Emerging strategies and challenges of molecular therapeutics in antileishmanial drug development

Insights into nucleoside hydrolase from Leishmania donovani inhibition: A new bioaffinity chromatography-based screening assay and docking studies

Leishmaniasis, a group of neglected infectious diseases, encompasses a serious health concern, particularly with visceral leishmaniasis exhibiting potentially fatal outcomes. Nucleoside hydrolase (NH) has a fundamental role in the purine salvage pathway, crucial for Leishmania donovani survival, and presents a promising target for developing new drugs for visceral leishmaniasis treatment. In this study, LdNH was immobilized into fused silica capillaries, resulting in immobilized enzyme reactors (IMERs). The LdNH-IMER activity was monitored on-flow in a multidimensional liquid chromatography system, with the IMER in the first dimension. A C18 analytical column in the second dimension furnished the rapid separation of the substrate (inosine) and product (hypoxanthine), enabling direct enzyme activity monitoring through product quantification. LdNH-IMER exhibited high stability and was characterized by determining the Michaelis-Menten constant. A known inhibitor (1-(β-d-Ribofuranosyl)-4-quinolone derivative) was used as a model to validate the established method in inhibitor recognition. Screening of three additional derivatives of 1-(β-d-Ribofuranosyl)-4-quinolone led to the discovery of novel inhibitors, with compound 2a exhibiting superior inhibitory activity (Ki = 23.37 ± 3.64 µmol/L) compared to the employed model inhibitor. Docking and Molecular Dynamics studies provided crucial insights into inhibitor interactions at the enzyme active site, offering valuable information for developing new LdNH inhibitors. Therefore, this study presents a novel screening assay and contributes to the development of potent LdNH inhibitors.

Quantification of Arbortristoside-A isolated from Nyctanthes arbor-tristis using HPLC: Method development and pharmaceutical applications

Arbortristoside-A (Arbor-A) is a naturally occurring iridoid glycoside and herbal-based lead molecule with proven medicinal potential. Aiming at the development of an efficient analytical tool for the quantification of Arbor-A in pharmaceutical dosage forms, in the presented work, we developed an economical, fast, and sensitive RP-HPLC-UV method and validated the procedure as per the ICH guidelines, Q2(R1). The chromatographic separation was accomplished under the optimised experimental conditions using an HPLC system with an LC-2010 autosampler, a PDA detector, and a Phenomenex C18 column with the mobile phase composed of a 70:30 (v/v) water-acetonitrile mixture eluting isocratically at a flow rate of 1 mL/min at ambient temperature, and UV detection at 310 nm. Arbor-A showed a sharp peak at the retention time of 5.60 min and exhibited linearity (R2 = 0.9988) with LOD and LOQ of 0.50 μg/mL and 1.50 μg/mL, respectively. The accuracy of the method was 98.33-101.36 % with acceptable intra-day and inter-day precisions as well as robustness (<2% RSD). To ratify the applicability of the presented approach in emerging pharmaceuticals, a nanoformulation loaded with Arbor-A was designed and analysed utilising the provided methodology. The method has also enabled to determine the degradation kinetics of Arbor-A under stress conditions, etcetera, employing forced degradation and short term stability studies.

Kaurane-Type Diterpenoids as Potential Inhibitors of Dihydrofolate Reductase-Thymidylate Synthase in New World Leishmania Species

The bifunctional enzyme Dihydrofolate reductase-thymidylate synthase (DHFR-TS) plays a crucial role in the survival of the Leishmania parasite, as folates are essential cofactors for purine and pyrimidine nucleotide biosynthesis. However, DHFR inhibitors are largely ineffective in controlling trypanosomatid infections, largely due to the presence of Pteridine reductase 1 (PTR1). Therefore, the search for structures with dual inhibitory activity against PTR1/DHFR-TS is crucial in the development of new anti-Leishmania chemotherapies. In this research, using the Leishmania major DHFR-TS recombinant protein, enzymatic inhibitory assays were performed on four kauranes and two derivatives that had been previously tested against LmPTR1. The structure 302 (6.3 µM) and its derivative 302a (4.5 µM) showed the lowest IC50 values among the evaluated molecules. To evaluate the mechanism of action of these structures, molecular docking calculations and molecular dynamics simulations were performed using a DHFR-TS hybrid model. Results showed that hydrogen bond interactions are critical for the inhibitory activity against LmDHFR-TS, as well as the presence of the p-hydroxyl group of the phenylpropanoid moiety of 302a. Finally, additional computational studies were performed on DHFR-TS structures from Leishmania species that cause cutaneous and mucocutaneous leishmaniasis in the New World (L. braziliensis, L. panamensis, and L. amazonensis) to explore the targeting potential of these kauranes in these species. It was demonstrated that structures 302 and 302a are multi-Leishmania species compounds with dual DHFR-TS/PTR1 inhibitory activity.