Inhibition of heterotrimeric G protein signaling by a small molecule acting on Galpha subunit.

The simultaneous activation of many distinct G protein-coupled receptors (GPCRs) and heterotrimeric G proteins play a major role in various pathological conditions. Pan-inhibition of GPCR signaling by small molecules thus represents a novel strategy to treat various diseases. To better understand such therapeutic approach, we have characterized the biomolecular target of BIM-46187, a small molecule pan-inhibitor of GPCR signaling. Combining bioluminescence and fluorescence resonance energy transfer techniques in living cells as well as in reconstituted receptor-G protein complexes, we observed that, by direct binding to the Galpha subunit, BIM-46187 prevents the conformational changes of the receptor-G protein complex associated with GPCR activation. Such a binding prevents the proper interaction of receptors with the G protein heterotrimer and inhibits the agonist-promoted GDP/GTP exchange. These observations bring further evidence that inhibiting G protein activation through direct binding to the Galpha subunit is feasible and should constitute a new strategy for therapeutic intervention.

IRC-083864, a novel bis quinone inhibitor of CDC25 phosphatases active against human cancer cells.

CDC25 phosphatases are key actors in cyclin-dependent kinases activation whose role is essential at various stages of the cell cycle. CDC25 expression is upregulated in a number of human cancers. CDC25 phosphatases are therefore thought to represent promising novel targets in cancer therapy. Here, we report the identification and the characterization of IRC-083864, an original bis-quinone moiety that is a potent and selective inhibitor of CDC25 phosphatases in the low nanomolar range. IRC-083864 inhibits cell proliferation of a number of cell lines, regardless of their resistance to other drugs. It irreversibly inhibits cell proliferation and cell cycle progression and prevents entry into mitosis. In addition, it inhibits the growth of HCT-116 tumor spheroids with induction of p21 and apoptosis. Finally, IRC-083864 reduced tumor growth in mice with established human prostatic and pancreatic tumor xenografts. This study describes a novel compound, which merits further study as a potential anticancer agent.

3D imaging of the response to CDC25 inhibition in multicellular spheroids.

Multicellular tumor spheroids closely mimic the 3D organization of avascular microregions within tumors and thereby represent a valuable model for the evaluation of anticancer drugs. In this study, we performed a 3D analysis of the response to the CDC25 phosphatase inhibitor IRC-083864 in HCT116 spheroids. Continuous exposure to IRC-083864 strongly inhibits the growth of spheroids and is shown to correlate with a decrease in Ki-67 positive cells. The cytotoxicity induced by IRC-083864 was examined by two-photon laser microscopy imaging and 3D reconstruction. Visualization in 3D allowed us to demonstrate that IRC-083864 treatment results in the inhibition of mitosis and induces cell death specifically localized in the outer proliferative cell layers of the spheroid structure. These results emphasize the importance of 3D models and of in toto analysis for the evaluation of anticancer drugs cytotoxicity.

Inhibitors of the CDC25 phosphatases.

As essential cell cycle regulators, the CDC25 phosphatases are currently considered as potential targets for the development of novel therapeutic approaches. Here, we review the function and regulation of CDC25 phosphatases, their involvement in cancer and Alzheimer's disease, and the properties of several recently identified inhibitors.