[Show abstract][Hide abstract] ABSTRACT: Histone deacetylase inhibitors (HDIs) are under investigation for the treatment of a number of human health problems. HDIs have proven therapeutic value in refractory cases of cutaneous T-cell lymphoma. Electrocardiographic ST segment morphological changes associated with HDIs were observed during development. Because ST segment morphology is typically linked to changes in ATP sensitive potassium (KATP) channel activity, we tested the hypothesis that HDIs affect cardiac KATP channel subunit expression. Two different HDIs, romidepsin and trichostatin A, caused ~20-fold increase in SUR2 (Abcc9) subunit mRNA expression in HL-1 cardiomyocytes. The effect was specific for the SUR2 subunit as neither compound causes a marked change in SUR1 (Abcc8) expression. Moreover, the effect was cell specific as neither HDI markedly altered KATP subunit expression in MIN6 pancreatic β-cells. We observe significant enrichment of the H3K9Ac histone mark specifically at the SUR2 promoter consistent with the conclusion that chromatin remodeling at this locus plays a role in increasing SUR2 gene expression. Unexpectedly, however, we also discovered that HDI-dependent depletion of cellular cholesterol is required for the observed effects on SUR2 expression. Taken together, the data in the present study demonstrate that KATP subunit expression can be epigenetically regulated in cardiomyocytes, defines a role for cholesterol homeostasis in mediating epigenetic regulation and suggests a potential molecular basis for the cardiac effects of the HDIs.
Frontiers in Pharmacology 08/2015; 6:168. DOI:10.3389/fphar.2015.00168 · 3.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The histone deacetylase inhibitor belinostat is eliminated through glucuronidation by UGT1A1. Polymorphisms that reduce UGT1A1 function could result in increased belinostat exposure and toxicities. We wanted to determine which SNPs alter belinostat exposure and toxicity. In a phase I (BPE) trial belinostat (400, 500, 600 or 800 mg/m(2) /24 h, 48 h continuous infusion) was administered to patients with cancer in combination with cisplatin and etoposide (n = 25). Patients were genotyped for UGT1A1 variants associated with reduced function: UGT1A1*6, UGT1A1*28 and UGT1A1*60. Endpoints were associations between UGT1A1 genotype and belinostat pharmacokinetics (PK), toxicities and global protein lysine acetylation (AcK). Belinostat AUC was increased (P = 0.003) and t1/2 increased (P = 0.0009) in UGT1A1*28 and *60 carriers, that received more than 400 mg/m(2) /24 h. The incidence of grade 3-4 thrombocytopenia (P = 0.0081) was associated with UGT1A1 polymorphisms. The FDA approved package insert recommends dose adjustment of belinostat for UGT1A1*28. However, our data suggest dose adjustment is also necessary for UGT1A1*60. UGT1A1 polymorphisms were associated with increased systemic belinostat exposure, increased AcK and increased incidence of toxicities, particularly at doses > 400 mg/m(2) /24 h. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
The Journal of Clinical Pharmacology 08/2015; DOI:10.1002/jcph.625 · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The development of new treatment options for central nervous system (CNS) metastases from breast cancer and fromother solid tumors lags far behindprogress in otherareasofoncology.Despite this lag, a series of paradigm shifts have made it possible to renew our efforts to make progress.
The Oncologist 12/2014; 20(1). DOI:10.1634/theoncologist.2014-0469 · 4.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ABCG2 was first identified due to its unusual phenotype, as several groups began reporting non-P-glycoprotein (Pgp), non-MRP1-mediated drug resistance in cell lines selected with mitoxantrone. Subsequent to the cloning of BCRP/ABCP/MXR, the Human Genome Nomenclature Committee assigned the name ABCG2. ABCG2 expression is complex and regulated in a tissue-specific, disease stage-specific, and tumor-specific way. ABCG2, composed of 655 amino acids, runs as a 72 kDa protein on SDS-PAGE and is organized into two main structural elements: an N-terminal ATP-binding domain (NBD) and a C-terminal transmembrane domain (TMD). ABCG2 appears to play a role in the physiologic efflux of multiple endogenous substrates. Porphyrin/heme was identified as the first endogenous ABCG2 substrate in ABCG2 knockout mice. Kinase inhibitors are an ever-growing class of compounds that act as ABCG2 inhibitors. Several studies have documented the expression of ABCG2 in multiple tissues, in a pattern consistent with multiple roles in xenobiotic protection.
