Synthesis of tritium-labeled PAM-43

New Allosteric Modulators of AMPA Receptors: Synthesis and Study of Their Functional Activity by Radioligand-Receptor Binding Analysis

The synthetic approaches to three new AMPA receptor modulators-derivatives of 1,11-dimethyl-3,6,9-triazatricyclo[7.3.1.1^3,11]tetradecane-4,8,12-trione-had been developed and all steps of synthesis were optimized. The structures of the compounds contain tricyclic cage and indane fragments necessary for binding with the target receptor. Their physiological activity was studied by radioligand-receptor binding analysis using [³H]PAM-43 as a reference ligand, which is a highly potent positive allosteric modulator of AMPA receptors. The results of radioligand-binding studies indicated the high potency of two synthesized compounds to bind with the same targets as positive allosteric modulator PAM-43 (at least on AMPA receptors). We suggest that the Glu-dependent specific binding site of [³H]PAM-43 or the receptor containing this site may be one of the targets of the new compounds. We also suggest that enhanced radioligand binding may indicate the existence of synergistic effects of compounds 11b and 11c with respect to PAM-43 binding to the targets. At the same time, these compounds may not compete directly with PAM-43 for its specific binding sites but bind to other specific sites of this biotarget, changing its conformation and thereby causing a synergistic effect of cooperative interaction. It can be expected that the newly synthesized compounds will also have pronounced effects on the glutamatergic system of the mammalian brain.

Characterization of a New Positive Allosteric Modulator of AMPA Receptors - PAM-43: Specific Binding of the Ligand and its Ability to Potentiate AMPAR Currents

BACKGROUND

Currently, the most dynamic areas in the glutamate receptor system neurobiology are the identification and development of positive allosteric modulators (PAMs) of glutamate ionotropic receptors. PAM-based drugs are of great interest as promising candidates for the treatment of neurological diseases, such as epilepsy, Alzheimer's disease, schizophrenia, etc. Understanding the molecular mechanisms underlying the biological action of natural and synthetic PAMs is a key point for modifying the original chemical compounds as well as for new drug design.

OBJECTIVE

We are trying to elaborate a system of molecular functional screening of ionotropic glutamate receptor probable PAMs.

METHODS

The system will be based on the radioligand - receptor method of analysis and will allow rapid quantification of new AMPAR probable PAMs molecular activity. We plan to use a tritiumlabeled analogue of recently elaborated ionotropic GluR probable PAM ([3H]PAM-43) as the main radioligand.

RESULTS

Here, we characterized the specific binding of the ligand and its ability to potentiate ionotropic GluR currents. The existence of at least two different sites of [3H]PAM-43 specific binding has been shown. One of the above sites is glutamate-dependent and is characterized by higher affinity. "Patchclamp" technique showed the ability of PAM-43 to potentiate ionotropic GluR currents in rat cerebellar Purkinje neurons in a concentration-dependent manner.

CONCLUSION

The possibility of using PAM-43 as a model compound to study different allosteric effects of potential regulatory drugs (AMPAR allosteric regulators) was shown. [3H]PAM-43 based screening system will allow rapid selection of new AMPAR probable PAM structures and quantification of their molecular activity.