Manuela Albertelli

Somatostatin and dopamine receptor interaction in prostate and lung cancer cell lines

Somatostatin analogues inhibit in vitro cell proliferation via specific membrane receptors (SSTRs). Recent studies on transfected cell lines have shown a ligand-induced formation of receptor dimers. The aim of this study is 1) to evaluate the role of specific ligands in modulating receptor interactions in the androgen-dependent prostate cancer cell line, LNCaP, and in the non-small cell lung cancer line, Calu-6, by co-immunoprecipitation and immunoblot; and 2) to correlate the antiproliferative effect of these compounds with their ability in modulating receptor interactions. In LNCaP, we have demonstrated the constitutive presence of sstr₁/sstr₂, sstr₂/sstr₅, sstr₅/dopamine (DA) type 2 receptor (D₂R), and sstr₂/D₂R dimers. BIM-23704 (sstr₁- and sstr₂-preferential compound) increased the co-immunoprecipitation of sstr₁/sstr₂ and significantly inhibited proliferation (-30.98%). BIM-23244 (sstr₂-sstr₅ selective agonist) significantly increased the co-immunoprecipitation of sstr₂/sstr₅, and induced a -41.36% inhibition of proliferation. BIM-23A760, a new somatostatin/DA chimeric agonist with a high affinity for sstr₂ and D₂R and a moderate affinity for sstr₅, significantly increased the sstr₅/D₂R and sstr₂/D₂R complexes and was the most powerful in inhibiting proliferation (-42.30%). The chimeric compound was also the most efficient in modulating receptor interaction in Calu-6, increasing the co-immunoprecipitation of D₂R/sstr₅ and inhibiting cell proliferation (-30.54%). However, behind BIM-23A760, BIM-53097 (D₂R-preferential compound) also significantly inhibited Calu-6 proliferation (-17.71%), suggesting a key role for D₂R in receptor cross talk and in controlling cell growth. Indeed, activation of monomeric receptors did not affect receptor co-immunoprecipitation, whereas cell proliferation was significantly inhibited when the receptors were synergistically activated. In conclusion, our data show a dynamic ligand-induced somatostatin and DA receptor interaction, which may be crucial for the antiproliferative effects of the new analogues.

Pasireotide and octreotide antiproliferative effects and sst2 trafficking in human pancreatic neuroendocrine tumor cultures

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) raise difficult therapeutic problems despite the emergence of targeted therapies. Somatostatin analogs (SSA) remain pivotal therapeutic drugs. However, the tachyphylaxis and the limited antitumoral effects observed with the classical somatostatin 2 (sst2) agonists (octreotide and lanreotide) led to the development of new SSA, such as the pan sst receptor agonist pasireotide. Our aim was to compare the effects of pasireotide and octreotide on cell survival, chromogranin A (CgA) secretion, and sst2 phosphorylation/trafficking in pancreatic NET (pNET) primary cells from 15 tumors. We established and characterized the primary cultures of human pancreatic tumors (pNETs) as powerful preclinical models for understanding the biological effects of SSA. At clinically relevant concentrations (1-10 nM), pasireotide was at least as efficient as octreotide in inhibiting CgA secretion and cell viability through caspase-dependent apoptosis during short treatments, irrespective of the expression levels of the different sst receptors or the WHO grade of the parental tumor. Interestingly, unlike octreotide, which induces a rapid and persistent partial internalization of sst2 associated with its phosphorylation on Ser341/343, pasireotide did not phosphorylate sst2 and induced a rapid and transient internalization of the receptor followed by a persistent recycling at the cell surface. These results provide the first evidence, to our knowledge, of striking differences in the dynamics of sst2 trafficking in pNET cells treated with the two SSAs, but with similar efficiency in the control of CgA secretion and cell viability.

