Phase I dose-escalation study of MEDI-573, a bispecific, antiligand monoclonal antibody against IGFI and IGFII, in patients with advanced solid tumors

Non-genetic heterogeneity and immune subtyping in breast cancer: Implications for immunotherapy and targeted therapeutics

Breast cancer (BC) is a complex and multifactorial disease, driven by genetic alterations that promote tumor growth and progression. However, recent research has highlighted the importance of non-genetic factors in shaping cancer evolution and influencing therapeutic outcomes. Non-genetic heterogeneity refers to diverse subpopulations of cancer cells within breast tumors, exhibiting distinct phenotypic and functional properties. These subpopulations can arise through various mechanisms, including clonal evolution, genetic changes, epigenetic changes, and reversible phenotypic transitions. Although genetic and epigenetic changes are important points of the pathology of breast cancer yet, the immune system also plays a crucial role in its progression. In clinical management, histologic and molecular classification of BC are used. Immunological subtyping of BC has gained attention in recent years as compared to traditional techniques. Intratumoral heterogeneity revealed by immunological microenvironment (IME) has opened novel opportunities for immunotherapy research. This systematic review is focused on non-genetic variability to identify and interlink immunological subgroups in breast cancer. This review provides a deep understanding of adaptive methods adopted by tumor cells to withstand changes in the tumor microenvironment and selective pressure imposed by medications. These adaptive methods include alterations in drug targets, immune system evasion, activation of survival pathways, and alterations in metabolism. Understanding non-genetic heterogeneity is essential for the development of targeted therapies.

Decoding the Role of Insulin-like Growth Factor 1 and Its Isoforms in Breast Cancer

Insulin-like Growth Factor-1 (IGF-1) is a crucial mitogenic factor with important functions in the mammary gland, mainly through its interaction with the IGF-1 receptor (IGF-1R). This interaction activates a complex signaling network that promotes cell proliferation, epithelial to mesenchymal transition (EMT) and inhibits apoptosis. Despite extensive research, the precise molecular pathways and intracellular mechanisms activated by IGF-1, in cancer, remain poorly understood. Recent evidence highlights the essential roles of IGF-1 and its isoforms in breast cancer (BC) development, progression, and metastasis. The peptides that define the IGF-1 isoforms-IGF-1Ea, IGF-1Eb, and IGF-1Ec-act as key points of convergence for various signaling pathways that influence the growth, metastasis and survival of BC cells. The aim of this review is to provide a detailed exami-nation of the role of the mature IGF-1 and its isoforms in BC biology and their potential use as possible therapeutical targets.

Nephrotoxicity in Bispecific Antibodies Recipients: Focus on T-Cell-Engaging Bispecific Antibodies

Recently, bispecific antibodies (BsAbs) are evolving the landscape of cancer treatment and have significantly improved the outcomes of relapsed or refractory cancer patients. As increasing BsAbs entered clinical practice, specific toxicities have emerged, and renal side-effects have been described. However, there are a lack of studies analyzing the nephrotoxicity in the anti-cancer BsAbs recipients systematically. In this review, we demonstrate the etiologies, mechanisms, other risk factors and treatment options of kidney injury in the BsAbs recipients to provide a more comprehensive insight into the nephrotoxicity post-BsAbs therapy. Significantly, due to the limited clinical trial data on each subject, we mainly conclude the related etiologies, mechanisms, and risk factors of nephrotoxicity that occur in T-cell-engaging BsAbs recipients. Nephrotoxicity associated with non-T-cell BsAbs may be associated with adverse nephrotoxicity of related monoclonal antibodies to two specific antigens. The aim of this paper is to provide nephrologists and oncologists with theoretical knowledge to provide better medical management for recipients who receive BsAbs, especially T-cell-engaging BsAbs treatment.

Extracellular Interactors of the IGF System: Impact on Cancer Hallmarks and Therapeutic Approaches

Dysregulation of the insulin-like growth factor (IGF) system determines the onset of various pathological conditions, including cancer. Accordingly, therapeutic strategies have been developed to block this system in tumor cells, but the results of clinical trials have been disappointing. After decades of research in the field, it is safe to say that one of the major reasons underlying the poor efficacy of anti-IGF-targeting agents is derived from an underestimation of the molecular complexity of this axis. Genetic, transcriptional, post-transcriptional and functional interactors interfere with the activity of canonical components of this axis, supporting the need for combinatorial approaches to effectively block this system. In addition, cancer cells interface with a multiplicity of factors from the extracellular compartment, which strongly affect cell destiny. In this review, we will cover novel extracellular mechanisms contributing to IGF system dysregulation and the implications of such dangerous liaisons for cancer hallmarks and responses to known and new anti-IGF drugs. A deeper understanding of both the intracellular and extracellular microenvironments might provide new impetus to better decipher the complexity of the IGF axis in cancer and provide new clues for designing novel therapeutic approaches.

Role of Insulin-like Growth Factor-1 Receptor in Tobacco Smoking-Associated Lung Cancer Development

Cancer remains a significant global health concern, with lung cancer consistently leading as one of the most common malignancies. Genetic aberrations involving receptor tyrosine kinases (RTKs) are known to be associated with cancer initiation and development, but RTK involvement in smoking-associated lung cancer cases is not well understood. The Insulin-like Growth Factor 1 Receptor (IGF-1R) is a receptor that plays a critical role in lung cancer development. Its signaling pathway affects the growth and survival of cancer cells, and high expression is linked to poor prognosis and resistance to treatment. Several reports have shown that by activating IGF-1R, tobacco smoke-related carcinogens promote lung cancer and chemotherapy resistance. However, the relationship between IGF-1R and cancer is complex and can vary depending on the type of cancer. Ongoing investigations are focused on developing therapeutic strategies to target IGF-1R and overcome chemotherapy resistance. Overall, this review explores the intricate connections between tobacco smoke-specific carcinogens and the IGF-1R pathway in lung carcinogenesis. This review further highlights the challenges in using IGF-1R inhibitors as targeted therapy for lung cancer due to structural similarities with insulin receptors. Overcoming these obstacles may require a comprehensive approach combining IGF-1R inhibition with other selective agents for successful cancer treatment.

Insulin receptor alternative splicing in breast and prostate cancer

Cancer etiology represents an intricate, multifactorial orchestration where metabolically associated insulin-like growth factors (IGFs) and insulin foster cellular proliferation and growth throughout tumorigenesis. The insulin receptor (IR) exhibits two splice variants arising from alternative mRNA processing, namely IR-A, and IR-B, with remarkable distribution and biological effects disparities. This insightful review elucidates the structural intricacies, widespread distribution, and functional significance of IR-A and IR-B. Additionally, it explores the regulatory mechanisms governing alternative splicing processes, intricate signal transduction pathways, and the intricate association linking IR-A and IR-B splicing variants to breast and prostate cancer tumorigenesis. Breast cancer and prostate cancer are the most common malignant tumors with the highest incidence rates among women and men, respectively. These findings provide a promising theoretical framework for advancing preventive strategies, diagnostic modalities, and therapeutic interventions targeting breast and prostate cancer.

