Detection and measurement of in vitro gene transfer by gamma camera imaging

The purpose of this work was to develop a high capacity method to image gene transfer to cancer cells growing as monolayers in cell culture plates. A sensitive and high capacity nuclear-imaging method for detection of gene transfer in vitro will allow rapid validation of vectors in different cell lines under various conditions. Human cancer cell lines (A-427 non-small cell lung, SKOV3.ip1 ovarian, MDA-MB-468 breast, and BxPC-3 pancreatic) were infected with a replication-incompetent adenoviral vector encoding the human type 2 somatostatin receptor (Ad-hSSTr2). Expression of the hSSTr2 reporter protein in cells was detected by imaging an internalized ^99mTc-labeled, hSSTr2 binding peptide (P2045, Diatide, Inc.). Imaging provided an accurate measure of internally bound ^99mTc as evidenced by equivalence of results for imaging region of interest (ROI) analyses and gamma counter measurements. Internally bound ^99mTc-P2045 was linearly correlated (R² = 0.98) with the percentage of hSSTr2-positive cells following gene transfer. Excess P2045 blocked binding and internalization of the ^99mTc-P2045, indicating the specificity of the technique. Up to four 96-well plates could be imaged simultaneously, thereby demonstrating the high capacity of the system. This novel in vitro approach provides a new method to test enhanced gene transfer as new vectors are developed.