Chemotherapeutic evaluation of 4-hydroxybenzylretinone (4-HBR), a nonhydrolyzable C-linked analog of N-(4-hydroxyphenyl) retinamide (4-HPR) against mammary carcinogenesis.

The antitumor effects of N-(4-hydroxyphenyl)retinamide (4-HPR), and its stable C-linked analog, 4-hydroxybenzylretinone (4-HBR) on the regression of established 7,12-dimethylbenz(a)anthracene(DMBA)-induced rat mammary tumors were compared. 4-HBR is a stable and nonhydroyzable derivative which cannot be converted in vivo to retinoic acid (RA). The results indicate that 4-HBR decreased mammary tumor volumes to the same extent as equimolar concentration (2 mmol/kg diet) of 4-HPR (-45% for 4-HBR vs. -42% for 4-HPR, p<0.01). Both 4-HPR and 4-HBR bind very poorly to nuclear retinoid receptors RARs and RXRs. The similarity of physicochemical properties of 4-HPR and 4-HBR as well as their equal antitumor potency suggests that 4-HPR like 4-HBR, is acting directly rather than through hydrolysis to free RA. Treatment with 4-HPR caused an almost 65% decrease in serum retinol levels. These results suggest that 4-HBR may have a significant chemotherapeutic advantage over 4-HPR, as the nonhydrolyzable analog may not cause night blindness which occurs as a significant side effect of 4-HPR usage.

Dose-response effects of the COX-2 inhibitor, celecoxib, on the chemoprevention of mammary carcinogenesis.

Recent chemopreventive studies in our laboratories showed that the COX-2 inhibitor, celecoxib, inhibited the induction of mammary cancer by 7,12-dimethylbenz(a)anthracene (DMBA). In this study, we examined the relative chemopreventive effect of varying doses of celecoxib on the development and growth of DMBA-induced rat mammary tumors. At 10 days prior to receiving a single intragastric dose of 15 mg DMBA/rat, female Sprague-Dawley rats were fed a control chow diet or diets containing 250, 500, 1000 or 1500 ppm celecoxib until termination of the experiment. Administration of increasing doses of celecoxib inhibited mammary tumor incidence and multiplicity as well as tumor volume in a dose-dependent manner. At 122 days post DMBA-intubation, mammary tumor incidence was 100% in the control rats compared to 80%, 50%, 45% and 25% in rats receiving 250, 500, 1000 or 1500 ppm celecoxib, respectively (p<0.001). Similarly, tumor multiplicity and tumor volume were significantly reduced by increasing the dose of celecoxib from 250 to 1500 ppm in the diet. The control rats had an average of 3.46 tumors/rat compared to 1.80, 1.00, 0.75 and 0.50 tumors/rat in animals receiving 250, 500, 1000 or 1500 ppm celecoxib, respectively (p<0.001). Average tumor volumes in rats fed 250, 500, 1000 or 1500 ppm celecoxib were 0.42, 0.34, 0.31 and 0.16 cm3 compared to 1.29 cm3 in the control rats (p<0.001). There was a concomitant increase in the steady-state serum concentration of celecoxib with the dose. These results indicate that, in this rat model, the chemopreventive effect of celecoxib against breast cancer is dose-dependent and that celecoxib is effective even at lower dose levels.

Chemotherapeutic evaluation of Celecoxib, a cyclooxygenase-2 inhibitor, in a rat mammary tumor model.

Epidemiological and experimental studies have shown that non-steroidal anti-inflammatory drugs (NSAIDs) reduce the relative risk of human cancer, including breast cancer. Recently, research studies in our laboratories have shown that the selective cyclooxygenase-2 (COX-2) blocker, Celecoxib, given daily in the diet, significantly inhibited the induction of rat mammary tumors by 7, 12-dimethylbenz(a)anthracene (DMBA). These studies were extended to evaluate Celecoxib for its effectiveness as an antineoplastic agent in this rat mammary tumor model. We examined the growth inhibitory effects of Celecoxib, given daily in the diet, on the volume and the number of established mammary tumors, vis-a-vis the cancer load (CL). Tumors continued to grow actively in control rats fed chow diet only. In contrast, the Celecoxib-supplemented diet (1500 mg/kg diet) significantly decreased the size of the mammary tumors in rats over the 6 week treatment period, resulting in an average reduction in tumor volume of approximately 32%, relative to the baseline volume (p<0.04). At the end of the 6 week treatment period, average tumor volume was 1.45 cm3 and 0.13 cm3 in the control and Celecoxib treated rats respectively. Tumor regression occurred in 90% of the rats. In addition, new tumors continued to emerge in the control group, in contrast to their significantly decreasing numbers in the Celecoxib treated group over the same time period (p<0.05). These results indicate that Celecoxib has significant antineoplastic activity, in addition to its anticarcinogenic effects.

Chemoprevention of breast cancer in rats by celecoxib, a cyclooxygenase 2 inhibitor.

