INTRODUCTION

Hypertension affects more than 1.2 billion individuals globally and remains the most significant modifiable risk factor for cardiovascular morbidity and mortality [1]. It is directly associated with an increased incidence of ischemic heart disease, stroke, heart failure, and chronic kidney disease [2]. Despite the availability of various antihypertensive agents from multiple classes—including angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), calcium channel blockers, diuretics, and β-blockers—only about 20% to 25% of patients achieve optimal blood pressure control [3,4].

Multiple factors contribute to this persistent therapeutic gap. Nonadherence to daily oral medications, clinical inertia, drug side effects, and the complex pharmacokinetics of some agents remain significant challenges. In addition, the phenomenon of "renin-angiotensin-aldosterone system (RAAS) escape," in which the body compensates for pharmacological RAAS inhibition through alternative regulatory mechanisms, undermines long-term efficacy in some patients [5]. The RAAS plays a crucial role in regulating blood pressure. RAAS inhibitors, including ACE inhibitors and ARBs, are the most commonly prescribed agents due to their demonstrated benefits in preventing complications related to cardiorenal disease [6]. However, despite these existing medications, more than 10% of patients have resistant hypertension.

Therefore, novel drugs are being developed to target alternative components of the RAAS pathway, in pursuit of innovative antihypertensive therapies.

Zilebesiran, which has advanced to phase 2b trials, is an investigational agent that utilizes RNA interference technology to silence hepatic expression of angiotensinogen (AGT), the sole precursor of all angiotensin peptides in the RAAS cascade. Unlike conventional agents (e.g., ACE inhibitors or ARBs) that inhibit downstream effectors, zilebesiran targets the source of the cascade, offering a novel and comprehensive approach to RAAS suppression. It is capable of maintaining substantial reductions in blood pressure for up to 6 months following a single subcutaneous dose, representing a paradigm shift in hypertension therapy.

MECHANISM OF ACTION

Zilebesiran is a chemically modified small interfering RNA (siRNA) designed to selectively inhibit AGT synthesis in hepatocytes [7]. The siRNA is conjugated to a triantennary N-acetylgalactosamine (GalNAc) ligand, facilitating specific uptake by asialoglycoprotein receptors on liver cells. Once internalized, zilebesiran is incorporated into the RNA-induced silencing complex (RISC), a ribonucleoprotein assembly that guides the siRNA to its complementary target on AGT messenger RNA (mRNA).

Upon binding, RISC-mediated cleavage of the AGT mRNA results in its degradation, effectively halting protein translation. As AGT is exclusively synthesized in the liver and circulates systemically as the substrate for renin, its depletion profoundly suppresses the RAAS axis. This significantly reduces the production of angiotensin I (by renin) and angiotensin II (by ACE), leading to attenuated vasoconstriction, decreased aldosterone secretion, reduced sodium retention, and ultimately, lower blood pressure (Fig. 1).

Notably, zilebesiran’s GalNAc-mediated liver specificity minimizes off-target effects in extrahepatic tissues such as the kidneys, brain, and vasculature. In addition, the molecule’s chemical modifications improve its in vivo stability, resistance to nuclease degradation, and prolong its half-life, enabling sustained pharmacodynamic activity and administration as infrequently as biannually or quarterly. Notably, zilebesiran’s GalNAc-mediated liver specificity minimizes off-target effects in extrahepatic tissues such as the kidneys, brain, and vasculature. In addition, the molecule’s chemical modifications improve its in vivo stability, resistance to nuclease degradation, and prolong its half-life, enabling sustained pharmacodynamic activity and administration as infrequently as biannually or quarterly. The underlying mechanism is as follows [8]. Like other siRNA therapeutics, unmodified siRNAs are cleared from circulation within minutes. Zilebesiran’s chemical modifications moderately extend its plasma stability, but more importantly, GalNAc targeting rapidly delivers the siRNA from plasma into hepatocytes. This minimizes systemic exposure and concentrates the drug in the liver shortly after injection. Once in hepatocytes, a substantial fraction of internalized zilebesiran is sequestered in acidic endosomal and lysosomal compartments. Rather than being rapidly degraded, the siRNA remains stable within these vesicles. Over time, active siRNA molecules are gradually released into the cytosol, where they can be incorporated into RISC. In effect, the liver cell’s endosomes act as a sustained-release depot, continually providing siRNA to maintain RISC-mediated silencing for weeks to months after a single dose. This unique pharmacokinetic property underlies the “remarkable durability” of GalNAc-conjugated siRNAs in humans (observable for over 6 months post-dose). In addition, with continuous replenishment of RISC and the inherent stability of RISC–siRNA complexes, zilebesiran’s effective duration allows for quarterly or even semi-annual dosing.

