Implications of insulin-like growth factor-I for prostate cancer therapies

In the last decade, abundant evidence has suggested that the insulin-like growth factor (IGF) family comprises a multi-component network of molecules involved in the regulation of both physiological and pathological growth processes in the prostate. The IGF axis plays an important role in the tumorigenesis and neoplastic growth of prostate cancer. Epidemiological observations indicate that circulating IGF-I levels are positively associated with increased risk of prostate cancer. Activation of IGF-I receptor (IGF-IR) by IGF-I has mitogenic and anti-apoptotic effects on normal and malignant prostate cells. Therapeutic alternatives in men with progressive prostate cancer after androgen ablation are very limited and more effective therapies are needed for such patients. Inactivation of the IGF-I axis represents a potential target to treat androgen-independent prostate cancer. This review addresses epidemiological studies of IGF-I and therapeutic strategies including reduction of IGF-I levels, inhibition of IGF-IR and the signaling mechanisms involved.     

Compensatory renal growth: role of growth hormone and insulin-like growth factor-I

Recent experimental evidence suggests that insulin-like growth factor-I (IGF-I) may be involved in compensatory renal growth (CRG). This study was designed to determine the relative contribution of IGF-I and growth hormone (GH) to the CRG that takes place in rats following uninephrectomy (UNx). We also studied the respective role of GH and IGF-I in the stimulation of CRG induced by a high protein diet (HPD). CRG was studied 7 days after UNx in Wistar rats and in a new mutant strain of dwarf rats, selectively deficient in GH. Prior to UNx, rats of both strains were pre-fed (14 days) either a medium-protein diet (MPD, casein 18%) or a HPD (54%). On MPD, CRG was comparable in Wistar (17.6 +/- 3.1%, M +/- SD) and dwarf (14.4 +/- 4.8%) rats. The HPD enhanced CRG in the Wistars (27 +/- 3.9%, P less than 0.005) but not in the dwarfs (14.9 +/- 2%). CRG in both experimental groups involved renal hypertrophy and hyperplasia. Control (baseline) serum, liver and kidney IGF-I were significantly less in dwarf rats. However, following UNx, on a MPD, kidney IGF-I increased significantly in both Wistar and dwarf rats: Wistar, pre-UNx, 310 +/- 46 ng/g tissue; post-UNx, 405 +/- 54 ng/g, P less than 0.005; dwarfs, pre-UNx, 205 +/- 35 ng/g; post-UNx 426 +/- 90 ng/g, P less than 0.001. On a HPD a further significant increase in renal IGF-I was only observed in Wistar rats (505 +/- 46 ng/g). No change in serum or liver IGF-I was observed after UNx in either strain.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gene mediated insulin-like growth factor-I delivery to the synovium.

The feasibility of articular gene therapy using insulin-like growth factor-I transgene expression in synovial tissues was assessed in vitro by transfection of synovial explant and monolayer cultures. Synovial membrane was harvested from horses and distributed for explant culture in multiwell plates or digested for monolayer culture in multiwell plates and chamber slides. Synovial monolayers were cultured for 48 h after infection with 0, 100, 200, or 500 moi adenovirus-IGF-I (AdeIGF-I) to establish an optimum dose. Explants were then either infected with AdeIGF-I or adenoviral LacZ and cultured for 8 days, treated with 100 ng/ml recombinant IGF-I as a positive control, or remained as uninfected untreated culture controls. Expression of IGF-I in explants and monolayers was assessed by in situ hybridization and quantitative polymerase chain reaction (PCR), and translation confirmed by IGF-I radioimmunoassay (RIA) and tissue immunoreaction. Effects of IGF-I on synovial function was assessed by proteoglycan and hyaluronan assay, and northern blot assessment of decorin and collagen type I expression. Significant transgene expression in synovial cells was present for all AdeIGF-I concentrations. Similarly, medium IGF-I concentrations were significantly elevated in AdeIGF-I infected synovial monolayer and explant cultures at all time points. Peak IGF-I concentration of 246 +/- 43 ng/ml developed in explant cultures on day 4; IGF-I levels in control explant groups were unchanged over baseline values. In situ hybridization and immunolocalization for IGF-I indicated focal IGF-I expression in intimal and subintimal layers of infected explants, with diffuse immunoreaction throughout infected subintimal and fibrous layers. For monolayer cultures, intracellular immunoreaction to IGF-I was markedly higher in infected cells, and was most prominent at 100 moi. Effects of IGF-I on synoviocyte cultures were evident on northern blots, which showed decreased decorin expression and elevated type I collagen production in AdeIGF-I infected monolayers. Proteoglycan concentration in the medium from explant cultures rose over the initial 4 days but was similar between treatment groups. The concentration of hyaluronan in medium from explant cultures did not differ significantly within or between treated and control groups during the 8-day study period. These data indicate that IGF-I can be successfully introduced to synovial structures by adenoviral vectors and results in effective IGF-I ligand synthesis without untoward synovial morphologic effects.     

