Synergistic efficacy of 3n-butyrate and 5-fluorouracil in human colorectalcancer xenografts via modulation of DNA synthesis

Background & Aims: Butyrate, produced in the colon lumen, maintains mucosal cell homeostasis, Poorly diffusible, its access is compromised in growing colon cancers and absent in distant metastases. Butyrate regulates DNA synt hesis, We postulated that systemic administration of butyrate should reduce colon cancer growth and enhance 5-fluorouracil (5-FU) efficacy, Methods: A stable derivative of butyrate (Bn-But) was used, The antitumoral efficacy of 5-FU and 3n-But, alone or combined, was evaluated in human colorectal ca ncers (hCRCs) subcutaneously, orthotopically, or intrasplenically grafted i nto nude mice, Thymidylate synthase (TS) and thymidine kinase (TH) mRNA exp ression, proliferation, apoptosis, and cell cycle alterations were studied, Results: In vivo, 5-FU alone inhibited growth of only 3 of the 12 hCRCs te sted and Bn-But alone had no effect; the 5-FU/3n-But combination inhibited growth of all 16 hCRCs tested. The hCRCs differed in their p53 and microsat ellite instability status. 5-FU/3n-But decreased TH and TS mRNA expression by 20- and 40-fold, respectively, and TS activity by 75%, stopped cell prol iferation without affecting cell differentiation, and significantly enhance d apoptosis. 3n-But potentiated the efficacy of Tomudex and methotrexate, 2 TS inhibitors, but not that of oxaliplatin, In vitro, 5-FU/3n-But inhibite d [H-3]thymidine but not bromodeoxyuridine incorporation and induced apopto sis in hCRC cell lines. Cells treated with 5-FU/Bn-But did not accumulate i n G(1) nor in S phase of the cell cycle, while 5-FU and 3n-But arrested the cycle in S and in G(1) phase, respectively, 3n-But prevented the cell resc ue from 5-FU-induced cytotoxicity by uridine or thymidine, Conclusions: 3n- But and TS inhibitors acted synergistically against colorectal cancers, ind ependently of the genetic alterations of the hCRCs, The mechanism of action of 5-FU/Bn-But could be enhanced reduction of TS and prevention of thymidi ne salvage in DNA synthesis.