Routine screening for potential babesicides using cultures of Babesia bovis

A procedure for screening of potential anti-malarial agents, based on the incorporation of [3H]hypoxanthine by the parasite, was adapted for the testing of anti-metabolites against Babesia bovis (Lismore and Samford isolates) cultured in vitro. A close correlation was found between [3H]hypoxanthine incorporation in a standard assay and percentage of parasitized cells as determined by microscopic examination. The concentrations of compounds causing 50% inhibition of [3H]hypoxanthine incorporation (ID50 values) for the established babesicides, Imidocarb and Amicarbalide, were determined to be 3 ng ml-1 (8.6 nM) and 5-10 ng ml-1 (17-34 nM), respectively. A variety of other anti-metabolites were tested in the system. ID50 values for some of the more effective compounds were tubercidin (75 nM), tetracycline (25 microM), menoctone (100 nM) and TN 108, a di-Mannich base derived from 4-(7'-trifluoromethyl-quinolin-4'-ylamino)phenol (0.13 microM). No significant differences between results with the two isolates of B. bovis were observed.