Inhibition of proliferation of HT-29 colon adenocarcinorna cells by carboxylate NSAIDs and their acyl glucuronides

Many nonsteroidal anti-inflammatory drugs (NSAIDs) which have antiprolifera tive activity in colon cancer cells are carboxylate compounds forming acyl glucuronide metabolites. Acyl glucuronides are potentially reactive, able t o hydrolyse, rearrange into isomers, and covalently modify proteins under p hysiological conditions. This study investigated whether the acyl glucuroni des (and isomers) of the carboxylate NSAIDs diflunisal, zomepirac and diclo fenac had antiproliferative activity on human adenocarcinoma. HT-29 cells i n culture. Included as controls were the carboxylate NSAIDs themselves, the non-carboxylate NSAID piroxicam, and the carboxylate non-NSAID valproate, as well as its acyl glucuronide and isomers. The compounds were incubated a t 1-3000 muM with HT-29 cells for 24 hr, with [H-3]-thymidine added for an additional 2 hr incubation. IC50 values were calculated from the concentrat ion-inhibition response curves for thymidine uptake. The four NSAIDs inhibi ted thymidine uptake, with IC50 values about 200-500 muM. All of the NSAID acyl glucuronides (and isomers, tested in the case of diflunisal) showed an tiproliferative activity broadly comparable to the parent drugs. This activ ity may stem from direct uptake of intact glucuronide/isomers followed by c ovalent modification of proteins critical in the cell replication process. However, hydrolysis during incubation and cellular uptake of liberated pare nt NSAID will play a role. In HT-29 cells incubated with zomepirac, covalen tly modified proteins in cytosol were detected by immunoblotting with a zom epirac antibody, suggesting that HT-29 cells do have the capacity to glucur onidate zomepirac. The anti-epileptic drug valproate had no effect on inhib ition of thymidine uptake, though, surprisingly, its acyl glucuronide and i somers were active. The reasons for this are unclear at present. (C) 2001 E lsevier Science Inc. All rights reserved.