The move by Acelyrin’s board comes as the venture capital firm has taken larger and larger stakes in the company in an attempt to disrupt a merger with Alumis.
Acelyrin is executing a poison pill defense strategy to fend off an unwanted takeover bid from Tang Capital. The move comes as the San Diego-based venture capital fund has accrued a growing stake in Acelyrin over the past few weeks.
Acelyrin is employing a “limited-duration stockholder rights plan,” commonly known as a poison pill, according to a Thursday release. The plan will grant current stockholders the option to buy more shares at a significant discount to guard against any investor acquiring 10% or more of the company’s shares in an effort to dilute that outside investor’s voting power. That unwelcome investor is excluded from being able to buy discounted shares.
The move against Tang Capital, announced by the L.A.-based biotech company early Thursday, comes as the firm tries to intervene in an acquisition between Acelyrin and Alumis. The two biotechs had planned to pool about $700 million in resources in a deal expected to close in the second quarter of 2025. The resultant company would take Alumis’ name and continue working on the only actively developed molecule currently between the two companies, an antibody in Phase II trials for thyroid eye disease.
Concentra Biosciences, owned by Tang Capital, offered to preempt the merger and buy Acelyrin in early February. On March 4, Acelyrin rejected Concentra’s offer.
Meanwhile, Tang Capital has steadily scooped up more and more shares of Acelyrin, climbing closer to the 10% threshold. Tang reached a 5.3% share in mid-February, 7.3% one week later, and 8.8% on March 10th, according to SEC filings.
Tang Capital and Concentra are extremely active buyers, often bidding for small, struggling companies and later shutting them down. In the past two years, the firms have made unsolicited offers to buy Singular Genomics and LianBio. Singular was eventually bought by Deerfield Management, while LianBio rejected the offer outright and then shut down completely.
BioSpace has reached out to Acelyrin and Tang Capital for comment.
