Case Nos: CA-2024-002655/002675/002676 - [2025] EWCA Civ 936

Lord Justice Arnold:

Introduction

This is an appeal by the Claimants against an order made by Mellor J on 7 November 2024 dismissing the Claimants’ claims for revocation of European Patent (UK) No. 1 893 196 (“the Patent”) and SPC No. SPC/GB13/079 (“the SPC”) for the reasons the judge gave in a judgment dated 8 October 2024 [2024] EWHC 2524 (Pat). The Patent discloses and claims enzalutamide as a treatment for prostate cancer, and in particular hormone refractory prostate cancer (“HRPC”). The Patent and the SPC are owned by the First Defendant and exclusively licensed to the Second Defendant. Like the judge, I shall refer to the Defendants collectively as “Astellas”. Astellas did not maintain any claim to priority from the three priority applications referenced in the Patent, and so the relevant date is the filing date of the Patent, 29 March 2006.

Before the judge, the Claimants challenged the validity of the Patent, and hence of the SPC, on the ground that the claimed invention was obvious in the light of each of two items of prior art referred to as “the Poster” and “the Slides”. In the alternative, the Claimants contended the Patent did not plausibly disclose a technical contribution. They also argued that it was insufficient if not obvious. The judge heard the trial over six days. His judgment runs to no less than 448 paragraphs. On the appeal, for which I granted permission, the Claimants confined their case to obviousness over the Poster and the Slides. Furthermore, in the case of the Poster they confined their case to their primary argument, and did not pursue a secondary argument advanced at trial. Nor did they maintain two other arguments which were explored in cross-examination although not pursued in closing submissions at trial. As a result, the case advanced on appeal appears much simpler than the one which confronted the judge.

It is also pertinent to note that the Claimants originally relied only on the Slides. It was only at a later stage that they found the Poster and introduced it into the case. The judge thought that the arguments on obviousness were finely balanced, but particularly so in the case of the Slides. Nevertheless, on the appeal the Claimants concentrated on the Poster, although they maintained their case on the Slides. It is common ground that the Poster and the Slides must be considered separately.

The Poster and the Slides both report work done by the inventors of the Patent. They were made available to the public during the year before the filing date of the Patent, but can be relied upon as prior art by the Claimants due to the absence of priority. Each discloses a compound identified as RD162. The compound claimed in the Patent is identified as RD162' (now known as enzalutamide). The structures of these compounds are as follows:

The only difference between RD162 and RD162' is in the substituent at the bottom right of the central thiohydantoin ring at what the judge called position X: RD162 has a cyclobutyl group and RD162' has a geminal dimethyl substituent (i.e. two methyl groups on the same carbon atom).