A first-in-class Alzheimer’s therapeutic met its primary endpoint in a Phase 2a trial, according to topline results released by the drug’s sponsor, Probiodrug in Halle, Germany. The compound, PQ912, inhibits an enzyme that produces pyroglutamate Aβ, a particularly sticky form of the peptide that may give rise to amyloid plaques. The main goal of the Phase 2a SAPHIR trial was to determine the safety and tolerability of a high dose of PQ912 over a three-month period. The compound appeared safe, though some participants had trouble tolerating it, with gastrointestinal and skin reactions that faded over time. The researchers did not expect to see a clinical effect in this short time frame, so they were pleasantly surprised to see brain electrical rhythms normalize in the treatment group; this measure suggests more coordinated synapse function. Participants taking PQ912 also bested controls on one of seven neuropsychology tasks. Biomarkers of synapse health and inflammation moved in the hoped-for direction in the treatment group, as well.
“These preliminary results encourage us to go on to a longer study with more endpoints,” said Philip Scheltens at VU University Medical Center, Amsterdam, who was the principal investigator on the study.
Other researchers agreed that the findings merit further development of the drug. “Although I am a bit concerned about the adverse events, the results obtained after such a short treatment period show that the target, the treatment strategy, and the compound are very promising,” Dieter Willbold at Forschungszentrum Jülich, Germany, wrote to Alzforum.
The story around pyroGlu Aβ, which forms when Aβ loses its first two amino acids and the enzyme glutaminyl cyclase (QC) links up the ends of the exposed glutamate residue to make a circle, has been building for a decade. Independent studies have found that pyroGlu Aβ correlates with disease severity and abounds in amyloid plaques in both AD animal models and postmortem brains. Some researchers suggest it may seed plaques, though that is not universally accepted (see May 2007 conference news; Apr 2008 conference news; Dec 2009 conference news). Oligomers of pyroGlu Aβ appear particularly neurotoxic and can corrupt normal Aβ42 (see Nov 2010 conference news; May 2012 news).
Researchers at Probiodrug developed their QC inhibitor PQ912 to turn down production of pyroGlu Aβ. Phase 1 trials on healthy young and elderly volunteers demonstrated that several different doses of the drug were safe for short periods (see Mar 2013 conference news). The maximum dose of 800 mg twice daily demonstrated no ill effects when given for 11 days, Inge Lues at Probiodrug told Alzforum. In the present Phase 2a trial, the researchers wanted find out how well a high dose would be tolerated over longer treatment periods, Lues said.
The researchers recruited 120 people with biomarker evidence of AD at 21 sites in seven European countries. Participants were at early stages of the disease, with a mean MMSE of 25.5. The trial enrolled only people who were not taking acetylcholinesterase inhibitors or memantine. This was done to minimize noise in the data and better detect any signal on cognitive testing and brainwave activity, Lues noted. Scheltens said this requirement made recruitment difficult at first, but as the trial progressed, positive word of mouth allowed the researchers to attract more patients than the original goal. Participants were randomized to receive either 800 mg twice daily of PQ912 or placebo for 12 weeks.
The treatment appeared safe, with no difference in the number of adverse events or serious adverse events between the placebo and treatment arms. However, tolerability was an issue. During the first eight weeks of the study, 27 people in the treatment arm either temporarily or prematurely stopped taking the medication due to side effects, compared with six people in the placebo group. The most common problem was skin rashes or itching, which resolved when the drug was stopped. In the final month of the study, participants reported no problems. This suggests people adapt to the dosage over time, Lues said. In future trials, the researchers are considering titrating the dose up to give the body more time to adapt, she added.
On the exploratory measures, the researchers saw a highly significant (p=0.002) effect on brainwave activity, as measured by EEG. In early AD, theta rhythms peak while alpha power wanes (see Moretti et al., 2009; Montez et al., 2009). In the PQ912 treatment arm, both measures became more normal, with theta power decreasing and alpha rising. The results fit with the hypothesis that pyroGlu Aβ oligomers poison synapses, and that their absence allows brain function to normalize, Lues noted. The researchers are still analyzing fMRI data to find out if functional connectivity changed in the participants.
In keeping with the EEG results, people on PQ912 performed better on the One Card Back test, which measures working memory, compared to their baseline performance. The placebo group remained stable on this measure. The treatment group also had a trend toward improvement on a test of attention, but no difference from placebo on five other measures.
Finally, the researchers saw encouraging trends on several cerebrospinal fluid markers. The synaptic protein neurogranin rises in CSF during AD, apparently reflecting synaptic damage (see Sep 2015 news; Sep 2015 news). On drug, neurogranin edged down. The decline missed significance, but the researchers noted that if they excluded from analysis three patients who started taking donepezil during the trial, the results became significant.
Meanwhile, the inflammatory marker YKL40 fell in treated patients, also just shy of significance. Besides modifying Aβ, the enzyme QC also activates chemokines and spurs an inflammatory response. Thus, QC inhibitors may have a second mechanism of action that quiets the immune response, noted Hans-Ulrich Demuth from the Fraunhofer Institute for Cell Therapy & Immunology, Leipzig, Germany. Demuth helped found Probiodrug and now advises the company. The researchers examined CSF Aβ and tau as well, but saw no change in these AD biomarkers. Lues noted this was not expected in such a short study.
The CSF also provided signals that PQ912 was hitting its target. QC was inhibited by 92 percent in patients on drug, in agreement with Phase 1 data for this dose. Levels of pyroGlu Aβ oligomers in CSF appeared to drop, but Lues noted that this data should be interpreted cautiously, since levels in the CSF are so low that they are at the limit of detection for the assay. Additional analysis from the SAPHIR trial will be presented at the 2017 Clinical Trials on Alzheimer’s Disease conference in Boston in November.
The researchers plan to test several doses in future trials, and for longer time periods, Lues said. Animal studies show that inhibiting QC by 60 percent is sufficient for cognitive benefits. This level of inhibition can be achieved with a dose of 150 or 200 mg twice daily in people, she noted. “That makes us confident we can lower the dose,” Lues told Alzforum. In future trials, participants will be allowed to take acetylcholinesterase inhibitors.
Probiodrug also develops an antibody against pyroGlu Aβ that it plans to take to the clinic (see Nov 2015 conference news). Eli Lilly tested a similar antibody; it lowered brain amyloid load in Phase 1, but produced an adverse immune reaction (see Aug 2016 conference news).—Madolyn Bowman Rogers
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- Moretti DV, Fracassi C, Pievani M, Geroldi C, Binetti G, Zanetti O, Sosta K, Rossini PM, Frisoni GB. Increase of theta/gamma ratio is associated with memory impairment. Clin Neurophysiol. 2009 Feb;120(2):295-303. PubMed.
- Montez T, Poil SS, Jones BF, Manshanden I, Verbunt JP, van Dijk BW, Brussaard AB, van Ooyen A, Stam CJ, Scheltens P, Linkenkaer-Hansen K. Altered temporal correlations in parietal alpha and prefrontal theta oscillations in early-stage Alzheimer disease. Proc Natl Acad Sci U S A. 2009 Feb 3;106(5):1614-9. PubMed.