Duchenne muscular dystrophy specialist Sarepta Therapeutics Inc. gained $125 million by selling to Gilead Sciences Inc. an FDA priority review voucher (PRV) won with its approval of Exondys 51 (eteplirsen). The rare pediatric disease PRV will allow Gilead to trim four months from a standard 10-month agency review. Sarepta said the sale – for about $72 million less than the average fetched by past PRVs – will support development of its follow-on exon-skipping candidates and RNA targeted antisense platform.

It's at least the second PRV purchased by Gilead, which paid Knight Therapeutics Inc. $125 million for a neglected tropical disease PRV in November 2014. A Gilead representative said the company would offer no comment on the latest purchase.

In announcing the sale, Sarepta characterized Gilead's payment as an "up front," language usually reserved for deals that include potential milestone payments. Though such an arrangement would be unusual, it was unclear if any future payments could be part of the deal since Sarepta representatives did not respond to requests for comment.

Credit Suisse served as Sarepta's advisor in the transaction and conducted what the Cambridge, Mass.-based company called an "extensive sales process, which included outreach to multiple pharmaceutical and biotech companies."

Commenting on the sale via Twitter, Duke University health economist David Ridley, co-author of the PRV concept, said that it "reminded us that the laws of supply and demand apply to the priority review market, too." Over the past two years, he wrote, nine PRVs have been awarded, "and the price has fallen as a result."

Jefferies analyst Gena Wang called the sale "positive for near-term inflow of nondilutive cash," though noted that it ranks in the "lower-mid range" of past PRV sales, pointing to past vouchers that have fetched between $125 million and a high of $350 million, paid by Abbvie Inc. to United Therapeutics Corp. The average price fetched for four prior vouchers sold since the program's start is around $197 million. (See BioWorld Today, July 5, 2016.)

The sale remains subject to customary closing conditions.

Exondys 51 won a surprise accelerated approval in September 2016 for the treatment of patients with Duchenne muscular dystrophy amenable to exon 51 skipping.

Even then, the firm had planned to sell the PRV, Sarepta's senior vice president and chief financial officer, Sandy Mahatme, told BioWorld Today at the time. (See BioWorld Today, Sept. 20, 2016.)

Though for a time, it seemed that Congress could allow the pediatric PRV program to expire, with the passage of the 21st Century Cures Act, it been extended through Sept. 30, 2020. The vouchers never expire.

Sarepta stock (NASDAQ:SRPT) closed Tuesday at $28.48, up 40 cents. Gilead shares (NASDAQ:GILD) slipped slighty, down 56 cents, to close at $69.29.