Sierra doubles down on ex-Gilead drug, deprioritizes other assets

Myelofibrosis, reticulin stain. (euthman/CC BY 2.0)

Sierra Oncology is betting its future on the phase 3 myelofibrosis drug it picked up from Gilead for a knockdown price. The JAK 1/2 inhibitor underwhelmed in the clinic at Gilead but Sierra has decided to focus its resources on the drug, leading it to search for non-dilutive ways to fund other assets.

Gilead let the drug, momelotinib, go for $3 million upfront in 2018, despite having paid around $500 million for it six years earlier. The low price Sierra paid reflected the tarnishing of momelotinib’s prospects during its time at Gilead, which oversaw clinical trials that raised doubts about the drug.

Sierra focused on momelotinib’s potential to address myelofibrosis-related anemia, a characteristic that could give it an edge over other JAK inhibitors such as Incyte’s Jakafi. Now, Sierra has affirmed its belief momelotinib.

Going forward, Sierra will focus on momelotinib amd seek non-dilutive ways to fund development of SRA737 and SRA141, DNA damage response assets that are in or near the clinic. Sierra, formerly known as ProNAi Therapeutics, licensed SRA737 and SRA141 in 2016 to rebuild its pipeline following the failure of its lead candidate but is now focusing its resources on momelotinib.

Sierra disputes that it is deprioritizing SRA737 and SRA141, instead saying to FierceBiotech: "SRA737 and SRA141 are being actively developed by Sierra; our press release only states our intention to seek non-dilutive options to support the future development of these assets and that we are prioritizing our capital for the future development of our lead drug momelotinib."

SRA737, a Chk1 inhibitor, is the more advanced of the two assets. Sierra recently linked the drug to a 30% response rate in the second-line treatment of metastatic anogenital cancer. At the time, Sierra talked up a path to registration for SRA737.

The second affected asset, SRA141, is a Cdc7 inhibitor that has been through the IND process. Sierra has designed a phase 1/2 trial but now looks unlikely to forge ahead until a non-dilutive way of bankrolling the study is secured.

Sierra ended March with $90 million in cash. Having seen its share price fall 80% over the past year, Sierra is poorly placed to raise additional money through stock offerings. Sierra turned to Silicon Valley Bank for a debt facility to acquire and advance momelotinib. Back then, Sierra thought it was “well capitalized” to advance SRA737 and SRA141 alongside momelotinib.

Ten months later Sierra has decided the multifront clinical development strategy is too much. The decision ties Sierra’s future to a phase 3 momelotinib trial it plans to start in the fourth quarter. Sierra expects to have top-line data from the study late in 2021.