21 Dec 2019

For therapies taking aim at Alzheimer’s disease, exerting an effect in the brain seems critical. And obvious. But according to results on display at 12th Clinical Trials on Alzheimer’s Disease conference, held December 4–7 in San Diego, California, a therapy might also influence the brain without ever entering it. Researchers reported that apabetalone, a drug that tweaks expression of hundreds of genes via an epigenetic mechanism, reduced inflammatory proteins in the blood, including those that make inflammation-stoking leukocytes cling to blood vessel walls. Apabetalone appeared to slow cognitive decline, but only among those who were most impaired at baseline. Separately, a fresh statistical analysis of AMBAR—a trial that evaluated a plasma-exchange protocol—claimed a cognitive benefit in people with moderate AD, and hinted it could work in people with milder disease. Both trials were plagued by the limitation that they did not use biomarkers to select people who truly had AD, muddling signs of efficacy.

Apabetalone exerts its sway by inhibiting Bromodomain Extraterminal Domain (BET) proteins, which bind to the acetylated lysines that mark open, active stretches of chromatin. BET proteins then recruit transcription factors to the scene to switch on gene expression. Apabetalone essentially blocks the association between BET and acetylated lysines, squelching transcription of hundreds of genes. Previously, researchers reported that BET proteins drove the expression of myriad genes involved in inflammation, lipid metabolism, and vascular function, casting apabetalone as a candidate treatment for cardiovascular and other chronic diseases of aging.

At the AD/PD meeting in Lisbon earlier this year, Ewelina Kulikowski of Resverlogix, the Calgary-based company developing the drug, reported that in cell culture, apabetalone blocked expression of pro-inflammatory cytokines and leukocyte adhesion molecules on vascular endothelial cells; this kept monocytes from latching onto them (May 2019 conference news). Apabetalone also spared LPS-ravaged mice from damaging neuroinflammation.

At CTAD, Kulikowski presented data suggesting the drug douses vascular inflammation in people, too. She measured more than 1,300 proteins within plasma samples collected from 94 participants in the ASSURE trial, which evaluated a 26-week course of 200 mg of apabetalone for its effect on atherosclerotic plaques in people with cardiovascular disease (Nicholls et al., 2016). Kulikowski found that between baseline and 26 weeks, samples from the apabetalone group had significant drops in inflammatory mediators, particularly chemokines and cell adhesion receptors known to snag circulating leukocytes and rev up vascular inflammation.

Many of the genes targeted by apabetalone were downstream of tumor necrosis factor α (TNFα), a master regulator of inflammation. Overall, her findings suggested that apabetalone could nip TNFα-driven inflammatory responses in the bud, quell vascular inflammation—and just maybe limit the chronic activation of glial cells on the other side of the blood-brain barrier.

The potential role of TNFα in neuroinflammation and neurodegenerative disease jibes with other findings presented at CTAD. Mark Gurney of Tetra Therapeutics in Grand Rapids, Michigan, and Mengshi Zhou of Case Western Reserve University in Cleveland accessed medical records on more than 56 million people—roughly 20 percent of the U.S. population. They reported that among people with chronic inflammatory conditions such as rheumatoid arthritis, psoriasis, inflammatory bowel disease, and Crohn’s disease, those who took TNFα-blocking drugs had as much as a 60 percent lower risk of AD, depending on the condition and drug used.

Jeffrey Cummings of the Cleveland Clinic’s Lou Ruvo Center for Brain Health in Las Vegas followed Kulikowski’s talk with cognitive data from the BETonMACE trial, a Phase 3 study that tested whether apabetalone could prevent major cardiovascular events in people with high cardiovascular risk. Participants in the trial had Type 2 diabetes, a recent brush with acute coronary syndrome, and low levels of high-density lipoprotein (HDL) at baseline. The trial continued until 250 cardiovascular events had occurred. Though the drug trended toward reducing cardiovascular events, the effect did not meet statistical significance. Of the 2,425 people enrolled in the trial, 469 people over the age of 70 took part in a prespecified cognitive sub-study. It assessed scores on the Montreal Cognitive Assessment (MoCA) at baseline, at one year, and at the last treatment visit, which was at an average of 27 months. Participants were split into three groups based on their baseline MoCA score: 26 or higher (cognitively normal); 22–25 (MCI); or 22 and below (MCI to AD).