Insulin-like growth factor-I and insulin-like growth factor-binding proteins in the nephrotic syndrome

Similar to findings in the nephrotic syndrome in humans, rats with the doxorubicin-induced nephrotic syndrome (which resembles minimal change disease) have reduced serum levels of insulin-like growth factor-I (IGF-I). This is mainly caused by glomerular ultrafiltration of IGF-I-containing binding protein complexes, primarily of a molecular weight of approximately 50 kilodaltons, and urinary losses of the peptide. Despite urinary excretion of IGF-binding protein (IGFBP)-2, serum levels are increased more than twofold in the nephrotic syndrome compared with controls, because of increased synthesis of this binding protein by the liver. In contrast, the liver synthesis of IGFBP-3, the predominant binding protein in normal serum, is unchanged in the nephrotic syndrome. However, binding and serum levels of IGFBP-3 are reduced in nephrotic rat serum, apparently due to proteolytic degradation of IGFBP-3. The glomerular ultrafiltration of IGF-I, which leads to biologically significant IGF-I concentrations of about 1.35 nM in proximal tubule fluid, may have metabolic consequences, such as increased tubular phosphate absorption. Hypothetically, tubule fluid IGF-I may also contribute to progressive tubulointerstitial fibrosis which is sometimes present in protractive nephrotic glomerulopathies. The profound changes in the IGF-I/IGFBP system in the nephrotic syndrome may also contribute to systemic metabolic abnormalities and growth failure.     

Experimental diabetic renal growth: role of growth hormone and insulin-like growth factor-I

We have compared the kidneys of two inbred strains of rats (Lewisand Lewis-Dwarf) 7 days after the induction of diabetes mellituswith streptozotocin, in order to examine the influence of aselective growth hormone (GH) deficiency on diabetic renal growthand insulin-like growth factor-I (IGF-I) content of the kidneys.Insulin-like growth factor-I was measured by radioimmunoassayand its distribution within the kidney by immunohistochemicalstaining. We detected a significant increase in both the wetweight (32.9±5.3%, P=0.0085) and dry weight (16.3±6.3%,P=0.046) of the kidneys of diabetic Lewis rats but dwarf rats,selectively deficient in GH, did not show a significant increasein either parameter. Extractable IGF-I increased within thekidneys of diabetic rats of both strains but to a lesser extentin the dwarf rats (+105±28% and +65±21% respectively,P<0.0l). In diabetic Lewis rats a positive correlation wasnoted between the severity of glycaemia and kidney IGF-I content(r=0.604, P<0.05) but no such correlation was noted in dwarfrats. Insulin-like growth factor-I immunostaining increased in diabeticrats of both strains, mainly within cells of the thick ascendinglimb of the loop of Henle including damaged and vacuolated cells.However, morphometric analysis of the staining showed that itwas significantly less widespread in the diabetic dwarf rats(P=0.026). We conclude that growth hormone deficiency bluntsexperimental diabetic renal growth and restricts the increasein the kidney IGF-I content. These findings raise further questionsconcerning the contribution of GH and IGF-I to the early stagesof experimental diabetic renal disease.     

