Development of Thioredoxin Monothiol Derivatives for Mitigating Radiation Induced Hematopoietic Injury

• Published in: Blood 2023-11, Vol.142 (Supplement 1), p.3639-3639
• Main Authors: Kang, Yubin, Wu, Jian, Wang, Xiaobei, Mathews, Parker, Jabbar, Shaima, Schaaf, George William, Olson, John, Ross, Joel, Chao, Nelson J., Cline, Mark, Heifetz, Peter B.
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2023-185355

Hematopoietic stem cells (HSCs) are among the most sensitive cells to radiation injury and contribute to many of the manifestations of acute radiation syndrome. There is an unmet need for effective agents that can be used to rescue radiation injury and enhance HSC recovery especially when administered post-irradiation. We previously identified the stress-protective human thioredoxin-1 protein (TRX) as a novel molecule for enhancing HSC recovery in mouse models of radiation injury. Treatment of lethally irradiated mice with recombinant TRX 24 hours after irradiation increased survival by 45%. However, native or recombinant TRX has a very short half-life (0.5-1 hr), which limits its clinical application, and the ability of exogenous TRX to internalize to the cytosol and support cellular proliferation is a potential concern. To overcome these limitations, an engineered monocysteinic, chemically pre-reduced TRX variantin which the second active-site Cys at position 35 has been replaced by Ser was developed (ORP100S). This modification stabilizes the mixed-disulfide transition state intermediate formed during docking and reduction of TRX-specific target protein Cys disulfide bonds. The resulting ORP100S Cys 32-target Cys linkage shifts the thiol-disulfide equilibrium and confers a longer duration and more potent activity compared to native TRX. Compared to TRX, ORP100S does not increase multiplication of EML hematopoietic cells in vitro, consistent with enhanced extracellular regulatory/stress-protective activity and attenuated intracellular proliferative activity. We first tested the effectiveness of ORP100S in mitigating lethal total body irradiation (TBI) in C57Bl/6 mice. Animals were irradiated (9.5 Gy) and 24 hours later were administered (IV, tail-vein injection) either PBS control buffer or ORP100S in PBS at 32 μg/mouse, every other day for a total of five doses. While all lethally-irradiated mice receiving PBS alone died within 2 weeks, half of the mice receiving ORP100S survived through termination of the study at 40 days. We further performed a dose-ranging efficacy study. At 24 hrs after TBI (8.45Gy), C57Bl/6 mice were given PBS or ORP100S in PBS (32 μg, 64 μg, 128 μg, 320 μg IV; 128μg SQ) every other day for a total of five doses. Nine of ten 128 μg SQ ORP100S-treated mice and all treatment groups given ORP100S at greater than 64 μg IV survived to the end of study on Day 45. Because subcutaneous injection is a preferred route of administration in th