Insulin-like growth factor physiology and cancer risk

In the past few years, both laboratory investigations and population studies have provided strong circumstantial evidence that insulin-like growth factor (IGF) physiology influences cancer risk. In contrast to the influence of germ line mutations that are rare but are associated with very high risks, the impact of inter-individual variability in IGF physiology on risk appears to be modest but to effect a relatively high percentage of the population. Although this field of investigation is young, attention is already being given to the possibility that it may be relevant to clinical assessment of risk and/or to the identification of novel prevention strategies and intermediate endpoints. This review summarises key results in this field and provides a hypothesis concerning the mechanism by which IGF physiology influences risk of common epithelial cancers including those of breast, prostate, lung and colon.

Castration-induced up-regulation of insulin-like growth factor binding protein-5 potentiates insulin-like growth factor-I activity and accelerates progression to androgen independence in prostate cancer models

Although insulin-like growth factor binding protein-5 (IGFBP-5) has been shown to be implicated in prostate cancer progression, the functional role of IGFBP-5 in progression to androgen-independence remains largely undefined. Here, we demonstrate substantial up-regulation of IGFBP-5 during castration-induced regression and androgen-independent (AI) progression in the mouse androgen-dependent (AD) Shionogi tumor model. To analyze the functional significance of these changes in IGFBP-5, human AD LNCaP prostate cancer cells were stably transfected with IGFBP-5 gene, and IGFBP-5-overexpressing LNCaP tumors progressed significantly faster to androgen independence after castration compared with controls. Antisense mouse IGFBP-5 oligodeoxynucleotides (ODNs) were then designed that reduced IGFBP-5 expression in Shionogi tumor cells in vitro in a dose-dependent and sequence-specific manner. Growth of Shionogi tumor cells was inhibited by antisense IGFBP-5 ODN treatment in a time- and dose-dependent manner, which could be reversed by exogenous IGF-I. However, antisense IGFBP-5 ODN treatment had no additive inhibitory effect on Shionogi tumor cell growth when IGF-I activity was neutralized by anti-IGF-I antibody. Antisense IGFBP-5 ODN treatment resulted in decreased mitogen-activated protein kinase activity and number of cells in the S + G2-M phases of the cell cycle that directly correlated with reduced proliferation rate of Shionogi tumor cells. Systemic administration of antisense IGFBP-5 ODN in mice bearing Shionogi tumors after castration significantly delayed time to progression to androgen independence and inhibited growth of AI recurrent tumors. These findings suggest that up-regulation of IGFBP-5 after castration serves to enhance IGF bioactivity and raise the possibility that the response of prostate cancer to androgen withdrawal can be enhanced by strategies, such as antisense IGFBP-5 ODN therapy, that target IGF signal transduction.

Aging effects in an anderson insulator

Aging, commonly observed in glasses, is a manifestation of breakdown of time-translational invariance. Here we demonstrate experimentally aging effects in the electronic system of an Anderson insulator. The aging phenomenon in the electron glass appears to be much less sensitive to temperature than in other systems. The differences in the behavior of the electron glass and a spin glass system are discussed in terms of some microscopic differences between the two systems.

The question of a link between insulin-like growth factor physiology and neoplasia

The results of both population and laboratory studies suggest that the physiology of insulin-like growth factors (IGFs) has important influences on cancer biology and cancer risk. This review highlights recent laboratory and epidemiological results in this rapidly evolving area of investigation. There is no direct evidence to suggest that growth hormone (GH) treatment of GH-deficient patients increases their risk of neoplasia, but recent research reinforces the need for careful surveillance. The monitoring of serum IGF-I levels may be advisable to help avoid inadvertent over-treatment, particularly in individuals undergoing long-term GH replacement therapy.

