New Human Antibodies for CNS Drug Delivery

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ABSTRACT Millions of people worldwide suffer from neurological diseases such as Alzheimer’s disease, stroke, and brain cancer. Advances in protein/gene profiling techniques and high throughput drug screening technologies have spawned many new drug candidates. However, the blood-brain barrier (BBB) has impeded the development and clinical realization of this new generation of neurotherapeutics by restricting the brain uptake of most small molecule therapeutics, and prohibiting brain uptake of protein- and gene-based medicines. A promising noninvasive brain delivery strategy takes advantage of endogenous BBB transport mechanisms as a means to shuttle drug cargo from the blood to the brain. Such receptor-mediated transport systems can be targeted using the exquisite specificity of antibodies that are in turn linked to a drug payload that can include small molecules, proteins, or DNA therapeutics. After binding to the receptor on the blood side, the antibody- drug conjugate acts as an artificial substrate for the transporter and is transcytosed from the blood, across the BBB, and into the brain. However, current approaches have yielded limited brain uptake because the targeted transporters are ubiquitously expressed and the antibody targeting reagents have low BBB permeability. Therefore, this proposal is focused on the identification and validation of a new panel of antibodies and cognate transporters that can mediate BBB crossing of therapeutics. The antibodies were identified by mining a large phage display antibody library against a BBB model comprising human induced pluripotent stem cell- derived brain microvascular endothelial-like cells (BMECs). The barrier characteristics of these BMECs are well- suited to screen large antibody libraries for those antibodies capable of crossing the BBB in vitro. Moreover, at the transcriptome level, the transporter profiles in these cells correlate quite well to freshly isolated human BMECs. Finally, the human sourcing ensures that identified antibodies recognize human BBB transporters. Using this innovative platform, we have identified a panel of high value antibodies that preliminary data indicate are capable of binding both the human and murine BBB and delivering pharmacologically relevant amounts of drug cargo to the murine brain. We propose to further validate these brain targeting antibodies by identifying their cognate transporters. Next, we will determine their pharmacokinetic properties, biodistribution and brain regiospecificity. Finally, the antibodies will be tested for their ability to mediate brain uptake of conjugated drug cargo to normal brain and to diseased brain in the form of a murine stroke model. Those antibodies that exhibit significant and selective brain uptake would represent new, noninvasive drug delivery vectors with potential application in many neurological disease settings.