Mode of action of the 2-phenylquinoline efflux inhibitor PQQ4R againstEscherichia coli

Abstract

Efflux pump inhibitors are of great interest since their use as adjuvants of bacterial chemotherapy can increase the intracellular concentrations of the antibiotics and assist in the battle against the rising of antibiotic-resistant bacteria. In this work, we have described the mode of action of the 2-phenylquinoline efflux inhibitor (4-(2-(piperazin-1-yl)ethoxy)-2-(4-propoxyphenyl) quinolone – PQQ4R), against Escherichia coli, by studding its efflux inhibitory ability, its synergistic activity in combination with antibiotics, and compared its effects with the inhibitors phenyl-arginine-β-naphthylamide (PAβN) and chlorpromazine (CPZ). The results showed that PQQ4R acts synergistically, in a concentration dependent manner, with antibiotics known to be subject to efflux in E. coli reducing their MIC in correlation with the inhibition of their efflux. Real-time fluorometry assays demonstrated that PQQ4R at sub-inhibitory concentrations promote the intracellular accumulation of ethidium bromide inhibiting its efflux similarly to PAβN or CPZ, well-known and described efflux pump inhibitors for Gram-negative bacteria and whose clinical usage is limited by their levels of toxicity at clinical and bacteriological effective concentrations. The time-kill studies showed that PQQ4R, at bactericidal concentrations, has a rapid antimicrobial activity associated with a fast decrease of the intracellular ATP levels. The results also indicated that the mode of action of PQQ4R involves the destabilization of the E. coli inner membrane potential and ATP production impairment, ultimately leading to efflux pump inhibition by interference with the energy required by the efflux systems. At bactericidal concentrations, membrane permeabilization increases and finally ATP is totally depleted leading to cell death. Since drug resistance mediated by the activity of efflux pumps depends largely on the proton motive force (PMF), dissipaters of PMF such as PQQ4R, can be regarded as future adjuvants of conventional therapy against E. coli and other Gram-negative bacteria, especially their multidrug resistant forms. Their major limitation is the high toxicity for human cells at the concentrations needed to be effective against bacteria. Their future molecular optimization to improve the efflux inhibitory properties and reduce relative toxicity will optimize their potential for clinical usage against multi-drug resistant bacterial infections due to efflux.

Asiatic Acid (AA) Sensitizes Multidrug-Resistant Human Lung Adenocarcinoma A549/DDP Cells to Cisplatin (DDP) via Downregulation of P-Glycoprotein (MDR1) and Its Targets

“…P-gp encoded by the MDR1 gene is a transmembrane protein, which belongs to the ABC transporter protein superfamily. It functions as an ATP-dependent drug efflux pump [29] and is known to decrease the intracellular concentration of chemotherapeutic agents [30]. MDR1 (P-gp) is deeply involved in tumor chemoresistance [31].…”

Efflux pump inhibitors of clinically relevant multidrug resistant bacteria

“…PAβN was shown to increase the permeability of the outer membrane of the P. aeruginosa PAM2035 strain, that lacks the functional MexAB‐OprM pump, in a dose‐dependent manner due to its dicationic character, which has raised concerns concerning toxicity . In vivo cytotoxicity data showed that PAβN was toxic to mice (LD 50 < 25 mg/kg) and its further developed analogs were proven to be nephrotoxic as a result of their accumulation in lysosomes …”

“…72 In vivo cytotoxicity data showed that PAβN was toxic to mice (LD 50 < 25 mg/kg) 243 and its further developed analogs were proven to be nephrotoxic as a result of their accumulation in lysosomes. 244,245 To determine the initial SAR, more than 500 analogs were synthesized and tested. Analog 70 ( Figure 21) showed an MPC 8 of 11.9 µM for levofloxacin against PAM1032 and nearly twofold increase in activity against all the strains tested when compared to the parent compound PAβN (1; Figure 1), while retaining the broad-spectrum inhibitory characteristics.…”

Thermodynamic secrets of multidrug resistance: A new take on transport mechanisms of secondary active antiporters

“…Such inhibitors synergistically enhance effects of other antibiotics by reducing their minimum inhibitory concentration (MIC). A non‐specific inhibitor may abolish the activity of PMF‐driven efflux pumps by depleting the TM potential, albeit such an inhibitor is likely to be toxic to all cells . In contrast, an inhibitor specific to an MDR transporter may either reduce the expression of the transporter or block its conformational transitions.…”

“…In fact, Dm W is assumed to drive and/or regulate functions of many membrane proteins, for example the PMF-driven rotational ATP synthase F 0 -F 1 , 21,22 voltage-gated ion channels, 19 GPCR signal-transduction proteins, 23,24 and integral membrane enzymes, 25 additional to secondary-active transporters. 18,26 The same electrostatic TM potential also guides correct folding and orientation of bacterial membrane proteins 27 and is likely to facilitate cationic drugs to penetrate plasma membranes. In addition, the function of certain membraneresident pH sensors 28 can be explained by interaction between pH-induced protonation and DW.…”