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DOI: 10.1055/a-2535-2003
Green Tea Catechins: A Promising Anticancer Approach for Leukaemia
Abstract
Green tea catechins are bioactive polyphenolic compounds that possess a number of biological activities and potential health benefits. This review will focus on discussing the effects of green tea catechins, with a particular emphasis on clinical studies that evaluate their anticancer potential. Epigallocatechin gallate (EGCG), either as a stand-alone treatment or in conjunction with conventional anticancer therapies, represents a promising alternative strategy for the management of leukaemia. This review was based on a search of the scientific sources indexed in the databases PubMed and Scopus using the following keywords: ‘Camellia sinensis’, ‘tea catechins’, ‘anticancer’, ‘antioxidant’, ‘hematological cancer’, and ‘leukaemia’ in combination. A deeper comprehension of the multifaceted mechanisms and findings of research could facilitate the development of novel strategies and the integration of green tea catechins into clinical practice, thus enhancing treatment outcomes for patients with leukaemia.
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Keywords
antioxidants - Camellia sinensis - Camelliaceae - catechin - epigallocatechin gallate - leukaemiaAbbreviations
Introduction
The term neoplasm is used to describe abnormal tissue growth that results from unlimited replicative potential [1]. Chronic inflammation represents a significant contributing factor to the initiation of carcinogenesis, whereby the production of reactive oxygen species (ROS) and reactive nitrogen species, leads to oxidative and nitrative damage to DNA, proteins, and lipids, which results in tissue damage and the accumulation of mutations, ultimately leading to the formation of cancer cells. Additionally, these processes can foster epigenetic alterations, such as aberrant DNA methylation and microRNA dysregulation, creating an environment conducive to tumour initiation and progression, ultimately culminating in the formation of cancer cells [2].
In 2022, approximately 20 million new cancer cases and 9.7 million cancer-related deaths were reported globally across 185 countries. The most prevalent cancers were lung (12.4% of all cases, 2.48 mln cases), breast (11.6%, 2.31 mln cases), colorectal (9.6%, 1.93 mln cases), prostate (7.3%, 1.47 mln cases), and stomach cancer (4.9%, 0.97 mln cases), reflecting their significant contribution to the global cancer burden [3], [4].
Cancer is a pervasive health concern, with a higher prevalence in developed countries. The incidence of cancer is approximately two to three times higher in developed countries compared to less developed ones [5], [6]. It is projected that the global incidence of cancer will continue to increase throughout the forthcoming two decades, with an estimated 28.4 million cases anticipated by 2040 [6]. There is substantial evidence to suggest that plant secondary metabolites possess pharmacological activity and efficacy in the treatment of a diverse range of diseases [7].
Haematological cancers, which encompass leukaemia and lymphoma, represent approximately 10% of all cancer diagnoses. Approximately 130 different types and subtypes of haematological malignancies have been identified. Notwithstanding the considerable advances in diagnostic techniques and pharmacological treatments, the incidence of relapse remains relatively high, and the lack of efficacious therapies persists [8]. The incorporation of polyphenols into oneʼs diet represents a promising strategy for the prevention of specific types of cancer [9]. Researchers are currently exploring innovative therapeutic approaches that transform existing treatments into targeted therapies. They are also combining herbal substances with synthetic compounds as complementary or alternative therapies to traditional pharmacological methods.
A variety of plant-based foods, including vegetables, fruits, grains, nuts, herbs, seeds, stems, and flowers, are rich in polyphenolic compounds. Due to their anti-inflammatory and antioxidant properties, these compounds may offer a potential method of prevention and treatment for a range of metabolic disorders, autoimmune diseases, neurodegenerative diseases, and cancer [10], [11], [12], [13]. According to the US National Health and Nutrition Examination Survey (NHANES), approximately 40% of US adults use herbal supplements, which encompass a range of spices and herbs, to achieve health-related benefits [14]. The United States Department of Agriculture (USDA) [15] indicates that there has been a notable increase in the consumption of herbs and spices within the United States over the past five decades. The utilisation of herbs and spices, such as ginger, cinnamon, garlic, and turmeric, has become increasingly prevalent in recent times. This is likely attributable to the perception that these substances have minimal side effects, are more readily accessible than conventional pharmaceuticals, and are recognised for their established health benefits [16].
In the pursuit of novel pharmaceutical agents with therapeutic properties, the re-examination of medicinal plants that have been utilised for millennia is a prominent area of research. The majority of these botanical species and their corresponding phytochemical derivatives are employed globally as components of a nutritionally balanced diet [17], [18], [19]. One particularly promising raw material is green tea. In a research study conducted in China by Zhang et al. [20] involving 107 individuals diagnosed with leukaemia and 110 controls, it was observed that the likelihood of developing leukaemia decreased in correlation with an increase in the frequency, amount, and duration of green tea consumption. Published data showed that green-tea drinkers had a 49% lower risk of developing leukaemia compared with non-tea drinkers (OR = 0.51, 95% CI: 0.27 – 0.96, p = 0.04). Consumption of green tea for more than 20 years was associated with an 80% lower risk of leukaemia (OR = 0.20, 95% CI: 0.06 – 0.60, p < 0.01). Drinking at least one cup per day was associated with a 60% reduced risk (OR = 0.40, 95% CI: 0.19 – 0.82, p < 0.01). Protective effects were observed particularly in acute lymphoblastic leukaemia (ALL) and chronic lymphocytic/myeloid leukaemia (CML/CLL). Similar effects were not observed in acute myeloid leukaemia (AML). A further study by Kuo et al. [21] involving 252 cases of leukaemia patients and 637 control patients in the China–Taiwan area revealed a significant association between green tea consumption and the risk of leukaemia in individuals aged 16 – 29 years. In this age group, a significant reduction in the risk of leukaemia was observed in response to a high intake of catechins (OR = 0.47, 95% CI: 0.23 – 0.97, p = 0.04). The definition of a high intake is more than 550 catechin units (1 unit = 50 ml of green tea), which can be achieved with regular consumption of one or more cups of green tea per day over a longer period of time. In the younger age group (under 15 years), no significant association was observed. The mechanism of this action was explained by the presence of catechins in green tea, including epigallocatechin gallate (EGCG).
Green tea, which has its origins in Southeast Asia, is one of the worldʼs oldest and most widely consumed beverages [22]. The catechins, a type of flavonoid subgroup, present in the green tea (Camellia sinensis (L.) Kuntze) may confer potential health benefits including anticancer effects. EGCG, the most abundant catechin found in green tea, has been demonstrated to effectively limit tumour growth by inhibiting the proliferation and metastasis of cancer cells, including lung, breast, oesophageal, stomach, liver, prostate, colorectal, pancreatic, bladder cancers, and melanoma. It functions as an antioxidant, enhances immune function, and improves the efficacy of chemotherapy [23].
It has recently been demonstrated that EGCG has a multitude of beneficial effects in the fight against cancer. It has been demonstrated that EGCG can enhance the immune response against cancer cells, while simultaneously reducing the immunosuppression caused by T cells and myeloid-derived suppressor cells. Additionally, EGCG has been demonstrated to impede the tumour-promoting functions of various cells, including tumour-associated macrophages, neutrophils, cancer-associated fibroblasts, and endothelial cells. Moreover, EGCG has been demonstrated to inhibit multiple metabolic reprogramming pathways, including glucose uptake, aerobic glycolysis, and fatty acid anabolism [24].
EGCG, a catechin found in green tea, has been shown to possess anti-tumour properties in a number of different cancers, including lung, breast, prostate, colorectal, liver, cervical, ovarian, oral, pancreatic cancers, melanoma, and leukaemia, as well as therapeutic potential in various metabolic disorders such as obesity, insulin resistance, hyperglycaemia, dyslipidaemia, hypertension, non-alcoholic fatty liver disease (NAFLD), and metabolic syndrome [25], [26]. Currently, various nano-formulations are being employed to enhance the bioavailability and efficacy of tea catechins [27].