PRECLINICAL EVIDENCE

Merck initially conducted a preclinical study in which lipid nanoparticle-encapsulated siRNA targeting the AGT gene was intravenously administered at a dose of 3 mg/kg into the tail veins of spontaneously hypertensive male rats [9]. Administration resulted in an immediate reduction in hepatic AGT mRNA expression and circulating AGT levels, with the effect lasting about 7 days. Blood pressure reached its lowest point on day 4 post-injection, with mean systolic blood pressure (SBP) decreased to 154±4 mmHg in the treatment group, compared to 188±2 mmHg in the control group. Liver and kidney function markers, including aspartate aminotransferase, alanine aminotransferase, and blood urea nitrogen, remained within normal ranges, indicating no signs of organ toxicity.

The drug now used in clinical trials is linked to the following preclinical research [10]. In a study by Alnylam Pharmaceuticals, the efficacy of GalNAc-conjugated siRNA targeting AGT was evaluated in spontaneously hypertensive rats, both as monotherapy and in combination with ACE inhibitor captopril and ARB valsartan. Reductions in mean arterial pressure were observed with each monotherapy: −23±2 mmHg with captopril, −10±2 mmHg with valsartan, and −14±2 mmHg with siRNA. Among combination therapies, valsartan+siRNA achieved the greatest mean arterial pressure reduction at −68±4 mmHg, followed by captopril+valsartan at −54±4 mmHg. After initial siRNA administration, plasma AGT levels were reduced by about 97%, and by 99% when combined with valsartan. While renin levels increased in all groups—as expected due to substrate depletion—angiotensin I levels remained low, except in the valsartan with siRNA group, where suppression was sustained. Additionally, rats treated with valsartan with siRNA showed improved cardiac hypertrophy, as evidenced by decreased N-terminal pro–B-type natriuretic peptide levels. Similar improvements were observed in the captopril with valsartan group. Across all treatment groups, kidney function remained stable, with no evidence of acute kidney injury, as indicated by a preserved glomerular filtration rate and stable albuminuria.

CLINICAL EVIDENCE

Phase 1 trial

Zilebesiran, a GalNAc-conjugated siRNA targeting hepatic AGT, was evaluated in a randomized, double-blind, placebo-controlled phase 1 clinical trial sponsored by Alnylam Pharmaceuticals [11]. The study enrolled 107 adult patients aged 18 to 65 years, each with a mean 24-hour SBP of 130 mmHg or higher. Key exclusion criteria included secondary hypertension, smoking, postural hypotension, diabetes, a history of cardiovascular events, and treatment with β-adrenergic blockers. The average participant age was 53.5 years, and 62% were male. The population was predominantly composed of White and Black participants, accounting for over 90% of those enrolled.

In part A, 84 participants were randomized to receive a single subcutaneous injection of zilebesiran (at doses of 10, 25, 50, 100, 200, 400, or 800 mg) or placebo to evaluate the blood pressure–lowering effects and AGT response across different doses. A dose-dependent reduction in both serum AGT (correlation coefficient, –0.56; 95% confidence interval [CI], –0.69 to –0.39) and SBP (correlation coefficient, –0.41; 95% CI, –0.58 to –0.21) was observed. Patients receiving 100 to 400 mg of zilebesiran showed a 90% reduction in AGT sustained for 12 weeks, and those receiving 800 mg maintained this level of suppression for 24 weeks. In addition, part B assessed the effect of zilebesiran in relation to dietary salt intake, while part E evaluated its efficacy when combined with an ARB. In part B, under low-salt conditions, the zilebesiran treatment group experienced greater reductions in blood pressure (SBP, –18.8±4.3 mmHg; diastolic blood pressure [DBP], –8.4±2.5 mmHg), confirming that zilebesiran’s antihypertensive effect was enhanced by sodium restriction. In part E, at week 6, the 10 participants who had received 800 mg of zilebesiran but still had persistent SBP ≥120 mmHg were subsequently treated with 300 mg of irbesartan daily for 2 weeks. This add-on therapy resulted in an additional average reduction in SBP of –6.3±3.1 mmHg and DBP of –3.0±1.9 mmHg. Across all parts of the study, zilebesiran was generally well tolerated. The most common adverse event was mild injection-site reaction. There were no occurrences of hypotension, hyperkalemia, or renal impairment requiring intervention. Zilebesiran in the phase 1 study demonstrated a favorable safety profile and a sustained, dose-dependent antihypertensive effect, supporting its potential for long-acting blood pressure control with quarterly or twice-yearly dosing. Safety and tolerability will be further discussed in the following section.

