Polyamines are downstream mediators of genetic risk factors in human intestinal cancers. The adenomatous polyposis coli (APC) tumour-suppressor gene, which is mutated in essentially all human colon cancers, regulates the expression of several e-box transcription factors. These factors, in turn, regulate the transcription of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis. The Kirsten ras (K-ras) oncogene regulates the expression of several genes, including suppressing the expression of peroxisomal proliferator-activated receptor γ (PPARγ). This PPAR, in turn, activates the expression of the spermidine/spermine-N1-acetyltransferase (SSAT), the first enzyme in polyamine catabolism. The non-steroidal anti-inflammatory drug (NSAID) sulindac induces the transcription of SSAT via activation of PPARγ. Inactivation of the APC tumour-suppressor gene, and the activation of K-ras, have a combined effect on increasing tissue polyamine contents due to increased synthesis and decreased catabolism of the polyamines. Pharmacological strategies for suppressing ODC (e.g. the enzyme-activated inhibitor α-difluoromethylornithine) and activating SSAT (e.g. NSAIDs) are potent inhibitors of intestinal carcinogenesis in rodent models. Clinical trials combining these classes of agent in humans with risk factors for colon cancer are in progress.
Abbreviations used: NSAID, non-steroidal anti-inflammatory drug; ODC, ornithine decarboxylase; PAO, polyamine oxidase; FAP, familial adenomatous polyposis; APC, adenomatous polyposis coli; Tcf, T-cell factor; HLH, helix-loop-helix; K-ras, Kirsten ras; MAPK, mitogen-activated protein kinase; PPAR, peroxisomal proliferator-activated receptor γ; PPRE, peroxisome proliferator-response element; COX, cyclo-oxygenase; α-DFMO, α-difluoromethylornithine; SSAT, spermidine/spermine-N1-acetyltransferase; Zip, leucine zipper; Min, multiple intestinal neoplasia; ERK, extracellular-signal-regulated kinase.
678th Meeting of the Biochemical Society, held at Imperial College, London, 16–18 December 2002