Prolonged inhibition of 5‐HT₃ receptors by palonosetron results from surface receptor inhibition rather than inducing receptor internalization

Abstract

Background and PurposeThe 5-HT3 receptor antagonist palonosetron is an important treatment for emesis and nausea during cancer therapy. Its clinical efficacy may result from its unique binding and clearance characteristics and receptor down-regulation mechanisms. We investigated the mechanisms by which palonosetron exerts its long-term inhibition of 5-HT3 receptors for a better understanding of its clinical efficacy.Experimental ApproachCell surface receptors (recombinantly expressed 5HT3A or 5HT3AB in COS-7 cells) were monitored using [3H]granisetron binding and ELISA after exposure to palonosetron. Receptor endocytosis was investigated using immunofluorescence microscopy.Key ResultsChronic exposure to palonosetron reduced the number of available cell surface [3H]granisetron binding sites. This down-regulation was not sensitive to either low temperature or pharmacological inhibitors of endocytosis (dynasore or nystatin) suggesting that internalization did not play a role. This was corroborated by our observation that there was no change in cell surface 5-HT3 receptor levels or increase in endocytic rate. Palonosetron exhibited slow dissociation from the receptor over many hours, with a significant proportion of binding sites being occupied for at least 4 days. Furthermore, our observations suggest that chronic receptor down-regulation involved interactions with an allosteric binding site.Conclusions and ImplicationsPalonosetron acts as a pseudo-irreversible antagonist causing prolonged inhibition of 5-HT3 receptors due to its very slow dissociation. In addition, an irreversible binding mode persists for at least 4 days. Allosteric receptor interactions appear to play a role in this phenomenon.

In silico investigation into the interactions between murine 5-HT3 receptor and the principle active compounds of ginger (Zingiber officinale)

“…[13][14][15][16] Recently observations of multiple modes of inhibition by palonosetron, for example, exhibiting pseudo irreversible inhibition at the serotonin site but also acting at a distinct allosteric site, exemplifies the complexity of modulation and challenges to medicinal chemists. [17][18][19][20][21] …”

Comparative investigation of the anti-emetic effects of granisetron and palonosetron during the treatment of acute myeloid leukemia

“…Hothersall et al (19) reported that palonosetron acts as a 5-HT3 receptor over a prolonged period or even as an irreversible antagonist for at least 4 days. Allosteric receptor-receptor interactions may play a significant role in this phenomenon (19). The key objective of the present study was to identify a continuous daily regimen of anti-emetic drugs that may be used during remission induction therapy.…”

Evaluation of the ability of continuous palonosetron infusion, using a patient-controlled analgesia device, to reduce postoperative nausea and vomiting

“…In a recent report, palonosetron treatment was shown to down-regulate the amount of available 5-HT 3 receptor binding sites, rather than cell surface expression levels of 5-HT 3 receptors [18]. This result suggests that palonosetron inhibits 5-HT 3 receptors by interacting with an allosteric binding site rather than by inducing receptor internalization.…”

“…Palonosetron exhibits significant receptor occupation for as long as 4 days [18]. Given this characteristic of palonosetron, we investigated the effects of continuous infusion in the context of a PCA on the incidence of PONV in high-risk patients.…”