Effects of Recombinant α1-Microglobulin on Early Proteomic Response in Risk Organs after Exposure to 177Lu-Octreotate.

Recombinant α1-microglobulin (A1M) is proposed as a protector during 177Lu-octreotate treatment of neuroendocrine tumors, which is currently limited by bone marrow and renal toxicity. Co-administration of 177Lu-octreotate and A1M could result in a more effective treatment by protecting healthy tissue, but the radioprotective action of A1M is not fully understood. The aim of this study was to examine the proteomic response of kidneys and bone marrow early after 177Lu-octreotate and/or A1M administration. Mice were injected with 177Lu-octreotate and/or A1M, while control mice received saline or A1M vehicle solution. Bone marrow, kidney medulla, and kidney cortex were sampled after 24 h or 7 d. The differential protein expression was analyzed with tandem mass spectrometry. The dosimetric estimation was based on 177Lu activity in the kidney. PHLDA3 was the most prominent radiation-responsive protein in kidney tissue. In general, no statistically significant difference in the expression of radiation-related proteins was observed between the irradiated groups. Most canonical pathways were identified in bone marrow from the 177Lu-octreotate+A1M group. Altogether, a tissue-dependent proteomic response followed exposure to 177Lu-octreotate alone or together with A1M. Combining 177Lu-octreotate with A1M did not inhibit the radiation-induced protein expression early after exposure, and late effects should be further studied.

Clinical Evaluation of Response to Octreotide and Chemotherapy in High-Grade Malignant Neuroendocrine Tumors and Promising In Vitro Preclinical Results with Pasireotide.

Background and Objectives: High-grade malignant neuroendocrine tumors (G3 NETs) and neuroendocrine carcinomas (NECs) are characterized by rapid proliferation, high metastatic capacity, and strong expression of somatostatin receptors (SSTRs). We aimed to analyze the presence of SSTRs in NET G3 and NEC, and to correlate their expression with the use of octreotide and pasireotide. Materials and Methods: For this purpose, we first performed a retrospective study of G3 NET and NEC patients, which included the determination of SSTR expression and response to octreotide treatment. Second, we selected the H69 small cell lung cancer cell line to determine the effect of octreotide and pasireotide. Results: Our results showed the traditional somatostatin analog (SSA) octreotide was ineffective in patients with NET G3 and NEC. On the other hand, RT-qPCR showed a high expression of SSTR2 and SSTR5 in H69 cells. Interestingly, while octreotide did not modify H69 cell proliferation, a strong inhibition of proliferation was detected with the use of pasireotide. Conclusions: In view of these results, a clinical trial in NET G3 and NEC patients using pasireotide is necessary to determine the usefulness of this drug in improving patient treatment.

Structural basis for activation of somatostatin receptor 5 by cyclic neuropeptide agonists.

Somatostatin receptor 5 (SSTR5) is an important G protein-coupled receptor and drug target for neuroendocrine tumors and pituitary disorders. This study presents two high-resolution cryogenicelectron microscope structures of the SSTR5-Gi complexes bound to the cyclic neuropeptide agonists, cortistatin-17 (CST17) and octreotide, with resolutions of 2.7 Å and 2.9 Å, respectively. The structures reveal that binding of these peptides causes rearrangement of a "hydrophobic lock", consisting of residues from transmembrane helices TM3 and TM6. This rearrangement triggers outward movement of TM6, enabling Gαi protein engagement and receptor activation. In addition to hydrophobic interactions, CST17 forms conserved polar contacts similar to somatostatin-14 binding to SSTR2, while further structural and functional analysis shows that extracellular loops differently recognize CST17 and octreotide. These insights elucidate agonist selectivity and activation mechanisms of SSTR5, providing valuable guidance for structure-based drug development targeting this therapeutically relevant receptor.

Nanotechnology-Based Strategy for Enhancing Therapeutic Efficacy in Pancreatic Cancer: Receptor-Targeted Drug Delivery by Somatostatin Analog.

