Statins synergistically potentiate 7-hydroxystaurosporine (UCN-01) lethality in human leukemia and myeloma cells by disrupting Ras farnesylation and activation

Targeting myeloma metabolism: How abnormal metabolism contributes to multiple myeloma progression and resistance to proteasome inhibitors

Multiple myeloma is a hematological malignancy that has evolved from antibody-secreting B lymphocytes. Like other types of cancers, myeloma cells have acquired functional capabilities which are referred to as "Hallmarks of Cancer", and one of their most important features is the metabolic disorders. Due to the high secretory load of the MM cells, the first-line medicine proteasome inhibitors have found their pronounced effects in MM cells for blocking the degradation of misfolded proteins, leading to their accumulation in the ER and overwhelming ER stress. Moreover, proteasome inhibitors have been reported to be effective in myeloma by targeting glucose, lipid, amino acid metabolism of MM cells. In this review, we have described the abnormal metabolism of the three major nutrients, such as glucose, lipid and amino acids, which participate in the cellular functions. We have described their roles in myeloma progression, how they could be exploited for therapeutic purposes, and current therapeutic strategies targeting these metabolites, hoping to uncover potential novel therapeutic targets and promote the development of future therapeutic approaches.

Evaluation of the Biological Effect of Non-UV-Activated Bergapten on Selected Human Tumor Cells and the Insight into the Molecular Mechanism of Its Action

There is some evidence that non-photoactivated psoralens may be active against breast and colon tumor cells. Therefore, we evaluated the antiproliferative, proapoptotic, and anti-migrative effect of 5-methoxypsoralen (5-MOP) isolated from Peucedanum tauricum MB fruits in human colorectal adenocarcinoma (HT-29 and SW620), osteosarcoma (Saos-2 and HOS), and multiple myeloma (RPMI8226 and U266). Dose- and cell-line-dependent effects of 5-MOP on viability and proliferation were observed, with the strongest inhibitory effect against Saos-2 and a moderate effect against the HOS, HT-29, and SW620 cells. Multiple myeloma showed low sensitivity. The high viability of human normal cell cultures (HSF and hFOB) in a wide range of 5-MOP concentrations tested (6.25-100 µM) was confirmed. Moreover, the migration of treated Saos-2, SW620, and HT-29 cell lines was impaired, as indicated via a wound healing assay. Flow cytometry analysis conducted on Saos-2 cells revealed the ability of 5-MOP to block the cell cycle in the G2 phase and trigger apoptosis, which was accompanied by a loss of mitochondrial membrane potential, caspases (-9 and -3) activation, the altered expression of the Bax and Bcl-2 proteins, and decreased AKT phosphorylation. This is the first report evaluating the antiproliferative and antimigratory impact of non-UV-activated bergapten on the abovementioned (except for HT-29) tumor cells, which provides new data on the potential role of 5-MOP in inhibiting the growth of various types of therapeutic-resistant cancers.

Statins markedly potentiate aminopeptidase inhibitor activity against (drug-resistant) human acute myeloid leukemia cells

Aim: This study aimed to decipher the molecular mechanism underlying the synergistic effect of inhibitors of the mevalonate-cholesterol pathway (i.e., statins) and aminopeptidase inhibitors (APis) on APi-sensitive and -resistant acute myeloid leukemia (AML) cells. Methods: U937 cells and their sublines with low and high levels of acquired resistance to (6S)-[(R)-2-((S)-Hydroxy-hydroxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3,3 dimethyl-butyric acid cyclopentyl ester (CHR2863), an APi prodrug, served as main AML cell line models. Drug combination effects were assessed with CHR2863 and in vitro non-toxic concentrations of various statins upon cell growth inhibition, cell cycle effects, and apoptosis induction. Mechanistic studies involved analysis of Rheb prenylation required for mTOR activation. Results: A strong synergy of CHR2863 with the statins simvastatin, fluvastatin, lovastatin, and pravastatin was demonstrated in U937 cells and two CHR2863-resistant sublines. This potent synergy between simvastatin and CHR2863 was also observed with a series of other human AML cell lines (e.g., THP1, MV4-11, and KG1), but not with acute lymphocytic leukemia or multiple solid tumor cell lines. This synergistic activity was: (i) specific for APis (e.g., CHR2863 and Bestatin), rather than for other cytotoxic agents; and (ii) corroborated by enhanced induction of apoptosis and cell cycle arrest which increased the sub-G1 fraction. Consistently, statin potentiation of CHR2863 activity was abrogated by co-administration of mevalonate and/or farnesyl pyrophosphate, suggesting the involvement of protein prenylation; this was experimentally confirmed by impaired Rheb prenylation by simvastatin. Conclusion: These novel findings suggest that the combined inhibitory effect of impaired Rheb prenylation and CHR2863-dependent mTOR inhibition instigates a potent synergistic inhibition of statins and APis on human AML cells.

Cholesterol metabolism in cancer and cell death

SIGNIFICANCE

Cholesterol is a type of lipid that plays a crucial role in building and maintaining cell membranes, producing certain hormones, and aiding in digestion. The two main types of cholesterol are low-density lipoprotein and high-density lipoprotein, and maintaining a healthy balance between them is essential for cellular function and organism health.

RECENT ADVANCES

Cholesterol metabolism is a complex and dynamic process that involves biosynthesis, uptake, efflux, transport, and esterification. Disruptions in cholesterol metabolism are implicated in all stages of cancer, contributing to drug resistance, immune evasion, and autophagy dysfunction. These disruptions have also been linked to various types of regulated cell death, such as apoptosis, anoikis, lysosome-dependent cell death, pyroptosis, NETosis, necroptosis, entosis, ferroptosis, alkaliptosis, immunogenic cell death, and paraptosis.

CRITICAL ISSUES

Understanding the complex interplay between cholesterol metabolism and cell death and their impact on cancer development and progression is still a significant challenge. Additionally, there is currently a lack of reliable biomarkers that can accurately reflect cholesterol metabolism dysregulation in cancer.

FUTURE DIRECTIONS

To develop more specific and effective cholesterol metabolism-targeted therapies, a better understanding of the mechanisms by which cholesterol metabolism dysregulation contributes to cell death and cancer progression is needed. Additionally, improving the accuracy and reliability of biomarkers will be crucial for monitoring and diagnosing cholesterol-related cancer subtypes and evaluating the effectiveness of cholesterol metabolism-targeted therapies. These efforts will require ongoing research and collaboration among multidisciplinary teams of scientists and clinicians.

Targeting the Isoprenoid Biosynthetic Pathway in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell malignancy for which there is currently no cure. While treatment options for MM have expanded over the last two decades, all patients will eventually become resistant to current therapies. Thus, there is an urgent need for novel therapeutic strategies to treat MM. The isoprenoid biosynthetic pathway (IBP) is responsible for the post-translational modification of proteins belonging to the Ras small GTPase superfamily, such as Ras, Rho and Rab family members. Given the important roles these GTPase proteins play in various cellular processes, there is significant interest in the development of inhibitors that disturb their prenylation and consequently their activity in MM cells. Numerous preclinical studies have demonstrated that IBP inhibitors have anti-MM effects, including the induction of apoptosis in MM cells and inhibition of osteoclast activity. Some IBP inhibitors have made their way into the clinic. For instance, nitrogenous bisphosphonates are routinely prescribed for the management MM bone disease. Other IBP inhibitors, including statins and farnesyltransferase inhibitors, have been evaluated in clinical trials for MM, while there is substantial preclinical investigation into geranylgeranyl diphosphate synthase inhibitors. Here we discuss recent advances in the development of IBP inhibitors, assess their mechanism of action and evaluate their potential as anti-MM agents.

