Antibacterial activity and pharmacokinetic profile of a promising antibacterial agent: 14-O-[(4-Amino-6-hydroxy-pyrimidine-2-yl)thioacetyl] mutilin

Anti-methicillin-resistant Staphylococcus aureus activity and safety evaluation of 14-O-[(5-ethoxycarbonyl-4,6-dimethylpyrimidine-2-yl) thioacetyl] mutilin (EDT)

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have threated the public health worldwide, which emphasizes the urgent need for new drugs with novel mechanism of actions. 14-O-[(5-ethoxycarbonyl-4,6-dimethylpyrimidine-2-yl) thioacetyl] mutilin (EDT) is a pleuromutilin compound with high activity against several Gram-positive bacteria in vitro and in vivo. This study aimed to verifying the potential anti-MRSA activity and evaluating the safety of EDT. In in vitro antibacterial activity assays, EDT exhibited potent antibacterial activity against MRSA isolated from clinic (minimum inhibitory concentration = 0.0313-0.125 μg/mL), increased post-antibiotic effect (PAE) values and limited potential for the development of resistance. Docking model and green fluorescent protein (GFP) inhibition assay further elucidated the higher antibacterial activities of EDT via mechanism of action. In safety evaluation, EDT exhibited low cytotoxic effect and acute oral toxicity in mice and avoided to significantly increase the number of revertant colonies of six tested strains in the Ames study. Furthermore, EDT displayed a moderate inhibitory effect on CYP3A4 and moderate stability in mouse and human liver microsomes, providing a promising agent for the development of new antimicrobial candidate.

Design, synthesis and antibacterial activity of novel pleuromutilin derivatives with thieno[2,3-d]pyrimidine substitution

A series of novel pleuromutilin derivatives with substituted thienopyrimidines were designed, synthesized, and evaluated for antibacterial act ivity. In this study, the activities of these compounds were investigated using the inhibition circle test, the minimum inhibitory concentration (MIC) test, real-time growth curves, time-kill kinetic assays, cytotoxicity assays, and molecular docking. Most of the tested compounds exhibited moderate antibacterial activity against Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli. Compound A11 was the most active and displayed bacteriostatic activities against methicillin-resistant S. aureus, with MIC values as low as 0.00191 μg/mL, which is 162 and 32 times lower than that of the marketed antibiotics tiamulin and retapamulin, respectively. Furthermore, the mechanism of action of A11 was confirmed by molecular docking studies.

Antibacterial Activity of a Promising Antibacterial Agent: 22-(4-(2-(4-Nitrophenyl-piperazin-1-yl)-acetyl)-piperazin-1-yl)-22-deoxypleuromutilin

A novel pleuromutilin derivative, 22-(4-(2-(4-nitrophenyl-piperazin-1-yl)-acetyl)-piperazin-1-yl)-22-deoxypleuromutilin (NPDM), was synthesized in our laboratory and proved excellent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). In this study, more methods were used to further study its preliminary pharmacological effect. The antibacterial efficacy and toxicity of NPDM were evaluated using tiamulin as the reference drug. The in vitro antibacterial activity study showed that NPDM is a potent bactericidal agent against MRSA that induced time-dependent growth inhibition and a concentration-dependent post-antibiotic effect (PAE). Toxicity determination showed that the cytotoxicity of NPDM was slightly higher than that of tiamulin, but the acute oral toxicity study proved that NPDM was a low-toxic compound. In an in vivo antibacterial effect study, NPDM exhibited a better therapeutic effect than tiamulin against MRSA in a mouse thigh infection model as well as a mouse systemic infection model with neutropenia. The 50% effective dose (ED50) of NPDM in a Galleria mellonella infection model was 50.53 mg/kg. The pharmacokinetic properties of NPDM were also measured, which showed that NPDM was a rapid elimination drug in mice.

