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.

Effects of an anti-IGF-1 receptor monoclonal antibody on laminitis induced by prolonged hyperinsulinaemia in Standardbred horses

Currently, there are no registered veterinary drugs for the treatment of endocrinopathic equine laminitis, and although this form of the disease is known to be caused by prolonged hyperinsulinaemia, the mechanism of insulin toxicity is unclear. One possibility is that high concentrations of insulin activate IGF-1 receptors (IGF-1R) in lamellar tissue, leading to uncontrolled cell proliferation and epidermal lamellar dysregulation. An equinized version of a human anti-IGF-1R therapeutic monoclonal antibody (mAb11) was generated to test this theory, using a modification of the prolonged euglycaemic-hyperinsulinaemic clamp technique. Healthy Standardbred horses were infused for 48 h with 0.9% saline (negative-control, n = 6), a combination of insulin (4.5 mIU/kgBW/min) and a variable infusion of 50% glucose to maintain euglycaemia (positive-control, n = 6), or insulin and glucose, preceded by a low dose of mAb11 (20 mg), designed to treat one foot only and delivered by retrograde infusion into one forelimb (mAb-treated, n = 7). Maximum insulin concentrations were 502 ± 54.4 and 435 ± 30.4 μIU/mL in the positive-control and mAb11-treated groups, respectively (P = 0.33). While the control group remained healthy, all the insulin-treated horses developed laminitis within 30 h, as judged by clinical examination, foot radiographs and histological analysis. Some effects of insulin were not attenuated by the antibody, however, relative to the positive-control group, horses treated with mAb11 showed less sinking of the distal phalanx (P < 0.05) and milder histological changes, with markedly less elongation at the tips of the secondary epidermal lamellae (P < 0.05). These differences were apparent in both front feet and were statistically significant when the values for both feet were combined. The results confirm that IGF-1R may have a role in insulin-induced laminitis and suggest that mAb11 warrants further research as a potential agent to prevent or treat the disease.

Evaluating Changes in Immune Function and Bone Microenvironment During Radium-223 Treatment of Patients with Castration-Resistant Prostate Cancer

The effects of radium-223 on the immune system and the bone tumor microenvironment are incompletely understood. The authors describe mechanisms by which radium-223 may interact with the immune system, specifically through STAT-3 and impact on tumor and circulating lymphocyte populations. They review mechanisms through which effects of radium-223 and androgen-targeted therapy on bone microenvironment could be better elucidated. These knowledge gaps currently limit development of optimal combination therapy approaches for radium-223. Tissue based studies are currently underway in a prospective clinical trial to enhance therapeutic perspective on radium-223 treatment in the prostate cancer landscape.

A Phase I Trial of IGF-1R Inhibitor Cixutumumab and mTOR Inhibitor Temsirolimus in Metastatic Castration-resistant Prostate Cancer

BACKGROUND

Despite frequent PTEN (phosphatase and tensin homologue) loss and Akt/mammalian target of rapamycin (mTOR) signaling in prostate cancer, the disease is insensitive to single-agent mTOR inhibition. Insulin-like growth factor-1 receptor inhibition might mitigate the feedback inhibition by Torc1 inhibitors, suppressing downstream Akt activation and, thus, potentiating the antitumor activity of mTOR inhibition.

PATIENTS AND METHODS

In the present phase I study, patients with metastatic castration-resistant prostate cancer received 6 mg/kg cixutumumab and 25 mg temsirolimus intravenously each week. The primary objective was safety and tolerability. Temsirolimus was decreased if ≥ 2 dose-limiting toxicities (DLTs) were observed in 6 patients. The correlative analyses included measurement of circulating tumor cells, [18F]-fluoro-2-deoxyglucose positron emission tomography, 16β-[18F]-fluoro-α-dihydrotestosterone positron emission tomography, and tumor biopsy.

RESULTS

A total of 16 patients were enrolled across 3 cohorts (1, -1, -2). Two DLTs (grade 3 oral mucositis) were observed in cohort 1 (temsirolimus, 25 mg), and 1 DLT (grade 3 lipase) in cohort -1 (temsirolimus, 20 mg). The most common adverse events included hyperglycemia (100%; 31% grade 3), oral mucositis (63%; 19% grade 3), and diarrhea (44%; 0 grade 3). Low-grade pneumonitis occurred in 7 of 11 patients (44%; 0 grade 3), prompting the opening of a 3-weekly cohort (temsirolimus, 20 mg/kg), without pneumonitis events. No patient had a >50% decline in prostate-specific antigen from baseline. The best radiographic response was stable disease, with median study duration of 22 weeks (range, 7-63 weeks).

