BBOX1 Is a Metabolic Checkpoint That Mediates Metastatic Cancer Cell Evasion from Immunosurveillance by NK Cells

Abstract Primary tumors constantly shed cancer cells into the circulation, yet only a fraction of these cells manage to give rise to metastatic tumors. Successful metastatic seeding and growth seem to depend on metabolic changes within cancer cells. In this study, using a metabolism-focused CRISPR screen in a spontaneous metastasis model, we found that the expression of the enzyme γ-butyrobetaine hydroxylase 1 (BBOX1) in a subpopulation of tumor cells in various carcinomas enables immune evasion. The metabolite carnitine produced by BBOX1 inhibited the small GTPase RhoA in NK cells, preventing immunologic synapse formation and thereby protecting metastatic cells. Loss of BBOX1 in tumor cells promoted their destruction by NK cells in vitro and improved the efficacy of NK cell adoptive transfer therapy in vivo. These findings illustrate how BBOX1-positive tumor cells hijack carnitine production to evade immunosurveillance during metastasis and propose BBOX1 as a potential metabolic checkpoint for antimetastatic strategies. Significance: BBOX1-generated carnitine enables metastatic cell immune evasion by suppressing NK cell immunological synapse formation and cytotoxicity, providing a targetable metabolic vulnerability in metastasis and redefining carnitine as an immunosuppressive metabolite.