A non-invasive approach for monitoring breast tumor cells during therapeutic intervention

Objective: This study was performed to develop a non-invasive imaging method to evaluate non-palpable tumors in a breast xenograft model undergoing therapy. Methods. Human breast cancer cells were infected with an adenoviral (Ad) vector encoding enhanced Green Fluorescent Protein (GFP). GFP-positive breast cancer cells were treated with doxorubicin 12h after plating cells and sequentially imaged. Nude mice were implanted with GFP-positive tumor cells, treated with doxorubicin 24h after implantation, and imaged at 1, 3, and 5 days after treatment. In vitro and in vivo images of the GFP-positive cells were collected using an inverted microscope and a fluorescent stereomicroscope, respectively. The fluorescence of GFP and of doxorubicin was simultaneously detected using two different GFP filters. Results. Over 99% of tumor cells were GFP-positive following Ad-GFP infection. Doxorubicin therapy killed GFP-positive cancer cells and gradually eliminated GFP fluorescence in vitro and in vivo. Loss of GFP fluorescence was verified as cell death. Incorporation of doxorubicin into tumor cells and detection of single GFP-positive cells was observed in vivo through light-based imaging. Conclusion. The response of GFP-positive breast tumor cells to doxorubicin treatment was non-invasively imaged using light-based microscopy. This approach provides many useful applications for the evaluation of new anti-tumor drugs.