Immediate utility of two approved agents to target both the metabolic mevalonate pathway and its restorative feedback loop

A High-Throughput Screening Platform Identifies FDA-Approved Drugs That Inhibit SREBP Pathway Activation

Sterol regulatory element-binding protein (SREBP) transcription factors are central regulators of lipid homeostasis and are essential for lipid metabolic reprogramming that supports tumor growth in multiple cancers. SREBP pathway inhibitors have been identified, but bioavailable compounds are lacking. To address this need, we designed a novel approach for screening a collection of 4,474 FDA-approved drugs. SREBPs are conditionally essential and required under low lipid conditions. Leveraging this property, we screened for drugs that inhibited pancreatic cancer cell growth in lipid-poor, but not lipid-rich, medium. The primary screen identified 83 drugs that inhibited cell growth in a lipid-dependent manner. Secondary assays examining SREBP target gene expression, SREBP proteolytic cleavage, and effects on human breast cancer cells identified 13 FDA-approved drugs that inhibit SREBP pathway activation. Taken together, we demonstrated that our screening approach can identify SREBP inhibitors from a small library of compounds. This high-throughput screening platform enables screening of large compound collections to discover novel small molecule SREBP inhibitors.

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.

In vivo CRISPR screening identifies geranylgeranyl diphosphate as a pancreatic cancer tumor growth dependency

OBJECTIVE

Cancer cells must maintain lipid supplies for their proliferation and do so by upregulating lipogenic gene programs. The sterol regulatory element-binding proteins (SREBPs) act as modulators of lipid homeostasis by acting as transcriptional activators of genes required for fatty acid and cholesterol synthesis and uptake. SREBPs have been recognized as chemotherapeutic targets in multiple cancers, however it is not well understood which SREBP target genes are essential for tumorigenesis. In this study, we examined the requirement of SREBP target genes for pancreatic ductal adenocarcinoma (PDAC) tumor growth.

METHODS

Here we constructed a custom CRISPR knockout library containing known SREBP target genes and performed in vitro 2D culture and in vivo orthotopic xenograft CRISPR screens using a patient-derived PDAC cell line. In vitro, we grew cells in medium supplemented with 10% fetal bovine serum (FBS) or 10% lipoprotein-deficient serum (LPDS) to examine differences in gene essentiality in different lipid environments. In vivo, we injected cells into the pancreata of nude mice and collected tumors after 4 weeks.

RESULTS

We identified terpenoid backbone biosynthesis genes as essential for PDAC tumor development. Specifically, we identified the non-sterol isoprenoid product of the mevalonate pathway, geranylgeranyl diphosphate (GGPP), as an essential lipid for tumor growth. Mechanistically, we observed that restricting mevalonate pathway activity using statins and SREBP inhibitors synergistically induced apoptosis and caused disruptions in small G protein prenylation that have pleiotropic effects on cellular signaling pathways. Finally, we demonstrated that geranylgeranyl diphosphate synthase 1 (GGPS1) knockdown significantly reduces tumor burden in an orthotopic xenograft mouse model.

CONCLUSIONS

These findings indicate that PDAC tumors selectively require GGPP over other lipids such as cholesterol and fatty acids and that this is a targetable vulnerability of pancreatic cancer cells.

Targeting HMGCS1 restores chemotherapy sensitivity in acute myeloid leukemia

Acute myeloid leukemia (AML) is a common hematological malignancy with overall poor prognosis. Exploring novel targets is urgent and necessary to improve the clinical outcome of relapsed and refractory (RR) AML patients. Through clinical specimens, animal models and cell-level studies, we explored the specific mechanism of 3-hydroxy-3-methylglutaryl coenzyme A synthase 1 (HMGCS1) in AML and the mechanism of targeting HMGCS1 to attenuate cell proliferation, increase chemotherapy sensitivity and improve the occurrence and development of AML. Here, we reveal that HMGCS1 is overexpressed in RR patients and negatively related to overall survival (OS). Knocking out HMGCS1 in AML cells attenuated cell proliferation and increased chemotherapy sensitivity, while stable overexpression of HMGCS1 had the opposite effects. Mechanistically, we identified that knockout of HMGCS1 suppressed mitogen-activated protein kinase (MAPK) pathway activity, while overexpression of HMGCS1 could remarkably enhance the pathway. U0126, a MEK1 inhibitor, offset the effects of HMGCS1 overexpression, indicating that HMGCS1 promotes RR AML through the MAPK pathway. Further, we verified that hymeglusin, a specific inhibitor of HMGCS1, decreases cell growth both in AML cell lines and primary bone marrow cells of AML patients. Furthermore, combination of hymeglusin and the common chemotherapeutic drug cytarabine and adriamycin (ADR) had synergistic toxic effects on AML cells. Our study demonstrates the important role of HMGCS1 in AML, and targeting this protein is promising for the treatment of RR AML.

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.

In vivo CRISPR screening identifies geranylgeranyl diphosphate as a pancreatic cancer tumor growth dependency

Cancer cells must maintain lipid supplies for their proliferation and do so by upregulating lipogenic gene programs. The sterol regulatory element-binding proteins (SREBPs) act as modulators of lipid homeostasis by acting as transcriptional activators of genes required for fatty acid and cholesterol synthesis and uptake. SREBPs have been recognized as chemotherapeutic targets in multiple cancers, however it is not well understood which SREBP target genes are essential for tumorigenesis. Using parallel in vitro and in vivo CRISPR knockout screens, we identified terpenoid backbone biosynthesis genes as essential for pancreatic ductal adenocarcinoma (PDAC) tumor development. Specifically, we identified the non-sterol isoprenoid product of the mevalonate pathway, geranylgeranyl diphosphate (GGPP), as an essential lipid for tumor growth. Mechanistically, we observed that restricting mevalonate pathway activity using statins and SREBP inhibitors synergistically induced apoptosis and caused disruptions in small G protein prenylation that have pleiotropic effects on cellular signaling pathways. Finally, we demonstrated that geranylgeranyl diphosphate synthase 1 ( GGPS1 ) knockdown significantly reduces tumor burden in an orthotopic xenograft mouse model. These findings indicate that PDAC tumors selectively require GGPP over other lipids such as cholesterol and fatty acids and that this is a targetable vulnerability of pancreatic cancer cells.

SREBPs as the potential target for solving the polypharmacy dilemma

The phenomenon of polypharmacy is a common occurrence among older people with multiple health conditions due to the rapid increase in population aging and the popularization of clinical guidelines. The prevalence of metabolic syndrome is growing quickly, representing a serious threat to both the public and the worldwide healthcare systems. In addition, it enhances the risk of cardiovascular disease as well as mortality and morbidity. Sterol regulatory element binding proteins (SREBPs) are basic helix-loop-helix leucine zipper transcription factors that transcriptionally modulate genes that regulate lipid biosynthesis and uptake, thereby serving an essential role in biological systems regulation. In this article, we have described the structure of SREBPs and explored their activation and regulation of signals. We also reveal that SREBPs are intricately involved in the modulation of metabolic diseases and thus have tremendous potential as the novel target for single-drug therapy for multiple diseases.

Enhanced SREBP2-driven cholesterol biosynthesis by PKCλ/ι deficiency in intestinal epithelial cells promotes aggressive serrated tumorigenesis

The metabolic and signaling pathways regulating aggressive mesenchymal colorectal cancer (CRC) initiation and progression through the serrated route are largely unknown. Although relatively well characterized as BRAF mutant cancers, their poor response to current targeted therapy, difficult preneoplastic detection, and challenging endoscopic resection make the identification of their metabolic requirements a priority. Here, we demonstrate that the phosphorylation of SCAP by the atypical PKC (aPKC), PKCλ/ι promotes its degradation and inhibits the processing and activation of SREBP2, the master regulator of cholesterol biosynthesis. We show that the upregulation of SREBP2 and cholesterol by reduced aPKC levels is essential for controlling metaplasia and generating the most aggressive cell subpopulation in serrated tumors in mice and humans. Since these alterations are also detected prior to neoplastic transformation, together with the sensitivity of these tumors to cholesterol metabolism inhibitors, our data indicate that targeting cholesterol biosynthesis is a potential mechanism for serrated chemoprevention.