In San Diego, Cummings reported that while MoCA scores declined slightly or remained stable in treatment and placebo groups among participants in the two high MoCA groups, those with the lowest baseline MoCA scores appeared to benefit from treatment. Among the 97 participants in this subgroup, those taking apabetalone improved by an average of three points on the test between baseline and 27 months, whereas those on placebo, oddly, improved by 1 point. Breaking the scores down by cognitive domain, Cummings reported that the treatment group posted significant improvements on the abstraction and recall portions of the MoCA. Interestingly, Cummings found that differences between the treatment and placebo groups only emerged between 52 weeks and the final visit. The MoCA is a cognitive screen, which includes 30 questions and takes about 10 minutes to administer.

Based on these results in people with cardiovascular disease, as well as apabetalone’s effects on markers of vascular inflammation, Cummings believes the drug assuages cognitive impairment by targeting the inflamed vasculature. Whether it is more effective at treating people with vascular dementia or AD remains to be determined. BETonMACE was not designed as an AD trial, so the researchers did not measure AD biomarkers. However, given recent advances in plasma biomarker tests, Cummings told the audience that existing plasma samples from the participants will be tested for Aβ42/40 ratio, p-tau-181, neurofilament light (NfL), YKL-40, and other markers.

The idea that an inflamed vascular endothelium—especially within the vessels that comprise the blood brain barrier—might damage brain health and cognition jibes with recent studies from Tony Wyss-Coray’s group at Stanford University. He reported that with age, brain endothelial cells ramp up expression of vascular adhesion molecule 1 (VCAM1), which tethers circulating leukocytes to the endothelium and transmits inflammation-stoking, neurogenesis-dousing signals into the brain (Jul 2018 news; May 2019 news). More recently, the group took stock of the plasma proteome in more than 4,000 people between the ages of 18–95. In this month’s issue of Nature Medicine, the scientists report waves of proteomic changes correlating with specific biological pathways and age-related disease, rising in the plasma in the fourth, seventh, and eighth decades of life (Lehallier et al., 2019). 

Similarly, researchers at Alkahest, a San Carlos, California-based company co-founded by Wyss-Coray, recently identified specific proteins in the plasma that helped transmit damaging effects to the brain (Dec 2018 news). As they are hunting for bad actors in aging plasma, Alkahest scientists are also looking for good ones.

At CTAD, Jonas Hannestad presented data from the company’s trial of GRF6019, a plasma fraction that reportedly contains factors that promote a youthful brain. Forty-seven participants with mild to moderate AD were randomized to receive 100 mL or 250 mL doses, infused daily during two five-day inpatient stints at weeks one and 13. There was no placebo. Hannestad reported that participants did not decline on either the ADAS-Cog or MMSE over the six-month trial period, but did slide on the ADCS-ADL over that time. Hannestad used data from placebo groups in published clinical trials as well as in ADNI to argue that GRF6019 slowed cognitive decline. The true test will come from a placebo-controlled trial, which is being planned, Hannestad said.

AMBAR—Elaborate Sham Procedure, or Intensive Alzheimer’s Therapy?
A new look at results from another plasma-based therapy stirred up debate at CTAD. In a roundtable discussion, scientists sliced and diced results from Alzheimer’s Management by Albumin Replacement (AMBAR), a Phase 2b/3 trial performed between 2012 and 2018 that tested a 14-month regimen of repeated plasmapheresis with albumin replacement. In a nutshell, researchers had proposed that removing plasma albumin—which is laden with Aβ and myriad other proteins—and replacing it with fresh albumin could cleanse the blood and act as a peripheral Aβ sink. The trial enrolled 322 participants, of whom 232 completed the trial. It had three treatment arms—one that replaced albumin, and two that added different doses of intravenous immunoglobulin (IVIG) to the replacement fluid. The placebo group received a complicated sham procedure, in which only small volumes of plasma were removed.

