Neuropeptide growth factors

Synthesis of novel cyclopeptides containing heterocyclic skeletons

Cyclopeptides can be considered as naturally biologically active compounds. Over the last several decades, many attempts have been made to synthesize complex naturally occurring cyclopeptides, and great progress has been achieved to advance the field of total synthesis. Moreover, cyclopeptides containing heterocyclic skeletons have been recently developed into powerful reactions and approaches. This review aims to highlight recent advances in the synthesis of cyclopeptides containing heterocyclic skeletons such as triazole, oxazole, thiazole, and tetrazole.

The relationship between angiogenesis and the immune response in carcinogenesis and the progression of malignant disease

Recent studies have demonstrated that angiogenesis and suppressed cell-mediated immunity (CMI) play a central role in the pathogenesis of malignant disease facilitating tumour growth, invasion and metastasis. In the majority of tumours, the malignant process is preceded by a pathological condition or exposure to an irritant which itself is associated with the induction of angiogenesis and/or suppressed CMI. These include: cigarette smoking, chronic bronchitis and lung cancer; chronic oesophagitis and oesophageal cancer; chronic viral infections such as human papilloma virus and ano-genital cancers, chronic hepatitis B and C and hepatocellular carcinoma, and Epstein-Barr virus (EBV) and lymphomas; chronic inflammatory conditions such as Crohn's disease and ulcerative colitis and colorectal cancer; asbestos exposure and mesothelioma and excessive sunlight exposure/sunburn and malignant melanoma. Chronic exposure to growth factors (insulin-like growth factor-I in acromegaly), mutations in tumour suppressor genes (TP53 in Li Fraumeni syndrome) and long-term exposure to immunosuppressive agents (cyclosporin A) may also give rise to similar environments and are associated with the development of a range of solid tumours. The increased blood supply would facilitate the development and proliferation of an abnormal clone or clones of cells arising as the result of: (a) an inherited genetic abnormality; and/or (b) acquired somatic mutations, the latter due to local production and/or enhanced delivery of carcinogens and mutagenic growth factors. With progressive detrimental mutations and growth-induced tumour hypoxia, the transformed cell, to a lesser or greater extent, may amplify the angiogenic process and CMI suppression, thereby facilitating further tumour growth and metastasis. There is accumulating evidence that long-term treatment with cyclo-oxygenase inhibitors (aspirin and indomethacin), cytokines such as interferon-alpha, anti-oestrogens (tamoxifen and raloxifene) and captopril significantly reduces the incidence of solid tumours such as breast and colorectal cancer. These agents are anti-angiogenic and, in the case of aspirin, indomethacin and interferon-alpha have proven immunomodulatory effects. Collectively these observations indicate that angiogenesis and suppressed CMI play a central role in the development and progression of malignant disease.

Growth stimulation of normal melanocytes and nevocellular nevus cells by gastrin releasing peptide (GRP)

In order to know the possible effects of gastrin releasing peptide (GRP) on nevus cells and melanocytes, we studied the effect of GRP on the proliferation of cultured human nevus cells and normal melanocytes. MTS assay showed that GRP stimulated the growth of viable melanocytes at 1000 ng/ml. GRP also stimulated the growth of nevus cells in a dose dependent manner and maximum stimulation was obtained at 100 ng/ml of GRP. GRP was less effective for growth stimulation of normal melanocytes than nevus cells. The cytoplasm of nevus cells were positively stained by polyclonal anti-GRP antibody. We also detected the expression of GRP and GRP receptor mRNAs in these cells by RT-PCR. These results suggest that GRP acts as an autocrine growth factor for nevus cells and normal melanocytes.

