Antiproliferative activity induced by the somatostatin analogue, TT-232, in human pancreatic cancer cells

Bioenergetic alteration in gastrointestinal cancers: The good, the bad and the ugly

Cancer cells exhibit metabolic reprogramming and bioenergetic alteration, utilizing glucose fermentation for energy production, known as the Warburg effect. However, there are a lack of comprehensive reviews summarizing the metabolic reprogramming, bioenergetic alteration, and their oncogenetic links in gastrointestinal (GI) cancers. Furthermore, the efficacy and treatment potential of emerging anticancer drugs targeting these alterations in GI cancers require further evaluation. This review highlights the interplay between aerobic glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation (OXPHOS) in cancer cells, as well as hypotheses on the molecular mechanisms that trigger this alteration. The role of hypoxia-inducible transcription factors, tumor suppressors, and the oncogenetic link between hypoxia-related enzymes, bioenergetic changes, and GI cancer are also discussed. This review emphasizes the potential of targeting bioenergetic regulators for anti-cancer therapy, particularly for GI cancers. Emphasizing the potential of targeting bioenergetic regulators for GI cancer therapy, the review categorizes these regulators into aerobic glycolysis/ lactate biosynthesis/transportation and TCA cycle/coupled OXPHOS. We also detail various anti-cancer drugs and strategies that have produced pre-clinical and/or clinical evidence in treating GI cancers, as well as the challenges posed by these drugs. Here we highlight that understanding dysregulated cancer cell bioenergetics is critical for effective treatments, although the diverse metabolic patterns present challenges for targeted therapies. Further research is needed to comprehend the specific mechanisms of inhibiting bioenergetic enzymes, address side effects, and leverage high-throughput multi-omics and spatial omics to gain insights into cancer cell heterogeneity for targeted bioenergetic therapies.

The heptapeptide somatostatin analogue TT-232 exerts analgesic and anti-inflammatory actions via SST4 receptor activation: In silico, in vitro and in vivo evidence in mice

Since the conventional and adjuvant analgesics have limited effectiveness frequently accompanied by serious side effects, development of novel, potent pain killers for chronic neuropathic and inflammatory pain conditions is a big challenge. Somatostatin (SS) regulates endocrine, vascular, immune and neuronal functions, cell proliferation through 5 G_i protein-coupled receptors (SST₁-SST₅). SS released from the capsaicin-sensitive peptidergic sensory nerves mediates anti-inflammatory and antinociceptive effects without endocrine actions via SST₄. The therapeutic use of the native SS is limited by its diverse biological actions and short plasma elimination half-life. Therefore, SST₄ selective SS analogues could be promising analgesic and anti-inflammatory drug candidates with new mode of action. TT-232 is a cyclic heptapeptide showing great affinity to SST₄ and SST₁. Here, we report the in silico SST₄ receptor binding mechanism, in vitro binding (competition assay) and cAMP- decreasing effect of TT-232 in SST₄-expressing CHO cells, as well as its analgesic and anti-inflammatory actions in chronic neuropathic pain and arthritis models using wildtype and SST₄-deficient mice. TT-232 binds to SST₄ with similar interaction energy (-11.03 kcal/mol) to the superagonist J-2156, displaces somatostatin from SST₄ binding (10 nM to 30 µM) and inhibits forskolin-stimulated cAMP accumulation (EC₅₀: 371.6 ± 58.03 nmol; E_max: 78.63 ± 2.636 %). Its i.p. injection (100, 200 µg/kg) results in significant, 35.7 % and 50.4 %, analgesic effects upon single administration in chronic neuropathic pain and repeated injection in arthritis models in wildtype, but not in SST₄-deficient mice. These results provide evidence that the analgesic effect of TT-232 is mediated by SST₄ activation, which might open novel drug developmental potentials. Chemical compounds Chemical compounds studied in this article TT-232 (PubChem CID: 74053735).

