A Phase II Study of Coltuximab Ravtansine (SAR3419) Monotherapy in Patients with Relapsed or Refractory Acute Lymphoblastic Leukemia

Background Long-term disease-free survival in adult patients with acute lymphoblastic leukemia (ALL) remains unsatisfactory, and the treatment options are limited for those patients with relapse or a failure to respond after initial therapy. We conducted a dose-escalation/expansion phase II, multicenter, single-arm study to determine the optimal dose of coltuximab ravtansine (SAR3419), an anti-CD19 antibody-drug conjugate, in this setting. Patients and Methods The dose-escalation part of the study determined the selected dose of coltuximab ravtansine for the evaluation of efficacy and safety in the dose-expansion phase. Patients received coltuximab ravtansine induction therapy (≤ 8 weekly doses). The responding patients were eligible for maintenance therapy (biweekly administration for ≤ 24 weeks). Three dose levels of coltuximab ravtansine were examined: 55, 70, and 90 mg/m². The primary endpoint was the objective response rate (ORR). The secondary endpoints included the duration of response (DOR) and safety. Results A total of 36 patients were treated: 19 during dose escalation and 17 during dose expansion. One dose-limiting toxicity was observed at 90 mg/m² (grade 3 peripheral motor neuropathy); therefore, 70 mg/m² was selected for the dose-expansion phase. Five patients discontinued therapy because of adverse events (AEs). The most common AEs were pyrexia, diarrhea, and nausea. Of the 17 evaluable patients treated at the selected dose, 4 had a disease response (estimated ORR using the Bayesian method: 25.5% (80% confidence interval, 14.2%-39.6%). The DOR was 1.9 months (range, 1-5.6 months). Because of these results, the study was prematurely discontinued. Conclusion Coltuximab ravtansine was well tolerated but was associated with a low clinical response rate in patients with relapsed or refractory ALL.