Gergely Szakács

Hungarian Academy of Sciences, Budapeŝto, Budapest, Hungary

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Publications (64)434.03 Total impact

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    ABSTRACT: Cells cope with the threat of xenobiotic stress by activating a complex molecular network that recognizes and eliminates chemically diverse toxic compounds. This "chemoimmune system" consists of cellular Phase I and Phase II metabolic enzymes, Phase 0 and Phase III ATP Binding Cassette (ABC) membrane transporters, and nuclear receptors regulating these components. In order to provide a systems biology characterization of the chemoimmune network, we designed a reaction kinetic model based on differential equations describing Phase 0-III participants and regulatory elements, and characterized cellular fitness to evaluate toxicity. In spite of the simplifications, the model recapitulates changes associated with acquired drug resistance and allows toxicity predictions under variable protein expression and xenobiotic exposure conditions. Our simulations suggest that multidrug ABC transporters at Phase 0 significantly facilitate the defense function of successive network members by lowering intracellular drug concentrations. The model was extended with a novel toxicity framework which opened the possibility of performing in silico cytotoxicity assays. The alterations of the in silico cytotoxicity curves show good agreement with in vitro cell killing experiments. The behavior of the simplified kinetic model suggests that it can serve as a basis for more complex models to efficiently predict xenobiotic and drug metabolism for human medical applications.
    PLoS ONE 02/2015; 10(2):e0115533. DOI:10.1371/journal.pone.0115533 · 3.53 Impact Factor
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    ABSTRACT: ABCB6 is a homodimeric ATP-binding cassette (ABC) transporter present in the plasma membrane and in intracellular organelles. The intracellular localization of ABCB6 has been a matter of debate, as it has been suggested to reside in the mitochondria and the endo-lysosomal system. Using a variety of imaging modalities including confocal and electron microscopy we confirm the endo-lysosomal localization of ABCB6 and show that the protein is internalized from the plasma membrane through endocytosis, to be distributed to multivesicular bodies and lysosomes. In addition to the canonical nucleotide binding (NBD) and transmembrane domains (TMD), ABCB6 contains a unique N-terminal transmembrane domain (TMD0), which does not show sequence homology to known proteins. We investigated the functional role of these domains through the molecular dissection of ABCB6. We find that the folding, dimerization, membrane insertion and ATP binding/hydrolysis of the core ABCB6 complex devoid of TMD0 is preserved. However, in contrast to the full-length transporter, the core ABCB6 construct is retained at the plasma membrane, and does not appear in Rab5-positive endosomes. TMD0 is directly targeted to the lysosomes, without a passage to the plasma membrane. Collectively, our results reveal that TMD0 represents an independently folding unit, which is dispensable for catalysis, but has a crucial role in the lysosomal targeting of ABCB6.
    Biochemical Journal 01/2015; DOI:10.1042/BJ20141085 · 4.78 Impact Factor
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    ABSTRACT: Three novel pyrimidinylhydrazones substituted at either the aromatic moiety or at the imine carbon atom were synthesized and characterized by standard analytical methods. All compounds were found to be toxic in the micro- to submicromolar range against a diverse panel of cancer cell lines including multidrug resistant (MDR) derivatives expressing P-glycoprotein (Pgp). Using UV-visible spectrophotometry experiments demonstrated that the most active compound (3) forms highly stable complexes with iron(III) and copper(II) in a wide pH range with a stronger preference towards iron(III). The redox activity of the iron and copper complexes of ligand 3 was investigated using cyclic voltammetry and was tested with cellular reductants. The impact of reactive oxygen species (ROS) in the mechanism of toxicity was assessed using the ROS-sensitive cell permeable dye 2′,7′-dichlorofluorescin diacetate (DCFDA). Our results demonstrate that the studied pyrimidinylhydrazones form redox-active iron and copper complexes that are capable of producing intracellular ROS, which might lead to cellular damage and cell death in cancer cells regardless of their resistance status.
