On a morning that cardiologists will long remember for the wrong reasons, a small Alameda, California, biotech stepped to the podium at the AHA Scientific Sessions 2026 to argue that the future of cholesterol and lipoprotein(a) control looks nothing like its past.

Scribe Therapeutics Inc. (Nasdaq: SCTX), the clinical-stage company co-founded by Nobel laureate Jennifer Doudna, presented two datasets Saturday that together sketch an ambitious vision: a single injection, given once, that keeps the heart’s two most stubborn lipid threats suppressed for years — through epigenetics and gene editing — without permanently altering a single letter of DNA.

The timing is striking. Just hours earlier, in the same convention center, Novartis, the Swiss drugmaker, disclosed that investigational drug pelacarsen — the most closely watched drug ever designed to lower lipoprotein(a), and licensed by Novartis from antisense pioneer Ionis Pharmaceuticals in a deal potentially worth $825 million — had reduced Lp(a) levels by approximately 78 percent but produced no statistically significant reduction in heart attacks, strokes, cardiovascular deaths, or emergency revascularizations in the Phase 3 Lp(a)HORIZON outcomes trial of 8,323 patients. The result, described by researchers as “stunning,” has redrawn the competitive map for every approach still pursuing Lp(a) as a target — including Scribe’s.

A Single Injection Held Cholesterol Down for Two Years

The headline number from Scribe’s late-breaking abstract is striking by any cardiovascular medicine standard: a single dose of investigational therapy STX-1150 provided persistent LDL cholesterol (LDL-C) control for at least two years in non-human primates — with the effect still ongoing at the time of reporting.

STX-1150 is not a statin, not a monoclonal antibody like PCSK9 antibody evolocumab, and not a small interfering RNA like inclisiran. It is an epigenetic gene silencer — a therapy that uses Scribe’s proprietary Epigenetic Long-Term X-Repressor (ELXR) platform to switch off the PCSK9 gene in liver cells without cutting or rewriting the genetic code underneath. The company describes the approach as a middle path: more durable than RNA-silencing drugs that need periodic re-dosing, but less permanent — and potentially reversible — compared to outright gene editing.

CEO Benjamin Oakes, who delivered Saturday’s 10:45 a.m. CT presentation, has described the ambition as replicating in a vial what nature already proved works: people born with PCSK9 loss-of-function variants experience up to 88 percent lower coronary risk over a lifetime, with no apparent ill effects. What ELXR aims to do is engineer that state pharmacologically — without the permanence of DNA alteration — using a programmable epigenetic machinery delivered by the same lipid nanoparticle technology that carried COVID-19 mRNA vaccines into cells.

Earlier Scribe data, reported at the European Atherosclerosis Society Congress in May 2026, showed greater than 22 months’ durability in non-human primates at doses below 1.0 mg/kg. Saturday’s late-breaking data extends that window to at least 24 months — a milestone that meaningfully strengthens the case for annual or potentially even lifetime single-dose therapy in patients. STX-1150 is currently being evaluated in a first-in-human Phase 1 trial in Australia under principal investigator Prof. Stephen Nicholls of the Victorian Heart Institute.

How ELXR Works: A Two-Lock Epigenetic Safety System

The mechanism deserves careful unpacking, because it is what makes ELXR distinct from first-generation epigenetic editing attempts — and what gives Scribe’s scientific founders confidence that the approach is both durable and specific.

STX-1150 is delivered via lipid nanoparticles (LNPs) — the same general vehicle platform used in COVID mRNA vaccines — that carry two payloads to liver cells: a messenger RNA encoding the ELXR protein, and a single guide RNA programmed to find the PCSK9 gene. Once inside hepatocytes, ELXR homes in on the target and installs what the company calls “epigenetic marks” — molecular modifications that sit on top of the DNA and effectively switch the gene off, without altering the underlying genetic sequence.

Epigenetic silencing through DNA methylation is not new. What distinguishes ELXR is a built-in proofreading system that determines where the silencing machinery can act.