A novel nanotechnology-based drug delivery system (DDS) targeted at pancreatic cancer cells was developed, characterized, and tested. The system consisted of liposomes as carriers, an anticancer drug (paclitaxel) as a chemotherapeutic agent, and a modified synthetic somatostatin analog, 5-pentacarbonyl-octreotide, a ligand for somatostatin receptor 2 (SSTR2), as a targeting moiety for pancreatic cancer. The cellular internalization, cytotoxicity, and antitumor activity of the DDS were tested in vitro using human pancreatic ductal adenocarcinoma (PDAC) cells with different expressions of the targeted SSTR2 receptors, and in vivo on immunodeficient mice bearing human PDAC xenografts. The targeted drug delivery system containing paclitaxel exhibited significantly enhanced cytotoxicity compared to non-targeted DDS, and this efficacy was directly related to the levels of SSTR2 expression. It was found that octreotide-targeted DDS proved exceptionally effective in suppressing the growth of PDAC tumors. This study underscores the potential of octreotide-targeted liposomal delivery systems to enhance the therapeutic outcomes for PDAC compared with non-targeted liposomal DDS and Paclitaxel-Cremophor® EL, suggesting a promising avenue for future cancer therapy innovations.

Octreotide attenuates intestinal barrier damage by maintaining basal autophagy in Caco2 cells.

The intestinal mucosal barrier is of great importance for maintaining the stability of the internal environment, which is closely related to the occurrence and development of intestinal inflammation. Octreotide (OCT) has potential applicable clinical value for treating intestinal injury according to previous studies, but the underlying molecular mechanisms have remained elusive. This article is based on a cell model of inflammation induced by lipopolysaccharide (LPS), aiming to explore the effects of OCT in protecting intestinal mucosal barrier function. A Cell Counting Kit­8 assay was used to determine cell viability and evaluate the effectiveness of OCT. Gene silencing technology was used to reveal the mediated effect of somatostatin receptor 2 (SSTR2). The changes in intestinal permeability were detected through trans­epithelial electrical resistance and fluorescein isothiocyanate­dextran 4 experiments, and the alterations in tight junction proteins were detected using immunoblotting and reverse transcription fluorescence­quantitative PCR technology. Autophagosomes were observed by electron microscopy and the dynamic changes of the autophagy process were characterized by light chain (LC)3­II/LC3­I conversion and autophagic flow. The results indicated that SSTR2­dependent OCT can prevent the decrease in cell activity. After LPS treatment, the permeability of monolayer cells decreased and intercellular tight junctions were disrupted, resulting in a decrease in tight junction protein zona occludens 1 in cells. The level of autophagy­related protein LC3 was altered to varying degrees at different times. These abnormal changes gradually returned to normal levels after the combined application of LPS and SSTR2­dependent OCT, confirming the role of OCT in protecting intestinal barrier function. These experimental results suggest that OCT maintains basal autophagy and cell activity mediated by SSTR2 in intestinal epithelial cells, thereby preventing the intestinal barrier dysfunction in inflammation injury.

The Novel SSTR3 Agonist ITF2984 Exerts Antimitotic and Proapoptotic Effects in Human Non-Functioning Pituitary Neuroendocrine Tumor (NF-PitNET) Cells.

Somatostatin receptor ligands (SRLs) with high affinity for somatostatin receptors 2 and 5 (SSTR2 and SSTR5) are poorly efficacious in NF-PitNETs, expressing high levels of SSTR3. ITF2984 is a pan-SSTR ligand with high affinity for SSTR3, able to induce SSTR3 activation and to exert antitumoral activity in the MENX rat model. The aim of this study was to test ITF2984's antiproliferative and proapoptotic effects in NF-PitNET primary cultured cells derived from surgically removed human tumors and to characterize their SSTR expression profile. We treated cells derived from 23 NF-PitNETs with ITF2984, and a subset of them with octreotide, pasireotide (SRLs with high affinity for SSTR2 or 5, respectively), or cabergoline (DRD2 agonist) and we measured cell proliferation and apoptosis. SSTR3, SSTR2, and SSTR5 expression in tumor tissues was analyzed by qRT-PCR and Western blot. We demonstrated that ITF2984 reduced cell proliferation (-40.8 (17.08)%, p < 0.001 vs. basal, n = 19 NF-PitNETs) and increased cell apoptosis (+41.4 (22.1)%, p < 0.001 vs. basal, n = 17 NF-PitNETs) in all tumors tested, whereas the other drugs were only effective in some tumors. In our model, SSTR3 expression levels did not correlate with ITF2984 antiproliferative nor proapoptotic effects. In conclusion, our data support a possible use of ITF2984 in the pharmacological treatment of NF-PitNET.