HMG-CoA reductase degrader, SR-12813, counteracts statin-induced upregulation of HMG-CoA reductase and augments the anticancer effect of atorvastatin

Statins are cholesterol-lowering drugs that have exhibited potential as cancer therapeutic agents. However, as some cancer cells are resistant to statins, broadening an anticancer spectrum of statins is desirable. The upregulated expression of the statin target enzyme, 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase (HMGCR), in statin-treated cancer cells is a well-known mechanism of statin resistance, which can be counteracted by the downregulation of HMGCR gene expression, or degradation of the HMGCR protein. However, the mechanism by which HMGCR degradation influences the anticancer effects of statins remain unreported. We tested the effect of the HMGCR degrader compound SR-12813 at a concentration that did not affect the growth of eight diverse tumor cell lines. Combined treatment with atorvastatin and a low concentration of SR-12813 led to lowering of increased HMGCR expression, and augmented the cytostatic effect of atorvastatin in both statin-resistant and -sensitive cancer cells compared with that of atorvastatin treatment alone. Dual-targeting of HMGCR using statins and SR-12813 (or similar compounds) could provide an improved anticancer therapeutic approach.

Functional significance of cholesterol metabolism in cancer: from threat to treatment

Cholesterol is an essential structural component of membranes that contributes to membrane integrity and fluidity. Cholesterol homeostasis plays a critical role in the maintenance of cellular activities. Recently, increasing evidence has indicated that cholesterol is a major determinant by modulating cell signaling events governing the hallmarks of cancer. Numerous studies have shown the functional significance of cholesterol metabolism in tumorigenesis, cancer progression and metastasis through its regulatory effects on the immune response, ferroptosis, autophagy, cell stemness, and the DNA damage response. Here, we summarize recent literature describing cholesterol metabolism in cancer cells, including the cholesterol metabolism pathways and the mutual regulatory mechanisms involved in cancer progression and cholesterol metabolism. We also discuss various drugs targeting cholesterol metabolism to suggest new strategies for cancer treatment.

Caffeine Supplementation and FOXM1 Inhibition Enhance the Antitumor Effect of Statins in Neuroblastoma

High-risk neuroblastoma exhibits transcriptional activation of the mevalonate pathway that produces cholesterol and nonsterol isoprenoids. A better understanding of how this metabolic reprogramming contributes to neuroblastoma development could help identify potential prevention and treatment strategies. Here, we report that both the cholesterol and nonsterol geranylgeranyl-pyrophosphate branches of the mevalonate pathway are critical to sustain neuroblastoma cell growth. Blocking the mevalonate pathway by simvastatin, a cholesterol-lowering drug, impeded neuroblastoma growth in neuroblastoma cell line xenograft, patient-derived xenograft (PDX), and TH-MYCN transgenic mouse models. Transcriptional profiling revealed that the mevalonate pathway was required to maintain the FOXM1-mediated transcriptional program that drives mitosis. High FOXM1 expression contributed to statin resistance and led to a therapeutic vulnerability to the combination of simvastatin and FOXM1 inhibition. Furthermore, caffeine synergized with simvastatin to inhibit the growth of neuroblastoma cells and PDX tumors by blocking statin-induced feedback activation of the mevalonate pathway. This function of caffeine depended on its activity as an adenosine receptor antagonist, and the A2A adenosine receptor antagonist istradefylline, an add-on drug for Parkinson's disease, could recapitulate the synergistic effect of caffeine with simvastatin. This study reveals that the FOXM1-mediated mitotic program is a molecular statin target in cancer and identifies classes of agents for maximizing the therapeutic efficacy of statins, with implications for treatment of high-risk neuroblastoma.

SIGNIFICANCE

Caffeine treatment and FOXM1 inhibition can both enhance the antitumor effect of statins by blocking the molecular and metabolic processes that confer statin resistance, indicating potential combination therapeutic strategies for neuroblastoma. See related commentary by Stouth et al., p. 2091.

Targeting the mevalonate pathway suppresses ARID1A-inactivated cancers by promoting pyroptosis

ARID1A, encoding a subunit of the SWI/SNF complex, is mutated in ∼50% of clear cell ovarian carcinoma (OCCC) cases. Here we show that inhibition of the mevalonate pathway synergizes with immune checkpoint blockade (ICB) by driving inflammasome-regulated immunomodulating pyroptosis in ARID1A-inactivated OCCCs. SWI/SNF inactivation downregulates the rate-limiting enzymes in the mevalonate pathway such as HMGCR and HMGCS1, which creates a dependence on the residual activity of the pathway in ARID1A-inactivated cells. Inhibitors of the mevalonate pathway such as simvastatin suppresses the growth of ARID1A mutant, but not wild-type, OCCCs. In addition, simvastatin synergizes with anti-PD-L1 antibody in a genetic OCCC mouse model driven by conditional Arid1a inactivation and in a humanized immunocompetent ARID1A mutant patient-derived OCCC mouse model. Our data indicate that inhibition of the mevalonate pathway simultaneously suppresses tumor cell growth and boosts antitumor immunity by promoting pyroptosis, which synergizes with ICB in suppressing ARID1A-mutated cancers.

Metabolism in acute myeloid leukemia: mechanistic insights and therapeutic targets

Metabolic rewiring and cellular reprogramming are trademarks of neoplastic initiation and progression in acute myeloid leukemia (AML). Metabolic alteration in leukemic cells is often genotype specific, with associated changes in epigenetic and functional factors resulting in the downstream upregulation or facilitation of oncogenic pathways. Targeting abnormal or disease-sustaining metabolic activities in AML provides a wide range of therapeutic opportunities, ideally with enhanced therapeutic windows and robust clinical efficacy. This review highlights the dysregulation of amino acid, nucleotide, lipid, and carbohydrate metabolism in AML; explores the role of key vitamins and enzymes that regulate these processes; and provides an overview of metabolism-directed therapies currently in use or development.

Acetyl-CoA metabolism in cancer

Few metabolites can claim a more central and versatile role in cell metabolism than acetyl coenzyme A (acetyl-CoA). Acetyl-CoA is produced during nutrient catabolism to fuel the tricarboxylic acid cycle and is the essential building block for fatty acid and isoprenoid biosynthesis. It also functions as a signalling metabolite as the substrate for lysine acetylation reactions, enabling the modulation of protein functions in response to acetyl-CoA availability. Recent years have seen exciting advances in our understanding of acetyl-CoA metabolism in normal physiology and in cancer, buoyed by new mouse models, in vivo stable-isotope tracing approaches and improved methods for measuring acetyl-CoA, including in specific subcellular compartments. Efforts to target acetyl-CoA metabolic enzymes are also advancing, with one therapeutic agent targeting acetyl-CoA synthesis receiving approval from the US Food and Drug Administration. In this Review, we give an overview of the regulation and cancer relevance of major metabolic pathways in which acetyl-CoA participates. We further discuss recent advances in understanding acetyl-CoA metabolism in normal tissues and tumours and the potential for targeting these pathways therapeutically. We conclude with a commentary on emerging nodes of acetyl-CoA metabolism that may impact cancer biology.

Inhibiting the glycerophosphodiesterase EDI3 in ER-HER2+ breast cancer cells resistant to HER2-targeted therapy reduces viability and tumour growth

BACKGROUND

Intrinsic or acquired resistance to HER2-targeted therapy is often a problem when small molecule tyrosine kinase inhibitors or antibodies are used to treat patients with HER2 positive breast cancer. Therefore, the identification of new targets and therapies for this patient group is warranted. Activated choline metabolism, characterized by elevated levels of choline-containing compounds, has been previously reported in breast cancer. The glycerophosphodiesterase EDI3 (GPCPD1), which hydrolyses glycerophosphocholine to choline and glycerol-3-phosphate, directly influences choline and phospholipid metabolism, and has been linked to cancer-relevant phenotypes in vitro. While the importance of choline metabolism has been addressed in breast cancer, the role of EDI3 in this cancer type has not been explored.