Phase 2 trials (KARDIA-1 and KARDIA-2)

Zilebesiran is currently under investigation in three phase 2 clinical trials, all employing a randomized, double-blind, placebo-controlled design; findings from two have been published, and one trial remains ongoing (Table 1) [11–14].

The KARDIA-1 trial (ClinicalTrials.gov identifier: NCT04936035) was a phase 2, randomized, double-blind, placebo-controlled study designed to evaluate the efficacy and safety of zilebesiran in patients with mild to moderate hypertension [12]. The trial enrolled 394 adults who had a daytime ambulatory SBP between 135 and 160 mmHg after washout of prior antihypertensive medications. Patients were randomized to receive zilebesiran at doses of 150, 300, or 600 mg every 6 months; or 300 mg every 3 months; or placebo every 3 months, with follow-up for 6 months.

The primary endpoint was the change from baseline to month 3 in 24-hour mean ambulatory SBP. Zilebesiran produced significant, dose-dependent reductions in SBP compared to placebo. The placebo-adjusted reduction in SBP at month 3 ranged from –14.1 mmHg (150 mg every 6 months) to –16.7 mmHg (300 mg every 3 or 6 months), and –15.7 mmHg (600 mg every 6 months), all with P<0.001. The antihypertensive effect was maintained through 6 months for all doses ≥300 mg. Reductions in blood pressure were consistent across the 24-hour cycle, including both daytime and nighttime periods.

Serum AGT levels were reduced by more than 90% at month 6 with zilebesiran doses of 300 mg or greater. These pharmacodynamic effects supported the observed durable blood pressure reductions.

In the KARDIA-1 study, zilebesiran demonstrated clinically meaningful, sustained reductions in blood pressure with the potential for quarterly or biannual dosing, offering a promising long-acting treatment option for hypertension that could improve adherence and reduce visit-to-visit blood pressure variability. The trial supports further development of zilebesiran in larger, longer-term studies.

KARDIA-2 was a multicenter, phase 2, randomized, double-blind, placebo-controlled clinical trial designed to assess the efficacy and safety of zilebesiran as an add-on therapy to standard-of-care antihypertensive treatment in patients with inadequately controlled hypertension [13]. Eligible participants included adults aged 18 to 75 years with either untreated hypertension (seated office SBP, 155 to 180 mmHg) or treated hypertension on one to two antihypertensive agents (office SBP, 145 to 180 mmHg). After a run-in phase with background therapy (indapamide, amlodipine, or olmesartan), patients with 24-hour mean ambulatory SBP of 130 to 160 mmHg and at least 80% adherence were randomized to receive a single subcutaneous injection of zilebesiran 600 mg or placebo. The primary endpoint was the change from baseline to month 3 in 24-hour mean ambulatory SBP. In total, 667 participants were randomized across the three background therapy cohorts. Zilebesiran treatment resulted in statistically significant and clinically meaningful reductions in 24-hour ambulatory SBP at 3 months compared to placebo in both the indapamide and amlodipine cohorts (least-squares mean difference, −11.0 −7.9 mmHg, respectively; both P<0.001). At 6 months, the proportion of patients achieving blood pressure control without the need for rescue therapy was higher in the zilebesiran arms, particularly in the indapamide and amlodipine groups. In contrast, the olmesartan cohort showed attenuated ambulatory SBP reduction, potentially due to a ceiling effect from the use of maximum-dose ARB therapy. Overall, the KARDIA-2 trial supports the potential of biannual subcutaneous zilebesiran administration as an effective adjunct to conventional antihypertensive therapy, especially in patients with mild to moderate hypertension not adequately controlled by monotherapy or dual therapy. These findings provide a rationale for further investigation in high-risk populations and those with resistant hypertension, as being pursued in the ongoing KARDIA-3 trial.