Does Telotristat Have a Role in Preventing Carcinoid Heart Disease?

Carcinoid heart disease (CHD) is a frequent and life-threatening complication in patients with carcinoid tumors. Its clinical management is challenging is some cases since serotonin-induced valve fibrosis leads to heart failure. Telotristat is an inhibitor of tryptophan-hydroxylase (TPH), a key enzyme in serotonin production. Telotristat use in patients with carcinoid syndrome and uncontrollable diarrhea under somatostatin analogs is approved, but its specific role in patients with CHD is still not clear. IN this context, we aimed to explore the effect of telotristat in heart fibrosis using a mouse model of serotonin-secreting metastasized neuroendocrine neoplasm (NEN). To this aim, four treatment groups (n = 10/group) were evaluated: control, monthly octreotide, telotristat alone, and telotristat combined with octreotide. Plasma serotonin and NT-proBNP levels were determined. Heart fibrosis was histologically evaluated after 6 weeks of treatment or when an individual mouse's condition was close to being terminal. Heart fibrosis was observed in all groups. Non-significant reductions in primary tumor growth were observed in all of the treated groups. Feces volume was increased in all groups. A non-significant decrease in feces volume was observed in the octreotide or telotristat-treated groups, while it was significantly reduced with the combined treatment at the end of the study compared with octreotide (52 g reduction; p < 0.01) and the control (44.5 g reduction; p = 0.05). Additionally, plasma NT-proBNP decreased in a non-significant, but clinically relevant, manner in the octreotide (28.2% reduction), telotristat (45.9% reduction), and the octreotide + telotristat (54.1% reduction) treatment groups. No significant changes were observed in plasma serotonin levels. A similar non-significant decrease in heart valve fibrosis was observed in the three treated groups. In conclusion, Telotristat alone and especially in combination with octreotide decreases NT-proBNP levels in a mouse model of serotonin-secreting metastasized NEN, when compared with the control and octreotide, but its effect on heart valve fibrosis (alone and in combination) was not superior to octreotide in monotherapy.

Octreotide improves human lymphatic fluid transport a translational trial.

OBJECTIVES: Chylothorax is a complex condition and many different pharmacological agents have been tried as treatment. Octreotide is used off-label to treat chylothorax, but the efficacy of octreotide remains unclear. A decrease in lymph production is suggested as the mechanism. In this cross-over study, we explore the direct effect of octreotide on human lymphatic drainage. METHODS: Pre-clinical: the effect of octreotide on force generation was assessed during acute and prolonged drug incubation on human lymphatic vessels mounted in a myograph. Clinical: in a double-blinded, randomized, cross-over trial including 16 healthy adults, we administered either octreotide or saline as an intravenous infusion for 2.5 h. Near-infrared fluorescence imaging was used to examine spontaneous lymphatic contractions and lymph pressure in peripheral lymphatic vessels and plethysmography was performed to assess the capillary filtration rate, capillary filtration coefficient and isovolumetric pressures of the lower leg. RESULTS: Pre-clinical: human thoracic duct (n = 12) contraction rate was concentration-dependently stimulated by octreotide with a maximum effect at 10 and 100 nmol/l in the myograph chamber. Clinical: spontaneous lymphatic contractions and lymph pressure evaluated by near-infrared fluorescence did not differ between octreotide or placebo (P = 0.36). Plethysmography revealed similar capillary filtration coefficients (P = 0.057), but almost a doubling of the isovolumetric pressures (P = 0.005) during octreotide infusion. CONCLUSIONS: Octreotide stimulated lymphatic contractility in the pre-clinical setup but did not affect the spontaneous lymphatic contractions or lymph pressure in healthy individuals. Plethysmography revealed a doubling in the isovolumetric pressure. These results suggest that octreotide increases lymphatic drainage capacity in situations with high lymphatic afterload.

Somatostatin affects GnRH neuronal development and migration and stimulates olfactory-related fiber fasciculation.

