Continuous administration of the mTORC1 inhibitor everolimus induces tolerance and decreases autophagy in mice

Background and PurposeEverolimus is an allosteric inhibitor of the mechanistic target of rapamycin complex 1 (mTORC1) widely known for its potent autophagy stimulating properties. Because everolimus shows poor solubility and stability in aqueous solutions, long-term in vivo administration in preclinical models is challenging. The aim of the present study was to evaluate the effects of short-term and long-term everolimus administration on mTORC1 inhibition and autophagy induction in mice. Experimental ApproachWe developed a vehicle in which everolimus was solubilized and stable at 37 degrees C for at least 1month. Using osmotic minipumps, GFP microtubule-associated protein light chain 3 transgenic mice were treated continuously either with vehicle or everolimus (1.5mgkg(-1) per day) for 3 or 28days. Alternatively, a regimen consisting of intermittent everolimus administration (every other day) for 56days by oral gavage was used. Autophagy markers and mTORC1 activation status were investigated in the liver. Key ResultsAs expected, everolimus inhibited mTORC1 and stimulated autophagy in the liver after 3days of treatment. However, continuous administration for 28days resulted in hyperactivation of the Akt1-mTORC1 pathway accompanied by a remarkable decrease in autophagy markers. Everolimus given intermittently for 56days partially rescued mTORC1 sensitivity to the drug but without inducing autophagy. The failure to induce autophagy following long-term everolimus administration was due to uncoupling of the mTORC1 substrate unc-51 like autophagy activating kinase 1. Conclusions and ImplicationsOur data encourage the use of intermittent everolimus regimens to prevent tolerance and to extend its activity.