Search

Somatostatin is a cyclopeptide that has a broad inhibitory effect on the secretion of hormones such as growth hormone, glucagon, and insulin. The molecular basis of the use of radiolabeled octreotide in scintigraphy and radionuclide therapy is receptor-mediated internalization and cellular retention of the radionuclide. A large variety of radiolabeled somatostatin derivatives have been prepared for radionuclide therapy purposes and are in various stages of investigation. The chapter shows that radionuclide therapy with radiolabeled somatostatin analogs is a most promising new treatment modality for patients bearing sst2-positive tumors. The molecular basis of the use of radiolabeled octreotide in scintigraphy and radionuclide therapy is receptor-mediated internalization and cellular retention of the radionuclide. Several reports have been published on the in vitro receptor binding to somatostatin receptors of another somatostatin analog, the octapeptide RC-160. In conclusion, radiolabeled peptides have opened a new era in nuclear oncology, not only for diagnosis but also for radionuclide therapy.

Patients with longstanding achalasia have an increased risk of developing esophageal cancer. Surveillance is hampered by chronic stasis. We investigated whether aberrant expressions of tumor suppressor gene p53 and proliferation marker ki67 are early predictors for progression to malignancy. In 399 achalasia patients, 4% died of esophageal cancer despite surveillance. We performed a cohort study, using surveillance biopsies from 18 patients (11 carcinoma, one high-grade dysplasia [HGD], and six low-grade dysplasia [LGD]) and 10 controls (achalasia patients without cancer or dysplasia development). One hundred sixty-four biopsies were re-evaluated and studied for p53 and ki67 expression using immunohistochemistry. Eighty-two percent of patients with cancer/HGD showed p53 overexpression in surveillance biopsies at a mean of 6 (1-11) years prior to cancer development. In 67% of patients with LGD and only in 10% of the controls p53 overexpression was present. The proportion of samples with p53 overexpression increased with increasing grades of dysplasia. We found no difference for ki67 overexpression. p53 overexpression may identify achalasia patients at increased risk of developing esophageal carcinoma. Further study is needed to determine if patients with p53 overexpression would benefit from intensive surveillance to detect esophageal neoplasia at a potential curable stage.

OBJECTIVES: Barrett's esophagus (BE) is a premalignant condition of the esophagus. It is a consequence of mucosal injury from chronic gastroesophageal reflux in which bile acids are an important toxic component. The farnesoid X receptor (FXR) is a nuclear receptor involved in the regulation of bile acid synthesis, transport, and absorption. FXR activation is also involved in the induction of the innate immune response. This suggests that FXR is involved in the pathogenesis and the inflammation seen in BE. METHODS: mRNA levels of FXR and the FXR-regulated genes, ileal bile acid-binding protein (IBABP), small heterodimer partner (SHP), and chemokines interleukin (IL)-8 and macrophage inflammatory protein 3 alpha (MIP3 alpha), were determined by real time-polymerase chain reaction (RT-PCR). Protein expression was determined by immunohistochemistry. RESULTS: FXR was not expressed in squamous epithelium of healthy subjects (N = 7), but was present in both squamous and columnar epithelium of BE patients. Compared to the squamous epithelium of BE patients, their columnar epithelium displayed a 2.3-fold (P = 0.02) increase in FXR mRNA. Also, IBABP (2.2-fold; P = 0.0029), SHP (2.7-fold; P = 0.007), IL-8 (1.5-fold; P = 0.04), and MIP3 alpha (1.7-fold; P = 0.019) transcription levels were increased. Exposure of esophageal cell line TE7 to deoxycholic acid (DCA) resulted in a similar induction. The induction was abolished by the FXR antagonist guggulsterone. CONCLUSIONS: Expression levels of the bile acid receptor FXR, the bile acid metabolism genes IBABP and SHP, and the chemokines IL-8 and MIP3 alpha are increased in Barrett's epithelium. The in vitro induction of FXR by DCA suggests that bile acids can actively induce the inflammatory response in BE by recruiting immune cells.

