Identification of new inhibitors of Plasmodium falciparum hypoxanthine-guanine-xanthine Phosphoribosyltransferase (HG(X)PRT): An outlook towards the treatment of malaria.

Plasmodium, a protozoan parasite responsible for causing malaria relies on the purine salvage pathway to synthesize purine as they are incapable of synthesizing them de novo. This pathway is crucial for the survival of the parasite and hence enzymes of this pathway can serve as antimalarial drug targets. One of the enzymes of this pathway is hypoxanthine guanine (xanthine) phosphoribosyltransferase [HG(X)PRT] that serves as novel target, potentially less prone to existing resistance mechanisms seen with the use of traditional antimalarial drugs. HGXPRT inhibition disrupts the parasite's ability to synthesize nucleotides, essential for its growth and replication. In this regard, the current study was designed to identify the inhibitors of HGXPRT enzyme. For this purpose, the enzyme was produced through recombinant technology and purified with 10 mg/ L yield. Followed this, UV-based enzyme inhibition assay was optimized and >200 fully characterized compounds were evaluated for their HGXPRT inhibitory activity. Out of them fourteen compounds 1-14 showed significant to weak inhibition of HGXPRT enzyme with IC values in the range of 15.7 to 229.6 μM, as compared to the standard inhibitor i.e. 9-deazaguanine (IC = 12 ± 1.0 μM). In- silico and biophysical studies were further performed on active compounds to get structural insights into enzyme-inhibitor complex at the atomic level. Docking studies predicted that these inhibitors accommodate the purine binding site of enzyme and interacted with critical residues such as Asp148, Phe197, and Val198. Biophysical studies showed that these identified inhibitors interacted with HGXPRT enzyme in a non-ambiguous manner. Furthermore, these inhibitors were found to be non-cytotoxic against human fibroblast cell line (BJ). Hence, this study identified 14 hits that could lead to further research towards anti-malarial drug design and development.