Imaging CXCR4 expression in orthotopic and metastatic models of breast cancer

Objectives Chemokine receptor 4 (CXCR4) is expressed in a variety of cancers including breast, brain, ovarian and prostate. CXCR4/CXCL12 interactions are critical for tumor development, growth and metastasis. Neoplastic breast tissue and metastases express elevated levels of CXCR4. Previous observations suggest that CXCR4 levels could be used as a predictive marker of metastatic potential. We report SPECT/CT imaging of CXCR4 expression in orthotopic, lung and bone metastatic models of breast cancer using ¹²⁵I-anti-CXCR4 antibodies.

Methods The monoclonal hCXCR4 and control antibodies were radiolabeled by the Iodogen method. MDAMB231 cells were used to generate orthotopic xenografts, lung and bone metastases. After IV injection of rMAbs (37 MBq), SPECT/CT images were acquired until 96 h in all the three models. For biodistribution studies mice receiving rMAbs (148 kBq) were sacrificed and tissues harvested at selected time intervals. CXCR4 expression of orthotopic tumors and metastases were analyzed by flow cytometry and immunoblot analysis.

Results Radiolabeled antibodies (rMAbs) were obtained in 40% yield with > 95% purity. Imaging and biodistribution studies showed specific accumulation of rMAbs in MDAMB231 tumors with tumor/muscle ratios of 7±2 and 16±3 at 24 and 96 h post injection, respectively. Lung and bone metastases showed significant accumulation of radioactivity relative to control rMAb. Flow cytometry and immunoblot analyses demonstrated elevated CXCR4 in metastases.

Conclusions These data demonstrate the feasibility of imaging CXCR4 expression in breast xenografts, lung and bone metastases.

Research Support U24 CA092871 and 1P50CA103175