Abstract 5936: Comparison of carbonic anhydrase & activity between triple-negative & luminal breast cancer cells
Authors: Chen Zhijuan , Mboge Mam Y. , Tu Chingkuang , Ai Lingbao , Heldermon Coy , Frost Susan C. 
Published: July 2017

Tumor microenvironment substantially influences the process of tumorigenesis. Extracellular acidification within the tumor microenvironment is an indicator of an aggressive cancer and a marker for poor patient outcome. In solid tumors, hypoxia leads to extracellular acidosis. Carbonic anhydrases (CA) are thought to regulate intracellular and extracellular pH (pHi and pHe, respectively). To explore the effect of CAs in breast cancer, we compared the expression and activity of two membrane bound CAs, CAIX and CAXII, between triple negative breast cancer cells (TNBCs) and luminal breast cancer cells (LBCs).

We chose five different TNBC and LBC lines. Our data show that, among the TNBC lines, CAIX expression increased in three of the five lines: HBL100, SUM159, and the new UFH-001 cells under hypoxic condition. UFH-001 cells also showed strong constitutive expression. None of these TNBC lines expressed CAXII or estrogen receptor (ER). In LBC lines, four of the five lines constitutively expressed CAXII: T47D, MCF7, SKBR and SUM52 cells. CAXII expression was not hypoxia-dependent. Each of the five luminal lines expressed ER. We also examined CA expression in a tumor graft model. In tumors grown from cells derived from TNBC patients, we observed CAIX expression in four of six sample sets. In tumors derived from ER-positive LBC patients, all five expressed CAXII.

We also used the 18O exchange method to assess CA activity. Two TNBC lines: UFH-001 and HBL100 cells showed that CAIX activity increased in hypoxic conditions which was blocked by an impermeant sulfonamide CA inhibitor (N3500). In the luminal lines, we detected CAXII activity in T47D and MCF7 cells that was also inhibited by N3500. Like CAXII protein expression in these cells, CAXII activity was not affected by hypoxia. We also evaluated the effect of pH on CA activity in TNBC and LBC lines. Both CAIX and CAXII showed increased activity in response to reduced pH, which is expected in a bicarbonate-based system. However, UFH-001 cells also exhibited a hypoxic-dependent increase in CAIX activity which is associated with increased protein expression.

In conclusion, these observations demonstrate that CAIX expression is associated with the TNBC phenotype. Based on our activity data, we would predict that CA activity in TNBC tumors will be sensitive to both hypoxia (based on enhanced expression) and reduced pH. This change in activity may serve to regulate pH in the tumor microenvironment favoring an aggressive phenotype. On the other hand, LBC tumors, which are ER-positive, are only associated with CAXII expression. In luminal cells, we expect that only pH and not hypoxia will affect CAXII activity. This may, in part, explain the more positive prognosis in patients with CAXII expression.

Note: This abstract was not presented at the meeting.

Citation Format: Zhijuan Chen, Mam Y. Mboge, Chingkuang Tu, Lingbao Ai, Coy Heldermon, Susan C. Frost. Comparison of carbonic anhydrase & activity between triple-negative & luminal breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5936. doi:10.1158/1538-7445.AM2017-5936