S. Food and Drug Administration (FDA) for the treatment of myelodysplastic syndrome since 2006. 5-Aza-dC is known to reactivate silenced TSG by demethylation of their promoter regions in MB and other tumor cells after incorporation into the DNA during the replication process [8–10]. DNA-integrated

5-aza-dC traps de novo methyltransferases (DNMT) and induces DNA damage including double-strand breaks (DSB) [11, 12]. We have recently shown that 5-aza-dC treatment of human MB cells reduces their vitality, proliferation rate, and clonogenic GS-1101 solubility dmso survival significantly [8]. Others have described similar effects in leukemia and lung cancer cell lines [13, 14]. VPA, an HDACi, has already been established in the treatment of epilepsy and depression, and clinical trials for its application in HIV and cancer patients are ongoing. VPA leads to hyperacetylation

of histone proteins resulting in activation of cell cycle arrest and apoptosis in human MB cells [15]. In xenograft MB mouse models, it was shown that VPA alone reduces tumor growth and prolonges survival [16]. It was also reported that combinatorial treatment with 5-aza-dC and VPA is able to diminish tumor initiation in a Ptch-deficient MB mouse model [17]. SAHA (vorinostat, Zolinza™) is the first HDACi approved by the FDA for cancer treatment. SAHA directly interacts with the catalytic domain of histone deacetylases [18]. As a result, gene promoter-bound histones stay Ferrostatin-1 clinical trial hyperacetylated and facilitate the selective transcription of genes [19]. Additionally, SAHA exerts chemosensitizing effects in oral squamous cell carcinoma and medulloblastoma cells [20, 21]. Abacavir, a 2-deoxyguanine analog, is approved for HIV and AIDS therapy in the EU since 1999. Two ways of an abacavir-mediated reduction of telomerase activity are reported: 1) indirect, by incorporation into the DNA strand which leads to polymerization stop [22], and 2) direct, by downregulation

of hTERT (human gene for telomerase reverse transcriptase) mRNA transcription [3]. In recent years, abacavir attracted attention for cancer therapy for its ability to inhibit telomerase activity, which however is known to be overexpressed in the vast majority of cancers [23]. Also in 70% of MBs, telomerase activity is enhanced in contrast to normal cerebellum [24]. It was previously shown that treatment of human MB cell lines with abacavir results in proliferation inhibition and neuronal differentiation [3]. ATRA is the prototype of differentiation therapy in cancer cells and, therefore, it is approved for treatment of acute promyelocytic leukemia (APL) in the EU since 1996. Inhibition of proliferation and induction of apoptosis and differentiation have been observed in many tumor cells including MB cells after treatment with ATRA [25–30]. Resveratrol, a plant polyphenol, is described to exhibit tumor-preventive as well as anticancer effects dependent on concentration, cell type, and microenvironment [31–33].