Motuporamine Derivatives as Antimicrobial Agents and Antibiotic Enhancers against Resistant Gram-Negative Bacteria

Abstract

Dihydromotuporamine C and its derivatives were evaluated for their in vitro antimicrobial activities and antibiotic enhancement properties against Gram-negative bacteria and clinical isolates. The mechanism of action of one of these derivatives, MOTU-N44, was investigated against Enterobacter aerogenes by using fluorescent dyes to evaluate outer-membrane depolarization and permeabilization. Its efficiency correlated with inhibition of dye transport, thus suggesting that these molecules inhibit drug transporters by de-energization of the efflux pump rather than by direct interaction of the molecule with the pump. This suggests that depowering the efflux pump provides another strategy to address antibiotic resistance.

Keywords: antibiotics; antimicrobial agents; bacterial resistance; membranes; motuporamine; polyamine derivatives.

Scheme 1

Motuporamine compounds 1–6, anthracenyl compounds 1–7 squalamine 8, and spermine 9.

Figure 1

The effect of squalamine (100 μg mL⁻¹), spermine (100 μg mL⁻¹), and 5 b (MOTU‐N44, 100 μg mL⁻¹) on ATP release kinetics for Gram‐positive bacteria S. aureus.

Figure 2

Depolarization of the bacterial membrane of S. aureus in the presence of 2.6 and 5.2 μm squalamine, spermine, or 5 b (MOTU‐N44).

Figure 3

MOTU‐N44 (5 b) has multiple effects on the cell membrane of the Gram‐negative bacterium E. aerogenes EA289. a) Outer‐membrane permeabilization detected by nitroceflin hydrolysis, in a dose‐and time‐dependent manner. b) Dose‐dependent inner‐membrane depolarization quantified by the release of DiSC₃(5). c) Membrane disruption revelaed by APT efflux. d) Inhibition of glucose‐triggered 1,2′‐diNA release via effux pumps.

Figure 4

Time‐kill curves of 5 b (MOTU‐N44, 4×MIC) over 4 h against EA289 bacteria.

Figure 5

Cell viability of EA289 in the presence of 5 b (MOTU‐N44, 4×MIC).