Plasma insulin-like growth factor binding protein-3 proteolysis is increased in primary breast cancer

Insulin Receptor Isoforms and Insulin Growth Factor-like Receptors: Implications in Cell Signaling, Carcinogenesis, and Chemoresistance

This comprehensive review thoroughly explores the intricate involvement of insulin receptor (IR) isoforms and insulin-like growth factor receptors (IGFRs) in the context of the insulin and insulin-like growth factor (IGF) signaling (IIS) pathway. This elaborate system encompasses ligands, receptors, and binding proteins, giving rise to a wide array of functions, including aspects such as carcinogenesis and chemoresistance. Detailed genetic analysis of IR and IGFR structures highlights their distinct isoforms, which arise from alternative splicing and exhibit diverse affinities for ligands. Notably, the overexpression of the IR-A isoform is linked to cancer stemness, tumor development, and resistance to targeted therapies. Similarly, elevated IGFR expression accelerates tumor progression and fosters chemoresistance. The review underscores the intricate interplay between IRs and IGFRs, contributing to resistance against anti-IGFR drugs. Consequently, the dual targeting of both receptors could present a more effective strategy for surmounting chemoresistance. To conclude, this review brings to light the pivotal roles played by IRs and IGFRs in cellular signaling, carcinogenesis, and therapy resistance. By precisely modulating these receptors and their complex signaling pathways, the potential emerges for developing enhanced anti-cancer interventions, ultimately leading to improved patient outcomes.

IGF2 and cancer

Insulin-like growth factor 2 (IGF2) is a 7.5  kDa mitogenic peptide hormone expressed by liver and many other tissues. It is three times more abundant in serum than IGF1, but our understanding of its physiological and pathological roles has lagged behind that of IGF1. Expression of the IGF2 gene is strictly regulated. Over-expression occurs in many cancers and is associated with a poor prognosis. Elevated serum IGF2 is also associated with increased risk of developing various cancers including colorectal, breast, prostate and lung. There is established clinical utility for IGF2 measurement in the diagnosis of non-islet cell tumour hypoglycaemia, a condition characterised by a molar IGF2:IGF1 ratio >10. Recent advances in understanding of the pathophysiology of IGF2 in cancer have suggested much novel clinical utility for its measurement. Measurement of IGF2 in blood and genetic and epigenetic tests of the IGF2 gene may help assess cancer risk and prognosis. Further studies will determine whether these tests enter clinical practice. New therapeutic approaches are being developed to target IGF2 action. This review provides a clinical perspective on IGF2 and an update on recent research findings.

Serum levels of IGF-1 and IGFBP-3 during adjuvant chemotherapy for primary breast cancer

High serum concentrations of insulin-like growth factor-1 (IGF-1) are associated with an increased risk of breast, prostate, colorectal, and lung cancer whereas IGF binding protein-3 (IGFBP-3) seems to exert a protective effect. Therefore, patients may benefit from low IGF-1 levels and high IGFBP-3 levels. This study evaluated whether adjuvant anthracycline-containing chemotherapy modulates IGF-1 and/or IGFBP-3 serum levels in breast cancer patients. In 18 patients undergoing adjuvant treatment for primary breast cancer, IGF-1 and IGFBP-3 serum levels were measured with immunoassays during chemotherapy regimens of either 5-fluorouracil, epirubicin and cyclophosphamide (FEC) or epirubicin and cyclophosphamide (EC). Mean pre-treatment values of IGF-1 and IGFBP-3 were 124+/-13 and 3698+/-186 ng/ml, respectively. No significant changes in IGF-1 and IGFBP-3 serum concentrations were observed during adjuvant anthracycline-containing chemotherapy. IGF-1 levels significantly correlated with IGFBP-3 levels before and during chemotherapy. In conclusion, these chemotherapy regimens do not seem to modulate IGF-1 or IGFBP-3 levels in a favourable or unfavourable way.

