Abstract 3014: PHGDH- A therapeutic vulnerability in melanoma

Abstract Recurrently amplified oncogenes may represent melanoma vulnerabilities that can be exploited for therapy. The genomic locus containing the Phosphoglycerate Dehydrogenase (PHGDH) gene at chromosome 1p12 is frequently amplified in melanoma. PHGDH is the rate limiting enzyme that converts the glycolytic intermediate 3-Phospho Glycerate (3-PG) to serine through the serine synthesis pathway (SSP). Serine is utilized to make glycine, glutathione, one carbon metabolites, proteins and lipids. PHGDH inhibition suppresses proliferation of 1p12 amplified melanoma cells. However, the role of PHGDH in chromosome 1p12 non-amplified melanoma is poorly understood. We observed that 1p12 non-amplified melanoma cell lines have enhanced expression of the SSP enzymes as compared to melanocytes cultured in tetradecanoyl-phorbol acetate (TPA, a growth factor that stimulates MAPK pathway). Moreover, TPA starvation in melanocytes increased PHGDH expression. This led us to hypothesize that activation of oncogenic MAPK signaling leads to high expression of PHGDH which can serve as therapeutic vulnerability in melanomagenesis. Acute expression of oncogenic BRAFV600E in melanocytes resulted in upregulation of SSP enzymes, while treatment of melanoma cells with either BRAF or MEK inhibitor resulted in downregulation of SSP enzymes. We confirmed that PHGDH is regulated by BRAF-ERK-mTOR axis. Downregulation of PHGDH in 1p12 non-amplified melanoma cell lines decreased their cell proliferation and colony formation ability in vitro. We also observed that Phgdh knockdown in a BrafV600E/WT and Pten-/- (BPP) melanoma mouse model significantly increased survival. Furthermore, serine-glycine starvation (external source of Serine-glycine) in BPP chimeras did not affect the survival of these mice while on the other end, it suppressed the growth of the xenograft tumors injected in the NSG mice, which warrants further investigation. These results suggest the importance of PHGDH for melanoma cell proliferation and tumor growth irrespective of its amplification status. The exact mechanism of PHGDH regulation by BRAFV600E and the therapeutic effect of PHGDH inhibition in melanoma initiation and progression are the focus of our studies. Citation Format: Neel N. Jasani, Florian Karreth. PHGDH- A therapeutic vulnerability in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3014.