Deciphering the signaling networks underlying simvastatin-induced apoptosis in human cancer cells: evidence for non-canonical activation of RhoA and Rac1 GTPases

Additional statin treatment enhances the efficacy of HER2 blockade and improves prognosis in Rac1-high/HER2-positive breast cancer

The prognosis of HER2-positive breast cancer (BC) has improved with the development of anti-HER2 therapies; however, the problem remains that there are still cases where anti-HER2 therapies do not respond well. We found that the expression of SREBF2, a master transcriptional factor in the mevalonate pathway, was correlated with ERBB2 (HER2) expression and a poor prognosis in HER2-positive BC. The target gene expressions of SREBF2 were associated with higher expression of ERBB2 in HER2-positive BC cells. Statins, anti-hypercholesterolemia drugs that inhibit the mevalonate pathway, enhanced the efficacy of HER2-targeting agents with inducing apoptosis in a geranylgeranylation-dependent manner. Mechanistically, statins specifically inhibited membrane localization of Rac1, a target protein of geranylgeranylation, and suppressed the activation of HER2 downstreams AKT and ERK pathways. Consistently, retrospective analysis showed a longer recurrence-free survival in Rac1-high/HER2-positive BC patients treated with HER2-targeting agents with statins than without statins. Our findings thus suggest that Rac1 expression could be used as a biomarker to stratify HER2-positive BC patients that could benefit from dual blockade, i.e., targeting HER2 with inhibition of geranylgeranylation of Rac1 using statins, thereby opening avenues for precision medicine in a new subset of Rac1-high/HER2-positive BC.

Simvastatin activates the spindle assembly checkpoint and causes abnormal cell division by modifying small GTPases

Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, which is a rate-limiting enzyme of the cholesterol synthesis pathway. It has been used clinically as a lipid-lowering agent to reduce low-density lipoprotein (LDL) cholesterol levels. In addition, antitumor activity has been demonstrated. Although simvastatin attenuates the prenylation of small GTPases, its effects on cell division in which small GTPases play an important role, have not been examined as a mechanism underlying its cytostatic effects. In this study, we determined its effect on cell division. Cell cycle synchronization experiments revealed a delay in mitotic progression in simvastatin-treated cells at concentrations lower than the IC50. Time-lapse imaging analysis indicated that the duration of mitosis, especially from mitotic entry to anaphase onset, was prolonged. In addition, simvastatin increased the number of cells exhibiting misoriented anaphase/telophase and bleb formation. Inhibition of the spindle assembly checkpoint (SAC) kinase Mps1 canceled the mitotic delay. Additionally, the number of cells exhibiting kinetochore localization of BubR1, an essential component of SAC, was increased, suggesting an involvement of SAC in the mitotic delay. Enhancement of F-actin formation and cell rounding at mitotic entry indicates that cortical actin dynamics were affected by simvastatin. The cholesterol removal agent methyl-β-cyclodextrin (MβCD) accelerated mitotic progression differently from simvastatin, suggesting that cholesterol loss from the plasma membrane is not involved in the mitotic delay. Of note, the small GTPase RhoA, which is a critical factor for cortical actin dynamics, exhibited upregulated expression. In addition, Rap1 was likely not geranylgeranylated. Our results demonstrate that simvastatin affects actin dynamics by modifying small GTPases, thereby activating the spindle assembly checkpoint and causing abnormal cell division.

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.

Correlations between preoperative statin treatment with short- and long-term survival following colorectal cancer surgery: a propensity score-matched national cohort study

INTRODUCTION

The pleiotropic effects of statins have attracted considerable attention in oncological treatment. Several preclinical and epidemiological studies have highlighted their potential anti-tumor properties in patients with colorectal cancer, although results have been conflicting. This study aimed to examine the association between statin exposure before colorectal cancer surgery with long and short-term survival outcomes.

METHODS

This retrospective propensity score-adjusted study was conducted on a Danish cohort of patients who underwent elective curative-intended surgery for stage I-III colorectal cancer in 2008-2020, using four national patient databases. The primary and secondary outcomes were overall, 90-day, and disease-free survival. Propensity scores were calculated using all available data to match patients with and without statin exposure in a 1:1 ratio.

RESULTS

Following propensity score matching, 7120 patients were included in the primary analysis. The median follow-up time was 5 years. A Cox proportional hazards model showed no statistically significant difference in overall survival between patients with or without statin exposure 365 days before surgery (HR 0.93, 95% CI 0.85-1.02) and no association with 90-day survival (OR 0.91, 95% CI 0.76-1.10). However, a subgroup analysis examining a 90-day exposure before surgery found a statistically significant association with increased overall survival (HR 0.85, 95% CI 0.77-0.93).

CONCLUSION

Although a subgroup of patients with a preoperative exposure time of 90 days showed statistically significant better overall survival, we found no statistically significant association between statin exposure 1 year before colorectal cancer surgery and overall survival.

Blockade of isoprenoids biosynthesis by simvastatin induces autophagy-mediated cell death via downstream c-Jun N-terminal kinase activation and cell cycle dysregulation in canine T-cell lymphoma cells

Statins are inhibitors of the mevalonic acid pathway that mediates cellular metabolism by producing cholesterol and isoprenoids and are widely used in treating hypercholesterolaemia in humans. Lipophilic statins, including simvastatin, induce death in various tumour cells. However, the cytotoxic mechanisms of statins in tumour cells remain largely unexplored. This study aimed to elucidate the cytotoxic mechanisms of simvastatin in canine lymphoma cells. Simvastatin induced cell death via c-Jun N-terminal kinase (JNK) activation and autophagy in canine T-cell lymphoma cell lines Ema and UL-1, but not in B-cell lines. Cell death was mediated by induction of caspase-dependent apoptosis in UL-1 cells, but not in Ema cells. Blockade of autophagy by lysosomal inhibitors attenuated simvastatin-induced JNK activation and cell death. Isoprenoids, including farnesyl pyrophosphate and geranylgeranyl pyrophosphate, attenuated simvastatin-induced autophagy, JNK activation, and cell death. In UL-1 cells, simvastatin treatment resulted in the cell cycle arrest at the G2/M phase, which was altered to G0/1 phase cell cycle arrest by treatment with lysosomal inhibitors. These findings demonstrate that depletion of isoprenoids by simvastatin induces autophagy-mediated cell death via downstream JNK activation and cell cycle dysregulation in canine T-cell lymphoma cells.

Geranylgeranyl isoprenoids and hepatic Rap1a regulate basal and statin-induced expression of PCSK9

LDL-C lowering is the main goal of atherosclerotic cardiovascular disease prevention, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is now a validated therapeutic strategy that lowers serum LDL-C and reduces coronary events. Ironically, the most widely used medicine to lower cholesterol, statins, has been shown to increase circulating PCSK9 levels, which limits their efficacy. Here, we show that geranylgeranyl isoprenoids and hepatic Rap1a regulate both basal and statin-induced expression of PCSK9 and contribute to LDL-C homeostasis. Rap1a prenylation and activity is inhibited upon statin treatment, and statin-mediated PCSK9 induction is dependent on geranylgeranyl synthesis and hepatic Rap1a. Accordingly, treatment of mice with a small-molecule activator of Rap1a lowered PCSK9 protein and plasma cholesterol and inhibited statin-mediated PCSK9 induction in hepatocytes. The mechanism involves inhibition of the downstream RhoA-ROCK pathway and regulation of PCSK9 at the post-transcriptional level. These data further identify Rap1a as a novel regulator of PCSK9 protein and show that blocking Rap1a prenylation through lowering geranylgeranyl levels contributes to statin-mediated induction of PCSK9.

