Chemical Biology Seminar
Due to their specificity and favorable pharmacological properties, monoclonal antibodies (mAbs) are being rapidly developed and armed to image and treat disease. Invariably, chemical methods and/or extensive genetic engineering efforts are required to add novel functionality to mAbs. Through diffraction methods, we have identified a novel peptide interface within a cavity formed by the light and heavy chains of the cetuximab Fab that may provide an entirely novel, noncovalent route to functionalize and/or manipulate mAbs. Distinct from other Fab binding proteins such as protein A or protein L, we show that this peptide interaction is exclusive to cetuximab. In other words, the peptide binding site absent in human mAbs. Moreover, we demonstrate that the presence of the peptide (which we have named a meditope) does not affect antigen binding. Anticipating that this non-covalent method could be used to direct an imaging agent to a tumor cell, we created a bivalent meditope analog and show that this bivalent analog targets with antigen presenting cells with high specificity and affinity only in the presence of cetuximab. Furthermore, we have successfully grafted the meditope binding site onto other mAbs including trastuzumab and rituximab through a minimal set of mutations (12 or less). Finally, we demonstrated that the combination of the meditope-enabled mAbs and the bivalent meditope selectively targets antigen-bearing cells. In toto, these biophysical and in vitro studies suggest an entirely novel means to leverage the antigen specificity of mAbs coupled to a meditope site for imaging, drug delivery and/or tethering multiple mAbs bound to receptors.
Key words: Protein Engineering, Crystallography and Biophysics, Energy Additivity and Avidity, Cancer Therapeutics (Antibody-drug conjugates).