Abstract 2211: Quantitative analysis of IGF-1R expression and signaling pathway activation in FFPE xenograft and human tumor tissues

Abstract

Abstract The IGF-1R signal pathway is activated in many cancer types which has led to active clinical development of both antibody and small molecule IGF1R targeted therapeutics. Multiple clinical trials targeting IGF1R are currently underway, however after initial optimism in NSCLC and Ewing's sarcoma, several trials have failed to show efficacy or had severe toxicity. Pretreatment quantitation of tumor IGF1R protein expression remains a challenge due to high homology between IGF1R and the insulin receptor. Thus, there is a need for a specific and quantitative clinical assay for IGF-1R protein expression. The ability to quantify IGF1R expression and determine signaling pathway activation status directly in formalin-fixed paraffin-embedded (FFPE) patient tissue biopsies should help identify and select patients most likely to benefit from anti-IGF1R therapies. We have developed a quantitative IGF1R assay which can be performed directly in FFPE patient tissue. This approach is based on the Liquid Tissue®-SRM technology platform which enables relative and absolute quantification of proteins and their phosphorylation status directly in formalin fixed tissue. The IGF1R- specific SRM assay was developed and preclinically validated on cell lines expressing a range of IGF1R protein. The final assay has a LOD of <20 attomol/ug and an LOQ of ∼35 attomol/ug, values that are well in line with expected levels of expression in primary tumor sourced cell lines and xenograft explants. The expression levels of IGF1R in seven formalin fixed rhabdomyosarcoma (RMS) cell lines were measured by SRM mass spectrometry. We detected a range of IGF1R expression from 68 to 333 amol/ug for these cell lines, values that showed extremely high correlation with antibody based techniques (Cao et al, Cancer Res. 68:8039). We extended this quantitation study by measuring expression of IGF-1R in human rhabdomyosarcoma xenograft explants and a cohort of ∼40 embryonal and alveolar rhabdomyosarcoma tumors. Interestingly, in xenografts treated with a therapeutic IGF1R antibody, tumor regression was seen, and a loss of IGF1R expression was noted by SRM analysis. Our goal is to define expression levels of IGF1R in these tumors, and to validate this assay for use as a companion diagnostic in follow on clinical trials of IGF1R inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2211. doi:10.1158/1538-7445.AM2011-2211