Probing the mechanism of SIRT1 activation by a 1,4-dihydropyridine.

The NAD+-dependent deacetylase SIRT1 plays important roles in several physiological processes such as transcription, genome stability, stress responses, and aging. Due to its diverse role in metabolisms, SIRT1 has emerged as a potential therapeutic target in many human disorders such as type II diabetes, cardiovascular and neurodegenerative diseases, and cancer. Recent studies have reported that modulation of SIRT1 activity by phenolic activators like resveratrol and some 1,4-dihydropyridines (1,4-DHPs) can inhibit tumor growth by promoting apoptosis in cancer cells. However, the mechanism of SIRT1 activation is still not clear. In this report, we have tried to elucidate the mechanism of SIRT1 activation from studies on its interaction with a synthetic 1,4-DHP derivative (DHP-8; 3,5-diethoxy carbonyl-4-(4-nitrophenyl)-2,6-dimethyl-1,4-dihydropyridine) using molecular modeling, docking, simulation, and free energy analyses. Owing to the absence of full-length human SIRT1 structure, multi-template based modeling approach was opted followed by docking of DHP-8 at its allosteric site. In presence of DHP-8, the overall conformation of SIRT1 was found to be more stable (especially at its substrate binding sites) with a large structural variation at its N-terminal domain while bound to substrate p53 or p53-W. Determination of the MM/PBSA free energy indicated that the binding of DHP-8 to SIRT1 significantly increased the binding affinity of SIRT1 to its substrate p53-W as well as to NAD+. Overall, this study depicts the atomistic detailed mechanism for the direct activation of SIRT1 by a 1,4-DHP. This would serve to develop new SIRT1 activators for future therapeutic perspectives.