Genentech's Rituxan Faces Stiff Competition

Rituxan, a longtime blockbuster drug for Genentech (DNA Quote), is likely to contend with increased competition out of Denmark next year.

Rituxan is approved for non-Hodgkin's lymphoma (NHL) and rheumatoid arthritis, but is also used off label for a host of other indications. In fact, Rituxan combined with chemotherapy is one of the most common forms of treatment for chronic lymphocytic leukemia (CLL).

The drug is expected to generate more than $2 billion in sales in 2006 for marketing partners Genentech and Biogen Idec (BIIB Quote), with Genentech as majority partner.

Rituxan, a monoclonal antibody, targets the CD20 protein, which exists on the outside of B cells, the type of white blood cells that help fight infections. The antibody sticks to the protein, which alerts the body's immune system to kill the cell. If the immune system cannot destroy the cell, the antibody can bore a hole into the cell and kill it. Rituxan is a hybrid of both human and mouse antibodies.

The HuMax Factor

Danish drug company Genmab has developed a humanized antibody called HuMax CD20. Recent studies have shown that HuMax appears to work better in CLL patients than Rituxan.

CLL patients have lower levels of CD20 on their cells than NHL patients do. While Rituxan is able to find the CD20 proteins on NHL patients' B cells, it has more difficulty finding them on the cells of CLL patients. HuMax does not have that problem.

Despite CLL patients having far fewer CD20 proteins on the cells, HuMax can still locate enough of them to signal the body's immune system to attack, which leads to the death of more cancerous B cells. Additionally, HuMax attaches to the protein closer to the cell, enabling it to more easily reach into the cell to kill it if the immune system doesn't do the job first.