Pfizer’s experimental rheumatoid arthritis drug tasocitinib has shown strong promise in a late-stage clinical trial, reducing the signs and symptoms of the disease in the majority of patients without any new safety issues.

Top-line data from the six-month, placebo-controlled, Phase III Oral Solo (1045) study, involving 611 patients, showed ACR20 response rates (20% improvement from baseline) of 60% in the group taking 5mg of tasocitinib, 66% in those given 10mg of the drug, and 27% in the placebo arm after three months’ of twice-daily treatment.

In addition, the drug also met its secondary endpoint of inducing a significant improvement in physical functionality – ie the ability of patients to carry out every-day tasks – as measured by mean change in HAQ-DI (Health Assessment Questionnaire Disability Index), the drug giant said.

On the down side, while tasocitinib appeared to improve disease remission, results on the DAS (Disease Activity Score)-28 showed that this benefit was not statistically significant, with scores of 6% for the 5mg group, 9.6% for the 10mg group, and 4.4% for the control arm.

But the drug also fared well on the safety side of things, with no new issues emerging during the trial. In ORAL Solo, a similar frequency of adverse events was seen across all treatment groups, with serious adverse events reported in 4.1% of patients. Decreases in neutrophil count and haemoglobin and an increase in cholesterol were observed by month three, but the changes tended to stabilise thereafter, Pfizer said.

Tasocitinib is a novel, oral Janus kinase (JAK) inhibitor that, unlike current therapies for RA, takes a novel approach to treatment by targeting intracellular signalling pathways as opposed to the more common extracellular targets such as pro-inflammatory cytokines, and there are certainly high hopes that the drug could be the first new RA pill in over 10 years, offering an alternative to biologic injections such as Abbott Laboratories’ Humira (adalimumab).

Multi-billion-dollar sales?

Rheumatoid arthritis affects 1.3 million people in the US and around 1% of the adult population around the globe, and if the drug makes it to market analyst expect muli-billion-dollar peak sales, which could help to fill some of the void left by generic competition to Pfizer’s cholesterol buster Lipitor, currently the world’s number one selling drug, from next year.

Pfizer is reportedly planning on completing a further four studies on tasocitinib in the first half of next year, gunning for a very broad label for the drug. “This might be the first drug that is going for the original filing with everything: signs and symptoms, quality of life, X- ray data, and then really looking at the various types where the drug could be used,” Saeed Fatenejad, head of late-stage trials in inflammation and immunology at Pfizer, told Bloomberg.

Results of Oral Solo and Oral Sequel - an open label, follow-up Phase II/III study assessing long-term safety and efficacy of the drug - will be presented at the American College of Rheumatology (ACR) Annual Meeting in Atlanta this week.