Cationic Polypeptide Research Articles

Abstract 6272: Redirecting tumor extracellular proteases to target radiosensitizer delivery

Abstract Patients with locally advanced cancers are treated with combined radiotherapy and chemotherapy, however curability is poor and side effects severe. Drugs that sensitize tumors to radiotherapy have been tried to improve cure, but tumor specificity remains a challenge. To achieve tumor selectivity of small molecule radiosensitizers, we tested as a strategy active tumor targeting utilizing peptide-based drug conjugates that split the responsibilities for targeting and radiosensitization into distinct molecular tasks. The tumor milieu possesses localizing beacons that can guide drug delivery using tumor cell surface receptors and microenvironment extracellular matrix metalloproteinases (MMPs). Here we applied peptide-based linkers to test for tumor selective drug delivery and radiosensitization by chemically conjugating the DNA damage checkpoint kinase 1/2 inhibitor AZD7762 to antibody to or cell penetrating peptides. AZD7762 governs DNA damage response and irradiated cell fate. We synthesized drug conjugates of AZD7762 and compared their anti-tumor efficacy in combination with ionizing radiation (IR). An antibody drug conjugate (ADC) was built by attaching AZD7762 to the anti-EGFR antibody cetuximab. Polycationic cell penetrating peptide drug conjugates were constructed by linking AZD7762 to a 9 amino acid repeat of D-arginine and keeping it bare (r9-AZD7762) or cloaking r9 within a MMP-2/9 triggered activatable cell penetrating peptide scaffold (ACPP-AZD7762). In contrast to receptor directed ADCs, ACPPs redirect extracellular tumor microenvironment proteases to guide drug delivery. Intact, ACPPs are charge neutral which blocks the conjugated drug from cell entry. Upon cleavage by tumor overexpressed MMPs, the ACPP scaffold releases drug conjugated polycationic peptide which is then internalized by cells. We found that while cetuximab-AZD7762 ADC had high affinity for EGFR overexpressing tumor cells and prolonged blood circulation in murine models, cetuximab-AZD7762 lacked anti-tumor efficacy. On the other extreme, naked r9-AZD7762 drug conjugate was indiscriminately cytotoxic and radiosensitized a panel of tumor cell lines in cell culture: CAL27, A549, PANC1 and HCT116. However, r9 cell penetrating peptides lacked tumor specificity when intravenously injected into mice. In contrast, MMP-2/9 sensitive ACPPs balanced tumor selectivity with drug efficacy. Intact, ACPPs held conjugated AZD7762 in a pro-drug inactive state that upon tumor microenvironment ACPP cleavage resulted in tumor selective drug accumulation and anti-tumor efficacy in combination with IR. Importantly, a control non-cleavable ACPP-AZD7762 did not improve tumor control with IR, demonstrating the necessity of ACPP cleavage to release active drug. These results highlight the utility of the ACPP technology platform to target amine containing radiosensitizing drugs to tumor tissues based on extracellular protease activity that overcome the limitations of ADC conjugated radiosensitizers. Citation Format: Dina V. Hingorani, Maria F. Camargo, Maryam A. Quraishi, Joseph Aguilera, Stephen R. Adams, Sunil J. Advani. Redirecting tumor extracellular proteases to target radiosensitizer delivery [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6272.

Polylysine effect on thylakoid membranes

Thylakoid membranes of photosynthetic plant chloroplasts are involved in a wide range of energy producing pathways. Their stacking can be employed in order to provide increased surface area for biocatalytic purposes. Here we probe the aggregate formation of higher plants' thylakoids using low-molecular poly-l-lysine as an electrostatic polymer linker in low ionic strength media. Microelectrophoresis, actinic light scattering, millisecond-delayed fluorescence and free radical production of thylakoid membranes are measured and analyzed in the presence of the cationic polypeptide to track its influence on the surface electrical properties, the electron-transport processes and the proton gradient accumulation across membranes. Enhanced proton gradient in polylysine-treated thylakoids is obtained upon illumination due to alterations of the proton intake across the membrane resulting from the non-specific electrostatic interactions of the cationic polypeptide with thylakoids. We report lower rates of lipid peroxidation in polylysine-treated thylakoids measured both in the dark and under illumination in salt-free medium. The gained insight on the effect of polycations on photosynthetic membranes may be used in future developments of thylakoid-based approaches for energy transfer applications.

Phosphate-dependent aggregation of [KL]n peptides affects their membranolytic activity

In this study, we investigate how the length of amphiphilic β-sheet forming peptides affects their interaction with membranes. Four polycationic model peptides with lengths from 6 to 18 amino acids were constructed from simple Lys-Leu repeats, giving [KL]n=3,5,7,9. We found that (1) they exhibit a pronounced antimicrobial activity with an intriguing length dependent maximum for [KL]5 with 10 amino acids; (2) their hemolytic effect, on the other hand, increases steadily with peptide length. CD analysis (3) and TEM (4) show that all peptides-except for the short [KL]3-aggregate into amyloid-like fibrils in the presence of phosphate ions, which in turn has a critical effect on the results in (1) and (2). In fact, (5) vesicle leakage reveals an intrinsic membrane-perturbing activity (at constant peptide mass) of [KL]5 > [KL]9 > [KL]7 in phosphate buffer, which changes to [KL]5 ≈ [KL]7 ≈ [KL]9 in PIPES. A specific interaction with phosphate ions thus explains the subtle balance between two counteracting effects: phosphate-induced unproductive pre-aggregation in solution versus monomeric membrane binding and vigorous lipid perturbation due to self-assembly of the bound peptides within the bilayer. This knowledge can now be used to control and optimize the peptides in further applications.

Antineoplastic Drug‐Free Anticancer Strategy Enabled by Host‐Defense‐Peptides‐Mimicking Synthetic Polypeptides

An antineoplastic drug-free anticancer strategy enabled by host defense peptides (HDPs)-mimicking synthetic polypeptides is reported. The polypeptide exhibits a broad spectrum of anticancer activity in 12 cancer cell lines, including drug-resistant and highly metastatic tumor cells. Detailed mechanistic studies reveal that the cationic anticancer polypeptide (ACPP) can directly induce rapid necrosis of cancer cells within minutes through a membrane-lytic mechanism. Moreover, a pH-sensitive zwitterionic derivative of ACPP (DA-ACPP) is prepared for in vivo application. DA-ACPP shows negligible hemolysis under neutral physiological conditions, and can be converted back to ACPP in slightly acidic tumor environments, resulting in selective killing of cancer cells. Consequently, DA-ACPP shows an effective inhibition of tumor growth in both 4T1 orthotopic breast tumor models and B16-F10 melanoma pulmonary metastatic models. Overall, these findings demonstrate that synthetic HDPs-mimicking polypeptides represent safe and effective antineoplastic agents, which sheds new light on the development of drug-free synthetic polymers for cancer therapy.

Inhalable Nanocomposite Microparticles with Enhanced Dissolution and Superior Aerosol Performance.

Previous studies have shown that combining colistin (Col), a cationic polypeptide antibiotic, with ivacaftor (Iva), a cystic fibrosis (CF) drug, could achieve synergistic antibacterial effects against Pseudomonas aeruginosa. The purpose of this study was to develop dry powder inhaler formulations for co-delivery of Col and Iva, aiming to treat CF and lung infection simultaneously. In order to improve solubility and dissolution for the water-insoluble Iva, Iva was encapsulated into bovine serum albumin (BSA) nanoparticles (Iva-BSA-NPs). Inhalable composite microparticles of Iva-BSA-NPs were produced by spray-freeze-drying using water-soluble Col as the matrix material and l-leucine as an aerosol enhancer. The optimal formulation showed an irregularly shaped morphology with fine particle fraction (FPF) values of 73.8 ± 5.2% for Col and 80.9 ± 4.1% for Iva. Correlations between "" and FPF were established for both Iva and Col. The amorphous solubility of Iva is 66 times higher than the crystalline solubility in the buffer. Iva-BSA-NPs were amorphous and remained in the amorphous state after spray-freeze-drying, as examined by powder X-ray diffraction. In vitro dissolution profiles of the selected DPI formulation indicated that Col and Iva were almost completely released within 3 h, which was substantially faster regarding Iva release than the jet-milled physical mixture of the two drugs. In summary, this study developed a novel inhalable nanocomposite microparticle using a synergistic water-soluble drug as the matrix material, which achieved reduced use of excipients for high-dose medications, improved dissolution rate for the water-insoluble drug, and superior aerosol performance.