CONCLUSIONS

Despite a strong scientific rationale for the combination, temsirolimus plus cixutumumab demonstrated limited antitumor activity and a greater than expected incidence of toxicity, including low-grade pneumonitis and hyperglycemia. Hence, the trial was stopped in favor of alternative androgen receptor/phosphatidylinositol 3-kinase-directed combinatorial therapies.

SWOG S0925: A Randomized Phase II Study of Androgen Deprivation Combined With Cixutumumab Versus Androgen Deprivation Alone in Patients With New Metastatic Hormone-Sensitive Prostate Cancer

PURPOSE

Cixutumumab, formerly IMC-A12, is a recombinant human monoclonal immunoglobulin G1 antibody that targets insulin-like growth factor I receptor (IGF-IR). Cixutumumab was synergistic with castration in a hormone-sensitive prostate cancer xenograft model.

PATIENTS AND METHODS

Patients with new metastatic prostate cancer were randomly assigned within 30 days of initiating androgen deprivation (AD) to cixutumumab added to a luteinizing hormone-releasing hormone agonist with bicalutamide versus AD alone. With 180 patients and one-sided alpha of 0.10, there would be 90% power to detect an absolute 20% difference in undetectable prostate-specific antigen (PSA; ≤ 0.2 ng/mL) rate at 28 weeks (relative risk, 1.44); this end point was previously strongly correlated with survival. Secondary end points included the proportion of patients with PSA > 4.0 ng/mL, safety and tolerability, circulating tumor cell (CTC) levels, and seven plasma IGF-IR biomarkers. Fisher's exact test was used for the primary end point, and extended Mantel-Haenszel χ(2) test was used for three PSA response categories.

RESULTS

The trial accrued 210 eligible patients (105 randomly assigned to each arm). Patient characteristics were similar in both arms. Undetectable PSA rate was 42 (40.0%) of 105 for cixutumumab plus AD and 34 (32.3%) of 105 for AD alone (relative risk, 1.24; one-sided P = .16). Lower baseline CTCs (0 v 1 to 4 v ≥ 5/7.5 mL whole blood) were associated with higher rate of PSA response (three categories; P = .036) in 39 evaluable patients. IGF-IR biomarkers were not correlated with PSA outcome, and cixutumumab did not significantly change these biomarker levels.

CONCLUSION

Cixutumumab plus AD did not significantly increase the undetectable PSA rate in men with new metastatic hormone-sensitive prostate cancer. CTCs at baseline may carry prognostic value.

Insulin-like growth factor receptor-1 (IGF-IR) as a target for prostate cancer therapy

Prostate cancer is the most commonly diagnosed cancer in men and is the second leading cause of cancer-related deaths in men each year. Androgen deprivation therapy is and has been the gold standard of care for advanced or metastatic prostate cancer for decades. While this treatment strategy initially shows benefit, eventually tumors recur as castration-resistant prostate cancer for which there are limited treatment options with only modest survival benefit. Upregulation of the insulin-like growth factor receptor type I (IGF-IR) signaling axis has been shown to drive the survival of prostate cancer cells in many studies. As many IGF-IR blockades have been developed, few have been tested preclinically and even fewer have entered clinical trials for prostate cancer therapy. In this review, we will update the most recent preclinical and clinical studies of IGF-IR therapy for prostate cancer. We will also discuss the challenges for IGF-IR targeted therapies to achieve clinical benefit for prostate cancer.

Growth factor and signaling pathways and their relevance to prostate cancer therapeutics

Treatments that target the androgen axis represent an effective strategy for patients with advanced prostate cancer, but the disease remains incurable and new therapeutic approaches are necessary. Significant advances have recently occurred in our understanding of the growth factor and signaling pathways that are active in prostate cancer. In conjunction with this, many new targeted therapies with sound preclinical rationale have entered clinical development and are being tested in men with castration-resistant prostate cancer. Some of the most relevant pathways currently being exploited for therapeutic gain are HGF/c-Met signaling, the PI3K/AKT/mTOR pathway, Hedgehog signaling, the endothelin axis, Src kinase signaling, the IGF pathway, and angiogenesis. Here, we summarize the biological basis for the use of selected targeted agents and the results from available clinical trials of these drugs in men with prostate cancer.

