Epidemiological studies have demonstrated an association between type 2 diabetes and cancer. Type 2 diabetes is characterized by insulin resistance and hyperinsulinemia. Hyperinsulinemia may lead to cancer through insulin's effect on its cognate receptor and the insulin-like growth factor system. The effects of insulin and insulin-like growth factor I on cancer development and progression have been demonstrated in animal and human studies. Type 2 diabetes has been positively associated with cancers of the breast, colon, and pancreas. An inverse relationship has been observed between type 2 diabetes and prostate cancer, and this may be due to lower testosterone levels in men with type 2 diabetes. Medications used to treat type 2 diabetes may affect cancer cells directly or indirectly by affecting serum insulin levels. Hyperinsulinemia may be an important risk factor for cancer as well as a target for cancer therapy.

Animal studies have shown that IGF-I is essential for mammary gland development. Previous studies have suggested that local IGF-I rather than circulating IGF-I is the major mediator of mammary gland development. In the present study we used the hepatic IGF-I transgenic (HIT) and IGF-I knockout/ HIT (KO-HIT) mouse models to examine the effects of enhanced circulating IGF-I on mammary development in the presence and absence of local IGF-I. HIT mice express the rat IGF-I transgene under the transthyretin promoter in the liver and have elevated circulating IGF-I and normal tissue IGF-I levels. The KO-HIT mice have no tissue IGF-I and increased circulating IGF-I. Analysis of mammary gland development reveals a greater degree of complexity in HIT mice as compared to control and KO-HIT mice, which demonstrate similar degrees of mammary gland complexity. Immunohistochemical evaluation of glands of HIT mice also suggests an enhanced degree of proliferation of the mammary gland, whereas KO-HIT mice exhibit mammary gland proliferation similar to control mice. In addition, HIT mice have a higher percentage of proliferating myoepithelial and luminal cells than control mice, whereas KO-HIT mice have an equivalent percentage of proliferating myoepithelial and luminal cells as control mice. Thus, our findings show that elevated circulating IGF-I levels are sufficient to promote normal pubertal mammary epithelial development. However, HIT mice demonstrate more pronounced mammary gland development when compared to control and KO-HIT mice. This suggests that both local and endocrine IGF-I play roles in mammary gland development and that elevated circulating IGF-I accelerates mammary epithelial proliferation. (Endocrinology 151: 5751-5761, 2010)

Androgen deprivation therapy remains the treatment of choice for metastatic prostate cancer; however, it is not without its adverse effects, and most men with advanced disease eventually develop castration resistance. Newer compounds that more specifically and effectively target androgen and androgen receptor signaling in prostate cancer cells may provide more long-lasting remissions in advanced disease.

SUMMARYUnderstanding insulin-like growth factor-1 (IGF1) biology is of particular importance because, apart from its role in mediating growth, it plays key roles in cellular transformation, organ regeneration, immune function, development of the musculoskeletal system and aging. IGF1 bioactivity is modulated by its binding to IGF-binding proteins (IGFBPs) and the acid labile subunit (ALS), which are present in serum and tissues. To determine whether IGF1 binding to IGFBPs is necessary to facilitate normal growth and development, we used a gene-targeting approach and generated two novel knock-in mouse models of mutated IGF1, in which the native Igf1 gene was replaced by Des-Igf1 (KID mice) or R3-Igf1 (KIR mice). The KID and KIR mutant proteins have reduced affinity for the IGFBPs, and therefore present as unbound IGF1, or ‘free IGF1’. We found that both KID and KIR mice have reduced serum IGF1 levels and a concomitant increase in serum growth hormone levels. Ternary complex formation of IGF1 with the IGFBPs and the ALS was markedly reduced in sera from KID and KIR mice compared with wild type. Both mutant mice showed increased body weight, body and bone lengths, and relative lean mass. We found selective organomegaly of the spleen, kidneys and uterus, enhanced mammary gland complexity, and increased skeletal acquisition. The KID and KIR models show unequivocally that IGF1-complex formation with the IGFBPs is fundamental for establishing normal body and organ size, and that uncontrolled IGF bioactivity could lead to pathological conditions.

No abstract