Serotonin and Dopamine Receptor Expression in Solid Tumours Including Rare Cancers.

In preclinical studies serotonin stimulates and dopamine inhibits tumour growth and angiogenesis. Information regarding serotonin and dopamine receptor (5-HTR and DRD) expression in human cancers is limited. Therefore, we screened a large tumour set for receptor mRNA overexpression using functional genomic mRNA (FGmRNA) profiling, and we analysed protein expression and location of 5-HTR1B, 5-HTR2B, DRD1, and DRD2 with immunohistochemistry in different tumour types. With FGmRNA profiling 11,756 samples representing 43 tumour types were compared to 3,520 normal tissue samples to analyse receptor overexpression. 5-HTR2B overexpression was present in many tumour types, most frequently in uveal melanomas (56%). Receptor overexpression in rare cancers included 5-HTR1B in nasopharyngeal carcinoma (17%), DRD1 in ependymoma (30%) and synovial sarcoma (21%), and DRD2 in astrocytoma (13%). Immunohistochemistry demonstrated high 5-HTR2B protein expression on melanoma and gastro-intestinal stromal tumour cells and endothelial cells of colon, ovarian, breast, renal and pancreatic tumours. 5-HTR1B expression was predominantly low. High DRD2 protein expression on tumour cells was observed in 48% of pheochromocytomas, and DRD1 expression ranged from 14% in melanoma to 57% in renal cell carcinoma. In conclusion, 5-HTR1B, 5-HTR2B, DRD1, and DRD2 show mRNA overexpression in a broad spectrum of common and rare cancers. 5-HTR2B protein is frequently highly expressed in human cancers, especially on endothelial cells. These findings support further investigation of especially 5HTR2B as a potential treatment target.

Quantitative Profiling of Platelet-Rich Plasma Indole Markers by Direct-Matrix Derivatization Combined with LC-MS/MS in Patients with Neuroendocrine Tumors.

BACKGROUND: Currently, several indole markers are measured separately to support diagnosis and follow-up of patients with neuroendocrine tumors (NETs). We have developed a sensitive mass spectrometry method that simultaneously quantifies all relevant tryptophan-related indoles (tryptophan, 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid) in platelet-rich plasma. Direct-matrix derivatization was used to make the chemical properties of the indoles uniform and to improve the analytical sensitivity and specificity of the assay. METHODS: In situ derivatization was performed directly in platelet-rich plasma with propionic anhydride at an ambient temperature. The derivatized indoles were extracted by online solid-phase extraction and eluted to the analytical column for separation followed by mass spectrometric detection. The method was validated according to international guidelines. Platelet-rich plasma samples from 68 healthy individuals and 40 NET patients were analyzed for tryptophan, 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid. RESULTS: The method reproducibly quantified relevant indoles in 8.5 min, including online sample cleanup. Intra- and interassay imprecision, evaluated at 3 different concentrations, ranged from 2.0% to 12% and 1.9% to 13%, respectively. The limit of quantification was sufficient to measure endogenous concentrations of all 4 indoles. Healthy individuals and NET patients had different concentrations of 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid, but tryptophan concentrations were the same. CONCLUSIONS: Direct-matrix derivatization in combination with LC-MS/MS is a powerful tool for the simultaneous quantification of all tryptophan-related indoles in platelet-rich plasma. Simultaneous profiling of relevant indoles improves the biochemical characterization and follow-up of NETs.

Melatonin is not stored in platelets.

BACKGROUND: Melatonin is one of numerous biologically active compounds reported to be stored in platelets. As melatonin is increasingly linked to several diseases, we wanted to confirm the storage of melatonin in platelets using sensitive liquid chromatography in combination with isotope dilution tandem mass spectrometry (LC-MS/MS). The difference between melatonin levels analyzed in platelet-rich plasma (PRP) and platelet-poor plasma (PPP) served as proxy for platelet levels of melatonin. METHODS: Melatonin concentrations were analyzed in PRP and PPP from nineteen healthy volunteers by ELISA and LC-MS/MS. A Wilcoxon signed-rank test was performed to assess if the melatonin levels measured in PRP and PPP were different. Results for melatonin concentrations obtained by LC-MS/MS or ELISA were compared using Passing-Bablok regression. RESULTS: Comparison of the ELISA with the LC-MS/MS method showed poor agreement for melatonin concentrations in PRP and PPP. No indication was found for storage of melatonin in platelets by either LC-MS/MS or ELISA (P = .89 and P = .53 for the LC-MS/MS and ELISA analysis, respectively). CONCLUSION: In this study we could find no evidence for melatonin storage in platelets.

Dopamine concentration in blood platelets is elevated in patients with head and neck paragangliomas.

BACKGROUND: Plasma 3-methoxytyramine (3-MT), a metabolite of dopamine, is elevated in up to 28% of patients with head and neck paragangliomas (HNPGLs). As free dopamine is incorporated in circulating platelets, we determined dopamine concentration in platelets in patients with a HNPGL. METHODS: A single center cohort study was performed between 2012 and 2014. Thirty-six patients with a HNPGL were compared to healthy controls (68 for dopamine in platelets and 120 for plasma 3-MT). RESULTS: Dopamine concentration in platelets was elevated in HNPGL patients compared to healthy controls (median [interquartile ranges] 0.48 [0.32-0.82] pmol/109 platelets vs. 0.31 [0.24-0.47] pmol/109 platelets; p<0.05), whereas plasma 3-MT concentration did not differ between both groups (0.06 [0.06-0.08] nmol/L vs. 0.06 [0.06-0.06] nmol/L; p=0.119). Based on 68 healthy controls, the reference interval for dopamine concentration in platelets was 0.12-0.97 pmol/109 platelets. Six (16.7%) patients with a HNPGL demonstrated an increased dopamine concentration in platelets compared to three (8.3%) patients with an increased plasma 3-MT level (p=0.053). The sensitivity and specificity were 16.7% and 98.5% for platelet dopamine and 8.3% and 97.5% for plasma 3-MT concentration (p=0.37). CONCLUSIONS: Dopamine concentration in platelets is elevated in patients with a HNPGL compared to healthy subjects, and may be a novel biomarker for dopamine producing paraganglioma.

Dopamine and serotonin regulate tumor behavior by affecting angiogenesis.

The biogenic amines dopamine and serotonin are neurotransmitters and hormones, which are mainly produced in the central nervous system and in the gastro-intestinal tract. They execute local and systemic functions such as intestinal motility and tissue repair. Dopamine and serotonin are primarily stored in and transported by platelets. This review focuses on the recently recognized role of dopamine and serotonin in the regulation of tumor behavior by affecting angiogenesis and tumor cell proliferation. Preclinical studies demonstrate that dopamine inhibits tumor growth via activation of dopamine receptor D2 on endothelial and tumor cells. Serotonin stimulates tumor growth via activation of serotonin receptor 2B on endothelial cells and serotonin receptors on tumor cells. Drugs that stimulate dopamine receptor D2 or inhibit serotonin receptors are available and therefore clinical intervention studies for cancer patients are within reach.