D1 dopamine receptors are not expressed in human melanoma

Anticancer efficacy of endo- and exogenous potent ligands acting at dopaminergic receptor-expressing cancer cells

Cancer is one of the most common and dreaded diseases affecting the vastness of society. Unfortunately, still some people die especially when cancer is not diagnosed and thus caught early enough. On the other hand, using available chemo- or radiotherapy may result in serious side effects. Therefore, cancer-specific medications seem to be the most desired and safe therapy. Knowing that some cancers are characterized by overexpression of specific receptors on the cell surface, target-mediated drugs could serve as a unique and effective form of therapy. In line with this, recently dopaminergic receptors were presented important in cancer therapy as several dopaminergic ligands revealed their efficacy in tumor growth reduction as well as in apoptosis mediation. Unfortunately, the indication of whether DA receptor agonists or antagonists are the best choices in cancer treatment is quite difficult, since both of them may exert either pro- or anticancer effects. In this review, we analyze the therapeutic efficacy of compounds, both of exogenous and endogenous origin, targeting dopaminergic receptor-expressing cancers.

Roles of dopamine receptors and their antagonist thioridazine in hepatoma metastasis

Tumor metastasis is the most common cause of death and poor prognosis for cancer patients. Therapeutics that prevent tumor metastasis are the key to prolonging the lifespan of cancer patients. Cancer stem cells are believed to be critical in the metastatic process. Recently, drug screening for cancer stem cells reports that antipsychotic drugs displayed potential anticancer activity. Thioridazine, one of the antipsychotic drugs for dopamine receptors (DRs), is shown to induce the differentiation of cancer stem cells in leukemic disease and breast cancer, but it is not known if this drug would affect liver cancer. In this study, expression of DR5 was higher in tumors than in nontumor adjacent tissues, while DR1 was lower in human hepatocellular carcinoma (HCC) than those in the adjacent tissues. Other DRs were very low or undetectable. Treatment of HCC cells with thioridazine displays a dose-dependent response in HCC cell lines SNU449, LM3, and Huh7. Thioridazine treatment reduced cell viability and sphere formation of HCC cell lines through induction of G0/G1 cell cycle arrest and suppression of stemness genes CD133, OCT4, and EpCam. It also inhibited cell migration via suppression of epithelial–mesenchymal transition (EMT)-related genes such as twist2 and E-cadherin. Thioridazine-pretreated LM3 cells decreased the capacity of tumorigenesis in nude mice. Taken together, our data suggest that thioridazine may have the potential role in treatment of HCC.

Antitumor activity of histamine and clozapine in a mouse experimental model of human melanoma

BACKGROUND

Functional presence of histamine H4 receptor (H4R) was demonstrated in human melanoma cell lines and biopsies.

OBJECTIVE

The purposes of this work were to investigate signal transduction pathways and biological responses triggered by the activation of H4R in human primary (WM35) and metastatic (M1/15) melanoma cell lines and to evaluate the in vivo antitumor activity of histamine (HA) and clozapine (CLZ) on human M1/15 melanoma xenografts.

METHODS

Clonogenic assay, incorporation of BrdU, cell cycle distribution, phosphorylation levels of ERK1/2 and cAMP production were evaluated in vitro. An experimental human melanoma model was developed into athymic nude mice. Tumor growth, survival and histochemical studies were performed in order to investigate the expression levels of H4R, HA, PCNA, mitotic index (MI), and angiogenesis.

RESULTS

The results indicate that H4R agonists inhibited forskolin-induced cAMP levels only in M1/15 cells while increased phosphorylation levels of ERK1/2 and decreased proliferation in both cell types. In vivo studies show that HA and CLZ (1mgkg(-1), sc) significantly increased median survival and decreased tumor volume. These effects were associated to a reduction in MI, in the expression of proliferation marker and in intratumoral neovascularization.

CONCLUSIONS

We conclude that HA and CLZ exhibit an antitumoral effect in vitro and in vivo on human melanoma, suggesting the therapeutic potential of these compounds for the treatment of malignant melanoma.

DRD2/DARPP-32 expression correlates with lymph node metastasis and tumor progression in patients with esophageal squamous cell carcinoma

BACKGROUND

Dopamine receptors (DRs) are members of seven transmembrane domain trimeric guanosine 5'-triphosphate (GTP)-binding protein-coupled receptor family. Through dopamine receptor activation, dopamine plays a significant role in regulating gene expression, such as induced tumor cell migration.

