In-vitro activity of ramoplanin (a novel lipoglycopeptide), vancomycin, and teicoplanin against gram-positive clinical isolates from cancer patients

Local Drug Delivery Strategies towards Wound Healing

A particular biological process known as wound healing is connected to the overall phenomena of growth and tissue regeneration. Several cellular and matrix elements work together to restore the integrity of injured tissue. The goal of the present review paper focused on the physiology of wound healing, medications used to treat wound healing, and local drug delivery systems for possible skin wound therapy. The capacity of the skin to heal a wound is the result of a highly intricate process that involves several different processes, such as vascular response, blood coagulation, fibrin network creation, re-epithelialisation, collagen maturation, and connective tissue remodelling. Wound healing may be controlled with topical antiseptics, topical antibiotics, herbal remedies, and cellular initiators. In order to effectively eradicate infections and shorten the healing process, contemporary antimicrobial treatments that include antibiotics or antiseptics must be investigated. A variety of delivery systems were described, including innovative delivery systems, hydrogels, microspheres, gold and silver nanoparticles, vesicles, emulsifying systems, nanofibres, artificial dressings, three-dimensional printed skin replacements, dendrimers and carbon nanotubes. It may be inferred that enhanced local delivery methods might be used to provide wound healing agents for faster healing of skin wounds.

Identification of potential drug targets in human pathogen Bacillus cereus and insight for finding inhibitor through subtractive proteome and molecular docking studies

Bacillus cereus is a gram-positive, anaerobic, spore-forming bacterium related to food poisoning in humans. Vomit and diarrhea are the symptoms of foodborne B. cereus infection caused by emetic toxins and three enterotoxins, respectively. This bacterium is broadly present in soil and foods such as vegetables, spices, milk, and meat. The antibiotics impenem, vancomycin, chloramphenicol, gentamicin, and ciprofloxacin are used for all susceptible strains of B. cereus. But these antibiotics cause side effects in the host due to the drug-host interaction; because the targeted proteins by the drugs are not pathogen specific proteins, they are similar to human proteins also. To overcome this problem, this study focused on identifying putative drug targets in the pathogen B. cereus and finding new drugs to inhibit the function of the pathogen. The identification of drug targets is a pipeline process, starting with the identification of targets non-homologous to human and gutmicrobiota proteins, finding essential proteins, finding other proteins that highly interact with these essential proteins that are also highly important for protein network stability, finding cytoplasmic proteins with a clear pathway and known molecular function, and finding non-druggable proteins. Through this process, two novel drug targets were identified in B. cereus. Among the various antibiotics, Gentamicin had showed good binding affinity with the identified novel targets through molecular modeling and docking studies using Prime and GLIDE module of Schrödinger. Hence, this study suggest that the identified novel drug targets may very useful in drug therapeutic field for finding inhibitors which are similar to Gentamicin and designing new formulation of drug molecules to control the function of the foodborne illness causing pathogen B. cereus.

Inhibitory effects of aptamer targeted teicoplanin encapsulated PLGA nanoparticles for Staphylococcus aureus strains

Emergence of resistance to traditional antibiotic treatments necessitates alternative delivery systems. Teicoplanin is a glycopeptide antibiotic used in the treatments of serious infections caused by Gram-positive bacteria, including Methicillin Resistant Staphylococcus aureus (MRSA). One strategy to keep up with antibiotic resistance development is to limit dose and amount during treatments. Targeted delivery systems of antibiotics have been suggested as a mechanism to slow-down the evolution of resistance and to increase efficiency of the antimicrobials on already resistant pathogens. In this study, we report teicoplanin delivery nanoparticles of Poly Lactic-co-Glycolic Acid (PLGA), which are functionalized with S. aureus specific aptamers. A 32-fold decrease in minimum inhibitory concentration (MIC) values of teicoplanin for S. aureus was demonstrated for susceptible strains and about 64-fold decline in MIC value was achieved for moderately resistant clinical isolates of MRSA upon teicoplanin treatment with aptamer-PLGA nanoparticles. Although teicoplanin delivery in PLGA nanoparticles without targeting demonstrated eightfold decrease in MIC of susceptible strains of S. aureus and S. epidermidis and twofold in MIC of resistant strains, the aptamer targeting specifically decreased MIC for S. aureus, but not for S. epidermidis. Therefore, aptamer-targeted PLGA delivery of antibiotic can be an attractive alternative to combat with some of the multi-drug resistant bacterial pathogens.

