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Background The overexpression of (basic)helix-loop-helix ((b)HLH) transcription factors (TFs) is frequent in malignant glioma. We investigated molecular effects upon disruption of the (b)HLH network by a dominant-negative variant of the E47 protein (dnE47). Our goal was to identify novel molecular subgroup-specific therapeutic strategies. Methods Glioma cell lines LN229, LNZ308, and GS-2/GS-9 were lentivirally transduced. Functional characterization included immunocytochemistry, immunoblots, cytotoxic, and clonogenic survival assays in vitro, and latency until neurological symptoms in vivo. Results of cap analysis gene expression and RNA-sequencing were further validated by immunoblot, flow cytometry, and functional assays in vitro. Results The induction of dnE47-RFP led to cytoplasmic sequestration of (b)HLH TFs and antiglioma activity in vitro and in vivo. Downstream molecular events, ie, alterations in transcription start site usage and in the transcriptome revealed enrichment of cancer-relevant pathways, particularly of the DNA damage response (DDR) pathway. Pharmacologic validation of this result using ataxia telangiectasia and Rad3 related (ATR) inhibition led to a significantly enhanced early and late apoptotic effect compared with temozolomide alone. Conclusions Gliomas overexpressing (b)HLH TFs are sensitive toward inhibition of the ATR kinase. The combination of ATR inhibition plus temozolomide or radiation therapy in this molecular subgroup are warranted.

RATIONALE Herpes virus thymidine kinase (HSV-TK) suicide gene therapy is a well-established approach for in situ tumor cell killing after administration of ganciclovir (GCV), due to the induction of lethal DNA damage in HSV-TK expressing cells. Here we investigated the effects of HSV-TK gene delivery with a non-replicating serotype 5 adenovirus (AdTK) in murine glioblastoma models in combination with the ATR-inhibitor AZD6738 to disrupt the DNA damage response (DDR). METHODS We investigated the effects of disrupted DDR signaling on AdTK therapy in vitro using cytotoxicity, cytokine and flow cytometry assays in glioblastoma cell lines and in vivo with an orthotopic syngeneic murine glioblastoma model. Therapy response was monitored with MRI. Changes in the tumor microenvironment were analyzed with CyTOF. RESULTS The combination of AZD6738 with AdTK was synergistic in cytotoxicity assays, which was complemented by a significant increase of γH2AX foci. Complex modulations of the tumor microenvironment were observed with significantly reduced expression of PD-L1, MICA/B and the pro-tumorigenic cytokines IL1b and IL-4. In vivo, the combination with AZD6738 led to an increase in long-term surviving animals (66.7%) compared to GMCI (50%) and proved to be highly significant in contrast to untreated controls (p=0.0022). However, the combination treatment did not block the growth of tumors upon rechallenge in long-term survivors. CONCLUSION DDR signaling is crucial in the therapeutic efficacy of AdTK/GCV. It significantly enhances cytotoxicity in vitro and in vivo while having complex ramifications at the immunological level, requiring further studies to determine ideal conditions for a maximized therapeutic benefit.

Background The impact of prolonging temozolomide (TMZ) maintenance beyond six cycles in newly diagnosed glioblastoma (GBM) remains a topic of discussion. We investigated the effects of prolonged TMZ maintenance on progression-free survival (PFS) and overall survival (OS). Patients and methods In this retrospective single-center cohort study, we included patients with GBM who were treated with radiation therapy with concomitant and adjuvant TMZ. For analysis, patients were considered who either completed six TMZ maintenance cycles (group B), continued with TMZ therapy beyond six cycles (group C), or stopped TMZ maintenance therapy within the first six cycles (group A). Patients with progression during the first six TMZ maintenance cycles were excluded. Results Clinical data from 107 patients were included for Kaplan-Meier analyses and 102 for Cox regressions. Median PFS times were 8.1 months (95% confidence interval [CI] 6.1-12.4) in group A, 13.7 months (95% CI 10.6-17.5) in group B, and 20.9 months (95% CI 15.2-43.5) in group C. At first progression, response rates of TMZ/lomustine rechallenge were 47% in group B and 13% in group C. Median OS times were 12.7 months (95% CI 10.3-16.8) in group A, 25.2 months (95% CI 17.7-55.5) in group B, and 28.6 months (95% CI 24.4-open) in group C. Nevertheless, multivariate Cox regression for patients in group C compared with group B that accounted for imbalances of other risk factors showed no different relative risk (RR) for OS (RR 0.77, p = .46). Conclusion Our data do not support a general extension of TMZ maintenance therapy beyond six cycles. The Oncologist 2017;22:570-575 IMPLICATIONS FOR PRACTICE: Radiation therapy with concomitant and adjuvant temozolomide (TMZ) maintenance therapy is still the standard of care in patients below the age of 65 years in newly diagnosed glioblastoma. However, in clinical practice, many centers continue TMZ maintenance therapy beyond six cycles. The impact of this continuation is controversial and has not yet been addressed in prospective randomized clinical trials. We compared the effect of more than six cycles of TMZ in comparison with exactly six cycles on overall survival (OS) and progression-free survival (PFS) by multivariate analysis and found a benefit in PFS but not OS. Thus, our data do not suggest prolonging TMZ maintenance therapy beyond six cycles, which should be considered in neurooncological practice.