Growth-Inhibitory Effects of Human Anti-Insulin-Like Growth Factor-I Receptor Antibody (A12) in an Orthotopic Nude Mouse Model of Anaplastic Thyroid Carcinoma

Abstract

The insulin-like growth factor-I receptor (IGF-IR) and its ligands have been implicated in the pathogenesis and progression of various cancers, including those arising in the thyroid gland. We therefore evaluated whether the IGF-IR could serve as a potential target for therapy of anaplastic thyroid carcinoma (ATC). The expression and activation of the IGF-IR and some of its downstream signaling pathway components were evaluated in both human thyroid cancer specimens and thyroid cancer cell lines. The therapeutic potential of a humanized monoclonal antibody (A12) directed against IGF-IR was assessed in vitro and in vivo in an orthotopic model of ATC. Tumor volume and overall survival time were analyzed to evaluate the efficacy of A12 in vivo. IGF-IR was overexpressed in 94% of the thyroid cancers. Blockade of IGF-IR with A12 was effective in attenuating IGF-IR signaling both in vitro and in vivo. However, the inhibitory effects of A12 on cell proliferation were cell line dependent, as those ATC cell lines that had detectable levels of pIGF-IR were more sensitive to A12 treatment. A12 was equally effective in vivo, where it brought approximately 57% (P = 0.041) inhibition in tumor volume. The concomitant use of A12 and irinotecan produced additive effects and resulted in a 93% (P < 0.001) reduction in tumor volume. Blocking IGF-IR blocked Akt phosphorylation and decreased proliferation and microvessel density but increased apoptosis within the tumor xenografts. Our results also highlighted a previously undefined IGF-IR-mediated antiangiogenic effect on tumor-associated endothelium in thyroid cancers. Blocking the IGF-IR with A12 seems to be a potential avenue for treating patients with ATC by its direct antitumor effects and its effects on the tumor vasculature.