Pfizer Inc announced that data from a phase-2 efficacy and safety study of tasocitinib (proposed INN name for CP-690,550), the company's investigational oral JAK inhibitor, met its primary endpoint of a statistically significant greater proportion of patients achieving at least a 75 per cent reduction from baseline in PASI (Psoriasis Area and Severity Index) at week 12 in individuals with chronic moderate to severe plaque psoriasis.

At week 12, PASI 75 responses for tasocitinib 2, 5 and 15 mg twice daily groups were 25.0%, 40.8% and 66.7% respectively, versus placebo, 2.0% (all doses, p<0.001). As early as week 4, treatment with 5 and 15 mg twice daily of tasocitinib significantly improved patient reported health-related quality of life outcomes. These results were presented in two posters at the annual meeting of the European Academy of Dermatology and Venereology (EADV).

The double-blind, placebo-controlled, dose-ranging phase-2 study was conducted in 197 adult patients with moderate to severe plaque psoriasis. Study participants were randomized to receive 2, 5 or 15 mg tasocitinib or placebo twice daily. In the study, the most frequently reported treatment-emergent adverse events were upper respiratory tract infection and headache.

Three patients experienced a total of five serious adverse events during the study. Dose dependent decreases in mean neutrophil counts and haemoglobin values and increases in mean LDL, HDL and total cholesterol levels were observed.

Tasocitinib is a Janus Kinase (JAK) inhibitor. It is believed that the JAK pathways play an important role in the psoriasis disease cascade. Researchers are conducting clinical trials to test the hypothesis that inhibiting the JAK pathways modulates the immune and inflammatory responses involved in psoriasis, which may lead to clinically meaningful improvement for patients.

More than 4,000 people have participated in tasocitinib clinical trials to date. The most frequently reported adverse events include headaches, infections and gastrointestinal symptoms such as nausea, vomiting and diarrhoea: most were mild to moderate in severity and were manageable with routine medical care.

Pfizer has initiated its study of tasocitinib in people with chronic moderate to severe plaque psoriasis in a phase-3 programme called the OPT (Oral Psoriasis Treatment) Trials to further characterize the efficacy and safety profile.

Tasocitinib is also being studied for the potential treatment of rheumatoid arthritis in a group of trials called the ORAL trials. Additionally, tasocitinib is being studied in dry eye, Crohn's disease, ulcerative colitis and solid organ transplant.

Tasocitinib was discovered by Pfizer scientists in the company's Groton, Connecticut laboratories and is being developed solely by Pfizer.