Dual-Targeted Therapy Circumvents Non-Genetic Drug Resistance to Targeted Therapy

The introduction of various targeted agents into the armamentarium of cancer treatment has revolutionized the standard care of patients with cancer. However, like conventional chemotherapy, drug resistance, either preexisting (primary or intrinsic resistance) or developed following treatment (secondary or acquired resistance), remains the Achilles heel of all targeted agents with no exception, via either genetic or non-genetic mechanisms. In the latter, emerging evidence supports the notion that intracellular signaling pathways for tumor cell survival act as a mutually interdependent network via extensive cross-talks and feedback loops. Thus, dysregulations of multiple signaling pathways usually join forces to drive oncogenesis, tumor progression, invasion, metastasis, and drug resistance, thereby providing a basis for so-called “bypass” mechanisms underlying non-genetic resistance in response to targeted agents. In this context, simultaneous interruption of two or more related targets or pathways (an approach called dual-targeted therapy, DTT), via either linear or parallel inhibition, is required to deal with such a form of drug resistance to targeted agents that specifically inhibit a single oncoprotein or oncogenic pathway. Together, while most types of tumor cells are often addicted to two or more targets or pathways or can switch their dependency between them, DTT targeting either intrinsically activated or drug-induced compensatory targets/pathways would efficiently overcome drug resistance caused by non-genetic events, with a great opportunity that those resistant cells might be particularly more vulnerable. In this review article, we discuss, with our experience, diverse mechanisms for non-genetic resistance to targeted agents and the rationales to circumvent them in the treatment of cancer, emphasizing hematologic malignancies.

Fluvastatin enhances IL-33-mediated mast cell IL-6 and TNF production

Statins are HMG-CoA reductase inhibitors prescribed for lowering cholesterol. They can also inhibit inflammatory responses by suppressing isoprenylation of small G proteins. Consistent with this, we previously found that fluvastatin suppresses IgE-mediated mast cell function. However, some studies have found that statins induced pro-inflammatory cytokines in macrophages and NK cells. In contrast to IgE signaling, we show that fluvastatin augments IL-33-induced TNF and IL-6 production by mast cells. This effect required the key mast cell growth factor, stem cell factor (SCF). Treatment of IL-33-activated mast cells with mevalonic acid or isoprenoids reduced fluvastatin effects, suggesting fluvastatin acts at least partly by reducing isoprenoid production. Fluvastatin also enhanced IL-33-induced NF-κB transcriptional activity and promoted neutrophilic peritonitis in vivo, a response requiring mast cell activation. Other statins tested did not enhance IL-33 responsiveness. Therefore, this work supports observations of unexpected pro-inflammatory effects of some statins and suggests mechanisms by which this may occur. Because statins are candidates for repurposing in inflammatory disorders, our work emphasizes the importance of understanding the pleiotropic and possible unexpected effects of these drugs.

Simvastatin regulates the proliferation, apoptosis, migration and invasion of human acute myeloid leukemia cells via miR-19a-3p/HIF-1α axis

Statins are mainly used to lower plasma cholesterol level. In addition, the anti-leukemia effect of statins has been reported, but the mechanism remains unclear.

This study aimed to explore the bioregulation of simvastatin and its mechanism in acute leukemia cell lines. Cell viability was detected by CCK-8 analysis. Apoptosis was detected through flow cytometry. Cell invasion and migration both were observed by transwell and wound healing separately. RT-qPCR and Western blot were used for determination of genes and proteins. We found that that simvastatin could regulate the biological functions of acute myeloid leukemia (AML) cells, including its proliferation, migration, invasion and apoptosis, which may be carried out by down-regulating miR-19a-3p. Overexpression of miR-19a-3p had the opposite effect in AML cells, suggesting simvastatin-inhibited AML by reducing miR-19a-3p expression. Following researches showed that HIF-1α was directly regulated by the target of miR-19a-3p. Simvastatin could reverse the adverse effects caused by miR-19a-3p mimics. Conversely, the increased expression of Mcl-1, the inhibition of caspase-3 could promote the growth of AML cells. In conclusion, simvastatin could inhibit the proliferation, migration, invasion and promote apoptosis in AML cells through miR-19a-3p/HIF-1α axis.

The Role of Arginine Metabolism in Oral Tongue Squamous Cell Carcinoma

Simple Summary

Cancers that are ‘arginine auxotrophic’ rely on extracellular arginine as a crucial substrate for proliferation and growth. Capitalizing on this vulnerability, there are numerous clinical trials evaluating the therapeutic benefits of depleting arginine in multiple types of cancer, including those occurring in the head and neck. However, head and neck cancers are different and are nonauxotrophic for arginine. Here, we explored the intricacies of arginine metabolism in tongue cancer in order to better understand the therapeutic potential of this biological vulnerability. We showed that reprogramming arginase 1 (ARG1) expression in tongue cancer cells inhibits growth compared with controls. Further, RNA-sequencing showed that HIFα, natural killer cell and interferon signaling were concordantly deregulated.

Abstract

Early diagnosis and treatment do not prevent the high morbidity and poor prognosis of oral tongue squamous cell carcinoma (TSCC). Earlier studies have shown that ARG1 signaling is deregulated in TSCC. Here, we investigated the complexity of ARG1 metabolism in this cancer subsite to appreciate the therapeutic potential of this potential biological vulnerability. Various functional studies show that ARG1 overexpression in oral cancer cells inhibits cell proliferation and invasion compared with controls. Further, RNA-sequencing revealed numerous differentially expressed genes (DEGs) and associated networks were dysregulated by ARG1 overexpression, including hypoxia-inducible factor (HIFα) signaling, the natural killer cell signaling pathway and interferon signaling. Our work provides a foundation for understanding the mechanism of action of disrupted arginine metabolism in oral tongue squamous cell carcinoma. This may impact the community for developing further therapeutic approaches.

Simvastatin enhances the efficacy of nilotinib in chronic myeloid leukaemia by post-translational modification and drug transporter modulation

The resistance of chronic myeloid leukaemia (CML) to tyrosine kinase inhibitors (TKIs) remains a significant clinical problem. Targeting alternative pathways, such as protein prenylation, is known to be effective in overcoming resistance. Simvastatin inhibits 3-hydroxy-3-methylglutaryl-CoA reductase (a key enzyme in isoprenoid-regulation), thereby inhibiting prenylation. We demonstrate that simvastatin alone effectively inhibits proliferation in a panel of TKI-resistant CML cell lines, regardless of mechanism of resistance. We further show that the combination of nilotinib and simvastatin synergistically kills CML cells via an increase in apoptosis and decrease in prosurvival proteins and cellular proliferation. Mechanistically, simvastatin inhibits protein prenylation as shown by increased levels of unprenylated Ras and rescue experiments with mevalonate resulted in abrogation of synergism. The combination also leads to an increase in the intracellular uptake and retention of radio-labelled nilotinib, which further enhances the inhibition of Bcr-Abl kinase activity. In primary CML samples, this combination inhibits clonogenicity in both imatinib-naive and resistant cells. Such combinatorial effects provide the basis for utilising these Food and Drug Administration-approved drugs as a potential clinical approach in overcoming resistance and improving CML treatment.

