Parabilis Medicines, the developer of drugs and antibody-drug conjugates targeting historically undruggable protein targets and based on stabilized helical peptides or Helicons, has filed for an initial public offering (IPO), joining a growing parade of companies seeking to raise capital by tapping into the improving market for first time biotech stocks. The company’s IPO filing came a day after Parabilis inked an up-to-$2.3 billion-plus strategic research collaboration with Regeneron Pharmaceuticals to discover and develop an initial five candidates encompassing “antibody-Helicon conjugates,” a new form of antibody-drug conjugates aimed at challenging and historically undruggable targets. Regeneron has agreed to purchase approximately $75 million of Parabilis common stock in a concurrent private placement, at 90% of the IPO price per share. It’s too soon to know how much money Parabilis plans to raise through the IPO. The company’s Form S-1 registration statement, filed Tuesday with the U.S. Securities and Exchange Commission (SEC), includes a placeholder “$100 million” figure that will inevitably be revised, and doesn’t say how many shares will be sold. Parabilis has applied to list its shares on The Nasdaq Global Market under the ticker symbol “PBLS.” It’s also too early to know how much of the proceeds will go toward the four priorities it highlighted in its registration statement. Two of the four priorities relate to Parabilis’ lead Helicon peptide candidate zolucatetide (formerly FOG-001), a first and only direct inhibitor of the elusive β-catenin:TCF interaction, according to the company. Parabilis stated that it plans to continue ongoing clinical development of…