Dopamine 2 and somatostatin 1-5 receptors coexpression in clinically non-functioning pituitary adenomas

Hybrid Somatostatin Receptor PET/MRI of the Head and Neck

Hybrid PET/MRI has the potential to transform neuro-oncologic imaging, particularly in diagnosis and treatment planning of somatostatin receptor-expressing tumors of the head and neck. Hybrid PET/MRI combines high-resolution MRI with functional information from PET, providing precise anatomic information and overcoming difficulties in localization inherent to PET alone. There is a range of tumors in the head and neck that overexpress somatostatin receptors and are therefore amenable to evaluation with somatostatin receptor PET/MRI. These include meningiomas, paragangliomas, olfactory neuroblastomas, pituitary neuroendocrine tumors, middle ear neuroendocrine tumors, and medullary thyroid carcinomas. The combination of PET and MRI is superior to either modality alone and can address several unique diagnostic challenges associated with these lesions. The authors discuss the superior capabilities of somatostatin receptor PET/MRI, including improved lesion localization, more sensitive demonstration of disease extent, enhanced surveillance, optimized radiation therapy planning, and accurate prediction of response to somatostatin analog therapy. Although there are only a few dedicated PET/MRI units available in clinical practice, commercial software is now available that can automatically fuse PET/CT data with recently acquired MRI data, increasing the availability of this approach. Radiologists should be aware of the advantages of somatostatin receptor PET/MRI in evaluation of head and neck tumors as well as the potential pitfalls of this approach so that they can accurately advise clinicians and better interpret these studies. ©RSNA, 2024 See the invited commentary by Shatzkes and Strauss in this issue.

Agonists, Antagonists and Receptors of Somatostatin: Pathophysiological and Therapeutical Implications in Neoplasias

Somatostatin is a peptide that plays a variety of roles such as neurotransmitter and endocrine regulator; its actions as a cell regulator in various tissues of the human body are represented mainly by inhibitory effects, and it shows potent activity despite its physiological low concentrations. Somatostatin binds to specific receptors, called somatostatin receptors (SSTRs), which have different tissue distributions and associated signaling pathways. The expression of SSTRs can be altered in various conditions, including tumors; therefore, they can be used as biomarkers for cancer cell susceptibility to certain pharmacological agents and can provide prognostic information regarding disease evolution. Moreover, based on the affinity of somatostatin analogs for the different types of SSTRs, the therapeutic range includes conditions such as tumors, acromegaly, post-prandial hypotension, hyperinsulinism, and many more. On the other hand, a number of somatostatin antagonists may prove useful in certain medical settings, based on their differential affinity for SSTRs. The aim of this review is to present in detail the principal characteristics of all five SSTRs and to provide an overview of the associated therapeutic potential in neoplasias.

Pre-and post-surgical non-functional pituitary adenomas and their relationship with high levels of serum glucose

OBJECTIVES

This clinical, analytical, retro-prospective, auto-controlled, not randomized, and not blinded study, aimed to investigate the association of changes in the serum glucose levels with the pre-and-post changes in the size tumor in mm3 in the Non-Functional pituitary adenomas.

METHODS

Pre-and post-surgical MRI, as well as the measurements in the serum glucose levels and immunohistochemical techniques were performed in all the patients in the study, with a mean followed-up until 208.57 days. A comparison was made between the reductions in tumor size of hormonally active pituitary adenomas (HSPAs) vs NFPAs.

RESULTS

Seventy-four patients were included in this study, of whom, 46 were NFPAs. The decrease in the NFPAs tumor size after surgery was statistically significant (P ≤ 0.0001). The Mean of the differences of both type of tumors in mm3 were -9552 ± 10287. Pre-surgery, the mean of the HSPAs were 8.923 ± 2.078; and the NFPAs were 14.161 ± 1.912. The differences in the tumor size were statistically significant (p = 0.039). Post-surgical, the mean of the HSPAs were 2.079 ± 971, with a (p = 0.14): and the NFPAs were 4.609 ± 1.205. After surgery of the NFPAs, most of the patients-maintained serum levels ≤ 100 mg/dL, with a statistical significance (P ≤ 0.0003).

