Phase I Study of Forodesine (BCX1777), An Oral PNP Inhibitor In Patients with Relapsed or Refractory T/NK Malignancies.

Forodesine is a rationally designed potent inhibitor of purine nucleoside phosphorylase (PNP) that leads to elevation of plasma deoxyguanosine (dGuo) and intracellular accumulation of dGTP levels and then apoptosis mainly in T cells. Oral forodesine has shown clinical activity in patients with cutaneous T-cell lymphoma (CTCL) (M. Duvic et al, ASH 2007). The objective of this phase I study was to evaluate the safety, PK profile, and efficacy of oral forodesine in patients with recurrent or refractory T/NK malignancies in Japan.

An open-label dose-escalation study of forodesine, 100 to 300 mg/body qd for 4 weeks, was conducted to evaluate safety profile (dose-limiting toxicities, DLT), tolerability and PK profile as primary endpoints. Forodesine was administered until disease progression or unacceptable toxicity is observed. Relapsed or refractory T/NK malignancies with PS 0 to 1 and without major organ dysfunction were eligible.

Overall, 13 Japanese patients, 8 males and 5 females, with a median age of 69 (range 30–77) years were enrolled in the study: 5 patients in the 100mg cohort, 3 in the 200mg cohort and 5 in the 300mg cohort. Patients’ histopathologic subtypes were as follows: peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) (6 patients), anaplastic large cell lymphoma (ALCL) (3), primary cutaneous ALCL (C-ALCL) (2) and mycosis fungoides (MF) (2). Median stage and prior treatment regimen were IIIA (range IA-IVA) and 2 (range 1, 8), respectively.

No DLT was observed and a maximum tolerated dose was never defined. The most common toxicities of grade 2 or less were constipation (39 %), rash (31%), lymphopenia (31 %), neutropenia (23 %), nausea (23 %), peripheral edema (23 %), LDH elevation (23 %) and leukopenia (23 %). The toxicities of grade 3 or greater were lymphopenia (62 %), anemia (15 %), leukopenia (8 %), thrombocytopenia (8 %) and viral infection (8 %). Median baseline, nadir, and last visit lymphocytes counts (1,000/μL) were 0.69 (95% CI: 0.56, 1.18), 0.35 (95% CI: 0.14, 0.60) and 0.60 (95% CI: 0.24, 0.95), respectively.

Plasma levels for forodesine showed less than dose-proportional increase in exposure as mean AUC at Day 1 was 1,948 (ng·h/mL) in the 100mg cohort, 4,608 (ng·h/mL) in the 200mg cohort, and 4,596 (ng·h/mL) in the 300mg cohort. The levels for dGuo displayed a similar trend, with mean AUC at Day 1 4,023 (ng·h/mL) in the 100mg cohort, 5,705 (ng·h/mL) in the 200mg cohort, and 6,074 (ng·h/mL) in the 300mg cohort.

One patient with ALCL reached complete response (CR) in the 100mg cohort and 2 patients with MF reached partial response in the 200mg cohort. In addition, 4 patients with stable disease (SD) were observed: 1 patient with PTCL-NOS in the 100mg cohort, 1 with C-ALCL in the 200mg cohort and 2 with C-ALCL and PTCL-NOS in the 300mg cohort. As of Aug, 2010, 2 patients with ALCL (CR patient in the 100mg cohort) and PTCL-NOS (SD patient in the 300mg cohort) have continued the treatment for more than 510 days and 290 days, respectively.

Conclusion: Oral forodesine was well tolerated at all the dose levels tested with similar PK findings to those in the CTCL study in USA, demonstrating potential efficacy against relapsed or refractory T/NK lymphomas including PTCL for the first time. Based on these promising data, we are planning a phase I /II study of forodesine in patients with relapsed or refractory PTCL.

No relevant conflicts of interest to declare.