Dopamine Agonist Resistance Research Articles

MicroRNA-Mediated Drug Repurposing Unveiled Potential Candidate Drugs for Prolactinoma Treatment

Introduction: Prolactinomas, also called lactotroph adenomas, are the most encountered type of hormone-secreting pituitary neuroendocrine tumors in the clinic. The preferred first-line therapy is a medical treatment with dopamine agonists (DAs), mainly cabergoline, to reduce serum prolactin levels, tumor volume, and mass effect. However, in some cases, patients have displayed DA resistance with aggressive tumor behavior or are faced with recurrence after drug withdrawal. Also, currently used therapeutics have notorious side effects and impair the life quality of the patients. Methods: Since the amalgamation of clinical and laboratory data besides tumor histopathogenesis and transcriptional regulatory features of the tumor emerges to exhibit essential roles in the behavior and progression of prolactinomas; in this work, we integrated mRNA- and microRNA (miRNA)-level transcriptome data that exploit disease-specific signatures in addition to biological and pharmacological data to elucidate a rational prioritization of pathways and drugs in prolactinoma. Results: We identified 8 drug candidates through drug repurposing based on mRNA-miRNA-level data integration and evaluated their potential through in vitro assays in the MMQ cell line. Seven repurposed drugs including 5-fluorocytosine, nortriptyline, neratinib, puromycin, taxifolin, vorinostat, and zileuton were proposed as potential drug candidates for the treatment of prolactinoma. We further hypothesized possible mechanisms of drug action on MMQ cell viability through analyzing the PI3K/Akt signaling pathway and cell cycle arrest via flow cytometry and Western blotting. Discussion: We presented the transcriptomic landscape of prolactinoma through miRNA and mRNA-level data integration and proposed repurposed drug candidates based on this integration. We validated our findings through testing cell viability, cell cycle phases, and PI3K/Akt protein expressions. Effects of the drugs on cell cycle phases and inhibition of the PI3K/Akt pathway by all drugs gave us promising output for further studies using these drugs in the treatment of prolactinoma. This is the first study that reports miRNA-mediated repurposed drugs for prolactinoma treatment via in vitro experiments.

Predictors of dopamine agonist resistance in prolactinoma patients

BackgroundSurgical resection of prolactinomas resistant to dopamine agonists is frequently incomplete due to fibrotic changes of the tumour under pharmacological therapy. In order to identify a subgroup of patients who may benefit from early surgery, we thought to investigate possible predictive factors of pharmacological resistance of prolactinomas to dopamine agonists.MethodsWe retrospectively analyzed a database of a Belgian tertiary reference center for patients with pituitary tumours from 2014 to 2016. The groups of interest were patients with dopamine agonist responsive and resistant prolactinomas. The possible predictive factors, including MRI findings, endocrinological parameters, response of tumour and patient factors for dopamine agonist resistance were investigated.ResultsWe included 69 patients of whom 52 were women (75,4%) and 17 were men (24,6%). Rate of dopamine agonist resistance was 15.9%. We identified four significant predictors of dopamine agonist resistance: male gender, a large tumour volume, prolonged time to prolactin normalization and presence of a cystic, hemorrhagic and/or necrotic component. In addition, symptoms due to mass effect, high baseline prolactin level and a high contrast capture on MRI are factors that can be taken into consideration.ConclusionWe identified predictive factors for pharmacological resistance and developed a scoring system for patient specific prediction of resistance to dopamine agonists. This scoring system may have impact on the timing and decision of surgery in prolactinoma patients after further prospective evaluation.

