Targeting fatty acid metabolism in prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed malignancy in men and the second leading cause of cancer-related mortality in the developed world. Prostate cancers are androgen-dependent and rely on androgen receptor signalling for growth and survival. Hence, the mainstay treatment for patients with advanced metastatic PCa is androgen deprivation therapy. Although initially effective, most patients eventually relapse with castrate-resistant prostate cancer (CRPC), and this stage of the disease is ultimately fatal. Despite the clinical development of more potent anti-androgens, these agents are not curative. Alternative treatment strategies are urgently sought to overcome treatment resistance and progression to CRPC. Targeting cancer metabolism has emerged as a promising therapeutic avenue for cancer treatment, especially by targeting upregulated metabolic pathways that promote cancer cell survival. Dysregulation of lipid metabolism is a prominent feature of prostate cancer, and overexpression of key enzymes involved in lipid metabolism is characteristic of both primary and advanced stages of the disease. Moreover, androgens have been shown to regulate lipid metabolism pathways, either directly or indirectly by coordinating with other oncogenic signalling or metabolic networks. Hence, lipid metabolism represents a promising therapeutic vulnerability for the treatment of PCa and could potentially circumvent treatment resistance. While most studies have focused on targeting de novo lipogenesis and, more recently, lipid uptake pathways in cancer, fatty acid oxidation (FAO) remains an underexplored aspect of lipid metabolism. FAO is the dominant bioenergetic pathway in prostate cancer, which has led to interest in exploiting FAO inhibitors as a potential therapeutic strategy to suppress cancer tumorigenesis and overcome treatment resistance. Despite promising preclinical data, FAO inhibitors (ie. etomoxir and perhexiline) used for metabolic diseases have seen rapid decline in their use due to their severe toxicity and side effects. This is attributed to their broad specificity and subsequent off-target effects by targeting the rate limiting enzyme of mitochondrial FAO, carnitine palmitoyltransferase 1 (CPT1). Therefore, it is important that we identify new and more selective targets of FAO. In this dissertation, we characterise two novel and potential targetable FAO enzymes, 2,4-Dienoyl CoA Reductase 1 and 2 (DECR1 and DECR2) respectively. In Chapter 3, we identified DECR1 as a robustly overexpressed gene in prostate cancer compared to normal or benign tissues and associated with shorter relapse-free survival rates. DECR1 is an auxiliary enzyme involved in polyunsaturated fatty acid (PUFA) oxidation in the mitochondria. Intriguingly, DECR1 is an androgen-repressed gene and besides its fundamental function to produce energy from mitochondrial FAO, DECR1 plays an important role to protect prostate cancer cells from oxidative stress and lipid peroxidation-induced cell death, ferroptosis (caused by the accumulation of peroxidation-prone PUFAs). In Chapter 4, we investigated its peroxisomal counterpart, DECR2, an auxiliary enzyme involved in peroxisomal FAO. To date, there is very limited knowledge on the roles of peroxisomal FAO in PCa and its potential as a therapeutic target. We found that DECR2 is significantly upregulated in prostate cancer and markedly suppressed prostate tumour oncogenesis. Moreover, we uncovered an association between peroxisomal FAO and treatment resistance, as well as a novel link with mitochondrial FAO whereby mitochondrial respiration was maintained in DECR2 knockdown cells likely to support tumour survival. We also provide evidence of cell cycle arrest, a mechanism by which DECR2 or peroxisomal FAO inhibition attenuates prostate cancer cell growth. We utilised thioridazine, a peroxisomal FAO inhibitor as a proof-of-concept that targeting peroxisomal FAO is efficacious and a promising avenue for therapeutic targeting. In Chapter 5, we were also interested whether FAO could play a role as an adaptive survival response in the context of treatment resistance. We analysed a proteomics dataset of AUY922 (heat shock protein 90 inhibitor) treated prostate tumours and found that FAO was a significantly enriched pathway in response to treatment. We then proceeded to evaluate the efficacy of the combination treatment with AUY922 and a clinical FAO inhibitor, perhexiline, and demonstrated enhanced suppressive effects on prostate tumour proliferation compared with individual treatments alone. Taken together, the findings of this thesis support the notion that FAO is a critical survival pathway in PCa progression and treatment resistance. Moreover, targeting FAO represents an exciting and novel therapeutic avenue for PCa treatment and provides a strong rationale for further investigation and clinical development of specific DECR1/2 inhibitors. This thesis also provided novel insights into previously unexplored areas and links of cancer metabolism and opens up new opportunities or questions for future exploration.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 202

Peroxisomal β-oxidation enzyme, DECR2, regulates lipid metabolism and promotes treatment resistance in advanced prostate cancer