Regulatory effects of curcumin on nitric oxide signaling in the cardiovascular system

The continuously rising prevalence of cardiovascular disease (CVD) globally substantially impacts the economic growth of developing countries. Indeed, one of the leading causes of death worldwide is unfavorable cardiovascular events. Reduced nitric oxide (NO) generation is the pathogenic foundation of endothelial dysfunction, which is regarded as the first stage in the development of a number of CVDs. Nitric oxide exerts an array of biological effects, including vasodilation, the suppression of vascular smooth muscle cell proliferation and the functional control of cardiac cells. Numerous treatment strategies aim to increase NO synthesis or upregulate downstream NO signaling pathways. The major component of Curcuma longa, curcumin, has long been utilized in traditional medicine to treat various illnesses, especially CVDs. Curcumin improves CV function as well as having important pleiotropic effects, such as anti-inflammatory and antioxidant, through its ability to increase the bioavailability of NO and to positively impact NO-related signaling pathways. In this review, we discuss the scientific literature relating to curcumin's positive effects on NO signaling and vascular endothelial function.

Exploring the Role of Plasma Lipids and Statin Interventions on Multiple Sclerosis Risk and Severity: A Mendelian Randomization Study

BACKGROUND AND OBJECTIVES

There has been considerable interest in statins because of their pleiotropic effects beyond their lipid-lowering properties. Many of these pleiotropic effects are predominantly ascribed to Rho small guanosine triphosphatases (Rho GTPases) proteins. We aimed to genetically investigate the role of lipids and statin interventions on multiple sclerosis (MS) risk and severity.

METHOD

We used two-sample Mendelian randomization (MR) to investigate (1) the causal role of genetically mimic both cholesterol-dependent (through low-density lipoprotein cholesterol (LDL-C) and cholesterol biosynthesis pathway) and cholesterol-independent (through Rho GTPases) effects of statins on MS risk and MS severity, (2) the causal link between lipids (high-density lipoprotein cholesterol [HDL-C] and triglycerides [TG]) levels and MS risk and severity, and (3) the reverse causation between lipid fractions and MS risk. We used summary statistics from the Global Lipids Genetics Consortium (GLGC), eQTLGen Consortium, and the International MS Genetics Consortium (IMSGC) for lipids, expression quantitative trait loci, and MS, respectively (GLGC: n = 188,577; eQTLGen: n = 31,684; IMSGC (MS risk): n = 41,505; IMSGC (MS severity): n = 7,069).

RESULTS

The results of MR using the inverse-variance weighted method show that genetically predicted RAC2, a member of cholesterol-independent pathway (OR 0.86 [95% CI 0.78-0.95], p-value 3.80E-03), is implicated causally in reducing MS risk. We found no evidence for the causal role of LDL-C and the member of cholesterol biosynthesis pathway on MS risk. The MR results also show that lifelong higher HDL-C (OR 1.14 [95% CI 1.04-1.26], p-value 7.94E-03) increases MS risk but TG was not. Furthermore, we found no evidence for the causal role of lipids and genetically mimicked statins on MS severity. There is no evidence of reverse causation between MS risk and lipids.

DISCUSSION

Evidence from this study suggests that RAC2 is a genetic modifier of MS risk. Because RAC2 has been reported to mediate some of the pleiotropic effects of statins, we suggest that statins may reduce MS risk through a cholesterol-independent pathway (that is, RAC2-related mechanism(s)). MR analyses also support a causal effect of HDL-C on MS risk.

Geranylgeranyl Isoprenoids and Hepatic Rap1a Regulate Basal and Statin-Induced Expression of PCSK9

Low-density lipoprotein cholesterol (LDL-C) lowering is the main goal of atherosclerotic cardiovascular disease prevention, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is now a validated therapeutic strategy that lowers serum LDL-C and reduces coronary events. Ironically, the most widely used medicine to lower cholesterol, statins, has been shown to increase circulating PCSK9 levels, which limits their efficacy. Here, we show that geranylgeranyl isoprenoids and hepatic Rap1a regulate both basal and statin induced expression of PCSK9 and contribute to LDL-C homeostasis. Rap1a prenylation and activity is inhibited upon statin treatment, and statin mediated PCSK9 induction is dependent on geranylgeranyl synthesis and hepatic Rap1a. Accordingly, treatment of mice with a small molecule activator of Rap1a lowered PCSK9 protein and plasma cholesterol and inhibited statin mediated PCSK9 induction in hepatocytes. The mechanism involves inhibition of the downstream RhoA-ROCK pathway and regulation of PCSK9 at the post transcriptional level. These data further identify Rap1a as a novel regulator of PCSK9 protein and show that blocking Rap1a prenylation through lowering geranylgeranyl levels contributes to statin-mediated induction of PCSK9.

Repositioning of HMG-CoA Reductase Inhibitors as Adjuvants in the Modulation of Efflux Pump-Mediated Bacterial and Tumor Resistance

Efflux pump (EP)-mediated multidrug resistance (MDR) seems ubiquitous in bacterial infections and neoplastic diseases. The diversity and lack of specificity of these efflux mechanisms raise a great obstacle in developing drugs that modulate efflux pumps. Since developing novel chemotherapeutic drugs requires large investments, drug repurposing offers a new approach that can provide alternatives as adjuvants in treating resistant microbial infections and progressive cancerous diseases. Hydroxy-methyl-glutaryl coenzyme-A (HMG-CoA) reductase inhibitors, also known as statins, are promising agents in this respect. Originally, statins were used in the therapy of dyslipidemia and for the prevention of cardiovascular diseases; however, extensive research has recently been performed to elucidate the functions of statins in bacterial infections and cancers. The mevalonate pathway is essential in the posttranslational modification of proteins related to vital eukaryotic cell functions. In this article, a comparative review is given about the possible role of HMG-CoA reductase inhibitors in managing diseases of bacterial and neoplastic origin. Molecular research and clinical studies have proven the justification of statins in this field. Further well-designed clinical trials are urged to clarify the significance of the contribution of statins to the lower risk of disease progression in bacterial infections and cancerous diseases.

Investigating potential anti-proliferative activity of different statins against five cancer cell lines

Statins have been reported to have potential anti-proliferative effects through an unknown mechanism. This study aims to investigate the anti-proliferative activities of five statins, including simvastatin, rosuvastatin, fluvastatin, atorvastatin, and pravastatin, against five different cancer cell lines; cervical epithelial carcinoma DoTc2 4510, malignant melanoma A-375, muscle Ewing's sarcoma A-673, hepatocellular carcinoma HUH-7, as well as breast cancer cells MCF-7. At 100 µM, simvastatin and atorvastatin significantly inhibited 70% of cellular proliferation. At the same concentration, rosuvastatin and fluvastatin showed about 50% of inhibition only in A-375 and A-673 cancer cells in a time- and dose-dependent manner. Of all the statin drugs used, pravastatin had the least inhibitory effect on all the cancer cell lines. Western Blot analysis showed a decrease in mTOR level, and the expression of p53 tumour suppression and BCL-2 proteins was relatively elevated compared to the untreated cells. Simvastatin and atorvastatin may inhibit cellular proliferation via BCL-2/p53, Bax/Bak, and PI3K/Akt/mTOR signalling pathways. This is the first research to evaluate the anti-cancer effects of simvastatin, rosuvastatin, fluvastatin, atorvastatin, and pravastatin against five different cell lines from distinct origins and provided a relevant comparison of their efficacies for their anti-proliferative activity.