In vivo effects of the association of the psychoactive phenotiazine thioridazine on antitumor activity and hind limb paralysis induced by the native polypeptide crotamine

Crotamine is a cationic polypeptide composed by 42 amino acid residues with several pharmacological and biological properties, including the selective ability to enter and kill actively proliferating tumour cells, which led us to propose its use as a theranostic agent for cancer therapy. At the moment, the improvement of crotamine antitumoral efficacy by association with chemotherapeutic adjuvants is envisioned. In the present work, we evaluated the association of crotamine with the antitumoral adjuvant phenotiazine thioridazine (THD). In spite of the clear efficacy of these both compounds as anticancer agents in long-term in vivo treatment of animal model bearing implanted xenograph melanoma tumor, the expected mutual potentiation of the antitumor effects was not observed here. Moreover, this association revealed for the first time the influence of THD on crotamine ability to trigger the hind limb paralysis in mice, and this discovery may represent the first report suggesting the potential involvement of the CNS in the action of this snake polypeptide on the skeletal muscle paralysis, which was classically believed to be essentially limited to a direct action in peripheral tissues as the skeletal muscle. This is also supported by the observed ability of crotamine to potentiate the sedative effects of THD which action was consistently demonstrated to be based on its central action. The better characterization of crotamine properties in CNS may certainly bring important insights for the knowledge needed to pave the way toward the use of this molecule as a theranostic compound in human diseases as cancer.

Synthesis and Properties of Mono- or Diamine-Initiated Imidazolium-Based Cationic Polypeptides.

A series of cationic polypeptide imidazolium conjugates were prepared by ring-opening polymerization (ROP) of γ-4-(3-chloropropoxycarbonyl)benzyl-L- glutamic acid-based N-carboxyanhydride (CPBLG-NCA) initiated by various mono- or diamine initiators and subsequent side-chain modification with high grafting efficiency. Rapid and controlled ROP was achieved by polymerizing CPBLG-NCA in a dichloromethane/NaHCO3/H2O solvent mixture with the amine initiators. The resulting polypeptides bearing imidazolium iodide pendants showed reversible upper critical solution temperature (UCST)-type thermoresponsive properties in both ethanol and DI water while the polypeptides with tetrafluoroborate counter-anions showed a UCST in phosphate buffer saline (PBS). The cloud point temperature (Tcp) in ethanol and aqueous solutions can be tuned by both molecular weight and the end- or linkage-groups in the main chain. The cationic polypeptides showed good antibacterial activity against Staphylococcus aureus and low hemolysis. Our results provide a facile and rapid ROP strategy to develop new families of stimuli-responsive polypeptides with tunable properties as well as antibacterial polypeptides with optimized selectivity.

Corrigendum: Vancomycin Resistance is Overcome by Conjugation of Polycationic Peptides

The authors of this Communication omitted to cite the following publications: A vancomycin–arginine conjugate that is effective against Gram-negative bacteria,1 and a D-octaarginine conjugate of vancomycin that eliminates biofilm-associated MRSA in a murine wound infection model, MRSA persister cells, and vancomycin-resistant enterococci2 have previously been reported. A review has also been published on oligoarginine- and oligoguanidine-enabled drug delivery.3 The authors thank Professors L. Cegelski and P. A. Wender for drawing attention to this issue.

