Amplified Ca ²⁺ dynamics and accelerated cell proliferation in breast cancer tissue during purinergic stimulation

Abstract Intracellular Ca 2+ dynamics shape malignant behaviors of cancer cells. Whereas previous studies focused on cultured cancer cells, we here used breast organoids and colonic crypts freshly isolated from human and murine surgical biopsies. We performed fluorescence microscopy to evaluate intracellular Ca 2+ concentrations in breast and colon cancer tissue with preferential focus on intracellular Ca 2+ release in response to purinergic and cholinergic stimuli. Inhibition of the sarco‐/endoplasmic reticulum Ca 2+ ATPase with cyclopiazonic acid elicited larger Ca 2+ responses in breast cancer tissue, but not in colon cancer tissue, relative to respective normal tissue. The resting intracellular Ca 2+ concentration was elevated, and ATP, UTP and acetylcholine induced strongly augmented intracellular Ca 2+ responses in breast cancer tissue compared with normal breast tissue. In contrast, resting intracellular Ca 2+ levels and acetylcholine‐induced increases in intracellular Ca 2+ concentrations were unaffected and ATP‐ and UTP‐induced Ca 2+ responses were smaller in colon cancer tissue compared with normal colon tissue. In accordance with the amplified Ca 2+ responses, ATP and UTP substantially increased proliferative activity—evaluated by bromodeoxyuridine incorporation—in breast cancer tissue, whereas the effect was minimal in normal breast tissue. ATP caused cell death—identified with ethidium homodimer‐1 staining—in breast cancer tissue only at concentrations above the expected pathophysiological range. We conclude that intracellular Ca 2+ responses are amplified in breast cancer tissue, but not in colon cancer tissue, and that nucleotide signaling stimulates breast cancer cell proliferation within the extracellular concentration range typical for solid cancer tissue.