In Vitro Activity of Novel Rifamycins against Gram-positive Clinical Isolates

Rifamycin W Analogues from Amycolatopsis mediterranei S699 Δrif-orf5 Strain

Rifamycin W, the most predominant intermediate in the biosynthesis of rifamycin, needs to undergo polyketide backbone rearrangement to produce rifamycin B via an oxidative cleavage of the C-12/C-29 double bond. However, the mechanism of this putative oxidative cleavage has not been characterized yet. Rif-Orf5 (a putative cytochrome P450 monooxygenase) was proposed to be involved in the cleavage of this olefinic moiety of rifamycin W. In this study, the mutant strain Amycolatopsis mediterranei S699 Δrif-orf5 was constructed by in-frame deleting the rif-orf5 gene to afford thirteen rifamycin W congeners (1-13) including seven new ones (1-7). Their structures were elucidated by extensive analysis of 1D and 2D NMR spectroscopic data and high-resolution ESI mass spectra. Presumably, compounds 1-4 were derivatized from rifamycin W via C-5/C-11 retro-Claisen cleavage, and compounds 1-3, 9 and 10 featured a hemiacetal. Compounds 5-7 and 11 showed oxygenations at various sites of the ansa chain. In addition, compounds 1-3 exhibited antibacterial activity against Staphylococcus aureus with minimal inhibitory concentration (MIC) values of 5, 40 and 0.5 µg/mL, respectively. Compounds 1 and 3 showed modest antiproliferative activity against HeLa and Caco-2 cells with half maximal inhibitory concentration (IC50) values of about 50 µM.

Evaluation of current dosing guidance for oral rifampicin treatment in adult patients with osteoarticular infections

For management of osteoarticular infections, rifampicin appears to be the key antibiotic. We aimed to evaluate the actual rifampicin dosing regimens using a population pharmacokinetic model of rifampicin in patients with osteoarticular infections. A Monte Carlo simulation study was performed to simulate steady-state plasma concentrations for 1000 randomly sampled subjects using a total daily dose between 600 and 1200 mg (600 and 900 mg once daily, 450 and 600 mg twice daily, or 300 mg 3 times daily). When rifampicin was administered with fusidic acid, the pharmacokinetic/pharmacodynamic (PK/PD) target (area under the curve/minimum inhibitory concentration ≥952) was achieved with all tested dosing regimen, except 600 mg once daily for Staphylococcus epidermidis infections. Without coadministration of fusidic acid, none of tested dosing regimens achieved this PK/PD target. Most recommended drug-dosing regimens allow attaining the fixed area under the curve/minimum inhibitory concentration target for Staphylococcus aureus and coagulase-negative staphylococcal osteoarticular infections. In future studies, PK/PD target for osteoarticular infections in human should also be confirmed.

Isolation of 11,12- seco-Rifamycin W Derivatives Reveals a Cleavage Pattern of the Rifamycin Ansa Chain

This study reported the isolation and characterization of 11 rifamycin congeners including six new ones (1-6) from the agar fermentation extract of Amycolatopsis mediterranei S699. Compounds 1 and 2 are rifamycin glycosides named as rifamycinosides A and B, respectively. Their polyketide skeleton represents a novel cleavage pattern of the rifamycin ansa chain. Compounds 6 and 8 showed potential T3SS inhibitory activity, and 6 induced G2/M phase arrest and caused DNA damage in HCT116 cells.

Population pharmacokinetics of rifampicin in adult patients with osteoarticular infections: interaction with fusidic acid

AIMS

Rifampicin represents the key antibiotic for the management of osteoarticular infections. An important pharmacokinetic variability has already been described, particularly for absorption and metabolism. All previous pharmacokinetic studies have been focused only on patients treated for tuberculosis. The objective of the present study was to describe a population pharmacokinetic model of rifampicin in patients with staphylococcal osteoarticular infections, which has not been investigated to date.

METHOD

Rifampicin concentrations were collected retrospectively from 62 patients treated with oral rifampicin 300 mg three times daily. Plasma concentration-time data were analysed using NONMEM to estimate population pharmacokinetic parameters. Demographic data, infection characteristics and antibiotics taken in addition to rifampicin antibiotics were investigated as covariates.

RESULTS

A one-compartment model, coupled to a transit absorption model, best described the rifampicin data. Fusidic acid coadministration was identified as a covariate in rifampicin pharmacokinetic parameters. The apparent clearance and apparent central volume of distribution mean values [95% confidence interval (CI)] were 5.1 1 h^-1 (1.2, 8.2 1 h^-1 )/23.8 l (8.9, 38.7 l) and 13.7 1 h^-1 (10.6, 18.0 1 h^-1 )/61.1 1 (40.8, 129.0 1) for patients with and without administration of fusidic acid, respectively. Interindividual variability (95% CI) in the apparent clearance and apparent central volume of distribution were 72.9% (49.5, 86.0%) and 59.1% (5.5, 105.4%), respectively. Residual variability was 2.3 mg l^-1 (1.6, 2.6 mg l^-1 ).