Transient expression of somatostatin (SST) has been observed in the olfactory epithelium (OE) and nerves of chick embryos. Intense expression of SST in these regions on embryonic days (E) 5-8 coincides with the migration of neurons producing gonadotropin-releasing hormone (GnRH) from the OE to the forebrain (FB), suggesting that SST plays a role in the development of GnRH neurons. Using in ovo electroporation of small interfering RNA, we found that the suppression of SST mRNA in the olfactory placode (OP) of E3.5 chick embryos significantly reduced the number of GnRH and Islet-1-immunoreactive neurons in the nasal region without affecting the entry of GnRH neurons into the FB at E5.5-6. SST knockdown did not lead to changes in the number of apoptotic, proliferating, or HuC/D-positive neuronal cells in the OE; therefore, it is possible that SST is involved in the neurogenesis/differentiation of GnRH neurons and OP-derived GnRH-negative migratory neurons. In whole OP explant cultures, we also found that SST or its analog octreotide treatment significantly increased the number of migratory GnRH neurons and the migratory distance from the explants. The co-application of an SST antagonist blocked the octreotide-induced increase in the number of GnRH neurons. Furthermore, the fasciculation of polysialylated neural cell adhesion molecule-immunoreactive fibers emerging from the explants was dependent on octreotide. Taken together, our results provide evidence that SST exerts facilitatory effects on the development of neurons expressing GnRH or Islet-1 and on GnRH neuronal migration, in addition to olfactory-related fiber fasciculation.

Pantoprazole-Induced Bone Loss through Gastrin Secretion: A Stereological Study.

Background: Recent researches have failed to uncover a clear explanation for proton pump inhibitors' bone-loss effects. In light of pantoprazole's effects on gastrin secretion, the goal of this study was to see if it caused bone loss through gastrin secretion. Methods: Forty male rats were divided into control, octreotide (Oct), pantoprazole (Pan), and pantoprazole plus octreotide (Pan+Oct) groups. Serum calcium, phosphorous, alkaline phosphatase, parathyroid hormone, and gastrin were measured before and three months after the treatment, and bone densitometry was examined. The rats' femoral bones were examined stereologically at the end of the investigation. Results: The Pan group had considerably greater levels of serum alkaline phosphatase, parathyroid hormone (PTH), and gastrin, but this was prevented in the presence of Oct, a gastrin secretion inhibitor. All parameters of femoral bone densitometry in the Pan group were significantly lower than the control after treatment which was considerably inhibited in the presence of Oct. Furthermore, when compared to the control and Oct groups, the rats in the Pan group had a lower trabecular volume, femur bone weight, and volume, as well lower number of osteocytes. The amount of osteoclasts, on the other hand, was much higher in the Pan group than in the other groups. Conclusion: Overall findings revealed that pantoprazole caused bone loss, which could be prevented by adding octreotide. Because these detrimental effects were not detected in rats given both Oct and Pan, it was suggested that the effect of Pan on bone was produced by a hypergastrinemic condition.

Primary weight loss failure after Roux-en-Y gastric bypass is characterized by impaired gut-hormone mediated regulation of food intake.

BACKGROUND/OBJECTIVES: After Roux-en-Y gastric bypass (RYGB) a subset of patients never obtain excess BMI loss (EBMIL) > 50% and are categorized as having primary weight loss (WL) failure. We hypothesized that postprandial concentrations of glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) would be lower in patients with primary WL failure compared with patients with successfully maintained WL. Furthermore, that inhibition of gut hormone secretions would increase ad libitum food intake less in patients with primary WL failure. SUBJECTS/METHODS: Twenty women with primary WL failure (LowEBMIL < 50%) were individually matched to twenty women with successful WL (HighEBMIL > 60%) on age, preoperative BMI and time from RYGB. On separate days performed in a random order, patient-blinded subcutaneous injections of octreotide or saline (placebo) were followed by a fixed breakfast and an ad libitum lunch with blood sampling for appetite regulating hormones and Visual-Analogue-Scale (VAS)-scoring of hunger/satiety. Furthermore, participants underwent gene variant analysis for GLP-1, PYY and their receptors, indirect calorimetry, dual-energy X-ray absorptiometry (DXA)-scans, 4-days at-home food registration and 14-days step counting. RESULTS: On placebo days, postprandial GLP-1, PYY and cholecystokinin (CCK) concentrations were similar between groups after breakfast. Fasting ghrelin was lower in LowEBMIL, but the postprandial suppression was similar. LowEBMIL had lower satiety VAS-scores and less suppression of hunger VAS-scores. Gene variants did not differ between groups. Octreotide diminished GLP-1, PYY, CCK and ghrelin concentrations in both groups. Octreotide did not affect ad libitum food intake in LowEBMIL (-1% [-13, 12], mean [95%CI]), while food intake increased in HighEBMIL (+23% [2,44]). CONCLUSIONS: Primary WL failure after RYGB was not characterized by impaired secretions of appetite regulating gut hormones. Interestingly, inhibition of gut hormone secretions with octreotide only increased food intake in patients with successful WL post-RYGB. Thus, an impaired central anorectic response to gut hormones may contribute to primary WL failure after RYGB.

