Discovery of Two Brominated Oxindole Alkaloids as Staphylococcal DNA Gyrase and Pyruvate Kinase Inhibitors via Inverse Virtual Screening.

Ahmed M Sayed,Mostafa E Rateb,Usama Ramadan Abdelmohsen,Seham S El-Hawary,Hani A Alhadrami,Hossam M Hassan,Walid Bakeer,Rabab Mohammed

doi:10.3390/microorganisms8020293

Abstract

In the present study, a small marine-derived natural products library was assessed for antibacterial potential. Among 36 isolated compounds, a number of bis-indole derivatives exhibited growth-inhibitory activity towards Gram-positive strains (Bacillus subtilis and multidrug-resistant Staphylococcus aureus). 5- and 6-trisindoline (5-Tris and 6-Tris) were the most active derivatives (minimum inhibitory concentration, MIC, 4–8 µM) that were subsequently selected for anti-biofilm activity evaluation. Only 5-Tris was able to inhibit the staphylococcal biofilm formation starting at a 5 µM concentration. In order to investigate their possible molecular targets, both natural products were subjected to in silico inverse virtual screening. Among 20 target proteins, DNA gyrase and pyruvate kinase were the most likely to be involved in the observed antibacterial and anti-biofilm activities of both selected natural products. The in vitro validation and in silico binding mode studies revealed that 5-Tris could act as a dual enzyme inhibitor (IC50 11.4 ± 0.03 and 6.6 ± 0.05 µM, respectively), while 6-Tris was a low micromolar gyrase-B inhibitor (IC50 2.1 ± 0.08 µM), indicating that the bromine position plays a crucial role in the determination of the antibacterial lead compound inhibitory activity.

Highlights

Staphylococci are considered dangerous opportunistic microorganisms, and are associated with many serious infections, including those that are hospital-acquired
The antibacterial evaluation was performed for our small natural products library (Compounds 1–36, Table S1) in terms of Minimum Inhibitory Concentration (MIC) values in μM using standard antibacterial agents
The results suggested that the position of the bromine atom in 6-position favored the antibacterial activity; the 5- position favored the antibiofilm properties

Summary

Introduction

Staphylococci are considered dangerous opportunistic microorganisms, and are associated with many serious infections, including those that are hospital-acquired. Fluoroquinolones are well-known DNA gyrase inhibitors that target the enzyme’s A subunit They have achieved great success as antibacterial agents over the last 20 years; a number of resistant strains have emerged recently. They are more active towards the Gram-negative bacteria in comparison with Gram-positive ones such as S. aureus and S. epidermidis [11]. Many research groups worldwide are focusing on the development of novel antibacterial drugs by targeting DNA gyrase B subunits [12,13,14] Besides their bactericidal activity, DNA gyrase inhibitors have recently been identified as active anti-biofilm agents toward a wide range of pathogenic bacteria, most notably staphylococci (MRSA and MRSE) [15].

Methods

Results

Conclusion