Novel positron emission tomography/computed tomography of diffuse parenchymal lung disease combining a labeled somatostatin receptor analogue and 2-deoxy-2[18F]fluoro-D-glucose

We prospectively investigated the potential of positron emission tomography (PET) using the somatostatin receptor (SSTR) analogue ⁶⁸Ga-DOTATATE and 2-deoxy-2[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) in diffuse parenchymal lung disease (DPLD). Twenty-six patients (mean age 68.9 ± 11.0 years) with DPLD were recruited for ⁶⁸Ga-DOTATATE and ¹⁸F-FDG combined PET/high-resolution computed tomography (HRCT) studies. Ten patients had idiopathic pulmonary fibrosis (IPF), 12 patients had nonspecific interstitial pneumonia (NSIP), and 4 patients had other forms of DPLD. Using PET, the pulmonary tracer uptake (maximum standardized uptake value [SUV(max)]) was calculated. The distribution of PET tracer was compared to the distribution of lung parenchymal changes on HRCT. All patients demonstrated increased pulmonary PET signal with ⁶⁸Ga-DOTATATE and ¹⁸F-FDG. The distribution of parenchymal uptake was similar, with both tracers corresponding to the distribution of HRCT changes. The mean SUV(max) was 2.2 ± 0.7 for ⁶⁸Ga-DOTATATE and 2.8 ± 1.0 (t-test, p  =  .018) for ¹⁸F-FDG. The mean ⁶⁸Ga-DOTATATE SUV(max) in IPF patients was 2.5 ± 0.9, whereas it was 2.0 ± 0.7 (p  =  .235) in NSIP patients. The correlation between ⁶⁸Ga-DOTATATE SUV(max) and gas transfer (transfer factor of the lung for carbon monoxide [TLCO]) was r  =  -.34 (p  =  .127) and r  =  -.49 (p  =  .028) between ¹⁸F-FDG SUV(max) and TLCO. We provide noninvasive in vivo evidence in humans showing that SSTRs may be detected in the lungs of patients with DPLD in a similar distribution to sites of increased uptake of ¹⁸F-FDG on PET.

Novel Positron Emission Tomography/Computed Tomography of Diffuse Parenchymal Lung Disease Combining a Labeled Somatostatin Receptor Analogue and 2-Deoxy-2 [18F] Fluoro-D-Glucose

We prospectively investigated the potential of positron emission tomography (PET) using the somatostatin receptor (SSTR) analogue 68Ga-DOTATATE and 2-deoxy-2[18F]fluoro-D-glucose (18F-FDG) in diffuse parenchymal lung disease (DPLD). Twenty-six patients (mean age 68.9 ± 11.0 years) with DPLD were recruited for 68Ga-DOTATATE and 18F-FDG combined PET/high-resolution computed tomography (HRCT) studies. Ten patients had idiopathic pulmonary fibrosis (IPF), 12 patients had nonspecific interstitial pneumonia (NSIP), and 4 patients had other forms of DPLD. Using PET, the pulmonary tracer uptake (maximum standardized uptake value [SUVmax]) was calculated. The distribution of PET tracer was compared to the distribution of lung parenchymal changes on HRCT. All patients demonstrated increased pulmonary PET signal with 68Ga-DOTATATE and 18F-FDG. The distribution of parenchymal uptake was similar, with both tracers corresponding to the distribution of HRCT changes. The mean SUVmax was 2.2 ± 0.7 for 68Ga-DOTATATE and 2.8 ± 1.0 ( t-test, p = .018) for 18F-FDG. The mean 68Ga-DOTATATE SUVmax in IPF patients was 2.5 ± 0.9, whereas it was 2.0 ± 0.7 ( p = .235) in NSIP patients. The correlation between 68Ga-DOTATATE SUVmax and gas transfer (transfer factor of the lung for carbon monoxide [TLCO]) was r = .34 ( p = .127) and r = .49 ( p = .028) between 18F-FDG SUVmax and TLCO. We provide noninvasive in vivo evidence in humans showing that SSTRs may be detected in the lungs of patients with DPLD in a similar distribution to sites of increased uptake of 18F-FDG on PET.

