Acelyrin readies biggest biotech IPO so far this year with $540M upsized offering

In what looks set to be one of the biggest biotech IPOs of 2023, Acelyrin has revealed that it’s expecting to raise $540 million to push its immune drug candidates through the clinic.

The upsized public offering will now see the California biotech offer 30 million shares of common stock at $18 apiece. There will also be the option for underwriters to snap up a further 4.5 million shares at the same price, which could potentially boost proceeds to around $620 million.

It would mark a significant cash injection for a company that has already raised $408 million from private investors in recent years. The biotech’s backers have been attracted by izokibep, a small therapeutic protein inhibitor of IL-17A that Acelyrin licensed from Affibody and is in late-phase development in three immunological diseases.

So far, the outlook has been promising, with a midphase trial linking izokibep to complete clearance of psoriasis skin lesions in 67% of patients. Top-line data from a phase 2b/3 trial in the skin condition hidradenitis suppurativa are due in the second half of the year, to be followed by results from phase 2b/3 studies in psoriatic arthritis and uveitis around the middle of 2024.

The company also has an IGF-1R candidate called lonigutamab in development for thyroid eye disease and a c-KIT prospect called SLRN-517 for chronic urticaria. The spread of potential indications gives Acelyrin a shot at a number of lucrative markets. Or, in the words of the company’s latest Securities and Exchange Commission filing, “multi-billion-dollar opportunities in the aggregate.”

The game plan is for Acelyrin to have part of the data package for approval in three indications in a little over 12 months. It marks a far more sturdy footing in the clinic than many of the biotechs that went public during the recent IPO boom years, when companies were in some cases as much as a year away from being able to show any clinical data at all.

With expectations of raking in north of half a billion dollars for the IPO, Acelyrin is clearly confident that it will be able to entice new shareholders. The IPO size dwarfs the few other biotechs that have ventured onto the public markets so far this year—such as Structure Therapeutics’ $161 million offering and Mineralys Therapeutics’ $192 million IPO.

Acelyrin’s shares are due to begin trading on Nasdaq May 5 under the symbol "SLRN," with the offering expected to close May 9.