Astellas and Medivation Sue MSN on Four Xtandi Patents Over ANDA No. 221866.

The complaint

The case is Astellas Pharma Inc. et al. v. MSN Pharmaceuticals Inc., MSN Laboratories Private Limited, and Novadoz Pharmaceuticals, LLC, No. 3:26-cv-13220 (D.N.J.), filed October 9, 2026, ECF No. 1. Astellas Pharma Inc. is a Japanese corporation based in Tokyo; Astellas US LLC and Astellas Pharma US, Inc. are Delaware entities based in Northbrook, Illinois; and Medivation LLC and Medivation Prostate Therapeutics LLC are Delaware limited liability companies based in New York. The complaint alleges, on information and belief, that MSN Pharmaceuticals Inc. is a Delaware corporation and Novadoz Pharmaceuticals, LLC a New Jersey company, both based in Piscataway, New Jersey; that MSN Laboratories Private Limited is an Indian corporation based in Hyderabad; and that the two U.S. companies are its subsidiaries. The docket lists the case as assigned to Judge Michael A. Shipp and Magistrate Judge Rukhsanah L. Singh. The complaint's Local Rule 11.2 certification identifies a related action, No. 3:26-cv-12995 (D.N.J.).

The application and the notice letter

The complaint says that by a letter dated August 26, 2026, MSN advised Astellas Pharma Inc. and Medivation Prostate Therapeutics LLC that it had submitted ANDA No. 221866 seeking approval of enzalutamide 40 mg and 80 mg tablets before the patents expire, with a certification that the claims are invalid, unenforceable, or not infringed. It alleges that the notice letter does not raise invalidity under 35 U.S.C. 101, 102, or 112 or unenforceability for three of the patents, nor invalidity under 35 U.S.C. 101, 102, 103, or 112 or unenforceability for the '128 patent, and it argues that MSN thereby admits those defenses are unavailable. Plaintiffs say they sued within 45 days of receiving the letter.

The patents

The complaint asserts U.S. Patent 11,839,689, titled Formulations of Enzalutamide (issued December 12, 2023); U.S. Patent 12,161,628, titled Combination Therapy (issued December 10, 2024); U.S. Patent 12,502,357, titled Formulations of Enzalutamide (issued December 23, 2025); and U.S. Patent 12,447,128, titled Formulations of Enzalutamide (issued October 21, 2025). It says the patents issued to Astellas Pharma Inc. and Medivation Prostate Therapeutics LLC, that Astellas Pharma Inc. holds an exclusive license with sublicenses to the other Astellas plaintiffs, and that each patent is listed in the Orange Book for Xtandi tablets (the '128 patent for the 80 mg tablet).

The complaint recites one claim of each patent. Claim 1 of the '689 patent covers a pharmaceutical composition comprising a solid dispersion consisting essentially of amorphous enzalutamide and hydroxypropyl methylcellulose acetate succinate (HPMCAS). Claim 1 of the '628 patent covers a method of treating prostate cancer in a patient to whom rifampin is administered, by co-administering a daily dose of 240 mg enzalutamide. Claim 1 of the '357 patent covers a method of treating prostate cancer by administering a tablet comprising a solid dispersion of amorphous enzalutamide and HPMCAS. Claim 3 of the '128 patent covers a method of treating prostate cancer by orally administering two tablets, each with a spray-dried dispersion consisting essentially of 80 mg amorphous enzalutamide and 400 mg HPMCAS plus one or more inactive excipients, where the enzalutamide remains amorphous after the dispersion is stored for one month at 40 degrees C and 75 percent relative humidity.

What the lawsuit alleges

Counts I through IV allege that filing ANDA No. 221866 infringed each patent under 35 U.S.C. 271(e)(2)(A). The complaint also alleges, on information and belief, that commercial sales would directly infringe the '689 patent, would induce infringement of the '628, '357, and '128 patents through the proposed label, and would contributorily infringe the '357 and '128 patents, and that MSN copied the claimed inventions. It alleges, on information and belief, that MSN's stated bases for noninfringement and invalidity lack an objective good-faith basis and that the case is exceptional.

The prayer asks for judgments of infringement, a permanent injunction under 35 U.S.C. 271(e)(4)(B) and 283, an order under 35 U.S.C. 271(e)(4)(A) that any FDA approval of the ANDA take effect no earlier than the patents' expiration, inclusive of any extensions, an exceptional-case finding with attorney fees under 35 U.S.C. 285, and costs.

What to watch next

Watch for the MSN defendants' answer and any counterclaims, and whether the court coordinates this case with No. 3:26-cv-12995. The case can end at any time, including by settlement or voluntary dismissal.