Highlights d Kinase inhibitors (KIs) and biguanides synergistically target cancer cells d mTORC1/4E-BP axis regulates aspartate, asparagine, and serine biosynthetic enzymes d 4E-BPs and HIF-1a determine responses to KI/biguanide combinations d Cancer cell metabolic plasticity limits efficacy of the KI/ biguanide combinations

Tyrosine kinase signalling within cancer cells is central to the establishment of an immunosuppressive microenvironment. Although tyrosine kinase inhibitors act, in part, to augment adaptive immunity, the increased heterogeneity and functional redundancy of the tyrosine kinome is a hurdle to achieving durable responses to immunotherapies. We previously identified the Shc1 (ShcA) scaffold, a central regulator of tyrosine kinase signalling, as essential for promoting breast cancer immune suppression. Herein we show that the ShcA pathway simultaneously activates STAT3 immunosuppressive signals and impairs STAT1-driven immune surveillance in breast cancer cells. Impaired Y239/Y240-ShcA phosphorylation selectively reduces STAT3 activation in breast tumours, profoundly sensitizing them to immune checkpoint inhibitors and tumour vaccines. Finally, the ability of diminished tyrosine kinase signalling to initiate STAT1-driven immune surveillance can be overcome by compensatory STAT3 hyperactivation in breast tumours. Our data indicate that inhibition of pY239/240-ShcA-dependent STAT3 signalling may represent an attractive therapeutic strategy to sensitize breast tumours to multiple immunotherapies.

ShcA (SHC1) is an adapter protein that possesses an SH2 and a PTB phosphotyrosine-binding motif. ShcA generally uses its PTB domain to engage activated receptor tyrosine kinases (RTK), but there has not been a definitive determination of the role of this domain in tumorigenesis. To address this question, we employed a ShcA mutant (R175Q) that no longer binds phosphotyrosine residues via its PTB domain. Here, we report that transgenic expression of this mutant delays onset of mammary tumors in the MMTV-PyMT mouse model of breast cancer. Paradoxically, we observed a robust increase in the growth and angiogenesis of mammary tumors expressing ShcR175Q, which displayed increased secretion of fibronectin and expression of integrin a5/b1, the principal fibronectin receptor. Sustained integrin engagement activated Src, which in turn phosphorylated proangiogenic RTKs, including platelet-derived growth factor receptor, fibroblast growth factor receptor, and Met, leading to increased VEGF secretion from ShcR175Q-expressing breast cancer cells. We defined a ShcR175Q-dependent gene signature that could stratify breast cancer patients with a high microvessel density. This study offers the first in vivo evidence of a critical role for intracellular signaling pathways downstream of the ShcA PTB domain, which both positively and negatively regulate tumorigenesis during various stages of breast cancer progression. Cancer Res; 73(14); 4521-32. Ó2013 AACR.