Silencing liver angiotensinogen synthesis as a novel approach to hypertension management: promises and challenges

Comment on the article ‘Zilebesiran, an RNA Interference Therapeutic Agent for Hypertension’ published in the New England Journal of Medicine; https://doi.org/10.1056/NEJMoa2208391. In this industry-funded, phase 1, placebo-controlled study, the tolerability (primary endpoint), pharmacokinetic (PK), and pharmacodynamic (PD) features of zilebesiran were tested in patients with mild-to-moderate hypertension.1 Zilebesiran is a first-in-class, small interfering RNA (siRNA) that prevents the hepatic synthesis of angiotensinogen (AGT), a key precursor of angiotensin peptides, that play a pathogenetic role in hypertension. The siRNA is covalently linked to an N-acetylgalactosamine (GalNAc) ligand that binds with high affinity to the hepatic asialoglycoprotein receptor, limiting off-target effects in other tissues, especially in the kidney. Conducted at four sites in the UK, this study included 107 patients [mean age, 53.5 years (range 35–65), 62% men, 25% Black; mean ± standard deviation 24-h systolic blood pressure (BP), 140 ± 9 mmHg] who participated in three of five study parts. In Part A, patients (12 per cohort) were randomly assigned in a 2:1 ratio to receive a single increasing subcutaneous dose of zilebesiran (10, 25, 50, 100, 200, 400, or 800 mg) or placebo. Add-on antihypertensive therapy was permitted at investigator discretion at 8 weeks for uncontrolled hypertension. In Part B, after sequential administration of a low-salt diet (0.23 g per day) and a high-salt diet (5.75 g per day) from days −21 through −8, patients were randomly assigned in a 2:1 ratio to a single dose of 800 mg zilebesiran (n = 8) or placebo (n = 4) and rechallenged with the same dietary protocol from days 43 through 56 (the expected peak effect of zilebesiran). In Part E, all patients received zilebesiran 800 mg. Patients with a systolic BP > 120 mm Hg at week 6 received additional treatment with 300 mg irbesartan once-daily for 2 weeks. After the conclusion of the treatment period at week 12, all zilebesiran-treated patients entered an extended safety follow-up period. Adverse events (AEs) were reported during the treatment period (12 weeks) in 58 patients receiving zilebesiran (72%) and 28 receiving placebo (88%). Zilebesiran was well tolerated. The most frequent treatment-related AEs were mild-to-moderate reactions at the site of the injection (6% of patients who received zilebesiran) with no serious treatment-related AEs, hypotension, or significant changes in kidney or liver function. Secondary and exploratory endpoints included PK characteristics, change from baseline in serum AGT, and change from baseline in BP as measured by 24-h ambulatory BP monitoring. The drug PK profile was suggestive of dose-proportionality and a relatively short half-life. In Part A, zilebesiran was associated with dose-dependent reductions in serum AGT that were negatively correlated with the zilebesiran dose [at week 8, r = −0.56; 95% confidence interval (CI), −0.69 to −0.39] and sustained for up to 6 months. The peak reduction in circulating AGT occurred after approximately 3 weeks. No additional effect of irbesartan on AGT levels was observed in Part E. Consistent and prolonged PD effects of zilebesiran offer the potential for sustained reductions in BP. In Part A, single doses of zilebesiran (≥200 mg) resulted in reductions in 24-hour ambulatory systolic (>10 mm Hg) and diastolic (>5 mm Hg) BP by week 8, which were consistent throughout the diurnal cycle and sustained for up to 6 months. At the 800 mg dose, zilebesiran treatment resulted in mean (± standard error) systolic and diastolic BP reductions of 22.5 ± 5.1 mmHg and 10.8 ± 2.7 mmHg at 6 months. In Parts B and E of the study, zilebesiran-associated BP changes were attenuated on high-salt intake and were augmented by irbesartan co-administration. Hypertension is associated with an increased burden in mortality, and healthcare and socioeconomic costs worldwide.2,3 Despite the availability of effective antihypertensive treatments, nearly half of patients with hypertension fail to achieve blood pressure (BP) goals recommended by guidelines.3,4 Contributing factors include the frequent need to adopt complex therapeutic schemes, poor adherence to lifestyle changes and drug therapy, and resistance to one or more antihypertensive drugs. For these reasons as well as for the persisting excess of cardiovascular diseases associated with hypertension, the search for new effective pharmacological strategies was recently boosted by the availability of novel technologies. The study by Desai et al.1 has explored the tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) of a small interfering RNA (siRNA) agent that inhibits the hepatic synthesis of angiotensinogen (AGT), the precursor of the renin-angiotensin (RAS) cascade. Upstream inhibition of RAS represents an attractive and rational therapeutic