Background

AL001 is a recombinant human anti-human sortilin (SORT1) monoclonal IgG1 developed by Alector in partnership with Abbvie. In June 2018, this antibody received orphan drug designation from the U.S. FDA for the treatment of frontotemporal dementia.

Sortilin is a type I membrane glycoprotein in the vacuolar protein sorting 10 protein (Vps10p) family. Sortilin is abundantly expressed in the central nervous system. As a sorting receptor in the trans-Golgi network, sortilin is involved in neurotrophin signaling, lysosomal degradation, and APP metabolism. Sortilin regulates the endocytosis and degradation of progranulin, and this process has been implicated in FTD pathophysiology (Hu et al., 2010). Progranulin mutations are a leading cause of frontotemporal dementia, and are associated with 50 to 70 percent reduction in progranulin protein levels. Blocking sortilin with AL001 is a strategy to increase progranulin levels. 

The SORL1 gene is one of the strongest genetic risk factors for Alzheimer's disease, and is associated with frontotemporal dementia, as well (Rogaeva et al., 2007; Pottier et al., 2012; Holstege et al., 2017; Raghavan et al., 2018; Pallesen and Vægter et al., 2012; Philtjens et al., 2018).

Targeting the sortilin-progranulin axis was reported to improve outcomes associated with progranulin insufficiency in preclinical models (Lee et al., 2013).

In cell assays, latozinemab blocked the interaction of sortilin with progranulin, reduced sortilin protein levels, and increased progranulin. In a mouse model of FTD-PGN, a rodent cross-reactive form of AL001 decreased sortilin levels in white blood cells, restored plasma proganulin to normal levels, and rescued a social behavior deficit. In cynomolgus monkeys, latozinemab decreased sortilin levels in blood cells, and increased plasma and CSF progranulin by two to three times (Kurnellas et al., 2023).

Findings

In September 2018, a first-in-human trial started enrolling 64 healthy adults and people with progranulin mutations causative for FTD at eight sites across North America and the U.K. Called INFRONT, the plan was to compare up to six single-ascending doses of AL001 intravenous infusion to placebo on outcomes including safety, pharmacokinetics, and exposure. The trial was completed in December 2019. At AAIC in July 2019, Alector reported results from 50 healthy volunteers and four FTD-GRN patients. According to the abstract and press release, AL001 infusion was “generally safe and well tolerated,” and resulted in a dose-dependent increase in progranulin levels in plasma and CSF in healthy adults and FTD patients. The press release notes a doubling of progranulin concentration in CSF of asymptomatic and symptomatic patients, restoring progranulin levels to the normal range. The results were published after peer review (Kurnellas et al., 2023).

Details of the complete cohort of 14 FTD-GRN mutation carriers were presented at AAIC July 2020. In six asymptomatic FTD-GRN mutation carriers, CSF progranulin levels were restored to normal 12 days after a single dose of 60 mg/kg. Among eight symptomatic patients, three doses of 30 mg/kg over four weeks raised progranulin into the normal range for at least eight weeks after the last dose. CSF markers of lysosomal function, inflammation, and gliosis were partially normalized. A non-significant 14 percent reduction in plasma neurofilament light chain (NfL) was observed eight weeks after dosing.

In September 2019, recruitment began for INFRONT-2, an open-label, multi-dose Phase 2 study in people with progranulin or C9ORF72 mutations causative of FTD. This trial is assessing safety, tolerability, PK, and pharmacodynamics in 40 participants receiving 60 mg/kg monthly infusions for nearly two years. The study is running at 12 sites in North America, Europe, and the U.K. It was slated to end in 2021, but the date has been pushed back to early 2026. According to an AAIC 2020 presentation, by May 2020 the trial had enrolled 15 patients, including some rollovers from the Phase 1 study. The longest-treated patient had received six months of drug, which remained safe and well-tolerated. CSF progranulin reached normal levels within 10 days after the first dose in all participants, and stayed elevated with continued treatment. Due to the COVID-19 pandemic, two patients missed a dose, and some missed biomarker evaluations. A preliminary analysis based on this incomplete data indicated that plasma NfL declined in six of eight participants who received all scheduled infusions. In one patient, plasma NfL decreased during the Phase 1 trial, rebounded off drug, and decreased again when treatment recommenced in Phase 2.

At the July 2021 AAIC, Alector presented 12-month data from 12 symptomatic FTD-GRN patients in INFRONT-2. Participants maintained normal plasma and CSF progranulin levels, with no new safety issues. The company also reported normalization of lysosomal and inflammatory biomarkers, and stabilization of NfL in this group. A comparison with historical controls showed potential for slowing decline on exploratory clinical endpoints of brain atrophy and dementia (Aug 2021 conference news). A cohort of 10 symptomatic FTD-CORF72 patients posted similar results, according to a company presentation at the March 2022 AD/PD conference (press release).

In July 2020, Alector started a Phase 3, placebo-controlled trial. Called INFRONT-3, it with the aim of enrolling 180 people between 25 and 85 who are at risk of or have frontotemporal dementia due to heterozygous mutations in the progranulin gene. Participants are receiving a monthly intravenous infusion of AL001 60 mg/kg or placebo in a blinded fashion, or open-label AL001, for up to two years. The primary outcome is change in a combination of the Clinical Dementia Rating plus the NACC FTLD-Sum of Boxes, a measure adapted for frontotemporal dementia patients. Secondary clinical outcomes include standard measures of disease severity or improvement. The study will evaluate volumetric MRI, as well as CSF and blood pharmacodynamic biomarkers. It is taking place at 65 sites in North America, Australia, and Europe, and will run through 2025. In October 2023, the trial was declared fully enrolled at 101 symptomatic patients; an open-label continuation study of once-monthly 60 mg/kg latonizemab is recruiting (press release).

In July 2021, the company announced an agreement with GlaxoSmithKline to co-develop AL001 for FTD and ALS (press release). In September 2021, the first patient was enrolled in Phase 2 for ALS due to C9ORF72 mutations. The study planned to randomize 45 participants to six monthly infusions of AL001 or placebo, added to their current treatment. The primary endpoints were to be safety, tolerability, pharmacokinetics and pharmacodynamics, including plasma and CSF progranulin levels, with blood and CSF neurofilament light chain concentration as a secondary outcome. The study was terminated in October 2022, after enrolling 5 patients. The reason given was that Alector is considering a different study in ALS.

Alector has a related sortilin antibody, AL101, in Phase 1 for Alzheimer’s disease.

For all clinical trials of AL001, see clinicaltrials.gov.