Preclinical evaluation of half-life extended Affimer (R) biotherapeutics targeting the PD-L1 pathway

Programmed Cell Death-Ligand 1 (PD-L1) binds to its receptor, Programmed Cell Death protein (PD-1) and is expressed on a range of activated immune cells and is upregulated by tumor cells and by immune cells in the tumor microenvironment. PD-L1 immunotherapies have emerged as effective treatments both as monotherapies and in combinations, providing long term responses in a subset of patients. Phage display selections have identified a range of potent Affimer biotherapeutic antagonists to both human and mouse programmed death-ligand 1 (PD-L1). We have demonstrated when formatted as bivalent molecules they have improved sub nM affinity, half-life extension in a mouse PK study, blocking activity in vitro and in vivoefficacy in syngeneic or xenograph mouse models. Affimer biotherapeutics are a 14kDa monomeric scaffold protein based on the human protease inhibitor Stefin A, lacking post-translational modifications such as disulfide bonds and glycosylation. Large diverse phage display libraries have been created by engineering in two nine amino acid peptide loops into the scaffold backbone. We have identified a range of affinity competitive binders to mouse or human PD-L1 confirmed by performing competition ELISA and SPR using Fc formatted antigen. Half-life extension of lead Affimer proteins was achieved by fusing to human IgG1Fc or as an in-line fusion (ILF) fused to serum albumin binding Affimers. We demonstrated avidity for binding to target antigen, binding to cells in vitro and blockade of the PD-1L/PD-1 interaction using Promega cell based assay. The PK properties of the formatted Affimers in mouse showed half-life extension from 40-120 hours depending on the clone and half-life extension technology used. We have demonstrated that the Affimer scaffold has the necessary properties to be developed as an immunotherapy. The anti-PD-L1 Affimer scaffold proteins were formatted as Fc fusion and in-line fusion formats which showed in vivo efficacy. These molecules will be developed further for both bispecific and drug conjugates to generate new novel biotheraputics that will give greater efficacy in the clinic. Citation Format: Amrik Basran, Emma Jenkins, Estelle Adam, Floriane Laurent, Michele Writer, Assa Oumie, Jyrki Sivula, Maureen West, Emma Stanley, Jennifer Hillman, Viviana Robles-munoz. Preclinical evaluation of half-life extended Affimer® biotherapeutics targeting the PD-L1 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4108.