GSK Just Dropped $950 Million on a Drug That Hasn't Treated a Single Patient
GSK just wrote a $950 million check for a drug that's never been tested in a patient. The target: a potentially massive pulmonary hypertension market projected to hit $18 billion. The gamble hinges on whether one molecule can outperform Merck's blockbuster Winrevair.
Nearly a billion dollars. For a company most people have never heard of. For a drug that's only been tested in healthy volunteers.
That's the bet GSK just made on 35Pharma, a small biotech whose lead asset, HS235, has completed Phase 1 healthy volunteer trials and is now moving into patient trials. The price tag: $950 million in cold, hard, upfront cash. No milestones, no earn-outs, no "we'll pay you more if it works" safety nets. GSK is all in.
The question isn't whether $950 million is a lot of money (it is). The question is what GSK sees that justifies writing that check before a single sick person has taken the drug.
The answer? A market that could be worth $18 billion by 2032, and a molecule that might just be the best way to crack it.
The Lung Disease That's Quietly Becoming a Blockbuster Market
Pulmonary hypertension (PH) is high blood pressure in the lungs. It sounds manageable; it's not. The blood vessels in the lungs narrow and stiffen, forcing the heart to work harder until, eventually, it fails. For decades, treatments focused on dilating those blood vessels: think of it like widening a clogged pipe without actually cleaning out the gunk.
Then came a new approach: activin signaling inhibitors. Instead of just opening the pipes wider, these drugs target the biological signals that cause the vessels to thicken and scar in the first place. It's the difference between treating symptoms and treating the disease itself.
Merck proved this concept with Winrevair (sotatercept), which became the first disease-modifying therapy approved for pulmonary arterial hypertension (PAH, the most severe form of PH). The drug hit the market in 2024 and has been ramping fast, pulling in $280 million in a single quarter by early 2025. Analyst projections for peak annual sales have climbed as high as $6.1 billion. A Phase 3 trial called ZENITH showed it could reduce major complications, including death and lung transplant, by about 76%.
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The global PAH market sits at roughly $8 to $9.5 billion today. Multiple forecasters project it'll grow to $11.5 to $15 billion by 2032, with activin inhibitors expected to capture about half of that total value.
GSK looked at those numbers and decided it wanted a seat at the table.
What Makes HS235 Different (at Least on Paper)
If Merck already has the first activin inhibitor on the market, why would GSK pay nearly a billion dollars for another one? Because Winrevair has a problem, and it's the kind of problem that creates opportunity.
Winrevair is linked to bleeding risks and a complication called telangiectasia (abnormal blood vessel formations on the skin). For a drug prescribed to patients who often take blood thinners, that's a meaningful concern. A survey of over 100 cardiologists and pulmonologists found that many doctors use dose reductions or temporary pauses to manage these side effects.
HS235 was designed to avoid this. The drug is engineered to spare two proteins called BMP9 and BMP10, which are believed to be connected to the bleeding and vascular side effects seen with older activin-pathway drugs. Think of it as a more selective filter: it blocks the bad actors while leaving the helpful ones alone.
On top of that, early healthy-volunteer data showed some intriguing metabolic effects. HS235 appeared to reduce fat mass while preserving lean muscle and improve insulin sensitivity. That matters because obesity and insulin resistance are extremely common in PH patients, especially those with PH-HFpEF (pulmonary hypertension driven by a type of heart failure).
PH-HFpEF is a huge, underserved population with zero approved disease-modifying therapies. If HS235 works there, it opens an entirely separate market on top of PAH.
The Risk: GSK Paid Full Price for an Unproven Asset
Let's be clear about what GSK doesn't have yet. HS235 has completed Phase 1 testing in healthy volunteers. Two trials in patients are just getting started: one in PAH patients (NCT07143448) and one in PH-HFpEF patients (NCT07123779), both Phase 1b studies designed to test safety, dosing, and early signs of efficacy.
No clinical efficacy data in actual patients. No proof it works better, or even as well as, Winrevair. The preclinical models look promising (improved lung blood flow, better heart function in mice), but mice aren't people. The graveyard of drugs that looked great in mice is deep.
And yet GSK paid $950 million upfront with no contingent payments. Compare that to GSK's 2024 acquisition of IDRx, where the company paid $1 billion upfront plus up to $150 million in milestones for a drug that was further along in development. With 35Pharma, they're taking on more risk with less of a cushion.
So why the urgency?
A New CEO, a New Playbook
This deal lands as Luke Miels steps into the CEO role at GSK. And it's not happening in a vacuum. GSK recently acquired Rapt Therapeutics for $2.2 billion and snapped up IDRx, signaling an aggressive, deal-driven approach to filling pipeline gaps.
Management has explicitly said that respiratory and inflammation will be a core priority for business development in 2025 and beyond, right alongside oncology. The company's internal pipeline is heavy on asthma and COPD (depemokimab in Phase 3 for asthma, a new siRNA asset entering trials), but it had nothing in the pulmonary hypertension space. HS235 fills that hole.
The strategic logic is straightforward. If the PH market really does hit $18 billion by 2032, and if activin inhibitors grab roughly half of it, then even a modest market share for HS235 could return multiples on a $950 million investment. The math works, but only if the drug works.
The Competitive Chessboard
GSK isn't the only one eyeing this space. Merck's Winrevair has a massive head start, an expanding label, and rock-solid clinical data. Only about 10% of U.S. PAH patients are currently on the drug, meaning there's enormous room for Winrevair to grow before competitors even arrive.
Meanwhile, other activin-pathway attempts have stumbled. Keros Therapeutics had to halt all dosing of its PAH candidate and ultimately terminated its TROPOS trial due to pericardial effusion (fluid around the heart), which spooked some investors about the entire drug class.
HS235's pitch, a cleaner safety profile with metabolic benefits, is compelling. But it's still theoretical. The earliest we'd see meaningful patient data is probably 2027 or later, and a potential approval wouldn't come until the end of the decade.
The Bottom Line
GSK is placing a big, early bet that HS235 can become a best-in-class activin inhibitor for pulmonary hypertension, one that's safer than Winrevair and useful across a broader patient population. The market opportunity is real; the question is whether the science will cooperate.
At $950 million for a Phase 1 asset, there's no margin for error. If HS235 stumbles in Phase 2, this deal becomes an expensive lesson in paying too much, too early. But if it works? GSK will have bought its way into one of the fastest-growing markets in cardiopulmonary medicine for what might look like a bargain.
Sometimes the best poker hands are the ones you buy before anyone else sees the cards. Whether GSK just made a brilliant move or an expensive mistake won't be clear for years. But one thing is certain: the race for the next generation of pulmonary hypertension drugs just got a lot more interesting.
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