Targeted delivery of small-molecule drugs has the potential to enhance selective killing of tumor cells. We have identified previously an internalizing single chain [single chain variable fragment (scFv)] antibody that targets prostate cancer cells and identified the target antigen as CD166. We report here the development of immunoliposomes using this anti-CD166 scFv (H3). We studied the effects of a panel of intracellularly delivered, anti-CD166
We have used a naive human single-chain fragment variable (scFv) library as a source of random shape repertoire to directly probe the altered surface chemistry of tumor cells. We reported previously the identification of more than 90 internalizing phage monoclonal antibodies targeting prostate cancer cells, including those that are hormone refractory. In this report, we describe the conversion of a panel of those scFvs into full-length human immunoglobulins (IgGs) and show that tumor specificity is retained. We have further shown that antibodies isolated from a naive phage display library can nevertheless be of high affinity towards target tumor cells. In addition, full-length IgGs retain the functionality of parental scFvs including the ability to rapidly enter target cells through receptor-mediated endocytosis and thereby to mediate efficient and specific intracellular payload delivery to tumor cells. We have used recombinant IgGs to immunoprecipitate target antigens and analyzed their molecular composition by mass spectrometry. We have identified one target antigen as activated leukocyte cell adhesion molecule (ALCAM)/MEMD/CD166 and have further studied tissue specificity of this internalizing ALCAM epitope by immunohistochemistry. Our study shows that cell type-specific internalizing human antibody can be readily identified from a naive phage antibody display library, characterized with regards to sequence, affinity, tissue specificity, and antigen identity, and modified genetically and chemically to generate various forms of targeted therapeutics.
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