Recombinant α1-Microglobulin (rA1M) Protects against Hematopoietic and Renal Toxicity, Alone and in Combination with Amino Acids, in a 177Lu-DOTATATE Mouse Radiation Model.

177Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) is used clinically to treat metastasized or unresectable neuroendocrine tumors (NETs). Although 177Lu-DOTATATE is mostly well tolerated in patients, bone marrow suppression and long-term renal toxicity are still side effects that should be considered. Amino acids are often used to minimize renal radiotoxicity, however, they are associated with nausea and vomiting in patients. α1-microglobulin (A1M) is an antioxidant with heme- and radical-scavenging abilities. A recombinant form (rA1M) has previously been shown to be renoprotective in preclinical models, including in PRRT-induced kidney damage. Here, we further investigated rA1M's renal protective effect in a mouse 177Lu-DOTATATE model in terms of administration route and dosing regimen and as a combined therapy with amino acids (Vamin). Moreover, we investigated the protective effect of rA1M on peripheral blood and bone marrow cells, as well as circulatory biomarkers. Intravenous (i.v.) administration of rA1M reduced albuminuria levels and circulatory levels of the oxidative stress-related protein fibroblast growth factor-21 (FGF-21). Dual injections of rA1M (i.e., at 0 and 24 h post-177Lu-DOTATATE administration) preserved bone marrow cellularity and peripheral blood reticulocytes. Administration of Vamin, alone or in combination with rA1M, did not show any protection of bone marrow cellularity or peripheral reticulocytes. In conclusion, this study suggests that rA1M, administered i.v. for two consecutive days in conjunction with 177Lu-DOTATATE, may reduce hematopoietic and kidney toxicity during PRRT with 177Lu-DOTATATE.

Cardioprotective Effects of Octreotide against Sepsis-Induced Cardiotoxicity in Mice.

Sepsis is a systemic inflammatory consequence resulting from microbial infection, assessed as a worldwide healthcare issue. Sepsis can result in multiorgan dysfunction, including cardiac, renal, hepatic, and cerebral dysfunction. Cardiotoxicity can occur in humans and rodents during sepsis, leading to increased mortality. The current study aims to explore the possible cardioprotective effects of octreotide during sepsis-induced cardiotoxicity. This study was done with a total of forty male albino Swiss mice, aged 8-12 weeks and weighing 25-30 gm. These animals had free access to food and water. After two weeks of adaptation, mice were divided into four groups (n=10): 1) Normal group: healthy mice; 2) CLP group: mice underwent CLP operation; 3) Vehicle group: mice received DMSO. 4) Octreotide group: mice received octreotide (10 mg/kg) subcutaneously in 2 divided doses for 5 consecutive days. All groups underwent CLP operation on the 4th day, then sacrificed on the 5th day then blood, and tissue sampling was done. The Octreotide group demonstrated a significant (P<0.05) decrease in the myocardial levels of cardiac troponin-I as compared to the CLP group. Furthermore, the octreotide group demonstrated a significant (P<0.05) decrease in the serum level of inflammatory cytokines (TNF-α, IL-6, & IL-1ß) as compared to the CLP group. Additionally, the octreotide group showed a significant (P<0.05) elevation in the myocardial activity of SOD and a reduction in MDA level compared to the CLP group. Histologically, all mice in the CLP group showed a significant (P<0.05) cardiac tissue injury, while the octreotide groups showed a significant (P<0.05) reduced level of cardiac tissue injury. The results of the present study revealed that octreotide attenuates sepsis-induced cardiotoxicity through different protective effects; they include the anti-inflammatory effect through their ability to decrease serum levels of inflammatory cytokines (TNF-α, IL-1ß, and IL-6). Also, the anti-oxidant effect through their ability to decrease myocardial levels of MDA and increase the myocardial activity of SOD. Additionally, the direct cardiac protective effect through the lower level of cardiac troponin- I and the reduction of histopathological changes during sepsis-induced cardiotoxicity.

