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 normally do not cross the blood-brain barrier (BBB), to brain drug delivery vectors. The murine 83-14 MAb to the human insulin receptor (HIR) is a potential brain drug 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 chimeric HIRMAb, expression and characterization of the protein, radiolabeling of the chimeric HIRMAb with 111-indium and 125-iodine, and quantitative autoradiography of living primate brain taken 2 hours after intravenous administration of the [¹¹¹In]chimeric HIRMAb. Results. The chimeric HIRMAb had identical affinity to the target antigen as the murine HIRMAb based on Western blotting and immunoradiometric assay using partially purified HIR affinity purified from serum free conditioned media produced by a CHO cell line secreting soluble HIR. The [¹²⁵I]chimeric HIRMAb was avidly bound to isolated human brain capillaries, and this binding was blocked by the murine HIRMAb. The [¹¹¹In]chimeric HIRMAb was administered intravenously to an anesthetized Rhesus monkey, and the 2 hour brain scan showed robust uptake of the chimeric antibody by the living primate brain. Conclusions. A genetically engineered chimeric HIRMAb has been produced, and the chimeric antibody has identical reactivity to the human and primate BBB HIR as the original murine antibody. This chimeric HIRMAb may be used in humans for drug targeting through the BBB of neurodiagnostic or neurotherapeutic drugs that normally do not cross the BBB.