Pharmacological properties of NAI-603, a well-tolerated semisynthetic derivative of ramoplanin

NAI-603 is a ramoplanin derivative designed to overcome the tolerability issues of the parent drug as a systemic agent. NAI-603 is highly active against aerobic and anaerobic Gram-positive bacteria, with MICs ranging from 0.008 to 8 μg/ml. MICs were not significantly affected by pH (range, 6 to 8), by inoculum up to 10(8) CFU/ml, or by addition of 50% human serum. Against staphylococci and enterococci, NAI-603 was rapidly bactericidal, with minimum bactericidal concentration (MBC)/MIC ratios never exceeding 4. The frequency of spontaneous resistance was low at 2× to 4× MIC (≤1×10(-6) to ≤1×10(-8)) and below the detection limit (about ≤1×10(-9)) at 8×MIC. Serial subcultures at 0.5×MIC yielded at most an 8-fold increase in MICs. In a systemic infection induced by methicillin-resistant Staphylococcus aureus (MRSA), the 50% effective dose (ED50) of intravenous (i.v.) NAI-603 was 0.4 mg/kg, lower than that of oral (p.o.) linezolid (1.4 mg/kg) and subcutaneous (s.c.) teicoplanin (1.4 mg/kg) or vancomycin (0.6 mg/kg). In neutropenic mice infected with vancomycin-resistant enterococci (VRE), the ED50s for NAI-603 were 1.1 to 1.6 mg/kg i.v., compared to 0.5 mg/kg i.v. of ramoplanin. The bactericidal activity was confirmed in vivo in the rat granuloma pouch model induced by MRSA, where NAI-603, at 40 mg/kg i.v., induced about a 2- to 3-log10-reduction in viable bacteria in the exudates, which persisted for more than 72 h. The pharmacokinetic (PK) profiles of NAI-603 and ramoplanin at 20 mg/kg show similar half-lives (3.27 and 3.80 h, respectively) with the maximum concentration (Cmax) markedly higher for NAI-603 (207 μg/ml versus 79 μg/ml). The favorable pharmacological profile of NAI-603, coupled with the absence of local tolerability issues, supports further investigation.

Generation of ramoplanin-resistant Staphylococcus aureus

Ramoplanin is a lipoglycodepsipeptide antimicrobial active against clinically important Gram-positive bacteria including methicillin-resistant Staphylococcus aureus. To proactively examine ramoplanin resistance, we subjected S. aureus NCTC 8325-4 to serial passage in the presence of increasing concentrations of ramoplanin, generating the markedly resistant strain RRSA16. Susceptibility testing of RRSA16 revealed the unanticipated acquisition of cross-resistance to vancomycin and nisin. RRSA16 displayed phenotypes, including a thickened cell wall and reduced susceptibility to Triton X-100-induced autolysis, which are associated with vancomycin intermediate-resistant S. aureus strains. Passage of RRSA16 for 18 days in a drug-free medium yielded strain R16-18d with restored antibiotic susceptibility. The RRSA16 isolate may be used to identify the genetic and biochemical basis for ramoplanin resistance and to further our understanding of the evolution of antibiotic cross-resistance mechanisms in S. aureus.

Ramoplanin: a lipoglycodepsipeptide antibiotic

OBJECTIVE

To review the pharmacology, antimicrobial activity, pharmacokinetics, clinical applications, and safety of ramoplanin, a lipoglycodepsipeptide antibiotic.

DATA SOURCES

Information was obtained from MEDLINE and BIOSIS databases (1984-August 2004) and Oscient Pharmaceuticals using the key words ramoplanin, A 16686, A 16686A, and MDL 62198.

STUDY SELECTION AND DATA EXTRACTION

Available English-based articles and abstracts were reviewed, along with information from Oscient Pharmaceuticals.

DATA SYNTHESIS

Ramoplanin exerts its bactericidal activity against gram-positive aerobic and anaerobic bacteria by blocking peptidoglycan synthesis via lipid II. In vitro susceptibility reports have demonstrated efficacy against antibiotic-resistant gram-positive pathogens. Cross-resistance has not been documented with vancomyin and other glycopeptides. Clinical trials are investigating ramoplanin's oral administration for treatment of Clostridium difficile-associated diarrhea. Previous clinical trials had evaluated the suppression of colonization of vancomycin-resistant Enterococcus with ramoplanin. Adverse effects are minimal, and drug-drug interactions have not been documented.

CONCLUSIONS

The completion of clinical trials will determine whether ramoplanin has a promising role as a treatment option for diarrhea due to C. difficile.