Surgical Outcome of Endoscopic Transsphenoidal Surgery in Prolactinoma

Abstract Background: Prolactinoma represent approximately 30% of pituitary adenomas, they are the most common type of functioning pituitary adenoma, few studies have recently reexamined efficacy of transsphenoidal surgery in prolactin-oma. Aim of Study: The aim of this work is to evaluate the outcome of patients with prolactinoma treated by transsphe-noidal surgery, to identify the factors that affect the surgical outcome leading to remissions or recurrence. Patients and Methods: This is a retrospective study of 27 patients with prolactinoma treated in Neurosurgery Department in Benha University in the period between January 2015 and January 2018 of which 21 were women and 6 were men, the mean age was 40(±) 15 years. Results: Post-operative remission was obtained in 70% of cases. Better outcome was associated with smaller pre-operative tumor size, amount of removed tumor intraopera-tively, lack of invasion of nearby structures and lack of suprasellar extension. The mean follow-up period was 36 months. Recurrence was observed in 20% of cases during this period (5 cases). In patients with pre-operative dopamine agonist resistance treated again after surgery there was signif-icant reduction of prolactin level in about half of cases. Conclusion: Gross total removal, smaller tumor size, lack of cavernous sinus invasion and lack of suprasellar extension is associated with better outcome. Dopamine agonist resistant cases show better response to dopamine agonist after debulking.

Expression patterns of ERα66 and its novel variant isoform ERα36 in lactotroph pituitary adenomas and associations with clinicopathological characteristics.

The regulatory effects of estradiol on pituitary homeostasis have been well documented. However, the expression patterns of ERα66 and ERα36 and their correlations with the clinical course of postoperative prolactinoma tumors remain unclear. The expression of ERα36, ERα66, Ki67, p53, and CD31 were determined by immunohistochemistry in 62 prolactinoma patients. Snap-frozen tumors and normal pituitaries were also examined by western blotting for estrogen receptor detection. A broad expression of ERα36 was identified in normal pituitaries. The median scores of ERα36 and ERα66 expression were 8 and 6 in normal pituitaries and 4 and 0 in tumors, respectively. Four phenotypes of ERα36 and ERα66 expression were explored in tumors with regard to sex, invasiveness, dopamine resistance, and recurrence. Low ERα36 expression was associated with tumor invasion and increased Ki67. Low ERα66 expression was associated with tumor invasion, dopamine-agonist resistance, and enhanced tumor size. Multivariable logistic regression analysis showed that low ERα36 expression is an independent risk factor for invasiveness. The significant inverse association of ERα66 with invasiveness, dopamine resistance, and tumor size remained significant after adjustment for sex as a potential confounder. After controlling for sex, the low ERα66/low ERα36 phenotype was 6.24 times more prevalent in invasive tumors than in noninvasive tumors. Although the decreasing trend of CD31 expression from surrounding nontumoral lactotroph adenomas to tumors was similar to that of the estrogen receptors, a significant correlation was not observed here. The decreasing trends of ERα36 and ERα66 expression from normal pituitaries to tumors are associated with aggressive clinical behavior.

Surgery for prolactinomas: a better choice?

Renewed interest in transsphenoidal surgery (TSS) as a therapeutic option for prolactinomas has emerged. Based on contemporary literature and own experience, the changing role of surgery for treatment of prolactinomas is discussed. Today, TSS is performed by minimally invasive microscopic or endoscopic techniques. Normoprolactinemia is obtained in 71-100% of patients with microprolactinomas by TSS. Almost equal results are found in circumscribed intrasellar macroprolactinomas. In experienced hands, pituitary function is preserved in TSS. The risk of cardiac valve disease is still a concern with ergot-derived dopamine-agonists (DAs) in patients requiring long-term, high-dose dopamine-agonist (DA) treatment. Cost-utility analysis favors TSS over DA treatment. The possible negative impact of DA treatment on future surgical results is still a controversial and unsettled issue. In patients who wish to become pregnant, the advantages of microprolactinoma removal to avoid DAs and macroprolactinoma debulking to avoid symptomatic enlargement during pregnancy should be discussed with the patients. Young patients' age is an argument for surgery to circumvent the unpredictable sequelae of long-term DA treatment. Surgery should be discussed in male gender because of a higher likelihood of DA resistance and aggressive behavior of prolactinoma. Given excellent results of TSS and concerns about medical treatment, the scale of indications for TSS as an alternative to DAs has increased. The patient's wishes concerning a chance at a cure with TSS instead of a long-term treatment with DAs has become an important and accepted indication. With DA medication and TSS, two effective treatment modalities for prolactinomas are available that can be used in a complementary fashion.

