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

PURPOSE: 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. EXPERIMENTAL DESIGN: 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). RESULTS: 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. CONCLUSION: 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.

Targeting gastrin-releasing peptide receptors for cancer treatment.

Growth factor receptors play critical roles in cancer cell proliferation and progression. A number of such receptors have been targeted for cancer treatment by either a monoclonal antibody or a specifically designed small molecule to inhibit the receptor function. Bombesin/gastrin-releasing peptide receptors (BN/GRP-Rs) are expressed in a variety of cancer cells and have limited distribution in normal human tissue. Inhibition of BN/GRP-Rs has been shown to block small cell lung cancer growth in vitro. Early phase clinical trials targeting human GRP-R showed anti-cancer activity. This review will focus on the study of the distribution of BN/GRP-Rs in normal and malignant tissues, and various approaches to targeting BN-GRP-Rs for cancer diagnosis and treatment.

Bombesin/gastrin-releasing peptide receptor: a potential target for antibody-mediated therapy of small cell lung cancer.

PURPOSE: Bombesin/gastrin releasing peptide (BN/GRP) is a growth factor for small cell lung cancer (SCLC). The receptor (R) for BN/GRP is overexpressed on SCLC cells and other solid tumors. BN/GRP and its receptor form an autocrine loop to promote tumor growth. We developed a novel immunotherapeutic approach targeting cell surface BN/GRP-R on SCLC cells and an immune trigger molecule on host immune effector cells to direct immune effector cells to SCLC cells and mediate targeted cancer cell destruction. Targeted immunotherapy combined with chemotherapy enhanced cell killing. EXPERIMENTAL DESIGN: We designed a synthetic BN/GRP antagonist (Antag 2) and constructed a bispecific molecule (BsMol), H22xAntag 2 (humanized monoclonal antibody) for FcgammaRI. We tested the binding of the BsMol to several SCLC cell lines, its ability to mediate cytotoxicity of SCLC by IFN-gamma-activated human monocytes with chemotherapy, and BsMol-mediated immunotherapy in an animal model of SCLC human xenograft. RESULTS: Common chemotherapy (cisplatin, etoposide, and paclitaxel) inhibited thymidine uptake into SCLC cells in a dose-dependent pattern. Antibody-dependent cellular cytotoxicity mediated by the BsMol inhibited thymidine uptake into SCLC cells and was largely dependent on E:T cell ratio. When SCLC cells were treated with antibody-dependent cellular cytotoxicity followed by exposure to chemotherapy agents an additional 25-40% inhibition of thymidine uptake into SCLC cells was observed consistently. With BsMol and IFN-gamma-activated human monocytes, tumor burdens were reduced significantly in immunodeficient mice bearing human SCLC xenografts. CONCLUSIONS: Combined chemotherapy and immunotherapy targeting BN/GRP-R with a BsMol significantly enhances targeted SCLC cell killing.

Efficient intracellular delivery of oligonucleotides formulated in folate receptor-targeted lipid vesicles.

In this study, a novel lipid vector has been developed for targeted delivery of oligodeoxynucleotides (ODN) to tumors that overexpress folate receptor. This is based on a method developed by Semple et al. (1), which utilizes an ionizable aminolipid (1,2-dioleoyl-3-(dimethylammonio)propane, DODAP) and an ethanol-containing buffer system for encapsulating large quantities of polyanionic ODN in lipid vesicles. Folate is incorporated into the lipid vesicles via a distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG) spacer. These vesicles are around 100-200 nm in diameter with an ODN entrapment efficiency of 60-80%. Folate mediated efficient delivery of ODN to KB cells that overexpress folate receptor. Uptake of folate-targeted lipidic ODN by KB cells is about 8-10-fold more efficient than that of lipidic ODN without a ligand or free ODN. This formulation is resistant to serum. Thus, targeted delivery of ODN via this novel lipid vector may have potential in treating tumors that overexpress folate receptors.