Effect of Statins on Lung Cancer Molecular Pathways: A Possible Therapeutic Role

Lung cancer is a common neoplasm, usually treated through chemotherapy, radiotherapy and/or surgery. Both clinical and experimental studies on cancer cells suggest that some drugs (e.g., statins) have the potential to improve the prognosis of cancer. In fact, statins blocking the enzyme "hydroxy-3-methylglutaryl-coenzyme A reductase" exert pleiotropic effects on different genes involved in the pathogenesis of lung cancer. In this narrative review, we presented the experimental and clinical studies that evaluated the effects of statins on lung cancer and described data on the effectiveness and safety of these compounds. We also evaluated gender differences in the treatment of lung cancer to understand the possibility of personalized therapy based on the modulation of the mevalonate pathway. In conclusion, according to the literature data, statins exert multiple effects on lung cancer cells, even if the evidence for their use in clinical practice is lacking.

Underappreciated roles for Rho GDP dissociation inhibitors (RhoGDIs) in cell function: Lessons learned from the pancreatic islet β-cell

Rho subfamily of G proteins (e.g., Rac1) have been implicated in glucose-stimulated insulin secretion from the pancreatic β-cell. Interestingly, metabolic stress (e.g., chronic exposure to high glucose) results in sustained activation of Rac1 leading to increased oxidative stress, impaired insulin secretion and β-cell dysfunction. Activation-deactivation of Rho G proteins is mediated by three classes of regulatory proteins, namely the guanine nucleotide exchange factors (GEFs), which facilitate the conversion of inactive G proteins to their active conformations; the GTPase-activating proteins (GAPs), which convert the active G proteins to their inactive forms); and the GDP-dissociation inhibitors (GDIs), which prevent the dissociation of GDP from G proteins. Contrary to a large number of GEFs (82 members) and GAPs (69 members), only three members of RhoGDIs (RhoGDIα, RhoGDIβ and RhoGDIγ) are expressed in mammalian cells.Even though relatively smaller in number, the GDIs appear to play essential roles in G protein function (e.g., subcellular targeting) for effector activation and cell regulation. Emerging evidence also suggests that the GDIs are functionally regulated via post-translational modification (e.g., phosphorylation) and by lipid second messengers, lipid kinases and lipid phosphatases. We highlight the underappreciated regulatory roles of RhoGDI-Rho G protein signalome in islet β-cell function in health and metabolic stress. Potential knowledge gaps in the field, and directions for future research for the identification of novel therapeutic targets to loss of functional β-cell mass under the duress of metabolic stress are highlighted.

Statins: a repurposed drug to fight cancer

As competitive HMG-CoA reductase (HMGCR) inhibitors, statins not only reduce cholesterol and improve cardiovascular risk, but also exhibit pleiotropic effects that are independent of their lipid-lowering effects. Among them, the anti-cancer properties of statins have attracted much attention and indicated the potential of statins as repurposed drugs for the treatment of cancer. A large number of clinical and epidemiological studies have described the anticancer properties of statins, but the evidence for anticancer effectiveness of statins is inconsistent. It may be that certain molecular subtypes of cancer are more vulnerable to statin therapy than others. Whether statins have clinical anticancer effects is still an active area of research. Statins appear to enhance the efficacy and address the shortcomings associated with conventional cancer treatments, suggesting that statins should be considered in the context of combined therapies for cancer. Here, we present a comprehensive review of the potential of statins in anti-cancer treatments. We discuss the current understanding of the mechanisms underlying the anti-cancer properties of statins and their effects on different malignancies. We also provide recommendations for the design of future well-designed clinical trials of the anti-cancer efficacy of statins.

Role of Small GTPase RhoA in DNA Damage Response

Accumulating evidence has suggested a role of the small GTPase Ras homolog gene family member A (RhoA) in DNA damage response (DDR) in addition to its traditional function of regulating cell morphology. In DDR, 2 key components of DNA repair, ataxia telangiectasia-mutated (ATM) and flap structure-specific endonuclease 1 (FEN1), along with intracellular reactive oxygen species (ROS) have been shown to regulate RhoA activation. In addition, Rho-specific guanine exchange factors (GEFs), neuroepithelial transforming gene 1 (Net1) and epithelial cell transforming sequence 2 (Ect2), have specific functions in DDR, and they also participate in Ras-related C3 botulinum toxin substrate 1 (Rac1)/RhoA interaction, a process which is largely unappreciated yet possibly of significance in DDR. Downstream of RhoA, current evidence has highlighted its role in mediating cell cycle arrest, which is an important step in DNA repair. Unraveling the mechanism by which RhoA modulates DDR may provide more insight into DDR itself and may aid in the future development of cancer therapies.

Comparative Study of Lipophilic Statin Activity in 2D and 3D in vitro Models of Human Breast Cancer Cell Lines MDA-MB-231 and MCF-7

Introduction

Statins are a type of drugs that are used to lower cholesterol level in blood. Since the early 1990s, it has been known that statins could be beneficial in cancer therapy. However, data remain controversial, especially regarding estrogen receptors status. Despite many studies in breast cancer models in vitro, the correlations of effects of separate statins in various model systems remain unclear.

Aim

Our aim was to evaluate the anticancer activity of lovastatin, mevastatin, pitavastatin and simvastatin on different subtypes of human breast cancer (MDA-MB-231 and MCF-7 cell lines) in spatially different 2D and 3D cultures in vitro.

Materials and Methods

Cell viability was tested using MTT assay. Effect of statins on cell colony formation was evaluated by calculating breast cancer cell colony area and number. The effect on cell migration was estimated by “wound healing” assay. The activity of compounds in 3D cultures was evaluated by measuring the spheroid size changes during incubation.

Results

Among the tested statins, pitavastatin had the greatest effect on the viability of breast cancer MDA-MB-231 and MCF-7 cell lines. The mevastatin and pitavastatin mostly decreased the MDA-MB-231 and MCF-7 cell colony formation. All statins at 90% of their estimated effective concentration (EC₅₀) and simvastatin at 10% of its EC₅₀ concentration suppressed the MCF-7 cells migration in “wound healing” assay. Only higher concentrations of mevastatin and pitavastatin slowed down the MDA-MB-231 cell migration. Statins showed different activity on 3D cell cultures growth. Lovastatin and simvastatin delayed the growth of MDA-MB-231 cell spheroids, while mevastatin and pitavastatin reduced the growth of MCF-7 spheroids.

