Targeting the liver X receptor with dendrogenin A differentiates tumour cells to secrete immunogenic exosome-enriched vesicles

Cholesterol metabolism in tumor immunity: Mechanisms and therapeutic opportunities for cancer

Cholesterol is an essential component of the cell membrane which plays a critical role in the survival of immune and tumor cells. Reprogramming of cholesterol metabolism in both tumor cells and immune cells can impact tumor progression and anti-tumor immune responses. Strategies aimed at modulating cholesterol metabolism have been demonstrated to be effective in hindering tumor growth and boosting anti-tumor immune functions. This review provides a thorough analysis of intracellular cholesterol homeostasis regulation in cells, focusing on key genes and signaling pathways. It particularly emphasizes the regulatory mechanisms and importance of the cholesterol presence state (esterified/free), levels of cholesterol, and its metabolites in immune and tumor cells. Additionally, the review thoroughly explores how cholesterol metabolism and sources (endogenous/exogenous) in the tumor microenvironment (TME) contribute to the interplay among tumor cells, immune suppressor cells, and immune effector cells, promoting cancer progression and immune evasion. It also delves into current insights on the influence of cholesterol metabolites and related drugs in regulating tumor development or immunotherapy. Finally, it presents an overview of recent advancements in clinical and preclinical trials investigating the efficacy of targeted cholesterol metabolism treatments and combination therapies in cancer management, while proposing potential future research directions in tumor immunity. This review is poised to offer fresh perspectives and avenues for examining the potential of cancer immunotherapy centered on cholesterol metabolism regulation.

Insights into tumor-derived exosome inhibition in cancer therapy

Exosomes are critical mediators of cell-to-cell communication in physiological and pathological processes, due to their ability to deliver a variety of bioactive molecules. Tumor-derived exosomes (TDEs), in particular, carry carcinogenic molecules that contribute to tumor progression, metastasis, immune escape, and drug resistance. Thus, TDE inhibition has emerged as a promising strategy to combat cancer. In this review, we discuss the key mechanisms of TDE biogenesis and secretion, emphasizing their implications in tumorigenesis and cancer progression. Moreover, we provide an overview of small-molecule TDE inhibitors that target specific biogenesis and/or secretion pathways, highlighting their potential use in cancer treatment. Lastly, we present the existing obstacles and propose corresponding remedies for the future development of TDE inhibitors.

Role of Protein Regulators of Cholesterol Homeostasis in Immune Modulation and Cancer Pathophysiology

Cholesterol metabolism and homeostasis have emerged as important factors governing various aspects of cancer biology. Clinical associations between circulating cholesterol and poor prognosis or use of cholesterol-lowering medication and improved prognosis have been noted for several different solid tumors. Mechanistically, cholesterol has many different direct and indirect effects on cancer cells themselves but is also critically involved in shaping the function of other cells of the tumor microenvironment, especially immune cells. There are 2 major feedback loops regulating cholesterol homeostasis. Here we highlight the major proteins involved in the so-called oxysterol-bile acid feedback loop and discuss how each has been implicated in cancer biology. We focus on roles within the immune system with implications for cancer. Given that many of these proteins are enzymes or nuclear receptors, both of which are amenable to small molecule intervention, we posit that this axis may represent a promising area for therapeutic intervention.

Tackling exosome and nuclear receptor interaction: an emerging paradigm in the treatment of chronic diseases