Emerging Role of IGF-1 in Prostate Cancer: A Promising Biomarker and Therapeutic Target

Prostate cancer (PCa) is a highly heterogeneous disease driven by gene alterations and microenvironmental influences. Not only enhanced serum IGF-1 but also the activation of IGF-1R and its downstream signaling components has been increasingly recognized to have a vital driving role in the development of PCa. A better understanding of IGF-1/IGF-1R activity and regulation has therefore emerged as an important subject of PCa research. IGF-1/IGF-1R signaling affects diverse biological processes in cancer cells, including promoting survival and renewal, inducing migration and spread, and promoting resistance to radiation and castration. Consequently, inhibitory reagents targeting IGF-1/IGF-1R have been developed to limit cancer development. Multiple agents targeting IGF-1/IGF-1R signaling have shown effects against tumor growth in tumor xenograft models, but further verification of their effectiveness in PCa patients in clinical trials is still needed. Combining androgen deprivation therapy or cytotoxic chemotherapeutics with IGF-1R antagonists based on reliable predictive biomarkers and developing and applying novel agents may provide more desirable outcomes. This review will summarize the contribution of IGF-1 signaling to the development of PCa and highlight the relevance of this signaling axis in potential strategies for cancer therapy.

The Insulin-like Growth Factor Signaling Pathway in Breast Cancer: An Elusive Therapeutic Target

In this review, we provide an overview of the role of the insulin-like growth factor (IGF) signaling pathway in breast cancer and discuss its potential as a therapeutic target. The IGF pathway ligands, IGF-1 and IGF-2, and their receptors, primarily IGF-1R, are important for normal mammary gland biology, and dysregulation of their expression and function drives breast cancer risk and progression through activation of downstream signaling effectors, often in a subtype-dependent manner. The IGF signaling pathway has also been implicated in resistance to current therapeutic strategies, including ER and HER2 targeting drugs. Unfortunately, efforts to target IGF signaling for the treatment of breast cancer have been unsuccessful, due to a number of factors, most significantly the adverse effects of disrupting IGF signaling on normal glucose metabolism. We highlight here the recent discoveries that provide enthusiasm for continuing efforts to target IGF signaling for the treatment of breast cancer patients.

Dual Inhibition of EGFR and IGF-1R Signaling Leads to Enhanced Antitumor Efficacy against Esophageal Squamous Cancer

Both the epidermal growth factor receptor (EGFR) and insulin-like growth factor 1 receptor (IGF-1R) have been implicated in the development of cancers, and the increased expression of both receptors has been observed in esophageal cancer. However, the tyrosine kinase inhibitors of both receptors have thus far failed to provide clinical benefits for esophageal cancer patients. Studies have confirmed the complicated crosstalks that exist between the EGFR and IGF-1R pathways. The EGFR and IGF-1R signals act as mutual compensation pathways, thereby conveying resistance to EGFR or IGF-1R inhibitors when used alone. This study evaluated the antitumor efficacy of the EGFR/HER2 inhibitors, gefitinib and lapatinib, in combination with the IGF-1R inhibitor, linsitinib, on the esophageal squamous cell carcinoma (ESCC). Gefitinib or lapatinib, in combination with linsitinib, synergistically inhibited the proliferation, migration, and invasion of ESCC cells, caused significant cell cycle arrest, and induced marked cell apoptosis. Their combination demonstrated stronger inhibition on the activation of EGFR, HER2, and IGF-1R as well as the downstream signaling molecules. In vivo, the addition of linsitinib to gefitinib or lapatinib also potentiated the inhibition effects on the growth of xenografts. Our results suggest the next clinical exploration of the combination of gefitinib or lapatinib with linsitinib in the treatment of ESCC patients.

Targeting the IGF/PI3K/mTOR Pathway and AXL/YAP1/TAZ pathways in Primary Bone Cancer

Primary bone cancers (PBC) belong to the family of mesenchymal tumors classified based on their cellular origin, extracellular matrix, genetic regulation, and epigenetic modification. The three major PBC types, Ewing sarcoma, osteosarcoma, and chondrosarcoma, are frequently aggressive tumors, highly metastatic, and typically occur in children and young adults. Despite their distinct origins and pathogenesis, these sarcoma subtypes rely upon common signaling pathways to promote tumor progression, metastasis, and survival. The IGF/PI3K/mTOR and AXL/YAP/TAZ pathways, in particular, have gained significant attention recently given their ties to oncogenesis, cell fate and differentiation, metastasis, and drug resistance. Naturally, these pathways – and their protein constituents – have caught the eye of the pharmaceutical industry, and a wide array of small molecule inhibitors and antibody drug-conjugates have emerged. Here, we review how the IGF/PI3K/mTOR and AXL/YAP/TAZ pathways promote PBC and highlight the drug candidates under clinical trial investigation.

Targeting the IGF-1R in prostate and colorectal cancer: reasons behind trial failure and future directions

IGF-1Rs enact a significant part in cancer growth and its progress. IGF-1R inhibitors were encouraged in the early trials, but the patients did not benefit due to the unavailability of predictive biomarkers and IGF-1R system complexity. However, the linkage between IGF-1R and cancer was reported three decades ago. This review will shed light on the IGF-1R system, targeting IGF-1R through monoclonal antibodies, reasons behind IGF-1R trial failure and future directions. This study presented that targeting IGF-1R through monoclonal antibodies is still effective in cancer treatment, and there is a need to look for future directions. Cancer patients may benefit from using mAbs that target existing and new cancer targets, evidenced by promising results. It is also essential that the academician, trial experts and pharmaceutical companies play their role in finding a treatment for this deadly disease.

A phase 1 trial of xentuzumab, an IGF-neutralizing antibody, in Japanese patients with advanced solid tumors

Xentuzumab is an insulin‐like growth factor (IGF) ligand‐neutralizing antibody. This phase 1 trial assessed xentuzumab in Japanese patients with solid tumors. Patients aged ≥20 y old with solid tumors that were refractory or not amenable to standard therapy were enrolled. Patients received xentuzumab intravenously at a starting dose of 750 mg/wk. Dose escalation used a 3 + 3 design with dose de‐escalation. The primary endpoint was to determine the maximum tolerated dose (MTD) of xentuzumab. Safety, pharmacokinetics, pharmacodynamics, and anti‐tumor activity were also assessed. Fifteen patients received xentuzumab in the dose escalation part (750 mg/wk [n = 6]; 1000 mg/wk [n = 3]; 1400 mg/wk [n = 6]). There were no dose‐limiting toxicities at any dose; the MTD of xentuzumab was not reached. Xentuzumab 1000 mg/wk was recommended as the relevant biological dose. Six further patients received xentuzumab 1000 mg/wk in an expansion cohort. Of 21 patients, 13 (61.9%) experienced a drug‐related adverse event, most commonly fatigue (23.8%), neutropenia (19.0%), diarrhea, nausea, white blood cell count decrease, and muscle spasms (14.3% each). No relevant deviations from dose linearity of xentuzumab exposure were observed during dose escalation. Total IGF‐1 and IGF‐2 levels increased and bioactive IGF levels decreased from baseline to 24 h after the first infusion in cycle 1. Partial response was observed in 2 (9.5%) patients with desmoid‐type fibromatosis. Disease control was achieved in 6 (28.6%) patients (median duration 42.4 mo). Xentuzumab monotherapy was well tolerated in Japanese patients and showed evidence of anti‐tumor activity. This study was registered with www.clinicaltrials.gov (NCT02145741).

Molecular targets and therapeutics in chemoresistance of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a specific subtype of breast cancer (BC), which shows immunohistochemically negative expression of hormone receptor i.e., Estrogen receptor and Progesterone receptor along with the absence of Human Epidermal Growth Factor Receptor-2 (HER2/neu). In Indian scenario the prevalence of BC is 26.3%, whereas, in West Bengal the cases are of 18.4%. But the rate of TNBC has increased up to 31% and shows 27% of total BC. Conventional chemotherapy is effective only in the initial stages but with progression of the disease the effectivity gets reduced and shown almost no effect in later or advanced stages of TNBC. Thus, TNBC patients frequently develop resistance and metastasis, due to its peculiar triple-negative nature most of the hormonal therapies also fails. Development of chemoresistance may involve various factors, such as, TNBC heterogeneity, cancer stem cells (CSCs), signaling pathway deregulation, DNA repair mechanism, hypoxia, and other molecular factors. To overcome the challenges to treat TNBC various targets and molecules have been exploited including CSCs modulator, drug efflux transporters, hypoxic factors, apoptotic proteins, and regulatory signaling pathways. Moreover, to improve the targets and efficacy of treatments researchers are emphasizing on targeted therapy for TNBC. In this review, an effort has been made to focus on phenotypic and molecular variations in TNBC along with the role of conventional as well as newly identified pathways and strategies to overcome challenge of chemoresistance.

