Breaking Immune Tolerance For The Treatment Of Glioblastoma: Phase Iib Clinical Trial Experience.

71 Background: Intratumoral heterogeneity (IH) resulting in the temporal and spatial diversification of tumor subclones. IH occurs progressively during tumor development inherent to the individual predilection to mutation and in the face of counterselections by exogenous therapies and/or endogenous immune surveillance. The xenogenization is countered by immunosuppression via overexpression of TGF-β. Here we compare the use of temozolomide (TMZ) and OT-101/TMZ to break immune tolerance to glioblastoma (GBM) for the cure. OT-101 is an antisense against TGF-β2. Methods: This is a phase IIb, multi-national, multi-center, open-label, active-controlled, randomized parallel group dose-finding study to evaluate the efficacy and safety of OT-101 in adult patients with recurrent high-grade glioma, administered intratumorally as continuous high-flow microperfusion over a 7-day period every other week. A total of 134 patients, 89 patients in the OT-101 test group and 45 patients in the standard chemotherapy (TMZ) control group were assessed. Results: Multiple rounds of TMZ broke the immune tolerance as shown by increase in overall survival (OS). mOS increased from 5.6 mos, 7.9 mos, to 36.6 mos with 1 round, 2 rounds, and 3 rounds of TMZ, respectively (p<0.0001). For OT-101, mOS increased from 4.6 mos to 21.6 mos with just one round of TMZ (p<0.0001) reducing the negative side effects of TMZ. Treatment sequencing was important as lead-in OT101 followed with subsequent TMZ was more effective than TMZ prior to OT-101 (26.2 mos vs. 4.8 mos, p<0.0001). Conclusions: The MOA for OT-101/TMZ is consistent with the reactivation of immunity during TGF-β suppression and subsequent boosting/expansion of immunity during TMZ. Contrary to traditional tumor vaccine- this is universally applicable to all patients.