Updates on protein-prenylation and associated inherited retinopathies.

Membrane-anchored proteins play critical roles in cell signaling, cellular architecture, and membrane biology. Hydrophilic proteins are post-translationally modified by a diverse range of lipid molecules such as phospholipids, glycosylphosphatidylinositol, and isoprenes, which allows their partition and anchorage to the cell membrane. In this review article, we discuss the biochemical basis of isoprenoid synthesis, the mechanisms of isoprene conjugation to proteins, and the functions of prenylated proteins in the neural retina. Recent discovery of novel prenyltransferases, prenylated protein chaperones, non-canonical prenylation-target motifs, and reversible prenylation is expected to increase the number of inherited systemic and blinding diseases with aberrant protein prenylation. Recent important investigations have also demonstrated the role of several unexpected regulators (such as protein charge, sequence/protein-chaperone interaction, light exposure history) in the photoreceptor trafficking of prenylated proteins. Technical advances in the investigation of the prenylated proteome and its application in vision research are discussed. Clinical updates and technical insights into known and putative prenylation-associated retinopathies are provided herein. Characterization of non-canonical prenylation mechanisms in the retina and retina-specific prenylated proteome is fundamental to the understanding of the pathogenesis of protein prenylation-associated inherited blinding disorders.

Sensitive quantification of mevalonate pathway intermediates and prediction of relative novel analogs by chemical derivatization-based LC-MS/MS.

The mevalonate (MVA) pathway plays a crucial role in the occurrence and progression of various diseases, such as osteoporosis, breast cancer, and lung cancer, etc. However, determining all the MVA pathway intermediates is still challenging due to their high polarity, low concentration, chelation effect with metal compartments, and poor mass spectrometric response. In this study, we established a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method coupled with N2, N2, N4, N4-tetramethyl-6-(4-(piperazin-1-ylsulfonyl) phenyl)-1,3,5-triazine-2,4-diamine (Tmt-PP) labeling for the simultaneous analysis of all MVA intermediates in biospecimens. Chemical derivatization significantly improved the chromatographic retention, peak shape, and detection sensitivity of the analytes. Moreover, we employed a method named mass spectrum calculation to achieve the absolute quantification of the isomers, i.e., isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). The established method was fully qualified and applied to explore the difference of these metabolites in cisplatin-resistant non-small cell lung cancer (NSCLC) cells. Additionally, several MVA intermediate analogs, including isopentenyl monophosphate or dimethylallyl monophosphate (IMP/DMAMP), geranyl monophosphate (GMP), 5-triphosphomevalonate (MTP), and isopentenyl triphosphate or dimethylallyl triphosphate (ITP/DMATP), were identified for the first time using a knowledge-driven prediction strategy. We further explored the tissue distribution of these novel metabolites. Overall, this work developed a sensitive quantification method for all MVA intermediates, which will enhance our understanding of the role of this pathway in various health and disease conditions. The novel metabolites we discovered warrant further investigations into their biosynthesis and biological functions.

Conventional and Novel Treatment Strategies for Porokeratoses: A Narrative Review.

Porokeratoses are a heterogenous group of autoinflammatory keratinization disorders all characterized by the presence of a cornoid lamella. In addition to gene mutations affecting the mevalonate pathway, environmental factors such as UV radiation, immunosuppression, trauma, and infection are also thought to contribute to porokeratoses. To date, there are no management guidelines or levels of evidence for commonly used pharmacologic and non-pharmacologic treatment options for porokeratoses. Conventional treatment strategies encompass topical and systemic drugs (e.g., salicylic acid, topical glucocorticoids, and retinoids), phototherapy, laser, and surgical interventions. Better insights into the pathogenesis of porokeratoses have paved the way for the development of novel therapeutic approaches, such as topical statins or the use of monoclonal antibodies. This narrative review aims to summarize both conventional and novel treatment options, including their level of evidence, advantages, and disadvantages.

Gypenoside L inhibits hepatocellular carcinoma by targeting the SREBP2-HMGCS1 axis and enhancing immune response.

