Abstract 3654: Clofarabine: factors influencing cytotoxicity and resistance in hematologic and solid malignancies

Abstract

Abstract Clofarabine is a new-generation nucleoside analog that was synthesized to combine the most favorable pharmacological properties of its congener fludarabine and cladribine. It acts as a strong inhibitor of DNA polymerase, DNA synthesis and ribonucletide reductase (R1/R2). Like other nucleoside analogues, clofarabine must be activated within cells to the 5′-triphodphate form initially by deoxycytidine kinase (dCK). In this study, the anticancer effect of clofarabine was investigated in three solid tumor cell lines, HCT116 (a colon carcinoma cell line), U1810 (a human non-small cell lung carcinoma cell line), and MCF7 (a mammary carcinoma cell line) and compared to four leukemic cell lines, CCRF-CEM, HL60, K562 and MOLT4. Clofarabine was investigated to enter into HCT116, U1810, and MCF7 in a clearly detectable manner by LigandTracer® White. At 10 µM a high signal is achieved and approaches equilibrium after 1∼2 hrs. Pre-incubation with 10 µM clofarabine resulted in rapid inhibition of thymidine incorporation and DNA synthesis. Induction of apoptosis by clofarabine was cell line dependent, but the average apoptotic level was higher in leukemic cell lines than solid tumor cell lines; however it seemed the sensitivity for apoptosis of cell line is correlated with the activity of dCK and thymidine kinase 1 (TK1) in the solid tumor cell lines. Upon treatment with 10 μM clofarabine for 24 hrs, apoptosis induction increased compared to untreated cells 3.1-, 2.9- and 2.1-fold; the activity of dCK 7.3-, 3.7- and 3.1-fold and the activity of TK1 4.2-, 1.4- and 1.2-fold in U1810, HCT116 and MCF7 cells, respectively. In general, the expression of R1, dCK and TK1 in leukemic cells was higher than in solid tumor cells, but the expression of R2, p53R2 and p53 varied among the cell lines. However, there was an inverse correlation between induction of apoptosis at 100nM clofarabine (upon 24 hours incubation) and the expression of p53R2 (spearman rank test −0.67, p=0.1). In addition, clofarabine treatment causes retardation in S-phase, which seems to be related to the activity of TK1 and the protein expression of R2 in U1810, HCT116 and MCF7 cells. This study is a first step to extend the application of clofarabine toward the solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3654.