Biological evaluation of 9-thioansamitocin P3.

Highly cytotoxic maytansine derivatives are widely used in targeted tumor delivery. Structure-activity studies published earlier suggested the C9 carbinol to be a key element necessary to retain the potency. However, in 1984 a patent was published by Takeda in which the synthesis of 9-thioansamitocyn (AP3SH) was described and its activity in xenograft models was shown. In this article we summarize the results of an extended study of the anti-tumor properties of AP3SH. Like other maytansinoids, it induces apoptosis and arrests the cell cycle in the G2/M phase. It is metabolized in liver microsomes predominately by C3A4 isoform and doesn't inhibit any CYP isoforms except CYP3A4 (midazolam, IC50 7.84 µM). No hERG inhibition, CYP induction or mutagenicity in Ames tests were observed. AP3SH demonstrates high antiproliferative activity against 25 tumor cell lines and tumor growth inhibition in U937 xenograft model. Application of AP3SH as a cytotoxic payload in drug delivery system was demonstrated by us earlier.

The antimicrobial peptides and their potential clinical applications.

Nowadays, the bacterial drug resistance leads to serious healthy problem worldwide due to the long-term use and the abuse of traditional antibiotics result in drug resistance of bacteria. Finding a new antibiotic is becoming more and more difficult. Antimicrobial peptides (AMPs) are the host defense peptides with most of them being the cationic (positively charged) and amphiphilic (hydrophilic and hydrophobic) α-helical peptide molecules. The membrane permeability is mostly recognized as the well-accepted mechanism to describe the action of cationic AMPs. These cationic AMPs can bind and interact with the negatively charged bacterial cell membranes, leading to the change of the electrochemical potential on bacterial cell membranes, inducing cell membrane damage and the permeation of larger molecules such as proteins, destroying cell morphology and membranes and eventually resulting in cell death. These AMPs have been demonstrated to have their own advantages over the traditional antibiotics with a broad-spectrum of antimicrobial activities including anti-bacteria, anti-fungi, anti-viruses, and anti-cancers, and even overcome bacterial drug-resistance. The natural AMPs exist in a variety of organisms and are not stable with a short half-life, more or less toxic side effects, and particularly may have severe hemolytic activity. To open the clinical applications, it is necessary and important to develop the synthetic and long-lasting AMP analogs that overcome the disadvantages of their natural peptides and the potential problems for the drug candidates.

Pituitary adenylate cyclase-activating polypeptide is a potent broad-spectrum antimicrobial peptide: Structure-activity relationships.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a naturally occurring cationic peptide with potent immunosuppressant and cytoprotective activities. We now show that full length PACAP38 and to a lesser extent, the truncated form PACAP27, and the closely related vasoactive intestinal peptide (VIP) and secretin had antimicrobial activity against the Gram-negative bacteria Escherichia coli in the radial diffusion assay. PACAP38 was more potent than either the bovine neutrophil antimicrobial peptide indolicidin or the synthetic antimicrobial peptide ARVA against E. coli. PACAP38 also had activity against the Gram-positive bacteria Staphylococcus aureus in the same assay with comparable potency to indolicidin and ARVA. In the more stringent broth dilution assay, PACAP38 had moderate sterilizing activity against E. coli, and potent sterilizing activity against the Gram-negative bacteria Pseudomonas aeruginosa. PACAP27, VIP and secretin were much less active than PACAP38 in this assay. PACAP38 also had some activity against the Gram-positive bacteria Bacillus cereus in the broth dilution assay. Many exopeptidase-resistant analogs of PACAP38, including both receptor agonists and antagonists, had antimicrobial activities equal to, or better than PACAP38, in both assays. PACAP38 made the membranes of E. coli permeable to SYTOX Green, suggesting a classical membrane lytic mechanism. These data suggest that analogs of PACPAP38 with a wide range of useful biological activities can be made by judicious substitutions in the sequence.

