They are difficult to isolate, hard to quantify, and virtually uncharacterized structurally. No matter the maddening vagueness of the target, scientists think they have therapies to go after Aβ oligomers. At this year’s Clinical Trials in Alzheimer’s Disease meeting, held November 1–4 in Boston, researchers outlined a handful of strategies to sweep these toxic molecules out of the brain. They include small molecules said to prevent oligomer formation or block their toxicity, such as the sigma-2 antagonist CT1812 and the glutaminyl cyclase inhibitor PQ912. They include immunotherapies, both known ones such as crenezumab and two newcomers called KHK6640 and UB-311. Even the failed-and-resurrected tramiprosate is being presented to fit the bill. Most of these drugs are in early clinical development.
Lon Schneider, University of Southern California, Los Angeles, reviewed safety data from a multicenter, double-blind, placebo-controlled Phase 1b/2a study of CT1812, which was developed by Cognition Therapeutics, Inc., in Pittsburgh. Susan Catalano and colleagues at that company identified this molecule as a sigma-2 receptor allosteric antagonist that prevents Aβ oligomers from binding oligomer receptors and compromising synaptic function (Dec 2014 conference news). A prior Phase 1 trial conducted in Australia indicated that the compound was safe and well tolerated up to a dose of 560mg in healthy elderly volunteers.
The second Phase 1b/2a trial enrolled 19 patients with mild to moderate AD between the ages of 50 and 80, whose MMSEs ranged from 18–26. They were randomized to receive 90, 280, or 560 mg CT1812 or placebo once daily for 28 days. While incidence of treatment-emergent adverse events was the primary outcome, the study also measured cognition, a fleet of CSF biomarkers, and changes in protein expression patterns in the CSF and plasma.
Schneider reported that most patients, including 60 percent of placebo-treated patients, experienced mild, transient, unintended effects, including nausea, vomiting, headache, post-lumbar puncture headache, fatigue, and lethargy. The incidence of adverse events was slightly higher in the highest dose group, he said. Four patients developed a reduction in T cells in the blood called lymphocytopenia, which resolved before the end of the study. “Generally, the drug is safe and well tolerated at the doses given,” said Schneider.
The study was not powered to detect changes in cognition, and clinicians observed no change on the ADAS-Cog14, a verbal-fluency test, or a category-fluency test.
Both Schneider and Catalano claimed that the trial yielded evidence for synapse protection. Collaborators at Kaj Blennow’s lab at the University of Gothenburg, Sweden, used a sandwich ELISA to measure fragments of neurogranin in CSF samples from the trial. Considered a marker of postsynaptic damage, neurogranin fragments tick up in AD CSF compared to controls (Jan 2015 news; Kvartsberg et al., 2014). Indeed, over this 28-day trial, CSF neurogranin rose slightly in the placebo and fell slightly in the treated groups. There was no apparent dose response, however. The difference from placebo was statistically significant only in the 90 mg group and pooled treatments groups, which had 33 and 18 percent less neurogranin, respectively.
More indirect evidence for neuroprotection came from liquid chromatography–mass spec analysis of CSF and plasma samples carried out by researchers at Caprion Biosciences, Inc., in Montreal. Catalano reported that synaptotagmin-1, another synaptic marker that is elevated in AD CSF (Öhrfelt et al., 2016), decreased 59 percent in treated patients compared with controls. Catalano told Alzforum that changes in expression of additional proteins supported the idea of a synaptic benefit, as well. Cognition Therapeutics has filed a patent on a protein signature she considers a promising indicator of target engagement; she expects to disclose the signature next year. “We need to replicate these findings in another, longer-duration clinical trial and look at them in the context of cognitive function,” she said.