MicroRNA-93 mediates cabergoline-resistance by targeting ATG7 in prolactinoma.

To date, the management of dopamine agonist (DA)-resistant prolactinomas remains a major clinical problem. Previously, we determined that miRNA-93 expression increases in DA-resistant prolactinomas; however, the role of miRNA-93 in the DA resistance remains largely unexplored. Hence, this study aimed to investigate the susceptibility of tumor cells to cabergoline (CAB) and the autophagy changes in MMQ and GH3 cells after miRNA-93 overexpression or inhibition. We used bioinformatics to identify the potential target of miRNA-93. Subsequently, we analyzed the correlation between miRNA-93 and autophagy-related 7 (ATG7) using protein expression analysis and luciferase assays. Furthermore, the change in the effect of miRNA-93 was measured after ATG7 overexpression. miRNA-93 expression was elevated in DA-resistant prolactinomas, whereas the expression of its identified target, ATG7, was downregulated. miRNA-93 overexpression suppressed the cytotoxic effect of CAB in MMQ and GH3 cells. In contrast, miRNA-93 downregulation enhanced CAB efficiency and promoted cell autophagy, eventually resulting in apoptosis. These results were further confirmed in vivo xenograft models in nude mice. ATG7 overexpression could reverse the inhibitory effect of miRNA-93 on CAB treatment. Taken together, our results suggest that miRNA-93 mediates CAB resistance via autophagy downregulation by targeting ATG7 and serves as a promising therapeutic target for prolactinoma.

Giant Prolactinomas: Outcomes of Multimodal Treatments for 42 Cases with Long-Term Follow-Up.

Giant prolactinomas represent a rare entity of pituitary tumors so that the management of these patients is still a prevalent challenge at present. Paying special attention to the treatment strategy and outcomes, we presented a large series of 42 cases looking forward to share our understanding and experience in management of these patients. Male patients accounted for 71.4% of this series and were relatively younger (35.70±2.42 vs. 52.00±3.55 years, p=0.0011) and harbored bigger tumors (14.57 vs. 7.74 cm3, p=0.0179) compared to females. Almost all of these tumors showed suprasellar extension (97.6%) and cavernous sinus invasion (92.9%). Dopamine agonist represented an efficient method to control PRL concentrations (98.8%) and reduce tumor burdens (81.2 %). PRL normalization was detected in 13 out of the 27 patients initially treated with bromocriptine (BRC) whereas none of the 14 patients with first-line operation gained a normalization of PRL concentration after surgery. Although there was no reliable predictor of tumor response, First PRL reduction was a predictive criterion for the nadir PRL level during the long-time period of follow-up for first-line bromocriptine treatment. In conclusion, patients with giant prolactinomas did not gain more benefits from initial surgery. Dopamine agonist (BRC) should be first-line treatment for giant prolactinomas whereas operation merely served as a remedy for acute compression symptoms and dopamine agonist resistance. Consecutive monitoring of serum PRL levels in the early stage of initial BRC treatment is useful for evaluation of therapeutic effect and further therapeutic decision.

The Balance of PI3K and ERK Signaling Is Dysregulated in Prolactinoma and Modulated by Dopamine.

