In vivo activity of epiroprim, a dihydrofolate reductase inhibitor, singly and in combination with dapsone, against Mycobacterium leprae.

The antimicrobial effects of a new dihydrofolate reductase inhibitor, epiroprim, either singly or in combination with dapsone against Mycobacterium leprae, were evaluated in vivo using a mouse footpad model. When fed to mice at concentration of 0.05% in diet, epiroprim completely inhibited the growth of both dapsone-sensitive and dapsone-resistant strains of M. leprae in the footpads of mice and the effects were bactericidal. To achieve similar effects, the concentration of dapsone in the diet had to be 0.0005 and 0.01%, respectively. When used in combination, the concentrations of the drugs in the diet could be lowered by 50-80% and still achieve bactericidal effects. The data support the earlier results on in vitro studies and suggest the use of epiroprim in the multidrug regimen in the treatment of leprosy.

Search for newer antileprosy drugs.

In 1991 World Health Organization proclaimed the goal of global elimination of leprosy as a public health problem by year 2000 by implementing multidrug therapy (MDT). Since then the prevalence rate has declined by 85%. However, during the same period the incidence rate of leprosy has remained constant or even has been increasing. This suggests that it will take a long time for the eradication of leprosy and that without in-vitro cultivation of M. leprae, eradication of leprosy is not likely to be achieved. While in-vitro cultivation is a long-term goal, as an immediate measure, there is an urgent need for the development of newer drugs and newer multidrug therapy regimens. Using the in-vitro system for screening potential antileprosy drugs and also using the mouse foot-pad system we have evaluated several compounds in four classes of drugs--dihydrofolate reductase inhibitors, fluoroquinolones, rifampicin analogues and phenazines--and identified at least two compounds that appear to be more potent than dapsone, rifampicin and clofazimine. Newer combinations of rifampicin analogues and fluoroquinolones have also been identified that seem to be better than the combination of rifampicin and ofloxacin.

In vitro activity of epiroprim, a dihydrofolate reductase inhibitor, singly and in combination with brodimoprim and dapsone, against Mycobacterium leprae.

The antimicrobial effects of a new dihydrofolate reductase inhibitor, epiroprim, alone and in combination with dapsone and brodimoprim against Mycobacterium leprae were evaluated in vitro in cell-free culture system. Two biochemical parameters were used to measure metabolic activity (and growth) of the organism. The minimal inhibitory activity of epiroprim against M. leprae was 10 mg/l and the action was bactericidal. When combined with dapsone, epiroprim exhibited a strong synergism; on the other hand, combination of epiroprim and brodimoprim provided only additive effects. The results suggest that epiroprim can be a component in multidrug therapy regimen in leprosy.

Diaminodiphenylsulfone resistance of Mycobacterium leprae due to mutations in the dihydropteroate synthase gene.

The nucleotide sequence analysis of the dihydropteroate synthase (DHPS) gene of six diaminodiphenylsulfone-resistant Mycobacterium leprae strains revealed that the mutation was limited at highly conserved amino acid residues 53 or 55. Though the mutation at amino acid residue 55 or its homologous site has been reported in other bacteria, the mutation at residue 53 is the first case in bacteria. This is the first paper which links the mutations in DHPS and sulfonamide resistance in M. leprae. This finding is medically and socially relevant, since leprosy is still a big problem in certain regions.

In vitro and in vivo activity of K-130, a dihydrofolate reductase inhibitor, against Mycobacterium leprae.

The antimicrobial effects of a new dihydrofolate reductase inhibitor, K-130 (2,4-diaminodiphenyl sulfone substituted 2,4-diamino-5-benzylpyrimidine), alone and in combination with dapsone (CAS 80-08-0) against both dapsone-sensitive and dapsone-resistant strains of Mycobacterium leprae were evaluated in vitro, in cell-free culture system, and in vivo, in mouse foot pads. The minimal inhibitory concentration of K-130 against dapsone-sensitive as well as dapsone resistant strains of M, leprae was 0.03 microgram/ml, and the activity was bactericidal in both cases. However, when combined with dapsone, K-130 exhibited synergism in case of dapsone-sensitive M. leprae, while in case of dapsone-resistant M. leprae, the effect was merely additive. Similar synergistic effects were also observed in the mouse foot pad system for both types of M. leprae strains.

Mechanism of action of the folate blocker diaminodiphenylsulfone (dapsone, DDS) studied in E. coli cell-free enzyme extracts in comparison to sulfonamides (SA).

The antibacterial activity of DDS has been studied in whole cell (E. coli), cell-free folate synthesizing enzyme extracts and compared to effects obtained for sulfonamides (SA). It is shown that DDS acts as a synthetase inhibitor in the folate synthesizing enzyme system. DDS reacts with the substrate 7,8-dihydro-6-hydroxymethylpterinopyrophosphate to form a 7,8-dihydropteroic acid analog. Bacterial growth kinetic studies were performed to test for possible synergistic activity of the analog in combination with DDS. Possible reasons for the extremely large inhibitory power of DDS against M. leprae are discussed.