Characteristics and response cutoff of octreotide suppression test in thyrotrophin (TSH)-secreting pituitary adenomas.

CONTEXT: Somatostatin analogs are recommended for preoperative therapy in thyrotrophin secreting pituitary adenomas (TSHomas). Octreotide suppression test (OST) was designed to differentiate TSHomas with resistance to thyroid hormones, while its ability to test the sensitivity of SSA has not been fully studied. OBJECTIVE: To test the sensitivity of SSA in TSHomas with OST. PATIENTS: We collected 48 pathologically confirmed TSHoma patients with complete 72 h' data of OST into analysis. INTERVENTION: Octreotide suppression test. MAIN OUTCOME: Sensitivity timepoint and cutoff of OST. RESULTS: During the entire OST, the TSH descended maximally 89.07% (73.85%, 96.77%), while the FT3 and FT4 declined slowly [43.40% (37.80%, 54.44%) and 26.59% (19.01%, 33.13%), respectively]. The 24th hour was the timepoint wherein the stability occurs for TSH, and the 48th hour for FT3 and FT4 during OST. In the patients who received both short- and long-acting somatostatin analogs (SSA), the 24-h timepoint was the most predictive timepoint for the percentage of TSH decline (Spearman's rank correlation analysis, r = .571, p < .001), while the 72-h timepoint was optimal for predicting the magnitude of TSH decline (Spearman's rank correlation analysis, r = .438, p = .005). In the 24th timepoint, a positive correlation was also observed between TSH suppression rate and the percentage decrease and absolute value decrease of FT3 and FT4. Furthermore, in patients treated with long-acting SSA, the 72-h timepoint was optimal for predicting both the percentage (Spearman's rank correlation analysis, r = .587, p = .01) and magnitude (Spearman's rank correlation analysis, r = .474, p = .047) of TSH decline. The 24th hour was the optimal timepoint with 44.54% (50% of median value of TSH in 72-hOST) decrease of TSH being the observing cutoff. The adverse effect of OST was predominantly occurred in the gastrointestinal system and no severe event occurred during OST. Paradoxical response could occur in OST and it did not influence the effect of SSA as long as sensitivity was confirmed. A high level of hormonal control was achieved in the SSA-sensitive patients. CONCLUSION: OST can be used as an efficient tool to guide the adequate use of SSA.

Co-administration with A1M does not influence apoptotic response of 177Lu-octreotate in GOT1 neuroendocrine tumors.

Recombinant α1-microglobulin (A1M) is a proposed radioprotector during 177Lu-octreotate therapy of neuroendocrine tumors (NETs). To ensure a maintained therapeutic effect, we previously demonstrated that A1M does not affect the 177Lu-octreotate induced decrease in GOT1 tumor volume. However, the underlying biological events of these findings are still unknown. The aim of this work was to examine the regulation of apoptosis-related genes in GOT1 tumors short-time after i.v. administration of 177Lu-octreotate with and without A1M or A1M alone. Human GOT1 tumor-bearing mice received 30 MBq 177Lu-octreotate or 5 mg/kg A1M or co-treatment with both. Animals were sacrificed after 1 or 7 days. Gene expression analysis of apoptosis-related genes in GOT1 tissue was performed with RT-PCR. In general, similar expression patterns of pro- and anti-apoptotic genes were found after 177Lu-octreotate exposure with or without co-administration of A1M. The highest regulated genes in both irradiated groups compared to untreated controls were FAS and TNFSFRS10B. Administration of A1M alone only resulted in significantly regulated genes after 7 days. Co-administration of A1M did not negatively affect the transcriptional apoptotic response of 177Lu-octreotate in GOT1 tumors.

Prospect of acromegaly therapy: molecular mechanism of clinical drugs octreotide and paltusotine.

