Abstract B004: Enhanced efficacy of immune modulators with albumin binding domains
Authors: Cini John 
Published: August 2018

Abstract
Numerous approaches to improve the biologic half-life and tumor targeting of small therapeutic proteins (e.g., interleukins), peptides, and fragment-based antibodies (scFv) have been described. The attractiveness of these smaller biologic formats includes improved tumor penetration and the ability to engineer a single molecule that can modulate several tumor targets. However, the limitation of these smaller biologic-based therapeutics (less than 150kd) is their short half-life and lack of tumor targeting. Here we describe a unique (24Kd) single-chain fragment antibody (ScFv) that binds to serum albumin across a range of pHs and that retains binding to, and recycling by, the neonatal Fc-receptor (FcRn), resulting in a significant extension of the biologic half-life of three different therapeutic proteins that were molecularly linked to this albumin binding domain (ABD) fragment antibody. A second advantage to having an ABD construct is enhanced tumor targeting. Numerous studies have shown that albumin-mediated delivery of therapeutic proteins and small molecules results in tumor accumulation that was higher than that produced by PEGylation, Thus, fusion with an ABD is a promising approach for improving the therapeutic/safety window of small recombinant therapeutic proteins (e.g., interleukins, receptor ligands) or enhancing the targeting of receptor-directed scFv therapeutic proteins. Using the XOMA phage library, we discovered an scFv ABD that has high binding affinity to mouse, human, and cynomolgus serum albumin. We demonstrate that fusion constructs of this scFv ABD with several different small therapeutic proteins (recombinant interleukin proteins and scFvs targeting relevant immune-oncology receptors) demonstrated improved serum half-life and greater efficacy compared to the naked proteins without the ABD present. We have further characterized our scFV-ABD and have demonstrated that (1) biologic activity is retained when the therapeutic protein is attached via the N- or C-terminus, suggesting utility for delivering more than one therapeutic protein; and (2) half-life in mouse serum in vivo was extended from minutes to hours/days for three different recombinant proteins with MWs of 10-80Kd. Additionally, we have demonstrated markedly superior reductions in tumor growth and improved overall survival with our ABD constructs vs free recombinant protein in an established B6F10 melanoma model. Moreover, superior efficacy was observed at lower doses and with a single dose of the ABD constructs vs free recombinant protein. The versatility of this ABD construct to attached combinations of various types of recombinant immune stimulators and/or scFv to immune checkpoint inhibitors can result in significantly enhanced clinical efficacy.
Citation Format: John Cini. Enhanced efficacy of immune modulators with albumin binding domains [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B004.