Conformational mimicry: synthesis and solution conformation of a cyclic somatostatin hexapeptide containing a tetrazole cis amide bond surrogate

Potent, cyclic hexapeptide analogues of somatostatin are generally believed to adopt some common secondary structural features: a II' beta turn at one end of the cycle, and a type VI turn with a cis amide bond at the other. A proposed cis amide surrogate, the 1,5-disubstituted tetrazole, has been placed into a cyclic hexapeptide analog of somatostatin in order to constrain the putative cis amide bond. The final cyclization was done by either chemical or enzymatic means. The product, cyclo(Ala6-Tyr7-D-Trp8-Lys9-Val10-Phe11-psi[CN4] ), was found to have 83% of the activity of somatostatin. Solution nmr analysis in DMSO/water revealed that the backbone as well as side chain chi1 and chi2 were well ordered. Relaxation matrix methods were used to extract distance restraints from the nuclear Overhauser effect spectroscopy data set, and these were used in a systematic search of torsional space to identify structures consistent with the nmr data. Restrained minimizations of these structures using a number of different force fields produced structures having the expected beta II' turn at D-Trp8-Lys9 and a beta VIa turn in the Phe11-psi[CN4]-Ala6 portion of the molecule. The similarity of the minimized structures to those previously reported for cyclic hexapeptide analogues of somatostatin confirms the similarity of the tetrazole geometry to that of the cis amide in solution.

A metastatic neuroendocrine anaplastic small cell tumor in a patient with multiple endocrine neoplasia type 1 syndrome. Assessment of disease status and response to doxorubicin, cyclophosphamide, etoposide chemotherapy through scintigraphic imaging with 111In-pentetreotide

Extrapulmonary small cell and small cell neuroendocrine tumors of unknown primary site are, in general, aggressive neoplasms with a short median survival. Like small cell lung cancer (SCLC), they often are responsive to chemotherapy and radiotherapy. Small cell lung cancer and well differentiated neuroendocrine carcinomas of the gastrointestinal tract and pancreas tend to express somatostatin receptors. These tumors may be localized in patients by scintigraphic imaging using radiolabeled somatostatin analogues. A patient with anaplastic neuroendocrine small cell tumor arising on a background of multiple endocrine neoplasia type 1 syndrome is reported. The patient had a known large pancreatic gastrinoma and previously treated parathyroid adenopathy. At presentation, there was small cell cancer throughout the liver and skeleton. Imaging with a radiolabeled somatostatin analogue, 111In-pentetreotide (Mallinckrodt Medical B. V., Petten, Holland), revealed all sites of disease detected by routine biochemical and radiologic methods. After six cycles of chemotherapy with doxorubicin, cyclophosphamide, and etoposide, there was almost complete clearance of the metastatic disease. 111In-pentetreotide scintigraphy revealed uptake consistent with small areas of residual disease in the liver, the abdomen (in mesenteric lymph nodes), and posterior thorax (in a rib). The primary gastrinoma present before the onset of the anaplastic small cell cancer showed no evidence of response to the treatment. The patient remained well for 1 year and then relapsed with brain, lung, liver, and skeletal metastases. Despite an initial response to salvage radiotherapy and chemotherapy with carboplatin and dacarbazine, the patient died 6 months later.

Scintigraphic imaging of small-cell lung cancer with [111In]pentetreotide, a radiolabelled somatostatin analogue

Recent work suggests that between 50 and 75% of small-cell lung cancer (SCLC) tumours have specific high-affinity binding sites for somatostatin. This study evaluated the potential role of the radiolabelled somatostatin analogue, [111In]pentetreotide, in the detection and staging of SCLC in patients prior to and after chemotherapy using scintigraphic imaging techniques. Thirteen patients were studied prior to chemotherapy. Following standard staging six patients had limited stage disease and seven extensive disease. [111In]pentetreotide imaging led to the detection of all primary sites of disease, including a primary site of disease not detectable with chest radiograph or computerised tomography (CT) of the thorax. Five of ten metastatic sites detected by standard staging were also imaged. Furthermore, a cerebellar metastasis was detected in a patient thought to have disease confined to the right hemithorax. This was subsequently confirmed with a CT brain scan. Following chemotherapy [111In]pentetreotide imaging detected residual intrathoracic disease in two of three patients with complete remissions by standard staging and in two patients who had had a partial response to chemotherapy. These results suggest that [111In]pentetreotide imaging may have a role to play in the clinical evaluation of patients with SCLC. Specifically, this technique may be of particular value in detecting residual intrathoracic disease in patients thought to be in complete remission by conventional staging methods.