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Background: Angiotensinogen (AGT) is the sole precursor of all angiotensin peptides and plays a key role in hypertension pathogenesis. We evaluated the effect of ALN-AGT01, a subcutaneous investigational RNAi therapeutic targeting hepatic AGT synthesis, on blood pressure in hypertensive patients. Methods: As part of a phase 1 program designed to assess the safety and tolerability of ALN-AGT01, we conducted a multicenter study randomizing patients aged 18-65 years with mild to moderate hypertension (mean seated systolic blood pressure [SBP] of >130 and ≤165 mmHg after washout of antihypertensive medication) 2:1 to ascending single doses of ALN-AGT01 or placebo. Change from baseline in BP at 8 weeks was measured by ambulatory BP monitoring (ABPM). We report interim results as of May 14, 2020. Results: Sixty patients (mean age 52 years, 45% female, mean baseline 24h SBP 139 +/- 7 mm Hg) were enrolled in ascending dose cohorts of 10 mg, 25 mg, 50 mg, 100 mg, or 200 mg. Dose-related reductions in serum AGT levels were observed (figure), with reductions >90% in the 100 and 200 mg dose cohorts. AGT remained durably reduced through 12 weeks after single dose administration. Concomitant reductions in BP from baseline were observed with AGT knockdown, with an over 10 mm Hg reduction of mean 24-hour SBP observed at Week 8 after single doses of 100 mg or 200 mg. No symptomatic hypotension, treatment-related serious adverse events, or clinically significant elevations in blood creatinine or potassium were seen. Conclusions: Single dose administration of ALN-AGT01 to hypertensive patients resulted in dose-related reductions in serum AGT and BP over 8 weeks without hypotension or other related serious adverse events. Durable AGT knockdown to 12 weeks supports further evaluation of once quarterly or potentially less frequent dose administration.