Graduation Date

Spring 5-4-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Biochemistry & Molecular Biology

First Advisor

Surinder K. Batra

Second Advisor

Parthasarathy Seshacharyulu

Abstract

Resistance to chemotherapy poses a significant challenge in the treatment of advanced-stage prostate cancer (PCa), specifically with chemotherapy drugs like docetaxel (Doce), which is often employed after the failure of hormone therapy. However, 50-90% of PCa patients develop resistance to docetaxel within three years of post-chemo treatment, compounded by serious adverse side effects necessitating dose reductions. Various strategies are being investigated to address this issue, including identifying new therapeutic targets or mechanisms, developing novel combination therapies, and optimizing dosing regimens. In particular, our research is focused on uncovering the underlying mechanisms of resistance to docetaxel, such as the activation of survival pathways or changes in the expression of differential gene responders. By understanding these mechanisms, new strategies can be developed to enhance the efficacy of docetaxel treatment and reduce the emergence of resistance. We developed a docetaxel-resistant in vitro PCa cell-based model to address these challenges by treating the PCa cells for 6 months. By chronic Docetaxel exposure, we identified Leukemia Inhibitory Factor Receptor (LIFR) as a potential contributor to docetaxel resistance, supported by elevated LIFR expression in metastatic and primary tumors compared to benign counterparts. LIFR, a transmembrane receptor, interacts with leukemia inhibitory factor (LIF), forming a heterodimer crucial in cancer progression, including prostate cancer. Consequently, screening through 800 small molecule inhibitors, we identified EC914, a potent inhibitor against LIFR, to overcome docetaxel resistance in PCa. First, we investigated EC914's potential to bind with receptors by demonstrating its strong binding affinity to LIFR, lack of steroid receptor affinity, and ability to compete with physiological ligands through SPR and confocal analysis. Second, significant reductions in cell viability, proliferation, colony growth, and induction of apoptosis were observed upon treatment with EC914 in synergy with docetaxel in human and mouse PCa Doce-resistant cells. Thirdly, these 2D studies and synergy between EC914 and Docetaxel were complemented and validated with human and mouse PCa organoids. Studies of human and mouse cell-based xenografts (CBX) and PCa patient-derived xenografts (PDX) showed significant reduction in tumor growth, volume, and weight with EC914 treatment alone and combined with docetaxel, which was devoid of observed toxicity. Finally, our global transcriptomic profiling unveiled alterations in 1249 differentially responded genes associated with the MYC pathway upon LIFR inhibition, highlighting mechanisms of action for EC914. Our promoter analysis also revealed several STAT family members as transcription factors associated with MYC regulation. Among STAT family members, we found that STAT 1 and 4 regulate the MYC pathway in chronic docetaxel treatment and respond to EC914 in PCa cells. Specifically, among the 25 top differentially responded MYC target genes, DDX21 emerged as a critical target, exhibiting significant downregulation upon EC914 treatment. Additionally, EC914 demonstrated the ability to induce cell cycle arrest by suppressing MYC activity, further emphasizing its therapeutic potential to impede PCa progression towards advancement. Our findings provide new insights into potential therapeutic options to overcome docetaxel resistance in prostate cancer and cancers with MYC amplification regulated by the STAT pathway.

Comments

2024 Copyright, the authors

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