Prolactin-secreting adenomas, or prolactinomas, cause hypogonadism, osteoporosis, and infertility. Although dopamine agonists (DAs) are used clinically to treat prolactinoma and reduce prolactin secretion via cAMP inhibition, the precise mechanism by which DAs inhibit lactotrope proliferation has not been defined. In this study, we report that phosphatidylinositol 3-kinase (PI3K) signals through AKT and mTOR to drive proliferation of pituitary somatolactotrope GH4T2 cells. We demonstrate that the DA cabergoline reduces activity of the mTOR effector s6K and diminishes GH4T2 cell proliferation primarily via activation of the long isoform of the dopamine D2 receptor (D2R). Dysfunctional D2R-mediated signaling and/or downregulated D2R expression is thought be the primary mechanism of DA resistance, which is observed in 10% to 20% of prolactinoma tumors. Dopamine-mediated D2R activation results in ERK stimulation and PI3K inhibition, suggesting that these two pathways act in an inverse manner to maintain lactotrope homeostasis. In this study, we found that ERK1/2-mediated prolactin transcription is inhibited by PI3K/CDK4-driven cell cycle progression, emphasizing that the ERK and PI3K signaling pathways oppose one another in lactotrope cells under homeostatic conditions. Lastly, we show that both ERK1/2 and AKT are activated in prolactinoma, demonstrating that the balance of ERK and AKT is dysregulated in human prolactinoma. Our findings reveal a potential use for dual pharmacological inhibitors of ERK and AKT as an alternative treatment strategy for DA-resistant prolactinomas.

Clinicopathological significance of baseline T2-weighted signal intensity in functional pituitary adenomas.

To assess baseline T2-weighted signal intensity (T2-WSI) of functional pituitary adenomas (FPA), and to investigate the relationship of baseline T2-WSI with clinical features, histopathological granulation patterns, and response to treatment in patients with acromegaly, prolactinoma and Cushing's disease (CD). Somatotroph adenomas (n = 87), prolactinomas (n = 78) and corticotroph adenomas (n = 29) were included in the study. Baseline T2-WSI findings (grouped as hypo-, iso- and hyperintense) were compared with hormone levels, tumor diameter, granulation patterns and response to treatment. Somatotroph adenomas were mostly hypointense (53%), prolactinomas were dominantly hyperintense (55%), and corticotroph adenomas were generally hyperintense (45%). Hyperintense somatotroph adenomas were larger in size with sparsely granulated pattern and tumor shrinkage rate was lower after somatostatin analogues (SSA) (p = 0.007, p = 0.035, p = 0.029, respectively). T2 hypointensity was related with higher baseline IGF-1% ULN (upper limit of normal) levels and a better response to SSA treatment (p = 0.02, p = 0.045, respectively). In female prolactinomas, hyperintensity was correlated with a smaller adenoma diameter (p = 0.001). Hypointense female prolactinomas were related to younger age at diagnosis, higher baseline PRL levels and dopamine agonist (DA) resistance (p = 0.009, p = 0.022, p < 0.001, respectively). Hyperintense corticotroph adenomas were related to larger adenoma size and sparsely granulated pattern (p = 0.04, p = 0.017, respectively). There was no significant difference in the recurrence with T2WSI in CD. Baseline hypointense somatotroph adenomas show a better response to SSA, whereas hypointensity was related to DA resistance in female prolactinomas.

Cabergoline and prolactinomas: lack of association between DRD2 polymorphisms and response to treatment.

About 80% of prolactinomas respond to dopamine agonists (DA) with hormonal normalization and tumor shrinkage. Mechanisms of DA resistance include reduction of dopamine receptor subtype 2 (DRD2) expression, short and long isoform ratio and post-receptor mechanisms. It was suggested that polymorphisms in the gene encoding dopamine receptor subtype 2 gene (DRD2) could be associated with variable effectiveness of cabergoline (CAB). To assess the influence of DRD2 polymorphisms in responsiveness of CAB treatment in patients with prolactinoma. Cross-sectional retrospective case-control study analyzing the frequency of five DRD2 polymorphisms in 148 patients with prolactinoma and 349 healthy subjects. The association of genetic variants and clinical characteristics with CAB responsiveness was performed in 118 patients (mean age at diagnosis 29years; range 11-61years) with hormonal evaluation. Patients with prolactin (PRL) normalization were considered as responders. No association in genotypes and allele proportions was found comparing patients and controls. On pharmacogenetic study, 118 patients on CAB were included and 20% were non-responders. No association was found between clinical characteristics (gender, age, PRL level and tumor size at diagnosis) and polymorphisms of DRD2 with CAB responsiveness. Otherwise, there was association between polymorphisms rs1076560 (allele A) and rs1800497 (allele T) and the presence of macroadenomas. No correlation was found between DRD2 polymorphisms and CAB responsiveness in patients with prolactinoma. More data are necessary in order to assess the influence of DRD2 genotyping on DA treatment response.

