Synthesis and biological evaluation of new naphthalimide-thiourea derivatives as potent antimicrobial agents active against multidrug-resistant Staphylococcus aureus and Mycobacterium tuberculosis.

The emergence of antibiotic resistance to S. aureus and M. tuberculosis, particularly MRSA, VRSA, and drug-resistant tuberculosis, poses a serious threat to human health. Towards discovering new antibacterial agents, we designed and synthesized a series of new naphthalimide-thiourea derivatives and evaluated them against a panel of bacterial strains consisting of E. coli, S. aureus, K. pneumoniae, P. aeruginosa, A. baumannii and various mycobacterial pathogens. Compounds 4a, 4l, 4m, 4n, 4q, 9f, 9l, 13a, 13d, 13e, 17a, 17b, 17c, 17d, and 17e demonstrated potent antibacterial activity against S. aureus with MIC 0.03-8 µg mL-1. In addition, these compounds have also exhibited potent inhibition against MDR strains of S. aureus, including VRSA with MICs 0.06-4 µg mL-1. Compounds 4h, 4j, 4l, 4m, 4q, 4r, 9a, 9b, 9c, 9d, 9e, 9g, 9h, 9j, 13f and 17e also exhibited good antimycobacterial activity against M. tuberculosis with MIC 2-64 µg mL-1. The cytotoxicity assay using Vero cells revealed that all the compounds were non-toxic and exhibited a favorable selectivity index (SI >40). Time kill kinetics data indicated that compounds exhibited concentration-dependent killing. Furthermore, in silico studies were performed to decipher the possible mechanism of action. Comprehensively, these results highlight the potential of naphthalimide-thiourea derivatives as promising antibacterial agents.

Polycationic phosphorous dendrimer potentiates multiple antibiotics against drug-resistant mycobacterial pathogens.

Mycobacterium tuberculosis (Mtb), causative agent of tuberculosis (TB) and non-tubercular mycobacterial (NTM) pathogens such as Mycobacterium abscessus are one of the most critical concerns worldwide due to increased drug-resistance resulting in increased morbidity and mortality. Therefore, focusing on developing novel therapeutics to minimize the treatment period and reducing the burden of drug-resistant Mtb and NTM infections are an urgent and pressing need. In our previous study, we identified anti-mycobacterial activity of orally bioavailable, non-cytotoxic, polycationic phosphorus dendrimer 2G0 against Mtb. In this study, we report ability of 2G0 to potentiate activity of multiple classes of antibiotics against drug-resistant mycobacterial strains. The observed synergy was confirmed using time-kill kinetics and revealed significantly potent activity of the combinations as compared to individual drugs alone. More importantly, no re-growth was observed in any tested combination. The identified combinations were further confirmed in intra-cellular killing assay as well as murine model of NTM infection, where 2G0 potentiated the activity of all tested antibiotics significantly better than individual drugs. Taken together, this nanoparticle with intrinsic antimycobacterial properties has the potential to represents an alternate drug candidate and/or a novel delivery agent for antibiotics of choice for enhancing the treatment of drug-resistant mycobacterial pathogens.

Structural and biophysical characterization of PadR family protein Rv1176c of Mycobacterium tuberculosis H37Rv.

Rv1176c of Mycobacterium tuberculosis H37Rv belongs to the PadR-s1 subfamily of the PadR family of protein. Rv1176c forms a stable dimer in solution. Its stability is characterized by a thermal melting transition temperature (Tm) of 39.4 °C. The crystal structure of Rv1176c was determined at a resolution of 2.94 Å, with two monomers in the asymmetric unit. Each monomer has a characteristic N-terminal winged-helix-turn-helix DNA-binding domain. Rv1176c C-terminal is a coiled-coil dimerization domain formed of α-helices α5 to α7. In the Rv1176c dimer, there is domain-swapping of the C-terminal domain in comparison to other PadR homologs. In the dimer, there is a long inter-subunit tunnel in which different ligands can bind. Rv1176c was found to bind to the promoter region of its own gene with high specificity. M. smegmatis MC2 155 genome lacks homolog of Rv1176c. Therefore, it was used as a surrogate to characterize the functional role of Rv1176c. Expression of Rv1176c in M. smegmatis MC2 155 cells imparted enhanced tolerance towards oxidative stress. Rv1176c expressing M. smegmatis MC2 155 cells exhibited enhanced intracellular survival in J774A.1 murine macrophage cells. Overall, our studies demonstrate Rv1176c to be a PadR-s1 subfamily transcription factor that can moderate the effect of oxidative stress.

