Page 124 - Haematologica Vol. 107 - September 2022

ARTICLE - Effects of BT200 on VWF/FVIII in humans
K.D. Kovacevic et al.
and desmopressin was supplied as a commercially avail- able sterile solution for injection in 4.0 mg/mL ampoules (Octostim, Ferring, Austria).
A description of analytical methods and the statistical analysis is provided in the Online Supplementary Data.
Results
Randomization of 112 subjects was planned; due to slower recruitment during the COVID pandemic, 20 sub- jects from part A were re-exposed (once) in part B, C or D. Thus, a total of 92 individual subjects were enrolled in 14 cohorts.
Single subcutaneous doses and intravenous bioavailability study
In part A, 86 subjects were screened, 60 were random- ized to BT200 and 20 to placebo. Cohort 9 included one early termination and cohort 10 two early terminations due to COVID-19. Two volunteers were Asian, one African, and the rest Caucasian. The male:female sex ratio of par- ticipants was 72:8, and their age ranged from 18 to 60 years. Complete demographic characteristics are given in Online Supplementary Table S1.
In part D, eight subjects from part A (including 1 woman and the 2 Asian volunteers) were re-exposed and they re- ceived intravenous doses of placebo or BT200; their mean age was 31.3 years (Online Supplementary Table S2).
Pharmacokinetics
The rate and extent of exposure to BT200 increased with increasing doses over the dose range of 0.18 mg to 24 mg after single SC injections (Figure 1). The increase over the dose range for areas under the concentration curve (AUC) and maximum concentration (Cmax) appeared to be pro- portional to dose for dose levels ≥6 mg. For SC infusions, the rate and extent of exposure to BT200 also increased in a dose-proportional manner. Geometric mean half- lives (t1/2) ranged from 121 to 279 h (Table 2). Clearance (CL/F) decreased as a function of body weight and age. The half-life was 204 h after a 24 h IV infusion and the Cmax reached 4.8 mg/mL, the geometric mean clearance (CL) was 0.0264 L/h and the volume of distribution (Vss) was 4.54 L. Therefore, as had been expected, clearance was much lower than glomerular filtration rate (7.5 L/h). The volume of distribution was consistent with the blood volume of human volunteers (5 L), and similar to that seen for other pegylated aptamers22 which are not pri- marily eliminated via passive renal filtration.
The bioavailability of BT200 was approximately 64% fol- lowing SC injection and 75% following SC infusion. Bio- availability was lower for doses below 1.8 mg (33 to 50%), as expected from the dose proportionality analysis.
Multiple ascending dose cohorts (cohorts 13, 14)
In part B, 16 subjects (14 men and 2 women )were in- cluded (8 of whom were re-exposed from part A). One subject was Asian and the rest were Caucasian. The mean age was 43 years (standard deviation [SD] 13), mean height was 180 cm (SD 11), mean weight was 87 kg (SD 17) and the mean body mass index was 26.8 kg/m2 (SD 4.5) (On- line Supplementary Table S3).
Pharmacokinetics
As expected, the combination of IV infusions over 2 h and SC injections in a split SC/IV loading dose resulted in peak levels being observed much earlier than was seen after the same dose was administered via the SC route alone (Figure 1). The exposure (AUC and Cmax) was only slightly higher that that of an equivalent injected or SC infused dose in part A. Mean trough concentrations of BT200 ap- peared to plateau by day 7 and remained consistent through to day 28 following weekly maintenance doses of 12 mg BT200 (Online Supplementary Figure S1). Subjects in cohort 14 received only the initial dose but not any of the subsequent maintenance doses, because the maxi- mum tolerated dose had been reached and the aims of the trial fulfilled.
Pharmacodynamic effects in all cohorts
BT200 concentration-dependently inhibited VWF-depend- ent platelet function (Online Supplementary Figures S2 and S3): a 12 mg dose was necessary to fully prolong col- lagen-ADP closure times as measured by the Platelet Function Analyzer (PFA) (Online Supplementary Figures S4 and S5) to a median of 300 s (range: 148-300 s; P<0.001) 48 h after sc injection, which coincided with the nadir of free VWF A1-domains in this cohort (Figure 2). Maximal PFA closure prolongation was short lived and did not per- sist even until the maximal plasma concentration of 1.2 mg/mL was observed at 72 h following the 12 mg dose. Likewise, ristocetin-induced platelet aggregation de- creased from 92 U (range, 69-117 U) to a nadir of 34 U (range, 13-58 U; P<0.001) after 96 h (Online Supplementary Figures S5 and S6).
All three lower SC doses of BT200 had a minimal effect on free VWF A1-domains which was comparable to that observed for placebo (Figure 2). The 6 mg dose moder- ately suppressed free VWF A1-domains by ~30% (P<0.001). Doses of 12-48 mg invariably decreased free VWF A1-do- mains to <50% of normal values, although the extent of decrease appeared to be more pronounced in subjects with low baseline levels of VWF. The 48 mg dose reduced median free VWF A1-domains to 2% (range, 2-6%) at 48 h, and the 24-h IV infusion of 24 mg BT200 quickly reduced free VWF A1-domains to 1% (range, 0-7%). At equivalent exposure, the IV infusion yielded a greater extent of sup- pression compared to the SC injection, consistent with
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