Biasing Receptor Mediated Signaling in Metastatic Breast Cancer
thesisposted on 16.12.2020, 02:52 by Sherry Liang
The epidermal growth factor receptor (EGFR) is a well-recognized proto-oncogene and mediator of cancer cell growth and proliferation. Emerging evidence suggests the paradoxical role of EGFR activation, unique to metastatic breast cancer cells. Previously studies elucidated the role of EGFR mediated activation of Signal Transducer and Activator of Transcription 1, STAT1, is required to induce apoptosis in cells with increased metastatic potential. In this current study, we evaluate the effects of cells with mutations leading to aberrations in phosphatidylinositol 3-kinase, PI3K/AKT/protein kinase B signaling. Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit α (PIK3CA) is a key regulator of the PI3K/Akt pathway and is one of the most commonly mutated genes in breast cancer patients. Utilizing human breast cancer cells, MDA-MB-468 and BT-20s, characterized by amplified protein levels of EGFR and mutations in the PI3K signaling, we demonstrate activation of EGFR with EGF leads to increased pSTAT1 expression. We further demonstrate biased EGFR signaling toward STAT1 activation by pharmacological inhibition of downstream kinase activity with MEK1/2 inhibitor, trametinib, and the AKT inhibitor, Uprosertib or in combination with the PI3Kα specific inhibitor Alpelisib, trade name, PIQRAY. Combination MEK and Akt signaling inhibition followed by EGF stimulation show marked increase in apoptotic activity and decreased cell viability. Moreover, we demonstrate changes in EGFR mediated apoptosis in murine breast cancer cell line derived from metastatic lung nodules, delineate from cells derived from the primary tumor. These finding support the notion of differential evolution of cancer cells as they metastasize to secondary organs. Furthermore, EGFR expression was observed to be vital in EGF mediated pSTAT1 in human breast cancer cell lines. To this end we explored alternative stimulators of pSTAT1 using interferon activation. Addition of INFγ led to robust pSTAT1 in cells that did not respond to EGF and levels of pSTAT1 were not attenuated with our combination treatment. Together, our findings demonstrate the differential role of EGFR expression and signaling in metastatic cells and tolerance for novel combination therapies for patients of late stage breast cancer.