Antonio Páez of Grifols, based in Barcelona, presented top-line results of the Phase 2b/3 study last year at CTAD (Nov 2018 news). Essentially, the trial met one of its two co-primary endpoints, and when the three treatment groups were pooled, they declined 52 percent less on the ADCS-ADL than those on the sham procedure, with a p value of 0.03. The combined group declined by 66 percent less on the ADAS-Cog, but this result missed significance, with a p value of 0.06. In a prespecified analysis that split the cohort into two groups based on baseline MMSE scores, people with mild dementia barely declined, while those with moderate dementia did. The treatment thus had no effect on either endpoint in the mild group, though the moderate group had a highly significant treatment effect on the ADCS-ADL and a near-significant one—with a p value of 0.054—on the ADAS-Cog.

In San Diego, Páez presented a more detailed analysis of that data and new findings from secondary outcome measures. Among all participants, the combined treatment groups had 71 percent less decline on the Clinical Dementia Rating Scale Sum of Boxes (CDR-SB) and 100 percent less decline on the Alzheimer Disease Research Center Clinical Global Impression of Change (ADCS-CGIC) over 14 months, he said. Participants in the mild group significantly improved on both these measures in response to treatment, while the treatment appeared to slow decline within the moderate AD group. Across all cognitive outcome measures, participants in all three treatment groups appeared to perform similarly, while the placebo group diverged.

Páez showed some CSF biomarker data, reporting stabilization of Aβ42, tau, and p-tau in the treatment groups relative to placebo. These effects were only significant in the moderate group, for Aβ42 and tau.

Páez also reported that according to CSF Aβ42 measures, 72 percent of people in the trial had brain amyloid accumulation. Amyloid status was not confirmed at screening. Fewer people in the mild AD group—65 percent—had abnormal CSF Aβ42 than in the moderate group, in which 79 percent did. This suggests that 35 and 21 percent of the participants in the mild and moderate groups, respectively, had an underlying reason for their cognitive impairment or dementia other than Alzheimer’s disease. At CTAD, Páez did not present outcome measures broken down by amyloid status.

Suzanne Hendrix of Pentara Corporation followed Páez’s talk with additional statistical analyses of the trial data. She emphasized that her analyses were intended to inform the design of future trials, not “rewrite the story with post hoc analysis.” Hendrix normalized and combined data from the ADAS-Cog, ADCS-ADL, and CDR-SB into one overall score, called a global statistical test. Hendrix considers GST a way to assess consistency between multiple outcome measures. In so doing, she found a statistically significant effect of treatment, with an effect size of 100 percent on the GST at nine, 12, and 14 months.

Analyzing potential consequences of the 28 percent of people who left the trial; Hendrix concluded that, if anything, the dropouts reduced any apparent treatment effect. She also looked at interactions between treatment responses and MMSE scores as a continuum, as opposed to mild versus moderate groups, and concluded that the treatment had an effect on some measures within some people classified as mild. Given the consistency of responses across outcome measures, and large effect sizes, the treatment is likely to be exerting a true effect, and should be further tested in people in both mild and moderate stages of impairment, she believes.

In questions following the talks, and in hallway conversations outside, researchers discussed what, if anything, the new data added to the interpretation. Like many others, Stephen Salloway of Brown University in Rhode Island was unmoved by data from additional outcome measures, noting they were not corrected for multiple comparisons. Paul Aisen at the University of Southern California, San Diego, questioned how “alpha spending” was done, given the myriad analyses and outcomes presented. Hendrix responded that beyond the two co-primary outcome measures analyzed by the MMSE subgroup, all analyses were purely descriptive.

Others questioned whether the sham procedure adequately blinded participants. It used a lower volume than the real procedure, and Salloway noted that plasmapheresis triggers a consistent physiological response, including a lowering of body temperature, so it could have been obvious whether a person was undergoing the real deal or not. Larry Honig of Columbia University in New York pointed out to the panel that the fact that all three treatment groups tracked together across measures, while the placebo group declined, suggests that participants knew whether they were receiving plasma exchange or not. He was unconvinced that the sham worked.