Hepatocellular carcinoma (HCC) is a malignant tumor that occurs in the liver, with a high degree of malignancy and relatively poor prognosis. Gypenoside L has inhibitory effects on liver cancer cells. However, its mechanism of action is still unclear. This study aims to investigate the inhibitory effects of gypenoside L on HCC in vitro and in vivo, and explore its potential mechanisms. The results showed that gypenoside L reduced the cholesterol and triglyceride content in HepG2 and Huh-7 cells, inhibited cell proliferation, invasion and metastasis, arrested cell cycle at G0/G1 phase, promoted cell apoptosis. Mechanistically, it targeted the transcription factor SREPB2 to inhibit the expression of HMGCS1 protein and inhibited the downstream proteins HMGCR and MVK, thereby regulating the mevalonate (MVA) pathway. Overexpression HMGCS1 led to significant alterations in the cholesterol metabolism pathway of HCC, which mediated HCC cell proliferation and conferred resistance to the therapeutic effect of gypenoside L. In vivo, gypenoside L effectively suppressed HCC growth in tumor-bearing mice by reducing cholesterol production, exhibiting favorable safety profiles and minimal toxic side effects. Gypenoside L modulated cholesterol homeostasis, enhanced expression of inflammatory factors by regulating MHC I pathway-related proteins to augment anticancer immune responses. Clinical samples from HCC patients also exhibited high expression levels of MVA pathway-related genes in tumor tissues. These findings highlight gypenoside L as a promising agent for targeting cholesterol metabolism in HCC while emphasizing the effectiveness of regulating the SREBP2-HMGCS1 axis as a therapeutic strategy.

Induction of resistance to neurotrophic tropomyosin-receptor kinase inhibitors by HMGCS2 via a mevalonate pathway.

INTRODUCTION: A neurotrophic tropomyosin receptor kinase (NTRK)-tyrosine kinase inhibitor (TKI) has shown dramatic efficacy against malignant tumors harboring an NTRK fusion gene. However, almost all tumors eventually acquire resistance to NTRK-TKIs. METHOD: To investigate the mechanism of resistance to NTRK-TKIs, we established cells resistant to three types of NTRK-TKIs (larotrectinib, entrectinib, and selitrectinib) using KM12 colon cancer cells with a TPM3-NTRK1 rearrangement. RESULT: Overexpression of 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2) was observed in three resistant cells (KM12-LR, KM12-ER, and KM12-SR) by microarray analysis. Lower expression of sterol regulatory element-binding protein 2 (SREBP2) and peroxisome proliferator activated receptor α (PPARα) was found in two cells (KM12-ER and KM12-SR) in which HMGCS2 was overexpressed compared to the parental KM12 and KM12-LR cells. In resistant cells, knockdown of HMGCS2 using small interfering RNA improved the sensitivity to NTRK-TKI. Further treatment with mevalonolactone after HMGCS2 knockdown reintroduced the NTRK-TKI resistance. In addition, simvastatin and silibinin had a synergistic effect with NTRK-TKIs in resistant cells, and delayed tolerance was observed after sustained exposure to clinical concentrations of NTRK-TKI and simvastatin in KM12 cells. In xenograft mouse models, combination treatment with entrectinib and simvastatin reduced resistant tumor growth compared with entrectinib alone. CONCLUSION: These results suggest that HMGCS2 overexpression induces resistance to NTRK-TKIs via the mevalonate pathway in colon cancer cells. Statin inhibition of the mevalonate pathway may be useful for overcoming this mechanistic resistance.

Endogenous p53 inhibitor TIRR dissociates systemic metabolic health from oncogenic activity.

It is unclear whether metabolic health corresponds to reduced oncogenesis or vice versa. We study Tudor-interacting repair regulator (TIRR), an inhibitor of p53 binding protein 1 (53BP1)-mediated p53 activation, and the physiological consequences of enhancing tumor suppressor activity. Deleting TIRR selectively activates p53, significantly protecting against cancer but leading to a systemic metabolic imbalance in mice. TIRR-deficient mice are overweight and insulin resistant, even under normal chow diet. Similarly, reduced TIRR expression in human adipose tissue correlates with higher BMI and insulin resistance. Despite the metabolic challenges, TIRR loss improves p53 heterozygous (p53HET) mouse survival and correlates with enhanced progression-free survival in patients with various p53HET carcinomas. Finally, TIRR's oncoprotective and metabolic effects are dependent on p53 and lost upon p53 deletion in TIRR-deficient mice, with glucose homeostasis and orexigenesis being primarily regulated by TIRR expression in the adipose tissue and the CNS, respectively, as evidenced by tissue-specific models. In summary, TIRR deletion provides a paradigm of metabolic deregulation accompanied by reduced oncogenesis.

