Journal Article

Chemoprevention of colonic aberrant crypt foci by an inducible nitric oxide synthase-selective inhibitor

Chinthalapally V. Rao, Toshihiko Kawamori, Rachid Hamid and Bandaru S. Reddy

in Carcinogenesis

Volume 20, issue 4, pages 641-644
Published in print April 1999 | ISSN: 0143-3334
Published online April 1999 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/20.4.641
Chemoprevention of colonic aberrant crypt foci by an inducible nitric oxide synthase-selective inhibitor

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Inducible nitric oxide synthase (iNOS) is overexpressed in colonic tumors of humans and also in rats treated with a colon carcinogen. iNOS appear to regulate cyclooxygenase-2 (COX-2) expression and production of proinflammatory prostaglandins, which are known to play a key role in colon tumor development. Experiments were designed to study the inhibitory effects of S,S′-1,4-phenylene-bis(1,2-ethanediyl)bis-isothiourea (PBIT) a selective iNOS-specific inhibitor, measured against formation of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF). Beginning at 5 weeks of age, male F344 rats were fed experimental diets containing 0 or 50 p.p.m. of PBIT, or 2000 p.p.m. of curcumin (non-specific iNOS inhibitor). One week later, rats were injected s.c. with AOM (15 mg/kg body wt, once weekly for 2 weeks). At 17 weeks of age, all rats were killed, colons were evaluated for ACF formation and colonic mucosa was assayed for isoforms of COX and NOS activities. Both COX and iNOS activities in colonic mucosa of the AOM-treated rats were significantly induced. Importantly, 50 p.p.m. PBIT suppressed AOM-induced colonic ACF formation to 58% (P < 0.0001) and crypt multiplicity containing four or more crypts per focus to 78% (P < 0.0001); it also suppressed AOM-induced iNOS activity. Curcumin inhibited colonic ACF formation by 45% (P < 0.001). These observations suggest that iNOS may play a key regulatory role in colon carcinogenesis. Developing iNOS-specific inhibitors may provide a selective and safe chemopreventive strategy for colon cancer treatment.

Keywords: ACF, aberrant crypt foci; AOM, azoxymethane; COX, cyclooxygenase; eNOS, endothelial nitric oxide synthase; iNOS, inducible nitric oxide synthase; nNOS, neuronal nitric oxide synthase; NO, nitric oxide; NOS, nitric oxide synthase; PBIT, S,S′-1,4-phenylene-bis(1,2-ethanediyl)bis-isothiorea; TLC, thin layer chromatography.

Journal Article.  3360 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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