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 (modified peptide with multiple backbone cyclizations rather than the classic Verdine-style hydrocarbon-stapled architecture) engineered to enforce α-helicity, minimize solvent-exposed amide hydrogen-bond donors, and achieve cytosolic exposure adequate for binding intracellular targets. Disclosed chemistry: molecular formula C102H134N18O25S2, molecular weight 2,076.4 Da, CAS 3044032-95-0; the molecule was discovered via peptide phage display library screening. Zolucatetide is administered intravenously on a continuous 28-day cycle schedule. Phase 1/2 NCT05919264 is enrolling locally advanced or metastatic solid tumors with Wnt-pathway activating mutations across CRC, HCC, desmoid, prostate, and endometrial baskets, plus combination cohorts with mFOLFOX-6 + bevacizumab, nivolumab, and trifluridine/tipiracil + bevacizumab. Parabilis's May 19, 2026 S-1 disclosed the desmoid efficacy data driving the Phase 3 plan: tumor reductions in 100% of evaluable patients and 74% RECIST 1.1 objective response rate in patients with at least two post-baseline scans, with responses in both gamma-secretase-inhibitor (GSI)-naive and GSI-failed patients and independent of CTNNB1 versus APC mutation status. FDA Orphan Drug Designation was granted March 11, 2026 for desmoid tumors. Parabilis raised a $305M Series F in 2026 and inked a Regeneron partnership ahead of the May 19, 2026 IPO filing, targeting ~$100M in proceeds earmarked for the registrational Phase 3 desmoid program planned for H1 2027.

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. Zolucatetide is the first molecule to directly engage the β-catenin:TCF interaction itself, and the 74% ORR figure disclosed in Parabilis's May 2026 IPO S-1 represents roughly 1.8× nirogacestat's randomized-trial response rate. Honest caveats are substantial. The 74% comes from an open-label Phase 1/2 with small evaluable n (19 reported as of February 2026), is not a randomized head-to-head against nirogacestat, includes both GSI-naive and GSI-failed patients (a mixed population), and predates peer-reviewed publication. No FOG-001 paper exists in PubMed; conference disclosures (AACR-NCI-EORTC October 2025 abstract B031, JPMorgan January 2025, ESMO 2025, S-1 May 2026) are the primary data sources. 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, founded by Gregory Verdine — a Harvard chemical biologist who pioneered stabilized α-helical peptide chemistry as a strategy for drugging intracellular protein-protein interactions over the prior two decades. The lineage runs from Verdine's hydrocarbon-stapled SAH-BCL9 peptide that disrupted the BCL9/β-catenin interaction (Sci Transl Med 2012, PMID 22914623), through Fog Pharmaceuticals' evolution of the Helicon platform — polymacrocyclic α-helical peptides with multiple backbone cyclizations engineered for cytosolic accumulation — to FOG-001 itself, identified via peptide phage display library screening against β-catenin and the TCF-binding interface. The Phase 1/2 trial NCT05919264 opened in May 2023 across solid tumors with Wnt-pathway-activating mutations, with expansion baskets in colorectal cancer, hepatocellular carcinoma, desmoid tumors, endometrial cancer, and prostate cancer, 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 progressed through AACR-NCI-EORTC October 2025 (abstract B031), ESMO 2025, JPMorgan January 2025, and ESMO Sarcoma 2026, building the clinical story. Fog Pharmaceuticals rebranded as Parabilis Medicines and announced an oversubscribed $305M Series F financing in early 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. Parabilis filed its IPO S-1 on May 19, 2026, targeting approximately $100M in proceeds; the S-1 disclosed the 74% RECIST 1.1 ORR figure in evaluable desmoid patients with at least two post-baseline scans, tumor reductions in 100% of evaluable patients, and clinical activity in both GSI-naive and GSI-failed populations. The S-1 also disclosed a Regeneron partnership and outlined plans for a registrational Phase 3 in desmoid tumors targeted for H1 2027. 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. Vendor-reported binding affinity is IC50 <50 nM. 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 publication — no PubMed-indexed primary paper on FOG-001 exists; conference abstracts and S-1 disclosures are the only data sources.
• 02Durability of response and median PFS — disclosed ORR data does not yet include time-to-event endpoints.
• 03Head-to-head comparison versus nirogacestat — no randomized comparison exists.
• 04Performance in non-desmoid baskets — CRC, HCC, endometrial, and prostate efficacy data have not been disclosed at the same maturity as desmoid.
• 05Combination signal — combination cohorts (mFOLFOX/bevacizumab, nivolumab, FTD/TPI/bevacizumab) are early; mature efficacy data pending.
• 06Long-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