Aggregation induced emission of an anionic tetraphenylethene derivative for efficient protamine sensing

Protamine, an arginine rich polycationic peptide, is the only clinically approved antidote of Heparin and has been successfully used in reversing the action of Heparin in case of Heparin overdose, a situation which can have fatal outcomes. Therefore, developing sensors for Protamine is of uttermost importance in clinical diagnosis. However, only limited reports are available on optical detection of Protamine, since it is relatively difficult to detect Protamine due to its composition, which is devoid of aromatic amino acids. In the present contribution, we describe a fluorescence turn-on sensing scheme for Protamine which utilizes the phenomenon of aggregation induced emission of an anionic derivative of tetraphenylethene, i.e. sodium 1,2-bis[4-(3-sulfonatopropoxyl)phenyl]-1,2-diphenylethene (BSPOTPE) on interaction with Protamine. The interaction between BSPOTPE and Protamine has been thoroughly investigated using various photophysical techniques, which include, ground state absorption, steady-state and time-resolved emission spectroscopy, and molecular docking calculations. The interaction of BSPOTPE with Protamine leads to large modulation in its photophysical properties, with an enhancement of ~70-fold in emission intensity and significant modulation in excited-state lifetime. Apart from being simple and selective, the present sensor system is highly sensitive for Protamine with a LOD of 47 pM in aqueous solution. Importantly, BSPOTPE is a commercially available probe molecule which provides freedom from the tedious and time-consuming protocols to develop synthetic probe molecules for sensor applications, which normally serves as an impediment for real-life applications.

Eukaryotic phosphatase inhibitors enhance colistin efficacy in gram-negative bacteria.

The mounting threat of multi-drug-resistant (MDR) bacteria places a tremendous strain on the antimicrobial clinical arsenal, forcing physicians to revert to near-obsolete antibiotics to treat otherwise intractable infections. Antibiotic adjuvant therapy has emerged as a viable alternative to the development of novel antimicrobial agents. This method uses combinations of an existing antibiotic and a non-antimicrobial small molecule, where the combination either breaks drug resistance or further potentiates antibiotic activity. Through a high-content screen of eukaryotic kinase inhibitors, our group previously identified two highly potent adjuvants that synergize with colistin, a cyclic, polycationic antimicrobial peptide that serves as a drug of last resort for the treatment of MDR Gram-negative bacterial infections. Cell signaling proteins implicated in colistin resistance mechanisms display both kinase and phosphatase activities. Herein, we explore the potential for eukaryotic phosphatase inhibitors to be repurposed as colistin adjuvants. From a panel of 48 unique structures, we discovered that the natural product kuwanon G breaks colistin resistance, while the non-antimicrobial macrolide ascomycin potentiates colistin in polymyxin-susceptible bacteria.

Vancomycin-Lipopeptide Conjugates with High Antimicrobial Activity on Vancomycin-Resistant Enterococci.

Multidrug-resistant bacteria represent one of the most important health care problems worldwide. While there are numerous drugs available for standard therapy, there are only a few compounds capable of serving as a last resort for severe infections. Therefore, approaches to control multidrug-resistant bacteria must be implemented. Here, a strategy of reactivating the established glycopeptide antibiotic vancomycin by structural modification with polycationic peptides and subsequent fatty acid conjugation to overcome the resistance of multidrug-resistant bacteria was followed. This study especially focuses on the structure–activity relationship, depending on the modification site and fatty acid chain length. The synthesized conjugates showed high antimicrobial potential on vancomycin-resistant enterococci. We were able to demonstrate that the antimicrobial activity of the vancomycin-lipopeptide conjugates depends on the chain length of the attached fatty acid. All conjugates showed good cytocompatibility in vitro and in vivo. Radiolabeling enabled the in vivo determination of pharmacokinetics in Wistar rats by molecular imaging and biodistribution studies. An improved biodistribution profile in comparison to unmodified vancomycin was observed. While vancomycin is rapidly excreted by the kidneys, the most potent conjugate shows a hepatobiliary excretion profile. In conclusion, these results demonstrate the potential of the structural modification of already established antibiotics to provide highly active compounds for tackling multidrug-resistant bacteria.