HDAC inhibitors suppressed small cell lung cancer cell growth and enhanced the suppressive effects of receptor-targeting cytotoxins via upregulating somatostatin receptor II.

Small cell lung cancer (SCLC) is a malignant human cancer and patients have very limited benefit from traditional anticancer treatments, with a poor five-year survival rate being 10% less. In present study, we observed that Notch signalling activation induced SCLC cell growth suppression via overexpressing Notch active fragments (ICN1, ICN2, ICN3 and ICN4), implying its tumor suppressive role. The histone deacetylase (HDAC) inhibitors also displayed their suppressive effects. Valproic acid (VPA) as a HDAC inhibitor was found to suppress SCLC cell growth and cell cycle arrest at phase G1, and observed to decrease HDAC4 and increase acetylation of histone H4 (AcH4) while activating Notch signalling with an increase of Notch1, Notch target gene HES1 and p21. Meanwhile, we also observed that VPA greatly stimulated the expression of somatostatin receptor type II (SSTR2) that is usually overexpressed in many cancer cells and is used as a target for anticancer drug development, providing a combination therapy with VPA and the SSTR2-targeting cytotoxins. Thus, VPA was investigated in combination with SSTR2-targeted cytotoxins captothecine-somatostatin conjugate (CPT-SST) and colchicine-somatostatin conjugate (COL-SST). Our assays showed that these combination treatments strongly led to a greater suppression as compared to each alone. In conclusion, we found that VPA suppressed SCLC cell growth and increased the expression of SSTR2. These may provide a novel clinical opportunity for enhanced anticancer therapy using the combination strategy of Notch signalling regulator and SSTR2-targeting cytotoxins in SCLC treatments.

Pituitary adenylate cyclase-activating polypeptide (PACAP) protects against mitoxantrone-induced cardiac injury in mice.

Mitoxantrone (MXT) is an androstenedione that is used to treat cancers and progressive forms of multiple sclerosis; however, its use is limited by its cardiotoxicity. Pituitary adenylate cyclase activating polypeptide (PACAP) is a member of the secretin/growth hormone-releasing hormone/vasoactive intestinal peptide family and has many functions, including cytoprotection and immunosuppression. We tested the hypothesis that PACAP can protect against MXT-induced cardiotoxicity in mice. Female BALB/c mice were treated once weekly for 4 weeks with saline (n=14) or MXT (3mg/kg, i.p.; n=14). Half of the mice in each group received PACAP (10µg, i.p.) 1h before and 24 and 48h after MXT, while the remaining mice received injections of saline on the same schedule. Echocardiography was used to assess cardiac structure and function. In mice treated with MXT and saline, body weight was significantly reduced after the third dose of MXT. PACAP significantly attenuated the reduction in body weight; however, the weights did not return to control level. Compared to controls, MXT-treated mice had significantly increased left ventricular (LV) diameter and LV volume and decreased LV posterior wall thickness. Fractional shortening (FS) and ejection fraction (EF) were also significantly decreased. Treatment with PACAP prevented MXT-induced LV dilation and significantly attenuated the reductions in FS and EF, although FS and EF did not return to control level. PACAP38 did not prevent MXT-induced decreases in LV posterior wall thickness. MXT dose-dependently decreased the viability of cultured U937 (human leukemia) cells; PACAP did not protect cultured U937 cells from MXT-mediated cell death. In conclusion, PACAP can attenuate MXT-mediated LV dilation and dysfunction in mice.

Activated Notch signaling augments cell growth in hepatocellular carcinoma via up-regulating the nuclear receptor NR4A2.

Hepatocellular carcinoma (HCC) is one of the most malignant cancers. Conventional therapies are limited due to the human liver being such a unique organ and easily showing side-effects. The unclear molecular mechanisms are tough challenges for scientists searching for new and effective anti-HCC targeting drugs. We identified that the nuclear receptor NR4A2 is a novel oncogene in HCC progression. In this study, we show that NR4A2 and the notch recceptor Notch1 were expressed highly in primary HCC tissues and immortal HCC cells by using qPCR, western blot and immuno-histochemistry assays. Both genes were observed to stimulate HCC cell proliferation, anti-apoptosis and cell cycle arrest by using cell proliferation assays and FACS assays. We also observed that the four notch receptor subtypes (Notch1-4) displayed different effects on HCC cell growth. The over-expression of Notch1 by transiently transfecting the intracellular domain of Notch1 (ICN1, Notch1 active form) increased the expression of NR4A2, with the knockdown of Notch1 decreasing NR4A2. This indicates that NR4A2 is one of the Notch-mediated downstream genes. Moreover, both NR4A2 and Notch1 suppressed the expression of tumor suppressors p21 and p63. These findings support that Notch1/NR4A2 co-regulate HCC cell functions by playing oncogenic roles and regulating the associated downstream signaling pathways. Novel Notch1/NR4A2-mediated oncogenic signaling may provide us a great opportunity for anti-HCC drug development.

Notch Signaling Activation in Cervical Cancer Cells Induces Cell Growth Arrest with the Involvement of the Nuclear Receptor NR4A2.

Cervical cancer is a second leading cancer death in women world-wide, with most cases in less developed countries. Notch signaling is highly conserved with its involvement in many cancers. In the present study, we established stable cervical cell lines with Notch activation and inactivation and found that Notch activation played a suppressive role in cervical cancer cells. Meanwhile, the transient overexpression of the active intracellular domain of all four Notch receptors (ICN1, 2, 3, and 4) also induced the suppression of cervical cancer Hela cell growth. ICN1 also induced cell cycle arrest at phase G1. Notch1 signaling activation affected the expression of serial genes, especially the genes associated with cAMP signaling, with an increase of genes like THBS1, VCL, p63, c-Myc and SCG2, a decrease of genes like NR4A2, PCK2 and BCL-2. Particularly, The nuclear receptor NR4A2 was observed to induce cell proliferation via MTT assay and reduce cell apoptosis via FACS assay. Furthermore, NR4A2's activation could reverse ICN1-induced suppression of cell growth while erasing ICN1-induced increase of tumor suppressor p63. These findings support that Notch signaling mediates cervical cancer cell growth suppression with the involvement of nuclear receptor NR4A2. Notably, Notch/NR4A2/p63 signaling cascade possibly is a new signling pathway undisclosed.

Glucagon responses to exercise-induced hypoglycaemia are improved by somatostatin receptor type 2 antagonism in a rat model of diabetes.

AIMS/HYPOTHESIS: Regular exercise is at the cornerstone of care in type 1 diabetes. However, relative hyperinsulinaemia and a blunted glucagon response to exercise promote hypoglycaemia. Recently, a selective antagonist of somatostatin receptor 2, PRL-2903, was shown to improve glucagon counterregulation to hypoglycaemia in resting streptozotocin-induced diabetic rats. The aim of this study was to test the efficacy of PRL-2903 in enhancing glucagon counterregulation during repeated hyperinsulinaemic exercise. METHODS: Diabetic rats performed daily exercise for 1 week and were then exposed to saline (154 mmol/l NaCl) or PRL-2903, 10 mg/kg, before hyperinsulinaemic exercise on two separate occasions spaced 1 day apart. In the following week, animals crossed over to the alternate treatment for a third hyperinsulinaemic exercise protocol. RESULTS: Liver glycogen content was lower in diabetic rats compared with control rats, despite daily insulin therapy (p < 0.05). Glucagon levels failed to increase during exercise with saline but increased three-to-six fold with PRL-2903 (all p < 0.05). Glucose concentrations tended to be higher during exercise and early recovery with PRL-2903 on both days of treatment; this difference did not achieve statistical significance (p > 0.05). CONCLUSIONS/INTERPRETATION: PRL-2903 improves glucagon counterregulation during exercise. However, liver glycogen stores or other factors limit the prevention of exercise-induced hypoglycaemia in rats with streptozotocin-induced diabetes.