Statin use and the risk of multiple myeloma: a PRISMA-compliant meta-analysis

Previous studies exploring associations between statin use and risk of multiple myeloma (MM) showed inconsistent results. We searched for articles published in English in databases (PubMed, Web of Science, EMBASE, Medline, and Google Scholar) before October 2019. The multivariate odds ratio (OR)/relative risk (RR) and 95% confidence intervals (CI) were computed to explore associations between statin use and risk of MM. The study indicated that statin users showed significantly lower risks of MM with a random effects model (OR/RR = 0.77, 95% CI 0.63 to 0.95, I² = 63.1%, p for Q test = 0.001). Subgroup analyses showed that statin users showed significantly lower risks of MM in Caucasian populations with a fixed effects model (OR/RR = 0.72, 95% CI 0.59 to 0.88, I² = 43.5%, p for Q test = 0.060), whereas no significant association was shown between statin use and risks of MM in Asian populations with a random effects model. Additionally, Subgroup analyses showed that statin users showed significantly lower risks of MM in cohort studies with a fixed effects model (RR = 0.83, 95% CI 0.74 to 0.93, I² = 0.0%, p for Q test = 0.429), whereas no significant association was shown between statin use and risks of MM in case-control studies with a random effects model. In conclusion, the present study indicated that statin use might be a protective factor for MM incidence. However, the relationship between statin use and MM risk requires repeated and large prospective studies to be verified.

Fluvastatin Induces Apoptosis in Primary and Transformed Mast Cells

Statin drugs are widely employed in the clinic to reduce serum cholesterol. Because of their hydroxymethylglutaryl coenzyme A reductase antagonism, statins also reduce isoprenyl lipids necessary for the membrane anchorage and signaling of small G-proteins in the Ras superfamily. We previously found that statins suppress immunoglobulin E (IgE)-mediated mast cell activation, suggesting these drugs might be useful in treating allergic disease. Although IgE-induced function is critical to allergic inflammation, mast cell proliferation and survival also impact atopic disease and mast cell neoplasia. In this study, we describe fluvastatin-mediated apoptosis in primary and transformed mast cells. An IC₅₀ was achieved between 0.8 and 3.5 μM in both cell types, concentrations similar to the reported fluvastatin serum C_max value. Apoptosis was correlated with reduced stem cell factor (SCF)-mediated signal transduction, mitochondrial dysfunction, and caspase activation. Complementing these data, we found that p53 deficiency or Bcl-2 overexpression reduced fluvastatin-induced apoptosis. We also noted evidence of cytoprotective autophagy in primary mast cells treated with fluvastatin. Finally, we found that intraperitoneal fluvastatin treatment reduced peritoneal mast cell numbers in vivo These findings offer insight into the mechanisms of mast cell survival and support the possible utility of statins in mast cell-associated allergic and neoplastic diseases. SIGNIFICANCE STATEMENT: Fluvastatin, a statin drug used to lower cholesterol, induces apoptosis in primary and transformed mast cells by antagonizing protein isoprenylation, effectively inhibiting stem cell factor (SCF)-induced survival signals. This drug may be an effective means of suppressing mast cell survival.

The combination of UCN-01 and ATRA triggers differentiation in ATRA resistant acute promyelocytic leukemia cell lines via RAF-1 independent activation of MEK/ERK

With the introduction of arsenic trioxide and all-trans retinoic acid, the prognosis of acute promyelocytic leukemia has greatly improved. However, all-trans retinoic acid resistance is still unresolved in acute promyelocytic leukemia relapsed patients. In this study, the clinical achievable concentration of 7-hydroxystaurosporine synergized with all-trans retinoic acid to induce terminal differentiation in all-trans retinoic acid resistant acute promyelocytic leukemia cell lines. Though 7-hydroxystaurosporine is a PKC inhibitor, PKC might not be involved in the combination-induced differentiation since other PKC selective inhibitors, Gö 6976 and rottlerin failed to cooperate with all-trans retinoic acid to trigger differentiation. The combination significantly enhanced the protein level of CCAAT/enhancer binding protein β and/or PU.1 as well as activated MEK/ERK. U0126 (MEK specific inhibitor) not only suppressed the combination-induced differentiation but also restored the protein level of CCAAT/enhancer binding protein β and/or PU.1. However, RAF-1 inhibitor had no inhibitory effect on MEK activation and the combination-induced differentiation. Therefore, the combination overcame differentiation block via RAF-1 independent MEK/ERK modulation of the protein level of CCAAT/enhancer binding protein β and/or PU.1. These findings may provide a preclinical rationale for the potential role of this combination in the treatment of all-trans retinoic acid resistant acute promyelocytic leukemia patients.

Statins Perturb Gβγ Signaling and Cell Behavior in a Gγ Subtype Dependent Manner

Guanine nucleotide-binding proteins (G proteins) facilitate the transduction of external signals to the cell interior, regulate most eukaryotic signaling, and thus have become crucial disease drivers. G proteins largely function at the inner leaflet of the plasma membrane (PM) using covalently attached lipid anchors. Both small monomeric and heterotrimeric G proteins are primarily prenylated, either with a 15-carbon farnesyl or a 20-carbon geranylgeranyl polyunsaturated lipid. The mevalonate [3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase] pathway synthesizes lipids for G-protein prenylation. It is also the source of the precursor lipids for many biomolecules, including cholesterol. Consequently, the rate-limiting enzymes of the mevalonate pathway are major targets for cholesterol-lowering medications and anticancer drug development. Although prenylated G protein γ (Gγ) is essential for G protein-coupled receptor (GPCR)-mediated signaling, how mevalonate pathway inhibitors, statins, influence subcellular distribution of Gβγ dimer and Gαβγ heterotrimer, as well as their signaling upon GPCR activation, is poorly understood. The present study shows that clinically used statins not only significantly disrupt PM localization of Gβγ but also perturb GPCR-G protein signaling and associated cell behaviors. The results also demonstrate that the efficiency of prenylation inhibition by statins is Gγ subtype-dependent and is more effective toward farnesylated Gγ types. Since Gγ is required for Gβγ signaling and shows a cell- and tissue-specific subtype distribution, the present study can help understand the mechanisms underlying clinical outcomes of statin use in patients. This work also reveals the potential of statins as clinically usable drugs to control selected GPCR-G protein signaling.

Cholesterol Serum Levels and Use of Statins in Graves' Orbitopathy: A New Starting Point for the Therapy

Graves' Orbitopathy (GO) is the most frequent extrathyroidal manifestation of Graves' disease (GD). Its ultimate cause remains unclear, but it is commonly considered an autoimmune disorder due to self recognition of autoantigens constitutively expressed by orbital fibroblasts (OFs), and thyroid epithelial cells. High dose intravenous glucocorticoids (ivGC) are the most commonly used treatment for moderately severe and active GO. However, based on the complex pathogenesis of GO, a number of factors may have a protective and maybe a therapeutic role. The use of other medications improving the effect of GC may increase the overall effectiveness of the therapy and reduce GC doses, thereby limiting side effects. Recently, a possible protective role of 3-hydroxy-3-methylglutaryl-coenzyme reductase inhibitors, the so-called statins, and perhaps of lowering cholesterol levels, has been proposed. Thus, statins have been reported to be associated with a reduced frequency of GO in GD patients and in recent cross-sectional and retrospective studies a significant correlation was found between the occurrence of GO and both total and LDL-cholesterol in patients with a GD of relatively recent onset, suggesting a role of cholesterol in the development of GO. Moreover, a correlation was found between the GO clinical activity score and total as well as LDL-cholesterol in untreated GO patients, depending on GO duration, indicating a role of cholesterol on GO activity. Therefore, statin treatment may be beneficial for GO. Here we review this subject, which offers new therapeutic perspectives for patients with GO.

ERRα suppression enhances the cytotoxicity of the MEK inhibitor trametinib against colon cancer cells

BACKGROUND

ERRα, a constitutive transcription factor that regulates energy metabolism, plays an important role in the progression of various tumours. However, its role in cell survival and proliferation and its implication in targeted therapy in colon cancer remains elusive.

