Enhancement of radiation effects by combined treatment with 5-aza-2'-deoxycytidine and differentiation-inducing or epigenetic drugs in human MB cells

Medulloblastoma (MB) is the most common pediatric brain tumor. MB therapy includes surgery followed by irradiation and/or chemotherapy. However, survival rates remain poor with a 5-year survival of approximately 60%. Especially for patients with moderate or poor prognosis (about 90% of all MB patients), an improved therapy is urgently needed. In case of low-risk patients (5-year survival up to 95%), the current therapy has to be further developed to reduce adverse effects, like neurocognitive and endocrine disorders.

In this study, we tested the combination of epigenetic mediators (5-aza-2'-deoxycytidine, valproic acid, SAHA), differentiation inducers (retinoic acid, abacavir, resveratrol), and ionizing irradiation on the clonogenic survival of human MB cell lines.

Three human MB cell lines (DAOY, MEB-Med8a, D283-Med) were treated with 5-aza-2'deoxycytidine (5-aza-dC) alone or in combination for six days. Irradiation (IR) with 2 or 8 Gy was applied after three treatment days. In clonogenic assays the IC 90 values (concentration leading to 90% inhibition of clonogenic survival) were evaluated for the single compounds and then used in combination experiments.

We observed that 5-aza-dC (IC 90) radiosensitize human MB cells by reducing their clonogenic fraction 10- to 50-fold after 2 Gy. The triple combination of 5-aza-dC, 2 Gy, and one of the examined drugs mostly diminished the clonogenic survival further. Thereby, the strongest synergisms were found with abacavir or resveratrol added. Resveratrol enhanced the effect of 5-aza-dC/2 Gy between 100-fold (D283-Med, MEB-Med8a) and 10,000-fold (DAOY). This is of special interest because of the fact that the p53-mutated DAOY cells are most resistant to IR and 5-aza-dC treatment, and possibly depicts an interesting treatment option especially for highly aggressive MB tumor subtypes.

Using human MB cell lines, we could define a multimodal treatment option for MB patients, which we will translate into an orthotopic MB mouse model to be confirmed in-vivo.

An update on the current status and feasibility of the program, as well as future perspectives are presented.

Funding: National Center for Tumor Diseases – Interdisciplinary Research Program (NCT-IFP).