Designing a leucine-rich antibacterial nonapeptide with potent activity against mupirocin-resistant MRSA via a structure-activity relationship study

Staphylococcus aureus is the main aetiological agent responsible for the majority of human skin infections. Of particular concern is the methicillin-resistant variety, commonly known as MRSA. The extensive use of the first-line topical antibiotic of choice, mupirocin, has inevitably resulted in the emergence of resistant strains, signalling an urgent need for the development of new antibacterials with new mechanisms of action. In this work, we describe how we designed a novel cationic nonapeptide, containing only leucine and two lysine residues, with potent anti-MRSA activity and a rapid bactericidal mode of action. Coupled to a favourable safety profile towards human skin fibroblasts, we believe nonapeptide 11 has high potential for further development as a mupirocin replacement candidate to treat skin infections caused by MRSA.

Design, synthesis and biological activities of novel pleuromutilin derivatives with a substituted triazole moiety as potent antibacterial agents

A series of novel pleuromutilin derivatives possessing 1,2,3-triazole moieties were synthesized via click reactions under mild conditions. The in vitro antibacterial activities of these derivatives against 4 strains of S. aureus (MRSA ATCC 43300, ATCC 29213, AD 3, and 144) and 1 strain of E. coli (ATCC 25922) were tested by the broth dilution method. The majority of the synthesized derivatives displayed potent antibacterial activities against MRSA (MIC = 0.125-2 μg/mL). It was also found that most compounds had no significant inhibitory effect on the proliferation of RAW264.7 cells at the concentration of 8 μg/mL. Among these derivatives, compound 32 (∼1.71 log10 CFU/g) containing dimethylamine group side chain displayed more effective than tiamulin (∼0.77 log10 CFU/g) at the dose of 20 mg/kg in reducing MRSA load in thigh infected mice. Additionally, compound 32 (the survival rate was 50%) also displayed superior in vivo efficacy to that of tiamulin (the survival rate was 20%) in the mouse systemic model. Structure-activity relationship (SAR) studies resulted in compound 32 with the most potent in vitro and in vivo antibacterial activity among the series. Moreover, compound 32 was evaluated in CYP450 inhibition assay and showed moderate in vitro inhibition of CYP3A4 (IC50 = 6.148 μM).

A Validated HPLC-MS/MS Assay for 14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] Mutilin in Biological Samples and Its Pharmacokinetic, Distribution and Excretion via Urine and Feces in Rats

14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] mutilin (DPTM), a novel pleuromutilin candidate with a substituted pyrimidine moiety, has been confirmed to possess excellent antibacterial activity against Gram-positive bacteria. To illustrate the pharmacokinetic profile after intravenous (i.v.), intramuscular (i.m.) and oral (p.o.) administrations with DPTM, as well as tissue distribution and excretion via urine and feces in vivo, a specific, sensitive and robust HPLC-MS/MS method was first developed to determine DPTM in rat plasma, various tissues, urine and feces. The plasma, tissues, urine and feces samples were treated by protein precipitation with acetonitrile using tiamulin fumarate as an internal standard (IS). This method which was achieved on an HPLC system detector equipped with an ESI interface, was sensitive with 5 ng/mL as the lower limit of detection and exhibited good linearity (R² > 0.9900) in the range of 5⁻4000 ng/mL for plasma, various tissues, urine and feces, as well as intra-day precision, inter-day precision and accuracy. The matrix effects ranged from 94.2 to 109.7% with RSD ≤ 9.4% and the mean extraction recoveries ranged from 95.4 to 109.5% in plasma, tissue homogenates, urine and feces (RSD ≤ 9.9). After i.v., i.m. and p.o. administrations, DPTM was rapidly absorbed and metabolized in rats with the half-life (t1/2) of 1.70⁻1.86, 3.23⁻3.49 and 4.38⁻4.70 for 10, 25 and 75 mg/kg doses, respectively. The tissue distribution showed that DPTM was diffused into all the tested tissues, especially into the intestine and lung. Excretion via urine and feces studies demonstrated that DPTM was mainly excreted by feces after administration.