Potential RNA-dependent RNA polymerase inhibitors as prospective therapeutics against SARS-CoV-2.

Introduction. The emergence of SARS-CoV-2 has taken humanity off guard. Following an outbreak of SARS-CoV in 2002, and MERS-CoV about 10 years later, SARS-CoV-2 is the third coronavirus in less than 20 years to cross the species barrier and start spreading by human-to-human transmission. It is the most infectious of the three, currently causing the COVID-19 pandemic. No treatment has been approved for COVID-19. We previously proposed targets that can serve as binding sites for antiviral drugs for multiple coronaviruses, and here we set out to find current drugs that can be repurposed as COVID-19 therapeutics.Aim. To identify drugs against COVID-19, we performed an in silico virtual screen with the US Food and Drug Administration (FDA)-approved drugs targeting the RNA-dependent RNA polymerase (RdRP), a critical enzyme for coronavirus replication.Methodology. Initially, no RdRP structure of SARS-CoV-2 was available. We performed basic sequence and structural analysis to determine if RdRP from SARS-CoV was a suitable replacement. We performed molecular dynamics simulations to generate multiple starting conformations that were used for the in silico virtual screen. During this work, a structure of RdRP from SARS-CoV-2 became available and was also included in the in silico virtual screen.Results. The virtual screen identified several drugs predicted to bind in the conserved RNA tunnel of RdRP, where many of the proposed targets were located. Among these candidates, quinupristin is particularly interesting because it is expected to bind across the RNA tunnel, blocking access from both sides and suggesting that it has the potential to arrest viral replication by preventing viral RNA synthesis. Quinupristin is an antibiotic that has been in clinical use for two decades and is known to cause relatively minor side effects.Conclusion. Quinupristin represents a potential anti-SARS-CoV-2 therapeutic. At present, we have no evidence that this drug is effective against SARS-CoV-2 but expect that the biomedical community will expeditiously follow up on our in silico findings.

In vitro synergistic effect of retapamulin with erythromycin and quinupristin against Enterococcus faecalis.

To find a therapeutic alternative for the treatment of skin and soft tissue infections, we evaluated the effects of combinations of retapamulin with macrolide, lincosamide, and streptogramin (MLS) antibiotics against Staphylococcus aureus, Streptococcus pyogenes, Enterococcus faecium, and Enterococcus faecalis. Using both the disk diffusion test and checkerboard assay, we initially examined the effects of combinations of retapamulin with MLS antibiotics against standard strains of these species. Combinations of retapamulin with erythromycin, quinupristin/dalfopristin and quinupristin showed synergistic activity against E. faecalis only. Synergy of retapamulin with clindamycin and dalfopristin was not observed. Then, a checkerboard assay was performed to evaluate the effects of the combinations against 15 clinical strains of E. faecalis. Retapamulin and quinupristin, the most synergistic combination, showed activity against all erythromycin-susceptible, -intermediate, and -resistant strains tested. Among the eight strains with high-level erythromycin resistance, five strains were synergistically inhibited in the presence of only 1 µg of retapamulin per ml. Time-kill assay revealed that combinations of retapamulin with erythromycin and quinupristin were bacteriostatic. These results suggest that combinations of retapamulin with erythromycin and quinupristin have in vitro synergistic activity against E. faecalis, including strains with high-level erythromycin resistance.

[Therapeutic perspectives of linezolid in the management of infections due to multiresistant Gram-positive pathogens]. / Le prospettive terapeutiche di linezolid nelle infezioni da patogeni Gram-positivi multiresistenti.

