Pfizer has entered into an agreement to buy Rinat Neuroscience, in a move that will add new antibody-based treatments for pain and Alzheimer’s disease into its product pipeline, as well as furthering its push into biologic drugs.

Terms have not been disclosed, although speculation is that the price tag is several hundred million dollars.

Rinat’s lead product is RN624, which has just started Phase II testing as a treatment for acute and chronic pain in patients with osteoarthritis, and if approved could go some way to bolster Pfizer’s arthritis franchise, hit by declining sales of its former blockbuster painkiller Celebrex (celecoxib) on safety concerns.

The drug is a monoclonal antibody that blocks nerve growth factor (NGF), and Rinat claims its painkilling efficacy that rivals morphine and is superior to the non-steroidal anti-inflammatory drugs such as naproxen and diclofenac, but without the side effects associated with either of these classes.

Following behind – and possibly of more interest to Pfizer - is RN1219, an antibody against the amyloid beta peptide that accumulates in the brains of people with Alzheimer’s and is thought to contribute to the degeneration of neurons underlying the disease. Preclinical trials indicate that RN1219 can clear amyloid ‘plaques’ deposited in the brain, and the drug has now advanced into Phase I testing in humans.

Similar amyloid-busting drugs are being developed by Elan/Wyeth, Neurochem and Myriad Genetics. Analysts have suggested that a drug that proved effective treating the underlying causes of Alzheimer’s could reap sales of $4 billion or more at peak.

For Pfizer, the Rinat purchase comes on the heels of a string of other acquisitions aimed at boosting its pipeline as it copes with patent expiries on some of its top-selling drugs, competition to powerhouse cholesterol-lowerer Lipitor (atorvastatin) and the decline in Celebrex sales that has occurred as a result of the link between COX-2 inhibitors and an elevated risk of heart attack and stroke.

In February, the world’s largest drugmaker said its sales this year would be roughly level with 2005.

Last year, Pfizer paid $1.9 billion to purchase Vicuron Pharmaceuticals, and also acquired Idun Pharmaceuticals for an undisclosed amount, bolstering its oncology pipeline, and biotechnology firm Angiosyn for $275 million.