Conclusion

Statins possess different anticancer activity in human breast cancer MDA-MB-231 and MCF-7 cell cultures. Pitavastatin and simvastatin showed the highest activity in most tested assays, especially against MCF-7 cell line.

Pleiotropic effects of statins: A focus on cancer

The statin drugs ('statins') potently inhibit hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase by competitively blocking the active site of the enzyme. Statins decrease de novo cholesterol biosynthesis and thereby reduce plasma cholesterol levels. Statins exhibit "pleiotropic" properties that are independent of their lipid-lowering effects. For example, preclinical evidence suggests that statins inhibit tumor growth and induce apoptosis in specific cancer cell types. Furthermore, statins show chemo-sensitizing effects by impairing Ras family GTPase signaling. However, whether statins have clinically meaningful anti-cancer effects remains an area of active investigation. Both preclinical and clinical studies on the potential mechanisms of action of statins in several cancers have been reviewed in the literature. Considering the contradictory data on their efficacy, we present an up-to-date summary of the pleiotropic effects of statins in cancer therapy and review their impact on different malignancies. We also discuss the synergistic anti-cancer effects of statins when combined with other more conventional anti-cancer drugs to highlight areas of potential therapeutic development.

Hepatocellular Carcinoma and Statins

HMG-CoA reductase inhibitors (known as statins) are commonly prescribed worldwide for the management of coronary heart disease and the underlying dyslipidemia. This class of drugs has been shown to infer a significant decrease in the risk of cardiovascular morbidity and mortality. Only recently though have the beneficial effects of statins in other diseases such as non-alcoholic steatohepatitis been highlighted. Importantly, also, multiple studies have revealed that statin use was associated with lower cancer-associated mortality across multiple types of cancers. This work aims to review those studies with a particular focus on liver cancer. We also provide a review of the proposed mechanisms of action describing how statins can induce chemo-preventive and antitumor effects.

Effect of simvastatin on cell proliferation and Ras activation in canine tumour cells

Statins are inhibitors of the mevalonate cascade that is responsible for cholesterol biosynthesis and the formation of intermediate metabolites, farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) used in the prenylation of proteins. Although statins are widely used in the treatment of hypercholesterolemia, recent studies suggest that they also inhibit proliferation of tumour cells by reducing prenylation of small GTP-binding proteins, such as, Ras. This study aimed to evaluate the effect of simvastatin on cell proliferation and Ras activation in various canine tumour cell lines, including hemangiosarcoma (HSA), melanoma, and lymphoma cell lines. Simvastatin inhibited cell proliferation of all cell lines tested in a concentration- and time-dependent manner, but the susceptibilities were different amongst the cell lines. Simvastatin induced apoptotic cell death via activation of caspase-3 and cell cycle arrest. The cytotoxic effects of simvastatin were attenuated by GGPP and FPP. Simvastatin decreased the amount of prenylated Ras and GTP-bound Ras in HSA and melanoma cell lines, but not in lymphoma cell lines. These results indicate that simvastatin induces cytotoxic effects through the depletion of GGPP and FPP in a variety of canine tumour cells, whereas multiple mechanisms are involved in the effects. Further study is required to elucidate the underlying mechanisms of simvastatin-induced cytotoxic effects in a variety of canine tumour cells.

Receipt of Statins Is Associated With Lower Risk of Multiple Myeloma: Systematic Review and Meta-analysis

BACKGROUND

Studies on receipt of statins and risk of multiple myeloma (MM) yielded conflicting results. This systematic review and meta-analysis was conducted in order to comprehensively investigate the relationship between receipt of statins and risk of MM.

PATIENTS AND METHODS

Potentially eligible studies that compared the risk of MM between statin recipients and those who did not receive statins were identified from Medline and Embase databases from inception to August 2019 using a search strategy that comprised terms for "statin" and "multiple myeloma." To be eligible, cohort studies must have recruited 2 groups of participants, statin recipients and nonrecipients, and followed their participants for incident MM. Eligible case-control studies must have recruited cases of MM and controls without MM, and must have explored the history of receipt of statins. Relative risk, hazard risk ratio, standardized incidence ratio, or odds ratio (OR) of this association must be reported. Relative risk and standard error from each study were extracted and combined using random-effect generic inverse variance. Relative risk of cohort study was used as an estimate for OR to calculate the pooled effect estimate along with the OR of the case-control studies.

RESULTS

A total of 1744 articles were identified using the search strategy, and 10 studies were included in the meta-analysis. The odds of MM were significantly lower among statin recipients than nonrecipients, with a pooled OR of 0.80 (95% confidence interval, 0.68-0.93; I² 72%). The funnel plot was relatively symmetrical and did not suggest publication bias.

CONCLUSION

Receipt of statins is associated with a significant 20% reduction in the odds of MM.

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.

Cell adhesion to collagen promotes leukemia resistance to doxorubicin by reducing DNA damage through the inhibition of Rac1 activation

Chemoresistance is a major hurdle in anti-cancer therapy. Growing evidence indicates that integrin-mediated cell adhesion to extracellular matrix plays a major role in chemoresistance. However, the underlying mechanisms are not fully understood. We have previously shown that the collagen-binding integrin α2β1 promoted doxorubicin resistance in acute T cell lymphoblastic leukemia (T-ALL). In this study, we found that acute myeloid leukemia (AML) cell lines also express α2β1 integrin and collagen promoted their chemoresistance as well. Furthermore, we found that high levels of α2 integrin correlate with worse overall survival in AML. Our results showed that doxorubicin-induced apoptosis in leukemic cells is associated with activation of Ras-related C3 botulinum toxin substrate 1 (Rac1) and that collagen inhibited this pathway. The protective effect of collagen is associated with the inhibition of Rac1-induced DNA damage as evaluated by the comet assay and the phosphorylated levels of histone H2AX (γ-H2AX). Together these results show that by inhibiting pro-apoptotic Rac1, α2β1 integrin can be a major pathway protecting leukemic cells from genotoxic agents and may thus represent an important therapeutic target in anti-cancer treatment.

ADP-dependent glucokinase regulates energy metabolism via ER-localized glucose sensing

Modulation of energy metabolism to a highly glycolytic phenotype, i.e. Warburg effect, is a common phenotype of cancer and activated immune cells allowing increased biomass-production for proliferation and cell division. Endoplasmic reticulum (ER)-localized ADP-dependent glucokinase (ADPGK) has been shown to play a critical role in T cell receptor activation-induced remodeling of energy metabolism, however the underlying mechanisms remain unclear. Therefore, we established and characterized in vitro and in vivo models for ADPGK-deficiency using Jurkat T cells and zebrafish. Upon activation, ADPGK knockout Jurkat T cells displayed increased cell death and ER stress. The increase in cell death resulted from a metabolic catastrophe and knockout cells displayed severely disturbed energy metabolism hindering induction of Warburg phenotype. ADPGK knockdown in zebrafish embryos led to short, dorsalized body axis induced by elevated apoptosis. ADPGK hypomorphic zebrafish further displayed dysfunctional glucose metabolism. In both model systems loss of ADPGK function led to defective N- and O-glycosylation. Overall, our data illustrate that ADPGK is part of a glucose sensing system in the ER modulating metabolism via regulation of N- and O-glycosylation.