Targeting obesity-related dysfunction in hormonally driven cancers

Obesity is a risk factor for at least 13 different types of cancer, many of which are hormonally driven, and is associated with increased cancer incidence and morbidity. Adult obesity rates are steadily increasing and a subsequent increase in cancer burden is anticipated. Obesity-related dysfunction can contribute to cancer pathogenesis and treatment resistance through various mechanisms, including those mediated by insulin, leptin, adipokine, and aromatase signalling pathways, particularly in women. Furthermore, adiposity-related changes can influence tumour vascularity and inflammation in the tumour microenvironment, which can support tumour development and growth. Trials investigating non-pharmacological approaches to target the mechanisms driving obesity-mediated cancer pathogenesis are emerging and are necessary to better appreciate the interplay between malignancy, adiposity, diet and exercise. Diet, exercise and bariatric surgery are potential strategies to reverse the cancer-promoting effects of obesity; trials of these interventions should be conducted in a scientifically rigorous manner with dose escalation and appropriate selection of tumour phenotypes and have cancer-related clinical and mechanistic endpoints. We are only beginning to understand the mechanisms by which obesity effects cell signalling and systemic factors that contribute to oncogenesis. As the rates of obesity and cancer increase, we must promote the development of non-pharmacological lifestyle trials for the treatment and prevention of malignancy.

Unraveling the IGF System Interactome in Sarcomas Exploits Novel Therapeutic Options

Aberrant bioactivity of the insulin-like growth factor (IGF) system results in the development and progression of several pathologic conditions including cancer. Preclinical studies have shown promising anti-cancer therapeutic potentials for anti-IGF targeted therapies. However, a clear but limited clinical benefit was observed only in a minority of patients with sarcomas. The molecular complexity of the IGF system, which comprises multiple regulators and interactions with other cancer-related pathways, poses a major limitation in the use of anti-IGF agents and supports the need of combinatorial therapeutic strategies to better tackle this axis. In this review, we will initially highlight multiple mechanisms underlying IGF dysregulation in cancer and then focus on the impact of the IGF system and its complexity in sarcoma development and progression as well as response to anti-IGF therapies. We will also discuss the role of Ephrin receptors, Hippo pathway, BET proteins and CXCR4 signaling, as mediators of sarcoma malignancy and relevant interactors with the IGF system in tumor cells. A deeper understanding of these molecular interactions might provide the rationale for novel and more effective therapeutic combinations to treat sarcomas.

Randomized Phase II Trial of Capecitabine and Lapatinib with or without IMC-A12 (Cituxumumab) in Patients with HER2-Positive Advanced Breast Cancer Previously Treated with Trastuzumab and Chemotherapy: NCCTG N0733 (Alliance)

PURPOSE

To compare efficacy and safety of capecitabine and lapatinib with or without IMC-A12 (cituxumumab) in patients with HER2-positive metastatic breast cancer (MBC) previously treated with trastuzumab.

PATIENTS AND METHODS

Following an initial safety run-in cohort, patients were randomized 1:2 to Arm A (capecitabine and lapatinib) or to Arm B (capecitabine, lapatinib, and cituxumumab). Given the frequency of non-hematologic grade ≥ 3 adverse events in those receiving the three-drug combination in the safety cohort, lapatinib and capecitabine doses were reduced in Arm B only. The primary objective was to determine if the addition of cituxumumab to capecitabine and lapatinib improved progression-free survival (PFS) compared with capecitabine and lapatinib. Secondary objectives included a comparison between arms of other clinical endpoints, safety, change in overall quality of life (QOL) and self-assessed fatigue, rash, diarrhea, and hand-foot syndrome.

RESULTS

From July 2008 to March 2012, 68 patients (out of 142 planned) were enrolled and 63 were evaluable, including 8 for the safety run-in and 55 for the randomized cohort. Study enrollment was stopped early due to slow accrual. The addition of cituxumumab to capecitabine and lapatinib did not improve PFS (HR 0.93, 95% CI: 0.52-1.64). Furthermore, no difference in objective response rate or overall survival (OS) was observed. No difference between arms was observed in grade ≥ 3 adverse events, overall QOL change from baseline after 4 cycles of treatment.

CONCLUSION

The addition of cituxumumab to lapatinib and capecitabine did not improve PFS or OS compared with lapatinib and capecitabine in patients with HER2-positive MBC.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov Identifier: NCT00684983.

Disrupting Insulin and IGF Receptor Function in Cancer

The insulin and insulin-like growth factor (IGF) system plays an important role in regulating normal cell proliferation and survival. However, the IGF system is also implicated in many malignancies, including breast cancer. Preclinical studies indicate several IGF blocking approaches, such as monoclonal antibodies and tyrosine kinase inhibitors, have promising therapeutic potential for treating diseases. Uniformly, phase III clinical trials have not shown the benefit of blocking IGF signaling compared to standard of care arms. Clinical and laboratory data argue that targeting Type I IGF receptor (IGF1R) alone may be insufficient to disrupt this pathway as the insulin receptor (IR) may also be a relevant cancer target. Here, we review the well-studied role of the IGF system in regulating malignancies, the limitations on the current strategies of blocking the IGF system in cancer, and the potential future directions for targeting the IGF system.

Unraveling the Resistance of IGF-Pathway Inhibition in Ewing Sarcoma

Simple Summary

The insulin-like growth factor-1 receptor (IGF1R) is a receptor commonly overexpressed and overactivated in a variety of cancers, including Ewing sarcoma, and promotes cell growth and survival. After promising results with targeting and inhibiting the receptor in vitro, multiple different IGF1R targeting compounds have been clinically tried but showed limited efficacy. Here we discuss several possible resistance mechanisms which could explain why IGF1R targeting fails in the clinic and discuss possible ways to overcome these resistances.

Abstract

Insulin-like growth factor-1 receptor (IGF1R) inhibitors are effective in preclinical studies, but so far, no convincing benefit in clinical studies has been observed, except in some rare cases of sustained response in Ewing sarcoma patients. The mechanism of resistance is unknown, but several hypotheses are proposed. In this review, multiple possible mechanisms of resistance to IGF-targeted therapies are discussed, including activated insulin signaling, pituitary-driven feedback loops through growth hormone (GH) secretion and autocrine loops. Additionally, the outcomes of clinical trials of IGF1-targeted therapies are discussed, as well as strategies to overcome the possible resistance mechanisms. In conclusion, lowering the plasma insulin levels or blocking its activity could provide an additional target in cancer therapy in combination with IGF1 inhibition. Furthermore, because Ewing sarcoma cells predominantly express the insulin receptor A (IRA) and healthy tissue insulin receptor B (IRB), it may be possible to synthesize a specific IRA inhibitor.

