Adherent-suspension plasticity promotes the dissemination and colonization of circulating tumor cells

Background: The adherent-to-suspension transition (AST) describes how solid tumor cells reprograms their anchorage dependency via defined hematopoietic transcriptional regulators to disseminate into circulating tumor cells (CTCs). It remains unclear, however, whether the dissemination and colonization processes require dynamic plasticity of AST factor expression in CTCs to permit the completion of the metastatic cascade. Methods: We investigated AST factor-mediated adherent-suspension plasticity (ASP) in a newly developed cell-based dissemination assay. Here we identified a rare population of CTC-like cells spontaneously suspended from highly confluent breast cancer cells under chronic stress conditions that mimic the tumor microenvironment (TME). We investigated the oscillatory dynamics of AST factor expression in these CTC-like cells and their role in dissemination and colonization. Furthermore, we performed a single-cell transcriptomic analysis of matched primary tumors, CTCs, and metastatic lesions from newly enrolled de novo metastatic breast cancer patients, focusing on the plasticity of AST factor expression during the metastatic cascade in vivo. Results: Using data obtained from the dissemination assay and de novo metastatic breast cancer patients, we have demonstrated the dynamic regulation of AST factor expression during the dissemination and colonization of CTCs both in vitro and in vivo. From our dissemination assay of breast cancer cell lines, we show that AST factor induction is required for the reprogramming of anchorage dependency and spontaneous detachment of CTC-like cells. We also show that subsequent AST factor suppression is required for the reattachment of CTCs during colonization. Single-cell transcriptome analyses in matched specimens of primary tumor, CTC, and metastatic lesions obtained from de novo metastatic breast cancer patients confirmed the oscillatory dynamics of AST factors and related gene signatures related to the adherent-suspension plasticity. Conclusion: Our results show that the reprogramming of anchorage dependency in solid tumor cells via AST factor-mediated ASP plays a critical role in the dissemination and colonization of CTCs. These findings highlight the potential of targeting AST factors to develop effective anti-metastatic therapies.