In Accord v Astellas [1] the UK Court of Appeal upheld EP (UK) 1 893 196 (the “Patent”) [2], which claims enzalutamide as a treatment for prostate cancer. The judgment, which dismissed the appeal, demonstrates once again that when it comes to the assessment of obviousness, the Court of Appeal is unlikely to interfere with the multi-factorial evaluation at first instance, including especially as to the weight attributed to expert evidence. The decision also shows that what might appear to be a “small” modification to a chemical compound is nonetheless inventive.
Background
Accord [3] had originally sought revocation of the Patent (and SPC). Mr Justice Mellor heard the trial at first instance and held the Patent valid in his judgment on 7 November 2024. The case advanced on appeal was slimmed down to focus on the key issue of whether the Patent was obvious in light of two pieces of prior art – the “Poster” and the “Slides”. On appeal, Accord focussed on the Poster, even though it came into the case later. That had the knock-on effect that Accord’s medicinal chemistry expert, Prof Westwell, only saw the Poster after he had seen the Patent. Notwithstanding this, when giving his evidence on the Poster, Prof Westwell was told to put out of his mind what he had previously discussed with Accord’s solicitors. However, even with such instructions, these circumstances impacted hindsight, and accordingly the weight attributed to Prof Westwell’s evidence (discussed below).
The Poster and Slides report work that was done by the inventors of the Patent. They each disclose the compound RD162, while the Patent claims the compound RD162’ (now known as enzalutamide), which differs from RD162 by virtue of its geminal dimethyl group where RD162 has a cyclobutyl group at the bottom right of the central thiohydantoin ring (shown in yellow highlight below).
It was common ground that the Patent was addressed to a skilled team interested in seeking to develop a new drug for treating prostate cancer, and in particular a new antagonist to the androgen receptor. The team would include a cancer biologist, with knowledge and skills in the biology of prostate cancer, and a medicinal chemist, who would be well-versed in inter alia drug design, synthesis and characterisation.
The appeal
Accord’s starting point was that (1) the judge was correct in finding that no challenge was made to the technical reasoning which Accord’s expert, Prof Westwell, put forward in support of obviousness over the Poster; and (2) the judge had rejected each of the three reasons advanced by Astellas in support of non-obviousness, based on the evidence of their medicinal chemistry expert, Prof Ward.
Accord argued that, in reaching the opposite conclusion and finding the patent valid, the judge had erred in principle in two ways. First, they argued that the judge erred in looking for a “context” or “scenario” in which the skilled team was working in and deciding what steps to take. Second, they argued that there was an internal inconsistency in Mellor J’s judgment whereby he had, on the one hand, rejected an allegation that Prof Westwell’s evidence in cross-examination was approached with hindsight but, on the other hand, later in his judgment, held that Prof Westwell’s conclusion on obviousness was tainted with hindsight.
As regards the first argument, Accord emphasised that motivation to take a particular step (which, in this case, was changing the cyclobutyl group to a geminal dimethyl group) is not a requirement for a finding of obviousness. Lord Justice Arnold, who gave the leading judgment, did not consider Mellor J to have questioned this. Rather, Arnold LJ clarified that the point the judge had made was whether a particular change is characterised as “trivial” is highly fact-dependent and that there is a real danger in substituting the question of “triviality” for that of obviousness. Arnold LJ went on to explain that, crucially, Prof Westwell had not said that he was approaching the question of obviousness on the premise that the skilled team, having read the Poster, would be interested in developing an antagonist for prostate cancer that was simply an alternative to RD162. Indeed, as Arnold LJ emphasised, Prof Westwell had not explained in his evidence what objective the medicinal chemist would have in mind at all; that was what the judge had meant by the “absence of a proper description of the context” in which Prof Westwell considered the question of obviousness. The judge was entitled to take that omission into account when assessing his evidence.
As regards the second argument, Arnold LJ did not see any inconsistency in Mellor J’s reasoning. In the first instance, Mellor J had addressed Astellas’ submission that Prof Westwell’s cross-examination was tainted with hindsight, in particular because “he had had the target (RD162’) in mind”. This was rejected by the judge because he was not persuaded that was the case. The judge went on to give his conclusion on Prof Westwell’s evidence, namely that it was tainted with hindsight because the skilled team looking for a novel compound (i.e., an alternative to RD162) would not have considered close analogues of RD162; the focus on those had been driven by hindsight knowledge that the Patent claims RD162’.
As part of their response, Accord argued that Prof Westwell had been instructed to follow the Pozzoli approach, which he had faithfully followed, and that could not be criticised as leading. Arnold LJ did not consider the judge to have criticised Accord for instructing Prof Westwell to adopt the Pozzoli approach or Prof Westwell for doing his best to follow it. Rather, the judge’s concern was that the expert had been led to focus on the key modification of changing cyclobutyl to a dimethyl at a certain position and whether this would have a material effect, as opposed to considering what would have been an obvious way forward from RD162.
Arnold LJ went on to comment that “explicitly instructing an expert to follow the Pozzoli approach can create a risk of hindsight”. He further emphasised that “the Court will normally adopt the Pozzoli approach, but it does not follow that it is necessary to instruct the expert to do so”. In this case, it was clear what the difference between the prior art (RD162) and the Patent (RD162’) was in structural terms. Arnold LJ thought that hindsight would have been easier to avoid if Prof Westwell had been asked a more open-ended question such as: assuming the skilled team was interested in developing an alternative to RD162 which had similar therapeutic potential, and having read the Poster, what compound(s) would have been obvious choices to investigate?
Comment
This judgment highlights again the importance of the way in which experts are instructed in UK patent cases. In this decision, Arnold LJ highlights that whilst the Court usually adopts the Pozzoli approach when assessing obviousness, it is not necessary for the experts to do so. Indeed, Arnold LJ’s decision suggests that avoiding it altogether, and asking the more open question – “what would be the obvious next step(s)?” – may be the preferred approach. In addition, this decision emphasises the importance of the experts providing the context in which they are considering the question of obviousness.
[1] [2025] EWCA Civ 936.
[2] and related SPC No. SPC/GB13/079 (the “SPC”).
[3] Sandoz and Teva were co-claimants/appellants in these proceedings.