CONCLUSION

This study demonstrates for the first time the correlation between the presence of pre-and post- surgical changes in the NFPAs, with modifications in the levels of serum glucose, and the comparison, pre- and post-surgical between the tumor size of HSPAs and NFPAs.

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

Somatostatin Receptor-PET/CT/MRI of Head and Neck Neuroendocrine Tumors

BACKGROUND AND PURPOSE

Due to its high sensitivity, somatostatin receptor-PET may detect smaller lesions and more extensive disease than contrast-enhanced MR imaging, while the superior spatial resolution of MR imaging enables lesions to be accurately localized. We compared results of somatostatin receptor-PET/MRI with those of MR imaging alone and assessed the added value of vertex-to-thigh imaging for head and neck neuroendocrine tumors.

MATERIALS AND METHODS

Somatostatin receptor-PET/CT was acquired as limited brain or head and neck imaging, with optional vertex-to-thigh imaging, following administration of 64CU/68GA DOTATATE. Somatostatin receptor-PET was fused with separately acquired contrast-enhanced MR imaging. DOTATATE activity was classified as comparable, more extensive, and/or showing additional lesions compared with MR imaging. Vertex-to-thigh findings were classified as positive or negative for metastatic disease or incidental.

RESULTS

Thirty patients (with 13 meningiomas, 11 paragangliomas, 1 metastatic papillary thyroid carcinoma, 1 middle ear neuroendocrine adenoma, 1 external auditory canal mass, 1 pituitary carcinoma, 1 olfactory neuroblastoma, 1 orbital mass) were imaged. Five had no evidence of somatostatin receptor-positive lesions and were excluded. In 11/25, somatostatin receptor-PET/MRI and MR imaging were comparable. In 7/25, somatostatin receptor-PET/MRI showed more extensive disease, while in 9/25, somatostatin receptor-PET/MRI identified additional lesions. On vertex-to-thigh imaging, 1 of 17 patients was positive for metastatic disease, 8 of 17 were negative, and 8 of 17 demonstrated incidental findings.

CONCLUSIONS

Somatostatin receptor-PET detected additional lesions and more extensive disease than contrast-enhanced MR imaging alone, while vertex-to-thigh imaging showed a low incidence of metastatic disease. Somatostatin receptor-PET/MRI enabled superior anatomic delineation of tumor burden, while any discrepancies were readily addressed. Somatostatin receptor-PET/MRI has the potential to play an important role in presurgical and radiation therapy planning of head and neck neuroendocrine tumors.

[68 Ga]-DOTATATE PET/MR-based evaluation of physiologic somatostatin receptor 2 expression in the adult pituitary gland as a function of age and sex in a prospective cohort

PURPOSE

The pituitary gland has the fourth highest physiologic avidity of [68 Ga]-DOTATATE. In order to guide our understanding of [68 Ga]-DOTATATE PET in clinical contexts, accurate characterization of the normal pituitary gland is first required. This study aimed to characterize the normal pituitary gland using dedicated brain [68 Ga]-DOTATATE PET/MRI as a function of age and sex.

METHODS

A total of 95 patients with a normal pituitary gland underwent brain [68 Ga]-DOTATATE PET examinations for the purpose of diagnosing CNS SSTR2 positive tumors (mean age: 58.9, 73% female). Maximum SUV of the pituitary gland was obtained in each patient. SUV of superior sagittal sinus was obtained to calculate normalized SUV score (SUVR) of the gland. The anatomic size of the gland was collected as maximum sagittal height (MSH). Correlations with age and sex were analyzed.

RESULTS

The mean SUV and SUVR of the pituitary gland were 17.6 (range: 7-59.5, SD = 7.1) and 13.8 (range: 3.3-52.6, SD = 7.2), respectively. Older females had significantly higher SUV of the pituitary gland compared to younger females. When stratified by age and sex, both older and younger females had significantly higher pituitary SUV than older males. SUVR did not differ significantly by age or sex. MSH of the pituitary gland in younger females was significantly greater than in younger males at all age cutoffs.

