Evidence for a credit-card-swipe mechanism in the human PC floppase ABCB4

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Specific and Selective Bacteriophages in the Fight against Multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii causes serious infections especially in immunocompromised and/or hospitalized patients. Several A. baumannii strains are multidrug resistant and infect wounds, bones, and the respiratory tract. Current studies are focused on finding new effective agents against A. baumannii. Phage therapy is a promising means to fight this bacterium and many studies on procuring and applying new phages against A. baumannii are currently being conducted. As shown in animal models, phages against multidrug-resistant A. baumannii may control bacterial infections caused by this pathogen and may be a real hope to solve this dangerous health problem.     

Seco-4-methyl-DCK derivatives as potent chemosensitizers

Twenty-five seco-4-methyl-DCK derivatives were designed, synthesized and evaluated for chemoreversal activity when combined with paclitaxel or vincristine in two drug-resistant cancer cell lines (A2780/T and KB-V) respectively. Most of the new compounds displayed moderate to significant MDR reversal activities in the P-gp overexpressing A2780/T and KB-V cells. Especially, compounds 7o and 7y showed the most potent chemosensitization activities with more than 496 and 735 reversal ratios at a concentration of 10?μM. Unexpectedly the newly synthesized compounds did not show chemosensitization activities observed in a non-P-gp overexpressing cisplatin resistant human ovarian cancer cell line (A2780/CDDP), implying that the MDR reversal effects might be associated with P-gp overexpression. Moreover, these compounds did not exhibit significant antiproliferative activities against nontumorigenic cell lines (HUVEC, HOSEC and T29) compared to the positive control verapamil at the tested concentration, which suggested better safety than verapamil. The pharmacological actions of the compounds will be studied further to explore their merit for development as novel candidates to overcome P-gp mediated MDR cancer.     

核酸适配体介导的多药耐药性肿瘤的治疗

化疗是目前肿瘤治疗最常见的方法。然而,肿瘤细胞的多药耐药（multidrug resistance,MDR）常导致临床化疗失败及患者的死亡。因此,干预和逆转肿瘤多药耐药,提高化疗效果,对于肿瘤的治疗具有重要的意义。核酸适配体是一种短的单链寡核苷酸,通过折叠形成特定空间结构从而与靶标特异性结合。靶向肿瘤的核酸适配体可以选择性地将治疗性物质（抗癌药物,siRNA,miRNA）和药物载体递送至肿瘤中,对肿瘤进行靶向杀伤。利用核酸适配体靶向多药耐药性肿瘤,能够特异性干预甚至逆转肿瘤的多药耐药性。本文概述了核酸适配体介导的干预与逆转肿瘤多药耐药性的研究进展。     

Molecular characterization of clinical and environmental Pseudomonas aeruginosa isolated in a burn center

In burn centers, Pseudomonas aeruginosa acts as a major cause of nosocomial infections. Therefore, this study aimed to characterize molecularly P. aeruginosa isolates collected from environmental samples and burn patients. A total of 78 strains (including 58 clinical and 20 environmental isolates) of the P. aeruginosa were collected from Beasat hospital of Hamadan, west of Iran, and was identified using API 20NE. The disk diffusion method according to the CLSI was applied for determination of the antimicrobial resistance. Moreover, the microtiter plate test was used for the quantification of Biofilm formation. The genomic features of the isolated strains was evaluated using Pulsed Field Gel Electrophoresis (PFGE). We found that 94.8% of clinical and 80% environmental isolates were capable of forming biofilm. The rate of MDR in clinical and environmental isolates was 51.7% and 40%, respectively. A significant relationship was observed between biofilm formation capability and multiple drug resistance (p < 0.05). PFGE typing showed 11 different clusters with two major clusters A with 30 (38.5%) and B with 14 (17.9%) members, containing up to 56.4% of all isolates. There was no relationship between biofilm formation ability and antibiotic resistance patterns with PFGE patterns. According to the results, the clonal spread of environmental P. aeruginosa isolates is associated with clinical isolates, and both environmental and clinical isolates are attributed to a high prevalence of the antibiotic resistance and biofilm formation ability. This study highlighted that the prevention programs should be implemented in the hospital environment to control the spread of P. aeruginosa in burn units.     

Pheromone peptide cOB1 from native Enterococcus faecalis forms amyloid‐like structures: A new paradigm for peptide pheromones

Pheromone peptides are an important component of bacterial quorum‐sensing system. The pheromone peptide cOB1 (VAVLVLGA) of native commensal Enterococcus faecalis has also been identified as an antimicrobial peptide (AMP) and reported to kill the prototype clinical isolate strain of E. faecalis V583. In this study, the pheromone peptide cOB1 has shown to form amyloid‐like structures, a characteristic which is never reported for a pheromone peptide so far. With in silico analysis, the peptide was predicted to be highly amyloidogenic. Further, under experimental conditions, cOB1 formed aggregates displaying characteristics of amyloid structures such as bathochromic shift in Congo red absorbance, enhancement in thioflavin T fluorescence, and fibrillar morphology under transmission electron microscopy. This novel property of pheromone peptide cOB1 may have some direct effects on the binding of the pheromone to the receptor cells and subsequent conjugative transfer, making this observation more important for the therapeutics, dealing with the generation of virulent and multidrug‐resistant pathogenic strains.     

A Mutation within the Extended X Loop Abolished Substrate-induced ATPase Activity of the Human Liver ATP-binding Cassette (ABC) Transporter MDR3

The human multidrug resistance protein 3 (MDR3/ABCB4) belongs to the ubiquitous family of ATP-binding cassette (ABC) transporters and is located in the canalicular membrane of hepatocytes. There it flops the phospholipids of the phosphatidylcholine (PC) family from the inner to the outer leaflet. Here, we report the characterization of wild type MDR3 and the Q1174E mutant, which was identified previously in a patient with progressive familial intrahepatic cholestasis type 3 (PFIC-3). We expressed different variants of MDR3 in the yeast Pichia pastoris, purified the proteins via tandem affinity chromatography, and determined MDR3-specific ATPase activity in the presence or absence of phospholipids. The ATPase activity of wild type MDR3 was stimulated 2-fold by liver PC or 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine lipids. Furthermore, the cross-linking of MDR3 with a thiol-reactive fluorophore blocked ATP hydrolysis and exhibited no PC stimulation. Similarly, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin lipids did not induce an increase of wild type MDR3 ATPase activity. The phosphate analogues beryllium fluoride and aluminum fluoride led to complete inhibition of ATPase activity, whereas orthovanadate inhibited exclusively the PC-stimulated ATPase activity of MDR3. The Q1174E mutation is located in the nucleotide-binding domain in direct proximity of the leucine of the ABC signature motif and extended the X loop, which is found in ABC exporters. Our data on the Q1174E mutant demonstrated basal ATPase activity, but PC lipids were incapable of stimulating ATPase activity highlighting the role of the extended X loop in the cross-talk of the nucleotide-binding domain and the transmembrane domain.     

Infection of H69AR cells with retroviral particles harboring interfering RNAi significantly reduced the multidrug resistance of these small cell lung cancer cells

Incubation of the drug-sensitive H69, a small cell lung cancer cell line, with increased concentrations of adriamycin yielded multidrug resistant (MDR) H69AR cells that over-express multidrug resistance-associated protein (MRP1). MRP1 co-transports its substrate with glutathione (GSH), leading to lower intracellular GSH. In this report we tested whether depleting intracellular GSH in MRP1-expressing cells could hyper-sensitize them to anticancer drugs or not. We have found that the GSH contents in MRP1-expressing cells are significantly lower than their corresponding control cells. The treatment with MRP1 substrate verapamil or the GSH synthetase inhibitor buthionine sulfoxi-mine significantly reduced the intracellular GSH contents in MRP1-expressing cells. Interestingly, depleting intracellular GSH contents can hyper-sensitize the MRP1-cDNA transfected BHK cells to daunomycin, but not the adriamycin-selected H69AR cells. Further analyses indicated that anti-apoptotic factor Bcl2 might be a factor responsible for the fact that depleting intracellular GSH could not hyper-sensitize H69AR cells to daunomycin. We hypothesized that knocking down the expression of Bcl2 could hyper-sensitize H69AR cells to daunomycin. Interestingly, infection of H69AR cells with retroviral particles harboring Bcl2 interfering RNAi not only reduced the expression of Bcl2, but also many factors that contribute to MDR, such as Bcl-xl, MRP1 and ABCC3, etc., leading to the MDR H69AR cells more sensitive to daunomycin than the parental H69 cell. Thus, although the mechanisms of the down-regulation of the genes contributing to MDR remain to be elucidated, retroviral particles harboring Bcl2 interfering RNAi could be used as an alternative way to sensitize the MDR cancer cells to anticancer drugs.     

Mdm2 inhibitors as a platform for the design of P-glycoprotein inhibitors

Chemoresistance is thought to be the cause of low treatment efficacy and mortality in more than 90% of patients with advanced cancer. The activation of drug efflux by P-glycoprotein is the key mechanism of resistance. All known P-gp inhibitors are used only in the combination therapy. We propose a new approach based on the multitarget rational design of drugs, which possess both the antitumor and efflux pump inhibitory activity. In this work, the principle possibility of combining the ability to inhibit P-gp and p53-Mdm2 protein-protein interaction in one structure is considered. The biological activity of a number of known and newly synthesized compounds was evaluated using cell lines with different p53 status. The possibility of using computer modeling for the search for P-glycoprotein inhibitors among Mdm2 inhibitors was analyzed; P-gp interaction site and binding modes of substrates and inhibitors were identified. The results obtained in cells that have the native balance of drug resistance and sensitivity showed the ability of the cells to both actively throw out xenobiotics and to lose this ability using P-gp inhibitors. The data obtained indicate that Mdm2 inhibitors are a promising platform for the development of multitarget drugs that can overcome tumor resistance by inhibiting the P-glycoprotein activity.     

Veliparib overcomes multidrug resistance in liver cancer cells

Overexpression of ATP-binding cassette (ABC) transporter is one of the most important factors taking responsibility for the progress of multidrug resistance (MDR) in multiple cancers. In this study, we investigated that veliparib, a PARP inhibitor which is in clinical development, could overcome ABCB1-mediated MDR in liver cancer cells. Veliparib could significantly enhance the cytotoxic effects of a series of conventional chemotherapeutic drugs in ABCB1-overexpression liver cancer cells. Mechanism study showed that veliparib could significantly enhance the accumulation of doxorubicin in ABCB1-overexpression liver cancer cells, without down-regulating the expression level of ABCB1. Finally, veliparib could significantly inhibit the ATPase activity of ABCB1 transporter. This study could provide information that combine veliparib with other chemotherapeutic drugs may benefit liver cancer patients.