Drug Transporters, 08/2014: pages 187-221; , ISBN: 9781118489932
[Show abstract][Hide abstract] ABSTRACT: ABCG2 is a potential biomarker causing multidrug resistance (MDR) in Non-Small Cell Lung Cancer (NSCLC). We conducted this study to investigate whether Icotinib, a small-molecule inhibitor of EGFR tyrosine kinase, could interact with ABCG2 transporter in NSCLC. Our results showed that Icotinib reversed ABCG2-mediated MDR by antagonizing the drug efflux function of ABCG2. Icotinib stimulated the ATPase activity in a concentration-dependent manner and inhibited the photolabeling of ABCG2 with [125I]-Iodoarylazidoprazosin, demonstrating that it interacts at the drug-binding pocket. Homology modeling predicted the binding conformation of Icotinib at Asn629 centroid-based grid of ABCG2. However, Icotinib at reversal concentration did not affect the expression levels of AKT and ABCG2. Furthermore, a combination of Icotinib and topotecan exhibited significant synergistic anticancer activity against NCI-H460/MX20 tumor xenografts. However, the inhibition of transport activity of ABCG2 was insufficient to overcome pemetrexed resistance in NCI-H460/MX20 cells, which was due to the co-upregulated thymidylate synthase (TS) and ABCG2 expression. This is the first report to show that the up-regulation of TS in ABCG2-overexpressing cell line NCI-H460/MX20 may play a role of resistance to pemetrexate. Our findings suggested different possible strategies of overcoming the resistance of topotecan and pemetrexed in the NSCLC patients.
[Show abstract][Hide abstract] ABSTRACT: Romidepsin and vorinostat are histone deacetylase inhibitors (HDACis) that have activity in T-cell lymphomas, but have not gained traction in solid tumors. To gain deeper insight into mechanisms of HDACi efficacy, we systematically surveyed 19 cell lines with different molecular phenotypes, comparing romidepsin and vorinostat at equipotent doses. Acetylation at H3K9 and H4K8 along with 22 other histone lysine acetylation and methylation modifications were measured by reverse phase proteomics array (RPPA), and compared with growth inhibition (IC50), and cell cycle arrest. These assays typically used to assess HDACi effect showed that acetylation and methylation of specific lysine residues in response to HDACis were consistent across cell lines, and not related to drug sensitivity. Using a treatment duration more reflective of the clinical exposure, cell death detected by annexin staining following a 6 h drug exposure identified a subset of cell lines, including the T-cell lymphoma line, that was markedly more sensitive to HDAC inhibition. Kinetic parameters (Km values) were determined for lysine acetylation and for cell cycle data and were themselves correlated following HDACi exposure, but neither parameter correlated with cell death. The impact on cell survival signaling varied with the molecular phenotype. This study suggests that cellular response to HDACis can be viewed as two distinct effects: a chromatin effect and a cell death effect. All cells undergo acetylation, which is necessary but not sufficient for cell death. Cells not primed for apoptosis will not respond with cell death to the impact of altered histone acetylation. The divergent apoptotic responses observed reflect the variable clinical outcome of HDACi treatment. These observations should change our approach to the development of therapeutic strategies that exploit the dual activities of HDACis.
[Show abstract][Hide abstract] ABSTRACT: In this study we investigated the effect of linsitinib on the reversal of multidrug resistance (MDR) mediated by the overexpression of the ATP-binding cassette (ABC) subfamily members ABCB1, ABCG2, ABCC1 and ABCC10. Our results indicate for the first time that linsitinib significantly potentiate the effect of anti-neoplastic drugs mitoxantrone (MX) and SN-38, which are substrates of ABCG2 and paclitaxel, docetaxel and vinblastine which are substrates of ABCC10. Linsitinib moderately enhanced the cytotoxicity of vincristine in cell lines overexpressing ABCB1, whereas it did not alter the cytotoxicity of substrates of ABCC1. Furthermore, linsitinib significantly increased the intracellular concentration and significantly decreased the efflux of [(3)H]-MX in ABCG2-overexpressing cells and [(3)H]-paclitaxel in ABCC10-overexpressing cells. However, linsitinib, at a concentration that reversed MDR, did not significantly alter the expression levels of either the ABCG2 or ABCC10 transporter proteins. Furthermore, linsitinib did not significantly alter the intracellular localization of ABCG2 or ABCC10. Moreover, linsitinib stimulates the ATPase activity of ABCG2 in a concentration-dependent manner. Overall, our study suggests that linsitinib could attenuate ABCG2- and ABCC10-mediated MDR by directly inhibiting their function as opposed to altering ABCG2 or ABCC10 protein expression.
The international journal of biochemistry & cell biology 04/2014; 51(1). DOI:10.1016/j.biocel.2014.03.026 · 4.05 Impact Factor