Pyrrole-thiazolidinone hybrids as a new structural class of broad-spectrum anti-infectives.

A series of pyrrole-thiazolidinone hybrids was designed, synthesized and evaluated for activities against ESKAP bacteria panel and mycobacterial pathogens. From the series, compound 9d showed prominent activity against S. aureus (MIC = 0.5 µg/mL) and compound 9k showed the most promising activity against M. tuberculosis H37Rv (MIC = 0.5 µg/mL). Potent derivatives were found to be non-toxic when tested against Vero cells. Compound 9d upon evaluation in vitro against several MRSA and VRSA strains produced activity comparable or better than standard drugs. In the anti-biofilm assay, 9d reduced S. aureus biofilm by >11% at 10x MIC. The dual inhibitory effect exhibited by pyrrole-thiazolidinone hybrids confirms their potential as new class of promising anti-infective agents.

Synthesis and pharmacological evaluation of 1,3-diaryl substituted pyrazole based (thio)urea derivatives as potent antimicrobial agents against multi-drug resistant Staphylococcus aureus and Mycobacterium tuberculosis.

The urgent development of newer alternatives has been deemed a panacea for tackling emerging antimicrobial resistance effectively. Herein, we report the design, synthesis, and biological evaluation of 1,3-diaryl substituted pyrazole-based urea and thiourea derivatives as antimicrobial agents. Preliminary screening results revealed that compound 7a (3,4-dichlorophenyl derivative) exhibited potent activity against S. aureus (MIC = 0.25 µg mL-1) and compound 7j (2,4-difluorophenyl derivative) against Mycobacterium tuberculosis (MIC = 1 µg mL-1). Compounds 7a and 7j were non-toxic to Vero cells with a favorable selectivity index of 40 and 200, respectively, and demonstrated good microsomal stability. Compound 7a exhibited equipotent activity (MIC = 0.25 µg mL-1) against various multidrug-resistant strains of S. aureus, which include various strains of MRSA and VRSA, and elicited bacteriostatic properties. In an enzymatic assay, 7a effectively inhibited DNA gyrase supercoiling activity at a concentration of 8 times MIC. Further, molecular modeling studies suggested that compound 7a binds at the active site of DNA gyrase with good affinity.

Mycobacterial lipid-derived immunomodulatory drug- liposome conjugate eradicates endosome-localized mycobacteria.

Tuberculosis is a challenging disease due to the intracellular residence of its pathogen, Mycobacterium tuberculosis, and modulation of the host bactericidal responses. Lipids from Mycobacterium tuberculosis regulate macrophage immune responses dependent on the infection stage and intracellular location. We show that liposomes constituted with immunostimulatory lipids from mycobacteria modulate the cellular immune response and synergize with sustained drug delivery for effective pathogen eradication. We evaluate the pH-dependent release of Rifampicin from the mycobacterial-lipid-derived liposomes intracellularly and in vitro, their cell viability, long-term stability, and antimicrobial efficacy. Intracellular drug levels were higher following liposome treatment compared with the free drug in a temporal fashion underlying a sustained release. The drug-encapsulated liposomes were taken up by clathrin-mediated endocytosis and elicited a robust pro-inflammatory immune response while localizing in the recycling and late endosomes. Notably, these were the same cellular compartments that contained the pathogen underlying localized intracellular targeting. Our results also imply a lipid-centric and species-specific selectivity of the liposomal drug formulations. This work provides a proof-of-concept for the dual-action of liposomes derived from the pathogen itself for their effective eradication, in conjunction with the attuned host immunomodulation.

