Anti-factor IXa/X bispecific antibody ACE910 prevents joint bleeds in a long-term primate model of acquired hemophilia A

Abstract

ACE910 is a humanized anti-factor IXa/X bispecific antibody mimicking the function of factor VIII (FVIII). We previously demonstrated in nonhuman primates that a single IV dose of ACE910 exerted hemostatic activity against hemophilic bleeds artificially induced in muscles and subcutis, and that a subcutaneous (SC) dose of ACE910 showed a 3-week half-life and nearly 100% bioavailability, offering support for effective prophylaxis for hemophilia A by user-friendly SC dosing. However, there was no direct evidence that such SC dosing of ACE910 would prevent spontaneous bleeds occurring in daily life. In this study, we newly established a long-term primate model of acquired hemophilia A by multiple IV injections of an anti-primate FVIII neutralizing antibody engineered in mouse-monkey chimeric form to reduce its antigenicity. The monkeys in the control group exhibited various spontaneous bleeding symptoms as well as continuous prolongation of activated partial thromboplastin time; notably, all exhibited joint bleeds, which are a hallmark of hemophilia. Weekly SC doses of ACE910 (initial 3.97 mg/kg followed by 1 mg/kg) significantly prevented these bleeding symptoms; notably, no joint bleeding symptoms were observed. ACE910 is expected to prevent spontaneous bleeds and joint damage in hemophilia A patients even with weekly SC dosing, although appropriate clinical investigation is required.

Figure 1

Change in APTT after weekly IV injection of the mouse anti-primate FVIII neutralizing antibody VIII-2236 in cynomolgus monkeys. VIII-2236 was injected at 3 or 10 mg/kg IV doses to cynomolgus monkeys on days 0, 7, 14, and 21. Citrated blood was collected on days 0, 3, 7, 10, 14, 17, 21, 24, and 28 (before and 2 hours after VIII-2236 injection on days 0, 7, 14, and 21). The time course of APTT is shown for each monkey.

Figure 2

Comparison of the mouse-monkey chimeric anti-primate FVIII neutralizing antibody cyVIII-2236 with the original mouse antibody VIII-2236 in an APTT assay. (A) Effects of cyVIII-2236 and VIII-2236 on APTT in normal cynomolgus monkey plasma. (B) Influence of 300 µg/mL cyVIII-2236 and VIII-2236 on APTT-shortening activity of ACE910 in FVIII-deficient human plasma. Data are expressed as means ± SD (n = 3). The bars depicting SD are shorter than the height of the symbols. The symbols for the group without anti-FVIII antibody are hidden behind the symbols for the other groups in panel B.

Figure 3

Preventive effects of ACE910 on spontaneous joint bleeds in a long-term primate model of acquired hemophilia A. (A) Experimental protocol used for evaluating preventive effects of ACE910 in a long-term hemophilia A model induced by the weekly IV doses of 10 mg/kg cyVIII-2236. The 8 cynomolgus monkeys received weekly IV injections of cyVIII-2236 on days 0, 7, 14, 21, 28, 35, 42, and 49. ACE910 was administered as an initial 3.97 mg/kg SC dose 2 hours after cyVIII-2236 injection on day 0, and thereafter as a weekly 1 mg/kg SC dose on days 7, 14, 21, 28, 35, 42, and 49. Citrated blood was collected on days 0, 4, 7, 11, 14, 18, 21, 25, 28, 32, 35, 39, 42, 46, 49, 53, and 56 (before and 2 hours after cyVIII-2236 injection on day 0; just before cyVIII-2236, vehicle, and ACE910 injections on days 7, 14, 21, 28, 35, 42, and 49). (B) The time courses of APTT are shown as individual values for respective cynomolgus monkeys (#1-4) of the vehicle and ACE910 groups. The APTT of the vehicle #3 monkey on day 46 was not determined due to a handling failure. (C) The days in which limping was observed are shown in red for the individual cynomolgus monkeys. The gray boxes indicate that no data are available because the ACE910 #4 monkey was killed for humane reasons on day 28 (See “Results”). The number of days with limping (C) and the number of bleeding joints at necropsy (D) are shown as individual values (#1-4) and as means ± SD in the vehicle group (n = 4) and the ACE910 group (n = 3). **P < .01 indicates significant differences from the vehicle group (2-tailed Student t test). (E) Representative macroscopic findings of the joints at necropsy. Left hip joint with limping in the vehicle #1 monkey; dark-red area in the Af (i) and Hf (ii) is detected. Left hip joint without limping in the ACE910 #3 monkey; no abnormalities are noted in the Af (iii) and Hf (iv). Ac, acetabulum; Af, acetabular fossa; Hf, head of femur.

Figure 4

Histopathological findings in a representative joint in a long-term primate model of acquired hemophilia A. Left hip joint with limping in the vehicle #1 monkey (A-C) and left hip joint without limping in the ACE910 #3 monkey (D-F) are shown at original magnification ×5 (A, D), ×20 (B, E), and ×400 (C, F). Hemorrhagic changes (arrowheads) including hemosiderin deposition (arrows) and destruction of articular cartilage/underlying bone (*) are detected in the joint with limping (A-C). No hemorrhagic changes are noted in the joint without limping (D-F). Hematoxylin and eosin stain. Aca, articular cartilage of acetabulum; Hb, hip bone; Sm, synovial membrane.

Figure 5

Relative blood Hgb concentrations in a long-term primate model of acquired hemophilia A. The time courses of blood Hgb concentration relative to concentration on day 0 (2 hours after cyVIII-2236 injection) are shown as individual values in respective cynomolgus monkeys (#1-4) of the vehicle and ACE910 groups.

Figure 6

Plasma ACE910 concentrations in a long-term primate model of acquired hemophilia A. ACE910 was administered at an initial SC dose of 3.97 mg/kg on day 0 followed by weekly SC doses of 1 mg/kg on days 7, 14, 21, 28, 35, 42, and 49. The time courses of actual measured and simulated plasma concentrations of ACE910 are shown. The actual measured concentrations are presented as individual values for cynomolgus monkeys (#1-4) of the ACE910 group.