CHK1 inhibition as a strategy for targeting fanconi anemia (FA) DNA repair pathway deficient tumors

Background: DNA repair deficient tumor cells have been shown to accumulate high levels of DNA damage. Consequently, these cells become hyper-dependent on DNA damage response pathways, including the CHK1-kinase-mediated response. These observations suggest that DNA repair deficient tumors should exhibit increased sensitivity to CHK1 inhibition. Here we offer experimental evidence in support of this hypothesis. Results: Using isogenic pairs of cell lines differing only in the Fanconi Anemia ( FA) DNA repair pathway, we showed that FA deficient cell lines were hypersensitive to CHK1 silencing by independent siRNAs as well as CHK1 pharmacologic inhibition by Go6976 and UCN-01. In parallel, an siRNA screen designed to identify gene silencings synthetically lethal with CHK1 inhibition identified genes required for FA pathway function. To confirm these findings in vivo, we demonstrated that whole zebrafish embryos, depleted for FANCD2 by a morpholino approach, were hypersensitive to Go6976. Silencing of FA genes led to hyper-activation of CHK1 and vice versa. Furthermore, inactivation of CHK1 in FA deficient cell lines caused increased accumulation of DNA strand and chromosomal breakages. These results suggest that the functions subserved by CHK1 and the FA pathway mutually compensate in maintaining genome integrity. As CHK1 inhibition has been under clinical trial in combination with cisplatin, we showed that the FA specific tumoricidal effect of CHK1 inhibition and cisplatin was synergistic. Conclusion: Taken together, these results suggest CHK1 inhibition as a strategy for targeting FA deficient tumors.