Prolonged Survival and Improved Response Rates With ARRY-520 In Relapsed/Refractory Multiple Myeloma (RRMM) Patients With Low α-1 Acid Glycoprotein (AAG) Levels: Results From a Phase 2 Study

The availability of multiple immunomodulators (IMiDs) and proteasome inhibitors (PIs) has resulted in improved outcomes for patients (pts) with multiple myeloma (MM). Pts refractory to these 2 classes of drugs have a poor prognosis and new drugs with novel mechanisms of action are needed. ARRY-520, a potent, selective inhibitor of the novel drug target KSP, has shown single-agent activity in MM. The acute-phase protein AAG can bind ARRY-520, reducing free drug, possibly resulting in reduced treatment effect in pts with high AAG.

ARRAY-520-212 is a Phase 1/2 study. The Phase 2 portion was designed to evaluate the efficacy and safety of 1.5 mg/m²/day ARRY-520 administered intravenously on Days 1 and 2 every 2 weeks with filgrastim support. 2 Cohorts have been enrolled: Cohort 1 investigated single-agent ARRY-520 in pts with relapsed or refractory MM with ≥ 2 prior lines of therapy, including both bortezomib (BTZ) and an IMiD. Cohort 2 (cohort2) investigated ARRY-520 with Low-dose dexamethasone (LoDex -40mg weekly) in pts with RRMM with ≥ 2 prior lines of therapy, refractory (progression on or within 60 days of last treatment) to last line of therapy, and refractory to BTZ, lenalidomide (Len) and dexamethasone (triple-refractory). Pts intolerant to Len or BTZ were not included in cohort2. Baseline plasma AAG levels were measured in both cohorts.

Results are summarized in the attached table. In cohort 1, 32 pts have been treated, with a median age of 65 years and a median of 6 prior regimens. 41% of cohort 1 pts were refractory to BTZ and Len. 6/27 pts (22%) had high baseline AAG. In cohort 2, 50 pts have been treated to date, with a median age of 63 years and a median of 9 prior regimens. As described in the table, cohort 2 pts had more prior treatment regimens, were primarily triple refractory and had a short time to progression (TTP) on prior therapy. 13/44 (30%) of cohort 2 pts had high baseline AAG.

ARRY-520 showed a similar safety profile in both Cohorts. The most commonly reported (≥ 10% of pts) treatment-emergent Grade 3/4 adverse events, regardless of attribution, were thrombocytopenia (44% cohort 1, 42% cohort 2), anemia (38% and 50%), neutropenia (38% and 38%), fatigue (16% and 8%), leukopenia (13 and 4%) and pneumonia (3% and 12%). The incidence of febrile neutropenia was low in both cohorts (3% and 6%).

ARRY-520 has shown activity both alone and with LoDex (See table). To date, in both cohorts, pts with High AAG have had no objective responses as compared to pts with Low AAG. In the completed cohort 1, ARRY-520 showed a durable 16% overall response rate (ORR) with an 8.6 month (mo) duration of response. In pts with Low AAG a prolonged OS (median = 23 mo) was observed compared to pts with High AAG (OS = 4.5 mo). Follow-up in cohort 2 is ongoing and ARRY-520+LoDex has shown a 16% ORR to date in this very heavily pretreated population.

Notably in cohort 2, 4 PR were observed in the 16 patients (25%) who were previously treated with either a novel PI (carfilzomib or MLN9708) and/or IMiD (pomalidomide).

ARRY-520 is a novel first-in class agent in MM. In this Phase 2 analysis, ARRY-520 showed a similar activity and safety profile both alone and in combination with LoDex. While transient non-cumulative neutropenia is observed, the incidence of febrile neutropenia was low. ARRY-520 showed clear activity both alone and in combination with LoDex. Activity in pts refractory to novel PI and IMiDs suggests a lack of cross-resistance with drugs with existing mechanisms of action. High levels of AAG are associated with a lack of tumor responses and shorter OS following treatment with ARRY-520, suggesting AAG may be a potential patient selection marker identifying pts unlikely to benefit from ARRY-520.

Lonial:Millennium: Consultancy; Novartis: Consultancy; BMS: Consultancy; Sanofi: Consultancy; Onyx: Consultancy; Celgene Corporation: Consultancy. Off Label Use: ARRY-520 (Investigational Drug). 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 Pharmaceuticals: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Millenium: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Zonder:Celgene Corporation: Consultancy; Onyx: Consultancy; Skyline Diagnostics: Consultancy. Kaufman:Onyx: Consultancy; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Janssen: Consultancy; Millenium: Consultancy; Merck: Research Funding. Hilder:Array BioPharma: Employment. Rush:Array BioPharma: Employment. Ptaszynski:Array BioPharma: Employment. Walker:Array BioPharma: Employment. Orlowski: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; Resverlogix: Research Funding; Onyx Pharmaceuticals: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Millenium Pharmaceuticals: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Celgene Corporation: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Merck: Membership on an entity’s Board of Directors or advisory committees.