CARM1 arginine methyltransferase as a therapeutic target for cancer.

Coactivator-associated arginine methyltransferase 1 (CARM1) is an arginine methyltransferase that posttranslationally modifies proteins that regulate multiple levels of RNA production and processing. Its substrates include histones, transcription factors, coregulators of transcription, and splicing factors. CARM1 is overexpressed in many different cancer types, and often promotes transcription factor programs that are co-opted as drivers of the transformed cell state, a process known as transcription factor addiction. Targeting these oncogenic transcription factor pathways is difficult but could be addressed by removing the activity of the key coactivators on which they rely. CARM1 is ubiquitously expressed, and its KO is less detrimental in embryonic development than deletion of the arginine methyltransferases protein arginine methyltransferase 1 and protein arginine methyltransferase 5, suggesting that therapeutic targeting of CARM1 may be well tolerated. Here, we will summarize the normal in vivo functions of CARM1 that have been gleaned from mouse studies, expand on the transcriptional pathways that are regulated by CARM1, and finally highlight recent studies that have identified oncogenic properties of CARM1 in different biological settings. This review is meant to kindle an interest in the development of human drug therapies targeting CARM1, as there are currently no CARM1 inhibitors available for use in clinical trials.

Circulating vascular endothelial growth factor receptor 2/pAkt-positive cells as a functional pharmacodynamic marker in metastatic colorectal cancers treated with antiangiogenic agent.

OBJECTIVE: The anti-vascular endothelial growth factor (VEGF) antibody bevacizumab has received considerable attention as a first-line treatment of advanced colorectal cancers. Difficulties associated with effectively monitoring the activity of this drug have prompted us to seek a pharmacodynamic marker suitable for defining the optimum biological dose and schedule of bevacizumab administration against colon cancer in early clinical trials. METHODS: We evaluated inhibitory effects of bevacizumab on VEGF signaling and tumor growth in vitro and in vivo, and assessed phosphorylation of VEGF receptor 2 (VEGFR2) and downstream signaling in endothelial cells as pharmacodynamic markers using phospho-flow cytometry. We also validated markers in patients with metastatic colorectal cancer (mCRC) treated with bevacizumab-based chemotherapy. RESULTS: In in vitro studies, bevacizumab inhibited proliferation of human umbilical vein endothelial cells in association with reduced VEGF signaling. Notably, bevacizumab inhibited VEGF-induced phosphorylation of VEGFR-2, Akt, and extracellular signal-regulated kinase (ERK). In vivo, treatment with bevacizumab inhibited growth of xenografted tumors and attenuated VEGF-induced phosphorylation of Akt and ERK. The median percentages of VEGFR2 + pAkt + and VEGFR2 + pERK + cells, determined by phospho-flow cytometry, were approximately 3-fold higher in mCRC patients than in healthy controls. Bevacizumab treatment decreased VEGFR2 + pAkt + cells in 18 of 24 patients on day 3. CONCLUSION: Bevacizumab combined with chemotherapy decreased the number of VEGFR2 + pAkt + cells, reflecting impaired VEGFR2 signaling. Together, these data suggest that changes in the proportion of circulating VEGFR2 + pAkt + cells may be a potential pharmacodynamic marker of the efficacy of antiangiogenic agents, and could prove valuable in determining drug dosage and administration schedule.

Quantitation and pharmacokinetics of 1,4-diamino-2,3-dicyano-1,4-bis (2-aminophenylthio) butadiene (U0126) in rat plasma by liquid chromatography-tandem mass spectrometry.

A simple, robust, and rapid LC-MS/MS method was developed for the quantitation of U0126 and validated in rat plasma. Plasma samples (20 µL) were deproteinized using 200 µL ACN containing 30 ng/mL of chlorpropamide, internal standard. Chromatographic separation performed on an Agilent Poroshell 120 EC-C(18) column (4.6 × 50 mm, 2.7 µm particle size) with an isocratic mobile phase consisting of a 70:30 v/v mixture of ACN and 0.1% aqueous formic acid. Each sample was run at 0.6 mL/min for a total run time of 2 min per sample. Detection and quantification were performed using a mass spectrometer in selected reaction-monitoring mode with positive ESI at m/z 381 → 123.9 for U0126 and m/z 277 → 175 for the internal standard. The standard curve was linear over a concentration range of 20-5000 ng/mL with correlation coefficients greater than 0.9965. Precision, both intra- and interday, was less than 10.1% with an accuracy of 90.7-99.4%. No matrix effects were observed. U0126 in rat plasma degraded approximately 41.3% after 3-h storage at room temperature. To prevent degradation, sample handling should be on an ice bath and all solutions kept at 4°C. This method was successfully applied to a pharmacokinetic study of U0126 at various doses in rats.

