RNA Interference as a Therapeutic Approach for Managing Hypertension

Introduction More than one billion people worldwide have hypertension—a major risk factor for cardiovascular and kidney disease.1 The therapeutic landscape of first-line agents for treatment of hypertension has been transformed by the elucidation of the renin-angiotensin-aldosterone system (RAAS). This has culminated in the development of direct renin inhibitors, angiotensin-converting enzyme inhibitors (ACEis), angiotensin II-receptor blockers (ARBs), and mineralocorticoid receptor antagonists. Despite these advances, more than half of US adults with hypertension have mean BP above target goals. A prominent determinant of uncontrolled BP is nonadherence. A systematic review unveiled a composite nonadherence prevalence of approximately 50% when using metrics such as directly observed therapy and antihypertensive drug levels.2 In a small study focused on apparent treatment-resistant hypertension, one third of patients who underwent directly observed therapy experienced an average decline in systolic BP of 26 mm Hg.3 Another significant determinant of BP control is the efficiency of RAAS inhibition. Inhibition of RAAS with an ACEi or ARB results in lower levels of aldosterone and loss of the negative feedback on renin secretion. Thus, use of an ACEi or ARB causes a compensatory increase in plasma renin activity and downstream RAAS intermediates. The quest for complete RAAS suppression led to the use of a combination of an ACEi and ARB. However, up to one third of individuals who administered RAAS inhibitor therapy had a resurgence in plasma aldosterone levels after 3 months, reverting to the levels measured before initiation of RAAS blockade.4 The Randomized Evaluation of Strategies for Left Ventricular Dysfunction study also showed that the combination of enalapril with candesartan reduced serum aldosterone at week 17 of treatment, but not at week 43.5 This phenomenon is known as aldosterone breakthrough. Owing to high levels of the substrate, angiotensinogen, despite renin, angiotensin-converting enzyme, or AT1R blockade, restoration of angiotensin I, angiotensin II, and aldosterone is possible (Figure 1). Proximal depletion of hepatic angiotensinogen production may overcome these limitations of current therapy.Figure 1: RAAS and its therapeutic targets. ACE, angiotensin converting enzyme; ARB, angiotensin II-receptor blocker; AT1R, angiotensin II type 1 receptor; AT2R, angiotensin II type 2 receptor; RAAS, renin-angiotensin-aldosterone system; RISC, RNA-induced silencing complex; siRNA, small interfering RNA. Created with BioRender.com.Small interfering RNAs (siRNAs) have shown tremendous promise in multiple fields of medicine for long-term inhibition of gene expression. For example, inclisiran blocks PCSK9 expression and is approved for hypercholesterolemia, and nedosiran reduces glycolate oxidase expression and is approved for primary hyperoxaluria. Efficient targeting of siRNA to hepatocytes is achieved with the use of a trivalent GalNAc ligand that binds the asialoglycoprotein receptor, followed by cell internalization of the siRNA cargo.6 Recent studies have investigated siRNAs to target the upstream RAAS pathway. Zilebesiran selectively degraded hepatic angiotensinogen mRNA (angiotensinogen mRNA), leading to significant BP reduction in a phase I clinical trial.7 This trial involved 107 adults up to age 65 years with an average 24-hour systolic BP of 140.3±9.0 mm Hg, conducted in three parts: A, B, and E. Part A included patients randomly assigned to escalating doses of zilebesiran (n=56) or placebo (n=28). Those receiving zilebesiran showed substantial, dose-dependent reductions in BP after 8 weeks. A 200 and 800 mg dose lowered 24-hour ambulatory systolic BP by >10 and >15 mm Hg, respectively. Part B involved patients subjected to high sodium (5.75 g/d) and low sodium (0.23 g/d) diets, randomized to either zilebesiran (800 mg) (n=8) or placebo (n=4). Notably, a low sodium diet reduced systolic BP by an average of 9.1±4.5 mm Hg while zilebesiran further lowered systolic BP by 18.8±4.3 mm Hg. Importantly, this BP reduction was reversed on high sodium intake. In part E, 16 patients received zilebesiran (800 mg), and those with systolic BP ≥120 mm Hg at week 6 were assigned irbesartan (300 mg/d). Six patients