Isoxazole carboxylic acid methyl ester-based urea and thiourea derivatives as promising antitubercular agents.

In our continued efforts to find potential chemotherapeutics active against drug-resistant (DR) Mycobacterium tuberculosis (Mtb), causative agent of Tuberculosis (TB) and to curb the current burdensome treatment regimen, herein we describe the synthesis and biological evaluation of urea and thiourea variants of 5-phenyl-3-isoxazolecarboxylic acid methyl esters as promising anti-TB agent. Majority of the tested compounds displayed potent in vitro activity not only against drug-susceptible (DS) Mtb H37Rv but also against drug-resistant (DR) Mtb. Cell viability test against Vero cells deemed these compounds devoid of significant toxicity. 3,4-Dichlorophenyl derivative (MIC 0.25 µg/mL) and 4-chlorophenyl congener (MIC 1 µg/mL) among urea and thiourea libraries respectively exhibited optimum potency. Lead optimization resulted in the identification of 1,4-linked analogue of 3,4-dichlorophenyl urea derivative demonstrating improved selectivity. Further, in silico study complemented with previously proposed prodrug like attributes of isoxazole esters. Taken together, this molecular hybridization approach presents a new chemotype having potential to be translated into an alternate anti-Mtb agent.

In Vitro and In Vivo Activity of Gepotidacin against Drug-Resistant Mycobacterial Infections.

Mycobacterial pathogens, including nontuberculous mycobacteria (NTM) and Mycobacterium tuberculosis, are pathogens of significant worldwide interest owing to their inherent drug resistance to a wide variety of FDA-approved drugs as well as causing a broad range of serious infections. Identifying new antibiotics active against mycobacterial pathogens is an urgent unmet need, especially those antibiotics that can bypass existing resistance mechanisms. In this study, we demonstrate that gepotidacin, a first-in-class triazaacenapthylene topoisomerase inhibitor, demonstrates potent activity against M. tuberculosis and M. fortuitum, as well as against other clinically relevant NTM species, including fluoroquinolone-resistant M. abscessus. Furthermore, gepotidacin exhibits concentration-dependent bactericidal activity against various mycobacterial pathogens, synergizes with several drugs utilized for their treatment, and reduces bacterial load in macrophages in intracellular killing assays comparably to amikacin. Additionally, M. fortuitum ATCC 6841 was unable to generate resistance to gepotidacin in vitro. When tested in a murine neutropenic M. fortuitum infection model, gepotidacin caused a significant reduction in bacterial load in various organs at a 10-fold lower concentration than amikacin. Taken together, these findings show that gepotidacin possesses a potentially new mechanism of action that enables it to escape existing resistance mechanisms. Thus, it can be projected as a potent novel lead for the treatment of mycobacterial infections, particularly for NTM, where present therapeutic interventions are extremely limited.

Mechanistic insight into the role of mevalonate kinase by a natural fatty acid-mediated killing of Leishmania donovani.

We evaluated the anti-leishmanial efficacy of different saturated medium-chain fatty acids (FAs, C8-C18) where FA containing C8 chain, caprylic acid (CA), was found to be most potent against Leishmania donovani, the causative agent for visceral leishmaniasis (VL). Different analogs of CA with C8 linear chain, but not higher, along with a carboxyl/ester group showed a similar anti-leishmanial effect. Ergosterol depletion was the major cause of CA-mediated cell death. Molecular docking and molecular dynamic simulation studies indicated the enzyme mevalonate kinase (MevK) of the ergosterol biosynthesis pathway as a possible target of CA. Enzyme assays with purified recombinant MevK and CA/CA analogs confirmed the target with a competitive inhibition pattern. Using biochemical and biophysical studies; strong binding interaction between MevK and CA/CA analogs was established. Further, using parasites with overexpressed MevK and proteomics studies of CA-treated parasites the direct role of MevK as the target was validated. We established the mechanism of the antileishmanial effect of CA, a natural product, against VL where toxicity and drug resistance with current chemotherapeutics demand an alternative. This is the first report on the identification of an enzymatic target with kinetic parameters and mechanistic insights against any organism for a natural medium-chain FA.

