A number of cell surface protein receptors have been identified that distinguish malignant cancer cells from their normal counterparts. While several of these receptors have been shown to be more abundant on cancer cells (e.g. CD20, CD22), others have been confirmed to differ structurally (e.g. HLA-DR10, Muc-1) from the same or closely related receptors present on normal cells. This has led to the development of a variety of antibody-based, receptor-specific reagents conjugated to radioisotopes for use in radio-immunotherapy. Lym-1, an antibody developed to bind to a unique structural epitope on the abundant cell surface receptor HLA-DR10 found only on human lymphoma and normal B-cell lymphocytes, has been used with some success in the treatment of non Hodgkin’s lymphoma. In an effort to develop smaller and more effective therapeutics for treating non Hodgkin’s lymphoma, we have synthesized the first in a series of small (<3kD) selective high affinity ligands (SHALs) that bind to this same HLA-DR10 structural epitope. A homology model for HLA-DR10 was created using four known crystal structures of related HLA-DR molecules. Two unique “pockets” located on the surface of the protein adjacent to key amino acids required for Lym-1 binding were identified, and computational docking techniques were used to prescreen a large library of small molecules to predict which compounds should bind to each site. A small number of these compounds were tested experimentally using NMR spectroscopy to confirm their binding to the isolated HLA-DR10 protein, and pairs of compounds binding to the two different “pockets” were linked together using solid phase synthetic chemistry to create a series of bidentate reagents with different length linkers. The SHAL exhibiting the highest affinity for isolated HLA-DR10 (∼23nM) has been shown to bind selectively to nine different cultured cell lines containing HLA-DR10 and to frozen and fixed tissue sections obtained from patients with small cell and large cell human lymphomas. A bivalent form of this SHAL was also synthesized and shown to further enhance cell binding. This effort was supported by grants from the National Cancer Institute (PO1-CA47829) and LLNL Laboratory Directed Research Development awards 01-ERD-111 (R.B. and J.P.) and 01-ERD-046 (M.C.). The work at LLNL was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]