Acidic melanoma microenvironment selects for a senescence-like but also migratory-active subpopulation driving metastatic disease

One of the main characteristics of solid tumors, such as melanoma, is an acidic tumor microenvironment. Due to dysregulation of the cancer cell metabolism and an increased production of acidic metabolites, the tumor acidifies its microenvironment. We hypothesize that this has a strong impact on tumor heterogeneity and the formation of phenotypic subpopulations. Cell culture experiments are usually carried out at a physiological pH of 7.4. Here, we show that long-time acidosis results in the formation of a senescent subpopulation in melanoma cells. Interestingly, after reintroduction to physiological pH, these cells lose their senescence-associated attributes. We isolated this subpopulation using β-galactosidase-dependent C₁₂FDG staining and FACS. Live cell imaging, microscopy, and RNA sequencing analysis revealed that these apparent senescent cells show an increased migratory activity. With this study, we demonstrate that the acidic tumor microenvironment drives tumor plasticity in melanoma and results in the formation of a small subpopulation, which promotes metastasis.