CHK1 Inhibition Synergizes with Gemcitabine Initially by Destabilizing the DNA Replication Apparatus.
Boyce, Richard J
Boyle, Robert G
American Association for Cancer Research (AACR)
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Koh, S., Courtin, A., Boyce, R. J., Boyle, R. G., Richards, F., & Jodrell, D. (2015). CHK1 Inhibition Synergizes with Gemcitabine Initially by Destabilizing the DNA Replication Apparatus.. Cancer Res, 75 3583-3595. https://doi.org/10.1158/0008-5472.CAN-14-3347
Combining cell-cycle checkpoint kinase inhibitors with the DNA-damaging chemotherapeutic agent gemcitabine offers clinical appeal, with a mechanistic rationale based chiefly on abrogation of gemcitabine-induced G2-M checkpoint activation. However, evidence supporting this mechanistic rationale from chemosensitization studies has not been consistent. Here we report a systematic definition of how pancreatic cancer cells harboring mutant p53 respond to this combination therapy, by combining mathematical models with large-scale quantitative biologic analyses of single cells and cell populations. Notably, we uncovered a dynamic range of mechanistic effects at different ratios of gemcitabine and CHK1 inhibitors. Remarkably, effective synergy was attained even where cells exhibited an apparently functional G2-M surveillance mechanism, as exemplified by a lack of both overt premature CDK1 activation and S-phase mitotic entry. Consistent with these findings, S-G2 duration was extended in treated cells, leading to a definable set of lineage-dependent catastrophic fates. At synergistic drug concentrations, global replication stress was a distinct indicator of chemosensitization as characterized molecularly by an accumulation of S-phase cells with high levels of hyperphosphorylated RPA-loaded single-stranded DNA. In a fraction of these cells, persistent genomic damage was observed, including chromosomal fragmentation with a loss of centromeric regions that prevented proper kinetochore-microtubule attachment. Together, our results suggested a "foot-in-the-door" mechanism for drug synergy where cells were destroyed not by frank G2-M phase abrogation but rather by initiating a cumulative genotoxicity that deregulated DNA synthesis.
CHK1, gemcitabine, synergy, cell cycle checkpoint, DNA damage response
This study was funded by Cancer Research UK via Institute Senior Group Leader funding (C14303/A17197) to DI Jodrell, and by Sentinel Oncology through an award from Innovate UK.
Cancer Research UK (CB4270)
External DOI: https://doi.org/10.1158/0008-5472.CAN-14-3347
This record's URL: https://www.repository.cam.ac.uk/handle/1810/248827