Title: Targeting Lipid Oxidation for Prostate Cancer Imaging and Therapy Rationale: Increased aerobic glycolysis is only observed in advanced metastatic prostate cancer (PCa), while de novo lipid synthesis can be observed in both primary and advanced PCa. These differences may be the reason why PCa tumors respond differently to Positron Emission Tomography (PET)-glucose imaging techniques: Advanced disease is imaged by PET-glucose but low grade prostate cancer tumors are not, suggesting different metabolic pathways between early and advanced/metastatic PCa. This proposal speculates that lipid oxidation supports glycolysis in PCa, and blocking lipid oxidation will lead to enhanced PET signal in PCa xenograft models, even in early stages. The clinically safe fat burning inhibitor etomoxir is able to block 14C-lipid oxidation in LNCaP cells, resulting in increased 14C-lipid trapped inside the cells and concomitant increases in glucose uptake. However, these metabolic changes result in 40% decreased viability of LNCaP cells by 48 hours suggesting that blocking fat oxidation perturbs their ability to use glucose (aerobic glycolysis) as a fuel source, resultin in apoptosis. Survival of non-cancer cells was not affected by etomoxir, suggesting an ability to switch to glucose oxidation for their fuel needs. This has great implications for how glucose and lipid metabolism interrelate, leading to novel metabolic approaches to image and treat PCa tumors. Hypothesis: Safely blocking lipid oxidation will result in accumulation of lipid metabolites, increased compensatory glucose uptake, but failure to maintain glycolysis, resulting in increased PET imaging signal and decreased PCa survival.
Specific Aim 1 : Study the proliferation, apoptosis, signaling and metabolites of tumorigenic and non- tumorigenic PCa cells exposed to lipid oxidation inhibitors. Results will identify the apoptotic mechanisms of etomoxir and ranolazine fat burning inhibitors and the metabolic biomarkers associated with the decreased PCa cell viability. These biomarkers can be used to design better PET tracers (glucose or lipid-based) that can be explored in Aim 2.
Specific Aim 2 : Utilize mouse PCa xenograft experiments to study growth, metabolite profile, oxidative metabolism, and PET imaging of tumors after systemic treatment with lipid oxidation inhibitors. Xenograft studies will provide verification of the new role of lipid oxidation in PCa tumor survival and will offer novel PET tracers to improve PCa imaging when combined with safe fat burning inhibitors. Knowing the amount of metabolites trapped inside the cells will help us design more effective PET tracers for PCa tumors and move our protocols from the bench to the bedside. Innovation: Lipid synthesis in prostate cancer has been observed for many years and inhibitors of FASN enzyme are currently being developed. However, new observations suggest that PCa is also a lipolytic cancer that depends on lipid mitochondrial metabolism for its survival, but little is known about the lipid synthesis- oxidation cycling that occurs in PCa and how it supports tumor growth. This lipid-cycling of PCa is a novel research study concept that will be examined by adapting existing metabolic methods. Disruption of the lipid cycle at the mitochondrial oxidation level will also be exploited for improved diagnostics, since specific unoxidized lipid metabolites that accumulate in the cells can be used to design new radiotracers for more effective imaging of PCa tumors. Since increased glucose uptake is also a response to lipid oxidation inhibition, PET-glucose will be enhanced in PCa cells unable to oxidize lipids. Thus, the proposed studies offer a new way to look at lipid metabolism in PCa cells, with strong potential for imaging and therapeutic interventions. Impact: Currently, only glycolytic PCa tumors are visible by PET-glucose and lipogenic tracers like 11C-choline or 11C-acetate are unable to detect small metastasis. In the long term, blocking fat oxidation with FDA approved fat inhibitors like ranolazine could lead to increased image signal of most PCa tumors, since glucose or lipid-based tracers would accumulate inside PCa cells, improving tumor detection, staging and response to therapy in a safe and effective manner. This proposal targets lipid oxidation pathways of PCa cells new Achilles'heel to be exploited for therapeutic (decreased PCa viability) and imaging (PET) outcomes. Furthermore, PCa relapse has no potential curative therapy, but it is associated with a lipid-dependent phenotype that will be exploited in the proposed studies to generate more effective therapy and imaging approaches to recurrent PCa tumors. Additionally, recent trials suggest that routine screening does not reduce PCa death and may lead to overtreatment, emphasizing the need for additional tests to supplement PSA screening and differentiate indolent from lethal disease.
This proposal aims to investigate the therapeutic (in the long run) and imaging (short term intervention) avenues that stem from the blockade of lipid oxidation in prostate cancer. Additionally, our studies will provide solid evidence of the types of lipids preferentially oxidized by prostate cancer cells and the metabolic consequences of inhibiting their utilization by the cell, leading to the development of combinatorial therapies that can simultaneously target metabolic and molecular aspects of prostate cancer disease.
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