Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of Anti-Vwf Nanobody® ALX-0681 After Single and Multiple Subcutaneous Administrations to Healthy Volunteers.
Authors: Abd-Elaziz Khalid , Kamphuisen Pieter W. , Lyssens Christophe , Reuvers Mariska , den Daas Izaak , Van Bockstaele Femke , Vercruysse Kristof , Ulrichts Hans , Baumeister Judith , Crabbe Patricia , Compernolle Veerle , Holz Josefin-Beate 
Published: October 2019

Abstract
Abstract 1063
Poster Board I-85
ALX-0681 is a humanized bivalent Nanobody®, that binds to the A1 domain of von Willebrand factor (vWF) and hence blocks its interaction with platelet receptor GPIb-IX-V. Given its mode of action, ALX-0681 could provide an alternative treatment option for thrombotic thrombocytopenic purpura (TTP), a rare and life-threatening condition characterized by systemic platelet aggregation in the microcirculation mediated by activated vWF multimers. The goal of this Phase I trial in healthy volunteers was to determine the maximum tolerated dose (MTD) or biologically effective dose (BED) and the Phase II dosing and scheduling of ALX-0681, in order to support the further clinical development of ALX-0681 in TTP patients. In total, 36 healthy volunteers were included in this randomized, placebo-controlled study to evaluate the safety of single ascending doses and multiple doses of ALX-0681 administered subcutaneously (s.c.) (Table 1).
Table 1 Dosing schedule for Phase I trial with ALX-0681 Cohort Dose (mg) Number of daily doses Subjects receiving ALX-0681 Subjects receiving placebo Single dose Cohort 1 2 1 3 1 Cohort 2 4 1 3 1 Cohort 3 8 1 3 1 Cohort 4 16 1 3 1 Cohort 5 10 1 3 1 Multiple dose Cohort 6 10 7 6 2 Cohort 7 10 14 6 2 Study endpoints included safety (dose limiting toxicities, adverse events (AEs) and immunogenicity), pharmacokinetics (PK), pharmacodynamics (PD) and pharmacological efficacy of ALX-0681. The latter endpoint was addressed by measuring the ristocetin cofactor (RICO) biomarker, reflecting vWF mediated inhibition of platelet aggregation. ALX-0681 was safe and well tolerated at all dose levels (Table 2). One unrelated SAE (meniscus lesion) occurred. The number of observed signs of bleeding and bruises increased with increasing treatment duration. However, all these events were of mild intensity. No signs of immunogenicity were observed for a minimum of 45 days after the last injection.
Table 2 Summary of main safety results (number (%) of subjects with event) Dose level Subjects (n) AE SAE Bleeding Hematoma at injection site Hematoma at blood sampling site Other hematoma Single dose 2 mg 3 2 (67) 0 (0) 1 (33) 0 (0) 1 (33) 0 (0) 4 mg 3 2 (67) 0 (0) 1 (33) 0 (0) 0 (0) 0 (0) 8 mg 3 3 (100) 0 (0) 0 (0) 0 (0) 1 (33) 0 (0) 16 mg 3 3 (100) 0 (0) 0 (0) 0 (0) 0 (0) 1 (33) 10 mg 3 1 (33) 0 (0) 0 (0) 0 (0) 1 (33) 0 (0) Placebo 5 3 (60) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) Multiple dose 10 mg (7d) 6 6 (100) 1 (17) 5 (83) 1 (17) 0 (0) 3 (50) Placebo (7d) 2 2 (100) 0 (0) 1 (50) 0 (0) 1 (50) 0 (0) 10 mg (14d) 6 6 (100) 0 (0) 5 (83) 5 (83) 4 (67) 5 (83) Placebo (14d) 2 2 (100) 0 (0) 1 (50) 0 (0) 0 (0) 0 (0) PK analysis showed a rapid increase in ALX-0681 plasma concentration (tmax = 4-10 h post dose), followed by a slow elimination phase (t1/2 = 10-78 h). All subjects dosed with ALX-0681 at 8 mg or higher showed complete inhibition of RICO activity to < 20% with an onset of 1-6 h post dose. This inhibition was maintained until 12-360 h post dose, depending on the dose level (Table 3). Overall, 20 (74%) and 17 (63%) of ALX-0681 treated subjects experienced a drop in vWF and FVIII levels below 50% of pre-dose levels, respectively. These events were all transient and not clinically significant.
Table 3 Summary of main PD results (number (%) of subjects with event) Dose level Subjects (n) RICO < 20% vWF < 50% FVIII < 50% Subjects (%) Start (h)* Stop (h)* Single dose 2 mg 3 2 (67) 2-4 12-18 3 (100) 0 (0) 4 mg 3 2 (67) 4-6 18-36 1 (33) 1 (33) 8 mg 3 3 (100) 2-4 18-48 3 (100) 3 (100) 16 mg 3 3 (100) 1-4 48 0 (0) 2 (67) 10 mg 3 3 (100) 2-6 24-36 3 (100) 3 (100) Placebo 5 0 (0) NA NA 0 (0) 0 (0) Multiple dose 10 mg (7d) 6 6 (100) 2-4 168-192 5 (83) 3 (50) Placebo (7d) 2 0 (0) NA NA 0 (0) 0 (0) 10 mg (14d) 6 6 (100) 2-4 336-360 5 (83) 5 (83) Placebo (14d) 2 0 (0) NA NA 0 (0) 0 (0) * Time relative to first administration NA: not applicable In conclusion, ALX-0681 administered s.c. for up to 14 days was well tolerated and did not result in any clinically significant AEs. No local reactions, local intolerances or signs of clinically relevant bleeding were reported. The PD marker indicated complete inhibition of vWF mediated platelet aggregation following single daily s.c. injections of 10 mg, which was maintained over the 2 weeks treatment period. Multiple daily administration of s.c. injections of ALX-0681 did not result in an immunogenic reaction for a minimum of 45 days following completion of treatment. Based on the results of this study, ALX-0681 development will be advanced into a Phase II study in TTP patients to investigate the safety and efficacy of ALX-0681 in the target patient population.

Disclosures:
Abd-Elaziz: Ablynx NV: Consultancy. Kamphuisen:Ablynx NV: Consultancy. Lyssens:Ablynx NV: Employment. Reuvers:Ablynx NV: Consultancy. den Daas:Ablynx NV: Consultancy. Van Bockstaele:Ablynx NV: Employment. Vercruysse:Ablynx NV: Employment. Ulrichts:Ablynx NV: Employment. Baumeister:Ablynx NV: Employment. Crabbe:Ablynx NV: Employment. Compernolle:Ablynx NV: Employment. Holz:Ablynx NV: Employment.