Inhibiting IGF1R-mediated Survival Signaling in Head and Neck Cancer with the Peptidomimetic SSTN(IGF1R)

Previous studies have shown that the type I IGFR (IGF1R) suppresses apoptosis when it is autoactivated by coupling its extracellular domain to a matrix adhesion receptor complex consisting of syndecan-1 (Sdc1) and αvβ3 or αvβ5 integrin. We now report that head and neck squamous cell carcinoma (HNSCC) relies on this receptor complex. Disruption of the complex in HNSCC cells in vitro with a peptide mimetic of the organizer site in Sdc1 (called SSTN(IGF1R)) inactivates IGF1R, even in the presence of IGF1, and relieves the suppression of apoptosis signal-regulating kinase-1 (ASK1), dramatically reducing tumor cell survival. Normal epithelial cells do not assemble this receptor complex, require IGF1 to activate the IGF1R, and are refractory to SSTN(IGF1R). In vivo, SSTN(IGF1R) reduced the growth of patient-derived HNSCC tumors in immunodeficient mice by 85%–95%. IGF1R's assimilation into the matrix receptor complex, which is detected in these tumors using the proximity ligation assay (PLA), is quantitatively disrupted by SSTN(IGF1R), coinciding with ASK1 activation. PLA also detects the IGF1R-containing receptor complex in the archival sections of tonsil carcinomas, whereas the adjacent benign epithelium is negative. Likewise, PLA screening of oropharyngeal and adenoid cystic tumor microarrays demonstrated that over 95% of the tumors contained this unique receptor complex with no detectable expression in benign tissue. These findings suggest that HNSCC upregulates and is highly dependent on IGF1R signaling via this adhesion receptor complex. Targeting this mechanism with novel therapeutics, including highly specific SSTN(IGF1R), is likely to offer promising outcomes for patients with carcinoma. SIGNIFICANCE: A newly developed biomarker reveals upregulation of an antiapoptotic IGF1R-integrin-syndecan receptor complex in head and neck cancer and documents disruption of the complex in patient-derived tumor xenografts (PDX) treated with the inhibitor SSTN(IGF1R). A corresponding blockade in PDX growth in the presence of this inhibitor demonstrates that therapies designed to target this mechanism will likely offer promising outcomes for patients with head and neck cancer.