Updated: Mirum Pharmaceuticals Launches With Phase III-Ready Drug From Shire, $120 Million in Financing

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With $120 million secured in a Series A financial round, startup company Mirum Pharmaceuticals is hitting the ground running with a licensing deal from Shire for a Phase III-ready ASBT inhibitor in hand.

Based in San Diego, Mirum entered into the agreement with Shire for the exclusive global rights to develop and market maralixibat, a Phase II oral inhibitor of the apical sodium-dependent bile acid transporter (ASBT). Shire had initially intended to launch a Phase III program, but opted to hold off, which allowed Mirum to step in with a significant offer, Mirum Chief Executive Officer and Chairman Mike Grey told BioSpace in an exclusive interview Maralixibat is being developed for Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis (PFIC), both debilitating liver diseases that tend to strike pediatric patients. Early clinical data showed a clear proof of concept for the drugs and that was something that Mirum was interested in pursuing once it learned that Shire was not actively pursuing development of the drug. Backed by the impressive Series A financing, Mirum secured the two drugs and is

Mirum is evaluating the ability of maralixibat to prevent the accumulation of excess bile acids, as well as control extreme itching associated with cholestatic liver diseases, such as ALGS and PFIC, the company said. The company is initially focusing ondevelopment of maralixibat on the two conditions as treatments for pediatric patients. The company believes that there is potential for maralixibat to be developed for additional pediatric and adult cholestatic liver disease indications. For right now though, it is focused on the two named indications.

Mirum believes that maralixibat in oral form could be a first-in-class treatment for ALGS and other liver diseases. As of this morning, maralixibat has been administered to more than 230 cholestatic patients to date, which Mirum said has provided an extensive safety data set.

In an interim analysis of Shire’s Phase II trial of maralixibat, Mirum noted that ALGS patients who had been dosed with the treatment saw reductions in bile acids and pruritus, which is the extreme itching, compared to placebo. In a Phase IIb PFIC study, a subset of patients responded to maralixibat and some of the pediatric patients were able to come off a liver transplant list, Grey said. As a result of the PFIC study conducted by Shire, the U.S. Food and Drug Administration (FDA) gave maralixibat Breakthrough Therapy designation.

Mirum intends to launch Phase III trials in both indications next year. However, when those trials will begin is not yet known, Chris Peetz, Mirum’s president said in the interview. He noted though that the company will take advantage of the legwork previously done by Shire with maralixibat.

“We’re still getting down to specifics before we can start the Phase III’s,” Peetz said.

Grey said the data announced from Shire’s Phase IIb study in ALGS underscores his confidence in maralixibat and its potential to help patients with severe liver diseases. Grey noted that patients taking maralixibat saw reductions in bile acids and pruritus. The data announced as part of Mirum’s coming out party was based on the 48-week interim analysis. The company plans to present the data at a liver diseases meeting next year.

“Additionally, in a single-arm, open-label Phase II study, a subset of patients with PFIC2 responded to maralixibat, with a sustained reduction or normalization of serum bile acids and reduction of pruritus. These results led to the FDA’s Breakthrough Therapy designation for patients with PFIC2. These clinical studies demonstrate the potential of maralixibat to significantly impact patients’ lives,” Grey said in a statement.

Under terms of the arrangement with Shire, the pharma giant will receive an undisclosed upfront payment from Mirum, as well as an equity position in the new company. Shire also stands to pick up additional milestone payments and royalties as the drug moves forward in development toward potential commercialization. In addition to maralixibat, the deal with Shire also gave Mirum exclusive global rights to develop and market volixibat, another ASBT inhibitor.

In addition to Grey at the helm of Mirum, the company has tapped several leaders who garnered expertise in drug development in the liver disease space from former companies Lumena Pharmaceuticals, which was acquired by Shire in 2014, and Tobira Therapeutics, which was acquired by Allergan in 2016. Peetz will serve as president, Pamela Vig was named chief scientific officer, Lara Longpre serves as the company’s chief development officer and Shelly Xiong will be head of regulatory.

The Series A financing round was supported New Enterprise Associates, Deerfield Management, Frazier Healthcare Partners, Novo Holdings A/S, Pappas Capital, RiverVest Venture Partners and Rock Springs Capital.

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