Inhibition of the mechanistic Target Of Rapamycin (mTOR) signaling pathway by the FDA-approved drug rapamycin promotes lifespan in numerous model organisms and delays age-related disease in mice. However, the utilization of rapamycin as a therapy for age-related diseases will likely prove challenging due to the serious metabolic and immunological side effects of rapamycin in humans. While the beneficial effects of rapamycin are largely mediated by inhibition of mTOR complex 1 (mTORC1), which is acutely sensitive to rapamycin, many of the negative side effects are mediated by inhibition of mTOR complex 2 (mTORC2), which is chronically sensitive to rapamycin. We hypothesized that a more relaxed rapamycin dosing schedule or the use of rapamycin analogs might specifically target mTORC1, reducing mTORC2 mediated side effects and still promoting longevity. Here, we identified an intermittent rapamycin treatment regimen – 2 mg/kg administered every five days – with reduced impact on glucose metabolism and the immune system compared to daily rapamycin treatment. Further, we show that the FDA-approved rapamycin analogs everolimus and temsirolimus efficiently inhibit mTORC1 signaling while having a reduced impact on glucose metabolism compared to rapamycin. Finally, we find that intermittent rapamycin administration extends the lifespan of mice even to a greater degree than continuous fed rapamycin.
First, we tested in C57BL/6J mice, an inbred mouse line of which of which the lifespan can be extended by rapamycin, several intermittent dosing regimens and determined that IP administration of rapamycin once every 5 days was the most intensive dosing routing with no significant impact on glucose tolerance. We analyzed the impact of intermittent rapamycin administration on glucose homeostasis and determined that compared to daily treatment, intermittent rapamycin has reduced pyruvate intolerance (impaired gluconeogensis regualtion). Surprisingly, intermittent rapamycin resulted in similar fasting plasma insulin, insulin sensitivity, and ex vivo insulin secretion than vehicle treatment. We also determined that intermittent rapamycin has reduced impact on the immune system compared to daily rapamycin, as indicated by spleen T regulatory cells percent. We analyzed the effect of intermittent rapamycin on mTOR signaling and observed a sustained impact of this dosing routine on adipose, but not muscle, mTORC1 downstream marker S6 (S240/244) phosphorylation after 5 days of treatment. Remarkable, we observed no impact of intermittent rapamycin on the mTORC2 substrate Akt (S473) phosphorylation on either tissue. We compared the impact of daily treatment with equimolar doses of the FDA-approved rapamycin analogs everolimus and temsirolimus on glucose homeostasis. Despite both analogs had similar reduction on muscle mTORC1 signaling than rapamycin, they had improved glucose tolerance. In addition, everolimus had improved pyruvate tolerance, reduced testis weight loss, and reduced inhibition of mTORC2 signaling in muscle. Our results suggest that many of the negative side effects of rapamycin treatment can be mitigated through intermittent dosing or the use of rapamycin analogs, yet still extend lifespan. Therefore, we analyzed the impact of every 5 days rapamycin administration on longevity when treatment started at 20 months of age. Fascinatingly, intermittent rapamycin extended median and maximum lifespan compared to vehicle treated mice, with minimum impact on metabolism.
Our work demonstrates that the anti-aging potential of rapamycin is separable from many of its negative side-effects, and suggests that carefully designed dosing regimens may permit the safer use of rapamycin and its analogs for the treatment of age-related diseases in humans.
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