Synthesis, characterization and in vitro extracellular and intracellular activity against Mycobacterium tuberculosis infection of new second-line antitubercular drug-palladium complexes

OBJECTIVES

The aim of this work was to characterize novel palladium (Pd) complexes with second-line antitubercular drugs, namely capreomycin (C), kanamycin (K) and ofloxacin (Ofx), and to address the in vitro extracellular and intracellular activity against Mycobacterium tuberculosis infection.

METHODS

Synthesis reaction kinetics and complex properties were assessed. Kf was calculated from the transition state quasi-equilibrium approximation and Arrhenius plot. The complexes were characterized for qualitative solubility, stoichiometry, powder size and morphology, element analysis, and thermal behaviour. Structural analyses were performed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Activity was evaluated against H37Ra M. tuberculosis strain and in infected THP-1 cells, and compared with that of the parent drugs.

KEY FINDINGS

The complexes showed log Kf of 6 for CPd and OfxPd, and 10 for KPd indicating good stability. Stoichiometry of 1:1, 2: 3 and 1:3 resulted for OfxPd, KPd, and CPd. OfxPd structure matched that in literature, while K and C had more complex structures with possible multiple coexisting species. The complexes had extracellular activity comparable with drugs and an improved efficacy against intracellular infection of M. tuberculosis.

CONCLUSIONS

The novel anti-tuberculosis (TB) complexes had promising properties, and extracellular and intracellular activity, which makes them potential tools for intracellular targeting of pulmonary TB.

Unexpected N-acetylation of capreomycin by mycobacterial Eis enzymes

OBJECTIVES

The enhanced intracellular survival (Eis) protein from Mycobacterium tuberculosis (Eis_Mtb), a regio-versatile N-acetyltransferase active towards many aminoglycosides (AGs), confers resistance to kanamycin A in some cases of extensively drug-resistant tuberculosis (XDR-TB). We assessed the activity of Eis_Mtb and of its homologue from Mycobacterium smegmatis (Eis_Msm) against a panel of anti-tuberculosis (TB) drugs and lysine-containing compounds.

METHODS AND RESULTS

Both enzymes acetylated capreomycin and some lysine-containing compounds, but not other non-AG non-lysine-containing drugs tested. Modelling studies predicted the site of modification on capreomycin to be one of the two primary amines in its β-lysine side chain. Using Eis_Mtb, we established via nuclear magnetic resonance (NMR) spectroscopy that acetylation of capreomycin occurs on the ε-amine of the β-lysine side chain. Using Msm, we also demonstrated for the first time to our knowledge that acetylation of capreomycin results in deactivation of the drug.

CONCLUSIONS

Eis is a unique acetyltransferase capable of inactivating the anti-TB drug capreomycin, AGs and other lysine-containing compounds.

Antibacterial natural products in medicinal chemistry--exodus or revival?

To create a drug, nature's blueprints often have to be improved through semisynthesis or total synthesis (chemical postevolution). Selected contributions from industrial and academic groups highlight the arduous but rewarding path from natural products to drugs. Principle modification types for natural products are discussed herein, such as decoration, substitution, and degradation. The biological, chemical, and socioeconomic environments of antibacterial research are dealt with in context. Natural products, many from soil organisms, have provided the majority of lead structures for marketed anti-infectives. Surprisingly, numerous "old" classes of antibacterial natural products have never been intensively explored by medicinal chemists. Nevertheless, research on antibacterial natural products is flagging. Apparently, the "old fashioned" natural products no longer fit into modern drug discovery. The handling of natural products is cumbersome, requiring nonstandardized workflows and extended timelines. Revisiting natural products with modern chemistry and target-finding tools from biology (reversed genomics) is one option for their revival.