Engineering Highly Specific Fibronectin Type III domain-fused Elastin-like Polypeptides to the PD-L1 for Improved Immunotherapy
Junseon Min, Ashutosh Chilkoti*
Department of Biomedical Engineering, Duke University, Durham, NC
Cancer immunotherapy, a breakthrough that harnesses our immune system to cure cancer, has been greatly promoted by the recent success of clinical trials. One of the most promising strategies includes antibodies to block immune-checkpoint pathways (e.g. PD-1, PD-L1, or CTLA4) to activate T cells to capture tumors. Despite its substantial potential, inherent challenges to utilize antibody as a drug confine its versatile applications. Advances in protein engineering and phage display have contributed to the development of alternative non-antibody scaffolds (e.g. Fibronectin Type III (FN3) domain)(1) to replace complex antibodies. They are tremendously advantageous because of low manufacturing cost, the ease of precise control to reproduce and structural plasticity that is amenable to genetic and chemical modifications. However, the comparatively smaller size of them provides poorer retention behaviors within the body. To overcome all these hurdles, herein, we developed a novel approach whereby thermally sensitive elastin-like polypeptides (ELPs) are fused with the newly engineered multiple FN3 domain molecules that specifically bind to the PD-L1 using phage display. The ELP micelles(2) are triggered by body heat to rapidly form an insoluble and viscous coacervate in 2 minutes. These injectable hydrogels are expressed as soluble proteins in E. coli, permitting convenient production and purification at high yield, and they are also stable in near physiologic aqueous buffer without any reconstitution or further mixing. Most significantly, they can prolong its circulation time with the depot formation as well as modulate the release rate of therapeutics from the subcutaneous injection to enhance immunotherapeutic efficacy. Thus, this enables more practical utility to overcome the hurdles of traditional antibody-based immunotherapy.
1. A. Koide et al. J. Mol. Biol. 415, 393-405 (2012)
2. A. Chilkoti et al. Adv. Drug Deliv. Rev. 54, 613-630 (2002)