The KARDIA-3 trial (ClinicalTrials.gov identifier: NCT06272487) is a global, ongoing phase 2 clinical study designed to evaluate the efficacy and safety of zilebesiran as add-on therapy in patients with uncontrolled hypertension who are at high cardiovascular risk, with or without advanced chronic kidney disease [14]. Eligible patients include adults with a seated office SBP of 140 to 170 mmHg despite stable treatment with two to four standard-of-care antihypertensives. Participants must also have one or more of the following high-risk features: a history of major cardiovascular events, an estimated 10-year atherosclerotic cardiovascular disease risk score >15%, or reduced renal function defined as an estimated glomerular filtration rate (GFR) between 30 and <60 mL/min/1.73 m². The study population is divided into two cohorts: cohort A includes approximately 270 patients with estimated GFR ≥45 mL/min/1.73 m², while cohort B enrolls up to 120 patients with more advanced chronic kidney disease (estimated GFR, 30 to <45 mL/min/1.73 m²). During the 6-month double-blind treatment period, patients are randomized to receive a single subcutaneous dose of zilebesiran (150, 300, or 600 mg) or placebo, in addition to their background antihypertensive therapy. Antihypertensive intensification is permitted at the investigator’s discretion if clinically indicated.

Primary and secondary endpoints include changes from baseline in mean seated office SBP at month 3 (primary) and month 6 (secondary), as well as changes in 24-hour ambulatory blood pressure, DBP, serum AGT levels, and the proportion of patients reaching blood pressure targets without medication intensification. Safety is assessed through the incidence of adverse events during the treatment and follow-up periods.

SAFETY AND TOLERABILITY

Across all trials, zilebesiran was generally well tolerated with a favorable safety profile. The most commonly reported adverse events were mild to moderate injection-site reactions, such as erythema, tenderness, or swelling. These reactions were transient and resolved without intervention. Other observed adverse events included transient dizziness and mild orthostatic hypotension, neither of which required treatment discontinuation.

Importantly, no serious adverse events related to renal function, hepatic function, or electrolyte disturbances (e.g., hyperkalemia) were observed in phase 1 or 2 studies. Laboratory monitoring showed no clinically significant changes in serum creatinine, liver transaminases, or potassium levels. Infrequent administration (once every 3 to 6 months) may further reduce the risk of cumulative toxicity and support adherence in real-world settings.

Collectively, the safety data support zilebesiran’s potential as a long-acting, low-burden antihypertensive therapy with a tolerability profile that compares favorably to conventional oral agents.

CLINICAL IMPLICATIONS AND FUTURE DIRECTIONS

Zilebesiran introduces a paradigm shift in hypertension management. The primary goal of hypertension therapy is the effective reduction of blood pressure to mitigate the risk of cardiovascular morbidity and mortality. While lifestyle modifications remain foundational, consistent pharmacologic adherence is the essential first step to achieving target blood pressure. Zilebesiran offers a transformative approach to improving medication adherence by enabling infrequent dosing. In real-world clinical practice, many patients struggle with the daily pill burden due to demanding lifestyles or polypharmacy, which can compromise adherence and treatment efficacy. Zilebesiran, with its durable blood pressure–lowering effect following a single biannual subcutaneous injection, represents a promising alternative for these populations.

Another significant challenge in hypertension management is the treatment of resistant or uncontrolled hypertension. Despite multiple antihypertensive agents, a subset of patients fails to achieve adequate blood pressure control, underscoring the need for new therapeutic options. Recent developments in this area include the US Food and Drug Administration–approved endothelin receptor antagonist aprocitentan, nonsteroidal mineralocorticoid receptor antagonists such as finerenone, aldosterone synthase inhibitors like baxdrostat, and dual angiotensin receptor–neprilysin inhibitors—originally developed for heart failure, but now expanding their indications. In this context, zilebesiran may emerge as a strong candidate for adjunctive therapy in resistant or uncontrolled hypertension.

Finally, zilebesiran may also play a pivotal role in high-risk patient populations. Beyond blood pressure reduction, its potential to prevent target organ damage could contribute to broader cardiovascular risk reduction. The ongoing KARDIA-3 trial, enrolling patients with uncontrolled hypertension despite multiple therapies and elevated cardiovascular risk, is expected to provide further insights into the clinical utility of zilebesiran in this challenging population.

CONCLUSIONS

Zilebesiran represents a novel class of antihypertensive therapy that targets the root of the RAAS cascade through RNA interference. With promising early results showing sustained blood pressure reduction, minimal side effects, and infrequent dosing, it has the potential to address significant gaps in current hypertension treatment paradigms. Pending further data, zilebesiran may emerge as a cornerstone in the management of difficult-to-treat hypertension.

ARTICLE INFORMATION

Conflicts of interest

The author has no conflicts of interest to declare.

