P18.21.A MODULATION OF THE L-CYSTEINE/H₂S/L-SERINE/S1P AXIS IN GLIOBLASTOMA: IMPLICATIONS OF HYDROGEN SULFIDE IN TUMOR PROGRESSION

Abstract BACKGROUND Sphingosine-1-phosphate (S1P) is a key signaling molecule involved in the progression of several cancers, including glioblastoma multiforme (GBM), the most aggressive primary brain tumor. Recent findings suggest that S1P originates from L-serine, a product of the transsulfuration pathway during the cystathionine beta-synthase (CBS)-mediated conversion of L-cysteine to hydrogen sulfide (H₂S), a gaseous neurotransmitter with complex and still-debated roles in GBM development and progression. In this context this project aims to define the role of transsulfuration pathway-derived H2S and its interplay with S1P signaling in GBM, using in vivo model. MATERIAL AND METHODS We performed a xenograft model of GBM to investigate the modulation of the L-cysteine/H2S/L-serine/S1P axis. The expression of key enzymes involved in this pathway—CBS, 3-mercaptopyruvate sulfurtransferase (3-MST), serine palmitoyltransferase (SPT), as well as neuronal and inducible nitric oxide synthases (nNOS and iNOS)—were assessed by immunohistochemistry and RT-PCR. Concurrently, levels of H₂S, S1P, and nitric oxide (NO) were quantified in tumor tissues and compared to controls. RESULTS GBM xenografts showed a marked upregulation of CBS and 3-MST expression compared to control tissues, indicating an active transsulfuration pathway. In contrast, CSE expression remained unchanged, suggesting a specific enzymatic signature associated with GBM. Notably, SPT, the key enzyme initiating S1P biosynthesis, was significantly elevated, along with robust increases in both nNOS and iNOS expression. Biochemical analysis confirmed a substantial rise in intratumoral levels of H₂S, S1P, and NO, underscoring the coordinated activation of this metabolic axis. These results collectively point to a hyperactivated L-cysteine/H₂S/L-serine/S1P pathway in GBM, potentially driving tumor growth, invasiveness, and microenvironmental remodeling. CONCLUSION These findings highlight a potential mechanistic link between H₂S signaling and S1P production in GBM, mediated through the L-cysteine/H₂S/L-serine/S1P axis. This pathway may represent a novel target for therapeutic intervention aimed at modulating GBM progression and influencing both the tumor microenvironment and blood-brain barrier dynamics.