Current advances in the clinical development of anti-tubercular agents

Tuberculosis (TB) is a communicable airborne infectious disease caused by the Mycobacterium tuberculosis (MTB) that primarily affects the lungs, and can disseminate to other parts of the body. MTB is one of the most dangerous pathogens, killing about 1.4 million people annually worldwide. Although the standard treatment of TB is comprised of four anti-TB drugs, the emergence of multidrug-resistant (MDR) and extensive drug-resistant (XDR) strains in the recent past and associated side effects have affected the tailor-made regimens. Notably, existing therapies approved by the World Health Organisation (WHO) can only treat less than 50% of drug-resistant TB. Therefore, an expeditious pace in the TB research is highly needed in search of effective, affordable, least toxic novel drugs with shorter regimens to reach the goals viz. 2020 milestones End TB strategy set by the WHO. Currently, twenty-three drug-like molecules are under investigation in different stages of clinical trials. These newer agents are expected to be effective against the resistant strains. This article summarizes the properties, merits, demerits, and the probability of their success as novel potential therapeutic agents.

A feedback regulatory model for RifQ-mediated repression of rifamycin export in Amycolatopsis mediterranei

BACKGROUND

Due to the important role of rifamycin in curing tuberculosis infection, the study on rifamycin has never been stopped. Although RifZ, which locates within the rifamycin biosynthetic cluster, has recently been characterized as a pathway-specific regulator for rifamycin biosynthesis, little is known about the regulation of rifamycin export.

RESULTS

In this work, we proved that the expression of the rifamycin efflux pump (RifP) was regulated by RifQ, a TetR-family transcriptional regulator. Deletion of rifQ had little impact on bacterial growth, but resulted in improved rifamycin production, which was consistent with the reverse transcription PCR results that RifQ negatively regulated rifP's transcription. With electrophoretic mobility shift assay and DNase I Footprinting assay, RifQ was found to directly bind to the promoter region of rifP, and a typical inverted repeat was identified within the RifQ-protected sequences. The transcription initiation site of rifP was further characterized and found to be upstream of the RifQ binding sites, well explaining the RifQ-mediated repression of rifP's transcription in vivo. Moreover, rifamycin B (the end product of rifamycin biosynthesis) remarkably decreased the DNA binding affinity of RifQ, which led to derepression of rifamycin export, reducing the intracellular concentration of rifamycin B as well as its toxicity against the host.

CONCLUSIONS

Here, we proved that the export of rifamycin B was repressed by RifQ in Amycolatopsis mediterranei, and the RifQ-mediated repression could be specifically relieved by rifamycin B, the end product of rifamycin biosynthesis, based on which a feedback model was proposed for regulation of rifamycin export. With the findings here, one could improve the antibiotic yield by simply inactivating the negative regulator of the antibiotic transporter.

Epidemiological investigation of Clostridioides difficile colonization in Chinese community infants

Clostridioides difficile is a colonizer of the human gut; asymptomatic colonization has been reported to be more common in infants and is highly variable across regions even with no symptoms of diarrhea or death. Antibiotic treatment strategies might increase the antibiotic resistance of C. difficile. We performed a one-point study involving 1098 healthy infants (0-36 months) to address the deficiency of reports on C. difficile colonization in Chinese community infants. The C. difficile colonization rate was 22.8% (250/1098), and more than half of the strains (55.2%) were toxigenic isolates. Among the 138 toxigenic isolates, 111 were of the A⁺B⁺CDT^- genotype, 26 strains were A^-B⁺CDT^-, and one strain was A⁺B⁺CDT⁺. Fifteen different PCR ribotypes were found among the 250 isolates, and PCR-ribotype HB03 appeared to be dominant type, accounting for 19.6% (49/250). High levels of resistance to antimicrobial agents were observed. Our study showed that age and hospitalization before stool collection were positively correlated with the C. difficile colonization rate, whereas the delivery term was negatively related to the colonization rate. Particular attention should be paid to the increasing resistance of C. difficile to rifamycin.

