Abstract C153: Quantitative analysis of IGF-1R expression in FFPE human rhabdomyosarcoma tumor tissue by mass spectrometry.

The IGF-1R pathway is activated in many cancer types which has led to clinical development of many IGF1R targeted therapeutics. Multiple clinical trials targeting IGF1R are currently underway, however after initial optimism in NSCLC and Ewing9s 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 IGF1R 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 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 preclinically validated on cell lines expressing a range of IGF1R protein. 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. Analysis of FFPE human rhabdomyosarcoma xenograft explants demonstrates that variable levels of IGF1R expression can be measured accurately. In xenografts where treatment with a therapeutic IGF1R antibody caused tumor regression there was a concomitant loss of IGF1R expression. We have extended these studies by characterizing the expression of IGF1R in a clinical cohort of 25 RMS tumors. IGF1R was detected in 13/14 embryonal RMS tumors and all 11 syncytial RMS tumors. The range of expression in these tissues was 50–250 amol/ug of protein tissue. However, there was one tumor which expressed ∼4500 amol/ug of IGF1R and may represent a stable amplification, or mutation resulting in this extremely high level of IGF1R expression. Additional studies are underway to continue characterization of this tumor. These novel techniques for quantifying IGF1R protein expression in FFPE RMS tumor tissue may enhance our ability to select patients for IGF1R targeted therapy. We are extending this work in two ways. First we are initiating retrospective analysis of IGF1R levels in a sarcoma trial of an IGFR targeted therapy, and second, we are also preparing to use this assay for prospective analysis of FFPE sarcoma tissue in a future IGF1R targeted therapy trial. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C153.