Preneoplastic changes persist after IGF-IR downregulation and tumor regression.

Despite our incomplete understanding of the function of the type I insulin-like growth factor receptor (IGF-IR) in tumorigenesis, IGF-IR targeting agents have entered clinical trials for the treatment of human cancers. Previously, we have shown that downregulation of IGF-IR transgene in mammary tumors in MTB-IGFIR transengic mice results in tumor regression in a majority of the mice and most of these mice do not develop recurrent mammary tumors. In this study, we examined mammary tissue of mice that did not develop recurrent tumors. Areas of tumor regression were visible macroscopically and microscopically these lesions contained cell debris, individual cells, lipofuscin and doxycycline crystals. Three of the 12 mice also presented with considerable lobuloalveolar development. The re-expression of the IGF-IR transgene in mammary tissue with stably regressed tumors resulted in the rapid re-emergence of mammary tumors, some of which seemed to originate from the regressed mammary lesions. Thus, despite stable tumor regression after IGF-IR downregulation, mammary tissue contained preneoplastic lesions and tumors rapidly re-appear upon re-overexpression of IGF-IR transgene. Therefore, IGF-IR-targeting agents may be effective at regressing mammary tumors expressing IGF-IR, but these agents will not completely eradicate all tumor cells or restore the mammary stromal environment.

Effects of rosiglitazone on ovarian function and fertility in animals with reduced fertility following fetal and neonatal exposure to nicotine.

We have previously shown that in utero nicotine exposure causes impaired fertility, follicle immaturity, and ovarian dysfunction in adult female rat offspring. These characteristics overtly resemble the clinical profile of polycystic ovarian syndrome (PCOS) and recent studies have shown that thiazolidinediones such as rosiglitazone improve fertility in women with PCOS but the mechanism is not well defined. Our goal was to examine whether rosiglitazone would (1) ameliorate the altered ovarian physiology that occurs following fetal and neonatal exposure to nicotine and (2) to examine whether this could be due to normalization of ovarian vascularization. At weaning, offspring of nicotine-exposed dams were given either vehicle (NV) or rosiglitazone (3 mg kg(-1) day(-1); NR). Offspring of saline-exposed dams received vehicle (SV). Tissues were collected when the female offspring reached 26 weeks of age. NV animals had reduced granulosa cell proliferation and increased ovarian cell apoptosis. Treatment with rosiglitazone increased proliferation, and decreased apoptosis, compared NV animals. NV animals had decreased ovarian vascularity relative to controls, whereas NR animals had an intermediate level of ovarian vessel density. Moreover, ovaries from NV animals had decreased levels of the pro-angiogenic growth factors vascular endothelial growth factor (VEGF) and endocrine gland-derived VEGF both of which were increased with rosiglitazone treatment. Rosiglitazone reversed some of the nicotine effects in the ovary and increased ovarian vascularization, follicle maturation and improved oocyte competence. Rosiglitazone may be an important treatment option for PCOS and the present study provides a potential mechanism by which rosiglitazone may have beneficial effects on fertility in these patients.

Reversibility and recurrence of IGF-IR-induced mammary tumors.

The type-I insulin-like growth factor receptor (IGF-IR) is frequently overexpressed in breast cancer and therapeutic agents targeting IGF-IR are currently in development. The ultimate success of anti-IGF-IR therapies will depend on the extent to which established tumors remain dependent upon IGF-IR signaling for sustained growth. To investigate the potential benefits and pitfalls of targeting IGF-IR, we used a doxycycline inducible mouse model of IGF-IR initiated breast cancer. We found that downregulation of IGF-IR results in tumor-size-dependent regression to an undetectable state. Partially regressed tumors almost always resumed growth in the absence of doxycycline and a proportion of tumors that regressed to an undetectable state ultimately recurred. This re-emergence of tumor growth in the absence of doxycycline was facilitated by IGF-IR-dependent and IGF-IR-independent mechanisms. Tumor escape from IGF-IR dependence was associated with an epithelial to mesenchymal transition and upregulation of transcriptional repressors of E-cadherin. These results suggest that tumors initiated by IGF-IR have the ability to become independent of this initiating oncogene, and IGF-IR independence is associated with characteristics consistent with an epithelial to mesenchymal transition.

cAMP response element-binding protein is expressed at high levels in human ovarian adenocarcinoma and regulates ovarian tumor cell proliferation.