A novel surgical approach for the management of giant invasive prolactinoma compressing the brainstem.

SummaryProlactinomas constitute the largest subsection of all secretory pituitary adenomas. Most are microprolactinomas and are satisfactorily treated by medical management alone. Giant prolactinomas, measuring more than 4 cm in diameter, are rare and usually occur more commonly in men. Macroprolatinomas tend to present with symptoms of mass effect rather than those of hyperprolactinaemia. Dopamine agonists (DA) are the treatment of choice for all prolactinomas. Surgery is usually reserved for DA resistance or if vision is threatened by the mass effects of the tumour. We describe the case of a 52 year-old woman with a giant invasive prolactinoma who required multiple surgical procedures as well as medical management with DA. One of the surgical interventions required a posterior approach via the trans cranial sub occipital transtentorial approach, a surgical technique that has not been previously described in the medical literature for this indication. The giant prolactinoma was reduced significantly with the above approach and patient symptoms from the compressing effects of the tumour were resolved. This case highlights the importance of a multidisciplinary approach to the management of such patients who present with florid neurological sequelae secondary to pressure effects. Although this presentation is uncommon, surgery via a sub occipital transtentorial approach may be considered the treatment of choice in suitable patients with giant invasive prolactinomas compressing the brainstem.Learning points Giant prolactinomas present with symptoms of mass effect or those of hyperprolactinaemia.Interpretation of the pituitary profile is crucial to guide further investigations and management.Treatment of giant invasive prolactinomas may involve a combination of medical management and multiple surgical interventions.Treatment with DA may cause pituitary haemorrhage or infarction in patients with these tumours.A sub occipital transtetorial approach may be considered the treatment of choice in invasive prolactinomas compressing the brainstem.Multidisciplinary approach of such patients is fundamental for a better outcome.

Lower PRDM2 expression is associated with dopamine-agonist resistance and tumor recurrence in prolactinomas.

BackgroundDopamine agonists (DAs) are the first-line treatment for prolactinomas, which account for 25–30% of functioning pituitary adenomas, and bromocriptine (BRC) is the only commercially available DAs in China. However, tumors are resistant to therapy in 5–18% of patients.MethodsThe exomes of six responsive prolactinomas and six resistant prolactinomas were analyzed by whole-exome sequencing.ResultsUsing stringent variant calling and filtering parameters, ten somatic variants that were mainly associated with DNA repair or protein metabolic processes were identified. New resistant variants were identified in multiple genes including PRDM2, PRG4, MUC4, DSPP, DPCR1, RP1L1, MX2, POTEF, C1orf170, and KRTAP10-3. The expression of these genes was then quantified by real-time reverse-transcription PCR (RT–qPCR) in 12 prolactinomas and 3 normal pituitary glands. The mRNA levels of PRDM2 were approximately five-fold lower in resistant prolactinomas than in responsive tumors (p < 0.05). PRDM2 protein levels were lower in resistant prolactinomas than in responsive tumors, as determined by Western blotting and immunohistochemical analysis (p < 0.05). Overexpression of PRDM2 upregulated dopamine receptor D2 (D2DR) and inhibited the phosphorylation of ERK1/2 in MMQ cells. PRDM2 showed a synergistic effect with BRC on the inhibition of prolactin (PRL) secretion and MMQ cell viability, and low PRDM2 expression was associated with tumor recurrence.ConclusionsPRDM2 downregulation may play a role in dopamine-agonist resistance and tumor recurrence in prolactinomas.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-1267-0) contains supplementary material, which is available to authorized users.

