Biogen Idec (BIIB 2.21%) may be best known for its multiple sclerosis drugs, but the biotech giant is also giving itself a few more chances to succeed in the high-risk field of Alzheimer's disease therapies.

Cambridge, Mass.-based Biogen today cut a wide-ranging deal with Japan's Eisai. On one hand, Biogen grabbed the rights to co-develop and commercialize two experimental drugs for Alzheimer's disease that Eisai owns, which are in early- to mid-stage development -- E2609 and BAN2401. On the other hand, Biogen also gave Eisai an option to do the same with two of the Massachusetts company's in-house Alzheimer's drug candidates. One is an anti-amyloid beta antibody called BIIB037 and the other is an antibody that targets tau, another protein implicated in Alzheimer's.

Biogen didn't disclose any of the financial details behind the deal. It only said Eisai gets an up-front payment, and a "fixed" amount of development, approval, and milestone payments tied to sales targets. Eisai could also get a further unspecified onetime check from Biogen for joint development and commercialization rights in Japan.

Both companies will share the costs and potential profits, as well as co-promote the drug candidates should they eventually win approval from regulators. Even so, Eisai, which developed the palliative Alzheimer's treatment donepezil (Aricept), will lead the development of E2609 and BAN2401.

E2609 is what's known as a beta secretase, or BACE, inhibitor, a type of small molecule that binds with an enzyme that performs amyloid processing work. By doing so, this is supposed to reduce the production of amyloid beta peptides and ultimately the plaques that build up in the brains of people with Alzheimer's.

No BACE inhibitors have become marketed drugs as of yet, though several large companies have been trying. Merck is the closest, having put its candidate, MK-8931 into a phase 3 trial last year. AstraZeneca is close behind. It announced plans a month ago to put a similar drug candidate, known as AZD3293, into a late-stage trial. Both Eli Lilly and Roche have fallen off, however. Lilly's BACE inhibitor flunked a phase 2 trial in June due to safety issues, and Roche also recently killed off a BACE inhibitor program that was in phase 1.

Eisai's E2609 is "undergoing preparations" to begin a mid-stage trial, Biogen said Wednesday.

BAN-2401, meanwhile, is an immunotherapy that is also designed to bind to and break up amyloid beta plaques. Eisai got the drug candidate in a December 2007 deal with Sweden-based BioArctic Neuroscience. It's currently in phase 2 testing. Biogen's in-house candidate, BIIB037, is in a phase 1b study.

"Eisai's candidates have demonstrated compelling early data and complement our [Alzheimer's] research while extending our pipeline in this critical area," said Biogen CEO George Scangos in a statement.

Biogen has made a number of early-stage development deals over the past year, including pacts with Sangamo Biosciences, Amicus Therapeutics, and Isis Pharmaceuticals.

This article originally appeared on Xconomy, along with: