A new isoquinolinium derivative, cadein1, preferentially induces apoptosis in p53-defective cancer cells with functional mismatch repair via a p38-dependent pathway

We screened a protoberberine backbone derivative library for compounds with anti-proliferative effects on p53-defective cancer cells. A compound identified from this small molecule library, cadein1 (cancer-selective death inducer 1), an isoquinolinium derivative, effectively leads to a G₂/M delay and caspase-dependent apoptosis in various carcinoma cells with nonfunctional p53. The ability of cadein1 to induce apoptosis in p53-defective colon cancer cells was tightly linked to the presence ofa functionalDNAmismatch repair(MMR)system, which is an important determinant in chemosensitivity. Cadein1 was very effective in MMR⁺/p53^- cells, whereas it was not effective in p53⁺ cells regardless of theMMRstatus. Consistently, when the function ofMMRwas blocked with short hairpinRNAinSW620 (MMR⁺/p53 ^-) cells, cadein1 was no longer effective in inducing apoptosis. Besides, the inhibition of p53 increased the pro-apoptotic effect of cadein1 in HEK293(MMR⁺/p53⁺) cells, whereas it did not affect the response to cadein1 in RKO (MMR^-/p53⁺) cells. The apoptotic effects of cadein1 depended on the activation of p38 but not on the activation of Chk2 or other stress-activated kinases in p53-defective cells. Taken together, our results show that cadein1 may have a potential to be an anti-cancer chemotherapeutic agent that is preferentially effective on p53-mutant colon cancer cells with functional MMR.