Genome-wide in vivo CRISPR screen identifies CMTR2 as a potent suppressor of metastasis in triple-negative breast cancer.

AbstractTriple-negative breast cancer (TNBC) remains one of the most lethal breast cancer subtypes dueto its high metastatic potential and lack of targeted therapies. While oncogenic drivers of metastasishave been extensively characterized, metastasis suppressor genes (MSGs) in TNBC remain poorlyunderstood. Here, we performed an unbiased in vivo genome-wide CRISPR/Cas9 loss-of-functionscreen using a TNBC xenograft model to systematically identify regulators of metastaticprogression. The screen uncovered clinically relevant MSGs (VPS45, CMTR2, RBSN, and NF2),whose loss significantly enhanced lung metastasis. Functional and mechanistic validation revealedthat knockout of these genes promotes epithelial-to-mesenchymal transition, cell migration,invasion, intravasation, and angiogenesis, whereas CRISPR activation of their endogenouspromoters markedly suppressed metastatic dissemination in preclinical TNBC models. Multi-omicanalyses of patient datasets highlighted downregulation of these genes in primary breast tumors,particularly TNBC and showed consistent correlation with advanced stage and poor survival.Notably, CMTR2 loss induced profound intratumoral heterogeneity and vascular remodeling,highlighting its critical role in regulating tumor angiogenesis and circulating tumor celldissemination. Collectively, in this study, we identified a network of MSGs that constrainmetastatic progression in TNBC, underscoring the utility of in vivo CRISPR functional genomicsfor uncovering therapeutic vulnerabilities in aggressive breast cancers.