Flura-seq identifies organ-specific adaptations in metastasis-initiating cells

Metastasis-initiating cells dynamically adapt to the distinct microenvironments of different organs, but these early adaptations are poorly understood due to the limited sensitivity of in situ transcriptomics. We developed fluorouracil-labeled RNA sequencing (Flura-seq) for in situ analysis with unprecedented sensitivity. Flura-seq utilizes cytosine deaminase (CD) to convert fluorocytosine to fluorouracil, covalently labeling nascent RNA for purification and sequencing. Flura-seq revealed that breast cancer micrometastases in lung and brain exhibit unique, reversible gene signatures depending on the microenvironment. Specifically, the mitochondrial electron transport Complex I and the NRF2-driven antioxidant programs were induced in oxygen-rich pulmonary micrometastases, compared to mammary tumors or brain micrometastases. Loss of Complex I activity, and antioxidant supplementation potentiated pulmonary metastatic growth. We confirm lung metastasis-specific NRF2 overexpression in clinical samples, thus validating Flura-seq’s utility in identifying clinically actionable microenvironmental adaptations in early metastasis. The sensitivity, robustness and economy of Flura-seq are broadly applicable beyond cancer research. Examination of 5-FU labeled RNAs in cancer cells present in different organs