A rapid drug susceptibility test for Mycobacterium tuberculosis using the hybridization protection assay

Potentiating the Anti-Tuberculosis Efficacy of Peptide Nucleic Acids through Combinations with Permeabilizing Drugs

The emergence of antimicrobial resistance warrants for the development of improved treatment approaches. In this regard, peptide nucleic acids (PNAs) have shown great promise, exhibiting antibiotic properties through the targeting of cellular nucleic acids. We aimed to study the efficacy of PNA as an anti-tuberculosis agent. Since the efficacy of PNA is limited by its low penetration into the cell, we also investigated combinatorial treatments using permeabilizing drugs to improve PNA efficacy. Various concentrations of anti-inhA PNA, permeabilizing drugs, and their combinations were screened against extracellular and intracellular mycobacteria.0.625 to 5 μM anti-inhA PNA was observed to merely inhibit the growth of extracellular M. smegmatis, while low intracellular bacterial load was reduced by 2 or 2.5 log-fold when treated with 2.5 or 5 μM PNA, respectively. Anti-inhA PNA against M. tuberculosis H37Ra exhibited bactericidal properties at 2.5 and 5 μM and enabled a slight reduction in intracellular M. tuberculosis at concentrations from 2.5 to 20 μM. Of the permeabilizing drugs tested, ethambutol showed the most permeabilizing potential and ultimately potentiated anti-inhA PNA to the greatest extent, reducing its efficacious concentration to 1.25 μM against both M. smegmatis and M. tuberculosis. Furthermore, an enhanced clearance of 1.3 log-fold was observed for ethambutol-anti-inhA PNA combinations against intracellular M. tuberculosis. Thus, permeabilizing drug-PNA combinations indeed exhibit improved efficacies. We therefore propose that anti-inhA PNA could improve therapy even when applied in minute doses as an addition to the current anti-tuberculosis drug regimen.

IMPORTANCE Peptide nucleic acids have great potential in therapeutics as anti-gene/anti-sense agents. However, their limited uptake in cells has curtailed their widespread application. Through this study, we explore a PNA-drug combinatorial strategy to improve the efficacy of PNAs and reduce their effective concentrations. This work also focuses on improving tuberculosis treatment, which is hindered by the emergence of antimicrobial-resistant strains of Mycobacterium tuberculosis. It is observed that the antibacterial efficacy of anti-inhA PNA is enhanced when it is combined with permeabilizing drugs, particularly ethambutol. This indicates that the addition of even small concentrations of anti-inhA PNA to the current TB regimen could potentiate their therapeutic efficiency. We hypothesize that this system would also overcome isoniazid resistance, since the resistance mutations lie outside the designed anti-inhA PNA target site.

Phenothiazines: an alternative to conventional therapy for the initial management of suspected multidrug resistant tuberculosis. A call for studies

Increased frequency of multidrug resistant strains of Mycobacterium tuberculosis results from inappropriate treatment and lack of patient compliance. The Center for Disease Control/American Thoracic Society (CDC/ATS) guidelines issued for the management of newly diagnosed cases of tuberculosis (TB) will not be totally effective regardless of adherence to the guidelines and patient cooperation. The long interim period between the diagnosis of TB and confirmation of antibiotic susceptibility contributes to the infection rate. Consequently, the use of an adjuvant that is known to inhibit all encountered multidrug resistant strains of M. tuberculosis may be helpful until antibiotic susceptibility is known. Phenothiazines such as chlorpromazine, methdilazine and thioridazine are effective against strains of M. tuberculosis in vitro and in vivo. It is recommended that studies be designed and conducted for the purpose of managing new cases of TB that emanate from areas known to harbour multidrug resistant strains of M. tuberculosis, with phenothiazines as adjuvants to the regimen recommended by the CDC/ATS guidelines until antibiotic susceptibility is defined. Because the normal maximum period for obtaining conventional antibiotic susceptibility results is less than 7 or 8 weeks, the probability of serious side effects from the use of a phenothiazine is remote.