Sterol-like drugs potentiate statin-triggered prostate cancer cell death by inhibiting SREBP2 nuclear translocation.

There is an urgent need to provide immediate and effective options for the treatment of prostate cancer (PCa) to prevent progression to lethal castration-resistant PCa (CRPC). The mevalonate (MVA) pathway is dysregulated in PCa, and statin drugs commonly prescribed for hypercholesterolemia, effectively target this pathway. Statins exhibit anti-PCa activity, however the resulting intracellular depletion of cholesterol triggers a feedback loop that restores MVA pathway activity, thus diminishing statin efficacy and contributing to resistance. To identify drugs that block this feedback response and enhance the pro-apoptotic activity of statins, we performed a high-content image-based screen of a 1508 drug library, enriched for FDA-approved compounds. Two of the validated hits, Galeterone (GAL) and Quinestrol, share the cholesterol-related tetracyclic structure, which is also evident in the FDA-approved CRPC drug Abiraterone (ABI). Molecular modeling revealed that GAL, Quinestrol and ABI not only share structural similarity with 25-hydroxy-cholesterol (25HC) but were also predicted to bind similarly to a known protein-binding site of 25HC. This suggested GAL, Quinestrol and ABI are sterol-mimetics and thereby inhibit the statin-induced feedback response. Cell-based assays demonstrated that these agents inhibit nuclear translocation of sterol-regulatory element binding protein 2 (SREBP2) and the transcription of MVA genes. Sensitivity was independent of androgen status and the Fluva-GAL combination significantly impeded CRPC tumor xenograft growth. By identifying cholesterol-mimetic drugs that inhibit SREBP2 activation upon statin treatment, we provide a potent "one-two punch" against CRPC progression and pave the way for innovative therapeutic strategies to combat additional diseases whose etiology is associated with SREBP2 dysregulation.

Inhibition of human mevalonate kinase by allosteric inhibitors of farnesyl pyrophosphate synthase.

Mevalonate kinase is a key regulator of the mevalonate pathway, subject to feedback inhibition by the downstream metabolite farnesyl pyrophosphate. In this study, we validated the hypothesis that monophosphonate compounds mimicking farnesyl pyrophosphate can inhibit mevalonate kinase. Exploring compounds originally synthesized as allosteric inhibitors of farnesyl pyrophosphate synthase, we discovered mevalonate kinase inhibitors with nanomolar activity. Kinetic characterization of the two most potent inhibitors demonstrated Ki values of 3.1 and 22 nm. Structural comparison suggested features of these inhibitors likely responsible for their potency. Our findings introduce the first class of nanomolar inhibitors of human mevalonate kinase, opening avenues for future research. These compounds might prove useful as molecular tools to study mevalonate pathway regulation and evaluate mevalonate kinase as a potential therapeutic target.

Atorvastatin attenuates intestinal mucositis induced by 5-fluorouracil in mice by modulating the epithelial barrier and inflammatory response.

Chemotherapy-induced intestinal mucositis is a major side effect of cancer treatment. Statins are 3-hydroxy-3-methyl glutaryl coenzyme reductase inhibitors used to treat hypercholesterolemia and atherosclerotic diseases. Recent studies have demonstrated that atorvastatin (ATV) has antioxidant, anti-inflammatory, and resulting from the regulation of different molecular pathways. In the present study, we investigated the effects of ATV on intestinal homeostasis in 5-fluorouracil (5-FU)-induced mucositis. Our results showed that ATV protected the intestinal mucosa from epithelial damage caused by 5-FU mainly due to inflammatory infiltrate and intestinal permeability reduction, downregulation of inflammatory markers, such as Tlr4, MyD88, NF-κB, Tnf-a, Il1ß, and Il6 dose-dependent. ATV also improved epithelial barrier function by upregulating the mRNA transcript levels of mucin 2 (MUC2), and ZO-1 and occludin tight junction proteins. The results suggest that the ATV anti-inflammatory and protective effects on 5-FU-induced mice mucositis involve the inhibition of the TLR4/MYD88/NPRL3/NF-κB, iNos, and caspase 3.

Spectrum of activity and mechanisms of azole-bisphosphonate synergy in pathogenic Candida.

