Anna V. Semenchenko

Effect of metformin on life span and on the development of spontaneous mammary tumors in HER-2/neu transgenic mice.

Studies in mammals have led to the suggestion that hyperglycemia and hyperinsulinemia are important factors both in aging and in the development of cancer. Insulin/insulin-like growth factor 1 (IGF-1) signaling molecules that have been linked to longevity include DAF-2 and InR and their homologues in mammals, and inactivation of the corresponding genes is followed by increased life span in nematodes, fruit flies and mice. It is possible that the life-prolonging effects of calorie restriction are due to decreasing IGF-1 levels. A search of pharmacological modulators of insulin/IGF-1 signaling pathway (which mimetic effects of life span extending mutations or calorie restriction) could be a perspective direction in regulation of longevity. The chronic treatment of female transgenic HER-2/neu mice with metformin (100 mg/kg in drinking water) slightly decreased the food consumption but failed in reducing the body weight or temperature, slowed down the age-related rise in blood glucose and triglycerides level, as well as the age-related switch-off of estrous function, prolonged the mean life span by 8% (p < 0.05), the mean life span of last 10% survivors by 13.1%, and the maximum life span by 1 month in comparison with control mice. The demographic aging rate represented by the estimate of respective Gompertzs parameter was decreased 2.26 times. The metformin-treatment significantly decreased the incidence and size of mammary adenocarcinomas in mice and increased the mean latency of the tumors.

Rapamycin increases lifespan and inhibits spontaneous tumorigenesis in inbred female mice.

The nutrient-sensing TO R (target of rapamycin) pathway is involved in cellular and organismal aging. Rapamycin, an inhibitor of TO R, extends lifespan in yeast, fruit flies and genetically heterogeneous mice. Here, we demonstrate that lifelong administration of rapamycin extends lifespan in female 129/Sv mice characterized by normal mean lifespan of 2 y. Importantly, rapamycin was administrated intermittently (2 weeks per month) starting from the age of 2 mo. Rapamycin inhibited age-related weight gain, decreased aging rate, increased lifespan (especially in the last survivors) and delayed spontaneous cancer. 22.9% of rapamycin-treated mice survived the age of death of the last mouse in control group. Thus we demonstrated for the first time in normal inbred mice that lifespan can be extended by rapamycin. This opens an avenue to develop optimal doses and schedules of rapamycin as an anti-aging modality.

Metformin slows down aging and extends life span of female SHR mice.

Studies in mammals have led to the suggestion that hyperglycemia and hyperinsulinemia are important factors both in aging and in the development of cancer. It is possible that the life-prolonging effects of calorie restriction are due to decreasing IGF-1 levels. A search of pharmacological modulators of insulin/IGF-1 signaling pathway (which resemble effects of life span extending mutations or calorie restriction) could be a perspective direction in regulation of longevity. Antidiabetic biguanides are most promising among them. Here we show the the chronic treatment of female outbred SHR mice with metformin (100 mg/kg in drinking water) slightly modified the food consumption but decreased the body weight after the age of 20 months, slowed down the age-related switch-off of estrous function, increased mean life span by 37.8%, mean life span of last 10% survivors by 20.8%, and maximum life span by 2.8 months (+10.3%) in comparison with control mice. On the other side, treatment with metformin failed influence blood estradiol concentration and spontaneous tumor incidence in female SHR mice. Thus, antidiabetic biguanide metformin dramatically extends life span, even without cancer prevention in this model.

Rapamycin Extends Maximal Lifespan in Cancer-Prone Mice

Aging is associated with obesity and cancer. Calorie restriction both slows down aging and delays cancer. Evidence has emerged that the nutrient-sensing mammalian target of rapamycin (mTOR) pathway is involved in cellular and organismal aging. Here we show that the mTOR inhibitor rapamycin prevents age-related weight gain, decreases rate of aging, increases lifespan, and suppresses carcinogenesis in transgenic HER-2/neu cancer-prone mice. Rapamycin dramatically delayed tumor onset as well as decreased the number of tumors per animal and tumor size. We suggest that, by slowing down organismal aging, rapamycin delays cancer.

Insulin and longevity: antidiabetic biguanides as geroprotectors

The results of previous experimental studies of effects of antidiabetic biguanides (phenformin and buformin) on life span and spontaneous tumor incidence in mice and rats were recalculated and reanalyzed using standard demographic models of mortality. The chronic treatment of female C3H/Sn mice with phenformin prolonged the mean life span by 21.1% (P < 0.05), the mean life span of the last 10%survivors by 28.4% and the maximum life span by 5.5 months (by 26%) in comparison with the control. The demographic aging rate represented by the estimate of respective Gompertzs parameter decreased by 31.2% and MRDT increased 1.45-fold. The treatment significantly inhibited (4.0-fold, P < 0.01) the incidence of mammary adenocarcinomas in mice. Administration of phenformin to female LIO rats failed to influence the mean lifespan. At the same time, the mean life span of the last 10% survivors increased by 10.1% (P < 0.05), and maximum life span increased by 3 months (+9.8%). Phenformin attenuated the development of spontaneous tumors in comparison to the control. The treatment of female rats with another antidiabetic biguanide, buformin, slightly increased their mean life span (by 7.3%; P > 0.05). The mean life span of the last 10%survivors increased by 12% (P < 0.05) and the maximum life span increased by 2 months (+5.5%) as compared with controls. The population aging rate decreased by 18.1% (P < 0.05) and MRDT increased 1.22-foldunder the influence of buformin (P < 0.05). The total tumor incidence decreased by 49.5%in buformin-treated rats. Both antidiabetic biguanides slightly decreased the body weight, slowed down the age-related decline of there productive function in female rats. The results of our experiments provide evidence that antidiabetic biguanides are promising geroprotectors as well as drugs which can be used in the prevention of cancer.