Influence of growth hormone and insulin-like growth factor-I on kidney function and kidney growth

Decreased glomerular filtration rate (GFR) in hypopituitarism and increased GFR in acromegaly suggest that growth hormone (GH) has a substantial effect on renal haemodynamics. Extractive and recombinant human (rh) GH in healthy volunteers increased effective renal plasma flow (ERPF) and GFR by 10% and 15% respectively. Renal response to GH was delayed and occurred at the same time as an increase in plasma insulin-like growth factor (IGF)-I values, whereas infusion of rhIGF-I promptly increased GFR and ERPF, indicating that the haemodynamic response of the kidney to GH is mediated by IGF-I. In chronic renal failure (CRF), the acute effect of GH on GFR is obliterated. This might protect the diseased kidney against the undesired consequences of hyperfiltration. Indeed, rhGH treatment for 1 year in children with CRF did not lead to an accelerated decline in GFR compared with the year before treatment. GH and IGF-I also effect renal growth. Exposure to excessive GH in transgenic mice causes renomegaly and progressive glomerular selerosis. In acromegalic humans, increased renal size and weight and increased glomerular diameter are well known, whereas renal failure is not a long-term hazard. At least in normal and hypophysectomized rats treated with doses comparable with the therapeutic regimens used in stunted children, rhGH increased renal weight but in proportion to the increase in body weight indicating an isometric effect of GH on renal growth. From these data, major renal longterm side effects of rhGH treatment in children with CRF appear unlikely.     

Serum insulin-like growth factor-I and insulin-like growth factor binding protein-3 following chemotherapy for advanced breast cancer

Background: Insulin‐like growth factor‐I (IGF‐I) and IGF binding protein‐3 (IGFBP‐3) appear to influence the growth of breast cancer cells in vitro, and epidemiological studies suggest higher serum IGF‐I levels increase the risk of breast cancer. IGF‐I and IGFBP‐3 have therefore been measured in women with advanced breast cancer to determine if changes in serum levels predict the response to treatment by chemotherapy. Methods: Serum IGF‐I and IGFBP‐3 levels were measured in 14 patients before and after 1 week of chemotherapy. Changes in serum levels were compared with duration of survival. Results: Mean basal serum levels of IGF‐I and IGFBP‐3 were not significantly different between patients with advanced breast cancer and controls or women with early breast cancer. Serum IGFBP‐3 fell significantly 1 week after initiation of chemotherapy. Patient survival was not significantly related to baseline IGF‐I or IGFBP‐3 levels, but when the fall in serum levels 1 week after starting treatment was expressed either as absolute change or as a percentage of baseline, those individuals with a decrease in IGFBP‐3 greater than the median had significantly poorer survival (median survival 5.5 months vs 18 months). These results were independent of other prognostic variables such as previous disease‐free survival, and were also unaffected by the change in serum albumin with treatment. The fall in IGF‐I and IGFBP‐3 with chemotherapy mainly occurred in those with hepatic metastases, but prediction of survival was explained solely by the extent of the fall in IGFBP‐3. Conclusions: This preliminary study has shown that serum IGFBP‐3 falls significantly following initiation of chemotherapy and the extent of reduction significantly predicts the response to treatment.     

Increased specific binding of insulin-like growth factor-I in healing cutaneous wounds

Insulin-like growth factor-I is a polypeptide hormone structurally related to insulin. It is a potent mitogen that promotes growth and differentiation in many tissues. A role for insulin-like growth factor-I in wound healing is suggested by its rapid rise in levels and increased insulin-like growth factor-I messenger RNA expression in tissue after wounding. We designed our study to characterize possible changes in insulin-like growth factor-I receptor binding during wound healing. Surgical wounds created on the abdominal skin of anesthetized New Zealand White rabbits were either left open or closed primarily. Size- and weight-matched specimens were harvested at wounding time (day 0), and at 1, 4, 7, 38, and 50 days after wounding. Preliminary experiments showed that the greatest difference in specific binding occurred between day 0 and day 7. (125)I-insulin-like growth factor-I binding studies were performed on frozen tissue specimens and autoradiography was performed and analyzed by computerized densitometry. Scatchard analysis of the binding data showed a single class of insulin-like growth factor-I binding sites whose affinity that is, binding constant (K(d) = 0.6 x 10(-9)) did not change significantly over time; in contrast there was a threefold increase in the number of receptors per milligram tissue in day 7 wound tissue versus normal skin harvested at day 0 (17.3 +/- 2.6 x 10(10) versus 4.7 +/- 2.5 x 10(10), respectively, p < 0.05). Binding inhibition experiments showed that (125)I-insulin-like growth factor-I binding was most specific to insulin-like growth factor-I with insulin-like growth factor-I > insulin-like growth factor-II > insulin. This increase in binding was due to upregulation of insulin-like growth factor-I receptors rather than increased levels of insulin-like growth factor-I binding protein as less than 20% of the threefold increase in binding at day 7 could be attributed to insulin-like growth factor-I binding protein in membrane-free extracts. The presence of specific, high-affinity insulin-like growth factor-I receptors in the skin and their upregulation at day 7 after wounding suggest that insulin-like growth factor-I plays an important role during wound healing.     