Metabolism and immunity in breast cancer

Breast cancer is one of the most common malignancies that seriously threaten women's health. In the process of the malignant transformation of breast cancer, metabolic reprogramming and immune evasion represent the two main fascinating characteristics of cancer and facilitate cancer cell proliferation. Breast cancer cells generate energy through increased glucose metabolism. Lipid metabolism contributes to biological signal pathways and forms cell membranes except energy generation. Amino acids act as basic protein units and metabolic regulators in supporting cell growth. For tumor-associated immunity, poor immunogenicity and heightened immunosuppression cause breast cancer cells to evade the host's immune system. For the past few years, the complex mechanisms of metabolic reprogramming and immune evasion are deeply investigated, and the genes involved in these processes are used as clinical therapeutic targets for breast cancer. Here, we review the recent findings related to abnormal metabolism and immune characteristics, regulatory mechanisms, their links, and relevant therapeutic strategies.

Blockade of IGF/IGF-1R signaling axis with soluble IGF-1R mutants suppresses the cell proliferation and tumor growth of human osteosarcoma

Primary bone tumor, also known as osteosarcoma (OS), is the most common primary malignancy of bone in children and young adults. Current treatment protocols yield a 5-year survival rate of near 70% although approximately 80% of patients have metastatic disease at the time of diagnosis. However, long-term survival rates have remained virtually unchanged for nearly four decades, largely due to our limited understanding of the disease process. One major signaling pathway that has been implicated in human OS tumorigenesis is the insulin-like growth factor (IGF)/insulin-like growth factor-1 receptor (IGF1R) signaling axis. IGF1R is a heterotetrameric α2β2 receptor, in which the α subunits comprise the ligand binding site, whereas the β subunits are transmembrane proteins containing intracellular tyrosine kinase domains. Although numerous strategies have been devised to target IGF/IGF1R axis, most of them have failed in clinical trials due to the lack of specificity and/or limited efficacy. Here, we investigated whether a more effective and specific blockade of IGF1R activity in human OS cells can be accomplished by employing dominant-negative IGF1R (dnIGF1R) mutants. We engineered the recombinant adenoviruses expressing two IGF1R mutants derived from the α (aa 1-524) and β (aa 741-936) subunits, and found that either dnIGF1Rα and/or dnIGF1Rβ effectively inhibited cell migration, colony formation, and cell cycle progression of human OS cells, which could be reversed by exogenous IGF1. Furthermore, dnIGF1Rα and/or dnIGF1Rβ inhibited OS xenograft tumor growth in vivo, with the greatest inhibition of tumor growth shown by dnIGF1Rα. Mechanistically, the dnIGF1R mutants down-regulated the expression of PI3K/AKT and RAS/RAF/MAPK, BCL2, Cyclin D1 and most EMT regulators, while up-regulating pro-apoptotic genes in human OS cells. Collectively, these findings strongly suggest that the dnIGF1R mutants, especially dnIGF1Rα, may be further developed as novel anticancer agents that target IGF signaling axis with high specificity and efficacy.

IGF-1R/mTOR Targeted Therapy for Ewing Sarcoma: A Meta-Analysis of Five IGF-1R-Related Trials Matched to Proteomic and Radiologic Predictive Biomarkers

Background : Ten to fourteen percent of Ewing sarcoma (ES) study participants treated nationwide with IGF-1 receptor (IGF-1R)-targeted antibodies achieved tumor regression. Despite this success, low response rates and short response durations (approximately 7-weeks) have slowed the development of this therapy. Methods: We performed a meta-analysis of five phase-1b/2 ES-oriented trials that evaluated the anticancer activity of IGF-1R antibodies +/− mTOR inhibitors (mTORi). Our meta-analysis provided a head-to-head comparison of the clinical benefits of IGF-1R antibodies vs. the IGF-1R/mTOR-targeted combination. Available pretreatment clinical samples were semi-quantitatively scored using immunohistochemistry to detect proteins in the IGF-1R/PI3K/AKT/mTOR pathway linked to clinical response. Early PET/CT imaging, obtained within the first 2 weeks (median 10 days), were examined to determine if reduced FDG avidity was predictive of progression-free survival (PFS). Results: Among 56 ES patients treated at MD Anderson Cancer Center (MDACC) with IGF-1R antibodies, our analysis revealed a significant ~two-fold improvement in PFS that favored a combination of IGF-1R/mTORi therapy (1.6 vs. 3.3-months, p = 0.042). Low pIGF-1R in the pretreatment specimens was associated with treatment response. Reduced total-lesion glycolysis more accurately predicted the IGF-1R response than other previously reported radiological biomarkers. Conclusion: Synergistic drug combinations, and newly identified proteomic or radiological biomarkers of IGF-1R response, may be incorporated into future IGF-1R-related trials to improve the response rate in ES patients.

Insulin-like growth factor receptor signaling in tumorigenesis and drug resistance: a challenge for cancer therapy

Insulin-like growth factors (IGFs) play important roles in mammalian growth, development, aging, and diseases. Aberrant IGFs signaling may lead to malignant transformation and tumor progression, thus providing the rationale for targeting IGF axis in cancer. However, clinical trials of the type I IGF receptor (IGF-IR)-targeted agents have been largely disappointing. Accumulating evidence demonstrates that the IGF axis not only promotes tumorigenesis, but also confers resistance to standard treatments. Furthermore, there are diverse pathways leading to the resistance to IGF-IR-targeted therapy. Recent studies characterizing the complex IGFs signaling in cancer have raised hope to refine the strategies for targeting the IGF axis. This review highlights the biological activities of IGF-IR signaling in cancer and the contribution of IGF-IR to cytotoxic, endocrine, and molecular targeted therapies resistance. Moreover, we update the diverse mechanisms underlying resistance to IGF-IR-targeted agents and discuss the strategies for future development of the IGF axis-targeted agents.

Two first-in-human studies of xentuzumab, a humanised insulin-like growth factor (IGF)-neutralising antibody, in patients with advanced solid tumours

BACKGROUND

Xentuzumab, an insulin-like growth factor (IGF)-1/IGF-2-neutralising antibody, binds IGF-1 and IGF-2, inhibiting their growth-promoting signalling. Two first-in-human trials assessed the maximum-tolerated/relevant biological dose (MTD/RBD), safety, pharmacokinetics, pharmacodynamics, and activity of xentuzumab in advanced/metastatic solid cancers.

METHODS

These phase 1, open-label trials comprised dose-finding (part I; 3 + 3 design) and expansion cohorts (part II; selected tumours; RBD [weekly dosing]). Primary endpoints were MTD/RBD.

RESULTS

Study 1280.1 involved 61 patients (part I: xentuzumab 10-1800 mg weekly, n = 48; part II: 1000 mg weekly, n = 13); study 1280.2, 64 patients (part I: 10-3600 mg three-weekly, n = 33; part II: 1000 mg weekly, n = 31). One dose-limiting toxicity occurred; the MTD was not reached for either schedule. Adverse events were generally grade 1/2, mostly gastrointestinal. Xentuzumab showed dose-proportional pharmacokinetics. Total plasma IGF-1 increased dose dependently, plateauing at ~1000 mg/week; at ≥450 mg/week, IGF bioactivity was almost undetectable. Two partial responses occurred (poorly differentiated nasopharyngeal carcinoma and peripheral primitive neuroectodermal tumour). Integration of biomarker and response data by Bayesian Logistic Regression Modeling (BLRM) confirmed the RBD.

CONCLUSIONS

Xentuzumab was well tolerated; MTD was not reached. RBD was 1000 mg weekly, confirmed by BLRM. Xentuzumab showed preliminary anti-tumour activity.

CLINICAL TRIAL REGISTRATION

NCT01403974; NCT01317420.

