The position of the amino group on the benzene ring is critical for mesalamine's improvement of replication fidelity.

Background: Individuals with ulcerative colitis are at high risk of developing colitis-associated cancer. 5-Aminosalicylate (5-ASA) protects from cancer by its antiinflammatory activity as well as by altering cell growth, inducing apoptosis, and reducing replication errors. So far neither 5-ASA's structural specificity nor its pharmacophore group have been identified. Here we compared 5-ASA with its analogs (4-ASA and 3-ASA) and its metabolite N-acetyl-5-ASA (NAc-5-ASA).

Methods: Superoxide scavenging was analyzed by lucigenin-amplified chemiluminescence. Cell growth, cell cycle distribution, and replication fidelity at a (CA)13 microsatellite were measured in HCT116 and HT29 colon epithelial cells by MTT and flow cytometry. Nuclear protein extracts were blotted for replication protein A (RPA), claspin, p53, and p53(Ser15).

Results: All compounds inhibited the growth of colon epithelial cells at a similar level and displayed potent scavenging properties, with 3-ASA being the most active, followed by 5-ASA, 4-ASA, and NAc-5-ASA. Besides 5-ASA, only 4-ASA caused an increase in the S-phase population (56%-69% and 49%-62% in HCT116 and HT29 cells, respectively). This was accompanied by nuclear recruitment of replication proteins RPA and claspin as well as phosphorylation of p53(Ser15), both of which were weaker or absent with 3-ASA or NAc-5-ASA. 5-ASA was the only compound that lowered mutations at a (CA)13 microsatellite.

Conclusions: 5-ASA shares its growth inhibitory and superoxide scavenging properties with its structural analogs and metabolite, but the position of the amino group is critical for reducing replication errors.