Resveratrol prevents rapamycin-induced upregulation of autophagy and selectively induces apoptosis in TSC2-deficient cells

Abstract

The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway is hyperactivated in a variety of cancers and disorders, including lymphangioleiomyomatosis (LAM) and tuberous sclerosis complex (TSC), which are characterized by mutations in tumor suppressors TSC1 or TSC2. The concern with the use of mTORC1 inhibitors, such as rapamycin or its analogs (rapalogs), is that they cause upregulation of autophagy and suppress the negative feedback loop to Akt, which promotes cell survival, causing the therapy to be only partially effective, and relapse occurs upon cessation of treatment. In this study, we investigate the use of rapamycin in combination with resveratrol, a naturally occurring polyphenol, in TSC2-deficient cells. We tested whether such combination would prevent rapamycin-induced upregulation of autophagy and shift the cell fate toward apoptosis. We found that this combination treatment blocked rapamycin-induced upregulation of autophagy and restored inhibition of Akt. Interestingly, the combination of rapamycin and resveratrol selectively promoted apoptosis of TSC2-deficient cells. Thus, the addition of resveratrol to rapamycin treatment may be a promising option for selective and targeted therapy for diseases with TSC loss and mTORC1 hyperactivation.

Effects of Combining Rapamycin and Resveratrol on Apoptosis and Growth of TSC2-Deficient Xenograft Tumors

“…In this study, we observed that, in TSC2-null cells, the combination therapy prevented rapamycininduced up-regulation of Akt while maintaining inhibition of S6K1 signaling, indicating that this combination therapy can counter hyperactivation of mTORC1 signaling caused by the loss of TSC2. Additionally, resveratrol treatment was able to prevent rapamycin-induced upregulation of autophagy, as evidenced by stabilization of p62, in accord with our previous findings (23). Interestingly, expression of survivin, an inhibitor of apoptosis in TSC2-null cells, was found to correlate with resistance to chemotherapeutic agents (36).…”

“…In addition, LAM cells seem to be dependent on even the low levels of autophagy because further inhibition of autophagy induces cell death (21). Our previous studies showed that combination therapy of rapamycin with resveratrol was able to block autophagy and induce apoptosis in TSC2-null cells and in cells with mTORC1 pathway hyperactivation (22,23). In this study, we observed that, in TSC2-null cells, the combination therapy prevented rapamycininduced up-regulation of Akt while maintaining inhibition of S6K1 signaling, indicating that this combination therapy can counter hyperactivation of mTORC1 signaling caused by the loss of TSC2.…”

“…Five weeks after cell inoculation, mice bearing subcutaneous tumors were randomized into four groups: vehicle control (n = 5; 10% ethanol in 10% 2-hydroxypropylb-cyclodextrin, 200 ml/d, orally), rapamycin (n = 4; 3 mg/kg/d, intraperitoneally), resveratrol (n = 5; 200 mg/kg/d in 10% 2-hydroxypropyl-b-cyclodextrin, orally), and rapamycin plus resveratrol (n = 5; 3 mg/kg/d, intraperitoneally and 200 mg/kg/d, orally). The concentrations were selected based on effective doses as previously determined (23). Animal toxicity was analyzed using body weight as previously described (21).…”

“…We have previously demonstrated that the autophagy inhibitor resveratrol synergized with rapamycin in suppressing PI3K/mTORC1 activity, preventing rapamycin-induced autophagy and promoting death of TSC2-deficient cells in vitro (23). In this study we investigated whether the combination of rapamycin and resveratrol is effective in reducing TSC2-deficient tumor burden in vivo, thereby increasing the clinical usefulness of rapamycin therapy.…”

“…Thus, rapamycin causes reactivation of autophagy, which paradoxically allows LAM cells to survive. Therefore, the use of autophagy inhibitors in addition to rapamycin treatment could cause LAM cells to undergo apoptosis (22,23).…”