Management of hormone-sensitive metastatic prostate cancer

Targeting gonadal androgen synthesis (often in conjunction with blockade of androgen receptor) is the cornerstone of treatment of hormone-sensitive metastatic prostate cancer (HSPC). Despite the failure of androgen deprivation therapy, most tumors maintain some dependence on androgen or androgen receptor signaling for proliferation. This article reviews the current standard of care for metastatic HSPC, mechanisms of treatment resistance, novel drugs targeting the androgen signaling pathway, biomarkers predicting response to treatment and survival, future directions, and ongoing clinical trials in HSPC.

Diverse functions of IGF/insulin signaling in malignant and noncancerous prostate cells: proliferation in cancer cells and differentiation in noncancerous cells

The insulin-like growth factor (IGF) pathway represents one of the most studied molecular regulatory networks in oncology. Clinical trials investigating the therapeutic value of anti-IGF1 receptor (IGF1R) therapies in cancer, including prostate cancer, are ongoing. However, the multiple functions of the IGF network in the prostate are not entirely known. To elucidate the effects of IGF and insulin (INS) on prostate cells, we stimulated prostate cancer (PC3, DU145, LNCaP, DUCaP) and noncancerous prostate cells (EP156T, RWPE-1) and observed differing responses: whereas cancer cells responded to IGF and INS exposure by way of enhanced cell proliferation and glucose consumption, basal to luminal differentiation was induced in noncancerous cells. The same diverse responses were observed when the growth factor receptors IGF1R or INSR were overexpressed. Down-regulation of IGF1R or INSR isoform A (INSRA) also inhibited only proliferation of cancer cells. The proliferative response induced by the INSR in cancer cells was mediated solely by the INSRA. Moreover we observed that the receptors of the IGF network mutually influence their expression and exert redundant functions, thus underscoring the functional molecular network formed by IGF, INS, IGF1R, and INSR. Collectively we found that both IGF1R and INSRA have oncogenic effects in prostate cancer, but the IGF network also has important physiological functions in the noncancerous prostate. These data provide new insights into the biology of the IGF network in the prostate, thereby facilitating the design and interpretation of clinical studies investigating IGF1R targeting agents.

The role of the insulin-like growth factor signaling pathway in non-small cell lung cancer and other solid tumors

The type 1 insulin-like growth factor receptor (IGF-1R) and its downstream signaling components have become increasingly recognized as having a driving role in the development of malignancy, and consequently IGF-1R has become a potential target for cancer therapy. Several inhibitors of IGF-1R are in clinical development for the treatment of solid tumors, including non-small cell lung cancer (NSCLC). These IGF-1R-targeted agents include monoclonal antibodies such as cixutumumab (IMC-A12), AMG-479, AVE1642, BIIB022, dalotuzumab (MK-0646), and robatumumab (Sch717454), the ligand neutralizing antibody Medi-573, and the small molecule inhibitors BMS-754807, linsitinib (OSI-906), XL228, and AXL1717. Two phase III trials of the anti-IGF-1R monoclonal antibody, figitumumab (CP-751,871), were discontinued in 2010 as it was considered unlikely either trial would meet their primary endpoints. In light of disappointing clinical data with figitumumab and other targeted agents, it is likely that the use of molecular markers will become important in predicting response to treatment. This review outlines the role of IGF-1R signaling in solid tumors with a particular focus on NSCLC, and provides an overview of clinical data.

Emerging therapeutic approaches in the management of metastatic castration-resistant prostate cancer

Although treatment options for men with castration-resistant prostate cancer (CRPC) have improved with the recent and anticipated approvals of novel immunotherapeutic, hormonal, chemotherapeutic and bone-targeted agents, clinical benefit with these systemic therapies is transient and survival times remain unacceptably short. Thus, we devote the second section of this two-part review to discussing emerging therapeutic paradigms and research strategies that are entering phase II and III clinical testing for men with metastatic CRPC. We will discuss a range of emerging hormonal, immunomodulatory, antiangiogenic, epigenetic and cell survival pathway inhibitors in current clinical trials, with an emphasis on how these therapies may complement our existing treatment options.

