Nanoformulation of imipramine loaded resealed erythrocytes as potent anti-leishmanial, which targets unique 'prokaryotic TopA' homolog in Leishmania

Introduction: Uncontrolled use of traditional anti-leishmanials leading to the emergence of drug resistant parasites has necessitated the search for potent drugs against novel drug targets clear and evident. A serendipitous... [ view full abstract ]

Introduction:
Uncontrolled use of traditional anti-leishmanials leading to the emergence of drug resistant parasites has necessitated the search for potent drugs against novel drug targets clear and evident. A serendipitous BLAST search using prokaryotic TopA sequence led us to identify its homolog, LdBPK_210180.1 in Leishmania. The sequence corresponds to a unique Topoisomerase IA (LdTopIA), having prokaryotic homologs and being absent in higher eukaryotes. Previously anti-depressants have been shown to exhibit anti-leishmanial activity and imipramine, which is one such anti-depressant has been reported to inhibit mycobacterial Topoisomerase I (MttopoI), so we thought of testing efficacy of imipramine as an inhibitory agent against LdTopIA.
Methods:
Sequence similarity of E.coli TopA and LdTopIA was established using CLUSTAL-W and homology modeling of LdTopIA was performed using SWISS-MODEL using E.coli TopA as template (PDB ID-1CY1). Functional complementation studies were performed in RFM 475 (an E.coli TopoI null-DNA gyrasets mutant strain) in presence and absence of imipramine. In-silico docking was also studied for imipramine and LdTopIA. Nanoformulation of imipramine was carried out for entrapment in resealed erythrocytes for efficient delivery to the effected organs.
Results:
Homology modeling and functional characterization shows LdTopIA has active site residues similar to its prokaryotic homologs. Though the enzyme complements E.coli TopA in RFM 475 strain, it fails to do the same in presence of imipramine. In-silico docking studies also show that imipramine binds to the active site of LdTopIA suggesting that imipramine is a potent inhibitor of LdTopIA.
Discussion:
The results establish LdTopIA as a unique drug target capable of killing the parasite while respite the host. Since, liver and spleen are the effected organs in visceral leishmaniasis, nanoformulation of imipramine-loaded resealed erythrocytes can be an effective therapy to combat the disease as the reticuloendothelial system readily phagocytoses such RBCs. Such strategy can lead to personalized medicines where one’s own red blood cells can be used as drug delivery vessel and thereby prove to be a successful new strategy for treating leishmaniasis.