The Novel KSP Inhibitor ARRY-520 Is Active Both with and without Low-Dose Dexamethasone in Patients with Multiple Myeloma Refractory to Bortezomib and Lenalidomide: Results From a Phase 2 Study

ARRY-520 is a kinesin spindle protein (KSP) inhibitor that arrests cells in mitosis and induces apoptosis due to degradation of the BCL2 family survival protein MCL-1. As previously reported, ARRY-520 has demonstrated single-agent activity in relapsed and refractory multiple myeloma (RRMM). In preclinical myeloma models, the addition of dexamethasone (Dex) increases the activity of ARRY-520, supporting clinical investigation of ARRY-520 combined with low-dose Dex (LoDex). Here, the efficacy and safety of ARRY-520 is compared in 2 Phase 2 cohorts in RRMM: as a single agent (Cohort 1) and in combination with LoDex (Cohort 2).

Both cohorts were designed as 2-stage single-arm Phase 2 studies. Cohort 1 evaluated the efficacy and safety of 1.5 mg/m²/d ARRY-520 administered intravenously on Days 1 and 2 every 2 weeks with prophylactic granulocyte colony-stimulating factor (G-CSF) support. Eligible patients had RRMM with 2 prior lines of therapy that included both bortezomib (BTZ) and an immunomodulatory agent (IMiD), unless refusing or ineligible for this therapy. Cohort 2 is evaluating the efficacy and safety of the same dose and schedule of ARRY-520 and G-CSF with LoDex (40 mg PO weekly). Eligible patients had RRMM with 2 prior lines of therapy, and had disease refractory to (progressed on or ≤ 60 days of treatment) their last line of therapy and that was refractory to BTZ, lenalidomide (Len) and dexamethasone. Data from Cohort 1 and the first stage of Cohort 2 are reported.

At the time of data cutoff, a total of 32 patients were enrolled into Cohort 1 with a median age of 65 years (range 51–82) and a median of 6 prior regimens (range 2–19). All patients received prior IMiD, 90% received prior BTZ and 78% had prior autologous stem cell transplant (ASCT). The defined first stage of Cohort 2 has been enrolled with 18 evaluable patients. These patients had a median age of 67 years (range 53–78) and were more heavily pretreated, with a median of 10 prior therapies (range 5–13).

Safety was similar for both cohorts. A possible trend for more infections in Cohort 2 was noted. The most commonly reported (20% of patients) treatment-related adverse events (AEs) in both cohorts included thrombocytopenia, anemia, neutropenia and fatigue. No treatment-related events of neuropathy were observed in either cohort. The most common Gr 3/4 AEs (in Cohort 1, Cohort 2) included neutropenia (38%, 33%), thrombocytopenia (44%, 44%) anemia (28%, 50%), pneumonia (3%, 17%) and fatigue (16%, 11%). Treatment discontinuations due to AEs were infrequent (9%, 11%).

Of 32 patients in Cohort 1, confirmed responses (≥ Minor Response (MR)) were observed in 6 patients (19%) with 5 Partial responses (PR) (16%) per International Melanoma Working Group (IMWG) and European Group for Blood and Marrow Transplantation (EBMT) criteria. The median treatment time was 2.1 months. In the subset of patients with disease refractory to both BTZ and Len, a 15% overall response rate (ORR ≥ MR) was observed. Among the 18 evaluable patients in Cohort 2, the ORR (≥ MR) was 28% (5/18), with 4 patients ≥ PR (22%). At the time of data cutoff, the median treatment time was 3.9 months.

Patients with RRMM refractory to both IMiD and proteasome inhibitor therapy have a poor prognosis with median survival of as little as 6 months¹. New drugs with clinically meaningful activity in this population are needed. ARRY-520 is a novel agent with a distinct mechanism of action relative to other myeloma drugs and shows promising clinical activity both alone and combined with Dex in RRMM. Notably, in patients with triple-refractory MM, ARRY-520 + LoDex has shown a preliminary 28% ORR (≥ MR), with a manageable safety profile. These data are comparable to those reported for pomalidomide or carfilzomib in less heavily pretreated patients. Both the median time on study and ORR in Cohort 2 were greater than the activity seen for Cohort 1, despite the more advanced stage of these patients and the fact that they were heavily pretreated with Dex, suggesting that LoDex may enhance ARRY-520 activity. Based on this evidence of activity, further development of ARRY-520 + LoDex is warranted in patients who have exhausted other therapeutic options.

Shah:Array BioPharma: 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; Onyx: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau. Off Label Use: ARRY-520. Zonder:Millenium: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Kaufman:Onyx: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Millenium: Consultancy. Orlowski:Array BioPharma: Honoraria, Membership on an entity's Board of Directors or advisory committees. Walker:Array BioPharma: Employment. Hilder:Array BioPharma: Employment. Ptaszynski:Array BioPharma: Consultancy. Lonial:Onyx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bristol-Meyers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Millennium Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees.