Principia Biopharma has filed to raise up to $86.3 million in its IPO to carry its lead asset into phase 3. The company's BTK inhibitor is currently in phase 2 trials for the autoimmune skin disease pemphigus and is also being developed for immune thrombocytopenic purpura (ITP), a bleeding disorder.
PRN1008 is a small-molecule inhibitor of Bruton’s Tyrosine Kinase (BTK), a protein important to immune function. Blocking BTK down-regulates certain cellular processes that are activated in autoimmune and inflammatory diseases, the company says.
The IPO haul will also support the completion of a phase 1 trial testing Principia’s FGFR inhibitor, PRN1371, in FGFR translocated metastatic bladder cancer, as well as “fund our obligations” under a licensing deal with Sanofi.
South San Francisco-based Principia licensed a different BTK inhibitor, PRN2246, to Sanofi in November. This one is in development for multiple sclerosis and has been shown to cross the blood-brain barrier, opening the door to use in other neurological disorders. Principia picked up $40 million upfront and stands to reap up to $765 million in milestone payments.
“The agreement allows Principia to maximize the BTK opportunity in neurology with a strong partner for PRN2246 while focusing internal resources on our lead BTK inhibitor in another therapeutic area," Principia CEO Martin Babler said at the time. "PRN2246 is a blood brain barrier crossing, highly potent BTK inhibitor, that we believe is especially well suited for the treatment of MS and other neurological disorders."
BTK is perhaps best known as the target of Imbruvica, approved back in 2013 for patients with mantle cell lymphoma who have received at least one prior therapy. Interest in BTK has grown as scientists turned up evidence linking the protein to autoimmune disorders. Merck KGaA reported in March that its BTK drug evobrutinib bested placebo in a phase 2 trial in multiple sclerosis. The candidate reduced gadolinium-enhancing T1 lesions at a higher rate than placebo, but unanswered questions remain about its safety and efficacy. Merck has yet to quantify the difference or say how evobrutinib did against rival multiple sclerosis drug Tecfidera.
In 2016, Biogen quietly moved a BTK inhibitor for lupus into the clinic. But just because BTK has become a hot area doesn’t mean it’s a recipe for success. In July 2017, Redx Pharma sold off its BTK program to Loxo Oncology in a bid to stay alive. Loxo forked over $40 million for the assets, which Redx used to pay off an outstanding loan. Because Redx’s situation was so dire, Loxo snagged the early-stage asset without having to promise milestones and royalties.