International Union of Basic and Clinical Pharmacology. CVIII. Calcium-Sensing Receptor Nomenclature, Pharmacology, and Function.

The calcium-sensing receptor (CaSR) is a class C G protein-coupled receptor that responds to multiple endogenous agonists and allosteric modulators, including divalent and trivalent cations, L-amino acids, γ-glutamyl peptides, polyamines, polycationic peptides, and protons. The CaSR plays a critical role in extracellular calcium (Ca2+ o) homeostasis, as demonstrated by the many naturally occurring mutations in the CaSR or its signaling partners that cause Ca2+ o homeostasis disorders. However, CaSR tissue expression in mammals is broad and includes tissues unrelated to Ca2+ o homeostasis, in which it, for example, regulates the secretion of digestive hormones, airway constriction, cardiovascular effects, cellular differentiation, and proliferation. Thus, although the CaSR is targeted clinically by the positive allosteric modulators (PAMs) cinacalcet, evocalcet, and etelcalcetide in hyperparathyroidism, it is also a putative therapeutic target in diabetes, asthma, cardiovascular disease, and cancer. The CaSR is somewhat unique in possessing multiple ligand binding sites, including at least five putative sites for the "orthosteric" agonist Ca2+ o, an allosteric site for endogenous L-amino acids, two further allosteric sites for small molecules and the peptide PAM, etelcalcetide, and additional sites for other cations and anions. The CaSR is promiscuous in its G protein-coupling preferences, and signals via Gq/11, Gi/o, potentially G12/13, and even Gs in some cell types. Not surprisingly, the CaSR is subject to biased agonism, in which distinct ligands preferentially stimulate a subset of the CaSR's possible signaling responses, to the exclusion of others. The CaSR thus serves as a model receptor to study natural bias and allostery. SIGNIFICANCE STATEMENT: The calcium-sensing receptor (CaSR) is a complex G protein-coupled receptor that possesses multiple orthosteric and allosteric binding sites, is subject to biased signaling via several different G proteins, and has numerous (patho)physiological roles. Understanding the complexities of CaSR structure, function, and biology will aid future drug discovery efforts seeking to target this receptor for a diversity of diseases. This review summarizes what is known to date regarding key structural, pharmacological, and physiological features of the CaSR.

Next Generation Salivary Lubrication Enhancer Derived from Recombinant Supercharged Polypeptides for Xerostomia.

Insufficient retention of water in adsorbed salivary conditioning films (SCFs) because of altered saliva secretion can lead to oral dryness (xerostomia). Patients with xerostomia sometimes are given artificial saliva, which often lacks efficacy because of the presence of exogenous molecules with limited lubrication properties. Recombinant supercharged polypeptides (SUPs) improve salivary lubrication by enhancing the functionality of endogenously available salivary proteins, which is in stark contrast to administration of exogenous lubrication enhancers. This novel approach is based on establishing a layered architecture enabled by electrostatic bond formation to stabilize and produce robust SCFs in vitro. Here, we first determined the optimal molecular weight of SUPs to achieve the best lubrication performance employing biophysical and in vitro friction measurements. Next, in an ex vivo tongue-enamel friction system, stimulated whole saliva from patients with Sjögren syndrome was tested to transfer this strategy to a preclinical situation. Out of a library of genetically engineered cationic polypeptides, the variant SUP K108cys that contains 108 positive charges and two cysteine residues at each terminus was identified as the best SUP to restore oral lubrication. Employing this SUP, the duration of lubrication (Relief Period) for SCFs from healthy and patient saliva was significantly extended. For patient saliva, the lubrication duration was increased from 3.8 to 21 min with SUP K108cys treatment. Investigation of the tribochemical mechanism revealed that lubrication enhancement is because of the electrostatic stabilization of SCFs and mucin recruitment, which is accompanied by strong water fixation and reduced water evaporation.