Factors associated with circulating levels of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in 740 women at risk for breast cancer

Prospective studies have shown an association between elevated plasma levels of insulin-like growth factor-I (IGF-I) and/or decreased levels of its major circulating carrier protein insulin-like growth factor binding protein-3 (IGFBP-3) and increased risk of major cancers. Identifying the factors which affect these biomarkers is of particular interest as subjects at increased risk could benefit from lifestyle changes, and/or chemoprevention intervention. We evaluated the association between constitutional, hormonal and clinical factors and IGF-I and IGFBP-3 in 740 women, including 376 unaffected women and 364 women with intraepithelial neoplasia (IEN) or early invasive breast cancer enrolled in breast cancer chemoprevention trials, conducted at a single institution. Age, body mass index (BMI), height, waist to hip girth ratio (WHR), parity, menopausal status, age at menarche, number of affected first degree relatives, number of biopsies and breast cancer status were considered in the analysis. Women with early breast cancer had 21% higher IGF-I levels (p = 0.033) and 19% higher IGF-I/IGFBP-3 molar ratio (p = 0.047) than unaffected women. In unaffected women, age was negatively associated with IGF-I (p = 0.002) and IGF-I/IGFBP-3 (p = 0.001), while age at menarche was negatively associated with IGFBP-3 levels (p = 0.043). In women with IEN or early breast cancer, IGF-I levels were negatively associated with age (p < 0.001), and positively associated with prior biopsies for benign disease (p = 0.013), while age, parity and menopausal status were significant predictors of IGF-I/IGFBP-3 molar ratio. We conclude that circulating IGF-I levels are higher in women with prior breast cancer compared to unaffected women, and that IGF-I and/or IGFBP-3 levels are influenced by age and by reproductive and hormonal factors. These findings support their putative role as breast cancer risk biomarker.

Insulin-like growth factor (IGF)-I and IGF-II serum concentrations in patients with benign and malignant breast lesions: free IGF-II is correlated with breast cancer size

PURPOSE

Insulin-like growth factors (IGFs) are potent mitogens for breast cancer cells in vitro, and elevated IGF-I serum levels are a risk factor for breast malignancies. This study evaluated IGF-I and IGF-II serum levels in healthy women and in patients with benign and malignant breast lesions and correlated them with tumor size.

EXPERIMENTAL DESIGN

Serum levels of the total and unbound fractions of IGF-I and IGF-II were analyzed in 65 patients with benign and malignant breast lesions and in 38 women without breast disease. ELISAs were used to detect serum IGF levels, with (total IGF) or without (free IGF) prior acid-ethanol extraction.

RESULTS

Total IGF-I serum concentrations were lower in healthy women than in breast cancer patients (P < 0.001) or patients with benign breast lesions (P = 0.010), but no differences were observed in free IGF-I levels. Conversely, healthy women had higher serum levels of free IGF-II than women with breast lesions (P = 0.003), and the free/total IGF-II ratio was significantly reduced in patients with breast disease (P = 0.001). Although IGF-I or IGF-II serum concentrations of breast cancer patients were similar to those of patients with benign lesions, the size of a malignant tumor was correlated to the ratio free/total IGF-II (P = 0.002).

CONCLUSIONS

Malignant breast tumors cannot be distinguished from benign breast lesions by systemic IGF serum levels. However, women with breast lesions have decreased IGF-II concentrations, and free IGF-II levels are clearly correlated to the size of a breast cancer, indicating an involvement in tumor growth.