Novel approaches for the treatment of infections due to multidrug-resistant bacterial pathogens.

Antimicrobial resistance (AMR), which is a major challenge for global healthcare, emerging because of several reasons including overpopulation, increased global migration and selection pressure due to enhanced use of antibiotics. Antibiotics are the widely used therapeutic options to combat infectious diseases; however, unfortunately, inadequate and irregular antibiotic courses are also major contributing factors in the emergence of AMR. Additionally, persistent failure to develop and commercialize new antibiotics has created the scarcity of effective anti-infective drugs. Thus, there is an urgent need for a new class of antimicrobials and other novel approaches to curb the menace of AMR. Besides the conventional approaches, some novel approaches such as the use of antimicrobial peptides, bacteriophages, immunomodulation, host-directed therapy and antibodies have shown really promising potentials.

Bioevaluation of quinoline-4-carbonyl derivatives of piperazinyl-benzothiazinones as promising antimycobacterial agents.

The quinoline moiety remains a privileged antitubercular (anti-TB) pharmacophore, whereas 8-nitrobenzothiazinones are emerging potent antimycobacterial agents with two investigational candidates in the clinical pipeline. Herein, we report the synthesis and bioevaluation of 30 piperazinyl-benzothiazinone-based quinoline hybrids as prospective anti-TB agents. Preliminary evaluation revealed 24/30 compounds exhibiting substantial activity (minimum inhibitory concentration [MIC] = 0.06-1 µg/ml) against Mycobacterium tuberculosis (Mtb) H37Rv. Cytotoxicity analysis against Vero cells found these to be devoid of any significant toxicity, with the majority displaying a selectivity index of >80. Furthermore, potent nontoxic compounds, when screened against clinical isolates of drug-resistant Mtb strains, demonstrated equipotent inhibition with MIC values of 0.03-0.25 µg/ml. A time-kill study identified a lead compound exhibiting concentration-dependent bactericidal activity, with 10× MIC completely eliminating Mtb bacilli within 7 days. Along with acceptable aqueous solubility and microsomal stability, the optimum active compounds of the series manifested all desirable traits of a promising antimycobacterial candidate.

Contezolid in complicated skin and soft tissue infection.

Contezolid (MRX-I, Youxitai) is an oral oxazolidinone drug being developed by MicuRx Pharmaceutical Co., Ltd., Shanghai, China. It was approved by China's National Medical Products Administration (NMPA) in June 2021, attaining its first approval for the treatment of complicated skin and soft tissue infections (cSSTIs). It is also under clinical development for acute bacterial skin and skin structure infections (ABSSSIs) in the U.S. after receiving qualified infectious disease product (QIDP) classification and fast track status by U.S. Food and Drug Administration (FDA) in September 2018. Contezolid is effective against a broad range of Gram-positive bacteria including activity against methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae and vancomycin-resistant Enterococci (VRE). It provides a major benefit over the most popular drug of its class, linezolid (Zyvox), by offering an improved safety profile and minimal effects concerning myelosuppression and monoamine oxidase (MAO) inhibition, two independent adverse events limiting linezolid use in the clinic. The recommended dosage regimen of contezolid is 800 mg every 12 hours for 7-14 days with regular food intake and it can be extended if required. At the mentioned dose under fed conditions, satisfactory efficacy against MRSA with a 90%; or higher cumulative fraction of response and probability of target attainment was achieved. Additionally, contezolid also exhibits activity against Mycobacterium tuberculosis and Mycobacterium abscessus.

Synthesis and evaluation of triazole congeners of nitro-benzothiazinones potentially active against drug resistant Mycobacterium tuberculosis demonstrating bactericidal efficacy.