Investigational IGF1R inhibitors in early stage clinical trials for cancer therapy

Introduction: The insulin-like growth factors (IGFs) are a family of secreted peptide hormones with important roles in different cellular and organism functions. The biological activities of the IGFs are mediated by the IGF1 receptor (IGF1R), a cell surface, tyrosine kinase-containing heterotetramer that is linked to numerous cytoplasmic signaling cascades. The IGF1R displays potent antiapoptotic, pro-survival capacities and plays a key role in malignant transformation. Research has identified the IGF1R as a candidate therapeutic target in cancer.Areas covered: We offer a synopsis of ongoing efforts to target the IGF axis for therapeutic purposes. Our review includes a digest of early experimental work that led to the identification of IGF1R as a candidate therapeutic target in oncology.Expert opinion: Targeting of the IGF axis has yielded disappointing results in phase III trials, but it is important to learn from this to improve future trials in a rational manner. The potential of anti-IGF1R antibodies and small molecular weight inhibitors, alone or in combination with chemotherapy or other biological agents, should be investigated further in randomized studies. Moreover, the implementation of predictive biomarkers for patient selection will improve the outcome of future trials. Emerging personalized medicine could have a major impact on IGF1R targeting.

Overcoming platinum resistance in ovarian cancer by targeting pregnancy-associated plasma protein-A

OBJECTIVES

Inhibition of pregnancy-associated plasma protein-A (PAPP-A), an upstream activator of the insulin-like growth factor (IGF) pathway, is known to augment sensitivity to platinum-based chemotherapy. This study further tests the efficacy of PAPP-A inhibition with a monoclonal antibody inhibitor (mAb-PA) in ovarian cancer (OC) platinum-resistant patient-derived xenograft (PDX) models.

METHODS

PAPP-A expression was quantitated in platinum-resistant PDX models by ELISA. A subset with High (n = 5) and Low (n = 2) expression were revived in female SCID/beige mice for studies with either saline, carboplatin/paclitaxel (CP) + mAb-PA, or CP + IgG2a. The primary endpoint was tumor area by ultrasound on day 28 relative to baseline. Conversion to platinum-sensitive was defined by average tumor regression below baseline. Statistical analyses included linear mixed effects modeling and Kaplan Meier curves. Response to therapy was correlated with changes in the ratio of phosphorylated/total AKT and ERK 1/2 using Wes analysis.

RESULTS

The addition of mAb-PA to CP induced tumor regression below baseline in one High PAPP-A PDX model; another three models exhibited notable growth inhibition relative to CP + IgG2a. None of the Low PAPP-A PDX models regressed below baseline. The PDX model with the greatest magnitude of tumor regression from baseline after combination therapy was maintained on single agent mAb-PA or IgG2a, but no benefit was observed. Decreased phosphorylation of ERK1/2 correlated with conversion to platinum-sensitive.

CONCLUSIONS

The addition of mAb-PA to CP overcame platinum-resistance in one of five High PAPP-A PDX models; three other models demonstrated improved platinum-response. This supports further clinical development of this novel therapeutic.

Therapeutic Targeting of the IGF Axis

The insulin like growth factor (IGF) axis plays a fundamental role in normal growth and development, and when deregulated makes an important contribution to disease. Here, we review the functions mediated by ligand-induced IGF axis activation, and discuss the evidence for the involvement of IGF signaling in the pathogenesis of cancer, endocrine disorders including acromegaly, diabetes and thyroid eye disease, skin diseases such as acne and psoriasis, and the frailty that accompanies aging. We discuss the use of IGF axis inhibitors, focusing on the different approaches that have been taken to develop effective and tolerable ways to block this important signaling pathway. We outline the advantages and disadvantages of each approach, and discuss progress in evaluating these agents, including factors that contributed to the failure of many of these novel therapeutics in early phase cancer trials. Finally, we summarize grounds for cautious optimism for ongoing and future studies of IGF blockade in cancer and non-malignant disorders including thyroid eye disease and aging.

Insulin/IGF signaling and discoidin domain receptors: An emerging functional connection

The insulin/insulin-like growth factor system (IIGFs) plays a fundamental role in the regulation of prenatal and postnatal growth, metabolism and homeostasis. As a consequence, dysregulation of this axis is associated with growth disturbance, type 2 diabetes, chronic inflammation and tumor progression. A functional crosstalk between IIGFs and discoidin domain receptors (DDRs) has been recently discovered. DDRs are non-integrin collagen receptors that canonically undergo slow and long-lasting autophosphorylation after binding to fibrillar collagen. While both DDR1 and DDR2 functionally interact with IIGFs, the crosstalk with DDR1 is so far better characterized. Notably, the IIGFs-DDR1 crosstalk presents a feed-forward mechanism, which does not require collagen binding, thus identifying novel non-canonical action of DDR1. Further studies are needed to fully explore the role of this IIGFs-DDRs functional loop as potential target in the treatment of inflammatory and neoplastic disorders.

Bad to the Bone: The Role of the Insulin-Like Growth Factor Axis in Osseous Metastasis

Bone metastases are a frequent complication of cancer that are associated with considerable morbidity. Current treatments may temporarily palliate the symptoms of bone metastases but often fail to delay their progression. Bones provide a permissive environment because they are characterized by dynamic turnover, secreting factors required for bone maintenance but also stimulating the establishment and growth of metastases. Insulin-like growth factors (IGF) are the most abundant growth factors in bone and are required for normal skeletal development and function. Via activation of the IGF-1 receptors (IGF-1R) and variant insulin receptors, IGFs promote cancer progression, aggressiveness, and treatment resistance. Of specific relevance to bone biology, IGFs contribute to the homing, dormancy, colonization, and expansion of bone metastases. Furthermore, preclinical evidence suggests that tumor cells can be primed to metastasize to bone by a high IGF-1 environment in the primary tumor, suggesting that bone metastases may reflect IGF dependency. Therapeutic targeting of the IGF axis may therefore provide an effective method for treating bone metastases. Indeed, anti-IGF-1R antibodies, IGF-1R tyrosine kinase inhibitors, and anti-IGF-1/2 antibodies have demonstrated antitumor activity in preclinical models of prostate and breast cancer metastases, either alone or in combination with other agents. Several studies suggest that such treatments can inhibit bone metastases without affecting growth of the primary tumor. Although previous trials of anti-IGF-1R drugs have generated negative results in unselected patients, these considerations suggest that future clinical trials of IGF-targeted agents may be warranted in patients with bone metastases.

Protein Tyrosine Signaling and its Potential Therapeutic Implications in Carcinogenesis

Protein tyrosine phosphorylation is a crucial signaling mechanism that plays a role in epithelial carcinogenesis. Protein tyrosine kinases (PTKs) control various cellular processes including growth, differentiation, metabolism, and motility by activating major signaling pathways including STAT3, AKT, and MAPK. Genetic mutation of PTKs and/or prolonged activation of PTKs and their downstream pathways can lead to the development of epithelial cancer. Therefore, PTKs became an attractive target for cancer prevention. PTK inhibitors are continuously being developed, and they are currently used for the treatment of cancers that show a high expression of PTKs. Protein tyrosine phosphatases (PTPs), the homeostatic counterpart of PTKs, negatively regulate the rate and duration of phosphotyrosine signaling. PTPs initially were considered to be only housekeeping enzymes with low specificity. However, recent studies have demonstrated that PTPs can function as either tumor suppressors or tumor promoters, depending on their target substrates. Together, both PTK and PTP signal transduction pathways are potential therapeutic targets for cancer prevention and treatment.

