Vol.:(0123456789) 1 3 International Journal of Peptide Research and Therapeutics https://doi.org/10.1007/s10989-020-10033-7 Prolonged Beneft of Reltecimod Despite Short Plasma Half‑Life Rotem Edgar 1  · Avi Cohen 1  · Dalia Hillman 2  · Raymond Kaempfer 2  · Anat Shirvan 1 Accepted: 22 January 2020 © Springer Nature B.V. 2020 Abstract Reltecimod (previously AB103 or p2TA) is a short-peptide mimetic of the CD28 costimulatory receptor on T cells that attenuates CD28/B7-2 signaling, which are responsible for the hyperinfammatory response that is observed during severe infections. A single-dose of reltecimod provides sustained survival beneft in animal models of sepsis and clinical beneft in patients with necrotizing soft tissue infections. Here, the pharmacokinetic/pharmacodynamics profle of reltecimod was evaluated to determine the basis of its sustained single-dose efect. The half-life of reltecimod was assessed using bioana- lytical methods in diferent animals, and the biodistribution was studied in male BALB/c mice that were administered a single intravenous dose of [ 14 C]-reltecimod. Blood partitioning was performed, and the minimal time to observe efcacy of reltecimod was evaluated in vitro. The plasma half-life of reltecimod was short in humans and all tested animal models, ranging from 1 to 8 min. Upon leaving the blood vessels, reltecimod quickly redistributed to lymphatic tissues, where T cells are produced and exposed to antigens. Lymphatic concentration of reltecimod was 22 times higher than plasma concentra- tion by 20 min post-administration, and reltecimod was enriched in the white blood cell fraction of blood (6.8% after 2 h). Reltecimod had a rapid onset of efect (5 min) that lasted for at least 12 h based on levels of IFN-γ that were secreted by antigen-activated human peripheral blood mononuclear cells. This suggests that reltecimod’s prolonged clinical benefts are based on fast distribution to target organs and rapid intervention with signaling pathways, irrespective of its short residence time in the plasma. Keywords Reltecimod · AB103 · Necrotizing soft tissue infection (NSTI) · Sepsis · Cytokine storm · Half-life Abbreviations AAALAC Association for Assessment and Accredi- tation of Laboratory Animal Care Ci Curie ELISA Enzyme-linked immunosorbent assay g Gram h Hour/hours IFN Interferon IV Intravenous L Liter LC–MS/MS Liquid chromatography with tandem mass spectrometry LSC Liquid scintillation counting MCH-II Major histocompatibility complex class II Min Minute/s mmol Millimoles NSTI Necrotizing soft-tissue infection PAR Peak area ratio hPBMC Human peripheral blood mononuclear cell PBS Phosphate-bufered saline PD Pharmacodynamic PK Pharmacokinetic RBC Red blood cell rpm Revolutions per minute Superantigen/s SAg/s SEB Staphylococcal enterotoxin B Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10989-020-10033-7) contains supplementary material, which is available to authorized users. * Rotem Edgar rotem.edgar@gmail.com * Anat Shirvan anatshirvan@gmail.com.com 1 Atox Bio, Weizmann Science Park, 8 Pinhas Sapir St., 7403631 Ness Ziona, Israel 2 Department of Biochemistry and Molecular Biology, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel