Tumor microenvironment acidosis favors pancreatic cancer stem cell properties and in vivo metastasis.

The acidic tumor microenvironment (TME) favors cancer aggressiveness via incompletely understood pathways. Here, we asked whether adaptation to environmental acidosis (pH 6.5) selects for human pancreatic cancer stem cell (CSC) properties. RNA sequencing (RNA-seq) of acid-adapted (AA) Panc-1 cells revealed CSC pathway enrichment and upregulation of CSC markers. AA Panc-1 cells exhibited classical CSC characteristics including increased aldehyde dehydrogenase (ALDH) activity and β-catenin activity. Panc-1, PaTu8988s, and MiaPaCa-2 cells all exhibited increased pancreatosphere-forming efficiency after acid adaptation but differed in CSC marker expression and did not exhibit typical flow cytometric CSC populations. However, single-nucleus sequencing revealed the acid adaptation-induced emergence of Panc-1 cell subpopulations with clear CSC characteristics. In orthotopic mouse tumors, AA Panc-1 cells exhibited enhanced aggressiveness, liver and lung metastasis, compared to controls. Collectively, our work suggests that acid adaptation enriches for pancreatic CSC phenotypes with unusual traits via several trajectories, providing new insight into how acidic microenvironments favor cancer aggressiveness.