Helical peptides are short peptide chains engineered to lock into a stable alpha-helix conformation, the secondary-structure element that mediates many protein-protein interactions inside cells. Stabilization techniques (hydrocarbon stapling, lactam bridges, helicon framing) prevent the helix from unraveling in serum and let the peptide cross cell membranes, opening up intracellular targets that small molecules cannot bind and that antibodies cannot reach.
The modality has produced several clinical-stage programs in 2026. Parabilis Medicines (formerly FogPharma) is in dose-expansion with zolucatetide, a cell-penetrating helical peptide blocking beta-catenin, with a Phase 3 in desmoid tumors planned for the first half of 2027 and a Regeneron antibody-helicon conjugate collaboration worth up to $2.3 billion. Aileron Therapeutics's stapled peptides and Roche's Maxinox helical programs have explored MDM2/MDMX and other intracellular oncology targets. The shared thesis: where small molecules see flat undruggable surfaces and antibodies cannot enter the cell, a stabilized helix can do both.
Stories here cover helical-peptide program readouts and the platforms behind them. See [[parabilis-medicines]], [[zolucatetide]], and [[stapled-peptide]] for adjacent threads.
Parabilis Medicines (Nasdaq: PBLS) opened June 10 at $33.35 and closed at $31.60 on its Nasdaq debut, a 58% first-day gain after pricing an upsized $670 million IPO at $20 per share — above the previously announced $17-19 range and well past the $476 million initial target Parabilis set on June 4. The 33.5 million-share offering breaks the venture-backed biotech IPO record. Proceeds extend runway for the lead asset zolucatetide, a cell-penetrating helical peptide targeting Wnt/β-catenin in cancer, with a Phase 3 in desmoid tumors expected in the first half of 2027.
Parabilis Medicines (formerly FogPharma) set terms June 4 for a Nasdaq IPO under ticker PBLS: 25 million shares at $17-19, raising about $413 million, or up to $476 million if underwriters exercise the overallotment. Proceeds fund its lead asset zolucatetide, a cell-penetrating helical peptide that blocks beta-catenin, through dose expansion and into Phase 3 for desmoid tumors, plus studies in familial adenomatous polyposis and hepatocellular carcinoma. The offering follows a $75 million Regeneron investment tied to a collaboration worth up to $2.3 billion for antibody-helicon conjugates.
Parabilis Medicines (formerly FogPharma) filed its S-1 on May 19 to list on Nasdaq under ticker PBLS, seeking ~$100M to fund Phase 3 of zolucatetide (FOG-001), a stabilized helical peptide and the first direct inhibitor of the β-catenin:TCF interaction. As of February 16, 38 desmoid-tumor patients were dosed; 25 had sufficient follow-up to be response-evaluable, all showed tumor reduction, and 74% of the 19 patients with ≥2 post-baseline scans hit RECIST 1.1 objective response. The IPO follows a $305M Series F in January and a Regeneron research deal worth up to $2B. FDA granted fast track designation for desmoid tumors.