Despite well-defined etiology, effective therapeutic options for TSC-associated tumors are limited mainly to invasive surgery and in the case of LAM to lung transplant, with no pharmaceutical treatment capable of inducing long-term remission of tumor growth ( 5–7).
In addition, sporadic forms of AML and LAM characterized by mutation in TSC1 or TSC2 genes may develop in patients who do not carry germline mutation in these genes ( 5). Clinical manifestation of TSC is development of tumors and neoplastic lesions in kidney, lung, brain, heart and skin, among which renal cell carcinoma (RCC), renal angiomyolipoma (AML), pulmonary lymphangioleiomyomatosis (LAM), and brain tumors constitute the most common cause of TSC-associated deaths ( 3–6). The incidence of TSC has been estimated as 1 in 6,000 persons worldwide, with the average age at diagnosis being 7.5 years ( 2, 3). Tuberous sclerosis complex (TSC) is an autosomal-dominant multiorgan disorder caused by a germline-inactivating mutation in the tumor suppressor genes TSC1 or TSC2 ( 1). Together, this study identifies a previously unrecognized novel regulated necrotic death pathway that involves mitochondrial homeostasis, is suppressed by the RIP1/RIP3/MLKL signaling in TSC-deficient cells, and could be a promising therapeutic target for TSC-associated tumors. Finally, supplementation with the mitochondrial metabolite α-ketoglutarate, whose synthesis is regulated by RIP1/RIP3/MLKL, rescues cells from the sensitizing effect of Nec-1 and NSA. Expression analysis demonstrated that RIP1, RIP3, and MLKL protein levels are elevated in cells with TSC2 deficiency, and their inactivation enhances mitochondrial dysfunction in a glutaminolysis-dependent and autophagy-independent manner.
Furthermore, blocking RIP1/RIP3/MLKL–dependent signaling using chemical inhibitors necrostatin-1 (Nec-1) and necrosulfonamide (NSA) synergizes with BSO and auranofin in killing TSC-deficient cells.
The current study shows that simultaneous inhibition of two major pathways regulating redox homeostasis using l-buthionine-sulfoximine (BSO, glutathione synthesis inhibitor) and auranofin (thioredoxin reductase inhibitor) induces oxidative burst, mitochondrial damage, and necrotic cell death in TSC-deficient cells in a highly synergistic and cell context–specific manner. Despite its oncogenic effect, cells with TSC deficiency were more sensitive to oxidative stress and dependent on mitochondrial metabolism, providing a rationale for a new therapeutic approach. It is caused by an inactivating mutation in tumor suppressor genes coding the TSC1/TSC2 complex, resulting in the hyperactivation of mTOR- and Raf/MEK/MAPK–dependent signaling that stimulates tumor cell proliferation and metastasis. Tuberous sclerosis complex (TSC) is a genetic multiorgan disorder characterized by the development of neoplastic lesions in kidney, lung, brain, heart, and skin.
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