Vancomycin Resistance Is Overcome by Conjugation of Polycationic Peptides.

Multidrug‐resistant bacteria represent one of the biggest challenges facing modern medicine. The increasing prevalence of glycopeptide resistance compromises the efficacy of vancomycin, for a long time considered as the last resort for the treatment of resistant bacteria. To reestablish its activity, polycationic peptides were conjugated to vancomycin. By site‐specific conjugation, derivatives that bear the peptide moiety at four different sites of the antibiotic were synthesized. The most potent compounds exhibited an approximately 1000‐fold increased antimicrobial activity and were able to overcome the most important types of vancomycin resistance. Additional blocking experiments using d‐Ala‐d‐Ala revealed a mode of action beyond inhibition of cell‐wall formation. The antimicrobial potential of the lead candidate FU002 for bacterial infection treatments could be demonstrated in an in vivo study. Molecular imaging and biodistribution studies revealed that conjugation engenders superior pharmacokinetics.

Control of solvent exposure of cationic polypeptides in anionic environment

Here we study anionic biphosphate condensation around cationic HIV-1 Tat peptide to understand interaction between charged functional groups with counter-anion. Our all-atom molecular dynamics simulations show that the counter-anion condensation around the basic functional groups and the solvent accessible surface area of the peptide show non-monotonic dependence on biphosphate concentration. There is an optimum concentration of biphosphate ions in solution where the condensation is maximum, while the solvent exposed area is minimum. Thus, we show that the solvent exposure of the macromolecule can be controlled by tuning anion concentration in the solution which may help in designing drug delivery medium.

A bi-adjuvant nanovaccine that potentiates immunogenicity of neoantigen for combination immunotherapy of colorectal cancer.

Neoantigen vaccines have been enthusiastically pursued for personalized cancer immunotherapy while vast majority of neoantigens have no or low immunogenicity. Here, a bi-adjuvant neoantigen nanovaccine (banNV) that codelivered a peptide neoantigen (Adpgk) with two adjuvants [Toll-like receptor (TLR) 7/8 agonist R848 and TLR9 agonist CpG] was developed for potent cancer immunotherapy. Specifically, banNVs were prepared by a nanotemplated synthesis of concatemer CpG, nanocondensation with cationic polypeptides, and then physical loading with hydrophobic R848 and Adpgk. The immunogenicity of the neoantigen was profoundly potentiated by efficient codelivery of neoantigen and dual synergistic adjuvants, which is accompanied by reduced acute systemic toxicity. BanNVs sensitized immune checkpoint programmed death receptor 1 (PD-1) on T cells, therefore, a combination of banNVs with aPD-1 conspicuously induced the therapy response and led to complete regression of 70% neoantigen-specific tumors without recurrence. We conclude that banNVs are promising to optimize personalized therapeutic neoantigen vaccines for cancer immunotherapy.

Bioinspired and Mechanically Strong Fibers Based on Engineered Non-Spider Chimeric Proteins.

Silk-protein-based fibers have attracted considerable interest due to their low weight and extraordinary mechanical properties. Most studies on fibrous proteins focus on the recombinant spidroins, but these fibers exhibit moderate mechanical performance. Thus, the development of alternative structural proteins for the construction of robust fibers is an attractive goal. Herein, we report a class of biological fibers produced using a designed chimeric protein, which consists of the sequences of a cationic elastin-like polypeptide and a squid ring teeth protein. Remarkably, the chimeric protein fibers exhibit a breaking strength up to about 630 MPa and a corresponding toughness as high as about 130 MJ m-3 , making them superior to many recombinant spider silks and even comparable to some native counterparts. Therefore, this strategy is a novel concept for exploring bioinspired ultrastrong protein materials through the development of new types of structural chimeric proteins.