Effects of octreotide and insulin on colon cancer cellular proliferation and correlation with hTERT activity

Peptide hormone somatostatin and its receptors have a wide range of physiological functions and play a role in the treatment of numerous human diseases, including colorectal cancer. Octreotide, a synthetic somatostatin-analog peptide, inhibits growth of colonic cancer cells primarily by binding to G-protein coupled receptors and elicits cellular responses through second-messenger systems. Insulin also initiates mitogenic signals in certain cell types. The objective of the present study was to explore the effects of octreotide with or without insulin treatment, on Caco-2 and HT-29 human colon-cancer cell proliferation and to correlate their effects with the activation of telomerase reverse transcriptase (hTERT). The involvement of protein tyrosine phosphatases in the regulation of the anti-proliferative effect of octreotide was also evaluated. Sodium orthovanadate was used to reverse the anti- proliferative effect of octreotide. Telomerase activity was determined for each time point under octreotide and/or insulin treatment. Elevated expression of sst1, sst2 and sst5 was confirmed in both cell lines by RT-PCR. Immunocytochemistry detected sst1, sst2A, sst2B, sst3, sst4 and sst5 protein expression in the membranes of both cell lines. Octreotide inhibited the proliferation of Caco-2 and HT-29 cells in a time and dose-dependent manner. Insulin exerted proliferative effects in Caco-2 cells and octreotide reversed its effect in both cell lines. Sodium orthovanadate suppressed the anti-proliferative effect of octreotide both in Caco-2 and HT-29 cells. Telomerase activity was significantly reduced when Caco-2 cells were exposed to octreotide, under serum-free cultured medium. On the other hand, telomerase attenuation after octreotide treatment could not counteract the actions of insulin on both cells. Our data indicate that the use of octreotide could provide a possible therapeutic approach to the management of certain patients who suffer from colon cancer.

Synthesis and evaluation of biodegradable PCL/PEG nanoparticles for neuroendocrine tumor targeted delivery of somatostatin analog

PURPOSE

Neuroendocrine tumors often present a diagnostic and therapeutic challenge. We have aimed to synthesize and develop biodegradable nanoparticles of somatostatin analogue, octreotide for targeted therapy of human neuroendocrine pancreatic tumor.

METHODS

Direct solid phase peptide synthesis of octreotide was done. Octreotide loaded PCL/PEG nanoparticles were prepared by solvent evaporation method and characterized for transmission electron microscopy, differential scanning calorimetery (DSC), Zeta potential measurement studies. The nanoparticles were evaluated in vitro for release studies and peptide content. For biological evaluations, receptor binding & cytotoxicity studies were done on BON-1 neuroendocrine tumor cell line. Biodistribution of radiolabeled peptide and nanoparticles, tumor regression studies were performed on tumor-bearing mouse models.

RESULTS

We have synthesized and purified octreotide with the purity of 99.96% in our laboratory. PEG/PCL nanoparticles with an average diameter of 130-195 nm having peptide loading efficiency of 66-84% with a negative surface charge were obtained with the formulation procedure. Octreotide nanoparticles have a negative action on the proliferation of BON-1 cells. In vivo biodistribution studies exhibited major accumulation of octreotide nanoparticles in tumor as compared to plain octreotide. Octreotide nanoparticles inhibited tumor growth more efficiently than free octreotide.

CONCLUSIONS

Thus, it was concluded that the PCL/PEG nanoformulation of octreotide showed high tumor uptake due to the enhanced permeation and retention (EPR) effect and then peptide ligand imparts targetability to the sst2 receptor and there by showing increase tumor growth inhibition. Selective entry of nanoparticles to the tumor also give the reduce side effects both in vivo and in vitro.

Somatostatin stimulates the migration of hepatic oval cells in the injured rat liver

BACKGROUND

Somatostatin is a pleiotropic peptide, exerting a variety of effects through its receptor subtypes. Recently, somatostatin has been shown to act as a chemoattractant for haematopoietic progenitor cells and hepatic oval cells (HOC) via receptor subtype 2 and subtype 4 (SSTR4) respectively.

AIMS

We investigated the in vivo effect of somatostatin/SSTR4 on HOC migration in the injured liver model of rats and the type of signalling molecules associated with the chemotactic function.

METHODS

Migration assay, HOC transplantation and phosphatidylinositol-3-kinase (PI3K) signalling were assessed with or without somatostatin and an analogue of somatostatin (TT232) that specifically binds to SSTR4.