Targeting the Mevalonate Pathway to Overcome Acquired Anti-HER2 Treatment Resistance in Breast Cancer

Despite effective strategies, resistance in HER2⁺ breast cancer remains a challenge. While the mevalonate pathway (MVA) is suggested to promote cell growth and survival, including in HER2⁺ models, its potential role in resistance to HER2-targeted therapy is unknown. Parental HER2⁺ breast cancer cells and their lapatinib-resistant and lapatinib + trastuzumab-resistant derivatives were used for this study. MVA activity was found to be increased in lapatinib-resistant and lapatinib + trastuzumab-resistant cells. Specific blockade of this pathway with lipophilic but not hydrophilic statins and with the N-bisphosphonate zoledronic acid led to apoptosis and substantial growth inhibition of R cells. Inhibition was rescued by mevalonate or the intermediate metabolites farnesyl pyrophosphate or geranylgeranyl pyrophosphate, but not cholesterol. Activated Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) and mTORC1 signaling, and their downstream target gene product Survivin, were inhibited by MVA blockade, especially in the lapatinib-resistant/lapatinib + trastuzumab-resistant models. Overexpression of constitutively active YAP rescued Survivin and phosphorylated-S6 levels, despite blockade of the MVA. These results suggest that the MVA provides alternative signaling leading to cell survival and resistance by activating YAP/TAZ-mTORC1-Survivin signaling when HER2 is blocked, suggesting novel therapeutic targets. MVA inhibitors including lipophilic statins and N-bisphosphonates may circumvent resistance to anti-HER2 therapy warranting further clinical investigation. IMPLICATIONS: The MVA was found to constitute an escape mechanism of survival and growth in HER2⁺ breast cancer models resistant to anti-HER2 therapies. MVA inhibitors such as simvastatin and zoledronic acid are potential therapeutic agents to resensitize the tumors that depend on the MVA to progress on anti-HER2 therapies.

Combination simvastatin and metformin synergistically inhibits endometrial cancer cell growth

OBJECTIVE

Recent data show that simvastatin (SIM) and metformin (MET) have anti-proliferative effects in endometrial cancer cells. The combination (MET+SIM) inhibits tumor growth and metastasis in prostate cancer cells which possess similar molecular alterations to many early endometrial cancers. We tested the hypothesis that the anti-proliferative effects of MET+SIM in endometrial cancer cells would be greater than the effects of each agent alone.

METHODS

RL95-2, HEC1B, and Ishikawa endometrial cancer cell lines were treated with MET and/or SIM. Growth inhibition was measured by MTS cell proliferation assays. Apoptosis was evaluated by caspase-3, Annexin V, and TUNEL assays and by apoptosis markers (BAX, Bcl-2, Bim) using western blot. Bim was silenced using Bim siRNA to confirm this apoptotic pathway. Treatment effects on the mTOR pathway were investigated by western blot using antibodies to phosphorylated (phospho)-AMPK and phospho-S6.

RESULTS

MET+SIM synergistically inhibited growth in all three cell lines. The combination induced apoptosis as measured by TUNEL, Annexin V, and caspase-3 assays. Bim siRNA transfection abrogated this effect-silencing Bim in MET+SIM-treated RL95-2 cells rescued cell viability in MTS assays and reduced caspase-3 activity compared with control siRNA-transfected cells. Combination treatment upregulated phosphorylated AMPK and downregulated downstream phosphorylated S6, suggesting mTOR inhibition as a mechanism for these anti-proliferative effects.

CONCLUSIONS

MET+SIM treatment synergistically inhibits endometrial cancer cell viability. This may be mediated by apoptosis and mTOR pathway inhibition. Our results provide preclinical evidence that the combination of these well-tolerated drugs may warrant further clinical investigation for endometrial cancer treatment.

Biocatalyzed Synthesis of Statins: A Sustainable Strategy for the Preparation of Valuable Drugs

Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are the largest selling class of drugs prescribed for the pharmacological treatment of hypercholesterolemia and dyslipidaemia. Statins also possess other therapeutic effects, called pleiotropic, because the blockade of the conversion of HMG-CoA to (R)-mevalonate produces a concomitant inhibition of the biosynthesis of numerous isoprenoid metabolites (e.g., geranylgeranyl pyrophosphate (GGPP) or farnesyl pyrophosphate (FPP)). Thus, the prenylation of several cell signalling proteins (small GTPase family members: Ras, Rac, and Rho) is hampered, so that these molecular switches, controlling multiple pathways and cell functions (maintenance of cell shape, motility, factor secretion, differentiation, and proliferation) are regulated, leading to beneficial effects in cardiovascular health, regulation of the immune system, anti-inflammatory and immunosuppressive properties, prevention and treatment of sepsis, treatment of autoimmune diseases, osteoporosis, kidney and neurological disorders, or even in cancer therapy. Thus, there is a growing interest in developing more sustainable protocols for preparation of statins, and the introduction of biocatalyzed steps into the synthetic pathways is highly advantageous—synthetic routes are conducted under mild reaction conditions, at ambient temperature, and can use water as a reaction medium in many cases. Furthermore, their high selectivity avoids the need for functional group activation and protection/deprotection steps usually required in traditional organic synthesis. Therefore, biocatalysis provides shorter processes, produces less waste, and reduces manufacturing costs and environmental impact. In this review, we will comment on the pleiotropic effects of statins and will illustrate some biotransformations nowadays implemented for statin synthesis.

Simvastatin reduces the carcinogenic effect of 3-methylcholanthrene in renal epithelial cells through histone deacetylase 1 inhibition and RhoA reactivation

The therapeutic effects of simvastatin for renal cell carcinoma (RCC) are controversial. In this study, the effects of simvastatin on the carcinogenic properties of 3-methylcholanthrene (3MC; an aryl-hydrocarbon receptor [AhR] agonist) in human renal epithelial cells (hRECs) were investigated. We exposed in vitro and in vivo models to 3MC to induce RCC onset. 3MC upregulated the epithelial-mesenchymal transition (EMT) and tumor biomarkers; the models exhibited the reciprocal expression of histone deacetylase 1 (HDAC1) and RhoA, namely increased HDAC1 and decreased RhoA expression, through hypoxia-inducible-factor (HIF)- and AhR-dependent mechanisms. In addition to inducing EMT biomarkers, 3MC decreased von Hippel-Lindau protein levels (a risk factor for RCC) and increased CD44 expression in hRECs, which were reversed by digoxin (a HIF inhibitor) and HDAC inhibitors (suberoylanilide hydroxamic acid and trichostatin A [TSA]). Simvastatin abolished the detrimental effects of 3MC by reducing HDAC1 expression, with resulting RhoA upregulation, and reactivating RhoA in vitro and in vivo. Notably, the protective effects of simvastatin were negated by an HDAC activator (ITSA) through TSA suppression. The crucial role of RhoA in RCC carcinogenesis was verified by the overexpression of constitutively active RhoA. Collectively, these results demonstrate that simvastatin restores RhoA function through HDAC1 inhibition; therefore, simvastatin might serve as adjunct therapy for RCC induced by 3MC.

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison

SIGNIFICANCE

There is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.

CRITICAL ISSUES

Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.

FUTURE DIRECTIONS

Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins. Antioxid. Redox Signal.

