Identification of metabolic alterations and vulnerabilities in senescent cancer cells

Cellular senescence is a tumor suppressive mechanism that leads to cell cycle arrest under stress conditions. A variety of cancer treatments lead to therapy-induced senescence (TIS), which has traditionally been considered irreversible and hence a positive outcome. However, senescent cells secrete cytokines that enhance inflammation and cancer progression; a phenomenon referred to as senescence-associated secretory phenotype (SASP). Furthermore, new evidence suggests mechanisms of senescence escape which could lead to relapse. Our research aims to identify cellular metabolic alterations associated with TIS which could be drug targeted. We used LC-MS based metabolomics and isotope tracing to characterize metabolic alterations in melanoma cells treated with clinically relevant therapeutic agents inducing TIS: Braf inhibitor Vemurafenib, the chemotherapeutic drug Cisplatin, and radiation. ^­Our analysis reveals major metabolic alterations in TIS related to amino acid and lipid metabolism associated with the SASP phenotype: Isotope tracing experiments revealed increase in the relative contribution of glucose versus glutamine-derived TCA cycle anaplerosis (supporting amino acid biosynthesis) via pyruvate carboxylase in all studied TIS models, versus in proliferating as well as serum starved quiescent cells. Additionally, metabolomics shows more than 100-fold increase in the intracellular concentration of phosphoethanolamine; and lipidomics reveals alterations in the balance between phosphatidylethanolamine and phosphatidycholine, in accordance with an expected change in membrane lipid composition to support the secretion of vesicles. Our research is expected to lead to the identification of induced dependence of senescent cells on specific metabolic enzymes that could be targeted for eliminating TIS cells and improve anticancer therapy.