Development of a nanoparticle that releases nucleic acids in response to a mitochondrial environment

The delivery of nucleic acids targeting mutant mtDNA represent a potential strategy for addressing a variety of mitochondria-related diseases. We previously developed a MITO-Porter, a nano carrier that is capable of delivering nanoparticles of nucleic acids to mitochondria of human cells. Here, we report on an investigation of a series of nanoparticles formed with various poly cationic peptides that can release nucleic acids in response to a mitochondrial environment. A significant relationship was found between the number of and the location of arginine and histidine residues in the peptide sequence and the release of nucleic acids in a mitochondrial environment.

Gene interaction network studies to decipher the multi-drug resistance mechanism in Salmonella enterica serovar Typhi CT18 reveal potential drug targets

Salmonella enterica subsp. enterica serovar Typhi, a human enteric pathogen causing typhoid fever, developed resistance to multiple antibiotics over the years. The current study was dedicated to understand the multi-drug resistance (MDR) mechanism of S. enterica serovar Typhi CT18 and to identify potential drug targets that could be exploited for new drug discovery. We have employed gene interaction network analysis for 44 genes which had 275 interactions. Clustering analysis resulted in three highly interconnecting clusters (C1–C3). Functional enrichment analysis revealed the presence of drug target alteration and three different multi-drug efflux pumps in the bacteria that were associated with antibiotic resistance. We found seven genes (arnA,B,C,D,E,F,T) conferring resistance to Cationic Anti-Microbial Polypeptide (CAMP) molecules by membrane Lipopolysaccharide (LPS) modification, while macB was observed to be an essential controlling hub of the network and played a crucial role in MacAB-TolC efflux pump. Further, we identified five genes (mdtH, mdtM, mdtG, emrD and mdfA) which were involved in Major Facilitator Superfamily (MFS) efflux system and acrAB contributed towards AcrAB-TolC efflux pump. All three efflux pumps were seen to be highly dependent on tolC gene. The five genes, namely tolC, macB, acrA, acrB and mdfA which were involved in multiple resistance pathways, can act as potential drug targets for successful treatment strategies. Therefore, this study has provided profound insights into the MDR mechanism in S. Typhi CT18. Our results will be useful for experimental biologists to explore new leads for S. enterica.

Evaluation of colistin nephrotoxicity and urinary level of kidney injury molecule-1 in hospitalized adult ICU patients

Introduction: Colistin is a cationic polypeptide antibiotic used for treatment of gram-negative infections. Nephrotoxicity is one of the most common adverse effects of colistin. Objectives: To determine the epidemiology of colistin nephrotoxicity and also to compare the changing pattern of kidney injury molecule 1 (KIM-1) in urine with serum creatinine and urine during the treatment with colistin in patients admitted to intensive care unit (ICU). Patients and Methods: During 13 months, all patients admitted to adult ICUs of two university hospitals without any documented history of acute or chronic kidney diseases receiving at least one week of colistin were included. Required demographic, clinical, and paraclinical data of the study population was collected. Urinary and serum levels of creatinine, urea, sodium, potassium, magnesium, and KIM-1 were measured at six time points including days zero, 3, 5, 7, 10, and 14 of colistin treatment. Results: Six patients (18.18%) developed nephrotoxicity during colistin treatment. Nephrotoxicity was resolved without any intervention in three individuals. None of studied demographic, clinical and laboratory characteristics of the patients had a significant association with the incidence of colistin nephrotoxicity. The pattern of KIM-1 urine level during the course of colistin treatment did not differ significantly among patients with and without nephrotoxicity. The accuracy of KIM-1 urine level in detecting colistin nephrotoxicity was significantly lower than that of serum creatinine on days 0th, 3rd, 5th and 7th. Conclusion: Nephrotoxicity of colistin is a common complication, usually reversible, KIM-1 was not more accurate than serum creatinine or urine in detecting nephrotoxicity of colistin.