Prophylactic agent and therapeutic agent for fibrodysplasia ossificans progressiva

1. A method of suppressing onset of flare-up or ectopic ossification or treating fibrodysplasia ossificans progressiva, including administering, to a mammal, an effective dose of a binding inhibitor that inhibits interaction between activin and activin A receptor type I (ACVR1), wherein the binding inhibitor is selected from the group consisting of:

(a) a polypeptide fragment of activin receptor or a fusion protein of the polypeptide fragment and a carrier protein, wherein the polypeptide fragment is (i) a membrane receptor comprising the extracellular ligand-binding domain and transmembrane region, or (ii) a soluble receptor comprising the entire extracellular domain of a receptor, or a portion of the extracellular domain including the ligand-binding domain,

and

(b) an antibody for activin and an activin binding fragment thereof.

2. The method according to claim 1 , wherein the mammal is a human.

3. The method according to claim 2 , wherein the human has an amino acid mutation in ACVR1.

4. The method according to claim 3 , wherein the amino acid mutation includes an amino acid mutation in the GS domain or kinase domain of the ACVR1.

5. The method according to claim 4 , wherein the amino acid mutation in the GS domain or kinase domain includes at least one amino acid mutation selected from the group consisting of amino acid mutations in which the 196th amino acid residue is proline, amino acid mutations in which the 197th amino acid residue is leucine and the 198th amino acid is deleted, amino acid mutations in which the 202nd amino acid residue is isoleucine, amino acid mutations in which the 206th amino acid residue is histidine, amino acid mutations in which the 207th amino acid residue is glutamic acid, amino acid mutations in which the 258th amino acid residue is glycine or serine, amino acid mutations in which the 325th amino acid residue is alanine, amino acid mutations in which the 328th amino acid residue is glutamic acid, arginine or tryptophan, amino acid mutations in which the 356th amino acid residue is aspartic acid, and amino acid mutations in which the 375th amino acid residue is proline, in the amino acid sequence of SEQ ID NO: 10.

6. The method according to claim 4 , including an amino acid mutation in the ACVR1 GS domain, the amino acid mutation in the GS domain including an amino acid mutation in which the 206th amino acid residue of the amino acid sequence of SEQ ID NO: 10 is histidine.

7. The method according to claim 1 , wherein the activin receptor of the binding inhibitor (a) is ACVR2A or ACVR2B.

8. The method according to claim 7 , wherein the activin receptor of the binding inhibitor (a) is ACVR2A.

9. The method according to claim 8 , wherein the ACVR2A includes a protein including the amino acid sequence of SEQ ID NO: 12.

10. The method according to claim 1 , wherein the polypeptide fragment has an amino acid sequence corresponding to amino acid positions 20 to 135 of the amino acid sequence of SEQ ID NO: 12.

11. The method according to claim 7 , wherein the activin receptor of the binding inhibitor (a) is ACVR2B.

12. The method according to claim 11 , wherein ACVR2B includes a protein including the amino acid sequence of SEQ ID NO: 14.

13. The method according to claim 1 , wherein the polypeptide fragment has an amino acid sequence corresponding to amino acid positions 19 to 134 of the amino acid sequence of SEQ ID NO: 14.

14. The method according to claim 1 , wherein

the binding inhibitor is the fusion protein of the polypeptide fragment and the carrier protein,

the polypeptide fragment is the soluble receptor comprising the entire extracellular domain of ACVR2A, or a portion of its extracellular domain including the ligand-binding domain, and

the carrier protein is a Fc region of a human-derived antibody in which the soluble receptor linked either directly or via a linker sequence with the Fc region.

15. The method according to claim 1 , wherein the polypeptide fragment is the soluble receptor consisting of a polypeptide fragment of 100 to 140 amino acid residues having an amino acid sequence corresponding to the extracellular domain of the activin receptor and having the ability to bind with activin.

16. The method according to claim 1 , wherein the polypeptide fragment is the soluble receptor consisting of a polypeptide fragment of 100 to 120 amino acid residues having an amino acid sequence corresponding to the extracellular domain of the activin receptor and having the ability to bind with activin.

17. The method according the claim 1 , wherein the binding inhibitor is the fusion protein of the polypeptide fragment and the carrier protein, and the carrier protein is an antibody Fc fragment or a modified form of Fc fragment having an amino acid sequence with a deletion, substitution, insertion or addition of one or several amino acids.

18. The method according to claim 1 , wherein the binding inhibitor is the fusion protein of the polypeptide fragment and the carrier protein, wherein the polypeptide fragment is the polypeptide fragment comprising an amino acid sequence of positions 20 to 135 of an amino acid sequence listed as SEQ ID NO: 12, or an amino acid sequence of positions 19 to 134 of the amino acid sequence listed as SEQ ID NO: 14, and the carrier protein is a Fc region of human-derived antibody or a modified form of the Fc region having an amino acid sequence with a deletion, substitution, insertion, or addition of one or several amino acids.

19. The method according to claim 18 , wherein the fusion protein is a Sotatercept.

20. The method according to claim 1 , wherein the antibody for activin is an antibody whose antigen is at least one inhibin β chain selected from the group consisting of the inhibin βA chain, inhibin βB chain, inhibin βC chain and inhibin βE chain.

21. The method according to claim 1 , wherein the antibody for activin is an antibody whose antigen is inhibin βA chain or inhibin βB chain.

22. The method according to claim 1 , wherein the antibody for activin is a monoclonal antibody.

23. The method according to claim 1 , wherein isotype of the antibody is IgG, IgM or IgA.

24. The method according to claim 1 , wherein the antibody is selected from the group consisting of chimeric antibody, humanized antibody, fully humanized antibody, single-chain antibody or antibody fused with a protein.

25. The method according to claim 1 , wherein the method treats fibrodysplasia ossificans progressiva.

26. The method according to claim 1 , wherein the binding inhibitor is the polypeptide fragment of activin receptor or the fusion protein of the polypeptide fragment and a carrier protein, wherein the polypeptide fragment is (i) the membrane receptor comprising the extracellular ligand-binding domain and transmembrane region, or (ii) the soluble receptor comprising the entire extracellular domain of a receptor or a portion of the extracellular domain including the ligand-binding domain.