Eli Lilly and partner Incyte Corp have put their janus kinase (JAK) inhibitor baricitinib into Phase III trials for rheumatoid arthritis.

The move has come after 24-week results from the continuation of an ongoing Phase IIb study of baricitinib were presented at the American College of Rheumatology meeting in Washington DC. The trial is looking at the oral drug in patients with moderate-to-severe RA who had an inadequate response to treatment with methotrexate.

Positive results of the placebo-controlled 12-week portion of the study were presented at the European League Against Rheumatism meeting in June and in Washington this week, data from the 12- to 24-week portion of the study, which did not include a placebo control, showed that patients who continued to receive 2mg, 4mg or 8mg baricitinib once daily-doses maintained or improved ACR20 (ie a 20% improvement in their condition), ACR50 and ACR70 responses.

The trial also included a sub-study of 154 patients using magnetic resonance imaging, which showed a statistically significant improvement in both the total inflammation and total joint damage scores for both 4mg and 8mg baricitinib doses compared with placebo at 12 weeks. The effects persisted through 24 weeks.

Lilly and Incyte quoted Mark Genovese of the Stanford University School of Medicine in Palo Alto, USA, as saying that these data are important "because collectively they show patients experienced improvement with baricitinib as early as week two that was sustained through week 24". Also of note, he added, is that the percentage of patients achieving ACR50 and ACR70 "increased over time and no unexpected safety findings emerged with continued dosing".

Eiry Roberts, vice president of autoimmune product development at Lilly, said wWe believe the JAK inhibitors are an innovative class of molecules which we hope have the potential to improve outcomes for patients with diseases such as RA". Baricitinib is also in Phase II as a potential treatment for psoriasis and diabetic nephropathy. Four Phase III RA studies are planned, which will investigate baricitinib 2mg and 4mg in patients with active RA who are methotrexate-naive, biologic-naive or biologic-experienced.

Analysts at Credit Suisse said the data presented "continue to reinforce the potential of the drug and the class". They argue that "expectations are somewhat muted on this agent," less than $500 million in 2020, however the uptake of Pfizer's twice-daily JAK inhibitor Xeljanz ((tofacitinib), approved last week for RA by the US Food and Drug Administration, "should help build confidence in the category and drive estimates up".