Selective Chk1 inhibitors differentially sensitize p53‐deficient cancer cells to cancer therapeutics

Abstract

The majority of cancer therapeutics induces DNA damage to kill cells. Normal proliferating cells undergo cell cycle arrest in response to DNA damage, thus allowing DNA repair to protect the genome. DNA damage induced cell cycle arrest depends on an evolutionarily conserved signal transduction network in which the Chk1 kinase plays a critical role. In mammalian cells, the p53 and RB pathways further augment the cell cycle arrest response to prevent catastrophic cell death. Given the fact that most tumor cells suffer defects in the p53 and RB pathways, it is likely that tumor cells would depend more on the Chk1 kinase to maintain cell cycle arrest than would normal cells. Therefore Chk1 inhibition could be used to specifically sensitize tumor cells to DNA-damaging agents. We have previously shown that siRNA-mediated Chk1 knockdown abrogates DNA damage-induced checkpoints and potentiates the cytotoxicity of several DNA-damaging agents in p53-deficient cell lines. In this study, we have developed 2 potent and selective Chk1 inhibitors, A-690002 and A-641397, and shown that these compounds abrogate cell cycle checkpoints and potentiate the cytotoxicity of topoisomerase inhibitors and c-radiation in p53-deficient but not in p53-proficient cells of different tissue origins. These results indicate that it is feasible to achieve a therapeutic window with 1 or more Chk1 inhibitors in potentiation of cancer therapy based on the status of the p53 pathway in a wide spectrum of tumor types. ' 2006 Wiley-Liss, Inc.Key words: Chk1; Cdc25A; small molecule inhibitor; cell cycle checkpoint; topoisomerase inhibitors; camptothecin; doxorubicin DNA damaging agents are mainstays of cancer therapy. In response to DNA damage, proliferating cells arrest at distinct transition points along the cell cycle to allow time for DNA repair. The successful repair of DNA lesions is critical for clonogenic survival and the restoration of genome integrity. Excessive and persistent DNA damage, on the other hand, leads to cell death by causing premature senescence, apoptosis, necrosis or mitotic catastrophe.

Status of p53 in human cancer cells does not predict efficacy of CHK1 kinase inhibitors combined with chemotherapeutic agents

“…To confirm these findings, we used the non-selective CHK1 inhibitor UCN-01, which had been previously shown to abrogate the S and G2/M checkpoints and induce mitotic catastrophe in p53-deficient cells (Wang et al, 1996;Shao et al, 1997;Hirose et al, 2001;Tse and Schwartz 2004;Chen et al, 2006;Levesque et al, 2008). Like siRNA-mediated knockdown of CHK1, UCN-01 by itself reduced cell viability even without chemotherapeutics (Figures 4a and b).…”

“…Contrary to these results, other groups reported that UCN-01 and other CHK1 inhibitors, when combined with DNA damaging agents, reduced the efficacy of colony formation of p53-inactive cell lines more drastically than that of their isogenic p53-active cell lines (Wang et al, 1996;Shao et al, 1997;Chen et al, 2006). In these and other studies, UCN-01 and other CHK1 inhibitors, as well as CHK1 knockdown, were reported to potentiate the toxicity of DNA damaging agents (Wang et al, 1996;Shao et al, 1997;Hirose et al, 2001;Tse and Schwartz 2004;Chen et al, 2006;Levesque et al, 2008).…”

Harnessing the complexity of DNA-damage response pathways to improve cancer treatment outcomes

“…Other selective Chk1 inhibitors were also shown to abrogate the S-phase delay induced by topoisomerase inhibitors (Chen et al, 2006;Tse et al, 2007) and to potentiate the cytotoxicity of g-radiation in p53-deficient cells (Chen et al, 2006). These effects were associated with increased mitotic entry, induction of DSB and apoptosis, as well as marked inhibition of proliferation (Chen et al, 2006;Tse et al, 2007;Blasina et al, 2008;Zhang et al, 2009). The synergy between replication stress inducers and Chk1 inhibitors was translated into a dose-dependent increase in tumor growth delay in vivo (Tse et al, 2007;Blasina et al, 2008;Zhang et al, 2009).…”

“…PF-00477736 also inhibits the mitotic spindle checkpoint and the DNA-damage checkpoint induced by docetaxel . Other selective Chk1 inhibitors were also shown to abrogate the S-phase delay induced by topoisomerase inhibitors (Chen et al, 2006;Tse et al, 2007) and to potentiate the cytotoxicity of g-radiation in p53-deficient cells (Chen et al, 2006). These effects were associated with increased mitotic entry, induction of DSB and apoptosis, as well as marked inhibition of proliferation (Chen et al, 2006;Tse et al, 2007;Blasina et al, 2008;Zhang et al, 2009).…”

Protein Phosphorylation in Human Health

“…These inhibitors block a ssDNA repair pathway which is mostly dispensable for normal cells, but essential for cells deficient in HR, such as BRCA1/2 mutant cells [144]. Other examples of synthetic lethality could be the use of Chk1 inhibitors and ATR inhibitors, to treat p53 deficient tumors [145][146][147][148].…”