Candidiasis places a significant burden on human health and can range from common superficial vulvovaginal and oral infections to invasive diseases with high mortality. The most common Candida species implicated in human disease is Candida albicans, but other species like Candida glabrata are emerging. The use of azole antifungals for treatment is limited by increasing rates of resistance. This study explores repositioning bisphosphonates, which are traditionally used for osteoporosis, as antifungal synergists that can improve and revitalize the use of azoles. Risedronate, alendronate, and zoledronate (ZOL) were tested against isolates from six different species of Candida, and ZOL produced moderate antifungal activity and strong synergy with azoles like fluconazole (FLC), particularly in C. glabrata. FLC:ZOL combinations had increased fungicidal and antibiofilm activity compared to either drug alone, and the combination prevented the development of antifungal resistance. Mechanistic investigations demonstrated that the synergy was mediated by the depletion of squalene, resulting in the inhibition of ergosterol biosynthesis and a compromised membrane structure. In C. glabrata, synergy compromised the function of membrane-bound multidrug transporters and caused an accumulation of reactive oxygen species, which may account for its acute sensitivity to FLC:ZOL. The efficacy of FLC:ZOL in vivo was confirmed in a Galleria mellonella infection model, where combinations improved the survival of larvae infected with C. albicans and C. glabrata to a greater extent than monotherapy with FLC or ZOL, and at reduced dosages. These findings demonstrate that bisphosphonates and azoles are a promising new combination therapy for the treatment of topical candidiasis. IMPORTANCE: Candida is a common and often very serious opportunistic fungal pathogen. Invasive candidiasis is a prevalent cause of nosocomial infections with a high mortality rate, and mucocutaneous infections significantly impact the quality of life of millions of patients a year. These infections pose substantial clinical challenges, particularly as the currently available antifungal treatment options are limited in efficacy and often toxic. Azoles are a mainstay of antifungal therapy and work by targeting the biosynthesis of ergosterol. However, there are rising rates of acquired azole resistance in various Candida species, and some species are considered intrinsically resistant to most azoles. Our research demonstrates the promising therapeutic potential of synergistically enhancing azoles with non-toxic, FDA-approved bisphosphonates. Repurposing bisphosphonates as antifungal synergists can bypass much of the drug development pipeline and accelerate the translation of azole-bisphosphonate combination therapy.

Statins as anti-tumor agents: A paradigm for repurposed drugs.

BACKGROUND: Statins, frequently prescribed medications, work by inhibiting the rate-limiting enzyme HMG-CoA reductase (HMGCR) in the mevalonate pathway to reduce cholesterol levels. Due to their multifaceted benefits, statins are being adapted for use as cost-efficient, safe and effective anti-cancer treatments. Several studies have shown that specific types of cancer are responsive to statin medications since they rely on the mevalonate pathway for their growth and survival. RECENT FINDINGS: Statin are a class of drugs known for their potent inhibition of cholesterol production and are typically prescribed to treat high cholesterol levels. Nevertheless, there is growing interest in repurposing statins for the treatment of malignant neoplastic diseases, often in conjunction with chemotherapy and radiotherapy. The mechanism behind statin treatment includes targeting apoptosis through the BCL2 signaling pathway, regulating the cell cycle via the p53-YAP axis, and imparting epigenetic modulations by altering methylation patterns on CpG islands and histone acetylation by downregulating DNMTs and HDACs respectively. Notably, some studies have suggested a potential chemo-preventive effect, as decreased occurrence of tumor relapse and enhanced survival rate were reported in patients undergoing long-term statin therapy. However, the definitive endorsement of statin usage in cancer therapy hinges on population based clinical studies with larger patient cohorts and extended follow-up periods. CONCLUSIONS: The potential of anti-cancer properties of statins seems to reach beyond their influence on cholesterol production. Further investigations are necessary to uncover their effects on cancer promoting signaling pathways. Given their distinct attributes, statins might emerge as promising contenders in the fight against tumorigenesis, as they appear to enhance the efficacy and address the limitations of conventional cancer treatments.

Age-specific induction of mutant p53 drives clonal hematopoiesis and acute myeloid leukemia in adult mice.