CONCLUSION

This study provides an empiric profiling of the physiological [68 Ga]-DOTATATE avidity of the pituitary gland. The findings suggest that SUV may vary by age and sex and can help guide the use of [68 Ga]-DOTATATE PET/MRI in clinical and research settings. Future studies can build on these findings to investigate further the relationship between pituitary biology and demographic factors.

The Effects of Peptide Receptor Radionuclide Therapy on the Neoplastic and Normal Pituitary

Pituitary neuroendocrine tumours (PitNETs) are usually benign and slow-growing; however, in some cases, they may behave aggressively and become resistant to conventional treatments. Therapeutic options for aggressive or metastatic PitNETs are limited, and currently mainly consist of temozolomide, with little experience of other emerging approaches, including peptide receptor radionuclide therapy (PRRT). Somatostatin receptor expression in PitNETs explains the effectiveness of somatostatin analogues for treating PitNETs, particularly those hypersecreting pituitary hormones, such as growth hormone or adrenocorticotropic hormone. The expression of such receptors in pituitary tumour cells has provided the rationale for using PRRT to treat patients with aggressive or metastatic PitNETs. However, the PRRT efficacy in this setting remains unestablished, as knowledge on this today is based only on few case reports and small series of cases, which are reviewed here. A total of 30 PRRT-treated patients have been thus far reported: 23 aggressive PitNETs, 5 carcinomas, and 2 of malignancy status unspecified. Of the 27 published cases with information regarding the response to PRRT, 5 (18%) showed a partial response, 8 (30%) had stable disease, and 14 (52%) had progressive disease. No major adverse effects have been reported, and there is also no increased risk of clinically relevant hypopituitarism in patients with pituitary or non-pituitary neuroendocrine tumours following PRRT. PRRT may be regarded as a safe option for patients with aggressive or metastatic PitNETs if other treatment approaches are not feasible or have failed in controlling the disease progression, with tumour shrinkage occurring in up to a fifth of cases, while about a third of aggressive pituitary tumours may achieve stable disease. Here, the data on PRRT in the management of patients with aggressive pituitary tumours are reviewed, as well as the effects of PRRT on the pituitary function in other PRRT-treated cancer patients.

Targeting Aggressive Pituitary Adenomas at the Molecular Level-A Review

Pituitary adenomas (PAs) are mostly benign endocrine tumors that can be treated by resection or medication. However, up to 10% of PAs show an aggressive behavior with invasion of adjacent tissue, rapid proliferation, or recurrence. Here, we provide an overview of target structures in aggressive PAs and summarize current clinical trials including, but not limited to, PAs. Mainly, drug targets in PAs are based on general features of tumor cells such as immune checkpoints, so that programmed cell death 1 (ligand 1) (PD-1/PD-L1) targeting may bear potential to cure aggressive PAs. In addition, epidermal growth factor receptor (EGFR), mammalian target of rapamycin (mTOR), vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and their downstream pathways are triggered in PAs, thereby modulating tumor cell proliferation, migration and/or tumor angiogenesis. Temozolomide (TMZ) can be an effective treatment of aggressive PAs. Combination of TMZ with 5-Fluorouracil (5-FU) or with radiotherapy could strengthen the therapeutic effects as compared to TMZ alone. Dopamine agonists (DAs) are the first line treatment for prolactinomas. Dopamine receptors are also expressed in other subtypes of PAs which renders DAs potentially suitable to treat other subtypes of PAs. Furthermore, targeting the invasive behavior of PAs could improve therapy. In this regard, human matrix metalloproteinase (MMP) family members and estrogens receptors (ERs) are highly expressed in aggressive PAs, and numerous studies demonstrated the role of these proteins to modulate invasiveness of PAs. This leaves a number of treatment options for aggressive PAs as reviewed here.

