Nimesulide and melatonin in mammary carcinogenesis prevention in female Sprague-Dawley rats.

Tumorsuppressive effects of a selective inhibitor of cyclooxygenase-2 (COX-2) nimesulide (NIM) activity and pineal hormone melatonin (MEL) and their combination in two chemopreventive studies of mammary carcinogenesis were evaluated. Mamary tumors in female Sprague-Dawley rats were induced by N-methyl-N-nitrosourea (NMU) and by 7,12-dimethylbenz(a)anthracene (DMBA), respectively. The treatment with NIM (applied subcutaneously twice a week in the dose of 5 mg/kg b.w.) and MEL (given daily diluted in drinking water in concentration 20microg/ml) began several days before carcinogen administration and lasted until the end of the experiment. The tumor incidence, frequency, latency period and tumor volume as parameters of mammary carcinogenesis were evaluated. Moreover, the effect of chemopreventives on body weight, food and water intake were recorded. Changes of selected parameters of lipid and carbohydrate metabolism in the serum and chosen organs were evaluated in the NMU experiment. In the NIM-treated group in the NMU experiment, the tumor incidence decreased by 34.5% (p < 0.05), tumor frequency per group by 40% (p < 0.05) and tumor volume gain by 39% when compared to the control group. Tumorsuppressive effect of MEL was not observed. In DMBA-induced carcinogenesis an oncostatic effect of NIM was not observed; MEL administration decreased tumor incidence by 21.5% (p < 0.05), tumor frequency per group by 22.5% and tumor volume gain by 43.5%. Combined chemoprevention of NIM+MEL was very similar to that of chemopreventives administered alone. MEL lowered food and water intake and body weight gain in DMBA-induced carcinogenesis. It increased glycogen and cholesterol content in the liver, triacyglycerol and phospholipid concentrations in the bone marrow and decreased malondialdehyde concentration at the same tissue of tumor-bearing animals. NIM did not significantly influence the selected metabolic parameters, excepting the decrease in serum glucose concentration in tumor-bearing rats.

Variability of mammary carcinogenesis induction in female Sprague-Dawley and Wistar:Han rats: the effect of season and age.

It is important to determine and clarify the variability of mammary carcinogenesis induction in animal experimental studies particularly in connection with chemoprevention projects. The circannual seasonal rhythms of hormone levels or various parameters within the immune system may involve factors participating in mammary gland carcinogenesis. In our study, 19 experiments were conducted and all of them lasted for about 25 weeks after chemical carcinogen administration (DMBA or NMU) under standard laboratory conditions. Females of two rat strains - a medium susceptible Sprague-Dawley strain and a very low susceptible Wistar:Han were used. We observed not only the effect of seasonal changes but also the effect of age after single or repeated carcinogen administration. The seasonal dependence of mammary carcinogenesis with higher tumor incidence during long days in comparison with winter short days has been demonstrated in Sprague-Dawley rats. In experiments on the Wistar:Han strain, certain features of seasonal character were recorded, although the very low susceptibility of this strain to mammary carcinogenesis might have influenced the results. A limited period of carcinogen administration in early puberty around postnatal days 43-46 (higher susceptibility), when compared to the period after postnatal day 50, is the factor significantly increasing incidence and frequency of mammary carcinogenesis in the Sprague-Dawley strain. Our results indicate the need to consider the effect of season and age of animals at the time of carcinogen administration on rat mammary carcinogenesis induction. However, the application of the results obtained in one strain of experimental animals may only lead to misleading conclusions.

Preventive effects of raloxifene and melatonin in N-methyl-N-nitrosourea-induced mammary carcinogenesis in female rats.

The aim of this study was to evaluate preventive effects of raloxifene (RAL), melatonin (MEL) and their combination in N-methyl-N-nitrosourea (NMU)-induced rat mammary carcinogenesis. MEL-treatment began 12 days and RAL treatment began 10 days prior to carcinogen administration and continued till the end of experiment (24 weeks after first carcinogen administration). RAL was administered subcutaneously twice a week in the dose of 5 mg/kg b.w. MEL was administered diluted in drinking water in a concentration 4 microg/ml daily from 3 p.m. to 8 a.m. At the end of experiment, tumor incidence, frequency, latency period and tumor volume as parameters of mammary carcinogenesis were evaluated. Moreover, the effect of chemopreventives on body and uterine weight, food and water intake were recorded. In RAL-treated group, tumor incidence was decreased by 67% (p < 0.001), tumor frequency per group was reduced by 90% (p < 0.0002) and latency period lengthened by 27 days in comparison with control group. After MEL-treatment tumor incidence was decreased by 19%, tumor frequency per group was decreased by 50% (p < 0.05) when compared to control animals. The effect of RAL+MEL-treatment was very similar to that of RAL-treatment. In groups with RAL administration, significant decrease (p < 0.0001) in body weight gain and relative uterine weight was recorded. As to food intake no significant differences in comparison with control group were found. Consequently, groups were pooled and in RAL-treated groups (RAL, RAL+MEL) a decrease in food intake, when compared to groups without RAL administration (control group, MEL) was recorded (p<0.04). The water intake was markedly decreased in RAL-treated groups (P < 0.0001). RAL and RAL+MEL proved to be very effective in prevention of experimental mammary carcinogenesis in female rats, isolated MEL appeared to be of lower oncostatic activity.