N-Methylated sst2 Selective Somatostatin Cyclic Peptide Analogue as a Potent Candidate for Treating Neurogenic Inflammation

A focused multiply N-methylated library of a cyclic hexapeptidic somatostatin analogue: MK678 cyclo(-MeAYwKVF-) was generated, which resulted in the unexpected observation of an efficacious tetra-N-methylated analogue, cyclo(-MeAYMewMeKVMeF-) with a potent inhibitory action on sensory neuropeptide release in vitro and on acute neurogenic inflammatory response in vivo. The analogue shows selectivity toward somatostatin receptor subtype 2 (sst2). Extensive 2D NMR spectroscopy and molecular dynamics simulation revealed the solution conformation of the analogue, which can be adopted as a lead for the further structure-activity relationship studies targeting neurogenic inflammation.

Glucagon-like peptide-1 (GLP-1) receptors are not overexpressed in pancreatic islets from patients with severe hyperinsulinaemic hypoglycaemia following gastric bypass

AIMS/HYPOTHESIS

Glucagon-like peptide-1 (GLP-1) receptors are highly overexpressed in benign insulinomas, permitting in vivo tumour visualisation with GLP-1 receptor scanning. The present study sought to evaluate the GLP-1 receptor status in vitro in other pancreatic disorders leading to hyperinsulinaemic hypoglycaemia, specifically after gastric bypass surgery.

METHODS

Fresh frozen pancreatic tissue samples (n=7) from six gastric bypass surgery patients suffering from hyperinsulinaemic hypoglycaemia were evaluated for GLP-1 receptor content using in vitro receptor autoradiography, and compared with normal pancreas and with pancreatic insulinoma tissues.

RESULTS

GLP-1 receptor analysis of the pancreatic tissues, which histopathologically were compatible with nesidioblastosis and originated from post-bypass hypoglycaemic patients, revealed a mean density value of GLP-1 receptors in the islets of 1,483 ± 183 dpm/mg tissue. Pharmacological characterisation indicated the presence of specific GLP-1 receptors. The density of islet GLP-1 receptor in post-gastric bypass patients did not differ from that of normal pancreas (1,563 ± 104 dpm/mg tissue, n = 10). Receptor density in pancreatic acini was low in post-bypass and control conditions. In contrast, benign insulinomas showed a high density of GLP-1 receptors, with a mean value of 8,302 ± 1,073 dpm/mg tissue (n = 6).

CONCLUSIONS/INTERPRETATION

In contrast to insulinoma, hyperinsulinaemic hypoglycaemia after gastric bypass surgery is not accompanied by overexpression of GLP-1 receptor in individual islets. Thus, patients with post-gastric bypass hyperinsulinaemic hypoglycaemia are not candidates for GLP-1 receptor imaging in vivo using radiolabelled exendin. These GLP-1 receptor data support the notion that the islet pathobiology of post-gastric bypass hypoglycaemia is distinctly different from that of benign insulinomas.

Biodistribution of two octreotate analogs radiolabeled with indium and yttrium in rats

BACKGROUND

In this study, two octreotate derivatives N-[4-carboxy-4-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane-1-yl]butanoyl]-Tyr(3)-octreotate (DOTAGA-tate) and N-[[4,10-bis(carboxymethyl)-7-(1(1,3-dicarboxypropyl))-1,4,7,10-tetraaza-cyclododec-1-yl]acetyl]-Tyr(3)-octreotate (DOTA-t-GA-tate) were radio-labeled with (111)In or (88)Y and their biodistribution profiles together with their elimination characteristics in rats were compared.

MATERIALS AND METHODS

Radiolabeling of the peptides with high radiochemical purity was carried out in an acetate buffer with gentisic acid as radioprotective compound. Biodistribution profiles of the radiolabeled peptides were determined in intact male Wistar rats after an intravenous dose of 1 microg/kg. For elimination pathways analysis, studies in intact rats in metabolic cages and perfused rat kidney and liver were carried out.

RESULTS

Fast radioactivity clearance from rat tissues (excepting somatostatin receptor-rich organs and the kidney) was determined for all agents under study. Profound radioactivity uptake in organs with a high density of somatostatin receptors (namely the adrenals and pancreas as biomarkers of somatostatin receptor-positive tissue) was slightly higher for radiolabeled DOTAGA-tate when compared with DOTA-t-GA-tate. Significantly higher accumulation in kidney and somewhat lower urinary elimination of (111)In-labeled peptides in comparison with that of (88)Y-agents were determined. Perfused rat kidney experiments confirmed that glomerular filtration was the main elimination mechanism for the compounds under study; their bile clearances in the perfused rat liver were negligible.

CONCLUSION

(111)In((88)Y)-DOTAGA-tates exhibited higher distribution into somatostatin receptor-rich organs when compared with the corresponding radiolabeled DOTA-t-GA-tates. Higher uptake of (111)In-labeled peptides in the kidney is attributed to its different coordination properties.