With growing concerns regarding target residue mutation hovering over established anti-TB pharmacophores, it is imperative to have reserve chemotypes at our disposal to curb unrestrained spread of tuberculosis. In this context, we herein present the synthesis and bio-evaluation of a library of new nitrobenzothiazinone (BTZ) congeners comprising 2-mercapto/amino-benzothiazinone tethered 1,2,3-triazole hybrids as antitubercular agents. In preliminary screening, 10 out of 37 compounds displayed substantial in vitro potency against Mtb H37Rv (MIC 0.5-8 µg mL-1). Structural optimization of the initial hit 5o (MIC 0.5 µg mL-1) led to identification of linker variants 9a, 9b, 9c, and 9d exhibiting potent anti-TB activity (MIC 0.03-0.12 µg mL-1). When tested against Vero cells to determine their selectivity index (SI), these compounds displayed no appreciable cytotoxicity (SI >80). Further studies on activity against drug resistant (DR) Mtb indicated these compounds to be equally potent (MIC 0.03-0.25 µg mL-1). The in silico covalent docking study suggested a similar polar interaction to that of PBTZ169 with an additional and contrasting side chain interaction at the active site of Mtb DprE1 target protein. Further, the time kill kinetic study found compounds 9a and 9d to be demonstrating bactericidal efficacy, completely eliminating bacilli in 7 days at 10× MIC. The most promising compound 9d, considering its potent anti-TB activity (MIC 0.06 µg mL-1 against drug susceptible Mtb and MIC 0.06-0.25 µg mL-1 against DR Mtb) along with a broad therapeutic index (SI >640) demonstrating a comparable concentration dependent bactericidal efficacy to that of RIF, holds a significant edge to be translated into a potent anti-Mtb agent.

Exploration of Isoxazole-Carboxylic Acid Methyl Ester Based 2-Substituted Quinoline Derivatives as Promising Antitubercular Agents.

In pursuit of potent anti-TB agents active against drug resistant tuberculosis (DR-TB), herein we report synthesis and bio-evaluation of a new series of isoxazole-carboxylic acid methyl ester based 2-substituted quinoline derivatives. Preliminary evaluation indicated selectivity towards Mtb H37Rv, with no inhibition of non-tubercular mycobacterial (NTM) & bacterial pathogen panel. Out of 36 synthesized compounds, majority exhibited substantial inhibition of Mtb H37Rv (MIC 0.5-8 µg/mL). Cell viability test against Vero cells revealed no significant cytotoxicity. Further, screening against drug resistant strains (DR-Mtb) found hit compound displaying promising potency (MIC 1-4 µg/mL). Structure optimization of the hit led to the identification of lead compound demonstrating potent inhibition of both drug-susceptible Mtb (MIC 0.12 µg/mL) and drug-resistant Mtb (MIC 0.25-0.5 µg/mL) along with a high selectivity index (SI) >80. Taken together, with appreciable selectivity and potent activity, these chemotypes show prospect to be turned into a potential anti-TB candidate.

Identification of nitrofuranylchalcone tethered benzoxazole-2-amines as potent inhibitors of drug resistant Mycobacterium tuberculosis demonstrating bactericidal efficacy.

Ever increasing drug resistance has become an impeding threat that continues to hamper effective tackling of otherwise treatable tuberculosis (TB). Such dismal situation necessitates identification and exploration of multitarget acting newer chemotypes with bactericidal efficacy as a priority, that could efficiently hinder uncontrolled spread of TB. In this context, herein we present design, synthesis and bio-evaluation of chalcone tethered bezoxazole-2-amines as promising anti-TB chemotypes. Preliminary screening of 24 compounds revealed initial hits 3,4,5-trimethoxyphenyl and 5-nitrofuran-2-yl derivative exhibiting selective inhibition of Mycobacterium tuberculosis (Mtb) H37Rv. Further, structural optimization of hit compounds generated 12 analogues, amongst which 5-nitrofuran-2-yl derivatives displayed potent inhibition of not only drug-susceptible (DS) Mtb but also clinical isolates of drug-resistant (DR) Mtb strains equipotently. Moreover, cell viability test against Vero cells found these compounds with favourable selectivity. Time kill analysis led to the identification of the lead compound (E)-1-(4-((5-chlorobenzo[d]oxazol-2-yl)amino)phenyl)-3-(5-nitrofuran-2-yl)prop-2-en-1-one, that demonstrated bactericidal killing of Mtb bacilli. Together with acceptable microsomal stability, the lead compound of the series manifested all desirable traits of a promising antitubercular agent.