Characteristics of Dynamic Magnetic Resonance Image Enhancement in Prolactinomas Resistant to Dopamine Agonist Therapy

ObjectiveThe objective of this study was to determine whether dynamic magnetic resonance imaging (dMRI) enhancement parameters could predict dopamine agonist (DA) resistance in prolactinomas.MethodsWe retrospectively identified patients with prolactinomas who...

Retrospective analyses of clinical and laboratory features of 646 patients with prolactinoma in Turkey

Background: Prolactinomas are the most frequently occurring pituitary adenomas and consist of nearly 40% of all pituitary adenomas. Their prevalence varies from approximately 60 to 100 inhabitants per million. Objectives: This study aimed to determine demographic and clinical features of patients with prolactinoma. In addition, it targeted to determine success percentage of medical therapy and frequency of dopamine agonist (DA) resistance. Materials and Methods: Records of 646 patients who were admitted to Endocrinology and Metabolism Disease department of two hospitals in Turkey between 2007 and 2014 were evaluated retrospectively. Data of the study were obtained from file records for 53% patients and ICD-10 diagnosis code of electronic database of the hospital in 47% of patients. Results: Of patients who received medical therapy, 91.7% (n = 394) had received cabergoline (CAB) and 8.6% (n = 55) had received bromocriptine (BMC). While normalization rate of prolactin was 92.7% with medical therapy, size of the adenoma completely regressed in 59.7% patients. Size of the adenoma decreased more than 50% in 56% patients. Resistance was detected against DA drugs in 6.9% patients. DA resistance found in 3.9% of patients with microprolactinoma and 27% of patients with macroprolactinoma. Conclusion: Success percentage of CAB therapy was found greater than BMC therapy in patients with microprolactinoma, which was in line with the literature. And, frequency of DA resistance was found to be lower in patients with microprolactinoma and greater in patients with macroprolactinoma than that reported in the literature.

Macroprolactinomas in Children and Adolescents: Factors Associated With the Response to Treatment in 77 Patients

Pituitary adenomas are rare in children and adolescents. The response of macroprolactinomas to dopamine agonists (DA) in this age group has been less extensively studied than in adults. We retrospectively analyzed data on a large cohort of young patients with macroprolactinomas. Patients aged younger than 20 years at macroprolactinoma diagnosis and seen in three tertiary referral centers between 1983 and 2013 were studied by analyzing their clinical and genetic (AIP and MEN1) characteristics. Hormonal and tumoral responses to DA were analyzed, and the patients' status at their last visit, after a mean (±SD) follow-up of 8.2 ± 5.8 years, was assessed. The cohort comprised 77 patients (26 males, 51 females). Mean age at diagnosis was 16.1 ± 2.5 years (range, 4.5-20 y). In both sexes, the most frequent revealing symptom was a pubertal disorder (49%), followed by visual problems (24%) and growth retardation (24%). Basal prolactin (PRL) levels and maximal tumor diameter were significantly higher in boys than in girls (7168 ng/mL, 202-40 168 vs 1433 ng/mL, 115-20 000, P = .002; and 33 ± 14 mm, 15-64 vs 19 ± 9 mm; 10-50, P < .001, respectively). PRL levels normalized in 74% of the patients treated with DA. A mutation of AIP or MEN1 was found in 14% of the patients. Factors associated with resistance to DA were young age, higher PRL levels, larger volume, and the presence of a MEN1 (but not an AIP) mutation. Macroprolactinomas are rare below the age of 20 years, mainly occurring in girls and during adolescence. Like adults, young patients are very sensitive to DA, which should therefore be considered the first-line treatment. DA resistance is associated with a higher PRL level and larger tumor size, both parameters being closely linked together. About 14% of these young patients have an AIP or MEN1 mutation, this latter being an independent predictor of DA resistance.

