The Expression of Dopamine Receptors Gene and their Potential Role in Targeting Breast Cancer Cells with Selective Agonist and Antagonist Drugs. Could it be the Novel Insight to Therapy?

BACKGROUND: Breast cancer is one of the common causes of mortality for women in Iran and other parts of the world. The substantial increasing rate of breast cancer in both developed and developing countries warns the scientists to provide more preventive steps and therapeutic measures. This study is conducted to investigate the impact of neurotransmitters (e.g., Dopamine) through their receptors and the importance of cancers via damaging immune system. It also evaluates dopamine receptors gene expression in the women with breast cancer at stages II or III and dopamine receptor D2 (DRD2) related agonist and antagonist drug effects on human breast cancer cells, including MCF-7 and SKBR-3. METHODS: The patients were categorized into two groups: 30 native patients who were diagnosed with breast cancer at stages II and III, with the mean age of 44.6 years and they were reported to have the experience of a chronic stress or unpleasant life event. The second group included 30 individuals with the mean age of 39 years as the control group. In order to determine the RNA concentration in all samples, the RNA samples were extracted and cDNA was synthesized. The MCF-7 cells and SKBR-3 cells were treated with dopamine receptors agonists and antagonists. The MTT test was conducted to identify oxidative and reductive enzymes and to specify appropriate dosage at four concentrations of dopamine and Cabergoline on MCF-7 and SKBR-3 cells. Immunofluorescence staining was done by the use of a mixed dye containing acridine orange and ethidiume bromide on account of differentiating between apoptotic and necrotic cells. Flow cytometry assay was an applied method to differentiate necrotic from apoptotic cells. RESULTS: Sixty seven and thirty three percent of the patients were related to stages II and III, respectively. About sixty three percent of the patients expressed ER, while fifty seven percent expressed PR. Thirty seven percent of the patients were identified as HER-2 positive. All types of D2-receptors were expressed in PBMC of patients with breast cancer and healthy individuals. The expression of the whole dopamine receptor subtypes (DRD2-DRD4) was carried out on MCF-7 cell line. The results of RT-PCR confirmed the expression of DRD2 on SKBR-3 cells, whereas the other types of D2- receptors did not have an expression. The remarkable differences in gene expression rates between patients and healthy individuals were revealed in the result of the Real-time PCR analysis. The over expression in DRD2 and DRD4 genes of PBMCs was observed in the patients with breast cancer at stages II and III. The great amount of apoptosis and necrosis occurred after the treatment of MCF-7 cells by Cabergoline from 25 to 100 µmolL-1 concentrations. CONCLUSION: This study revealed the features of dopamine receptors associated with apoptosis induction in breast cancer cells. Moreover, the use of D2-agonist based on dopamine receptors expression in various breast tumoral cells could be promising as a new insight of complementary therapy in breast cancer.

Prototypical antipsychotic drugs protect hippocampal neuronal cultures against cell death induced by growth medium deprivation.

BACKGROUND: Several clinical studies suggested that antipsychotic-based medications could ameliorate cognitive functions impaired in certain schizophrenic patients. Accordingly, we investigated the effects of various dopaminergic receptor antagonists--including atypical antipsychotics that are prescribed for the treatment of schizophrenia--in a model of toxicity using cultured hippocampal neurons, the hippocampus being a region of particular relevance to cognition. RESULTS: Hippocampal cell death induced by deprivation of growth medium constituents was strongly blocked by drugs including antipsychotics (10(-10)-10(-6) M) that display nM affinities for D2 and/or D4 receptors (clozapine, haloperidol, (+/-)-sulpiride, domperidone, clozapine, risperidone, chlorpromazine, (+)-butaclamol and L-741,742). These effects were shared by some caspases inhibitors and were not accompanied by inhibition of reactive oxygen species. In contrast, (-)-raclopride and remoxipride, two drugs that preferentially bind D2 over D4 receptors were ineffective, as well as the selective D3 receptor antagonist U 99194. Interestingly, (-)-raclopride (10(-6) M) was able to block the neuroprotective effect of the atypical antipsychotic clozapine (10(-6) M). CONCLUSION: Taken together, these data suggest that D2-like receptors, particularly the D4 subtype, mediate the neuroprotective effects of antipsychotic drugs possibly through a ROS-independent, caspase-dependent mechanism.

Effect of substituted benzamides on feeding and hypothalamic neuropeptide Y-like immunoreactivity (NPY-LI) in rats.

The study was conducted: (i) to evaluate the effects of three substituted benzamides on feeding behaviour in rats with free access to food and in those with access to food limited either to the light or to the dark phase of the diurnal cycle; and (ii) to determine whether the hypothalamic neuropeptide Y (NPY) system is involved in the action of these drugs on feeding. In free-feeding rats, a single dose of eticlopride (1 mg/kg, i.p.) or raclopride (1 mg/kg, i.p.) decreased 24-h food intake, whereas remoxipride (3 mg/kg, i.p.) produced no effect. Single doses of eticlopride and raclopride but not of remoxipride decreased hypothalamic neuropeptide Y-like immunoreactivity (NPY-LI). Eticlopride administered once daily for 14 days decreased both food intake and hypothalamic NPY-LI. When given for 14 days, raclopride and remoxipride decreased food intake in rats with access to food in the dark (19.00-07.00) but not in thelight (07.00-19.00) phase of the diurnal cycle; both these compounds decreased hypothalamic NPY-LI only in the former group of rats. The results suggest that the effects of substituted benzamides on feeding behaviour depend on the drug and the time of administration and that these effects are related to the altered function of the hypothalamic NPY system.

An assessment of the peripheral antinociceptive potential of remoxipride, clonidine and fentanyl in sheep using the forelimb tourniquet.

A modification of the intravenous regional anaesthesia technique was used to assess the peripheral antinociceptive effect of remoxipride, clonidine and fentanyl. Drugs administered intravenously via peripheral catheters were restricted to the distal limb and nociceptive threshold test site by prior inflation of a tourniquet proximal to both the catheter and a threshold-testing device. Lignocaine (1 mg/kg) induced peripheral antinociception during tourniquet inflation. Clonidine (6 micrograms/kg) only induced significant elevations in thresholds after tourniquet deflation. A low dose of remoxipride (2 mg/kg), which had no systemic antinociceptive effect, produced antinociception after its restriction to the periphery. Peripheral administration of saline and tourniquet-induced restriction of blood flow to the distal limb did not alter threshold values. Peripheral administration of fentanyl was used to test a further modification of the injection protocol designed to reduce the incidence of leakage into the systemic circulation. Fentanyl administration (11.2 micrograms/kg) failed to elicit an increase in thresholds when it was restricted to the distal limb test site. The contribution of a peripheral mechanism to the antinociception induced by systemic administration of a higher remoxipride dose (7.5 mg/kg) was investigated using an inflated tourniquet to exclude remoxipride from the periphery. Exclusion of remoxipride from the periphery reduced its antinociceptive effect, i.e. threshold values were lower than if remoxipride was allowed free access to the limb prior to tourniquet inflation. The technique described here was effective in demonstrating that the increase in noninflammatory nociceptive thresholds seen with clonidine and fentanyl is not peripherally mediated whilst that seen with remoxipride has a peripheral component.

The atypical antipsychotic, remoxipride, blocks phencyclidine-induced disruption of prepulse inhibition in the rat.

The effect of various typical (haloperidol) and atypical (clozapine, raclopride, remoxipride) antipsychotics on phencyclidine (PCP)-induced disruption of sensorimotor gating was tested in rats using an acoustic startle paradigm. Clozapine (4-40 mumol/kg), haloperidol (1-5 mumol/kg) and raclopride (1-12 mumol/kg) failed to reverse PCP-induced disruption of prepulse inhibition (PPI) of the acoustic startle response. In contrast, remoxipride (12-60 mumol/kg) caused a dose-dependent block of this effect. PCP-induced disruption of PPI is a widely accepted animal model of a corresponding behavioural deficit observed in schizophrenia although little evidence has been presented that it is in fact sensitive to antipsychotic agents. The present results indicate that remoxipride behaves in a unique way in this model compared to clozapine, haloperidol and raclopride.