Mycobactin Analogues with Excellent Pharmacokinetic Profile Demonstrate Potent Antitubercular Specific Activity and Exceptional Efflux Pump Inhibition.

In this study, we have designed and synthesized pyrazoline analogues that partially mimic the structure of mycobactin, to address the requirement of novel therapeutics to tackle the emerging global challenge of antimicrobial resistance (AMR). Our investigation resulted in the identification of novel lead compounds 44 and 49 as potential mycobactin biosynthesis inhibitors against mycobacteria. Moreover, candidates efficiently eradicated intracellularly surviving mycobacteria. Thermofluorimetric analysis and molecular dynamics simulations suggested that compounds 44 and 49 bind to salicyl-AMP ligase (MbtA), a key enzyme in the mycobactin biosynthetic pathway. To the best of our knowledge, these are the first rationally designed mycobactin inhibitors to demonstrate an excellent in vivo pharmacokinetic profile. In addition, these compounds also exhibited more potent whole-cell efflux pump inhibition than known efflux pump inhibitors verapamil and chlorpromazine. Results from this study pave the way for the development of 3-(2-hydroxyphenyl)-5-(aryl)-pyrazolines as a new weapon against superbug-associated AMR challenges.

Co-drug of isoniazid and sulfur containing antioxidant for attenuation of hepatotoxicity and treatment of tuberculosis.

The prolonged use of isoniazid (INH) - a highly effective drug in the treatment of tuberculosis - causes fatal liver injury. In order to overcome this adverse effect, a unique amide codrug was designed by covalently linking INH with sulfur-containing antioxidant- alpha-lipoic acid for possible hepatoprotective and antimycobacterial effect. Co-drug LI was prepared by Schotten Baumann reaction and was characterized by spectroscopic analysis. To check the bioreversibility of LI, in vitro release tests were conducted in buffers of specific pH, stomach, and intestinal homogenates of rat employing HPLC. Male Wistar rats were used for the evaluation of the hepatoprotective activity. Liver function markers, oxidative stress markers, and biochemical parameters were estimated. The antimycobacterial efficacy of LI was examined in terms of its ability to decrease the lung bacillary load in Balb/c mice infected intravenously with Mycobacterium tuberculosis. LI resisted hydrolysis in buffers of pH 1.2 (acidic), pH 7.4 (basic), and stomach homogenate of the rat while displayed significant hydrolysis (88.19%) in intestinal homogenates over a period of 6 h. The effect of LI on liver function, antioxidant and biochemical paradigms was remarkable as it reestablished the enzyme levels and restored hepatic cytoarchitecture representing its abrogating effect. The findings of antimycobacterial activity assessment evidently demonstrated that LI was as potent as INH in lowering the mycobacterial load in mice. The outcome of this exploration confirmed that the described co-drug can offer desirable safety and therapeutic benefit in the management of tuberculosis.

EphH, a unique epoxide hydrolase encoded by Rv3338 is involved in the survival of Mycobacterium tuberculosis under in vitro stress and vacuolar pH-induced changes.

Introduction: Mycobacterium tuberculosis (Mtb), one of the deadliest human pathogen, has evolved with different strategies of survival inside the host, leading to a chronic state of infection. Phagosomally residing Mtb encounters a variety of stresses, including increasing acidic pH. To better understand the host-pathogen interaction, it is imperative to identify the role of various genes involved in the survivability of Mtb during acidic pH environment. Methods: Bio-informatic and enzymatic analysis were used to identify Mtb gene, Rv3338, as epoxide hydrolase. Subsequently, CRISPRi knockdown strategy was used to decipher its role for Mtb survival during acidic stress, nutrient starvation and inside macrophages. Confocal microscopy was used to analyse its role in subverting phagosomal acidification within macrophage. Results: The present work describes the characterization of Rv3338 which was previously known to be associated with the aprABC locus induced while encountering acidic stress within the macrophage. Bio-informatic analysis demonstrated its similarity to epoxide hydrolase, which was confirmed by enzymatic assays, thus, renamed EphH. Subsequently, we have deciphered its indispensable role for Mtb in protection from acidic stress by using the CRISPRi knockdown strategy. Our data demonstrated the pH dependent role of EphH for the survival of Mtb during nutrient starvation and in conferring resistance against elevated endogenous ROS levels during stress environment. Conclusion: To the best of our knowledge, this is the first report of an EH of Mtb as a crucial protein for bacterial fitness inside the host, a phenomenon central to its pathogenesis.