This study examines the potential anticancer properties of green tea catechins and their potential utility in the treatment of various haematological malignancies including types of leukaemia AML, CML, CLL, ALL, and APL. This paper presents an analysis of the health benefits of green tea, including an examination of the main active ingredient, EECG. However, the most noteworthy outcome is the possibility of a synergistic combination of green tea and EGCG with existing antineoplastic medications utilised in the management of leukaemia. Furthermore, a synopsis of the data on green tea and its constituents in the context of leukaemia prevention and treatment was presented.
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Literature Data Analysis
The examination of literary data was conducted using the PubMed and Scopus databases. The initial stage of the process involved the selection of papers based on the relevance of their abstracts to the studyʼs aim. If a paper was deemed to be relevant, it was subjected to further analysis. A preference was given to papers published more recently, with a particular focus on those published between 2020 and 2024. The initial search was conducted for review articles, with the aim of supplementing the findings through the inclusion of original research. The search strategy employed a general-to-specific approach, and only articles written in English were considered. All items have been imported into Mendeley Reference Manager software (version 2.86.0), and any duplicate data have been removed. The detailed review criteria are provided below for reference.
The literature was initially searched exclusively in the PubMed database using the following keywords: the search terms “green tea” were then entered. A total of 4460 results were returned. Accordingly, the time frame was narrowed to the last 12 years (2013 – 2024). A total of 2366 results were obtained, of which 12 publications were ultimately included in the analysis. Initially, the focus was on review articles that addressed the properties, phytochemistry, pharmacological activity, and toxicology of green tea. Following an analysis of the abstracts of the publications, an extension of the further analysis was conducted, whereby the term ʼcatechinsʼ was also included. A total of 352 results were obtained, of which 17 papers were included in the subsequent analysis. The subsequent phase of the process entailed the restriction of the dataset to encompass solely those publications that referenced the anticancer properties of green tea. To this end, the term “anticancer” was appended to the combination of “green tea” and the logical conjunction “and”, resulting in the retrieval of 77 results. The subsequent step was to incorporate the term “leukemia” into the search for literature on green tea. The objective was to identify publications examining the relationship between green tea consumption and the efficacy of leukaemia treatment. Eleven results were obtained, and earlier studies were also included (covering a period of 25 years, from 1998 to 2024). A total of 24 results were obtained, of which 12 papers were ultimately included.
It is regrettable that the data available for analysis in response to the query regarding the relationship between green tea and leukaemia were insufficient to yield conclusive results. Although the selected publications highlighted EGCG as a potential mechanism underlying the antitumour effects of green tea, they did not provide sufficient experimental evidence to draw definitive conclusions in this aspect. It was thus resolved to extend the analysed data to encompass the most active component, namely EGCG, with the term ʼleukaemiaʼ being appended to the term ʼEGCG′. A total of 132 results were retrieved. Subsequently, an analysis was conducted using the Scopus database, employing the terms ʼEECG′ and ʼleukaemiaʼ. The time range was set to the last 25 years (1998 – 2024) in accordance with the extended search algorithm for the terms ʼgreen teaʼ and ʼleukaemiaʼ. A total of 247 results were identified. The analysis commenced with the most recent articles. In the absence of satisfactory results, the scope was narrowed to the words EGCG and leukaemia, resulting in the retrieval of 187 results. Despite the acquisition of a substantial number of results, the broad scope of the query and the voluminous nature of the results precluded a comprehensive review and analysis of all publications. This underscores the necessity to employ more refined search criteria. For this reason, it was decided to proceed to the second stage of data selection, focusing on information about the role of epigenetic mechanisms of the green tea component (EGCG) in the treatment of leukaemia. In order to achieve this, the following keywords were employed: EGCG, leukaemia, and epigenetic. A search of the PubMed database yielded nine results, while the Scopus database yielded 13 results, of which five papers were included. Based on the analysis of abstracts, publications that directly addressed the role of epigenetic mechanisms of EGCG in leukaemia treatment were selected. At the same time, general articles or those marginally related to the topic were excluded.
The subsequent phase of the investigation entailed the identification of data pertaining to immunotherapy as a therapeutic modality for haematological disorders and the prospective impact of EGCG. A search for the terms ʼimmunotherapyʼ and ʼleukaemiaʼ returned 8324 results, of which five were selected to support the thesis. This was deemed an inadequate approach, and thus the analysis was narrowed down to specific types of leukaemia. The analysis was primarily focused on results from trials conducted within the past decade. The search was initiated in the PubMed database by entering the terms ʼEGCG′ and ʼacute myeloid leukaemiaʼ. A total of 15 results were retrieved, of which four were deemed pertinent for inclusion. Subsequently, the terms ʼEGCG′ and ʼacute promyelocytic leukaemiaʼ were employed. A total of 13 results were retrieved. The analysis was extended to the Scopus database, resulting in the retrieval of 17 records (2 papers were included). Subsequently, the search terms ʼEGCG′ and ʼchronic myeloid leukaemiaʼ were employed. A total of five articles were retrieved, prompting a modification of the search terms to encompass green tea and an extension of the time frame to encompass the past 25 years. This resulted in the retrieval of 20 articles, of which four were included. The terms ʼgreen teaʼ and ʼacute lymphoblastic leukemiaʼ were then employed. The period under consideration was the last 25 years. A total of 18 results were obtained, with four papers included in the analysis. Subsequently, the terms ʼgreen teaʼ and ʼchronic lymphocytic leukaemiaʼ were employed. A total of 20 results were obtained, with four papers included. The final review method employed focuses on the utilisation of green tea and EECG in the treatment of leukaemia, along with its various forms, and enables the hypothesis presented in the title to be tested.
Phytochemical composition and pharmacological potentials of green tea: Key bioactive compounds and their health-promoting and anti-cancer significance
The history of green tea can be traced back to antiquity, with its health benefits being acknowledged by civilisations in China and Southeast Asia approximately 5000 years ago [28]. Green tea is processed within 24 hours of harvesting. The initial stage is that of withering, which takes between two and three hours. This is followed by a reduction in the water content of the leaves to approximately one-third of the initial content. The subsequent stage is the treatment of the leaves with dry air or wet heating, typically with steam at a temperature of approximately 100 °C. The objective of this process is to inactivate polyphenol oxidases and peroxidases, which are enzymes that catalyse oxidation reactions. The fermentation process and oxidation of catechins to theaflavins are halted during the production of green tea, resulting in a higher concentration of catechin compounds with potent antioxidant properties compared to black tea [23]. The enzymes responsible for the breakdown of chlorophyll in the leaves are also inactivated, thus ensuring that the green tea retains its colour throughout the subsequent processing stages. The final stage in the production of green tea is drying, which aims to reduce the water content of the leaves to a level that will permit storage without loss of quality. The objective is to achieve a final water content of between 2 and 3% throughout the entire process. It is noteworthy that EGCG demonstrates optimal stability within slightly acidic conditions (pH 4 – 6). Consequently, the method of processing green tea leaves can influence the behaviour of this ingredient during storage and infusion preparation [23], [29].
