CCG-63802

CCG-63802 is a selective inhibitor of RGS4 with IC50 value of 1.9 μM [1].
RGS (regulators of G protein signaling) are multi-functional, GTPase-accelerating proteins and plays an important role in promoting GTP hydrolysis via heterotrimeric G proteins α subunit. RGS 4 is also known as RGP4 and plays a pivotal role in negatively regulating signaling upstream or at the level of the heterotrimeric G protein [1, 2].
CCG-63802 is a potent RGS inhibitor and is different from the reported RGS4 irreversibly inhibitor CCG-4986. Using the [32P] GTP single-turnover GAP assay, it was shown that CCG-63802 treatment inhibited GAP activity of RGS4 [1]. When tested with HEK-293 cells, administration of CCG-63802 successfully reversed 8-Br-cGMP inhibition on BK via inhibiting RGS4 [2].
References:
[1].Blazer, L.L., et al., Reversible, allosteric small-molecule inhibitors of regulator of G protein signaling proteins. Mol Pharmacol, 2010. 78(3): p. 524-33.
[2].Dobrivojevic, M., et al., Interaction between bradykinin and natriuretic peptides via RGS protein activation in HEK-293 cells. Am J Physiol Cell Physiol, 2012. 303(12): p. C1260-8.

Reversible, allosteric small-molecule inhibitors of regulator of G protein signaling proteins.[Pubmed:20571077]

Mol Pharmacol. 2010 Sep;78(3):524-33.

Regulators of G protein signaling (RGS) proteins are potent negative modulators of G protein signaling and have been proposed as potential targets for small-molecule inhibitor development. We report a high-throughput time-resolved fluorescence resonance energy transfer screen to identify inhibitors of RGS4 and describe the first reversible small-molecule inhibitors of an RGS protein. Two closely related compounds, typified by CCG-63802 [((2E)-2-(1,3-benzothiazol-2-yl)-3-[9-methyl-2-(3-methylphenoxy)-4-oxo-4H-pyrido[ 1,2-a]pyrimidin-3-yl]prop-2-enenitrile)], inhibit the interaction between RGS4 and Galpha(o) with an IC(50) value in the low micromolar range. They show selectivity among RGS proteins with a potency order of RGS 4 > 19 = 16 > 8 >> 7. The compounds inhibit the GTPase accelerating protein activity of RGS4, and thermal stability studies demonstrate binding to the RGS but not to Galpha(o). On RGS4, they depend on an interaction with one or more cysteines in a pocket that has previously been identified as an allosteric site for RGS regulation by acidic phospholipids. Unlike previous small-molecule RGS inhibitors identified to date, these compounds retain substantial activity under reducing conditions and are fully reversible on the 10-min time scale. CCG-63802 and related analogs represent a useful step toward the development of chemical tools for the study of RGS physiology.

Interaction between bradykinin and natriuretic peptides via RGS protein activation in HEK-293 cells.[Pubmed:23054060]

Am J Physiol Cell Physiol. 2012 Dec 15;303(12):C1260-8.

In this study, the interaction of natriuretic peptides (NP) and bradykinin (BK) signaling pathways was identified by measuring membrane potential (V(m)) and intracellular Ca(2+) using the patch-clamp technique and flow cytometry in HEK-293 cells. BK and NP receptor mRNA was identified using RT-PCR. BK (100 nM) depolarized cells activating bradykinin receptor type 2 (B(2)R) and Ca(2+)-dependent Cl(-) channels inhibitable by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 10 muM). The BK-induced Ca(2+) signal was blocked by the B(2)R inhibitor HOE 140. [Des-Arg(9)]-bradykinin, an activator of B(1)R, had no effect on intracellular Ca(2+). NP [atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and urodilatin] depolarized HEK-293 cells inhibiting K(+) channels. ANP, urodilatin, BNP [binding to natriuretic peptide receptor (NPR)-A] and 8-bromo-(8-Br)-cGMP inhibited the BK-induced depolarization while CNP (binding to NPR-Bi) failed to do so. The inhibitory effect on BK-triggered depolarization could be reversed by blocking PKG using the specific inhibitor KT 5823. BK-stimulated depolarization as well as Ca(2+) signaling was completely blocked by the phospholipase C (PLC) inhibitor U-73122 (10 nM). The inositol 1,4,5-trisphosphate receptor blocker 2-aminoethoxydiphenyl borate (2-APB; 50 muM) completely inhibited the BK-induced Ca(2+) signaling. UTP, another activator of the PLC-mediated Ca(2+) signaling pathway, was blocked by U-73122 as well but not by 8-Br-cGMP, indicating an intermediate regulatory step for NP via PKG in BK signaling such as regulators of G-protein signaling (RGS) proteins. When RGS proteins were inhibited by CCG-63802 in the presence of BK and 8-Br-cGMP, cells started to depolarize again. In conclusion, as natural antagonists of the B(2)R signaling pathway, NP may also positively interact in pathological conditions caused by BK.

Inhibition of the regulator of G protein signalling RGS4 in the spinal cord decreases neuropathic hyperalgesia and restores cannabinoid CB1 receptor signalling.[Pubmed:26478461]

Br J Pharmacol. 2015 Nov;172(22):5333-46.

BACKGROUND AND PURPOSE: Regulators of G protein signalling (RGS) are major determinants of metabotropic receptor activity, reducing the lifespan of the GTP-bound state of G proteins. Because the reduced potency of analgesic agents in neuropathic pain may reflect alterations in RGS, we assessed the effects of CCG 63802, a specific RGS4 inhibitor, on pain hypersensitivity and signalling through cannabinoid receptors, in a model of neuropathic pain. EXPERIMENTAL APPROACH: The partial sciatic nerve ligation (PSNL) model in male Sprague Dawley rats was used to measure paw withdrawal thresholds to mechanical (von Frey hairs) or thermal (Hargreaves method) stimuli, during and after intrathecal injection of CCG 63802. HEK293 cells expressing CB1 receptors and conditional expression of RGS4 were used to correlate cAMP production and ERK phosphorylation with receptor activation and RGS4 action. KEY RESULTS: Treatment of PSNL rats with CCG 63802, twice daily for 7 days after nerve injury, attenuated thermal hyperalgesia during treatment. Spinal levels of anandamide were higher in PSNL animals, irrespective of the treatment. Although expression of CB1 receptors was unaffected, HU210-induced CB1 receptor signalling was inhibited in PSNL rats and restored after intrathecal CCG 63802. In transfected HEK cells expressing CB1 receptors and RGS4, inhibition of cAMP production, a downstream effect of CB1 receptor signalling, was blunted after RGS4 overexpression. RGS4 expression also attenuated the CB1 receptor-controlled activation of ERK1/2. CONCLUSIONS AND IMPLICATIONS: Inhibition of spinal RGS4 restored endogenous analgesic signalling pathways and mitigated neuropathic pain. Signalling through CB1 receptors may be involved in this beneficial effect.