Tag Archives: enantiomers

Amgen Scores Partial Victory in Efforts to Maintain OTEZLA Exclusivity

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By Chris Holman

Amgen Inc. v. Sandoz Inc., 2023 WL 2994166, — 4th —   (Fed. Cir. Apr. 19, 2023)

In 2019, Amgen acquired worldwide rights to apremilast (OTEZLA) from Celgene $13.4 billion in cash, in connection with Celgene’s merger with Bristol-Myers Squibb. Apremilast was the only oral, non-biologic treatment for psoriasis and psoriatic arthritis, and in 2020 apremilast generated $2.2 billion for Amgen.

At the time Amgen’s acquired apremilast, Celgene was involved in Hatch-Waxman litigation with numerous generic challengers, including Sandoz. Celgene had asserted three of its 11 Orange Book-listed patents against Sandoz, and in 2020 Amgen was substituted as plaintiff.

The primary patent asserted is U. S. Patent 7,427,638, which is directed to pharmaceutical compositions comprising stereochemically pure apremilast. The original expiration date of this patent was in 2024, but the patent received a patent term extension of more than three years, resulting in an effective patent expiration date of February 16, 2028, according to the Orange Book.

Celgene also asserted U. S. Patent 7,893,101, which is directed to enantiomerically pure solid forms (e.g., crystalline polymorphic forms) of apremilast. This patent is due to expire December 9, 2023.

The third patent asserted by Celgene was U. S. Patent 10,092,541, directed to methods for treating a patient using dose titration of apremilast. According to the Orange Book, this patent was set to expire on May 29, 2034.

The district court found the claims of the ‘638 and ‘101 patents to be infringed and not invalid, and enjoined generic apremilast until the expiration of the ‘638 patent in February 2028. On appeal the Federal Circuit affirmed, an outcome that Amgen characterizes as a win.

On the other hand, the district court found the asserted claims of the ‘541 patent to be invalid for obviousness, which reportedly “pleased” Sandoz because the ruling “enables Sandoz to launch [its] generic apremilast product in the U. S. in 2028, six years prior to the expiry date of the latest-expiring Amgen patent asserted in litigation.”  On appeal, the Federal Circuit affirmed with respect to the obviousness of the ‘541 patent.

Here is a brief overview of the court’s decision regarding the asserted obviousness of these patents.

The ‘638 patent claims apremilast, which is the stereochemically pure (+) enantiomer of a compound falls that within a class of molecules referred to as phosphodiesterase-4 (“PDE4”) inhibitors.  Sandoz’s obviousness argument was based primarily upon a prior art Celgene patent, U. S. Patent 6,020,058, which includes an Example 12 that describes a racemic mixture containing apremilast, but that does not disclose the purified (+) enantiomer. The Federal Circuit found that the district court had not erred in holding that Sandoz had not proven that a skilled artisan would have had sufficient motivation to purify the (+) enantiomer from the racemic mixture disclosed in Example 12, nor that a skilled artisan would have had a reasonable expectation of success in resolving that mixture into its enantiomeric components, given the unpredictable nature of resolving racemic mixtures.

The Federal Circuit further found that the district court had not erred in its finding of strong objective indicia of nonobviousness, particularly given the unexpected potency of apremilast relative to the apremilast-containing racemic mixture disclosed in Example 12. The court credited testimony from a Celgene researcher listed as an inventor on the ‘638 patent, who noted a 20-fold difference in potency between apremilast alone and the racemic mixture, and stated that the inventors “didn’t expect a 20-fold difference in potency… Normally, if a racemate is a 50/50 mixture of two enantiomers, you might expect a two-fold difference in potency, all things being equal.” The district court also did not err in determining that apremilast satisfied a long felt need for an improved psoriasis treatment suitable for oral administration, that others in the field had tried and failed to develop other PDE4 inhibitors as drugs, and that there had been a degree of skepticism about the safety of apremilast because of its structural similarity to thalidomide, a drug notorious for its teratogenic effects in fetuses leading to severe and debilitating birth defects.

The issue with respect to the ‘101 patent was whether it could rely upon the filing date of a provisional application to which it claims priority. The ‘101 patent claims crystalline Form B of apremilast, and the provisional application includes an Example 2 which discloses a synthetic procedure for preparing apremilast. Although Example 2 does not explicitly disclose that the resulting apremilast has the Form B crystalline structure, Amgen provided the court with the results of over a dozen experiments following the procedure of Example 2, all of which resulted in crystalline Form B of apremilast, while Sandoz had provided no evidence to establish that Example 2 was capable of producing a crystalline Form other than Form B. Although the district court had based its holding on its conclusion that the provisional application inherently disclose crystalline Form B of apremilast, the Federal Circuit found that it did not need to reach the issue of inherent disclosure because the evidence established that Example 2 actually disclosed crystalline Form B of apremilast, albeit without specifically disclosing the crystal structure of the resulting product.

The ‘541 patent claimed a method of treating a patient with apremilast that basically involves starting with a relatively low dose and, over a course of days, gradually increasing the dosage to arrive at a full dosage which is significantly higher than the initial dosage, i.e., a dose-titration schedule. The court found this to be an obvious method, in view of prior art disclosing a similar dosage schedule. The Federal Circuit observed that, as a general matter, varying doses in response to the occurrence of side effects is well-known and obvious to the skilled artisan.

