O -methylguanine DNA methyltransferase (MGMT) promoter methylation is a predictive biomarker for benefit from alkylating chemotherapy, specifically temozolomide (TMZ), in glioblastoma, the most common malignant intrinsic brain tumor. Glioma-initiating cells (GIC) with stem-like properties have been associated with resistance to therapy and progression. We assessed the levels of MGMT mRNA and MGMT protein by real-time PCR and immunoblot and evaluated the impact of MGMT on TMZ sensitivity in clonogenicity assays in GIC sphere cultures (S) or differentiated adherent monolayer cultures (M). Nuclear factor kappa B (NF-κB) signaling was assessed by reporter assay and immunoblot. Compared to M cells, S cells expressed higher levels of MGMT. Differentiation of GIC induced by S-to-M transition resulted in a gradual loss of MGMT expression and increased TMZ sensitivity. This transcriptional regulation of MGMT was restricted to cell lines without MGMT promoter methylation and was not coupled to any specific neurobasal (NB) stem cell medium supplement or loss of cell adhesion. Expression levels of p50/p65 subunits of NF-κB, a transcriptional regulator of MGMT, were increased in S cells. Inhibition of NF-κB by the small molecule inhibitor, BAY 11-7082, or siRNA-mediated gene silencing, reduced MGMT levels. In summary, alkylator resistance of S cells is mainly promoted by over-expression of MGMT which results from increased activity of the NF-κB pathway in this cell culture model of glioma stem-like cells. Read the Editorial Highlight for this article on page 688.

Glioblastoma is the most aggressive brain tumor in adults with a median survival below 12 months in population-based studies. The main reason for tumor recurrence and progression is constitutive or acquired resistance to the standard of care of surgical resection followed by radiotherapy with concomitant and adjuvant temozolomide (TMZ/RT→TMZ). Here, we investigated the role of microRNA (miRNA) alterations as mediators of alkylator resistance in glioblastoma cells. Using microarray-based miRNA expression profiling of parental and TMZ-resistant cultures of three human glioma cell lines, we identified a set of differentially expressed miRNA candidates. From these, we selected miR-138 for further functional analyses as this miRNA was not only upregulated in TMZ-resistant versus parental cells, but also showed increased expression in vivo in recurrent glioblastoma tissue samples after TMZ/RT→TMZ treatment. Transient transfection of miR-138 mimics in glioma cells with low basal miR-138 expression increased glioma cell proliferation. Moreover, miR-138 overexpression increased TMZ resistance in long-term glioblastoma cell lines and glioma initiating cell cultures. The apoptosis regulator BIM was identified as a direct target of miR-138, and its silencing mediated the induced TMZ resistance phenotype. Altered sensitivity to apoptosis played only a minor role in this resistance mechanism. Instead, we identified the induction of autophagy to be regulated downstream of the miR-138/BIM axis and to promote cell survival following TMZ exposure. Our data thus define miR-138 as a glioblastoma cell survival-promoting miRNA associated with resistance to TMZ therapy in vitro and with tumor progression in vivo.

Aims Aberrant expression of microRNAs (miRNAs) is frequent in various cancers including gliomas. We aimed to characterize the role of miR‐16‐5p as a candidate tumour suppressor miRNA in gliomas. Methods Real‐time PCR‐based approaches were used for miRNA and mRNA expression profiling of glioma and non‐neoplastic brain tissues as well as glioma cell lines. Protein levels were determined by Western blotting. In vitro analyses were performed following overexpression of miR‐16‐5p, trichostatin A (TSA) treatment, and siRNA‐mediated knock‐down of HDAC3 in glioma cells. Effects of miR‐16‐5p on glioma cell viability, apoptosis and response to irradiation and temozolomide (TMZ) were assessed. Results Expression of miR‐16‐5p was reduced relative to control brain tissue in isocitrate dehydrogenase (IDH)‐mutant astrocytomas of World Health Organization (WHO) grades II, III and IV, and a subset of IDH‐wildtype glioblastomas WHO grade IV. MiR‐16‐5p expression was lower in IDH‐mutant than in IDH‐wildtype gliomas, and down‐regulated in IDH‐wildtype glioma lines. MiR‐16‐5p overexpression reduced expression of important cell cycle and apoptosis regulators in glioma cells, including CDK6, CDC25A, CCND3, CCNE1, WEE1, CHEK1, BCL2 and MCL1. In line, CDK6, WEE1, CHEK1, BCL2 and MCL1 transcript levels were increased in WHO grade III or IV gliomas. TSA treatment and HDAC3 knockdown in glioma cells induced miR‐16‐5p up‐regulation and reduced expression of its targets. Moreover, miR‐16‐5p overexpression inhibited proliferation and induced apoptosis in various glioma cell lines and increased sensitivity of A172 glioma cells to irradiation and TMZ. Conclusion Reduced expression of miR‐16‐5p contributes to glioma cell proliferation, survival and resistance to cytotoxic therapy.

BackgroundNeoadjuvant chemotherapy (CT) followed by radiotherapy (RT) and surgery showed a median survival of 28.7 months in resectable stage IIIB non-small-cell lung cancer (NSCLC) patients (pts). Here, we evaluate the impact of concomitant cetuximab to the same neoadjuvant chemo-radiotherapy (CRT) in selected patients (pts) with NSCLC, stage IIIB.MethodsResectable stage IIIB NSCLC received three cycles of CT (cisplatin 100 mg/m2 and docetaxel 85 mg/m2 d1, q3w) followed by RT (44 Gy in 22 fractions) with concomitant cetuximab (250 mg/m2, q1w) and subsequent surgery. The primary endpoint was 1-year progression-free survival (PFS).ResultsSixty-nine pts were included in the trial. Fifty-seven (83%) pts underwent surgery, with complete resection (R0) in 42 (74%) and postoperative 30 day mortality of 3.5%. Responses were: 57% after CT-cetuximab and 64% after CRT-cetuximab. One-year PFS was 50%. Median PFS was 12.0 months (95% CI: 9.0–15.6), median OS was 21.3 months, with a 2- and 3-yr survival of 41% and 30%, respectively.ConclusionsThis is one of the largest prospective phase 2 trial to investigate the role of induction CRT and surgery in resectable stage IIIB disease, and the first adding cetuximab to the neoadjuvant strategy. This trial treatment is feasible with promising response and OS rates, supporting an aggressive approach in selected pts.