Zolucatetide

What is Zolucatetide?

Zolucatetide (development code FOG-001) is Parabilis Medicines' lead clinical asset and the first direct inhibitor of the β-catenin:TCF protein-protein interaction to reach human trials — a target the oncology field considered undruggable for three decades because the binding interface (~4,800 Ų of flat, hydrophobic surface) is too large for traditional small molecules. The molecule is built on the Helicon platform, a class of polymacrocyclic α-helical peptides engineered to enforce α-helicity, minimize solvent-exposed amide hydrogen-bond donors, and achieve cytosolic exposure adequate for binding intracellular targets. Its WHO INN chemical name describes a 15-residue acetylated peptide rich in non-natural amino acids, braced by three cross-links: an all-hydrocarbon hexenediyl bridge (the classic stapled-peptide chemistry), a carbamate bridge, and a side-chain lactam. Disclosed chemistry: molecular formula C102H134N18O25S2, molecular weight 2,076.4 Da, CAS 3044032-95-0; the starting point was found through the Helicon platform's phage-display screening. Zolucatetide is administered intravenously on a continuous 28-day cycle schedule. Phase 1/2 NCT05919264 (estimated n=619) is enrolling locally advanced or metastatic solid tumors with Wnt-pathway activating mutations, with cohorts in colorectal cancer, hepatocellular carcinoma, desmoid tumors, castration-resistant prostate cancer, and familial adenomatous polyposis (FAP), plus combination cohorts with mFOLFOX-6 + bevacizumab, nivolumab, and trifluridine/tipiracil + bevacizumab. Parabilis's IPO prospectus disclosed the desmoid data driving the Phase 3 plan: as of February 16, 2026, 38 desmoid patients had been treated, all 25 response-evaluable patients showed tumor reductions, and 74% (14/19) of those with enough follow-up had a RECIST 1.1 objective response, including patients who had failed gamma-secretase inhibitors (GSIs) and regardless of CTNNB1 versus APC mutation status. The FDA granted Fast Track designation for desmoid tumors in November 2025 and Orphan Drug Designation on March 11, 2026. Parabilis closed a $305M Series F in January 2026, signed an antibody-Helicon conjugate collaboration with Regeneron in May 2026, and priced its IPO on June 9, 2026 (Nasdaq: PBLS) at $20 per share, raising $770.5M gross including the over-allotment. The registrational Phase 3 desmoid trial is planned for H1 2027, after FDA discussions in Q4 2026.

What Zolucatetide Is Investigated For

Zolucatetide is the clinical proof-of-concept for an undruggable target: the β-catenin:TCF protein-protein interaction that sits at the transcriptional output of the Wnt signaling pathway. Wnt-pathway dysregulation drives desmoid tumors (~85% CTNNB1-mutated, ~10–15% FAP-associated APC-loss), most colorectal cancers, hepatocellular carcinoma subsets, and Wnt-mutant endometrial and prostate cancers — collectively a large slice of the oncology landscape. Prior pharmacological approaches all targeted the pathway upstream of β-catenin nuclear function: tankyrase inhibitors (XAV939, AZ1366), porcupine inhibitors (LGK974/WNT974, ETC-159, CGX1321), and the indirect approach exemplified by nirogacestat (Ogsiveo), an oral γ-secretase inhibitor that became the first FDA-approved desmoid therapy in November 2023 with a 41% RECIST 1.1 ORR in the pivotal DeFi trial, rising to 45.7% with up to four years of treatment (J Clin Oncol 2025). A second γ-secretase inhibitor, Immunome's varegacestat, reported a 56% versus 9% ORR in the 156-patient RINGSIDE Phase 3 and has an FDA decision date of April 28, 2027. Zolucatetide is the first molecule to directly engage the β-catenin:TCF interaction itself, and its 74% ORR sits above both — but the comparison is cross-trial. Honest caveats are substantial. The 74% comes from an open-label Phase 1/2 with a small denominator (14 of 19 patients with enough follow-up as of February 2026), is not randomized, includes both GSI-naive and GSI-failed patients (a mixed population), and has not been peer-reviewed. The only PubMed-indexed zolucatetide publication is a 2026 NEJM letter describing a single patient with recurrent ameloblastoma; the desmoid data come from company disclosures (the AACR-NCI-EORTC October 2025 abstract B031, ESMO 2025, the November 2025 Fast Track announcement, and the 2026 IPO prospectus), with an ESMO 2026 oral presentation scheduled for late October. The platform validation story is industry-significant: if zolucatetide succeeds in Phase 3, it establishes that Helicon-style polymacrocyclic helical peptides can drug intracellular protein-protein interactions that resisted small-molecule chemistry for decades — a thesis that would justify the broader Parabilis pipeline targeting other previously intractable PPI targets in oncology.