Approximately 90% of human ovarian tumors result from transformation of ovarian surface epithelial cells. It has been hypothesized that repeated destruction of the epithelial cells during ovulation, followed by proliferation and migration of epithelial cells to restore the ovarian surface, renders these cells susceptible to mutagenic events. One of the proteins found to promote ovarian surface epithelial cell survival and proliferation was the transcription factor, cAMP response element-binding protein (CREB). Thus, the objective of this study was to determine whether CREB was also highly expressed in tumor cells originating from the ovarian epithelium. Using an ovarian cancer tissue array, it was observed that approximately 54% of the epithelial-derived human ovarian tumors displayed moderate or high levels of CREB immunostaining, while none of the normal ovarian samples did. Comparison of CREB levels in a human ovarian tumor cell line to those of a normal ovarian epithelial cell line revealed elevated levels of CREB and phosphorylated CREB in the ovarian tumor cells. To determine whether CREB regulated proliferation and/or apoptosis in the ovarian tumor cell line, CREB expression was suppressed using RNA interference. Decreased CREB expression significantly reduced ovarian tumor cell proliferation, while there was no effect on apoptosis in these cells. Finally, we showed that CREB is highly expressed in an in vivo murine model of ovarian tumorigenesis. Therefore, CREB is frequently overexpressed in ovarian cancer where it appears to promote cell proliferation.

Rosiglitazone prevents diabetes by increasing beta-cell mass in an animal model of type 2 diabetes characterized by reduced beta-cell mass at birth.

AIM: Interventions that preserve or increase beta-cell mass may also prevent type 2 diabetes. Rosiglitazone prevents diabetes in people with high glucose levels who have impaired glucose tolerance and/or impaired fasting glucose. The effect of this drug on both glucose levels and beta-cell mass was studied in a rat model of diabetes, characterized by reduced beta-cell mass at birth with normoglycaemia, and progression to dysglycaemia with age. METHODS: Female Wistar rats were given either saline (vehicle) or nicotine during pregnancy and lactation. Offspring of saline-exposed dams were given vehicle and offspring of nicotine-exposed dams were randomized to receive either vehicle or rosiglitazone starting at weaning. Beta-cell mass, proliferation and apoptosis were determined at birth and at 4 and 26 weeks of age. Glucose homeostasis was examined following sequential oral glucose tolerance tests (OGTT). RESULTS: Rosiglitazone treatment prevented the development of dysglycaemia in nicotine-exposed animals. The ability of rosiglitazone to preserve normoglycaemia appeared to be because of its ability to increase beta-cell mass through a combination of enhanced beta-cell proliferation and decreased beta-cell apoptosis. CONCLUSIONS: These results suggest that if rosiglitazone administration is started prior to the onset of glucometabolic abnormalities, it prevents the onset of dysglycaemia by partially restoring beta-cell mass in animals with reduced beta-cell mass at birth.

Influence of dichlorodiphenylchloroethylene on vascular endothelial growth factor and insulin-like growth factor in human and rat ovarian cells.

1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE, DDE), a metabolite of DDT is a persistent hormonally active environmental toxicant present in human serum and follicular fluid. The objective of this study was to investigate the effects of DDE on the expression of the ovarian vascular endothelial growth factor (VEGF) and insulin-like growth factor (IGF-1) in primary cultures of human granulosa cells and in the rat ovary. Granulosa cells were obtained at the time of oocyte retrieval for in vitro fertilization and cultured with environmentally relevant concentrations of DDE. Immature female rats were treated with 100 microg DDE/kg body weight or vehicle at 28 and 31 days of age and then euthanized at 50 days of age for collection of ovarian tissue. Expression of VEGF, the VEGF receptor fetal liver kinase (Flk-1) and IGF-1 were determined by Western blotting analysis of protein lysates from granulosa cell cultures and by immunohistochemistry in the rat ovary. DDE at concentrations of 100-1000 ng/mL increased the expression of VEGF, Flk-1 and IGF-1 in vitro in primary cultures of human granulosa cells, with the highest expression occurring at 1000 ng/mL. Similarly, acute administration of DDE resulted in a significant increase in immunoreactive VEGF, Flk-1 and IGF-1 in the rat ovary. We conclude that DDE, at levels, which have been detected in humans, alters the expression of the ovarian growth factors VEGF and IGF-1 both in vivo and in vitro. This alteration in expression of growth factors may lead to altered ovarian function as seen in polycystic ovaries and impaired fertility.

