Pharmacodynamics of the orexin type 1 (OX) receptor in colon cancer cell models: A two-sided nature of antagonistic ligands resulting from partial dissociation of Gq.

BACKGROUND AND PURPOSE

Orexins have important biological effects on the central and peripheral nervous systems. Their primary ability is to regulate the sleep-wake cycle. Orexins and their antagonists, via OX receptor have been shown to have proapoptotic and antitumor effects on various digestive cancers cell models. We investigated, (1) the ability of orexin-A and its antagonists to regulate OX receptor expression at the cell surface and (2), how OX antagonists induced proapoptotic effect in cancer cells models.

EXPERIMENTAL APPROACH

The OX receptor internalisation is determined by imaging flow cytometry in colon cancer cell models and the OX receptor coupling to G proteins via bioluminescence resonance energy transfer and molecular dynamic simulation.

KEY RESULTS

Orexin-A induced rapid receptor internalisation within 15 min via β-arrestin 2 recruitment, whereas antagonists had no effect. Furthermore, Gq is critical for receptor internalisation and signalling pathways, and no other G proteins appear to be recruited. Surprisingly, antagonists induced recruitment and conformational changes in Gq protein. Simulated molecular dynamics of agonists/orexin receptor/Gq complexes show that antagonists exhibits a similar binding mode, stable at the binding site and show conformational changes of ECL2, similar to that of the agonists.

CONCLUSION AND IMPLICATIONS

OX receptor activation induced orexin/β-arrestin-dependent internalisation, which was independent of the apoptotic pathway induced by orexins and antagonists. In addition, antagonists activate the Gq protein, suggesting its putative partial dissociation. These results suggest that the development of OX receptor targeting molecules, including orexin antagonists with antitumor properties, may pave the way for innovative cancer therapies.