Solid state fermentation and production of rifamycin SV using Amycolatopsis mediterranei

Production of Rifamycin SV from cheaper agro-industrial by-products using mutant strain of Amycolatopsis mediterranei OVA5-E7 in solid state fermentation (SSF) was optimized. Among the agro-based substrates used, ragi bran was found suitable for maximizing the yield of Rifamycin SV (1310 mg 100 g(-1) ds). The yield can be further enhanced to 19·7 g Kg(-1) of dry substrate by supplementing the substrate with deoiled cotton cake (10% w/w) using optimized fermentation parameters such as maintaining 80% moisture, pH 7·0, 30°C incubation temperature, inoculum 25% v/w and carrying the solid state fermenting for 9 days. Manipulating these seven specifications, the end product yield achieved in our experimentation was 20 g of Rifamycin SV Kg(-1) ds. Eventually, an overall 5-fold improvement in Rifamycin SV production was achieved.

SIGNIFICANCE AND IMPACT OF THE STUDY

Antibiotics such as rifamycin are broad-spectrum antimicrobial drugs used in large-scale worldwide as human medicine towards controlling diseases. Amycolatopsis mediterranei strain which produces this antibiotic was earlier used in submerged fermentation yielded lower amounts of rifamycin. By employing cheaper agro-industrial by-products, we produced upto 20 g rifamycin SV per Kg dry substrate used under optimized solid state fermentation conditions. Keeping in view, the role of rifamycin in meeting the medical demands of world's increasing population; we successfully used an improved strain on cheaper substrates with optimized fermentation parameters and achieved a 5-fold improvement in rifamycin SV production.

Antibacterial activity of rifamycins for M. smegmatis with comparison of oxidation and binding to tear lipocalin

A mutant of Mycobacterium smegmatis is a potential class I model substitute for Mycobacterium tuberculosis. Because not all of the rifamycins have been tested in this organism, we determined bactericidal profiles for the 6 major rifamycin derivatives. The profiles closely mirrored those established for M. tuberculosis. Rifalazil was confirmed to be the most potent rifamycin. Because the tuberculous granuloma presents a harshly oxidizing environment we explored the effects of oxidation on rifamycins. Mass spectrometry confirmed that three of the six major rifamycins showed autoxidation in the presence of trace metals. Oxidation could be monitored by distinctive changes including isosbestic points in the ultraviolet-visible spectrum. Oxidation of rifamycins abrogated anti-mycobacterial activity in M. smegmatis. Protection from autoxidation was conferred by binding susceptible rifamycins to tear lipocalin, a promiscuous lipophilic protein. Rifalazil was not susceptible to autoxidation but was insoluble in aqueous solution. Solubility was enhanced when complexed to tear lipocalin and was accompanied by a spectral red shift. The positive solvatochromism was consistent with robust molecular interaction and binding. Other rifamycins also formed a complex with lipocalin, albeit to a lesser extent. Protection from oxidation and enhancement of solubility with protein binding may have implications for delivery of select rifamycin derivatives.

Comparison of the effects of topical fusidic acid and rifamycin on wound healing in rats

Wound healing is an active and dynamic process that begins from the moment of injury. Any delay in the initiation of the response to injury can prolong the healing process. The aim of this study was to investigate the effects of topically applied fusidic acid and rifamycin on wound healing in a full-thickness wound model. Ten female Sprague-Dawley rats, aged 4 months and weighing 200-250 g, were used. Four rifamycin (R), four fusidic acid (F) and four control (K) areas were generated on their backs by using a 5-mm punch biopsy pen. On the 4th, 7th, 14th and 21st days, biopsies were taken from each wound area of all the rats. Fusidic acid group demonstrated a statistically significant increase of collagen and intensity of fibroblast proliferation on the 21st day of wound healing, whereas in the rifamycin group, healing time was, as expected, similar to physiological wound-healing phases. Despite the limited number of subjects, topical fusidic acid was found to delay wound healing by prolonging fibroblast proliferation.

Prediction of Transcription Factors and Their Involvement in Regulating Rifamycin Production in Amycolatopsis mediterranei S699

Amycolatopsis mediterranei S699 produces rifamycin B and successors of this strain are in use for the industrial production of rifamycin B. Semisynthetic derivatives of rifamycin B are used against Mycobacterium tuberculosis that causes tuberculosis. Although the rifamycin biosynthetic gene cluster was characterized two decades ago, the regulation of rifamycin B biosynthesis in Amycolatopsis mediterranei S699 is poorly understood. In this study, we analysed the genome and proteome of Amycolatopsis mediterranei S699 and identified 1102 transcription factors which comprise about 10% of the total genome. Using interactomics approaches we delineated 30 unique transcription factors directly involved in secondary metabolism that regulate rifamycin B biosynthesis. We also predict the role of RifN as hub in controlling the regulation of other genes involved in rifamycin biosynthesis. RifN is important for maintaining the integrity of the rifamycin-network. Thus, these transcription factor can be exploited to improve rifamycin B production in Amycolatopsis mediterranei S699.

Current strategies to treat tuberculosis

Tuberculosis (TB) has been a leading cause of death for more than a century. While effective therapies exist, treatment is long and cumbersome. TB control is complicated by the overlapping problems created by global inadequacy of public health infrastructures, the interaction of the TB and human immunodeficiency virus (HIV) epidemics, and the emergence of drug-resistant TB. After a long period of neglect, there is now significant progress in the development of novel treatment regimens for TB. Focusing on treatment for active disease, we review pathways to TB regimen development and the new and repurposed anti-TB agents in clinical development.

Degradation of rifamycin from mycelial dreg by activated persulfate: Degradation efficiency and reaction kinetics

Rifamycin mycelial dreg (RMD) is a biological waste, and its residual rifamycin (RIF) is potentially harmful to both the environment and human health. In this work, thermally activated persulfate (PDS) oxidative degradation of RIF in RMD was developed for the first time. The effects of reaction temperature, initial PDS concentration, and pH on RIF degradation in RMD were investigated, and the treatment conditions were optimized using response surface methodology (RSM). The results showed that 90 °C, 50 mg/g PDS, and pH = 5.3 were the optimal pretreatment conditions, and 100% degradation efficiency of RIF (734 mg/kg) was achieved. SEM and FTIR analyses confirmed that the RIF was destroyed and decomposed after the oxidation reaction. The possible degradation pathways of RIF in the thermally activated PDS system were discussed through HPLC/MS and ESR analyses. The intermediate product was identified, and the toxicity of the final product was predicted to be low or nontoxic. In this work, a degradation pathway of RMD was proposed by activating persulfate, which facilitates subsequent resource utilization and provides meaningful guidance for the practical treatment of antibiotic mycelium residue (AMR).

Redesign of Rifamycin Antibiotics to Overcome ADP-Ribosylation-Mediated Resistance

Rifamycin antibiotics are a valuable class of antimicrobials for treating infections by mycobacteria and other persistent bacteria owing to their potent bactericidal activity against replicating and non-replicating pathogens. However, the clinical utility of rifamycins against Mycobacterium abscessus is seriously compromised by a novel resistance mechanism, namely, rifamycin inactivation by ADP-ribosylation. Using a structure-based approach, we rationally redesign rifamycins through strategic modification of the ansa-chain to block ADP-ribosylation while preserving on-target activity. Validated by a combination of biochemical, structural, and microbiological studies, the most potent analogs overcome ADP-ribosylation, restored their intrinsic low nanomolar activity and demonstrated significant in vivo antibacterial efficacy. Further optimization by tuning drug disposition properties afforded a preclinical candidate with remarkable potency and an outstanding pharmacokinetic profile.

Which method is the most effective for preventing postoperative infection in spinal surgery?

BACKGROUND

Several methods have been used to reduce the infection rate in spinal surgeries with instrumentation.

