Epigenetic modulator UVI5008 inhibits MRSA by interfering with bacterial gyrase

Abstract

The impact of multi-drug resistant bacterial strains on human health is reaching worrisome levels. Over 2 million people are infected by resistant bacteria, and more than 700,000 people die each year because of the continuous spread of resistant strains. The development of new antibiotics and the prudent use of existing ones to prolong their lifespan require a constant effort by drug industries and healthcare workers. The re-purposing of existing drugs for use as antimicrobial agents would streamline the development of new antibacterial strategies. As part of this effort, we screened a panel of drugs previously characterized to be epigenetic modulators/pro-apoptotic/differentiative drugs. We selected a few compounds that alter Gram-positive growth. Among these, UVI5008, a derivative of the natural compound psammaplin A (Psa_A), was identified. The interaction of Psa_A with the DNA gyrase enzyme has been shown, and here, we hypothesized and confirmed the gyrase-specific activity by biochemical assays. UVI5008 exhibited growth inhibition activity against Staphylococcus aureus via structural modification of the cell wall, which was observed by SEM electron microscopy. Based on our findings, we propose UVI5008 as an alternative antibacterial compound against methicillin-resistant (Met.R) S. aureus strains.

Figure 1

Radar graph representation of the effect of epigenetic compounds on two Gram-negative (E. coli, K. pneumoniae) and two Gram-positive (S. aureus, E. faecalis) bacterias. Compounds and their concentrations (expressed in μM) are reported on the external radar graph circle. All absorbance values were recorded and converted to % of inhibition compared to controls. The results are representative of three independent experiments, and stringent statistical filters were applied

Figure 2

Radar graph representation of bacteria growth at 600 nm absorbance for ATCC MSSA (A), field MSSA (B), Met.R S. aureus (C), Beta-lactamase producer S. aureus (D), and macrolide resistant S. aureus (E) at 4 h, 6 h, and 20 h of incubation. Table of MIC and MBC values for the respective S. aureus strains (F).

Figure 3

Combinatorial experiments on biofilm degradation mediated by UVI5008 and vancomycin, ampicillin and ciprofloxacin for ATCC SA compared with FI MSSA and MRSA. The results are representative of three independent experiments, and stringent statistical filters were applied (p-value < 0,5).

Figure 4

UVI5008 analogues based on SAR (A). Heatmap representation of absorbance acquired for MSSA and MRSA in response to treatment with UVI5008 analogues. The distance between two clusters is the mean distance between all objects of the clusters (B). Structural analysis of UVI5008 characteristics needed for preservation of antibacterial properties (C).

Figure 5

UVI5008 biochemical mechanism of action on S. aureus recombinant DNA gyrase and supercoiled bacterial DNA (A) with the relative quantization obtained via ImageJ software (B). Inhibition activity of UVI5008 on two quinolone-resistant S. aureus strains compared with the FI MSSA strain (C–E). IC₅₀ on DNA gyrase was calculated by GraphPad Prism software (F).

Figure 6

S. aureus gyrase ATPase linked assay. Schematic representation of enzymatic reaction (A). Enzymatic evaluation of ATPase activity of S. aureus DNA gyrase in the presence of UVI5008 from 50 to 500 μM compared with the negative control (no enzyme) and the positive control (no inhibitor).

Figure 7

Two different magnifications of each surface morphology of MSSA ATCC and MRSA treated with UVI5008 at 3 μM and 50 μM compared to control, acquired via scanning electron microscopy.