Long term progression and therapeutic response of visceral metastatic disease non-invasively monitored in mouse urine using beta-human choriogonadotropin secreting tumor cell lines
Historically, the use of mouse models of metastatic disease to evaluate anticancer therapies has been hampered because of difficulties in detection and quantification of such lesions without sacrificing the mice, which in turn may also be dictated by institutional or ethical guidelines. Advancements in imaging technologies have begun to change this situation. A new method to non-invasively measure tumor burden, as yet untested to monitor spontaneous metastases, is the use of transplanted tumors expressing secretable human β-chorionic gonadotropin (β-hCG) that can be measured in urine. We describe examples of β-hCG–transfected tumor cell lines for evaluating the effect of different therapies on metastatic disease, which in some cases involved monitoring tumor growth for > 100 days. We used β-hCG–tagged mouse B16 melanoma and erbB-2/Her-2–expressing human breast cancer MDA-MB-231 models, and drug treatments included metronomic low-dose cyclophosphamide chemotherapy with or without a vascular endothelial growth factor receptor 2–targeting antibody (DC101) or trastuzumab, the erbB-2/Her-2–targeting antibody. Both experimental and spontaneous metastasis models were studied; in the latter case, an increase in urine β-hCG always foreshadowed the development of lung, liver, brain, and kidney metastases. Metastatic disease was unresponsive to DC101 or trastuzumab monotherapy treatment, as assessed by β-hCG levels. Our results also suggest that β-hCG levels may be set as an end point for metastasis studies, circumventing guidelines, which have often hampered the use of advanced disease models. Collectively, our data indicates that β-hCG is an effective noninvasive preclinical marker for the long term monitoring of untreated or treated metastatic disease.