Enhancement of radiolabeled antibody binding and tumor localization through adenoviral transduction of the human carcinoembryonic antigen gene.

Conventional radiolabeled antibody targeting utilized in radioimmunotherapy has resulted in limited success clinically due in part to inadequate tumor localization resulting from low expression of human tumor-associated antigens on target cells. We hypothesized that one could improve upon these limitations by genetically inducing tumor cells to express high levels of a new membrane-associated receptor with high affinity for a radioligand. As a preliminary strategy, we induced a human glioma cell line (D54 MG) to express human carcinoembryonic antigen (CEA) in vitro. To accomplish this, we constructed a recombinant adenoviral vector encoding the CEA cDNA inserted downstream of a cytomegalovirus (CMV) promoter (AdCMVCEA). D54 MG cells were transfected with AdCMVCEA or an adenoviral vector encoding lacZ reporter gene as a control (AdCMVlacZ). LS174T human colon cancer cells, known to express CEA constitutively, served as positive controls. Immunofluorescence and immunohistochemistry assays employing unlabeled anti-CEA COL-1 monoclonal antibody demonstrated expression of CEA antigen on the cell surface of transduced D54 MG cells in culture. In addition, assays utilizing 125I-labeled COL-1 indicated high binding to transduced D54 MG cells expressing CEA (4.7 +/- 0.5 x 10(5) COL-1 molecules bound per cell) as compared with minimal binding to nontransduced D54 MG cells. LS174T cells demonstrated only 2.7 +/- 0.5 x 10(6) COL-1 molecules bound per cell. Thus, AdCMVCEA was able to induce levels of cell surface CEA in target cells at a higher level than CEA-overexpressing tumor cells (P < 0.01). The efficacy of transduction of recombinant AdCMVCEA by direct intratumoral injection into D54 MG xenografts was investigated by immunohistochemical analysis, immunofluorescence and by measuring 131I-labeled COL-1 uptake through external scintigraphic imaging and biodistribution studies. Expression of CEA in the tumor xenografts by, and radiolabeled antibody tumor targeting to, AdCMVCEA transduced D54 MG xenografts was comparable to that seen with LS174T xenografts. Results of these studies indicate the potential of adenovirus-mediated delivery of targets to improve radiopharmaceutical tumor localization.