Nuclear receptors (NRs) function as crucial transcription factors in orchestrating essential functions within the realms of development, host defense, and homeostasis of body. NRs have garnered increased attention due to their potential as therapeutic targets, with drugs directed at NRs demonstrating significant efficacy in impeding chronic disease progression. Consequently, these pharmacological agents hold promise for the treatment and management of various diseases. Accumulating evidence emphasizes the regulatory role of exosome-derived microRNAs (miRNAs) in chronic inflammation, disease progression, and therapy resistance, primarily by modulating transcription factors, particularly NRs. By exploiting inflammatory pathways such as protein kinase B (Akt)/mammalian target of rapamycin (mTOR), nuclear factor kappa-B (NF-κB), signal transducer and activator of transcription 3 (STAT3), and Wnt/β-catenin signaling, exosomes and NRs play a pivotal role in the panorama of development, physiology, and pathology. The internalization of exosomes modulates NRs and initiates diverse autocrine or paracrine signaling cascades, influencing various processes in recipient cells such as survival, proliferation, differentiation, metabolism, and cellular defense mechanisms. This comprehensive review meticulously examines the involvement of exosome-mediated NR regulation in the pathogenesis of chronic ailments, including atherosclerosis, cancer, diabetes, liver diseases, and respiratory conditions. Additionally, it elucidates the molecular intricacies of exosome-mediated communication between host and recipient cells via NRs, leading to immunomodulation. Furthermore, it outlines the implications of exosome-modulated NR pathways in the prophylaxis of chronic inflammation, delineates current limitations, and provides insights into future perspectives. This review also presents existing evidence on the role of exosomes and their components in the emergence of therapeutic resistance.

27-Hydroxycholesterol Enhances Secretion of Extracellular Vesicles by ROS-Induced Dysregulation of Lysosomes

Extracellular vesicles (EVs) serve as crucial mediators of cell-to-cell communication in normal physiology as well as in diseased states; they have been largely studied in regard to their role in cancer progression. However, the mechanisms by which their biogenesis and secretion are regulated by metabolic or endocrine factors remain unknown. Here, we delineate a mechanism by which EV secretion is regulated by a cholesterol metabolite, 27-hydroxycholesterol (27HC), where treatment of myeloid immune cells (RAW 264.7 and J774A.1) with 27HC impairs lysosomal homeostasis, leading to shunting of multivesicular bodies (MVBs) away from lysosomal degradation, toward secretion as EVs. This altered lysosomal function is likely caused by mitochondrial dysfunction and subsequent increase in reactive oxygen species (ROS). Interestingly, cotreatment with a mitochondria-targeted antioxidant rescued the lysosomal impairment and attenuated the 27HC-mediated increase in EV secretion. Overall, our findings establish how a cholesterol metabolite regulates EV secretion and paves the way for the development of strategies to regulate cancer progression by controlling EV secretion.

Cholesterol Metabolite 27-Hydroxycholesterol Enhances the Secretion of Cancer Promoting Extracellular Vesicles by a Mitochondrial ROS-Induced Impairment of Lysosomal Function

Extracellular vesicles (EVs) serve as crucial mediators of cell-to-cell communication in normal physiology as well as in diseased states, and have been largely studied in regard to their role in cancer progression. However, the mechanisms by which their biogenesis and secretion are regulated by metabolic or endocrine factors remain unknown. Here, we delineate a mechanism by which EV secretion is regulated by a cholesterol metabolite, 27-Hydroxycholesterol (27HC), where treatment of myeloid immune cells (RAW 264.7 and J774A.1) with 27HC impairs lysosomal homeostasis, leading to shunting of multivesicular bodies (MVBs) away from lysosomal degradation, towards secretion as EVs. This impairment of lysosomal function is caused by mitochondrial dysfunction and subsequent increase in reactive oxygen species (ROS). Interestingly, cotreatment with a mitochondria-targeted antioxidant rescued the lysosomal impairment and attenuated the 27HC-mediated increase in EV secretion. Overall, our findings establish how a cholesterol metabolite regulates EV secretion and paves the way for the development of strategies to regulate cancer progression by controlling EV secretion.

The Cholesterol-5,6-Epoxide Hydrolase: A Metabolic Checkpoint in Several Diseases

Cholesterol-5,6-epoxides (5,6-ECs) are oxysterols (OS) that have been linked to several pathologies including cancers and neurodegenerative diseases. 5,6-ECs can be produced from cholesterol by several mechanisms including reactive oxygen species, lipoperoxidation, and cytochrome P450 enzymes. 5,6-ECs exist as two different diastereoisomers: 5,6α-EC and 5,6β-EC with different metabolic fates. They can be produced as a mixture or as single products of epoxidation. The epoxide ring of 5,6α-EC and 5,6β-EC is very stable and 5,6-ECs are prone to hydration by the cholesterol-5,6-epoxide hydrolase (ChEH) to give cholestane-3β,5α,6β-triol, which can be further oxidized into oncosterone. 5,6α-EC is prone to chemical and enzymatic conjugation reactions leading to bioactive compounds such as dendrogenins, highlighting the existence of a new metabolic branch on the cholesterol pathway centered on 5,6α-EC. We will summarize in this chapter current knowledge on this pathway which is controlled by the ChEH.