IGF system in sarcomas: a crucial pathway with many unknowns to exploit for therapy

The insulin-like growth factor (IGF) system has gained substantial interest due to its involvement in regulating cell proliferation, differentiation and survival during anoikis and after conventional and targeted therapies. However, results from clinical trials have been largely disappointing, with only a few but notable exceptions, such as trials targeting sarcomas, especially Ewing sarcoma. This review highlights key studies focusing on IGF signaling in sarcomas, specifically studies underscoring the properties that make this system an attractive therapeutic target and identifies new relationships that may be exploited. This review discusses the potential roles of IGF2 mRNA-binding proteins (IGF2BPs), discoidin domain receptors (DDRs) and metalloproteinase pregnancy-associated plasma protein-A (PAPP-A) in regulating the IGF system. Deeper investigation of these novel regulators of the IGF system may help us to further elucidate the spatial and temporal control of the IGF axis, as understanding the control of this axis is essential for future clinical studies.

A dual-specific IGF-I/II human engineered antibody domain inhibits IGF signaling in breast cancer cells

The insulin-like growth factors (IGFs), IGF-I and IGF-II, are essential for regulating cell growth, differentiation and metastasis of a broad range of malignancies. The IGF-I/II actions are mediated through the IGF receptor type 1 (IGF-1R) and the insulin receptor (IR), which are overexpressed in multiple types of tumors. Here, we have firstly identified a human engineered antibody domain (eAd) from a phage-displayed VH library. The eAd suppressed the signal transduction of IGF-1R mediated by exogenous IGF-I or IGF-II in breast cancer cell lines through neutralizing both IGF-I and IGF-II. It also significantly inhibited the growth of breast cancer cells. Therefore, the anti-IGF-I/II eAd offers an alternative approach to target both the IGF-1R signaling pathways through the inhibition of IGF-I/II.

Aiming for the Insulin-like Growth Factor-1 system in breast cancer therapeutics

Despite the major discoveries occurred in oncology the recent years, breast malignancies remain one of the most common causes of cancer-related deaths for women in developed countries. Development of HER2-targeting drugs has been considered a breakthrough in anti-cancer approaches and alluded to the potential of targeting growth factors in breast cancer (BrCa) therapeutics. More than twenty-five years have passed since the Insulin-like Growth Factor-1 (IGF-1) system was initially recognized as a potential target candidate in BrCa therapy. To date, a growing body of studies have implicated the IGF-1 signaling with the BrCa biology. Despite the promising experimental evidence, the impression from clinical trials is rather disappointing. Several reasons may account for this and the last word regarding the efficacy of this system as a target candidate in BrCa therapeutics is probably not written yet. Herein, we provide the theoretical basis, as well as, a comprehensive overview of the current literature, regarding the different strategies targeting the various components of the IGF-1/IGF-1R axis in several pathophysiological aspects of BrCa, including the tumor micro-environment and cancer stemness. In addition, we review the rationale for targeting the IGF-1 system in the different BrCa molecular subtypes and in treatment resistant breast tumors with a focus on both the molecular mechanisms and on the clinical perspectives of such approaches in specific population subgroups. We also discuss the future challenges, as well as, the development of novel molecules and strategies targeting the system and suggest potential improvements in the field.

Insulin Receptor Isoforms in Physiology and Disease: An Updated View

The insulin receptor (IR) gene undergoes differential splicing that generates two IR isoforms, IR-A and IR-B. The physiological roles of IR isoforms are incompletely understood and appear to be determined by their different binding affinities for insulin-like growth factors (IGFs), particularly for IGF-2. Predominant roles of IR-A in prenatal growth and development and of IR-B in metabolic regulation are well established. However, emerging evidence indicates that the differential expression of IR isoforms may also help explain the diversification of insulin and IGF signaling and actions in various organs and tissues by involving not only different ligand-binding affinities but also different membrane partitioning and trafficking and possibly different abilities to interact with a variety of molecular partners. Of note, dysregulation of the IR-A/IR-B ratio is associated with insulin resistance, aging, and increased proliferative activity of normal and neoplastic tissues and appears to sustain detrimental effects. This review discusses novel information that has generated remarkable progress in our understanding of the physiology of IR isoforms and their role in disease. We also focus on novel IR ligands and modulators that should now be considered as an important strategy for better and safer treatment of diabetes and cancer and possibly other IR-related diseases.

Insulin-Like Growth Factor (IGF) Pathway Targeting in Cancer: Role of the IGF Axis and Opportunities for Future Combination Studies

Despite a strong preclinical rationale for targeting the insulin-like growth factor (IGF) axis in cancer, clinical studies of IGF-1 receptor (IGF-1R)-targeted monotherapies have been largely disappointing, and any potential success has been limited by the lack of validated predictive biomarkers for patient enrichment. A large body of preclinical evidence suggests that the key role of the IGF axis in cancer is in driving treatment resistance, via general proliferative/survival mechanisms, interactions with other mitogenic signaling networks, and class-specific mechanisms such as DNA damage repair. Consequently, combining IGF-targeted agents with standard cytotoxic agents, other targeted agents, endocrine therapies, or immunotherapies represents an attractive therapeutic approach. Anti-IGF-1R monoclonal antibodies (mAbs) do not inhibit IGF ligand 2 (IGF-2) activation of the insulin receptor isoform-A (INSR-A), which may limit their anti-proliferative activity. In addition, due to their lack of specificity, IGF-1R tyrosine kinase inhibitors are associated with hyperglycemia as a result of interference with signaling through the classical metabolic INSR-B isoform; this may preclude their use at clinically effective doses. Conversely, IGF-1/IGF-2 ligand-neutralizing mAbs inhibit proliferative/anti-apoptotic signaling via IGF-1R and INSR-A, without compromising the metabolic function of INSR-B. Therefore, combination regimens that include these agents may be more efficacious and tolerable versus IGF-1R-targeted combinations. Herein, we review the preclinical and clinical experience with IGF-targeted therapies to-date, and discuss the rationale for future combination approaches as a means to overcome treatment resistance.

Revisiting the IGF-1R as a breast cancer target

The type I insulin-like growth factor-1 receptor is a well-described target in breast cancer and multiple clinical trials examining insulin-like growth factor-1 receptor have been completed. Unfortunately, monoclonal antibodies and tyrosine kinase inhibitors targeting insulin-like growth factor-1 receptor failed in phase III breast clinical trials for several reasons. First, insulin-like growth factor-1 receptor antibody therapy resulted in hyperglycemia and metabolic syndrome most likely due to disruption of insulin-like growth factor-1 homeostasis and subsequent growth hormone elevation. Growth hormone elevation induces insulin resistance, hence a subsequent elevation of insulin and the potential for activation of insulin receptor. Second, the insulin-like growth factor-1 receptor and insulin receptor are highly homologous in amino acid sequence, structure, and function. These two receptors bind insulin, insulin-like growth factor-1 and insulin-like growth factor-2, to regulate glucose uptake and other cellular functions. Hybrid receptors composed of one chain of insulin-like growth factor-1 receptor and insulin receptor also participate in signaling. Third, since all the monoclonal antibodies were specific for insulin-like growth factor-1 receptor, any pathophysiologic role for insulin receptor was not inhibited. While the insulin-like growth factor-1 receptor tyrosine kinase inhibitors effectively inhibited both insulin-like growth factor-1 receptor and insulin receptor, these drugs are not being further developed likely due to their metabolic toxicities. Insulin-like growth factor-1/2 neutralizing antibodies are still being studied in early phase clinical trials. Perhaps a more comprehensive strategy of targeting the insulin-like growth factor-1 receptor network would be successful. For example, targeting receptor, ligand and downstream signaling molecules such as phosphatidylinositol 3′-kinase or particularly the insulin receptor substrate adapter proteins might result in a complete blockade of insulin-like growth factor-1 receptor/insulin receptor biological functions.

