Phase 1 Study of Tabalumab, a Human Anti-BAFF Antibody and Bortezomib in Patients with Previously-Treated Multiple Myeloma

Tabalumab, a human mAb that neutralizes membrane-bound and soluble B cell activating factor (BAFF), has demonstrated both anti-myeloma activity and osteoclastogenesis inhibition in xenograft models of multiple myeloma (MM). We initially conducted a Phase 1 study with the combination of tabalumab and bortezomib in previously-treated MM patients who were not refractory to bortezomib. The results from the dose escalation (Part A) have been previously reported, where a tabalumab dose of 100 mg was selected based on several factors, most notably the stabilization of the peak to trough concentration ratio. The cohort expansion (Part B) has since completed enrollment, and we now report the preliminary results for the entire study.

The primary objective was to identify a safe and potentially efficacious dose of tabalumab to be combined with bortezomib. Bortezomib was given in a standard biweekly fashion, 1.3 mg/m² IV on days 1, 4, 8, and 11 of a 21 day cycle, and tabalumab at 1, 10, 30, 100, or 300 mg (Part A) or 100 mg (Part B) IV (30 min) on day 1 in Cycles 1 – 3, 5, and 7. The study was later amended to include dexamethasone to assess safety, and 12 patients received dexamethasone in combination with bortezomib and tabalumab. Response was assessed per IMWG criteria and adverse events per CTCAE v3.0. Pharmacokinetic (PK) and pharmacodynamic (PD) samples were obtained throughout the study, including BAFF, IL-1beta, IL-6, IL-10, VEGF, and TNF-alpha.

Forty-eight patients were enrolled to the study; 20 to dose escalation (Part A) and 28 to cohort expansion (Part B). The median age was 65.7 years and 56% were women. The median number of prior therapies was 3 (range 1–10). All patients received either bortezomib or an IMiD; 75% received prior bortezomib and 88% received prior IMiD therapy. The median number of cycles was 5.5 (range 1–28). Grade 3/4 toxicities occurring in two or more patients included peripheral sensory neuropathy, pneumonia, thrombocytopenia, neutropenia, diarrhea, musculoskeletal pain, renal failure acute, fatigue, anemia, neuralgia, and gastrointestinal hemorrhage. Most patients discontinued treatment due to progressive disease or adverse events (neuropathy, neuralgia, fatigue, and thrombocytopenia). Two patients died during study participation - one during treatment from acute respiratory distress syndrome and another during follow-up from multiple myeloma. Confirmed responses included 2 complete responses, 4 very good partial responses, and 16 partial responses. Response associated with lower baseline serum BAFF or IL-6 levels, independent of the tabalumab dose. Also, response in patients treated with tabalumab 100 mg appeared to associate with lower baseline serum levels of IL-10 and undetectable TNF-alpha. With 14 patients censored, the TTP was 4.9 months (95% CI: 4 – 8). With 6 patients censored, the median response duration was 7.3 months (95% CI: 3.5 – 13.9).

A 100 mg dose of tabalumab in combination with bortezomib was well tolerated; 22 patients achieved a PR or better despite prior bortezomib and/or IMiD therapy. Response correlated with lower baseline serum BAFF levels, supporting the hypothesis that a higher dose of tabalumab should be evaluated. A three-arm study randomizing patients to the combination(s) of bortezomib, dexamethasone, and tabalumab 100 mg vs. tabalumab 300mg vs. placebo is currently enrolling.

Raje:Onyx: Consultancy; Celgene: Consultancy; Millennium: Consultancy; Acetylon: Research Funding; Amgen: Research Funding; Eli-Lilly: Research Funding. Richardson:Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees. Schiller:Eli Lilly & Company: Research Funding. Cohen:Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Onyx: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Carpenter:Eli Lilly & Company: Employment. Cronier:Eli Lilly and Company: Employment. Kaiser:Eli Lilly and Company: Employment. Wooldridge:Eli Lilly and Company: Employment. Anderson:Acetylon, Oncopep: Scientific Founder, Scientific Founder Other; Celgene, Millennium, BMS, Onyx: Membership on an entity's Board of Directors or advisory committees.