    Journal of Inorganic Biochemistry 12/2014; 144. DOI:10.1016/j.jinorgbio.2014.12.015 · 3.27 Impact Factor
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    ABSTRACT: Human ABCG2 is a plasma membrane glycoprotein causing multidrug resistance in cancer. Membrane cholesterol and bile acids are efficient regulators of ABCG2 function, while the molecular nature of the sterol-sensing sites has not been elucidated. The cholesterol recognition amino acid consensus (CRAC, L/V-(X)(1-5)-Y-(X)(1-5)-R/K) sequence is one of the conserved motifs involved in cholesterol binding in several proteins. We have identified five potential CRAC motifs in the transmembrane domain of the human ABCG2 protein. In order to define their roles in sterol-sensing, the central tyrosines of these CRACs (Y413, 459, 469, 570 and 645) were mutated to S or F and the mutants were expressed both in insect and mammalian cells. We found that mutation in Y459 prevented protein expression; the Y469S and Y645S mutants lost their activity; while the Y570S, Y469F, and Y645F mutants retained function as well as cholesterol and bile acid sensitivity. We found that in the case of the Y413S mutant, drug transport was efficient, while modulation of the ATPase activity by cholesterol and bile acids was significantly altered. We suggest that the Y413 residue within a putative CRAC motif has a role in sterol-sensing and the ATPase/drug transport coupling in the ABCG2 multidrug transporter. Copyright © 2014. Published by Elsevier B.V.
    Biochimica et Biophysica Acta (BBA) - Biomembranes 11/2014; 1848(2):477-487. DOI:10.1016/j.bbamem.2014.11.006 · 3.43 Impact Factor
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    ABSTRACT: Lan is a high-incidence blood group antigen expressed in more than 99.9% of the population. Identification of the human ABC transporter ABCB6 as the molecular basis of Lan has opened the way for studies assessing the relation of ABCB6 function and expression to health and disease. To date, 34 ABCB6 sequence variants have been described in association with reduced ABCB6 expression based on the genotyping of stored blood showing weak or no reactivity with anti-Lan antibodies. In the present study we examined the red blood cell (RBC) surface expression of ABCB6 by quantitative flow cytometry in a cohort of 47 healthy individuals. Sequencing of the entire coding region of the ABCB6 gene in low RBC ABCB6 expressors identified a new allele (IVS9+1G>A, affecting a putative splice site at the boundary of exon 9) and two nonsynonymous SNPs listed in the SNP database (R192Q (rs150221689) and G588 S (rs145526996)). The R192Q mutation showed co-segregation with reduced RBC ABCB6 expression in a family, and we found the G588 S mutation in a compound heterozygous individual with undetectable ABCB6 expression, suggesting that both mutations result in weak or no expression of ABCB6 on RBCs. Analysis of the intracellular expression pattern in HeLa cells by confocal microscopy indicated that these mutations do not compromise overall expression or the endolysosomal localization of ABCB6. Genotyping of two large cohorts, containing 235 and 1039 unrelated volunteers, confirmed the high allele frequency of Lan-mutations. Our results suggest that genetic variants linked to lower or absent cell surface expression of ABCB6/Langereis may be more common than previously thought.