METHODS

EDI3 mRNA and protein expression in human breast cancer tissue were investigated using publicly-available Affymetrix gene expression microarray datasets (n = 540) and with immunohistochemistry on a tissue microarray (n = 265), respectively. A panel of breast cancer cell lines of different molecular subtypes were used to investigate expression and activity of EDI3 in vitro. To determine whether EDI3 expression is regulated by HER2 signalling, the effect of pharmacological inhibition and siRNA silencing of HER2, as well as the influence of inhibiting key components of signalling cascades downstream of HER2 were studied. Finally, the influence of silencing and pharmacologically inhibiting EDI3 on viability was investigated in vitro and on tumour growth in vivo.

RESULTS

In the present study, we show that EDI3 expression is highest in ER-HER2 + human breast tumours, and both expression and activity were also highest in ER-HER2 + breast cancer cell lines. Silencing HER2 using siRNA, as well as inhibiting HER2 signalling with lapatinib decreased EDI3 expression. Pathways downstream of PI3K/Akt/mTOR and GSK3β, and transcription factors, including HIF1α, CREB and STAT3 were identified as relevant in regulating EDI3 expression. Silencing EDI3 preferentially decreased cell viability in the ER-HER2 + cells. Furthermore, silencing or pharmacologically inhibiting EDI3 using dipyridamole in ER-HER2 + cells resistant to HER2-targeted therapy decreased cell viability in vitro and tumour growth in vivo.

CONCLUSIONS

Our results indicate that EDI3 may be a potential novel therapeutic target in patients with HER2-targeted therapy-resistant ER-HER2 + breast cancer that should be further explored.

The role of cholesterol metabolism in tumor therapy, from bench to bed

Cholesterol and its metabolites have important biological functions. Cholesterol is able to maintain the physical properties of cell membrane, play an important role in cellular signaling, and cellular cholesterol levels reflect the dynamic balance between biosynthesis, uptake, efflux and esterification. Cholesterol metabolism participates in bile acid production and steroid hormone biosynthesis. Increasing evidence suggests a strict link between cholesterol homeostasis and tumors. Cholesterol metabolism in tumor cells is reprogrammed to differ significantly from normal cells, and disturbances of cholesterol balance also induce tumorigenesis and progression. Preclinical and clinical studies have shown that controlling cholesterol metabolism suppresses tumor growth, suggesting that targeting cholesterol metabolism may provide new possibilities for tumor therapy. In this review, we summarized the metabolic pathways of cholesterol in normal and tumor cells and reviewed the pre-clinical and clinical progression of novel tumor therapeutic strategy with the drugs targeting different stages of cholesterol metabolism from bench to bedside.

A survival prediction model and nomogram based on immune-related gene expression in chronic lymphocytic leukemia cells

Introduction

There are many different chronic lymphoblastic leukemia (CLL) survival prediction models and scores. But none provide information on expression of immune-related genes in the CLL cells.

Methods

We interrogated data from the Gene Expression Omnibus database (GEO, GSE22762; Number = 151; training) and International Cancer Genome Consortium database (ICGC, CLLE-ES; Number = 491; validation) to develop an immune risk score (IRS) using Least absolute shrinkage and selection operator (LASSO) Cox regression analyses based on expression of immune-related genes in CLL cells. The accuracy of the predicted nomogram we developed using the IRS, Binet stage, and del(17p) cytogenetic data was subsequently assessed using calibration curves.

Results

A survival model based on expression of 5 immune-related genes was constructed. Areas under the curve (AUC) for 1-year survivals were 0.90 (95% confidence interval, 0.78, 0.99) and 0.75 (0.54, 0.87) in the training and validation datasets, respectively. 5-year survivals of low- and high-risk subjects were 89% (83, 95%) vs. 6% (0, 17%; p < 0.001) and 98% (95, 100%) vs. 92% (88, 96%; p < 0.001) in two datasets. The IRS was an independent survival predictor of both datasets. A calibration curve showed good performance of the nomogram. In vitro, the high expression of CDKN2A and SREBF2 in the bone marrow of patients with CLL was verified by immunohistochemistry analysis (IHC), which were associated with poor prognosis and may play an important role in the complex bone marrow immune environment.

Conclusion

The IRS is an accurate independent survival predictor with a high C-statistic. A combined nomogram had good survival prediction accuracy in calibration curves. These data demonstrate the potential impact of immune related genes on survival in CLL.

Sequential Delivery of Novel Triple Drug Combination via Crosslinked Alginate/Lactoferrin Nanohybrids for Enhanced Breast Cancer Treatment

While breast cancer remains a global health concern, the elaboration of rationally designed drug combinations coupled with advanced biocompatible delivery systems offers new promising treatment venues. Herein, we repurposed rosuvastatin (RST) based on its selective tumor apoptotic effect and combined it with the antimetabolite pemetrexed (PMT) and the tumor-sensitizing polyphenol honokiol (HK). This synergistic three-drug combination was incorporated into protein polysaccharide nanohybrids fabricated by utilizing sodium alginate (ALG) and lactoferrin (LF), inspired by the stealth property of the former and the cancer cell targeting capability of the latter. ALG was conjugated to PMT and then coupled with LF which was conjugated to RST, forming core shell nanohybrids into which HK was physically loaded, followed by cross linking using genipin. The crosslinked HK-loaded PMT-ALG/LF-RST nanohybrids exhibited a fair drug loading of 7.86, 5.24 and 6.11% for RST, PMT and HK, respectively. It demonstrated an eight-fold decrease in the IC50 compared to the free drug combination, in addition to showing an enhanced cellular uptake by MCF-7 cells. The in vivo antitumor efficacy in a breast cancer-bearing mouse model confirmed the superiority of the triple cocktail-loaded nanohybrids. Conclusively, our rationally designed triple drug-loaded protein/polysaccharide nanohybrids offer a promising, biocompatible approach for an effective breast tumor suppression.

Computational pharmacogenomic screen identifies drugs that potentiate the anti-breast cancer activity of statins

Statins, a family of FDA-approved cholesterol-lowering drugs that inhibit the rate-limiting enzyme of the mevalonate metabolic pathway, have demonstrated anticancer activity. Evidence shows that dipyridamole potentiates statin-induced cancer cell death by blocking a restorative feedback loop triggered by statin treatment. Leveraging this knowledge, we develop an integrative pharmacogenomics pipeline to identify compounds similar to dipyridamole at the level of drug structure, cell sensitivity and molecular perturbation. To overcome the complex polypharmacology of dipyridamole, we focus our pharmacogenomics pipeline on mevalonate pathway genes, which we name mevalonate drug-network fusion (MVA-DNF). We validate top-ranked compounds, nelfinavir and honokiol, and identify that low expression of the canonical epithelial cell marker, E-cadherin, is associated with statin-compound synergy. Analysis of remaining prioritized hits led to the validation of additional compounds, clotrimazole and vemurafenib. Thus, our computational pharmacogenomic approach identifies actionable compounds with pathway-specific activities.