The role of growth hormone and insulin-like growth factor-I in experimental renal growth and scarring

Recent evidence suggests a causal link between early renal/glomerular hypertrophy and late kidney scarring and glomerular sclerosis. Insulin-like growth factor-I (IGF-I) is a growth-promoting peptide likely to play a role in the development of kidney growth. We observed an increased renal IGF-I content in two experimental models of accelerated kidney growth in the rat. By contrast, diabetic renal hypertrophy is abolished in the absence of growth hormone (GH). Dietary protein manipulations affect the expression of compensatory renal growth (CRG), as well as renal IGF-I content. The renotrophic effect of a high-protein diet on CRG seems GH-dependent and IGF-I-mediated. GH also appears to have a permissive role on the development of progressive renal scarring following extensive renal ablation in rats, as dwarf rats seem somewhat resistant to the development of accelerated scarring and renal failure.     

Expression of insulin-like growth factor-I and transforming growth factor-beta in hypokalemic nephropathy in the rat

BACKGROUND: Potassium deficiency (KD) in the rat retards body growth but stimulates renal enlargement caused by cellular hypertrophy and hyperplasia, which is most marked in the outer medulla. If hypokalemia persists, interstitial infiltrates appear and eventually fibrosis. Since early in KD insulin-like growth factor-I (IGF-I) levels in the kidney are elevated, suggesting that it may be an early mediator of the exaggerated renal growth, and as transforming growth factor-beta (TGF-beta) promotes cellular hypertrophy and fibrosis, we examined the renal expression of these growth factors in prolonged KD. METHODS: Rats were given a K-deficient diet or were pair fed or ad libitum fed a K-replete diet for 21 days. Growth factor mRNA levels were measured in whole kidney and protein expression localized by immunohistochemistry. RESULTS: KD rats weighed less than pair-fed controls, while the kidneys were 49% larger. Their serum IGF-I and kidney IGF-I protein levels were depressed, as were their IGF-I mRNA levels in liver, kidney, and muscle. These changes can largely be attributed to decreased food intake. In contrast, kidney IGF binding protein-1 (IGFBP-1) mRNA and TGF-beta mRNA levels were increased significantly. Histology of outer medulla revealed marked hypertrophy and adenomatous hyperplasia of the collecting ducts and hypertrophy of the thick ascending limbs of Henle with cellular infiltrates in the interstitium. Both nephron segments immunostained strongly for IGF-I and IGFBP-1, but only the nonhyperplastic enlarged thick ascending Henle limb cells immunostained for TGF-beta, which was strongly positive. Prominent interstitial infiltrates with ED1 immunostained monocytes/macrophages were present. CONCLUSIONS: These findings are consistent with a sustained role for IGF-I in promoting the exaggerated renal growth of KD and appear to be mediated through local trapping of IGF-I by the overexpressed IGFBP-1, which together with IGF-I can promote renal growth. The selective localization of TGF-beta to hypertrophied nonhyperplastic nephron segments containing IGF-I raises the possibility that TGF-beta may be serving to convert the mitogenic action of IGF-I into a hypertrophic response in these segments. It is also conceivable that TGF-beta may be a cause of the tubulointerstitial infiltrate. Finally, the low circulating IGF-I levels likely contribute to the impaired body growth.     