Modulation of transforming growth factor beta1 gene expression in the mammary gland by insulin-like growth factor I and octreotide

Transforming growth factor beta1 (TGF-beta1) has been shown to exhibit anti-proliferative activity for mammary gland epithelial cells and for human breast cancer cells. Insulin-like growth factor I (IGF-I), in contrast, is a well-characterized mitogenic and anti-apoptotic factor involved in mammary gland physiology. In order to examine the hypothesis that IGF-I suppresses TGF-beta1 expression in the mammary gland, we studied the effect of various manipulations of the growth hormone - IGF-I axis on TGF-beta1 mRNA abundance. Administration of IGF-I to intact animal suppressed TGF-beta1 mRNA levels in a dose-dependent manner to approximately 20% of control levels. Administration of the somatostatin analogue octreotide in a manner previously shown to acutely suppress the growth hormone - IGF-I axis increased mammary gland TGF-beta1 expression approximately 3-fold. Transgenic mice overexpressing growth hormone expressed TGF-beta1 in the mammary gland at only approximately 12% of the level of control animals, while mice IGF-I deficient due to the mutation expressed TGF-beta1 at slightly higher levels than control animals. The large differences in TGF-beta1 expression between control and GH-transgenic animals were correlated with major differences in architecture of the mammary gland, while the appearance of mammary glands of normal and animals was similar. These data document a previously unrecognized relationship between TGF-beta1 and IGF-I physiology in the mammary gland, and suggest a novel mechanism by which somatostatin analogues influence the proliferative behaviour of breast epithelial cells.

[Neonatal hyperparathyroidism secondary to unknown maternal hypoparathyroidism]

Vitamin D or its analogue (calcitriol) is an effective treatment for hypoparathyroidism during pregnancy. Normal babies are delivered and very few cases of associated neonatal hyperparathyroidism are reported.

CASE REPORT

We report the case of a baby born to a mother suffering unknown hypoparathyroidism. He was delivered prematurely by cesarean section for birth asphyxia. His mother had had recurrent bouts of impetigo herpetiformis for several months. Severe demineralization associated with decreased plasma calcium level were observed at birth. The PTH level was very high (955 ng/mL) in the baby and very low in the mother, leading to the diagnosis. The baby was given intravenous calcium gluconate, oral 1 alpha-hydroxyvitamin D and mechanical ventilation. Normal plasma calcium level was reached on day 2. PTH level improved by one month of age. Because of impaired respiratory mechanics and bronchopulmonary dysplasia, the baby was kept on ventilation for 58 days. By 20 months of age, he was in good health despite a small height for his age.

CONCLUSION

In such cases 1 alpha-hydroxyvitamin D seems to be very effective but plasma and urinary calcium levels need careful monitoring.

Bicalutamide (Casodex)-induced prostate regression involves increased expression of genes encoding insulin-like growth factor binding proteins

OBJECTIVES

To examine the effects of bicalutamide (Casodex), a pure antiandrogen with high specificity for the androgen receptor, on insulin-like growth factor binding protein (IGFBP) expression and apoptotic regression of the rat ventral prostate.

METHODS

Rats were treated daily with 10 mg/kg body weight bicalutamide or vehicle alone. Ventral prostates were collected at various days of treatment. Northern blot analysis was performed to quantitate expression of genes encoding IGFBPs, and the TUNEL method was used to determine the extent of apoptosis in ventral prostate.

RESULTS

In rats treated daily with bicalutamide, increases in mRNA levels of IGFBP-2, -3, -4, and -5 were detectable by Northern blotting by 6 hours and reached 6 to 10-fold of control levels after 5 days of treatment. The time-course of induction of apoptosis in the ventral prostate by bicalutamide, as detected in situ by the TUNEL method, corresponded to the time-course of induction of IGFBP expression.

CONCLUSIONS

We demonstrate that apoptotic regression of the ventral prostate during bicalutamide treatment is accompanied by increased expression of IGFBP-2, -3, -4, and -5. Rapid induction of IGFBPs, which can limit access of insulin-like growth factors (IGFs) to the IGF-I receptor, may play a role in the induction of apoptosis by antiandrogens, particularly in view of the increasing evidence that IGF-I inhibits apoptosis. These results document a previously unrecognized effect of antiandrogens and extend our previous studies relating IGF physiology to prostate biology. Together with evidence that a strong positive correlation exists between plasma IGF-I levels and prostate cancer risk, our data suggest that IGF physiology may play a key role in prostate cancer biology and is strongly influenced by androgen-targeting therapies.

