ADARx Pharmaceuticals raises $446 million in first US RNAi biotech IPO in over a decade

ADARx Pharmaceuticals, a San Diego biotechnology company that has spent seven years building a pipeline of RNA-silencing drugs, priced an upsized initial public offering late Thursday at $17 a share, the top of its marketed range, and its stock was set to begin trading Friday on the Nasdaq Global Select Market under the ticker ADRX. The offering, disclosed in a company announcement distributed Thursday evening, raised roughly $446.3 million and marks one of the largest biotech listings of the year.

The deal is notable beyond its size. ADARx develops small interfering RNA, or siRNA, therapeutics, a class of drugs that silences the genetic instructions for disease-causing proteins rather than blocking the proteins themselves after they are made. According to BioPharma Dive's reporting on the pricing, ADARx is the first RNA interference-focused biotech to complete a U.S. IPO in more than a decade, and only the second RNA-focused biotech to go public in nearly two years, underscoring how narrow the public financing window has remained for the technology even as the broader biotech IPO market has revived. RNAi drugs have been approved for a handful of rare diseases over the past decade, led largely by Alnylam Pharmaceuticals, but the mechanism has struggled to attract fresh public capital compared with better-known categories such as obesity drugs and cell and gene therapy, making ADARx's reception on Wall Street a closely watched signal for the rest of the field.

The numbers

ADARx sold 26.25 million shares at $17 apiece, above the midpoint of the $15-to-$17 range it had set earlier in the week, according to its registration statement filed with the Securities and Exchange Commission. Underwriters — led by J.P. Morgan, Morgan Stanley, TD Cowen and UBS Investment Bank, with LifeSci Capital as a book-running manager — hold a 30-day option to buy roughly 3.94 million additional shares. The offering is expected to close Sept. 28.

Alongside the public offering, AbbVie agreed to buy up to $100 million of ADARx stock at the same $17 price in a concurrent private placement, a transaction that would leave the drugmaker with about a 4.9% stake once the deal closes. Combined, the IPO and the AbbVie placement are expected to generate approximately $535.2 million before expenses. Trading data compiled by stockanalysis.com put the company's market capitalization at roughly $1.74 billion at the offering price, ahead of the opening bell.

How ADARx got here

ADARx was founded in 2019 by Zhen Li, a chemist who led a small interfering RNA research team at Merck before becoming a senior vice president at Arrowhead Pharmaceuticals. The company has raised more than $350 million from venture investors, including OrbiMed, Bain Capital, TCGX and Venrock, before Friday's listing. It became a partner of choice for larger drugmakers seeking RNAi expertise: in May 2025, AbbVie agreed to pay ADARx a $335 million upfront fee, according to AbbVie's own announcement of the collaboration, for an option and license agreement covering future siRNA candidates in neuroscience, immunology and oncology, with several billion dollars in potential milestone payments and royalties still to come.

Li has previously said the company was in no hurry to test public markets. "The market's just too choppy, and we have cash. We are in control of the timing of our IPO," she said in an interview published last year. That posture changed this year as the broader biotech financing climate improved: the sector has completed roughly 21 U.S. IPOs in 2026 raising close to $7.85 billion, its strongest year since 2021, with drug startups banking more money through public offerings this year than in the prior four years combined by this point in the calendar, according to industry trackers.

"The market's just too choppy, and we have cash. We are in control of the timing of our IPO."

Who is affected

ADARx's most advanced program, onvuzosiran, is a twice-yearly injectable siRNA now in the Phase 3 STOP-HAE trial for hereditary angioedema, a rare and potentially life-threatening swelling disorder. Early-stage data cited by BioPharma Dive showed the drug produced roughly a 93% reduction in plasma kallikrein levels, the target implicated in angioedema attacks, and the drug has received FDA Fast Track designation, according to clinical data ADARx has presented at medical meetings this year. If approved, it would compete against CSL Behring's monthly-dosed garadacimab and Ionis Pharmaceuticals' donidalorsen, positioning ADARx's candidate as a longer-interval alternative for the roughly tens of thousands of Americans living with the condition. A second clinical candidate, agazisiran, is in mid-stage testing across kidney disease, geographic atrophy and a rare blood disorder called paroxysmal nocturnal hemoglobinuria.

The listing also affects a wider circle: venture backers who now have a path to liquidity, AbbVie shareholders exposed to a new equity stake tied to their partnership, and other clinical-stage RNA biotechs — a group that has largely relied on private financing and pharma partnerships rather than public markets over the past two years — watching to see whether investors reward the model. Employees at ADARx's San Diego headquarters, where the company has built out manufacturing and discovery operations since 2019, also gain a public valuation for the equity many were granted as private-company compensation.

Patient advocacy groups focused on hereditary angioedema have long pushed for treatments that reduce the burden of frequent injections, since existing prophylactic therapies typically require monthly or more frequent dosing to prevent swelling attacks that can affect the airway. A therapy dosed as infrequently as twice a year, if onvuzosiran clears late-stage testing and wins regulatory approval, would represent a meaningful change in treatment burden for a disease that current standards of care manage but do not cure.

What happens next

ADARx said Phase 3 data for onvuzosiran are expected by the end of 2027, a milestone that will likely dictate how the stock trades once the initial listing settles. In the nearer term, the offering's close on Sept. 28 will finalize AbbVie's stake and give underwriters until late October to exercise their option on additional shares. Investors and rival biotech executives are also expected to treat ADARx's reception on Nasdaq as an early test of appetite for RNA interference companies specifically, at a moment when the broader biotech IPO market has shown signs of recovery but remained selective about which technologies it will fund.