James, C. David

Abstract Background Acquired resistance to temozolomide (TMZ) chemotherapy due to DNA mismatch repair (MMR) enzyme deficiency is a barrier to improving outcomes for isocitrate dehydrogenase (IDH) wild-type glioblastoma (GBM) patients. KL-50 is a new imidazotetrazine-based therapeutic designed to induce DNA interstrand cross-links, and subsequent double-stranded breaks, in an MMR-independent manner in cells with O-6-methylguanine-DNA methyltransferase (MGMT) deficiency. Previous research showed its efficacy against LN229 glioma cells with MMR and MGMT knockdown. Its activity against patient-derived GBM that model post-TMZ recurrent tumors is unclear. Methods We created MMR-deficient GBM patient-derived xenografts through exposure to TMZ, followed by treatment with additional TMZ or KL-50. We also generated isogenic, MSH6 knockout (KO) patient-derived GBM and tested them for sensitivity to TMZ and KL-50. Results KL-50 extended the median survival of mice intracranially engrafted with either patient-derived TMZ-naïve GBM6 or TMZ-naïve GBM12 by 1.75-fold and 2.15-fold, respectively (P < 0.0001). A low dose (4 Gy) of fractionated RT further extended the survival of KL-50-treated GBM12 mice (median survival = 80 days for RT + KL-50 vs. 71 days KL-50 alone, P = 0.018). KL-50 also extended the median survival of mice engrafted with post-TMZ, MMR-deficient GBM6R-m185 (140 days for KL-50 vs. 37 days for vehicle, P < 0.0001). MSH6 KO increased TMZ IC50 for GBM6 and GBM12 cultures by >5-fold and >12-fold for cell death and live cell count outputs, respectively. In contrast, MSH6-KO actually decreased KL-50 IC50 by 10–80%. Conclusion KL-50-based compounds are a promising new strategy for the treatment of MGMT-deficient, MMR-deficient GBM that recurs after frontline TMZ.

Abstract Gliomas with mutations in isocitrate dehydrogenase 1 (IDH1mut) have global genomic hypermethylation, are less aggressive than IDH1 wild-type (IDH1wt) gliomas, and generally grow poorly in vitro and in vivo. Yet little data exist that connect specific hypermethylation events to this unique phenotype. We previously reported that the gene encoding Tissue Factor (TF), F3, is among the most hypermethylated and downregulated genes in IDH1mut gliomas relative to IDH1wt gliomas. TF was originally described in blood coagulation, but also can enhance tumor malignancy via protease-activated receptor 2 (PAR2) signaling, though its role in gliomas is not as well understood. In this study, we further explored the significance of TF on malignancy in IDH1wt and IDH1mut gliomas, and showed that receptor tyrosine kinases (RTKs) and β-catenin are downstream effectors of TF-PAR2 signaling. Studies were performed using 6 patient derived glioma cell lines, 3 IDH1wt (GBM6, GBM12, GBM43) and 3 IDH1mut (TB09, BT142, GBM164). DNA methylation was assessed by Illumina Human 850K. TF procoagulant activity (PCA) was determined by FXa generation, using conditioned medium. Markers of malignancy included BrdU incorporation for cell proliferation, transwell invasion, and soft agar colony formation. Nude mice (N≥6/group) were transplanted with glioma cells and monitored for growth using bioluminescence imaging. The TF gene, F3, was significantly hypermethylated in IDH1mut cells compared to IDH1wt cells, with corresponding lower TF protein in IDH1mut cells. Treatment of IDH1mut glioma cells with a demethylating agent, decitabine, increased F3 transcription 5-fold and PCA 19-fold in IDH1mut cells. TF increased the in vivo "take rate" of IDH1mut GBM164 from 0% to 100% (P=0.0001, Fisher's exact test). Conversely, TF knockdown in IDH1wt cells greatly reduced cell proliferation, invasion, colony formation, and extended median survival of engrafted mice by 86% (P=0.001). In both IDH1wt and IDH1mut cells, TF-PAR2 activated β-catenin, ERK1/2, and Akt, and was associated with multiple pathways that increase high-grade behavior. Disrupting TF-PAR2 signaling had the greatest impact on tumor growth in IDH1wt gliomas driven by epidermal growth factor receptor (EGFR), a major receptor tyrosine kinase (RTK) involved in glioma malignancy. TF-PAR2 transactivated EGFR through a Src-dependent intracellular pathway, even when extracellular stimulation of EGFR was blocked, and further enhanced phosphorylation of the constitutively activated EGFRvIII. In IDH1mut cells, TF-PAR2 signaled through another RTK, PDGFR. In contrast, TF-PAR2 stimulated invasion in all glioma cell lines through an RTK-independent, β-catenin-dependent mechanism. These results demonstrate the importance of TF-PAR2 in gliomas, and show that its suppression is a critical component of the IDH1mut phenotype. Citation Format: Dusten J. Unruh, Snezana Mirkov, Seamus Caragher, Jann Sarkaria, Atique Ahmed, C. David James, Craig Horbinski. Methylation-dependent suppression of Tissue Factor is a key contributor to the less aggressive phenotype in IDH1 mutant versus IDH1 wild-type gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5443.