METHODS

The expression of ERRα in colon cancer tissues and cell lines was detected by using western blotting and immunohistochemistry. A wound healing assay and a transwell assay were performed to examine the migration and invasion of the colon cancer cells. A cell viability assay, clonogenic assay, western blot assay and the dual-luciferase reporter assay were employed to study the interaction between trametinib (inhibitor of MEK) and EGF treatment. Flow cytometry, western blotting, quantitative reverse-transcription polymerase chain reaction and xenograft studies were used to identify whether the combination of trametinib and simvastatin had a synergistic effect.

RESULTS

ERRα positively regulated the cell proliferation, migration and invasion of colon cancer cells, and the suppression of ERRα completely reduced the EGF treatment-induced proliferation of colon cancer cells. Further investigation showed that trametinib partially restrained the up-regulation of ERRα induced by the EGF treatment, and ERRα inhibition increased the sensitivity of colon cancer cells to trametinib. At last, we combined trametinib with simvastatin, a common clinically used drug with a new reported function of transcriptional activity inhibition of ERRα, and found that this combination produced a synergistic effect in inhibiting the proliferation and survival of colon cancer cells in vitro as well as in vivo.

CONCLUSIONS

The present data indicated that ERRα acted as an oncogene in colon cancer cells, and the combined targeting of ERRα and MEK might be a promising therapeutic strategy for colon cancer treatment.

STK3 is a therapeutic target for a subset of acute myeloid leukemias

Acute myeloid leukemia (AML) is characterized by uncontrolled proliferation and accumulation of immature myeloblasts, which impair normal hematopoiesis. While this definition categorizes the disease into a distinctive group, the large number of different genetic and epigenetic alterations actually suggests that AML is not a single disease, but a plethora of malignancies. Still, most AML patients are not treated with targeted medication but rather by uniform approaches such as chemotherapy. The identification of novel treatment options likely requires the identification of cancer cell vulnerabilities that take into account the different genetic and epigenetic make-up of the individual tumors. Here we show that STK3 depletion by knock-down, knock-out or chemical inhibition results in apoptotic cells death in some but not all AML cell lines and primary cells tested. This effect is mediated by a premature activation of cyclin dependent kinase 1 (CDK1) in presence of elevated cyclin B1 levels. The anti-leukemic effects seen in both bulk and progenitor AML cells suggests that STK3 might be a promising target in a subset of AML patients.

ATR/CHK1 inhibitors and cancer therapy

The cell cycle checkpoint proteins ataxia-telangiectasia-mutated-and-Rad3-related kinase (ATR) and its major downstream effector checkpoint kinase 1 (CHK1) prevent the entry of cells with damaged or incompletely replicated DNA into mitosis when the cells are challenged by DNA damaging agents, such as radiation therapy (RT) or chemotherapeutic drugs, that are the major modalities to treat cancer. This regulation is particularly evident in cells with a defective G1 checkpoint, a common feature of cancer cells, due to p53 mutations. In addition, ATR and/or CHK1 suppress replication stress (RS) by inhibiting excess origin firing, particularly in cells with activated oncogenes. Those functions of ATR/CHK1 make them ideal therapeutic targets. ATR/CHK1 inhibitors have been developed and are currently used either as single agents or paired with radiotherapy or a variety of genotoxic chemotherapies in preclinical and clinical studies. Here, we review the status of the development of ATR and CHK1 inhibitors. We also discuss the potential mechanisms by which ATR and CHK1 inhibition induces cell killing in the presence or absence of exogenous DNA damaging agents, such as RT and chemotherapeutic agents. Lastly, we discuss synthetic lethality interactions between the inhibition of ATR/CHK1 and defects in other DNA damage response (DDR) pathways/genes.

Statins induce apoptosis through inhibition of Ras signaling pathways and enhancement of Bim and p27 expression in human hematopoietic tumor cells

Recently, statins have been demonstrated to improve cancer-related mortality or prognosis in patients of various cancers. However, the details of the apoptosis-inducing mechanisms remain unknown. This study showed that the induction of apoptosis by statins in hematopoietic tumor cells is mediated by mitochondrial apoptotic signaling pathways, which are activated by the suppression of mevalonate or geranylgeranyl pyrophosphate biosynthesis. In addition, statins decreased the levels of phosphorylated extracellular signal-regulated kinase 1/2 and mammalian target of rapamycin through suppressing Ras prenylation. Furthermore, inhibition of extracellular signal-regulated kinase 1/2 and mammalian target of rapamycin by statins induced Bim expression via inhibition of Bim phosphorylation and ubiquitination and cell-cycle arrest at G1 phase via enhancement of p27 expression. Moreover, combined treatment of U0126, a mitogen-activated protein kinase kinase 1/2 inhibitor, and rapamycin, a mammalian target of rapamycin inhibitor, induced Bim and p27 expressions. The present results suggested that statins induce apoptosis by decreasing the mitochondrial transmembrane potential, increasing the activation of caspase-9 and caspase-3, enhancing Bim expression, and inducing cell-cycle arrest at G1 phase through inhibition of Ras/extracellular signal-regulated kinase and Ras/mammalian target of rapamycin pathways. Therefore, our findings support the use of statins as potential anticancer agents or concomitant drugs of adjuvant therapy.

Statins do not inhibit the FGFR signaling in chondrocytes

OBJECTIVE

Statins are widely used drugs for cholesterol lowering, which were recently found to counteract the effects of aberrant fibroblast growth factor receptor (FGFR3) signaling in cell and animal models of FGFR3-related chondrodysplasia. This opened an intriguing therapeutic possibility for human dwarfing conditions caused by gain-of-function mutations in FGFR3, although the mechanism of statin action on FGFR3 remains unclear. Here, we determine the effect of statins on FGFR signaling in chondrocytes.

DESIGN

Cultured chondrocyte cell lines, mouse embryonic tibia cultures and limb bud micromasses were treated with FGF2 to activate FGFR signaling. The effects of atorvastatin, fluvastatin, lovastatin and pravastatin on FGFR3 protein stability and on FGFR-mediated chondrocyte growth-arrest, loss of extracellular matrix (ECM), induction of premature senescence and hypertrophic differentiation were evaluated.

RESULTS

Statins did not alter the level of FGFR3 protein expression nor produce any effect on FGFR-mediated inhibition of chondrocyte proliferation and hypertrophic differentiation in cultured chondrocyte cell lines, mouse tibia cultures or limb bud micromasses.

CONCLUSION

We conclude that statins do not inhibit the FGFR signaling in chondrocytes. Therefore the statin-mediated rescue of FGFR3-related chondrodysplasia, described before, is likely not intrinsic to the growth plate cartilage.

Statins Are Associated With Reduced Mortality in Multiple Myeloma

Purpose The 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) have activity in one of the pathways influenced by nitrogen-containing bisphosphonates, which are associated with improved survival in multiple myeloma (MM). To understand the benefit of statins in MM, we evaluated the association between statin use and mortality in a large cohort of patients with MM. Patients and Methods From the Veterans Administration Central Cancer Registry, we identified patients diagnosed with MM between 1999 and 2013. We defined statin use as the presence of any prescription for a statin within 3 months before or any time after MM diagnosis. Cox proportional hazards regression assessed the association of statin use with mortality, while controlling for known MM prognostic factors. Results We identified a cohort of 4,957 patients, of whom 2,294 received statin therapy. Statin use was associated with a 21% decrease in all-cause mortality (adjusted hazard ratio, 0.79; 95% CI, 0.73 to 0.86; P < .001) as well as a 24% decrease in MM-specific mortality (adjusted hazard ratio, 0.76; 95% CI, 0.67 to 0.86; P < .001). This association remained significant across all sensitivity analyses. In addition to reductions in mortality, statin use was associated with a 31% decreased risk of developing a skeletal-related event. Conclusion In this cohort study of US veterans with MM, statin therapy was associated with a reduced risk of both all-cause and MM-specific mortality. Our findings suggest a potential role for statin therapy in patients with MM. The putative benefit of statin therapy in MM should be corroborated in prospective studies.