Neuropeptide Y modulates steroid production of human adrenal H295R cells through Y1 receptors

Neuropeptide Y (NPY) is abundantly expressed in the nervous system and acts on target cells through NPY receptors. The human adrenal cortex and adrenal tumors express NPY receptor subtype Y1, but its function is unknown. We studied Y1-mediated signaling, steroidogenesis and cell proliferation in human adrenal NCI-H295R cells. Radioactive ligand binding studies showed that H295R cells express Y1 receptor specifically. NPY treatment of H295R cells stimulated the MEK/ERK1/2 pathway, confirming that H295R cells express functional Y1 receptors. Studies of the effect of NPY and related peptide PYY on adrenal steroidogenesis revealed a decrease in 11-deoxycortisol production. RIA measurements of cortisol from cell culture medium confirmed this finding. Co-treatment with the Y1 antagonist BIBP2336 reversed the inhibitory effect of NPY on cortisol production proving specificity of this effect. At mRNA level, NPY decreased HSD3B2 and CYP21A2 expression. However NPY revealed no effect on cell proliferation. Our data show that NPY can directly regulate human adrenal cortisol production.

Wild-type and splice-variant secretin receptors in lung cancer: overexpression in carcinoid tumors and peritumoral lung tissue

Gastrointestinal peptide hormone receptors, like somatostatin receptors, are often overexpressed in human cancer, allowing receptor-targeted tumor imaging and therapy. A novel candidate for these applications is the secretin receptor recently identified in pancreatic and cholangiocellular carcinomas. In the present study, secretin receptors were assessed in a non-gastrointestinal tissue, the human lung. Non-small-cell lung cancers (n=26), small-cell lung cancers (n=10), bronchopulmonary carcinoid tumors (n=29), and non-neoplastic lung (n=46) were investigated for secretin receptor protein expression with in vitro receptor autoradiography, using (125)I-[Tyr(10)] rat secretin and for secretin receptor transcripts with RT-PCR. Secretin receptor protein expression was found in 62% of bronchopulmonary carcinoids in moderate to high density, in 12% of non-small cell lung cancers in low density, but not in small cell lung cancers. In tumors found to be secretin receptor positive by autoradiography, RT-PCR revealed transcripts for the wild-type secretin receptor and for novel secretin receptor splice variants. In the non-neoplastic lung, secretin receptor protein expression was observed in low density along the alveolar septa in direct tumor vicinity in cases of acute inflammation, but not in histologically normal lung. In the autoradiographically positive peritumoral lung, RT-PCR showed transcripts for the wild-type secretin receptor and for a secretin receptor spliceoform different from those occurring in lung and gut tumors. In conclusion, secretin receptors are new markers for bronchopulmonary carcinoid tumors, and represent the molecular basis for an in vivo targeting of carcinoid tumors for diagnosis and therapy. Furthermore, secretin receptors may play a role in peritumoral lung pathophysiology. Secretin receptor mis-splicing specifically occurs in tumor and non-tumor lung pathology.

Up-regulation of somatostatin receptor density on rat CA20948 tumors escaped from low dose [177Lu-DOTA0,Tyr3]octreotate therapy

AIM

Peptide receptor radionuclide therapy using the somatostatin analogue [(177)Lu-DOTA(0),Tyr(3)]octreotate is a convincing treatment modality for metastasized neuroendocrine tumors. Therapeutic doses are administered in 4 cycles with 6-10 week intervals. A high somatostatin receptor density on tumor cells is a prerequisite at every administration to enable effective therapy. In this study, the density of the somatostatin receptor subtype 2 (sst2) was investigated in the rat CA20948 pancreatic tumor model after low dose [(177)Lu-DOTA(0), Tyr(3)]octreotate administration resulting in approximately 20 Gy tumor radiation absorbed dose, whereas 60 Gy is needed to induce complete tumor regression in these and the majority of tumors.

METHODS

Sixteen days after inoculation of the CA20948 tumor, male Lewis rats were injected with 185 MBq [(177)Lu-DOTA(0),Tyr(3)]octreotate to initiate a decline in tumor size. Approximately 40 days after injection, tumors re-grew progressively after initial response. Quantification of sst2 expression was performed using in vitro autoradiography on frozen sections of three groups: control (not-treated) tumors, tumors in regression and tumors in re-growth. Histology and proliferation were determined using HE- and anti-Ki-67-staining.

