Am. Aronov et al., Rational design of selective submicromolar inhibitors of Tritrichomonas foetus hypoxanthine-guanine-xanthine phosphoribosyltransferase, BIOCHEM, 39(16), 2000, pp. 4684-4691
All parasitic protozoa lack the ability to synthesize purine nucleotides de
novo, relying instead on purine salvage enzymes for their survival. Hypoxa
nthine-guanine-xanthine phosphoribosyltransferase (HGXPRT) from the protozo
an parasite Tritrichomonas foetus is a rational target for antiparasitic dr
ug design because it is the primary enzyme the parasite uses to salvage pur
ine bases from the host. The study presented here is a continuation of our
efforts to use the X-ray structure of the T.foetus HGXPRT-GMP complex to de
sign compounds that bind tightly to the purine pocket of HGXPRT. The goal o
f the current project was to improve the affinity and selectivity of previo
usly identified HGXPRT inhibitor TF1 [4-(3 -nitroanilino)phthalic anhydride
]. A virtual library of substituted 4-phthalimidocarboxanilides was constru
cted using methods of structure-based drug design, and was implemented synt
hetically on solid support. Compound 20 [(4'-phthalimido)carboxamido-3 -ben
zyloxybenzene] was then used as a secondary lead for the second round of co
mbinatorial chemistry, producing a number of low-micromolar inhibitors of H
GXPRT. One of these compounds, TF2 [(4'-phthalimido) carboxamido-3-(4-bromo
benzy loxy)benzene], was further characterized as a competitive inhibitor o
f T. foetus HGXPRT with respect to guanine with a K-I of 0.49 mu M and a 30
-fold selectivity over the human HGPRT. TF2 inhibited the growth of culture
d T. foetus cells in a concentration-dependent manner with an ED50 of 2.8 m
u M, and this inhibitory effect could be reversed by addition of exogenous
hypoxanthine. These studies underscore the efficiency of combining structur
e-based drug design with combinatorial chemistry to produce effective speci
es-specific enzyme inhibitors of medicinal importance.