Metformin decelerates aging and development of mammary tumors in HER-2/neu transgenic mice.

Transgenic FVB/N female mice carrying HER-2/neu mammary cancer gene received metformin (1200 mg/liter) with drinking water 5 days a week starting from the age of 2 months until natural death. Metformin slightly reduced food consumption, but did not change water consumption and dynamics of weight gain. Mean life span of mice increased by 8% (p<0.05), in 10% long-living mice it was prolonged by 13.1%, and the maximum life span was prolonged by 1 month under the effect of metformin in comparison with the control. The rate of populational aging decreased by 2.26 times. The total incidence of mammary adenocarcinoma and their multiplicity did not change under the effect of metformin, while the latency of tumor development increased and the mean diameter of tumors decreased. Hence, we first demonstrated a geroprotective effect of metformin and its suppressive effect towards the development of mammary tumors.

Deficiency in Poly(ADP-ribose) Polymerase-1 (PARP-1) Accelerates Aging and Spontaneous Carcinogenesis in Mice.

Genetic and biochemical studies have shown that PARP-1 and poly(ADP-ribosyl)ation play an important role in DNA repair, genomic stability, cell death, inflammation, telomere maintenance, and suppressing tumorigenesis, suggesting that the homeostasis of poly(ADP-ribosyl)ation and PARP-1 may also play an important role in aging. Here we show that PARP-1−/− mice exhibit a reduction of life span and a significant increase of population aging rate. Analysis of noninvasive parameters, including body weight gain, body temperature, estrous function, behavior, and a number of biochemical indices suggests the acceleration of biological aging in PARP-1−/− mice. The incidence of spontaneous tumors in both PARP-1−/− and PARP-1+/+ groups is similar; however, malignant tumors including uterine tumors, lung adenocarcinomas and hepatocellular carcinomas, develop at a significantly higher frequency in PARP-1−/− mice than PARP-1+/+ mice (72% and 49%, resp.; P < .05). In addition, spontaneous tumors appear earlier in PARP-1−/− mice compared to the wild type group. Histopathological studies revealed a wide spectrum of tumors in uterus, ovaries, liver, lungs, mammary gland, soft tissues, and lymphoid organs in both groups of the mice. These results demonstrate that inactivation of DNA repair gene PARP-1 in mice leads to acceleration of aging, shortened life span, and increased spontaneous carcinogenesis.

Effect of exposure to light-at-night on life span and spontaneous carcinogenesis in female CBA mice

The effect of constant illumination on the development of spontaneous tumors in female CBA mice was investigated. Fifty female CBA mice starting from the age of 2 months were kept under standard light/dark regimen (12 hr light:12hr dark; LD) and 50 CBA mice of similar age were kept under constant illumination (24 hr a day, 2,500 Lux, LL). Exposure to the LL regimen decreased food consumption but did not influence body weight, significantly accelerated age‐related disturbances in estrous function, and was followed by a significant increase in spontaneous tumor incidence in female CBA mice. Tumor incidence as well as the number of total or malignant tumors was significantly increased in the LL group compared to the LD group (p < 0.001). The incidence of lung adenocarcinomas, leukemias and hepatocarcinomas was 7/50; 6/50 and 4/50 in the LL group and 1/50; 0/50 and 0/50 in the LD group. Mice from the LL groups had shorter life spans then those from the LD group. The data demonstrate, for the first time, that exposure to constant illumination was followed by increases in the incidence of spontaneous lung carcinoma, leukemias and hepatocarcinoma in female CBA mice.

The effect of melatonin treatment regimen on mammary adenocarcinoma development in HER-2/neu transgenic mice.

The effect of various regimens of treatment with melatonin on the development of mammary tumors in HER2/neu transgenic mice was investigated. Female HER‐2/neu mice starting from the age of 2 months were kept under standard light/dark regimen and as given melatonin with tap water (20 mg/l) during the night time 5 times monthly (interrupted treatments) or constantly to natural death. Intact mice served as controls. Treatment with melatonin slowed down age‐related disturbances in estrous function most in the group exposed to interrupted treatment with the hormone. Constant treatment with melatonin decreased incidence and size of mammary adenocarcinomas, and incidence of lung metastases, compared to controls. The number of mice bearing 4 and more tumors was reduced in the group with constant melatonin treatment. Interrupted treatment with melatonin promote mammary carcinogenesis in HER‐2/neu transgenic mice. The data demonstrate the regimen‐dependent inhibitory effect of melatonin on the development of spontaneous mammary tumors in HER‐2/neu mice but not on overall survival with implication about the likely cause of the effect. Polycystic kidney disease is common in this transgenic line. Adverse effect of melatonin on the life span in our study may be unique to the transgenic model used and may not be relevant to the suppressive effect of melatonin in delay of mammary cancer.

Dose-dependent effect of melatonin on life span and spontaneous tumor incidence in female SHR mice

From the age of 3 months until their natural death, female Swiss-derived SHR mice were given melatonin with their drinking water (2 or 20mg/l) for 5 consecutive days every month. Intact mice served as controls. There were 54 mice in each group. The results of this study show that the treatment of melatonin did not significantly influence food consumption, but its administration at lower doses did decrease the body weight of mice; it slowed down the age-related switching-off of estrous function; it did not influence the frequency of chromosome aberrations in bone marrow cells; it did not influence mean life span; and it increased life span of the last 10% of the survivors in comparison to controls. We also found that treatment with low dose melatonin (2mg/l) significantly decreased spontaneous tumor incidence (by 1,9-fold), mainly mammary carcinomas, in mice whereas higher doses (20mg/l) failed to influence tumor incidence as compared to controls. For this reason, we conclude that the effect of melatonin as a geroprotector is dose-dependent.