Search

Reports that Harry Flood Byrd, crippled by arthritis and by generally failing health, resigned last November from the Senate seat he had held for 30 years. Information that his 51-year-old son, Harry Byrd Jr. had won nomination in his own right to his father's unexpired term; Evidence of his abiding friendship for the African American people in the traditional relationship of a segregated lifetime; Significance of his life-long support of the national parks of Virginia.

Suppression of T-cell immunity seen in children with inherited purine nucleoside phosphorylase (PNP) deficiency supports the potential application of PNP inhibitors for the therapy of T-cell malignancies. Forodesine (FodosineTM) is a specific PNP inhibitor that raises plasma 2′-deoxyguanosine (dGuo) and intracellular dGTP levels, leading to T-cell apoptosis. IV administration of forodesine has shown activity in cutaneous T-cell lymphoma (CTCL) patients. To determine the safety, pharmacokinetics and pharmacodynamics of oral forodesine in patients with refractory CTCL, as well as preliminary evidence of efficacy, five cohorts of patients (≥ 3patients per cohort) were evaluated sequentially, receiving forodesine at 40, 80, 160, 320, and 480 mg/m2 once per day for 28 days. At the end of the treatment cycle (Day 28), all patients with stable or improved disease could enter a long-term, follow-up period. To date, 12 patients have been treated, 11 completing the 28-day cycle. Forodesine is orally absorbed (40%–50%), mean terminal half-life of 12 to 20 h. dGuo levels were elevated in all patients (0.8–2.8 μM, predose levels ≤ 0.004 μM). Forodesine was generally safe and well tolerated in this population. Safety data is available for first 7 patients. No serious adverse events possibly related to the drug occurred. The most common adverse event possibly drug related was nausea (2 patients). Of the 11 patients completing the treatment cycle, 9 began long-term treatment. Of these 9 patients, 4 have received >3 months of treatment, while 1 patient continues to receive for >8 months. Efficacy data are available for 8 patients: 2 with partial response, 3 with minor response, 2 with progressive disease, and 1 with stable disease (Table). Forodesine showed preliminary evidence of clinical activity in refractory CTCL patients. Additional clinical and pharmacodynamic data will be presented. Clinical and Pharmacodynamic Activity of Oral Forodesine In CTCL Patients Patient Diagnosis Dose (mg/m2) Treatment Plasma dGuo (Cmax, M) μ Clinical Response PR = partial response; MR = minor response; SD = stable disease; PD = progressive disease; N/A = not available 2001 Sezary syndrome (IVA) 40 Completed 0.6 PR 3001 Mycosis fungoides (IVB) 40 Completed 1.7 PD 3002 Mycosis fungoides (IIB) 40 Completed 1.2 MR 3003 Mycosis fungoides (IB) 80 Completed 1.2 MR 3004 Sezary syndrome (IVA) 80 Completed 1.0 MR 3005 Sezary syndrome 80 Completed 1.6 PD 2002 IIA 80 Completed 1.1 PR 2003 III 80 Completed 1.7 N/A 3006 Mycosis fungoides/Sezary syndrome (IVB) 160 Completed 2.8 SD 4001 III 320 Completed 1.8 N/A 1001 Mycosis fungoides (IB) 320 Completed 1.3 N/A 3012 Mycosis fungoides/Sezary syndrome (IVA vs B) 320 Not Completed N/A Not evaluable

PNP represents an attractive target for drug development based on the profound, selective impairment of T-cell function seen in individuals with an inherited deficiency of PNP. Forodesine, a potent, specific transition-state analog inhibitor of PNP, is currently being investigated for safety and efficacy in T-cell and other malignancies. In a phase I/II single-center, intrapatient dose-escalation study, forodesine (starting dose: 40 mg/m2) was given to 5 patients with relapsed/refractory, aggressive T-cell leukemia/ lymphoma via a 30-min IV infusion, followed 24 hrs later by doses administered every 12 hrs for a total of 9 doses; courses could be repeated every 3–4 weeks, as required. Two patients with refractory T-cell prolymphocytic leukemia (T-PLL) and two patients with T-cell acute lymphoblastic leukemia (T-ALL) showed a decrease in leukemic or prolymphocytic counts in peripheral blood and/or bone marrow. All responders had increases in plasma 2′-deoxyguanosine (dGuo) (Cmax: 2.9 to 34 μM; baseline concentration: <.004 μM) and 4/5 responders showed elevated intracellular dGTP levels (10- to 60-fold). Forodesine was generally safe and well tolerated at all dose levels with no dose-limiting toxicities and only two adverse events (ie, acute renal failure and neutropenic infection) that were possibly drug-related. These promising results led to a phase II multi-center, open-label, repeat-dose trial in patients with advanced T-cell malignancies, in which forodesine (40 mg/m2) is infused for 30 mins for 5 days followed by at least 2 non-treatment days for up to 5 additional cycles. Out of 3 patients enrolled to-date, 2 T-ALL patients completed 6 courses of therapy with a dramatic reduction in WBC count (Fig 1A and 1B); 1 splenic T-cell lymphoma patient discontinued due to disease progression. Forodesine resulted in striking elevations in plasma dGuo. Peripheral blast cells in Patient 01 were undetectable at the start of the second course and remained undetectable after 6 courses (Fig 1A), and the bone marrow blast cells were reduced from >90% to near-normal levels. However, the contribution of a single dose of dexamethasone (40 mg IV given on Day 3) to the reduction in WBC count and blast cells is unknown. This patient’s peripheral blood hematologic profile (WBC, absolute neutrophil, platelet counts and hemoglobin level) returned to near-normal, indicating a specificity of forodesine for leukemic cell populations and supporting that forodesine is an important breakthrough in the development of less toxic ALL therapy. Additional phase II results will be presented. Figure Figure

bibliog