Hendrix and Grifols scientists countered that if the effects had all been due to unblinding, one would have expected larger treatment effects in subjective measures, which are more prone to a placebo effect, than in more objective measures. The one co-primary endpoint that was met—the ADCS-ADL—is a subjective measure; still, Hendrix considers the similar direction of effect across measures compelling. She noted that people in the placebo group became less depressed as the trial went on, suggesting they thought they were receiving a treatment. People in the mild dementia group also would have been more likely affected by knowledge of their treatment group than those in the moderate AD group, Hendrix and Grifols scientists agreed after the talk.

Lon Schneider of the University of Southern California, Los Angeles, commended the AMBAR investigators for responding to questions from the field, and running and presenting further analyses. Even so, he saw problems with the trial beyond the possibility of unblinding. For one, there was no dose response, and there were more infections in members of the treatment group who did not receive IVIG, which he found concerning and confusing. He wondered whether there were differences in outcomes, or infections, between people who received central versus peripheral lines to perform the procedure.

Babak Tousi of the Cleveland Clinic, a participating trial site, believes the sham procedure did blind participants. “If people knew they were receiving placebo, would they have come back to take part in this intensive procedure month after month?” he asked. The placebo group had fewer dropouts than the treatment groups. That all three treatment groups performed similarly across measures suggests removal of pathogenic proteins from the blood confers the treatment effect, rather than what was added back in, Tousi believes.

David Morgan of Michigan State University in Grand Rapids questioned the investigators on the premise of their trial. How, exactly, do they think their treatment works? Páez responded that drawing Aβ from the brain via removal of Aβ-albumin complexes from the blood was the initial premise, but it now appears likely that removal of other proteins from the blood contributed. The researchers did not present a subgroup analysis of people with or without brain amyloid, but Hendrix said such an analysis had been performed. She said even people without brain amyloid responded to treatment, at least on some measures. This suggests the procedure may confer broader benefits, Páez said.

Noting that the procedure was quite intensive, Morgan asked whether the scientists were attempting to zero in on which proteins needed to be removed, which would facilitate specific targeting. Páez responded that to do that, they would first need to figure out the etiology of AD.

Researchers wanted to know how Grifols would move forward, given the lack of difference between the treatment arms. Would they evaluate plasmapheresis with albumin replacement only, or continue to add back IVIG? Páez said that theoretically, any of the treatment regimens would be suitable for a future trial. However, he noted that they are considering the safety data. For example, fewer people in the IVIG groups came down with infections during the study. It is unclear why this was the case, Páez said, but this is something Grifols is investigating moving forward.—Jessica Shugart

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References

Therapeutics Citations

1. Apabetalone
2. GRF6019

News Citations

1. Antibodies Against Microglial Receptors TREM2 and CD33 Head to Trials 10 May 2019
2. VCAM1: Gateway to the Aging Brain? 17 Jul 2018
3. Paper Alert: VCAM1 Opens the Door to Brain Aging 18 May 2019
4. How Immune Cells From Blood Beget Aging in Brain 14 Dec 2018
5. Fits and Starts: Trial Results from the CTAD Conference 20 Nov 2018

Paper Citations

1. Nicholls SJ, Puri R, Wolski K, Ballantyne CM, Barter PJ, Brewer HB, Kastelein JJ, Hu B, Uno K, Kataoka Y, Herrman JP, Merkely B, Borgman M, Nissen SE. Effect of the BET Protein Inhibitor, RVX-208, on Progression of Coronary Atherosclerosis: Results of the Phase 2b, Randomized, Double-Blind, Multicenter, ASSURE Trial. Am J Cardiovasc Drugs. 2016 Feb;16(1):55-65. PubMed.
2. Lehallier B, Gate D, Schaum N, Nanasi T, Lee SE, Yousef H, Moran Losada P, Berdnik D, Keller A, Verghese J, Sathyan S, Franceschi C, Milman S, Barzilai N, Wyss-Coray T. Undulating changes in human plasma proteome profiles across the lifespan. Nat Med. 2019 Dec;25(12):1843-1850. Epub 2019 Dec 5 PubMed.

Further Reading

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