Statins: a new approach to combat temozolomide chemoresistance in glioblastoma

Patients with glioblastoma multiforme (GBM) have an average life expectancy of approximately 15 months. Recently, statins have emerged as a potential adjuvant cancer therapy due to their ability to inhibit cell proliferation and induce apoptosis in many types of cancer. The exact mechanisms that mediate the inhibitory actions of statins in cancer cells are largely unknown. The purpose of this proceeding paper is to discuss some of the known anticancer effects of statins, while focusing on GBM therapy that includes adjunct therapy of statins with chemotherapeutic agents.

Effect of survivin downregulation by simvastatin on the growth and invasion of salivary adenoid cystic carcinoma

Simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, is been used in the clinic due to its pleiotropic effects, such as breast cancer, prostate cancer, pancreatic cancer. Simvastatin has recently been demonstrated to serve a potential role in the prophylaxis and therapeutics of a number of human cancers. The majority of reports concerning simvastatin treatment in the majority of human cancers have demonstrated that survivin is significantly decreased as a result and has been implicated in tumorigenesis. However, only a limited number of studies have investigated the use of simvastatin for the treatment of salivary gland adenoid cystic carcinoma (SACC). Therefore, this agent is a candidate for further investigation. The aim of the present study was to investigate the effects of simvastatin on the proliferation, invasion and apoptosis of the human salivary adenoid cystic carcinoma cell line, SACC-83, as well as survivin expression in the cells. The Cell Counting kit-8 assay results revealed that simvastatin inhibited the proliferation of SACC-83 cells in a dose-dependent (10 to 50 µM) and time-dependent (24 to 48 h) manner when compared with the untreated cells. Flow cytometry analysis indicated that simvastatin increased the percentage of cells in early and late apoptosis. Invasion assays revealed that simvastatin treatment inhibited the invasiveness of SACC-83 cells in a dose-dependent manner. In addition, simvastatin downregulated survivin expression in SACC-83 cells. In conclusion, simvastatin significantly inhibited the proliferation and invasion of SACC-83 cells, induced apoptosis, and reduced the expression of survivin, which suggests that simvastatin may be a novel target for SACC therapy.

Mevalonate pathway blockage enhances the efficacy of mTOR inhibitors with the activation of retinoblastoma protein in renal cell carcinoma

Renal cell carcinoma (RCC) is the most common malignancy of kidney and remains largely intractable once it recurs after resection. mTOR inhibitors have been one of the mainstays used against recurrent RCC; however, there has been a major problem of the resistance to mTOR inhibitors, and thus new combination treatments with mTOR inhibitors are required. We here retrospectively showed that regular use of antilipidemic drug statins could provide a longer progression free survival (PFS) in RCC patients prescribed with an mTOR inhibitor everolimus than without statins (median PFS, 7.5 months vs. 3.2 months, respectively; hazard ratio, 0.52; 95% CI, 0.22-1.11). In order to give a rationale for this finding, we used RCC cell lines and showed the combinatorial effects of an mTOR inhibitor with statins induced a robust activation of retinoblastoma protein, whose mechanisms were involved in statins-mediated hindrance of KRAS or Rac1 protein prenylation. Finally, statins treatment also enhanced the efficacy of an mTOR inhibitor in RCC xenograft models. Thus, we provide molecular and (pre)clinical data showing that statins use could be a drug repositioning for RCC patients to enhance the efficacy of mTOR inhibitors.

Simvastatin exerts anticancer effects in osteosarcoma cell lines via geranylgeranylation and c-Jun activation

Osteosarcoma is the leading primary bone cancer in young adults and exhibits high chemoresistance rates. Therefore, characterization of both alternative treatment options and the underlying mechanisms is essential. Simvastatin, a cholesterol-lowering drug, has among its pleiotropic effects anticancer potential. Characterizing this potential and the underlying mechanisms in osteosarcoma is the subject of the present study. Human osteosarcoma cells (SaOS-2 and U2OS) were treated with simvastatin (4-66 µM) for 48 or 72 h. The effects of downstream substrate mevalonate (MA) or substrates for isoprenylation farnesyl pyrophosphate (FPP) and geranylgeranyl-pyrophosphate (GGPP) were evaluated using add-back experiments. Tumour growth using MTT assay, apoptosis, cell cycle and signalling cascades involved in simvastatin-induced manipulation were analysed. The results revealed that simvastatin dose-dependently inhibited cell growth. Simvastatin significantly induced apoptosis, increased the Bax/Bcl-2 ratio, and cleavage of caspase-3 and PARP protein. Simvastatin impaired cell cycle progression as shown by significantly increased percentages of cells in the G0/G1 phase and lower percentages of cells in the S phase. Gene expression levels of cell cycle-regulating genes (TP53, CDKN1A and CDK1) were markedly altered. These effects were not completely abolished by FPP, but were reversed by MA and GGPP. JNK and c-Jun phosphorylation was enhanced after simvastatin treatment, while those were abolished when either MA or GGPP were added. In conclusion, simvastatin acts primarily by reducing prenylation to induce apoptosis and reduce osteosarcoma cell growth. Particularly enhanced activation of c-Jun seems to play a pivotal role in osteosarcoma cell death.

Cholesterol Depletion by TASIN-1 Induces Apoptotic Cell Death through the ER Stress/ROS/JNK Signaling in Colon Cancer Cells

Truncated APC selective inhibitor-1 (TASIN-1) is a recently identified small molecule that selectively kills colorectal cancer cells that express truncated adenomatous polyposis coli (APC) by reducing cellular cholesterol levels. However, the downstream mechanism responsible for its cytotoxicity is not well understood. In this study, we show that TASIN-1 leads to apoptotic cell death via inducing ER stress-dependent JNK activation in human truncated APC colon cancer cells, accompanied by production of reactive oxygen species (ROS). In addition, TASIN-1 inhibits AKT activity through a cholesterol-dependent manner. Human colon tumor xenografts in immunodeficient mice also show the same TASIN-1 induced molecular mechanisms of tumor cell death as observed in vitro Taken together, cholesterol depletion by TASIN-1 treatment induces apoptotic cell death through activating ER stress/ROS/JNK axis and inhibiting AKT pro-survival signaling in colon cancer cells with truncated APC both in vitro and in vivoMol Cancer Ther; 17(5); 943-51. ©2018 AACR.