The key component is DNA methyltransferase DNMT3A — a DNA methylation enzyme — fused to Scribe’s engineered CRISPR enzyme CasX. DNMT3A carries a regulatory domain called the ADD domain (ATRX-DNMT3-DNMT3L domain) that reads the chromatin environment before acting. When an activating histone mark called H3K4me3 is present at a genomic site, the ADD domain allosterically blocks DNMT3A’s catalytic activity — the enzyme physically cannot methylate DNA there. Only when that activating mark has been removed and replaced with repressive marks (which ELXR’s histone effector components do first, in a mandatory earlier step) does the ADD domain release its inhibition and allow DNA methylation to occur.

This creates a sequential, two-step lock: histone rewriting must complete before DNA methylation can begin. At off-target genomic sites — even if the guide RNA briefly binds — the activating histone mark typically remains present, keeping the ADD domain in its blocking conformation. The DNA methylation machinery cannot fire. Only the intended PCSK9 promoter, where ELXR’s guide RNA holds the complex long enough for complete histone rewriting, receives permanent silencing.

In earlier NHP data, ELXR achieved greater than 90 percent PCSK9 protein silencing and LDL-C reductions exceeding 50 percent at a dose of 0.75 mg/kg, sustained now for over two years. No liver toxicity signals were detected. The company has also confirmed no detectable off-target epigenetic effects in NHP studies at relevant doses.

The Second Presentation: Editing the LPA Gene

Thirty minutes after Oakes concluded his STX-1150 presentation, Dr. Elena Smekalova, Scribe’s Associate Director of Discovery Biology, took the stage at 11:06 a.m. CT in a parallel precision cardiovascular genetics session to present LPA gene editor STX-1200 — a different approach to a different target, using an entirely different mechanism.

Where STX-1150 silences epigenetically, STX-1200 edits. This program uses Scribe’s X-Editor (XE) platform — the same CasX enzyme at the company’s core, but configured here to cut and permanently inactivate the LPA gene in the liver. The goal is to knock out the gene responsible for producing apolipoprotein(a), the structural protein that gives lipoprotein(a), or Lp(a), its uniquely dangerous cardiovascular properties.

Lp(a) is almost entirely genetically determined. Approximately one in five people worldwide carries Lp(a) levels elevated enough to independently increase their cardiovascular risk, and lifestyle changes and standard cholesterol drugs barely move the needle. That makes the LPA gene an attractive target for a one-time edit — in theory.

The abstract presented Saturday — “A Single Administration of STX-1200 CRISPR-CasX Gene Editor Achieves Robust and Durable Reduction of Lipoprotein(a) Across Preclinical Models” — reports that a single dose of an STX-1200 prototype achieved robust and durable Lp(a) reduction across multiple preclinical model systems. Earlier disclosed data showed greater than 90 percent editing of the LPA gene in primary human hepatocytes and greater than 90 percent reduction in secreted Lp(a). Crucially, the company also confirmed no detectable off-target editing — including at the PLG (plasminogen) gene, which shares close sequence similarity with LPA and represents the most important specificity risk for any LPA-targeting editor — even at ten times the effective dose.

The California Institute for Regenerative Medicine (CIRM) awarded approximately $12.7 million specifically to STX-1200 — part of more than $25.7 million in total CIRM grants for Scribe’s pipeline that also include $13 million for the companion triglyceride program STX-1400 — as part of a broader effort to accelerate both programs toward human trials.

CasX: The Engine Under Both Platforms

Both STX-1150 and STX-1200 are built on CRISPR enzyme CasX, first identified in groundwater bacteria through environmental metagenomic sequencing by the laboratories of Prof. Jillian Banfield and Jennifer Doudna at UC Berkeley — published in Liu et al. 2019 in Nature. CasX evolved entirely independently of the more familiar Cas9 protein, and the differences matter therapeutically.

CasX is smaller than SpCas9 (roughly 980 versus 1,368 amino acids), which matters for packaging into LNP delivery vehicles for large-scale liver dosing. More importantly for patient eligibility: CasX does not originate from the bacteria that commonly infect humans. SpCas9 derives from Streptococcus pyogenes — a frequent human pathogen to which a significant proportion of adults carry pre-existing neutralizing antibodies from prior exposure. Those antibodies can blunt Cas9’s therapeutic effectiveness, potentially excluding some patients from Cas9-based treatments. CasX, sourced from bacteria that do not infect people, does not carry that immune-recognition risk.

