2-Chlorodeoxyadenosine produces a high rate of complete hematologic remission in relapsed acute myeloid leukemia

The purine analog 2-chlorodeoxyadenosine (2-CDA) was well tolerated and showed promising anti-leukemic activity in a phase I trial conducted at St Jude Children's Research Hospital. To substantiate and extend this result, we performed a phase II trial in a representative group of children and young adults with relapsed acute leukemia.

Twenty-four patients (median age, 11 years) with acute myeloid or lymphoid leukemia in first or later relapse (acute myeloid leukemia [AML], 17; acute lymphoid leukemia [ALL], seven) were given continuous infusion 2-CDA for 5 days at 8.9 mg/m2/d. Patients with residual blast cells 10 days after treatment received a second course of 2-CDA that was identical to the first. Detailed pharmacokinetic studies were performed on plasma collected from five patients.

Eight (47%) of the 17 patients with AML had complete hematologic remissions (four after the initial course of 2-CDA), and two (12%) had partial remissions, for a total response rate of 59%. Only one child with ALL achieved remission. Seven of the responding patients underwent allogeneic or autologous bone marrow transplantation, with six remaining free of leukemia for a median of 7 months (range, 1 to 11 months). The major form of drug-induced toxicity was hematologic, with severe neutropenia and thrombocytopenia (National Cancer Institute [NCI] grade 3 or 4) developing in 34 of the 36 courses of 2-CDA. In responding patients, the median times to recovery of neutrophil counts greater than 0.5 x 10(9)/L and platelet counts greater than 50 x 10(9)/L were 18 and 21 days, respectively. There were no deaths due to toxicity. The mean steady-state plasma concentration of 2-CDA was 34.6 nmol/L (range, 20 to 54 nmol/L).

2-CDA given by prolonged continuous infusion has clinically significant activity against AML and merits further testing in multidrug regimens for this disease.