Somatostatin and Its Receptor System in Colorectal Cancer

Somatostatin (SST)/somatotropin release-inhibiting factor (SRIF) is a well-known neuropeptide, widely distributed in the central and peripheral nervous systems, that regulates the endocrine system and affects neurotransmission via interaction with five SST receptors (SST1-5). In the gastrointestinal tract, the main SST-producing cells include intestinal enteroendocrine cells (EECs) restricted to the mucosa, and neurons of the submucosal and myenteric plexuses. The action of the SRIF system is based on the inhibition of endocrine and exocrine secretion, as well as the proliferative responses of target cells. The SST1–5 share common signaling pathways, and are not only widely expressed on normal tissues, but also frequently overexpressed by several tumors, particularly neuroendocrine neoplasms (NENs). Furthermore, the SRIF system represents the only peptide/G protein-coupled receptor (GPCR) system with multiple approved clinical applications for the diagnosis and treatment of several NENs. The role of the SRIF system in the histogenesis of colorectal cancer (CRC) subtypes (e.g., adenocarcinoma and signet ring-cell carcinoma), as well as diagnosis and prognosis of mixed adenoneuroendocrine carcinoma (MANEC) and pure adenocarcinoma, is poorly understood. Moreover, the impact of the SRIF system signaling on CRC cell proliferation and its potential role in the progression of this cancer remains unknown. Therefore, this review summarizes the recent collective knowledge and understanding of the clinical significance of the SRIF system signaling in CRC, aiming to evaluate the potential role of its components in CRC histogenesis, diagnosis, and potential therapy.

The Role of Dopamine Agonists in Pituitary Adenomas

Dopamine agonist therapy is the primary therapy for prolactin-secreting adenomas and usually results in normoprolactinemia, eugonadism, and tumor reduction. Cabergoline is superior to bromocriptine with regard to efficacy and tolerance. Withdrawal of cabergoline can be attempted in patients with normal prolactin levels on low doses of medication and evidence of radiographic tumor involution. Dopamine agonists have been used off label in patients with acromegaly, Cushing disease, and nonfunctioning adenomas. A trial of cabergoline monotherapy can be effective in patients with biochemically mild acromegaly. Cabergoline combination with somatostatin receptor ligands or pegvisomant improves insulin-like growth factor level 1 in majority of patients.

The GALANT trial: study protocol of a randomised placebo-controlled trial in patients with a 68Ga -DOTATATE PET-positive, clinically non-functioning pituitary macroadenoma on the effect of lan reotide on t umour size

INTRODUCTION

At present, there is no approved medical treatment option for patients with non-functioning pituitary adenoma. A number of open-label studies suggest that treatment with somatostatin analogues may prevent tumour progression. In vivo somatostatin receptor imaging using ⁶⁸Ga-DOTATATE PET (PET, positron emission tomography) could help in preselecting patients potentially responsive to treatment. Our aim is to investigate the effect of the somatostatin analogue lanreotide as compared with placebo on tumour size in patients with a ⁶⁸Ga-DOTATATE PET-positive non-functioning pituitary macroadenoma (NFMA).

METHODS AND ANALYSIS

The GALANT study is a multicentre, randomised, double-blind, placebo-controlled trial in adult patients with a suprasellar extending NFMA. Included patients undergo a ⁶⁸Ga-DOTATATE PET/CT of the head and tracer uptake is assessed after coregistration with pituitary MRI. Forty-four patients with a ⁶⁸Ga-DOTATATE PET-positive NFMA are randomised in a 1:1 ratio between lanreotide 120 mg or placebo, both administered as subcutaneous injections every 28 days for 72 weeks. The primary outcome is the change in cranio-caudal tumour diameter on pituitary MRI after treatment. Secondary outcomes are change in tumour volume, time to tumour progression, change in quality of life and number of adverse events. Final results are expected in the second half of 2021.

