Researchers led by Martin Watterson at Northwestern University in Chicago, with colleagues near Strasbourg, France, have synthesized a series of small chemicals that could become the starting point for a drug development effort aimed at inhibiting inflammatory changes in glial cells without affecting inflammation elsewhere in the body. The paper also suggests a signal transduction pathway that might be a suitable target in trying to design glia-specific anti-inflammatory drugs. The paper was published online last week and will appear in the January 31 print edition of the Journal of Medicinal Chemistry.

These chemicals are 3-amino-6-phenyl-pyridazine derivatives, heterocyclic aromatics whose activity are reflected in what the authors call Compound 1. It inhibits the production of interleukin-1β (IL-1β ), inducible nitric oxide synthase (iNOS) and nitric oxide (NO) in cultured glial cells that were stimulated by treatment with Aβ1-42, an AβPP cleavage product shown to be neurotoxic. The study rests on the hypothesis that chronically activated glia produce excessive amounts of proinflammatory cytokines such as Il-1β, as well as oxidative-stress-related enzymes and acute-phase proteins, and that those together create an inflammatory state that damages neurons and spurs the onset of dementia. (See also polymorphism story below.)

Epidemiological results, though mixed, appear to support this notion in that non-steroidal antiinflammatory drugs (NSAIDs) can stem or slow AD (see related news item). However, currently available NSAIDs act systemically. Watterson's group has for the last three years tried to find compounds that would selectively inhibit glial signal transduction pathways leading to iNOS generation (Mirzoeva S. et al., 1999). They have focused on modulating glial-specific isoforms of calmodulin-dependent kinases (CaMKs). Yet the compounds they studied previously were analogs of natural products, which are generally too complex for the quick synthesis medicinal chemists require as they churn out derivatives to refine drug leads.

The present compound is different. It is based on a 1-(2-pyrimidyl) piperazine scaffold, a structure that can be manipulated easily and that is already present in other CNS-active compounds. In activated glia, Compound 1 inhibits Il-1β and iNOS production but leaves unaffected other glial functions, such as GFAP and glial apoE and COX-2 production.

While Watterson's group did not prove a definitive mechanism of action for their compound, further experiments suggest that it inhibits CaMKII but not p38 MAPK, which has been implicated in AD (Zhu X. et al. 2001) and is the target of drugs currently under development for rheumatoid arthritis. "We are especially interested in moving the effective concentration of Compound 1 lower while retaining selectivity and in extending the results to animal models of disease," said Watterson. The scientists hope to collaborate with industry to develop this early research further.—Gabrielle Strobel

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  1. Author's Response

    We read with interest the comments of Mark Smith and George Perry, which raise interesting philosophical points but do not directly address the results in our recent paper. In our peer-reviewed report, we describe a new class of synthetic compounds that selectively suppress certain glial activation processes, such as increases in oxidative stress-related enzymes and proinflammatory cytokines, and we demonstrate the mechanism of action is distinct from other classes of experimental therapeutics and FDA-approved drugs.

    Our comments in this and previous cited papers address the concept of homeostasis and its perturbation as a potential disease mechanism, especially of chronic diseases. Therefore, we agree with many of the points raised by Drs. Smith and Perry. We also agree that there are a number of potential pathways that can converge on a common disease end point. For this reason alone, it is important that early-stage discovery research seek to find new types of chemical compounds that have targets distinct from those that are the focus of currently available drugs or experimental therapeutics in late-stage drug development. Contemporary discovery research seeks to interfere early in the process, if the pathways being modulated by a new chemical compound are different, more selective, or have higher potency than what is currently available. Although our report deals with early- stage cell culture models, we show that our compounds have robust activity and target alternative pathways from current drugs, including aspirin and anti-oxidants. However, even if our current work in animal models shows efficacy of these new inhibitors, it is not until the stage of hypothesis-driven feasibility investigations in humans that reasonable arguments can be made about potential for success or failure. Even at the stage of human investigations, efficacy depends on choice of the appropriate treatment group and end points.

