Parabilis filed for an initial public offering (IPO) one day after signing a strategic research collaboration with Regeneron valued at up to $2.3 billion. The collaboration targets “antibody-Helicon conjugates,” a next-generation antibody-drug conjugate format designed to reach historically undruggable targets. Regeneron agreed to buy about $75 million of Parabilis stock in a concurrent private placement at 90% of the IPO price per share. In its registration statement, Parabilis outlined continued development of zolucatetide (formerly FOG-001), including dose expansion and a planned Phase 3 registrational trial in desmoid tumors. The company also plans further studies across additional indications including familial adenomatous polyposis and hepatocellular carcinoma. This sequence of deal + IPO filing signals Parabilis is positioning its Helicon platform and clinical asset development for near-term public-market scrutiny as biotech financing conditions remain active for companies with clinical catalysts.