A rapid imageable in vivo metastasis assay for circulating tumor cells

Circulating tumor cells (CTCs) are of great importance for cancer diagnosis, prognosis and treatment. It is necessary to improve the ability to image and analyze them for their biological properties which determine their behavior in the patient. In the present study, using immunomagnetic beads, CTCs were rapidly isolated from the circulation of mice orthotopically implanted with human PC-3 prostate cancer cells stably expressing green fluorescent protein (GFP). The PC-3-GFP CTCs were then expanded in culture in parallel with the parental PC-3-GFP cell line. Both cell types were then inoculated onto the chorioallentoic membrane (CAM) of chick embryos. Eight days later, embryos were harvested and the brains were processed for frozen sections. The IV-100 intravital laser scanning microscope enabled rapid identification of fluorescent metastatic foci within the chick embryonic brain. Inoculation of embryos with PC-3-GFP CTCs resulted in a 3 to 10-fold increase in brain metastasis when compared to those with the parental PC-3-GFP cells (p<0.05 in all animals). Thus, PC-3-GFP CTCs have increased metastatic potential compared to their parental counterparts. Furthermore, the chick embryo represents a rapid, sensitive, imageable assay of metastatic potential for CTCs. The chick embryo assay has future clinical application for individualizing patient therapy based on the metastatic profile of their CTCs.