History & Discovery

Zolucatetide originated at Fog Pharmaceuticals (FogPharma), founded in 2015 on technology licensed from the Harvard laboratory of Gregory Verdine — a chemical biologist who pioneered hydrocarbon-stapled α-helical peptides as a strategy for drugging intracellular protein-protein interactions. The lineage runs from the Verdine lab's 2012 report of a stapled peptide that bound β-catenin directly and blocked its coactivation of TCF (PNAS 2012, PMID 23071338) — published alongside a Dana-Farber group's stapled BCL9 helix targeting a different β-catenin partner (Sci Transl Med 2012, PMID 22914623) — through FogPharma's Helicon platform of multiply cross-linked helical peptides engineered for cytosolic accumulation, to FOG-001 itself, found through Helicon phage-display screening against β-catenin's TCF-binding interface. The company is now led by CEO Mathai Mammen, a former Johnson & Johnson R&D executive. The Phase 1/2 trial NCT05919264 opened in May 2023 across solid tumors with Wnt-pathway-activating mutations, with expansion cohorts in colorectal cancer, hepatocellular carcinoma, desmoid tumors, and castration-resistant prostate cancer (later adding FAP), plus combination cohorts. The desmoid signal emerged as the lead clinical opportunity through 2024–2025: desmoid tumors have ~85% CTNNB1-mutation prevalence, well-defined RECIST-evaluable disease, an established response benchmark (nirogacestat's 41% ORR in the DeFi trial), and an unmet need that produced the November 2023 FDA approval of nirogacestat as the first desmoid-specific drug. Conference disclosures at ESMO 2025 and AACR-NCI-EORTC in October 2025 (abstract B031) built the clinical story, and on November 12, 2025 the FDA granted Fast Track designation for desmoid tumors on data showing tumor reductions in all 10 evaluable desmoid patients at an August 2025 cut. Fog Pharmaceuticals rebranded as Parabilis Medicines and closed an oversubscribed $305M Series F financing on January 8, 2026 to support zolucatetide development across multiple indications and advance the broader Helicon pipeline. Zolucatetide received FDA Orphan Drug Designation for desmoid tumors on March 11, 2026. On May 18, 2026 Regeneron signed a research collaboration to develop antibody-Helicon conjugates, paying $50M upfront and buying $75M of stock, with up to about $2.2B in milestones — a platform deal rather than a zolucatetide license. Parabilis filed its IPO registration on May 19, 2026 and priced on June 9, 2026: 33.5 million shares at $20 (Nasdaq: PBLS), or $770.5M gross after the over-allotment. The prospectus disclosed the February 2026 desmoid data — tumor reductions in all 25 evaluable patients and a 74% (14/19) RECIST 1.1 ORR, in both GSI-naive and GSI-failed patients — and a registrational Phase 3 in desmoid tumors targeted for H1 2027. In June 2026 a New England Journal of Medicine letter reported a durable response in a patient with recurrent Wnt-mutant ameloblastoma, the first peer-reviewed zolucatetide publication. The scientific significance extends beyond desmoid. Zolucatetide is the first molecule ever to clinically validate direct β-catenin:TCF inhibition — a target the field considered undruggable since the interaction's structural characterization in the 1990s. If the Phase 3 confirms the early ORR signal and the molecule progresses to approval, it establishes the Helicon class as a viable platform for drugging the large class of intracellular protein-protein interactions historically out of reach for both small molecules and conventional biologics.

How It Works

In many cancers — including desmoid tumors, most colon cancers, and some liver, endometrial, and prostate cancers — a switch called the Wnt pathway is stuck on. The final step in that pathway is when β-catenin binds to a partner protein called TCF, which then turns on cancer-driving genes. Zolucatetide is a designed helical peptide that physically blocks β-catenin from binding TCF — interrupting the cancer-driving signal at its central point. It's the first drug to ever directly hit this target, which the field considered impossible to drug for thirty years.

