Abstract
The therapeutic efficacy of nucleoside analogues, e.g. gemcitabine, against cancer cells can be augmented by inhibitors of checkpoint kinases, including Wee1, ATR, and Chk1. We have compared the chemosensitizing effect of these inhibitors in cells derived from pancreatic cancer, a tumor entity where gemcitabine is part of the first-line therapeutic regimens, and in osteosarcoma-derived cells. As expected, all three inhibitors rendered cancer cells more sensitive to gemcitabine, but Wee1 inhibition proved to be particularly efficient in this context. Investigating the reasons for this potent sensitizing effect, we found that Wee1 inhibition or knockdown not only blocked Wee1 activity, but also reduced the activation of ATR/Chk1 in gemcitabine-treated cells. Combination of several inhibitors revealed that Wee1 inhibition requires Cyclin-dependent kinases 1 and 2 (Cdk1/2) and Polo-like kinase 1 (Plk1) to reduce ATR/Chk1 activity. Through activation of Cdks and Plk1, Wee1 inhibition reduces Claspin and CtIP levels, explaining the impairment in ATR/Chk1 activity. Taken together, these results confer a consistent signaling pathway reaching from Wee1 inhibition to impaired Chk1 activity, mechanistically dissecting how Wee1 inhibitors not only dysregulate cell cycle progression, but also enhance replicative stress and chemosensitivity towards nucleoside analogues.
Highlights
Gemcitabine (2’, 2’-difluorodeoxycytidine, dFdC), an analogue of deoxycytidine, is active against a broad spectrum of solid tumors, mostly pancreatic cancer [1], and breast cancer [2], bladder cancer [3] or non-small cell lung cancer [4]
Combination of several inhibitors revealed that Wee1 inhibition requires Cyclin-dependent kinases 1 and 2 (Cdk1/2) and Polo-like kinase 1 (Plk1) to reduce ATR/Chk1 activity
We found that Wee1 inhibition is potent to eliminate gemcitabine-treated cancer cells, as compared to the inhibition of Chk1 or ATR
Summary
Gemcitabine (2’, 2’-difluorodeoxycytidine, dFdC), an analogue of deoxycytidine, is active against a broad spectrum of solid tumors, mostly pancreatic cancer [1], and breast cancer [2], bladder cancer [3] or non-small cell lung cancer [4]. Cancer cells can evade the normal physiological signals controlling growth and survival by deregulating kinases. This notion initiated the design of small molecules that target and inhibit this class of enzymes [7]. Inhibitors of checkpoint kinases enhance replicative stress, DNA damage, and tumor cell death. There is a lack of quantitative comparisons between the efficacy of inhibiting different checkpoint kinases to sensitize cells towards gemcitabine. It remains to be determined how Wee and www.impactjournals.com/oncotarget
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