    PLoS ONE 10/2014; 9(10). DOI:10.1371/journal.pone.0111590 · 3.53 Impact Factor
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    ABSTRACT: Sucrose fatty acid esters are increasingly used as excipients in pharmaceutical products, but few data are available on their toxicity profile, mode of action, and efficacy on intestinal epithelial models. Three water-soluble sucrose esters, palmitate (P-1695), myristate (M-1695), laurate (D-1216), and two reference absorption enhancers, Tween 80 and Cremophor RH40, were tested on Caco-2 cells. Caco-2 monolayers formed a good barrier as reflected by high transepithelial resistance and positive immunostaining for junctional proteins claudin-1, ZO-1, and β-catenin. Sucrose esters in nontoxic concentrations significantly reduced resistance and impedance, and increased permeability for atenolol, fluorescein, vinblastine, and rhodamine 123 in Caco-2 monolayers. No visible opening of the tight junctions was induced by sucrose esters assessed by immunohistochemistry and electron microscopy, but some alterations were seen in the structure of filamentous actin microfilaments. Sucrose esters fluidized the plasma membrane and enhanced the accumulation of efflux transporter ligands rhodamine 123 and calcein AM in epithelial cells, but did not inhibit the P-glycoprotein (P-gp)-mediated calcein AM accumulation in MES-SA/Dx5 cell line. These data indicate that in addition to their dissolution-increasing properties sucrose esters can enhance drug permeability through both the transcellular and paracellular routes without inhibiting P-gp. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci
    Journal of Pharmaceutical Sciences 10/2014; 103(10). DOI:10.1002/jps.24085 · 3.01 Impact Factor
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    ABSTRACT: Background: ATP-binding Cassette (ABC) transporters have key roles in various physiological functions as well as providing chemical defense and stress tolerance in human tissues. In this study we have examined the expression pattern of all ABC proteins in pluripotent human embryonic stem cells (hESCs) and in their differentiated progenies. We paid special attention to the cellular expression and localization of multidrug transporter ABC proteins. Methods: Stem cell differentiation was carried out without chemical induction or cell sorting, and specialized cell types were separated mechanically. Cellular features regarding pluripotency and tissue identity, as well as ABC transporter expression were studied by flow cytomtery, immuno-microscopy and qPCR-based low-density arrays. Results: Pluripotent hESCs and differentiated cell types (cardiomyocytes, neuronal cells and mesenchymal stem cells) were distinguished by morphology, immunostaining markers and selected mRNA expression patterns. We found that the mRNA expression levels of the 48 human ABC proteins also clearly distinguished the pluripotent and the respective differentiated cell types. When multidrug and lipid transporter ABC protein expression was examined by using well characterized specific antibodies by flow cytometry and confocal microscopy, the protein expression data corresponded well to the mRNA expression results. Moreover, the cellular localization of these important human ABC transporter proteins could be established in the pluripotent and differentiated hESC derived samples. Conclusions: These studies provide valuable information regarding ABC protein expression in human stem cells and their differentiated offspring. The results may also help to obtain further information concerning the specialized cellular functions of selected ABC transporters. © 2014 Clinical Cytometry Society.
    Cytometry Part B Clinical Cytometry 09/2014; 86(5). DOI:10.1002/cytob.21168 · 2.28 Impact Factor
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    Chemical Reviews 04/2014; 114(11). DOI:10.1021/cr4006236 · 45.66 Impact Factor
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    ABSTRACT: We recently identified a chromone derivative, 5-(4-bromobenzyloxy)-2-(2-(5-methoxyindolyl)ethyl-1-carbonyl)-4H-chromen-4-one, named here chromone 1, as a potent, selective, non-toxic and non-transported inhibitor of ABCG2-mediated drug efflux (Valdameri et al. J. Med. Chem. 2012, 55, 966). We now synthesized a series of 14 derivatives to study structure-activity relationships controlling both drug efflux and ATPase activity of ABCG2, and to elucidate their molecular mechanism of interaction and inhibition. It was found that the 4-bromobenzyloxy substituent at position 5 and the methoxyindole are important for both inhibition of mitoxantrone efflux and inhibition of basal ATPase activity. Quite interestingly, methylation of the central amide nitrogen strongly altered the high-affinity and complete inhibition of mitoxantrone efflux, as well as the inhibition of coupled ATPase activity. These results allowed the identification of a critical central inhibitory moiety of chromones that has never been investigated previously, in any series of inhibitors.
    Journal of Medicinal Chemistry 12/2013; 56(24). DOI:10.1021/jm401649j · 5.48 Impact Factor
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    ABSTRACT: ABCG2 is a key human ATP-binding cassette (ABC) transporter mediating cancer cell chemoresistance. In the case of ABCC1, another multidrug transporter, earlier findings documented that certain modulators greatly increase ABCC1-mediated glutathione (GSH) efflux and, upon depletion of intracellular GSH, induce "collateral sensitivity" leading to the apoptosis of multidrug resistant cells. Recently, it has been suggested that ABCG2 may mediate an active GSH transport. In order to explore if ABCG2-overexpressing cells may be similarly targeted, we first looked for the effects of ABCG2 expression on cellular GSH levels, and for an ABCG2-dependent GSH transport in HEK293 and MCF7 cells. We found that, while ABCG2 overexpression altered intracellular GSH levels in these transfected or drug-selected cells, ABCG2 inhibitors or transport modulators did not influence GSH efflux. We then performed direct measurements of drug-stimulated ATPase activity and (3)H-GSH transport in inside-out membrane vesicles of human ABC transporter-overexpressing Sf9 insect cells. Our results indicate that ABCG2-ATPase is not modulated by GSH and, in contrast to ABCC1, ABCG2 does not catalyze any significant GSH transport. Our data suggest no direct interaction between the ABCG2 transporter and GSH, although a long-term modulation of cellular GSH by ABCG2 cannot be excluded.
