Substance P tachykininergic NK1 receptor emetic signal transduction pathways

Acute (day 1) and delayed (days 3-7) nausea and vomiting are the feared and debilitating side-effects of cancer therapeutics such as cisplatin. In the absence of prophylactic therapy, nearly all patients vomit from cisplatin-like drugs. These side-effects must be controlled to maintain patient compliance and quality of life. However, the cost of the best antiemetic regimen (Akynzeo) containing a serotonin 5-HT3 receptor (5-HT3R) antagonist and a substance P (SP) neurokinin NK1 receptor (NK1R)-antagonist is over $500 per pill in the USA and can only protect up to 80% of patients. Cisplatin-like drugs release serotonin (5-HT) and SP which stimulate their corresponding cell membrane-bound extracellular emetic receptors in both the gut and brainstem emetic loci to evoke vomiting. Of critical importance to this application, major gaps exist in the emesis field in that there is a lack of understanding of i) activation of emetic intracellular signaling mechanisms following stimulation of discussed emetic receptors; and ii) whether potential point(s) of signal convergence (e.g. Ca2+) exist among diverse emetic signaling cascades. As new cancer therapeutics are being developed, it becomes vital that we define shared fundamental intracellular signaling molecules that underlie induction of emesis versus cancer suppression, so that we can develop safer cancer therapeutics without emesis, which will save time, effort and research dollars. Although the emetic signaling cascade(s) downstream of NK1R remain unknown, we recently have identified the intracellular 5-HT3R emetic cascade [17,18]. Unlike the narrow-spectrum 5-HT3R blockers, NK1R antagonists exhibit broad-spectrum antiemetic efficacy against diverse causes of vomiting. Thus, a full understanding of NK1R emetic signals may allow us to identify unique intracellular signal(s) whose antagonists/inhibitors would suppress cancer formation without vomiting. Indeed, SP via NK1Rs plays a central role in the development of CNS tumors and its corresponding antagonists possess cancer chemotherapeutic potential [15,16]. Furthermore, our preliminary data strongly suggest that the phospholipase C (PLC) cascade and its interaction with the Akt/GSK-3aβ pathway are major players in NK1R-evoked vomiting. The purpose of this application is to take a broad approach involving pharmacological, behavioral, calcium imaging, immunohistochemical and Western blot techniques, to delineate the NK1R-mediated emetic signal transduction involving activation of phospholipase C and corresponding downstream signals including the role of extracellular Ca2+ influx and intracellular Ca2+ release in vomiting, as well as whether the evoked emesis can be modulated by the Akt/GSK-3αβ pathway. Not only there is scant information regarding intracellular mechanisms of emesis, but also there is an urgent and unmet need for alternative broad-spectrum antiemetics for protection of all cancer patients suffering from vomiting caused by cytotoxic chemotherapeutics. The findings of this proposal will introduce not only several new highly potent classes of antiemetics, but may also help reveal the potential of universal antiemetics, which will lower the cost of prevention of nausea and vomiting in diverse patient communities suffering from cancer, HIV or gastrointestinal disorders.