A small molecule protects mitochondrial integrity by inhibiting mTOR activity

Abstract

Significance Mitochondrial damage and ensuring cell death underline many neurodegenerative diseases such as Parkinson’s disease and stroke. Using cellular assays that mimic the activation of mitochondrial apoptosis pathway, we screened out a small molecule that blocks apoptosis by protecting mitochondrial integrity and function. Specifically, Compound R6 prevents apoptosis by activating autophagy through mTOR inhibition; it also confers significant, dose-dependent neuroprotective effects in a rat cerebral ischemia/reperfusion injury model. Given increasing appreciation that mitochondrial damage affects the etiology of several common and devastating neurodegenerative diseases, Compound R6’s ability to pass the blood−brain barrier and confer strong antiapoptotic effects should encourage preclinical and medicinal chemistry research efforts, perhaps even extending—as with other known mTOR inhibitors—into evaluation of possible antiaging effects. Apoptosis activation by cytochrome c release from mitochondria to cytosol is a normal cellular response to mitochondrial damage. Using cellular apoptosis assay, we have found small-molecule apoptosis inhibitors that protect cells from mitochondrial damage. Previously, we reported the discovery of a small molecule, Compound A, which blocks dopaminergic neuron death in a rat model of Parkinson’s disease through targeting succinate dehydrogenase subunit B (SDHB) of complex II to protect the integrity of the mitochondrial respiratory chain. Here, we report a small molecule, Compound R6, which saves cells from apoptosis via mammalian target of rapamycin (mTOR)-mediated induction of autophagy. Additionally, we show that Compound R6 protects mitochondrial integrity and respiration after induction of the intrinsic apoptosis pathway. Encouragingly, and supporting the potential further application of Compound R6 as a tool for basic and medicinal research, a pharmacokinetics (PK) profiling study showed that Compound R6 is metabolically stable and can pass the blood−brain barrier. Moreover, Compound R6 accumulates in the brain of test animals via intravenous and intraperitoneal administration. Finally, we found that Compound R6 confers significant neuroprotective effects on a rat cerebral ischemia/reperfusion model, demonstrating its potential as a promising drug candidate for neurodegenerative diseases.