HDAC Inhibitors as Epigenetic Regulators

(2013) Minimal Self peptides that inhibit phagocytic clearance and enhance delivery of nanoparticles. to ubiquitous expression of CD47. These factors reduce bioavailability and increase the risk of toxicity. Here, we present an alternative strategy to antagonize the CD47-SIRP pathway by engineering high affinity CD47 variants that target SIRP, which has restricted tissue expression. CD47 proved to be refractive to standard affinity maturation techniques targeting its binding interface with SIRP. Therefore, we developed a novel engineering approach, whereby we augmented the existing contact interface via N-terminal peptide extension, coined Velcro engineering. The high affinity variant (Velcro-CD47) bound to (R)-UT-155 the two most prominent Rabbit Polyclonal to ELOVL3 human SIRP alleles with greatly increased affinity relative to wild-type CD47 and potently antagonized CD47 binding to SIRP on human macrophages. Velcro-CD47 synergizes with tumor-specific monoclonal antibodies to enhance macrophage phagocytosis of tumor cells antibody-mediated killings of tumor cells by phagocytes have been generated to circumvent the potential issues associated with a (R)-UT-155 large antigen sink (12). One potential limitation is that an antibody has poor tissue penetration into solid tumors due to its large size (23), and tissue penetration in the case of targeting SIRP expressed on tumor-infiltrated macrophages is critical for therapeutic efficacy. Perhaps a smaller version of an anti-SIRP blocking agent could have benefits in this regard. In this study, we aimed to engineer a soluble high affinity variant of human CD47 ECD that binds human SIRP to turn off the don’t-eat-me transmission and thereby promote tumor clearance by macrophages. Blocking SIRP targets a much more defined cell populace than blocking CD47. In addition, compared with anti-SIRP antibodies (12), an designed CD47-ECD may exhibit superior tissue penetrance, utilize the natural CD47-SIRP-binding site so that resistance mechanisms are hard to evolve, and be suitable for further chemical manipulation in imaging applications. To this end, we have developed a novel protein-engineering technique, coined Velcro engineering, which increases affinity of receptor-ligand interactions by extending an existing contact interface via peptide extension at the N terminus. This approach should be quite general for affinity maturation of receptor-ligand interactions that are targets for therapeutic development. EXPERIMENTAL PROCEDURES Protein Expression and Purification Human SIRP allele 1 domain name 1 (a1d1), allele 2 domain name 1 (a2d1), and CV1 were expressed as explained previously (22). Briefly, SIRP variants were cloned into a altered pMal-p2X expression vector (New England Biolabs), made up of a 3C protease cleavage site (LEVLF(Q/G)P) after the maltose-binding protein tag and a C-terminal His8 tag, and were expressed in the periplasm of BL-21(DE3) (High Five) cells (Invitrogen) using the BaculoGold baculovirus expression system (BD Biosciences) for secretion and purified by Ni-NTA and size exclusion chromatography with a Superdex-75 column. Biotinylated CD47 and SIRP variants were expressed with a C-terminal biotin acceptor peptide tag (GLNDIFEAQKIEWHE) and purified as explained above. The purified proteins were biotinylated with BirA ligase and then re-purified from your reaction combination by size exclusion chromatography. For profiling human peripheral blood, CV1 A17C and N3612 F14C were expressed and purified as explained above to allow site-specific conjugation via maleimide linking chemistry. The proteins were conjugated to Alexa Fluorophore 647 (A647) maleimide (Life Technologies, Inc.) according to the manufacturer’s protocol and re-purified from your reaction combination by size exclusion chromatography. For phagocytosis assays, endotoxin was removed using Triton X-114 as explained previously (22), and endotoxin removal was confirmed using the ToxinSensor Chromogenic LAL endotoxin assay kit (R)-UT-155 (Genscript). Yeast Display and Construction of the CD47 Extension Library The human CD47 IgSF domain name, with a C15G mutation (25), was displayed on the surface of strain EBY100 as an N-terminal fusion to (R)-UT-155 Aga2 using the pYAL vector (26), leaving a free N terminus. To construct the CD47 extension library, the mutagenized CD47 DNA constructs from N3L0, N3L2, and N3L4 molecule designs were mixed and combined with linearized pYAL vector and EBY100 yeast. The.