The investigation of the mechanisms behind p53 mutations in acute myeloid leukemia (AML) has been limited by the lack of suitable mouse models, which historically have resulted in lymphoma rather than leukemia. This study introduces two new AML mouse models. One model induces mutant p53 and Mdm2 haploinsufficiency in early development, showing the role of Mdm2 in myeloid-biased hematopoiesis and AML predisposition, independent of p53. The second model mimics clonal hematopoiesis by inducing mutant p53 in adult hematopoietic stem cells, demonstrating that the timing of p53 mutation determines AML vs. lymphoma development. In this context, age-related changes in hematopoietic stem cells (HSCs) collaborate with mutant p53 to predispose toward myeloid transformation rather than lymphoma development. Our study unveils new insights into the cooperative impact of HSC age, Trp53 mutations, and Mdm2 haploinsufficiency on clonal hematopoiesis and the development of myeloid malignancies.

mTORC1-CTLH E3 ligase regulates the degradation of HMG-CoA synthase 1 through the Pro/N-degron pathway.

Mammalian target of rapamycin (mTOR) senses changes in nutrient status and stimulates the autophagic process to recycle amino acids. However, the impact of nutrient stress on protein degradation beyond autophagic turnover is incompletely understood. We report that several metabolic enzymes are proteasomal targets regulated by mTOR activity based on comparative proteome degradation analysis. In particular, 3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) synthase 1 (HMGCS1), the initial enzyme in the mevalonate pathway, exhibits the most significant half-life adaptation. Degradation of HMGCS1 is regulated by the C-terminal to LisH (CTLH) E3 ligase through the Pro/N-degron motif. HMGCS1 is ubiquitylated on two C-terminal lysines during mTORC1 inhibition, and efficient degradation of HMGCS1 in cells requires a muskelin adaptor. Importantly, modulating HMGCS1 abundance has a dose-dependent impact on cell proliferation, which is restored by adding a mevalonate intermediate. Overall, our unbiased degradomics study provides new insights into mTORC1 function in cellular metabolism: mTORC1 regulates the stability of limiting metabolic enzymes through the ubiquitin system.

Expanded Archaeal Genomes Shed New Light on the Evolution of Isoprenoid Biosynthesis.

Isoprenoids and their derivatives, essential for all cellular life on Earth, are particularly crucial in archaeal membrane lipids, suggesting that their biosynthesis pathways have ancient origins and play pivotal roles in the evolution of early life. Despite all eukaryotes, archaea, and a few bacterial lineages being known to exclusively use the mevalonate (MVA) pathway to synthesize isoprenoids, the origin and evolutionary trajectory of the MVA pathway remain controversial. Here, we conducted a thorough comparison and phylogenetic analysis of key enzymes across the four types of MVA pathway, with the particular inclusion of metagenome assembled genomes (MAGs) from uncultivated archaea. Our findings support an archaeal origin of the MVA pathway, likely postdating the divergence of Bacteria and Archaea from the Last Universal Common Ancestor (LUCA), thus implying the LUCA's enzymatic inability for isoprenoid biosynthesis. Notably, the Asgard archaea are implicated in playing central roles in the evolution of the MVA pathway, serving not only as putative ancestors of the eukaryote- and Thermoplasma-type routes, but also as crucial mediators in the gene transfer to eukaryotes, possibly during eukaryogenesis. Overall, this study advances our understanding of the origin and evolutionary history of the MVA pathway, providing unique insights into the lipid divide and the evolution of early life.

Unravelling the origin of isoprene in the human body-a forty year Odyssey.

In the breath research community's search for volatile organic compounds that can act as non-invasive biomarkers for various diseases, hundreds of endogenous volatiles have been discovered. Whilst these systemic chemicals result from normal and abnormal metabolic activities or pathological disorders, to date very few are of any use for the development of clinical breath tests that could be used for disease diagnosis or to monitor therapeutic treatments. The reasons for this lack of application are manifold and complex, and these complications either limit or ultimately inhibit the analytical application of endogenous volatiles for use in the medical sciences. One such complication is a lack of knowledge on the biological origins of the endogenous volatiles. A major exception to this is isoprene. Since 1984, i.e. for 40 years, it has been generally accepted that the pathway to the production of human isoprene, and hence the origin of isoprene in exhaled breath, is through cholesterol biosynthesis via the mevalonate (MVA) pathway within the liver. However, various studies between 2001 and 2012 provide compelling evidence that human isoprene is produced in skeletal muscle tissue. A recent multi-omic investigation of genes and metabolites has revealed that this proposal is correct by showing that human isoprene predominantly results from muscular lipolytic cholesterol metabolism. Despite the overwhelming proof for a muscular pathway to isoprene production in the human body, breath research papers still reference the hepatic MVA pathway. The major aim of this perspective is to review the evidence that leads to a correct interpretation for the origins of human isoprene, so that the major pathway to human isoprene production is understood and appropriately disseminated. This is important, because an accurate attribution to the endogenous origins of isoprene is needed if exhaled isoprene levels are to be correctly interpreted and for assessing isoprene as a clinical biomarker.