SPC-180002, a SIRT1/3 dual inhibitor, impairs mitochondrial function and redox homeostasis and represents an antitumor activity.

Since sirtuins (SIRTs) are closely associated with reactive oxygen species (ROS) and antioxidant system, the development of their selective inhibitors is drawing attention for understanding of cellular redox homeostasis. Here, we describe the pharmacological properties of SPC-180002, which incorporates a methyl methacrylate group as a key pharmacophore, along with its comprehensive molecular mechanism as a novel dual inhibitor of SIRT1/3. The dual inhibition of SIRT1/3 by SPC-180002 disturbs redox homeostasis via ROS generation, which leads to an increase in both p21 protein stability and mitochondrial dysfunction. Increased p21 interacts with and inhibits CDK, thereby interfering with cell cycle progression. SPC-180002 leads to mitochondrial dysfunction by inhibiting mitophagy, which is accompanied by a reduction in oxygen consumption rate. Consequently, SPC-180002 strongly suppresses the proliferation of cancer cells and exerts anticancer effect in vivo. Taken together, the novel SIRT1/3 dual inhibitor, SPC-180002, impairs mitochondrial function and redox homeostasis, thereby strongly inhibiting cell cycle progression and cancer cell growth.

GSK-3484862 targets DNMT1 for degradation in cells.

Maintenance of genomic methylation patterns at DNA replication forks by DNMT1 is the key to faithful mitotic inheritance. DNMT1 is often overexpressed in cancer cells and the DNA hypomethylating agents azacytidine and decitabine are currently used in the treatment of hematologic malignancies. However, the toxicity of these cytidine analogs and their ineffectiveness in treating solid tumors have limited wider clinical use. GSK-3484862 is a newly-developed, dicyanopyridine containing, non-nucleoside DNMT1-selective inhibitor with low cellular toxicity. Here, we show that GSK-3484862 targets DNMT1 for protein degradation in both cancer cell lines and murine embryonic stem cells (mESCs). DNMT1 depletion was rapid, taking effect within hours following GSK-3484862 treatment, leading to global hypomethylation. Inhibitor-induced DNMT1 degradation was proteasome-dependent, with no discernible loss of DNMT1 mRNA. In mESCs, GSK-3484862-induced Dnmt1 degradation requires the Dnmt1 accessory factor Uhrf1 and its E3 ubiquitin ligase activity. We also show that Dnmt1 depletion and DNA hypomethylation induced by the compound are reversible after its removal. Together, these results indicate that this DNMT1-selective degrader/inhibitor will be a valuable tool for dissecting coordinated events linking DNA methylation to gene expression and identifying downstream effectors that ultimately regulate cellular response to altered DNA methylation patterns in a tissue/cell-specific manner.

Protein arginine methyltransferases: promising targets for cancer therapy.

Protein methylation, a post-translational modification (PTM), is observed in a wide variety of cell types from prokaryotes to eukaryotes. With recent and rapid advancements in epigenetic research, the importance of protein methylation has been highlighted. The methylation of histone proteins that contributes to the epigenetic histone code is not only dynamic but is also finely controlled by histone methyltransferases and demethylases, which are essential for the transcriptional regulation of genes. In addition, many nonhistone proteins are methylated, and these modifications govern a variety of cellular functions, including RNA processing, translation, signal transduction, DNA damage response, and the cell cycle. Recently, the importance of protein arginine methylation, especially in cell cycle regulation and DNA repair processes, has been noted. Since the dysregulation of protein arginine methylation is closely associated with cancer development, protein arginine methyltransferases (PRMTs) have garnered significant interest as novel targets for anticancer drug development. Indeed, several PRMT inhibitors are in phase 1/2 clinical trials. In this review, we discuss the biological functions of PRMTs in cancer and the current development status of PRMT inhibitors in cancer therapy.