    Frontiers in Pharmacology 11/2013; 4:138. DOI:10.3389/fphar.2013.00138
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    ABSTRACT: Rationale: ABCC6 plays a crucial role in ectopic calcification; mutations of the gene cause pseudoxanthoma elasticum (PXE) and general arterial calcification of infancy (GACI). To elucidate the role of ABCC6 in cellular physiology and disease, it is crucial to establish the exact subcellular localization of the native ABCC6 protein. Objective: In a recent paper in Circulation Research, ABCC6 was reported to localize to the mitochondria-associated membrane (MAM) and not the plasma membrane. Since the suggested mitochondrial localization is inconsistent with published data and the presumed role of ABCC6, we performed experiments to determine the cellular localization of ABCC6 in its physiological environment. Methods and Results: We performed immunofluorescent labeling of frozen mouse and human liver sections as well as primary hepatocytes. We used several different antibodies recognizing human and mouse ABCC6. Our results unequivocally show that ABCC6 is expressed in the basolateral membrane of hepatocytes and is not associated with the mitochondria, MAM or the ER. Conclusions: Our findings support the model that ABCC6 is expressed in the basolateral membrane, mediating the sinusoidal efflux of a metabolite from the hepatocytes to the systemic circulation.
    Circulation Research 04/2013; 112(11). DOI:10.1161/CIRCRESAHA.111.300194 · 11.09 Impact Factor
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    ABSTRACT: We have developed a rapid, simple and reliable, antibody-based flow cytometry assay for the quantitative determination of membrane proteins in human erythrocytes. Our method reveals significant differences between the expression levels of the wild-type ABCG2 protein and the heterozygous Q141K polymorphic variant. Moreover, we find that nonsense mutations on one allele result in a 50% reduction in the erythrocyte expression of this protein. Since ABCG2 polymorphisms are known to modify essential pharmacokinetic parameters, uric acid metabolism and cancer drug resistance, a direct determination of the erythrocyte membrane ABCG2 protein expression may provide valuable information for assessing these conditions or for devising drug treatments. Our findings suggest that erythrocyte membrane protein levels may reflect genotype-dependent tissue expression patterns. Extension of this methodology to other disease-related or pharmacologically important membrane proteins may yield new protein biomarkers for personalized diagnostics.
    PLoS ONE 11/2012; 7(11):e48423. DOI:10.1371/journal.pone.0048423 · 3.53 Impact Factor
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    ABSTRACT: Seeding of bone implants with mesenchymal stem cells (MSCs) may promote osseointegration and bone regeneration. However, implant material surfaces, such as titanium or bovine bone mineral, fail to support rapid and efficient attachment of MSCs, especially under serum-free conditions that may be desirable when human applications or tightly controlled experiments are envisioned. Here we demonstrate that a branched poly[Lys(Ser(i)-DL-Ala(m))] polymer functionalized with cyclic arginyl-glycyl-aspartate, when immobilized by simple adsorption to tissue culture plastic, surgical titanium alloy (Ti6Al4V), or Bio-Oss(®) bovine bone substitute, significantly accelerates serum-free adhesion and enhances seeding efficiency of human adipose tissue-derived MSCs. Moreover, when exposed to serum-containing osteogenic medium, MSCs survived and differentiated on the peptide-coated scaffolds. In summary, the presented novel polypeptide conjugate can be conveniently used for coating various surfaces, and may find applications whenever quick and efficient seeding of MSCs is required to various scaffolds in the absence of serum.
