The biotech building peptides that go where small molecules can't - inside the cell, onto the flat protein surfaces driving cancer.
Above: CEO Mathai Mammen, the man steering a company that renamed itself to mean "beyond what's possible." No pressure.
It is May 2026, and a clinical-stage biotech most people have never heard of has just signed a collaboration with Regeneron worth up to $2.3 billion. One day later, it files to go public. The company is Parabilis Medicines. The thing it sells does not fit in a pill or an injection of antibodies. It sells a third option.
Parabilis lives at 30 Acorn Park Drive in Cambridge, Massachusetts, the kind of address where biotech either becomes a verb or quietly disappears. Roughly 170 people work here on a single, stubborn idea: that the protein targets everyone calls "undruggable" are only undruggable because the tools were wrong. Parabilis built a different tool. They call it the Helicon.
"Beyond what's possible" and "obtainable" - the company literally named itself after the gap it's trying to close.
On the meaning of "Parabilis," from Greek and Latin rootsIf you want to understand a company, watch where the smart money goes. RA Capital, Fidelity and Janus Henderson co-led a $305 million round in January. Regeneron then wrote a nine-figure check just for the privilege of building alongside them. That is not the behavior of investors hedging a bet. That is the behavior of people who have seen the data.
Here is the uncomfortable truth of modern medicine. Small molecules are tiny enough to slip inside cells, but they need a deep pocket to grab onto - and most disease-driving proteins are smooth, flat, and pocket-free. Antibodies can grab almost anything, but they are far too large to cross the cell membrane, so they are stuck patrolling the outside. Between "too small to be selective" and "too big to get in" lies the majority of biology.
The pie nobody wants to talk about. Roughly four out of five interesting targets sit in the orange. Parabilis decided that was the menu, not the wall.
The poster child for this frustration is beta-catenin, the protein at the heart of the Wnt signaling pathway. When it goes rogue, it drives colorectal cancer, desmoid tumors, liver cancer and a long tail of rarer tumors. For decades it sat there, biologically obvious and pharmacologically untouchable - the molecular equivalent of a celebrity who refuses interviews.
The target everyone wanted. The target nobody could hit. That contradiction is the entire reason this company exists.
On beta-catenin and the Wnt pathwayThe bet started in a Harvard lab. Gregory Verdine, a chemist with a taste for problems other people had given up on, published a landmark paper in 2000 on "stapling" peptides - locking floppy chains of amino acids into a rigid, drug-like helix using an all-hydrocarbon bridge. Peptides had always been dismissed as too unstable, too poorly absorbed, too floppy to be real medicines. Verdine's staple changed the physics.
In 2015 he turned the chemistry into a company. Its first name was, with admirable honesty, FogPharma - "Fog" being an acronym for "Friends of Greg," the well-heeled individuals who funded the seed round. The name had two problems: it couldn't be trademarked, and it kept getting confused with a company called Foghorn. In October 2024 the fog lifted and Parabilis Medicines appeared, complete with an AI- and physics-based discovery platform layered on top of Verdine's chemistry.
Today the company is run by Mathai Mammen, a physician-scientist whose name in pharma circles tends to make people sit up straight. The bet he inherited and is now scaling: that a 26-year-old staple, plus modern computation, can finally drug the undruggable.
Verdine invented the staple in 2000. It took a quarter-century to walk it into Phase 3-ready cancer trials. Patience, it turns out, is a platform.
On the long arc from bench to bedsideA Helicon is a stabilized, cell-penetrant alpha-helical peptide. In plain terms: it is small enough to get inside a cell, rigid enough to behave like a proper drug, and shaped to clamp onto the flat protein surfaces that defeat everything else. It takes the best trait of a small molecule (it gets in) and the best trait of an antibody (it can grab anything) and fuses them.
Crosses the cell membrane to reach intracellular targets - the address most drugs can't deliver to.
Binds smooth protein interfaces with no deep pocket, the ones small molecules slide right off.
Stapling adds stability, selectivity and drug-like properties peptides historically lacked.
Computation narrows a vast space of peptide candidates before a single one is synthesized.
The lead candidate is zolucatetide (formerly FOG-001), and it is a genuine first: the first direct inhibitor of the interaction between beta-catenin and the TCF family of transcription factors. That single mechanism reaches across a startling range of tumors - desmoid, colorectal, hepatocellular, and rare cancers like ameloblastoma and craniopharyngioma. One drug, many doors.
Zolucatetide doesn't dial the Wnt pathway down. It walks up to the exact handshake that drives the cancer and refuses to let go.
On the mechanism of the first direct beta-catenin/TCF inhibitorA platform is a promise. Data is the receipt. In a clinical trial of zolucatetide in desmoid tumors - aggressive, often disfiguring growths driven by the Wnt pathway - the early numbers are hard to look away from. Of the patients with sufficient follow-up, every single evaluable one showed a measurable tumor reduction. Among those with two post-baseline scans, nearly three in four had a confirmed objective response.
The chart that makes investors lean in. Approximate early figures from the ongoing FOG-001 desmoid study. Small numbers, but the direction is unmistakable.
Then came the validation that money can't fake. Regeneron - a company that does not hand out billions for science it doesn't believe in - signed on to build antibody-Helicon conjugates across multiple therapeutic areas: roughly $125 million upfront, up to about $2.2 billion in milestones, plus royalties. When one of the most discerning buyers in biotech licenses your toolkit, the "interesting idea" becomes an asset class.
You can argue with a press release. It's harder to argue with RA Capital, Fidelity, Janus Henderson and Regeneron all writing checks in the same six months.
On the proof that lives in the cap tableThe company has presented Helicon data at AACR-NCI-EORTC 2025 and reported craniopharyngioma results at SNO 2025. The platform is no longer a single drug riding a single mechanism. It is starting to look like a franchise.
Strip away the term sheets and the mission is plainly stated: create life-changing medicines for targets long considered out of reach. For patients with desmoid tumors, where surgery can be brutal and options thin, a peptide that shrinks the growth is not a slide in a deck. It is a different life. The Wnt pathway touches some of the most common and most stubborn cancers in oncology, which is exactly why nobody could afford to ignore it - and exactly why nobody had cracked it.
The targets aren't undruggable. They were just waiting for the right molecule to show up. Parabilis is betting it built that molecule.
The thesis, in one sentenceThere is an irony worth savoring here. The peptide - long dismissed as the awkward middle child of drug modalities, too big to be a small molecule, too small to be a biologic - turns out to be precisely the shape this problem needed. The thing nobody wanted is the thing that works.
Here is the wager beyond zolucatetide. If Helicons can drug one "undruggable" target, the same playbook should reach the others - the flat surfaces and intracellular drivers that account for most of disease biology. The Regeneron deal is the first sign that the world believes this is repeatable, not a one-off. Antibody-Helicon conjugates point toward a whole new modality, not just a new drug.
The skeptic's question is fair: early clinical data is early, IPO markets are fickle, and biology has humbled smarter companies. Parabilis has not won yet. But it has done the rare thing of turning a 26-year-old chemistry insight into a clinic-stage pipeline, a multibillion-dollar partner, and a believable shot at a category that medicine had quietly written off.
Return to that Cambridge office. A few years ago it was FogPharma, named after a circle of friends, chasing a target the textbooks called impossible. Today it is Parabilis Medicines, with a name that means "beyond what's possible," a drug shrinking tumors in real patients, and a buyer betting billions that the trick will repeat. The fog, as the headlines noted, has lifted. What's underneath is a company trying to make "undruggable" an outdated word.
"Undruggable" was always a confession dressed up as a fact. Parabilis is trying to retire the term.
The closing argumentLooking for video? Search "Parabilis Medicines" or "Mathai Mammen" on YouTube for interviews and platform explainers. (No official channel confirmed at publication.)