Hymeglusin Enhances the Pro-Apoptotic Effects of Venetoclax in Acute Myeloid Leukemia

Venetoclax is used for the priority treatment of elderly patients with acute myeloid leukemia (AML). Resistance or intolerance to venetoclax offsets its clinical benefits in some patients. Combination strategies with other drugs are promising alternatives to overcome the current complications associated with venetoclax use. Hymeglusin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A synthase 1 (HMGCS1), regulates the mevalonate pathway, which is vital for AML growth and chemosensitivity. The effects of the combination of venetoclax and hymeglusin on AML were explored in this study. The correlations between HMGCS1 and apoptosis-related genes were analyzed using the Gene Expression Profiling Interactive Analysis 2 and The Cancer Genome Atlas databases. Apoptosis and cell viability were detected in HL-60 and KG-1 cells after treatment with gradient concentrations of venetoclax or hymeglusin. The transcriptomic profiles of HL-60 and KG-1 cells were compared via RNA-Seq analysis. The effects of venetoclax and hymeglusin on apoptosis were validated in primary cells. The results showed that HMGCS1 expression was closely associated with apoptosis-related genes based on the data from large clinical databases. B cell lymphoma (BCL)-2 expression was elevated in AML and negatively associated with overall survival. Hymeglusin decreased BCL2 expression levels in HL-60 and KG-1 cells. Venetoclax and hymeglusin inhibited cell viability in both cell lines, but induced apoptosis in HL-60 cells. This discrepancy in sensitivity to hymeglusin may be attributed to the positive increase in the expression levels of HMGCS1 and multiple upregulated pro-leukemia genes in KG-1 cells. Combination treatment with venetoclax and hymeglusin significantly increased the apoptotic rates compared to single-agent treatment in both AML cell lines and primary AML cells. Furthermore, the combination strategy did not result in remarkably enhanced toxicity in normal mononuclear cells. Collectively, hymeglusin enhanced the effects of venetoclax on apoptosis. This combination strategy showed enhanced antileukemic activity with acceptable toxicity in AML.

Therapeutic targeting of the mevalonate-geranylgeranyl diphosphate pathway with statins overcomes chemotherapy resistance in small cell lung cancer

Small cell lung cancer (SCLC) lacks effective treatments to overcome chemoresistance. Here we established multiple human chemoresistant xenograft models through long-term intermittent chemotherapy, mimicking clinically relevant therapeutic settings. We show that chemoresistant SCLC undergoes metabolic reprogramming relying on the mevalonate (MVA)-geranylgeranyl diphosphate (GGPP) pathway, which can be targeted using clinically approved statins. Mechanistically, statins induce oxidative stress accumulation and apoptosis through the GGPP synthase 1 (GGPS1)-RAB7A-autophagy axis. Statin treatment overcomes both intrinsic and acquired SCLC chemoresistance in vivo across different SCLC PDX models bearing high GGPS1 levels. Moreover, we show that GGPS1 expression is negatively associated with survival in patients with SCLC. Finally, we demonstrate that combined statin and chemotherapy treatment resulted in durable responses in three patients with SCLC who relapsed from first-line chemotherapy. Collectively, these data uncover the MVA-GGPP pathway as a metabolic vulnerability in SCLC and identify statins as a potentially effective treatment to overcome chemoresistance.

Statins and prostate cancer-hype or hope? The biological perspective

Growing evidence suggests that men prescribed a statin for cholesterol control have a lower risk of advanced prostate cancer (PCa) and improved treatment outcomes; however, the mechanism by which statins elicit their anti-neoplastic effects is not well understood and is likely multifaceted. Statins are potent and specific inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), the rate-limiting enzyme of the mevalonate (MVA) metabolic pathway. This two-part series is a review of the observational and experimental data on statins as anti-cancer agents in PCa. In this article, we describe the functional role that deregulated MVA metabolism plays in PCa progression and summarize the biological evidence and rationale for targeting the MVA pathway, with statins and other agents, for the treatment of PCa.

Case Report: Mevalonic Aciduria Complicated by Acute Myeloid Leukemia After Hematopoietic Stem Cell Transplantation

Mevalonic aciduria (MA) is the most severe clinical subtype of mevalonate kinase deficiency (MKD) caused by an inherited defect in the mevalonate pathway. The treatment of MKD focuses on the suppression of recurrent hyperinflammatory attacks using anti-inflammatory drugs. Recently, allogeneic hematopoietic stem cell transplantation (HCT) was shown to successfully ameliorate autoinflammatory attacks in patients with MKD. Here, we report a case of an infant who showed severe recurrent systemic inflammation and was diagnosed with MA. Although she responded to steroids, her symptoms relapsed after the dose was tapered, and organ deterioration occurred. Therefore, at the age of 11 months, HCT from a matched, unrelated donor was performed for curative treatment. However, at 50 days after transplantation, acute myeloid leukemia was diagnosed, which was chemo-refractory. A second HCT from her haploidentical father was performed to treat the acute myeloid leukemia, but the patient died of sepsis on day 4 after transplantation. This is the first report of malignancy following HCT for MA. Our findings suggest that normalizing the mevalonate pathway after HCT in patients with MKD impacts patients differently depending on the clinical spectrum and severity of disease.

Targeting cholesterol homeostasis in hematopoietic malignancies

Cholesterol is a vital lipid for cellular functions. It is necessary for membrane biogenesis, cell proliferation and differentiation. In addition to maintaining cell integrity and permeability, increasing evidence indicates a strict link between cholesterol homeostasis, inflammation and haematological tumors. This makes cholesterol homeostasis an optimal therapeutic target for hematopoietic malignancies. Manipulating cholesterol homeostasis either interfering with its synthesis or activating the reverse cholesterol transport via the engagement of liver X receptors (LXRs), affects the integrity of tumor cells both in vitro and in vivo. Cholesterol homeostasis has also been manipulated to restore antitumor immune responses in preclinical models. These observations have prompted clinical trials in acute myeloid leukemia (AML) to test the combination of chemotherapy with drugs interfering with cholesterol synthesis, i.e. statins. We review the role of cholesterol homeostasis in hematopoietic malignancies, as well as in cells of the tumor microenvironment, and discuss the potential use of lipid modulators for therapeutic purposes.

Pan-cancer analysis reveals the oncogenic role of 3-hydroxy-3-methylglutaryl-CoA synthase 1

BACKGROUND

Emerging studies reveals that 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) plays vital oncogenic roles in a broad spectrum of human cancers, but there is no pan-cancer evidence on the relationship between HMGCS1 and various tumor types.

AIM

To explore the potential role of HMGCS1 across various tumor types based on big clinical data.

METHODS

We conducted a pan-cancer analysis across more than 30 tumor types, based on the most comprehensive database available, including TCGA, GSCA, clinical proteomic tumor analysis consortium, Kaplan-Meier Plotter dataset, GEPIA2, TIMER2, STRING, and GDSC dataset.

RESULTS

HMGCS1 was highly expressed and negatively correlated with the prognosis in most cancer types. The infiltration levels of cancer associated fibroblast and CD8+ T-cell were closely associated with HMGCS1 expression. Amplification was the most common genetic alteration of HMGCS1 in different cancers, while the frequency of mutation was low. Besides, ACAT2 and MVD were closely correlated and bind to HMGCS1. Pathway enrichment analysis indicated that HMGCS1 was actively involved in steroid biosynthesis. Moreover, high HMGCS1 expression could reduce the sensitivity to most drugs in the GDSC dataset.

CONCLUSIONS

Our study revealed the potential oncogenic role of HMGCS1 in cancers.

Nicotinamide phosphoribosyltransferase inhibitors selectively induce apoptosis of AML stem cells by disrupting lipid homeostasis

Current treatments for acute myeloid leukemia (AML) are often ineffective in eliminating leukemic stem cells (LSCs), which perpetuate the disease. Here, we performed a metabolic drug screen to identify LSC-specific vulnerabilities and found that nicotinamide phosphoribosyltransferase (NAMPT) inhibitors selectively killed LSCs, while sparing normal hematopoietic stem and progenitor cells. Treatment with KPT-9274, a NAMPT inhibitor, suppressed the conversion of saturated fatty acids to monounsaturated fatty acids, a reaction catalyzed by the stearoyl-CoA desaturase (SCD) enzyme, resulting in apoptosis of AML cells. Transcriptomic analysis of LSCs treated with KPT-9274 revealed an upregulation of sterol regulatory-element binding protein (SREBP)-regulated genes, including SCD, which conferred partial protection against NAMPT inhibitors. Inhibition of SREBP signaling with dipyridamole enhanced the cytotoxicity of KPT-9274 on LSCs in vivo. Our work demonstrates that altered lipid homeostasis plays a key role in NAMPT inhibitor-induced apoptosis and identifies NAMPT inhibition as a therapeutic strategy for targeting LSCs in AML.