Neuroendocrine tumors: insights into innovative therapeutic options and rational development of targeted therapies

Neuroendocrine tumors (NETs) are heterogeneous neoplasms with respect to molecular characteristics and clinical outcome. Although slow-growing, NETs are often late diagnosed, already showing invasion of adjacent tissues and metastases. Precise knowledge of NET biological and molecular features has opened the door to the identification of novel pharmacological targets. Therapeutic options include somatostatin analogs, alone or in combination with interferon-α, multi-targeted tyrosine kinase inhibitors (e.g. sunitinib) or mammalian target of rapamycin (mTOR) inhibitors (e.g. everolimus). Antiangiogenic approaches and anti insulin-like growth factor receptor (IGFR) compounds have been also proposed as combination therapies with the aforementioned compounds. This review will focus on recent studies that have improved therapeutic strategies in NETs, discussing management challenges such as drug resistance development as well as focusing on the need for predictive biomarkers to design distinct drug combinations and optimize pharmacological control.

Patient-derived xenograft in zebrafish embryos: a new platform for translational research in neuroendocrine tumors

Preclinical research on neuroendocrine tumors usually involves immortalized cell lines and few animal models. In the present study we described an in vivo model based on patient-derived xenografts of neuroendocrine tumor cells in zebrafish (Danio rerio) embryos, allowing a rapid analysis of the angiogenic and invasive potential. Patient-derived neuroendocrine tumor cells were transplanted in 48 hours post-fertilization Tg(fli1a:EGFP)y1 zebrafish embryos that express enhanced green fluorescent protein in the entire vasculature. Neuroendocrine tumor cells, stained with CM-Dil, were injected into the subperidermal (perivitelline) space, close to the developing subintestinal venous plexus. A proper control group, represented by zebrafish injected with only D-PBS, was included in this study. Angiogenic and invasive potentials of each patient-derived xenograft were evaluated by both epifluorescence and confocal microscopes. Six out of eight neuroendocrine tumor samples were successfully transplanted in zebrafish embryos. Although the implanted tumor mass had a limited size (about 100 cells for embryos), patient-derived xenografts showed pro-angiogenic (5 cases) and invasive (6 cases) behaviors within 48 hours post injection. Patient-derived xenograft in zebrafish embryos appears to be a reliable in vivo preclinical model for neuroendocrine tumors, tumors with often limited cell availability. The rapidity of this procedure makes our model a promising platform to perform preclinical drug screening and opens a new scenario for personalized treatment in patients with neuroendocrine tumors.

Optimization of flow reserve measurement using SPECT technology to evaluate the determinants of coronary microvascular dysfunction in diabetes

PurposeThe aim of this study was to validate a new method to measure regional myocardial perfusion reserve (MPR) with technetium-labelled tracers in patients with type 2 diabetes mellitus (DM2).MethodsA total of 40 consecutive DM2 patients without history of coronary artery disease (CAD) and 7 control subjects were recruited. Dipyridamole myocardial blood flow index (MBF) was assessed by measuring first transit counts in the pulmonary artery and myocardial count rate from gated SPECT images using 99mTc-labelled tracers. The corresponding MBF index was estimated 2 h later according to the same procedure. Regional myocardial perfusion reserve (MPR) was defined as the ratio between dipyridamole and baseline MBF using a 17-segment left ventricular (LV) model. Coronary flow reserve (CFR) was estimated by transthoracic contrast echo Doppler monitoring of flow velocity in the left anterior descending coronary artery (LAD) during the same session.ResultsEstimated MPR was higher in control subjects than in patients (3.36 ± 0.66 vs 1.91 ± 0.61, respectively, p < 0.01). In patients, LAD CFR and LAD MPR were 2.01 ± 0.78 vs 1.93 ± 0.63, respectively (p = ns). The agreement between the two techniques was documented by their close correlation (r = 0.92, p < 0.001) and confirmed by the Bland-Altman analysis. Reversible perfusion defects occurred in 13 patients (32%) who showed similar MPR values as the remaining 27 (2.10 ± 0.71 vs 1.83 ± 0.71, respectively, p = ns). Finally, MPR was closely correlated with age (r = −0.50, p < 0.01) and time elapsed from the diagnosis of DM2 (r = −0.51, p < 0.01).ConclusionLV regional MPR can be accurately estimated with the broadly available single photon technology. Application of this method to DM2 patients documents the presence of a microvascular dysfunction homogeneously distributed throughout the LV walls and most frequently not associated with reversible perfusion defects.

