EXHIBIT 1

AGREEMENT REGARDING JOINT FILING

The undersigned, Biotechnology Value Fund, L.P., a Delaware limited partnership, Biotechnology Value Fund II, L.P., a Delaware limited partnership, BVF Investments, L.L.C., a Delaware limited liability company, Investment 10, L.L.C., an Illinois limited liability company, BVF Partners L.P., a Delaware limited partnership, and BVF Inc., a Delaware corporation, hereby agree and acknowledge that the information required by Schedule 13D, to which this Agreement is attached as an exhibit, is filed on behalf of each of them.  The undersigned further agree that any amendments or supplements thereto shall also be filed on behalf of each of them.

Dated:  April 20, 2005

BIOTECHNOLOGY VALUE FUND, L.P.
By:	BVF Partners L.P., its general partner
	By:	BVF Inc., its general partner
		By:	/s/ Mark N. Lampert
			Mark N. Lampert
			President
BIOTECHNOLOGY VALUE FUND II, L.P.
By:	BVF Partners L.P., its general partner
	By:	BVF Inc., its general partner
		By:	/s/ Mark N. Lampert
			Mark N. Lampert
			President
BVF INVESTMENTS, L.L.C.
By:	BVF Partners L.P., its manager
	By:	BVF Inc., its general partner
		By:	/s/ Mark N. Lampert
			Mark N. Lampert
			President
INVESTMENT 10, L.L.C.
By:	BVF Partners L.P., its attorney-in-fact
	By:	BVF Inc., its general partner
		By:	/s/ Mark N. Lampert
			Mark N. Lampert
			President

BVF PARTNERS L.P.
By:	BVF Inc., its general partner
	By:	/s/ Mark N. Lampert
		Mark N. Lampert
		President
BVF INC.
By:	/s/ Mark N. Lampert
	Mark N. Lampert
	President