A Phase I Safety Study of Enzastaurin Plus Bortezomib in the Treatment of Relapsed or Refractory Multiple Myeloma.

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 clinical studies suggest activity and a favorable safety profile in a variety of hematological cancers. Enzastaurin has also demonstrated in-vitro synergy with bortezomib.

This phase I, open-label, multicenter, dose-escalation study was initiated to identify the recommended doses of enzastaurin and bortezomib in combination for phase II studies in patients (pts) with previously treated MM. Secondary objectives included evaluations of safety and response.

A conventional dose-escalation scheme was applied. In dose level 1, pts received enzastaurin as a loading dose of 500 mg (250 mg po BID) on day 1 followed by daily doses of 125 mg po BID plus bortezomib 1.0 mg/m² IV on days 8, 11, 15, and 18 in cycle 1 and days 1, 4, 8, and 11 thereafter. In dose level 2, pts received the same enzastaurin dose but a higher bortezomib dose (1.3 mg/m²). In dose level 3, pts received enzastaurin as a loading dose of 1125 mg (375 mg po TID) on day 1 followed by daily doses of 250 mg po BID plus 1.3 mg/m² bortezomib. All treated pts were evaluated for response using the International Uniform Response Criteria (IURC; Durie et al. 2006) and European Group for Blood and Bone Marrow Transplantation (EBMT) criteria (Blade et al. 1998). All adverse events (AEs) were graded according to Common Toxicity Criteria for Adverse Events (CTCAE) v3.0.

A total of 23 pts, 4 in dose level 1, 3 in dose level 2, and 16 in dose level 3, were enrolled in the study, which is now closed to enrollment. There were 8 women and 15 men, with a median age of 62 years (range, 37–78 years); 91% of the pts had an ECOG performance status of 1 or 0, and the median number of prior systemic therapies was 3 (range, 2–12), with 17 pts previously treated with bortezomib. The median number of cycles completed was 4 (range, 1–20). No dose-limiting toxicities (DLTs) were observed; thus, dose level 3 was the recommended phase II dose. The combination was well tolerated with few grade 3/4 AEs. CTCAE drug-related grade 3/4 laboratory toxicities included: thrombocytopenia in 5 (22%) pts, anemia in 2 (9%) pts, increased creatinine in 1 (4%) pt, and hyponatremia in 1 (4%) pt. Drug-related grade 3/4 non-laboratory toxicities included: sensory neuropathy, prolonged QTc interval, and renal/genitourinary in 1 (4%) pt each. Serious drug-related AEs were increased serum creatinine and renal tubular necrosis in 1 (4%) pt and thrombocytopenia in 1 (4%) pt. The thrombocytopenia was not considered a DLT as the baseline platelet count was low secondary to MM. Five (22%) pts were discontinued from the study due to drug-related toxicities: renal tubular necrosis (also a serious AE) in 1 (4%) pt, peripheral neuropathy in 2 (9%) pts, neuralgia in 1 (4%) pt, and pain in extremity in 1 (4%) pt. There were no deaths on therapy; 1 pt died within 30 days of treatment due to progressive disease. Of the 23 enrolled pts, objective responses based on IURC criteria included 1 (4%) pt with a very good partial response (dose level 1), 2 (9%) pts with a partial response (in dose levels 2 and 3), 9 (39%) pts with stable disease, and 3 (13%) pts with progressive disease; 2 pts had no post-baseline response assessment, and 6 pts had unconfirmed stable disease or progressive disease. Two (9%) pts had a minimal response based on EBMT criteria. Activity was seen in pts regardless of prior exposure to bortezomib.

The recommended phase II dose in patients with MM is enzastaurin 250 mg po BID with a loading dose of 1125 mg (375 mg po TID) on day 1 plus 1.3 mg/m² bortezomib on days 1, 4, 8, and 11 (days 8, 11, 15, and 18 in cycle 1 only). The combination was generally well tolerated, and responses were observed.

Ghobrial:Millenium: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Research Funding; Celgene: Honoraria, Speakers Bureau. Munshi:Millenium: 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; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Yuan:Eli Lilly and Company: Employment. Schlossman:Millenium: Speakers Bureau; Celgene: Speakers Bureau. Laubach:Novartis: Consultancy. Anderson:Celgene: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Millenium: Consultancy, Honoraria, Research Funding. Lin:Eli Lilly and Company: Employment. Wooldridge:Eli Lilly and Company: Employment. Richardson:Millenium: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keryx Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Merck: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bristol Meyers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gentium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.