A Phase II Study of Dasatinib in Relapsed and Refractory Chronic Lymphocytic Leukemia (CLL/SLL).

Preclinical studies have shown that proliferation and survival of CLL cells are associated with overexpression of the Lyn kinase protein, and in vitro inhibition of Lyn kinase leads to apoptosis of the CLL cells (Contri, J Clin Invest 2005). Because dasatinib inhibits Lyn kinase in CML cells at doses easily achievable in patients, we undertook this phase II study of dasatinib in patients with previously treated CLL/SLL. Patients were required to be over 18 years of age, have a diagnosis of CLL/SLL by flow cytometry/immunostains, and have failed at least 1 course of treatment with a fludarabine-containing regimen or at least 2 courses of non-fludarabine containing regimens. The starting dose of dasatinib was 140 mg daily by mouth. This dose could be reduced to 100 mg or 80 mg daily for toxicity. At baseline all patients had bone marrow biopsies and CT scans, and these were repeated at 2 months. Sequential blood and bone marrow samples were tested for Lyn kinase activity. The design of the study provided for 2 phases such that if 3 responses were seen among the first 15 patients, the trial would expand to enroll another 20 patients. Among the first 9 patients enrolled there were 4 male and 5 female subjects with a median age of 59 years (40–78 years). ECOG performance status was 0 in 4 subjects, 1 in 3, and 2 in 2 subjects. All patients had previously received fludarabine: 1 subject had 1 prior treatment, 3 had 2 prior treatments, 3 had 3 prior treatments, and 2 had 4 prior treatments. By cytogenetic/FISH analysis there were 2 patients with del(17p) and another 4 patients with del(11q). All patients required treatment by NCI Working Group criteria. The major toxicity encountered was myelosuppression: grade 3 + 4 neutropenia in 7 subjects, grade 3 + 4 thrombocytopenia in 5 subjects. Gastrointestinal toxicity was minor with only 1 subject experiencing grade 3 diarrhea. One subject developed a grade 2 pleural effusion. There was 1 patient with an electrolyte imbalance consisting of a transient serum K=6.8, and in 1 patient there was a transiently prolonged QTc of 516 ms. There were no fatal events, and all toxicities were reversible. The median duration of treatment on study was 9 weeks with a range of 4 to 23 weeks. The clinical response data of the first 15 patients will be presented along with the correlative studies of Lyn kinase inhibition by dasatinib.