Somatostatin and its Analogs.

Somatostatin (SST) is a cyclic hormone-release inhibitory peptide that has high binding affinity to all of its five SST receptors (SSTRs). SST negatively regulates cell proliferation and the release of multiple hormones via activation of its cognate receptors. A variety of SST analogs, some with high affinity and selectivity of receptor subtypes, have been synthesized and developed. Certain long-acting SST analogs such as octreotide, lanreotide and pasireotide have been clinically applied to the treatment of human diseases such as those caused by excessive release of growth hormone (acromegaly), or adrenocorticotropic hormone (Cushing's syndrome), and for the treatment of carcinoid syndrome. Investigations into new biological activities of these long-acting SSTs and their possible clinical applications are also still ongoing. Also, novel SST analogs are being designed and developed to target different receptor subtype(s) or mimic natural SST's multiple biological properties. Additionally, since SSTRs, especially SSTR2, are aberrantly expressed in many cancer cells and tumor blood vessels, internalizing SST analogs is currently being used as drug-delivery vehicle for the application of receptor-targeted therapeutics. This review will discuss recent advances in the development and applications of SST and its analogs.

Valproic acid induces NET cell growth arrest and enhances tumor suppression of the receptor-targeted peptide-drug conjugate via activating somatostatin receptor type II.

BACKGROUND: Human pancreatic carcinoids, a type of neuroendocrine tumors, are asymptomatic and difficult to diagnose, with the effects of traditional anti-cancer therapies being limited. The histone deacetylase (HDAC) inhibitor valproic acid (VPA) was evaluated for its effects alone and in combination with receptor-targeting peptide-drug conjugate via increasing drug internalization. MATERIALS AND METHODS: The in vitro and in vivo assays were used to evaluate the effects of VPA and somatostatin receptor-targeting camptothecin-somatostatin conjugate (CPT-SST). RESULTS: VPA induced proliferation suppression, cell apoptosis and cell cycle arrest. VPA acts as a HDAC inhibitor to induce a decrease of HDAC4 and an increase of acetylated histone 4 (AcH4). Meanwhile, most importantly, besides activating Notch signaling, VPA was observed to stimulate the expression of somatostatin receptor type 2 (SSTR2) that has been applied for receptor-targeting therapies. This characteristic was used for a combination therapy of VPA and CPT-SST. The combination displayed much more potent anti-tumor effects on carcinoid tumor growth by increasing SSTR2 density and drug internalization in target tumor cells. CONCLUSION: The combination of VPA and a SSTR2-targeting agent provides us a promising approach in treatment of carcinoid tumors.

The Histone Deacetylase Inhibitor Vaproic Acid Induces Cell Growth Arrest in Hepatocellular Carcinoma Cells via Suppressing Notch Signaling.

Hepatocellular carcinoma (HCC) is a type of malignant cancer. Notch signaling is aberrantly expressed in HCC tissues with more evidence showing that this signaling plays a critical role in HCCs. In the present study, we investigate the effects of the anti-convulsant drug valproic acid (VPA) in HCC cells and its involvement in modulating Notch signaling. We found that VPA, acting as a histone deacetylase (HDAC) inhibitor, induced a decrease in HDAC4 and an increase in acetylated histone 4 (AcH4) and suppressed HCC cell growth. VPA also induced down-regulation of Notch signaling via suppressing the expression of Notch1 and its target gene HES1, with an increase of tumor suppressor p21 and p63. Furthermore, Notch1 activation via overexpressing Notch1 active form ICN1 induced HCC cell proliferation and anti-apoptosis, indicating Notch signaling played an oncogenic role in HCC cells. Meanwhile, VPA could reverse Notch1-induced increase of cell proliferation. Interestingly, VPA was also observed to stimulate the expression of G protein-coupled somatostatin receptor type 2 (SSTR2) that has been used in receptor-targeting therapies. This discovery supports a combination therapy of VPA with the SSTR2-targeting agents. Our in vitro assay did show that the combination of VPA and the peptide-drug conjugate camptothecin-somatostatin (CPT-SST) displayed more potent anti-proliferative effects on HCC cells than did each alone. VPA may be a potential drug candidate in the development of anti-HCC drugs via targeting Notch signaling, especially in combination with receptor-targeting cytotoxic agents.

