Current oral medications for type 2 diabetes target a single main physiological mechanism. They either activate or inhibit receptors to enhance insulin sensitivity, increase insulin secretion, inhibit glucose absorption, or inhibit glucose production. In advanced stages, combination therapy may be required because of the limited efficacy of single-target drugs; however, medications are getting more costly, and there is also the risk of developing the combined side effects of each drug. Thus, identifying a multi-target drug, either plant-based or semi-synthetic, may be the best strategy to improve treatment efficacy. This study sees the potential of 3,083 Philippine phytochemicals as a source of natural inhibitors against four targets of diabetes: Protein-tyrosine phosphatase 1B (PTP1B), Dipeptidyl peptidase-4 (DPP-4), Sodium-glucose co-transporter 2 (SGLT-2), and Fructose 1,6-biphosphatase (FBPase). A wide array of computer-aided drug discovery techniques were employed to carry out the virtual screening process: ADMET profiling revealed 373 molecules with excellent bioavailability and toxicity properties; DFT optimization predicted their most accurate 3D structures; consensus docking identified the ten highest-scoring ligands per protein comparable to reference compounds' scores; molecular dynamics simulation elucidated the stability of the protein-ligand complexes trough RMSD, RMSF, and H-bond diagram analysis; and MM/PBSA energy calculations determined the binding affinity of the compounds against the four receptors and the key residues integral to binding. Through in silico methods, we have identified seven potential natural inhibitors against PTP1B, DPP-4, and FBPase, and ten against SGLT-2. Eight plants containing at least one natural inhibitor of each protein target were also identified (Eclipta prostata, Agave sisalana, Piper aduncum, Curculigo orchioides, Luffa cylindrica, Moringa oleifera, Alium cepa, and Helianthus annuus). It is recommended to investigate further the plants' potential to be transformed into a safe and scientifically validated multi-target drug to improve diabetes therapies.
In the first part of the study, phytosterols were found to primarily inhibit all four proteins. Stigmasterol and brassicasterol are potential inhibitors against PTP1B; campesterol against DPP-4; sitosterol, stigmasterol, and brassicasterol against SGLT-2; and campesterol and stigmasterol against FBPase. Since each protein is inhibited by at least one phytosterol, it is possible that a sterol or analog structure of a sterol will inhibit all four proteins. For this, we used the four phytosterols as parent compounds for creating 10,853 new sterol analogs. These analogs underwent the same virtual screening process employed in the first part of the study. Only 632 compounds with favorable ADMET properties underwent molecular docking, and the top ten ligands with the highest consolidated docking scores proceeded to the MD simulations and MM/PBSA calculations. Out of the ten candidates, eight sterol analogs demonstrated stable complex behaviors with all four protein targets and registered comparable binding affinity to the reference compounds (CID: 10905362, CID: 13831959, CID: 23724485, CID: 54307943, CID: 60030863, CID: 91041629, CID: 101306816, and CID:157570120). These semi-synthetic compounds are also recommended in the next stage of the drug discovery process to verify their viability as a multi-target drug against diabetes.