Date of Award

1-1-2014

Embargo Period

1-1-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Microbiology and Immunology

College

College of Graduate Studies

First Advisor

Christina Voelkel-Johnson

Second Advisor

Michael Lilly

Third Advisor

James Norris

Fourth Advisor

Chrystal Paulos

Fifth Advisor

Charles Smith

Sixth Advisor

Jennifer Wu

Abstract

Prostate cancer is the second leading cause of cancer death in American men. The interaction of androgen with its receptor (AR) is one of the major pathways that contributes to the progression of prostate cancer. As a result, hormone deprivation is a major strategy for prostate cancer treatment, but the emergence of castration resistant prostate cancer (CRPC) is a major clinical problem. Recently, the novel AR inhibitor, enzalutamide, demonstrated improved survival in men with metastatic CRPC by 4.8 months (13.8 vs 18.4 months in placebo vs treated groups) (18). While these results are encouraging, they also indicate that there is room for improvement to uncover new molecular targets for prostate cancers that have failed androgen deprivation therapy. Current literature provides increasing evidence for the role of inflammatory pathways and lipid mediators in cancer pathogenesis and drug resistance. Several studies have suggested the role of lipid mediator, sphingosine 1-phosphate (S1P), in mediating inflammatory responses by acting as a chemoattractant for immune cells. Sphingosine kinases (SK) 1 and 2 are responsible for the production of S1P, and both have overlapping functions that facilitate angiogenesis, cell proliferation, migration, and inflammatory responses through their downstream targets. Recent evidence suggests SK2 as target in cancer cells. A novel SK2 selective inhibitor, ABC294640 (ABC), has shown anti-tumor and anti-inflammatory effects in several preclinical models and is currently being evaluated for safety in a Phase I clinical trial at MUSC. Preliminary data indicates that ABC inhibits prostate cancer growth in vitro. We hypothesize that inhibition of SK2 through ABC will enhance the therapeutic efficacy of enzalutamide resulting in tumor inhibition and decreased inflammation in the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) cell line. To test this hypothesis, we investigated the mechanism by which ABC exerts anti-tumor effects as well as efficacy when combined with enzalutamide in vitro. We also investigated the anti-tumor and anti-inflammatory efficacy of enzalutamide and ABC combination in vivo. Our data demonstrates that ABC alone induces a nonapoptotic cell death that is directed by the accumulation of autophagic proteins, and when combined with enzalutamide, leads to a greater than additive effect against proliferation in vitro. We also observed an accumulation of dihydroceramides due to an off-target effect of ABC on dihydroceramide desaturase, which is responsible for converting dihydroceramide to ceramide. Further, ABC decreased c-Myc and AR expression, both of which contribute to maintaining the tumorigenic phenotype. NanoString analysis of cytokine and growth factors (NF-Kβ, VEGF, IL-6) were decreased in the presence of ABC in vitro. In vivo however, neither enzalutamide alone nor combination with ABC resulted in smaller tumors compared to vehicle. In contrast, ABC alone reduced the growth rate and resulted in smaller tumors. MALDI-MS Imaging demonstrated the presence of ABC within tumor tissue as well as elevated levels of dihydroceramides and glycoslyceramides. Cytokine analysis of inflammatory markers and growth factors in blood indicate a statistically significant decrease in TNF-α in ABC treated tumors compared to vehicle. Additional tissue cytokine and lymphocyte analysis is needed to fully understand the anti-inflammatory aspects of ABC in vivo. In summary, ABC shows promising evidence toward multifunctionality to shift sphingolipid metabolism toward cell death as well as compromise tumorigenic phenotype to enhance tumor inhibition.

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