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.

Simvastatin inhibits protein isoprenylation in the brain

Evidence suggests that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, may reduce the risk of Alzheimer's disease (AD). Statin action in patients with AD, as in those with heart disease, is likely to be at least partly independent of the effects of statins on cholesterol. Statins can alter cellular signaling and protein trafficking through inhibition of isoprenylation of Rho, Cdc42, and Rab family GTPases. The effects of statins on protein isoprenylation in vivo, particularly in the central nervous system, are poorly studied. We utilized two-dimensional gel electrophoresis approaches to directly monitor the levels of isoprenylated and non-isoprenylated forms of Rho and Rab family GTPases. We report that simvastatin significantly inhibits RhoA and Rab4, and Rab6 isoprenylation at doses as low as 50nM in vitro. We also provide the first in vivo evidence that statins inhibit the isoprenylation of RhoA in the brains of rats and RhoA, Cdc42, and H-Ras in the brains of mice treated with clinically relevant doses of simvastatin.

Repositioning of drugs for intervention in tumor progression and metastasis: Old drugs for new targets

The increasing unraveling of the molecular basis of cancer offers manifold novel options for intervention strategies. However, the discovery and development of new drugs for potential clinical applications is a tremendously time-consuming and costly process. Translating a novel lead candidate compound into an approved clinical drug takes often more than a decade, and the success rate is very low due to versatile efforts including defining its pharmacokinetics, pharmacodynamics, side effects as well as lack of sufficient efficacy. Thus, strategies are needed to minimize time and costs, while maximizing success rates. A very attractive strategy for novel cancer therapeutic options is the repositioning of already approved drugs. These medicines, approved for the treatment of non-malignant disorders, have already passed some early costs and time, have been tested in humans and are ready for clinical trials as anti-cancer drugs. Here we discuss the repositioning of nonsteroidal anti-inflammatory drugs (NSAID), statins, anti-psychotic drugs, anti-helminthic drugs and vitamin D as anti-tumor agents. We focus on their novel actions and potential for inhibition of cancer growth and metastasis by interfering with target molecules and pathways, which drive these malignant processes. Furthermore, important pre-clinical and clinical data are reviewed herein, which elucidate their therapeutic mechanisms which enable their repositioning for cancer therapy and disruption of metastasis.

A randomised, double-blind, placebo-controlled multi-centre phase III trial of XELIRI/FOLFIRI plus simvastatin for patients with metastatic colorectal cancer

Background:

The purpose of this randomised phase III trial was to evaluate whether the addition of simvastatin, a synthetic 3-hydroxy-3methyglutaryl coenzyme A reductase inhibitor, to XELIRI/FOLFIRI chemotherapy regimens confers a clinical benefit to patients with previously treated metastatic colorectal cancer.

Methods:

We undertook a double-blind, placebo-controlled phase III trial of 269 patients previously treated for metastatic colorectal cancer and enrolled in 5 centres in South Korea. Patients were randomly assigned (1 : 1) to one of the following groups: FOLFIRI/XELIRI plus simvastatin (40 mg) or FOLFIRI/XELIRI plus placebo. The FOLFIRI regimen consisted of irinotecan at 180 mg m⁻² as a 90-min infusion, leucovorin at 200 mg m⁻² as a 2-h infusion, and a bolus injection of 5-FU 400 mg m⁻² followed by a 46-h continuous infusion of 5-FU at 2400 mg m⁻². The XELIRI regimen consisted of irinotecan at 250 mg m⁻² as a 90-min infusion with capecitabine 1000 mg m⁻² twice daily for 14 days. The primary end point was progression-free survival (PFS). Secondary end points included response rate, duration of response, overall survival (OS), time to progression, and toxicity.

Results:

Between April 2010 and July 2013, 269 patients were enrolled and assigned to treatment groups (134 simvastatin, 135 placebo). The median PFS was 5.9 months (95% CI, 4.5–7.3) in the XELIRI/FOLFIRI plus simvastatin group and 7.0 months (95% CI, 5.4–8.6) in the XELIRI/FOLFIRI plus placebo group (P=0.937). No significant difference was observed between the two groups with respect to OS (median, 15.9 months (simvastatin) vs 19.9 months (placebo), P=0.826). Grade ⩾3 nausea and anorexia were noted slightly more often in patients in the simvastatin arm compared with with the placebo arm (4.5% vs 0.7%, 3.0% vs 0%, respectively).

Conclusions:

The addition of 40 mg simvastatin to the XELIRI/FOLFIRI regimens did not improve PFS in patients with previously treated metastatic colorectal cancer nor did it increase toxicity.

Rational Combinations of Targeted Agents in AML

Despite modest improvements in survival over the last several decades, the treatment of AML continues to present a formidable challenge. Most patients are elderly, and these individuals, as well as those with secondary, therapy-related, or relapsed/refractory AML, are particularly difficult to treat, owing to both aggressive disease biology and the high toxicity of current chemotherapeutic regimens. It has become increasingly apparent in recent years that coordinated interruption of cooperative survival signaling pathways in malignant cells is necessary for optimal therapeutic results. The modest efficacy of monotherapy with both cytotoxic and targeted agents in AML testifies to this. As the complex biology of AML continues to be elucidated, many “synthetic lethal” strategies involving rational combinations of targeted agents have been developed. Unfortunately, relatively few of these have been tested clinically, although there is growing interest in this area. In this article, the preclinical and, where available, clinical data on some of the most promising rational combinations of targeted agents in AML are summarized. While new molecules should continue to be combined with conventional genotoxic drugs of proven efficacy, there is perhaps a need to rethink traditional philosophies of clinical trial development and regulatory approval with a focus on mechanism-based, synergistic strategies.

New strategies for the treatment of ovarian cancer

Ovarian cancer usually responds well to chemotherapy, but once the disease becomes resistant to chemotherapy, the treatment options available are inadequate. A number of strategies are currently undergoing clinical evaluation, among which angiogenesis and PARP [poly(ADP-ribose) polymerase] inhibitors appear promising. Pre-clinical studies have identified several potential new therapeutic strategies, and we review the potential for use of BH3 (Bcl-2 homology) mimetics, autotaxin inhibitors and statins to treat ovarian cancer.

Suppressive effects of simvastatin on the human acute promyelocytic leukemia NB4 cell line through the regulation of the nuclear factor-κB signaling pathway

The present study examined the effects of simvastatin on the proliferation, apoptosis and gene expression levels involved in the nuclear factor-κB (NF-κB) signaling pathway in the human acute promyelocytic leukemia NB4 cell line by methyl thiazolyl tetrazolium assay, flow cytometry and the Human NF-κB Signaling Pathway RT² Profiler™ PCR Array profiles. The results showed that simvastatin significantly inhibited proliferation and induced apoptosis of the NB4 cells in a time- and dose-dependent manner. Changes were noted in the expression levels of 56 genes involved in the NF-κB signaling pathways in the NB4 cells treated with 15 μm simvastatin at 48 h post-incubation, among which, 47 genes were downregulated and 9 were upregulated. In conclusion, simvastatin potentially inhibits the proliferation and induces the apoptosis of NB4 cells through the regulation of the expression levels of genes involved in the NF-κB signaling pathway.