Lanreotide and its Potential Applications in Polycystic Kidney and Liver Diseases.

Multiple Gαi protein-coupled somatostatin receptors (SSTRs) are expressed in human kidney and liver tissues. Also, aberrant cAMP signaling has been shown to play a critical role in cysto-genesis and enlargement of the human kidney and liver. Thus, somatostatin (SST) analogs become potential and promising alternatives in treating human polycystic kidney disease (PKD) and polycystic liver disease (PLD) via interacting with Gαi protein-coupled SSTRs and further blocking cAMP production. Lanreotide is a synthetic, long-acting SST analog with high binding affinity to SSTR2, and has been clinically approved for the treatment of acromegaly due to excessive growth hormone. Recently, this SST analog has been applied in the treatment of PKD and PLD, and has shown an effective reduction of liver and kidney volume compared to placebo. This review will discuss the discovery of this peptide and its clinical applications in the treatment of PKD/PLD patients.

Insights into bombesin receptors and ligands: Highlighting recent advances.

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Is Notch Signaling a Specific Target in Hepatocellular Carcinoma?

Hepatocellular carcinoma (HCC) is one of the most malignant cancers, with the second highest cancer death rate world-wide, next to lung cancer. The signaling mechanisms in HCC are currently not clear. Notch signaling, which is highly conserved and plays a critical role in many cancers, was found to be aberrantly upregulated in HCC tissues compared to normal liver tissues. Accumulating evidence supports that Notch signaling plays a significantly important role in HCC carcinogenesis. This review discusses the functions of Notch signaling in HCC and its potential therapeutic applications against this cancer.

A structure-function study of PACAP using conformationally restricted analogs: Identification of PAC1 receptor-selective PACAP agonists.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has widespread physiological/pathophysiological actions and there is increased interest for its use therapeutically, especially in the CNS (neuroprotection). Unfortunately, no selective PACAP-analogs exist for PACAP-preferring PAC1-receptors, primarily because of its high sequence identity to VIP and particularly, because of the inability of structure-function studies to separate the pharmacophore of PAC1-R from VPAC1-R, which has high affinity for PACAP and VIP. The present study attempted to develop PAC1-R-selective agonists primarily by making conformationally restricted PACAP-analogs in positions important for receptor-selectivity/affinity. Forty-six PACAP-related-analogs were synthesized with substitutions in positions 1-4, 14-17, 20-22, 28, 34, 38 and receptor-selectivity determined in PAC1-R,VPAC1-R,VPAC2-R-transfected or native cells from binding or cAMP-generation experiments. Fifteen PACAP-analogs had 6-78-fold higher affinities for PAC1-R than VPAC1-R and 13 were agonists. Although binding-affinities correlated significantly with agonist potency, the degree of receptor-spareness varied markedly for the different PACAP-analogs, resulting in selective potencies for activating the PAC1 receptor over the VPAC1 receptor from 0- to 103-fold. In addition, a number of PACAP-analogs were identified that had high selectivity for PAC1-R over VPAC2-R as well as PACAP-analogs that could prove more useful therapeutically because of substitutions known to extend their half-lives (substitutions at potential sites of proteolysis and attachment of long-chain fatty acids). This study provides for the first time a separation of the pharmacophores for PAC1-R and VPAC1-R, resulting in PACAP-related analogs that are PAC1-R-preferring. Some of these analogs, or their modifications, could prove useful as therapeutic agents for various diseases.

