Many Alzheimer’s drugs that looked promising in animal and cell culture studies have failed in clinical trials. A paper in the December 17 Stem Cell Reports proposes a new explanation for one such class of drugs, namely γ-secretase modulators (GSMs) derived from nonsteroidal anti-inflammatory drugs (NSAIDs). Researchers led by Philipp Koch at the University of Bonn, Germany, found that these compounds failed to lower Aβ42 in human neurons when added at concentrations comparable to those achieved in human trials. By contrast, at these same concentrations the drugs robustly suppressed Aβ42 production in rodent and human cell lines typically used in preclinical studies. The data, published online December 5, highlight the importance of testing AD drugs in human neurons, the authors suggest. It is unclear if the findings have any relevance for the second-generation GSMs now under investigation. These drugs are as much as 1,000 times more potent than the NSAID derivatives, and have a different mechanism of action (see Sep 2011 news story; Kretner et al., 2011; Borgegard et al., 2012).  

“This is an important paper that highlights the need to develop human cell models to study AD,” Lawrence Rajendran at the University of Zurich wrote to Alzforum. He was not involved in the work. The study hints that γ-secretase might be regulated or localized differently in distinct cell populations, he suggested.

NSAID-based GSMs effectively lowered Aβ42 in preclinical studies both in vitro and in vivo, but Phase 2 and 3 trials were negative (see, e.g., Aug 2008 conference story; Vellas 2010). Because these compounds poorly enter the brain, researchers concluded that not enough of the drug reached its target.

Koch wondered if the target cell population might also play a role. To test this idea, first author Jerome Mertens generated human neuronal cultures from induced pluripotent stem cells made from fibroblasts of two familial AD patients and three controls (see image below). As expected, the AD neurons had higher ratios of secreted Aβ42/Aβ40 than did control cells. Addition of the high dose of 200 μM of four different NSAID-based GSMs (flurbiprofen, indometacin, diclofenac, and ibuprofen) cut this ratio by 25 percent or more in both AD and control neurons, showing that the drugs worked. However, in people these compounds are estimated to reach only the low micromolar range in the brain (see Bannwarth et al., 1990; Galasko et al., 2007). At these more realistic concentrations ranging from 1 to 80 μM, the authors saw no effect on secreted Aβ. By contrast, at these concentrations the GSMs squelched the Aβ42/Aβ40 ratio by around 50 percent in APP-overexpressing cell lines made from Chinese hamster ovaries and human embryonic kidney.

Neurons derived from iPS cells express tau (red) and beta III tubulin (green). They were used to test γ-secretase modulators. Image courtesy of Stem Cell Reports, Mertens et al. 2013

The findings show that, compared to other cell types, human neurons resist the effects of first-generation GSMs. The mechanism remains unclear. The authors did not test whether mouse neurons were also insensitive to these drugs. There is conflicting literature on this, with early pharmaceutical studies showing benefits in transgenic mouse models, while other studies have found little effect on Aβ in rodent brain and neuronal cultures (see Lanz et al., 2005; Stock et al., 2006; Carreras et al., 2013).—Madolyn Bowman Rogers

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References

News Citations

  1. Evidence Mounts That Some γ-Secretase Modulators Bind Presenilin
  2. Chicago: Flurizan Postmortem

Paper Citations

  1. . Attenuated Abeta42 responses to low potency gamma-secretase modulators can be overcome for many pathogenic presenilin mutants by second-generation compounds. J Biol Chem. 2011 Apr 29;286(17):15240-51. PubMed.
  2. . First and Second Generation γ-Secretase Modulators (GSMs) Modulate Amyloid-β (Aβ) Peptide Production through Different Mechanisms. J Biol Chem. 2012 Apr 6;287(15):11810-9. PubMed.
  3. . Tarenflurbil for Alzheimer's disease: a "shot on goal" that missed. Lancet Neurol. 2010 Mar;9(3):235-7. PubMed.
  4. . Plasma and cerebrospinal fluid concentrations of indomethacin in humans. Relationship to analgesic activity. Eur J Clin Pharmacol. 1990;38(4):343-6. PubMed.
  5. . Safety, tolerability, pharmacokinetics, and Abeta levels after short-term administration of R-flurbiprofen in healthy elderly individuals. Alzheimer Dis Assoc Disord. 2007 Oct-Dec;21(4):292-9. PubMed.
  6. . Lack of specific amyloid-beta(1-42) suppression by nonsteroidal anti-inflammatory drugs in young, plaque-free Tg2576 mice and in guinea pig neuronal cultures. J Pharmacol Exp Ther. 2005 Jan;312(1):399-406. PubMed.
  7. . The geminal dimethyl analogue of Flurbiprofen as a novel Abeta42 inhibitor and potential Alzheimer's disease modifying agent. Bioorg Med Chem Lett. 2006 Apr 15;16(8):2219-23. PubMed.
  8. . R-flurbiprofen improves tau, but not Aß pathology in a triple transgenic model of Alzheimer's disease. Brain Res. 2013 Dec 6;1541:115-27. Epub 2013 Oct 22 PubMed.

Further Reading

Primary Papers

  1. . APP Processing in Human Pluripotent Stem Cell-Derived Neurons Is Resistant to NSAID-Based γ-Secretase Modulation. Stem Cell Reports. 2013;1(6):491-8. Epub 2013 Dec 5 PubMed.