Differential roles of the mevalonate pathway in the development and survival of mouse Purkinje cells in culture

The cerebellum is an important locus for motor learning and higher cognitive functions, and Purkinje cells constitute a key component of its circuit. Biochemically, significant turnover of cholesterol occurs in Purkinje cells, causing the activation of the mevalonate pathway. The mevalonate pathway has important roles in cell survival and development. In this study, we investigated the outcomes of mevalonate inhibition in immature and mature mouse cerebellar Purkinje cells in culture. Specifically, we found that the inhibition of the mevalonate pathway by mevastatin resulted in cell death, and geranylgeranylpyrophosphate (GGPP) supplementation significantly enhanced neuronal survival. The surviving immature Purkinje cells, however, exhibited dendritic developmental deficits. The morphology of mature cells was not affected. The inhibition of squalene synthase by zaragozic acid caused impaired dendritic development, similar to that seen in the GGPP-rescued Purkinje cells. Our results indicate GGPP is required for cell survival and squalene synthase for the cell development of Purkinje cells. Abnormalities in Purkinje cells are linked to motor-behavioral learning disorders such as cerebellar ataxia. Thus, serious caution should be taken when using drugs that inhibit geranylgeranylation or the squalene-cholesterol branch of the pathway in the developing stage.

CHEK again: revisiting the development of CHK1 inhibitors for cancer therapy

CHEK1 encodes the serine/threonine kinase CHK1, a central component of the DNA damage response. CHK1 regulates cell cycle checkpoints following genotoxic stress to prevent the entry of cells with damaged DNA into mitosis and coordinates various aspects of DNA repair. Accordingly, CHK1 has become a target of considerable interest in oncology. CHK1 inhibitors potentiate the efficacy of DNA-damaging chemotherapeutics by abrogating CHK1-mediated cell cycle arrest and preventing repair of damaged DNA. In addition, CHK1 inhibitors interfere with the biological role of CHK1 as a principal regulator of the cell cycle that controls the initiation of DNA replication, stabilizes replication forks, and coordinates mitosis. Since these functions of CHK1 facilitate progression through an unperturbed cell cycle, CHK1 inhibitors are being developed not only as chemopotentiators, but also as single-agent therapies. This review is intended to provide information on the current progress of CHK1 inhibitors in pre-clinical and clinical development and will focus on mechanisms of single-agent activity and potential strategies for patient tailoring and combinations with non-genotoxic agents.

Emerging pathways as individualized therapeutic target of multiple myeloma

INTRODUCTION

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to the growing knowledge of disease pathobiology.

AREAS COVERED

Intrinsic genetic lesions, as well as the bone marrow microenvironment, contribute to the activation of proliferation and survival pathways, impairment of cell death mechanisms and drug resistance. The phosphatidylinositol 3-kinase (PI3K) and the Ras/mitogen-activated protein kinase (MAPK) cascades are the signaling pathways mainly involved in the MM development. In the last decade, several molecules interfering with growth and survival promoting signaling have been developed.

EXPERT OPINION

Despite the availability of novel therapeutics, MM still evolves into a drug-resistant phase and most patients die of progressive disease. Therefore, there is an urgent need of novel therapeutic strategies. Among a plethora of new investigational agents, microRNA (miRNA) represents the basis for the design of novel therapeutic strategies which basically rely on miRNA inhibition or miRNA replacement approaches and take benefit respectively from the use of miRNA inhibitors or synthetic miRNAs as well as from lipid-based nanoparticles as carriers for in vivo delivery.

JAK2-V617F-mediated signalling is dependent on lipid rafts and statins inhibit JAK2-V617F-dependent cell growth

Aberrant JAK2 signalling plays an important role in the aetiology of myeloproliferative neoplasms (MPNs). JAK2 inhibitors, however, do not readily eliminate neoplastic MPN cells and thus do not induce patient remission. Further understanding JAK2 signalling in MPNs may uncover novel avenues for therapeutic intervention. Recent work has suggested a potential role for cellular cholesterol in the activation of JAK2 by the erythropoietin receptor and in the development of an MPN-like disorder in mice. Our study demonstrates for the first time that the MPN-associated JAK2-V617F kinase localizes to lipid rafts and that JAK2-V617F-dependent signalling is inhibited by lipid raft disrupting agents, which target membrane cholesterol, a critical component of rafts. We also show for the first time that statins, 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors, widely used to treat hypercholesterolaemia, induce apoptosis and inhibit JAK2-V617F-dependent cell growth. These cells are more sensitive to statin treatment than non-JAK2-V617F-dependent cells. Importantly, statin treatment inhibited erythropoietin-independent erythroid colony formation of primary cells from MPN patients, but had no effect on erythroid colony formation from healthy individuals. Our study is the first to demonstrate that JAK2-V617F signalling is dependent on lipid rafts and that statins may be effective in a potential therapeutic approach for MPNs.

Apoptosis, autophagy and ER stress in mevalonate cascade inhibition-induced cell death of human atrial fibroblasts

3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors (statins) are cholesterol-lowering drugs that exert other cellular effects and underlie their beneficial health effects, including those associated with myocardial remodeling. We recently demonstrated that statins induces apoptosis and autophagy in human lung mesenchymal cells. Here, we extend our knowledge showing that statins simultaneously induces activation of the apoptosis, autophagy and the unfolded protein response (UPR) in primary human atrial fibroblasts (hATF). Thus we tested the degree to which coordination exists between signaling from mitochondria, endoplasmic reticulum and lysosomes during response to simvastatin exposure. Pharmacologic blockade of the activation of ER-dependent cysteine-dependent aspartate-directed protease (caspase)-4 and lysosomal cathepsin-B and -L significantly decreased simvastatin-induced cell death. Simvastatin altered total abundance and the mitochondrial fraction of proapoptotic and antiapoptotic proteins, while c-Jun N-terminal kinase/stress-activated protein kinase mediated effects on B-cell lymphoma 2 expression. Chemical inhibition of autophagy flux with bafilomycin-A1 augmented simvastatin-induced caspase activation, UPR and cell death. In mouse embryonic fibroblasts that are deficient in autophagy protein 5 and refractory to autophagy induction, caspase-7 and UPR were hyper-induced upon treatment with simvastatin. These data demonstrate that mevalonate cascade inhibition-induced death of hATF manifests from a complex mechanism involving co-regulation of apoptosis, autophagy and UPR. Furthermore, autophagy has a crucial role in determining the extent of ER stress, UPR and permissiveness of hATF to cell death induced by statins.

Statin-dependent activation of protein kinase Cδ in acute promyelocytic leukemia cells and induction of leukemic cell differentiation

Statins are HMG-CoA (3-hydroxy-3-methyl-glutaryl-coenzyme A) reductase inhibitors, which block the conversion of HMG-CoA to mevalonate and have potent cholesterol lowering properties. Beyond their importance in the generation of lipid lowering effects, the regulatory effects of statins on the mevalonate pathway have a significant impact on multiple other cellular functions. There is now extensive evidence that statins have anti-inflammatory and anti-neoplastic properties, but the precise mechanisms by which such responses are generated are not well understood. In the present study we demonstrate that statins engage a member of the protein kinase C (PKC) family of proteins, PKCδ, in acute promyelocytic leukemia (APL) cells. Our study shows that atorvastatin and fluvastatin induce proteolytic activation of PKCδ in the APL NB4 cell line, which expresses the t(15;17) translocation. Such engagement of PKCδ results in induction of its kinase domain and downstream regulation of pathways important for statin-dependent leukemia cell differentiation. Our research shows that the function of PKCδ is essential for statin-induced leukemic cell differentiation, as demonstrated by studies involving selective targeting of PKCδ using siRNAs. We also demonstrate that the potent enhancing effects of statins on all-trans retinoic acid (ATRA)-induced gene expression for CCL3 and CCL4 requires the function of PKCδ, suggesting a mechanism by which statins may promote ATRA-induced antileukemic responses. Altogether, our data establish a novel function for PKCδ as a mediator of statin-induced differentiation of APL cells and antileukemic effects.

