A Phase 1/2 Study Of KW-2478, An Hsp 90 Inhibitor, In Combination With Bortezomib (BTZ) In Patients (Pts) With Relapsed/Refractory (R/R) Multiple Myeloma (MM)

Background KW-2478 is a potent Hsp 90 inhibitor that binds to Hsp 90 with an IC50 value of 3.8 nmol/L. In preclinical studies, KW-2478 inhibited the in vitro growth of myeloma cell lines at GI50 values of 0.12 – 0.39 µM and markedly inhibited the growth of myeloma xenografts in SCID mice in a dose-dependent manner. In vitro, KW-2478 and BTZ demonstrated synergistic activity against OPM-2/GFP cells and in the NCI-H929 xenograft model, the combination of KW-2478 and BTZ showed greater anti-growth activity than either agent alone. A single-agent Phase 1 study (KW-2478 administered daily x 5 every 14 days), showed no dose limiting toxicity (DLT) and Hsp90 inhibition was observed at doses >71 mg/m2. Aim To establish safety, tolerability and recommended Phase 2 dose (RP2D) of KW-2478 plus BTZ in pts with R/R myeloma and assess overall response rate (ORR) based on International Myeloma Working Group (IMWG) response criteria. The PK and PD of KW-2478 plus BTZ were characterized and progression-free survival (PFS) was investigated. Methods All patients had MM by IMWG criteria, had received at least 1 and no more than 3 prior MM regimens and had not responded or had relapsed, and had adequate renal function. Patients who received prior BTZ could not be refractory. This open-label study had 2 parts: A Phase 1 dose escalation (3 + 3 design) part followed by a Simon 2-stage Phase 2. KW-2478 and BTZ were administered on Days 1, 4, 8 and 11 of a 21-day cycle. In Phase 1, the doses of KW-2478 and BTZ were sequentially escalated until observation of DLT, MTD, or achievement of the maximal planned dose levels (KW-2478 175 mg/m2, BTZ 1.3 mg/m2). PK and PD samples were collected in C1 on Days 1 and 11, and Days 1, 4, 8, and 11, respectively. In Phase 2, if 11 or more responses were observed in the first 27 evaluable pts, then an additional 50 evaluable pts would be enrolled. Response was assessed at the end of each cycle and safety was assessed continuously. Results The study enrolled 95 pts who received at least one dose of study drug: 15 in Phase 1 and 80 in Phase 2; 86 pts received the RP2D (highest planned dose of KW-2478 175 mg/m2 /bortezomib 1.3 mg/m2). Median age was 65; 57% of pts were male. There was 1 DLT (presyncope) in Phase 1. The most common adverse events (AEs) were diarrhea (74%), nausea (61%), fatigue (55%), constipation (46%), vomiting (40%) and peripheral neuropathy (30%). Most AEs were Grade 2; 5 pts had Grade 4 AEs. Five pts had a Grade 4 thrombocytopenia and 3 pts had a Grade 4 neutropenia. The PK profiles for KW-2478 plus BTZ in combination were comparable to each agent’s individual PK profile. In the Phase 1 portion of the trial, Hsp70 levels, a marker of Hsp90 inhibition, increased in the peripheral blood mononuclear cells in all subjects (N = 13). Of the pts who received the RP2D, 79 pts were evaluable for IMWG response. The ORR was 39% (4% CR, 14% VGPR, and 22% PR); in pts who were bortezomib naïve (n = 50), the ORR was 48%. Median PFS was 26.4 weeks and median duration of response had not been reached at the time of this report. Six pts continue treatment at the time of data cut-off. Conclusions KW-2478 plus BTZ was well-tolerated when administered at the doses and schedule studied. Clinical activity was demonstrated in pts with R/R MM (ORR of 39%). PFS was 26.4 weeks Disclosures: Akinaga: Kyowa Kirin Pharmaceuticals: Employment, Equity Ownership. Kurman:Kyowa Kirin Pharmaceuticals: Consultancy. Novak:Kyowa Kirin Pharmaceuticals: Employment.