Multi-antibiotic resistant Gram-positive cocci represent emerging pathogens especially in the setting of the immunocompromised, hospitalized patients, in particular when surgery, invasive procedures, or prosthetic implants are of concern, patients are admitted in intensive care units, or underlying chronic disorders and immunodeficiency are of concern, and broad-spectrum antibiotics and/or immunosuppressive drugs are widely administered. The spectrum of available antimicrobial compounds for an effective management of these relevant infections is significantly impaired in selection and clinical efficacy by the emerging and spread of methicillin-resistant and more recently glycopeptide-resistant Gram-positive microbial strains linezolid, together with the recently licensed quinupristin-dalfopristin, daptomycin and tigecycline, followed by a number of glycopeptides, fluoroquinolones, and other experimental compounds represent an effective response to these concerns, due to their innovative mechanisms of action, their maintained or enhanced activity against multiresistant pathogens, their effective pharmacokinetic/pharmacodynamic properties, their frequent possibility of synergistic activity with other compounds effective against Gram-positive pathogens, and a diffuse potential for a safe and easy administration, also when compromised patients are of concern. The main problems related to the epidemiological and clinical features of multiresistant Gram-positive infection, the potential clinical indications of all recently available compounds compared with the standard of treatment of resistant Gram-positive infections, and updated data on efficacy and tolerability of linezolid have to be clarified.

In vitro activity of linezolid & quinupristin/dalfopristin against Gram-positive cocci.

BACKGROUND & OBJECTIVES: Since the incidence of vancomycin- and methicillin-resistant Gram-positive infections continue to increase, novel antimicrobials such as linezolid and streptogramin may provide new options to treat patients. The aim of this study was to investigate in vitro susceptibility of Enterococcus faecium resistant to glycopeptides, coagulase negative staphylococci and S. aureus resistant to methicillin isolated mainly from blood and also rectal swab cultures of patients against quinupristin/dalfopristin and linezolid. METHODS: The in vitro susceptibility to linezolid and quinupristin/dalfopristin for a total of 332 isolates of Gram-positive cocci [127 methicillin-resistant Staphylococcus aureus, 109 methicillin-resistant coagulase negative staphylococci (71 S. epidermidis, 38 S. haemolyticus) and 96 vanA genotype vancomycin-resistant Enterococcus faecium] was investigated by E test. RESULTS: All MRSA and MRCoNS isolates were susceptible to linezolid (MICs < 4.0 mg/l). Ninety per cent of VRE isolates were inhibited by linezolid at concentration of 2.0 mg/l and presented similar activities to quinupristin/dalfopristin. MICs for quinupristin/dalfopristin against staphylococci were also low (MIC(90) = 1.0 mg/l for both MRSA and MRCoNS isolates). INTERPRETATION & CONCLUSION: The results of the present study demonstrated that quinupristin/ dalfopristin and linezolid, have good in vitro activity against MRSA, MRCoNS and vancomycin resistant E. faecium in Turkey. These drugs could be promising therapeutic options in an era of rapidly growing antibiotic resistance in all parts of world.

Endocarditis due to vancomycin-resistant Enterococcus faecium in an immunocompromised patient: cure by administering combination therapy with quinupristin/dalfopristin and high-dose ampicillin.

A 56-year-old man with diabetes mellitus and cadaveric renal transplantation had vancomycin-resistant Enterococcus faecium tricuspid valve endocarditis. Relapse followed 6 weeks of treatment with intravenous gentamicin and high-dose ampicillin. On the basis of previous data suggesting the potential for synergistic activity of quinupristin/dalfopristin plus high-dose ampicillin, therapy with this combination was administered for 63 days. Cure was achieved and later confirmed at 2-year follow-up.

Role of quinupristin/dalfopristin in the treatment of Gram-positive nosocomial infections in haematological or oncological patients.

Gram-positive pathogens, primarily Staphylococcus aureus, coagulase-negative staphylococci, viridans group streptococci, and enterococci, are now the predominant causes of infection in neutropenic haematology/oncology patients, but are often resistant to multiple antibiotics. Glycopeptides have been the only alternative antibiotic treatments for multidrug-resistant Gram-positive infections to date. However, glycopeptides are not always effective or well tolerated, and can produce nephrotoxic or ototoxic effects. Quinupristin/dalfopristin is a recently introduced streptogramin antibiotic that is active in vitro against most of the major Gram-positive pathogens causing infection in neutropenic patients. Recent studies of the in vitro susceptibility of clinical isolates of Gram-positive pathogens to quinupristin/dalfopristin are summarized. Pre-clinical and clinical studies of the efficacy and safety of quinupristin/dalfopristin in the treatment of Gram-positive infections are reviewed. Quinupristin/dalfopristin is active in vitro against the vast majority of recent isolates of relevant Gram-positive pathogens, including methicillin-resistant staphylococci, viridans group streptococci, and vancomycin-resistant Enterococcus faecium, but excluding Enterococcus faecalis. Pre-clinical and clinical data indicate the efficacy of quinupristin/dalfopristin in infections caused by these organisms, including bacteraemia and catheter-related infections. Quinupristin/dalfopristin is not associated with nephrotoxicity or ototoxicity. Quinupristin/dalfopristin is a potential alternative to glycopeptides in haematology or oncology patients with multidrug-resistant Gram-positive infections, especially those who are unresponsive to, or intolerant of, glycopeptides.

Telithromycin and quinupristin-dalfopristin resistance in clinical isolates of Streptococcus pyogenes: SMART Program 2001 Data.

This study evaluated the current status of antimicrobial resistance in clinical isolates of Streptococcus pyogenes in Taiwan as part of the SMART (Surveillance from Multicenter Antimicrobial Resistance in Taiwan) program. In 2001, 419 different isolates of S. pyogenes, including 275 from respiratory secretions, 87 from wound pus, and 31 from blood, were collected from nine hospitals in different parts of Taiwan. MICs of 23 antimicrobial agents were determined at a central location by the agar dilution method. All of the isolates were susceptible to penicillin (MIC at which 90% of the isolates were inhibited [MIC(90)], moxifloxacin > ciprofloxacin = levofloxacin = gatifloxacin > gemifloxacin) demonstrated potent activity against nearly all of the isolates of S. pyogenes tested. Thirty-two isolates (8%) were not susceptible to quinupristin-dalfopristin. Seventeen percent of isolates had telithromycin MICs of >or=1 microg/ml, and all of these isolates exhibited erythromycin MICs of >or=32 microg/ml. The high prevalence of resistance to telithromycin (which is not available in Taiwan) limits its potential use in the treatment of S. pyogenes infections, particularly in areas with high rates of macrolide resistance.

Safety and efficacy of quinupristin/dalfopristin for treatment of invasive Gram-positive infections in pediatric patients.

BACKGROUND: Antibiotic-resistant Gram-positive pathogens are an increasingly common cause of serious pediatric infections. Although quinupristin/dalfopristin demonstrates favorable activity against resistant Gram-positive pathogens (including many vancomycin-resistant and methicillin-resistant staphylococci), published experience in the pediatric patient population is limited. METHODS: We retrospectively analyzed data from the global quinupristin/dalfopristin Emergency-Use Program, which enrolled patients with serious Gram-positive infections who had no further therapy options because of resistance to, failure on or intolerance to standard antibiotic treatments. Our subset included safety and efficacy data from pediatric patients (age <18 years). There were no restrictions on underlying diseases, severity of illness or prior/concomitant antimicrobial use. RESULTS: Between May 1995 and October 1999, 127 pediatric patients with 131 infections were enrolled. Microbiologic confirmation of etiology was available in 124 patients. All patients had 1 or more concomitant conditions, including malignancy and solid organ or bone marrow transplantation. The most frequent causative pathogens were vancomycin-resistant (80%), spp. (7%), methicillin-resistant (6%) and (4%). All but 21 patients received intravenous quinupristin/dalfopristin 7.5 mg/kg every 8 h. The favorable clinical response rate of quinupristin/dalfopristin was 86 of 124 (69%); the favorable microbiologic response rate was 97 of 124 (78%). Eleven patients (8%) had nonvenous adverse events classified as possibly or probably related to quinupristin/dalfopristin. CONCLUSIONS: Quinupristin/dalfopristin demonstrated favorable response rates and was reasonably well-tolerated in pediatric patients with serious Gram-positive infections unable to receive alternative therapy. In our opinion quinupristin/dalfopristin is a therapeutic option for the management of such infections.

In vitro and in vivo effects of quinupristin-dalfopristin against Pneumocystis carinii.

Quinupristin-dalfopristin (Q-D), which is active against bacteria and Toxoplasma gondii, was examined for its activity against Pneumocystis carinii. After 72 h of incubation with rat P. carinii in an ATP cytotoxicity assay, the 50% inhibitory concentration of Q-D was 10.6 microg/ml, a level that can be achieved in serum with high-dose administration. Q-D administered intraperitoneally at doses of 50 to 200 mg per kg of body weight per day in the treatment and 100 mg/kg/day three times per week in the prophylaxis of pneumocystosis in immunosuppressed mice reduced the organism burden up to 15- and 302-fold, respectively. We conclude that Q-D has activity against P. carinii in vitro and in vivo.

Influence of resistance to streptogramin A type antibiotics on the activity of quinupristin-dalfopristin in vitro and in experimental endocarditis due to Staphylococcus aureus.

We evaluated the activity of quinupristin-dalfopristin (Q-D) against three clinical strains of Staphylococcus aureus susceptible to Q (MIC, 8 microg/ml) and Q-D (MICs, 0.5 to 1 microg/ml) but displaying various levels of susceptibility to D. D was active against S. aureus HM 1054 (MIC, 4 microg/ml) and had reduced activity against S. aureus RP 13 and S. aureus N 95 (MICs, 32 and 64 microg/ml, respectively). In vitro, Q-D at a concentration two times the MIC (2xMIC) produced reductions of 4.3, 3.9, and 5.8 log(10) CFU/ml after 24 h of incubation for HM 1054, RP 13, and N 95, respectively. Comparable killing was obtained at 8xMIC. Q-D-resistant mutants were selected in vitro at a frequency of 2 x 10(-8) to 2 x 10(-7) for the three strains on agar containing 2xMIC of Q-D; no resistant bacteria were detected at 4xMIC. Rabbits with aortic endocarditis were treated for 4 days with Q-D at 30 mg/kg of body weight intramuscularly (i.m.) three times a day (t.i.d.) or vancomycin at 50 mg/kg i.m. t.i.d. In vivo, Q-D and vancomycin were similarly active and bactericidal against the three tested strains compared to the results for control animals (P < 0.01). Among animals infected with RP 13 and treated with Q-D, one rabbit retained Q-D-resistant mutants that were resistant to Q and to high levels of D (MICs, 64, >256, and 8 microg/ml for Q, D, and Q-D, respectively). We conclude that the bactericidal activity of Q-D against strains with reduced susceptibility to D and susceptible to Q-D is retained and is comparable to that of vancomycin. Acquisition of resistance to both Q and D is necessary to select resistance to Q-D.

Streptogramins and their potential role in geriatric medicine.

Despite advances in antimicrobial chemotherapy over recent decades, morbidity and mortality secondary to infection continues to rise. In addition, the incidence of infection caused by resistant organisms has also increased. Concurrently, the elderly are living longer than prior generations, often with disabling chronic diseases. The more debilitated of the geriatric population are at greater risk for infection, and more likely to acquire or develop antimicrobial resistant organisms. Gram-positive organisms are a source of resistance and commonly cause infection in older patients. Whereas resistance is a concern in all patients, in the elderly this is magnified by limitations in treatment options because of differences in pharmacokinetics and tolerance as compared with younger counterparts. Pharmacokinetic differences include changes in drug distribution and may arise as a result of diminished end organ function. Age-related decreases in renal function often impact on commonly prescribed antimicrobials. In addition, the elderly are more susceptible to drug-drug interactions because polypharmacy is common in this patient population. Streptogramins may offer a useful alternative in the treatment of infections in the elderly due to their coverage of organisms commonly causing infections in this population and because of their favourable pharmacokinetic profiles. While published experience is limited, streptogramins are not appreciably eliminated by the kidney and, therefore, they are less subject to age-related changes in renal elimination. What is required is multi-dose pharmacokinetic analysis of streptogramins in geriatric populations and subset analysis of patient use data on file. The following will provide the reader with the most recently presented data on streptogramin use and their potential. While focusing on potential use in the elderly, we have cited data and issues which we believe will be relevant in the geriatric population.