Translating Unconventional T Cells and Their Roles in Leukemia Antitumor Immunity

Recently, cell-mediated immune response in malignant neoplasms has become the focus in immunotherapy against cancer. However, in leukemia, most studies on the cytotoxic potential of T cells have concentrated only on T cells that recognize peptide antigens (Ag) presented by polymorphic molecules of the major histocompatibility complex (MHC). This ignores the great potential of unconventional T cell populations, which include gamma-delta T cells (γδ), natural killer T cells (NKT), and mucosal-associated invariant T cells (MAIT). Collectively, these T cell populations can recognize lipid antigens, specially modified peptides and small molecule metabolites, in addition to having several other advantages, which can provide more effective applications in cancer immunotherapy. In recent years, these cell populations have been associated with a repertoire of anti- or protumor responses and play important roles in the dynamics of solid tumors and hematological malignancies, thus, encouraging the development of new investigations in the area. This review focuses on the current knowledge regarding the role of unconventional T cell populations in the antitumor immune response in leukemia and discusses why further studies on the immunotherapeutic potential of these cells are needed.

The effect of statin treatment on intratumoral cholesterol levels and LDL receptor expression: a window-of-opportunity breast cancer trial

Background

Deregulated lipid metabolism is common in cancer cells and the mevalonate pathway, which synthesizes cholesterol, is central in lipid metabolism. This study aimed to assess statin-induced changes of the intratumoral levels of cholesterol and the expression of the low-density lipoprotein receptor (LDLR) to enhance our understanding of the role of the mevalonate pathway in cancer cholesterol metabolism.

Methods

This study is based on a phase II clinical trial designed as a window-of-opportunity trial including 50 breast cancer patients treated with 80 mg of atorvastatin/day for 2 weeks, between the time of diagnosis and breast surgery. Lipids were extracted from frozen tumor tissue sampled pre- and post-atorvastatin treatment. Intratumoral cholesterol levels were measured using a fluorometric quantitation assay. LDLR expression was evaluated by immunohistochemistry on formalin-fixed paraffin-embedded tumor tissue. Paired blood samples pre- and post-atorvastatin were analyzed for circulating low-density lipoprotein (LDL), high-density lipoprotein (HDL), apolipoprotein A1, and apolipoprotein B. In vitro experiments on MCF-7 breast cancer cells treated with atorvastatin were performed for comparison on the cellular level.

Results

In the trial, 42 patients completed all study parts. From the paired tumor tissue samples, assessment of the cholesterol levels was achievable for 14 tumors, and for the LDLR expression in 24 tumors. Following atorvastatin treatment, the expression of LDLR was significantly increased (P = 0.004), while the intratumoral levels of total cholesterol remained stable. A positive association between intratumoral cholesterol levels and tumor proliferation measured by Ki-67 expression was found. In agreement with the clinical findings, results from in vitro experiments showed no significant changes of the intracellular cholesterol levels after atorvastatin treatment while increased expression of the LDLR was found, although not reaching statistical significance.

Conclusions

This study shows an upregulation of LDLR and preserved intratumoral cholesterol levels in breast cancer patients treated with statins. Together with previous findings on the anti-proliferative effect of statins in breast cancer, the present data suggest a potential role for LDLR in the statin-induced regulation of breast cancer cell proliferation.

Trial registration

The study has been registered at ClinicalTrials.gov (i.e., ID number: NCT00816244, NIH), December 30, 2008.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40170-020-00231-8.

Lipid Regulatory Proteins as Potential Therapeutic Targets for Ovarian Cancer in Obese Women

Obesity has become a recognized global epidemic that is associated with numerous comorbidities including type II diabetes, cardiovascular disease, hypertension, and cancer incidence and progression. Ovarian cancer (OvCa) has a unique mechanism of intra-peritoneal metastasis, already present in 80% of women at the time of diagnosis, making it the fifth leading cause of death from gynecological malignancy. Meta-analyses showed that obesity increases the risk of OvCa progression, leads to enhanced overall and organ-specific tumor burden, and adversely effects survival of women with OvCa. Recent data discovered that tumors grown in mice fed on a western diet (40% fat) have elevated lipid levels and a highly increased expression level of sterol regulatory element binding protein 1 (SREBP1). SREBP1 is a master transcription factor that regulates de novo lipogenesis and lipid homeostasis, and induces lipogenic reprogramming of tumor cells. Elevated SREBP1 levels are linked to cancer cell proliferation and metastasis. This review will summarize recent findings to provide a current understanding of lipid regulatory proteins in the ovarian tumor microenvironment with emphasis on SREBP1 expression in the obese host, the role of SREBP1 in cancer progression and metastasis, and potential therapeutic targeting of SREBPs and SREBP-pathway genes in treating cancers, particularly in the context of host obesity.

Dipyridamole Inhibits Lipogenic Gene Expression by Retaining SCAP-SREBP in the Endoplasmic Reticulum

Sterol regulatory element-binding proteins (SREBPs) are master transcriptional regulators of the mevalonate pathway and lipid metabolism and represent an attractive therapeutic target for lipid metabolic disorders. SREBPs are maintained in the endoplasmic reticulum (ER) in a tripartite complex with SREBP cleavage-activating protein (SCAP) and insulin-induced gene protein (INSIG). When new lipid synthesis is required, the SCAP-SREBP complex dissociates from INSIG and undergoes ER-to-Golgi transport where the N-terminal transcription factor domain is released by proteolysis. The mature transcription factor translocates to the nucleus and stimulates expression of the SREBP gene program. Previous studies showed that dipyridamole, a clinically prescribed phosphodiesterase (PDE) inhibitor, potentiated statin-induced tumor growth inhibition. Dipyridamole limited nuclear accumulation of SREBP, but the mechanism was not well resolved. In this study, we show that dipyridamole selectively blocks ER-to-Golgi movement of the SCAP-SREBP complex and that this is independent of its PDE inhibitory activity.

Cyclic AMP-hydrolyzing phosphodiesterase inhibitors potentiate statin-induced cancer cell death

Dipyridamole, an antiplatelet drug, has been shown to synergize with statins to induce cancer cell-specific apoptosis. However, given the polypharmacology of dipyridamole, the mechanism by which it potentiates statin-induced apoptosis remains unclear. Here, we applied a pharmacological approach to identify the activity of dipyridamole specific to its synergistic anticancer interaction with statins. We evaluated compounds that phenocopy the individual activities of dipyridamole and assessed whether they could potentiate statin-induced cell death. Notably, we identified that a phosphodiesterase (PDE) inhibitor, cilostazol, and other compounds that increase intracellular cyclic adenosine monophosphate (cAMP) levels potentiate statin-induced apoptosis in acute myeloid leukemia and multiple myeloma cells. Additionally, we demonstrated that both dipyridamole and cilostazol further inhibit statin-induced activation of sterol regulatory element-binding protein 2, a known modulator of statin sensitivity, in a cAMP-independent manner. Taken together, our data support that PDE inhibitors such as dipyridamole and cilostazol can potentiate statin-induced apoptosis via a dual mechanism. Given that several PDE inhibitors are clinically approved for various indications, they are immediately available for testing in combination with statins for the treatment of hematological malignancies.

Statins as Anticancer Agents in the Era of Precision Medicine

Statins are widely prescribed cholesterol-lowering drugs that inhibit HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the mevalonate metabolic pathway. Multiple lines of evidence indicate that certain cancers depend on the mevalonate pathway for growth and survival, and, therefore, are vulnerable to statin therapy. However, these immediately available, well-tolerated, and inexpensive drugs have yet to be successfully repurposed and integrated into cancer patient care. In this review, we highlight recent advances and outline important considerations for advancing statins to clinical trials in oncology.

