Dasatinib Has Activity in Relapsed/Refractory Chronic Lymphocytic Leukemia (CLL/SLL), a Phase II Trial

Background: Preclinical studies have shown that CLL cells overexpress lyn kinase protein, and in vitro inhibition of lyn kinase leads to apoptosis of the CLL cells (Contri, J Clin Invest 2005). Because dasatinib has been shown to inhibit lyn kinase in CML cells at concentrations easily achievable in patients, we undertook this phase II study in patients with previously treated CLL/SLL.

Methods: Patients were required to be over 18 years of age, have a diagnosis of CLL/SLL by flow cytometry or immunohistochemistry, and have failed either 1 course of treatment with a fludarabine-containing regimen or 2 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.

Results: Among the 15 patients enrolled there were 10 male and 5 female subjects with a median age of 59 years (40–78 years). ECOG performance status was 0 in 9 subjects, 1 in 3, and 2 in 3 subjects. All patients had previously received fludarabine, and 5 patients required treatment within 6 months of their last regimen. The median number of prior treatments was 3 (range: 1 to 7). By cytogenetic/FISH analysis there were 5 patients with del(17p) and 6 patients with del(11q). All patients required treatment by NCI–WG criteria. The major toxicity encountered was myelosuppression: grade 3 + 4 neutropenia in 10 subjects, grade 3 + 4 thrombocytopenia in 4 subjects. Gastrointestinal toxicity was minor with only 1 subject experiencing grade 3 diarrhea. Other toxicities: 1 patient had a grade 2 pleural effusion, 1 patient had a transient serum K=9.9 (likely an artifact of high white count and without clinical sequelae), and 1 patient had a transiently prolonged QTc of 516 ms. There were no fatal events, and all toxicities were reversible. The median duration on study was 10 weeks, but 5 responding or stable patients have remained on treatment for over 9 months. Partial responses (PR) by NCI-WG criteria were achieved in 2 of the 15 patients (13% with 90% CI 2%–36%). An additional 2 patients would have qualified for PR (lasting >2 months) except for myelosuppression. Among the remaining 11 patients, 6 had nodal responses (2 CR and 4 PR) by physical exam (PE) without a 50% reduction in lymphocytosis. CT scans confirmed nodal responses in 3 of the 10 patients with nodal responses by PE. The relationship between clinical response and lyn kinase, bcl-2, and mcl-1 expression will be presented at the meeting.

Conclusions: Dasatinib has modest activity in CLL, and combinations with standard agents, perhaps in an intermittent schedule, should be considered in subsequent trials.