    Journal of Materials Science Materials in Medicine 11/2012; 24(2). DOI:10.1007/s10856-012-4809-x · 2.38 Impact Factor
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    ABSTRACT: ABCB6, a member of the adenosine triphosphate-binding cassette (ABC) transporter family, has been proposed to be responsible for the mitochondrial uptake of porphyrins. Here we show that ABCB6 is a glycoprotein present in the membrane of mature erythrocytes and in exosomes released from reticulocytes during the final steps of erythroid maturation. Consistent with its presence in exosomes, endogenous ABCB6 is localized to the endo/lysosomal compartment, and is absent from the mitochondria of cells. Knock-down studies demonstrate that ABCB6 function is not required for de novo heme biosynthesis in differentiating K562 cells, excluding this ABC transporter as a key regulator of porphyrin synthesis. We confirm the mitochondrial localization of ABCB7, ABCB8 and ABCB10, suggesting that only three ABC transporters should be classified as mitochondrial proteins. Taken together, our results challenge the current paradigm linking the expression and function of ABCB6 to mitochondria.
    PLoS ONE 05/2012; 7(5):e37378. DOI:10.1371/journal.pone.0037378 · 3.53 Impact Factor
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    ABSTRACT: Human ABCG2 is a plasma membrane glycoprotein that provides physiological protection against xenobiotics. ABCG2 also significantly influences biodistribution of drugs through pharmacological tissue barriers and confers multidrug resistance to cancer cells. Moreover, ABCG2 is the molecular determinant of the side population that is characteristically enriched in normal and cancer stem cells. Numerous tumors depend on unregulated EGFR signaling, thus inhibition of this receptor by small molecular weight inhibitors such as gefitinib, and the novel second generation agents vandetanib, pelitinib and neratinib, is a promising therapeutic option. In the present study, we provide detailed biochemical characterization regarding the interaction of these EGFR inhibitors with ABCG2. We show that ABCG2 confers resistance to gefitinib and pelitinib, whereas the intracellular action of vandetanib and neratinib is unaltered by the presence of the transporter. At higher concentrations, however, all these EGFR inhibitors inhibit ABCG2 function, thereby promoting accumulation of ABCG2 substrate drugs. We also report enhanced expression of ABCG2 in gefitinib-resistant non-small cell lung cancer cells, suggesting potential clinical relevance of ABCG2 in acquired drug resistance. Since ABCG2 has important impact on both the pharmacological properties and anti-cancer efficiencies of drugs, our results regarding the novel EGFR inhibitors should provide useful information about their therapeutic applicability against ABCG2-expressing cancer cells depending on EGFR signaling. In addition, the finding that these EGFR inhibitors efficiently block ABCG2 function may help to design novel drug-combination therapeutic strategies.
    Biochemical pharmacology 04/2012; 84(3):260-7. DOI:10.1016/j.bcp.2012.04.010 · 4.65 Impact Factor
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    ABSTRACT: The phenomenon of multidrug resistance in cancer is often associated with the overexpression of the ABC (ATP-binding cassette) transporters Pgp (P-glycoprotein) (ABCB1), MRP1 (multidrug resistance-associated protein 1) (ABCC1) and ABCG2 [BCRP (breast cancer resistance protein)]. Since the discovery of Pgp over 35 years ago, studies have convincingly linked ABC transporter expression to poor outcome in several cancer types, leading to the development of transporter inhibitors. Three generations of inhibitors later, we are still no closer to validating the 'Pgp hypothesis', the idea that increased chemotherapy efficacy can be achieved by inhibition of transporter-mediated efflux. In this chapter, we highlight the difficulties and past failures encountered in the development of clinical inhibitors of ABC transporters. We discuss the challenges that remain in our effort to exploit decades of work on ABC transporters in oncology. In learning from past mistakes, it is hoped that ABC transporters can be developed as targets for clinical intervention.