There are numerous varieties of Japanese green tea as Mecha, Genmaicha, Kukicha, Kamairicha, Kariganecha, Koncha, Kokeicha, Fukamushicha, and Tamaryokucha, as well as Chinese varieties such as Gunpowder, Chun Mee, Lung Ching, Mao Feng, and China Sencha, varying in terms of both taste and antioxidant properties. The most widely consumed type is Sencha tea [30]. Following appropriate processing, Sencha tea yields the varieties Bancha, Matcha, and Gyokuro, with Matcha exhibiting the highest concentrations of caffeine and L-theanine ([Fig. 1]). The presence of caffeine is responsible for the distinctive aroma and flavour of the green tea infusion, while the amino acid L-theanine plays a role in the synthesis of proteins that are essential for the production of neurotransmitters, including insulin and adrenaline [29]. L-theanine is readily absorbed by the blood–brain barrier, where it affects serotonin and dopamine levels. It mitigates the stimulatory effects of caffeine and exerts a beneficial influence on brain function, enhancing cognitive performance, mood, and concentration [23]. The objective of the research study conducted by Hidese et al. [31] was to investigate the effects of a four-week course of L-theanine on stress-related manifestations and cognitive function in a cohort of 30 healthy individuals (comprising 9 men and 21 women; mean age: 48.3 ± 11.9 years) with no significant mental disorders (classified according to the Mini-International Neuropsychiatric Interview (M. I. N. I.) criteria and according to the DSM-5 classification). In a double-blind, placebo-controlled trial, participants were administered L-theanine tablets at a dosage of 200 mg per day. Following a four-week period, the incidence of stress-related symptoms was evaluated in comparison with the placebo. The administration of the L-theanine tablets resulted in a reduction in or absence of symptoms such as depression, anxiety, and sleep disturbances, while verbal fluency and executive function exhibited improvement [31]. As demonstrated by Kochman et al. [29], the concentration of caffeine in the majority of green teas ranges from 11.3 to 24.67 mg/g, whereas in matcha it ranges from 18.9 to 44.4 mg/g. In contrast, the caffeine content of most coffee beans is reported to range from 10.0 to 12.0 mg per gram of bean.
It is important to note that the content of EGCG in the raw material is also influenced by its geographical origin. Japanese varieties, such as Sencha and Matcha, are frequently reported to contain higher levels of EGCG compared to Chinese or Indian teas. For instance, green tea from Japan, particularly the Sencha variety, has been found to contain up to 124 mg of EGCG per 100 ml of infusion, whereas the Chinese equivalent contains 107 mg/100 ml of infusion. Consequently, the processing method and geographical location exert an influence on the EECG in row material content, which may result in the manifestation of potential health-promoting properties [32], [33], [34].
The principal bioactive constituents of green tea are the catechins, a subgroup of polyphenolic compounds whose concentration can range from 20 to 36% of the dry weight of the leaves [28]. The principal catechins present in green tea are epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate (EGCG) ([Fig. 1]). A minimum of 12 distinct catechin varieties have been identified in green tea, among which EGCG represents the predominant form, constituting approximately 50 – 75% of the total catechin content [35]. Catechins possess analogous basic structural features, namely two aromatic rings (referred to as rings A and B) linked by three carbon atoms and one oxygen atom to form a cyclic pyran structure (ring C). However, they exhibit variability in the number and configuration of hydroxyl groups located on ring B, the type of stereochemistry (cis or trans isomers), and the presence or absence of a galloyl moiety (ring D). This distinctive chemical configuration endows them with a diverse range of biological activities. However, it also renders these compounds inherently unstable and susceptible to various chemical, physical, and biological fluctuations, including temperature shifts, oxygen exposure, pH alterations, and the presence of metal ions [36]. The antioxidant characteristics exhibited by catechins can be attributed to the abundance of hydroxyl groups integrated into the molecular structure of these compounds. The quantity and spatial arrangement of these groups significantly influence the efficacy of the antioxidant properties, as they determine the ability of polyphenols, such as EGCG, to engage in redox reactions. This includes their capacity to neutralise a wide range of ROS and nitrogen species, including superoxide radicals, singlet oxygen, hydroxyl radicals, and peroxynitrite. Structural features, such as the number and positioning of hydroxyl groups, enhance the antioxidant potential by facilitating hydrogen atom transfer and electron delocalisation, which are critical in disrupting oxidative chain reactions [35]. The ingestion of green tea has been evidenced to augment the functional activity of phase II antioxidant enzymes, particularly superoxide dismutase, glutathione S-transferase, glutathione peroxidase, and glutathione reductase [37]. The antioxidant activity of catechins, the capacity to scavenge reactive oxygen and nitrogen species, the inhibition of free radical formation, and the ability to chelate metal ions in redox reactions are the reasons why tea catechins are attributed with anticancer and antimutagenic properties [28]. Since the 1980 s, the anti-cancer effects of tea catechins have been reported, and this has been corroborated by contemporary epidemiological studies indicating that Asian residents, who typically consume an average of 5 to 6 capfuls of green tea per day, exhibit a lower incidence of cancer than Westerners [9]. In a prospective 9-year cohort study conducted by Imai and colleagues on 8552 Japanese adults, it was found that regular consumption of substantial amounts of green tea may confer a significant protective effect against cancer. The incidence of cancer was reduced by eight years in women and three years in men who consumed ten or more cups of green tea daily, in comparison with those who consumed three or fewer cups. It is imperative to elucidate that women who consumed more than 10 cups of green tea per day exhibited a reduced relative risk (RR = 0.57; 95% CI = 0.33 – 0.98). A comparable risk reduction was observed in the male population; however, these findings did not attain statistical significance due to the impact of smoking as a confounding factor [38]. A further prospective cohort investigation conducted by the UK Biobank, encompassing more than 500,000 individuals aged between 38 and 73 years at the time of enrolment (2006 – 2010), revealed a markedly negative correlation between tea consumption and cancer-related mortality among both male and female subjects. A summary of trials examining the active ingredients and therapeutic effects of green tea in the prevention and treatment of cancer is presented in [Table 1].
|
Type of study |
Active ingredient |
Therapeutic effect |
Reference |
|---|---|---|---|
|
Epidemiological |
Green tea |
5 – 6 capfuls of green tea daily reduces the risk of cancer |
[57] |
|
Prospective cohort |
Green tea |
The onset of cancer was delayed by eight years in women and by three years in men consuming ≥ 10 cups of green tea per day |
[38] |
|
Prospective cohort |
Green tea |
Green tea drinking showed a negative correlation with cancer mortality in both men and women |
[60] |
|
In vitro
|
Green tea polyphenols |
↑ H2O2 level |
[61] |
|
In vitro
|
EGCG |
↑ ROS levels |
[62] |
|
In vitro
|
EGCG |
↑ apoptosis (formation of apoptotic bodies, DNA ladder formation) |
|
|
In vitro
|
EGCG |
↓ Bcl-2 and Bcl-xL |
[39] |
|
In vitro (PEL cells Model) |
EGCG |
↑ oxidative stress in HHV8-harboring PEL cells |
[87] |
|
In vitro
|
EGCG |
↓ proangiogenic factors |
[43] |
|
In vitro
|
EGCG |
↑ p21 and p27 |
[57] |
|
In vitro
|
Catechin |
↓ IL-1α, IL-1β, IL-6, IL-12p35, |
[45] |
|
In vivo
|
EC31 |
↓ P-gp |
[46] |
The most potent and dominant bioactive component of green tea is EGCG, which contains eight hydroxyl groups [23]. EGCG is acknowledged for its capacity to regulate diverse signalling pathways and enzymatic functions, which have the potential to induce apoptosis and inhibit cell proliferation, invasion, angiogenesis, and metastasis in oncological contexts [39]. The overproduction of ROS induces oxidative stress, which has the potential to impair cellular constituents and facilitate the proliferation and sustainability of neoplastic cells. ROS have the capacity to damage DNA, induce mutations, and alter gene expression, which may play a role in the aetiology of cancer. Consequently, the levels of ROS and their effects on tumour cells are contingent upon a multitude of factors, including the specific type and stage of the tumour, as well as the tumour microenvironment (TME), which encompasses the network of diverse cells and extracellular substances that surround the tumour [35].
