A Subcutaneously Administered Investigational RNAi Therapeutic (ALN-CC5) Targeting Complement C5 for Treatment of PNH and Complement-Mediated Diseases: Preliminary Phase 1/2 Study Results in Patients with PNH

Background:Uncontrolled complement activation plays a pivotal role in a variety of disorders such as paroxysmal nocturnal hemoglobinuria (PNH). Challenges to be addressed with eculizumab therapy include inter-individual variation in clearance of eculizumab, economic burden, and improvements in the current biweekly intravenous infusion maintenance schedule. ALN-CC5 is a subcutaneous (SC) investigational RNA interference (RNAi) therapeutic targeting hepatic complement C5 (C5) synthesis. Previously presented data from our ongoing Phase 1/2 study showed that ALN-CC5 was generally well tolerated and exhibited a clamped C5 knockdown and complement activity inhibition in healthy volunteers (Hill et al. Haematologica 2016; 101, Suppl 1). The aim of this abstract is to report updated tolerability and clinical activity of ALN-CC5 in patients with PNH.

Methods: A phase 1/2 single-ascending dose (Part A) and multiple-ascending dose study (Part B) of ALN-CC5 was conducted in healthy adult volunteers and in patients with PNH (Part C). In Part C, patients with PNH received weekly doses of 200 mg or 400 mg of ALN-CC5 for 2 to 16 weeks; ALN-CC5 is administered subcutaneously at a concentration of 200 mg/mL. The primary endpoints are safety and tolerability and secondary endpoints include: pharmacokinetics (PK), reduction of circulating C5 and complement activity, as measured by CAP/CCP Wieslab ELISA assays and sheep erythrocyte hemolysis assay, as well as reduction in LDH.

Results: Part C included 6 patients with PNH (treatment naïve n=3; patients receiving eculizumab n=3), including 1 patient who was experiencing breakthrough hemolysis despite receiving 1200mg eculizumab q2wk. ALN-CC5 was generally well tolerated in patients with PNH after multiple doses with the majority of adverse events (AEs) being mild or moderate in severity. There were no serious AEs or discontinuations due to AEs. One patient, who was also taking eculizumab, cyclosporine and anabolic steroids as concomitant medications, experienced a transient asymptomatic grade 3 elevation of liver transaminases that was deemed possibly related to study drug. In eculizumab naïve patients (n=3), ALN-CC5 monotherapy achieved a mean maximum C5 knockdown of 98.2% ± 0.3%, residual C5 levels of 0.9 mcg/mL and a mean maximum CCP inhibition of 94.2 ± 1.7%. During treatment with ALN-CC5, maximum reduction in LDH was 37% and 50% in 2 patients who received 17 doses of ALN-CC5 but remained above the goal of less than 1.5 times the ULN. In the remaining eculizumab naïve patient, LDH lowering was not observed following 8 doses of ALN-CC5. After completion of ALN-CC5 dosing and in the setting of ongoing >95% ALN-CC5-mediated KD of serum C5, treatment naïve patients received a single 600 mg dose of eculizumab (labeled induction dose is 600 mg weekly x 4) for the treatment of residual hemolysis followed by close clinical monitoring. An exploratory analysis was conducted to understand the potential for ALN-CC5 to reduce eculizumab dose and frequency. All 3 patients achieved sustained lowering of LDH <1.5 ULN for out to 4 weeks. In patients entering the study on a stable dose of eculizumab (n=3), ALN-CC5 was also able to achieve a robust C5 KD (mean max 86.7% ± 5.6%) with residual complement activity of <2% as measured by CCP assay from day 21 onward. The addition of ALN-CC5 resulted in LDH lowering to within reference range by day 35 post treatment (maintained out to Day 112) in an inadequate response patient who entered the study on higher than labeled dose of eculizumab. As a result, this patient's subsequent dosing of eculizumab was lowered from 1200mg q2wk to 900mg q2wk. Updated safety, pharmacodynamics (PD) and clinical activity for all 6 patients with PNH in Part C of this ongoing Phase 1/2 study will be presented.

Conclusion: ALN-CC5 was shown to be generally well tolerated in patients with PNH. The PD effects of ALN-CC5 were found to be durable, with clamped C5 knockdown and complement activity inhibition. Collectively, the data suggest that clamped inhibition of hepatic C5 synthesis may provide the foundation to potentially reduce the dose and frequency of eculizumab administration for patients with PNH, and to improve disease control in patients with inadequate response to eculizumab.