A novel synthetic microtubule inhibitor exerts antiproliferative effects in multidrug resistant cancer cells and cancer stem cells.

The success of cancer chemotherapy is limited by multidrug resistance (MDR), which is mainly caused by P-glycoprotein (P-gp) overexpression. In the present study, we describe a novel microtubule inhibitor, 5-(N-methylmaleimid-3-yl)-chromone (SPC-160002), that can be used to overcome MDR. A synthetic chromone derivative, SPC-160002, showed a broad spectrum of anti-proliferative effects on various human cancer cells without affecting P-gp expression and its drug efflux function. Treatment with SPC-160002 arrested the cell cycle at the M phase, as evidenced using fluorescence-activated cell sorting analysis, and increased the levels of mitotic marker proteins, including cyclin B, pS10-H3, and chromosomal passenger complex. This mitotic arrest by SPC-160002 was mediated by promoting and stabilizing microtubule polymerization, similar to the mechanism observed in case of taxane-based drugs. Furthermore, SPC-160002 suppressed the growth and sphere-forming activity of cancer stem cells. Our data herein strongly suggest that SPC-160002, a novel microtubule inhibitor, can be used to overcome MDR and can serve as an attractive candidate for anticancer drugs.

PRMT5 promotes DNA repair through methylation of 53BP1 and is regulated by Src-mediated phosphorylation.

PRMT5 participates in various cellular processes, including transcription regulation, signal transduction, mRNA splicing, and DNA repair; however, its mechanism of regulation is poorly understood. Here, we demonstrate that PRMT5 is phosphorylated at residue Y324 by Src kinase, a negative regulator of its activity. Either phosphorylation or substitution of the Y324 residue suppresses PRMT5 activity by preventing its binding with the methyl donor S-adenosyl-L-methionine. Additionally, we show that PRMT5 activity is associated with non-homologous end joining (NHEJ) repair by methylating and stabilizing p53-binding protein 1 (53BP1), which promotes cellular survival after DNA damage. Src-mediated phosphorylation of PRMT5 and the subsequent inhibition of its activity during the DNA damage process blocks NHEJ repair, leading to apoptotic cell death. Altogether, our findings suggest that PRMT5 regulates DNA repair through Src-mediated Y324 phosphorylation in response to DNA damage.

PRMT6-mediated H3R2me2a guides Aurora B to chromosome arms for proper chromosome segregation.

The kinase Aurora B forms the chromosomal passenger complex (CPC) together with Borealin, INCENP, and Survivin to mediate chromosome condensation, the correction of erroneous spindle-kinetochore attachments, and cytokinesis. Phosphorylation of histone H3 Thr3 by Haspin kinase and of histone H2A Thr120 by Bub1 concentrates the CPC at the centromere. However, how the CPC is recruited to chromosome arms upon mitotic entry is unknown. Here, we show that asymmetric dimethylation at Arg2 on histone H3 (H3R2me2a) by protein arginine methyltransferase 6 (PRMT6) recruits the CPC to chromosome arms and facilitates histone H3S10 phosphorylation by Aurora B for chromosome condensation. Furthermore, in vitro assays show that Aurora B preferentially binds to the H3 peptide containing H3R2me2a and phosphorylates H3S10. Our findings indicate that the long-awaited key histone mark for CPC recruitment onto mitotic chromosomes is H3R2me2a, which is indispensable for maintaining appropriate CPC levels in dynamic translocation throughout mitosis.

Protein arginine methyltransferase 6 suppresses adipogenic differentiation by repressing peroxisome proliferator­activated receptor γ activity.