ETHICS AND DISSEMINATION

The study protocol has been approved by the Medical Research Ethics Committee of the Academic Medical Centre (AMC) of the Amsterdam University Medical Centres and by the Dutch competent authority. It is an investigator-initiated study with financial support by Ipsen Farmaceutica BV. The AMC, as sponsor, remains owner of all data. Results will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NL5136 (Netherlands Trial Register); pre-recruitment.

TBR-760, a Dopamine-Somatostatin Compound, Arrests Growth of Aggressive Nonfunctioning Pituitary Adenomas in Mice

TBR-760 (formerly BIM-23A760) is a chimeric dopamine (DA)-somatostatin (SST) compound with potent agonist activity at both DA type 2 (D2R) and SST type 2 (SSTR2) receptors. Studies have shown that chimeric DA-SST compounds are more efficacious than individual DA and/or SST analogues, either alone or combined, in inhibiting secretion from primary cultures of human somatotroph and lactotroph tumor cells. Nonfunctioning pituitary adenomas (NFPAs) express both D2R and SSTR2 and, consequently, may respond to TBR-760. We used a mouse model with the pro-opiomelanocortin (POMC) gene knocked out that spontaneously develops aggressive NFPAs. Genomic microarray and DA and SST receptor messenger RNA expression analysis indicate that POMC KO mouse tumors and human NFPAs have similar expression profiles, despite arising from different cell lineages, establishing POMC KO mice as a model for study of NFPAs. Treatment with TBR-760 for 8 weeks resulted in nearly complete inhibition of established tumor growth, whereas tumors from vehicle-treated mice increased in size by 890 ± 0.7%. Comparing TBR-760 with its individual DA and SST components, TBR-760 arrested tumor growth. Treatment with equimolar or 10×-higher doses of the individual SST or DA agonists, either alone or in combination, had no significant effect. One exception was the lower dose of DA agonist that induced modest suppression of tumor growth. Only the chimeric compound TBR-760 arrested tumor growth in this mouse model of NFPA. Further, significant tumor shrinkage was observed in 20% of the mice treated with TBR-760. These results support the development of TBR-760 as a therapy for patients with NFPA.

Targeted systemic and peptide radio-ligand therapy for aggressive pituitary tumors and carcinomas

Aggressive pituitary tumors comprise a rare but challenging subset of pituitary tumors. A major issue currently is the absence of a holistic definition that reliably identifies these tumors in a prospective manner. Although comprehensive evaluation of patient gender, age, local invasiveness, treatment responses, radiological and histopathological features may be informative to assess the potential for aggressiveness, a definitive diagnosis of this entity cannot be confidently made until disease progression is actually observed despite standard medical and surgical therapy. Failure to diagnose these aggressive pituitary tumors early may impede initiation of suitable intensive stepwise multimodal treatments, and lessen their ultimate therapeutic success. Even though current therapeutic options for aggressive pituitary tumors are suboptimal in many cases, large-scale randomized prospective clinic trials are impractical and will likely never be conducted due to the rarity of this disease entity. Therefore, the majority of novel therapies in this subset of tumors derive from case reports or small case series, which greatly reduces their validity to make strong recommendations. This chapter, as part of this series on aggressive pituitary tumors, focuses on the role of systemic targeted medical and peptide radio-receptor therapy in treatment of aggressive pituitary tumors and carcinomas, and discusses future directions in these fields.

68Ga-DOTATATE PET imaging in clinically non-functioning pituitary macroadenomas

Purpose

Clinically non-functioning pituitary macroadenomas (NFMA) have been reported to express somatostatin receptors (SSTR), but results are inconsistent across different studies. This may be related to limited sensitivity and specificity of techniques used to date, i.e. immunohistochemistry in surgical specimens and ¹¹¹In-DTPA-octreotide scintigraphy in vivo. The aim of this study was to assess SSTR expression in NFMA in vivo using ⁶⁸Ga-DOTATATE PET, which offers superior sensitivity and spatial resolution as compared with planar scintigraphy or SPECT.