Insulin-like growth factor-I and insulin-like growth factor-II induce c-fos in mouse osteoblastic cells

Summary We investigated the expression of c-fos in mouse osteoblast-like cultures treated with insulin-like growth factor (IGF)-I and IGF-II. The IGFs are present in bone, are produced by osteoblast-like cells in culture, and stimulate osteoblast cell proliferation. Quiescent, subconfluent cultures of the clonal osteoblast-like mouse calvarial cell line, MC3T3-E1, were treated with 10 ng/ml of IGF-I or IGF-II. RNA was extracted at 0, 15, 30, 60, 120 and 240 minutes, and c-fos messenger RNA (mRNA) was analyzed on Northern blots. Both IGFs transiently increased c-fos mRNA levels 25–28 fold at 15–30 min. To determine if c-fos induction was unique to the MC3T3-E1 cell line, effects of IGF-1 and IGF-II (3 ng/ml) were also tested in quiescent, serum-free primary mouse calvarial cells. Levels of c-fos mRNA were increased at 15 and 30 minutes (40-fold with IGF-I and 5-fold with IGF-II). These results indicate that IGF-I and IGF-II caused a rapid and transient induction of c-fos mRNA in murine osteoblasts.     

Transgenic mice with osteoblast-targeted insulin-like growth factor-I show increased bone remodeling

To determine the effects of locally-expressed insulin-like growth factor (IGF-I) on bone remodeling, a transgene was produced in which murine IGF-I cDNA was cloned downstream of a gene fragment comprising 3.6 kb of 5' upstream regulatory sequence and most of the first intron of the rat Col1a1 gene. The construct was expressed at the mRNA and protein level in transfected osteoblasts. Five lines of transgenic mice were generated by embryo microinjection. Transgene mRNA levels were highest in calvaria, long bone and tendon, and lower in skin. Serum IGF-I and body weight were increased in males and females only in the highest expressing line. Histomorphometry showed that transgenic calvaria were wider and had greater marrow area and bone area. Transgenic calvaria had increased osteoclast number per bone surface. Percent collagen synthesis and cell replication were increased in transgenic calvaria. Femur length, cortical width and cross-sectional area were increased in transgenic femurs of the highest expressing line, while femoral trabecular bone volume was little affected. Thus, broad overexpression of IGF-I in cells of the osteoblast lineage increased indices of bone formation and resorption.     

Renal function in Laron syndrome patients treated by insulin-like growth factor-I

Eight children with Laron syndrome (5 males, 3 females) aged 3–14.5 years received daily subcutaneous injections of 150 g/kg recombinant insulin-like growth factor-I (IGF-I) for 5 months. The children were examined weekly for the 1st month and then once monthly. At each visit, overnight fasting blood was drawn for serum IGF-I and blood chemistry measurements and a 24-h urine collection was performed for the determination of calcium, phosphorus, creatinine and nitrogen. The main effects related to kidney function were: an initial weight gain with a mild transitory reduction in the urinary volume, an increase in serum electrolyte concentrations and a decrease in urinary electrolyte excretion. The lower than normal mean (± SEM) basal creatinine clearance (76.7±15.8 ml/min per 1.73 m²) increased towards the normal range during treatment to 124.9±13 ml/min per 1.73 m², with a mean increment of 73.4±28% (P<0.02) from basal values after 2 months of treatment, without changes in the serum creatinine. Initially an increase in blood urea nitrogen was observed together with a reduction in urinary nitrogen excretion. During the IGF-I therapy the urinary calcium excretion increased from 0.7±0.2 nmol/day to 1.5±0.3 nmol/day and the tubular reabsorption of phosphate increased from 1.24±0.06 to more than 1.38±0.04 nmol/l (P<0.002), resulting in a significant increase in serum phosphate levels from 1.51±0.06 to more than 1.63±0.04 nmol/l (P<0.005). The present study shows for the first time that long-term IGF-I deficiency in man results in a subnormal glomerular filtration rate and that chronic substitution therapy with IGF-I has marked renotropic effects identical to those ascribed to growth hormone.     

Circulating insulin-like growth factor-I and benign prostatic hyperplasia--a prospective study.

