Resuscitation promoting factors (Rpfs) are the proteins involved in the process of reactivation of the dormant cells of mycobacteria. Recently a new class of nitrophenylthiocyanates (NPTs), capable of inhibiting the biological and enzymatic activities of Rpfs has been discovered. In the current study the inhibitory properties of the compounds containing both nitro and thiocyanate groups alongside with the compounds with the modified number and different spatial location of the substituents are compared. New benzoylphenyl thiocyanates alongside with nitrophenylthiocyanates were tested in the enzymatic assay of bacterial peptidoglycan hydrolysis as well as against strains of several actinobacteria (Mycobacterium smegmatis, Mycobacterium tuberculosis) on in-lab developed models of resuscitation of the dormant forms. Introduction of the additional nitro and thiocyanate groups to the benzophenone scaffold did not influence the inhibitory activity of the compounds. Removal of the nitro groups analogously did not impair the functional properties of the molecules. Among the tested compounds two molecules without nitro group: 3-benzoylphenyl thiocyanate and 4-benzoylphenyl thiocyanate demonstrated the maximum activity in both enzymatic assay (inhibition of the Rpf-mediated peptidoglycan hydrolysis) and in the resuscitation assay of the dormant M. tuberculosis cells. The current study demonstrates dispensability of the nitro group in the NPT’s structure for inhibition of the enzymatic and biological activities of the Rpf protein molecules. These findings provide new prospects in anti-TB drug discovery especially in finding of molecular scaffolds effective for the latent infection treatment.

Background/Objectives: The escalating crisis of antibiotic resistance and the inherent limitations of conventional antibiotics necessitate the development of innovative therapeutic strategies. Targeted drug delivery (TDD) offers a powerful approach to enhance efficacy, minimize systemic toxicity, and circumvent bacterial resistance. This systematic review aims to evaluate the potential of unique bacterial transport systems (BTSs), surface specific receptors and intracellular enzymes as platforms for TDD via the “Trojan Horse” strategy (THS). Methods: A comprehensive literature review was conducted, focusing on studies that investigated the specificity and mechanisms of BTSs responsible for the uptake of metabolites that are essential for and unique to bacteria. This includes an analysis of transport systems for siderophores, bacteria-specific sugars, cell wall components, D-amino acids, and vitamins. We assessed preclinical and clinical examples of drug conjugates utilizing these pathways, as well as emerging platforms such as bacteriophage-derived proteins, antibody–antibiotic conjugates, and bacterial extracellular vesicles (EVs). Results: BTSs demonstrate high specificity for their cognate substrates, providing effective molecular gateways for TDD of drugs photosensitizers and diagnostic probes in form of conjugates. The siderophore–cephalosporin conjugate cefiderocol represents a clinically validated example, having received FDA approval. Preclinical studies further reveal that conjugates utilizing sugars (e.g., maltose, trehalose) and vitamins (e.g., B12) can significantly enhance antibiotic uptake and activity against both Gram-positive and Gram-negative pathogens, including drug-resistant strains. Emerging platforms like bacteriophage endolysins and engineered EVs show promise for overcoming biological barriers such as bacterial outer membranes and intracellular host niches. Conclusions: The THS leveraging BTSs represents a clinically viable and promising avenue for next-generation antibacterial therapies. Advantages of BTS include overcoming bacterial resistance, such as reduced membrane permeability and efflux pumps, enabling the “revival” of antibiotics that are poorly permeable or toxic, increasing their local concentration at the target site and reducing side effects on host cells. While significant progress has been made, a striking disconnect persists between the hundreds of conjugates demonstrating potent in vitro activity and the limited agent that has achieved clinical use. This in vitro–in vivo gap reflects, in large part, the early stage of this field rather than a fundamental failure. Further research is critically needed not only to identify novel BTSs and optimize drug-linker chemistry, but also to systematically address the translational barriers—including poor pharmacokinetics, immunogenicity, and unexpected toxicity—that have prevented most promising candidates from advancing beyond preclinical evaluation.

