Endoplasmic reticulum stress and cell death in mTORC1‐overactive cells is induced by nelfinavir and enhanced by chloroquine

Abstract

Inappropriate activation of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is common in cancer and has many cellular consequences including elevated endoplasmic reticulum (ER) stress. Cells employ autophagy as a critical compensatory survival mechanism during ER stress. This study utilised drug-induced ER stress through nelfinavir in order to examine ER stress tolerance in cell lines with hyper-active mTORC1 signalling. Our initial findings in wild type cells showed nelfinavir inhibited mTORC1 signalling and upregulated autophagy, as determined by decreased rpS6 and S6K1 phosphorylation, and SQTSM1 protein expression, respectively. Contrastingly, cells with hyper-active mTORC1 displayed basally elevated levels of ER stress which was greatly exaggerated following nelfinavir treatment, seen through increased CHOP mRNA and XBP1 splicing. To further enhance the effects of nelfinavir, we introduced chloroquine as an autophagy inhibitor. Combination of nelfinavir and chloroquine significantly increased ER stress and caused selective cell death in multiple cell line models with hyper-active mTORC1, whilst control cells with normalised mTORC1 signalling tolerated treatment. By comparing chloroquine to other autophagy inhibitors, we uncovered that selective toxicity invoked by chloroquine was independent of autophagy inhibition yet entrapment of chloroquine to acidified lysosomal/endosomal compartments was necessary for cytotoxicity. Our research demonstrates that combination of nelfinavir and chloroquine has therapeutic potential for treatment of mTORC1-driven tumours.

The HIV protease inhibitor, nelfinavir, as a novel therapeutic approach for the treatment of refractory pediatric leukemia

“…The autophagy induction is further characterized by the application of autophagy inhibitors, 3-methyladenine and thapsigargin, which greatly reduce cell survival when combined with NFV (Figure 3C–H). This is consistent with previous findings where, when similar inhibitors resulted in lethal or near-lethal cellular toxicity 40. When the cancer cells’ homeostatic mechanisms are overwhelmed, cells undergo apoptosis.…”

Loss of tuberous sclerosis complex 2 sensitizes tumors to nelfinavir−bortezomib therapy to intensify endoplasmic reticulum stress-induced cell death

“…To stratify therapy, we wanted to determine whether inactivation of TSC2, a key regulator of mTORC1, would sensitize cell and tumor models to combined nelfinavir and bortezomib treatment. Previously we showed that combined treatment with nelfinavir and the autophagy inhibitor, chloroquine, was sufficient to kill cancer cell lines with a high level of mTORC1 [15]. In this study, we reveal that both in vitro and in vivo mTORC1-hyperactive tumor models are sensitive to combined nelfinavir and bortezomib-induced cytotoxicity via ER stress, while normal cells tolerate this drug combination through intact compensatory mechanisms.…”

Mourning Dr. Alfred G. Knudson: the two‐hit hypothesis, tumor suppressor genes, and the tuberous sclerosis complex

“…Many other important phenomena downstream of mTORC1, such as autophagy and ER stress, have now been characterized . Pathways involved in those phenomena are already being exploited to develop new therapeutic targets and combination treatments with inhibitors of such pathways and rapalogs have been tested at the basic research level.…”