Figure 3 Combinatorial effects of 5-aza-dC with valproic acid, SAHA, abacavir, retinoic acid, and resveratrol on metabolic activity. Three medulloblastoma cell lines were treated with

5-aza-dC PLX4032 and/or indicated drugs for three days at concentrations listed in Table 1 and WST-1 test perfomed. Treated samples were normalized to the untreated control. Data show means ± SEM of at least three experiments done in triplicates. The statistical significance of differences between 5-aza-dC and combinatorial treatments is indicated by asterisks: *, p ≤ 0.05; **, p ≤ 0.001. Also, SAHA induced a concentration-dependent decrease of metabolic activity (Figure 2b). The IC 30 values were 60 nM ‒ 260 nM (MEB-Med8a,

D283-Med). After simultaneous treatment with 5-aza-dC, the metabolic activity of D283-Med and DAOY cells was only slightly reduced, compared to 5-aza-dC alone. Similarly to 5-aza-dC/VPA treatment response, MEB-Meb8a cells exhibited a significant enhancement of metabolic activity after combined treatment with SAHA (Figure 3b). Corresponding to these cell line-specific findings, differential results have also been published showing minor effects in colon carcinoma cells, but significantly Selleck C59 wnt enhanced cell death in ovarian cancer and leukemia cells after combinatorial 5-aza-dC/SAHA treatment [38–40]. Treatment of MB cells with abacavir resulted in a dose-dependent reduction of metabolic activity (Figure 2c). Thereby, D283-Med revealed to be the most resistant among the examined cell lines showing an IC 30 value of 340 μM, whereas MEB-Med8a and DAOY cells exhibited IC 30 values of 70 μM and 150 μM. The higher resistance is possibly due to a higher expression out of human telomerase reverse transcriptase (hTERT) in D283-Med cells compared to DAOY cells [3, 24]. Applying higher abacavir concentrations (350 μM to 750 μM, treated for 24 to 96 h), Rossi et al. reported that abacavir induces enhanced

mortality in D283-Med cells, but differentiation and growth arrest in DAOY cells [3]. We found here that simultaneous treatment with 5-aza-dC led to an additive response of two MB cell lines (DAOY, D283-Med) in metabolic activity (Figure 3c). This is the first time showing intensifying in vitro effects of an epigenetic modifier and a telomerase inhibitor on metabolic activity of tumor cells. Retinoic acid treatment induced differential, cell line-specific effects: MEB-Med8a cells showed no response to ATRA; DAOY cells exhibited only a moderate reduction of metabolic activity with a maximum of 30%; and in D283-Med cells, a dose-dependent reduction of metabolic activity with up to 70% inhibition could be observed (Figure 2d). This goes along with findings of other groups [28, 30, 41]. In the highly sensitive D283-Med cell line, an ATRA-mediated caspase 3 induction followed by apoptosis has been reported [28].