RESULTS

TT232 was shown to have an antimigratory action on HOC induced by somatostatin in vitro. In HOC transplantation experiments, a lower number of donor-derived cells were detected in TT232-treated animals, as compared with control animals. Activation of PI3K was observed in HOC exposed to somatostatin, and this activation was suppressed by either SSTR4 antibody or TT232-pretreatment. In addition, a PI3K inhibitor abrogated the motility of HOC.

CONCLUSION

Together, these data suggest that somatostatin stimulates the migration of HOC within injured liver through SSTR4, and this action appears to be mediated by the PI3K pathway.

TT232, A Novel Signal Transduction Inhibitory Compound in the Therapy of Cancer and Inflammatory Diseases

TT-232 is a structural analogue of somatostatin exhibiting strong and selective growth-inhibitory effects, inhibition of neurogenic inflammation, as well as general anti-inflammatory and analgesic potential without the wide-ranging endocrine side effects of the parent hormone and its "traditional" analogues. The anti-inflammatory action of TT-232 is mediated through the SSTR4 receptor, and its antitumor activity is mediated through the SSTR1 receptor and by the tumor-specific isoform of pyruvate kinase. Its mechanism of action is in line with a new era of molecular medicine called signal transduction therapy, where "false" intracellular or intercellular communication is inhibited or corrected without interfering with basic cell functions and machinery. TT232 has passed phase I clinical trials without toxicity and significant side effects, and phase II studies are running for oncological and anti-inflammatory indications, respectively. This compound has the perspective to become the first drug in molecularly targeted therapy of inflammation where a combined effect of anti-inflammatory, analgesic, and neurogenic inflammation-inhibiting activity can be achieved.

An update on somatostatin receptor signaling in native systems and new insights on their pathophysiology

The peptide somatostatin (SRIF) has important physiological effects, mostly inhibitory, which have formed the basis for the clinical use of SRIF compounds. SRIF binding to its 5 guanine nucleotide-binding proteins-coupled receptors leads to the modulation of multiple transduction pathways. However, our current understanding of signaling exerted by receptors endogenously expressed in different cells/tissues reflects a rather complicated picture. On the other hand, the complexity of SRIF receptor signaling in pathologies, including pituitary and nervous system diseases, may be studied not only as alternative intervention points for the modulation of SRIF function but also to exploit new chemical space for drug-like molecules.

Receptor-Mediated Tumor Targeting with Radiopeptides. Part 1. General Concepts and Methods: Applications to Somatostatin Receptor-Expressing Tumors

Radiolabeled peptides have become important tools in nuclear oncology, both as diagnostics and more recently also as therapeutics. They represent a distinct sector of the molecular targeting approach, which in many areas of therapy will implement the old "magic bullet" concept by specifically directing the therapeutic agent to the site of action. In this three-part review, we present a comprehensive overview of the literature on receptor-mediated tumor targeting with the different radiopeptides currently studied. Part I summarizes the general concepts and methods of targeting, the selection of radioisotopes, chelators, and the criteria of peptide ligand development. Then, the >400 studies on the application to somatostatin/somatostatin-release inhibiting factor receptor-mediated tumor localization and treatment will be reviewed, demonstrating that peptide radiopharmaceuticals have gained an important position in clinical medicine.

Cortistatin production by HepG2 human hepatocellular carcinoma cell line and distribution of somatostatin receptors

BACKGROUND/AIMS

Recently, trials of octreotide have shown a significant survival benefit in the treatment of advanced hepatocellular carcinoma but new data are controversial. We, therefore, examined the production of somatostatin and cortistatin, the expression and distribution of somatostatin receptors (sst) in HepG2 human hepatocellular carcinoma cells, and the possible antiproliferative effect of octreotide on these cells.

METHODS

Radioimmunoassay and RT-PCR studies were performed for the detection of somatostatin and cortistatin. RT-PCR, radioligand binding and immunocytochemistry assays were employed for the detection of the ssts. Growth and viability of cells were measured by the tetrazolium salt assay.

RESULTS

HepG2 cells were found to express sst(2), sst(3) and sst(5) receptors. Immunocytochemistry revealed a mainly intracellular distribution of all ssts with unique patterns for each of them. Membrane binding sites for somatostatin were mainly of the sst(3) (39+/-8%) and sst(5) (59+/-5%) types, while only minor sst(2) binding could be detected (5+/-12%). Octreotide was found to inhibit the proliferation of HepG2 cells (IC(50) 1.25 x 10(-9)M) via protein tyrosine phosphatases. HepG2 cells produced cortistatin while somatostatin expression was not detected.