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been observed to reduce the relative risk of breast cancer. This prompted our investigation of the chemopreventive potential of celecoxib, a specific cyclooxygenase 2 blocker, against mammary carcinogenesis induced by 7,12-dimethyl-benz(a)anthracene in female Sprague Dawley rats. Treatment with celecoxib was examined and compared to treatment with the general NSAID, ibuprofen, and to a control group receiving only dimethylbenz(a)anthracene. Dietary administration of celecoxib (1500 ppm) produced striking reductions in the incidence, multiplicity, and volume of breast tumors relative to the control group (68%, 86%, and 81%, respectively; P < 0.001). Ibuprofen also produced significant effects, but of lesser magnitude (40%, 52%, and 57%, respectively; P < 0.001). These results help confirm the chemopreventive activity of NSAIDs against breast cancer and provide the first evidence that a cyclooxygenase 2 blocking agent, celecoxib, possesses strong chemopreventive activity against mammary carcinogenesis.

Chemopreventive activity of a C-glucuronide analog of N-(4-hydroxyphenyl) retinamide-O-glucuronide against mammary tumor development and growth.

The long term chemopreventive effects of the N-(4-hydroxyphenyl) retinamide-O-glucuronide (4-HPROG), and its stable C-linked benzyl glucuronide analog, retinamidobenzyl glucuronide (4-HPRCG) on the growth and development of 7,12-dimethylbenz[a]anthracene-induced mammary tumors were compared. The retinamidobenzyl glucuronide is stable toward acid hydrolysis and resists the actions of beta-glucuronidase. The results indicate that the C-linked glucuronide analog, 4-HPRCG has a greater chemopreventive potency than an equimolar concentration of 4-HPROG. Tumor latency was 15% longer in rats fed 2 mmol/kg diet of 4-HPRCG as compared to 4-HPROG. At 80 days post DMBA-intubation, tumor incidence was 57% and 27% in the 4-HPROG and 4-HPRCG treated rats, respectively. Tumor multiplicity was also markedly decreased in the 4-HPRCG treated rats. At 80 days post DMBA intubation the control rats had an average of 1.43 tumors/rat compared to 0.71 and 0.36 tumors/rat in the 4-HPROG and 4-HPRCG respectively. The higher potency and low toxicity of 4-HPRCG suggest that this stable analog may have an in vivo chemopreventive advantage over its analog, 4-HPROG. The results also demonstrated that these glucuronide analogs do not bind effectively in vitro either to the nuclear retinoid receptors or to the cellular retinoid binding proteins. Regardless of the mode of action of these retinoids, they are clearly effective chemopreventive agents.

Comparative chemopreventive activity of ibuprofen and N-(4-hydroxyphenyl) retinamide against the development and growth of rat mammary adenocarcinomas.

The chemopreventive effects of Ibuprofen on the development and growth of 7,12-dimethylbenz(a)anthracene (DMBA) induced rat mammary tumors were examined. A well known breast cancer chemopreventive retinoid, N-(4-hydroxyphenyl) retinamide (4-HPR) was also included in this study for comparison. At 7 days prior to receiving a single intragastric dose of 15 mg DMBA, rats were fed a control chow diet, as well as diets containing either 1000 mg/kg diet of Ibuprofen or 1.5 mmol/kg diet of 4-HPR. Ibuprofen and 4-HPR markedly increased tumor latency. At 112 days post DMBA intubation, tumor incidence was 86% in control rats as compared to 74% and 62% in rats receiving Ibuprofen, and 4-HPR diets respectively (p < 0.05). Ibuprofen and 4-HPR reduced tumor burden and tumor volume almost to the same extent. The control rats had an average of 2.26 tumors/rat compared to 1.42 and 1.46 tumors/rat in the Ibuprofen or 4-HPR groups respectively (p < 0.05). Similarly, average tumor volume was 3.25 cm3 in the control rats compared to 0.86 cm3 and 0.83 cm3 in rats receiving Ibuprofen and 4-HPR diets respectively (p < 0.05). These results suggest that Ibuprofen may have potential in the chemoprevention and treatment of breast cancer.

Chemotherapeutic evaluation of N-(4-hydroxyphenyl) retinamide-O-glucuronide in the rat mammary tumor model.

The growth inhibitory effects of N-(4- Hydroxyphenyl) retinamide (4-HPR) and its glucuronide derivative, N-(4-Hydroxyphenyl) retinamide-O-glucuronide (4-HPROG) on established DMBA induced rat mammary tumors were compared. The results indicate that the glucuronide analog had a greater antitumor potency than equimolar concentration of the free retinoid. Tumor regression occurred in 75% of the rats fed 2 mmol/Kg diet of 4-HPROG. In a 6-week study, the maximum tolerated dietary dose (MTD) was found to be 3.5 mmol/Kg diet for 4-HPR and 5 mmol/Kg diet in the case of 4-HPROG. The higher potency and lower toxicity of the glucuronide suggests that this conjugate may have an in vivo chemotherapeutic advantage over the parent free retinoid.