Grade Increases in Gastroenteropancreatic Neuroendocrine Tumor Metastases Compared to the Primary Tumor

Background/Aim: The neuroendocrine tumor (NET) proliferation-based grading system (ENETS/WHO) for gastroenteropancreatic (GEP) tumors has proved reliable for prognostic stratification. To date, concerns exist regarding Ki-67 heterogeneity within the tumor and little is known on whether grade varies between primary and secondary sites. As tumor heterogeneity may have a significant impact on clinical management, our aim was to retrospectively evaluate Ki-67 on a series of GEP NETs in order to establish whether there is variability in different samples of the same lesion or between primary and metastatic disease (local/distant, synchronous/metachronous). Methods: Sixty patients with multiple samples of tumor were accrued from a total of 338 GEP NETs; 44 of them also had tissue from local/distant metastases and a further 5 had multiple metastatic foci from unknown primary tumors. Immunohistochemistry for Ki-67 was performed on all paraffin blocks from both primary and metastatic tumors. Results: Intratumor Ki-67 heterogeneity sufficient to change grade at first diagnosis was seen in 3/60 cases (5%). Out of 49 patients with primary NETs and/or multiple metastases, discrepancy in grade between sites was identified in 19 (39%) cases and in particular in 11/47 (23%) and in 10/12 (83%) patients with synchronous and metachronous metastases, respectively (p = 0.0002). Change in grade was more frequent in distant compared to locoregional metastases (p = 0.024) and in particular in distant sites other than the liver (p = 0.006). Conclusions: NETs show frequent differences in grade between primary sites and their synchronous/metachronous metastases; assessment of Ki-67 at all sites may prove to be significant for patient management.

Role of Dopamine Receptors in Normal and Tumoral Pituitary Corticotropic Cells and Adrenal Cells

The recent depiction of dopamine receptors (DRs) in tumors that cause Cushing’s syndrome (CS) has renewed the debate about the dopamine control on pituitary-adrenal axis, and opened interesting new perspectives for medical treatment of CS. The new insights arise from the recent accurate characterization of DR subtypes expression within tumors causing CS, the discovery of new mechanisms, such as the dimerization between DRs and other G-protein coupled receptors (CPCRs), including somatostatin receptors (SSTRs), and the recent availability of new agents targeting these receptor subtypes. Corticotropic adenomas express DR subtype 2 (D2R), together with different SSTR subtypes (ssts), in particular sst5. In vitro, activation of D2R inhibits ACTH release in the majority of cultures of corticotropic cells, whereas, in vivo, dopaminergic agents display an inhibitory effect on cortisol levels in a subset of patients with CS. In animal models the receptor profile can be deeply modulated in specific environmental conditions, that may resemble the different clinical phases of CS. The new insights about DRs and receptor-targeting drugs may offer different approaches for medical treatment of CS: combination therapies with different types of compounds, treatment with novel molecules (hybrid compounds) with a wider spectrum of activity, or even pretreatment manipulation of receptor profile. Finally, recent studies showed that D2R is also significantly expressed in ectopic ACTH-secreting tumors and in both normal and tumoral adrenal tissues. Dopamine-agonists may decrease cortisol levels in a number of these patients, strengthening the current (re)emerging interest in DRs as possible targets for medical treatment of CS.