Insulin-Like Growth Factor-I, IGF Binding Protein-3, and Breast Cancer in Young Women: A Comparison of Risk Estimates Using Different Peptide Assays

Circulating insulin-like growth factor-I (IGF-I) and its major binding protein IGF binding protein-3 (IGFBP-3) have been associated with increased risk of premenopausal breast cancer, although risk estimates varied broadly. An extension of a case-control study (138 cases, 259 matched controls) on IGF-I and breast cancer in premenopausal women nested in the New York University Women's Health Study cohort offered the opportunity to address the hypothesis that such variability may have been the result of variations in the ability of different IGFBP-3 assays to specifically measure intact/functional forms of the protein. IGF-I and IGFBP-3 had originally been measured using in-house RIAs. These measurements were repeated using commercially available ELISAs [Diagnostic System Laboratories (DSL), Webster, Texas], and a third ELISA with greater specificity for active forms for IGFBP-3. Pearson's correlations between IGF-I concentrations in the original study and DSL ELISA were very high [r = 0.92; 95% CI, 0.90-0.94]. Correlations with DSL ELISA were much lower for IGFBP-3 (r = 0.58; 0.49-0.66) and even lower still with the assay for functional IGFBP-3 (r = 0.33; 0.20-0.44). IGF-I and IGFBP-3 measurements by the DSL ELISA methods showed statistically significant relationships with risk. The odds ratios (OR) for top versus bottom quartiles were 1.93 (1.00-3.72; P = 0.02) and 2.03 (1.09-3.76; P = 0.02), respectively, in agreement with the original observations. In contrast, measurements of functional IGFBP-3 tended to be unrelated to risk [ORs for the top versus bottom quartile, 0.97 (0.44-2.11)]. The association with IGF-I became substantially weaker and lost statistical significance after adjustment for IGFBP-3 using DSL ELISA, but became considerably stronger when adjusting for the functional IGFBP-3 measurements [OR = 2.43 (1.21-4.90); P = 0.005], or when considering the molar ratio of IGF-I to IGFBP-3 [OR = 2.37 (1.13-5.00); P = 0.02]. These results are consistent with an association of breast cancer risk in young women with elevated IGF-I and IGFBP-3, and show that for IGFBP-3, the strength of such an association could vary substantially depending on the assay used.

Serum Insulin-Like Growth Factors, Insulin-Like Growth Factor Binding Proteins, and Breast Cancer Risk in Postmenopausal Women

Background: Studies have shown a positive association between serum insulin-like growth factor (IGF)-I and breast cancer risk in premenopausal but not postmenopausal women. IGF-II and estrogen receptor (ER) status has never been investigated. We examined the association between IGF-I, IGF-II, IGF binding protein (IGFBP)-2, IGFBP-3, and IGFBP-3 protease activity and breast cancer risk in postmenopausal women, taking ER status of the breast cancer into consideration.

Methods: We conducted this case-cohort study within a Danish follow-up study based on 24,697 postmenopausal women. We identified 411 cases with breast cancer and a matched control group including 397 cohort members. We estimated breast cancer risk using Cox regression analysis with adjustment for known breast cancer risk factors.

Results: We observed no association for IGF-I but a positive association between levels of IGFBP-3 and breast cancer risk. Per 500 units higher levels of IGFBP-3, an incidence rate ratio [IRR; 95% confidence interval (95% CI)] of 1.14 (1.00-1.30) was estimated. For ER-positive breast cancer, the IRR (95% CI) was 1.18 (1.05-1.33). IGFBP-3 protease activity was not associated with breast cancer risk. Per 275 units higher levels of IGF-II, an IRR (95% CI) of 1.35 (1.10-1.66) was observed for ER-positive tumors, whereas IGFBP-2 was not associated with breast cancer risk. Adjustment for potential confounders did not change the risk estimate. There was no association between IGF-I, IGF-II, IGFBP-2, or IGFBP-3 and risk of ER-negative breast cancer.

Conclusion: Serum IGFBP-3 and IGF-II levels were positively associated with ER-positive breast cancer risk. This may suggest an important relationship among IGFs, IGFBPs, the ER system, and breast cancer development in postmenopausal women.