The chemical composition of green tea is completed by proteins (15%), which include amino acids such as L-theanine, tyrosine, tryptophan, threonine, 5-N-ethyl glutamine, glutamic acid, serine, glycine, valine, leucine, aspartic acid, lysine, and arginine (4%). The remaining 25% is comprised of carbohydrates, including glucose, cellulose, and sucrose. Additionally, 3% is made up of sterols and lipids, including linoleic acid and alpha-linolenic acid. Finally, 3% is attributed to purine alkaloids, such as theophylline and caffeine. Additionally, trace amounts of enzymes (polyphenol oxidase), micro- and macronutrients (magnesium, phosphorus, chromium, manganese, calcium, copper, zinc, iron, selenium, cobalt, or nickel), and some vitamins (A, B2, B3, C, E, and K) are present. Green tea represents a significant source of iodine (content depends on local environmental conditions) and fluoride compounds (may contain from 0.3 to 4 mg of fluoride per litre of infusion). The chemical constituents of green tea include phenolic acids, such as gallic acid, as well as volatile compounds comprising alcohols, esters, hydrocarbons, and aldehydes (1.5%), in addition to plant pigments, namely carotenoids and chlorophyll, at a concentration of 0.5% [23].
The polyphenols present in green tea display both antioxidant and pro-oxidant characteristics that are pertinent to the prevention of cancer. These compounds may act as direct antioxidants by scavenging ROS, or alternatively, they may function as robust pro-oxidants by facilitating the generation of ROS, which in turn promotes apoptotic pathways [40]. The initiation of programmed cell death, commonly referred to as apoptosis, plays a pivotal role in oncological therapies, as it represents a deliberate approach for the elimination of this cell type [41]. The induction of programmed cell death, commonly referred to as apoptosis, is of pivotal importance in the field of oncological therapeutics, as it significantly contributes to the overall efficacy of cancer treatment. The suppression of neoplastic cell viability and the subsequent promotion of apoptosis by green tea polyphenols, specifically ECG and EGC, in vitro, can be attributed to the generation of reactive oxygen species, namely hydrogen peroxide and superoxide anion. This biochemical process induces the loss of mitochondrial transmembrane potential, which is followed by the release of cytochrome C from the mitochondria into the cytoplasm. This is then followed by the activation of the proteolytic caspase cascade, which, by cleaving the relevant proteins, indirectly leads to the degradation of genetic material, cell shape change, and cell division into apoptotic vesicles. These are then taken up by neutrophil granulocytes, monocytes, and neighbouring cells [35]. Additionally, catechins have been observed to alter the expression of Bcl-2 (B-cell lymphoma 2) family proteins, including Bcl-2 and Bcl-xL (B-cell lymphoma extra-large), which act as inhibitors of apoptosis. Green tea catechins (EGCG, EGC, ECG, and CG) bind to Bcl-2 and Bcl-xL, thereby preventing the anti-apoptotic effect of these proteins, which allows for the physiological elimination of tumour-transformed cells [39]. Tsai et al. [42] proposed that EGCG represents an efficacious strategy for the treatment of herpesvirus-8 infection and herpesvirus-8-associated lymphomas.
The induction of programmed cell death, or apoptosis, represents a crucial aspect of cancer treatment, as it serves as a targeted strategy for eliminating the pathological process that is cancerous [35]. Tumour cell infiltration and metastasis represent the predominant factors contributing to tumour recurrence and the failure of therapeutic interventions. The phenomenon of cancer cell metastasis is characterised by the dissociation of cellular adhesion, augmented cell motility, and invasiveness, as well as penetration into the circulatory system and dissemination to remote tissues. In vitro cellular studies and in vivo animal investigations have demonstrated that catechins, particularly EGCG, possess the capacity to negatively modulate these processes, thereby effectively inhibiting the metastasis and infiltration of diverse cancer cell types ([Table 2]). Fan et al. [43] demonstrated that catechins can inhibit carcinogenesis, tumour growth, tumour cell invasion, and tumour angiogenesis by inhibiting the induction of pro-angiogenic factors such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), human placental growth factor (PIGF), angiogenic factor (AF), and angiogenin. Additionally, heparin fragments (22 kDa molecular weight), chemokines, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), erythropoietin, and interleukin 8 (IL-8) have been identified as potential agents.
|
Drug/active substance |
Polyphenol |
Therapeutic effect |
Reference |
|---|---|---|---|
|
Cisplatin |
EGCG |
↑ sensitising cancer cells to cisplatin by stimulating CTR1 expression |
[57] |
|
Erlotinib |
EGCG |
↑ activity of cell cycle suppressors p21 and p27 |
[58] |
|
Docetaxel |
EGCG |
↓ side effects |
[60] |
|
Daunorubicin |
EGCG |
↑ myosin phospatase activity, leading to increased sensitivity of cancer cells |
[61] |
|
Irinotecan |
EGCG |
↓ P-glycoprotein activity |
[62] |
|
Doxorubicin |
EGCG |
↓ malondialdehyde |
EGCG exerts anti-cancer effects via the inhibition of metalloproteinases, which are pivotal in tumour advancement due to their function in stimulating tumour cell proliferation, migration, invasion, and metastasis, in addition to promoting angiogenesis. Green tea has been demonstrated to impede not only the commencement and advancement of the neoplastic process, but also its subsequent progression [44]. EGCG inhibits the coupling of growth factors to receptors, thereby preventing signal transduction and impeding the progression of tumour cells through the G1 phase of the cell cycle [9], [39]. The catechins present in green tea have been observed to influence the expression of genes and proteins associated with inflammatory processes, including tumour necrosis factor (TNF-α). When TNF-α is overexpressed, it activates the endogenous inflammatory cascade. EGCG was observed to antagonise TNF-α-induced inflammation by inhibiting the expression of the pro-inflammatory cytokines interleukin-12 (IL-12), interleukin (IL-6), interleukin 1β (IL-1β), and interleukin 1α (IL-1α). Furthermore, it has been demonstrated that green tea can inhibit the activity of inflammatory enzymes such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), while simultaneously stimulating the expression of anti-inflammatory cytokines, including interleukin-10 (IL-10) and interleukin-4 (IL-4) [45]. The interleukins IL-6 and IL-8 have been demonstrated to facilitate angiogenesis within neoplastic tissue. Administration of EGCG to tumour-bearing murine models resulted in the attenuation of IL-6 and IL-8 expression in a concentration-dependent manner. This observation suggests that IL-6 and IL-8 may play a role in anti-metastatic effects, as their overexpression has been linked to the formation and progression of metastatic tumours [40].
Additionally, catechins maintain equilibrium within the immune system and demonstrate an inhibitory effect against the majority of aberrant reactions induced by cancer. Catechins have been observed to exhibit dual regulatory mechanisms, which result in the attenuation of hyperactive immune responses while simultaneously reinstating immune tolerance induced by tumour cells. This is achieved through the modulation of cytokine secretion, which is targeted at pivotal pathways in order to uphold stable and orderly intracellular immune functionality [9]. Sun et al. [46] conducted an optimisation of tea polyphenol derivatives and identified epicatechin as a promising substance for further research in combination therapy for the treatment of breast cancer and leukaemia. EGCG has been demonstrated to enhance the protective role of nuclear factor–erythroid-2-related factor 2 and its downstream molecules in a range of disorders associated with cancer [47]. This is achieved through the regulation of a number of key proteins and enzymes, including Keap-1, NQO-1, HO-1, GPx, GCLc, GCLm, NF-kB cross-link, kinases, and apoptotic proteins.
EGCG effectively inhibits the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), a transcription factor involved in inflammation and cancer progression. EGCG suppresses both canonical and non-canonical NF-κB pathways by reducing the phosphorylation of IκB (inhibitor of kappa B) and its subsequent degradation, thereby limiting NF-κB translocation to the nucleus and the expression of pro-inflammatory genes such as TNF-α, IL-1β, and IL-6 [48], [49]. In RAW 264.7 macrophages exposed to lipopolysaccharides (LPS), EGCG significantly reduced nitric oxide (NO) levels to 32% and ROS to 45.4% of control values, alongside marked decreases in pro-inflammatory cytokine production (e.g., TNF-α from 27.1 pg/mL to 1.2 pg/mL; IL-6 from 2994 pg/mL to 408 pg/mL) [49]. Additionally, in pancreatic cancer cell lines, EGCG inhibited NF-κB activity, reduced the expression of its target genes (e.g., BCL-2, MMP9), and induced apoptosis [50].
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The use of green teaʼs anti-cancer properties in the treatment of leukaemia
Acute lymphoblastic leukaemia is a group of cancers characterised by the uncontrolled proliferation and development of leukocytes (white blood cells) in the blood and bone marrow. The leukocytes accumulate in the liver and spleen, which are affected by the disease [51]. It is typically, though not invariably, associated with peripheral blood leucocytosis. Additionally, leukopenia, a hallmark of hairy-cell leukaemia, presents with pancytopenia, a condition characterised by the deficiency of all normal blood morphological elements [52]. The current classification of leukaemia distinguishes between two principal categories: myeloid or lymphoid, which is contingent upon the cellular lineage of the leukaemic clone, and acute or chronic, which is contingent upon the velocity of progression and encompasses numerous subclassifications within each category [51]. The current range of therapeutic modalities for leukaemia includes chemotherapy, radiotherapy, immunotherapy, and haematopoietic stem-cell transplantation. Chemotherapy remains the primary intervention for the majority of leukaemia subtypes. These include antimetabolites (methotrexate), topoisomerase II inhibitors (e.g., doxorubicin), and alkaloids. In addition to general chemotherapeutic agents, targeted therapies are employed, including the use of tyrosine kinase inhibitors (imatinib) in BCR/ABL-positive leukaemia. BCR/ABL is a pathological gene encoding the p210 protein, which exhibits abnormal, increased tyrosine kinase activity in chronic myeloid leukaemia [51].
Chemotherapy and radiotherapy are frequently associated with adverse effects, including alopecia, decreased appetite, diarrhoeal episodes, emesis, hepatic impairment, and neurological anomalies. It is therefore imperative to explore novel therapeutic modalities that demonstrate enhanced efficacy while concomitantly minimising adverse effects. Research efforts have been directed towards the development of treatments for leukaemia that can selectively target malignant cells without affecting the integrity of non-malignant cells [53]. Della Via et al. [39] demonstrated that EGCG reduces the burden of leukaemia and induces apoptosis and cell differentiation, resulting in prolonged survival of mice diagnosed with leukaemia. This is achieved by affecting apoptosis and modulating the expression levels of anti-apoptotic Bcl-2 or pro-apoptotic Bax (Bcl-2 associated X protein) and Bad (Bcl-2-associated agonist of cell death), as well as modulating the activity of oxidative stress-inducing ROS production.
In cases of leukaemia, the administration of polyphenols prior to treatment could prove advantageous when used in conjunction with conventional chemotherapeutic modalities. The pro-apoptotic and pro-oxidative properties represent a valuable mechanism through which the susceptibility of neoplastic cells to forthcoming chemotherapy can be augmented, as well as through which diverse molecular signalling pathways can be amplified. Polyphenols, including green tea catechins, may also have the potential to protect against or possibly reverse multidrug resistance. Nevertheless, the majority of the existing empirical data has been derived from in vitro investigations utilising leukaemia cell lines. Consequently, it is imperative to conduct in vivo research and clinical trials to elucidate the potential efficacy and advantages of these polyphenolic compounds [51].
Total of 73 patients participated in clinical trials to investigate the effects of Polyphenon E, a standardised extract derived from the leaves of green tea, on early stage lymphocytic leukaemia [54]. In the initial phase of the trial, patients were administered a daily dose of the medication ranging from 0.4 to 1.8 grams for a period of six months [55]. Subsequently, during the second stage of the trial, the dosage was increased to a maximum of 2.0 g [56]. The majority of patients exhibited considerable and sustained reductions in their absolute lymphocyte count and lymphadenopathy throughout the course of both trial phases [55], [56]. It is noteworthy that no adverse effects were observed in either study.
Catechins have been demonstrated to exert a beneficial effect on chemotherapy-induced adverse effects, largely due to their multifaceted biological actions, including the capacity to counteract oxidative stress. The combination of anticancer pharmaceuticals with catechins, both prior to and subsequent to the administration of the drugs, may mitigate the toxicity and adverse effects associated with these agents to a certain degree, thereby facilitating enhanced apoptosis of tumour cells and augmenting the therapeutic efficacy of the drugs [9]. The impact of combining green tea catechins with specific anticancer drugs is illustrated in [Table 2]. Chen et al. [57] demonstrated that the combination of cisplatin with EGCG improved the chemotherapeutic sensitivity of cells to cisplatin, leading to a reduction in cisplatin dose by stimulating the expression of CTR1 (high-affinity copper transporter 1), the copper transporter responsible for cisplatin uptake. Amin et al. [58] demonstrate that EGCG exerts a synergistic effect on the activity of the cell cycle suppressors p21 and p27 when combined with erlotinib, resulting in enhanced tumour cell cycle arrest. Wang et al. [59] report that the use of EGCG with docetaxel reduces adverse effects and significantly improves the absorption and transport of the drug. It is worth noting that quercetin and green tea polyphenols, including ECGC, inhibit multidrug resistance proteins such as P-glycoprotein, which reduces the removal of the drug from cells and increases its intracellular concentration. EGCG enhanced the inhibitory effect of docetaxel on the phosphatidylinositol 3-kinase and protein kinase AKT (PI3K-AKT) signalling pathway, the transduction and activation of the STAT3 (signal transducers and activator of transcription) protein, and the expression of the multidrug resistance protein (MDR), resulting in the inhibition of cancer cell invasion and metastasis [60].
Toth et al. [61] demonstrated that EGCG enhances the sensitivity of leukaemic cells to daunorubicin by activating myosin phosphatase through the induction of dephosphorylation of MYPT1 (myosin phosphatase target subunit 1) to the phospho-Thr696 group (MYPT1pT696), which may confer increased chemosensitivity to cancer cells. Lin et al. [62] have demonstrated that EGCG increases the bioavailability of irinotecan by inhibiting P-glycoprotein (P-gp) activity, thereby inhibiting the biliary elimination of irinotecan and its active metabolite (SN-38). The pharmacokinetic data indicate that the area under the plasma concentration–time curve (AUC) for CPT-11 increased by 57.7%, while the AUC in bile decreased by 15.8% in the group pretreated with EGCG. This results in a significant increase in the plasma half-life of the drug. The combination of EGCG with irinotecan has been demonstrated to effectively reduce drug-induced toxicity, including the alleviation of symptoms such as diarrhoea and leukopenia. In a recent study, Bae et al. [63] developed a nanocomplex of gilteritinib with a hyaluronic acid-EGCG conjugate that demonstrated therapeutic efficacy as FMS-like tyrosine kinase receptor-3 inhibitors in the context of leukaemia therapy.
Doxorubicin is a widely used antibiotic with cytostatic activity, including in the treatment of acute leukaemia. However, it has a severe toxic effect on healthy cells, which is primarily caused by oxidative stress. Navarro-Hortal et al. [64] demonstrated that the administration of EGCG eliminates oxidative stress by enhancing antioxidant enzyme activity, regulating glutathione depletion, and reducing the level of malondialdehyde, a byproduct of lipid peroxidation.
Additionally, EGCG has been demonstrated to reduce the resistance of cancer cells to doxorubicin, thereby rendering them more susceptible to growth inhibition and apoptosis. The overexpression of P-gp in cancer cells can result in chemotherapy failure. EGCG has the capacity to inhibit the overexpression of P-gp, which is induced by doxorubicin. This results in a reduction in intracellular drug levels and the prevention of drug resistance. EGCG has the capacity to maintain drug levels in cancer cells by binding to P-gp [65].
