Abstract 1792: Synthetic lethal vulnerabilities stemming from inhibition of one carbon metabolism in anaplastic thyroid cancer
Authors: Forrest Alexander , Ahsan Anil , Cristofano Antonio Di 
Published: March 2024

Abstract
Reprogramming of metabolic processes by tumor cells is essential to cope with their increased proliferative activity, and with the challenges of the unique microenvironment they inhabit. These metabolic alterations are attractive targets to design novel therapeutic approaches.The most aggressive subtype of thyroid cancer, Anaplastic Thyroid Cancer (ATC), is often unresectable at presentation, highly resistant to therapy and usually lethal. We have recently discovered that ATCs overexpress several genes encoding enzymes involved in one-carbon metabolism (1C-Met), which utilizes serine and dietary folates to produce glycine and tetrahydrofolate-bound one-carbon units, required for nucleotide biosynthesis and for NADPH and glutathione (GSH) production. We have shown that i) the increased activity of the 1C-Met pathway supports the high purine demand of ATC; ii) inhibition of 1C-Met impairs tumor growth in vitro and in vivo, leading to growth arrest; iii) inhibition of 1C-Met renders thyroid cancer cells glycine-auxotroph.We now demonstrate that the profound addiction of ATC cells to 1C-Met creates a series of targetable vulnerabilities that can be harnessed to induce massive ATC cell death.Our new data demonstrate that:1- The purine depletion consequent impaired 1C-Met induces replicative stress and triggers the DNA Damage Response (DDR). Activation of DDR, coupled with the absence of functional TP53 in the vast majority of ATCs, leads to synthetic lethality between inhibition of 1C-Met and G2/M checkpoint kinases.2- Inhibition of 1C-Met in ATC cells generates an absolute dependence on extracellular glycine uptake. We have identified and validated the main glycine transporter(s) in ATC cells and show that inhibition of 1C-Met is synthetic lethal with inhibition of glycine uptake.3- Impaired 1C-Met leads to increased oxidative stress and decrease of NADPH and glutathione levels. These alterations create a synthetic lethality relationship with the glutathione-depleting activity of PRIMA-1 (APR246), a small molecule originally identified as a compound restoring mutant p53 conformation and function, but later shown to be converted within cells into the reactive electrophile methylene quinuclidinone, which acts in a p53-independent manner through a variety of mechanisms, including reduction of cellular GSH levels.Our data shed light on the molecular consequences of 1C-Met upregulation in ATC and support the efficacy of novel rationally designed therapeutic approaches with curative intent not only for ATC, but also for other aggressive, dedifferentiated solid tumors.
Citation Format: Alexander Forrest, Anil Ahsan, Antonio Di Cristofano. Synthetic lethal vulnerabilities stemming from inhibition of one carbon metabolism in anaplastic thyroid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1792.