Obviousness and Stereochemistry

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Amgen Inc., v. Sandoz Inc. 22-1147, — F.4th — (Fed. Cir. Apr. 19, 2023)

Jordan is a second-year law student at the University of Missouri and a registered patent agent.  He has an extensive background in chemistry and food science.

Amgen markets apremilast, a phosphodiesterase-4 (“PDE4”) inhibitor, which is used for treating psoriasis and related conditions, under the brand name Otezla® which is covered by three patents, U.S. Patents 7,427,638, 7,893,101, and 10,092,541. Sandoz submitted an Abbreviated New Drug Application (“ANDA”) seeking approval market a generic version of apremilast. Celgene, the original plaintiff, brought this Hatch-Waxman suit, asserting that Sandoz’s generic product would infringe the ’638 and ’101 patents. The Federal Circuit affirms the district court’s findings on all issues raised.

Sandoz asserts that U.S. Patent 6,020,358 renders the Amgen patents obvious. The ’358 patent is the first U.S. patent describing a racemic mixture containing apremilast. Enantiomers detail the orientation of the molecule around a chiral center and can have vastly different therapeutic outcomes and clinical results between the (+) and (-) enantiomers, particularly thalidomide analogues. The critical difference between the ‘358 and ‘638 patents is the composition of the mixture:

The ’358 patent is a racemic mixture comprised of 50% of the (+) enantiomer of 2-[1-(3-ethoxy-4-methoxyphenyl)-2-methylsulfonylethyl]-4acetylaminoisoindoline-1,3-dione and 50% of the (-) enantiomer.

Compare to an excerpt of Amgen’s language in claim three of ‘638:

A pharmaceutical composition comprising stereomerically pure (+)–2-[1-(3- ethoxy-4-methoxyphenyl)-2- methylsulfonylethyl]-4- acetylaminoisoindoline-1,3-dione, or a pharmaceutically acceptable salt, …

The ’638 Patent: Sandoz failed to provide clear and convincing evidence at the district court to show that a skilled artisan would have reasonably expected a benefit from separating the enantiomers or that the (+) enantiomer was the cause of the desirable properties of the ‘358 formulation. Sandoz’s appeal asserts that the district court erred in its findings.

At the Federal Circuit, Judge Lourie, writing for a unanimous panel of Judges Cunningham and Stark, focuses on the unexpected potency of apremilast discovered relative to the apremilast-containing racemic mixture during testing and experimentation. At the district court, the named inventor, Dr. Schafer, testified that the stereomerically pure apremilast reduces the production of tumor necrosis factor alpha (“TNFα”), the factor that is linked to psoriasis, 20 times more effectively than the previous patent.

Dr. Schafer also says that a skilled artisan would expect a twofold improvement in efficiency. The district court finds that the 20-fold difference, when an otherwise two-fold difference would have been expected by the skilled artisan was sufficient to support a finding of an unexpected result and subsequent nonobviousness. A 20-fold difference from the steromerically isolated formulation goes well beyond a difference in degree into a difference in kind.

It strikes me as interesting that the characteristics of apremilast were largely left undiscussed. Apremilast is a thalidomide analogue and safety concerns about the infamously teratogenic effects related to thalidomide were sufficient skepticism for a skilled artisan and the industry at large regarding stereomerically pure formulations. However, it would seem that this teratogenicity could cut both ways as a skilled artisan would have ample incentives to investigate the enantiomers separately for safety concerns in light of the thalidomide paradox.

The thalidomide paradox provides that racemic mixtures and pure enantiomers have different characteristics, despite in vivo racemization. If the molecule is sufficiently analogous to thalidomide, it seems that a skilled artisan would be inclined to be taught towards separating the enantiomers. Regardless, the unexpected result was found to be dispositive on appeal and the objective indicia weren’t necessary but the other findings of the objective indicia of long-felt need, others had tried and failed, industry skepticism, and commercial success were also affirmed.

           The ’101 Patent: Sandoz also alleges that the ’101 patent should have been found to be obvious. Sandoz says the ‘101 patent should not be entitled to the priority date of March 2002 because the  ’515 provisional application did not inherently disclose crystalline Form B of apremilast and therefore did not satisfy the written description requirements of 35 U.S.C. § 112. The district court relies on a finding that ‘515 application did inherently disclose the crystalline form.

The Federal Circuit did not find it necessary to delve into inherent disclosure because a review of the trial record shows Amgen provided multiple experiments, and expert testimony, showing that there was actual disclosure of the crystalline Form B. Absent any contrary evidence by Sandoz, the priority date and subsequent finding of nonobviousness were affirmed. Another win chalked up to Amgen’s excellent expert testimony.

            The ’541 Patent: On cross-appeal, Amgen asserts that the district court finding that the patent is obvious in light of prior art is erroneous. The district court found that the ’541 patent would have been obvious over the prior art or in crediting expert testimony stating that dose-titration modification would have been routine to a skilled artisan. Specifically, dose titration would be something that is regularly done in the treatment of psoriasis.