Radiomitigation and Tissue Repair Activity of Systemically Administered Therapeutic Peptide TP508 Is Enhanced by PEGylation

Abstract

TP508 is a synthetically derived tissue repair peptide that has previously demonstrated safety and potential efficacy in phase I/II clinical trials for the treatment of diabetic foot ulcers. Recent studies show that a single injection of TP508 administered 24 h after irradiation significantly increases survival and delays mortality in murine models of acute radiation mortality. Thus, TP508 is being developed as a potential nuclear countermeasure. Because of the short plasma half-life of TP508, we hypothesize that increasing the peptide bioavailability would increase TP508 efficacy or reduce the dosage required for therapeutic effects. We, therefore, evaluated the covalent attachment of various sizes of polyethylene glycol to TP508 at either its N-terminus or at an internal cysteine. A size-dependent increase in TP508 plasma half-life due to PEGylation was observed in blood samples from male CD-1 mice using fluorescently labeled TP508 and PEGylated TP508 derivatives. Biological activity of PEGylated TP508 derivatives was evaluated using a combination of biologically relevant assays for wound closure, angiogenesis, and DNA repair. PEG5k-TP508 enhanced wound closure after irradiation and enhanced angiogenic sprouting in murine aortic ring segments relative to equimolar dosages of TP508 without enhancing circulating half-life. PEG30k-TP508 extended the plasma half-life by approximately 19-fold while also showing enhanced biological activity. Intermediate-sized PEGylated TP508 derivatives had enhanced plasma half-life but were not active in vivo. Thus, increased half-life does not necessarily correlate with increased biological activity. Nevertheless, these results identify two candidates, PEG5k-TP508 and PEG30k-TP508, for potential development as second-generation TP508 injectable drugs.

A review of radiation countermeasures focusing on injury-specific medicinals and regulatory approval status: part III. Countermeasures under early stages of development along with ‘standard of care’ medicinal and procedures not requiring regulatory approval for use

“…This study, along with other data, suggests that increased survival following TP508 treatments may be due in part to the agent's effect on vascular endothelial cells. PEGylated TP508 enhanced wound closure after combined injury (8 Gy irradiation and wounding) in CD-1 outbred mice (McVicar et al 2017).…”

Conjugates for use in peptide therapeutics: a systematic review and meta-analysis

“…The mean half-lives of conjugated peptides are seen to increase overall as indicated in Table 3. There are, however, a few exceptions observed as in the cases of Fawaz et al (38) and McVicar, Rayavara & Carney (47). Note that the half-life of the control peptide for Fawaz et al came from Tang et al (38).…”

Drug discovery strategies for acute radiation syndrome

“…Out of these nine agents, only one agent, CBLB502, was identified based on well-characterized receptor as a target (Toll-like receptor-5, TLR5) for a ligand (truncated flagellin, TLR5 ligand) [67]. Several additional agents, such as cytokines and growth factors [62,82], indralin [83,84], tocols [85,86] metformin [87][88][89][90], lipopeptides [91][92][93], anti-ceramide antibody [94][95][96], cellular therapeutic agents [97][98][99][100], TP508 [101][102][103], inhibitors of various pathways [104][105][106], Oltipraz [107], and R-spondin1 [108][109][110] are under development as radiation countermeasures for various sub-syndromes of ARS (Table 3) and most of these agents are being developed following PBDD strategy. There are several agents under advanced development that show considerable promise and, accordingly, may very well receive FDA approval for human use in the near future.…”

“…TP508/Chrysalin/Rusalatide Tested in murine model of radiation and combined injury (radiation plus wound), mitigates H-ARS as well as GI-ARS Small peptide binding domain of human prothrombin and binds to thrombin receptor, counters chronic hypoxia TBDD/PBDD [101][102][103] Inhibitors of various pathways Several such agents inhibiting various cellular signaling pathways are being investigated. These agents interact with cell surface receptors transmitting various cellular signals which lead to changes at cellular and tissue levels TBDD/PBDD [104][105][106] Oltipraz/synthetic dithiolethione Improved survival of irradiated mice Reduces radiation-induced lipid peroxidation and acid phosphatase and modulated, glutathione and alkaline phosphatase PBDD [107] R-spondin1 A 263 amino acid protein, stimulates the repopulation of GI crypt cells and mitigates radiation-induced GI-ARS A mitogenic factor for GI stem cells, induces Wnt/β-catenin pathway and promotion of GI stem cell regeneration PBDD [108][109][110] ARS: acute radiation syndrome, GI-ARS: Gastrointestinal ARS; H-ARS: Hematopoietic-ARS.…”