We have recently reported the use of one-bead-one-compound (OBOC) combinatorial library methods to develop a high-affinity (IC50 = 2pM) peptidomimetic ligand (LLP2A) against activated α4β1 integrin of both T- and B-lymphoma and lymphocytic leukemia. When complexed with streptavidin-fluorphor in a tetravalent form, biotinylated LLP2A was able to image human lymphoma xenografts in nude mice with high specificity . Since then, we have designed and synthesized univalent LLP2A-Cy5.5 and [111In]-labeled LLP2A-DOTA conjugates, and evaluated their potential use as in vivo optical and radio imaging agents, respectively. Except for renal uptake, tumor targeting specificity by these conjugates was excellent. To increase circulation time and to decrease filtration through the glomeruli, we added a 30 Kd linear polyethylene glycol to the LLP2A-Cy5.5 conjugate, which resulted in a dramatic decrease in renal uptake. LLP2A was also found to bind to lymphoma biopsy specimens obtained from companion dogs with spontaneous lymphoma. Work is currently underway to evaluate LLP2A as canine lymphoma radio-imaging and radio-therapeutic agents.
We have also used OBOC combinatorial library method to develop peptidic ligands against breast cancer. A focused OBOC cyclic-peptide library (cXGXGXXc) with millions of permutations were synthesized and screened against live MDA-MB-231 breast cancer cells. Based on the chemical structure of the lead compounds and the SAR data, we designed two highly focused OBOC peptidomimetic libraries, and screened these libraries under high stringency. Anti-α3 integrin antibodies blocked the binding of the breast cancer cells to these peptide beads. K562 myeloid leukemia cells transfected with various mutant α3 integrins were used as probes to elucidate the molecular interaction between the ligands and the receptor. Mutations at T162A, G163A, M164A and T162F resulted in a complete loss of cell binding to the cyclic peptides. Work is currently underway to further improve the binding affinity and specificity of our candidate ligands and to evaluate their tumor targeting potential in vivo.
 Peng L, Liu R, Marik J, Wang X, Takada Y, Lam KS. Nature Chemical Biology, 2(7). 381-389, 2006.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA