SELECTIVE TIGHT-BINDING INHIBITORS OF TRYPANOSOMAL GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE VIA STRUCTURE-BASED DRUG DESIGN

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from the sleeping sic kness parasite Trypanosoma brucei is a rational target for anti-trypan osomatid drug design because glycolysis provides virtually all of the energy for the bloodstream form of this parasite. Glycolysis is also a n important source of energy for other pathogenic parasites including Trypanosoma cruzi and Leishmania mexicana. The current study is a cont inuation of our efforts to use the X-ray structures of T. brucei and L . mexicana GAPDHs containing bound NAD(+) to design adenosine analogue s that bind tightly to the enzyme pocket that accommodates the adenosy l moiety of NAD(+). The goal was to improve the affinity, selectivity, and solubility of previously reported 2'-deoxy-2'-(3-methoxybenzamido )adenosine (1). It was found that introduction of hydroxyl functions o n the benzamido ring increases solubility without significantly affect ing enzyme inhibition. Modifications at the previously unexploited N-6 -position of the purine not only lead to a substantial increase in inh ibitor potency but are also compatible with the 2'-benzamido moiety of the sugar. For N-6-substituted adenosines, two successive rounds of m odeling and screening provided a 330-fold gain in affinity versus that of adenosine. The combination of N-6- and 2'-substitutions produced s ignificantly improved inhibitors. N-6-Benzyl (9a) and N-6-2-methylbenz yl (9b) derivatives of 1 display IC50 values against L. mexicana GAPDH of 16 and 4 mu M, respectively (3100- and 12500-fold more potent than adenosine). The adenosine analogues did not inhibit human GAPDH. Thes e studies underscore the usefulness of structure-based drug design for generating potent and species-selective enzyme inhibitors of medicina l importance starting from a weakly binding lead compound.