Enzastaurin in Previously Treated Waldenstrom's Macroglobulinemia: An Open-Label, Multicenter, Phase II Study.

Enzastaurin is an oral serine/threonine kinase inhibitor that targets the PKC and PI3K/AKT pathways. Enzastaurin has demonstrated activity in preclinical models of multiple myeloma (MM) and Waldenstrom's macroglobulinemia (WM), and clinical studies suggest encouraging activity and a well-tolerated safety profile in a variety of hematologic cancers. We are conducting a multicenter, two (parallel) cohort, two-stage, phase II trial to determine whether further study of single-agent enzastaurin is warranted in patients with previously treated WM or MM. The primary objective is to assess the response rate (RR); secondary objectives include assessment of time to progression (TTP), safety, biomarkers, and the impact of adding dexamethasone to enzastaurin in patients with progressive disease (PD). Preliminary results for the WM cohort are reported here.

Eligible patients with WM and 1-5 prior therapies were enrolled and treated with 250 mg oral enzastaurin twice daily (1125-mg loading dose on day 1) in 28-day cycles. Patients continued for 8 cycles or until PD or unacceptable toxicity occurred. At the investigator's discretion, dexamethasone (20-40 mg po QD, days 1-4, 9-12, and 17-20 for 4 cycles; days 1-4 of each cycle thereafter) was added to enzastaurin in patients with PD. According to the Simon two-stage design, if 2 of the first 10 patients (in stage 1) experienced a minor response (MR) or better, then the study would be expanded to 29 patients (stage 2). Best response was determined according to the response assessment recommendations of the Third International Workshop on WM (IWWM). Adverse events were graded according to CTCAE version 3.0.

Twenty-nine patients (7 females, 22 males) with WM were enrolled. The median age was 65.6 years (range: 51.7-82.3 years) and 93% of patients had an Eastern Cooperative Oncology Group performance status of 0. Patients had a median of 2 prior systemic therapies and 26 patients (89.7%) had prior rituximab. Patients completed a median of 4 cycles. Six patients received ≥6 cycles of enzastaurin treatment. Twenty patients remain on study. There were no drug-related discontinuations. None of the patients had a complete response (CR). One patient had a partial response (PR) and 7 patients had a minor response (MR), for a RR (CR+PR+MR) of 27.6%. Immunoglobulin M decreased by ≥25% in 11 patients. Three (10.3%) patients had a PD. One patient had a drug-related grade 3 wound complication; there were no other drug-related grade ≥3 toxicities. One patient died on study due to infection unrelated to enzastaurin.

Although the results are preliminary, enzastaurin appears to have activity and is well tolerated in patients with previously treated WM. The WM cohort was expanded to allow up to 50 patients to be treated on study.

Ghobrial:Novartis: Honoraria, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millennium: Honoraria, Research Funding, Speakers Bureau. Lin:Eli Lilly and Company: Employment. Yuan:Eli Lilly and Company: Employment. Benhadji:Eli Lilly and Company: Employment. Wooldridge:Eli Lilly and Company: Employment. Leblond:Roche: 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; Amgen: Honoraria.