Abstracts Category : Other

Generation of engineered small protein scaffolds and insulin receptor targeting in human breast cancer

by Jie Ying Chan

The insulin-like growth factor (IGF) system is a well-studied growth regulatory pathway implicated in breast cancer tumorigenicity and drug resistance. The pivotal members of IGF system, the type I insulin-like growth factor (IGF1R) and insulin receptor (InsR) are homologous receptors necessary for signal transduction by their cognate ligands insulin, insulin-like growth factor-I and II. A number of drugs, including monoclonal antibodies (mAbs) directed against IGF1R, small molecule tyrosine kinase inhibitors (TKIs) and IGF ligand neutralizing antibodies have been developed and tested in clinical trials. Early trials suggested benefits in delaying tumor progression, unfortunately, none of the anti-IGF1R mAbs has, thus far, shown significant benefits in phase III clinical trials. Although preclinical studies of anti-IGF1R mAbs showed promising results using endocrine-sensitive models, these antibodies were evaluated in breast cancer patients with endocrine-resistant tumors. When our group generated endocrine-resistant breast cancer models, we showed that IGF1R expression was lacking and anti-IGF1R mAb treatment was inefficacious in treating these endocrine-resistant cells. Inaccurate recapitulation of human diseases explains the disappointing outcomes of the trials. This finding also suggests that IGF1R inhibition is not an appropriate treatment in treating breast cancer patients whom are resistant to endocrine treatments. Unlike IGF1R, InsR expression is not affected in the endocrine-resistant breast cancer model. Several studies have shown a shift in gene signatures from IGF- to insulin-mediated growth and differentiation in the absence of IGF1R. Our group has shown an increase of insulin sensitivity in breast cancer cells when IGF1R is downregulated and insulin/InsR alone is sufficient to drive metastasis and tumor growth in vivo. However, InsR has been intentionally avoided as a potential target in cancer therapy due to its major function in glucose homeostasis. There are, currently no InsR-specific inhibitor or molecular diagnostics available. This reason has become the motivation for my work. The first section of the work examines the roles of InsR and efficacy of InsR inhibition in endocrine-resistant breast cancer. The model we used was a tamoxifen resistant (TamR) cells derived from estrogen receptor positive breast cancer cell lines. These TamR cells did not simply lose IGF1R expression and function, but also gained sensitivity to insulin stimulation compared to their parental cells. We used three different targeting mechanisms to disrupt the functions of InsR: 1.) InsR short hairpin RNA (shIR) to knock down endogenous InsR expression, 2.) a small InsR-blocking peptide, S961 and 3.) an InsR down-regulator mAb (clone 83-7). These methods showed consistent results that suppression of InsR function in TamR cells successfully blocked insulin-mediated signaling, monolayer proliferation, cell cycle progression and anchorage-independent growth. This strategy, however was not effective in the parental cells,