Scribe’s engineering approach — which the company calls “CRISPR by Design” — has further optimized CasX far beyond its natural form. The company’s DeepXE AI platform now assists in predicting guide RNA efficiency and protein engineering outcomes across the two therapeutic modalities (epigenetic silencing and gene editing), allowing the team to design rather than simply discover.

Beyond the cardiovascular programs, Scribe has formed strategic research collaborations with pharmaceutical partner Sanofi and Eli Lilly and Company — a signal that larger pharmaceutical companies see meaningful potential in the platform. No licensing terms have been publicly disclosed, and neither partnership has announced a development commitment for a specific program.

What Pelacarsen’s Failure Means for the Gene-Editing Field

Scribe’s Lp(a) presentations land in a room where the air is thick with questions about whether lowering Lp(a) biochemically is sufficient to deliver cardiovascular outcomes benefit.

Pelacarsen — Novartis’s antisense oligonucleotide licensed from Ionis — reduced Lp(a) dramatically in Phase 2 and was widely expected to become the first approved Lp(a)-lowering therapy. Its failure in HORIZON was not a signal failure: the drug did what it was designed to do biochemically. The question the HORIZON data raises is whether the magnitude and duration of Lp(a) reduction achieved with antisense therapy is enough to move cardiovascular outcomes in patients who may already have established disease.

For LPA gene editor STX-1200, the HORIZON data cut both ways. On one hand, they remove the assumption that any Lp(a)-lowering drug will automatically produce cardiovascular benefit. The bar for future Lp(a) programs has moved outward. On the other, gene-editing programs capable of reducing Lp(a) by more than 90 percent — permanently abolishing LPA gene expression — may operate in a range the antisense approach never reached. When Novartis releases full HORIZON subgroup and pharmacodynamic analyses, the field will be watching to understand whether depth of Lp(a) reduction is what determines cardiovascular benefit, or whether something more fundamental about the biology is at play.

The Mendelian randomization data establishing Lp(a) as causal for ASCVD remain robust. Mendelian randomization epidemiological studies drawing on natural LOF LPA variants consistently show that people born with lower Lp(a) have meaningfully lower cardiovascular event rates. HORIZON does not overturn those findings. It raises questions about which Lp(a)-lowering strategy can translate genetic causality into therapeutic reality — and whether the gene-editing approach’s greater depth of reduction is the key difference.

STX-1200 is still a preclinical program. It has not entered human trials. Any path to cardiovascular outcomes data remains years away. But Saturday’s AHA presentation puts Scribe in the Lp(a) conversation at the precise moment the field is reckoning most urgently with what it needs to prove.

What to Watch Next

For STX-1150 (PCSK9 epigenetic silencing): The immediate focus is the Phase 1 trial now enrolling adults with elevated LDL-C and elevated cardiovascular risk at the Victorian Heart Institute in Melbourne, Australia. The first question the trial must answer is human safety — particularly any signs of off-target epigenetic effects or immune responses to the LNP delivery vehicle. The first LDL biomarker data in humans is expected in the first half of 2027. If the two-year NHP durability story holds in patients even at a fraction of its primate effect size, STX-1150 would become one of the most significant cardiovascular drug candidates in development.

For STX-1200 (LPA gene editing): Scribe’s next milestone is completing IND-enabling preclinical work to request regulatory clearance for a human study. The CIRM funding is intended to accelerate that timeline. The HORIZON data, by raising rather than answering the depth-of-reduction question, may actually make a head-to-head comparison between antisense and gene-editing approaches more compelling to regulators and funders.

For STX-1400 (APOC3, triglycerides): A third cardiovascular program using the same CasX platform targets the APOC3 gene to lower triglycerides — the third major lipid driver of atherosclerotic cardiovascular disease. Preclinical stage; no human data yet.

The larger picture: Scribe’s Scribe July 2026 IPO, which raised approximately $148 million gross after underwriters exercised their full overallotment option, provides funding runway for the Phase 1 trial and the STX-1200 IND push. The company’s ambition is a lipid-lowering platform where a single clinic visit — a single injection — could address LDL, Lp(a), and triglycerides permanently or near-permanently, using a single CasX-based delivery architecture. That vision remains years from clinical validation. But on a day when one era’s most watched Lp(a) drug collapsed in a Phase 3 trial, two presentations from a Berkeley spinout in the late-breaking and basic science sessions of the AHA’s flagship conference offered the clearest glimpse yet of what the next era might look like.