Browsing by Subject "Multidrug resistance"

Now showing 1 - 6 of 6
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    CONTRIBUTIONS OF TM5, ECL3 AND TM6 OF HUMAN BCRP TO ITS OLIGOMERIZATION ACTIVITIES AND TRANSPORT FUNCTIONS
    (2012-03-16) Mo, Wei; Safa, Ahmad R.; Zhang, Jian-Ting; Chou, Kai-Ming; Hocevar, Barbara A.; Smith, Martin L.
    Human BCRP is one of the major ATP-binding cassette transporters involved in the development of multidrug resistance in cancer chemotherapy. Overexpression of BCRP in the tumor cell plasma membrane and apical membrane of the gastrointestinal tract leads to decreased intracellular accumulation of various anticancer drugs as well as reduced drug bioavailability. BCRP has been shown to exist on the plasma membrane as higher forms of homo-oligomers. In addition, the oligomerization domain of BCRP has been mapped to the carboxyl-terminal TM5-ECL3-TM6 and this truncated domain, when co-expressed with the full-length BCRP, displays a dominant inhibitory activity on BCRP function. Thus, the oligomerization of BCRP could be a promising target in reversing multidrug resistance mediated by BCRP. To further dissect the oligomerization domains of human BCRP and test the hypothesis that TM5, ECL3, and TM6 each plays a role in BCRP oligomerization and function, we engineered a series of BCRP domain-swapping constructs with alterations at TM5-ECL3-TM6 and further generated HEK293 cells stably expressing wild-type or each domain-swapping construct of BCRP. Using co-immunoprecipitation and chemical cross-linking, we found that TM5, ECL3, and TM6 all appear to partially contribute to BCRP oligomerization, which are responsible for the formation of oligomeric BCRP. However, only TM5 appears to be a major contributor to the transport activity and drug resistance mediated by BCRP, while ECL3 or TM6 is insufficient for BCRP functions. Taken together, these findings suggest that homo-oligomeric human BCRP may be formed by the interactions among TM5, ECL3 and TM6, and TM5 is a crucial domain for BCRP functions and BCRP-mediated drug resistance. These findings may further be used to explore targets for therapeutic development to reverse BCRP-mediated drug resistance and increase the bioavailability of anti-cancer drugs for better treatment of multidrug resistant cancers.
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    Fatty Acid Synthase, a Novel Target for the Treatment of Drug Resistant Breast Cancers
    (2009-03-18T18:46:22Z) Liu, Hailan; Zhang, Jian-Ting
    Many cancers, including breast cancer, often develop resistance to chemotherapeutic drugs over a course of treatment. Many factors, including ABC transporter-mediated drug efflux, have been shown to play a role in acquired drug resistance. Fatty acid synthase (FASN), the key enzyme of lipid synthesis pathway, was found to be over-produced in an Adiamycin resistant breast cancer cell line MCF7/AdrVp3000, compared to its parental drug sensitive MCF7 cell line. Inhibition of FASN expression increased the drug sensitivity in breast cancer cells (MCF7/AdrVp3000 and MDA-MB-468), but not in the normal breast epithelia cell line MCF10A1. Enforced overexpression of FASN in MCF7 breast cancer cells decreased its drug sensitivity. These results indicated that FASN overexpression can induce drug resistance in breast cancers. Ectopic overexpression of FASN in MCF7 cells did not affect cell membrane permeability, transporter activity, nor did it affect cell proliferation rate. However, FASN overexpression protects cancer cells from drug-induced apoptosis by decreasing caspase-8 activation. In FASN over-expressing MCF7 cells, I discovered the positive feedback relationship between FASN and activation of Akt as previously reported. However, activation of Akt did not mediate FASN-induced drug resistance. Together with the findings that FASN expression associates with poor prognosis in several types of cancers, my investigations suggest that FASN overexpression is a novel mechanism of drug resistance in breast cancer chemotherapy. Inhibitors of FASN can be used as sensitizing agents in breast cancer chemotherapy.
