Description

Infection

Description

Sulfanilamide (Sulphanilamide) is a competitive inhibitor for bacterial enzyme dihydropteroate synthetase with IC50 of 320 μM.

Targets

IC₅₀

In Vitro

Sulfanilamide containing the sulfonamide functional group displays inhibitory activity for dihydropteroate synthetase partially purified from Escherichia coli which normally uses para-aminobenzoic acid (PABA) for synthesizing the necessary folic acid acting as a coenzyme in the synthesis of purine, pyrimidine and other amino acids, exhibiting an IC 50 of 320 μM for dihydropteroate synthetasea and Km of 2.5 uM for PABA. ^[1] Sulfanilamide shows IC50 of 286.8 μg/mL for recombinant S. cerevisiae strains with wild-type FOL1 genes, but the single mutation ⁵⁵Trp to ⁵⁵Ala or ⁵⁷Pro to ⁵⁷Ser within the putative active site of the fungal DHPS confers resistance to Sulfanilamide with IC50 of >800 μg/mL. ^[2] Sulfanilamide moderately inhibits the growth of bacterial cells harboring plasmodium falciparum pKOS-pfPPPK-DHPS (His) with IC50 of 380 uM. ^[3]

In Vivo

Administration of Sulfanilamide with the dosage of 100 mg/kg/day is effective in the prevention of P. carinii infection in the immunosuppressed rat model. When the dosage of sulfaguanidine and Sulfanilamide reduced to 10 mg/kg/day, breakthrough P. carinii infection occurs in the rats. ^[4]

Clinical Trials

Features

Assay of dihydropteroate synthetase activity

The dihydropteroate synthetase activity is measured by a modification of the radioactive assay based on the incorporation of ¹⁴C-PABA into dihydropteroate. The reaction mixture in test tubes (1 by 7 cm) is prepared in 0.4 mL of 100 mM Tris-HCl buffer (pH 8.5) (containing 10 mM of MgCl₂, 50 mM of 2-ME, 0.12 mM of hydroxymethyldihydropteridine pyrophosphate, 0.01 mM of 14C-PABA, a set of concentrations of Sulfanilamide and 0.2 mg partially purified dihydropteroate synthetase extract), and incubated for 1 hour at 37 °C. The reactions are stopped immediately by the addition of 25 μM of EDTA (pH 8.3) to each reaction mixture, then evaporated to dryness under reduced pressure and redissolved in 0.075 mL of 0.05 M Tris (pH 8.0). 0.05 mL of the above mixture is applied (each in an area of 1.0 by 4.0 cm) to Whatman 3MM chromatography paper. The chromatograms are developed by descending chromatography with 0.1 M potassium phosphate buffer (pH 7.0), for 4 hours at 25 °C. Under these conditions, pteroate (dihydropteroate is oxidized to pteroate during the evaporation step) remains at the origin, whereas unreacted ¹⁴C-PABA migrates with an Rf value of 0.78. Areas corresponding to the origin of the developed chromatograms are cut out and counted in a liquid scintillation counter. The concentration of Sulfanilamide required for 50% inhibition of dihydropteroate synthetase activity represents IC50.

Animal Models

Male Sprague-Dawley rats

Formulation

Thoroughly mixed into the daily ration of pulverized food and compounded into pellets.

Doses

100 mg/kg

Administration

Orally taken every day