Methods

Thirty-seven patients diagnosed with NFMA underwent ⁶⁸Ga-DOTATATE PET/CT of the head in the framework of a randomised controlled trial assessing the effect of the somatostatin analogue lanreotide on NFMA size. Individual co-registered T1-weighted pituitary MRIs were used to assess ⁶⁸Ga-DOTATATE uptake (SUV_mean) in the adenoma. An SUV_mean of > 2 was considered positive.

Results

⁶⁸Ga-DOTATATE uptake was positive in 34/37 patients (92%), with SUV_mean of positive adenomas ranging from 2.1 to 12.4 (mean ± SD 5.8 ± 2.6).

Conclusions

This is the first report of ⁶⁸Ga-DOTATATE PET performed in NFMA patients, demonstrating in vivo SSTR expression in the vast majority of cases. The high positivity rate when compared with results obtained with ¹¹¹In-DTPA-octreotide scintigraphy probably reflects the superior sensitivity of PET imaging.

Trial registration

Netherlands Trial Register, NL5136, registered on 18 August 2015; EudraCT, 2015-001234-22, registered on 10 March 2015, https://eudract.ema.europa.eu/

Multimodal therapy in aggressive pituitary tumors

The concept of aggressive pituitary tumor (APT) has been precisely defined in recent years. These tumors are characterized by morphological (radiological or histopathological) data of invasion, proliferative activity superior to that of typical adenomas and a clinical behavior characterized by resistance to standard therapies and frequent recurrences. The absence of cerebrospinal or distant metastases differentiates them from the pituitary carcinoma. APTs account for about 10% of all pituitary neoplasm. Proper diagnostic implies participation not only of radiological and hormonal investigation but also a thorough pathological assessment including proliferation markers and immunohistochemistry for hormones and transcription factors. Surgical resection, aiming gross total resection or tumor debulking, is the mainstay initial therapy in most patients. Most patients with APTs need more than one surgical intervention, pituitary radiation, sometimes on more than one occasion, and multiple sequential or combined medical treatments, to finally be doomed to unusual treatments, such as alkylating agents (temozolomide alone or in combination), molecular targeted therapies, or peptide receptor radionuclide therapy. Multimodal therapy, implemented by experts, preferably in specialized centers with high volume caseload, is the only way to improve the prognosis of patients with these uncommon tumors. The research needs in this area are multiple and include a greater knowledge of the molecular biology of these tumors, establishment of protocols for monitoring and sequencing of treatments, development of multicenter studies and international registries.

Cabergoline in the Management of Residual Nonfunctioning Pituitary Adenoma: A Single-Center, Open-Label, 2-Year Randomized Clinical Trial

BACKGROUND

Complete tumor removal by transsphenoidal surgery is usually difficult for large nonfunctioning pituitary adenomas (NFPAs). A validated medical treatment may be useful for their management. This study evaluates the clinical efficacy of the dopaminergic agonist cabergoline for residual NFPA.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a randomized, parallel, open-label clinical trial that compared cabergoline with nonintervention in patients with residual NFPA after transsphenoidal surgery over 2 years. The primary outcome was clinical efficacy (tumor reduction). The secondary outcome was the relationship between tumor dopamine D2 receptor (D2R) expression and clinical responsiveness. Tumor measurements and clinical evaluations were performed every 6 months.

RESULTS

In total, 59 and 57 individuals were randomly assigned to the study and control groups, respectively. At the end of the study, residual tumor shrinkage, stabilization, and enlargement were observed in 28.8%, 66.1%, and 5.1% of patients, respectively, in the medical-therapy group and in 10.5%, 73.7%, and 15.8% of patients, respectively, in the control group (P=0.01). The progression-free survival rate was 23.2 and 20.8 months for the study and control groups, respectively (P=0.01). D2R was not associated with cabergoline responsiveness. No major side effects were related to cabergoline use.

CONCLUSIONS

Cabergoline was an effective drug for treating residual NFPA, and its use was associated with a high rate of tumor shrinkage (ClinicalTrials.gov NCT03271918).