    Essays in Biochemistry 09/2011; 50(1):209-32. DOI:10.1042/bse0500209 · 4.39 Impact Factor
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    ABSTRACT: Phosphatidylinositol 4-kinase type IIIa (PI4KIIIα) is one of four mammalian PI 4-kinases that catalyzes the first committed step in polyphosphoinositide synthesis. PI4KIIIα has been linked to regulation of ER exit sites and to the synthesis of plasma membrane phosphoinositides and recent studies have also revealed its importance in replication of the Hepatitis C virus in liver. Two isoforms of the mammalian PI4KIIIα have been described and annotated in GenBank: a larger, ~230kDa (isoform 2) and a shorter splice variant containing only the ~97kDa C-terminus that includes the catalytic domain (isoform 1). However, Northern analysis of human tissues and cancer cells showed only a single transcript of ~7.5kb with the exception of the proerythroleukemia line K562, which contained significantly higher level of the 7.5kb transcript along with smaller ones of 2.4, 3.5 and 4.2kb size. Bioinformatic analysis also confirmed the high copy number of PI4KIIIα transcript in K562 cells along with several genes located in the same region in Chr22, including two pseudogenes that cover most exons coding for isoform 1, consistent with chromosome amplification. A panel of polyclonal antibodies raised against peptides within the C-terminal half of PI4KIIIα failed to detect the shorter isoform 1 either in COS-7 cells or K562 cells. Moreover, expression of a cDNA encoding isoform 1 yielded a protein of ~97kDa that showed no catalytic activity and failed to rescue hepatitis C virus replication. These data draw attention to PI4KIIIα as one of the genes found in Chr22q11, a region affected by chromosomal instability, but do not substantiate the existence of a functionally relevant short form of PI4KIIIα.
    Biochimica et Biophysica Acta 07/2011; 1811(7-8):476-83. DOI:10.1016/j.bbalip.2011.04.013 · 4.66 Impact Factor
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    ABSTRACT: INTRODUCTION: Anticancer tyrosine kinase inhibitors (TKIs) are small molecule hydrophobic compounds designed to arrest aberrant signaling pathways in malignant cells. Multidrug resistance (MDR) ATP binding cassette (ABC) transporters have recently been recognized as important determinants of the general ADME-Tox (absorption, distribution, metabolism, excretion, toxicity) properties of small molecule TKIs, as well as key factors of resistance against targeted anticancer therapeutics. AREAS COVERED: The article summarizes MDR-related ABC transporter interactions with imatinib, nilotinib, dasatinib, gefitinib, erlotinib, lapatinib, sunitinib and sorafenib, including in vitro and in vivo observations. An array of methods developed to study such interactions is presented. Transporter-TKI interactions relevant to the ADME-Tox properties of TKI drugs, primary or acquired cancer TKI resistance, and drug-drug interactions are also reviewed. EXPERT OPINION: Based on the concept presented in this review, TKI anticancer drugs are considered as compounds recognized by the cellular mechanisms handling xenobiotics. Accordingly, novel anticancer therapies should equally focus on the effectiveness of target inhibition and exploration of potential interactions of the designed molecules by membrane transporters. Thus, targeted hydrophobic small molecule compounds should also be screened to evade xenobiotic-sensing cellular mechanisms.
    Expert Opinion on Drug Metabolism &amp Toxicology 03/2011; 7(5):623-42. DOI:10.1517/17425255.2011.562892 · 2.93 Impact Factor
  • Balázs Sarkadi, Gergely Szakács
    dressNature Reviews Drug Discovery 11/2010; 9(11):897-8. DOI:10.1038/nrd3187-c1 · 37.23 Impact Factor

Publication Stats

4k Citations
434.03 Total Impact Points

Institutions

  • 1998–2015
    • Hungarian Academy of Sciences
      • • Institute of Enzymology
      • • Membrane Research Group
      Budapeŝto, Budapest, Hungary
  • 2012
    • Semmelweis University
      Budapeŝto, Budapest, Hungary
  • 2007
    • Kagoshima University
      • Department of Molecular Oncology
      Kagosima, Kagoshima, Japan
  • 2003–2006
    • National Institutes of Health
      • Laboratory of Cell Biology
      Bethesda, MD, United States
  • 2004
    • NCI-Frederick
      Maryland, United States