Phase I Study of IMGN901, Used as Monotherapy, in Patients with Heavily Pre-Treated CD56-Positive Multiple Myeloma - A Preliminary Safety and Efficacy Analysis.

Abstract Abstract 2883 Poster Board II-859 Background: IMGN901 (huN901-DM1/BB-10901) is a novel anticancer agent consisting of a potent cytotoxic maytansinoid, DM1, attached to a CD56-binding monoclonal antibody, huN901, using an engineered linker. Once bound to CD56 on a cancer cell, the conjugate is internalized and releases DM1. About 70% of multiple myeloma (MM) cases have surface expression of CD56. In preclinical settings, IMGN901 showed significant in vitro and in vivo anti-myeloma activity as a single agent and in combination with approved drugs such as lenalidomide. Objectives: To determine the maximum tolerated dose (MTD), pharmacokinetics (PK), and activity of IMGN901, used as monotherapy, in patients with MM. Methods: Patients with CD56+ relapsed or relapsed/refractory MM receive a single IV infusion of IMGN901 on 2 consecutive weeks every 3 weeks. Patients are enrolled into each dose level in cohorts of 3, with dose-limiting toxicity (DLT) triggering cohort expansion. The European Bone Marrow Transplant (EBMT) criteria were used for response assessment. Results: Twenty-three CD56+ MM patients have received IMGN901 at doses ranging from 40 to 140 mg/m2/week. Most of these 23 patients had been treated with 6 or more chemotherapy regimens prior to study entry. Two of 6 patients treated at the 140 mg/m2/week dose experienced DLT (grade 3 fatigue and grade 3 acute renal failure) and a lower dose has been defined as the MTD. Commonly reported adverse events that were at least possibly related to IMGN901 were fatigue, increased aspartate aminotransferase, increased uric acid, sensory neuropathy and headache. None of the patients experienced serious hypersensitivity reactions or demonstrated a humoral response against either the antibody or DM1 component of IMGN901. Sustained partial response (PR) was documented in 1 patient treated at 140 mg/m2/week and 3 minor responses (MR) were reported in 1 patient each at doses of 60, 90, and 112 mg/m2/week. Of the 23 patients receiving any dose level of IMGN901, 8 remained on IMGN901 treatment for at least 15 weeks. Five of these 8 patients continued treatment on IMGN901 for at least 24 weeks, and two of these 5 patients remained on IMGN901 for at least 50 weeks. Preliminary PK results indicate an approximately linear relationship between dose and observed maximal serum concentration. Conclusion: This is the first study of IMGN901 in patients with MM. The MTD of this agent in MM patients is now defined. Our experience with IMGN901 in this clinical trial demonstrates an overall favorable safety profile. Although the primary objective of this clinical trial was to determine the MTD of single agent IMGN901, exciting single agent activity was observed in heavily pretreated MM patients. This is particularly encouraging as the duration of treatment with IMGN901 in some patients was longer than duration of treatment with prior regimens of approved agents. Clinical observations noted here (including single agent efficacy and the favorable toxicity profile) as well as findings from preclinical combination studies warrant continued investigation of this novel agent in patients with MM especially in combination with approved anti-myeloma agents/regimens such as lenalidomide and dexamethasone. Disclosures: Chanan-Khan: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Immunogen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Jagannath:Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Merck: Honoraria. Miller:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millennium: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Guild:ImmunoGen, Inc: Employment. Zildjian:ImmunoGen, Inc: Employment. Qin:ImmunoGen, Inc.: Employment. O'Leary:ImmunoGen, Inc.: Employment.