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BackgroundThis phase I/II trial in patients with recurrent glioblastoma (GBM) evaluates the safety and preliminary efficacy of marizomib, an irreversible pan-proteasome inhibitor that crosses the blood-brain barrier.MethodsPart A assessed the safety and efficacy of marizomib monotherapy. In Part B, escalating doses of marizomib (0.5-0.8 mg/m2) in combination with bevacizumab were evaluated. Part C explored intra-patient dose escalation of marizomib (0.8-1.0 mg/m2) for the combination.ResultsIn Part A, 30 patients received marizomib monotherapy. The most common AEs were fatigue (66.7%), headache (46.7%), hallucination (43.3%), and insomnia (43.3%). One patient (3.3%) achieved a partial response. In Part B, the recommended phase II dose of marizomib was 0.8 mg/m2 when combined with bevacizumab 10 mg/kg. In Part C, dose escalation to 1.0 mg/m2 was not tolerated. Pooled analysis of 67 patients treated with marizomib ≤0.8 mg/m2 and bevacizumab showed a nonoverlapping safety profile consistent with the known safety profile of each agent: the most common grade ≥3 AEs were hypertension (16.4%), confusion (13.4%), headache (10.4%), and fatigue (10.4%). The overall response rate was 34.3%, including 2 patients with complete response. Six-month progression-free survival was 29.8%; median overall survival was 9.1 months.ConclusionsThe safety profile of marizomib as monotherapy and in combination with bevacizumab was consistent with previous observations that marizomib crosses the blood-brain barrier. Preliminary efficacy did not demonstrate a meaningful benefit of the addition of marizomib to bevacizumab for the treatment of recurrent GBM.

BackgroundThe proteasome plays a vital role in the physiology of glioblastoma (GBM), and proteasome inhibition can be used as a strategy for treating GBM. Marizomib is a second-generation, irreversible proteasome inhibitor with a more lipophilic structure that suggests the potential for penetrating the blood-brain barrier. While bortezomib and carfilzomib, the 2 proteasome inhibitors approved for treatment of multiple myeloma, have little activity against malignant gliomas in vivo, marizomib could be a novel therapeutic strategy for primary brain tumors.MethodsThe in-vitro antitumor activity of marizomib was studied in glioma cell lines U-251 and D-54. The ability of marizomib to cross the blood-brain barrier and regulate proteasome activities was evaluated in cynomolgus monkeys and rats. The antitumor effect of marizomib in vivo was tested in an orthotopic xenograft model of human GBM.ResultsMarizomib inhibited the proteasome activity, proliferation, and invasion of glioma cells. Meanwhile, free radical production and apoptosis induced by marizomib could be blocked by antioxidant N-acetyl cysteine. In animal studies, marizomib distributed into the brain at 30% of blood levels in rats and significantly inhibited (>30%) baseline chymotrypsin-like proteasome activity in brain tissue of monkeys. Encouragingly, the immunocompromised mice, intracranially implanted with glioma xenografts, survived significantly longer than the control animals (P < .05) when treated with marizomib.ConclusionsThese preclinical studies demonstrated that marizomib can cross the blood-brain barrier and inhibit proteasome activity in rodent and nonhuman primate brain and elicit a significant antitumor effect in a rodent intracranial model of malignant glioma.

Glioblastoma multiforme (GBM) is a highly aggressive brain tumor, which displays innate resistance to multiple treatment modalities. Previous studies have shown that proteasome inhibition can be used as a strategy for treating this malignancy. Marizomib (NPI-0052) is a second generation irreversible proteasome inhibitor, which has a more lipophilic structure and has a broader and more prolonged inhibition profile for 20S proteasome activities compared to bortezomib and carfilzomib. While bortezomib and carfilzomib have only modest activity in gliomas, marizomib might potentially be a novel therapeutic strategy for primary brain tumors. In these studies, we investigated the in vitro activities of marizomib in primary glioma cultures, neural stem/progenitor cells (NSC) and as well as in established human malignant glioma lines. The effect of marizomib on cell proliferation, proteasome activity, motility, apoptosis and Reactive Oxygen Species (ROS) were evaluated in glioma cell lines. The sensitivities varied in function of the pathology of the tumor, with the malignant glioma stem-like cells being the most severely affected, in contrast with the low-grade glioma and NSC-derived cultures. Marizomib inhibited the proliferation of U251-MG and D54-MG cell lines with a half maximal effective concentration (EC50) of 52nM and 20nM respectively, along with a significant decrease in cell migration and invasion. Marizomib treatment of human glioma cells was associated with increased ROS production and apoptosis, along with activation of caspase-3 and cleavage of PARP. Those effects of marizomib can be suppressed by exposure to the ROS quenching agent N-acetyl cysteine (NAC). These preclinical studies demonstrate a significant anti-glioma effect of marizomib. Marizomib has relatively little effect on neural stem/progenitor cells suggesting minimal neurotoxicity. But importantly, unlike bortezomib and carfilzomib, marizomib can cross the blood brain barrier. Additional research into the use of marizomib in malignant gliomas orthotropic models is in progress and will be presented during the meeting.