The Wnt pathway is a fundamental cellular signaling cascade with central roles in development, tissue regeneration, and oncogenesis. In the canonical pathway, β-catenin is normally targeted for proteasomal degradation by a destruction complex (APC, Axin, GSK3β, CK1). Wnt ligand engagement of Frizzled/LRP5/6 receptors inhibits the destruction complex, allowing β-catenin to accumulate, translocate to the nucleus, and bind TCF/LEF family transcription factors at Wnt-responsive promoters — driving transcription of MYC, CCND1, AXIN2, LGR5, and other targets that promote proliferation and survival. Loss-of-function APC mutations (familial adenomatous polyposis and most sporadic colorectal cancers) and gain-of-function CTNNB1 mutations (T41A, S45F, S45P — common in desmoid tumors, hepatocellular carcinoma, endometrial cancer) all converge on stabilized nuclear β-catenin. The downstream β-catenin:TCF protein-protein interaction is therefore the central transcriptional node where Wnt-pathway dysregulation drives oncogenesis. The interface itself is ~4,800 Ų of flat, hydrophobic surface — incompatible with conventional small-molecule drug discovery, which has historically required deeper pockets to achieve nanomolar affinity and selectivity. Zolucatetide is a polymacrocyclic α-helical peptide (Helicon class) engineered to bind β-catenin at the TCF-binding face; its helix is braced by an all-hydrocarbon staple, a carbamate bridge, and a side-chain lactam. Research-chemical vendors list its potency as IC50 <50 nM; Parabilis has not published full binding data in a peer-reviewed paper. The mechanism is direct: by occupying the TCF interaction surface, zolucatetide displaces TCF from β-catenin and prevents formation of the transcriptionally active β-catenin:TCF complex, shutting down Wnt-pathway transcriptional output downstream of stabilized β-catenin — regardless of whether the upstream driver is APC loss or CTNNB1 activation. This positions zolucatetide as a mechanistically unified therapy across the diverse spectrum of Wnt-pathway-activated cancers, in contrast to upstream-pathway agents whose effects depend on the specific level of pathway dysregulation.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about Zolucatetide:

• 01Peer-reviewed trial publication — the only PubMed-indexed zolucatetide paper is a single-patient NEJM letter (ameloblastoma); desmoid efficacy and safety data come from conference abstracts, press releases, and IPO filings.
• 02Durability of response and median PFS — disclosed ORR data does not yet include time-to-event endpoints.
• 03Head-to-head comparison versus nirogacestat or varegacestat — no randomized comparison exists, and both γ-secretase inhibitors are oral while zolucatetide is IV.
• 04Detailed safety data — grade 3 laboratory abnormalities, infusion-related effects, and the exposure-adjusted adverse-event profile have not been reported in a peer-reviewed format.
• 05Performance in non-desmoid cohorts — CRC, HCC, prostate, and other Wnt-mutant tumor data have been disclosed only as isolated responses (one HCC partial response, CRC ctDNA reductions), not at the same maturity as desmoid.
• 06Combination signal — combination cohorts (mFOLFOX/bevacizumab, nivolumab, FTD/TPI/bevacizumab) are early; mature efficacy data pending.
• 07Long-term safety — Phase 1/2 exposure timelines have not been reported in detail; chronic dosing safety is the question Phase 3 must address.

Forms & Administration

Intravenous infusion on continuous 28-day cycles per NCT05919264 protocol. Investigational — not commercially available. The Phase 1/2 protocol includes a subcutaneous arm, but disclosed clinical activity is IV. Oncology specialty supervision required for any trial participation.

Dosing & Protocols

The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.

Zolucatetide is investigational and Phase 1/2 stage. Specialty oncology supervision is required for any clinical trial participation. The molecule is not legitimately available outside registered clinical trials.

Timeline of Effects

Common Questions

Who Zolucatetide Is NOT For

Drug & Supplement Interactions

No established drug interaction profile because zolucatetide is investigational. The Phase 1/2 includes combination cohorts with mFOLFOX-6 + bevacizumab (CRC), nivolumab (multi-tumor), and trifluridine/tipiracil + bevacizumab (CRC), indicating manageable combinability with major cytotoxic and immunotherapy regimens. Specific drug-drug interaction analyses will be characterized in published trial results.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions