This page was produced as an assignment for Genetics 677, an undergraduate course at UW-Madison.

Chemical Genetics

The use of small organic molecules to perturb the function of a protein, called chemical genetics, is an approach complementary to gene-based methods that can be used to understand how a protein functions in an organism (Stockwell, 2004). Two chemicals that have been found to selectively perturb GRM7 function, AMN082 and MMPIP, are discussed below.

AMN082

AMN082 dihydrochloride (N,N'-Bis(diphenylmethyl)-1,2-ethanediamine dihydrochloride) is an orally active selective GRM7 agonist, capable of penetrating the blood/brain barrier (Figure 1) (Tocris bioscience, 2009; Flor, et al., 2005; Mitsukawa, et al., 2005). Directly activating GRM7 signaling through binding to a novel allosteric site located in the transmembrane domain of the protein,  AMN082 dihydrochloride inhibits cAMP accumulation and stimulates GTPγS signaling more effectively than glutamic acid, the normal ligand of the receptor (Flor, et al., 2005).

Figure 1. AMN082 dihydrochloride. AMN082 dihydrochloride (N,N'-Bis(diphenylmethyl)-1,2-ethanediamine dihydrochloride) acts as a selective GRM7 agonist (Tocris bioscience, 2009; Flor, et al., 2005; Mitsukawa, et al., 2005).
 

As alcohol preference in mice has been linked to lowered expression of GRM7, and, therefore, lowered overall activity of the GRM7 protein, one might predict that AMN082, by increasing GRM7 activity, would decrease alcohol preference (Vadasz, et al., 2007; Flor, et al., 2005). A study, conducted by Salling, et al., explored just this (2008). Two seperate groups of C57BL/6J male mice, one to which AMN082 was administered and one to which it was not (a control), were trained to self-administer ethanol on a fixed-ratio 4 schedule of reinforcement during 1 h sessions (Salling, et al., 2008). Salling, et al., found that mice to which AMN082 was administered exhibited decreased alcohol self-administration (2008). While this seems to suggest that AMN082 would be a good candidate for a drug to treat alcoholism, Salling, et al., also found that AMN082 administration caused general reductions in motivated behavior, as well as reduced locomotor activity and tremors (2008). Salling, et al., note that while these side effects may be due in part to off-target interactions not noticed in the orginal study by Flor, et al., that identified AMN082 as a selective agonist of GRM7, their study also indicates that GRM7, in general, may not be a good target for therapeutic interventions in alcoholism due to the importance of this receptor in stress response as well as learning and memory (2008; 2005).

MMPIP

MMPIP hydrochloride ( 6-(4-Methoxyphenyl)-5-methyl-3-(4-pyridinyl)-isoxazolo[ 4,5-c]pyridin-4(5H)-one hydrochloride) is potent selective antagonist of GRM7 (Figure 3) (Tocris bioscience, 2009; Suzuki, et al., 2007). While the specific region of GRM7 to which MMPIP binds is still unknown, this molecule has been shown to act allosterically in a reversible manner to cause forskolin-induced cAMP accumulation (Suzuki, et al., 2007). Additionally, MMPIP inhibits the effects of agonists like AMN082 (Suzuki, et al., 2007).

Figure 2. MMPIP hydrochloride. MMPIP hydrochloride ( 6-(4-Methoxyphenyl)-5-methyl-3-(4-pyridinyl)-isoxazolo[ 4,5-c]pyridin-4(5H)-one hydrochloride) acts as a selective GRM7 antagonist (Tocris bioscience, 2009; Suzuki, et al., 2007).

Although MMPIP has not yet been used for such a purpose, it is predicted that this molecule will be useful in elucidating the role GRM7 plays in modulating alcohol-related behaviors (Suzuki, et al., 2007). An interesting experiment that could be performed would be to look at alcohol preferences in mice that have been treated with MMPIP. As discussed above, lowered GRM7 expression, and therefore, lowered GRM7 functioning, has been linked to increased susceptibility to alcoholism (Vadasz, et al., 2007). Therefore, as compared to control mice not receiving MMPIP, mice that have received MMPIP would be predicted to show increased levels of alcohol preference. While the study on AMN082 and GRM7 by Salling, et al., suggested that GRM7 may not itself be a good target for therapeutic interventions in alcoholism, understanding how changes in the level of GRM7 function can lead to alcoholism through studies involving, among other things, drugs like MMPIP, will likely play an important role in finding treatments for alcoholism that are safe and effective (2008).

References

References

 

Flor, P.J., Vassout, A., Fendt, M., Mitsukawa, K., Jacobson, L., Yamamoto, R., Nozulak, J., Ofner, S., Pescott, O., Lukic, S., Stoehr, N., Urwyler, S., Kuhn, R., Herrling, P., McAllister, K., van der Putten, H., and Cryan, J.F. (2005). AMN082, the first selective mGluR7 agonist: activation of receptor signaling via an allosteric site in the transmembrane domain modulates stress parameters in vivo. [Abstract]. Neuropharmacology, 49 (Suppl. 1):244. doi: 10.1016/j.neuropharm.2005.06.013

Mitsukawa, K., Yamamoto, R., Ofner, S., Nozulak, J., Pescott, O., Lukic, S., Stoehr, N., Mombereau, C., Kuhn, R.,  McAllister, K., van der Putten, H., Cryan, J.F., and Flor, P.J. (2005). A selective metabotropic glutamate receptor 7 agonist: Activation of receptor signaling via an allosteric site modulates stress parameters in vivo. Proc. Natl. Acad. Sci. USA ,102(51):18712. doi: 10.1073/pnas.0508063102.

Salling, M.C., Faccidomo, S., Hodge, C.W. (2008). Nonselective suppression of operant ethanol and sucrose self-administration by the mGluR7 positive allosteric modulator AMN082. Pharmacology Biochemistry and Behavior, 91(1):14. doi: 10.1016/j.pbb.2008.06.006 

Stockwell, B.R. (2004). Exploring biology with small organic molecules. Nature, 432(7019):846. doi:10.1038/nature03196

Suzuki, G., Tsukamoto, N., Fushiki, H., Kawagishi, A., Nakamura, M., Kurihara, H., Mitsuya, M., Ohkubo, M., and Ohta, H. (2007). In Vitro Pharmacological Characterization of Novel Isoxazolopyridone Derivatives as Allosteric Metabotropic Glutamate Receptor 7 Antagonists . J Pharmacol Exp Ther, 323(1):147. doi: 10.1124/jpet.107.124701

Vadasz, C., Saito, M., Gyetvai, B. M., Oros, M., Szakall, I., Kovacs, K. M., Prasad, V. V. T. S., Toth, R. (2007). Glutamate receptor metabotropic 7 is cis-regulated in the mouse brain and modulates alcohol drinking. Genomics, 90(6):690. doi:10.1016/j.ygeno.2007.08.006

Tocris Bioscience. (2009). AMN082 dihydrochloride. Retrieved May 2, 2009, from http://www.tocris.com/dispprod.php?ItemId=145226.

Tocris Bioscience. (2009). MMPIP hydrochloride. Retrieved May 3, 2009, from http://www.tocris.com/dispprod.php?ItemId=5430.

 

Jennifer Wagner
wagner4@wisc.edu
Updated May 3, 2009
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