Medical therapy for non-functioning pituitary tumors-a critical approach

Non-functioning pituitary adenomas (NFPAs) are the second most common variant of pituitary tumors. When symptomatic, primary therapy is surgery. Recurrence rates are high. Since many NFPAs express dopamine and somatostatin receptors, medical therapy has been used after surgery in order to prevent recurrence. So far, dopamine agonists have been more widely tested with some promise when introduced immediately after surgery but with less efficacy when introduced later upon tumor regrowth. Currently, the role of medical therapy to prevent tumor regrowth in NFPAs is limited by imprecisions as to final outcome and uncertainties concerning on patient selection, dosing, duration, and side effects.

The Prospective Value of Dopamine Receptors on Bio-Behavior of Tumor

Dopamine receptors are belong to the family of G protein-coupled receptor. There are five types of dopamine receptor (DR), including DRD1, DRD2, DRD3, DRD4, and DRD5, which are divided into two major groups: the D1-like receptors (DRD1 and DRD5), and the D2-like receptors (DRD2, DRD3, and DRD4). Dopamine receptors are involved in all of the physiological functions of dopamine, including the autonomic movement, emotion, hormonal regulation, dopamine-induced immune effects, and tumor behavior, and so on. Increasing evidence shows that dopamine receptors are associated with the regulation of tumor behavior, such as tumor cell death, proliferation, invasion, and migration. Recently, some studies showed that dopamine receptors could regulate several ways of death of the tumor cell, including apoptosis, autophagy-induced death, and ferroptosis, which cannot only directly affect tumor behavior, but also limit tumor progress via activating tumor immunity. In this review, we focus mainly on the function of the dopamine receptor on Bio-behavior of tumor as a potential therapeutic target.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST₂ and SST₅ receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST₂ is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

Antipsychotic dopamine receptor antagonists, cancer, and cancer stem cells

Cancer is one of the deadliest diseases in the world. Despite extensive studies, treating metastatic cancers remains challenging. Years of research have linked a rare set of cells known as cancer stem cells (CSCs) to drug resistance, leading to the suggestion that eradication of CSCs might be an effective therapeutic strategy. However, few drug candidates are active against CSCs. New drug discovery is often a lengthy process. Drug screening has been advantageous in identifying drug candidates. Current understanding of cancer biology has revealed various clues to target cancer from different points of view. Many studies have found dopamine receptors (DRs) in various cancers. Therefore, DR antagonists have attracted a lot of attention in cancer research. Recently, a group of antipsychotic DR antagonists has been demonstrated to possess remarkable abilities to restrain and sensitize CSCs to existing chemotherapeutics by a process called differentiation approach. In this review, we will describe current aspects of CSC-targeting therapeutics, antipsychotic DR antagonists, and their extraordinary abilities to fight cancer.

Dopamine Agonists for Pituitary Adenomas

Dopamine agonists (DA) are well established as first-line therapy for prolactinomas. These tumors express high levels of dopamine 2 receptors (D2R), leading to the strong efficacy of DA in reducing tumor size and hormonal secretion. Other pituitary tumor subtypes express D2R to varying degrees, leading to an extensive body of research into potential off-label use of DA in non-prolactinoma pituitary tumors. Preclinical models of Cushing's disease, acromegaly, and nonfunctioning pituitary tumors (NFPT) demonstrate D2R expression in cell lines and cultured tumors as well as effectiveness of DA in reducing hormonal secretion in functioning tumors and arresting tumor proliferation. Clinical studies have shown some efficacy of DA in treatment of these tumors. In Cushing's disease, DA therapy results in normalization of urinary cortisol levels in approximately 25% of patients, but reported rates of tumor shrinkage are very low; in acromegaly, DA therapy leads to normalization of insulin-like growth factor I and tumor shrinkage in approximately one-third of patients, and improved responses when used in combination with somatostatin receptor ligands. Among patients with NFPT, pooled results show 30% experience reduction of tumor size and 58% show stabilization of disease. DA therapy appears to have some clinical benefit in patients with non-prolactinoma pituitary tumors, and may be an option for medical therapy in some clinical scenarios.