In vitro activities of ramoplanin, teicoplanin, vancomycin, linezolid, bacitracin, and four other antimicrobials against intestinal anaerobic bacteria

By using an agar dilution method, the in vitro activities of ramoplanin, teicoplanin, vancomycin, linezolid, and five other agents were determined against 300 gram-positive and 54 gram-negative strains of intestinal anaerobes. Ramoplanin was active at <or=2 microg/ml against 287 of 300 (95.7%) gram-positive organisms, including 18 strains of Clostridium difficile for which MICs of ramoplanin were 0.25 to 0.5 microg/ml; for 3 of these, linezolid MICs were 8 to 16 micro g/ml. Nineteen Clostridium innocuum strains for which the vancomycin MIC at which 90% of strains were inhibited was 16 microg/ml were susceptible to ramoplanin at 0.06 to 0.25 microg/ml and to teicoplanin at 0.125 to 1.0 microg/ml. All strains of Eubacterium, Actinomyces, Propionibacterium, and Peptostreptococcus spp. were inhibited by <or=0.25 microg of ramoplanin per ml and <or=1 microg of vancomycin per ml. Ramoplanin was also active at <or=4 microg/ml against 15 of 22 of the Prevotella and Porphyromonas strains tested, but ramoplanin MICs for all 31 strains of the Bacteroides fragilis group, the Fusobacterium mortiferum-Fusobacterium varium group, and Veillonella spp. were >or=256 microg/ml. Ramoplanin displays excellent activity against C. difficile and other gram-positive enteric anaerobes, including vancomycin-resistant strains; however, it has poor activity against most gram-negative anaerobes and thus potentially has a lesser effect on the ecological balance of normal fecal flora.

Chemistry and biology of the ramoplanin family of peptide antibiotics

The peptide antibiotic ramoplanin factor A2 is a promising clinical candidate for treatment of Gram-positive bacterial infections that are resistant to antibiotics such as glycopeptides, macrolides, and penicillins. Since its discovery in 1984, no clinical or laboratory-generated resistance to this antibiotic has been reported. The mechanism of action of ramoplanin involves sequestration of peptidoglycan biosynthesis Lipid intermediates, thus physically occluding these substrates from proper utilization by the late-stage peptidoglycan biosynthesis enzymes MurG and the transglycosylases (TGases). Ramoplanin is structurally related to two cell wall active lipodepsipeptide antibiotics, janiemycin, and enduracidin, and is functionally related to members of the lantibiotic class of antimicrobial peptides (mersacidin, actagardine, nisin, and epidermin) and glycopeptide antibiotics (vancomycin and teicoplanin). Peptidomimetic chemotherapeutics derived from the ramoplanin sequence may find future use as antibiotics against vancomycin-resistant Enterococcus faecium (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and related pathogens. Here we review the chemistry and biology of the ramoplanins including its discovery, structure elucidation, biosynthesis, antimicrobial activity, mechanism of action, and total synthesis.

Treatment options for vancomycin-resistant enterococcal infections

Serious infection with vancomycin-resistant enterococci (VRE) usually occurs in patients with significantly compromised host defences and serious co-morbidities, and this magnifies the importance of effective antimicrobial treatment. Assessments of antibacterial efficacy against VRE have been hampered by the lack of a comparator treatment arm(s), complex treatment requirements including surgery, and advanced illness-severity associated with a high crude mortality. Treatment options include available agents which don't have a specific VRE approval (chloramphenicol, doxycycline, high-dose ampicillin or ampicillin/sulbactam), and nitrofurantoin (for lower urinary tract infection). The role of antimicrobial combinations that have shown in vitro or animal-model in vivo efficacy has yet to be established. Two novel antimicrobial agents (quinupristin/ dalfopristin and linezolid) have emerged as approved therapeutic options for vancomycin-resistant Enterococcus faecium on the basis of in vitro susceptibility and clinical efficacy from multicentre, pharmaceutical company-sponsored clinical trials. Quinupristin/dalfopristin is a streptogramin, which impairs bacterial protein synthesis at both early peptide chain elongation and late peptide chain extrusion steps. It has bacteriostatic activity against vancomycin-resistant E. faecium [minimum concentration to inhibit growth of 90% of isolates (MIC(90)) = 2 microg/ml] but is not active against Enterococcus faecalis (MIC(90 )= 16 microg/ml). In a noncomparative, nonblind, emergency-use programme in patients who were infected with Gram-positive isolates resistant or refractory to conventional therapy or who were intolerant of conventional therapy, quinupristin/dalfopristin was administered at 7.5 mg/kg every 8 hours. The clinical response rate in the bacteriologically evaluable subset was 70.5%, and a 65.8% overall response (favourable clinical and bacteriological outcome) was observed. Resistance to quinupristin/dalfopristin on therapy was observed in 6/338 (1.8%) of VRE strains. Myalgia/arthralgia was the most frequent treatment-limiting adverse effect. In vitro studies which combine quinupristin/dalfopristin with ampicillin or doxycyline have shown enhanced killing effects against VRE; however, the clinical use of combined therapy remains unestablished. Linezolid, an oxazolidinone compound that acts by inhibiting the bacterial pre-translational initiation complex formation, has bacteriostatic activity against both vancomycin resistant E. faecium (MIC(90) = 2 to 4 microg/ml) and E. faecalis (MIC(90) = 2 to 4 microg/ml). This agent was studied in a similar emergency use protocol for multi-resistant Gram-positive infections. 55 of 133 evaluable patients were infected with VRE. Cure rates for the most common sites were complicated skin and soft tissue 87.5% (7/8), primary bacteraemia 90.9% (10/11), peritonitis 91.7% (11/12), other abdominal/pelvic infections 91.7% (11/12), and catheter-related bacteraemia 100% (9/9). There was an all-site response rate of 92.6% (50/54). In a separate blinded, randomised, multicentre trial for VRE infection at a variety of sites, intravenous low dose linezolid (200mg every 12 hours) was compared to high dose therapy (600 mg every 12 hours) with optional conversion to oral administration. A positive dose response (although statistically nonsignificant) was seen with a 67% (39/58) and 52% (24/46) cure rate in the high- and low-dose groups, respectively. Adverse effects of linezolid therapy have been predominantly gastrointestinal (nausea, vomiting, diarrhoea), headache and taste alteration. Reports of thrombocytopenia appear to be limited to patients receiving somewhat longer courses of treatment (>14 to 21 days). Linezolid resistance (MIC > or = 8 microg/ml) has been reported in a small number of E. faecium strains which appears to be secondary to a base-pair mutation in the genome encoding for the bacterial 23S ribosome binding site. At present a comparative study between the two approved agents for VRE (quinupristin/dalfopristin and linezolid) has not been performed. Several investigational agents are currently in phase II or III trials for VRE infection. This category includes daptomycin (an acidic lipopeptide), oritavancin (LY-333328; a glycopeptide), and tigilcycline (GAR-936; a novel analogue of minocycline). Finally, strategies to suppress or eradicate the VRE intestinal reservoir have been reported for the combination of oral doxycyline plus bacitracin and oral ramoplanin (a novel glycolipodepsipeptide). If successful, a likely application of such an approach is the reduction of VRE infection during high risk periods in high risk patient groups such as the post-chemotherapy neutropenic nadir or early post-solid abdominal organ transplantation.

Molecular characterization of vancomycin-resistant Enterococci repopulating the gastrointestinal tract following treatment with a novel glycolipodepsipeptide, ramoplanin

We characterized baseline and repopulating stool isolates recovered during a phase II trial of ramoplanin for the treatment of patients with stool carriage of vancomycin-resistant enterococci (VRE). Repopulation with a strain with a related genotype was found in 74, 60, and 53% of individuals in groups treated with placebo, 100 mg of ramoplanin, and 400 mg of ramoplanin, respectively. All ramoplanin-treated patients with a culture positive for VRE at day 7 had a relapse caused by a genotypically related isolate. In ramoplanin-treated patients, antibiotics with activities against anaerobic organisms were associated with positive cultures on day 7 (relative risk [RR] = 8.8; P = 0.004), and the avoidance of such antibiotics was significantly associated with culture negativity through day 21 (RR = 0.16; P = 0.02).

Effective suppression of vancomycin-resistant Enterococcus species in asymptomatic gastrointestinal carriers by a novel glycolipodepsipeptide, ramoplanin

Nosocomial bloodstream infections due to vancomycin-resistant enterococci (VRE) are associated with increased morbidity rates, mortality rates, and hospitalization costs. Gastrointestinal carriage of VRE is an important risk factor for subsequent infections. This 3-arm, phase II, double-blinded, randomized, multicenter, placebo-controlled study evaluated the safety and efficacy of oral ramoplanin (a novel, nonabsorbed glycolipodepsipeptide) versus placebo for suppression of gastrointestinal VRE colonization. Sixty-eight patients who were colonized with VRE were enrolled and received 2 daily doses of ramoplanin (100 mg or 400 mg) or placebo orally for 7 days. The primary end point was the proportion of persons per group from whom VRE were not recovered (VRE-free) on days 7, 14, and 21 after screening. After treatment, VRE-free status was as follows: day 7, none of the 20 patients in the placebo group, and 17 of 21 (P<.001) and 18 of 20 (P<.001) in the 100-mg and 400-mg ramoplanin groups, respectively; on day 14, 2 of 20 patients in the placebo group, and 6 of 21 (P=.134) and 7 of 17 (P=.028), in the 100-mg and 400-mg ramoplanin groups, respectively. By day 21, there were no differences between treatment groups. Adverse events were similar for all treatment groups. Ramoplanin was safe and effective in temporarily suppressing gastrointestinal VRE carriage.