Autophagy-Dependent Metabolic Reprogramming Sensitizes TSC2-Deficient Cells to the Antimetabolite 6-Aminonicotinamide

Abstract

The mammalian target of rapamycin complex 1 (mTORC1) is hyperactive in many human cancers and in tuberous sclerosis complex (TSC). Autophagy, a key mTORC1 targeted process, is a critical determinant of metabolic homeostasis. Metabolomic profiling was performed to elucidate the cellular consequences of autophagy dysregulation under conditions of hyperactive mTORC1. It was discovered that TSC2-null cells have distinctive autophagy-dependent pentose phosphate pathway (PPP) alterations. This was accompanied by enhanced glucose uptake and utilization, decreased mitochondrial oxygen consumption, and increased mitochondrial ROS production. Importantly, these findings revealed that the PPP is a key autophagy-dependent compensatory metabolic mechanism. Furthermore, PPP inhibition with 6-aminonicotinamide (6-AN) in combination with autophagy inhibition suppressed proliferation and prompted the activation of NF-kB and CASP1 in TSC2-deficient, but not TSC2-proficient cells. These data demonstrate that TSC2-deficient cells can be therapeutically targeted, without mTORC1 inhibitors, by focusing on their metabolic vulnerabilities. Implications: This study provides proof-of-concept that therapeutic targeting of diseases with hyperactive mTORC1 can be achieved without the application of mTORC1 inhibitors.

Rapamycin reversal of VEGF-C–driven lymphatic anomalies in the respiratory tract

“…daily) (23)(24)(25); (d) autophagy inhibitor chloroquine (50 mg/kg i.p. daily) (18,26); (e) antiinflammatory steroid dexamethasone (1 or 10 mg/kg i.p. daily) (13,19), or (f) mTOR inhibitor rapamycin (0.5 to 20 mg/kg i.p.…”

“…Our rationale for comparing the efficacy of six therapeutic strategies for reversing established lymphangiectasia was based on published reports of their use in prevention or treatment of lymphatic malformations, hemangiomas, and related conditions (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). Inhibition of VEGFR-2 and VEGFR-3 signaling by function-blocking antibodies prevents lymphatic growth in inflammation and in CCSP/VEGF-C mice (6,13).…”

“…Because activation of autophagy promotes cell survival (18,26), we reasoned that inhibition of autophagy could impair survival of abnormal lymphatic endothelial cells. However, chloroquine did not reverse lymphangiectasia in our model.…”

Tuberous Sclerosis Complex 2 Loss Increases Lysophosphatidylcholine Synthesis in Lymphangioleiomyomatosis

“…mTORC1 is a master regulator of cell growth, proliferation, and metabolism (5)(6)(7)(8)(9)(10)(11)(12). A downstream effector of mTORC1, the sterol regulatory elementbinding protein (SREBP), regulates the transcription of glucose metabolism and de novo fatty acid synthesis enzymes (8,12,13).…”

Towards personalised therapy for lymphangioleiomyomatosis: lessons from cancer

“…The hypothesis that the combination of mTORC1 inhibition plus autophagy inhibition has clinical benefit in LAM is currently being investigated in a phase I clinical trial, the SAIL (Sirolimus and Autophagy Inhibition in LAM) trial. Intriguingly, autophagy inhibition in TSC2-deficient cells leads to dependence on the pentose phosphate pathway, and the combination of chloroquine (to inhibit autophagy) and 6-aminonicotinamide (an antimetabolite that inhibits the pentose phosphate pathway) selectively inhibits the growth of TSC2-deficient but not TSC2-expressing cells [14].…”