CHEK1 and exocrine pancreatic carcinoma: Since Rac1 is a relevant target of statins5 and, moreover, is present in the nucleus,46 we speculate that it interferes with the ATM/ATR-regulated DDR.47 Accordingly, pharmacological inhibition of Rac1 blocks IR-stimulated ATM/Chk2 and ATR/Chk1 activity in pancreatic carcinoma cells.48, 49 Interestingly, zoledronic acid, which inhibits farnesylpyrophosphate (FPP) synthesis, also promotes the repair of IR-induced DSBs in mesenchymal stem cells.50