The Hypertension Drug That Worked Too Well (on One Dose)
Kardigan's hypertension drug crushed its biomarker target but completely missed on blood pressure. The twist? A single dose worked so well it accidentally ruined the trial's control group, leaving everyone scratching their heads about what happens next.
Imagine you're testing whether five cups of coffee keep you awake longer than one. You give everybody one cup first, then split the group: half get four more cups, half get nothing. At the end, everyone's equally wired. Did five cups fail? Or did that first cup just hit way harder than anyone expected?
That's basically what just happened to Kardigan's hypertension drug.
The Trial That Outsmarted Itself
Kardigan, a privately held biotech backed by over $550 million in funding from the likes of Fidelity, T. Rowe Price, ARCH Venture Partners, and Sequoia Heritage, presented Phase 2 results for tonlamarsen at the American College of Cardiology meeting (ACC.26) on March 28. Tonlamarsen is an antisense oligonucleotide, a type of genetic medicine designed to dial down production of angiotensinogen (AGT), a protein that sits near the top of the hormonal cascade controlling blood pressure.
Think of AGT as the first domino in a long chain. Knock it down, and a whole series of blood-pressure-raising signals follow. Tonlamarsen's job is to stop that domino from ever falling.
The KARDINAL trial enrolled 485 patients with stubborn, uncontrolled hypertension, of whom 198 were ultimately randomized after run-in periods. These weren't people skipping their meds; 80% or more were already on ACE inhibitors or ARBs, the standard blood pressure drugs. Their systolic readings still sat between 135 and 170 mmHg despite taking two to five medications. In other words, the hardest cases.
The design seemed straightforward: everyone got a single 90 mg dose of tonlamarsen during a run-in period. Then patients were randomized. Half received five additional monthly doses. The other half got placebo injections for the remaining 16 weeks. Two co-primary endpoints would tell the story: AGT levels and office systolic blood pressure at Week 20.
One Endpoint Crushed. One Completely Whiffed.
On the biomarker side, tonlamarsen was a star. Patients who received all five doses saw their AGT levels plummet by 67%. The single-dose group? Only a 23% drop. That 44-percentage-point gap was statistically bulletproof (p<0.0001).
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But here's where things got weird. When researchers measured the thing that actually matters to patients, blood pressure, both groups improved by the exact same amount: 6.7 mmHg. The between-group difference was not statistically significant, which is about as close to "no difference" as you can get. For context, a p-value of 0.05 is typically the bar for significance. This result didn't just miss the bar; it tripped in the parking lot.
So what happened? That single run-in dose apparently packed a much bigger and longer-lasting punch than anyone predicted. Luke Laffin, MD, the lead author from the Cleveland Clinic, said he was "surprised" by tonlamarsen's prolonged effects, noting the blood pressure drop after just one dose persisted well beyond what the drug's known biology would suggest.
When Your Control Group Refuses to Cooperate
This is one of the trickiest problems in clinical trials. Your comparison group is supposed to be your baseline, your "normal." But when everyone in the study gets an active drug first (even just one dose), you no longer have a clean placebo arm. You've got two treatment groups, one that got a little drug and one that got a lot.
It's like testing whether watering a plant daily is better than watering it once, but that single watering was a monsoon. By the end of the experiment, both plants look great, and your data says frequency doesn't matter. The real lesson might be that the drug is more potent than expected, not that it doesn't work.
Daniel W. Jones, MD, a past president of the American Heart Association and hypertension guidelines chair, noted that tonlamarsen effectively lowered AGT but that repeat dosing didn't add further blood pressure benefit. That's the polite way of saying the trial design accidentally sabotaged its own readout.
The Silver Lining for the Sickest Patients
Bury the lede and you'll find the most interesting nugget in the subgroup data. Patients with the highest blood pressure at baseline (above 150 mmHg) who received five doses saw a 8.9 mmHg drop at Week 20. The five-dose group also showed fewer dangerous blood pressure surges above 150 mmHg when measured at home.
This matters because these are the patients who need help the most, and they seemed to benefit the most from sustained treatment. It's a signal, not proof, but it's exactly the kind of signal that keeps a program alive.
Why Biomarkers and Blood Pressure Don't Always Agree
Cardiovascular drug development has a long, painful history of biomarkers telling one story while clinical outcomes tell another. The classic cautionary tale: Pfizer's torcetrapib crushed it on cholesterol biomarkers but actually increased heart attacks through off-target effects. The Normal Hematocrit trial hit its biomarker target beautifully while raising death and heart attack rates by 28%.
Tonlamarsen's situation isn't nearly that alarming. Nobody got worse. Both groups saw meaningful blood pressure reductions. The problem is more subtle: the trial simply couldn't demonstrate that more drug produces more benefit, because the single-dose arm responded so strongly.
The FDA has historically been skeptical of biomarker wins that don't come with clear clinical improvement. Blood pressure is itself a validated surrogate endpoint for cardiovascular events, particularly stroke. But when your drug hammers the biomarker upstream (AGT) without showing additional blood pressure improvement downstream, regulators are going to have questions.
Kardigan's Next Move: A Smarter Bet?
Rather than redesigning the same trial and hoping for a different result, Kardigan is pivoting to a potentially sharper use case: acute severe hypertension (ASH), the kind of dangerously high blood pressure that lands people in the hospital.
Jay Edelberg, MD, PhD, Kardigan's chief medical officer, confirmed plans for a Phase 2b trial called KARDINAL-ASH. The logic makes sense. If a single dose of tonlamarsen can durably lower blood pressure by nearly 7 mmHg in patients already on multiple medications, imagine what it could do in an acute crisis where rapid, reliable pressure reduction is life-or-death.
This is a classic biotech pivot: when your data surprises you, don't fight it. Lean into what the data actually showed.
The Bigger Picture
Kardigan isn't a one-trick pony. The company is running late-stage programs for danicamtiv (a cardiac myosin activator for genetic dilated cardiomyopathy) and ataciguat (an oral therapy for calcific aortic valve stenosis), both of which posted positive Phase 2 data in 2025. The $254 million Series B raised last October was designed to fund data readouts across all three programs in 2026.
For tonlamarsen specifically, the KARDINAL results are neither a triumph nor a death sentence. The drug clearly does something powerful to the biology of hypertension. It lowered AGT dramatically, and every patient who received it saw their blood pressure improve. The question is whether Kardigan can design a trial that captures that benefit cleanly, without the comparison group muddying the waters.
Sometimes in drug development, the most frustrating outcome isn't failure. It's a result so ambiguous that nobody knows what to do with it. Kardigan thinks it knows: go where the need is most urgent, and let the drug's surprising potency become a feature, not a bug.
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