Description:
21134 Background: Clofarabine (CLOLAR®) is a next-generation nucleoside analog designed as a hybrid molecule to improve the efficacy and minimize the extramedullary toxicity of other nucleoside analogs. Such analogs are known to have a variety of effects on both humoral and T-cell immune function. Fludarabine, the drug most closely related to clofarabine, causes major alterations in the CD4:CD8 lymphocyte ratios, associated with marked increases in the rate of opportunistic infections. In contrast, gemcitabine has a selective detrimental effect on the B-lymphocyte subset. Therefore, while conducting a phase I dose-finding trial of clofarabine in patients with solid tumors, we investigated its effects on lymphocyte sub-populations. Methods: A phase I dose-finding study is ongoing in patients with solid tumors who receive clofarabine once a week for 3 weeks every 28 days. Blood samples were collected from patients in the highest dose levels before, during, and after clofarabine administration for lymphocyte quantitation and phenotyping using flow cytometry. Results: Of the 11 patients who had samples collected, 5 currently have both baseline and postbaseline values available (1 at the 129 mg/m2 dose level and 4 at the 103 mg/m2 dose level). Overall, the percentage of T cells and CD8 suppressor cells did not decrease significantly with clofarabine administration. In 1 patient where data from 2 cycles were available, CD4 cells decreased slightly after the first cycle, suggesting a possible cumulative effect. However, in all 5 patients CD19 cells decreased significantly after the first infusion of clofarabine and remained suppressed for the duration of the study period. Conclusions: Although clofarabine is a purine analog (as is fludarabine), its effects on lymphocyte subsets more closely resemble gemcitabine, a pyrimidine analog. If substantiated, these findings should have bearing on future decisions about appropriate drug combinations involving clofarabine. No significant financial relationships to disclose.