Fresh off the press from the UK Court of Appeal is a decision concerning the pharmaceutical drug Xtandi (Enzalutamide). Xtandi is indicated in various oncology treatments in Australia and is listed at number 19 the of top 200 selling pharmaceuticals by retail in 2024.
Keen-eyed medicinal chemists will notice that the previously published compound RD162 and Xtandi share remarkably similar structures – the geminal-dimethyl group (highlighted in blue) and the cyclobutyl moiety (highlighted in red) differ only by a bridging methylene group, an overall difference of just one atom.
The Patentee’s own prior disclosure at a conference led to the publication of the RD162 structure. Nevertheless, relevant claims covering Xtandi have withstood an inventive step challenge both at first instance and now at the Appellate level in the UK.
The appeal Court found that there was insufficient motivation in the prior art and from existing knowledge at the relevant time to modify the molecular structure at the specified position with the aim of enhancing the biological properties of the compound. Ultimately, without the benefit of hindsight, this structural change could not be considered obvious, and the relevant claims were found inventive.
While Australian law on inventive step differs from the UK, the decision serves as a reminder to users of the patent system to be cautious with your own disclosures. Equally important however is that even small changes in chemical structures can be patentable.
As always, the devil is in the detail – specifically what has been disclosed in the prior art and what was commonly known at the priority date. It is interesting to consider how the inventive step considerations might play out in Australia and if Australia’s lenient ‘grace period’ provisions could be helpful.
Should you have any questions regarding your own medicinal chemistry projects, please feel free to contact me.