Fatty acid metabolism in human breast cancer cells (MCF7) transfected with heart-type fatty acid binding protein

The human breast cancer cell line MCF7 does not express heart-type fatty acid binding protein (H-FABP), a marker protein for differentiated mammary gland. MCF7 cells transfected with the bovine H-FABP cDNA expressed the corresponding protein and were characterized by growth inhibition and lower tumorgenicity in nude mice [22]. By enzyme linked immunoassay we now determined the amount of bovine H-FABP in these cells as 638 +/- 80 ng/mg protein and used the transfected cells to study the role of H-FABP in fatty acid metabolism. Compared to control cells the uptake of radioactively labelled palmitic acid and oleic acid into MCF7 cells after 30 or 60 min was increased by 67% in H-FABP expressing transfectants, demonstrating a stimulatory role for this FABP-type in fatty acid metabolism. However, preferential targeting of [14C]oleic acid into neutral or phospholipid classes was not observed by the criterion of high performance thin layer chromatography followed by autoradiography. A reason for the modest increase of fatty acid uptake in H-FABP transfected MCF7 cells may be the basal expression of epidermal-type FABP, which was detected for the first time in these cells. It appears that the small amount of E-FABP expressed in MCF7 cells fulfils the need of the cells for a cytosolic fatty acid carrier under culture conditions and that even high concentrations of another FABP do only slightly increase the uptake due to limitations of fatty acid transport through the plasma membrane or of metabolism.

Inhibition of insulin-like growth factor I receptor signaling by the vitamin D analogue EB1089 in MCF-7 breast cancer cells: A role for insulin-like growth factor binding proteins

Insulin-like growth factors I and II (IGF-I and IGF-II) are potent mitogens involved in growth regulation of breast epithelial cells and are implicated in the pathophysiology of breast cancer. Their bioactivity is enhanced or inhibited by specific IGF-binding proteins (IGFBPs). Vitamin D-related compounds (VDRCs) have been shown to inhibit proliferation and induce apoptosis of MCF-7 breast carcinoma cells. We have previously demonstrated that VDRCs antagonize the growth-promoting activity of IGF-I by stimulating autocrine production of IGFBP-5 in MCF-7 cells, but the effect of VDRCs on IGF-I receptor (IGF-IR) intracellular signaling has not been elucidated. We report here that the vitamin D analogue EB1089 interferes with the IGF-IR signaling pathway by attenuating IGF-I-induced tyrosine phosphorylation of IRS-1, and to a lesser extent, IRS-2. It does not affect protein levels of IRS-1, IRS-2 or IGF-IR. However, EB1089 does not inhibit tyrosine phosphorylation of IRS-1 induced by des(1-3) IGF-I, an IGF-I analogue with greatly reduced affinity for IGFBPs. Furthermore, we demonstrate that an antisense IGFBP-5 oligodeoxynucleotide attenuates EB1089-induced inhibition of IGF-I-stimulated tyrosine phosphorylation of IRS-1 and EB1089-induced IGFBP-5 accumulation. These data strongly suggest that IGFBP-5 plays a functional role in the interfering action of EB1089 with the IGF-IR signal transduction pathway.

Insulin-like growth factors and prostate cancer

Converging data from epidemiological and biological research implicate insulin-like growth factor (IGF) physiology in the regulation of prostate epithelial cell proliferation and in the pathophysiology of prostate cancer. This review (1) outlines elements of IGF physiology, (2) reviews recent evidence that circulating IGF-I level is related to risk of prostate cancer, (3) provides a hypothesis concerning the biological basis for the relationship between IGF-I level and risk of prostate cancer, (4) discusses IGF-I physiology in the context of neoplastic progression of prostate cancer, and (5) discusses clinical implications of these lines of research with respect to prevention and treatment.