Funding

The author received no financial support for this study.

Fig. 1.

Mechanism and clinical implication of zilebesiran. AGT, angiotensinogen; BP, blood pressure; GalNAc, N-acetylgalactosamine; mRNA, messenger RNA; RAAS, renin-angiotensin-aldosterone system; RISC, RNA-induced silencing complex; SBP, systolic blood pressure; siRNA, small interfering RNA.

REFERENCES

• 1. Bromfield S, Muntner P. High blood pressure: the leading global burden of disease risk factor and the need for worldwide prevention programs. Curr Hypertens Rep 2013;15:134–6. ArticlePubMedPMCPDF
• 2. Global Burden of Metabolic Risk Factors for Chronic Diseases Collaboration. Cardiovascular disease, chronic kidney disease, and diabetes mortality burden of cardiometabolic risk factors from 1980 to 2010: a comparative risk assessment. Lancet Diabetes Endocrinol 2014;2:634–47. ArticlePubMedPMC
• 3. Olsen MH, Angell SY, Asma S, Boutouyrie P, Burger D, Chirinos JA, et al. A call to action and a lifecourse strategy to address the global burden of raised blood pressure on current and future generations: the Lancet Commission on hypertension. Lancet 2016;388:2665–712. ArticlePubMed
• 4. Chobanian AV. Shattuck lecture. The hypertension paradox: more uncontrolled disease despite improved therapy. N Engl J Med 2009;361:878–87. ArticlePubMed
• 5. Lakkis J, Lu WX, Weir MR. RAAS escape: a real clinical entity that may be important in the progression of cardiovascular and renal disease. Curr Hypertens Rep 2003;5:408–17. ArticlePubMedPDF
• 6. Turner JM, Kodali R. Should angiotensin-converting enzyme inhibitors ever be used for the management of hypertension? Curr Cardiol Rep 2020;22:95.ArticlePubMedPMCPDF
• 7. Morgan ES, Tami Y, Hu K, Brambatti M, Mullick AE, Geary RS, et al. Antisense inhibition of angiotensinogen with IONIS-AGT-L: results of phase 1 and phase 2 studies. JACC Basic Transl Sci 2021;6:485–96. ArticlePubMedPMC
• 8. Ye D, Cruz-López EO, Tu HC, Zlatev I, Danser AH. Targeting angiotensinogen with N-acetylgalactosamine-conjugated small interfering RNA to reduce blood pressure. Arterioscler Thromb Vasc Biol 2023;43:2256–64. ArticlePubMedPMC
• 9. Olearczyk J, Gao S, Eybye M, Yendluri S, Andrews L, Bartz S, et al. Targeting of hepatic angiotensinogen using chemically modified siRNAs results in significant and sustained blood pressure lowering in a rat model of hypertension. Hypertens Res 2014;37:405–12. ArticlePubMedPDF
• 10. Uijl E, Mirabito Colafella KM, Sun Y, Ren L, van Veghel R, Garrelds IM, et al. Strong and sustained antihypertensive effect of small interfering RNA targeting liver angiotensinogen. Hypertension 2019;73:1249–57. ArticlePubMed
• 11. Desai AS, Webb DJ, Taubel J, Casey S, Cheng Y, Robbie GJ, et al. Zilebesiran, an RNA interference therapeutic agent for hypertension. N Engl J Med 2023;389:228–38. ArticlePubMed
• 12. Bakris GL, Saxena M, Gupta A, Chalhoub F, Lee J, Stiglitz D, et al. RNA interference with zilebesiran for mild to moderate hypertension: the KARDIA-1 randomized clinical trial. JAMA 2024;331:740–9. ArticlePubMedPMC
• 13. Desai AS, Karns AD, Badariene J, Aswad A, Neutel JM, Kazi F, et al. Add-on treatment with zilebesiran for inadequately controlled hypertension: the KARDIA-2 randomized clinical trial. JAMA 2025;334:46–55. ArticlePubMed
• 14. Havasi A, Pagidipati N, Bakris GL, Weber M, Bengus M, Daga S, et al. KARDIA-3 study design: zilebesiran as add-on therapy in patients with high cardiovascular risk and hypertension inadequately controlled by standard of care antihypertensives. Presented at: European Society of Hypertension (ESH) 2024 Annual Meeting (33rd European Meeting on Hypertension and Cardiovascular Protection); May 31–Jun 3, 2024; Berlin, Germany. J Hypertens 2024;42(Suppl 1):e120. Article

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References

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