Transport across the primate blood-brain barrier of a genetically engineered chimeric monoclonal antibody to the human insulin receptor

Purpose. Brain drug targeting may be achieved by conjugating drugs, that no rmally do not cross the blood-brain barrier (BBB), to brain drug delivery v ectors. The murine 83-14 MAb to the human insulin receptor (HIR) is a poten tial brain drugs targeting vector that could be used in humans, if this MAb was genetically engineered to form a chimeric antibody, where most of the immunogenic murine sequences are replaced by human antibody sequence., Methods. The present studies describe the production of the gene for the ch imeric HIRMAb, expression and characterization of the protein, radiolabelin g of the chimeric HIRMAb with 111-indium and 125-iodine, and quantitative a utoradiography of living primate brain taken 2 hours after intravenous admi nistration of the [(111)ln]chimeric HIRMAb. Results, The chimeric HIRMAb had identical affinity to the target antigen a s the murine HIRMAb based on Western blotting and immunoradiometric assay u sing partially purified HIR affinity purified from serum free conditioned m edia produced by a CHO cell line secreting soluble HIR. The [I-125]chimeric HIRMAb was avidly bound to isolated human brain capillaries, and this bind ing was blocked by the murine HIRMAb. The [(111)ln]chimeric HIRMAb was admi nistered intravenously to an anesthetized Rhesus monkey, and the 2 hour bra in scan showed robust uptake of the chimeric antibody by the living primate brain. Conclusions. A genetically engineered chimeric HIRMAb has been produced, an d the chimeric antibody has identical reactivity to the human and primate B BB HIR as the original murine antibody. This chimeric HIRMAb may be used in humans for drug targeting through the BBB of neurodiagnostic or neurothera peutic drugs that normally do not cross the BBB.