Conjugation to 10 kDa Linear PEG Extends Serum Half-Life and Preserves the Receptor-Binding Ability of mmTRAIL with Minimal Stimulation of PEG-Specific Antibodies.

The poor in vivo potencies of most therapeutic proteins might be attributed to their short serum half-lives. PEGylation is a well-established method and has been clinically proven to improve pharmacokinetics. mmTRAIL exhibited supercytotoxicity in a variety of tumor cells, but its serum half-life was less than 10 min in mice. Here, mmTRAIL-5K, mmTRAIL-10K, and mmTRAIL-20K were produced by N-terminus-specific PEGylation of mmTRAIL with 5, 10, or 20 kDa mPEG, respectively. The particle sizes of mmTRAIL-5K, mmTRAIL-10K, and mmTRAIL-20K were 9.09 ± 2.76, 12.62 ± 4.05, and 15.68 ± 4.95 nm, which were higher than the threshold (∼7 nm) of renal clearance. Accordingly, mmTRAIL-5K exhibited a serum half-life of 30 min only 3 times longer than that of mmTRAIL. However, both mmTRAIL-10K and mmTRAIL-20K exhibited similar serum half-lives ranging from 350 to 400 min, indicating that PEGylation with 10 or 20 kDa mPEG significantly improved the pharmacokinetics of mmTRAIL. However, death receptor binding of mmTRAIL-20K was reduced 5- to 8-fold, resulting in a 3-fold reduction of cytotoxicity. Additionally, repeated administration of mmTRAIL-20K elicited both mPEG-specific IgG and IgM antibody responses in rats. In contrast, the receptor binding and cytotoxicity of mmTRAIL-10K were similar to those of mmTRAIL. Repeated administration of mmTRAIL-10K did not obviously stimulate mPEG-specific antibody responses in rats and rhesus monkeys. Of the three PEGylated mmTRAIL analogues, mmTRAIL-10K exerted the greatest tumor suppression in mice bearing human tumor xenografts. These results demonstrated that conjugation of mmTRAIL to 10 kDa mPEG was better than that to 5 or 20 kDa mPEG for enhancing antitumor effects.

Fusion to an albumin-binding domain with a high affinity for albumin extends the circulatory half-life and enhances the in vivo antitumor effects of human TRAIL.

Clinical applications of recombinant human tumor necrosis factor-related apoptosis-inducing ligand (hTRAIL) have been limited by their poor pharmacokinetics. Using endogenous albumin as a carrier is an attractive approach for circulatory half-life extension. Here, we produced ABD-hTRAIL and hTRAIL-ABD by fusing the albumin-binding domain (ABD) from protein G to the N- or C-terminus of hTRAIL. We found that ABD-hTRAIL bound human serum albumin (HSA) with a high affinity (0.4 ± 0.18 nM) and formed nanoparticles with an average diameter (~12 nm) above the threshold (~7 nm) of renal filtration. ABD-hTRAIL also bound mouse serum albumin (MSA); thus, its half-life was 40-50-fold greater than that of hTRAIL (14.1 ± 0.87 h vs 0.32 ± 0.14 h). Tumor uptake of ABD-hTRAIL 8-48 h post-injection was 6-16-fold that of hTRAIL. Consequently, the tumor suppression of ABD-hTRAIL in mice bearing subcutaneous xenografts was 3-4 times greater than that of hTRAIL. Additionally, the time period during which ABD-hTRAIL could kill circulating tumor cells was approximately 8 times longer than that of hTRAIL. These results demonstrate that ABD fused to the N-terminus endows hTRAIL with albumin binding ability; once it enters the vasculature, ABD mediates binding with endogenous albumin, thus prolonging the half-life and enhancing the antitumor effect of hTRAIL. However, hTRAIL-ABD did not show a high affinity for albumin and therefore did not display the prolonged circulatory half-life and enhanced antitumor effects. These results demonstrate that N-terminal, but not C-terminal, ABD-fusion is an efficient technique for enhancing the antitumor effects of hTRAIL by using endogenous albumin as a carrier.