13 Dec 2013

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.

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 16 Sep 2011
2. Chicago: Flurizan Postmortem 20 Aug 2008

Paper Citations

1. Kretner B, Fukumori A, Gutsmiedl A, Page RM, Luebbers T, Galley G, Baumann K, Haass C, Steiner H. 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. Borgegard T, Juréus A, Olsson F, Rosqvist S, Sabirsh A, Rotticci D, Paulsen K, Klintenberg R, Yan H, Waldman M, Stromberg K, Nord J, Johansson J, Regner A, Parpal S, Malinowsky D, Radesater AC, Li T, Singh R, Eriksson H, Lundkvist J. 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. Vellas B. Tarenflurbil for Alzheimer's disease: a "shot on goal" that missed. Lancet Neurol. 2010 Mar;9(3):235-7. PubMed.
4. Bannwarth B, Netter P, Lapicque F, Péré P, Thomas P, Gaucher A. Plasma and cerebrospinal fluid concentrations of indomethacin in humans. Relationship to analgesic activity. Eur J Clin Pharmacol. 1990;38(4):343-6. PubMed.
5. Galasko DR, Graff-Radford N, May S, Hendrix S, Cottrell BA, Sagi SA, Mather G, Laughlin M, Zavitz KH, Swabb E, Golde TE, Murphy MP, Koo EH. 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. Lanz TA, Fici GJ, Merchant KM. 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. Stock N, Munoz B, Wrigley JD, Shearman MS, Beher D, Peachey J, Williamson TL, Bain G, Chen W, Jiang X, St-Jacques R, Prasit P. 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.

Other Citations

1. Carreras et al., 2013

Further Reading

News

1. Surprise! Some γ-Secretase Modulators Work by Targeting APP 13 Jun 2008
2. Research Brief—Flurizan Fails Final Hurdle, Company Discontinues Drug 2 Jul 2008
3. New γ-Secretase Modulators Reduce Aβ42, Avoid Notch 12 Sep 2010
4. Barcelona: Allosteric γ Modulation Moves Toward Clinic 1 Apr 2011
5. Paper Alert: γ-Secretase Modulators Trump Inhibitors 9 Feb 2012
6. More Evidence that γ-Secretase Modulators Spare Essential Substrates 9 Aug 2013