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Clin Cancer Res. 2006 Apr 1;12(7 Pt 1):2224-31.

Targeting gastrin-releasing peptide receptors on small cell lung cancer cells with a bispecific molecule that activates polyclonal T lymphocytes.

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Division of Blood and Marrow Transplantation, Department of Medicine and Moores University of California at San Diego Cancer Center, University of California San Diego, La Jolla, California, USA.



Gastrin-releasing peptide (GRP) is a growth factor for small cell lung cancer (SCLC). GRP belongs to the bombesin peptide family and has significant homology to bombesin. We constructed a bispecific molecule, OKT3xAntag2, by conjugating a monoclonal antibody OKT3 (anti-CD3) with a bombesin/GRP antagonist (Antag2) and evaluated cytotoxicity against SCLC cells.


We tested binding of the bispecific molecule to SCLC cell lines and T cells by flow cytometry, antibody-dependent cellular cytotoxicity (ADCC) of SCLC cells in vitro and in a murine SCLC xenograft model. We studied SCLC apoptosis and necrosis during ADCC and the activity and cleavage of caspase-3, caspase-9, and poly(ADP-ribose) polymerase (PARP).


The bispecific molecule functions as a cross-linker between T cells and SCLC cells, induces T cell activation, and mediates ADCC of SCLC cells; 40% to 80% growth inhibition of SCLC cells mediated by the bispecific molecule at low effector to target cell ratios was achieved. Activation of T cells by the bispecific molecule resulted in significant increases in IFNgamma production and apoptosis and necrosis of SCLC cells associated with cleavage of PARP and caspase-3. Targeted immunotherapy with the bispecific molecule-armed human T cells significantly reduced SCLC tumor burdens in a mouse model.


The bispecific molecule OKT3xAntag2 mediates growth inhibition and apoptosis of SCLC cells by activated T cells through activation and cleavage of caspase-3 and PARP in vitro and in vivo. Clinical trials of this bispecific molecule through adoptive transfer of ex vivo activated T cells in GRP receptor-positive tumors, such as SCLC, are warranted.

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