Insulin-Like Growth Factor-1 Receptor Signaling Blockade Modulates Cellular Proliferation, Angiogenesis, Xenograft Growth and Radiation-Induced Apoptosis

Purpose/Objective: The insulin-like growth factor-1 receptor (IGF-1R) is implicated in cellular proliferation, apoptosis, carcinogenesis, metastasis and response to cytotoxic therapies. Targeted disruption of IGF-1R signaling may therefore yield additional anti-cancer efficacy over cytotoxic therapies alone. In this study, a fully human anti-IGF-1R monoclonal antibody A12 (ImClone Systems) is examined as an adjunct to radiation therapy to explore whether targeted disruption of this signaling pathway confers additional anti-cancer efficacy.Materials/Methods: A panel of cancer cell lines was assessed for in vitro anchorage-dependent and anchorage-independent proliferation inhibition in the presence or absence of A12. Human tumor xenografts were established in athymic mice from non-small cell lung cancer (H226) cells to assess in vivo proliferation, angiogenesis and radiation response in the presence or absence of A12. Apoptosis assays measuring caspase activation were conducted to characterize the interaction between A12 and radiation.Results: IGF-1R blockade with A12 inhibits proliferation in a diverse cohort of cell lines representing breast, lung, prostate, head and neck, and colorectal cancers in a dose-dependent manner under both anchorage-dependent and anchorage-independent conditions. Proliferation inhibition under anchorage-dependent conditions ranges from 10–50% depending on cell line, while greater antiproliferative effects are observed for the same lines grown under anchorage-independent conditions. In H226 xenografts, A12 exhibits anti-tumor activity either alone or in combination with radiation. Xenografts in animals receiving A12 exhibit four-fold greater growth inhibition relative to controls (Fig. 1Fig. 1A). Immunohistochemistry of xenograft specimens demonstrates depletion of IGF-1R and downregulated PCNA in animals receiving A12. Angiogenesis assays using H226 cells embedded in a Matrigel plug demonstrate significantly impaired neovasculature formation after A12 treatment compared to controls. Finally, A12 increases radiation-induced apoptosis as measured by caspase activation approximately three-fold compared to radiation alone (Fig. 1Fig. 1B).Fig. 1A: IGF-1R signaling blockade inhibits human tumor xenograft growth. H226 xenografts were established in athymic mice. Animals received either human IgG (black line) or A12 (gray line), 1 mg i.p. twice weekly. Fig. 1Fig. 1B: IGF-1R signaling blockade enhances radiation-induced apoptosis. H226 cells were exposed to 8 Gy irradiation (black bar), A12 100 nM (white bar) or both treatments (gray bar). Apoptosis as measured by pan-caspase activation was assayed at 48 hours and normalized to control, unirradiated cells.View Large Image | Download PowerPoint SlideConclusions: These results validate IGF-1R signal transduction blockade as a molecular strategy to increase the anti-tumor effectiveness of radiation therapy by direct targeting of tumor cell proliferation, angiogenesis, and through promotion of radiation-induced apoptosis. Additional animal studies investigating the capacity of A12 to influence tumor response to focal radiation therapy are in progress. These data will contribute to the design of phase I clinical trials that examine the efficacy of IGF-1R targeting as an anti-cancer strategy in humans.