Four new trials for CT1812 are planned. One, in collaboration with Yvette Sheline at the University of Pennsylvania, Philadelphia, and John Cirrito at Washington University, St. Louis, will examine CSF hourly after single injections of CT1812 to look for displacement of Aβ oligomers from the brain parenchyma. In another, Philip Scheltens and colleagues at VU Medical Center, Amsterdam, will use EEG to look for evidence of synaptic network changes in a one-month placebo/drug crossover design trial. With the same goal in mind, Chris van Dyck and Richard Carson and colleagues at Yale University, New Haven, Connecticut, will use the investigational PET tracer UCB-J in a third trial to look for changes in synaptic vesicle glycoprotein 2A, a marker of synapse count, (see Part 2 of this series; Jul 2016 news). This six-month, NIA-supported trial will also conduct FDG PET and fMRI scans on, and collect CSF from, 21 volunteers taking placebo or one of two drug doses. Catalano said participants may opt to donate brain tissue after death to enable a comparison between in vivo UCB-J binding and postmortem counting of synapses. The fourth trial, a Phase 2 of 160 patients, will be similar in concept, but use less imaging, Catalano told Alzforum.
For another early stage treatment, the glutaminyl cyclase (QC) inhibitor PQ912, Scheltens reviewed previously presented data from the Phase 2a SAPHIR trial. The QC enzyme cyclizes the leading glutamate in N-terminally truncated Aβ3-x peptides, turning them into pyroglutamate forms (pGlu-Aβ), which are highly prone to oligomerize and aggregate (Apr 2008 conference news; Mar 2013 conference news). The drug appeared largely safe, though treated participants had more gastrointestinal problems and skin reactions than those on placebo. CSF analysis indicated a 91 percent inhibition of QC, and a future trial will focus on dose-ranging to find a more tolerable but still-effective dose.
In this trial, the median CSF GluAβ oligomer level in the treatment group dropped from 0.51 arbitrary units to 0.44 AUs by the end of the trial. The study used a proprietary assay to quantify this species of Aβ. By comparison, the median pGluAβ oligomer level rose from 0.01 AU to 0.26 AU in the placebo group. Overall pGluAβ oligomer fell by 18 percent in treated patients while increasing by 17 percent in controls. Rachelle Doody of F. Hoffmann-La Roche in Basel, Switzerland, wondered why the baseline values were so different between controls and treatment groups. Scheltens said this likely reflected difficulty in measuring oligomers. “The assay is not that sensitive, so we have to be very careful in how we interpret the data,” he said. “The only message I want to convey is that upon treatment over time, the amount of measurable oligomers went down in the active group and up in the placebo group, suggesting an effect of the drug on these oligomers.” He noted that the field has struggled to measure oligomers and hinted that a better assay might be in the works. “In the next trial we will have a more sensitive assay,” he predicted.
Also at CTAD, Jeff Cummings from the Cleveland Clinic Lou Ruvo Center for Brain Health, Las Vegas, stressed that oligomers likely play an important role in AD pathogenesis, and may well be present throughout the course of the disease, not only in its early stages. Cummings agreed that a validated assay for Aβ oligomers in the CSF would aid development of treatments. Case in point, Alzhemed, aka homotaurine, aka tramiprosate, aka Vivimind, was recently revived once more in a new pro-drug formulation called ALZ-801. Researchers at Alzheon Inc., Framingham, Massachusetts, claim an “enveloping mechanism” by which this compound keeps Aβ from oligomerizing (Kocis et al., 2017).
In his talk, Cummings ascribed efficacy signals reported in post hoc subgroup analysis of an otherwise failed North American Phase 3 trial of tramiprosate (Aug 2007 news) to an anti-oligomer effect. Among ApoE4 homozygotes who completed the trial, the 18 patients who received the highest dose declined more slowly than those on placebo, with differences seen on the CDR-SB beginning at week 26, on the ADAS-Cog beginning at week 52, and both continuing to diverge from placebo scores through the 78-week trial.
