Antiproliferative activity, mechanism of action and oral antitumor activity of CP-4126, a fatty acid derivative of gemcitabine, in in vitro and in vivo tumor models

Abstract

Gemcitabine is a deoxycytidine (dCyd) analog with activity in leukemia and solid tumors, which requires phosphorylation by deoxycytidine kinase (dCK). Decreased membrane transport is a mechanism of resistance to gemcitabine. In order to facilitate gemcitabine uptake and prolong retention in the cell, a lipophilic pro-drug was synthesized (CP-4126), with an elaidic fatty acid esterified at the 5'position. CP-4126 was tested in cell lines resistant to cytarabine, another dCyd analog or gemcitabine. Activity of gemcitabine and the derivative was comparable in the parent cell lines, while in dCK deficient cells all compounds were inactive. However, inhibition of nucleoside transport increased the IC(50) for gemcitabine up to 200-fold, but not for CP-4126, underlining the independence of a nucleoside transporter. For in vivo evaluation, nude mice bearing a human xenograft were treated intraperitoneally every third day for five doses at the maximal tolerated dose. In melanoma, sarcoma, lung, prostate, pancreatic and breast cancer xenografts, gemcitabine and CP-4126 were equally and highly effective; in four other xenografts moderately but equally active. In contrast to gemcitabine, CP-4126 could be administered orally, with a schedule and dose dependent toxicity and antitumor activity. In a colon cancer xenograft, antitumor activity of orally administered CP-4126 was equal to the intraperitoneally administered drug. In conclusion, CP-4126 is membrane transporter independent. Intraperitoneally administered CP-4126 was as effective as gemcitabine in several xenografts and CP-4126 is tolerated when orally administered. CP-4126 seems to be a promising new anticancer drug.

Fig. 1

a Chemical structure of gemcitabine and the fatty acid derivative CP-4126. b Mean IC₅₀, TGI and LC₅₀ graphs of CP-4126 on the NCI60 cell lines. Values represent Log values (M). Bars represent deviations of the means of all tested cell lines. Over all 60 cell lines the average IC₅₀ for CP-4126 was 0.1 μM, the TGI 12.6 μM and the LC₅₀ 70.9 μM. For dFdC the IC₅₀ was 0.2 μM, the TGI 0.9 μM and the LC₅₀ 1.0 μM. The dFdC data were obtained from the NCI60 database (dtp.nci.nih.gov), which also lists the separate disease specific cell lines. c COMPARE analysis of CP-4126 (NSC 735837) with standard agents of the NCI database including gemcitabine (NSC613327). 1 DNA antimetabolite, 2 topoisomerase 1 inhibitor, 3 topoisomerase 2 inhibitor, 4 alkylating agent

Fig. 2

Antitumor efficacy of CP-4126 as an oral drug in the human colon cancer xenograft Co6044. Mice treated with saline, qd 1–5 (▲), 100 mg/kg CP-4126, qd 1,7 (●), 20 mg/kg CP-4126. qd 1, 4, 7, 10, 13, (∇) and 10 mg/kg CP-4126, qd 1–5 (□). The curve for the optimal schedule of gemcitabine (not shown) was in between that of the control and q3d schedule