The insulin-like growth factor system in advanced breast cancer

Despite improvements in therapy, the prognosis for advanced breast cancer is poor and a search for new treatment targets and key regulators of tumour growth is warranted. Extensive data are available on the importance of the insulin-like growth factor (IGF) system in growth regulation of breast cancer cell lines in vitro, indicating that the IGF-I receptor (IGF-IR), IGF-I (and IGF-II) function as survival factors, while IGF binding protein (IGFBP)-3 may act as a growth inhibitor. There is a tight link between the growth regulatory pathways of IGFs and oestrogens in oestrogen-receptor(OR)-positive breast cancer cells. In vivo studies indicate a role of IGF-I and IGF-IR in breast cancer development. However, the importance of the IGF system in metastatic and highly aggressive breast tumours in vivo is not clear, and therapeutic strategies designed to interrupt IGF signalling have not yet proved to be an effective treatment modality in patients with metastatic breast cancer.

Mechanisms by which IGF-I may promote cancer

Multiple large case-control studies in the past five years have reported positive associations between high circulating levels of the insulin-like growth factor (IGF)-I and risk for different types of cancer. Correlations certainly do not prove causation, but the reproducibility of this finding implies this is a hypothesis worth further examination through more mechanistic studies. IGF-I binds to the IGF-I receptor, a tyrosine kinase receptor that transduces signals to the nucleus and mitochondrion primarily via the mitogen-activated protein kinase (MAPK) and PI3K/Akt pathways. Examples will be provided to illustrate how IGF-I signaling may contribute to each stage of cancer progression: malignant transformation, tumor growth, local invasion and distant metastases, and resistance to treatment. In addition to direct contributions to each of these stages, IGF-I may promote cancer indirectly, through interactions with oncogenes and tumor suppressors, interactions with other hormones (especially the sex steroids in breast and prostate cancers) and interactions with the IGF binding proteins (IGFBPs). Finally, circulating IGF-I may facilitate cancer development though it likely does not cause cancer to form. Prompted by the accumulating evidence, investigations are also being pursued to modulate the IGF system as a possible means of cancer prevention or treatment.

Insulin-like growth factor binding protein proteolysis

High-affinity interactions between insulin-like growth factors (IGF-I and IGF-II) and insulin-like growth factor-binding proteins (IGFBP-1, -2, -3, -4, -5 and -6) antagonize the binding of IGF to the type 1 IGF receptor. Proteases found in a variety of biological fluids can degrade IGFBP 1-6 into fragments that have a greatly reduced affinity for IGF-I and IGF-II, increasing the concentration of free IGFs at the cell surface and allowing IGFs to bind to and activate the IGF receptor. Therefore, IGFBP proteolysis directly modulates the first step in IGF receptor signaling and thereby indirectly modulates cell survival, mitogenesis and differentiation. Our understanding of IGFBP proteolysis has grown exponentially over the past five years, with the identification of several new IGFBP proteases, a growing appreciation of the potential for IGF-independent actions of IGFBP fragments and the realization that perturbations of IGFBP proteolysis are seen in, and might contribute to, several pathological conditions.

Serum insulinlike growth factor is not elevated in patients with multiple myeloma but is still a prognostic factor

Insulinlike growth factor 1 (IGF-1) has growth-promoting effects on myeloma cells in vitro as well as in vivo. In this study, we measured the concentration of IGF-1 and its major binding protein, IGF- binding protein 3 (IGFBP-3), in serum from 127 patients with multiple myeloma. Serum had been drawn at the time of diagnosis, before treatment with high-dose melphalan. IGFBP-3 in myeloma patients (1.6 +/- 0.73 microg/mL; mean +/- SD) was significantly decreased compared to healthy age- and sex-matched controls (2.2 +/- 0.42 microg/mL). However, IGFBP-3 had no prognostic value in this study. The mean IGF-1 level did not differ between myeloma patients (17.8 +/- 7.7 nM) and controls (17.3 +/- 5.6 nM). Nevertheless, IGF-1 was a strong indicator of prognosis. After 80 months of follow-up, myeloma patients with low levels (< 13 nM) of serum IGF-1 had not reached median survival. In the patient group with IGF-1 levels above 13 nM, median survival was 62 months (P =.006). These findings support the hypothesis of a role for IGF-1 in myeloma disease progression.