Cotargeting of CYP-19 (aromatase) and emerging, pivotal signalling pathways in metastatic breast cancer

Aromatase inhibition is one of the cornerstones of modern endocrine therapy of oestrogen receptor-positive (ER+) metastatic breast cancer (MBC). The nonsteroidal aromatase inhibitors anastrozole and letrozole, as well as the steroidal aromatase inactivator exemestane, are the preferred drugs and established worldwide in all clinical phases of the disease. However, although many patients suffering from MBC experience an initial stabilisation of their metastatic burden, drug resistance and disease progression occur frequently, following in general only a few months on treatment. Extensive translational research during the past two decades has elucidated the major pathways contributing to endocrine resistance and paved the way for clinical studies investigating the efficacy of novel drug combinations involving aromatase inhibitors and emerging drugable targets like mTOR, PI3K and CDK4/6. The present review summarises the basic research that provided the rationale for new drug combinations involving aromatase inhibitors and the main findings of pivotal clinical trials that have already started to change our way to treat hormone-sensitive MBC. The challenging situation of oestrogen receptor-positive and human epidermal growth factor receptor 2-positive (HER2+) MBC is also shortly reviewed to underline the complexity of the clinical scenario in the heterogeneous subgroups of hormone receptor-positive breast cancer patients and the increasing need for personalised medicine. Finally, we summarise some of the promising findings made with the combination of aromatase inhibitors with other potent endocrine treatment options like fulvestrant, a selective oestrogen receptor downregulator.

Combination therapy approaches to target insulin-like growth factor receptor signaling in breast cancer

Insulin-like growth factor receptor (IGF1R) signaling as a therapeutic target has been widely studied and clinically tested. Despite the vast amount of literature supporting the biological role of IGF1R in breast cancer, effective clinical translation in targeting its activity as a cancer therapy has not been successful. The intrinsic complexity of cancer cell signaling mediated by many tyrosine kinase growth factor receptors that work together to modulate each other and intracellular downstream mediators in the cell highlights that studying IGF1R expression and activity as a prognostic factor and therapeutic target in isolation is certainly associated with problems. This review discusses the current literature and clinical trials associated with IGF-1 signaling and attempts to look at new ways of designing novel IGF1R-directed breast cancer therapy approaches to target its activity 
and/or intracellular downstream signaling pathways in IGF1R-expressing breast cancers.

Insulin-like growth factor axis targeting in cancer and tumour angiogenesis - the missing link

Numerous molecular players in the process of tumour angiogenesis have been shown to offer potential for therapeutic targeting. Initially denoted to be involved in malignant transformation and tumour progression, the insulin-like growth factor (IGF) signalling axis has been subject to therapeutic interference, albeit with limited clinical success. More recently, IGFs and their receptors have received attention for their contribution to tumour angiogenesis, which offers novel therapeutic opportunities. Here we review the contribution of this signalling axis to tumour angiogenesis, the mechanisms of resistance to therapy and the interplay with other pro-angiogenic pathways, to offer insight in the renewed interest in the application of IGF axis targeting agents in anti-cancer combination therapies.

Clinical studies in humans targeting the various components of the IGF system show lack of efficacy in the treatment of cancer

The insulin-like growth factors (IGFs) system regulates cell growth, differentiation and energy metabolism and plays crucial role in the regulation of key aspects of tumor biology, such as cancer cell growth, survival, transformation and invasion. The current focus for cancer therapeutic approaches have shifted from the conventional treatments towards the targeted therapies and the IGF system has gained a great interest as anti-cancer therapy. The proliferative, anti-apoptotic and transformation effects of IGFs are mainly triggered by the ligation of the type I IGF receptor (IGF-IR). Thus, aiming at developing novel and effective cancer therapies, different strategies have been employed to target IGF system in human malignancies, including but not limited to ligand or receptor neutralizing antibodies and IGF-IR signaling inhibitors. In this review, we have focused on the clinical studies that have been conducted targeting the various components of the IGF system for the treatment of different types of cancer, providing a description and the challenges of each targeting strategy and the degree of success.

Molecular Pathways: Clinical Applications and Future Direction of Insulin-like Growth Factor-1 Receptor Pathway Blockade

The IGF1R signaling pathway is a complex and tightly regulated network that is critical for cell proliferation, growth, and survival. IGF1R is a potential therapeutic target for patients with many different malignancies. This brief review summarizes the results of clinical trials targeting the IGF1R pathway in patients with breast cancer, sarcoma, and non-small cell lung cancer (NSCLC). Therapeutic agents discussed include both monoclonal antibodies to IGF1R (dalotuzumab, figitumumab, cixutumumab, ganitumab, R1507, AVE1642) and newer IGF1R pathway targeting strategies, including monoclonal antibodies to IGF1 and IGF2 (MEDI-573 and BI 836845) and a small-molecule tyrosine kinase inhibitor of IGF1R (linsitinib). The pullback of trials in patients with breast cancer and NSCLC based on several large negative trials is noted and contrasted with the sustained success of IGF1R inhibitor monotherapy in a subset of patients with sarcoma. Several different biomarkers have been examined in these trials with varying levels of success, including tumor expression of IGF1R and its pathway components, serum IGF ligand levels, alternate pathway activation, and specific molecular signatures of IGF1R pathway dependence. However, there remains a critical need to define predictive biomarkers in order to identify patients who may benefit from IGF1R-directed therapies. Ongoing research focuses on uncovering such biomarkers and elucidating mechanisms of resistance, as this therapeutic target is currently being analyzed from the bedside to bench.

Overproduction of IGF-2 drives a subset of colorectal cancer cells, which specifically respond to an anti-IGF therapeutic antibody and combination therapies

Colorectal cancer (CRC) is a heterogeneous disease with a broad spectrum of genetic and epigenetic changes. A comprehensive molecular characterization of CRC by The Cancer Genome Atlas Network detected the overexpression of the insulin-like growth factor 2 (IGF2) gene, encoding a ligand for the insulin-like growth factor 1 receptor (IGF-1R), in a subset of CRC tumors. In this study, we investigated the oncogenic potential of IGF-2 in IGF2-overexpressing CRC models and the efficacy of MEDI-573, an IGF-1/2-neutralizing antibody. We found that a subset of CRC cell lines express high IGF-2 levels owing to an increased DNA copy number and hypermethylation in the H19 promoter of the IGF2 gene. MEDI-573 efficiently neutralized IGF-2 and induced apoptosis, which resulted in significant tumor growth inhibition in CRC mouse models that express high levels of IGF-2. These effects were specific to CRCs overexpressing IGF-2, as MEDI-573 did not affect the growth CRC cell lines with normal levels. Moreover, blockade of IGF-2 by MEDI-573 modulated other signaling pathways, suggesting combination therapies with inhibitors of these pathways. Indeed, in vivo efficacy was significantly enhanced when MEDI-573 was used in combination with trastuzumab, AZD2014 (dual mTORC1/2i), AZD5363 (AKTi) and selumetinib (AZD6244/ARRY-142886, MEK1/2i) or cetuximab. These results demonstrate that overexpressed IGF-2 is the major tumorigenic driver in a subset of CRCs and encourage testing of MEDI-573, alone and in combinations, in IGF2-overexpressing CRC patients.

