Background

ACI-3024 is a small-molecule inhibitor of tau aggregation. It originated from screening of AC Immune’s proprietary compound library of low-molecular-weight compounds that disrupt Aβ-sheet structures (Kroth et al., 2012). With additional medicinal chemistry, the company has created conformation-specific candidates targeting tau, Aβ, α-synuclein, and the NLRP3-ASC inflammasome; ACI-3024 is the first to enter clinical trials.

No preclinical information on ACI-3024 is formally published. According to data presented at conferences, the compound disrupts tau aggregates in vitro, independent of the presence of pathogenic mutations (see March 2019 AAT-AD/PD slides). Reportedly, ACI-3024 does not cross-react with monomeric tau, or with Aβ or α-synuclein aggregates from human brain, and it disaggregates tau neurofibrillary tangles in human brain sections ex vivo, even in the presence of amyloid plaques. In cell-based assays, nanomolar concentrations of ACI-3024 were claimed to cause a dose-dependent reduction of intracellular pathological tau, and to prevent microglial activation and neuron death induced by tau paired helical filaments in primary brain cell cultures. One month of ACI-3024 treatment was claimed to reduce brain aggregated and insoluble tau in the rTg4510 mouse model of tauopathy due to expression of mutated human tau. Treatment also reportedly reduced microglia activation and CSF total tau in these mice, in proportion to plasma drug concentration. 

In December 2018, AC Immune struck up a partnership with Lilly to develop ACI-3024 (Genetic Engineering & Biotechnology News story). AC Immune has used the same technology to discover PET ligands, and is developing the tau tracer PI-2620 in partnership with Life Molecular Imaging (Kroth et al., 2019; Jan 2020 news; Bullich et al., 2019).

Findings

In July 2019, the company began a Phase 1 safety and tolerability study in healthy young volunteers (press release). The placebo controlled, single- and multiple-ascending-dose study will also evaluate ACI-3024’s pharmacokinetics, food effects, and pharmacodynamics. No registry entry for this trial was found. However, in March 2020, AC Immune announced that recruitment and treatment were complete, and data release is anticipated in the second half of 2020 (press release).

In its 2020 annual report filed March 2021 with the U.S. Securities and Exchange Commission, ACImmune disclosed that this study was conducted as planned, and completed in 2020. It showed dose-dependent exposure and brain penetration of ACI-3024, a long half-life of 47.5 to 101 hours, steady-state levels reached after 12-13 days, and CSF drug concentrations exceeding the target levels that had been expected based on animal studies. The filing notes that plans for further clinical trials of ACI-3024 are suspended, and that the drug will be evaluated in models of other, rare tauopathies. As of October 2021, ACImmune's pipeline listed ACI-3024 as a preclinical candidate.