Somatostatin receptor 2 (SSTR2) is highly expressed in neuroendocrine tumors and represents as a therapeutic target. Several peptide analogs mimicking the endogenous ligand somatostatin are available for clinical use, but poor therapeutic effects occur in a subset of patients, which may be correlated with subtype selectivity or cell surface expression. Here, we clarify the signal bias profiles of the first-generation peptide drug octreotide and a new-generation small molecule paltusotine by evaluating their pharmacological characteristics. We then perform cryo-electron microscopy analysis of SSTR2-Gi complexes to determine how the drugs activate SSTR2 in a selective manner. In this work, we decipher the mechanism of ligand recognition, subtype selectivity and signal bias property of SSTR2 sensing octreotide and paltusotine, which may aid in designing therapeutic drugs with specific pharmacological profiles against neuroendocrine tumors.

Resistance of neuroendocrine tumours to somatostatin analogs.

INTRODUCTION: A common feature shared by most neuroendocrine tumors (NETs) is the expression on their surface of somatostatin receptors (SSTRs) that are essential for their pathophysiological regulation, diagnosis, and management. The first-generation synthetic somatostatin analogs (SSAs), octreotide and lanreotide, constitute the cornerstone of treatment for growth hormone secreting pituitary adenomas and functioning, progressive functioning, and non-functioning gastro-entero-pancreatic (GEP-NETs). SSAs exert their mechanism of action through binding to the SSTRs; however, their therapeutic response is frequently attenuated or diminished by the development of resistance. The phenomenon of resistance is complex implicating the presence of additional epigenetic and genetic mechanisms. AREAS COVERED: We aim to analyze the molecular, genetic, and epigenetic mechanisms of resistance to SSA treatment. We also summarize recent clinical data related to the development of resistance on conventional and non-conventional modes of administration of the first-generation SSAs and the second-generation SSA pasireotide. We explore mechanisms used to counteract the resistance to SSAs using higher doses or more frequent mode of administration of SSAs and/or combination treatments. EXPERT OPINION: There is considerable heterogeneity in the development of resistance to SSAs that is tumor-specific necessitating the delineation of the underlying pathophysiological processes to further expand their therapeutic applications.

Dissecting the In Vitro Efficacy of Octreotide and Cabergoline in GH- and GH/PRL-Secreting Pituitary Tumors.

CONTEXT: Cabergoline (CAB) is an off-label medical therapy for acromegaly, overshadowed by first-generation somatostatin receptor ligands, eg, octreotide (OCT). OBJECTIVE: This was a head-to-head comparison between OCT and CAB in inhibiting growth hormone (GH) secretion in primary cultures of GH- and GH/prolactin (PRL)-secreting tumors; we also investigated the role of somatostatin (SST) and dopamine type 2 (D2R) receptor expression. METHODS: We evaluated the antisecretory effect of OCT and CAB, together with receptor mRNA expression, in 23 tumor cultures obtained from acromegaly patients referred to the Erasmus Medical Center (Rotterdam, The Netherlands). GH concentrations in cell culture media were determined after 72-hour OCT and CAB treatment (10 nM). RESULTS: OCT showed a slightly higher efficacy compared with CAB (GH decrease -39.5% vs -32.5%, P = 0.079). The effect of the 2 drugs was superimposable in GH/PRL co-secreting tumors (-42.1% vs -44.8%), where SST1 and D2R had a higher expression compared with the pure GH-secreting tumors (P = 0.020 and P = 0.026). OCT was more effective than CAB in 8/23 cultures, while CAB was more effective than OCT in 3/23 (CAB+ group). In CAB+ tumors, SST1 expression was higher compared with the other groups (P = 0.034). At receiver operating characteristic (ROC) curve analysis, SST1 and D2R discriminated between GH and GH/PRL co-secretion (AUC 0.856, P = 0.013; AUC 0.822, P = 0.024). SST1 was the best predictor of CAB response (≥50% GH reduction, AUC 0.913, P = 0.006; 80% sensitivity, 94% specificity). CONCLUSION: OCT is 5% to 10% more effective than CAB in vitro. SST1 mRNA expression can represent a reliable marker of GH/PRL co-secreting tumors showing a preferential response to CAB treatment.

Effects of GLP-1 Infusion Upon Whole-body Glucose Uptake and Skeletal Muscle Perfusion During Fed-state in Older Men.

