Identification of candidate cancer chemopreventive agents and their evaluation in animal models and human clinical trials: a review.

A search of the literature using National Library of Medicine databases and individual cancer journal articles yielded over 500 compounds with published chemopreventive activity in animals. From these, an initial 16 agents or agent combinations have been evaluated in the following animal tumor models: mouse skin papillomas/carcinomas induced by 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate; rat breast adenocarcinoma induced by N-methyl-N-nitrosourea or 7,12-dimethylbenz(a)anthracene; hamster lung carcinoma induced by N-methyl-N-nitrosourea or diethylnitrosamine; mouse bladder papillary carcinoma induced by N-butyl-N-(4-hydroxybutyl)nitrosamine; and rat and mouse colon cancer induced by azoxymethane/methylazoxymethanol acetate. Some of the most interesting positive results observed include 4-hydroxyphenyl retinamide plus tamoxifen in breast cancer, piroxicam in colon cancer, dimethylfluoroornithine in breast and bladder cancer, oltipraz in lung cancer, dehydroepiandrosterone in colon cancer, and molybdate in bladder cancer. Eighteen human intervention trials in progress are described that involve the following agents: beta-carotene (eight trials). Retinol/retinoic acid (seven trials), vitamins C and E (three trials), 4-hydroxyphenyl retinamide (one trial), piroxicam (one trial), and calcium (one trial). By organ site these studies involve cancer of the lung (six studies), skin (five studies), colon (four studies), breast (one study), and uterine cervix (two studies).