In Vivo and in Vitro Activity And Mechanism Of Action of the Multidrug Cytarabine-L-Glycerylyl-Fluorodeoxyuridine

Abstract

Multidrugs have the potential to bypass resistance. We investigated the in vitro activity and resistance circumvention of the multidrug cytarabine-L-fluorodeoxyuridine (AraC-L-5FdU), linked via a glycerophospholipid linkage. Cytotoxicity was determined using sensitive (A2780, FM3A/0) and resistant (AG6000, AraC resistant, deoxycytidine kinase deficient; FM3A/TK-, 5FdU resistant, thymidine kinase deficient) cell lines. Circumvention of nucleoside transporter and activating enzymes was determined using specific inhibitors, HPLC analysis and standard radioactivity assays. AraC-L-5FdU was active (IC50: 0.03 μM in both A2780 and FM3A/0), had some activity in AG6000 (IC50: 0.28 μ M), but no activity in FM3A/TK⁻ (IC50: 18.3 μM). AraC-nucleotides were not detected in AG6000. 5FdU-nucleotides were detected in all cell lines. AraC-L-5FdU did not inhibit TS in FM3A/TK⁻ (5%). Since phosphatase/nucleotidase-inhibition reduced cytotoxicity 7–70-fold, cleavage seems to be outside the cell, presumably to nucleotides, and then to nucleosides. The multidrug was orally active in the HT-29 colon carcinoma xenografts which are resistant toward the single drugs.

Keywords:

• Multidrugs
• cytarabine
• fluorodeoxyuridine
• resistance

This study was supported by a mini-grant from Drug Development Committee (DDC) of the EORTC PAMM group.