With an assist from AstraZeneca, the salvage crew at Sierra bets another $216M they can resurrect an old Gilead JAK drug

05 Aug 2021
endpts.com
Almost a decade ago, Gilead shelled out $510 million in cash for YM BioSciences and its only drug, a JAK inhibitor for a rare type of bone marrow cancer called myelofibrosis. But when the candidate didn’t show any benefit over its rival, Incyte’s Jakafi, the molecule ended up in the hands of Sierra Oncology. Now, confident it’s got a diamond in the rough, Sierra $SRRA is putting that drug, momelotinib, through another Phase III trial in myelofibrosis. And on Thursday, the biotech unveiled a $216 million deal for the rights to AstraZeneca’s BRD4 BET inhibitorBRD4 BET inhibitor AZD5153, which it plans on putting through a Phase II trial in combination with momelotinib. “Sierra, from a company perspective, has been very highly focused on single asset development in myelofibrosis, that being momelotinib,” CMO Barbara Klencke told Endpoints News . “So I think it’s very exciting for us to start to have a pipeline.” Recent research has shown the promise of BET and JAK inhibitors in myelofibrosis, Klencke said, including data released in December showing that patients who took Constellation’s BET inhibitorBET inhibitor with Jakafi saw a 67% spleen volume response rate. “The JAK/STAT pathway that is so active in myelofibrosis causes cytokines, inflammatory proteins, to be abnormally high. That causes fibrosis,” Klencke said. “Whereas the BET inhibitorBET inhibitor can actually reduce some of the inflammation and can potentially reduce that fibrosis as well, so I think they’re very complementary biologic systems.” But unlike other currently available JAK inhibitors, momelotinib doesn’t cause a reduction in platelet count, meaning it could potentially be given in higher doses. Plus, AZD5153 binds at two active binding sites within BRD4, as opposed to one at a time, which the company believes contributes to its potency. Sierra’s putting down $8 million upfront for AZD5153, plus another $208 million in biobucks and tiered royalties on global sales from the “high single-digits to low double-digits.” The team plans on launching the Phase II combination trial in the first half of next year. They’re also on track to read out results from the Phase III monotherapy study in the first quarter. Jakafi was approved back in 2011 to treat myelofibrosis and raked in over $1.9 billion last year. While it was in Gilead’s pipeline, momelotinib proved statistically non-inferior to Jakafi on a key measure of efficacy, but didn’t look any better and didn’t hit its mark on a key secondary for the total symptom score. The studies were also hit with a high washout rate for patients due to side effects. What makes Sierra think this time around will be different? “We have used our prior data from Gilead and from earlier Phase IIs to design the right trial. MOMENTUM is designed knowing the patient type and the expected level of activity,” Klencke said. “So we have a very high level of confidence around MOMENTUM being a trial that should be able to confirm the efficacy of momelotinib.”
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