Gene-specific somatic epigenetic mosaicism of FDFT1 underlies a non-hereditary localized form of porokeratosis.

Porokeratosis is a clonal keratinization disorder characterized by solitary, linearly arranged, or generally distributed multiple skin lesions. Previous studies showed that genetic alterations in MVK, PMVK, MVD, or FDPS-genes in the mevalonate pathway-cause hereditary porokeratosis, with skin lesions harboring germline and lesion-specific somatic variants on opposite alleles. Here, we identified non-hereditary porokeratosis associated with epigenetic silencing of FDFT1, another gene in the mevalonate pathway. Skin lesions of the generalized form had germline and lesion-specific somatic variants on opposite alleles in FDFT1, representing FDFT1-associated hereditary porokeratosis identified in this study. Conversely, lesions of the solitary or linearly arranged localized form had somatic bi-allelic promoter hypermethylation or mono-allelic promoter hypermethylation with somatic genetic alterations on opposite alleles in FDFT1, indicating non-hereditary porokeratosis. FDFT1 localization was uniformly diminished within the lesions, and lesion-derived keratinocytes showed cholesterol dependence for cell growth and altered expression of genes related to cell-cycle and epidermal development, confirming that lesions form by clonal expansion of FDFT1-deficient keratinocytes. In some individuals with the localized form, gene-specific promoter hypermethylation of FDFT1 was detected in morphologically normal epidermis adjacent to methylation-related lesions but not distal to these lesions, suggesting that asymptomatic somatic epigenetic mosaicism of FDFT1 predisposes certain skin areas to the disease. Finally, consistent with its genetic etiology, topical statin treatment ameliorated lesions in FDFT1-deficient porokeratosis. In conclusion, we identified bi-allelic genetic and/or epigenetic alterations of FDFT1 as a cause of porokeratosis and shed light on the pathogenesis of skin mosaicism involving clonal expansion of epigenetically altered cells.

Overcoming statin resistance in prostate cancer cells by targeting the 3-hydroxy-3-methylglutaryl-CoA-reductase.

Prostate cancer is the most prevalent malignancy in men. While diagnostic and therapeutic interventions have substantially improved in recent years, disease relapse, treatment resistance, and metastasis remain significant contributors to prostate cancer-related mortality. Therefore, novel therapeutic approaches are needed. Statins are inhibitors of the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme of the mevalonate pathway which plays an essential role in cholesterol homeostasis. Numerous preclinical studies have provided evidence for the pleiotropic antitumor effects of statins. However, results from clinical studies remain controversial and have shown substantial benefits to even no effects on human malignancies including prostate cancer. Potential statin resistance mechanisms of tumor cells may account for such discrepancies. In our study, we treated human prostate cancer cell lines (PC3, C4-2B, DU-145, LNCaP) with simvastatin, atorvastatin, and rosuvastatin. PC3 cells demonstrated high statin sensitivity, resulting in a significant loss of vitality and clonogenic potential (up to - 70%; p < 0.001) along with an activation of caspases (up to 4-fold; p < 0.001). In contrast, C4-2B and DU-145 cells were statin-resistant. Statin treatment induced a restorative feedback in statin-resistant C4-2B and DU-145 cells through upregulation of the HMGCR gene and protein expression (up to 3-folds; p < 0.01) and its transcription factor sterol-regulatory element binding protein 2 (SREBP-2). This feedback was absent in PC3 cells. Blocking the feedback using HMGCR-specific small-interfering (si)RNA, the SREBP-2 activation inhibitor dipyridamole or the HMGCR degrader SR12813 abolished statin resistance in C4-2B and DU-145 and induced significant activation of caspases by statin treatment (up to 10-fold; p < 0.001). Consistently, long-term treatment with sublethal concentrations of simvastatin established a stable statin resistance of a PC3SIM subclone accompanied by a significant upregulation of both baseline as well as post-statin HMGCR protein (gene expression up to 70-fold; p < 0.001). Importantly, the statin-resistant phenotype of PC3SIM cells was reversible by HMGCR-specific siRNA and dipyridamole. Our investigations reveal a key role of a restorative feedback driven by the HMGCR/SREBP-2 axis in statin resistance mechanisms of prostate cancer cells.