Ectopic Cushing and Other Paraneoplastic Syndromes in Thoracic Neuroendocrine Tumors

Overproduction of corticotropin by the pituitary gland or extrapituitary tumors leads to hypercortisolism or Cushing syndrome. Diagnosis of suspected Cushing syndrome involves 3 major steps: confirmation of hypercortisolism, differentiation between corticotropin-independent and corticotropin-dependent causes of Cushing syndrome, and distinction between pituitary and ectopic corticotropin production. A definitive diagnosis of ectopic corticotropin secretion requires stringent criteria, including reversal of the clinical picture after resection of the tumor and/or demonstration of corticotropin immunohistochemical staining within the tumor tissue.

Characterization and sub-cellular localization of SS1R, SS2R, and SS5R in human late-stage prostate cancer cells: Effect of mono- and bi-specific somatostatin analogs on cell growth

Somatostatin (SST) and SST receptors (SS1R, SS2R, SS3R, SS4R and SS5R) appear to play a significant role in the progression of human prostate cancer (PCa), which is associated with heterogeneity of SSRs expression and specific cell localization as we already demonstrated in the LNCaP cell line, an in vitro model of human androgen-dependent PCa. In this study, PC-3 and DU-145 human castration-resistant PCa cells were found to express all SSRs, while LNCaP expressed all but SS4R. A 48-h treatment with BIM-23244 (SS2R/SS5R) or BIM-23926 (SS1R) SST analogs was more effective in inhibiting cell proliferation, compared to BIM-23120 (SS2R), BIM-23206 (SS5R) and BIM-23704 (SS1R/SS2R). BIM-23926 (SS1R) treatment increased the amount of p21 and decreased phosphorylated (p) ERK1/2. BIM-23244 (SS2R/SS5R) led to p21 increment only in PC-3 cells, and to pERK1/2 reduction in both cell lines. SS1R/SS2R and SS2R/SS5R receptor dimers were natively present on cell membrane and their amount was increased by BIM-23704 (SS1R/SS2R) or BIM-23244 (SS2R/SS5R) treatment, respectively. SS1R, SS2R and SS5R were differently distributed among nuclear, lysosomal and microsomal compartment, according to their different recycling dynamics. These results show that, in PC-3, DU-145 and LNCaP cells, activation of SS1R and SS2R/SS5R leads to relevant antiproliferative effects.

Prognostic factors in ectopic Cushing's syndrome due to neuroendocrine tumors: a multicenter study

OBJECTIVE Evidence is limited regarding outcome of patients with ectopic Cushings syndrome (ECS) due to neuroendocrine tumors (NETs). DESIGN We assessed the prognostic factors affecting the survival of patients with NETs and ECS. METHODS Retrospective analysis of clinicopathological features, severity of hormonal syndrome, treatments from a large cohort of patients with NETs and ECS collected from 17 Italian centers. RESULTS Our series included 110 patients, 58.2% female, with mean (±s.d.) age at diagnosis of 49.5 ± 15.9 years. The main sources of ectopic ACTH were bronchial carcinoids (BC) (40.9%), occult tumors (22.7%) and pancreatic (p)NETs (15.5%). Curative surgery was performed in 56.7% (70.2% of BC, 11% of pNETs). Overall survival was significantly higher in BC compared with pNETs and occult tumors (P = 0.033) and in G1-NETs compared with G2 and G3 (P = 0.007). Negative predictive factors for survival were severity of hypercortisolism (P < 0.02), hypokalemia (P = 0.001), diabetes mellitus (P = 0.0146) and distant metastases (P < 0.001). Improved survival was observed in patients who underwent NET removal (P < 0.001). Adrenalectomy improved short-term survival. CONCLUSIONS Multiple factors affect prognosis of ECS patients: type of NET, grading, distant metastases, severity of hypercortisolism, hypokalemia and diabetes mellitus. BCs have the highest curative surgical rate and better survival compared with occult tumors and pNETs. Hypercortisolism plays a primary role in affecting outcome and quality of life; therefore, prompt and vigorous treatment of hormonal excess by NET surgery and medical therapy should be a key therapeutic goal. In refractory cases, adrenalectomy should be considered as it affects outcome positively at least in the first 2 years.