CONCLUSIONS

In conclusion, HepG2 cells express cortistatin, which regulates somatostatin receptors. Cell proliferation was reduced by octreotide via a protein tyrosine phosphatase dependent mechanism.

Antineoplastic effects of octreotide on human gallbladder cancer cells in vitro

AIM: To investigate whether octreotide can inhibit the growth of human gallbladder cancer cells in vitro and to elucidate the antineoplastic mechanism of octreotide in gallbladder cancer.

METHODS: A human gallbladder cancer cell line, GBC-SD, was cultured in vitro. The antiproliferative effects of octreotide were examined by means of an MTT assay and a colony forming ability assay. Morphological variation was investigated under scanning electron microscopy and transmission electron microscopy. Cell cycle analysis and apoptosis rate was evaluated by flow cytometry (FCM) after staining by propidium iodide. DNA fragmentation was assayed by agarose gel electrophoresis. Immunohistochemical staining was performed to evaluate the expressions of mutant-type p53 and bcl-2.

RESULTS: The growth curve and colony forming ability assay showed significant inhibition of octreotide to the proliferation of GBC-SD cells in culture in a time- and dose-dependent manner. After exposure to octreotide, GBC-SD cells showed typically apoptotic characteristics, including morphological changes of chromatin condensation, vacuolar degeneration, nucleus fragmentation and apoptotic body formation. In FCM profile apoptotic cells showed increased sub-G₁ peaks in the octreotide group, significantly higher than the control group (P = 0.013). There was also an augmentation in the cell proportion of G₀/G₁ phase (P = 0.015), while the proportion of S phase and G₂/M phase remained unchanged (P = 0.057 and P = 0.280, respectively). DNA agarose gel electrophoresis displayed a ladder after exposure to 1 000 nmol/L octreotide. After being treated with octreotide, the expressions of both mutant-type p53 and bcl-2 decreased considering the percentage of positive cells (P < 0.05).

CONCLUSION: Octreotide has a negative action to the proliferation of GBC-SD cells, and the mechanism may be related to cytostatic and cytotoxic effects. The reduction of mutant-type p53 and bcl-2 expressions may be associated with the apoptosis induced by octreotide.

TT-232: a somatostatin structural derivative as a potent antitumor drug candidate

TT-232 (D-Phe-Cys-Tyr-D-Trp-Lys-Cys-Thr-NH2) has been developed as an antitumor somatostatin analog. TT-232 has no growth hormone release inhibitory effect and does not inhibit the secretion of gastric acid. This analog induces apoptosis in and exerts pronounced antiproliferative effects on various human tumors (colon, pancreas, lymphoma, leukemia, melanoma, hepatoma) cell lines. The growth of human xenografts (prostate, breast carcinoma, lymphoma, melanoma) and animal tumors (colon-26, P-388, S-180, B16, MXT) was inhibited by TT-232 (dose range: 30-750 microg/kg/day) in 54-98% of cases. Continuous long-term infusion proved to be the most effective way of administration. TT-232 combined with decarbazine or etoposide treatment enhanced the antitumor activity of these drugs on human melanoma and lymphoma xenografts, respectively. Regarding the mode of action, TT-232 activates cell cycle inhibitors via SSTR receptors, inhibits tyrosine kinases through interfering with the proliferative signaling cascades, and interacts with an intracellular receptor and an enzyme involved in glycolysis causing translocation of this enzyme to the nucleus, thus inducing apoptosis. TT-232 may be a promising candidate in the therapy of human malignancies.

