Treatment with Genentech and Roche’s MabThera/Rituxan can halt the damage to joints seen in patients with rheumatoid arthritis, even if they have already failed to respond well to biologic treatments for the disease.

The findings – marking the first time that a drug has been shown to stop joint damage in patients refractory to treatment with the tumor necrosis factor (TNF) inhibitors – give an early boost to MabThera (rituximab) in rheumatoid arthritis. The drug has just been cleared for this use in the USA, adding to its indications in cancer, and it was recommended for approval for the new use in Europe earlier this month. It has also just been approved in Canada.

The anti-TNF drugs have combined annual sales of around $4.6 billion out of a total RA market estimated at around $5.5 billion. Between 30% and 40% of patients taking anti-TNF drugs fail to respond to or are intolerant of therapy, although studies have suggested that some may be helped by switching from one anti-TNF therapy to another.

The results of the REFLEX study presented at the European League Against Rheumatism (EULAR) conference in Amsterdam compared MabThera to placebo, on top of standard therapy with methotrexate, in more than 500 patients who had failed treatment with one or more TNF blockers.

Edward keystone of the University of Toronto in Canada told the EULAR meeting that bone erosions were cut in half with MabThera therapy after one year compared to placebo, as was the narrowing of joint spaces, another indicator of joint damage in rheumatoid arthritis.

The REFLEX formed the basis of Roche and Genentech’s marketing applications for rituximab in rheumatoid arthritis based on its effects on the signs and symptoms of the disease.

“Stopping joint damage indicates that the disease pathway has been interrupted, a goal we strive for in the treatment of rheumatoid arthritis,” said Keystone. He said the expectation is that just two injections of the drug, given two weeks apart, should provide a therapeutic effect for up to nine months.

Analysts have suggested that rheumatoid arthritis could add a billion dollars to rituximab’s sales. Roche reported MabThera sales of 1.15 billion Swiss francs ($921m) in the first quarter of this year, while Genentech said it booked $477 million from Rituxan in the same period.

Two-year Orencia data

Meanwhile, there was also positive data for Bristol-Myers Squibb’s Orencia (abatacept), another drug vying to grab a slice of the market for rheumatoid arthritis patients who do not respond to anti-TNF drugs.

Orencia, approved for treating rheumatoid arthritis earlier this year, was shown to slow the progression of structural damage in patients out to two years, building on earlier one-year data in this setting.

The data came from a long-term, open-label extension of the AIM study, which was used to support Orencia’s approval in the USA at the end of last year. The extension phase involved 539 patients who received Orencia plus methotrexate, and revealed that there was a 57% decrease in the rate of progression compared to the first year, indicating that there was some acceleration in effect, according to Harry Genant of the University of California San Francisco.

This suggests “progressive improvement and sustained reduction of damage which could equate to increased patient quality of life measures such as mobility and independence,” he said.

While rituximab exerts its effects in rheumatoid arthritis by inhibiting the function of white blood cells known as B cells, abatacept targets the T cell population. B-MS’s drug is also expected to be a big seller, with $1 billion-plus potential.