OBJECTIVE: The aim of this study was to investigate the role of insulin-like growth factor-I (IGF-I), a strongly mitogenic and anti-apoptotic factor, in the development of benign prostatic hyperplasia (BPH). The bioactivity of IGF-I within tissues depends on circulating levels, as well as on the local production of IGF-I and the presence of IGF-binding proteins (IGFBPs). The IGFBPs regulate the efflux of IGF-I to the extravascular space and the bioavailability of IGF-I within tissues. MATERIAL AND METHODS: Within the Northern Sweden Health and Disease Study, 60 cases of BPH defined by a history of prostate resection were identified, and two controls per case were selected. IGF-I, IGFBP-1, IGFBP-3 and insulin were measured by immuno-radiometric assays in stored plasma samples drawn a mean of 3.2 years before surgery. RESULTS: The risk of BPH increased with increasing quartile levels of IGF-I adjusted for IGFBP-3 (p(trend) = 0.10) up to a relative risk of 2.16 (95% confidence interval 0.83-5.64) for the highest quartile. The risk decreased with increasing levels of IGFBP-1 (p(trend) = 0.10). CONCLUSIONS: Our results suggest that elevated IGF-I bioactivity may stimulate the development of BPH; however, they were not statistically significant and require confirmation from larger studies.     

The growth hormone/insulin-like growth factor-I system: implications for organ growth and development

Growth hormone (GH) and insulin-like growth factors (IGFs) are essential for normal growth and development during embryonic stages as well as postnatally. While GH has little effect on these processes prenatally, the IGFs are important during these stages. On the other hand the GH-IGF-I axis is important for pubertal growth. To determine whether postnatal growth and development are dependent on circulating or locally produced IGF-I, we deleted the IGF-I gene in the liver using the cre/LoxP system used for tissue-specific gene deletion. These animals demonstrated approximately 75%–80% reduction in circulating IGF-I and an approximate fourfold increase in circulating GH. Despite the marked reductions in circulating IGF-I, growth and development was apparently normal. Thus the original somatomedin hypothesis needs to be re-evaluated in the light of these new findings. Received: 5 September 1999 / Revised: 11 December 1999 / Accepted: 18 December 1999     

Seminal plasma cotinine and insulin-like growth factor-I in idiopathic oligoasthenoteratozoospermic smokers

OBJECTIVE

To assess seminal plasma insulin‐like growth factor‐I (IGF‐I) levels in cigarette smokers with idiopathic oligoasthenoteratozoospermia (iOAT).

PATIENTS AND METHODS

In all, 110 men were divided into fertile healthy non‐smokers, fertile smokers, infertile non‐smokers with iOAT and infertile smokers with iOAT. Semen was analysed, and seminal cotinine and seminal IGF‐I levels estimated.

RESULTS

There were significantly lower seminal IGF‐I levels in the smokers and in men with iOAT than in controls, and in both iOAT groups. Smokers, either fertile or with iOAT had significantly lower levels than in controls in mean semen volume, sperm production index, percentage of motile sperms, rapid linear forward progressive motility, linear velocity and sperm normal forms. Smokers with iOAT had significantly lower levels than non‐smokers with iOAT in mean sperm production index, rapid linear forward progressive motility and linear velocity. In smokers, seminal cotinine was significantly and negatively correlated with both seminal IGF‐I and sperm motility, while seminal IGF‐I was positively correlated with the percentage of motile spermatozoa.

CONCLUSION

Smoking effects on sperm variables could be mediated by decreased seminal IGF‐I.     

Molecular physiology, pathology, and regulation of the growth hormone/insulin-like growth factor-I system

Since the somatomedin hypothesis of growth hormone (GH) action was first formulated nearly 50 years ago, the key roles of both GH and insulin-like growth factor (IGF)-I in human growth have been confirmed and extended to include local effects on tissue maintenance and repair. More recent insights have revealed a dark side to the GH/IGF-I signaling system. Both proteins have been implicated as potential contributing factors in selected human cancers, and normal activity through this signaling pathway has been linked to diminished lifespan in experimental animals. This review highlights both the positive and negative aspects of the GH/IGF-I-growth pathway. The overall goal is to reinforce the need for more complete understanding of the mechanisms of signaling and action of GH and IGF-I, in order to separate, if possible, the potentially beneficial outcomes on growth and on tissue maintenance and repair from deleterious effects on cancer risk and lifespan.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany