Fig. 4: NBCn1-directed inhibitory antibodies block net acid extrusion from human breast cancer tissue, especially from patients with macrometastases in the axillary lymph nodes.

a Fluorescence image of BCECF-loaded primary organoid freshly isolated from human breast cancer tissue. The diameter of organoids is 100–150 µm [3, 9]. b Average traces of pH_i during NH₄⁺-prepulse-induced intracellular acidification of organoids isolated from primary breast carcinomas. The illustrated experiments were performed in the presence of CO₂/HCO₃^– on tissue from patients with macrometastases in the axillary lymph nodes. The 5H2.1 antibody was added at 10 nM from 30 min before addition of NH₄Cl until the end of the experiment. c Na⁺-dependent net acid extrusion calculated at pH_i 6.5 under conditions with and without CO₂/HCO₃^–, as indicated. Data are presented for the whole group of patients (n = 25). d + e 5H2.1-sensitive net acid extrusion calculated at pH_i 6.5 (d) and 5H2.1-dependent changes in steady-state pH_i (e) in the presence and absence of CO₂/HCO₃^– and stratified between patients without lymph node metastases (n = 12), with isolated tumor cells or micrometastases (n = 5), and with macrometastases (n = 8) in the axillary sentinel lymph nodes. Data in (c, d) were compared by two-way ANOVA followed by Šidák’s post-tests. Data in (e) were compared by one-way ANOVA and one-sample t-test. Reported P-values relate to comparisons vs. control in similar buffer (c) or matched recordings without CO₂/HCO₃^– (d).