The present study demonstrated that protein arginine methyltransferase 6 (PRMT6) negatively regulates the activity of peroxisome proliferator­activated receptor γ (PPARγ). The results indicated that the overexpression of PRMT6 inhibited the transactivity of PPARγ and subsequently decreased the expression levels of PPARγ target genes. Contrarily, the depletion or inhibition of PRMT6 increased PPARγ reporter activity and the expression of its target genes. It was also confirmed that PRMT6 was involved in the process of adipocyte differentiation. In addition, PRMT6 interacted with, but did not methylate, PPARγ. PRMT6 bound to the PPAR­responsive regulatory element of the adipocyte Protein 2 (aP2) promoter in conjunction with PPARγ and generated the repressive epigenetic mark arginine 2 on histone H3 asymmetric di­methylation, which suppressed aP2 gene expression. Therefore, PRMT6 may serve as an important regulator of PPARγ activity in adipogenic differentiation and may be an attractive therapeutic target for human metabolic diseases.

Histone deacetylase inhibitor apicidin-mediated drug resistance: involvement of P-glycoprotein.

Multidrug resistance (MDR), which is a significant impediment to the success of cancer chemotherapy, is attributable to the overexpression of membrane transport proteins, such as P-glycoprotein (P-gp), resulting in an increased drug efflux. In this study, we show that the histone deacetylase (HDAC) inhibitor apicidin leads to resistance of HeLa cells to paclitaxel through the induction of P-gp expression. Furthermore, apicidin dramatically increases the release of a fluorescent P-gp substrate, rhodamine 123, from cells. In parallel, apicidin resistance to the apoptotic potential of paclitaxel is associated with induction of P-gp expression in HeLa cells, as evidenced by specific inhibition of P-gp function using either the pharmacological inhibitor verapamil or RNA silencing. We also demonstrate the contribution of apicidin-induced functional P-gp expression to drug resistance using KB cells. Failure of P-gp induction by apicidin does not reverse paclitaxel-induced cytotoxicity in the cells. Although HDAC inhibitors are widely appreciated as a new class of anti-tumor agent, our findings clearly demonstrate that apicidin treatment may lead to P-gp-mediated resistance to other anti-tumor agents, suggesting a need for careful design of clinical applications using HDAC inhibitors.

Trichostatin A increases the thermosensitivity of human glioblastoma A172 cells.

Trichostatin A (TSA), histone deacetylase inhibitor, shows a promising therapeutic effect on cancer cells in combination with radiotherapy or chemotherapy. However, little has been reported on the combined treatment of TSA with hyperthermia. Here, we have assessed the effect of TSA/hyperthermia on human glioblastoma A172 cells and found that TSA increases the thermosensitivity of A172 cells, resulting in cellular apoptosis. The underlying mechanism of this effect consists of reduction in the level of phosphorylated STAT3 (Tyr705), a transcription factor required for survival of A172 cells, which leads to down-regulation of STAT3 target genes, cyclin D1 and Bcl-xL. Furthermore, the level of VEGF mRNA was also decreased by TSA/hyperthermia, suggesting the antiangiogenic effect of TSA/hyperthermia on human glioblastoma. Collectively, our results show the role of TSA as a chemical thermosensitizer, suggesting the possible therapeutic application of combined treatment of TSA/hyperthermia on STAT3-dependent tumors.

The synthetic ajoene analog SPA3015 induces apoptotic cell death through crosstalk between NF-κB and PPARγ in multidrug-resistant cancer cells.

Multidrug resistance (MDR) caused by P-glycoprotein (P-gp) overexpression impedes successful cancer chemotherapy. In this study, we investigated the anticancer effects of SPA3015, a synthetic ajoene analog, in P-gp-overexpressing MDR cancer cells (KBV20C and MES-SA/DX5). Treatment with SPA3015 caused a dramatic decrease in the cell viabilities of both KBV20C and MES-SA/DX5 cells. This decrease was accompanied by apoptotic cell death without affecting the expression level or drug efflux function of P-gp. SPA3015 selectively suppressed NF-κB reporter gene activity, which led to decreased expression of NF-κB target genes such as CIAP1, CIAP2, XIAP, and Bcl-XL. Surprisingly, nuclear localization and DNA binding affinity of the p65 subunit were not affected by SPA3015, suggesting that SPA3015 inhibits the transcriptional activity of NF-κB at the nucleus. Indeed, SPA3015 treatment led to an increase in the physical interaction of p65 with PPARγ, which resulted in the inhibition of NF-κB activity. Our findings support the hypothesis that SPA3015 inhibits NF-κB transcriptional activity by facilitating the physical interaction of the p65 subunit and PPARγ, which leads to apoptotic cell death in MDR cancer cells.

