Methods and compositions for treatment of myotonic dystrophy

1. A chimeric polypeptide comprising: (i) a functional fragment of an MBNL polypeptide comprising four zinc finger motifs and (ii) a targeting moiety, wherein the targeting moiety comprises an antibody or antigen-binding fragment, which antibody or antigen-binding fragment comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14, or which is a humanized antibody or antigen-binding fragment thereof; wherein the MBNL polypeptide is selected from the group consisting of a functional fragment of an MBNL1 polypeptide, an MBNL2 polypeptide, and an MBNL3 polypeptide; and wherein the chimeric polypeptide is capable of binding CUG repeats.

2. The chimeric polypeptide of claim 1 , wherein the functional fragment of the MBNL1 polypeptide lacks a portion of the C-terminus.

3. The chimeric polypeptide of claim 1 , wherein the targeting moiety comprises an antibody.

4. The chimeric polypeptide of claim 1 , wherein the targeting moiety comprises an antigen-binding fragment.

5. The chimeric polypeptide of claim 4 , wherein said antigen-binding fragment is a single chain Fv fragment (scFv).

6. The chimeric polypeptide of claim 1 , wherein the chimeric polypeptide is produced by chemically conjugating the functional fragment of the MBNL polypeptide to the targeting moiety.

7. The chimeric polypeptide of claim 1 , wherein the chimeric polypeptide is produced by a recombinant vector encoding both the functional fragment of the MBNL polypeptide and the targeting moiety.

8. The chimeric polypeptide of claim 1 , wherein the targeting moiety transits cellular membranes via an equilibrative nucleoside transporter 2 (ENT2) transporter.

9. The chimeric polypeptide of claim 1 , wherein said antibody or antigen-binding fragment thereof is an antigen binding fragment of 3E10.

10. The chimeric polypeptide of claim 1 , wherein the chimeric polypeptide is produced recombinantly to recombinantly conjugate the functional fragment of the MBNL polypeptide to the targeting moiety.

11. The chimeric polypeptide of claim 10 , wherein the chimeric polypeptide is produced in a prokaryotic or eukaryotic cell.

12. The chimeric polypeptide of claim 1 , wherein the functional fragment of the MBNL polypeptide is conjugated or joined to the targeting moiety by a linker.

13. The chimeric polypeptide of claim 1 , wherein the functional fragment of the MBNL polypeptide is conjugated or joined directly to the targeting moiety.

14. The chimeric polypeptide of claim 12 , wherein the targeting moiety is conjugated to the N-terminal or C-terminal amino acid of the functional fragment of the MBNL polypeptide.

15. A composition comprising the chimeric polypeptide of claim 1 , and a pharmaceutically acceptable carrier.

16. The chimeric polypeptide of claim 1 , wherein the chimeric polypeptide is a fusion protein.

17. The chimeric polypeptide of claim 1 , wherein said functional fragment of said MBNL polypeptide is a functional fragment of human MBNL1 isoform b, wherein said functional fragment is at least 250 amino acids in length and lacks a portion of the C-terminus of the MBNL1 polypeptide; and wherein the targeting moiety is an scFv.

18. The chimeric polypeptide of claim 17 , wherein the targeting moiety comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14.

19. A nucleic acid construct, comprising a nucleotide sequence that encodes a functional fragment of an MBNL polypeptide comprising four zinc finger motifs, operably linked to a nucleotide sequence that encodes a targeting moiety, wherein the targeting moiety comprises an antibody or antigen-binding fragment, which antibody or antigen-binding fragment comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14, or a humanized antibody or antigen-binding fragment thereof;

wherein the nucleic acid construct encodes a chimeric polypeptide having MBNL biological activity and having the targeting activity of the targeting moiety; and wherein the chimeric polypeptide is capable of binding CUG repeats.

20. The nucleic acid construct of claim 19 , wherein the targeting moiety targets muscle cells to promote transport into muscle cells.

21. The nucleic acid construct of claim 19 , wherein the targeting moiety transits cellular membranes via an ENT2 transporter.

22. The nucleic acid construct of claim 19 , wherein said wherein said functional fragment of said MBNL polypeptide is a functional fragment of human MBNL1 isoform b, wherein said functional fragment is at least 250 amino acids in length and lacks a portion of the C-terminus of the MBNL1 polypeptide; and wherein the targeting moiety is an scFv.

23. The nucleic acid construct of claim 22 , wherein the targeting moiety comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14.

24. A method of delivering a chimeric polypeptide into a cell via an equilibrative nucleoside transporter (ENT2) pathway, comprising contacting a cell with a chimeric polypeptide, which chimeric polypeptide comprises (i) a functional fragment of an MBNL polypeptide and (ii) a targeting moiety which mediates transport across a cellular membrane via an ENT2 pathway, thereby delivering the chimeric polypeptide into the cell; wherein said functional fragment of said MBNL polypeptide comprises four zinc finger motifs, wherein the chimeric polypeptide is capable of binding CUG repeats; and wherein the targeting moiety comprises an antibody or antigen-binding fragment, which antibody or antigen-binding fragment comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14, or a humanized antibody or antigen binding fragment thereof.

25. The method of claim 24 , wherein the functional fragment of the MBNL polypeptide is the functional fragment of an MBNL1 polypeptide having an amino acid sequence at least 90% identical to any of SEQ ID NOs: 1-7.

26. The method of claim 24 , wherein said antibody or antigen-binding fragment is an antigen binding fragment of 3E10.

27. A method of delivering a chimeric polypeptide into a muscle cell, comprising contacting a muscle cell with a chimeric polypeptide, which chimeric polypeptide comprises (i) a functional fragment of an MBNL polypeptide comprising four zinc finger motifs and (ii) a targeting moiety which promotes transport into muscle cells, thereby delivering the chimeric polypeptide into the muscle cell; wherein the chimeric polypeptide is capable of binding CUG repeats; and wherein the targeting moiety comprises an antibody or antigen-binding fragment, which antibody or antigen-binding fragment comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14, or a humanized antibody or antigen binding fragment thereof.

28. The method of claim 27 , wherein the functional fragment of the MBNL polypeptide is a functional fragment of an MBNL1 polypeptide having an amino acid sequence at least 90% identical to any of SEQ ID NOs: 1-7, or a functional fragment thereof.

29. The method of claim 27 , wherein said antibody or antigen-binding fragment is an antigen binding fragment.

30. A method of increasing MBNL bioactivity in a muscle cell, comprising contacting a muscle cell with a chimeric polypeptide, which chimeric polypeptide comprises (i) a functional fragment of an MBNL polypeptide and (ii) a targeting moiety which promotes transport into muscle cells, thereby increasing MBNL bioactivity in the muscle cell; wherein said functional fragment of said MBNL polypeptide comprises four zinc finger motifs, and wherein the chimeric polypeptide is capable of binding CUG repeats; and wherein the targeting moiety comprises an antibody or antigen binding fragment, which antibody or antigen binding fragment comprises a heavy chain variable domain (VH) comprising the amino acid sequence set forth in SEQ ID NO: 12 and a light chain variable domain (VL) comprising the amino acid sequence set forth in SEQ ID NO: 14, or a humanized variant of said antibody or antigen binding fragment.

31. The method of claim 30 , wherein the functional fragment of the MBNL polypeptide is a functional fragment of an MBNL1 polypeptide having an amino acid sequence at least 90% identical to any of SEQ ID NOs: 1-7, or a functional fragment thereof.

32. The method of claim 30 , wherein said antibody or antigen-binding fragment is an antigen binding fragment.