Pfizer bails on a $70M rare disease deal with Repligen

Pfizer ($PFE) is walking away from a $70 million collaboration with Waltham, MA's Repligen ($RGEN), handing back some early-stage treatments for the rare spinal muscular atrophy.

Under the initial deal, signed in late 2012, Pfizer handed over $5 million up front and promised another $65 million in milestones to get its hands on RG3039, a Phase I drug designed to block enzyme DcpS and improve survival and motor function in SMA patients.

This week, Pfizer informed its partner that it's backing out of the agreement effective April 26, Repligen said, relinquishing RG3039 and an undisclosed number of preclinical candidates. The biotech's shares fell more than 10% on the news Friday morning.

Repligen's not providing any further detail on the issue, and Pfizer isn't disclosing why it chose to cut ties to RG3039. One potential clue: Over the summer, Pfizer's director of rare disease R&D told Cure SMA's annual conference that RG3039 successfully lowered blood DcpS levels in Phase I but failed to increase production of the protein SMN, whose deficiency is a mark of the disease. That said, just last month, Pfizer dished out a $1 million milestone milestone payment to its partner.

In a statement, Pfizer said moving away from RG3039 will have no effect on its overall work in rare diseases, which includes 7 in-development programs.

Meanwhile, Roche ($RHHBY) entered the SMA space earlier this month with its €470 million ($545 million) deal to acquire Trophos and its lead candidate, now in Phase II. And Isis ($ISIS) is working through a Phase III trial with an SMA treatment of its own, awaiting word on whether partner Biogen Idec ($BIIB) will buy into the program.

There are currently no approved treatments for SMA, which affects between one in 6,000 to one in 10,000 children around the world.

- read Repligen's filing