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The use of EGCG as an epigenetic therapy for leukaemia
The latest research in epigenetics indicates that, in addition to genetic alterations, human cancer cells exhibit epigenetic abnormalities. These genetic and epigenetic changes are of critical importance at all stages of tumour development [35], [36]. The most significant epigenetic modifications include DNA methylation, histone protein modifications, and gene regulation by non-coding RNA molecules [66]. Epigenetic abnormalities can result in a defective chromatin structure, which in turn leads to the deregulation of gene transcription and contributes to the development of leukaemia. This process involves the abnormal proliferation of blast cells and the inhibition of their maturation. Areas of DNA that are susceptible to hypermethylation in leukaemia cells are CpG islands, which are rich in cytosine and guanine [67]. Leukaemia, like other cancers, exhibits aberrant methylation profiles. The presence of tumour cells with high levels of methylation of CpG islands has the potential to suppress the expression of neighbouring genes by preventing the binding of transcription factors, which is associated with rapid tumour progression [68].
EGCG has recently been the subject of scientific investigation as a potential demethylating agent. EGCG is subject to methylation via the enzyme catechol-O-methyltransferase (COMT). This particular enzyme plays a role in the addition of a methyl group to the catecholamine group, a process that utilises S-adenosylmethionine (SAM) as a methyl donor. The demethylation process of SAM results in the production of S-adenosyl-L-homocysteine (SAH), which acts as an inhibitor of DNA methyltransferase (DNMT), the enzyme responsible for catalysing the transfer of the methyl group from SAM to the cytosine residue within DNA. It has been proposed that the generation of SAH represents one of the biochemical mechanisms through which EGCG exerts its demethylating effects. Moreover, EGCG is capable of forming hydrogen bonds with a range of amino acid residues within the catalytic domain of DNMT, thereby acting as a direct inhibitor of this enzyme. The inhibition of DNMT can impede the methylation of newly synthesised DNA strands, thereby facilitating the reversal of hypermethylation and the re-expression of genes that have been silenced [35]. Furthermore, EGCG has been shown to act as an effective inhibitor of human dihydrofolate reductase. EGCG exerts effects on folate metabolism within cellular environments, inhibits both DNA and RNA synthesis, and induces modifications in DNA methylation patterns [35].
The aberrant activation or excessive expression of histone-modifying enzymes results in a disruption in gene transcription regulation, which may be manifested as an interplay between the repression of tumour suppressor genes and the stimulation of developmental genes that facilitate thermal progression. As demonstrated by Moradzadeh et al. [69], EGCG exhibits distinctive modulatory characteristics that target pivotal epigenetic enzymes and signalling pathways. In an in vitro assay using NB4 and HL60 cell lines, EGCG was observed to decrease the expression of histone deacetylases (HDACs), which are often overexpressed in therapeutic contexts.
The use of EGCG as an epigenetic therapy in the white cap is a promising avenue of research, yet further studies are needed to fully elucidate its molecular actions, determine optimal doses and treatment regimens, and address safety concerns [35]. It is important to note that, like other phytochemicals, EGCG acts as a pleiotropic regulator through multiple mechanisms. The inhibitor is characterised by properties that hinder its pharmacological action.
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Immunotherapy as a treatment for haematological cancers
The dynamic evolution of cancer has rendered immunotherapy an innovative strategy for cancer treatment, whereby the immune system is activated, which possesses intrinsic anti-cancer defence mechanisms. As medicine progresses, novel concepts are emerging and clinical trials are being conducted to evaluate the efficacy, safety, and feasibility of utilising immunotherapy as a primary treatment for malignant tumours, in conjunction with surgery, radiotherapy, chemotherapy, and molecular therapies. Specific focus is being directed towards the potential utilisation of macrophage functions in the combat against leukaemia. Macrophages play a pivotal role in maintaining tissue equilibrium; however, they are also present within the TME [66].
In both primary tumours and metastases, tumour-associated macrophages (TAMs) exhibit characteristics of M2 macrophages and serve as a conduit between the inflammatory response and the tumour process. TAMs have been observed to promote tumour cell proliferation and metastasis, stimulate angiogenesis, and inhibit the T-cell-mediated immune response, thereby contributing to tumour progression. However, two distinct populations of macrophages have been identified, each with opposing effects. The pro-inflammatory M1 population is characterised by phagocytosis and destruction of bacteria, tumour suppression, and the activation of cells with cytotoxic properties. Additionally, it produces pro-inflammatory cytokines. In contrast, the anti-inflammatory M2 population is involved in IL-4- and IL-10-mediated immunosuppression, as well as the stimulation of angiogenesis through the release of VEGF. TAMs can constitute up to 50% of the tumour mass in the TME, which is associated with a poor prognosis [70]. Researchers are attempting to modify the M2 to M1 state by targeting key modulators of macrophage biology, including macrophage colony-stimulating factor (M-CSF) and the pro-inflammatory cytokine interferon gamma (IFN-γ) [71].
In a study utilising RAW 264.7 mouse macrophage cells, Li and Kuemmerle demonstrated that EGCG inhibits macrophage polarisation from M1 to M2 in mouse bone-marrow-derived macrophages, consequently reducing the proportion of M2 macrophages [72]. A subsequent investigation conducted by Calgarotto et al. [73] involved a cohort of 10 individuals diagnosed with AML-MRC (acute myeloid leukaemia with myelodysplasia-related changes), with a median age of 77 years (minimum–maximum: 64 – 87). This revealed considerable alterations in the immune profile of AML-MRC patients who were administered green tea extract at a cumulative dosage of 1000 mg daily for no less than six months. As early as 30 days after treatment, a significant increase in the number of naive and effector CD8+ T cells (cluster of differentiation 8) and natural killer (NK) cells was observed. Increase in cytotoxic immune response: after 30 days of treatment, a statistically significant increase was observed in the frequency of naive and effector CD8+ T cells (from 15.6% to 24.5%, p < 0.05) and granzyme B+/perforin+ CD8+ T cells in PB (from 12.4% to 42%, p < 0.05), as well as granzyme B+ NK cells in PB (from 70% to 87%, p < 0.05). These cells are responsible for recognising and destroying tumour-transformed cells. Other results indicate a significant reduction in the mRNA expression of immunosuppressive cytokines, including transforming growth factor beta (TGF-β) and interleukin 4 (IL-4), with no effect on the pro-inflammatory cytokines interleukin 1 beta (IL-1β) and TNF-α. Reduction in immunosuppressive cytokine expression: after 30 days of treatment, a significant reduction in mRNA expression levels of TGF-β (from 1.04 to 0.43, p = 0.03) and IL-4 (from 1.22 to 0.35, p = 0.03) was observed, with no changes detected in IL-1β or TNF-α levels (p > 0.05). A reduction in the number of regulatory T cells (Treg) was observed, which are responsible for suppressing an overstimulated immune response [73]. Although the study sample was limited in size and included older AML-MRC patients who were ineligible for conventional chemotherapy and bone marrow transplantation, the median survival of patients who received green tea treatment was longer than that of the control sample (164 days vs. 266 days, respectively). Despite the observed prolongation of median survival in the group receiving green tea extract, this difference was not statistically significant, suggesting the need for further studies in larger groups of patients to confirm the potential effect of green tea on prolonging survival [73]. Nevertheless, further investigation is required to ascertain the potential of plant constituents in the immunotherapy treatment of haematological malignancies.
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The use of EGCG in the treatment of various types of leukaemia
Acute leukaemia is classified into four main categories: myeloid leukaemia (AML, acute myeloid leukaemia), lymphoblastic leukaemia (ALL, acute lymphoblastic leukaemia), chronic myeloid leukaemia (CML, chronic myeloid leukaemia), and chronic lymphocytic leukaemia (CLL, chronic lymphocytic leukaemia). [Fig. 2] demonstrates the mechanisms of EGCGʼs action in the context of treating acute and chronic leukaemia.
Acute myeloid leukaemia (AML) is a clinically heterogeneous malignancy that originates from early progenitor cells of myelopoiesis that have become independent of regulatory mechanisms and are capable of clonal proliferation. Approximately 80% of acute leukaemia cases in adults and approximately 15% of leukaemia cases in children are attributed to AML. It is hypothesised that genetic alterations in haematopoietic stem cells result in irreversible dysregulation of key gene functions responsible for processes of differentiation, proliferation, or apoptosis [39].
