A potent Chk1 inhibitor is selectively cytotoxic in melanomas with high levels of replicative stress

Abstract

There are few effective treatments for metastatic melanoma. Checkpoint kinase 1 (Chk1) inhibitors are being trialled for their efficacy in enhancing conventional chemotherapeutic agents, but their effectiveness as single agents is not known. We have examined the effectiveness of two novel Chk1 selective inhibitors, AR323 and AR678, in a panel of melanoma cell lines and normal cell types. We demonstrate that these drugs display single-agent activity, with IC50s in the low nanomolar range. The drugs produce cytotoxic effects in cell lines that are most sensitive to these drugs, whereas normal cells are only sensitive to these drugs at the higher concentrations where they have cytostatic activity. The cytotoxic effect is the consequence of inhibition of S-phase Chk1, which drives cells prematurely from late S phase into an aberrant mitosis and results in either failure of cytokinesis or cell death through an apoptotic mechanism. The sensitivity to the Chk1 inhibitors was correlated with the level of endogenous DNA damage indicating replicative stress. Chk1 inhibitors are viable single-agent therapies that target melanoma cells with high levels of endogenous DNA damage. This sensitivity suggests that Chk1 is a critical component of an adaptation to replicative stress in these cells. It also suggests that markers of DNA damage may be useful in identifying the melanomas and potentially other tumour types that are more likely to be sensitive to Chk1 inhibitors as single agents.

E1a promotes c-Myc-dependent replicative stress

“…33 In addition, our data provides a novel explanation for the observed pattern of H2AX phosphorylation associated to E1a expression trough RS mediated by c-Myc rather than through ATM-dependent mechanism. 37 Finally, regarding the role of Chk1 in E1a-expressing cells, our data support the idea that this could be a key element to maintain viability in these cells, as has been shown in c-Myc-driven tumorgenesis or in melanoma, 32,38 and even could be implicated in the transforming properties of E1a as has been shown in other experimental systems.…”

“…4D and E). Considering recent evidences showing how Chk1 inhibitors selectively kill cells with a marked RS, 32,38 we decided to challenge E1a-expressing cells to Chir-124, a known inhibitor for Chk1. 39 Interestingly, E1a cells showed a higher toxicity in response to Chir-124 (Fig.…”

Combination Drug Scheduling Defines a “Window of Opportunity” for Chemopotentiation of Gemcitabine by an Orally Bioavailable, Selective ChK1 Inhibitor, GNE-900

“…Although targeting such intra-S functions of ChK1 in the face of mounting replication stress can result in replication fork collapse and a significant induction of DSBs, we have found that chemo combinations with this mechanism of action are poorly tolerated in animals, even with extensive modification to both dose and schedule (e.g., thymidine monophosphate depletion with Xeloda; data not shown). However, the synthetic lethal potential of ChK1 inhibition may provide single-agent activity in cancers with a high degree of replicative stress (43,44).…”

Mitogen-Activated Protein Kinase–Activated Protein Kinase 2 in Neuroinflammation, Heat Shock Protein 27 Phosphorylation, and Cell Cycle: Role and Targeting

“…Finally, based on the concept that many tumors exhibit high levels of replicative stress, the sole inhibition of Chk1 has been shown to effectively target melanoma cells with significant intrinsic DNA damage (Brooks et al, 2013). The cytotoxic effect of Chk1 inhibitors resulted from inhibition of Chk1 activity in the S phase driving premature exit from the S phase into an aberrant mitosis, resulting in either failure of cytokinesis or cell death by an apoptotic mechanism.…”