Phase 1 Study Of The Novel Kinesin Spindle Protein Inhibitor ARRY-520 + Carfilzomib (Car) In Patients With Relapsed and/Or Refractory Multiple Myeloma (RRMM)

ARRY-520, a kinesin spindle protein (KSP) inhibitor, has demonstrated promising clinical activity, both as a single agent and combined with dexamethasone in patients (pts) with bortezomib- and lenalidomide-refractory MM with a single agent response rate (≥ MR) of 19-33%. The maximum tolerated dose (MTD) of ARRY-520 as a single agent was 1.5 mg/m² administered on days 1 and 2 every 2 weeks with minimal non-hematologic toxicity. Carfilzomib, an irreversible proteasome inhibitor (PI), also has demonstrated single agent activity in RRMM and received accelerated approval by the Food & Drug Administration (FDA). Preclinical data demonstrate synergy between the combination of a PI and ARRY-520 and the minimal overlapping side effect profile support the hypothesis that the combination of carfilzomib and ARRY-520 could be an attractive regimen.

The primary objective was to determine the MTD and the safety/tolerability of carfilzomib and ARRY-520 in RRMM. Secondary objectives were to determine efficacy as measured by the overall response rate (ORR), time to progression, progression free survival and time to next therapy. Pts had to be ineligible for autologous stem cell transplant (ASCT), have disease refractory/intolerant to bortezomib, and have had prior lenalidomide exposure. ARRY-520 was administered intravenously (iv) on days 1, 2, 15 and 16; carfilzomib was administered intravenously on days 1, 2, 8, 9, 15 and 16 of a 28 day cycle. All pts received growth factor support in cycle 1. Dose-escalation used a standard 3+3 schema with dose-limiting toxicities (DLTs) assessed during cycle 1. Four dose levels were studied with ARRY-520 escalated from 0.75 to 1.5 mg/m² with the approved fixed dose of carfilzomib 20/27 mg/m². Adverse events (AEs) were graded by NCI-CTCAE v4, while responses were assessed by the modified International Uniform Response Criteria.

20 pts were enrolled in the completed phase 1 dose escalation portion of the study. The median age was 61 (range 43-80), and pts had received a median of 4 lines of prior therapy (range 2-10). 16/20 pts were lenalidomide refractory/intolerant; 20/20 pts were bortezomib refractory/intolerant; and 18/20 pts had prior ASCT. Two pts in cohort 2 were not DLT evaluable due to non-compliance with study-related therapy in cycle 1 and replaced for assessment of DLT.

No DLTs were observed in 3 patients dosed in cohort 1, with ARRY-520 at 0.75 mg/m². In cohort 2, 1/6 patients encountered a DLT with influenza pneumonia and non-neutropenic fever. In cohort 3, 5 patients were enrolled, ARRY-520 was dose escalated to 1.25 mg/m², 2 patients were unevaluable for assessment of DLT, and no DLTs were encountered in the remaining 3 patients. The final planned cohort 4 was full dose ARRY-520 at 1.5 mg/m² and carfilzomib 20/27 mg/m², where 1/6 patients encountered a DLT of non-neutropenic fever and pneumonia. Therefore, the MTD of ARRY-520 with carfilzomib 20/27 mg/m² was established at 1.5 mg/m².

Among 19/20 patients evaluable for efficacy, for an ORR (≥ MR) was 58%: including nCR (n=1), uPR/PR (n=6), MR (n=4), uSD/SD (n=4) and PD (n=4). Among 20 pts enrolled to date, 10 patients remain on study, 6 discontinued due to progressive disease, 1 pt was lost to follow-up, 1 patient died with febrile neutropenia in cycle 4 related to treatment, and 2 pts withdrew consent after 1 cycle of therapy.

Treatment emergent SAEs included 5 pts with 6 incidences of pneumonia (influenza; n=1), 1 patient each with G3 bacteremia, G2 lethargy, G3 febrile neutropenia(FN) and G5 FN.

MTD has been established at the maximum planned dose level 4, with carfilzomib 20/27mg/m² and ARRY-520 at 1.5 mg/m². ARRY-520 can be safely combined carfilzomib in patients with RRMM and the combination is well tolerated with limited hematologic toxicity with growth factor support. The combination is very active in a heavily pretreated patient population with an ORR (≥MR) of 58%. Enrollment in a dose expansion at dose level 4 is underway. In addition a second dose escalation of ARRY-520 and increasing doses of carfilzomib in a 30 minute infusion is also enrolling.

Shah:Array biopharma: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Research Funding; Onyx: Honoraria, Research Funding; Millennium: Research Funding; Novartis: Honoraria, Research Funding. Off Label Use: ARRY-520 in relapsed/refractory myeloma. Thomas:Celgene: Research Funding; Novartis: Research Funding; Millenium: Research Funding; Immunomedics: Research Funding; Pharmacyclics: Membership on an entity’s Board of Directors or advisory committees; Onyx: Membership on an entity’s Board of Directors or advisory committees. Hilder:Array BioPharma: Employment. Orlowski:Bristol-Myers Squibb: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Millennium: The Takeda Oncology Company: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Onyx: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Resverlogix: Research Funding; Array Biopharma: Honoraria, Membership on an entity’s Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity’s Board of Directors or advisory committees; Merck: Membership on an entity’s Board of Directors or advisory committees.