An image-based small-molecule screen identifies vimentin as a pharmacologically relevant target of simvastatin in cancer cells

Vimentin is a cytoskeletal intermediate filament protein that is expressed in mesenchymal cells and cancer cells during the epithelial-mesenchymal transition. The goal of this study was to identify vimentin-targeting small molecules by using the Tocriscreen library of 1120 biochemically active compounds. We monitored vimentin filament reorganization and bundling in adrenal carcinoma SW13 vimentin-positive (SW13-vim⁺) cells via indirect immunofluorescence. The screen identified 18 pharmacologically diverse hits that included 2 statins-simvastatin and mevastatin. Simvastatin induced vimentin reorganization within 15-30 min and significant perinuclear bundling within 60 min (IC₅₀ = 6.7 nM). Early filament reorganization coincided with increased vimentin solubility. Mevastatin produced similar effects at >1 µM, whereas the structurally related pravastatin and lovastatin did not affect vimentin. In vitro vimentin filament assembly assays revealed a direct targeting mechanism, as determined biochemically and by electron microscopy. In SW13-vim⁺ cells, simvastatin, but not pravastatin, reduced total cell numbers (IC₅₀ = 48.1 nM) and promoted apoptosis after 24 h. In contrast, SW13-vim^- cell viability was unaffected by simvastatin, unless vimentin was ectopically expressed. Simvastatin similarly targeted vimentin filaments and induced cell death in MDA-MB-231 (vim⁺), but lacked effect in MCF7 (vim^-) breast cancer cells. In conclusion, this study identified vimentin as a direct molecular target that mediates simvastatin-induced cell death in 2 different cancer cell lines.-Trogden, K. P., Battaglia, R. A., Kabiraj, P., Madden, V. J., Herrmann, H., Snider, N. T. An image-based small-molecule screen identifies vimentin as a pharmacologically relevant target of simvastatin in cancer cells.

Targeting protein geranylgeranylation slows tumor development in a murine model of prostate cancer metastasis

The isoprenoid biosynthetic pathway (IBP) plays a critical role in providing substrates and enzymes necessary for the post-translational modification and thus activation of a number of proteins involved in prostate cancer metastasis. Previous work by our lab found novel compound disodium [(6Z,11E,15E)-9-[bis(sodiooxy)phosphoryl]-17-hydroxy-2,6,12,16-tetramethyheptadeca-2,6,11,15-tetraen-9-yl]phosphonate (GGOHBP), which inhibits the IBP enzyme geranylgeranyl diphosphate synthase (GGDPS), reduced protein geranylgeranylation without altering protein farnesylation. This activity significantly reduced adrenal gland tumor burden in a murine model of human prostate cancer metastasis which relied on treatment of established disease. The present study determined the ability of GGDPS inhibition to slow the development of prostate cancer metastasis in a preventative murine model. Using tail vein injection of human derived PC-3 prostate cancer cells 4 d after initiating daily GGOHBP or vehicle treatments, we found GGOHBP significantly reduced whole body tumor burden, significantly slowed the development of tumors, and prolonged overall survival as compared to vehicle treated animals. The observed reduction in soft tissue tumor burden corresponded to a biochemical reduction in Rap1A geranylgeranylation, which for prostate cancer is important in its own merit and which serves as a surrogate marker for Rho family, i.e. Rac, protein modification. This effect was present in all treated mice pointing to strong target engagement, which was not observed in non-tumor burdened tissues or control mice. Our findings reiterate a role for protein geranylgeranylation in the development of prostate cancer metastasis in vivo.

A screen for inducers of bHLH activity identifies pitavastatin as a regulator of p21, Rb phosphorylation and E2F target gene expression in pancreatic cancer

The average survival for patients with Pancreatic Ductal Adenocarcinoma (PDA) is merely 6 months, underscoring the need for new therapeutic approaches. During PDA progression, pancreatic acinar cells lose activity of the ClassI/II bHLH factors that regulate quiescence. We previously found that promoting transcriptional activity of the Class I bHLH factor E47 in highly aggressive PDA cells induced stable growth arrest in vitro and in vivo. To translate these findings for clinical utility, we developed a high throughput screening platform to identify small molecule inducers of Class I/II bHLH activity. A screen of 4,375 known drugs identified 70 bHLH activators. Prominent among the hits were members of the statin class of HMG-CoA reductase inhibitors, cholesterol lowering drugs that are also being evaluated in cancer. Studies with pitavastatin in primary patient derived tumor cells and established PDA lines, revealed dose dependent growth inhibition. At the molecular level, pitavastatin induced expression of the cyclin dependent kinase (CDK) inhibitor p21 in a cholesterol independent manner, blocked repressive phosphorylation of the Retinoblastoma tumor suppressor protein at CDK targeted sites, and reduced expression of E2F target genes required for progression through the G1/S boundary. Together, the data provide new insight into mechanisms by which statins constrain proliferation in cancer and establish the effectiveness of a novel screening platform to identify small molecules of clinical relevance in pancreatic cancer.

Geranylgeranyl diphosphate synthase inhibition induces apoptosis that is dependent upon GGPP depletion, ERK phosphorylation and caspase activation

Bisphosphonates are diphosphate analogs that inhibit the intermediate enzymes of the mevalonate pathway. Here, we compared the effects of a farnesyl diphosphate synthase inhibitor, zoledronate, and a geranylgeranyl diphosphate synthase (GGDPS) inhibitor, digeranyl bisphosphonate (DGBP), on lymphocytic leukemia cell proliferation and apoptosis. Both zoledronate and DGBP inhibited proliferation with DGBP doing so more potently. DGBP was markedly less toxic than zoledronate toward the viability of healthy human peripheral blood mononuclear cells. Addition of GGPP, but not farnesyl diphosphate (FPP), prevented the anti-proliferative effects of DGBP. Both GGPP and FPP partially rescued the effects of zoledronate. Co-treatment with DGBP and zoledronate was antagonistic. To further assess the effects of the bisphosphonates, we analyzed annexin V and propidium iodide staining via flow cytometry and found that DGBP induced apoptosis more potently than zoledronate. Western blots show that DGBP treatment altered expression and membrane affinity of some but not all geranylgeranylated small GTPases, activated caspases and increased ERK phosphorylation. Importantly, the anti-proliferative effects of DGBP were blocked by treatment with a caspase inhibitor and by treatment with a MEK inhibitor. Together, our findings indicate that DGBP is a more potent and selective compound than zoledronate in inducing apoptosis mediated through pathways that include caspases and MEK/ERK. These findings support the further development of GGDPS inhibitors as anticancer therapeutics.

RhoA Proteolysis Regulates the Actin Cytoskeleton in Response to Oxidative Stress

The small GTPase RhoA regulates the actin cytoskeleton to affect multiple cellular processes including endocytosis, migration and adhesion. RhoA activity is tightly regulated through several mechanisms including GDP/GTP cycling, phosphorylation, glycosylation and prenylation. Previous reports have also reported that cleavage of the carboxy-terminus inactivates RhoA. Here, we describe a novel mechanism of RhoA proteolysis that generates a stable amino-terminal RhoA fragment (RhoA-NTF). RhoA-NTF is detectable in healthy cells and tissues and is upregulated following cell stress. Overexpression of either RhoA-NTF or the carboxy-terminal RhoA cleavage fragment (RhoA-CTF) induces the formation of disorganized actin stress fibres. RhoA-CTF also promotes the formation of disorganized actin stress fibres and nuclear actin rods. Both fragments disrupt the organization of actin stress fibres formed by endogenous RhoA. Together, our findings describe a novel RhoA regulatory mechanism.

Combined strategy for suppressing breast carcinoma MCF-7 cell lines by loading simvastatin on alpha lipoic acid nanoparticles

BACKGROUND

Augmentation of simvastatin (SMV) cytotoxicity in breast carcinoma cell lines MCF-7, by: improvement of cellular uptake and loading on alpha lipoic acid (ALA).

METHODS

In this study, SMV was loaded on ALA nanoparticles and characterized for surface morphology, SMV entrapment efficiency percent (%EE), zeta potential and release profile. Cellular viability, morphology and uptake and DNA fragmentations were analyzed as a hallmark of cellular apoptosis.