Castration-induced apoptosis of androgen-dependent shionogi carcinoma is associated with increased expression of genes encoding insulin-like growth factor-binding proteins

Insulin-like growth factor (IGF)-I has well-characterized mitogenic and antiapoptotic effects that are essential for maintenance of the normal prostate and may be important during regression of the normal prostate and/or prostate tumors induced by androgen-targeting therapies for prostate cancer. IGF-I activity is modulated by IGF-binding proteins (IGFBPs). Here we examine IGFBP expression during regression of androgen-dependent Shionogi carcinoma tumors after castration. In this model, we observe a 90% reduction in Shionogi tumors by 10 days postcastration. Northern blotting of RNA from tumors collected at various times after castration indicates a rapid induction of IGFBP-5 concomitant with apoptotic regression of tumors, as detected by Apoptag staining of tumor sections after castration. IGFBP-5 mRNA was not detectable in tumors from control animals, but levels increased 120-fold in tumors 3 days after castration. The mRNAs for IGFBP-3 and 4 were abundant in Shionogi tumors from intact mice and decreased to -33% and -20% of control, respectively. Castration had no significant effect on IGFBP-2 expression. Treatment with calcium channel blockers inhibited castration-induced apoptosis and tumor regression and also significantly inhibited up-regulation of IGFBP-5 after castration. These data provide strong evidence for a functional role of IGFBP-5 expression in mediating the apoptosis induced by androgen deprivation in androgen-dependent neoplasia.

Regression of DMBA-induced breast carcinoma following ovariectomy is associated with increased expression of genes encoding insulin-like growth factor binding proteins

Insulin-like growth factor I (IGF-I) has well characterized mitogenic and antiapoptotic effects in both normal and neoplastic mammary epithelial cells which are mediated through the IGF-I receptor. IGF activity is modulated by a family of high affinity IGF binding proteins (IGFBPs 1-6). Here we show that gene expression of IGFBP-2, -3, -4 and -5 increases rapidly in DMBA-induced rat mammary tumors following ovariectomy. We observed a 90% reduction in volume of DMBA-induced rat mammary tumors by 14 days post-ovariectomy. The time course of maximal tumor regression was associated with increased gene expression of IGFBPs, as detected by Northern blot analysis. IGFBP-2, -3, -4 and -5 mRNA levels increased from 2- to 16-fold of control by 14 days of estrogen-ablation. These results are compatible with the hypothesis that response of DMBA-induced mammary tumors to estrogen deprivation therapies involves reduction of IGF bioactivity secondary to upregulation of expression of IGF binding proteins.

IGF-I physiology and breast cancer

Recent studies imply that IGF-I levels vary greatly between normal women, and that premenopausal breast cancer risk is increased among women with higher IGF-I levels. It is known that tamoxifen lowers IGF-I levels, but further research is needed to determine whether antiestrogens will be of particular value in risk reduction for women with high IGF-I levels, and also to determine if IGF-I levels can indeed be used as an intermediate endpoint in risk reduction interventions. With respect to adjuvant therapy, we currently have convincing data that antiestrogens have moderate IGF-I lowering actions, but it remains unclear to what extent these contribute to the therapeutic effect of these compounds. Ongoing trials are addressing this question, as well as the hypothesis that interventions that increase IGF-I suppression will be associated with reduced relapse rates.

Antiproliferative action of tumor necrosis factor-alpha on MCF-7 breastcancer cells is associated with increased insulin-like growth factor binding protein-3 accumulation

Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional cytokine involved in host response to neoplasia. TNF-alpha has been shown to inhibit proliferation and induce apoptosis of MCF-7 breast carcinoma cells. Insulin-like growth factors I and II (IGF-I and IGF-II) are potent mitogens involved in growth regulation of breast epithelial cells and are implicated in the pathophysiology of breast cancer. Their bioactivity is strongly influenced by specific IGF-binding proteins (IGFBPs). We report that accumulation of IGFBP-3 in the conditioned media of MCF-7 cells is increased over control values in the presence of TNF-alpha. The increased IGFBP-3 accumulation induced by TNF-alpha is correlated with increased IGFBP-3 mRNA abundance. TNF-alpha also decreases IGF-I receptor levels in MCF-7 cells. Estradiol-stimulated MCF-7 cell proliferation is associated with reduced IGFBP-3 accumulation, and we show that TNF-alpha attenuation of estradiol-stimulated proliferation is associated with increased IGFBP-3 accumulation. Finally, we demonstrate that an IGFBP-3 antisense oligodeoxynucleotide antagonizes TNF-alpha-induced inhibition of cell proliferation and TNF-alpha-induced IGFBP-3 accumulation. These data strongly suggest that IGFBP-3 plays a role in modulation of breast cancer cell proliferation by TNF-alpha.