exhibited a mean reduction of 21.8±2.9 mm Hg in systolic BP. Conversely, the remaining ten patients on irbesartan showed incremental changes in systolic BP of −6.3±3.1 mm Hg by week 8, suggesting a synergistic effect of ARB with zilebesiran. The study showed a dose-dependent decrease in serum angiotensinogen with zilebesiran at week 1. By week 24, patients in part A who received zilebesiran (800 mg) exhibited a remarkable decrease of >90% in serum angiotensinogen. The study also revealed a trend of decreased plasma renin activity, angiotensin I, angiotensin II, and aldosterone with zilebesiran. Patients undergoing treatment were monitored until their serum angiotensinogen returned close to baseline or up to 1 year after their last zilebesiran dose. Treatment-related adverse events were mild, transient injection-site reactions. There were no occurrences of hypotension, hyperkalemia, or deterioration of kidney function, with the caveat that patients with an eGFR <60 ml/min per 1.73 m2 were excluded. Similarly, an antisense oligonucleotide directed to hepatocyte-derived AGT, made by Ionis Pharmaceuticals, an antisense oligonucleotide that targets hepatocyte-derived angiotensinogen, caused 67% reduction in circulating angiotensinogen levels in patients with uncontrolled hypertension, without hypotension or AKI.8 Unlike preclinical studies,9 plasma renin activity did not rise in patients treated with angiotensinogen siRNA.7,8 One could speculate that participants had a higher sodium intake at baseline compared with rodent studies or alternate mechanisms, but a lack of elevated plasma renin activity may underscore the benefit of zilebesiran to prevent aldosterone breakthrough. Therefore, the use of zilebesiran may yield several advantages including but not limited to (1) improved adherence due to infrequent dosing,2 (2) prevention of aldosterone breakthrough, and (3) preservation of intrarenal RAAS to allow for modulation of RAAS (e.g., by high sodium diet or concomitant use of irbesartan). Upstream versus sequential blockade of the RAAS may have differing safety profiles. Sequential blockade with multiple agents is known to carry risk of adverse events. Previous trials (ONTARGET, VA-NEPHRON) revealed an increased risk of AKI and hyperkalemia with a combination of an ACEi and ARB. In addition, combination therapy with aliskiren and an ACEi/ARB resulted in a higher rate of hyperkalemia.10 However, in the study by Desai et al., among the ten patients who received both irbesartan and zilebesiran, there were no significant changes to eGFR, sodium, and potassium at week 12.7 However, longer-term studies are still needed. The safety of siRNA targeting angiotensinogen is unknown in scenarios necessitating abrupt activation of the RAAS. Part B of the zilebesiran phase I trial showed that a high sodium diet attenuates BP reduction, and Part E showed additional benefit of an ARB (irbesartan) beyond loss of hepatic angiotensinogen. These data suggest that reduction in angiotensinogen can reduce BP but that acute modulation of RAAS is still possible. Similarly, preclinical studies using spontaneously hypertensive rats treated with siRNA showed that intravenous administration of angiotensin II or norepinephrine swiftly reversed siRNA-mediated BP reduction while fludrocortisone or high sodium intake led to gradual reversal of the BP back up to baseline on days 5–7.9 Alternatively, a GalNAc-conjugated single-stranded high-affinity oligonucleotide that complements a siRNA guide strand has also been shown to reverse siRNA-mediated gene silencing in vivo.11 A comprehensive BP management scheme could include semiannual administration of siRNA. The ongoing phase II trials of zilebesiran, KARDIA-1 and KARDIA-2, are poised to address current challenges of treating hypertension. This new mechanism of action will also have to be compared with other traditional and novel agents that target RAAS (e.g., steroidal and nonsteroidal mineralocorticoid receptor antagonists and aldosterone synthase inhibitors). Effective control of hypertension could lead to a 30.4% decrease in cardiovascular disease mortality for men and a 38.0% decrease for women.1 The use of siRNA in hypertension treatment holds promise for reduction of cardiovascular mortality by improving medication adherence, treatment response, and safety.