Abstract CT074: Phase I/II study of VAL-083 in patients with recurrent glioblastoma

Abstract Glioblastoma (GBM) is the most common brain cancer. Front-line systemic therapy with temozolomide (TMZ) is often ineffective due to O6-methylguanine-DNA-methyltransferase (MGMT)-mediated resistance and patients with recurrent glioma have limited treatment options and very poor prognosis. Dianhydrogalactitol (VAL-083) is a bi-functional alkylating agent that readily crosses the blood-brain barrier and has demonstrated activity against GBM in prior NCI-sponsored clinical trials. VAL-083 induces cross-links at N7 of guanine causing double-strand DNA breaks and apoptosis independent of MGMT expression against multiple GBM cell lines and cancer stem cells in vitro. VAL-083 cytotoxic activity also appears to be less dependent on wild type p53 compared to other alkylating agents. The main goal of this clinical trial was to determine an appropriate dose for VAL-083 for advancement to Phase II/III trials as a potential new treatment for refractory GBM. METHOD: Open-label, single-arm Phase I dose-escalation study (3+3 design) of IV treatment with VAL-083 on days 1, 2, 3 of a 21-day cycle, until MTD was reached. In Phase II, additional patients with GBM are treated at the MTD to gather further safety and outcomes data. Patients must have histologically confirmed GBM, previously treated with surgery and radiation and must have failed both TMZ and bevacizumab, unless contraindicated. RESULTS: Phase I has been completed and 40 mg/m2/d confirmed as the MTD. 29 GBM patients were enrolled in Phase I across 9 dose cohorts (1.5 - 50 mg/m2/d). Myelosuppression was mild; no drug-related serious adverse events were reported at doses ?40 mg/m2/d. Dose limiting toxicities (DLT), consisting of thrombocytopenia, were observed at 50 mg/m2/d and at an interim 45 mg/m2/d cohort. Platelet nadir occurred around day 20 and resolved rapidly and spontaneously. Pharmacokinetic analyses show dose-dependent linear systemic exposure with a short 1-2h plasma terminal half-life; average Cmax 781 ng/mL (5.3μM) at 40 mg/m2/d resulting in estimated CNS concentrations within the IC50 range observed for GBM cell-lines in vitro. A 14 patient Phase II expansion cohort was enrolled at 40 mg/m2/d. Safety observations in the Phase II expansion cohort to date are consistent with Phase I: Observed myelosuppression is mild, with the exception of 1 patient previously treated with CCNU who developed grade 4 thrombocytopenia. To date, 20 GBM patients (6 patients in Phase I and 14 patients in Phase II) have been treated with VAL-083 at therapeutic doses of 30 or 40 mg/m2/d. CONCLUSIONS: VAL-083 at 40 mg/m2/d on days 1, 2, 3 of a 21-day cycle exhibits a favorable safety profile and the Phase I part of the study showed a trend toward clinically meaningful improved survival in refractory GBM patients. Updated safety and outcomes data from the Phase II expansion cohort will be presented. ClinicalTrials.gov Identifier NCT01478178. Citation Format: Kent C. Shih, Manish R. Patel, Nicholas Butowski, Gerald S. Falchook, Sani H. Kizilbash, Jeffrey A. Bacha, Dennis M. Brown, Anne Steino, Richard Schwartz, Sarath Kanekal, Lorena M. Lopez, Howard A. Burris. Phase I/II study of VAL-083 in patients with recurrent glioblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT074.

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