Gilead and Galapagos’ JAK inhibitor filgotinib works in patients with ulcerative colitis, but maybe not well enough to displace rival drugs in the class.

That was the overall impression from the two partner’s phase 2b/3 readout in UC, a form of inflammatory bowel disease, in which only the higher of two doses on test had a significant impact on symptoms.

Filgotinib is already under regulatory review in the US, Europe and Japan as a treatment for rheumatoid arthritis, but Gilead and Galapagos will need to extend the use of the drug into additional indications as well if they hope to compete with other JAK inhibitors, including AbbVie’s recently-launched Rinvoq (upadacitinib), considered its closest rival.

The SELECTION trial is the first evidence to support filgotinib in UC, and the results were mixed. At a dose of 200mg, filgotinib improved remission rates in biologic-naïve or biologic-experienced adult patients, but the lower 100mg dose wasn’t able to hit that objective.

In biologic-naïve patients, 26.1% of patients in the 200mg achieved clinical remission at week 10 – the primary endpoint – compared to 15.3% of those in the placebo arm. In biologic-experienced patients, the remission rates were 11.5% and 4.2%, respectively.

For comparison – although that’s almost impossible between two different trials – Rinvoq achieved statistically significant clinical remission of 14-20% at its highest dose versus placebo after eight weeks.

Gilead chief medical officer Merdad Parsey said the company was “encouraged” by the data, adding that it suggested that filgotinib could play a role in helping more patients achieve a meaningful and sustained improvement in treatment response with an oral therapy.

Investors seemed unsure, however, and shares in Gilead slipped around 1% after the update, while Amsterdam-listed Galapagos fell almost 8%.

The results showed that filgotinib 200mng was able to induce clinical remission and also maintain it, with the drug still outperforming placebo after 58 weeks’ follow-up.

Added to that, the drug seemed to be well tolerated. Gilead and Galapagos are hoping to avoid a black box warning for potential thrombosis side effects that has been applied by the FDA on all other drugs in the JAK inhibitor class, although opinion is divided on whether that is likely to happen.

Rates of adverse events such as serious infections, herpes zoster, venous thrombosis, pulmonary embolism and gastrointestinal perforation were “low and comparable across treatment groups”, said Gilead and Galapagos.

The two companies have aspirations to launch filgotinib for no fewer than six indications in the next four years, namely rheumatoid arthritis and ulcerative colitis – where Gilead reckons it could be first to market – as well as Crohn’s disease, psoriatic arthritis, ankylosing spondylitis and uveitis.