Sotatercept-csrk, a recombinant activin receptor type IIA-Fc (ActRIIA-Fc) fusion protein, is an activin signaling inhibitor that binds to activin A and other TGF-β superfamily ligands. As a result, sotatercept-csrk improves the balance between the pro-proliferative (ActRIIA/Smad2/3-mediated) and anti-proliferative (BMPRII/Smad1/5/8-mediated) signaling to modulate vascular proliferation. In rat models of PAH, a sotatercept-csrk analog reduced inflammation and inhibited proliferation of endothelial and smooth muscle cells in diseased vasculature. These cellular changes were associated with thinner vessel walls, partial reversal of right ventricular remodeling, and improved hemodynamics.
A statistically significantly greater decrease from baseline in PVR was observed in the sotatercept group compared to the placebo group in the Phase 3 STELLAR study. The median treatment difference in PVR between sotatercept-csrk and placebo was -235 dynes*sec/cm5 (95% CI: -288, -181; p<0.001). Sotatercept-csrk steady state exposure at 0.7 mg/kg dose was associated with near maximal reduction in PVR based on exposure-response analysis.
A statistically significantly greater decrease from baseline in NT-proBNP was observed in the sotatercept group compared to the placebo group in the Phase 3 STELLAR study. The median treatment difference in NT-proBNP between the sotatercept-csrk and placebo was -442 pg/mL (95% CI: -574, -310; p<0.001).
Following subcutaneous administration of 0.7 mg/kg sotatercept every three weeks to PAH patients, the steady state geometric mean (CV) area under the time concentration curve (AUC) is 172 mcg×d/mL (34.2), and peak concentration (Cmax) is 9.7 mcg/mL (30%). Sotatercept-csrk AUC and Cmax increased proportionally with dose. Steady state is achieved after approximately 15 weeks following initiation of multiple dosing. The accumulation ratio of sotatercept-csrk AUC is approximately 2.2.
Following subcutaneous administration, the absolute bioavailability of sotatercept-csrk is approximately 66%. The sotatercept-csrk median time to peak drug concentration (Tmax) is approximately 7 days (range from 2 to 8 days) following multiple SC administration every 4 weeks.
The population PK model estimated volume of distribution (CV) of sotatercept-csrk at steady state is approximately 5.3 L (27.3) in patients with PAH.
The sotatercept-csrk effective half-life is approximately 24 days and its clearance is approximately 0.18 L/day.
Sotatercept-csrk is expected to be metabolized into small peptides by catabolic pathways.
No clinically significant differences in sotatercept-csrk pharmacokinetics (PK) were observed based on age (18 to 81 years of age), sex, race, mild to moderate (eGFR ranging from 30 to 89 mL/min) renal impairment (PAH patients), or end-stage kidney disease (eGFR <15 mL/min) with dialysis. Severe renal impairment (eGFR ranging from 15 to 30 mL/min) is not expected to impact the PK of sotatercept-csrk. Sotatercept-csrk is not dialyzable. The effect of hepatic impairment on the PK of sotatercept-csrk has not been studied.
The clearance (CL) and central volume of distribution (Vc) increase with increase in body weight. This effect is not clinically significant when sotatercept-csrk is administered using weight-based dosing as recommended.
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