Squalene Epoxidase: Its Regulations and Links with Cancers.

Squalene epoxidase (SQLE) is a key enzyme in the mevalonate-cholesterol pathway that plays a critical role in cellular physiological processes. It converts squalene to 2,3-epoxysqualene and catalyzes the first oxygenation step in the pathway. Recently, intensive efforts have been made to extend the current knowledge of SQLE in cancers through functional and mechanistic studies. However, the underlying mechanisms and the role of SQLE in cancers have not been fully elucidated yet. In this review, we retrospected current knowledge of SQLE as a rate-limiting enzyme in the mevalonate-cholesterol pathway, while shedding light on its potential as a diagnostic and prognostic marker, and revealed its therapeutic values in cancers. We showed that SQLE is regulated at different levels and is involved in the crosstalk with iron-dependent cell death. Particularly, we systemically reviewed the research findings on the role of SQLE in different cancers. Finally, we discussed the therapeutic implications of SQLE inhibitors and summarized their potential clinical values. Overall, this review discussed the multifaceted mechanisms that involve SQLE to present a vivid panorama of SQLE in cancers.

Repurposing of the Cardiovascular Drug Statin for the Treatment of Cancers: Efficacy of Statin-Dipyridamole Combination Treatment in Melanoma Cell Lines.

Metastatic melanoma has a very poor prognosis. Statins, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) inhibitors, are cholesterol-lowering agents with a potential for cancer treatment. The inhibition of HMGCR by statins, however, induces feedback, which paradoxically upregulates HMGCR expression via sterol regulatory element-binding protein-2 (SREBP2). Dipyridamole, an antiplatelet agent, is known to inhibit SREBP2 upregulation. We aimed to demonstrate the efficacy of statin-dipyridamole combination treatment in both human and spontaneously occurring canine melanoma cell lines. The half maximal inhibitory concentration (IC50) of atorvastatin showed a 68-92% reduction when combined with dipyridamole, compared with that of atorvastatin alone. In some melanoma cell lines, cell proliferation was suppressed to almost zero by the combination treatment (≥3 µM atorvastatin). Finally, the BRAF inhibitor, vemurafenib, further potentiated the effects of the combined statin-dipyridamole treatment in BRAF V600E mutation-bearing human melanoma cell lines. In conclusion, the inexpensive and frequently prescribed statin-dipyridamole combination therapy may lead to new developments in the treatment of melanoma and may potentiate the effects of vemurafenib for the targeted therapy of BRAF V600E-mutation bearing melanoma patients. The concordance between the data from canine and human melanoma cell lines reinforces this possibility.

Pitavastatin induces autophagy-dependent ferroptosis in MDA-MB-231 cells via the mevalonate pathway.

Triple-negative breast cancer (TNBC) is more prone to recurrence and metastasis relative to other subtypes of breast cancer, leading to an extremely poor prognosis. The increasing potential chemoresistance of TNBC patients is mainly due to that tumor cells escape from apoptosis. In recent years, statins have demonstrated extensive anti-tumor effects. It is worth noting that statins have more effective anti-tumor effects on TNBC cells and drug-resistant breast cancer cells. Therefore, this study examines the superior cytotoxic effects of statins on TNBC cell lines and further explores their potential therapeutic mechanisms. We detected different cell phenotypes and found that statins significantly reduced the cell viability of TNBC cells. Specifically, pitavastatin showed an obvious induction in cell death, cell cycle arrest and oxidative stress in TNBC MDA-MB-231 cells. The reversal effect of iron chelator desferrioxamine (DFO) on the morphological and molecular biological changes induced by pitavastatin has revealed a new mode of cell death induced by pitavastatin: ferroptosis. This ferroptotic effect was strengthened by the decreased expression of glutathione peroxidase 4 (GPx4) as well as newly discovered ferroptosis suppressor protein 1 (FSP1). The data showed that ferroptotic death of MDA-MB-231 cells is autophagy-dependent and mediated by the mevalonate pathway. Finally, we found that therapeutic oral doses of statins can inhibit the growth of transplanted tumors, which establishes statins as a potential treatment for TNBC patients. In conclusion, we found pitavastatin could induce autophagy-dependent ferroptosis in TNBC cells via the mevalonate pathway which may become a potential adjuvant treatment option for TNBC patients.