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    Five-year resistance trends in pathogens causing healthcare-associated infections at a multi-hospital healthcare system in Saudi Arabia, 2015-2019
    (Elsevier, 2021) Al Mutair, Abbas; Alhumaid, Saad; Al Alawi, Zainab; Zaidi, Abdul Rehman Z.; Alzahrani, Ahmed J.; Al-Tawfiq, Jaffar A.; Al-Shammari, Haifa; Rabaan, Ali A.; Khojah, Osamah; Al-Omari, Awad; Medicine, School of Medicine
    Objectives: Awareness of antimicrobial resistance (AMR) patterns in a given healthcare setting is important to inform the selection of appropriate antimicrobial therapy to reduce the further rise and spread of AMR as well as the rate of healthcare-associated infections (HAIs) and multidrug-resistant (MDR) organisms. We aimed to describe resistance patterns to several antimicrobial agents in pathogens causing HAIs isolated from patients using data gathered at three private tertiary-care hospitals in Saudi Arabia. Methods: Data on trends in AMR among bacteria causing HAIs and MDR events in children and adults at three private hospitals were collected retrospectively (2015-2019) using surveillance data. Results: Over the 5-year period, 29 393 pathogens caused 17 539 HAIs in 15 259 patients. Approximately 57.3% of patients were female and the mean age was 38.4 ± 16.8 years (81.4% adults, 18.6% children). Gram-negative pathogens were four times more likely to cause HAIs compared with Gram-positive bacteria (79.3% vs. 20.7%). Ranking of causative pathogens in decreasing order was Escherichia coli (42.2%), Klebsiella spp. (16.8%) and Staphylococcus aureus (13.9%). Acinetobacter spp. were the only pathogens to decrease significantly (7% reduction; P = 0.033). The most common resistant pathogens were extended-spectrum cephalosporin-resistant E. coli (37.1%), extended-spectrum cephalosporin-resistant Klebsiella (27.8%), carbapenem-non-susceptible Acinetobacter spp. (19.5%), carbapenem-non-susceptible Pseudomonas aeruginosa (19.2%) and methicillin-resistant S. aureus (18.6%). Conclusion: National collaboration is required by prompt feedback to local authorities to tackle regional differences in AMR. This can help plan timely containment interventions to stop and contain microbial threats and swiftly assess their impact.
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    Identification and characterization of the binding sites of P-glycoprotein for multidrug resistance-related drugs and modulators
    (Bentham Science, 2004-01) Safa, Ahmad R.; Department of Pharmacology and Toxicology, IU School of Medicine
    A major problem in cancer treatment is the development of resistance to multiple chemotherapeutic agents in tumor cells. A major mechanism of this multidrug resistance (MDR) is overexpression of the MDR1 product P-glycoprotein, known to bind to and transport a wide variety of agents. This review concentrates on the progress made toward understanding the role of this protein in MDR, identifying and characterizing the drug binding sites of P-glycoprotein, and modulating MDR by P-glycoprotein-specific inhibitors. Since our initial discovery that P-glycoprotein binds to vinblastine photoaffinity analogs, many P-glycoprotein-specific photoaffinity analogs have been developed and used to identify the particular domains of P-glycoprotein capable of interacting with these analogs and other P-glycoprotein substrates. Furthermore, significant advances have been made in delineating the drug binding sites of this protein by studying mutant P-glycoprotein. Photoaffinity labeling experiments and the use of site-directed antibodies to several domains of this protein have allowed the localization of the general binding domains of some of the cytotoxic agents and MDR modulators on P-glycoprotein. Moreover, site-directed mutagenesis studies have identified the amino acids critical for the binding of some of these agents to P-glycoprotein. Furthermore, equilibrium binding assays using plasma membranes from MDR cells and radioactive drugs have aided our understanding of the modes of drug interactions with P-glycoprotein. Based on the available data, a topological model of P-glycoprotein and the approximate locations of its drug binding sites, as well as a proposed classification of multiple drug binding sites of this protein, is presented in this review.