AML predominantly affects the elderly population, with a median age at diagnosis of 68 years, and over two-thirds of diagnoses occurring in individuals aged 55 years or older. Although acute myeloid leukaemia is predominantly sporadic in nature, there is an elevated risk associated with prolonged environmental or occupational exposure to benzene compounds, as well as in individuals with a history of exposure to cytotoxic agents or radiotherapy. Prognostic expectations for survival are significantly influenced by age. For instance, the estimated 5-year survival rate for patients younger than 50 years is 62%, while the 5-year survival rate for patients aged 50 – 64 years is 37%. In contrast, the 5-year survival rate for patients over the age of 65 years at the point of diagnosis is a mere 9.4% [74].
A significant challenge in the management of AML is the phenomenon of chemoresistance. This occurs when CD34+ AML haematopoietic stem cells demonstrate a poor prognosis and exhibit resistance to intrinsic apoptotic processes [75]. Recently, the inhibition of FMS-like tyrosine kinase 3 (FLT3) activity has emerged as a potentially efficacious therapeutic strategy, given that FLT3 mutation represents the predominant genetic modification correlated with decreased survival rates and an elevated risk of disease recurrence. Sorafenib, an FLT3 inhibitor, has been employed in clinical practice to treat patients with FLT3-positive AML in a range of settings. However, sorafenib has been demonstrated to exhibit limited efficacy against leukaemic cells within the bone marrow, which is primarily responsible for relapse and treatment failure. Two principal justifications for this phenomenon have been discerned: firstly, inadequate deposition of sorafenib within the bone marrow, and secondly, heightened drug resistance exhibited by AML cells within the bone marrow microenvironment. Bae et al. [76] developed a bone-marrow-targeted micellar nano complex (Sora-MNC) through the self-assembly of a sorafenib and EGCG conjugate.
The nano complex demonstrated efficacy in reducing the leukaemic burden in the bone marrow, exhibiting significantly enhanced cytotoxicity and anti-clonogenic activity, as well as prolonging survival more effectively than the free sorafenib formulation in studies conducted on human AML cell lines MOLM-14 and MV-4 – 11, with Sora-MNC eliminating over 99% of MOLM-14 AML cells compared to only 14% by free sorafenib at 200 nM, completely inhibiting colony formation (p < 0.001) and extending survival in AML-PDX mice, where all treated animals survived the 23-day treatment period, whereas mortality in the free sorafenib group began by day 12 (p < 0.05). The administration of the nano complex was observed to effectively eliminate residual leukaemic blasts in the bone marrow and to improve survival [76]. The nano complex was found to enhance the anti-leukaemic effect of sorafenib in a synergistic manner by selectively interfering with the mTOR (mechanistic target of rapamycin) pathway of the threonine-serine protein kinase. Dysregulation of this pathway may be a factor in the pathogenesis of human diseases, including cancer. An in vivo biodistribution study demonstrated that the nanocomplex exhibited an approximately 11-fold higher accumulation in the bone marrow compared to free sorafenib [76].
Acute promyelocytic leukaemia (APL) is a variant of AML that accounts for approximately 10 – 15% of new cases of AML. It frequently manifests with diminished platelet and fibrinogen levels, coagulopathy, and prolonged clotting times, which necessitate expeditious diagnosis and treatment (features characteristic of DIC, or disseminated intravascular coagulation). The primary consequence of a balanced translocation, most commonly t(15;17) (q22;q12 – 21), is the formation of a fusion gene between the promyelocytic leukaemia (PML) gene and the retinoic acid receptor alpha (RARA) gene, which is the underlying cause of APL. The formation of the PML-RARA fusion oncoprotein results in the inhibition of normal differentiation processes within the bone marrow, which in turn precipitates the onset of leukaemia [77]. Those diagnosed with APL receive therapeutic intervention through the administration of all-trans-retinoic acid (ATRA), and in certain instances, they may also be treated with arsenic trioxide [78].
A study by Torello et al. [78] demonstrated that administering a dosage of 250 mg/kg green tea extract to leukaemic mice over a period of four days resulted in a notable reduction in leucocytosis and the quantity of immature blastic cells observed in the peripheral blood, bone marrow, and spleen. The results indicate that green tea extract exerts an anti-proliferative effect in a leukaemia model by impeding the proliferation of malignant clones, as evidenced by a reduction in CD34 and CD11 antigens, which are expressed as a marker in the diagnosis and prognosis of APL. A concurrent investigation demonstrated that the administration of green tea extract precipitated apoptosis in leukaemic cells located within the bone marrow and spleen of murine models. This was substantiated by the activation of caspases-3, -8, and − 9, alongside a notable increase in the population of apoptotic cells. This increase may potentially have been achieved through the modulation of intracellular ROS production within these cellular entities. The progression of the disease was evaluated through in vivo fluorescence imaging techniques, which corroborated the infiltration of immature cellular populations within the spleen and bone marrow of leukemic subjects.
Chronic myeloid leukaemia (CML) is a disease of haematopoietic stem cells (HSC) that is characterised in 95% of cases by a t(9;22) translocation (q34;q11), resulting in the fusion of the BCR (breakpoint cluster region, locus 22q11). The fusion of the BCR and ABL1 (V-abl Abelson murine leukaemia viral oncogene homolog 1, locus 9 q34.1) results in the formation of the pathogenic oncogene BCR-ABL1, which is responsible for the production of an abnormal protein (called BCR-ABL tyrosine kinase). The incidence of this disease is 1 to 2 cases per 100 000 adults [53]. The primary consequence of this synergistic oncogene is the stimulation of the tyrosine kinase signalling cascade, which culminates in a proliferative superiority of mutant haematopoietic stem cells (HSCs) in comparison to their normal counterparts, leading to the gradual substitution of normal HSCs. The course of CML is characterised by three distinct phases: chronic, accelerated, and blast phase. In a controlled in vitro investigation, Xiao et al. [79] demonstrated that EGCG suppresses the proliferation of CML cell lines and primary CML cells, diminishes the permeability of the mitochondrial membrane in CML cell lines, and triggers apoptosis through caspase-independent cellular death mechanisms and apoptosis-inducing factor (AIF) [79]. A further study by Bange et al. [70] demonstrated that EGCG can effectively inhibit the viability of CML cells in a dose-dependent manner. EGCG was observed to increase autophagy gene expression (Atg5, autophagy-related 5), indicating that autophagy function is enhanced and may be implicated in EGCG-mediated cell apoptosis. The administration of EGCG resulted in a reduction in BCR/ABL protein expression within primary CML cells and across all utilised cell lines, with a clear correlation between dosage and efficacy. This suggests that EGCG may promote the degradation of the BCR/ABL protein, which is a product of this pathological gene.
Acute lymphoblastic leukaemia (ALL) is a malignant neoplasm of B or T lymphoblasts characterised by the uncontrolled proliferation of abnormal, immature lymphocytes. This proliferation typically results in the replacement of normal bone marrow and blood cells by the malignant lymphocytes. It is the most prevalent form of paediatric leukaemia. Patients with acute lymphoblastic leukaemia typically present with symptoms associated with anaemia, thrombocytopenia, and neutropenia. Involvement of the central nervous system is a common occurrence and may be accompanied by symptoms indicative of increased intracranial pressure. The current treatment protocols for ALL include the administration of high doses of chemotherapeutic agents, including anthracycline, vincristine, l-asparaginase, and corticosteroid [80]. EGCG has been demonstrated to inhibit the activity of the enzyme PIN1 (peptidyl-prolyl isomerase, peptidyl-prolyl cis-trans isomerase NIMA-interacting 1), which plays a pivotal role in the development of tumours and the formation of new blood vessels in a multitude of cancers, including acute lymphoblastic leukaemia. Inhibition of PIN1 can disrupt the equilibrium between oncogenes and tumour suppressors that facilitate oncogenesis [39], [77]. In an in vitro study conducted by Ghasemi-Pirbalut et al. [66], a Jurkat cell line was used. Jurkat cells were incubated with varying concentrations of EGCG (30 – 100 µM) over intervals of 24, 48, and 72 hours, and the determination of cell viability and metabolic activity was conducted utilising the MTS assay for assessment. The assessment of apoptosis and caspase-3 alterations was conducted using flow cytometry, while the assessment of Fas expression was conducted using reverse transcription-polymerase chain reaction (RT-PCR). EGCG was observed to effectively reduce cell viability, induce apoptosis, and increase the expression levels of caspase 3 and Fas, which are responsible for stimulating the apoptotic process. One study demonstrated that treatment with EGCG for 48 hours resulted in a significant increase in Fas expression at a concentration of 100 µM. This increase was over threefold compared to control levels (p < 0.05), highlighting the dose-dependent activation of the Fas-mediated apoptotic pathway in Jurkat T-lymphoblastic leukaemia cells.
