Phase I Study of IMGN901 in Patients with Relapsed and Relapsed/Refractory CD56-Positive Multiple Myeloma

Background: IMGN901 (huN901-DM1) is a novel conjugate of the cytotoxic maytansinoid, DM1, with the humanized CD56-binding monoclonal antibody, N901. 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. Preclinical investigations demonstrated significant in vitro and in vivo anti-myeloma activity of IMGN901.

Objectives: To determine the maximum tolerated dose (MTD), the dose-limiting toxicities (DLTs), and pharmacokinetics (PK) of increasing doses of IMGN901 given for MM on a weekly schedule.

Methods: Patients with relapsed or relapsed/refractory MM who have failed at least one prior therapy and have CD56-expressing MM received a single IV infusion of IMGN901 on 2 consecutive weeks every 3 weeks. Patients are enrolled in cohorts of 3 at each dose level, with DLT triggering cohort expansion.

Results: Eighteen patients have received IMGN901 to date in this study - 3 patients each at 40, 60, 75, 90, 112, and 140 mg/m²/week. One patient experienced a DLT (grade 3 fatigue) on 140 mg/m²/week, and this cohort is being expanded to enroll up to 6 patients. No patients have experienced serious hypersensitivity reactions or evidence of presence of humoral responses against the huN901 antibody component (HAHA) or against the DM1 component (HADA). Preliminary PK results indicate an approximately linear relationship between dosing and observed maximal serum concentration. A confirmed minor response (MR) was documented in 3 heavily pretreated patients (1 patient each at 60, 90, and 112 mg/m²/week) using the European Bone Marrow Transplant criteria. Durable stable disease was reported at doses of 60, 90, 112, and 140 mg/m²/week. Of the 18 patients treated in the study, eight patients remained on treatment with IMGN901 for at least 15 weeks, five of these 8 patients remained on treatment for at least 24 weeks, and two of these 5 patients remained on treatment for at least 42 weeks. This phase I study provides preliminary evidence of safety as well as clinical activity of IMGN901 in patients with CD56-positive MM who have failed established MM treatments. Updated results of this ongoing study will be presented.