Antituberculosis and Antiproliferative Activities of the Extracts and Tetrahydrobisbenzylisoquinoline Alkaloids from Phaeanthus ophthalmicus: In Vitro and In Silico Investigations

Abstract

Tuberculosis (TB) and cancer are among the maladies with high morbidity and mortality rates to date. This prompted the utilization of natural products in the discovery and development of new anti-TB and anticancer derivatives. In this study, we explored the antitubercular and antiproliferative activities of extracts and tetrahydrobisbenzylisoquinoline alkaloids tetrandrine (1) and limacusine (2) from the Philippine medicinal plant Phaeanthus ophthalmicus. Antitubercular evaluation using colorimetric MABA (microplate Alamar blue assay) assays revealed antitubercular activities of the extracts and fractions [minimum inhibitory concentration (MIC) = 15.6 to < 64 μg/mL]. Among the two isolated alkaloids, limacusine (2) exhibited inhibitory activity against Mycobacterium tuberculosis (MIC = 42.6 μg/ml). In addition, CellTiter-Blue cell viability assay showed antiproliferative activity for limacusine (2) against K-562. Both tetrahydrobisbenzylisoquinoline alkaloids exhibited cytotoxicity on HeLa cells. To probe the binding mechanisms of 1 and 2 against putative protein targets, molecular docking simulations were carried out. Limacusine (2) showed high binding propensities to mycobacterial enzymes ATP-dependent murE ligase and enoyl acyl carrier protein reductase, thus illustrating possibilities of cell wall and mycolic biosynthesis inhibitory mechanisms, respectively. High binding affinity was also observed in 2 vs. FLT3, a protein target implicated in myeloid leukemia cell proliferation. Additionally, the limacusine-InhA and limacusine-FLT3 complexes were found to be dynamically stable as per molecular dynamics (MD) simulations. The results of in vitro experiments and molecular docking studies suggest tetrahydrobisbenzylisoquinoline alkaloids from P. ophthalmicus, especially limacusine (2), as promising natural products against TB and myeloid leukemia.