Efficacy of ocaratuzumab (AME-133v) in relapsed follicular lymphoma patients refractory to prior rituximab.

Abstract

8081 Background: Ocaratzumab, previously known as AME-133v, is a humanized next-generation anti-CD20 monoclonal antibody. It has been optimized with a 13 to 20-fold increase in binding affinity to CD20 and improved binding to the low-affinity (F/F and F/V) polymorphisms of FcγRIIIa (CD16), which are thought to predict lower response rates and shorter duration of responses to rituximab. Methods: In a phase I dose escalation study in relapsed follicular lymphoma (FL) patients, ocaratuzumab was well-tolerated at doses up to 375 mg/m2 (Forero-Torres et al. CCR 2012). In a follow-on phase II trial, 44 patients with relapsed FL following prior rituximab and the low-affinity FcγRIIIa polymorphism (F-carriers) received 375 mg/m2 of ocaratuzumab weekly for 4 doses. In this study, overall response rate (ORR) was 36% and median progression free survival (PFS) was 91 weeks (Ganjoo et al. Haematologica 2011). Results: Amongst the 56 patients receiving 100 and 375 mg/m2 of ocaratuzumab, 8 patients had a previous time to progression of ≤ 180 days following their last rituximab treatment. These patients had a median of 2 prior rituximab treatments, (range 1-6 treatments), and median PFS following last treatment of 159 days. Five of the 8 patients showed a longer PFS after ocaratuzumab administration, compared with last rituximab treatment. All 5 patients expressed the homozygous low-affinity genotype of FcγRIIIa (F/F). At the time of study closure, 3 of the patients were still in remission (indicated by * in the table). Conclusions: This retrospective analysis suggests that ocaratuzumab may be non-cross-resistant to rituximab in patients with the low-affinity FcγRIIIa polymorphism. Prolonged PFS in selected patients following ocaratuzumab suggests that the increased binding affinity to CD16 and improved antibody-dependent cell-mediated cytotoxicity (ADCC) of this antibody is clinically relevant. As a single agent, ocaratuzumab may provide prolonged clinical benefit in relapsed FL patients and a clinical trial comparing ocaratuzumab to rituximab is in preparation. [Table: see text]