Alexion Pharmaceuticals Inc. and Zealand Pharma A/S will collaborate to discover and develop peptide-based therapies that target diseases related to the body's complement system.

Under the agreement, Boston-based Alexion will pay $25 million up front and make a $15 million equity investment in Denmark-based Zealand.

Alexion will have exclusive worldwide licenses and commercial rights for up to four targets within the complement pathway. The complement system is a part of the immune system which enhances the ability of antibodies to fight damaged cells. The system is thought to play a role in many diseases.

Zealand Pharma will lead discovery and research activities in the preclinical stage, while Alexion will oversee development from filing the investigational new drug application and phase 1 trials.

Zealand Pharma may receive up to $115 million in development-related milestones, and up to $495 million in sales-related milestones and potential royalty for the lead target.

Alexion has the option to select the remaining three target therapies for $15 million each, plus potential development and sales-related milestone payments along with royalties at a lower price than the lead candidate.