Comparative pharmacology of bombesin receptor subtype-3, nonpeptide agonist MK-5046, a universal peptide agonist, and peptide antagonist Bantag-1 for human bombesin receptors.

Bombesin-receptor-subtype-3 (BRS-3) is an orphan G-protein-coupled receptor of the bombesin (Bn) family whose natural ligand is unknown and which does not bind any natural Bn-peptide with high affinity. It is present in the central nervous system, peripheral tissues, and tumors; however, its role in normal physiology/pathophysiology is largely unknown because of the lack of selective ligands. Recently, MK-5046 [(2S)-1,1,1-trifluoro-2-[4-(1H-pyrazol-1-yl)phenyl]-3-(4-{[1-(trifluoromethyl)cyclopropyl]methyl}-1H-imidazol-2-yl)propan-2-ol] and Bantag-1 [Boc-Phe-His-4-amino-5-cyclohexyl-2,4,5-trideoxypentonyl-Leu-(3-dimethylamino) benzylamide N-methylammonium trifluoroacetate], a nonpeptide agonist and a peptide antagonist, respectively, for BRS-3 have been described, but there have been limited studies on their pharmacology. We studied MK-5046 and Bantag-1 interactions with human Bn-receptors-human bombesin receptor subtype-3 (hBRS-3), gastrin-releasing peptide receptor (GRP-R), and neuromedin B receptor (NMB-R)-and compared them with the nonselective, peptide-agonist [d-Tyr6,ßAla11,Phe13,Nle14]Bn-(6-14) (peptide #1). Receptor activation was detected by activation of phospholipase C (PLC), mitogen-activated protein kinase (MAPK), focal adhesion kinase (FAK), paxillin, and Akt. In hBRS-3 cells, the relative affinities were Bantag-1 (1.3 nM) > peptide #1 (2 nM) > MK-5046 (37-160 nM) > GRP, NMB (>10 µM), and the binding-dose-inhibition curves were broad (>4 logs), with Hill coefficients differing significantly from unity. Curve-fitting demonstrated high-affinity (MK-5046, Ki = 0.08 nM) and low-affinity (MK-5046, Ki = 11-29 nM) binding sites. For PLC activation in hBRS-3 cells, the relative potencies were MK-5046 (0.02 nM) > peptide #1 (6 nM) > GRP, NMB, Bantag-1 (>10 µM), and MK-5046 had a biphasic dose response, whereas peptide #1 was monophasic. Bantag-1 was a specific hBRS-3-antagonist. In hBRS-3 cells, MK-5046 was a full agonist for activation of MAPK, FAK, Akt, and paxillin; however, it was a partial agonist for phospholipase A2 (PLA2) activation. The kinetics of activation/duration of action for PLC/MAPK activation of MK-5046 and peptide #1 differed, with peptide #1 causing more rapid stimulation; however, MK-5046 had more prolonged activity. Our study finds that MK-5046 and Bantag-1 have high affinity/selectivity for hBRS-3. The nonpeptide MK-5046 and peptide #1 agonists differ markedly in their receptor coupling, ability to activate different signaling cascades, and kinetics/duration of action. These results show that their hBRS-3 receptor activation is not always concordant and could lead to markedly different cellular responses.

Somatostatin receptor type 2 antagonism improves glucagon counterregulation in biobreeding diabetic rats.

