Favorable safety and therapeutic efficacy of a novel humanized anti-ADAMTS13 antibody in acquired von willebrand syndrome: A preclinical study

Abstract Introduction Acquired von Willebrand syndrome (AVWS) results from the excessive proteolytic cleavage of von Willebrand factor (VWF) by its specific protease, ADAMTS13. AVWS has been identified as a potential risk factor for bleeding in patients undergoing mechanical circulatory support (MCS). Current management strategies for AVWS associated with MCS include VWF supplementation with fresh frozen plasma or VWF concentrate; however, the therapeutic effect is transient due to persistent VWF degradation. We developed a mouse-derived anti-ADAMTS13 antibody targeting the disintegrin-like domain of ADAMTS13 (Uemura, et al., Blood, 2005) and subsequently achieved its humanization (designated HA10) (Ito, et al., Sci Rep, 2021). In this study, we investigated HA10 as a potential therapeutic approach for AVWS mediated by excessive VWF cleavage. Aim We investigated HA10 inhibitory effect on VWF degradation in MCS-implanted male cynomolgus monkeys following single-dose HA10 administration (Efficacy pharmacological study). Additionally, we assessed the tolerability and toxicity of a single HA10 dose in male cynomolgus monkeys (toxicity study). Methods Efficacy pharmacological study: MCS circuits equipped with a MERA centrifugal pump (Senko Medical, Tokyo, Japan) were implanted in four male cynomolgus monkeys. Perfusion experiments were conducted at 3,000 rpm and the maximum flow rate maintaining stable flow (0.5–1 L/min). We evaluated temporal changes in VWF multimers in animals treated with (n = 2, 10 μg/mL) or without (n = 2) HA10 over 3 hours. VWF multimer analysis was conducted using 1.0% sodium dodecyl sulfate (SDS)-agarose gels. Toxicity studies: In a preliminary non-GLP single-dose study, HA10 was intravenously administered at 6.5 or 32.5 mg/kg to two male cynomolgus monkeys per group, targeting plasma concentrations of 100 and 500 μg/mL. Hematological and biochemical parameters were evaluated at 1, 3, and 6 days post-administration. Histopathological examinations of the heart and brain were conducted on day 14. In the definitive single-dose GLP study, HA10 was intravenously administered at 3 and 25 mg/kg to three males per group. The 3 mg/kg dose was selected to sustain plasma levels above the estimated effective concentration (10 μg/mL) for approximately 1 week. The control group (n = 3) received 146 mM purified sucrose/0.05% (w/v) polysorbate 80 in PBS (-), administered identically to HA10. During the observation period, blood biochemical analyses were performed on days 1, 3, 6, and 14; necropsy and histopathological examinations were conducted on day 14. The efficacy pharmacological study and the toxicity studies were approved by the Institutional Animal Care and Use Committees of Nissei Bilis Co., Ltd. and SHIN NIPPON BIOMEDICAL LABORATORIES, Ltd., respectively. Results Efficacy pharmacological study: We observed VWF degradation in untreated animals. In contrast, large VWF multimers were preserved in HA10-treated animals throughout the experiment. Toxicity studies: In the preliminary non-GLP toxicity study, no deaths occurred during the observation period, and no HA10-related abnormalities were observed in the histopathological examinations of the heart and brain. The mean HA10 concentration at 0.167 hours post-administration was 175 μg/mL in the 6.5 mg/kg group and 942 μg/mL in the 32.5 mg/kg group. The mean elimination half-life of HA10 was 64.9 hours in the 6.5 mg/kg group and 69.5 hours in the 32.5 mg/kg group. In the definitive GLP toxicity study, no mortality occurred during the study period. In the 25 mg/kg group, thrombocytopenia was observed in one animal; however, this finding was considered to have low toxicological significance, as it resolved by day 14. Additionally, elevated levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and creatinine kinase were observed on days 1, 3, and 6 in this group. However, no corresponding histopathological abnormalities were observed in the affected organs or tissues, suggesting these changes had low toxicological relevance. Conclusion Studies in cynomolgus monkeys demonstrated HA10 efficacy in inhibiting VWF degradation under high shear stress conditions and established its safety profile. Although thrombotic thrombocytopenic purpura (TTP) represents a potentially severe complication of HA10, no TTP-associated findings were reported. Additional basic research data have been collected to further characterize HA10 preclinical safety profile.

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