Arrowhead Announces First Patient Enrolled in Phase 1 Trial Evaluating HZN-457 for the Treatment of Gout

Arrowhead Pharmaceuticals Inc. (NASDAQ: ARWR) today announced that Horizon Therapeutics plc (Nasdaq: HZNP) has enrolled the first subject, earning Arrowhead a $15 million milestone payment, in a Phase 1 randomized, placebo-controlled trial to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of its development-stage medicine HZN-457, previously known as ARO-XDH. HZN-457 is a small interfering RNA (siRNA) candidate designed to treat gout by silencing liver xanthine dehydrogenase. The development of HZN-457 is part of a global collaboration and license agreement that the Company entered in 2021 with Horizon.

“Our partnership with Horizon has moved forward rapidly and we are excited that HZN-457, formerly ARO-XDH, has begun clinical studies,” said Christopher Anzalone, Ph.D., Arrowhead’s president and CEO. “Horizon is a clear leader in gout and we look forward to continuing to work with them to help bring this potentially important new medicine to the patients who need it.”

“As a clinical and commercial leader in gout, Horizon understands the critical need to develop innovative approaches and advance novel treatments to reach more patients who live with this disease,” said Elizabeth H.Z. Thompson, Ph.D., executive vice president, research and development, Horizon. “The HZN-457 Phase 1 clinical trial marks an important milestone for Horizon to advance our research and development in this space, fostered by our partnership with Arrowhead.”

Gout is a serious and painful form of inflammatory arthritis that is caused by excess uric acid. In the United States, there are more than 9 million gout patients and approximately a third are treated with oral urate-lowering therapies.^1,2 However, a meaningful portion of those patients do not respond sufficiently and continue to experience painful and debilitating gout symptoms.³ High uric acid levels, if left untreated or undertreated, can lead to acute and persistent inflammatory arthritis,⁴ bone and joint damage, exacerbate comorbidities, and severely impact patients’ lives.⁵ Preclinical studies suggest that HZN-457 has the potential to maintain lower uric acid levels and offer several benefits above standard of care for the treatment of gout.