The efficacy of molecular based therapies directed at receptor tyrosine kinases (RTKs) depends not only on binding but on biologic effects mediated through direct or indirect effects on receptor ft1nction. We hypothesize that the ability to simultaneously profile receptor function, as well as receptor density, will be essential to identify patients who will respond to novel anti-RTK therapies. For this project, we propose to develop antibody based tools and assays that will permit rapid in vitro assessment of the density, phosphorylation state, and endocytic activity of RTKs. Phosphorylation state is likely to prove predictive of responders to drugs that inhibit tumor growth by inhibiting receptor signaling (for example Herceptin and TK inhibitors). Assessment of endocytic activity is likely to predict therapeutic response to drugs that use receptor binding as a means of delivering drugs intracellularly (for example immunoliposomes). Endocytosis may also serve as a surrogate marker for receptor phosphorylation status in some instances. For the purposes of this proposal, we will focus on generating probes for the functional assessment of the ErbB family of RTKs, including the EGF receptor, ErbB2, ErbB3, and ErbB4. The probes will be used for mechanism-based evaluation of novel molecular based therapeutic strategies directed against ErbB receptors, an important and expanding group of therapeutic strategies and agents. By providing functional information regarding ErbB activity, these tools will facilitate early, mechanism-based assessments of therapeutic strategies requiring ErbB receptor function for anti-tumor activity (e.g., anti-ErbB2 immunoliposomes for receptor-mediated endocytotic drug delivery) as well as those therapies designed to be antagonists of ErbB function (e.g., small molecule TK inhibitors or ErbB-down modulators). These tools and assays will be based on recombinant monoclonal phage antibodies which permit: 1) optimal engineering of the assay reagent; and 2) the reliable generation of a reproducible reagent.
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