The influence of charge transfer complex formation on the antibacterial activity of some tricyclic drugs

Infectious plasmid resistance and efflux pump mediated resistance

Various bacterial plasmids can be eliminated from bacterial species cultured as pure or mixed bacterial cultures by non-mutagenic heterocyclic compounds at subinhibitory concentrations. For plasmid curing, the replication should be inhibited at three different levels simultaneously: the intracellular replication of plasmid DNA, partition and intercellular transconjugal transfer. The antiplasmid action of the compounds depends on the chemical structure. The targets for antiplasmid compounds were analysed in detail. It was found that amplified extrachromosomal DNA in the superhelical state binds more drug molecules than does the linear or open-circular form of the plasmid or the chromosome, without stereospecificity which leads to functional inactivation of the extrachromosomal genetic code. Plasmid elimination also occurs in ecosystems containing numerous bacterial species simultaneously, but the elimination of antibiotic resistance-encoding plasmids from all individual cells of the population is never complete. The medical significance of plasmid elimination in vitro is, it provides a method to isolate plasmid-free bacteria for biotechnology without any risk of mutations, and it opens up a new perspective in rational drug design against bacterial plasmids. Hypothetically, the combination of antiplasmid drugs and antibiotics may improve the effectivity of antibiotics against resistant bacteria; therefore, the results cannot be exploited until the curing efficiency reaches 100%. Inhibition of the conjugational transfer of antibiotic resistance plasmids can be exploited to reduce the spreading of these plasmids in ecosystems.

Phenothiazines: potential alternatives for the management of antibiotic resistant infections of tuberculosis and malaria in developing countries

The in vitro and in vivo activity of phenothiazines against antibiotic susceptible and antibiotic resistant Mycobacterium tuberculosis and malaria-causing Plasmodia is reviewed. Given the facts that pulmonary tuberculosis and malaria are the major causes of death in developing countries, that both of these infections continue to escalate in their resistance to antibiotics, that the cost for the management of these infections is beyond that afforded by most developing nations, and lastly, that new and effective agents are not forthcoming from the pharmaceutical industry, the scientific rationale for the potential use of select phenothiazines for the management of these infections is presented.

Guanine-cytosine rich regions of plasmid DNA can be the target in anti-plasmid effect of phenothiazines

The antiplasmid effects of promethazine on E. coli is the consequence of special complex formed with a covalently closed circular (ccc) form of plasmid DNA. The exact target in this macromolecule, however, was not clarified until recently. Caffeine and the chemically similar guanosine-5'- monophosphate (GMP) could compete with the antiplasmid effect of promethazine, showing that promethazine or other phenothiazines preferentially bind to xanthine type molecules. Among the xanthines, GMP was more effective at complex-forming than adenosine-5'-monophosphate (AMP). In addition, the Z-DNA was more susceptible than B-DNA. Therefore, one could suppose that guanine-cytosine (G-C) rich regions have higher affinity than adenine-thymine (A-T) rich region on phenothiazines. Because the G-C rich regions have a special role in the DNA stability via three hydrogen bonds, we suppose that these regions could have a key role in some biological effects such as antiplasmid and anticancer activity.

Inhibition of HIV infection of H9 cells by chlorpromazine derivatives

The binding between the HIV surface protein, gp120, and the CD4 coreceptor is known to be initiated by electrostatic interactions. Because of the ability of chlorpromazine to interact with proteins by charge transfer, we tested several derivatives for their ability to block binding of HIV to CD4+ cells. We have shown that 7,8-dioxo-chlorpromazine blocks binding of fluorescein isothiocyanate-labeled anti-Leu3a and rgp120 to peripheral human blood T4 cells and blocks syncytia formation between gp120- and CD4-expressing cells. We also found that 7,8-dioxo-chlorpromazine blocks HIV infectivity of H9 cells and acts synergistically with zidovudine.

Mechanism of chlorpromazine binding by gram-positive and gram-negative bacteria

Chlorpromazine forms charge-transfer complexes with xanthene dyes in bacteria. These complexes permit the differentiation of Gram-positive and Gram-negative bacteria in both light and polarization microscopy. The birefringence induced by the charge-transfer complex might explain the molecular basis of bacterial staining. The charge-transfer complexes formed between chlorpromazine and xanthene dyes accumulate in the bacterial cell, mainly inside the bacterial cell wall. The complexes give the cells a color, which depends on the chemical composition of the staining structure, and in particular the polysaccharides of the cell wall in bacteria. Metachromatic granules were seen inside Gram-positive bacteria after chlorpromazine and rose bengal staining. Although the nature of these granules remains unclear, this type of binding may have a role in the inhibition of biochemical processes in the bacterial cells.