On Jul 29, 2019, Federal Circuit affirmed district court & found
Coherus' biosimilar non-infringing under Doctrine of Equivalents (DOE) because
of prosecution history estoppel (PHE).
Coherus filed aBLA with USFDA which sought approval of biosimilar
version of Amgen’s pegfilgrastim product, Neulasta®. Amgen sued Coherus over US 8,273,707
which claims methods of purifying proteins using hydrophobic interaction
chromatography (“HIC”). All of the ’707 claims require a salt combination
chosen from one of three pairs: citrate and sulfate, citrate and acetate, or
sulfate and acetate for effective purification.
Claim 1 recites:
1. A process for
purifying a protein on a hydrophobic interaction chromatography column such
that the dynamic capacity of the column is increased for the protein comprising
mixing a preparation
containing the protein with a combination
of a first salt and a second salt,
loading the mixture onto a hydrophobic
interaction chromatography column, and eluting the protein,
wherein the first and
second salts are selected from the group consisting of citrate and sulfate,
citrate and acetate, and sulfate and acetate, respectively, and
wherein the
concentration of each of the first salt and the second salt in the mixture is
between about 0.1 M and about 1.0.
Amgen during prosecution argued that prior art did not teach
or suggest the claimed particular combination of salts. It supported this
arguments with Declaration from inventor. Amgen further argued that the claimed invention
is directed to increasing dynamic
capacity of a HIC column and prior art does not teach dynamic capacity at
all. Examiner first rejected the arguments but finally allowed the claims as Amgen
pointed out that choosing a working salt combination was a “lengthy development
path” and that “merely adding a second salt” would not result in the invention.
During litigation, Delaware Court dismissed Amgen's infringement claim under
DOE for failure to state the claim based on PHE. Amgen
appealed. During appeal Federal Circuit sided with district court & said
that argument based prosecution history estoppel prohibits Amgen from asserting
infringement under DOE. Amgen clearly and unmistakably surrendered salt
combinations other than the particular combinations recited in the claims. Notably,
Amgen’s response to the examiner’s office action quotes the Declaration’s
conclusion that “use of this particular combination of salts greatly improves
the cost-effectiveness of commercial manufacturing by reducing the number of
cycles required for each harvest and reducing the processing time for each
harvest.”
Amgen argued that its statement regarding the “particular
combinations” of salts “simply observes (correctly) as a factual matter that prior
art does not disclose using combinations of salts in the first instance,” and
thus does not clearly and unmistakably surrender unclaimed salt pairs. Amgen
argued that PHE does not apply because it made three bases/statements along
with the one which states that prior art failed to teach particular salt
combination. But Federal Circuit said that PHE can apply to single statement or
base also unless the combine effect is argued. Amgen did not rely on the
combination of its asserted grounds to distinguish prior art, so prosecution
history estoppel applies to the “particular combinations” ground regardless of
the other two arguments Amgen made. Therefore, single statement or base can
give rise to estoppel.
Amgen next argued that the statements made during
prosecution were not final ones which resulted in notice of allowance. Court
again disregarded this & held that it is not necessary that to apply the
PHE only final response is taken into consideration. Any response made against
the rejection at any stage can give rise to estoppel. Federal Circuit thus held
that the district court did not err in determining that prosecution history
estoppel bars Amgen from succeeding on its infringement claim under the
doctrine of equivalents.