27-Hydroxylation of oncosterone by CYP27A1 switches its activity from pro-tumor to anti-tumor

Oncosterone (6-oxo-cholestane-3β,5α-diol; OCDO) is an oncometabolite and a tumor promoter on estrogen receptor alpha-positive breast cancer (ER(+) BC) and triple-negative breast cancers (TN BC). OCDO is an oxysterol formed in three steps from cholesterol: 1) oxygen addition at the double bond to give α- or β- isomers of 5,6-epoxycholestanols (5,6-EC), 2) hydrolyses of the epoxide ring of 5,6-ECs to give cholestane-3β,5α,6β-triol (CT), and 3) oxidation of the C6 hydroxyl of CT to give OCDO. On the other hand, cholesterol can be hydroxylated by CYP27A1 at the ultimate methyl carbon of its side chain to give 27-hydroxycholesterol ((25R)-Cholest-5-ene-3beta,26-diol, 27HC), which is a tumor promoter for ER(+) BC. It is currently unknown whether OCDO and its precursors can be hydroxylated at position C27 by CYP27A1, as is the impact of such modification on the proliferation of ER(+) and TN BC cells. We investigated, herein, whether 27H-5,6-ECs ((25R)-5,6-epoxycholestan-3β,26-diol), 27H-CT ((25R)-cholestane-3β,5α,6β,26-tetrol) and 27H-OCDO ((25R)-cholestane-6-oxo-3β,5α,26-triol) exist as metabolites and can be produced by cells expressing CYP27A1. We report, for the first time, that these compounds exist as metabolites in humans. We give pharmacological and genetic evidence that CYP27A1 is responsible for their production. Importantly, we found that 27-hydroxy-OCDO (27H-OCDO) inhibits BC cell proliferation and blocks OCDO and 27-HC-induced proliferation in BC cells, showing that this metabolic conversion commutes the proliferative properties of OCDO into antiproliferative ones. These data suggest an unprecedented role of CYP27A1 in the control of breast carcinogenesis by inhibiting the tumor promoter activities of oncosterone and 27-HC.

Chemical synthesis and biochemical properties of cholestane-5α,6β-diol-3-sulfonate: A non-hydrolysable analogue of cholestane-5α,6β-diol-3β-sulfate

Cholestane-3β,5α,6β-triol (CT) is a primary metabolite of 5,6-epoxycholesterols (5,6-EC) that is catalyzed by the cholesterol-5,6-epoxide hydrolase (ChEH). CT is a well-known biomarker for Niemann-Pick disease type C (NP-C), a progressive inherited neurodegenerative disease. On the other hand, CT is known to be metabolized by the 11β-hydroxysteroid-dehydrogenase of type 2 (11β-HSD2) into a tumor promoter named oncosterone that stimulates the growth of breast cancer tumors. Sulfation is a major metabolic transformation leading to the production of sulfated oxysterols. The production of cholestane-5α,6β-diol-3β-O-sulfate (CDS) has been reported in breast cancer cells. However, no data related to CDS biological properties have been reported so far. These studies have been hampered because sulfate esters of sterols and steroids are rapidly hydrolyzed by steroid sulfatase to give free steroids and sterols. In order to get insight into the biological properties of CDS, we report herein the synthesis and the characterization of cholestane-5α,6β-diol-3β-sulfonate (CDSN), a non-hydrolysable analogue of CDS. We show that CDSN is a potent inhibitor of 11β-HSD2 that blocks oncosterone production on cell lysate. The inhibition of oncosterone biosynthesis of a whole cell assay was observed but results from the blockage by CDSN of the uptake of CT in MCF-7 cells. While CDSN inhibits MCF-7 cell proliferation, we found that it potentiates the cytotoxic activity of post-lanosterol cholesterol biosynthesis inhibitors such as tamoxifen and PBPE. This effect was associated with an increase of free sterols accumulation and the appearance of giant multilamellar bodies, a structural feature reminiscent of Type C Niemann-Pick disease cells and consistent with a possible inhibition by CDSN of NPC1. Altogether, our data showed that CDSN is biologically active and that it is a valuable tool to study the biological properties of CDS and more specifically its impact on immunity and viral infection.

Is cholesterol a risk factor for breast cancer incidence and outcome?

Cholesterol plays important roles in many physiological processes, including cell membrane structure and function, hormone synthesis, and the regulation of cellular homeostasis. The role of cholesterol in breast cancer is complex, and some studies have suggested that elevated cholesterol levels may be associated with an increased risk of developing breast cancer, while others have found no significant association. On the other hand, other studies have shown that, for total cholesterol and plasma HDL-associated cholesterol levels, there was inverse association with breast cancer risk. One possible mechanism by which cholesterol may contribute to breast cancer risk is as a key precursor of estrogen. Other potential mechanisms by which cholesterol may contribute to breast cancer risk include its role in inflammation and oxidative stress, which have been linked to cancer progression. Cholesterol has also been shown to play a role in signaling pathways regulating the growth and proliferation of cancer cells. In addition, recent studies have shown that cholesterol metabolism can generate tumor promoters such as cholesteryl esters, oncosterone, 27-hydroxycholesterol but also tumor suppressor metabolites such as dendrogenin A. This review summarizes some of the most important clinical studies that have evaluated the role of cholesterol or its derivatives in breast cancer. It also addresses the role of cholesterol and its derivatives at the cellular level.

Targeting NR1H/liver X receptor with dendrogenin A differentiates tumor cells to activate a new secretory pathway releasing immunogenic anti-tumor vesicles enriched in LC3-II-associated exosomes

Normal cells secrete small extracellular vesicles (sEV), containing exosomes and/or ectosomes, which play a beneficial role in monitoring tissue integrity and immune response, whereas cancer cells constitutively secrete sEV, which contribute to inhibit the immune defenses and promote tumor progression and aggressiveness. Therefore, there is a great interest in reprograming tumor sEV functions toward normal ones. We hypothesized that this could be realized by inducing tumor cell re-differentiation with dendrogenin A (DDA), an endogenous oxysterol and a ligand of NR1 H/LXR (nuclear receptor subfamily 1 group H). At low doses, DDA induces tumor cell differentiation, tumor growth inhibition and immune cell infiltration into tumors. At high doses, DDA induces lethal macroautophagy/autophagy in tumors by increasing LC3 expression at the mRNA and protein level, through NR1H2/LXRβ. In the present study, we showed that low doses of DDA re-differentiate tumor cells by interacting with NR1H2. This results in an increased formation of multivesicular bodies (MVB) in tumor cells and an enhanced secretion of LC3-II-associated exosome-enriched sEV, with immune and anticancer properties. This study highlights the original LC3-II-associated exosome secretory pathway driven by the DDA-NR1H2 complex and paves the way to the development of new therapeutic strategies against pro-tumor exosomes.

Exosome biogenesis: machinery, regulation, and therapeutic implications in cancer

Exosomes are well-known key mediators of intercellular communication and contribute to various physiological and pathological processes. Their biogenesis involves four key steps, including cargo sorting, MVB formation and maturation, transport of MVBs, and MVB fusion with the plasma membrane. Each process is modulated through the competition or coordination of multiple mechanisms, whereby diverse repertoires of molecular cargos are sorted into distinct subpopulations of exosomes, resulting in the high heterogeneity of exosomes. Intriguingly, cancer cells exploit various strategies, such as aberrant gene expression, posttranslational modifications, and altered signaling pathways, to regulate the biogenesis, composition, and eventually functions of exosomes to promote cancer progression. Therefore, exosome biogenesis-targeted therapy is being actively explored. In this review, we systematically summarize recent progress in understanding the machinery of exosome biogenesis and how it is regulated in the context of cancer. In particular, we highlight pharmacological targeting of exosome biogenesis as a promising cancer therapeutic strategy.