While small molecules might prevent Aβ oligomers from forming or interacting with other proteins, immunotherapy is being tried in an effort to rid the brain of these nefarious peptides. At CTAD, researchers debuted an antibody developed by Kyowa Hakko Kirin, Tokyo. Perhaps better known for making Japanese Kirin beer, Kyowa is a global pharmaceutical company and has therapeutic antibodies in the pipeline for several disorders, including asthma and psoriasis. KHK6640, a humanized form of a mouse antibody, purportedly recognizes Aβ aggregates, though a search of KHK6640 on PubMed pulls up no publications.
Marc Cantillon, Kyowa Kirin Pharmaceutical Development, Princeton, New Jersey, told Alzforum that the company designed the antibody, a modified IgG4, to have little effector function to reduce the risk of ARIA. Cantillon said it was crafted to only bind an epitope on aggregated Aβ and that, unlike crenezumab or solanezumab, KHK6640 did not bind Aβ monomers.
Cantillon and colleagues detailed safety and tolerability data from a Phase 1 trial. A total of 51 AD patients with MMSEs ranging from 19.45 to 27.6 were randomized to placebo or immunotherapy in single-ascending, followed by multiple-ascending, doses. The primary outcome was safety and tolerability; pharmacokinetics, immunogenicity, and CSF level of KHK6640 were measured as secondary outcomes. Changes in CSF Aβ oligomers and cognitive scores were determined as exploratory objectives.
For the SAD study, 46 patients were randomized to either placebo or 1, 3, 10, or 20 mg/Kg of KHK6640 given intravenously, or 0.3 mg/Kg given subcutaneously. After three to 12 months, 40 of these volunteers were re-randomized to placebo or the same dose given five times at 28-day intervals. Another 11 patients who had not been tested in the SAD part were tested in the MAD study.
Overall, KHK6640 seemed well tolerated, the scientists reported. The incidence of treatment-emergent adverse events was slightly lower in the treatment groups in both SAD and MAD studies, and none of them were dose-related. Two people discontinued, one in the SAD placebo group and one in the MAD treatment group, but neither discontinuance was deemed related to drug. One person in the MAD placebo group died, and another in the MAD treatment group developed severe hypotension and was hospitalized. The hypotension resolved during the study. Nobody dropped out due to drug-related treatment-emergent events. No evidence of ARIA-E emerged, but four patients showed signs of ARIA-H, one being in the placebo group. In all cases ARIA was asymptomatic.
Pharmacokinetics showed that KHK6640 reached maximum levels in the blood within minutes, and its concentration rose with dose. Its half-life in the blood was about 17 days. Three volunteers in the SAD part and three in the MAD part tested positive for antibodies to KHK6640. Strong immunogenicity posed a problem for Eli Lilly’s pGlu-Aβ antibody LY3002813, where almost everyone who received the therapy mounted an immune response against it (Aug 2016 conference news).
In the KHK664 trial, MMSE scores trended toward higher in patients than controls, but the differences were not statistically significant and scores for the CDR and a computerized cognitive test battery were inconsistent. CSF analysis indicated that the amount of KHK6640-bound Aβ oligomers increased in a dose-dependent manner, up to 10-20 mg/kg. According to Cantillon, this may be a first AD trial to show human oligomer target engagement. The poster gave no details on how oligomers were measured.
Cantillon told Alzforum that Kirin Kyowa plans a Phase 2 global trial in prodromal AD. Details are not final yet, but Cantillon expects that outcome measures will include tau PET and scores on a cognitive composite.
Hiroyuki Shimada and colleagues from Kyowa Kirin detailed data from a similar Phase 1 study conducted in Japan. The same single-ascending doses were administered to 16 volunteers with mild to moderate AD. Again, the drug seemed well tolerated, with two drug-related treatment-emergent adverse events. Investigators concluded that one SAE, a lacunar infarction, was unrelated to the drug. No ARIA turned up in this trial, and none of the treated patients developed antibodies to KHK6640.
