Phase 2 and pharmacodynamic study of oral forodesine in patients with advanced, fludarabine-treated chronic lymphocytic leukemia.

Forodesine is a new and potent purine nucleoside phosphorylase (PNP) inhibitor. Patients with chronic lymphocytic leukemia (CLL) with primary resistance to fludarabine-based therapy or with progressive disease were eligible for oral forodesine (200 mg/d) for up to 24 weeks. Eight patients with median lymphocyte count of 35.9 × 109/L and median serum β2 microglobulin level of 6.45 mg/L were treated. Six had Rai stage III to IV and were previously heavily treated (median prior therapy = 5). Two had transient decrease in lymphocyte count to normal, whereas in 5, disease progressed. Adverse events were mild. Steady-state level of forodesine ranged from 200 to 1300nM and did not reach desired 2μM level. PNP inhibition ranged from 57% to 89% and steady-state 2′-deoxyguanosine (dGuo) concentration median was 1.8μM. Intracellular deoxyguanosine triphosphate (dGTP) increase was very modest, from median of 6μM to 10μM. Compared with in vivo, in vitro incubations of CLL lymphocytes with 10 or 20μM dGuo and forodesine (2μM) resulted in accumulation of higher levels of dGTP (40-250μM) which resulted in increase in apoptosis. Forodesine has biologic activity in CLL; pharmacodynamic parameters suggest that an alternate dosing schedule and/or higher doses to achieve greater intracellular dGTP may be beneficial in this patient population. This study is registered at www.clinicaltrials.gov as #NCT00289549.