At AD/PD Meeting, New BACE Inhibitor Struts Its Stuff
Striving to be noticed in the hoopla over Biogen’s Phase 1 aducanumab data, other investigational therapies presented clinical data at the 12th International Conference on Alzheimer’s and Parkinson’s diseases, held March 18 to 22 in Nice on France’s Cote d’Azur. Consider JNJ-54861911. As recently as two years ago, a once-a-day drug that cuts CSF Aβ levels near to the ground in Phase 1 would have been big news. But by 2015, the field is not only replete with β-secretase inhibitors, but also enraptured—at least at the moment—by an antibody that teased an audience far beyond this research conference with hints of potential efficacy (see Part 1 of this series).
Yet the new BACE inhibitor is well worth noting. For one thing, some of its competition has since fallen by the wayside (e.g., Feb 2015 news, RG7129). For another, in offering details on the compound’s performance thus far, its developers showcased how the science of evaluating this type of drug is evolving. In Nice, Johannes Streffer of Janssen Research and Development in Beerse, Belgium, described the behavior, in the plasma and CSF of healthy volunteers, of a BACE inhibitor Janssen had licensed in 2012 from the Japanese pharmaceutical company Shionogi. Streffer’s talk afforded a peek at how early human trials nowadays are using continuous CSF monitoring and beginning to look more broadly at APP cleavage products beyond Aβ40 and 42.
Streffer and colleagues evaluated this molecule in volunteers of the same age range as Alzheimer’s patients who were willing not only to take an unproven drug, but also to live for 36 hours with a catheter implanted in their back so the researchers could sample their CSF frequently and learn how the levels of certain biomarkers change over time. For a single-ascending-dose study, people wore the catheter for the whole study. For a second, multiple-ascending-dose study that lasted two weeks, volunteers agreed to a lumbar puncture at baseline followed by a 36-hour CSF catheter at the end of the study. The goal was to learn about the drug’s safety and tolerability, its reach into plasma and CSF, and its target engagement as measured by various effects on APP processing.
On safety—a closely watched subject for BACE inhibitors—Streffer said what most BACE inhibitor developers have said early in Phase 1, that is, no worrisome side effects related to the drug are yet in sight. Two people vomited, but most side effects were a consequence of the lumbar catheter and all were mild or moderate. In the studies Streffer reported at AD/PD, 94 people were exposed to the drug. “Overall, the inhibitor was very well tolerated,” Streffer told the audience. Unlike therapy with anti-Aβ antibodies, the participants’ ApoE genotype had no influence on safety or any outcome measured thus far for this small-molecule drug, Streffer reported.
JNJ-5486911 shoots into the plasma fast, reaching its peak concentration after one to two hours and washing out over nine to 16 hours. In the CSF the curve is slower, peaking at two to three hours and waning over the course of 36 hours. Importantly, drug levels in CSF are proportional to those in plasma, and dose-dependent, Streffer said. In people who took their randomized dose for two weeks, the drug reached a steady-state level after about a week. Studying a drug’s concentration in the body over time is important so researchers know it neither accumulates to dangerous levels nor gets metabolized to toxic byproducts before it reaches its target.
To measure what the drug does to APP, the scientists used an electrochemiluminescence-detection platform by Meso Scale Discovery, one of the companies competing with Roche Diagnostics and Fujirebio Europe (formerly Innogenetics) to make more robust assays for CSF analysis. On it, they used their own antibodies to quantify Aβ1-37, Aβ1-38, Aβ1-40 and Aβ1-42 simultaneously. They also used a combination of in-house and commercial MSD antibodies to quantify sAPPα, sAPPβ, and sAPP total in the presence of inhibitor. This set of tests captures aspects of what happens to BACE’s substrate when the enzyme is blocked. It includes some known Aβ species, though not the whole range that has emerged in recent mass spectrometry work, such as Aβ1-16, Aβ1-43, or N-terminally extended or N-terminally truncated or pyroglutamated species. Streffer said that reagents for some of these other species were in hand and would be studied, as well.
