Rationale and design of the SHASTA-3 and SHASTA-4 studies: randomized, double-blind, placebo-controlled, phase 3 studies of plozasiran in patients with severe hypertriglyceridemia

Abstract Severe hypertriglyceridemia (sHTG) confers an increased risk of atherosclerotic cardiovascular disease (ASCVD) and acute pancreatitis (AP). sHTG-associated AP is a substantial source of morbidity, mortality, reduced quality of life and financial burden to health care systems. Currently available therapeutic approaches for sHTG are often insufficient to reduce triglyceride (TG) levels and prevent AP. Plozasiran, an investigational siRNA therapeutic, inhibits hepatic production of apolipoprotein C3 (APOC3), a key regulator of lipoprotein lipase-mediated TG metabolism and clearance. In a phase 2 study of sHTG patients [TG ≥500 mg/dL (≥5.65 mmol/L)], plozasiran demonstrated durable reductions in TG levels of up to -80%, 12 weeks after the last dose, and decreased TG below 500 mg/dL (5.65 mmol/L), a threshold of increased risk for AP in most participants. The SHASTA-3 and SHASTA-4 trials will evaluate safety and efficacy of plozasiran, including AP rates, in patients with sHTG. SHASTA-3 and SHASTA-4 are phase 3, randomized, double-blind, placebo-controlled, multi-center trials. Key inclusion criteria are prior sHTG and fasting TG ≥500 mg/dL (≥5.65 mmol/L), at screening. Key exclusion criteria include use of any hepatocyte targeted siRNA treatments that target lipids and/or TGs within 1 year (except inclisiran at least 4 weeks prior to enrollment), siRNA or ASO within 60 days, known FCS diagnosis, and AP within 4 weeks of screening. 700 adults with sHTG will be enrolled in these two trials in several sites across multiple countries. Patients will be randomized 2:1 to receive 4 quarterly subcutaneous injections of plozasiran 25 mg or matching placebo over a 1-year double-blinded period, followed by post-treatment evaluation or entry into the open-label extension study. The randomization will be stratified based on TG levels (≥880 mg/dL vs <880 mg/dL [≥ vs <10 mmol/L]) and prior history of AP, within 5 years of screening. The primary efficacy endpoint of the studies is placebo-adjusted percent change in fasting TG from baseline to month 12 with plozasiran. Secondary endpoints include percent change in fasting TG from baseline to month 10 compared to placebo, percent of patients achieving fasting TGs of <500 mg/dL (<5.65 mmol/L) and TGs of <150 mg/dL (<1.69 mmol/L) at month 10 and 12 compared to placebo, and event rate of adjudicated abdominal clinical events including ER visits and hospitalization for abdominal pain attributed to HTG and events of documented pancreatitis. The effect of plozasiran on other lipids and lipoproteins, inflammatory biomarkers, and liver fat content using magnetic resonance imaging-proton density fat fraction will be assessed. Adjudicated major adverse cardiovascular event rates, safety and tolerability will be assessed. SHASTA-3 and SHASTA-4 are designed to determine whether the quarterly-dosed APOC3 siRNA plozasiran, added to standard of care, safely reduces TG levels and the rate of AP in patients with sHTG.

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