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.

Combination of the mTOR inhibitor ridaforolimus and the anti-IGF1R monoclonal antibody dalotuzumab: preclinical characterization and phase I clinical trial

PURPOSE

Mammalian target of rapamycin (mTOR) inhibition activates compensatory insulin-like growth factor receptor (IGFR) signaling. We evaluated the ridaforolimus (mTOR inhibitor) and dalotuzumab (anti-IGF1R antibody) combination.

EXPERIMENTAL DESIGN

In vitro and in vivo models, and a phase I study in which patients with advanced cancer received ridaforolimus (10-40 mg/day every day × 5/week) and dalotuzumab (10 mg/kg/week or 7.5 mg/kg/every other week) were explored.

RESULTS

Preclinical studies demonstrated enhanced pathway inhibition with ridaforolimus and dalotuzumab. With 87 patients treated in the phase I study, main dose-limiting toxicities (DLT) of the combination were primarily mTOR-related stomatitis and asthenia at doses of ridaforolimus lower than expected, suggesting blockade of compensatory pathways in normal tissues. Six confirmed partial responses were reported (3 patients with breast cancer); 10 of 23 patients with breast cancer and 6 of 11 patients with ER(+)/high-proliferative breast cancer showed antitumor activity.

CONCLUSIONS

Our study provides proof-of-concept that inhibiting the IGF1R compensatory response to mTOR inhibition is feasible with promising clinical activity in heavily pretreated advanced cancer, particularly in ER(+)/high-proliferative breast cancer (ClinicalTrials.gov identifier: NCT00730379).

A phase I pharmacokinetic and pharmacodynamic study of dalotuzumab (MK-0646), an anti-insulin-like growth factor-1 receptor monoclonal antibody, in patients with advanced solid tumors

PURPOSE

Insulin-like growth factor-1 receptor (IGF-1R) mediates cellular processes in cancer and has been proposed as a therapeutic target. Dalotuzumab (MK-0646) is a humanized IgG1 monoclonal antibody that binds to IGF-1R preventing receptor activation. This study was designed to evaluate the safety and tolerability of dalotuzumab, determine the pharmacokinetic (PK) and pharmacodynamic (PD) profiles, and identify a recommended phase II dose.

EXPERIMENTAL DESIGN

Patients with tumors expressing IGF-1R protein were allocated to dose-escalating cohorts of three or more patients each and received intravenous dalotuzumab weekly, every 2 or 3 weeks. Plasma was collected for PK analysis. Paired baseline and on-treatment skin and tumor biopsy samples were collected for PD analyses.

RESULTS

Eighty patients with chemotherapy-refractory solid tumors were enrolled. One dose-limiting toxicity was noted, but a maximum-tolerated dose was not identified. Grade 1 to 3 hyperglycemia, responsive to metformin, occurred in 15 (19%) patients. At dose levels or more than 5 mg/kg, dalotuzumab mean terminal half-life was 95 hours or more, mean C(min) was more than 25 μg/mL, clearance was constant, and serum exposures were approximately dose proportional. Decreases in tumor IGF-1R, downstream receptor signaling, and Ki67 expression were observed. (18)F-Fluorodeoxy-glucose positron emission tomography metabolic responses occurred in three patients. One patient with Ewing's sarcoma showed a mixed radiologic response. The recommended phase II doses were 10, 20, and 30 mg/kg for the weekly, every other week, and every third week schedules, respectively.

CONCLUSIONS

Dalotuzumab was generally well-tolerated, exhibited dose-proportional PK, inhibited IGF-1R pathway signaling and cell proliferation in treated tumors, and showed clinical activity. The low clearance rate and long terminal half-life support more extended dosing intervals.