Preventive effect of indomethacin and melatonin on 7, 12-dimethybenz/a/anthracene-induced mammary carcinogenesis in female Sprague-Dawley rats. A preliminary report.

The aim of the experiment was to analyse the oncostatic effect of nonsteroidal antiinflammatory drug INDO, hormone MEL and combination of both substances in DMBA-induced mammary carcinogenesis in female SD rats. Chemoprevention started 10 days before the application of the first dose of DMBA to 35-day-old rats. INDO was administered in tap water (20 microg/ml of water) for 3 days in a week (days 2, 4 and 6), MEL solution in the concentration of 20 microg/ml of tap water was administered between 3 p.m. and 8 a.m. for 4 days in a week (days 1, 3, 5 and 7); during other days the animals drank tap water only. In combined chemoprevention, rats were drinking solutions of INDO and MEL according to the above-mentioned scheme. DMBA in the dose of 10 mg/rat was administered intragastrically using a probe to all rats 3 times on postnatal days 45, 50 and 55. There were four experimental groups: group 1--without chemoprevention, group 2--INDO treatment, group 3 --MEL treatment, group 4--application of INDO + MEL. The experiment lasted 26 weeks from the first administration of DMBA, when the final incidence and frequency of tumours per animal and group, as well as latency and average volume of tumours were evaluated. The content/concentration of malondialdehyde (MDA) was determined in selected tissues as a criterion of lipoperoxidation, considering its potential influencing by chemoprevention. The tumour incidence in controls was 100%; INDO reduced the incidence (36.84%) and frequency per group and animal, decreased the mean volume of tumours and prolonged the latency. Chemoprevention using combination of INDO with MEL was successful like that with INDO; however, it did not influence the tumour volume. MEL decreased the incidence to 42.11% and pronouncedly reduced the tumour frequency per group. INDO, administered alone or in combination with MEL, reduced an increased content/concentration of MDA in the liver, bone marrow and serum of tumour-bearing rats. INDO, MEL and INDO + MEL had a pronounced chemopreventive effect and showed to be a favourable combination in prevention of experimental mammary carcinogenesis.

Effects of tamoxifen and melatonin on mammary gland cancer induced by N-methyl-N-nitrosourea and by 7,12-dimethylbenz(a)anthracene, respectively, in female Sprague-Dawley rats.

Chemopreventive effects were analysed of antioestrogen TAM and of MEL on NMU- or DMBA-induced mammary gland cancer, respectively, in female Sprague-Dawley rats. NMU was administered intraperitoneally in two doses each of 50 mg/kg b.w. between 46th-57th postnatal days. DMBA was given by gavage in one dose (20 mg per animal) between 50th-54th postnatal days. The treatment with MEL began 12 days and the treatment with TAM 10 days before carcinogen administration; both chemopreventive substances were administered until the end of the experiment (24 weeks after carcinogen application). TAM was administered subcutaneously twice a week in a dose 2.5 mg/kg b.w. MEL was given in tap water (20 mg/ml) daily between 3 p.m. to 8 a. m. The tumour incidence, tumour frequency per group and animal, latency period, tumour volume, body weight gain in the rats and weight of uterus (in the experiment with NMU) were evaluated. TAM suppressed carcinogenesis to 0% incidence like TAM+MEL in both the NMU and DMBA models. In NMU-induced mammary carcinogenesis MEL lowered the tumour volume (although statistically non-significantly) by 30% in comparison with the control group; in DMBA-induced mammary carcinogenesis it lowered the tumour volume (2.70 +/- 0.81 cm3 vs. 0.90 +/- 0.33 cm3) and lengthened (non-significantly) the latency period (by 12 days). The weight gain of animals in both NMU and DMBA models and relative uterus weight in the NMU model were significantly lower in the groups treated with TAM and TAM+MEL as compared to the control group and the group treated with MEL. Evaluation of the combined effect of TAM+MEL was not possible due to total suppression of carcinogenesis by TAM. TAM and TAM+MEL are highly effective agents in rat mammary carcinogenesis prevention, but the side effects of TAM in humans limits its use in clinical oncology.