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly attributable to inadequate glucagon secretion. Intra-islet somatostatin (SST) suppression of hypoglycemia-stimulated α-cell glucagon release plays an important role. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by SST receptor type 2 (SSTR2) antagonism of α-cells, which relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes-prone (BBDP) rats mimic insulin-dependent human autoimmune T1D, whereas nondiabetic BBDP rats mimic prediabetes. Diabetic and nondiabetic rats underwent a 3-h infusion of vehicle compared with SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycemia clamped at 3 ± 0.5 mmol/L. Diabetic rats treated with SSTR2a needed little or no glucose infusion compared with untreated rats. We attribute this effect to SSTR2a restoration of the attenuated glucagon response. Direct effects of SSTR2a on α-cells was assessed by resecting the pancreas, which was cut into fine slices and subjected to perifusion to monitor glucagon release. SSTR2a treatment enhanced low-glucose-stimulated glucagon and corticosterone secretion to normal levels in diabetic rats. SSTR2a had similar effects in vivo in nondiabetic rats and promoted glucagon secretion from nondiabetic rat and human pancreas slices. We conclude that SST contributes to impaired glucagon responsiveness to hypoglycemia in autoimmune T1D. SSTR2a treatment can fully restore hypoglycemia-stimulated glucagon release sufficient to attain normoglycemia in both diabetic and prediabetic stages.

Amelioration of hypoglycemia via somatostatin receptor type 2 antagonism in recurrently hypoglycemic diabetic rats.

Selective antagonism of somatostatin receptor type 2 (SSTR2) normalizes glucagon and corticosterone responses to hypoglycemic clamp in diabetic rats. The purpose of this study was to determine whether SSTR2 antagonism (SSTR2a) ameliorates hypoglycemia in response to overinsulinization in diabetic rats previously exposed to recurrent hypoglycemia. Streptozotocin diabetic rats (n = 19), previously subjected to five hypoglycemia events over 3 days, received an insulin bolus (10 units/kg i.v.) plus insulin infusion (50 mU/kg/min i.v.) until hypoglycemia ensued (≤3.9 mmol/L) (experimental day 1 [Expt-D1]). The next day (Expt-D2), rats were allocated to receive either placebo treatment (n = 7) or SSTR2a infusion (3,000 nmol/kg/min i.v., n = 12) 60 min prior to the same insulin regimen. On Expt-D1, all rats developed hypoglycemia by ∼90 min, while on Expt-D2, hypoglycemia was attenuated with SSTR2a treatment (nadir = 3.7 ± 0.3 vs. 2.7 ± 0.3 mmol/L in SSTR2a and controls, P < 0.01). Glucagon response to hypoglycemia on Expt-D2 deteriorated by 20-fold in the placebo group (P < 0.001) but improved in the SSTR2a group (threefold increase in area under the curve [AUC], P < 0.001). Corticosterone response deteriorated in the placebo-treated rats on Expt-D2 but increased twofold in the SSTR2a group. Catecholamine responses were not affected by SSTR2a. Thus, SSTR2 antagonism after recurrent hypoglycemia improves the glucagon and corticosterone responses and largely ameliorates insulin-induced hypoglycemia in diabetic rats.

Valproic acid suppresses cervical cancer tumor progression possibly via activating Notch1 signaling and enhances receptor-targeted cancer chemotherapeutic via activating somatostatin receptor type II.

PURPOSE: We investigated the effects of the anti-epilepsy drug valproic acid (VPA) alone and in combination in treating cervical cancer. METHODS: VPA was investigated for its effects on cervical cancer Hela cell proliferation and tumor growth via in vitro and in vivo assays. RESULTS: VPA induce cell growth suppression and cell cycle arrest, with an increase of Notch1 that acts as a tumor suppressor and the change of other tumor-associated genes such as p21, p63 and PCNA. VPA was also found to induce cell morphological change, with an increase of certain cell transformation markers such as snail1, snail2 and N-cadherin. Moreover, VPA could significantly up-regulate somatostatin receptor type II (SSTR2). Our in vivo study further demonstrated that VPA via inducing SSTR2 up-regulation extremely enhanced the anti-tumor ability of the SSTR2-preferential cytotoxic COL-SST conjugate in xenografts. CONCLUSIONS: VPA could not only suppress tumor progression but also provide a novel promising therapeutic choice in combination with a receptor-targeted cytotoxic conjugate via activating the specific receptor.