Synthesis and structure-activity relationship of new chalcone linked 5-phenyl-3-isoxazolecarboxylic acid methyl esters potentially active against drug resistant Mycobacterium tuberculosis.

In search of novel therapeutic agents active against emerging drug-resistant Mycobacterium tuberculosis and to counter the long treatment protocol of existing drugs, herein we present synthesis and biological evaluation of a new series of 5-phenyl-3-isoxazolecarboxylic acid methyl ester-chalcone hybrids. Among 35 synthesized compounds, 32 analogues displayed potent in-vitro activity against Mycobacterium tuberculosis H37Rv with MIC 0.12-16 µg/mL. Cell viability test against Vero cells indicated 29 compounds to be non-cytotoxic (CC50 > 20 µg/mL & SI > 10). Most potent compounds with MIC 0.12 µg/mL (7 b, 7j, 7 ab) exhibited selectivity index (SI) in excess of 320. Further studies on activity against drug-resistant Mycobacterium tuberculosis revealed 7j as the most potent compound with MIC 0.03-0.5 µg/mL. Time-kill kinetic study suggested compound 7j displaying concentration-dependent bactericidal killing activity with relatively comparable potency to that of current first-line anti-TB drugs. Taken together, 7j presents a novel hit with potential to be translated into a potent antimycobacterial.

Safe Polycationic Dendrimers as Potent Oral In Vivo Inhibitors of Mycobacterium tuberculosis: A New Therapy to Take Down Tuberculosis.

The long-term treatment of tuberculosis (TB) sometimes leads to nonadherence to treatment, resulting in multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis. Inadequate bioavailability of the drug is the main factor for therapeutic failure, which leads to the development of drug-resistant cases. Therefore, there is an urgent need to design and develop novel antimycobacterial agents minimizing the period of treatment and reducing the propagation of resistance at the same time. Here, we report the development of original and noncytotoxic polycationic phosphorus dendrimers essentially of generations 0 and 1, but also of generations 2-4, with pyrrolidinium, piperidinium, and related cyclic amino groups on the surface, as new antitubercular agents active per se, meaning with intrinsic activity. The strategy is based on the phenotypic screening of a newly designed phosphorus dendrimer library (generations 0-4) against three bacterial strains: attenuated Mycobacterium tuberculosis H37Ra, virulent M. tuberculosis H37Rv, and Mangora bovis BCG. The most potent polycationic phosphorus dendrimers 1G0,HCl and 2G0,HCl are active against all three strains with minimum inhibitory concentrations (MICs) between 3.12 and 25.0 µg/mL. Both are irregularly shaped nanoparticles with highly mobile branches presenting a radius of gyration of 7 Å, a diameter of maximal 25 Å, and a solvent-accessible surface area of dominantly positive potential energy with very localized negative patches arising from the central N3P3 core, which steadily interacts with water molecules. The most interesting is 2G0,HCl, showing relevant efficacy against single-drug-resistant (SDR) M. tuberculosis H37Rv, resistant to rifampicin, isoniaid, ethambutol, or streptomycin. Importantly, 2G0,HCl displayed significant in vivo efficacy based on bacterial counts in lungs of infected Balb/C mice at a dose of 50 mg/kg oral administration once a day for 2 weeks and superior efficacy in comparison to ethambutol and rifampicin. This series of polycationic phosphorus dendrimers represents first-in-class drugs to treat TB infection, could fulfill the clinical candidate pipe of this high burden of infectious disease, and play a part in addressing the continuous demand for new drugs.