INTRODUCTION: Ageing skeletal muscles become both insulin resistant and atrophic. The hormone glucagon-like peptide 1 (GLP-1) facilitates postprandial glucose uptake as well as augmenting muscle perfusion, independent of insulin action. We thus hypothesized exogenous GLP-1 infusions would enhance muscle perfusion and positively affect glucose metabolism during fed-state clamps in older people. METHODS: Eight men (71 ± 1 years) were studied in a randomized crossover trial. Basal blood samples were taken before postprandial (fed-state) insulin and glucose clamps, accompanied by amino acid infusions, for 3 hours. Reflecting this, following insertions of peripheral and femoral vessels cannulae and baseline measurements, peripheral IV infusions of octreotide, insulin (Actrapid), 20% glucose, and mixed amino acids; Vamin 14-EF with or without a femoral arterial GLP-1 infusion were started. GLP-1, insulin, and C-peptide were measured by ELISA. Muscle microvascular blood flow was assessed via contrast enhanced ultrasound. Whole-body glucose handling was assayed by assessing glucose infusion rate parameters. RESULTS: Skeletal muscle microvascular blood flow significantly increased in response to GLP-1 vs feeding alone (5.0 ± 2.1 vs 1.9 ± 0.7 fold-change from basal, respectively; P = 0.008), while also increasing whole-body glucose uptake (area under the curve 16.9 ± 1.7 vs 11.4 ± 1.8 mg/kg-1/180 minutes-1, P = 0.02 ± GLP, respectively). CONCLUSIONS: The beneficial effects of GLP-1 on whole-body glycemic control are evident with insulin clamped at fed-state levels. GLP-1 further enhances the effects of insulin on whole-body glucose uptake in older men, underlining its role as a therapeutic target. The effects of GLP-1 in enhancing microvascular flow likely also affects other glucose-regulatory organs, reflected by greater whole-body glucose uptake.

The effect of Nateglinide and Octreotide on follicular morphology and free radical scavenging system in letrazole-induced rat model of PCOS.

OBJECTIVE: To investigate the effects of octreotide and nateglinide on ovarian follicle count, ovarian tissue damage, biochemical parameters and free radical scavenging system in letrazole-induced rat model of PCOS. MATERIALS AND METHODS: Forty-two female Sprague-Dawley rats were divided into six groups. Group 1 (Control Group): after localizing the ovaries and the uterine horns, the abdominal wall was closed without any surgical procedure. Group 2 (PCOS Group): PCOS was induced by administrating Letrozole orally for 21 successive days. At the end of 21 days, rats underwent ovarian biopsies. The experimental PCOS model was considered successful in the presence of atretic follicles without granulosa cell stratification. Group 3 (PCOS + Nateglinide Group): Nateglinide was administered by oral dropper for 30 days to the rats in which PCOS model was created. Group 4 (Nateglinid only Group): 30 days of NG was applied to the rats without PCOS. Group 5 (PCOS+Octreotide Group): 0.1 mg/kg/day Octreotide was given intraperitoneally for 4 weeks to the rats in which PCOS model was created. Group 6 (Octreotide only Group): animals without PCOS given 0.1 mg/kg/day Octreotide at the end of the treatment, bilateral oophorectomy was performed and blood samples were collected from all groups. Ovarian tissue was stained immunohistochemically with TLR-4 in addition to conventional staining. In addition to follicle classification, ovarian damage was graded. Serum insulin, FSH and LH, TNF-α, IL-6, SHBG, SOD, IGF-1, MDA and GSH levels were also measured. RESULTS: The cystic and degenerated follicle density of PCOS group was high compared with the other groups. Both cystic and degenerated follicles were significantly reduced in PCOS+NG and PCOS+OC groups compared to PCOS group. There was no difference between the groups in terms of serum LH, FSH and insulin levels (p>0.05). Serum testosterone level was significantly higher in the PCOS group compared to the other groups (p<0.01). Adding OC or NG to PCOS groups did not cause significant changes in testosterone levels. TNF-α and IL-6 levels were high in PCOS group (p<0.03). IGF-1 and MDA levels were higher in PCOS than in other groups (p<0.03, p<0.01 respectively). Adding OC or NG to the treatment normalized IGF-1 and MDA levels. Serum GSH levels were significantly lower in the PCOS group (p<0.05). Adding NG to the treatment increased GSH levels. CONCLUSIONS: Both NG and OCT reverses atretic and degenerate follicle damage due to PCOS through TLR-4, antioxidant and anti-inflammatory pathways.