SummaryBackgroundMetastasis is one of the most lethal hallmarks of esophageal squamous cell carcinoma (ESCC), yet the mechanisms remain unclear due to a lack of reliable experimental models and systematic identification of key drivers. There is urgent need to develop useful therapies for this lethal disease.MethodsA genome-wide CRISPR/Cas9 screening, in combination with gene profiling of highly invasive and metastatic ESCC sublines, as well as PDX models, was performed to identify key regulators of cancer metastasis. The Gain- and loss-of-function experiments were taken to examine gene function. Protein interactome, RNA-seq, and whole genome methylation sequencing were used to investigate gene regulation and molecular mechanisms. Clinical significance was analyzed in tumor tissue microarray and TCGA databases. Homology modeling, modified ELISA, surface plasmon resonance and functional assays were performed to identify lead compound which targets MEST to suppress cancer metastasis.FindingsHigh MEST expression was associated with poor patient survival and promoted cancer invasion and metastasis in ESCC. Mechanistically, MEST activates SRCIN1/RASAL1-ERK-snail signaling by interacting with PURA. miR-449a was identified as a direct regulator of MEST, and hypermethylation of its promoter led to MEST upregulation, whereas systemically delivered miR-449a mimic could suppress tumor metastasis without overt toxicity. Furthermore, molecular docking and computational screening in a small-molecule library of 1,500,000 compounds and functional assays showed that G699-0288 targets the MEST-PURA interaction and significantly inhibits cancer metastasis.InterpretationWe identified the MEST-PURA-SRCIN1/RASAL1-ERK-snail signaling cascade as an important mechanism underlying cancer metastasis. Blockade of MEST-PURA interaction has therapeutic potential in management of cancer metastasis.Funding: This work was supported by10.13039/501100012166National Key Research and Development Program of China(2021YFC2501000, 2021YFC2501900, 2017YFA0505100);10.13039/501100001809National Natural Science Foundation of China(31961160727, 82073196, 81973339, 81803551);NSFC/RGC Joint Research Scheme(N_HKU727/19);10.13039/501100003453Natural Science Foundation of Guangdong Province(2021A1515011158, 2021A0505030035);Key Laboratory of Guangdong Higher Education Institutes of China(2021KSYS009).