Abstract 5398: Inhibition of PHGDH suppresses mTOR signaling and metabolic reprogramming in TSC2-deficient lymphangioleiomyomatosis cells

Abstract Lymphangioleiomyomatosis (LAM) is a rare, progressive neoplastic disease primarily affecting women, characterized by TSC1/2 mutations’ driven mTORC1 hyperactivation and the proliferation of abnormal smooth muscle-like cells within the lungs and lymphatics. Despite rapalogs ability to stabilize lung function and limit LAM tumorigenesis, they are cytostatic and tumors regrow post treatment cessation. As such, with mTORC1 being nutrient sensitive, it is of note that understanding and targeting metabolic vulnerabilities in the disease could induce LAM tumor cell death and limit associated lesions. Emerging evidence suggests that serine and the serine biosynthesis enzyme, PHGDH (phosphoglycerate dehydrogenase), may support mTOR-driven anabolic processes in LAM. This study investigated the effects of PHGDH inhibition on mTOR signaling, cell survival, mitochondrial function, and metabolic reprogramming in TSC2-deficient LAM cells. PHGDH expression was evaluated in human LAM lung tissue and nodules using immunohistochemical staining. In HPLM media, TSC2-deficient LAM (621-101) and their control TSC2-add back (621-103) cells were treated with a selective PHGDH inhibitor. mTOR, S6, and their phosphorylated levels were measured via Western blot, and autophagic flux was monitored by immunofluorescence staining targeting LC3-II expression. Mitochondrial membrane potential and biogenesis were assessed using TMRE staining and Western blot targeting PGC-1a and TFAM. Additionally, the effect of PHGDH on LAM cell growth and in metabolic reprogramming in LAM cells was analyzed respectively using CCK-8 and by examining the expression of key Warburg effect and anabolic synthesis markers such as G6PD and PKM2. PHGDH was highly expressed in LAM lung tissues and nodules, implicating its role in LAM progression. PHGDH inhibition in TSC2-deficient LAM cells significantly reduced mTOR, ATF4 and S6 ribosomal protein phosphorylation, suppressed mitochondrial membrane potential, and decreased mitochondrial biogenesis by inhibiting PGC-1a and TFAM protein levels. Furthermore, PHGDH inhibition induced RB1 phosphorylation with a reduction in E2F1 alongside total RB1 protein expression inhibition while, with rapamycin, upregulated autophagy, as indicated by increased LC3-II expression in autophagic flux quantification. This study, thus, discovers a significant LAM cell growth and Warburg effect inhibition by a downregulated G6PD and PKM2 protein expression post PHGDH inhibition. These results suggest that PHGDH supports mTOR-driven metabolic reprogramming in LAM. Targeting PHGDH significantly reduces mTOR signaling, mitochondrial function, and impairs glycolysis and PKM2 mediated Warburg effect in LAM cells. PHGDH inhibition may offer a novel therapeutic strategy to enhance mTORC1 inhibitors’ efficacy and overcome resistance in LAM management. Citation Format: Evans K. Abor, Erik Y. Zhang, Jane J. Yu. Inhibition of PHGDH suppresses mTOR signaling and metabolic reprogramming in TSC2-deficient lymphangioleiomyomatosis cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5398.