BACKGROUND: Peroxisomes are central metabolic organelles that have key roles in fatty acid homoeostasis. As prostate cancer (PCa) is particularly reliant on fatty acid metabolism, we explored the contribution of peroxisomal β-oxidation (perFAO) to PCa viability and therapy response.METHODS: Bioinformatic analysis was performed on clinical transcriptomic datasets to identify the perFAO enzyme, 2,4-dienoyl CoA reductase 2 (DECR2) as a target gene of interest. Impact of DECR2 and perFAO inhibition via thioridazine was examined in vitro, in vivo, and in clinical prostate tumours cultured ex vivo. Transcriptomic and lipidomic profiling was used to determine the functional consequences of DECR2 inhibition in PCa.RESULTS: DECR2 is upregulated in clinical PCa, most notably in metastatic castrate-resistant PCa (CRPC). Depletion of DECR2 significantly suppressed proliferation, migration, and 3D growth of a range of CRPC and therapy-resistant PCa cell lines, and inhibited LNCaP tumour growth and proliferation in vivo. DECR2 influences cell cycle progression and lipid metabolism to support tumour cell proliferation. Further, co-targeting of perFAO and standard-of-care androgen receptor inhibition enhanced suppression of PCa cell proliferation.CONCLUSION: Our findings support a focus on perFAO, specifically DECR2, as a promising therapeutic target for CRPC and as a novel strategy to overcome lethal treatment resistance.</p

Human DECR1 is an androgen-repressed survival factor that regulates PUFA oxidation to Protect prostate tumor cells from ferroptosis

Fatty acid β-oxidation (FAO) is the main bioenergetic pathway in human prostate cancer (PCa) and a promising novel therapeutic vulnerability. Here we demonstrate therapeutic efficacy of targeting FAO in clinical prostate tumors cultured ex vivo, and identify DECR1, encoding the rate-limiting enzyme for oxidation of polyunsaturated fatty acids (PUFAs), as robustly overexpressed in PCa tissues and associated with shorter relapse-free survival. DECR1 is a negatively-regulated androgen receptor (AR) target gene and, therefore, may promote PCa cell survival and resistance to AR targeting therapeutics. DECR1 knockdown selectively inhibited β-oxidation of PUFAs, inhibited proliferation and migration of PCa cells, including treatment resistant lines, and suppressed tumor cell proliferation and metastasis in mouse xenograft models. Mechanistically, targeting of DECR1 caused cellular accumulation of PUFAs, enhanced mitochondrial oxidative stress and lipid peroxidation, and induced ferroptosis. These findings implicate PUFA oxidation via DECR1 as an unexplored facet of FAO that promotes survival of PCa cells.status: publishe

Lipidomic Profiling of Clinical Prostate Cancer Reveals Targetable Alterations in Membrane Lipid Composition.

peer reviewedDysregulated lipid metabolism is a prominent feature of prostate cancer that is driven by androgen receptor (AR) signaling. Here we used quantitative mass spectrometry to define the "lipidome" in prostate tumors with matched benign tissues (n = 21), independent unmatched tissues (n = 47), and primary prostate explants cultured with the clinical AR antagonist enzalutamide (n = 43). Significant differences in lipid composition were detected and spatially visualized in tumors compared with matched benign samples. Notably, tumors featured higher proportions of monounsaturated lipids overall and elongated fatty acid chains in phosphatidylinositol and phosphatidylserine lipids. Significant associations between lipid profile and malignancy were validated in unmatched samples, and phospholipid composition was characteristically altered in patient tissues that responded to AR inhibition. Importantly, targeting tumor-related lipid features via inhibition of acetyl-CoA carboxylase 1 significantly reduced cellular proliferation and induced apoptosis in tissue explants. This characterization of the prostate cancer lipidome in clinical tissues reveals enhanced fatty acid synthesis, elongation, and desaturation as tumor-defining features, with potential for therapeutic targeting. SIGNIFICANCE: This study identifies malignancy and treatment-associated changes in lipid composition of clinical prostate cancer tissues, suggesting that mediators of these lipidomic changes could be targeted using existing metabolic agents

ELOVL5 is a critical and targetable fatty acid elongase in prostate cancer

The androgen receptor (AR) is the key oncogenic driver of prostate cancer, and despite implementation of novel AR targeting therapies, outcomes for metastatic disease remain dismal. There is an urgent need to better understand androgen-regulated cellular processes to more effectively target the AR dependence of prostate cancer cells through new therapeutic vulnerabilities. Transcriptomic studies have consistently identified lipid metabolism as a hallmark of enhanced AR signaling in prostate cancer, yet the relationship between AR and the lipidome remains undefined. Using mass spectrometry-based lipidomics, this study reveals increased fatty acyl chain length in phospholipids from prostate cancer cells and patient-derived explants as one of the most striking androgen-regulated changes to lipid metabolism. Potent and direct AR-mediated induction of ELOVL fatty acid elongase 5 (ELOVL5), an enzyme that catalyzes fatty acid elongation, was demonstrated in prostate cancer cells, xenografts, and clinical tumors. Assessment of mRNA and protein in large-scale data sets revealed ELOVL5 as the predominant ELOVL expressed and upregulated in prostate cancer compared with nonmalignant prostate. ELOVL5 depletion markedly altered mitochondrial morphology and function, leading to excess generation of reactive oxygen species and resulting in suppression of prostate cancer cell proliferation, 3D growth, and in vivo tumor growth and metastasis. Supplementation with the monounsaturated fatty acid cis-vaccenic acid, a direct product of ELOVL5 elongation, reversed the oxidative stress and associated cell proliferation and migration effects of ELOVL5 knockdown. Collectively, these results identify lipid elongation as a protumorigenic metabolic pathway in prostate cancer that is androgen-regulated, critical for metastasis, and targetable via ELOVL5. </p