Phase III Study of Denileukin Diftitox (ONTAK®) To Evaluate Efficacy and Safety in CD25+ and CD25- Cutaneous T-Cell Lymphoma (CTCL) Patients.

Denileukin diftitox (ONTAK®) is a genetically engineered fusion protein composed of the enzymatically active domain of diphtheria toxin and the full length sequence of interleukin-2 (IL-2), designed to target malignancies expressing the IL-2 receptor. The drug is approved for the treatment of CTCL in patients expressing the CD-25 component of the IL-2 receptor. L4389-14 is a phase III study designed to further evaluate the efficacy and safety of denileukin diftitox (DD) in distinct subgroups of CTCL patients. The study met its accrual goal of 90 patients and included three subgroups of patients: 1) CD25 (+) patients that crossover from a placebo course of treatment in a companion study (L4389-11) and had progressed or failed to respond during an 8-course placebo treatment (N=34); 2) CD25 (−) patients (N=36) and 3) CD25 (+) patients that had previously been treated with DD, responded, and subsequently relapsed (retreatment group, N=22). Patients entered the study at stages Ia to III and received DD at a dose schedule of 18mcg/Kg/day by IV infusion once daily for 5 days every 3 weeks for up to 8 cycles. Efficacy of treatment was assessed based on tumor burden, lymph nodes, lymphocyte count, and patient status (PGA) at every cycle, beginning on cycle 2. A response assessment required confirmation in two subsequent cycles. Responses were evaluated by an independent Drug Evaluation Review Committee. Assessment of activity of DD across the 3 groups based on an analysis of the data is shown in the table below. Patient demographics were consistent across subgroups and representative of a general CTCL population. Disease status at baseline was Stage IIa or earlier 66% of patients and stage IIb or higher 34% of patients. About 46% of patients presented with mild to severe erythroderma. Adverse events were similar to those previously observed with ONTAK. Serious adverse events of ≥5% incidence were nausea (9%), vomiting (5%), capillary leak syndrome (5%), pyrexia (9%) and infections (10%). The results of this large phase III trial showed very consistent efficacy of denileukin diftitox across treatment-naïve CD25 (+) and CD25 (−) patients, as well as in patients undergoing retreatment with DD. Duration of response and progression free survival were also quite favorable across the different CTCL subgroups.