Low levels of PRB3 mRNA are associated with dopamine-agonist resistance and tumor recurrence in prolactinomas

Prolactinomas, or prolactin-secreting adenomas, constitute the most common type of hyperfunctioning pituitary adenoma. Dopamine agonists are used as first-line medication for prolactinomas, but the tumors are resistant to the therapy in 5-18% of patients. To explore potential mechanisms of resistance to bromocriptine (a dopamine agonist), we analyzed six responsive prolactinomas and six resistant prolactinomas by whole-exome sequencing. We identified ten genes with sequence variants that were differentially found in the two groups of tumors. The expression of these genes was then quantified by real-time reverse-transcription PCR (RT-qPCR) in the 12 prolactinomas and in six normal pituitary glands. The mRNA levels of one of the genes, PRB3, were about fourfold lower in resistant prolactinomas than in the responsive tumors (p=0.02). Furthermore, low PRB3 expression was also associated with tumor recurrence. Our results suggest that low levels of PRB3 mRNA may have a role in dopamine-agonist resistance and tumor recurrence of prolactinomas.

Outcomes of transsphenoidal surgery in prolactinomas: improvement of hormonal control in dopamine agonist-resistant patients

Few studies have recently re-examined the efficacy of neurosurgery in prolactinoma patients operated for various indications. To analyze outcomes of patients with a prolactinoma treated by transsphenoidal surgery, to identify factors associated with remission and relapse, and to evaluate if surgical debulking allows for better hormonal control in patients with preoperative resistance to dopamine agonists (DAs). This was a retrospective review of patients with a benign prolactinoma followed preoperatively and postoperatively in our department and treated by transsphenoidal surgery (n=63; 45 women; mean age: 31 ± 14 years). Postoperative remission was obtained in 63% of microprolactinomas, 60% of noninvasive macroprolactinomas, and none of the invasive macroprolactinomas. Better remission rate was independently predicted by lower diagnostic prolactin (PRL) levels and by the lack of abnormal postoperative residual tissue (P<0.05). A recurrence of hyperprolactinemia was observed in 34% of patients after a median follow-up period of 36 (7-164) months. In patients with preoperative DA resistance treated again after surgery, there was a significant reduction in PRL levels postoperatively (26 (6-687) ng/ml) vs preoperatively (70 (22-1514) ng/ml; P<0.01) under a lower DA dose, and about half of the patients had PRL normalization. Recurrence of hyperprolactinemia is observed in one-third of prolactinoma patients after surgical remission and may occur as late as 13 years after surgery. Resistance to DA can be considered as a good surgical indication, as partial tumor resection allows for better hormonal control with a lower dose of DAs.

Resistance to dopamine agonists in prolactinoma is correlated with reduction of dopamine D2 receptor long isoform mRNA levels

Dopamine agonists normalize prolactin (PRL) levels and reduce tumour size in responsive prolactinoma. However, several cases have shown resistance to dopamine agonists upon initial treatment. Infrequently, prolactinoma initially responds, but then becomes refractory to prolonged treatment (secondary resistance). We investigated the possible mechanisms of resistance to dopamine agonists. Twelve cases of prolactinoma were surgically resected and classified according to the responsiveness of PRL levels and tumour size to dopamine agonists: good responders (n = 5), poor responders (n = 5), or secondary resistance (n = 2). We examined the expression of dopamine D(2) receptor (D(2)R) isoform (short: D(2)S and long: D(2)L) mRNA and protein. We investigated DNA methylation patterns in the promoter region of the DRD2 gene. The predominant D(2)R isoform expressed in prolactinoma was D(2)L. Levels of D(2)L mRNA were significantly lower in secondary resistance and poor responders than in good responders. Expression of D(2)R protein was variable among cases. Almost no CpG sites of the DRD2 gene promoter region were methylated. Resistance of prolactinoma to dopamine agonists is correlated with a reduction in D(2)L isoform mRNA levels. Silencing of the DRD2 gene by methylation in the promoter region is unlikely to play a role in dopamine agonist resistance in prolactinoma.

