AstraZeneca has reported top-line results of OSKIRA-1, a phase III study to assess the efficacy and safety of fostamatinib, the first oral spleen tyrosine kinase (SYK) inhibitor in development for rheumatoid arthritis (RA). OSKIRA-1 had two primary endpoints: assessing signs and symptoms of RA as measured by ACR20 response rates, and an X-ray endpoint known as mTSS (modified Total Sharp Score).

In the OSKIRA-1 study, fostamatinib achieved a statistically significant improvement in ACR20 response rate at 24 weeks in both the 100 mg twice daily group and the group that received 100 mg twice daily for four weeks followed by 150 mg once daily (49%, p<0.001 and 44%, p=0.006 respectively) compared to placebo (34%). Fostamatinib did not demonstrate a statistically significant difference in mTSS compared to placebo at 24 weeks for either dose (p=0.252 and p=0.170, respectively).

The safety and tolerability findings for fostamatinib observed in the OSKIRA-1 study were generally consistent with those previously reported for the TASKi Phase II programme.

The most commonly reported adverse events were typical of those seen in earlier studies, including hypertension, diarrhoea, nausea, headache and nasopharyngitis (common cold).

Briggs Morrison, MD, executive vice president of Global Medicines Development and chief medical officer, said, “These top-line results provide important information on the efficacy and safety of fostamatinib and demonstrate that the compound has an effect on the signs and symptoms of rheumatoid arthritis. We will await the results of the remaining phase III studies, OSKIRA-2 and OSKIRA-3, to further evaluate and characterise the profile of fostamatinib as a potential treatment for rheumatoid arthritis.”

OSKIRA-1 randomised 923 patients who had experienced an inadequate response to methotrexate (MTX) and, over a 24 week period, evaluated the effectiveness of two dosing regimens of fostamatinib (100 mg twice daily or fostamatinib 100 mg twice daily for four weeks followed by 150 mg once daily) in combination with MTX versus placebo in combination with MTX. Patients on fostamatinib remained on treatment in OSKIRA-1 for 12 months.

The OSKIRA-2 and OSKIRA-3 results are expected later in the second quarter of 2013.

The American College of Rheumatology (ACR) score represents a percentage improvement in symptoms (tenderness and swelling in the joints). 28 joints are evaluated for tenderness and swelling respectively (prior to taking any required analgesic that day if possible). To qualify for an ACR20 score, a person with RA must have at least 20 per cent fewer tender joints and at least 20 per cent fewer swollen joints. He or she must also show a 20 per cent improvement in at least three of the following five areas: the person’s overall (global) assessment of his or her own RA, the physician’s global assessment of the person’s RA, the person’s assessment of his or her own pain, the person’s assessment of his or her own physical functioning, and the results of an erythrocyte sedimentation rate or C-reactive protein blood test (both of which test for inflammation).

Radiographic mTSS is measured in the hands and feet using X-rays. mTSS is a measure of bone erosion and joint space narrowing on X-rays. In each hand, 16 areas are measured for erosions and 15 areas are measured for joint space narrowing. In each foot, six areas are measured for erosions and six areas are measured for joint space narrowing. A smaller change in mTSS over a given time period, given in percentage change of mTSS score, reflects less progression of joint damage.

The ongoing (Oral SYK Inhibition in Rheumatoid Arthritis) OSKIRA programme, has been designed to investigate fostamatinib as a potential new oral treatment option for rheumatoid arthritis and an alternative to injectable therapies for patients with an inadequate response to conventional Disease Modifying Anti-Rheumatic Drugs (DMARDs), including methotrexate (OSKIRA-1 and OSKIRA-2) and those with an inadequate response to TNF-a antagonists (OSKIRA-3).

Fostamatinib (previously referred to as R788), is the first oral spleen tyrosine kinase (SYK) inhibitor in development for rheumatoid arthritis. In February 2010, AstraZeneca and Rigel Pharmaceuticals announced a worldwide license agreement whereby AstraZeneca would develop and commercialise fostamatinib.

Rheumatoid Arthritis (RA) is a systemic autoimmune disease whereby the immune system attacks the joints, causing pain, swelling to the surrounding tissue and damage to the cartilage and bone. If not adequately treated, RA can destroy cartilage and bone within joints, leading to serious disability and can be associated with reduced life expectancy. Not all RA patients have a satisfactory response to existing therapies because the disease pathology may differ from one individual to another and a considerable unmet need remains.

Rigel Pharmaceuticals, Inc. is a clinical-stage drug development company that discovers and develops novel, small-molecule drugs for the treatment of inflammatory and autoimmune diseases, as well as muscle disorders.

AstraZeneca is a global, innovation-driven biopharmaceutical business that focuses on the discovery, development and commercialisation of prescription medicines, primarily for the treatment of cardiovascular, metabolic, respiratory, inflammation, autoimmune, oncology, infection and neuroscience diseases.