A recent Appeal Court judgment concerning the University of California European patent (UK) covering the prostate cancer drug enzalutamide and exclusively licensed to Astellas has resulted in generic versions of the drug remaining barred from entering the UK market. Beyond the commercial significance of this judgment (full copy via this link Accord Healthcare Ltd & Ors v Regents of the University of California & Anor [2025] EWCA Civ 936 (23 July 2025)), an aspect of particular interest is the approach taken by the appeal judges to assessing lack of obviousness in a mere single group substitution in a chemical scaffold. This is especially so given that the prior art starting point was a poster and slides of the inventors as presented at a research meeting and might be regarded as arising from structure-activity studies to be expected by research teams in the pharmaceutical field.
At appeal, the sole issue was whether the judge at first instance had erred in assessing expert evidence and thereby rejecting as obvious the claim to enzalutamide due to prior disclosure of a compound RD162 – a compound differing from enzalutamide (RD162’) only by substitution of a cyclobutyl group by a geminal dimethyl group (i.e. two methyl groups on the same carbon atom) as shown below.
The appeal judges affirmed that it was appropriate to adopt the structured ‘Pozzoli approach’ to assessment of obviousness as commonly adopted by the UK courts in relation to patent claims, this approach consisting of four steps with step 3 being:
Identify what if any, differences exist between the matter cited as forming part of the ‘state of the art’ and the inventive concept of the claim or the claim as construed.
However, they qualified need to consider this step in the correct context – the context of a drug design project rather than mere ability of a medicinal chemist to recognise a particular group substitution as feasible. In this respect, the appeal judgment expresses concern that the technical expert for the generic companies had been led to focus unduly on changing cyclobutyl to dimethyl as an exercise of a medicinal chemist without dealing sufficiently with the scenario for the skilled person in the context of drug development.
In providing the lead judgment, Lord Justice Arnold took the opportunity to emphasise that in such a prior art situation it may be more desirable to ask an expert a more open question avoiding reference to the precise modification and thereby lessen risk of hindsight unduly overshadowing thought on obviousness of the choice of route, in this case:
Supposing that the skilled team, after having read the Poster, wanted to develop an alternative to RD162 which had similar therapeutic potential, what compounds(s) would have been obvious choices to investigate?
The message to those wishing to attack invention in chemical modification in the therapeutic field is clear- guard against equating the technically simple in chemistry terms with obviousness of choice of route – the scenario or context matters.
More detailed report on the judgment is due to appear in the on-line version of the CIPA J. here.