The rat pancreatic CA20948 tumor cell line is widely used in receptor-targeted preclinical studies because many different peptide receptors are expressed on the cell membrane. The response of the tumor cells to peptide radionuclide therapy, however, is dependent on the cell line's radiosensitivity. Therefore, we measured the radiosensitivity of the CA20948 tumor cells by using clonogenic survival assays after high-energy external-beam radiotherapy (XRT) in vitro. It can, however, be expected that results of high-dose-rate XRT are not representative for those after low-dose-rate radionuclide therapy (RT), such as peptide-receptor radionuclide therapy. Therefore, we compared clonogenic survival in vitro in CA20948 tumor cells after increasing doses of XRT or RT, the latter using (131)I.Survival of CA20948 cells was investigated using a clonogenic survival assay after RT by incubation with increasing amounts of (131)I, leading to doses of 1-10 Gy after 12 days of incubation (maximum dose rate, 0.92 mGy/min), or with doses of 1-10 Gy using an X-ray machine (dose rate, 0.66 Gy/min). Colonies were scored after a 12-day-incubation period. Also, the doubling time of this cell line was calculated.We observed a dose-dependent reduction in tumor-cell survival, which, at low doses, was similar for XRT and RT. For high-dose-rate XRT, the quadratic over linear component ratio (alpha/beta) for CA20948 was 8.3 Gy, whereas that ratio for low-dose-rate RT was calculated to be 86.5 Gy. The calculated doubling time of CA20948 cells was 22 hours.Despite the huge differences in dose rate, RT tumor cell-killing effects were approximately as effective as those of XRT at doses of 1 and 2 Gy, the latter being the common daily dose given in fractionated external-beam therapies. At higher doses, RT was less effective than XRT.

Peptide receptor scintigraphy with [(111)In-DTPA(0)]octreotide (a stabilized radiolabeled somatostatin (SS) analogue, OctreoScan) is widely used for the visualization and staging of somatostatin receptor-positive tumors. The application of likewise somatostatin analogues as vehicle for the deliverance of radionuclides to somatostatin receptor-positive targets are now in use for peptide receptor-targeted radionuclide therapy (PRRT). Currently preclinical and clinical investigation are ongoing trying to find the optimal combination of radionuclide and ligand. The anti-tumoral effects of such combinations, like [90Y-DOTA degrees, Tyr(3)]octreotide and [(177)Lu-DOTA degrees, Tyr(3)]octreotate, on SSR-positive solid tumors have been reported. In this study we present the anti-tumor effects of (177)Lu-DOTA-tate on: a) a single SSR-positive cell model and b) on a SSR-positive tumor in a rat liver micrometastatic model, mimicking disseminated disease. (177)Lu-DOTA-tate showed anti-tumoral effects in both cases and significant survival in the PRRT-treated rats. (177)Lu-DOTA-tate is a very promising new treatment modality for SSR-positive tumors, including disseminated disease.

Background The continuous exposure of esophageal epithelium to refluxate may induce ectopic expression of bile-responsive genes and contribute to the development of Barrett's esophagus (BE) and esophageal adenocarcinoma. In normal physiology of the gut and liver, the nuclear receptor Pregnane × Receptor (PXR) is an important factor in the detoxification of xenobiotics and bile acid homeostasis. This study aimed to investigate the expression and genetic variation of PXR in reflux esophagitis (RE), Barrett's esophagus (BE) and esophageal adenocarcinoma. Methods PXR mRNA levels and protein expression were determined in biopsies from patients with adenocarcinoma, BE, or RE, and healthy controls. Esophageal cell lines were stimulated with lithocholic acid and rifampicin. PXR polymorphisms 25385C/T, 7635A/G, and 8055C/T were genotyped in 249 BE patients, 233 RE patients, and 201 controls matched for age and gender. Results PXR mRNA levels were significantly higher in adenocarcinoma tissue and columnar Barrett's epithelium, compared to squamous epithelium of these BE patients (P < 0.001), and RE patients (P = 0.003). Immunohistochemical staining of PXR showed predominantly cytoplasmic expression in BE tissue, whereas nuclear expression was found in adenocarcinoma tissue. In cell lines, stimulation with lithocholic acid did not increase PXR mRNA levels, but did induce nuclear translocation of PXR protein. Genotyping of the PXR 7635A/G polymorphism revealed that the G allele was significantly more prevalent in BE than in RE or controls (P = 0.037). Conclusions PXR expresses in BE and adenocarcinoma tissue, and showed nuclear localization in adenocarcinoma tissue. Upon stimulation with lithocholic acid, PXR translocates to the nuclei of OE19 adenocarcinoma cells. Together with the observed association of a PXR polymorphism and BE, this data implies that PXR may have a function in prediction and treatment of esophageal disease.