Akt regulation of Aven contributes to the sensitivity of cancer cells to chemotherapeutic agents.

In the present study, it was demonstrated that the protein level of the apoptosis inhibitor Aven is regulated by the Akt signaling pathway, evidenced by the observation that Aven levels were significantly increased in MCF7 constitutively active (CA)­Akt cells and significantly inhibited following treatment with LY294002. This increase in Aven appears not to be mediated by transcriptional regulation and protein stabilization. However, the level of Aven was inversely correlated with the level of cathepsin D, which is a protease responsible for generating the C­terminal of Aven, ΔN­Aven, indicating that the level of Aven appears to be regulated by cathepsin D activity. It has previously been reported that ΔN­Aven is the active form of Aven, which functions as an anti­apoptotic molecule. Notably, low levels of ΔN­Aven were detected in MCF7 CA­Akt cells, which were more sensitive to anticancer drugs. Taken together, the current results suggest that the expression of Aven is regulated by the Akt signaling pathway through cathepsin D activity, which contributes to the sensitivity of cancer cells to chemotherapeutic agents.

Combination of CYP inhibitor with MEK/ERK inhibitor enhances the inhibitory effect on ERK in BRAF mutant colon cancer cells.

BACKGROUND/AIM: To investigate mechanisms of discrepancy in response to a MEK/ERK inhibitor, U0126, in KRAS- and BRAF-mutant colorectal cancer cells. MATERIALS AND METHODS: Multiparametric flow cytometry was performed on two colon cancer cell lines, HCT116 and HT29. Cells were treated with U0126, and phospho-specific antibodies were used to monitor ERK signaling. RESULTS: HCT116 and HT29 cells were treated with increasing amounts of U0126. The western blot analysis revealed that by increasing the amount of U0126 resulted in inhibition of phospho-ERK, in HCT116 and to a lesser degree in HT29 cells. Microarray profiling identified CYP1A1 and 1A2 overexpression in HT29 cells and that inhibition of CYP1A1 with α-naphthoflavone and furanfylline restored sensitivity to U0126 in HT29 cells. CONCLUSION: Combination of a CYP inhibitor with MEK/ERK inhibitor enhances the inhibitory effect on ERK in BRAF-mutant colon cancer cells.

Quantitative analysis of ERK signaling inhibition in colon cancer cell lines using phospho-specific flow cytometry.

OBJECTIVE: To evaluate the activity of U0126, a MEK1/2 inhibitor, in downregulating the phosphorylation of ERK in colon cancer cell lines and to explore the correlation of phospho-flow cytometry with standardized methods to validate its use in clinical settings. Phospho-specific flow cytometry provides an optimal platform for the analysis of signaling abnormalities in cancer. In this study, we used phospho-specific flow cytometry to monitor intracellular signaling in cells stimulated with phorbol 12-myristate 13-acetate (PMA). STUDY DESIGN: Multiparametric flow cytometry was performed on two colon cancer cell lines, HCT116 and HT29. PMA-stimulated cells were treated with U0126, and phospho-specific antibodies were used to monitor ERK signaling. The resulting data were compared to western blotting and immunofluorescence staining. RESULTS: HCT116 and HT29 cells were treated with increasing amounts of U0126 after PMA stimulation. The western blot analysis revealed that increasing the amount of U0126 resulted in inhibition of phospho-ERK (p-ERK). Fluorescence-activated cell sorting plots of phosphorylation of ERK demonstrated that the levels of p-ERK decreased with increasing concentrations of U0126. Results of immunofluorescence staining indicated that the staining density of the immunofluorescent dye decreased as the concentration of U0126 increased from 0.1 microM to 100 microM. CONCLUSION: Quantitative and correlated expression profiles for ERK signaling suggest that phospho-specific flow cytometry will provide new insights into mechanisms underlying defective signaling in cancer and enable us to predict drug responses in cancer cell lines.