The chemopreventive action of 40 and 80% maximum tolerated dose (MTD) levels of piroxicam, d,l-α-difluoromethylornithine (DMFO), 16α-fluoro-5-androsten-17-one (DHEA analogue 8354), and ellagic acid (EA) administered in diet individually and in combination before and during initiation and postinitiation phases of azoxymethane-induced neoplasia of the intestine was studied in male F344 rats. The MTD levels of piroxicam, DFMO, DHEA analogue, and EA were determined in male F344 rats and found to be 500, 5,000, 500, and 10,000 ppm, respectively, in modified AIN-76A diet. When these agents were fed in combination, the MTD levels were: piroxicam plus DFMO, 250 and 2500 ppm; piroxicam plus DHEA analogue, 250 and 250 ppm; piroxicam plus EA, 250 and 5000 ppm; piroxicam plus DFMO plus DHEA analogue, 250, 2500, and 250 ppm; and piroxicam plus DFMO plus EA, 250, 2500, and 5000 ppm. From these MTD values, 40 and 80% MTD levels were calculated and tested for their efficacy. At 5 weeks of age, animals were fed the modified AIN-76A (control) diet and experimental diets containing 40 and 80% MTD levels of piroxicam, DFMO, DHEA analogue, and EA individually and in combination. At 7 weeks of age, all animals except the vehicle-treated groups were administrated s.c. injections of azoxymethane (15 mg/kg body weight/week for 2 weeks). Animals intended for vehicle treatment received s.c. injections of an equal volume of normal saline. Fifty-two weeks after azoxymethane and saline treatment all the animals were necropsied, and colon and small intestinal tumor incidence (percentage of animals with tumors) and multiplicity (tumors/animal) were compared among various dietary groups. The results indicate that 40 and 80% MTD levels of dietary piroxicam and DFMO significantly (P < 0.001) inhibited colon and small intestinal tumor incidence and multiplicity. DHEA analogue at 40% MTD level significantly decreased the small intestinal and colon tumor incidences (P < 0.05), whereas 80% MTD of DHEA analogue inhibited only small intestinal tumor incidence. EA at 40 and 80% MTDs had no significant effect on colon tumor incidence (P > 0.05), but 80% MTD of EA showed a significant inhibitory effect on the incidence of small intestinal adenocarcinomas (P < 0.01). In the combination study, 40 and 80% MTD levels of piroxicam plus DFMO significantly (P < 0.001) inhibited colon adenocarcinoma incidence (8.3%) and multiplicity (0.08 ± 0.04) (SE) when compared to colon adenocarcinoma incidence (72.2%) and multiplicity (1.14 ± 0.18) in control diet-fed animals. These results also demonstrate that low levels of piroxicam and DFMO administered together possess an effective chemopreventive action. Administration of DHEA analogue or EA in combination with piroxicam and DFMO had no additional effect on colon and small intestinal tumorigenesis.
Supported by USPHS Contract NOI-CN-85095-01 and Grant CA-17613 from the National Cancer Institute. Animals were maintained under the guidelines set forth in the Guide for Care and Use of Laboratory Animals Resources, National Research Council.