Targeting the insulin-like growth factor receptor pathway in lung cancer: problems and pitfalls

The insulin-like growth factor (IGF) pathway is a complex pathway involving interactions between membrane-bound receptors, ligands, binding proteins, downstream effectors, and other receptor tyrosine kinase signaling cascades. The IGF pathway has been identified as a potential therapeutic target in non-small cell lung cancer (NSCLC) based on the following provocative factors. Preclinical observations in NSCLC have shown that this pathway is involved in tumor cell proliferation, survival, and invasiveness. In addition, IGF-1R protein expression is found in a significant number of non-small cell tumor specimens. Initial therapeutic efforts involved the development of monoclonal antibodies and tyrosine kinase inhibitors that target IGF-1R, a transmembrane receptor tyrosine kinase. Enthusiasm for targeting this pathway increased when a randomized phase II study showed that combining an anti-IGF-1R monoclonal antibody (figitumumab) with a platinum doublet resulted in a higher response rate and trends for superior progression-free survival and overall survival. Subsequently, a phase III study failed to confirm the promising results observed in the phase II trial. Currently, investigators are studying different monoclonal antibodies and tyrosine kinases targeting IGF-1R. In unselected patients, results presented thus far do not suggest efficacy of this agent. However, retrospective subgroup analyses suggest that circulating IGF-1 levels might identify patients who could benefit from treatment with an IGF-1R monoclonal antibody and may warrant further exploratory studies for predictive molecular markers. The purpose of this paper is to briefly discuss the IGF pathway and its relationship with other signaling pathways in lung cancer and to review the ongoing IGF clinical trials and efforts to identify predictive molecular markers.

The role of EGFR inhibition in the treatment of non-small cell lung cancer

The identification of certain molecular mechanisms underlying lung carcinogenesis and progression has led to the development of targeted agents against different families of growth factors and receptors. The epidermal growth factor receptor (EGFR) is one such target for therapeutic exploitation. Inhibition of EGFR downstream signaling can be accomplished through two primary mechanisms: (a) the direct blocking of intracellular kinase activity with small-molecule tyrosine kinase inhibitors (TKIs) (e.g., gefitinib, erlotinib) and (b) the blocking of EGFR ligand binding using antibodies directed against the extracellular domain of the receptor (e.g., cetuximab). Resistance to available EGFR-targeted treatments has emerged as a substantial clinical issue in non-small cell lung cancer (NSCLC). Several novel agents with the potential to overcome such resistance are currently in clinical development, including irreversible EGFR TKIs, monoclonal antibodies, and TKIs directed against multiple signaling pathways. Here we discuss the clinical application of the currently available EGFR-targeted agents in NSCLC, the underlying mechanisms of resistance, and the novel agents in clinical development that may overcome resistance.

Insulin-like growth factor receptor 1 (IGF1R) expression and survival in surgically resected non-small-cell lung cancer (NSCLC) patients

BACKGROUND

The purpose of this study is to investigate the prognostic role of insulin-like growth factor receptor 1 (IGF1R) expression in surgically resected non-small-cell lung cancer (NSCLC). Patient characteristics and methods: This retrospective study was conducted in 369 stage I-II-IIIA, surgically resected, NSCLC patients. Patients exposed to anti-epidermal growth factor receptor (EGFR) agents were excluded. IGF1R expression was evaluated by immunohistochemistry in tissue microarray sections.

RESULTS

A positive IGF1R expression (score > or = 100) was observed in 282 cases (76.4%) and was significantly associated with squamous cell histology (P = 0.04) and with grade III differentiation (P = 0.02). No difference in survival was observed between the positive and negative group when score 100 was used as cut-off for discriminating a positive versus a negative IGF1R result (52 versus 48 months, P = 0.99) or when median value of IGF1R expression was used (45 versus 55 months, P = 0.36). No difference in survival was observed between IGF1R-positive and -negative patients in a subgroup of stage I-II adenocarcinoma (n = 137) with known EGFR mutation and copy number status.

CONCLUSIONS

IGF1R expression does not represent a prognostic factor in resected NSCLC patients. Patients with squamous cell carcinoma overexpress IGF1R more frequently than patients with nonsquamous histology, justifying the different sensitivity to anti-IGF1R agents observed in clinical trials.