Management of breast cancer with targeted agents: importance of heterogeneity. [corrected]

Breast cancer is a heterogeneous disease with different molecular drivers regulating its growth, survival and response to therapy. Breast cancer is divided in three major subtypes based on the pattern of expression of hormone receptors and HER2: luminal tumors (or HR positive), HER2 amplified tumors, and the remaining subtypes being collectively referred to as triple-negative breast cancer. While tumors within these subtypes have similar gene-expression patterns, clinical outcomes, and response to therapy, this division is far from perfect and subgroups within these groups are beginning to be identified. In terms of therapy, an increasingly rational drug development effort has resulted in agents against new molecular targets that are active against only those tumors with the targeted molecular alteration or phenotype. These agents include receptor and non-receptor tyrosine kinase inhibitors (HER1, HER2, HER3, insulin-like growth factor receptor, c-met, fibroblast growth factor receptor and HSP 90 inhibitors), intracellular signaling pathways (PI3K, AKT, mTOR), angiogenesis inhibitors and agents that interfere with DNA repair (PARP inhibitors). Thus, the overall management of breast cancer will increasingly require an understanding of breast cancer heterogeneicity, the biological nature of any given tumor as well the existence of increased personalized treatment options.

Optimal treatment strategies in postmenopausal women with hormone-receptor-positive and HER2-negative metastatic breast cancer

Metastatic breast cancer (MBC) is unfortunately still considered incurable; treatment aims to prolong progression-free and overall survival, relieve disease symptoms, and maintain quality of life. Treatment can include endocrine therapy, radiotherapy, chemotherapy, bisphosphonates, and/or targeted therapy; which is used depends on the characteristics of the disease [e.g., hormone receptor status, disease site(s), and response to previous treatment] and the patient (age, comorbidity, and personal preferences). For most patients with hormone-receptor-positive tumors, the first choice of treatment is further endocrine therapy, but endocrine resistance is a common problem in advanced disease. Several novel anticancer agents have been developed with the aim of overcoming endocrine resistance, many of which target intracellular signaling pathways implicated in disease progression or resistance. Among these, inhibitors of growth factor receptor tyrosine kinases and of mammalian target of rapamycin have shown the most promise in clinical trials. Chemotherapy is the cornerstone of MBC treatment in most women. Important considerations when choosing chemotherapy include the choice of agents, and whether to use single-agent or combination therapy. Anthracyclines are one of the most active cytotoxic agents currently used for the treatment of breast cancer, and for many women, further anthracycline therapy at progression or relapse would be the preferred option. However, lifetime exposure to anthracyclines is limited by cumulative cardiotoxicity, which often prevents rechallenge in later lines of therapy. Newer anthracycline formulations have been developed with lower cardiotoxicity than the conventional anthracycline doxorubicin, but these agents still impair cardiac function, and have maximum recommended lifetime doses. Recently, the concomitant use of cardioprotective agents, such as dexrazoxane, has emerged as an effective approach to reducing the cardiotoxic effects of anthracyclines, thus permitting retreatment. Bisphosphonates, which are not associated with the acute toxicities of cytotoxic chemotherapy drugs, are the established standard of care for patients with metastatic bone disease, and have greatly improved outcomes over the last decade. The search is ongoing for novel agents that will, hopefully, bring a cure closer to reality.

New drug development in digestive neuroendocrine tumors

The traditional cytotoxic agents are of limited efficacy in the treatment of neuroendocrine tumors of the gastrointestinal tract (NETs). Recent investigations have brought up a number of biological features in this family of neoplasms that could represent targets for anticancer treatment. NETs seem to have an extraordinary tumor vascularization with high expression of proangiogenic molecules such as the vascular endothelial growth factor along with overexpression of certain tyrosine kinase receptors such as the epidermal growth factor receptor (EGFR), the insulin growth factor receptor (IGFR) and their downstream signaling pathway components (PI3K-AKT-mTOR). The rationale of an antiangiogenic approach in the treatment of NETs and the use of other pharmacological strategies such as EGFR, IGFR and mammalian target of rapamycin inhibitors are discussed. Additionally, the emerging results of recent clinical trials with these targeted drugs are presented.