Researchers at other companies are developing active vaccines to target oligomers. On a poster, Ajay Verma of United Neuroscience, Inc., Hauppauge, New York, reported data from a completed Phase 1 and an ongoing Phase 2a trial of UB-311, an active vaccine against Aβ1-14. The scientists claim this vaccine generates antibodies that bind oligomers and fibrils without causing ARIA.
Verma and colleagues used dot blots to determine antigen specificity. They reported that antibodies in serum from vaccinated patients failed to recognize α-helical monomers and Aβ monomers, but did bind Aβ oligomers and fibrils. The antibodies also bound amyloid plaques in tissue sections taken postmortem from AD brains.
While it remains to be seen exactly what these antibodies recognize, the vaccine elicited no ARIA so far in these trials. In the Phase 1, 19 people with mild to moderate AD, aged 51–78, were vaccinated; 24 weeks later, none had MRI abnormalities. Likewise, no evidence for ARIA has emerged so far in the 18–month Phase 2a study, which enrolled 43 mild to moderate AD patients, aged 60–86. They are being monitored quarterly by MRI. Twenty-five patients have completed the 12-month assessment, and none has shown signs of ARIA-E or meningo-encephalopathy. The latter sank AN1792, the first clinical Aβ immunotherapy, which was a vaccine made of Aβ1-42 (Jan 2002 news).
Further along than these new immunotherapies, crenezumab is wending its way through a Phase 3 program in autosomal-dominant and early stage, late-onset AD. This antibody is said to bind oligomers, though scientists have questioned how. At CTAD, Genentech’s Jasvinder Atwal explained crenezumab’s penchant for oligomers.
Atwal reported that crenezumab binds to stable oligomers that survive passage through SDS polyacrylamide gels, whereas commercially available Aβ antibodies do not. Crenezumab also immune-precipitates high-molecular-weight Aβ species from the CSF of AD patients, and from brain extracts of PS2APP mice. In these animals, Atwal found that crenezumab, which the scientists covalently labeled with the fluorescent dye methoxy-XO4, bound to regions of the brain that are known to accumulate Aβ multimers. These include the halo surrounding Aβ plaques, and mossy fiber axons in the hippocampus. The antibody never bound to tissue from wild-type mice, which produce monomers of murine Aβ.
Perhaps most importantly, Atwal reported that crenezumab does not bind to blood vessel Aβ in the transgenic mice. “We now think that the reason crenezumab causes no ARIA is not just because it has reduced microglial effector function, but also because it fails to bind vascular amyloid,” Atwal said.—Tom Fagan
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Research Models Citations
- Kvartsberg H, Duits FH, Ingelsson M, Andreasen N, Öhrfelt A, Andersson K, Brinkmalm G, Lannfelt L, Minthon L, Hansson O, Andreasson U, Teunissen CE, Scheltens P, Van der Flier WM, Zetterberg H, Portelius E, Blennow K. Cerebrospinal fluid levels of the synaptic protein neurogranin correlates with cognitive decline in prodromal Alzheimer's disease. Alzheimers Dement. 2014 Dec 19; PubMed.
- Öhrfelt A, Brinkmalm A, Dumurgier J, Brinkmalm G, Hansson O, Zetterberg H, Bouaziz-Amar E, Hugon J, Paquet C, Blennow K. The pre-synaptic vesicle protein synaptotagmin is a novel biomarker for Alzheimer's disease. Alzheimers Res Ther. 2016 Oct 3;8(1):41. PubMed.
- Kocis P, Tolar M, Yu J, Sinko W, Ray S, Blennow K, Fillit H, Hey JA. Elucidating the Aβ42 Anti-Aggregation Mechanism of Action of Tramiprosate in Alzheimer's Disease: Integrating Molecular Analytical Methods, Pharmacokinetic and Clinical Data. CNS Drugs. 2017 Jun;31(6):495-509. PubMed.
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