Phase 1 Study of the Novel Kinesin Spindle Protein Inhibitor ARRY-520 + Carfilzomib in Patients with Relapsed and/or Refractory Multiple Myeloma

ARRY-520, a novel kinesin spindle protein (KSP) inhibitor, has been studied as a single agent and in combination with dexamethasone, and demonstrated promising clinical activity in patients with bortezomib- and lenalidomide-refractory multiple myeloma (MM). Carfilzomib, a novel irreversible proteasome inhibitor (PI), has also demonstrated single agent activity in relapsed and refractory MM, and recently received regulatory approval for this indication. Preclinical data support the presence of synergy with the combination of a PI and a KSP inhibitor via the latter's ability to down-regulate Mcl-1, supporting our hypothesis that the combination of carfilzomib and ARRY-520 (Car-ARRY) would be highly active in relapsed and/or refractory myeloma. We therefore aimed to combine these two agents for the first time, and here report the initial findings from the phase I dose-escalation in patients with relapsed and/or refractory MM.

The primary objective was to determine the maximum tolerated dose (MTD) and the safety/tolerability of the Car-ARRY combination. Secondary objectives were to determine efficacy as measured by the overall response rate, time to progression, progression free survival and time to next therapy. Patients had to have myeloma that was relapsed and/or refractory, be ineligible for autologous stem cell transplant, bortezomib refractory/intolerant, and prior lenalidomide exposure. ARRY-520 was administered intravenously over 1 hour on days 1, 2, 15 and 16, while carfilzomib was administered intravenously over 30 minutes on days 1, 2, 8, 9, 15 and 16 on a 28 day cycle. All patients received growth factor support with filgrastim.

Dose-escalation used a standard 3+3 schema proceeded based on dose-limiting toxicities (DLTs) during cycle 1, with planned escalation of the dose of ARRY-520. Dose level 1 was ARRY-520 0.75 mg/m², and carfilzomib was dosed at 20 mg/m² for cycle 1 on days 1 and 2 and all subsequent dose were at 27 mg/m². Adverse events (AEs) were graded by NCI-CTCAE v4, while responses were assessed by the modified International Uniform Response Criteria.

To date, 8 patients have been enrolled in the ongoing dose escalation phase. The median age was 66 (range 47–80), 6/8 were males, and the median number of prior therapies was 4 (range 2–10). 7/8 patients had undergone prior autologous stem cell transplant, and all patients were bortezomib refractory or intolerant. In the first cohort, 3 patients were enrolled and no dole limiting toxicity (DLT) was observed. During the second cohort, ARRY-520 was escalated to 1 mg/m² with carfilzomib at 20/27 mg/m², and among the first 3 patients, one patient suffered a DLT in the form of an admission for influenza pneumonia with non-neutropenic fever. Expansion of cohort 2 is currently underway.

Among the 6 patients who completed the first cycle of therapy, 5 remain on study. In the first cohort, one patient remains on study with 6 cycles and achieved a near complete remission, 1 patient achieved stable disease, and 1 patient suffered disease progression after first cycle. In the second cohort, all three patients who completed the first cycle have stable disease and remain on trial.

In the first 6 toxicity-evaluable patients who have completed one cycle, grade (G) 3 events included one each of pneumonia, diarrhea, and hyperglycemia. There was limited hematologic toxicity with 4/6 patients with G1/2 thrombocytopenia, 3/6 patients with G1/2 anemia, and 1/6 patient with G1/2 neutropenia. Additional G1/2 non-hematologic toxicity included 3/6 patients with diarrhea, 3/6 patients with dyspnea, 3/6 patients with transient elevations in creatinine and 3/6 patients with aspartate aminotransferase elevations.

An MTD has not been established and enrollment is ongoing in cohort 2 with carfilzomib at 20/27mg/m² and ARRY-520 at 1.0 mg/m².

The combination of ARRY-520 and carfilzomib is well tolerated with limited hematologic toxicity and a manageable side effect profile. Notably, in this patient population, with patients who have bortezomib refractory/intolerant myeloma, the combination has demonstrated early signals of activity. Updated safety and efficacy data for all patients will be presented at the meeting.

Shah:Onyx: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Array BioPharma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Research Funding, Speakers Bureau. Off Label Use: This presentation will include information about Arry-520 which is not yet approved for use in patients with multiple myeloma. Wang:Pharmacyclic: Research Funding; onyx: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Hilder:Array BioPharma: Employment. Orlowski:onyx: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; array biopharma: Honoraria, Membership on an entity's Board of Directors or advisory committees.