Abstract P1-03-01: Circulating CAIX as a biomarker in breast cancer
Authors: Brown-Glaberman U , Chalasani P , Livingston R , Iannone M , Marron M , Specht J , Stopeck A 
Published: August 2014

Abstract
Introduction: Carbonic anhydrase-IX (CAIX) facilitates the reversible hydration of carbon dioxide to bicarbonate and protons, a process integral to maintaining pH differences across the cancer cell plasma membrane. CAIX is regulated by hypoxia inducible factor-1 alpha (HIF-1 alpha) and is essential for the elimination of acid loads generated by glycolysis. High CAIX expression is associated with poor prognosis and chemoresistance in breast cancer patients (pts) (1-3). To explore the role of CAIX as a possible biomarker for predicting breast cancer therapies, we measured plasma CAIX levels in response to various chemotherapy regimens, including anti-angiogenics, in several breast cancer clinical trials.
Methods: Circulating plasma CAIX was quantified using a commercially available enzyme-linked immunosorbent assay (ELISA) kit (R & D Systems). We evaluated the plasma stability of CAIX by quantifying levels within 1 hour as well as at 24 and 48 hours post phlebotomy in healthy controls (n = 10). We also evaluated the ideal anticoagulant for sample collection and stability of CAIX levels over time in healthy controls. For our analysis in breast cancer pts, we quantified plasma CAIX levels in two populations treated on chemotherapeutic clinical trials: 1) locally advanced breast cancer (LABC) pts treated in the neoadjuvant setting with paclitaxel in combination with sunitinib followed by anthracycline (AC) based chemotherapy (n = 63); 2) metastatic breast cancer (MBC) pts treated with systemic chemotherapy with either irinotecan + etoposide; or paclitaxel + a novel immunomodulatory agent (n = 22).
Results: In healthy control subjects, plasma levels of CAIX were stable at all time points tested (within1 hour, 24 hrs, 48 hours post phlebotomy) with no significant change on repeat testing at 6 months. Average baseline plasma CAIX levels were lowest in normal controls (20.5 pg/ml) compared to pts with LABC (34.1 pg/ml) or MBC (90.7 pg/ml) (p = &lt;0.001). In pts with LABC, CAIX rose significantly in response to paclitaxel/sunitinib (TS) therapy (p = 0.01) but not further with anthracycline based therapy (p = 0.37). The rise in response to TS was primarily in pts with baseline levels below the median. In pts with MBC treated with cytotoxic chemotherapies (without an anti-angiogenic) CAIX levels did not change in response to therapy.
Discussion: Plasma CAIX is a robust biomarker that is stable at room temperature in plasma for at least 48hrs and over time in healthy controls. Plasma CAIX levels are elevated in pts with MBC when compared to those with LABC or normal controls. CAIX levels rise in response to anti-angiogenic therapy but not in response to cytotoxic chemotherapy. Our results suggest CAIX may be a robust and easily measured pharmacodynamic biomarker of anti-angiogenic induced hypoxia and HIF-1 alpha upregulation.
1. Potter CP and Harris AL. Br J Cancer. 89:2-7, 2003.
2. Betof AS, Rabbani ZN, Hardee ME, et al. BJ Cancer. 106:916-922, 2012.
3. Generali D, Fox Berruti A, et al. Endocrine-Related Cancer. 13:921-30, 2006.
Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-03-01.