Chemoprevention for pancreatic cancer

For a number of solid tumors, including pancreatic cancer, efforts aimed at disease prevention may be more successful than currently available anticancer treatments. While specific interventions are emerging to prevent breast, prostate, lung, and colorectal cancer, no trials of chemoprevention are being conducted in pancreatic cancer. Importantly, there are significant obstacles to the conduct of such research. However, preclinical and epidemiologic studies suggest that several drugs may have chemopreventive potential in pancreatic cancer. These include aspirin and other non-steroidal antiinflammatory drugs (NSAIDs), selective cyclooxygenase inhibitors, somatostatin analogs, selective estrogen receptor modulators (SERMs), and anti-androgenic agents. As the oncology community evaluates some of these agents in large chemoprevention trials for breast, colon, and prostate cancer, it may be found that pancreatic cancer prevention occurs as an unintended, but desirable consequence. Moreover, other general societal trends, such as smoking cessation and the widespread use of cholesterol-lowering agents and aspirin, could have a role in reducing the risk of pancreatic cancer, and in the future, may lead to a decrease in its incidence.

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A cyclic peptide, L1AD3, induces early signs of apoptosis in human leukemic T-cell lines

L1AD3 is a small cyclic synthetic peptide designed to resemble the first loop of a cobra venom cytotoxin. Instead of inducing membrane disruption similar to that caused by the parent toxin, L1AD3 promotes extensive and unusually rapid apoptosis in leukemic T-cells without making the plasma membrane permeable to small fluorescent dyes. Within 4 h, micromolar concentrations of L1AD3 almost totally inhibit thymidine incorporation, and ATP levels decrease significantly. By contrast, normal human white blood cells are not affected by L1AD3, nor is heart cell function affected by it. If L1AD3 kills by interacting with targets that are different from those of currently applied agents, this peptide, or a derivative of it, could become a useful adjunct for cancer chemotherapy.

Antiproliferative effect of octreotide on gastric cancer cells mediated by inhibition of Akt/PKB and telomerase

AIM: To investigate the antiproliferative effect of octreotide, a long-acting analogue of somatostatin, on gastric cancer cell line SGC7901 and its possible molecular mechanisms.

METHODS: Gastric cancer cell line SGC7901 employed in the study was treated with 0.008, 0.04, 0.2, 1, 5 and 25 μg·mL^-1 of octreotide respectively for 24 h to evaluate the antiproliferative effect of somatostatin analog on the tumor cells by MTT assay method. To elucidate the underlying mechanism, the cells were exposed to 1 μg·mL^-1 of octreotide for 0, 12, 24 and 48 h, when their Akt/PKB and telomerase activities were respectively determined using PCR-ELSIA and nonradioactive protein kinase assay protocols. The same experimental procedures were also performed in the control cells that were treated with corresponding vehicles instead of somatostatin analog.

RESULTS: After exposed to octreotide for 24 h at the concentrations of more than 1 μg·mL^-1, SGC7901 cells exhibited a dose-dependent inhibition of growth with the inhibiting rate to be as high as 34.66% when 25 μg·mL^-1 of octreotide was applied. The Akt/PKB and telomerase activity of SGC7901 cells was significantly inhibited when the cells were exposed to 1 μg·mL^-1 of octreotide for 12, 24 and 48 h compared with that of their control counterparts (P < 0.01), both of which exhibited in a time-dependent manner.

CONCLUSION: The antiproliferative effect of octreotide on SGC7901 cells might be mediated by the inhibition of Akt/PKB and telomerase.

Pancreatic cancer - a continuing challenge in oncology

Pancreatic cancer is still one of the major health problems because of its rising incidence and the modest therapeutic results. The paper surveys the statistical data, the risk factors, the preneoplastic ductal lesions, the hormonal sensitivity, the possible transdifferentiation in the endocrine and exocrine parts and the possibilities for chemoprevention. Hungary is peculiar among the European countries because during the last 50 years the incidence of pancreatic cancer has displayed a 15-fold increase. Apart from smoking, additional risk factors seem to be important, and recently a puzzling association between Helicobacter pylori seropositivity and pancreatic cancer was found. First-degree relatives of patients with pancreatic cancer are also at increased risk of this tumor. The term pancreatic intraepithelial neoplasia (PanIN) seems yet to be established, but the dynamics of these lesions needs to be further elucidated. Several lines of firmly established data indicate the hormonal sensitivity of this tumor, but still an unexplained discrepancy exists between the experimental and the clinical results. In addition to the somatostatin analogs, anti-gastrin vaccine is being tested. The mixed exocrine-endocrine tumors might suggest a real possibility of transdifferentiation between different compartments of the pancreas. Finally, the paper outlines the available data about the possibility of chemoprevention, including the role of cyclooxygenase inhibitors.