PURPOSE

Which method is the most effective for preventing postoperative infection?

STUDY DESIGN

Basic science, animal model.

OBJECTIVE

In the present study, the efficiency of antibiotic prophylaxis, silver-plated screws, and local rifamycin application to the surgical site was investigated in an experimental animal model. Staphylococcus aureus was used as the pathogen.

METHODS

Fifty 6-month-old female Wistar albino rats were used. The animals were randomly numbered and divided into five groups of ten rats each (Group 1, control group; Group 2, titanium screw and S. aureus inoculation; Group 3, titanium screw, 0.1 ml rifamycin application to the surgical area, and bacterial inoculation; Group 4, titanium screw, single preoperative dose of IM cefazolin, and bacterial inoculation; Group 5, silver-plated screw and bacterial inoculation). Titanium micro-screws were placed into the pedicles. The control group received a sterile isotonic solution, and the other four groups received bacterial suspensions containing S. aureus. The animals were killed 15 days later.

RESULTS

Intensive S. aureus growth was observed in all tissue and screw samples from Group 2. The results for Group 3 were similar to those for Group 1, no growth was observed in the screw cultures. Intensive growth was observed in the five screw samples in Group 4 and in the eight samples in Group 5.

CONCLUSION

Our study suggests that rifamycin application to the surgical area in spinal operations with instrumentation is an effective method to prevent S. aureus infections.

Using phenotype microarrays in the assessment of the antibiotic susceptibility profile of bacteria isolated from wastewater in on-site treatment facilities

The scope of the study was to apply Phenotype Biolog MicroArray (PM) technology to test the antibiotic sensitivity of the bacterial strains isolated from on-site wastewater treatment facilities. In the first step of the study, the percentage values of resistant bacteria from total heterotrophic bacteria growing on solid media supplemented with various antibiotics were determined. In the untreated wastewater, the average shares of kanamycin-, streptomycin-, and tetracycline-resistant bacteria were 53, 56, and 42%, respectively. Meanwhile, the shares of kanamycin-, streptomycin-, and tetracycline-resistant bacteria in the treated wastewater were 39, 33, and 29%, respectively. To evaluate the antibiotic susceptibility of the bacteria present in the wastewater, using the phenotype microarrays (PMs), the most common isolates from the treated wastewater were chosen: Serratia marcescens ss marcescens, Pseudomonas fluorescens, Stenotrophomonas maltophilia, Stenotrophomonas rhizophila, Microbacterium flavescens, Alcaligenes faecalis ss faecalis, Flavobacterium hydatis, Variovorax paradoxus, Acinetobacter johnsonii, and Aeromonas bestiarum. The strains were classified as multi-antibiotic-resistant bacteria. Most of them were resistant to more than 30 antibiotics from various chemical classes. Phenotype microarrays could be successfully used as an additional tool for evaluation of the multi-antibiotic resistance of environmental bacteria and in preliminary determination of the range of inhibition concentration.

Gutierrez L, Reyes AG, Absalón AE, Kelly S. Improving rifamycin production in Amycolatopsis mediterranei by expressing a Vitreoscilla hemoglobin (vhb) gene fused to a cytochrome P450 monooxygenase domain

Expression of the vhb gene encoding hemoglobin from Vitreoscilla stercoraria in several organisms, clearly enhances oxygen-dependent product formation. In a previous work, we expressed the vhb gene that encodes hemoglobin from V. stercoraria in Amycolatopsis mediterranei, resulting in an increase (oxygen-dependent formation) in rifamycin B production. In the present work, we first confirm; by heterologous expression in Escherichia coli, that rif-orf5 from the rifamycin biosynthetic gene cluster, really encodes a cytochrome P450 enzyme, which is the key step for oxygen incorporation in the final biosynthetic product. Likewise, we fused rif-orf5 to the vhb gene, as part of a genetic engineering strategy. The fused genes were used to generate an Amycolatopsis mediterranei transformant (Msb-HbCYP5). Interestingly, the fermentation of Msb-HbCYP5 manifested 1.5-fold higher rifamicin B production than the transformant with only the hemoglobin gene, and 2.2-fold higher than the parental strain.