RESULTS

TEM images demonstrated spherical nanoparticles with particle size 104.7 ± 5.5 nm, SMV %EE was 95.8 ± 2.1% with a zeta potential - 23.6 ± 5.4 mV, and release properties were significantly enhanced. IC₅₀ was decreased to 22.2 ± 2.4 µM while raw SMV was 49.3 ± 6.6 µM. Cellular uptake of SMV-ALA nanoparticles was increased by about 3- and 2-folds after 2 and 4 h, respectively. DNA fragments confirmed the apoptosis property of ALA, which is associated with SMV cytotoxicity.

CONCLUSION

This study suggests evidence that SMV loaded on ALA nanoparticles increases the MCF-7 cellular uptake and cytotoxic effects induced by SMV as revealed by significantly enhanced cell death rates in MCF-7 cells. These findings demonstrate that ALA induces cell death, which makes the combination a candidate for tumor therapy.

Molecular mechanisms linking geranylgeranyl diphosphate synthase to cell survival and proliferation

Geranylgeranyl diphosphate is a 20-carbon isoprenoid phospholipid whose lipid moiety can be post-translationally incorporated into proteins to promote membrane association. The process of geranylgeranylation has been implicated in anti-proliferative effects of clinical agents that inhibit enzymes of the mevalonate pathway (i.e. statins and nitrogenous bisphosphonates) as well as experimental agents that deplete geranylgeranyl diphosphate. Inhibitors of geranylgeranyl diphosphate synthase are an attractive way to block geranylgeranylation because they possess a calcium-chelating substructure to allow localization to bone and take advantage of a unique position of the enzyme within the biosynthetic pathway. Here, we describe recent advances in geranylgeranyl diphosphate synthase expression and inhibitor development with a particular focus on the molecular mechanisms that link geranylgeranyl diphosphate to cell proliferation via geranylgeranylated small GTPases.

Repositioning antipsychotic chlorpromazine for treating colorectal cancer by inhibiting sirtuin 1

Investigating existing drugs for repositioning can enable overcoming bottlenecks in the drug development process. Here, we investigated the effect and molecular mechanism of the antipsychotic drug chlorpromazine (CPZ) and identified its potential for treating colorectal cancer (CRC). Human CRC cell lines harboring different p53 statuses were used to investigate the inhibitory mechanism of CPZ. CPZ effectively inhibited tumor growth and induced apoptosis in CRC cells in a p53-dependent manner. Activation of c-jun N-terminal kinase (JNK) was crucial for CPZ-induced p53 expression and the subsequent induction of tumor apoptosis. Induction of p53 acetylation at lysine382 was involved in CPZ-mediated tumor apoptosis, and this induction was attenuated by sirtuin 1 (SIRT1), a class III histone deacetylase. By contrast, knocking down SIRT1 sensitized tumor cells to CPZ treatment. Moreover, CPZ induced the degradation of SIRT1 protein participating downstream of JNK, and JNK suppression abrogated CPZ-mediated SIRT1 downregulation. Clinical analysis revealed a significant association between high SIRT1 expression and poor outcome in CRC patients. These data suggest that SIRT1 is an attractive therapeutic target for CRC and that CPZ is a potential repositioned drug for treating CRC.

Activation of surrogate death receptor signaling triggers peroxynitrite-dependent execution of cisplatin-resistant cancer cells

Platinum-based drugs remain as the cornerstone of cancer chemotherapy; however, development of multidrug resistance presents a therapeutic challenge. This study aims at understanding the molecular mechanisms underlying resistance to cisplatin and unraveling surrogate signaling networks that could revert sensitivity to apoptosis stimuli. We made use of three different sets of cell lines, A549 and H2030 non-small-cell lung cancer (NSCLC) and A2780 ovarian cancer cells and their cisplatin-resistant variants. Here we report that cisplatin-resistant cell lines displayed a multidrug-resistant phenotype. Changes in mitochondrial metabolism and defective mitochondrial signaling were unraveled in the resistant cells. More interestingly, a marked increase in sensitivity of the resistant cells to death receptor-induced apoptosis, in particular TRAIL (TNF-related apoptosis-inducing ligand)-mediated execution, was observed. Although this was not associated with an increase in gene transcription, a significant increase in the localization of TRAIL death receptor, DR4, to the lipid raft subdomains of plasma membrane was detected in the resistant variants. Furthermore, exposure of cisplatin-resistant cells to TRAIL resulted in upregulation of inducible nitric oxide synthase (iNOS) and increase in nitric oxide (NO) production that triggered the generation of peroxynitrite (ONOO⁻). Scavenging ONOO⁻ rescued cells from TRAIL-induced apoptosis, thereby suggesting a critical role of ONOO⁻ in TRAIL-induced execution of cisplatin-resistant cells. Notably, preincubation of cells with TRAIL restored sensitivity of resistant cells to cisplatin. These data provide compelling evidence for employing strategies to trigger death receptor signaling as a second-line treatment for cisplatin-resistant cancers.

Exploitation of pleiotropic actions of statins by using tumour-targeted delivery systems

Statins are drugs traditionally used to lower cholesterol levels in blood. At concentrations 100- to 500-fold higher than those needed for reaching cholesterol lowering activity, they have anti-tumour activity. This anti-tumour activity is based on statins pleiotropic effects derived from their ability to inhibit the mevalonate synthesis and include anti-proliferative, pro-apoptotic, anti-angiogenic, anti-inflammatory, anti-metastatic actions and modulatory effects on intra-tumour oxidative stress. Thus, in this review, we summarise the possible pleiotropic actions of statins involved in tumour growth inhibition. Since the administration of these high doses of statins is accompanied by severe side effects, targeted delivery of statins seems to be the appropriate strategy for efficient application of statins in oncology. Therefore, we also present an overview of the current status of targeted delivery systems for statins with possible utilisation in oncology.

Mevalonate Pathway Blockade, Mitochondrial Dysfunction and Autophagy: A Possible Link

The mevalonate pathway, crucial for cholesterol synthesis, plays a key role in multiple cellular processes. Deregulation of this pathway is also correlated with diminished protein prenylation, an important post-translational modification necessary to localize certain proteins, such as small GTPases, to membranes. Mevalonate pathway blockade has been linked to mitochondrial dysfunction: especially involving lower mitochondrial membrane potential and increased release of pro-apoptotic factors in cytosol. Furthermore a severe reduction of protein prenylation has also been associated with defective autophagy, possibly causing inflammasome activation and subsequent cell death. So, it is tempting to hypothesize a mechanism in which defective autophagy fails to remove damaged mitochondria, resulting in increased cell death. This mechanism could play a significant role in Mevalonate Kinase Deficiency, an autoinflammatory disease characterized by a defect in Mevalonate Kinase, a key enzyme of the mevalonate pathway. Patients carrying mutations in the MVK gene, encoding this enzyme, show increased inflammation and lower protein prenylation levels. This review aims at analysing the correlation between mevalonate pathway defects, mitochondrial dysfunction and defective autophagy, as well as inflammation, using Mevalonate Kinase Deficiency as a model to clarify the current pathogenetic hypothesis as the basis of the disease.