Transgenic overexpression of IGF-IR disrupts mammary ductal morphogenesis and induces tumor formation.

Overexpression and hyperactivation of the type I insulin-like growth factor receptor (IGF-IR) has been observed in human breast tumor biopsies. In addition, in vitro studies indicate that overexpression of IGF-IR is sufficient to transform cells such as mouse embryo fibroblasts and this receptor promotes proliferation and survival in breast cancer cell lines. To fully understand the function of the IGF-IR in tumor initiation and progression, transgenic mice containing human IGF-IR under a doxycycline-inducible MMTV promoter system were generated. Administration of 2 mg/ml doxycycline in the animals' water supply beginning at 21 days of age resulted in elevated levels of IGF-IR in mammary epithelial cells as detected by Western blotting and immunohistochemistry. Whole mount analysis of 55-day-old mouse mammary glands revealed that IGF-IR overexpression significantly impaired ductal elongation. Moreover, histological analyses revealed multiple hyperplasic lesions in the mammary glands of these 55-day-old mice. The formation of palpable mammary tumors was evident at approximately 2 months of age and was associated with increased levels of IGF-IR signaling molecules including phosphorylated Akt, Erk1/Erk2 and STAT3. Therefore, these transgenic mice provide evidence that IGF-IR overexpression is sufficient to induce mammary epithelial hyperplasia and tumor formation in vivo and provide a model to further understand the function of IGF-IR in mammary epithelial transformation.

Fetal and neonatal exposure to nicotine disrupts ovarian function and fertility in adult female rats.

Women born to mothers who smoked during pregnancy have been shown to have impaired fertility, although the mechanisms underlying this association are unknown. Nicotine administration in adult animals has adverse effects on the ovary and uterus; however, the effects of fetal exposure to nicotine on postnatal ovarian function have not been determined. The goal of this study was to assess the effect of fetal and neonatal exposure to nicotine on ovarian function and fertility of the offspring. Nulliparous female Wistar rats were given 1 mg.kg-1.d-1 nicotine bitartrate, subcutaneously for 14 d prior to mating, during pregnancy and throughout lactation until weaning. Measures of fertility, breeding success, and serum levels of ovarian steroid hormones in offspring were assessed at 4 and 6 mo of age. Fetal and neonatal exposure to nicotine significantly increased the time to pregnancy as the animals aged. Similarly, evidence of altered ovarian steroidogenesis including increased serum progesterone concentrations and a decreased estrogen:progesterone ratio was observed in 6-mo-old animals. We conclude that fetal and neonatal exposure to nicotine results in delayed ovarian dysfunction in adult female offspring.

Fetal and neonatal exposure to nicotine in Wistar rats results in increased beta cell apoptosis at birth and postnatal endocrine and metabolic changes associated with type 2 diabetes.

AIMS/HYPOTHESIS: Epidemiological studies report an increased risk of obesity and type 2 diabetes in children born to women who smoked during pregnancy. This study examines the effect of fetal and neonatal exposure to nicotine, the major addictive component of cigarettes, on postnatal growth, adiposity and glucose homeostasis. METHODS: Female Wistar rats were given either saline (vehicle) or nicotine (1 mg kg(-1) day(-1)) during pregnancy and lactation. Serum and pancreas tissue were collected from the infant rats at birth. Postnatal growth was assessed weekly until the rats reached 26 weeks of age and glucose homeostasis was examined by OGTTs performed at 7 and 26 weeks of age. RESULTS: Exposure to nicotine resulted in increased postnatal growth and adiposity. Nicotine exposure also resulted in dysglycaemia at 7 and 26 weeks of age. Serum insulin concentrations were decreased in the pups exposed to nicotine at birth. This was associated with increased beta cell apoptosis (pups of saline-treated mothers 8.8+/-1.21% apoptotic beta cells; pups of nicotine-treated mothers 27.8+/-3.1% apoptotic beta cells). CONCLUSIONS/INTERPRETATION: Fetal and neonatal exposure to nicotine results in metabolic changes in the offspring that are consistent with obesity and type 2 diabetes. We propose that these metabolic changes may be a consequence of the initial insult to the beta cell during fetal life and that this animal model has many characteristics of diabetes in humans.