Targeting the tumor micro-environment and oncogenic signaling pathways to combat therapeutic resistance in liver cancer and breast cancer brain metastases: Targeting the tumor micro-environment and oncogenic signaling pathways: Innovative multidisciplinary strategies to combat therapeutic resistance in cancer

Chapter 1 of this thesis focuses on uncovering and overcoming mechanisms of anti-cancer drug resistance by using alternative anti-tumor treatments that address the tumor microenvironment (TME). Other aims include identifying an anti-cancer drug with a high cytotoxicity profile that inhibits a different oncogenic signaling cascade than the first-line regimen, characterizing the role of the TME in therapy effectiveness, and simultaneously addressing the TME and cancer cells. Chapter 2 reviews the literature on tumor angiogenesis, various anti-angiogenesis therapies, anti-angiogenic resistance mechanisms, cancer immunotherapy and discusses the integration of cancer immunotherapy to anti-angiogenics to battle resistance to anti-angiogenic agents. Preceding studies have shown that hypoxia upregulated the immune-modulating ligand- PD-L1, restricting the activation of CD8+ T-cells and anti-tumor immunity. Following these data, we observed in Chapter 3 that sorafenib-induced hypoxia was associated with elevated PD-L1 expression in the hepatocellular carcinoma (HCC) mice models. Anti-PD-1 therapy with sorafenib plus AMD3100 was successful in expanding the distribution and activation (IL-2, IFN-, TNF-) of CD8+ T cells. In short, we demonstrated that combining cancer immunotherapy with anti-angiogenesis agents is efficacious in treating resistance to anti-angiogenic drugs. Chapter 4 is dedicated to overcoming sorafenib resistance by targeting the reactivation of oncogenic signaling pathways in tumor cells. Treatment with sorafenib rapidly paradoxically activated RAF-MEK-ERK signaling, which stimulated the proliferation and survival of cancer cells and conferred resistance to sorafenib. The addition of MEK inhibition with selumetinib to sorafenib prevented RAF-MEK-ERK paradoxical activation and restored the effectiveness of sorafenib. Chapter 5 exploited different anti-cancer drugs that exceed the cytotoxicity profile of sorafenib, which is linked with an alternative oncogenic pathway. Using a large-scale high throughput drug screen, we revealed that dasatinib surpassed sorafenib's cytotoxicity profile in a distinct panel of HCC cell lines. Further studies unveiled that YES1 inhibition with dasatinib inhibited the activity of YAP/Hippo pathway signaling. Here, we demonstrated that pharmacological inhibition of YES1 inhibited YAP/Hippo signaling and ultimately reduced YAP-dependent tumor growth in the dasatinib-sensitive HCCs. In Chapter 6, we inquired if dasatinib restrained HCC advancement by shifting the pro-TME into an anti-TME. Dasatinib modified the pro-TME into an anti-TME by reversing hepatic cirrhosis/fibrosis, inhibiting the differentiation and viability of activated HSC, alleviating tumor hypoxia, and ending in depreciated primary tumor growth and frequency of lung metastases. Further analyses ascertained that dasatinib inhibited Akt and ERK signaling due to this adjusted anti-TME in HCCs. In contrast, treatment was ineffective in suppressing Akt and ERK activity in in vitro models, lacking the TME. In Chapters 3-8, we utilized preclinical animal models that resemble human disease and are extremely valuable for fundamental and translational research. These preclinical murine models uniquely allow us to induce hepatic fibrosis/cirrhosis prior to HCC development and concurrently study these diseases. In Chapter 7, we outline how to produce HCC and hepatic cirrhosis in the liver of mice. Chapter 8 highlighted another route of therapeutic resistance that is solely mediated by the brain TME at the breast cancer brain metastatic site. In this chapter, we dissected what resistance mechanism was culpable for this refractoriness to HER2 inhibition in breast cancer brain metastases (BCBM) with HER2-amplified and/or PIK3CA-mutant. The brain TME induced HER3/NRG1 signaling, prompting this resistance to anti-PI3K/HER2 drugs in BCBM. The addition of pharmacological blockade of HER3 to PI3K inhibition or anti-HER2 therapy restored the efficacy of monotherapy of anti-PI3K and anti-HER2 regimens. This combination therapy overcame resistance to PI3K or HER2 inhibition alone in BCBM with HER2-amplified and/or PIK3CA-mutant. Summing up, in this thesis, it is emphasized that distinct multidisciplinary modalities are demanded to inhibit tumor progression and overcome resistance to anti-cancer therapies in HCC and BCBM.