Segaran P. Pillai

Multiple drug resistance

Multiple drug resistance to antibacterial agents, antifungals, antivirals, antiprotozoals, and antitumor agents has risen spectacularly in the last decade or so and presently threatens eventually to put an end to successful chemotherapy in all of the above fields. This review summarizes the known origins of the problem, its present dimensions, the means employed to combat the phenomenon and promising avenues for future developments.

The ability of certain antimutagenic agents to prevent development of antibiotic resistance.

Resistance to multiple antimicrobial agents has now become a prominent fact of contemporary life. It is believed that poor patient compliance, e.g. interrupted or premature cessation of therapy; and misuse or abuse of antibiotics, e.g. wrong antibiotic or insufficient dose, play important roles in resistance development. We present evidence that, this form of resistance often stems from spontaneous mutations accompanied by the positive selecting pressure of the doses of antibiotics being between the MIC and MBC levels. A number of antimutagenic agents, e.g. green tea catechins, and other antioxidants, etc. are able to suppress the emergence of resistance. In many cases, these agents are capable of exerting these effects at doses which by themselves produce no visible effect on growth. In a number of cases antimutagenic substances capable of preventing resistance emergence are present in normal food stuffs. These effects are exerted against resistance to tetracyclines, fluoroquinolones, macrolides, beta-lactams, aminoglycosides and the like. The implications of these laboratory findings for practical chemotherapy are discussed.

Polyamines and their potential to be antimutagens

In order to determine the antimutagenic potential of polyamines, modified Ames tests were performed. Polyamines spermine, spermidine and putrescine all showed antimutagenic potential against EMS-induced reversions. In addition, the polyamines spermidine and putrescine showed potential to reduce the number of spontaneous revertants in modified Ames tests. Since spermidine and putrescine have the potential to reduce spontaneous mutations, we decided to perform DNA fidelity assays. DNA fidelity assays confirmed that putrescine has the potential to reduce the mutation frequency. However, spermidine had no effect. This suggests that putrescine may play a vital role in DNA synthesis and possibly be the active compound that plays a role in affecting EMS-induced mutations in the modified Ames tests. This is possible since all cells have the potential to convert spermine and spermidine to putrescine. However, since the DNA fidelity assay is an in vitro assay, the enzymes required for the conversion of spermine and spermidine to putrescine are absent. The possibility of conversion and the rate of conversion need further study.

Effects of antimutagens on development of drug/antibiotic resistance in microorganisms.

The effects of polyamines and related compounds on the development of drug/antibiotic resistance in a variety of bacterial strains were studied. Methods employed included standard toxicity assays, modified Ames tests for mutation frequencies and antimutagenic effects, prophage induction assays, and recA-lacZ and ada-lacZ induction assays. Using these methods, we have shown that the polyamines produce strong antimutagenic effects against EMS and MMS-induced antibiotic resistance. Spermidine also seems to have antimutagenic potential against 4NQO-induced mutations. DNA fidelity assays suggest that polyamines play a vital role in DNA synthesis, and several polyamines prevent the development of resistance to dihydrostreptomycin. The polyamine putrescine appears to be required for streptomycin action and also enhances the activity of some antibiotics (e.g., neomycin, kanamycin) but shows no enhancing effect on tetracycline or erythromycin. The potential significance of these studies for infectious diseases and tumor therapy is discussed.

A parallel synthesis demonstration library of tri-substituted indazoles containing new antimutagenic/antioxidant hits related to benzydamine.

A solution phase strategy for the multiple parallel synthesis of a demonstration library of indazoles is described by which regio-selectivity problems inherent to previous syntheses of this nucleus are largely overcome. Synthesis of selected components proceeded satisfactorily indicating that a fully realized library of indazole analogs could readily be produced using this methodology. Simple modifications of the basic nucleophilic aromatic substitution route unambiguously produce a range of N-1 substitutions (alkyl, aryl and aralkyl) in 50-75% yields. Next a range of substituents was introduced at the C-3 position in 50-80% yields by O-alkylation. Careful choice of reagents and reaction conditions were required to prevent by-product formation due to competing alkylation at N-2 (trace to 15% yields). When present, these contaminants were readily removed by chromofiltration. A third diversity site was sketched in at C-5 in 75-90% yield by reductive alkylation or acylation. Screening of some of the demonstration library members in vitro revealed highly active antioxidants suggesting that producing a full library would be worthwhile.