Chronic lymphocytic leukaemia (CLL) is a slow-growing malignant disease affecting mature B lymphocytes, present in the blood, bone marrow, lymphoid tissues, and other organs. Due to its high biological heterogeneity, the clinical course is characterised by significant variability and unpredictability. CLL is the most prevalent haematopoietic malignancy in Western countries, affecting 22 – 30% of the population. The median age of patients is 72 years, with 81% of patients being older than 60 years of age [53]. The presence of deletions of the short arm of chromosome 17 (del [17 p]) or mutations of the TP53 gene are significant factors in the selection of an appropriate therapeutic regimen for patients, given their correlation with resistance to immunochemotherapy and adverse prognostic factors. A variety of treatment options are available, including a Bcl-2 inhibitor (venetoclax), its combination with obinutuzumab, tyrosine kinase inhibitor monotherapy (ibrutinib, acalabrutinib), or chemo-immunotherapy [81]. One potential mechanism through which green tea may influence CLL is via the modulation of regulatory T cells (T-reg). Treg lymphocytes represent a minor subset of CD4+ (cluster of differentiation 4) cells that play a crucial role in modulating excessive immune responses, thereby contributing to the preservation of immune system equilibrium, fostering tolerance towards self-antigens, preventing the onset of autoimmune disorders, and inhibiting the activation of effector T cells. Elevated T-cell levels have been identified as a contributing factor in the development and progression of numerous cancers, including CLL, due to the inhibition of the anti-tumour T-cell response [70]. In a research investigation conducted by Cornwall, a comparative analysis of CLL cells derived from four untreated CLL patients alongside healthy control specimens was undertaken. The subjects were subjected to escalating concentrations of EGCG (0, 25, 50, 75, or 100 µg/ml). The findings revealed that the cells from healthy controls exhibited no signs of apoptosis. Conversely, a significant 90% of CLL B cells underwent apoptosis when exposed to maximal concentrations of EGCG. This effect was dose-dependent, with apoptosis levels increasing from approximately 65% at 50 µg/mL to 90% at 100 µg/mL after 60 hours of treatment (p < 0.001), demonstrating the potent pro-apoptotic activity of EGCG in CLL B cells [82].
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Green tea and catechin adverse effects
Green tea and its catechins, including EGCG, are widely consumed for their health benefits, including antioxidant and anti-inflammatory effects and, as demonstrated above, anticancer properties. However, excessive consumption can lead to adverse effects that should be considered in the context of potential therapy. Adverse effects include hepatotoxicity, gastrointestinal disorders, nervous system stimulation, as well as renal and cardiovascular disorders, and drug interactions. High doses of EGCG, particularly from green tea extracts, have been linked to liver injury. Clinical trials indicate that doses ≥ 800 mg/day can significantly elevate serum transaminases, a biomarker of liver dysfunction. A study on individuals consuming 843 mg/day of EGCG for one year revealed that 5.1% of them developed moderate to severe liver abnormalities (p = 0.0002) [83], [84]. Animal studies further support these findings, showing hepatotoxic effects at doses of 750 mg EGCG/kg body weight/day in rats and 40 mg/kg/day in fasted dogs [84]. Excessive green tea consumption, particularly over 5 litres per day, can cause gastrointestinal symptoms, including nausea, vomiting, diarrhoea, and flatulence [85]. The caffeine content in green tea, exceeding 400 mg/day, exacerbates these effects. The caffeine in green tea, at doses between 80 – 87 mg per serving, can induce anxiety and restlessness, with higher doses (≥ 1200 mg/day) associated with insomnia, irritability, and tremors [84]. Green tea catechins interfere with the metabolism of certain drugs, including statins, warfarin, and NSAIDs, primarily through cytochrome P450 enzyme inhibition. These interactions are particularly concerning for drugs with narrow therapeutic windows [86]. Excess caffeine intake from green tea can increase urinary calcium excretion, potentially leading to kidney stones. Furthermore, high caffeine doses (> 10 mg/kg/day) have been associated with tachycardia, arrhythmias, and hypotension in cases of green tea overdose [84], [85]. To minimise risks, green tea consumption should be limited to 2 – 3 cups per day (approximately 300 mg EGCG/day) [83], [84], [85].
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Conclusions
The available data indicate that green tea catechins, in particular EGCG, exhibit a diverse range of pharmacological activities and demonstrate promising results in treating various types of leukaemia. This renders them a promising prospect for the treatment of cancer, either as a standalone therapy or in conjunction with traditional chemotherapy. EGCG inhibits the proliferation and metastasis of cancer cells, promotes their apoptosis, and acts as an inhibitor of DNA methyltransferase, leading to the demethylation of tumour suppressor genes. Additionally, it reduces the expression of histone deacetylases, thereby aiding in the regulation of gene transcription involved in tumour suppression. EGCG also enhances the sensitivity of cancer cells to conventional anticancer drugs, such as doxorubicin, cisplatin, and daunorubicin. Green tea and EGCG exhibit multifaceted anticancer effects and hold significant potential to support leukaemia therapy by modulating molecular, immunological, and epigenetic pathways. Nevertheless, further empirical research and clinical investigations are essential to comprehensively assess the bioavailability, efficacy, safety, and appropriate dosing protocols of green tea catechins. Various nano-formulations are being employed to enhance the bioavailability and efficacy of tea catechins. Furthermore, research should concentrate on identifying the regulatory mechanisms of plant-derived bioactive compounds on cancer epigenetics, with the objective of enhancing the efficacy of current anti-cancer therapies while reducing adverse effects.
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Contributorsʼ Statement
Conceptualization and design of the work: L. M. and R. B.; data collection: L. M., K.M, W. M., P. B. and R. B.; analysis and interpretation of the data: L. M., K. M., W. M., P. B., M. S. and A. J. B.; drafting the manuscript: L. M., K.M, W. M., M. S. and R. B.; critical revision of the manuscript: I. J.M, T. B. and R. B.
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Conflict of Interest
The authors declare that they have no conflict of interest.
Acknowledgements
During the preparation of this work, the author used an AI tool called DeepL Write to check the linguistic accuracy of chosen text fragments. After using this tool, the author reviewed and edited the content as needed and takes full responsibility for the content of the publication.
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Correspondence
Publication History
Received: 09 October 2024
Accepted: 27 January 2025
Article published online:
18 February 2025
© 2025. Thieme. All rights reserved.
Georg Thieme Verlag KG
Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany
-
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- 42 Tsai CY, Chen CY, Chiou YH, Shyu HW, Lin KH, Chou MC, Huang MH, Wang YF. Epigallocatechin-3-gallate suppresses human herpesvirus 8 replication and induces ROS leading to apoptosis and autophagy in primary effusion lymphoma cells. Int J Mol Sci 2017; 19: 16
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- 44 Oh JW, Muthu M, Pushparaj SSC, Gopal J. Anticancer therapeutic effects of Green Tea Catechins (GTCs) when integrated with antioxidant natural components. Molecules 2023; 28: 2151
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