Detection of “Non-culturable” Mycobacterium tuberculosis Cells by Culture Methods Выявление “некультивируемых” клеток Mycobacterium tuberculosis культуральными методами

The specific features of the reactivation of “non-culturable” (NC) Mycobacterium tuberculosis (MTB) cells for the following multiplication in liquid medium were defined, as well as the approach for the quantification of these cells by culture methods was suggested. When NC cells obtained in vitro were inoculated into the standard Sauton’s liquid medium, a prolonged (up to 20-day) lag phase was observed, in which no cell multiplication was occurred. During the lag phase, dormant cells secreted substances of an unknown nature that inhibited or completely arrested the reactivation and growth of cultures when the initial dormant cell concentration was above 10⁷–10⁸ cells/mL. Addition of meat-peptone broth (3.25 g/L) into a standard Sauton’s medium with a 10-fold reduced concentration of glycerol significantly stimulated the reactivation and multiplication of the initially dormant cells inoculated at a concentration above the threshold. This modification of the medium made it possible to detect up to 10³ times more cells in the MTB population by the method of the Most Probable Number (MPN) of cells. An increased number of the detected dormant cells in the population (up to an average of 2.5 orders of magnitude) was also achieved by adding RpfB recombinant protein (5 ng/mL) (a protein of the Rpf family, resuscitation promoting factor of dormant bacteria) to the reactivation medium. Perhaps, the action of the Rpf enzyme is related to the products of its enzymatic activity, since an increased MPN value in the dormant cells population was also observed when the products of mycobacteria peptidoglycan hydrolysis obtained by the coaction of RpfB and endopeptidase RipA were added. The addition of sonicated peptidoglycan fragments at a concentration up to 1 μg/mL had a similar effect. These results may be used in approaches to optimize the liquid media composition and culture conditions to identify the pathogen of tuberculosis in clinical samples in a nonculturable state.

Background/Objectives: The escalating crisis of antibiotic resistance and the inherent limitations of conventional antibiotics necessitate the development of innovative therapeutic strategies. Targeted drug delivery (TDD) offers a powerful approach to enhance efficacy, minimize systemic toxicity, and circumvent bacterial resistance. This systematic review aims to evaluate the potential of unique bacterial transport systems (BTSs) and surface specific receptors as platforms for TDD via the "Trojan Horse" strategy (THS). Methods: A comprehensive literature review was conducted, focusing on studies that investigated the specificity and mechanisms of BTSs responsible for the uptake of essential metabolites. This includes an analysis of transport systems for siderophores, bacteria-specific sugars, cell wall components, D-amino acids, and vitamins. We assessed preclinical and clinical examples of drug conjugates utilizing these pathways, as well as emerging platforms such as bacteriophage-derived proteins, antibody-antibiotic conjugates, and bacterial extracellular vesicles (EVs). Results: BTSs demonstrate high specificity for their cognate substrates, providing effective molecular gateways for drug conjugate import. The siderophore-cephalosporin conjugate cefiderocol represents a clinically validated example, having received FDA approval. Preclinical studies further reveal that conjugates utilizing sugars (e.g., maltose, trehalose) and vitamins (e.g., B12) can significantly enhance antibiotic uptake and activity against both Gram-positive and Gram-negative pathogens, including drug-resistant strains. Emerging platforms like bacteriophage endolysins and engineered EVs show promise for overcoming biological barriers such as bacterial outer membranes and intracellular host niches. Conclusions: The THS leveraging BTSs represents a clinically viable and promising avenue for next-generation antibacterial therapies. While significant progress has been made, including regulatory approval of cefiderocol, further research is critically needed to identify novel BTSs, optimize drug-linker chemistry, improve the pharmacokinetics and biosafety of conjugates, and translate these innovative platforms into effective treatments for drug-resistant infections.