MATERIALS AND METHODS

We investigated DRD1 and DRD2 expressions in patients with esophageal squamous cell carcinoma (ESCC) for immunohistochemistry and analyzed differences between DRD1, DRD2, and DARPP-32 expressions of clinicopathological features in 122 patients with ESCC.

RESULTS

DRD1 immunostaining correlated with the pathologic grade (P = 0.0127), and DRD2 immunostaining correlated with the pathologic stage (P = 0.0432) and pN classification (P = 0.0112). A significant correlation was found between DRD1 and DRD2 expression (P = 0.0292). However, no correlation was observed between DRD1/DRD2 expression and DARPP-32 expression (P = 0.4555 and 0.4774, respectively). No correlation was observed between the DRD1/DRD2 expression and patient prognosis. To find the cooperative role between DRD1, DRD2, and DARPP-32 expressions, patients were classified into the different groups. In the DRD2/DARPP-32 combination, the (+/-) group was significantly correlated with pathologic stage (P = 0.0006), lymph node metastasis (P = 0.0001), pT (P = 0.0287), and tumor size (P = 0.0202). Moreover, patients with this combination showed a lower survival rate compared with the other three groups (P = 0.0287).

CONCLUSIONS

We conclude that DRD2/DARPP-32 expression is associated with tumor progression and that DRD2/DARPP-32 expressions may help predict prognosis in patients with ESCC.

In vivo and in vitro detection of dopamine d2 receptors in uveal melanomas

Scintigraphy with radiolabeled benzamides was used in melanoma patients. Studies with a newer benzamide called 123I-epidepride, a high-affinity D2 receptor (D2R) antagonist, showed high sensitivity in D2R-positive pituitary adenomas. We evaluated the presence of D2R in patients with uveal melanomas in vivo with 123I-epidepride, and in vitro in melanomas, using immunohistochemistry (IHC) and 125I-epidepride autoradiography. We studied the in vivo tumor-to-background (TB) ratios in six patients with posterior uveal melanoma (one previously enucleated). IHC was performed in 3 of 6 tumors after enucleation and in another 20 uveal melanomas, 7 metastatic lymph nodes from skin melanoma, and 2 normal specimens. 125I-epidepride autoradiography was performed in 10 uveal melanomas (3 of which were studied in vivo), 7 metastases, and 2 normal samples. Radioligand uptake was present in the affected eye of 5 patients with uveal melanoma (TB = 3.1-6.1) and absent in the operated one (TB = 1). Eight uveal tumors were positive at IHC (35%), 14 weakly positive (61%), and 1 negative (4%). Two metastases were positive (29%), 2 weakly positive (29%), and 3 negative (42%). Two uveal tumors were positive at autoradiography (20%), 7 had nonspecific binding (70%), and 1 was negative (10%). One metastasis was positive (14%), while 6 were negative (86%). 123I-epidepride scintigraphy in uveal melanomas seems promising for sensitivity and image quality. D2R was demonstrated in a significant proportion of the melanomas, although 123I-epidepride uptake might also be nonspecific and unrelated to D2R binding. Although further studies on larger series are needed, 123I-epidepride could represent a future tool to study the expression of D2R in other classes of neuroendocrine tumors.

Melanin pigmentation in mammalian skin and its hormonal regulation

Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.

The cytotoxicity of dopamine may be an artefact of cell culture

Administration of L-DOPA is commonly used to treat Parkinson's disease, yet controversy continues as to whether the dopamine arising from it aggravates neuronal loss. Several authors have reported cytotoxic effects of L-DOPA and dopamine on cultured cells, but others have not. In this report using the rat pheochromocytoma cell line PC12 and the M14 human melanoma cell line we show that dopamine-mediated cell death is not specific for neuronal cells. Moreover, our data show that both L-DOPA and dopamine interact with commonly used cell culture media, undergoing oxidation to generate hydrogen peroxide and dopamine semiquinones/quinones. Catalase and reduced glutathione could protect against cytotoxicity. These results suggest that caution needs to be employed when using cell culture studies to predict effects of L-DOPA and/or dopamine in vivo because of the extracellular generation of reactive species in the culture media.