Effect of intense exercise on inflammatory cytokines and growth mediators in adolescent boys

OBJECTIVE

Exercise can enhance growth and development in children, but recent investigations have revealed an intriguing paradox. Namely, the early (4-5 weeks) response to training programs in children lead to a catabolic, growth hormone (GH)-resistant state rather than the expected anabolic activation of the GH-->insulin-like growth factor-I (IGF-I) axis. This paradox led us to hypothesize that single bouts of exercise in children could stimulate proinflammatory cytokines known to inhibit directly anabolic activity of the GH-->IGF-1 axis (interleukin [IL]-6, IL-1beta, and tumor necrosis factor-alpha [TNF-alpha]).

METHODS

Eleven healthy high school-age boys, age 14 to 18.5 years, performed a single, typical, 1.5-hour wrestling practice session. Blood was sampled before and after the session.

RESULTS

We found significant decreases in anabolic mediators: total IGF-I (-11.2 +/- 2.3%), bound IGF-I (-11.2 +/- 2.4%), and insulin (-42 +/- 10%. However, there was no change in unbound IGF-I. Remarkable increases were found in proinflammatory cytokines IL-6 (795 +/- 156%), TNF-alpha (30 +/- 12%), and IL-1beta (286 +/- 129%) and in IGF-binding protein-1 (835 +/- 234%), which itself is stimulated by inflammatory cytokines and is known to inhibit IGF-I. Evidence for compensatory mechanisms to counter the antianabolic inflammatory response to acute exercise were also noted: IL-1ra increased (80 +/- 20%) and IGF-binding protein-3 proteolysis (which can maintain unbound, biologically active IGF-I despite losses in total IGF-I) increased significantly (101 +/- 39%) as well.

CONCLUSIONS

These data demonstrate that an intense exercise bout in male adolescents leads to reductions in anabolic mediators and profound increases in inflammatory cytokines. This might explain the development of what seems to be a paradoxical catabolic state in the initial phases of exercise training programs.

Update on anorexia and cachexia

Declining physical, emotional, and social function as a result of anorexia and cachexia are considerable contributors to discomfort for cancer patients and their families, and they impair the patient's ability to express optimal physical and psychosocial potential as long as possible. This decline no longer has to be accepted as an indispensable sequel to advanced cancer, just as pain is no longer considered to be unavoidable. A routine screening for anorexia and cachexia and associated symptoms is necessary, as is a careful, comprehensive assessment, because the condition is not always obvious. Decisions about anorexia and cachexia treatment are guided by prioritizing the different, concurrent physical, psychosocial, and existential problems and by considering the natural course of the cancer and the effects of antineoplastic therapies. Reversible causes for anorexia and cachexia need to be identified and treated, if appropriate. Nutritional interventions are often indicated; patients with a predominant starvation component and without inflammation may profit the most. New pharmacologic therapies for primary anorexia and cachexia syndrome are expected to enter clinical practice soon; however, until then, treatment with corticosteroids, progestins, or prokinetics may be indicated for some patients. To understand a multicausal syndrome, multimodal and interdisciplinary therapy is required. Specialist palliative care services can be helpful to provide, hand-in-hand with the disease specialists [172], assessment and management of psychophysical symptoms and sociospiritual needs of patients during the course of the illness and at the end of life [173]. Research efforts aim to better characterize subgroups of patients suffering from secondary causes of anorexia and cachexia and to elucidate the mechanisms involved in the primary anorexia and cachexia syndrome. Increasingly individualized treatments are expected with combination treatments that involve different mechanisms including nutrition.