No abstract

Background Py-mulin is a new pleuromutilin derivative with potent antibacterial activities in vitro and in vivo, suggesting this compound may lead to a promising antibacterial drug after further development. The present study is aimed to evaluate the acute and subacute oral toxicity, and the genotoxicity with the standard Ames test according to standard protocols. Methods Acute oral toxicity of Py-mulin was determined using Kunming mice. The 28-day repeated dose oral toxicity study in SD rats was performed according to OECD guideline No. 407. The bacterial reverse mutation (Ames test) was carried out using four Salmonella typhimurium (S. typhimurium) strains TA97, TA98, TA100 and TA1535 with and without S9 metabolic activation. Results The LD50 values in acute oral toxicity were 2973 mg/kg (female mice) and 3891 mg/kg (male mice) calculated by the Bliss method. In subacute toxicity study, 50 mg/kg Py-mulin did not induce any abnormality in body weight, food consumption, clinical sign, hematology, clinical chemistry, organ weight, and histopathology in all of the treatment groups. However, high doses of Py-mulin (100 and 300 mg/kg) displayed slightly hepatotoxicity to female rats. Furthermore, Py-mulin did not significantly increase the number of revertant colonies of four standard S. typhimurium strains with the doses of 0.16–1000 μg/plate in the Ames study. Conclusions Based on our findings, our study provides some information for the safety profile of Py-mulin.

14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] mutilin (DPTM) is a promising drug candidate with excellent antibacterial activity against Gram-positive bacteria. The present study was designed to characterize its Cytochrome P450 (CYP) enzymes inhibition activities and the genotoxicity with the standard Ames test. We determined the inhibitory effects of DPTM on CYP1A2, CYP2D1/6, CYP2E1, CYP2C11/9 and CYP3A/4 in rat liver microsomes (RLMs) and in human liver microsomes (HLMs). The mRNA expressions of the above CYP isoforms and their transcriptional regulators were also evaluated using the Hep G2 cell model. The results showed DPTM exhibited a moderate inhibitory potential against CYP3A/4 (IC 50 values of 10 ± 2 and 8 ± 2 μM, respectively) and weak against the other CYP enzymes based on their IC 50 values. Compared to the control, CYP isoforms and their transcriptional regulators mRNA expressions significantly increased when the Hep G2 cells were treated with DPTM for a certain period of time. In the Ames test, Salmonella strains TA97, TA98, TA100, TA102 and TA1535 were treated with or without the metabolic activation (S9). Analysis showed the average number of revertant colonies per plate was less in double in the groups treated with DPTM than that in the negative control plate and showed no dose-related increase. Pleuromutilin (Fig. 1), a 5-6-8 tricycle diterpene, was first discovered and isolated from two basidiomycete species in 1951 1. Pleuromutilin class of antibiotics selectively inhibits bacterial protein synthesis by interacting with the peptidyl transferase centre (PTC) of prokaryotic ribosomes at the A-and P-site through hydrophobic interactions and hydrogen bonds 2-4. The modifications of pleuromutilin side chain led to tiamulin (Fig. 1) and valnemulin (Fig. 1) for veterinary use 5,6. Retapamulin (Fig. 1) is a topically administered pleuromutilin that was first approved for human use in 2007 7,8. Lefamulin (BC-3781, Fig. 1) developed by Nabriva Therapeutics was approved by FDA for human use in 2019 9,10. Azamulin (Fig. 1), an azole pleuromutilin derivative designed for human use, has entered phase I clinical trials in volunteers in 1980s 11. Unfortunately, azamulin did not undergo further clinical trials because of its Cytochrome P450 (CYP) inhibition and limited bioavailability 12,13. Tiamulin is also a potent inhibitor and inducer of CYP, via the formation of a metabolic intermediate complex 14. Lefamulin showed relative high inhibition for CYP3A4 with IC 50 < 5 μM 15. Therefore, the investigation of inhibition potency of pleuromutilin analogues against CYP was subsequently emphasized to avoid the risk for development a new drug. A novel pleuromutilin derivative, 14-O-[(4,6-Diaminopyrimidine-2-yl)thioacetyl] mutilin (DPTM, Fig. 1), was synthesized and reported in ours previous work 16. This compound showed the excellent in vitro activities against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), as w...