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    Resistance to Cell Death and Its Modulation in Cancer Stem Cells
    (Begell, 2016) Safa, Ahmad R.; Department of Pharmacology and Toxicology, IU School of Medicine
    Accumulating evidence has demonstrated that human cancers arise from various tissues of origin that initiate from cancer stem cells (CSCs) or cancer-initiating cells. The extrinsic and intrinsic apoptotic pathways are dysregulated in CSCs, and these cells play crucial roles in tumor initiation, progression, cell death resistance, chemo- and radiotherapy resistance, and tumor recurrence. Understanding CSC-specific signaling proteins and pathways is necessary to identify specific therapeutic targets that may lead to the development of more efficient therapies selectively targeting CSCs. Several signaling pathways-including the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR), maternal embryonic leucine zipper kinase (MELK), NOTCH1, and Wnt/Β-catenin&and expression of the CSC markers CD133, CD24, CD44, Oct4, Sox2, Nanog, and ALDH1A1 maintain CSC properties. Studying such pathways may help to understand CSC biology and lead to the development of potential therapeutic interventions to render CSCs more sensitive to cell death triggered by chemotherapy and radiation therapy. Moreover, recent demonstrations of dedifferentiation of differentiated cancer cells into CSC-like cells have created significant complexity in the CSCs hypothesis. Therefore, any successful therapeutic agent or combination of drugs for cancer therapy must eliminate not only CSCs but differentiated cancer cells and the entire bulk of tumor cells. This review article expands on the CSC hypothesis and paradigm with respect to major signaling pathways and effectors that regulate CSC apoptosis resistance. Moreover, selective CSC apoptotic modulators and their therapeutic potential for making tumors more responsive to therapy are discussed. The use of novel therapies, including small-molecule inhibitors of specific proteins in signaling pathways that regulate stemness, proliferation and migration of CSCs, immunotherapy, and noncoding microRNAs may provide better means of treating CSCs.
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    TgPRELID, a Mitochondrial Protein Linked to Multidrug Resistance in the Parasite Toxoplasma gondii
    (American Society for Microbiology, 2017-02) Jeffers, Victoria; Kamau, Edwin T.; Srinivasan, Ananth R.; Harper, Jonathan; Sankaran, Preethi; Post, Sarah E.; Varberg, Joseph M.; Sullivan, William J., Jr.; Boyle, Jon P.; Department of Pharmacology and Toxicology, IU School of Medicine
    New drugs to control infection with the protozoan parasite Toxoplasma gondii are needed as current treatments exert toxic side effects on patients. Approaches to develop novel compounds for drug development include screening of compound libraries and targeted inhibition of essential cellular pathways. We identified two distinct compounds that display inhibitory activity against the parasite's replicative stage: F3215-0002, which we previously identified during a compound library screen, and I-BET151, an inhibitor of bromodomains, the "reader" module of acetylated lysines. In independent studies, we sought to determine the targets of these two compounds using forward genetics, generating resistant mutants and identifying the determinants of resistance with comparative genome sequencing. Despite the dissimilarity of the two compounds, we recovered resistant mutants with nonsynonymous mutations in the same domain of the same gene, TGGT1_254250, which we found encodes a protein that localizes to the parasite mitochondrion (designated TgPRELID after the name of said domain). We found that mutants selected with one compound were cross resistant to the other compound, suggesting a common mechanism of resistance. To further support our hypothesis that TgPRELID mutations facilitate resistance to both I-BET151 and F3215-0002, CRISPR (clustered regularly interspaced short palindromic repeat)/CAS9-mediated mutation of TgPRELID directly led to increased F3215-0002 resistance. Finally, all resistance mutations clustered in the same subdomain of TgPRELID. These findings suggest that TgPRELID may encode a multidrug resistance factor or that I-BET151 and F3215-0002 have the same target(s) despite their distinct chemical structures. IMPORTANCE We report the discovery of TgPRELID, a previously uncharacterized mitochondrial protein linked to multidrug resistance in the parasite Toxoplasma gondii. Drug resistance remains a major problem in the battle against parasitic infection, and understanding how TgPRELID mutations augment resistance to multiple, distinct compounds will reveal needed insights into the development of new therapies for toxoplasmosis and other related parasitic diseases.