There is currently no effective treatment for recurrent small-cell lung cancer (rSCLC). The objective of this project is to utilize a monoclonal antibody, Abner, to develop new, rational, and successful treatment of rSCLC. The hypothesis being tested is that an abnormal vasopressin type 2 receptor (AbnV2R) present on these tumors will provide a sensitive, tumor-specific, and reliable target for the effective treatment by Abner antibodies. The data from the studies of Phase 1 of the project clearly show that treatment of variant SCLC tumor xenografts, with native and 90Yttrium-labelled mouse Abner significantly slows growth, but this growth is completely impaired when antibody treatment follows cyclophosphamide. Our data indicate AbnV2R expression is a feature common to all, or most, SCLC and that AbnV2R is a surface protein. Phase 2 is directed at advancing treatment of rSCLC with Abner by developing a human chimeric form (cAbner) of the mouse monoclonal antibody, and then a humanized form (hAbner) as potential clinical candidates. The ability of cAbner and hAbner to target and prevent growth of human variant SCLC xenografts in mice will then be tested. Phase 2 goals are directed towards (i) generating a chimeric form (cAbner) of mouse Abner with the constant regions of human IgG1; (ii) establishing that the targeting, recognition, and treatment profiles of mAbner are retained by cAbner; (iii) modeling a humanized form (hAbner) of Abner from the cAbner with genetically grafting CDRs from the VH and VL regions of mMAG-1 into the DNA framework of a human antibody; (iv) establishing that the targeting, recognition, and treatment profiles of mAbner are retained by hAbner. These investigations will employ, RT-PCR, ligation, and cloning, DNA recombinance, DNA sequencing, immunohistochemistry, antibody modification, Northern and Western analysis with densiometric quantitation, ELISA, RIA, tumor-directed targeting, whole-body scintigraphy for 99mTechnetium, cytofluorographic and radiometric quantitation, confocal microscopy, radioligand binding, flow cytometry, and cell and tumor growth assessments with mechanism analysis in vitro and for nu/nu mice. A successful end-point of our Phase 2 studies would be the generation of cAbner and/or hAbner forms of our antibody that show a similar binding affinity as mAbner, recognize all or most recurrent (and primary) cancers, do not react with normal tissues, and can reduce the size of tumors, and/or prevent their growth in vivo. The proposed research is expected to rapidly lead to new and successful therapeutic approaches for managing recurrent small-cell lung cancer.