Background

Cinpanemab is a human-derived monoclonal antibody directed against α-synuclein. Genetic and pathology evidence implicate this protein in the molecular pathogenesis of Parkinson's disease (PD) and other α-synucleinopathies such as dementia with Lewy bodies (DLB). In 2010, Biogen licensed cinpanemab from Neurimmune (see company press release). The antibody was generated with reverse translational medicine technology from naturally occurring, presumably protective antibodies found in healthy aged donors, as were aducanumab and other antibodies in the Biogen-Neurimmune partnership.

The antibody, previously known as BIIB054, binds to α-synuclein residues 1-10, with 800-fold higher affinity for aggregated over monomeric α-synuclein. The antibody inhibits α-synuclein spreading in cell-based assays, and slows pathology and motor symptoms in mice (Weihofen et al., 2019).

Cinpanemab is one of several α-synuclein antibodies being investigated for PD. Others include ABBV-0805, MEDI1341, LU AF82422, and prasinezumab.

Findings

From July 2015 through 2017, Biogen evaluated single-ascending, intravenous doses of cinpanemab in 48 healthy volunteers and 18 people with early Parkinson's, at eight sites in the U.S. Outcomes included safety measures, the MOCA cognition screen, cinpanemab serum levels and pharmacokinetics, as well as presence of anti-cinpanemab antibodies.

In 2017 at AD/PD, Biogen reported some data on the healthy participants, aged 40 to 65. They had received infusions of 1, 5, 15, 45, 90, or 135 mg/kg, had MRI scans at baseline, day three, and week four, and had CSF samples drawn at baseline, eight hours, 24 hours, and week three. Participants were followed for 16 weeks after dosing with clinical assessments and electrocardiograms. Doses up to 90 mg/kg were reported to have been well tolerated; in the 135 mg/kg cohort, one participant developed asymptomatic ischemia in the right parietal lobe. Side effects included headache, dizziness, pain, or skin rash related to the infusion. Cinpanemab’s half-life was 28 days, the CSF/serum ratio was 0.2 percent at all doses, and maximum concentration in blood was dose-proportional (see May 2017 conference news).

At the 2018 AAN conference, Biogen presented first results of the same trial's PD cohort. Thirteen men and five women, aged 47 to 75, had received a single infusion of either zero, 15, or 45 mg/kg of cinpanemab. Nine were not on PD medication, five were on levodopa, two on rasagiline, two on both. The pharmacokinetics of cinpanemab in patients were similar to those in healthy volunteers, with a 33-day serum half-life, a threefold higher plasma concentration in the high-dose versus low-dose group, and 0.4 and 0.3 percent reaching CSF in the high- and low-dose groups, respectively. None of the patients developed anti-cinpanemab antibodies.

According to Biogen, cinpanemab formed plasma complexes with α-synuclein in both cohorts. Both doses formed similar amounts of complex, suggesting saturation of blood synuclein with antibody. Cinpanemab is more selective for aggregated than soluble α-synuclein, but at high doses binds soluble protein, according to Biogen. No serious adverse events were reported, and trial results were subsequently published (May 2018 conference news; Brys et al., 2019).

In December 2017, Biogen started SPARK, a two-year Phase 2 study originally meant as a safety trial, in 357 people with PD. Year one compared monthly infusions of three doses of cinpanemab—250 mg, 1,250 mg, or 3,500 mg—to placebo to evaluate safety, pharmacodynamic effects on nigrostriatal dopaminergic nerve terminals, pharmacokinetics and immunogenicity of cinpanemab. Doses were selected to attain 50 percent, 90 percent and greater than 90 percent target binding, respectively, in brain interstitial fluid, based on modeling of Phase 1 and other data (Kuchimanchi et al., 2020). In year two, placebo recipients switched to receive cinpanemab, as well. The trial ran at 75 sites in the U.S., Canada, and Europe; enrollment is complete. The one-year placebo-controlled treatment period ended in May 2020, with trial completion planned for summer 2021.

Primary outcome measures were listed as adverse events, clinical labs, vital signs, neurological exam, as well as EKG and MRI, with secondary measures being I123 SPECT (DaTscan), cinpanemab serum concentration, and percent of participants generating anti-cinpanemab serum antibodies. However, in August 2020, Biogen changed this trial into a clinical-efficacy study. The primary outcome was change from baseline in Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Total Score.

In March 2019, a Phase 1 trial in 24 people with Parkinson's started at nine sites in Japan.

In February 2021, Biogen announced to investors that it had halted development of cinpanemab after the SPARK study missed its primary and secondary endpoints (see slide 14 here).

For all trials on this antibody, see clinicaltrials.gov.