Cytotoxic activity of the native Australian plant Acacia ligulata

This study forms part of an ongoing investigation into the phytochemistry and pharmacological activities of the native Australian plant Acacia ligulata. Leaves and bark of the plant has been used as a traditional medicine for cough, colds and general illness whereas the seeds have been eaten and described to “make your hair fall off”. Only a few bioactivity studies have included A. ligulata, however none have investigated the plant for its cytotoxic activities.

Crude extracts of leaves, bark and different developmental stages of seedpods and seeds were prepared using 80% ethanol. The extracts were tested against a panel of cancer cell lines including melanoma, breast and leukaemia. A tetrazolium-based (MTS) assay was used to screen for active extracts and calculate IC₅₀ values and active extracts were further validated using the Sulforhodamine B cell viability assay.

Bark and seedpod extracts showed cell toxicity effects against a melanoma cell line with IC₅₀ values from 37.9 – 131.8 µg/mL for the MTS assay with similar results obtained from the Sulforhodamine B assay with IC₅₀ values of 38.4 – 134.7 µg/mL. Chromatographic profiles of the crude extracts were obtained using Liquid Chromatography/Mass Spectrometry (LC/MS), which indicated a similar chemical profile of the different stages of seedpod growth. Further activity-guided fractionation was performed with the mature seedpod extract that gave the best IC₅₀ value in the screening.

The crude extract has further been fractionated by solid phase extraction (SPE) and centrifugal radial thin-layer chromatography to identify active fractions. Additional fractionation by HPLC will be performed in order to purify active compounds, which will be analysed by structural elucidation techniques. Through this study it has been shown that crude extracts of bark and seedpods of A. ligulata have cytotoxic activity against melanoma cells and may contain novel cytotoxic compounds.