Synthesis and evaluation of dual-action kanglemycin-fluoroquinolone hybrid antibiotics

Bacterial resistance threatens the utility of currently available antibiotics. Rifampicin, a cornerstone in the treatment of persistent Gram-positive infections, is prone to the development of resistance resulting from single point mutations in the antibiotic's target, RNA polymerase. One strategy to circumvent resistance is the use of 'hybrid' antibiotics consisting of two covalently linked antibiotic entities. These compounds generally have two distinct cellular targets, reducing the probability of resistance development and potentially providing simplified pharmacological properties compared to combination therapies using the individual antibiotics. Here we evaluate a series of semi-synthetic hybrid antibiotics formed by linking kanglemycin A (Kang A), a rifampicin analog, and a collection of fluoroquinolones. Kang A is a natural product antibiotic which contains a novel dimethyl succinic acid moiety that offers a new attachment point for the synthesis of hybrid antibiotics. We compare the activity of the Kang A hybrids generated via the acid attachment point to a series of hybrids linked at the compound's naphthoquinone ring system. Several hybrids exhibit activity against bacteria resistant to Kang A via the action of the partnered antibiotic, suggesting that the Kang scaffold may provide new avenues for generating antibiotics effective against drug-resistant infections.

Site-specific aptamer inhibitors of Thermus RNA polymerase

Bacterial RNA polymerase (RNAP) is an RNA-synthesizing molecular machine and a target for antibiotics. In transcription, RNAP can interact with DNA sequence-specifically, during promoter recognition by the σ-containing holoenzyme, or nonspecifically, during productive RNA elongation by the core RNAP. We describe high-affinity single-stranded DNA aptamers that are specifically recognized by the core RNAP from Thermus aquaticus. The aptamers interact with distinct epitopes inside the RNAP main channel, including the rifamycin pocket, and sense the binding of other RNAP ligands such as rifamycin and the σ^A subunit. The aptamers inhibit RNAP activity and can thus be used for functional studies of transcription and development of novel RNAP inhibitors.

Evaluation of the efficacy of topical rifamycin application on postoperative complications after lower impacted wisdom teeth surgery

PURPOSE

This study aimed to evaluate the efficacy of a single-dose topical rifamycin application on postoperative complications after impacted lower third molar surgery.

MATERIALS AND METHODS

This prospective, controlled clinical study consisted of individuals with bilaterally impacted lower third molars that would be extracted for orthodontic reasons. The extraction sockets were irrigated with 3 ml/250 mg of rifamycin solution in Group 1, while in Group 2 (control group) the extraction sockets were irrigated with 20 ml of physiological saline. Pain intensity was measured daily for 7 days by using visual analog scale. Trismus and edema were evaluated preoperatively and on the postoperative days 2 and 7 by calculating the proportional changes in maximum mouth opening and mean distance between reference points of the face, respectively. Paired samples t-test, Wilcoxon signed rank test and Chi-square test were used to analyze the study variables.

RESULTS

35 patients (19 female, 16 male) were included in the study. The mean age of all participants was 22.19±4.98. Alveolitis was observed in 8 patients, (6 in the control group, 2 in the rifamycin group). There was no statistically significant difference between groups in terms of trismus and swelling measurements on the 2nd and 7th postoperative days (p>0.05). VAS scores were significantly low in rifamycin group on postoperative days 1 and 4 (p<0.05).

CONCLUSION

Within the limits of the present study, topical rifamycin application reduced the incidence of alveolitis, prevented infection, and provided analgesic effect after surgical removal of impacted third molars.

[Conservative treatment of exacerbation of chronic purulent otitis media]

THE PURPOSE OF THE WORK

Is to study the efficacy of treatment of exacerbation of chronic tubotympanic purulent otitis media with Otofa drug with the active substance Rifamycin.

