Targeting antigens with antibodies exhibiting pH/Ca2+-dependent binding against an antigen is an attractive strategy to mitigate target-mediated disposition and antigen buffering. Studies have reported improved serum exposure of antibodies exhibiting pH/Ca2+-binding against membrane-bound receptors. Asialoglycoprotein receptor 1 (ASGR1) is a membrane-bound receptor primarily localized in hepatocytes. With a high expression level of approximately one million receptors per cell, high turnover, and rapid recycling, targeting this receptor with a conventional antibody is a challenge. In this study, we identified an antibody exhibiting pH/Ca2+-dependent binding to ASGR1 and generated antibody variants with increased binding to neonatal crystallizable fragment receptor (FcRn). Serum exposures of the generated anti-ASGR1 antibodies were analyzed in transgenic mice expressing human FcRn. Contrary to published reports of increased serum exposure of pH/Ca2+-dependent antibodies, the pH/Ca2+-dependent anti-ASGR1 antibody had rapid serum clearance in comparison to a conventional anti-ASGR1 antibody. We conducted sub-cellular trafficking studies of the anti-ASGR1 antibodies along with receptor quantification analysis for mechanistic understanding of the rapid serum clearance of pH/Ca2+-dependent anti-ASGR1 antibody. The findings from our study provide valuable insights in identifying the antigens, especially membrane bound, that may benefit from targeting with pH/Ca2+-dependent antibodies to obtain increased serum exposure.

Bispecific antibodies, engineered to recognize two targets simultaneously, demonstrate exceptional clinical potential for the therapeutic intervention of complex diseases. However, these molecules are often composed of multiple polypeptide chains of differing sequences. To meet industrial scale productivity, enforcing the correct quaternary assembly of these chains is critical. Here, we describe Chain Selectivity Assessment (CSA), a high-throughput method to rationally select parental monoclonal antibodies (mAbs) to make bispecific antibodies requiring correct heavy/light chain pairing. By deploying CSA, we have successfully identified mAbs that exhibit a native preference toward cognate chain pairing that enables the production of hetero-IgGs without additional engineering. Furthermore, CSA also identified rare light chains (LCs) that permit positive binding of the non-cognate arm in the common LC hetero-IgGs, also without engineering. This rational selection of parental mAbs with favorable developability characteristics is critical to the successful development of bispecific molecules with optimal manufacturability properties.

Inhibitors that block the programmed cell death-1 (PD-1) pathway can potentiate endogenous antitumor immunity and have markedly improved cancer survival rates across a broad range of indications. However, these treatments work for only a minority of patients. The efficacy of anti-PD-1 inhibitors may be extended by cytokines, however, the incorporation of cytokines into therapeutic regimens has significant challenges. In their natural form when administered as recombinant proteins, cytokine treatments are often associated with low response rates. Most cytokines have a short half-life which limits their exposure and efficacy. In addition, cytokines can activate counterregulatory pathways, in the case of immune-potentiating cytokines this can lead to immune suppression and thereby diminish their potential efficacy. Improving the drug-like properties of natural cytokines using protein engineering can yield synthetic cytokines with improved bioavailability and tissue targeting, allowing for enhanced efficacy and reduced off-target effects. Using structure guided engineering we have designed a novel class of antibody-cytokine fusion proteins consisting of a PD-1 targeting antibody fused together with an interleukin-21 (IL-21) cytokine mutein. Our bifunctional fusion proteins can block PD-1/programmed death-ligand 1 (PD-L1) interaction whilst simultaneously delivering IL-21 cytokine to PD-1 expressing T cells. Targeted delivery of IL-21 can improve T cell function in a manner that is superior to anti-PD-1 monotherapy. Fusion of engineered IL-21 variants to anti-PD1 antibodies can improve the drug-like properties of IL-21 cytokine leading to improved cytokine serum half-life allowing for less frequent dosing. In addition, we show that targeted delivery of IL-21 can minimize any potential detrimental effect on local antigen-presenting cells. A highly attenuated IL-21 mutein variant (R9E:R76A) fused to a PD-1 antibody provides protection in a humanized mouse model of cancer that is refractory to anti-PD-1 monotherapy. Collectively, our preclinical data demonstrate that this approach may improve upon and extend the utility of anti-PD-1 therapeutics currently in the clinic.

Designing drugs to treat diseases associated with articular joints, particularly those targeting chondrocytes, is challenging due to unique local environmental constraints including the avascular nature of cartilage, the absence of a closed joint compartment, and a highly cross-linked extracellular matrix. In an effort to address these challenges, we developed a novel strategy to prolong residence time of intra-articularly administered protein therapeutics. Avimer domains are naturally found in membrane polypeptides and mediate diverse protein-protein interactions. Screening of a phage Avimer domain library led to identification of several low affinity type II collagen-binding Avimers. Following several rounds of mutagenesis and reselection, these initial hits were transformed to high affinity, selective type II collagen-binding Avimers. One such Avimer (M26) persisted in rat knees for at least 1 month following intra-articular administration. Fusion of this Avimer to a candidate therapeutic payload, IL-1Ra, yielded a protein construct which simultaneously bound to type II collagen and to IL-1 receptor. In vitro, IL-1Ra_M26 bound selectively to cartilage explants and remained associated even after extensive washing. Binding appeared to occur preferentially to pericellular regions surrounding chondrocytes. An acute intra-articular IL-1-induced IL-6 challenge rat model was employed to assess in vivo pharmacodynamics. Whereas both IL-1Ra_M26 and native IL-1Ra inhibited IL-6 output when co-administered with the IL-1 challenge, only IL-1Ra_M26 inhibited when administered 1 week prior to IL-1 challenge. Collagen-binding Avimers thus represent a promising strategy for enhancing cartilage residence time of protein therapeutics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1238-1247, 2018.

Joanne T. Hulme†, Warren N. D’Souza†*, Helen J. McBride, Bo-Rin Park Yoon, Angela M. Willee, Amy Duguay, Melissa Thomas, Bin Fan, Maria Rosalyn Dayao, James B. Rottman, Kim Merriam, Jiansong Xie, Richard Smith, Benjamin M. Alba, Ryan B. Case, Khue Dang, Anielka Montalvan, Natalia Grinberg, Hong Sun, Roy A. Black, Christopher A. Gabel, John E. Sims, Kevin Moore, Alice Bakker & Peng Li* Affiliations: Inflammation, Amgen Inc., Seattle, WA, USA Inflammation, Amgen Inc., Thousand Oaks, CA. Therapeutic Discovery, Amgen Inc., South San Francisco, California, USA Comparative Biology & Safety Sciences, Amgen Inc., Cambridge, MA, USA Clinical Immunology, Amgen Inc., Thousand Oaks, CA. *Corresponding authors: wdsouza@amgen.com, pengl@amgen.com † Equal contributors