Descriptive Proteome Analysis to Investigate Context-Dependent Treatment Responses to OXPHOS Inhibition in Colon Carcinoma Cells Grown as Monolayer and Multicellular Tumor Spheroids

We have previously identified selective upregulation of the mevalonate pathway genes upon inhibition of oxidative phosphorylation (OXPHOS) in quiescent cancer cells. Using mass spectrometry-based proteomics, we here investigated whether these responses are corroborated on the protein level and whether proteomics could yield unique insights into context-dependent biology. HCT116 colon carcinoma cells were cultured as monolayer cultures, proliferative multicellular tumor spheroids (P-MCTS), or quiescent (Q-MCTS) multicellular tumor spheroids and exposed to OXPHOS inhibitors: nitazoxanide, FCCP, oligomycin, and salinomycin or the HMG-CoA-reductase inhibitor simvastatin at two different doses for 6 and 24 h. Samples were processed using an in-depth bottom-up proteomics workflow resulting in a total of 9286 identified protein groups. Gene set enrichment analysis showed profound differences between the three cell systems and confirmed differential enrichment of hypoxia, OXPHOS, and cell cycle progression-related protein responses in P-MCTS and Q-MCTS. Treatment experiments showed that the observed drug-induced alterations in gene expression of metabolically challenged cells are not translated directly to the protein level, but the results reaffirmed OXPHOS as a selective vulnerability of quiescent cancer cells. This work provides rationale for the use of deep proteome profiling to identify context-dependent treatment responses and encourages further studies investigating metabolic processes that could be co-targeted together with OXPHOS to eradicate quiescent cancer cells.

The mevalonate pathway is an actionable vulnerability of t(4;14)-positive multiple myeloma

Multiple myeloma (MM) is a plasma cell malignancy that is often driven by chromosomal translocations. In particular, patients with t(4;14)-positive disease have worse prognosis compared to other MM subtypes. Herein, we demonstrated that t(4;14)-positive cells are highly dependent on the mevalonate (MVA) pathway for survival. Moreover, we showed that this metabolic vulnerability is immediately actionable, as inhibiting the MVA pathway with a statin preferentially induced apoptosis in t(4;14)-positive cells. In response to statin treatment, t(4;14)-positive cells activated the integrated stress response (ISR), which was augmented by co-treatment with bortezomib, a proteasome inhibitor. We identified that t(4;14)-positive cells depend on the MVA pathway for the synthesis of geranylgeranyl pyrophosphate (GGPP), as exogenous GGPP fully rescued statin-induced ISR activation and apoptosis. Inhibiting protein geranylgeranylation similarly induced the ISR in t(4;14)-positive cells, suggesting that this subtype of MM depends on GGPP, at least in part, for protein geranylgeranylation. Notably, fluvastatin treatment synergized with bortezomib to induce apoptosis in t(4;14)-positive cells and potentiated the anti-tumor activity of bortezomib in vivo. Our data implicate the t(4;14) translocation as a biomarker of statin sensitivity and warrant further clinical evaluation of a statin in combination with bortezomib for the treatment of t(4;14)-positive disease.

Mevalonate Pathway Enzyme HMGCS1 Contributes to Gastric Cancer Progression

The 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) is a potential regulatory node in the mevalonate pathway that is frequently dysregulated in tumors. This study found that HMGCS1 expression is upregulated in stomach adenocarcinoma samples of patients and tumorspheres of gastric cancer cells. HMGCS1 elevates the expression levels of the pluripotency genes Oct4 and SOX-2 and contributes to tumorsphere formation ability in gastric cancer cells. HMGCS1 also promotes in vitro cell growth and progression and the in vivo tumor growth and lung metastasis of gastric cancer cells. After blocking the mevalonate pathway by statin and dipyridamole, HMGCS1 exerts nonmetabolic functions in enhancing gastric cancer progression. Furthermore, the level and nuclear translocation of HMGCS1 in gastric cancer cells are induced by serum deprivation. HMGCS1 binds to and activates Oct4 and SOX-2 promoters. HMGCS1 also enhances the integrated stress response (ISR) and interacts with the endoplasmic reticulum (ER) stress transducer protein kinase RNA-like endoplasmic reticulum kinase (PERK). Our results reveal that HMGCS1 contributes to gastric cancer progression in both metabolic and nonmetabolic manners.

Cholesterol and beyond - The role of the mevalonate pathway in cancer biology

Cancer is a multifaceted global disease. Transformation of a normal to a malignant cell takes several steps, including somatic mutations, epigenetic alterations, metabolic reprogramming and loss of cell growth control. Recently, the mevalonate pathway has emerged as a crucial regulator of tumor biology and a potential therapeutic target. This pathway controls cholesterol production and posttranslational modifications of Rho-GTPases, both of which are linked to several key steps of tumor progression. Inhibitors of the mevalonate pathway induce pleiotropic antitumor-effects in several human malignancies, identifying the pathway as an attractive candidate for novel therapies. In this review, we will provide an overview about the role and regulation of the mevalonate pathway in certain aspects of cancer initiation and progression and its potential for therapeutic intervention in oncology.

Enhanced anticancer activity of combined treatment of imatinib and dipyridamole in solid Ehrlich carcinoma-bearing mice

The current study was designed to evaluate potential enhancement of the anticancer activity of imatinib mesylate (IM) with dipyridamole (DIP) and to investigate the underlying mechanisms of the combined therapy (IM/DIP) to reduce hepatotoxicity of IM in solid Ehrlich carcinoma (SEC)-bearing mice. SEC was induced in female albino mice as a model for experimentally induced breast cancer. Mice were randomly divided into seven groups (n = 10): SEC vehicle, IM₅₀ (50 mg/kg), IM₁₀₀ (100 mg/kg), DIP (35 mg/kg), a combination of IM₅₀/DIP and IM₁₀₀/DIP. On day 28th, mice were sacrificed and blood samples were collected for hematological studies. Biochemical determination of liver markers was evaluated. Glutamic oxaloacetic transaminase (SGOT), glutamic pyruvic transaminase (SGPT) and alkaline phosphatase (ALP) levels were assessed. In addition, MDR-1 gene expression and immunohistochemical staining of BAX and BCL-2 was done. Also, in vitro experiment for determination of IC50 of different treatments and combination index (CI) were assessed in both MCF-7 and HCT-116 cell lines. IM- and/or DIP-treated groups showed a significant reduction in tumor volume, weight, and serum levels of SGOT, SGPT, and AIP compared to vehicle group. In addition, reduction of VEGF, Ki67, and adenosine contents was also reported by treated groups. Also, IM/DIP combination showed lower IC50 than monotherapy. Combination index is less than 1 for IM/DIP combination in both cell lines. DIP as an adjuvant therapy potentiated the cytotoxic effect of IM, ameliorated its hepatic toxicity, and showed synergistic effect with IM in vitro cell lines. Furthermore, the resistance against IM therapy may be overcome by the use of DIP independent on mdr-1 gene expression.

RORγ is a targetable master regulator of cholesterol biosynthesis in a cancer subtype

Tumor subtype-specific metabolic reprogrammers could serve as targets of therapeutic intervention. Here we show that triple-negative breast cancer (TNBC) exhibits a hyper-activated cholesterol-biosynthesis program that is strongly linked to nuclear receptor RORγ, compared to estrogen receptor-positive breast cancer. Genetic and pharmacological inhibition of RORγ reduces tumor cholesterol content and synthesis rate while preserving host cholesterol homeostasis. We demonstrate that RORγ functions as an essential activator of the entire cholesterol-biosynthesis program, dominating SREBP2 via its binding to cholesterol-biosynthesis genes and its facilitation of the recruitment of SREBP2. RORγ inhibition disrupts its association with SREBP2 and reduces chromatin acetylation at cholesterol-biosynthesis gene loci. RORγ antagonists cause tumor regression in patient-derived xenografts and immune-intact models. Their combination with cholesterol-lowering statins elicits superior anti-tumor synergy selectively in TNBC. Together, our study uncovers a master regulator of the cholesterol-biosynthesis program and an attractive target for TNBC.

