Design, synthesis, and evaluation of substrate - analogue inhibitors of Trypanosoma cruzi ribose 5-phosphate isomerase type B

Ribose 5-phosphate isomerase type B (RPI-B) is a key enzyme of the pentose phosphate pathway that catalyzes the isomerization of ribose 5-phosphate (R5P) and ribulose 5-phosphate (Ru5P). Trypanosoma cruzi RPI-B (TcRPIB) appears to be a suitable drug-target mainly due to: (i) its essentiality (as previously shown in other trypanosomatids), (ii) it does not present a homologue in mammalian genomes sequenced thus far, and (iii) it participates in the production of NADPH and nucleotide/nucleic acid synthesis that are critical for parasite cell survival. In this survey, we report on the competitive inhibition of TcRPI-B by a substrate - analogue inhibitor, Compound B (K-i = 5.5 +/- 0.1 mu M), by the Dixon method. This compound has an iodoacetamide moiety that is susceptible to nucleophilic attack, particularly by the cysteine thiol group. Compound B was conceived to specifically target Cys-69, an important active site residue. By incubating TcRPI-B with Compound B, a trypsin digestion LC-MS/MS analysis revealed the identification of Compound B covalently bound to Cys-69. This inhibitor also exhibited notable in vitro trypanocidal activity against T. cruzi infective life-stages co-cultured in NIH3T3 murine host cells (IC50 = 17.40 +/- 1.055 mu M). The study of Compound B served as a proof-of-concept so that next generation inhibitors can potentially be developed with a focus on using a prodrug group in replacement of the iodoacetamide moiety, thus representing an attractive starting point for the future treatment of Chagas' disease.

Automated summary

The study discovered a competitive inhibitor Compound B targeting ribose 5-phosphate isomerase type B (RPI-B), which exhibited significant trypanocidal activity against T. cruzi infective life-stages. By targeting the active site residue Cys-69, this inhibitor provided a proof-of-concept for the development of next generation inhibitors with potential prodrug groups to treat Chagas' disease in the future.