Athira Pharma has joined an attempt to rescue an asset abandoned by Pfizer. The biotech has secured near-global rights to a phase 3 breast cancer prospect in a deal with Sermonix Pharmaceuticals.
Pfizer developed the selective estrogen receptor modulator lasofoxifene in collaboration Ligand Pharmaceuticals, as a treatment for conditions including osteoporosis. The FDA issued a complete response letter in 2009, leading Pfizer to return rights to Ligand two years later. Sermonix in-licensed the asset in 2015 and pivoted to oncology, kicking off a phase 3 trial in locally advanced or metastatic breast cancer in 2023.
With phase 3 data expected in mid-2027, Athira has stepped up to help get lasofoxifene over the finish line. The biotech is issuing Sermonix about $34.9 million in equity as part of a deal that gives it rights to the molecule outside of Asia and in certain Middle Eastern countries.
Athira has agreed to pay third-party service providers $16.8 million and give Sermonix $75,000 a month. The monthly payments will be credited against future milestones that could total $100 million. Athira disclosed the outlay alongside a $90 million private placement and warrants that could give it another $146 million. Perceptive Advisors, whose affiliate owns 29% of Sermonix, co-led the financing.
Athira CEO Mark Litton, Ph.D., discussed the thinking behind the deal on a call with investors, pointing to “compelling signals of clinical activity, including double-digit months progression-free survival in combination therapy in phase 2, and a differentiated mechanism designed to overcome the very resistance that limits current endocrine agents.”
Litton added that the drug candidate’s “tissue-selective pharmacology and strong combinability profile position it uniquely within a landscape that is rapidly shifting towards precision, durability and improved patient experience.” Sermonix’s phase 3 is pitting lasofoxifene against fulvestrant, which AstraZeneca sells as Faslodex, in people with ER-positive, HER2-negative breast cancer with an ESR1 mutation.
Fulvestrant is a selective estrogen receptor degrader. Lasofoxifene, in contrast, modulates the receptor. The drug candidate may spare healthy estrogen receptors in bone and urogenital tissue, avoiding the tolerability and quality-of-life issues associated with complete receptor degradation or blockade. Phase 3 endpoints include patient-reported assessments of vaginal and sexual health.
Litton predicted that lasofoxifene could achieve peak annual U.S. sales of approximately $1 billion. The forecast reflects the tolerability profile seen in phase 2 and the potential for extended treatment duration when the drug candidate is combined with Eli Lilly’s Verzenio. Licensing lasofoxifene could accelerate Athira’s path to becoming a commercial biotech, with its next most advanced asset set to enter phase 2 in 2026.
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