harmine and harmicine

The rise of the resistance of the malaria parasite to the currently approved therapy urges the discovery and development of new efficient agents. Previously we have demonstrated that harmicines, hybrid compounds composed from β-carboline alkaloid harmine and cinnamic acid derivatives, linked via either triazole or amide bond, exert significant antiplasmodial activity. In this paper, we report synthesis, antiplasmodial activity and cytotoxicity of expanded series of novel triazole- and amide-type harmicines. Structure-activity relationship analysis revealed that amide-type harmicines 27, prepared at N-9 of the β-carboline core, exhibit superior potency against both erythrocytic stage of P. falciparum and hepatic stages of P. berghei. Notably, harmicine 27a, m-(trifluoromethyl)cinnamic acid derivative, exhibited the most favourable selectivity index (SI = 1105). Molecular dynamics simulations revealed the ATP binding site of P. falciparum heat shock protein 90 as a druggable binding location, confirmed the usefulness of the harmine's N-9 substitution and identified favourable N-H … π interactions involving Lys45 and the aromatic phenyl unit in the attached cinnamic acid fragment as crucial for the enhanced biological activity. Thus, those compounds were identified as promising and valuable leads for further derivatization in the search of novel, more efficient antiplasmodial agents.

Topics: Amides; Antimalarials; Binding Sites; Erythrocytes; HSP90 Heat-Shock Proteins; Humans; Indole Alkaloids; Life Cycle Stages; Molecular Dynamics Simulation; Plasmodium berghei; Plasmodium falciparum; Protozoan Proteins; Structure-Activity Relationship; Triazoles

Harmicines constitute novel hybrid compounds that combine two agents with reported antiplasmodial properties, namely β-carboline harmine and a cinnamic acid derivative (CAD). Cu(I) catalyzed azide-alkyne cycloaddition was employed for the preparation of three classes of hybrid molecules: N-harmicines 6a-i, O-harmicines 7a-i and N,O-bis-harmicines 8a-g,i. In vitro antiplasmodial activities of harmicines against the erythrocytic stage of Plasmodium falciparum (chloroquine-sensitive Pf3D7 and chloroquine-resistant PfDd2 strains) and hepatic stage of P. berghei, as well as cytotoxicity against human liver hepatocellular carcinoma cell line (HepG2), were evaluated. Remarkably, most of the compounds exerted significant activities against both stages of the Plasmodium life cycle. The conjugation of various CADs to harmine resulted in the increased antiplasmodial activity relative to harmine. In general, O-harmicines 7 exhibited the highest activity against the erythrocytic stage of both P. falciparum strains, whereas N,O-bis harmicines 8 showed the most pronounced activity against P. berghei hepatic stages. For the latter compound, molecular dynamics simulations confirmed binding within the ATP binding site of PfHsp90, while the weaker binders, namely 6b and harmine, were found to be positioned away from this structural element. In addition, decomposition of the computed binding free energies into contributions from individual residues suggested guidelines for further derivatization of harmine towards more efficient compounds. Cytotoxicity screening revealed N-harmicines 6 as the least, and O-harmicines 7 as the most toxic compounds. Harmicines 6g, 8b and 6d exerted the most selective action towards Plasmodium over human cells, respectively. These results establish harmicines as hits for future optimisation and development of novel antiplasmodial agents.

Topics: Antimalarials; Cinnamates; Dose-Response Relationship, Drug; Harmine; Indole Alkaloids; Molecular Dynamics Simulation; Molecular Structure; Parasitic Sensitivity Tests; Plasmodium berghei; Plasmodium falciparum; Structure-Activity Relationship