Functional evolution of IGF2:IGF2R domain 11 binding generates novel structural interactions and a specific IGF2 antagonist

Among the 15 extracellular domains of the mannose 6-phosphate/insulin-like growth factor-2 receptor (M6P/IGF2R), domain 11 has evolved a binding site for IGF2 to negatively regulate ligand bioavailability and mammalian growth. Despite the highly evolved structural loops of the IGF2:domain 11 binding site, affinity-enhancing AB loop mutations suggest that binding is modifiable. Here we examine the extent to which IGF2:domain 11 affinity, and its specificity over IGF1, can be enhanced, and we examine the structural basis of the mechanistic and functional consequences. Domain 11 binding loop mutants were selected by yeast surface display combined with high-resolution structure-based predictions, and validated by surface plasmon resonance. We discovered previously unidentified mutations in the ligand-interacting surface binding loops (AB, CD, FG, and HI). Five combined mutations increased rigidity of the AB loop, as confirmed by NMR. When added to three independently identified CD and FG loop mutations that reduced the koff value by twofold, these mutations resulted in an overall selective 100-fold improvement in affinity. The structural basis of the evolved affinity was improved shape complementarity established by interloop (AB-CD) and intraloop (FG-FG) side chain interactions. The high affinity of the combinatorial domain 11 Fc fusion proteins functioned as ligand-soluble antagonists or traps that depleted pathological IGF2 isoforms from serum and abrogated IGF2-dependent signaling in vivo. An evolved and reengineered high-specificity M6P/IGF2R domain 11 binding site for IGF2 may improve therapeutic targeting of the frequent IGF2 gain of function observed in human cancer.

Mechanisms of action of therapeutic antibodies for cancer

The therapeutic utility of antibodies and their derivatives is achieved by various means. The FDA has approved several targeted antibodies that disrupt signaling of various growth factor receptors for the treatment of a number of cancers. Rituximab, and other anti-CD20 monoclonal antibodies are active in B cell malignancies. As more experience has been gained with anti-CD20 monoclonal antibodies, the multifactorial nature of their anti-tumor mechanisms has emerged. Other targeted antibodies function to dampen inhibitory checkpoints. These checkpoint inhibitors have recently achieved dramatic results in several cancers, including melanoma. These and related antibodies continue to be investigated in the clinical and pre-clinical settings. Novel antibody structures that target two or more antigens have also made their way into clinical use. Tumor targeted antibodies can also be conjugated to chemo- or radiotherapeutic agents, or catalytic toxins, as a means to deliver toxic payloads to cancer cells. Here we provide a review of these mechanisms and a discussion of their relevance to current and future clinical applications.

Intrinsic Resistance to Cixutumumab Is Conferred by Distinct Isoforms of the Insulin Receptor

Despite a recent shift away from anti-insulin-like growth factor I receptor (IGF-IR) therapy, this target has been identified as a key player in the resistance mechanisms to various conventional and targeted agents, emphasizing its value as a therapy, provided that it is used in the right patient population. Molecular markers predictive of antitumor activity of IGF-IR inhibitors remain largely unidentified. The aim of this study is to evaluate the impact of insulin receptor (IR) isoforms on the antitumor efficacy of cixutumumab, a humanized mAb against IGF-IR, and to correlate their expression with therapeutic outcome. The data demonstrate that expression of total IR rather than individual IR isoforms inversely correlates with single-agent cixutumumab efficacy in pediatric solid tumor models in vivo. Total IR, IR-A, and IR-B expression adversely affects the outcome of cixutumumab in combination with chemotherapy in patient-derived xenograft models of lung adenocarcinoma. IR-A overexpression in tumor cells confers complete resistance to cixutumumab in vitro and in vivo, whereas IR-B results in a partial resistance. Resistance in IR-B-overexpressing cells is fully reversed by anti-IGF-II antibodies, suggesting that IGF-II is a driver of cixutumumab resistance in this setting. The present study links IR isoforms, IGF-II, and cixutumumab efficacy mechanistically and identifies total IR as a biomarker predictive of intrinsic resistance to anti-IGF-IR antibody.

IMPLICATIONS

This study identifies total IR as a biomarker predictive of primary resistance to IGF-IR antibodies and provides a rationale for new clinical trials enriched for patients whose tumors display low IR expression.

Bone Sarcomas in Pediatrics: Progress in Our Understanding of Tumor Biology and Implications for Therapy

The pediatric bone sarcomas osteosarcoma and Ewing sarcoma represent a tremendous challenge for the clinician. Though less common than acute lymphoblastic leukemia or brain tumors, these aggressive cancers account for a disproportionate amount of the cancer morbidity and mortality in children, and have seen few advances in survival in the past decade, despite many large, complicated, and expensive trials of various chemotherapy combinations. To improve the outcomes of children with bone sarcomas, a better understanding of the biology of these cancers is needed, together with informed use of targeted therapies that exploit the unique biology of each disease. Here we summarize the current state of knowledge regarding the contribution of receptor tyrosine kinases, intracellular signaling pathways, bone biology and physiology, the immune system, and the tumor microenvironment in promoting and maintaining the malignant phenotype. These observations are coupled with a review of the therapies that target each of these mechanisms, focusing on recent or ongoing clinical trials if such information is available. It is our hope that, by better understanding the biology of osteosarcoma and Ewing sarcoma, rational combination therapies can be designed and systematically tested, leading to improved outcomes for a group of children who desperately need them.

Understanding the Key to Targeting the IGF Axis in Cancer: A Biomarker Assessment

Type 1 insulin like growth factor receptor (IGF-1R) targeted therapies showed compelling pre-clinical evidence; however, to date, this has failed to translate into patient benefit in Phase 2/3 trials in unselected patients. This was further complicated by the toxicity, including hyperglycemia, which largely results from the overlap between IGF and insulin signaling systems and associated feedback mechanisms. This has halted the clinical development of inhibitors targeting IGF signaling, which has limited the availability of biopsy samples for correlative studies to understand biomarkers of response. Indeed, a major factor contributing to lack of clinical benefit of IGF targeting agents has been difficulty in identifying patients with tumors driven by IGF signaling due to the lack of predictive biomarkers. In this review, we will describe the IGF system, rationale for targeting IGF signaling, the potential liabilities of targeting strategies, and potential biomarkers that may improve success.

The Role of the Insulin/IGF System in Cancer: Lessons Learned from Clinical Trials and the Energy Balance-Cancer Link

Numerous epidemiological and pre-clinical studies have demonstrated that the insulin/insulin-like growth factor (IGF) system plays a key role in the development and progression of several types of cancer. Insulin/IGF signaling, in cooperation with chronic low-grade inflammation, is also an important contributor to the cancer-promoting effects of obesity. However, clinical trials for drugs targeting different components of this system have produced largely disappointing results, possibly due to the lack of predictive biomarker use and problems with the design of combination therapy regimens. With careful attention to the identification of likely patient responders and optimal drug combinations, the outcome of future trials may be improved. Given that insulin/IGF signaling is known to contribute to obesity-associated cancer, further investigation regarding the efficacy of drugs targeting this system and its downstream effectors in the obese patient population is warranted.

Insulin/Insulin-like growth factors in cancer: new roles for the aryl hydrocarbon receptor, tumor resistance mechanisms, and new blocking strategies

The insulin-like growth factor 1 receptor (IGF1R) and the insulin receptor (IR) are receptor tyrosine kinases that are expressed in cancer cells. The results of different studies indicate that tumor proliferation and survival is dependent on the IGF1R and IR, and that their inhibition leads to reductions in proliferation and increases in cell death. Molecular targeting therapies that have been used in solid tumors include anti-IGF1R antibodies, anti-IGF1/IGF2 antibodies, and small molecule inhibitors that suppress IGF1R and IR kinase activity. New advances in the molecular basis of anti-IGF1R blocking antibodies reveal they are biased agonists and promote the binding of IGF1 to integrin β3 receptors in some cancer cells. Our recent reports indicate that pharmacological aryl hydrocarbon receptor (AHR) ligands inhibit breast cancer cell responses to IGFs, suggesting that targeting AHR may have benefit in cancers whose proliferation and survival are dependent on insulin/IGF signaling. Novel aspects of IGF1R/IR in cancer, such as biased agonism, integrin β3 signaling, AHR, and new therapeutic targeting strategies will be discussed.