European patent 2 451 486 ("the patent") was granted with independent claim 1 relating to:
"A conjugate for use in medicine, the conjugate comprising an L-asparaginase from Erwinia chrysanthemi having at least 90% identity to the amino acid sequence of SEQ ID NO:1 and polyethylene glycol (PEG), wherein the PEG has a molecular weight less than or equal to about 5000 Da."
The grant of the patent was opposed and the appeal was filed by the opponent (appellant) against the interlocutory decision of the opposition division that the patent as amended in accordance with auxiliary request 1 was found to meet the requirements of the EPC.
The claims of auxiliary request 1 differed from the claims as granted in that claim 1 defined "A conjugate for use in therapy..." instead of the conjugate for use in medicine.
Sufficiency of disclosure
The patent presents results demonstrating that pegylation of Erwiniase**((R)) with 2000 Da or 5000 Da PEG allows for increased potency, prolonged half-life and reduced immunogenicity.
The Board is satisfied that the patent sufficiently discloses the suitability of the defined conjugate for the claimed use in therapy.
The failure of treatment using a conjugate as claimed in 3 out of 4 patients with pre-existing hypersensitivity to pegaspargase (PEGylated asparaginase from E. coli) due to hypersensitive responses reported in document D36 does not imply that the skilled person is confronted with an undue burden when carrying out the claimed invention aimed at effective treatment.
The skilled person is aware that a therapeutic treatment which is generally effective, may still fail in individual cases. Occasional failure do not necessarily call the validity of a generally effective method of therapeutic treatment into question, in particular in case such failure is reported in a subgroup of patients which would have been recognized by the skilled person as particularly difficult to treat.
The Board finds no basis that the treatment of patients with hypersensitivity to pegaspargase represented the core of the invention.
Accordingly, the Board concludes that the patent sufficiently discloses the claimed invention.
Inventive step
- Closest prior art
The patent is directed to stable PEGylated asparaginase conjugates with enhanced pharmacokinetics and reduced immunogenicity.
Document D8 reports on the preparation, activity, stability, pharmacokinetics and immunological properties of PEGylated Erwinia asparaginase conjugates.
Document D7 reports on a method for the evaluation of the polymer content in polyethylene glycol modified proteins, including chrysanthemi asparaginase. This document fails to specifically disclose any therapeutic utility of the described asparaginase conjugate.
Document D8 thus relates to the same purpose as the claimed invention and therefore represents a more promising starting point than document D7. Accordingly, document D8 represents the closest prior art.
- Problem to be solved
The difference between the claimed subject-matter and the teaching of document D8 concerns the definition of the L-asparaginase from Erwinia chrysanthemi having at least 90% identity to the amino acid sequence of SEQ ID NO:1 instead of the asparaginase from Erwinia carotovora.
The patent demonstrates that the pegylation of the defined aspariginase allows for increased potency, prolonged half-life and reduced immunogenicity with respect to the unmodified aspariginase. In the absence of comparative data with respect to the PEGylated asparaginase of document D8 the problem solved is seen in the provision of an alternative PEGylated asparaginase with therapeutic utility.
- Assessment of the solution
The pegylation described in document D8 involves the conjugation of activated PEG to the amino groups of the asparaginase. Document D11 indicates that the most common route for PEG conjugation of proteins is via the amino group of lysine residues. Document D11 notes that when multiple positions for conjugation are available, the pegylation typically results in heterogeneous mixtures due to differences in the degree and the positions of conjugation. D11 specifically cautions that the positional isomers are likely to influence whether or not the conjugate is active.
Asparaginase from Erwinia carotovora shows only 75-77% identity with asparaginase from Erwinia chrysanthemi. Moreover, alignment of the reference SEQ ID NO:1 presented in the patent for Erwinia chrysanthemi asparaginase with the sequence of the aspraraginase from Erwinia carotovora shows that the lysine residues are not well conserved.  Moreover, document D9 indicates that Erwinia chyrsanthemi asparaginase includes a lysine residue in its active site.
In view of the significant differences between the asparaginases from Erwinia carotovora and Erwinia chrysanthemi, including the positions of multiple sites for pegylation, and the unpredictability of the effects of these differences on the activity of the enzyme after pegylation, the person skilled in the art had no reasonable expectation of success that replacement of the asparaginase of document D8 by an asparaginase from Erwinia chrysanthemi having 90% identity to the amino acid sequence of SEQ ID NO:1 would yield a therapeutically active conjugate.
The subject-matter of claim 1 would therefore not be obvious to the skilled person as solution to the problem of providing an alternative therapeutically active PEGylated asparaginase conjugate.
Accordingly, the Board concludes that the claimed subject-matter also involves an inventive step.
The appeal is dismissed.