Expression of insulin-like growth factor receptor, IGF-1, and IGF-2 in primary and metastatic osteosarcoma

BACKGROUND AND OBJECTIVES

We have previously shown that insulin-like growth factor (IGF)-responsive murine sarcomas demonstrate inhibition of local and metastatic disease growth when implanted in an IGF-deficient host animal. In this experiment, we tested whether IGF receptor (IGF-R) and ligands were expressed in human primary and metastatic osteosarcomas.

METHODS

Fifty-two specimens of human osteosarcoma tumor from 48 patients were assayed for IGF-R, IGF-1, and IGF-2 using reverse transcriptase polymerase chain reaction.

RESULTS

Twenty-one of 46 tumors analyzed had levels of expression of IGF-R greater than or equal to the positive control cell line. Twenty-seven of 44 expressed levels of IGF-1 greater than or equal to the positive control, as did 21 of 38 cases assayed for IGF-2. No differences were found between 40 primary tumor samples and 12 metastatic lesions in mean levels of IGF-R, IGF-1, or IGF-2. There was a moderately strong correlation between expression of IGF-R and IGF-1, suggesting that autocrine stimulation may be an important mechanism for stimulation of osteosarcoma proliferation.

CONCLUSIONS

A significant proportion of osteosarcoma tumors express IGF-R and ligands. Higher levels of expression were not correlated with metastatic lesions.

Regulation of insulin-like growth factor (IGF) II and IGF binding protein 3 autocrine loop in human PC-3 prostate cancer cells by vitamin D metabolite 1,25(OH)2D3 and its analog EB1089

Prostate cancer and benign prostate hyperplasia (BPH) are major public health problems. Prostate epithelial cell proliferation is regulated by insulin-like growth factor I (IGF-I) which is mitogenic and anti-apoptotic, and IGF binding protein 3 (IGFBP-3) which is an apoptotic agent in these cells. We demonstrate that the 1,25(OH)2D3 and its analog EB1089-induced growth inhibition was associated with increased IGFBP-3 mRNA abundance, IGFBP-3 mRNA stability, IGFBP-3 protein accumulation, and decreased IGF-II gene expression. Anti-IGF-II antibody and exogenous recombinant human IGFBP-3 inhibit PC-3 cell proliferation. The results document the inhibitory effects of 1,25(OH)2D3 and EB1089 on the IGF system of mitogens in prostate cancer cells, and suggest a potential therapeutic use of EB1089 in treatment of BPH and prostate cancer.

Circulating concentrations of insulin-like growth factor-I and risk of breast cancer

BACKGROUND

Insulin-like growth factor (IGF)-I, a mitogenic and antiapoptotic peptide, can affect the proliferation of breast epithelial cells, and is thought to have a role in breast cancer. We hypothesised that high circulating IGF-I concentrations would be associated with an increased risk of breast cancer.

METHODS

We carried out a nested case-control study within the prospective Nurses' Health Study cohort. Plasma concentrations of IGF-I and IGF binding protein 3 (IGFBP-3) were measured in blood samples collected in 1989-90. We identified 397 women who had a diagnosis of breast cancer after this date and 620 age-matched controls. IGF-I concentrations were compared by logistic regression with adjustment for other breast-cancer risk factors.

FINDINGS

There was no association between IGF-I concentrations and breast-cancer risk among the whole study group. In postmenopausal women there was no association between IGF-I concentrations and breast-cancer risk (top vs bottom quintile of IGF-I, relative risk 0.85 [95% CI 0.53-1.39]). The relative risk of breast cancer among premenopausal women by IGF-I concentration (top vs bottom tertile) was 2.33 (1.06-5.16; p for trend 0.08). Among premenopausal women less than 50 years old at the time of blood collection, the relative risk was 4.58 (1.75-12.0; p for trend 0.02). After further adjustment for plasma IGFBP-3 concentrations these relative risks were 2.88 and 7.28, respectively.

INTERPRETATION

A positive relation between circulating IGF-I concentration and risk of breast cancer was found among premenopausal but not postmenopausal women. Plasma IGF-I concentrations may be useful in the identification of women at high risk of breast cancer and in the development of risk reduction strategies. Additional larger studies of this association among premenopausal women are needed to provide more precise estimates of effect.