PROJECT SUMMARY/ ABSTRACT The perturbation of phospho-tyrosine mediated signaling networks is an essential occurrence during the multistep process of tumor development and progression. As a result, the components of these phospho-tyrosine signaling networks, especially tyrosine kinases, have been shown to be a key reservoir of actionable molecular targets for the treatment of cancer. In recent years, it has been revealed that the tumor microenvironment plays a critical role in modulating the signaling pathways that govern tumor progression and metastasis. The features of a tumor's microenvironment have been shown to produce unique sensitivities and resistances to different treatment modalities. One major aspect of the tumor microenvironment which is often overlooked in preclinical studies is oxygen tension. This proposal seeks to understand the impact that oxygen tension has on phosphotyrosine-dependent signaling networks in solid tumors, and how the resultant vulnerabilities can be targeted to improve patient outcome. In Aim 1.1 (prior studies), we sought to identify alterations in signaling networks that occur when lung cancer cells colonize the brain, a hypoxic environment. We showed that brain- metastatic lung cancer cells elevate and have an increased dependence on a non-canonical HSF1-E2F transcriptional program for survival. Importantly, we identified that this transcriptional program is targetable through treatment with allosteric ABL2 tyrosine kinase inhibitors. In Aim 1.2 (proposed studies), using a small molecule screen, I have identified previously unrecognized modulators of the cellular response to hypoxia, a tumor microenvironment feature associated with increased metastasis and lower overall survival in patients with solid tumors. The top uncharacterized hit was the FDA-approved ABL1/2 tyrosine kinase inhibitor Dasatinib and my preliminary investigation has shown that the ABL kinases are critical regulators of HIF-1α protein stability. I will continue mechanistic investigation of the ABL- HIF-1α axis in vitro and in vivo. Finally, in Aim 2 (post-doctoral studies), I will focus on understanding the impact that tumor representative- oxygen tension has on protein tyrosine phosphatase activity. Extensive investigation has demonstrated that tumor hypoxia induces activation of phospho-tyrosine signaling networks, but current work has almost exclusively focused on the role of tyrosine kinases. I show that hypoxia induces inhibitory oxidation of protein tyrosine phosphatases (PTPs). Using mass- spectrometry based approaches, I will identify the oxidized- PTP landscape (ox-PTPome) of tumor samples and cancer cells at oxygen levels observed in tumors. Further, since PTPs restrain cellular signaling, I will employ high-throughput drug screening technologies in vitro to identify emergent sensitivities due to the loss of PTP activity that would not have been captured in the numerous normoxically (tumor-unrepresentative oxygen level) performed s...