Assessing Na+/H+ exchange and cell effector functionality in metastatic breast cancer

Abstract

Metastasis is the leading cause of mortality in patients with breast cancer. In triple-negative breast cancer, high recurrence rates, increased invasive capacity of cells, and their aggressive ability to metastasize at secondary sites dictate patient survival. The Na⁺/H⁺ exchanger isoform 1 (NHE1) plays a critical role in controlling the metastatic potential of these cells. Its activity results in an elevation of intracellular pH and in extracellular acidification, a key step in the establishment of the tumor microenvironment. Here, we describe assays for characterization of Na⁺/H⁺ exchanger activity and its related downstream physiological effects on triple-negative breast cancer cells. Na⁺/H⁺ exchanger activity can be routinely and rapidly measured in live cells with a fluorometric assay that assesses changes in intracellular pH. Characterization of downstream cell effector function as a result of Na⁺/H⁺ exchanger activation can be evaluated by measuring directed cell migration and invasion. Cell migration is assessed with wound-healing assays, where a gap is introduced in a confluent monolayer of cells and the rate of gap closure is measured over time. Cell invasion is assessed in the short-term by transwell invasion assays that track cell movement through an extracellular matrix. Long-term invasiveness, growth and proliferation can be assessed with 3-D invasion assays using transwell inserts fitted with specialized scaffolds optimized for 3-D cell culture. Taken together these assays provide powerful tools for testing the effects of altering Na⁺/H⁺ exchanger activity with chemical inhibition on the metastatic capacity of breast cancer cells.