Checkpoint kinase 1 down-regulation by an inducible small interfering RNA expression system sensitized in vivo tumors to treatment with 5-fluorouracil.

Clin Cancer Res

Laboratory of Molecular Pharmacology, Department of Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy.

Published: August 2008

Purpose: After DNA damage, checkpoints pathways are activated in the cells to halt the cell cycle, thus ensuring repair or inducing cell death. To better investigate the role of checkpoint kinase 1 (Chk1) in cellular response to different anticancer agents, Chk1 was knocked down in HCT-116 cell line and in its p53-deficient subline by using small interfering RNAs (siRNA).

Experimental Design: Chk1 was abrogated by transient transfection of specific siRNA against it, and stable tetracycline-inducible Chk1 siRNA clones were obtained transfecting cells with a plasmid expressing two siRNA against Chk1. The validated inducible system was then translated in an in vivo setting by transplanting the inducible clones in nude mice.

Results: Transient Chk1 down-regulation sensitized HCT-116 cells, p53-/- more than the p53 wild-type counterpart, to DNA-damaging agents 5-fluorouracil (5-FU), doxorubicin, and etoposide treatments, with no modification of Taxol and PS341 cytotoxic activities. Inhibition of Chk1 protein levels in inducible clones on induction with doxycycline correlated with an increased cisplatin and 5-FU activity. Such effect was more evident in a p53-deficient background. These clones were transplanted in nude mice and a clear Chk1 down-regulation was shown in tumor samples of mice given tetracycline in the drinking water by immunohistochemical detection of Chk1 protein. More importantly, an increased 5-FU antitumor activity was found in tumors with the double Chk1 and p53 silencing.

Conclusions: These findings corroborate the fact that Chk1 protein is a molecular target to be inhibited in tumors with a defective G1 checkpoint to increase the selectivity of anticancer treatments.

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http://dx.doi.org/10.1158/1078-0432.CCR-08-0304DOI Listing

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