Looking first at the most abundant type of Aβ, the 1-40 peptide, Streffer reported that plasma and CSF are a bit different. In plasma, Aβ40 goes down in lockstep with inhibitor concentration going up. The reduction is dose-dependent and lasts longer than 36 hours after a single dose, Streffer said. Lower doses—in the range the company will take forward—reduced Aβ40 for about a day. The CSF showed a delayed and more protracted reaction, with Aβ40 concentrations going down dose-dependently after about eight hours. Streffer related the time course of the inhibitor’s pharmacodynamic response to the time course of newly produced Aβ in the brains of healthy people as measured by the SILK method (Mawuenyega et al., 2013), and concluded that the drug inhibits production of Aβ in the brain.
At the end of two weeks on the inhibitor, plasma and CSF Aβ40 stayed where they had been for another 24 to 36 hours: 5 mg cut CSF Aβ40 in half, and the 30, 50, and 90 mg doses pushed it below 20 percent. Claiming that his team has focused intense effort on eliminating variability from its CSF measurements, Streffer showed spaghetti graphs—flat lines of Aβ40 levels below 20 percent of baseline—from five study participants who had taken 50 mg of inhibitor for two weeks. “We have very stable CSF Aβ measurements now,” Streffer said. Variability at many levels—between centers, manufacturing lots, and test-retest of the same sample—has bedeviled CSF analysis in AD research for years. This appears to be on the verge of changing with the advent of new assays (see upcoming story in this series).
Like most drug developers these days, Janssen draws design help for larger trials from a quantitative pharmacokinetics model, essentially an in-silico oracle that puts Phase 1 data through a set of mathematical algorithms and draws a dose-response curve, among other outputs. In response to audience questions, Streffer replied that no one truly knows yet how much Aβ reduction is necessary for a clinical benefit, but his company picked 10 and 50 mg for their latest Phase 1b and 2a safety studies in early Alzheimer’s. “Even 25 mg achieves a solid 80 percent reduction of Aβ,” Streffer said.
How this BACE inhibitor is being developed stands in contrast to the strategy behind Biogen’s antibody BIIB037/aducanumab. The latter underwent two Phase 1 studies in a total of about 230 people, and skips Phase 2 to enter Phase 3 later this year. For JNJ-54861911, clinicaltrials.gov lists 10 Phase 1 studies. Its first Phase 2 trial tests safety plus similar dose, exposure, and target engagement biomarkers, as summarized in this story, for a six-month course of the drug; it makes no mention of cognitive or clinical efficacy at all. For a summary of trials on this compound, see JNJ-5486911.
After BACE has cleaved APP, its product C99 undergoes sequential processing by γ-secretase that yields not only Aβ40, but also longer and shorter versions of the peptide. Basic researchers have long argued that drug developers should know how all of them change, not just one or two. For example, Bart De Strooper of KU Leuven, Belgium, has called for an unbiased, comprehensive accounting of all cleavage products with mass spectrometry before taking a potential Alzheimer’s drug into expensive, high-profile trials. That would catch any potentially toxic APP byproducts early on, before they could trip up an investigational therapy. “If you inhibit one enzyme, another will take over,” De Strooper told Alzforum. Pharma companies tend to resist collecting more data than they think they need or can explain, or to adopt scientific methods they consider research-grade.
That said, Streffer’s team did branch out beyond studying Aβ40 and 42. At AD/PD, he reported that Aβ37, 38, 40, and 42 were reduced equally in CSF. What happens to APP when BACE is blocked? To address this question, the scientists profiled sAPPβ, the other product of APP cleavage by BACE besides C99; sAPPα, the product of APP cleavage by α-secretase, and sAPP total. At any given inhibitor dose, Aβ40 and sAPPβ dropped down to identical levels, Streffer said. This would be expected if both arise one-to-one from APP cleavage blocked by this compound. The concentration of sAPPα rose with increasing inhibitor doses, up to about 2.5-fold. sAPP total stayed unchanged at all doses. To Streffer’s mind, the decrease of sAPPβ was “very reassuring,” and the increase of sAPPα was “not concerning for the therapy.” sAPPα is thought to be non-toxic.
APP processing is drawing renewed interest in the field. Researchers continue to hunt for additional enzymes they suspect might cleave APP when BACE is out of commission. This, some believe, could generate additional fragments that warrant further study.—Gabrielle Strobel
- Mawuenyega KG, Kasten T, Sigurdson W, Bateman RJ. Amyloid-beta isoform metabolism quantitation by stable isotope-labeled kinetics. Anal Biochem. 2013 Sep 1;440(1):56-62. PubMed.
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