    Clearly, multi-factorial diseases of a chronic nature are candidates for multiple types of therapy that target different pathways. It is from this perspective that we would not want readers to interpret philosophical comments as hinting that the fear of failure should preclude innovative approaches to such devastating diseases. Early-stage discovery research is by its very nature high-risk. Even late-stage drug development, which is more structured, has a higher risk level than other areas of manufacturing. We and others, who seek to discover new ligands to modulate disease-relevant biological responses, accept the high probability of long-term failure in view of the impact of one long-term success. In this regard, we believe the hypothesis that suppression of selective glial activation responses may be a potential therapeutic approach deserves to be rigorously tested.

  2. Our new compounds appear to have a different mechanism of action from
    currently available inhibitors that target COX-2 or p38 MAPK pathways,
    suggesting that additional signal transduction pathways exist that can be
    targeted for glial activation and neuroinflammation. If currently available
    drugs fail to show the desired activity in clinical trials for AD and
    related diseases, then the elucidation of these alternative pathways becomes
    more important.

  3. Findings associating the pathology of Alzheimer disease (AD) with inflammatory cells led to epidemiological and clinical investigations showing that broad-based anti-inflammatories reduce the incidence of AD. Mirzoeva et al. describe a new antiinflammatory agent, 3-amino-6-phenyl-pyridazine, that is one of a series of proposed "specific" remedies that started with the cyclooxygenase 2 inhibitors and continues here with other pathways, such as inhibition of IL-1 and nitric oxide (NO) production. Unfortunately, specificity may not be better. Antiinflammatories, such as aspirin, are also powerful antioxidants, which, like "antiinflammatories" (sic), are effective in lowering the incidence of AD (Smith et al., 1999).

    As an aside, but an important one, one must ask what is the function of inflammation in AD? NO can act as an antioxidant as much as an oxidant (Perry et al.,2001). Additionally, are we to believe that tissue damage is always met by self-destruction or is it instead met by a survival response? Biology tells us that responses are evolutionarily selected and will benefit the organism, if they are in balance. Therefore, senile plaques with activated inflammatory microglia are not associated with an increase but rather a reduction in oxidative stress (Nunomura et al., 2000, 2001), and the major site of oxidative damage in AD is the neuron, which is not the site of inflammation. Could it be that nitric oxide is being produced to reduce the oxygen radicals? The important issue here is that by focusing on the pathology of disease, we miss the point of the homeostatic nature of chronic disease. Silencing compensatory responses, such as amyloid or inflammation, may destabilize a delicate balance as appears to be the case for both the amyloid-β vaccine and the COX-2 inhibitor clinical trials.

    References:

    . Neuronal oxidative stress precedes amyloid-beta deposition in Down syndrome. J Neuropathol Exp Neurol. 2000 Nov;59(11):1011-7. PubMed.

    . Oxidative damage is the earliest event in Alzheimer disease. J Neuropathol Exp Neurol. 2001 Aug;60(8):759-67. PubMed.

    . Biochemistry of neurodegeneration. Science. 2001 Jan 26;291(5504):595-7. PubMed.

    . Diet and oxidative stress: a novel synthesis of epidemiological data on Alzheimer's disease. J Alzheimers Dis. 1999 Nov;1(4-5):203-6. PubMed.

References

News Citations

  1. Large Prospective Study Finds NSAIDs Reduce Risk of Developing AD

External Citations

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Further Reading

Papers

  1. . Screening in a cell-based assay for inhibitors of microglial nitric oxide production reveals calmodulin-regulated protein kinases as potential drug discovery targets. Brain Res. 1999 Oct 9;844(1-2):126-34. PubMed.
  2. . Activation of MKK6, an upstream activator of p38, in Alzheimer's disease. J Neurochem. 2001 Oct;79(2):311-8. PubMed.

Primary Papers

  1. . Discovery of a 3-amino-6-phenyl-pyridazine derivative as a new synthetic antineuroinflammatory compound. J Med Chem. 2002 Jan 31;45(3):563-6. PubMed.