Recently, RecA has established itself as a potential target for the development of antibacterial drugs. The dual function of recA allows bacteria both to control the damage associated with the action of antimicrobial agents and simultaneously promotes the development of the drug resistance [1] [2] [3] [4] [5].
RecA was identified as a critical component involved in the response of bacteria to antibiotics of hinolones series. Fluoroquinolones such as ciprofloxacin interfere with topoisomerase II, leading to the emergence of double-stranded breaks and stop the replication of DNA [6]. In this case, monomers RecA, polymerize, forming a spiral filament, which has both the enzymatic and signaling activity. RecA-DNA filaments mediate DNA repair by catalyzing the exchange of chains between the DNA molecules. That is why one of the first results of the activation of RecA is to reduce the sensitivity of bacteria to ciprofloxacin (bacteria lacking RecA (ΔrecA) have an increased sensitivity to ciprofloxacin [7]).
The role of RecA is not limited to DNA repair. Activated recA SOS mutagenesis in the long run lead to the emergence of drug resistance so that the SOS-deficient strains of the emergence of such resistance is severely hampered [8].
RecA is a highly conserved bacterial protein [9], which makes it a tempting target for the development of new drugs [10]. In our work we’ve taken a three-dimensional structure of RecA protein mycobacteria and identified novel small molecules-inhibitors of RecA. For each of the compound we studied experimentally the ability of inhibitors to increase the sensitivity of the sensitivity of E.coli to ciprofloxacin. This bacteriostatic effect was measured by using ciprofloxacin in the sub-lethal concentrations in combination with our agents.
The results of screening studies (one concentration of test substances, the concentration of one antibiotic) are shown in the chart:
The height of the blue column is proportional to the number of bacteria in the samples after 20 hours of study (relative to control: bacteria, increasing antibiotic, but in the same sublethal concentration). Best of the substances significantly reduce bacterial populations. Nonzero height columns explains nemomentalnym substance (most likely a threshold effect, the growth of population in the uncritical accumulation of damage to a certain point).
Currently, it is shown that the effect of suppressing the growth of bacteria is dose-dependent with respect to a change in the concentration of antibiotic (the higher the concentration of antibiotic, the greater the bacteriostatic effect). For some of the substances observed bactericidal effect. None of the substances does not significantly affect the growth of bacteria without antibiotic.
It’s worth to mention, that among the 40 compounds suggested by the Quantum Software and sent to the lab, roughly half turned out to be somewhat active in-vitro and a few compounds turned out to be sufficiently active to permit further optimization. Therefore the computer model-to-lab hit rate turned out to be about 50%.
References
[1] SOS response promotes horizontal dissemination of antibiotic resistance genes. Beaber et al 2003 Nature (http://www.ncbi.nlm.nih.gov/pubmed/14688795)
[2] Antibiotic-induced lateral transfer of antibiotic resistance. Hastings et al 2004 Trends in microbiology (http://www.ncbi.nlm.nih.gov/pubmed/15337159)
[3] Adaptive mutation and amplification in Escherichia coli: two pathways of genome adaptation under stress. Hersh et al 2004 Research in microbiology (http://www.ncbi.nlm.nih.gov/pubmed/15207867)
[4] Stress responses and genetic variation in bacteria. Foster et al 2004 Mutation research (http://www.ncbi.nlm.nih.gov/pubmed/15603749)
[5] Survival versus maintenance of genetic stability: a conflict of priorities during stress. Matic et al 2004 Research in microbiology (http://www.ncbi.nlm.nih.gov/pubmed/15207865)
[6] Induction of the SOS gene (umuC) by 4-quinolone antibacterial drugs. Power et al 1992 Journal of medical microbiology (http://www.ncbi.nlm.nih.gov/pubmed/1740787)
[7] A common mechanism of cellular death induced by bactericidal antibiotics. Kohanski et al 2007 Cell (http://www.ncbi.nlm.nih.gov/pubmed/17803904)
[8] Inhibition of mutation and combating the evolution of antibiotic resistance. Cirz et al 2005 PLoS biology (http://www.ncbi.nlm.nih.gov/pubmed/15869329)
[9] RecA protein: structure, function, and role in recombinational DNA repair. Roca et al 1997 Progress in nucleic acid research and molecular biology (http://www.ncbi.nlm.nih.gov/pubmed/9187054)
[10] A molecular target for suppression of the evolution of antibiotic resistance: inhibition of the Escherichia coli RecA protein by N (6) – (1-naphthyl)-ADP. Lee et al 2005 Journal of medicinal chemistry (http://www.ncbi.nlm.nih.gov/pubmed/16107138)
