NTP to Study 22 Chemicals

A NUMBER of recent studies have shown that the growth of certain rodent tumouirs may be inhibited by the oral administration of the H-2 antagonist cimetidine (Gifford et al., 1981; Osband et al., 1981). Furthermore, it has been proposed that the antitumour effects of this compound are due to its ability to inhibit histamineinduced T-suppressor-cell activation (Osband et al., 1980a, 1981; Ogden & Hill, 1980; Gifford et al., 1981). In view of the potential of this approach to immunotherapy we decided to undertake studies on the effect of similar cimetidine protocols on the growth of some of the experimental rodent tumours routinely used in our laboratories. The results of these studies are summarized below. Male syngeneic WAG/Ed (Edinburgh University Centre for Laboratory Animals strain of Wistar rats) were inoculated s.c. with 105 viable cells of the asbestosinduced mesothelioma MF3 (Bolton et al., in preparation ) and cimetidine (Smith, Kline and French Laboratories Ltd., Welwyn Garden City) was included in the drinking water from the date of tumour inoculation. Similarly, 105 or 106 viable cells of the 3-methylcholanthrene (MCA)induced fibrosarcoma CCH1 (WAoodruff et al., 1972) were inoculatedl s.c. into syngeneic CBA/Ca mice, and cimetidine included in the drinking water. In both experiments, the concentrations of cimetidine in the drinking water were such that each animal received 100 mg/kg/day AlkcceptedI 6 January 1982