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.

Abstract MRZ – an irreversible, brain-penetrant, pan-proteasome inhibitor with anti-glioma preclinical activity – was evaluated in BEV-naïve rGBM patients.

METHODS

Phase 1 (P1) MRZ+BEV, 3 + 3 MRZ dose-escalation (N=6, 3, 3 at 0.55, 0.7, 0.8 mg/m2) followed by dose-expansion (N=24, 0.8 mg/m2). Phase 2 (P2) MRZ monotherapy (N=30, 0.8 mg/m2). Treatments (IV, 28-day (D) cycles): MRZ (10min infusion) D1, 8, 15; BEV (10 mg/kg) D1, 15. Tumor response (RANO criteria) every other cycle; MRZ and BEV PK, and proteasome inhibition in blood evaluated in P1.

RESULTS

as of 14Apr2017: P1 mean age 55 yrs, 64% male, mean treatment duration 5.3 cycles, 1 patient active; P2 56 yrs, 57% male, 2.5 cycles, 6 patients active. One DLT (fatigue) in P1 at 0.55 mg/m2, no other DLTs. P1 treatment-related AEs (TRAEs Grade ≥3 in ≥2 patients): hypertension, headache, confusional state, fatigue, hallucination, proteinuria; three Grade 4 SAEs (appendicitis perforated, depressed level of consciousness, not-related; blindness, BEV-related), three Grade 5 SAEs (2 PD, not-related; intracranial hemorrhage, BEV-related). P2 TRAEs (Grade ≥3 in ≥2 patients): fatigue, hallucination, lethargy; one Grade 4 SAE (hallucination). P1 overall response (≥PR) 44% (16/36) including 1 CR, 15 PR; overall survival (OS) at 6/9/12 months (mos) 75/60/39%, median 9.4mos; OS 68/45/15% (median 7.2mos) in unmethylated MGMT (uMGMT, N=22), 78/78/67% (median not reached) in methylated MGMT (N=10). In P2: 1 PR, 6 SD; 4 patients (3 SD, 1 PR) ongoing at 5–10 cycles. P1 patients experiencing ≥1 CNS-related AEs (any grade: ataxia/balance disorder/dizziness/dysarthria/fall/gait disturbance/hallucination) have increased OS (83/74/45%, median 11.4mos, N=23) versus patients without these AEs (59/34/25%, median 6.3mos, N=13).

CONCLUSIONS

MRZ monotherapy and MRZ+BEV active in rGBM overall and in uMGMT. Possible therapeutic improvement in patients experiencing CNS AEs will be explored in ongoing P2 MRZ+BEV extension allowing intra-patient MRZ dose-escalation if no CNS AE in first cycle (0.8 mg/m2).

Background

The 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.

Methods

The 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.

Results

Marizomib 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.

Conclusions

These 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.

Background

This 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.

Methods

Part 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.

Results

In 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.

Conclusions

The 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.

Abstract Proteasome inhibition sensitizes glioma cells to TMZ and RT, providing a novel therapeutic strategy for ndGBM. MRZ -- an irreversible, brain-penetrant, pan-proteasome inhibitor with anti-glioma preclinical activity -- is being evaluated in ndGBM patients (NCT02903069). The phase 1 study (MRZ at 0.55, 0.7, 0.8, 1.0, and 1.2 mg/m2) is accruing in separate concomitant (MRZ+TMZ+RT) and adjuvant (MRZ+RT) treatment cohorts (3 + 3 design), followed by dose-expansion at the recommended phase 2 dose in concomitant followed by adjuvant treatment cohorts. Concomitant treatment (42 days (D)): MRZ (10 min IV infusion) D1, 8, 15, 29, 36; RT total dose 60 Gy; TMZ (75 mg/m2, PO QD). Adjuvant treatment (28D-cycle): MRZ D1, 8, 15; TMZ (150–200 mg/m2, PO QDX5). Tumor response (RANO criteria) measured at beginning and end of concomitant treatment, and every other cycle during adjuvant treatment; MRZ and TMZ PK in concomitant treatment D1-2, 8–9. Mean age 55 yrs (60% male) for 20 patients in 14Apr2017 interim analysis (cohorts 1–3 have completed accrual in concomitant treatment, cohorts 1 and 2 have completed accrual and 2 patients are enrolled in adjuvant cohort 3); one DLT (fatigue) in the 0.7 mg/m2 adjuvant cohort. Most common treatment-related AEs (≥4 pts): fatigue, nausea, vomiting, decreased appetite, dizziness, hallucination; three Grade 3 SAEs (fatigue, hallucination, vomiting; all MRZ-related); two Grade 2 SAEs (nausea, confusional state, MRZ-related). Seventeen of the 20 patients included in this interim analysis remain on study: 7 of 9 concomitant patients are continuing in adjuvant treatment (longest beginning adjuvant cycle 7); of 11 adjuvant pts, two beginning cycle 9. The study is ongoing at 1.0 mg/m2 for both concomitant and adjuvant dose-escalation cohorts. Together the data demonstrate that the combination of MRZ with standard of care in ndGBM is well tolerated and may provide novel therapeutic benefit in this unmet need.