Treatment with high-dose simvastatin inhibits geranylgeranylation in AML blast cells in a subset of AML patients

It is currently unknown whether the in vitro effects observed with statins in acute myeloid leukemia (AML) cells, including lowering of cholesterol, inhibition of isoprenylation, and sensitization to chemotherapy, also occur in vivo. Therefore, AML mononuclear cells (MNCs) were isolated from 12 patients before and after 7 days of high-dose (7.5-15 mg/kg/day) simvastatin treatment. Parallel mouse studies were performed to have, in addition to AML cells, access to liver tissue, a major target of statins. Serum cholesterol levels were lowered by simvastatin in all patients, however, only limited changes in the messenger RNA expression of cholesterol metabolism genes were seen in patient and mouse MNCs compared to murine liver cells. Still, two out of seven patients displayed an increased in vitro chemosensitivity of their AML cells upon simvastatin treatment. Gene set enrichment analysis on microarray data of AML patient cells and Western blot analysis for the isoprenylated proteins DnaJ and Rap1 on murine and AML patient MNCs demonstrated that in vivo simvastatin treatment resulted in inhibition of geranylgeranylation in murine MNCs and in a subset of patient AML MNCs. In summary, our data demonstrate that simvastatin treatment results in chemosensitization and inhibition of geranylgeranylation in AML cells of a subset of patients.

Involvement of Chk1-Cdc25A-cyclin A/CDK2 pathway in simvastatin induced S-phase cell cycle arrest and apoptosis in multiple myeloma cells

Statins have been demonstrated to effectively inhibit proliferation and induce apoptosis in cancer cells by inhibition of geranylgeranylation, however its novel molecular mechanism remains to be determined. Recently simvastatin has been found to result in the synergistic induction of apoptosis with 7-hydroxystaurosporine (UCN-01) (a Chk1 inhibitor) in myeloma cells. Therefore we hypothesized that Chk1 plays a role in the anti-myeloma effect of simvastatin. Interestingly, we found that simvastatin caused a dose-dependent increase in S phase cell cycle and induced significant apoptosis. The results of western blot showed that simvastatin-induced S-phase cell cycle arrest was associated with activation of Chk1, downregulation of Cdc25A, cyclin A and CDK2 expression. Additionally, simvastatin-induced apoptosis was accompanied by diminished Bcl-2 protein expression, increased cytosolic cytochrome c level, and activation of caspase 9 and caspase 3. Further investigation revealed that silence of Chk1 expression by Chk1 specific siRNA inhibited simvastatin-induced activation of Chk1, downregulation of Cdc25A, cyclin A and CDK2 expression, and diminished S phase cell cycle arrest. Additionally, inhibition of Chk1 expression enhanced simvastatin-induced downregulation of Bcl-2, caspase 9 cleavage and subsequent apoptosis. These results suggested that the Chk1-Cdc25A-cyclin A/CDk2 pathway was involved in simvastatin-induced S-phase cell cycle arrest and apoptosis in multiple myeloma cell lines.

12/15-Lipoxygenase gene knockout severely impairs ischemia-induced angiogenesis due to lack of Rac1 farnesylation

To understand the mechanisms by which 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) activates Rac1 in the induction of angiogenesis, we studied the role of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and αPix. 15(S)-HETE stimulated Rac1 in a sustained manner in human dermal microvascular endothelial cells (HDMVECs). Simvastatin, a potent inhibitor of HMG-CoA reductase, suppressed 15(S)-HETE-induced Rac1 activation in HDMVECs affecting their migration and tube formation. 15(S)-HETE by inducing HMG-CoA reductase expression caused increased farnesylation and membrane translocation of Rac1 where it became activated by Src-dependent αPix stimulation. Mevalonate rescued 15(S)-HETE-induced Rac1 farnesylation and membrane translocation in HDMVECs and the migration and tube formation of these cells from inhibition by simvastatin. Down-regulation of αPix inhibited 15(S)-HETE-induced HDMVEC migration and tube formation. Hind-limb ischemia induced Rac1 farnesylation and activation leading to increased angiogenesis and these effects were blocked by simvastatin and rescued by mevalonate in WT mice. In contrast, hind-limb ischemia failed to induce Rac1 farnesylation and activation as well as angiogenic response in 12/15-Lox(-/-) mice. Activation of Src and αPix were also compromised at least to some extent in 12/15-Lox(-/-) mice compared with WT mice in response to hind-limb ischemia. Together, these findings demonstrate for the first time that HMG-CoA reductase plays a determinant role in 12/15-Lox-induced angiogenesis.

CHK1 inhibitors in combination chemotherapy: thinking beyond the cell cycle

Cellular sensing of DNA damage, along with concomitant cell cycle arrest, is mediated by a great many proteins and enzymes. One focus of pharmaceutical development has been the inhibition of DNA damage signaling, and checkpoint kinases (Chks) in particular, as a means to sensitize proliferating tumor cells to chemotherapies that damage DNA. 7-Hydroxystaurosporine, or UCN-01, is a clinically relevant and well-studied kinase activity inhibitor that exerts chemosensitizing effects by inhibition of Chk1, and a multitude of Chk1 inhibitors have entered development. Clinical development of UCN-01 has overcome many initial obstacles, but the drug has nevertheless failed to show a high level of clinical activity when combined with chemotherapeutic agents. One very likely reason for the lack of clinical efficacy of Chk1 inhibitors may be that the inhibition of Chk1 causes the compensatory activation of ATM and ERK1/2 pathways. Indeed, inhibition of many enzyme activities, not necessarily components of cell cycle regulation, may block Chk1 inhibitor-induced ERK1/2 activation and enhance the toxicity of Chk1 inhibitors. This review examines the rationally hypothesized actions of Chk1 inhibitors as cell cycle modulatory drugs as well as the impact of Chk1 inhibition upon other cell survival signaling pathways. An understanding of Chk1 inhibition in multiple signaling contexts will be essential to the therapeutic development of Chk1 inhibitors.

Effect of simvastatin on cetuximab resistance in human colorectal cancer with KRAS mutations

BACKGROUND

Metastatic colorectal cancer (CRC) patients with v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations are resistant to treatment with cetuximab, a monoclonal antibody that targets the epidermal growth factor receptor. Statins have reported antitumor activity, but it is unknown whether simvastatin can reverse cetuximab resistance in KRAS mutant CRC.

METHODS

Human CRC cell lines with KRAS mutations (LS153, LS174T, DLD1, LoVo, SW403, SW480, SNU175, and LS1034) or with v-raf murine sarcoma viral oncogene homolog B1 (BRAF) mutations (DiFi, SW48, HT29, and RKO) were used to test the effect of cetuximab, simvastatin, and cetuximab plus simvastatin on cell proliferation and apoptosis in vitro. Because BRAF(V600E) mutant may be responsible for cetuximab resistance in KRAS wild-type cells, we measured the growth of xenograft tumors originating from KRAS mutant and BRAF mutant cells in mice treated with cetuximab alone or plus simvastatin (n = 5 mice per treatment group). We used immunoblot assays to study RAS-regulated activation of BRAF protein after simvastatin treatment. All statistical tests were two-sided.