HER2/ErbB2 Receptor Signaling in Rat and Human Prolactinoma Cells: Strategy for Targeted Prolactinoma Therapy

Dopamine agonist resistance or intolerance is encountered in approximately 20% of prolactinoma patients. Because human epidermal growth factor receptor 2 (HER2)/ErbB2 is overexpressed in prolactinomas and ErbB receptor ligands regulate prolactin (PRL) gene expression, we tested the role of HER2/ErbB2 in prolactinoma hormone regulation and adenoma cell proliferation to assess the rationale for targeting this receptor for prolactinoma therapy. As we showed prolactinoma HER2 overexpression, we generated constitutively active HER2-stable GH3 cell transfectants (HER2CA). PRL mRNA levels were induced approximately 250-fold and PRL secretion was enhanced 100-fold in HER2CA cells, which also exhibited increased proliferation. Lapatinib, a dual tyrosine kinase inhibitor (TKI) of both epidermal growth factor receptor (EGFR)/ErbB1 and HER2, blocked receptor signaling, and suppressed PRL expression more than gefitinib, a TKI of EGFR/ErbB1. Lapatinib also suppressed colony formation in soft agar more than gefitinib. Oral lapatinib treatment caused tumor shrinkage and serum PRL suppression both in HER2CA transfectant-inoculated Wistar-Furth rats and in estrogen-induced Fischer344 rat prolactinomas. In cultured human cells derived from resected prolactinoma tissue, lapatinib suppressed both PRL mRNA expression and secretion. These results demonstrate that prolactinoma HER2 potently induces PRL and regulates experimental prolactinoma cell proliferation. Because pituitary HER2 signaling is abrogated by TKIs, this receptor could be an effective target for prolactinoma therapy.

Use of the Leksell Gamma Knife in the Treatment of Prolactinoma Patients

The current treatment of choice for prolactinomas is pharmacologic therapy with dopamine agonists (DA). However, these drugs must be taken long-term or even life-long, and they are unsuccessful in adenoma patients who are resistant to or intolerant of DA. Other options in such patients include surgical treatment or radiosurgery with the Leksell gamma knife (LGK). This non-randomized trial was designed to examine the effectiveness of LGK irradiation in treating prolactinoma patients who were resistant to or intolerant of DA. A secondary aim was to investigate the effect of LGK in improving the effects of DA on the size of adenomas, shortening the length of administration of DA, and normalizing prolactin levels permanently. The study population was comprised of 35 patients with prolactin secreting pituitary adenomas (27 females and 8 males), with an average age of 40.3 years (range: 18-71). Nine of the 35 patients (25.7%) had microprolactinomas and 26 of the 35 (74.3%) had macroprolactinomas. The mean ± SD follow-up period was 75.5 ± 34.4 months. Twenty-five patients (71.4%) received only pharmacologic therapy with DA before LGK and 10 patients (28.6%) underwent pituitary adenoma surgery in addition to DA therapy. LGK irradiation was indicated because of drug intolerance (31.4%), partial or complete DA resistance (45.7%), and attempts to shorten the period of treatment with DA or reduce the dosage (22.9%). Pituitary function was monitored regularly by measuring hormone levels at 6-month intervals. The median central radiation dose was 70 Gy (range: 40-80 Gy) and the median minimal peripheral dose was 34 Gy (range: 20-49 Gy). Normoprolactinemia was achieved in 80% (28/35) of the study patients. This included 37.1% (13/35 patients) who discontinued DA treatment and 42.9% (15/35 patients) who continued DA treatment after irradiation. After discontinuation of DA in the study subjects, the median time for hormonal normalization was 96 months. None of the patients achieving normoprolactinemia with LGK experienced any disease relapse. Only 1 patient (2.5%) experienced further growth of the adenoma after LGK irradiation. These findings suggest that LGK may achieve normoprolactinemia in 80.0% of the patients with pituitary adenomas who fail pharmacological therapy due to resistance to, or intolerance of, DAs and insufficient response to DA before radiation. The absence of relapse after normalization with LGK contrasts with DA therapy which produces a permanent remission in less than 50% of patients after discontinuation.