MATERIAL AND METHODS

Performed a retrospective analysis of 37 medical histories of patients who applied to the otorhinolaryngology clinic with a diagnosis of exacerbation of chronic purulent tubotympanic otitis media in the period from January 2019 to December 2019.

RESULTS

Noted relief of symptoms such as throbbing noise and pain in patients receiving the topical Otofa drug (active ingredient Rifamycin) by the 3th day of therapy. Otofa also reduced otorrhea by the 5th day of therapy.

CONCLUSION

The study showed the high clinical efficacy of Otofa ear drops containing the Rifamycin antibiotic.

In vitro activity of rifampicin, rifapentine and rifabutin in combination with their 25-deacetyl-metabolites against various Mycobacterium tuberculosis lineages

OBJECTIVES

Rifamycin agents (rifampicin (RIF), rifapentine (RFP), rifabutin (RFB)) are the cornerstone of tuberculosis (TB) therapy. Rifamycins are metabolized into 25-deacetyl-metabolites, which have been described has active and may contribute to in vivo drug effect. However, little is known about the combined effect of rifamycins and their metabolites across different Mycobacterium tuberculosis complex (MTBC) lineages.

METHODS

This study included 14 MTBC strains representing the main lineages. Minimum inhibitory concentrations (MICs) were determined using microdilution assays for the three rifamycins and their metabolites. A checkerboard assay was used to assess drug interactions, with the fractional inhibitory concentration (FIC) index calculated for synergy or antagonism.

RESULTS

MICs varied across rifamycins, RIF and its metabolite showed the highest MICs, followed by RFP and RFB and their respective metabolites. FIC indices for rifamycin-metabolite combinations indicated additive effects (FIC between 0.5 and 1.25), with no antagonism observed, even at clinically relevant metabolite-to-parent drug ratios, and without impact of MTBC lineage.

CONCLUSIONS

Rifamycin metabolites exhibit additive effects with parent drugs, potentially enhancing bactericidal activity. This highlights that rifamycin susceptibility testing should account for both parent drugs and their metabolites, as these metabolites also exhibit antimicrobial activity. Additionally, these findings support further pharmacokinetic/pharmacodynamic studies to optimize TB treatment regimens, particularly in relation to metabolite-to-parent drug ratios in patients.

Possible Ototoxic Effects of Topical Rifamycin Application: An Electrophysiological and Ultrastructural Study

Objective

This study aimed to investigate possible ototoxicity associated with topical rifamycin application via electrophysiological tests and ultrastructural examinations.

Methods

Electrophysiological assessment was performed with tympanometry, auditory brainstem response (ABR), and distortion product otoacoustic emission (DPOAE) measurements. This study was conducted on 40 ears of 20 guinea pigs that were detected to have normal hearing thresholds. The animals were randomly assigned to three groups: Group 1 (n=12) received 0.1 mL rifamycin, Group 2 (n=8) received 0.1 ml gentamycin, and Group 3 (n=20) received 0.1 mL physiological saline. The antibiotics and saline solutions were administered via intratympanic injections. After five injections every other day, electrophysiological tests were performed again on the 15th day. After electrophysiological measurements, the temporal bones of all guinea pigs were prepared for ultrastructural examinations and the cochlear surface morphology was examined by scanning electron microscopy (SEM).

Results

The animals in group 3 did not show a statistically significant change in their DPOAE signal/noise ratio (SNR) or ABR thresholds (p>0.05). In groups 1 and 2, the reduction in the DPOAE SNR and the increase in the ABR threshold were statistically significant (p<0.05). Regarding SEM examination results, the animals in groups 1 and 2 showed statistically significant outer hair cell damage and cochlear degeneration due to the ototoxic effect of the drugs (p<0.05), whereas the animals in group 3 showed no significant damage (p>0.05).

Conclusion

The results indicate that rifamycin application to the middle ears of guinea pigs has mild ototoxic effects on their inner ears.