RESULTS

Addition of simvastatin (0.2 μM) to cetuximab (0.03-1.0 μM) reduced cell proliferation of KRAS mutant (P < .001) but not of BRAF mutant CRC cells in vitro. Treatment of KRAS mutant cells with simvastatin reduced BRAF activity and induced apoptosis. Treatment with cetuximab and simvastatin reduced the growth of xenograft tumors originating from KRAS mutant cells compared with cetuximab alone (eg, for tumors originating from DLD1 cells, cetuximab vs cetuximab + simvastatin, mean tumor volume = 49.4 vs 20.2 cm(3), mean difference = 29.2 cm(3), 95% confidence interval = 19.7 to 38.5, P < .001); treatment with cetuximab alone or in combination with simvastatin had no effect on the growth of BRAF mutant tumors.

CONCLUSION

Simvastatin may overcome cetuximab resistance in colon cancer cells with KRAS mutations by modulating BRAF activity and inducing apoptosis.

Disruption of Src function potentiates Chk1-inhibitor-induced apoptosis in human multiple myeloma cells in vitro and in vivo

Ras/MEK/ERK pathway activation represents an important compensatory response of human multiple myeloma (MM) cells to checkpoint kinase 1 (Chk1) inhibitors. To investigate the functional roles of Src in this event and potential therapeutic significance, interactions between Src and Chk1 inhibitors (eg, UCN-01 or Chk1i) were examined in vitro and in vivo. The dual Src/Abl inhibitors BMS354825 and SKI-606 blocked Chk1-inhibitor-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation, markedly increasing apoptosis in association with BimEL up-regulation, p34(cdc2) activation, and DNA damage in MM cell lines and primary CD138(+) MM samples. Loss-of-function Src mutants (K297R, K296R/Y528F) or shRNA knock-down of Src prevented the ERK1/2 activation induced by Chk1 inhibitors and increased apoptosis. Conversely, constitutively active Ras or mitogen-activated protein kinase/ERK kinase 1 (MEK1) significantly diminished the ability of Src inhibitors to potentiate Chk1-inhibitor lethality. Moreover, Src/Chk1-inhibitor cotreatment attenuated MM-cell production of vascular endothelial growth factor and other angiogenic factors (eg, ANG [angiogenin], TIMP1/2 [tissue inhibitor of metalloproteinases 1/2], and RANTES [regulated on activation normal T-cell expressed and secreted]), and inhibited in vitro angiogenesis. Finally, coadministration of BMS354825 and UCN-01 suppressed human MM tumor growth in a murine xenograft model, increased apoptosis, and diminished angiogenesis. These findings suggest that Src kinase is required for Chk1-inhibitor-mediated Ras → ERK1/2 signaling activation, and that disruption of this event sharply potentiates the anti-MM activity of Chk1 inhi-bitors in vitro and in vivo.

Combined inhibitory effects of celecoxib and fluvastatin on the growth of human hepatocellular carcinoma xenografts in nude mice

This study was designed to investigate the in vivo growth inhibitory effects of celecoxib, a cyclo-oxygenase-2 inhibitor, and fluvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, on the hepatocellular carcinoma (HCC) cell line, BEL-7402. Athymic nude mice implanted with BEL-7402 cells were given celecoxib and fluvastatin, either alone or in combination, and the effect of treatment on tumour growth was evaluated after 6 weeks. The combination of celecoxib and fluvastatin enhanced inhibition of tumour growth, induction of apoptosis, inhibition of tumour cell proliferation, and inhibition of tumour angiogenesis compared with either treatment alone. The combination of celecoxib and fluvastatin also increased levels of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1), decreased levels of p-Akt, myeloid cell leukaemia-1 (Mcl-1) and survivin protein, but had no effect on Akt protein levels in tumours. These results suggest that celecoxib combined with fluvastatin would be more efficacious for the treatment of HCC than either treatment alone and this combination of therapy warrants further research.

Statins can modulate effectiveness of antitumor therapeutic modalities

Despite significant, frequently very strong, antiproliferative and tumoricidal effects of statins demonstrated in vitro, their antitumor effects in animal models are modest, and their efficacy in clinical trials has not been proven. As such, statins seem unlikely to be ever regarded as antitumor agents. However, statins are regularly taken by many elderly cancer patients for the prevention of cardiovascular events. Owing to their pleiotropic effects in normal and tumor cells, statins interact in various ways with many antitumor treatment modalities, either potentiating or diminishing their effectiveness. Elucidation of these interactions might affect the choice of treatment to be planned in cancer patients as some combinations might be contraindicated, whereas others might elicit potentiated antitumor effects but at a cost of increased general toxicity. Some other combinations might induce either comparable or even stronger antitumor effects, but with a beneficial concomitant reduction of specific side effects. Most of the studies reviewed in this article have been carried in vitro or in experimental tumor models, but clinical relevance of the findings is also discussed.

Role of matrix metalloproteinase-9 in the development of diabetic retinopathy and its regulation by H-Ras

PURPOSE

Diabetes activates a small molecular weight G-protein, H-Ras, in the retina and its capillary cells, and H-Ras activation is implicated in the apoptosis of retinal capillary cells. Matrix metalloproteinase (MMP)-9 is regulated by H-Ras, and in diabetes its activation is associated with increased vascular permeability. The goal of this study was to investigate the role of sustained activation of MMP-9 in the pathogenesis of diabetic retinopathy and to illustrate the mechanism through which it is upregulated in diabetes.

METHODS

Retinal MMP-9 activation and its tissue inhibitor, TIMP-1, were quantified in streptozotocin-induced diabetic rats. Inhibition of H-Ras by simvastatin on diabetes-induced activation of H-Ras was evaluated. The mechanism by which diabetes regulates retinal MMP-9 was confirmed by determining the effect of genetic or pharmacologic regulation of H-Ras on its activation in retinal endothelial cells.

RESULTS

In rats, MMP-9 was activated and expression of TIMP-1 was decreased in the retina and its microvasculature at both 2 months and 12 months of diabetes. In retinal endothelial cells, high glucose activated MMP-9, and inhibition of its activation (by pharmacologic inhibitor or siRNA) ameliorated accelerated apoptosis. Inhibition of H-Ras, both in diabetic rats (simvastatin) and in isolated endothelial cells (H-Ras siRNA), abrogated the activation of MMP-9 and prevented the reduction of TIMP-1.

CONCLUSIONS

Hyperglycemia-induced activation of MMP-9 accelerates apoptosis of retinal capillary cells, a phenomenon that predicts the development of diabetic retinopathy, and the activation of MMP-9 is downstream of H-Ras. Characterizing the role of MMP-9 in the development of diabetic retinopathy will help explore novel molecular targets for future pharmacological interventions.

New insights into checkpoint kinase 1 in the DNA damage response signaling network

The DNA damage response (DDR) represents a complex network of multiple signaling pathways involving cell cycle checkpoints, DNA repair, transcriptional programs, and apoptosis, through which cells maintain genomic integrity following various endogenous (metabolic) or environmental stresses. In cancer treatment, the DDR occurs in response to various genotoxic insults by diverse cytotoxic agents and radiation, representing an important mechanism limiting chemotherapeutic and radiotherapeutic efficacy. This has prompted the development of agents targeting DDR signaling pathways, particularly checkpoint kinase 1 (Chk1), which contributes to all currently defined cell cycle checkpoints, including G1/S, intra-S-phase, G2/M, and the mitotic spindle checkpoint. Although numerous agents have been developed with the primary goal of enhancing the activity of DNA-damaging agents or radiation, the therapeutic outcome of this strategy remains to be determined. Recently, new insights into DDR signaling pathways support the notion that Chk1 represents a core component central to the entire DDR, including direct involvement in DNA repair and apoptotic events in addition to checkpoint regulation. Together, these new insights into the role of Chk1 in the DDR machinery could provide an opportunity for novel approaches to the development of Chk1 inhibitor strategies.