CONCLUSION

We developed the first population pharmacokinetic model of rifampicin in patients with osteoarticular infections. Our model demonstrated that fusidic acid affects rifampicin pharmacokinetics, leading to potential high drug exposure. This finding suggests that fusidic acid dosing regimens should be reconsidered.

Overexpression of div8 increases the production and diversity of divergolides in Streptomyces sp. W112

Isolation and structure elucidation of divergolides from Streptomyces sp. HKI0576 revealed unusual ansamycin diversification reactions and the biosynthetic flexibility of the divergolide family.

Optimizing combination rifampin therapy for staphylococcal osteoarticular infections

Staphylococcus spp. causes more than half of all osteoarticular infections of native structures or implanted material. The ability of Staphylococcus spp. to persist within infected bone tissue and to produce a bacterial biofilm, most notably in infections of implanted material, can lead to treatment failures and microbiological relapses. Rifampin is a cornerstone of the treatment of staphylococcal osteoarticular infections, particularly those of implanted material. Rifampin is a bactericidal antibiotic that diffuses very well within bone tissue and bacterial biofilms. The mechanism of action is inhibition of bacterial DNA transcription to mRNA independently from bacterial division, which results in activity against even dormant Staphylococcus spp. organisms. However, the high risk of emergence of rifampin-resistant mutants requires the concomitant administration of another antibiotic. Several antibiotics are recommended in the French guidelines issued by the French-Speaking Society for Infectious Diseases (Société de Pathologie Infectieuse de Langue Française [SPILF]). Here, we discuss the results from in vitro, animal, and clinical studies that explain the advantages and drawbacks of each antibiotic used with rifampin to treat osteoarticular infections due to Staphylococcus spp.

Rifamycins--obstacles and opportunities

With nearly one-third of the global population infected by Mycobacterium tuberculosis, TB remains a major cause of death (1.7 million in 2006). TB is particularly severe in parts of Asia and Africa where it is often present in AIDS patients. Difficulties in treatment are exacerbated by the 6-9 month treatment times and numerous side effects. There is significant concern about the multi-drug-resistant (MDR) strains of TB (0.5 million MDR-TB cases worldwide in 2006). The rifamycins, long considered a mainstay of TB treatment, were a tremendous breakthrough when they were developed in the 1960's. While the rifamycins display many admirable qualities, they still have a number of shortfalls including: rapid selection of resistant mutants, hepatotoxicity, a flu-like syndrome (especially at higher doses), potent induction of cytochromes P450 (CYP) and inhibition of hepatic transporters. This review of the state-of-the-art regarding rifamycins suggests that it is quite possible to devise improved rifamycin analogs. Studies showing the potential of shortening the duration of treatment if higher doses could be tolerated, also suggest that more potent (or less toxic) rifamycin analogs might accomplish the same end. The improved activity against rifampin-resistant strains by some analogs promises that further work in this area, especially if the information from co-crystal structures with RNA polymerase is applied, should lead to even better analogs. The extensive drug-drug interactions seen with rifampin have already been somewhat ameliorated with rifabutin and rifalazil, and the use of a CYP-induction screening assay should serve to efficiently identify even better analogs. The toxicity due to the flu-like syndrome is an issue that needs effective resolution, particularly for analogs in the rifalazil class. It would be of interest to profile rifalazil and analogs in relation to rifampin, rifapentine, and rifabutin in a variety of screens, particularly those that might relate to hypersensitivity or immunomodulatory processes.

Rifamycin antibiotic resistance by ADP-ribosylation: Structure and diversity of Arr

The rifamycin antibiotic rifampin is important for the treatment of tuberculosis and infections caused by multidrug-resistant Staphylococcus aureus. Recent iterations of the rifampin core structure have resulted in new drugs and drug candidates for the treatment of a much broader range of infectious diseases. This expanded use of rifamycin antibiotics has the potential to select for increased resistance. One poorly characterized mechanism of resistance is through Arr enzymes that catalyze ADP-ribosylation of rifamycins. We find that genes encoding predicted Arr enzymes are widely distributed in the genomes of pathogenic and nonpathogenic bacteria. Biochemical analysis of three representative Arr enzymes from environmental and pathogenic bacterial sources shows that these have equally efficient drug resistance capacity in vitro and in vivo. The 3D structure of one of these orthologues from Mycobacterium smegmatis was determined and reveals structural homology with ADP-ribosyltransferases important in eukaryotic biology, including poly(ADP-ribose) polymerases (PARPs) and bacterial toxins, despite no significant amino acid sequence homology with these proteins. This work highlights the extent of the rifamycin resistome in microbial genera with the potential to negatively impact the expanded use of this class of antibiotic.