Abstract 1105: Redundancy of growth factor utilization and complex molecular analyses in human primary tumors highlights potential resistance mechanisms for targeted agents.
Authors: Rossi John , Loberg Robert D. , Bass Michael B. , Deshpande Chetan , Baker Dan , Baker Dan , Rizk Maha , Paweletz Katherine , Damore Michael A. , Patterson Scott D. , McCaffery Ian 
Published: August 2014

Redundancy in growth factor (GF) pathway utilization in human tumors has been hypothesized to be a primary resistance mechanism to targeted therapeutics. Little evidence has been reported in primary tumors to demonstrate functional differences between tumors to GF receptor activation. Data is presented that demonstrates variable response between EGF, HGF, and IGF-1 stimulation of primary tumors that is not attributed solely to receptor expression. Growth factor receptor expression (EGFR, MET, and IGF-1R) and function was investigated in viable, non-apoptotic disaggregated primary tumors by flow cytometry (n= 199) from multiple tumor types including breast, NSC lung, colorectal, and ovarian cancer. Analyses were performed under conditions shown to preserve receptor expression and function in positive cell line controls. Cell surface GF receptor expression was evaluated by flow cytometry. Evidence of GF receptor function was investigated by analysis of intracellular signaling pathways using phospho-specific antibodies following ex vivo GF stimulation (EGF- 100ng/ mL, HGF - 500ng/mL, IGF1 - 200ng/mL; 5 minutes). Combination of receptor expression and pathway utilization revealed approximately 38 unique combinations defining the 199 tumors analyzed. Receptor expression was highly variable and analysis of intracellular signaling pathways demonstrated functional differences and redundancy in pathway utilization following stimulation with EGF, HGF, or IGF-1 (see Table). The presence of GF receptor alone did not account for the differences to GF stimulation observed suggesting alternative contributing factors to these biological differences. Using this robust and sensitive platform we provide evidence for growth factor pathway redundancy in primary tumors. Additional analyses of mutations and targeted mRNA analyses were explored to identify signatures that correlate with response to GF stimulation.

Redundancy in growth factor response in tumors. Tissue Type n % No Response % EGF only %HGF only %IGF1 only %EGF/HGF %EGF/IGF1 %HGF/IGF1 %EGF/HGF/IGF1 Colon 85 16 11 0 12 1 27 4 29 Lung 52 6 8 2 6 8 33 0 38 Breast 25 4 24 0 4 0 40 1 24 Ovarian 19 11 5 0 5 11 37 5 26 Other 18 6 17 0 22 17 33 0 6 TOTAL 199 11 12 1 10 5 32 3 29

Citation Format: John Rossi, Robert D. Loberg, Michael B. Bass, Chetan Deshpande, Dan Baker, Dan Baker, Maha Rizk, Katherine Paweletz, Michael A. Damore, Scott D. Patterson, Ian McCaffery. Redundancy of growth factor utilization and complex molecular analyses in human primary tumors highlights potential resistance mechanisms for targeted agents. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1105. doi:10.1158/1538-7445.AM2013-1105