Phase 1 Clinical Trial of NPI-0052, a Novel Proteasome Inhibitor in Patients with Multiple Myeloma

Background: NPI-0052 is a novel proteasome inhibitor that produces prolonged inhibition of all three catalytic activities (C-L, T-L, CT-L) of the 20S proteasome. Preclinical data suggest NPI-0052 may demonstrate an improved therapeutic ratio, with significant activity in hematologic and solid tumor malignancies including multiple myeloma (MM) resistant to bortezomib and other agents (Chauhan et al, Blood 2006). Studies have therefore been initiated in patients with multiple myeloma, lymphoma, leukemia and solid tumors.

Materials and Methods: This Phase 1 dose escalation study evaluated NPI-0052 monotherapy in patients with relapsed and relapsed/refractory MM, including those that have received bortezomib and/or lenalidomide. Patients were assessed for safety, pharmacodynamics (including ex vivo proteasome inhibition), plasma pharmacokinetics (PK), and clinical activity (with response assessed by modified EBMT criteria). Patients were treated with NPI-0052 administered as a weekly IV injection on Days 1, 8 and 15 every 4 weeks with concomitant hydration. The dose of NPI-0052 was escalated in cohorts of 3 patients dependent on observed adverse events utilizing a 3+3 design. Proteasome inhibition and PK were assayed after the 1^st and 3^rd dose and upon any intra-patient dose escalation. Proteasome inhibition was also assessed in CD138 positive cells isolated from bone marrow aspirates obtained at baseline and after the 3^rd dose in a subset of patients.

Preliminary Results: To date, 10 patients have been treated at doses ranging from 0.025 mg/m² to 0.075 mg/m² without reaching an MTD. One patient experienced reversible elevation in serum creatinine that responded to drug cessation and steroids; this event may have been related to progression of his underlying light chain nephropathy (as interval worsening of renal function was noted prior to enrollment). Drug-related adverse events have been otherwise unremarkable at all dose levels tested. PK data demonstrate a rapid elimination half life (estimated to be 3–4 minutes) with clearance between 8–21 mL/min and Vz of 44–99L; no change in PK has been observed comparing the 1^st and 3^rd injection. Proteasome inhibition in whole blood suggests drug-dependent CT-L inhibition, with inhibition up to 28% observed (inhibition up to 100% at doses of up to 0.7 mg/m² has been observed in other clinical trials with NPI-0052 without producing the profile of toxicity reported with standard doses of bortezomib). Whilst no responses have been confirmed, two patients with relapse/refractory MM remained on study for over 6 months and one year, respectively, with stable disease and no significant toxicity. Importantly, no peripheral neuropathy or myelosuppression has been seen in 41 treatment cycles in patients to date.

Conclusions: In patients with relapsed and relapsed, refractory MM, NPI-0052 affects parameters relevant to pharmacodynamics, PK and demonstrated potential clinical benefit at doses well below the MTD anticipated from Phase 1 clinical trials with NPI-0052 in lymphoma and solid tumors. Drug administration to date has been well tolerated. Dose escalation continues to define DLT and MTD, and to recommend a phase 2 dose for further study in patients with advanced MM.