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Amgen Inc. v. Coherus Biosciences Inc.

United States Court of Appeals, Federal Circuit

July 29, 2019

AMGEN INC., AMGEN MANUFACTURING LTD., Plaintiffs-Appellants
v.
COHERUS BIOSCIENCES INC., Defendant-Appellee

          Appeal from the United States District Court for the District of Delaware in No. 1:17-cv-00546-LPS, Chief Judge Leonard P. Stark.

          Nicholas P. Groombridge, Paul, Weiss, Rifkind, Wharton & Garrison LLP, New York, NY, argued for plaintiffs-appellants. Also represented by Jennifer Gordon, Golda Lai, Peter Sandel, Jacob Whitt, Jennifer H. Wu; Lois M. Kwasigroch, Kimberlin L. Morley, Wendy A. Whiteford, Amgen Inc., Thousand Oaks, CA.

          Adam G. Unikowsky, Jenner & Block LLP, Washington, DC, argued for defendant-appellee. Also represented by Bradford Peter Lyerla, Aaron A. Barlow, Louis Fogel, Susan O'Brien, Chicago, IL.

          Before Reyna, Hughes, and Stoll, Circuit Judges.

          STOLL, CIRCUIT JUDGE

         Amgen Inc. and Amgen Manufacturing Ltd. (collectively, "Amgen") sued Coherus BioSciences Inc. for patent infringement in the District of Delaware. The district court dismissed Amgen's complaint for failure to state a claim, and Amgen appeals. Because prosecution history estoppel bars Amgen from succeeding on its infringement claim under the doctrine of equivalents, we affirm the order of the district court.

         Background

         I

         Recombinant therapeutic proteins are a class of biologic medicines that are manufactured inside living cells. Before a protein can be therapeutically useful, it must first be purified from contaminants. Amgen's U.S Patent No. 8, 273, 707 claims methods of purifying proteins using hydrophobic interaction chromatography ("HIC"). A HIC column contains a solid, hydrophobic matrix and "is used to separate proteins on the basis of hydrophobic interactions between the hydrophobic moieties of the protein and insoluble, immobilized hydrophobic groups on the matrix." '707 patent col. 1 ll. 36-39. In a HIC purification, a buffered salt solution containing the desired protein and associated impurities is first poured onto a HIC column. Id. at col. 1 ll. 40-41. This is known as the "loading" step. The salt in the buffer exposes the hydrophobic regions of the protein and causes them to adsorb (i.e., attach) onto the hydrophobic groups on the column matrix. See id. at col. 1 ll. 41-44. The impurities are then washed out of the column with a buffered salt solution while the desired protein remains attached to the matrix. See id. at col. 4 ll. 27-29. Finally, molecules of the desired protein are detached (or "eluted") by pouring a buffer solution with a lower salt concentration through the column. See id. at col. 1 ll. 44-49. "Usually, a decreasing salt gradient is used to elute proteins from a column. As the ionic strength decreases, the exposure of the hydrophilic regions of the protein increases and proteins elute from the column in order of increasing hydrophobicity." Id. at col. 1 ll. 45-49.

         During the loading step, only a finite amount of protein can bind to the matrix. If too much protein is loaded on the column, "'breakthrough' or loss of protein to the solution phase before elution" will occur. Id. at col. 3 ll. 40-41. The '707 patent claims a process that reduces breakthrough, or in other words, increases the "dynamic capacity" of a HIC column. Dynamic capacity refers to "the maximum amount of protein in solution which can be loaded onto a column without significant breakthrough or leakage of the protein into the solution phase of a column before elution." Id. at col. 3 l. 65-col. 4 l. 3.

         Prior art methods of increasing a HIC column's dynamic capacity included using a higher salt concentration in the buffer solution. See id. at col. 3 ll. 37-38. This resulted in other problems, however, as "high salt can be detrimental to protein stability. High salt increases the viscosity of a solution, results in increased formation of aggregates, results in protein loss due to dilution and filtration of the protein after elution from the column, and can lead to reduced purity." Id. at col. 3 ll. 41-45. Instead of increasing the concentration of a single salt, the '707 invention:

provides combinations of salts useful for increasing the dynamic capacity of an HIC column compared with the dynamic capacity of the column using separate salts alone. These combinations of salts allow for a decreased concentration of at least one of the salts to achieve a greater dynamic capacity, without compromising the quality of the protein separation.

Id. at col. 2 ll. 9-15. 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. Representative 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 ...

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