Regulation of the Notch-ATM-abl axis by geranylgeranyl diphosphate synthase inhibition

Notch proteins drive oncogenesis of many cancers, most prominently T-cell acute lymphoblastic leukemia (T-ALL). Because geranylgeranylated Rab proteins regulate Notch processing, we hypothesized that inhibition of geranylgeranyl diphosphate synthase (GGDPS) would impair Notch processing and reduce viability of T-ALL cells that express Notch. Here, we show that GGDPS inhibition reduces Notch1 expression and impairs the proliferation of T-ALL cells. GGDPS inhibition also reduces Rab7 membrane association and depletes Notch1 mRNA. GGDPS inhibition increases phosphorylation of histone H2A.X, and inhibitors of ataxia telangiectasia-mutated kinase (ATM) mitigate GGDPS inhibitor-induced apoptosis. GGDPS inhibition also influences c-abl activity downstream of caspases, and inhibitors of these enzymes prevent GGDPS inhibitor-induced apoptosis. Surprisingly, induction of apoptosis by GGDPS inhibition is reduced by co-treatment with γ-secretase inhibitors. While inhibitors of γ-secretase deplete one specific form of the Notch1 intracellular domain (NICD), they also increase Notch1 mRNA expression and increase alternate forms of Notch1 protein expression in cells treated with a GGDPS inhibitor. Furthermore, inhibitors of γ-secretase and ATM increase Notch1 mRNA stability independent of GGDPS inhibition. These results provide a model by which T-ALL cells use Notch1 to avoid DNA-damage-induced apoptosis, and can be overcome by inhibition of GGDPS through effects on Notch1 expression and its subsequent response.

Dipyridamole Enhances the Cytotoxicities of Trametinib against Colon Cancer Cells through Combined Targeting of HMGCS1 and MEK Pathway

Both the MAPK pathway and mevalonate (MVA) signaling pathway play an increasingly significant role in the carcinogenesis of colorectal carcinoma, whereas the cross-talk between these two pathways and its implication in targeted therapy remains unclear in colorectal carcinoma. Here, we identified that HMGCS1 (3-hydroxy-3-methylglutaryl-CoA synthase 1), the rate-limiting enzyme of the MVA pathway, is overexpressed in colon cancer tissues and positively regulates the cell proliferation, migration, and invasion of colon cancer cells. In addition, HMGCS1 could enhance the activity of pERK independent of the MVA pathway, and the suppression of HMGCS1 could completely reduce the EGF-induced proliferation of colon cancer cells. Furthermore, we found that trametinib, a MEK inhibitor, could only partially abolish the upregulation of HMGCS1 induced by EGF treatment, while combination with HMGCS1 knockdown could completely reverse the upregulation of HMGCS1 induced by EGF treatment and increase the sensitivity of colon cancer cells to trametinib. Finally, we combined trametinib and dipyridamole, a common clinically used drug that could suppress the activity of SREBF2 (sterol regulatory element-binding transcription factor 2), a transcription factor regulating HMGCS1 expression, and identified its synergistic effect in inhibiting the proliferation and survival of colon cancer cells in vitro as well as the in vivo tumorigenic potential of colon cancer cells. Together, the current data indicated that HMGCS1 may be a novel biomarker, and the combination of targeting HMGCS1 and MEK might be a promising therapeutic strategy for patients with colon cancer.

Epidemiologic Analysis Along the Mevalonate Pathway Reveals Improved Cancer Survival in Patients Who Receive Statins Alone and in Combination With Bisphosphonates

PURPOSE

Cohort studies report associations between statin use and improved survival in patients with cancer. We used pharmacoepidemiologic methods to evaluate the survival of patients with cancer who received statins alone or in ostensibly synergistic drug combinations.

MATERIALS AND METHODS

Patients with cancer who were diagnosed from 2010 to 2013 were identified in a large health care claims database. The rate of all-cause death up to 1 year after diagnosis was compared by Cox proportional hazard regression. Sensitivity analyses included age stratification, statin type and intensity, and comparison with or without bisphosphonates and dipyridamole.

RESULTS

Among 312,907 identified patients with cancer, treatment groups included statin users (n = 65,440), nonstatin users who received medications that block cholesterol absorption (n = 9,289), and nonusers (n = 226,007). Statin use before diagnosis was associated with improved overall survival compared with no treatment (hazard ratio [HR], 0.85; 95% CI, 0.80 to 0.91) and specifically in patients with leukemia, lung, or renal cancers. Nonstatin users had increased overall survival compared with no treatment (HR, 0.73; 95% CI, 0.62 to 0.85); when stratified, this difference held true only for pancreatic cancer and leukemia. No differences were observed between statin and nonstatin groups. Bisphosphonate use alone had no effect (n = 4,528), but patients who used both statins and bisphosphonates (n = 4,090) had increased survival compared with no treatment (HR, 0.60; 95% CI, 0.45 to 0.81). The effect of the combination of dipyridamole and statin use (n = 651) was not significant compared with no treatment.

CONCLUSION

This study suggests that the combination of statins with drugs that affect isoprenylation, such as bisphosphonates, improves survival in patients with cancer. Consideration of pathway-specific pharmacology allows for hypotheses testing with the pharmacoepidemiologic approach. Prospective evaluation of these findings warrants clinical investigation and preclinical mechanistic studies.

Screening a library of approved drugs reveals that prednisolone synergizes with pitavastatin to induce ovarian cancer cell death

The survival rate for patients with ovarian cancer has changed little in the past three decades since the introduction of platinum-based chemotherapy and new drugs are needed. Statins are drugs used for the treatment and prevention of cardiovascular diseases. Recent work from our laboratory has shown that pitavastatin has potential as a treatment for ovarian cancer if dietary geranylgeraniol is controlled. However, relatively high doses of statins are required to induce apoptosis in cancer cells, increasing the risk of myopathy, the most common adverse effect associated with statins. This makes it desirable to identify drugs which reduce the dose of pitavastatin necessary to treat cancer. A drug-repositioning strategy was employed to identify suitable candidates. Screening a custom library of 100 off-patent drugs for synergistic activity with pitavastatin identified prednisolone as the most prominent hit. Prednisolone potentiated the activity of pitavastatin in several assays measuring the growth, survival or apoptosis in several ovarian cancer cells lines. Prednisolone, alone or in some cases in combination with pitavastatin, reduced the expression of genes encoding enzymes in the mevalonate pathway, providing a mechanistic explanation for the synergy.

An actionable sterol-regulated feedback loop modulates statin sensitivity in prostate cancer

OBJECTIVE

The statin family of cholesterol-lowering drugs has been shown to induce tumor-specific apoptosis by inhibiting the rate-limiting enzyme of the mevalonate (MVA) pathway, HMG-CoA reductase (HMGCR). Accumulating evidence suggests that statin use may delay prostate cancer (PCa) progression in a subset of patients; however, the determinants of statin drug sensitivity in PCa remain unclear. Our goal was to identify molecular features of statin-sensitive PCa and opportunities to potentiate statin-induced PCa cell death.

METHODS

Deregulation of HMGCR expression in PCa was evaluated by immunohistochemistry. The response of PCa cell lines to fluvastatin-mediated HMGCR inhibition was assessed using cell viability and apoptosis assays. Activation of the sterol-regulated feedback loop of the MVA pathway, which was hypothesized to modulate statin sensitivity in PCa, was also evaluated. Inhibition of this statin-induced feedback loop was performed using RNA interference or small molecule inhibitors. The achievable levels of fluvastatin in mouse prostate tissue were measured using liquid chromatography-mass spectrometry.

RESULTS

High HMGCR expression in PCa was associated with poor prognosis; however, not all PCa cell lines underwent apoptosis in response to treatment with physiologically-achievable concentrations of fluvastatin. Rather, most cell lines initiated a feedback response mediated by sterol regulatory element-binding protein 2 (SREBP2), which led to the further upregulation of HMGCR and other lipid metabolism genes. Overcoming this feedback mechanism by knocking down or inhibiting SREBP2 potentiated fluvastatin-induced PCa cell death. Notably, we demonstrated that this feedback loop is pharmacologically-actionable, as the drug dipyridamole can be used to block fluvastatin-induced SREBP activation and augment apoptosis in statin-insensitive PCa cells.

CONCLUSION

Our study implicates statin-induced SREBP2 activation as a PCa vulnerability that can be exploited for therapeutic purposes using clinically-approved agents.

Induction of 3-hydroxy-3-methylglutaryl-CoA reductase mediates statin resistance in breast cancer cells

The mevalonate pathway has emerged as a promising target for several solid tumors. Statins are inhibitors of the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme of this pathway, and are commonly used to treat patients with hypercholesterolemia. Pleiotropic antitumor mechanisms of statins have been demonstrated for several human cancer types. However, cancer cells differ in their individual statin sensitivity and some cell lines have shown relative resistance. In this study we demonstrate, that the human breast cancer cell lines MDA-MB-231, MDA-MB-468, MCF-7, and T47D are differentially affected by statins. Whereas the vitality of MDA-MB-231 and MDA-MB-468 cells was reduced by up to 60% using atorvastatin, simvastatin, or rosuvastatin (p < 0.001), only marginal effects were seen in T47D and MCF-7 cells following exposure to statins. Statin treatment led to an upregulation of HMGCR mRNA and protein expression by up to sixfolds in the statin-resistant cells lines (p < 0.001), but no alterations of HMGCR were observed in the statin-sensitive MDA-MB-231 and MDA-MB-468 cells. The knockdown of HMGCR prior to statin treatment sensitized the resistant cell lines, reflected by a 70% reduction in vitality, increased apoptotic DNA fragmentation (sixfold) and by accumulation of the apoptosis marker cleaved poly-ADP ribose polymerase. Statins induced a cleavage of the sterol-regulatory element-binding protein (SREBP)-2, a transcriptional activator of the HMGCR, in T47D and MCF-7 cells. The inhibition of SREBP-2 activation by co-administration of dipyridamole sensitized MCF-7 and T47D cells for statins (loss of vitality by 80%; p < 0.001). Furthermore, assessment of a statin-resistant MDA-MB-231 clone, generated by long-term sublethal statin exposure, revealed a significant induction of HMGCR expression by up to 12-folds (p < 0.001). Knockdown of HMGCR restored statin sensitivity back to levels of the parental cells. In conclusion, these results indicate a resistance of cancer cells against statins, which is in part due to the induction of HMGCR.

CircHMGCS1 Promotes Hepatoblastoma Cell Proliferation by Regulating the IGF Signaling Pathway and Glutaminolysis

Circular RNAs (circRNAs), a novel class of endogenous RNAs, have been recently shown to participate in cellular development and several pathophysiological processes. The identification of dysregulated circRNAs and their function in cancer have attracted considerable attention. Nevertheless, the expression profile and role of circRNAs in human hepatoblastoma (HB) remain to be studied. In this report, we analyzed the expression prolife of circRNAs in HB tissues and identified circHMGCS1 (3-hydroxy-3-methylglutaryl-CoA synthase 1; hsa_circ_0072391) as a remarkably upregulated circRNA. Methods: The expression prolife of circRNAs in HB tissues were investigated through circRNA sequencing analyses. ISH and qRT-PCR assays were performed to measure the expression level of circHMGCS1. The effect of knocking down circHMGCS1 in HB cells in vitro and in vivo were evaluated by colony formation assay, flow cytometry, xenograft tumors assay and untargeted metabolomics assay. MRE analysis and dual luciferase assay were performed to explore the underlying molecular mechanisms. Results: HB patients with high circHMGCS1 expression have shorted overall survival. Knockdown of circHMGCS1 inhibits HB cells proliferation and induces apoptosis. CircHMGCS1 regulates IGF2 and IGF1R expression via sponging miR-503-5p, and affects the downstream PI3K-Akt signaling pathway to regulate HB cell proliferation and glutaminolysis. Conclusions: The circHMGCS1/miR-503-5p/IGF-PI3K-Akt axis regulates the proliferation, apoptosis and glutaminolysis of HB cells, implying that circHMGCS1 is a promising therapeutic target and prognostic marker for HB patients.

The poor design of clinical trials of statins in oncology may explain their failure - Lessons for drug repurposing

Statins are widely used to treat hypercholesterolaemia. However, by inhibiting the production of mevalonate, they also reduce the production of several isoprenoids that are necessary for the function of small GTPase oncogenes such as Ras. As such, statins offer an attractive way to inhibit an "undruggable" target, suggesting that they may be usefully repurposed to treat cancer. However, despite numerous studies, there is still no consensus whether statins are useful in the oncology arena. Numerous preclinical studies have provided evidence justifying the evaluation of statins in cancer patients. Some retrospective studies of patients taking statins to control cholesterol have identified a reduced risk of cancer mortality. However, prospective clinical studies have mostly not been successful. We believe that this has occurred because many of the prospective clinical trials have been poorly designed. Many of these trials have failed to take into account some or all of the factors identified in preclinical studies that are likely to be necessary for statins to be efficacious. We suggest an improved trial design which takes these factors into account. Importantly, we suggest that the design of clinical trials of drugs which are being considered for repurposing should not assume it is appropriate to use them in the same way as they are used in their original indication. Rather, such trials deserve to be informed by preclinical studies that are comparable to those for any novel drug.

Thyroid transcription factor 1 enhances cellular statin sensitivity via perturbing cholesterol metabolism

We have discovered an unexpected connection between a critical lung development and cancer gene termed thyroid transcription factor 1 (TTF-1 also known as NKX2-1) and cholesterol metabolism. Our published work implicates that TTF-1 positively regulates miR-33a which is known to repress ATP-binding cassette transporter 1 (ABCA1) and thus its cholesterol efflux activity. We set out to demonstrate that a higher TTF-1 expression would presumably inhibit cholesterol efflux and consequently raise intracellular cholesterol level. Surprisingly, raising TTF-1 expression actually lowers intracellular cholesterol level, which, we believe, is attributed to a direct transactivation of ABCA1 by TTF-1. Subsequently, we show that lung cancer cells primed with a TTF-1-driven decrease of cholesterol were more vulnerable to simvastatin, a frequently prescribed cholesterol biosynthesis inhibitor. In view of the fact that pathologists routinely interrogate human lung cancers for TTF-1 immunopositivity to guide diagnosis and the prevalent use of statins, TTF-1 should be further investigated as a putative biomarker of lung cancer vulnerability to statins.

Lipid metabolism reprogramming and its potential targets in cancer

Reprogramming of lipid metabolism is a newly recognized hallmark of malignancy. Increased lipid uptake, storage and lipogenesis occur in a variety of cancers and contribute to rapid tumor growth. Lipids constitute the basic structure of membranes and also function as signaling molecules and energy sources. Sterol regulatory element-binding proteins (SREBPs), a family of membrane-bound transcription factors in the endoplasmic reticulum, play a central role in the regulation of lipid metabolism. Recent studies have revealed that SREBPs are highly up-regulated in various cancers and promote tumor growth. SREBP cleavage-activating protein is a key transporter in the trafficking and activation of SREBPs as well as a critical glucose sensor, thus linking glucose metabolism and de novo lipid synthesis. Targeting altered lipid metabolic pathways has become a promising anti-cancer strategy. This review summarizes recent progress in our understanding of lipid metabolism regulation in malignancy, and highlights potential molecular targets and their inhibitors for cancer treatment.