The changing therapeutic landscape of castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) has a poor prognosis and remains a significant therapeutic challenge. Before 2010, only docetaxel-based chemotherapy improved survival in patients with CRPC compared with mitoxantrone. Our improved understanding of the underlying biology of CRPC has heralded a new era in molecular anticancer drug development, with a myriad of novel anticancer drugs for CRPC entering the clinic. These include the novel taxane cabazitaxel, the vaccine sipuleucel-T, the CYP17 inhibitor abiraterone, the novel androgen-receptor antagonist MDV-3100 and the radioisotope alpharadin. With these developments, the management of patients with CRPC is changing. In this Review, we discuss these promising therapies along with other novel agents that are demonstrating early signs of activity in CRPC. We propose a treatment pathway for patients with CRPC and consider strategies to optimize the use of these agents, including the incorporation of predictive and intermediate end point biomarkers, such as circulating tumor cells.

Insulin-like growth factor pathway: a link between androgen deprivation therapy (ADT), insulin resistance, and disease progression in patients with prostate cancer?

Androgen deprivation therapy (ADT) is standard of care for patients with metastatic hormone-sensitive prostate cancer (HSPC), yet through its induction of a hypogonadal state leads to metabolic perturbations, including insulin resistance (IR) and obesity. IR and obesity have been associated with an increased risk of progression to castrate-resistant prostate cancer (CRPC) and ultimately increased prostate cancer-specific mortality. On a molecular level, this association between obesity/IR and prostate cancer progression may be mediated by alterations in the insulin-like growth factor (IGF) axis, which has been shown to be up-regulated upon disease progression to CRPC. Targeting the IGF axis, either by anti-IGF therapy or via enhancement of peripheral insulin sensitivity, represents a viable therapeutic target in patients with prostate cancer. Using the development of IR and/or obesity may represent a clinically available biomarker that may predict those patients most likely to respond to such therapy, and warrants testing in future prospective clinical trials.

Horizon scanning for novel therapeutics for the treatment of prostate cancer

IMPORTANCE OF THE FIELD

Treatment options for patients with advanced prostate cancer (PCa) remain limited. Improved understanding of the underlying molecular drivers of prostate cancer pathogenesis, progression and resistance development has provided the fundamental basis for rational targeted drug design.

AREAS COVERED IN THIS REVIEW

This review will discuss the most recent developments in the field of prostate cancer therapies including key findings such as the identification of ETS gene rearrangements, the dissection of prostate cancer molecular heterogeneity and the discovery that castration-resistant prostate cancer (CRPC) remains androgen-driven despite the androgen-depleted milieu, thus making androgen receptor signaling a continued focus of molecularly targeted treatments. A multitude of new molecularly targeted agents are in clinical development and are highly likely to change the current treatment paradigm.

WHAT THE READER WILL GAIN

This review will outline the current clinical development of molecular targeted treatments in CRPC.

TAKE HOME MESSAGE

Unraveling the complex molecular biology that underpins this heterogeneous disease may pave the way to personalized therapy with a wide range of rationally targeted agents and combination treatments. In conclusion, we can predict that the rational clinical development of new targeted drugs will improve the outcome of men with prostate cancer in the years ahead.

Novel targeted therapies for prostate cancer

This article reviews the concepts and rationale behind targeted agents that are currently in clinical testing for patients with castration resistant prostate cancer (CRPC). Advances in our understanding of the molecular mechanisms underlying prostate cancer progression has translated into a variety of treatment approaches. Agents targeting androgen receptor activation and local steroidogenesis, angiogenesis, apoptosis, chaperone proteins, the insulinlike growth factor pathway, RANK ligand, endothelin receptors, and Src family kinases are entering, or have recently completed, accrual to phase III trials for patients with CRPC. There has also been interest generated by data from early-phase studies evaluating multitargeted tyrosine kinase inhibitors, agents effecting signal transduction pathways, and novel cytotoxics.

Novel targets in esophageal and gastric cancer: beyond antiangiogenesis

Cancers of the stomach, gastroesophageal junction and esophagus are a major cause of cancer-related deaths worldwide. In Western countries, adenocarcinomas of the distal esophagus, gastroesophageal junction and proximal stomach have been increasing in frequency more rapidly than other malignancies. The majority of newly diagnosed patients present with advanced disease and the overall survival remains dismal at approximately 10% at 5 years. Better understanding of tumor biology has led to the development of promising novel therapeutic strategies. There is therefore increasing optimism that some of these approaches will improve the outcomes in these increasingly common cancers. Given the success of antiangiogenesis as a therapeutic strategy in various types of cancer, there are ongoing efforts to investigate the utility of other targeted therapies in the treatment of gastric and esophageal cancers. This review will focus on novel therapeutic targets other than angiogenesis and provide a rationale for the further clinical evaluation of these agents in patients with upper gastrointestinal tract cancers.