Forward genetic screening in engineered colorectal cancer organoids identifies regulators of metastasis.

Metastatic outgrowth requires that cancer cells delaminate from the primary tumor, intravasate, survive in circulation, extravasate, migrate to, and proliferate at a distal site. Recurrent genetic drivers of metastasis remain elusive, suggesting that unlike the early steps of oncogenesis, metastasis drivers may be variable. We develop a framework for identifying metastasis regulators using CRISPR/Cas9-based screening in a genetically defined organoid model of colorectal adenocarcinoma. We conduct in vitro screens for invasion and migration alongside orthotopic, in vivo screens for gain of metastasis in a syngeneic mouse model. We identify CTNNA1 and BCL2L13 as bona fide metastasis-specific suppressors which do not confer any selective advantage in primary tumors. CTNNA1 loss promotes cell invasion and migration, and BCL2L13 loss promotes anchorage-independent survival and non-cell-autonomous changes to macrophage polarization. This study demonstrates proof of principle that large-scale genetic screening can be performed in tumor-organoid models in vivo and identifies novel regulators of metastasis.