target because it may prevent the renin rise, which follows downstream blockade with angiotensin converting enzyme-inhibitors or angiotensin receptor blockers.5 AGT suppression in the liver by siRNA may offer specific and persistent inhibition of RAS and sustained BP-lowering effect. This therapeutic strategy may override the issue of non-adherence, because the compound may be administered as a single subcutaneous injection every few months. With regard to the upstream blockade of RAS, an approach based on aliskiren, a once-daily, orally effective, direct renin inhibitor was introduced a few years ago. The drug provided consistent reductions of angiotensin production, by inhibiting the rate-limiting enzyme renin, as well as of BP.6 However, clinical studies did not support the use of aliskiren as first-line treatment in hypertensive patients as it did not reduce mortality and major cardiovascular outcomes, and it was harmful in combination with other RAS blockers in diabetic patients.7 The primary objective of this phase 1 study was to assess the tolerability of zilebesiran.1 While all doses of the investigational drug only produced mild-to-moderate injection site reactions as the most frequent treatment-related AEs, the authors acknowledged the limitations represented by the small sample size and the short follow-up for a reliable safety assessment. Consistent with the design of a phase 1 study, single drug administrations were performed, and the findings in terms of adverse reactions and effect size on BP cannot predict the effects of multiple administrations. Moreover, findings cannot be generalized, as exclusion criteria included secondary hypertension, postural hypotension, diabetes, previous cardiovascular events, and current or anticipated treatment with beta-blockers. As additional limiting aspects of the present study, power calculations were not used to determine sample size, and data were analysed primarily by means of descriptive statistics. No formal statistical hypothesis testing was performed. Finally, the sponsor contribution in conceiving, designing, and interpreting the study is perhaps over-represented.1 Although zilebesiran overcomes many key PK and PD challenges for the use of siRNA therapy (i.e. poor tissue penetration, nuclease inactivation, rapid renal elimination, immune activation, and off-target effects) by means of innovative chemical modifications and GalNAc-conjugated delivery, several other issues remain. An important potential safety concern in the wider therapeutic use of zilebesiran is its long-acting RAS-inhibiting and BP-lowering effect in hypovolemic and hypotensive circumstances. In this regard, a platform called REVERSIR has been developed for providing rapid and potent reversal of siRNA-mediated gene silencing.8 Furthermore, hypotension produced by zilebesiran could be partially reversed by increasing salt intake, as shown in the present report, in addition to standard interventions, including volume and pressure support. With regard to the downstream adjustments of the RAS components following liver-targeted AGT silencing, it would have been of key interest to test the dose-related effects and the time trends of plasma levels of renin, angiotensin, and aldosterone also in relation to manipulation of sodium intake. Within the limitations of assessing an exploratory endpoint, the promise of a liver-targeted AGT RNA silencer as a solution for the long-term BP control does not seem to be supported by the moderate BP reductions observed in the present study, which may predict the need for an association with other antihypertensive therapies for optimal BP control.1 It should be also considered that RNA interference may have a slow onset of action, whereas current guidelines recommend early achievement of BP goals (ideally within 12 weeks).9,10 Overall, the results of this study with zilebesiran are quite encouraging and support further clinical development. In fact, the safety and efficacy of zilebesiran are being currently evaluated in a phase 2 clinical programme either as a monotherapy (KARDIA-1) or in combination with a standard-of-care antihypertensive treatment (KARDIA-2). These studies will provide preliminary answers for some of the safety and efficacy challenges related to the use of the drug in the management of hypertension as well as to assess the potential added value of this novel approach with respect to current therapeutic strategies. Supplementary data are not available at European Heart Journal online. G.L. received grant support (to the Institution) for investigator-initiated research from American Heart Association, Italian National Health Service and Italian Minister of Education, University and Research. She is currently involved in the Research Programs of the Italian Cardiovascular Network. She reports personal fees for speaker bureau from Astra Zeneca, Boehringer Ingelheim, Novo Nordisk, Daiichi Sankyo, Sanofi, and Novartis, outside the submitted work.