Combination Treatment of the Bruton's Tyrosine Kinase Inhibitor Ibrutinib and Carfilzomib in Patients with Relapsed or Relapsed and Refractory Multiple Myeloma: Initial Results from a Multicenter Phase 1/2b Study

Background: Recent advances have improved outcomes for patients (pts) with multiple myeloma (MM); however, novel agents targeting different pathways are still needed. Ibrutinib (ibr) is a first-in-class, once-daily, oral, covalent inhibitor of Bruton's tyrosine kinase (BTK), an enzyme overexpressed in malignant plasma cells, whose expression may positively regulate the myeloma stem cell-like population (Yang 2015). Clinical activity was observed at the 840-mg dose of ibr in heavily pretreated pts with relapsed or relapsed/refractory MM (RRMM), when combined with weekly dexamethasone (dex) (Vij 2014). Furthermore, BTK-mediated upregulation of NF-κB p65 contributes to proteasome inhibitor (PI) resistance in MM cell lines; thus, BTK inhibition with ibr may help overcome PI resistance (Murray 2015). In vitro, ibr has demonstrated synergy with PIs in MM (Rushworth 2013) and mantle cell lymphoma cells (Ou 2013). PCYC-1119 (NCT01962792) is an ongoing phase 1/2b study of ibr + carfilzomib (CFZ) ± dex in RRMM.

Methods: Eligible pts received ≥2 prior therapies, including bortezomib (BTZ) and an immunomodulatory agent (IMiD) and had either no response or documented disease progression following the most recent treatment. Dose escalation followed a 3+3 design, followed by expansion of 2 cohorts (Table). Phase 1 primary objectives were maximum tolerated dose/recommended phase 2 dose (RP2D) determination and safety.

Results: As of July 8, 2015, 40 pts were enrolled and received ibr combined with CFZ ± dex across multiple dose levels during the phase 1 portion. No dose-limiting toxicities (DLTs) were observed, and cohorts 2b and 3b were chosen for expansion to further evaluate safety and efficacy. Pts had a median age of 63 y (range, 44-83) and a median time from diagnosis of 4.3 y (range, 0.5-25.3). Cytogenetic assessment by FISH identified that 20% and 8% of pts had t4;14 and del17p, respectively. Overall, pts received a median of 3 prior lines of therapy (range, 2-11), including 10% prior CFZ, 25% pomalidomide, 25% thalidomide, 73% autologous stem cell transplant, and 100% BTZ and lenalidomide. Moreover, 88% of pts were refractory to their last therapy, with 73% refractory to BTZ, 73% refractory to lenalidomide, and 58% refractory both to IMiD and PI. No relevant differences were observed across cohorts. Thirty-six pts were evaluable for efficacy. With early follow-up, the initial objective response rate (ORR) was 58% and the clinical benefit rate (CBR) was 67%. In cohort 3b, the ORR and CBR were 65% and 77%, respectively, including 3 very good partial responses (VGPRs) and 1 stringent complete response (sCR). No clinically meaningful tolerability differences were seen between cohorts, and no new safety findings were observed. Across all cohorts, the most common all-grade nonhematologic adverse events (AEs) were diarrhea (43%), cough (35%), constipation and fatigue (30% each), and nausea (28%). Grade ≥3 hematologic AEs included thrombocytopenia (15%), anemia (13%), and neutropenia (5%). Grade ≥3 nonhematologic AEs occurring in ≥10% of pts were pneumonia and hypertension (15% each), diarrhea (13%), and fatigue (10%). Eleven pts reported treatment related SAEs. No clinically relevant differences in AEs were observed across cohorts. Ten pts discontinued study treatment due to progressive disease; an additional 6 pts discontinued due to an AE, and 6 pts discontinued due to investigator or pt decision. Duration of treatment ranged from 0.3 to 13.6 months, and 17 pts remain on treatment. Updated data will be presented.

Conclusions: The initial phase 1 data indicated promising clinical potential for ibr + CFZ + dex, as it is well tolerated with no DLTs, no new toxicities, and no increase in the severity of known toxicities for the individual agents. The preliminary ORR of 58%, with 1 sCR and 3 VGPRs in cohort 3b, is encouraging in this mostly refractory patient population, especially with the high number refractory to BTZ. Cohort 3b was established as the RP2D and will be further evaluated in the phase 2 portion of the study.