A common action of clozapine, haloperidol, and remoxipride on D1- and D2-dopaminergic receptors in the primate cerebral cortex.

The potencies of the major neuroleptics used in the treatment of schizophrenia, including haloperidol and remoxipride, correlate with their ability to bind D2-dopaminergic receptors in subcortical structures. On the other hand, the neuroleptic clozapine has a low affinity for these sites, and the pharmacological basis of its beneficial action is less clear. We have found that chronic treatment with clozapine, haloperidol, and remoxipride up-regulates D2 receptors in specific cortical areas of the rhesus monkey frontal, parietal, temporal, and occipital lobes. Of particular interest, all three neuroleptics down-regulated D1 receptors in prefrontal and temporal association regions--the two areas most often associated with schizophrenia. This latter finding raises the possibility that down-regulation of D1 receptors in prefrontal and temporal cortex may be an important component of the therapeutic response to neuroleptic drugs. Further, the common effects of three neuroleptics with different pharmacological profiles in the cerebral cortex is consistent with the idea that this structure is a major therapeutic target in the treatment of schizophrenia.

Preclinical findings with new antipsychotic agents: what makes them atypical?

Many early antipsychotics such as haloperidol, while effective in treating the symptoms of schizophrenia, cause detrimental side effects and moreover induce nonspecific sedation in many patients. Newer drugs such as remoxipride are as effective as the classical antipsychotics but induce fewer debilitating side effects. These clinical properties are reflected to some extent in their preclinical pharmacology, with drugs such as remoxipride having effects on various preclinical behavioural and biochemical models that are quite different to those exerted by drugs such as haloperidol. This article reports some new behavioural data and discusses the various mechanisms that can underlie the effect of new atypical antipsychotics.

On dopaminergic modulation of temporal information processing.

Temporal processing of durations in the range of seconds or more (i.e. time estimation) is cognitively mediated, whereas processing of brief durations in the range of milliseconds (i.e. time perception) appears to be beyond cognitive control and based on neural counting mechanisms. Although there is some evidence from animal and human studies suggesting that the internal timing mechanism underlying time perception is modulated by the effective level of brain dopamine, the findings are not conclusive. Therefore, the effects of pharmacologically induced changes in D2 receptor activity on temporal information processing were evaluated. In a double-blind design, either 3 mg of haloperidol, 150 mg of remoxipride, or placebo were administered in a single oral dose. Performance on time estimation was significantly impaired by both haloperidol and remoxipride as compared with placebo. Both drugs obviously affected cognitive mechanisms underlying temporal processing of durations in the range of seconds. On the other hand, only haloperidol produced a significant decrease in performance on time perception as compared with placebo and remoxipride, whereas the remoxipride and placebo groups did not differ significantly. The differential effects of haloperidol and remoxipride on performance on time perception suggest that D2 receptor activity in the basal ganglia may play a critical role in timing of brief durations in the range of milliseconds.

Remoxipride and raclopride differentially alter the activity of incertohypothalamic dopaminergic neurons.

The effects of two dopaminergic (DA) antagonists, raclopride (S-(-)-3,5-dichloro-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-hydroxy- 6-methoxybenzamide(+)-tartrate) and remoxipride (S(-)-3-bromo-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2, 6-dimethoxybenzamide hydrochloride monohydrate), were compared on the DA receptor-mediated regulation of incertohypothalamic and nigrostriatal DA neurons. Both drugs produced dose- and time-related increases in concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum, which contains the terminals of the nigrostriatal DA neurons. On the other hand, raclopride but not remoxipride increased concentrations of DOPAC in the medial zona incerta and dorsomedial hypothalamic nucleus, regions that contains cell bodies and terminals, respectively, of incertohypothalamic DA neurons. These results suggest that raclopride blocks a population of DA receptors that regulates the activity of incertohypothalamic DA neurons, whereas remoxipride does not.