CHIR-124, a novel potent inhibitor of Chk1, potentiates the cytotoxicity of topoisomerase I poisons in vitro and in vivo.

Purpose: Chk1 kinase is a critical regulator of both S and G(2)-M phase cell cycle checkpoints in response to DNA damage. This study aimed to evaluate the biochemical, cellular, and antitumor effects of a novel Chk1 inhibitor, CHIR124.

Experimental Design: CHIR-124 was evaluated for its ability to abrogate cell cycle checkpoints, to potentiate cytotoxicity, and to inhibit Chk1-mediated signaling induced by topoisomerase I poisons in human tumor cell line and xenograft models.

Tezacitabine enhances the DNA-directed effects of fluoropyrimidines in human colon cancer cells and tumor xenografts.

Tezacitabine is a nucleoside analogue characterized by a dual mechanism of action. Following intracellular phosphorylation, the tezacitabine diphosphate irreversibly inhibits ribonucleotide reductase, while the tezacitabine triphosphate can be incorporated into DNA during replication or repair, resulting in DNA chain termination. In the present study we have investigated the effect of the combination of tezacitabine and 5-fluorouracil (5-FU) or 5-fluoro-2'-deoxyuridine (FUdR) on HCT 116 human colon carcinoma cells and xenografts.