RESULTS

The sst2 expression on CA20948 tumor cells decreased significantly after therapy to 5% of control level. However, tumors escaping from therapy showed an up-regulated sst2 level of 2-5 times higher sst2 density compared to control tumors.

CONCLUSION

After a suboptimal therapeutic dose of [(177)Lu-DOTA(0),Tyr(3)]octreotate, escape of tumors is likely to occur. Since these cells show an up-regulated sst2 receptor density, a next therapeutic administration of radiolabelled sst2 analogue can be expected to be highly effective.

Novel 111In-labelled bombesin analogues for molecular imaging of prostate tumours

PURPOSE

It has been shown that some primary human tumours and their metastases, including prostate and breast tumours, overexpress gastrin-releasing peptide (GRP) receptors. Bombesin (BN) is a neuropeptide with a high affinity for these GRP receptors. We demonstrated successful scintigraphic visualisation of BN receptor-positive tumours in preclinical studies using the radiolabelled BN analogue [(111)In-DTPA-Pro(1),Tyr(4)]BN. However, the receptor affinity as well as the serum stability of this analogue leave room for improvement. Therefore new (111)In-labelled BN analogues were synthesised and evaluated in vitro and in vivo.

METHODS AND RESULTS

The receptor affinity of the new BN analogues was tested on human GRP receptor-expressing prostate tumour xenografts and rat colon sections. Analogues with high receptor affinity (low nM range) were selected for further evaluation. Incubation in vitro of GRP receptor-expressing rat CA20948 and human PC3 tumour cells with the (111)In-labelled analogues resulted in rapid receptor-mediated uptake and internalisation. The BN analogue with the best receptor affinity and in vitro internalisation characteristics, Cmp 3 ([(111)In-DTPA-ACMpip(5),Tha(6),betaAla(11),Tha(13),Nle(14)]BN(5-14)), was tested in vivo in biodistribution studies using rats bearing GRP receptor-expressing CA20948 tumours, and nude mice bearing human PC3 xenografts. Injection of (111)In-labelled Cmp 3 in these animals showed high, receptor-mediated uptake in receptor-positive organs and tumours which could be visualised using planar gamma camera and microSPECT/CT imaging.

CONCLUSION

With their enhanced receptor affinity and their rapid receptor-mediated internalisation in vitro and in vivo, the new BN analogues, and especially Cmp 3, are promising candidates for use in diagnostic molecular imaging and targeted radionuclide therapy of GRP receptor-expressing cancers.

Are radiogallium-labelled DOTA-conjugated somatostatin analogues superior to those labelled with other radiometals?

PURPOSE

Gallium-68 is a metallic positron emitter with a half-life of 68 min that is ideal for the in vivo use of small molecules, such as [68Ga-DOTA,Tyr3]octreotide, in the diagnostic imaging of somatostatin receptor-positive tumours. In preclinical studies it has shown a striking superiority over its 111In-labelled congener. The purpose of this study was to evaluate whether third-generation somatostatin-based, radiogallium-labelled peptides show the same superiority.

METHODS

Peptides were synthesised on solid phase. The receptor affinity was determined by in vitro receptor autoradiography. The internalisation rate was studied in AR4-2J and hsst-HEK-transfected cell lines. The pharmacokinetics was studied in a rat xenograft tumour model, AR4-2J.

RESULTS

All peptides showed high affinities on hsst2, with the highest affinity for the Ga(III)-complexed peptides. On hsst3 the situation was reversed, with a trend towards lower affinity of the Ga(III) peptides. A significantly increased internalisation rate was found in sst2-expressing cells for all 67Ga-labelled peptides. Internalisation into HEK-sst3 was usually faster for the 111In-labelled peptides. No internalisation was found into sst5. Biodistribution studies employing [67Ga-DOTA,1-Nal3]octreotide in comparison to [111In-DOTA,1-Nal3]octreotide and [67Ga-DOTA,Tyr3]octreotide showed a significantly higher and receptor-mediated uptake of the two 67Ga-labelled peptides in the tumour and somatostatin receptor-positive tissues. A patient study illustrated the potential advantage of a broad receptor subtype profile radiopeptide over a high-affinity sst2-selective radiopeptide.

CONCLUSION

This study demonstrates that 67/68Ga-DOTA-octapeptides show distinctly better preclinical, pharmacological performances than the 111In-labelled peptides, especially on sst2-expressing cells and the corresponding animal models. They may be excellent candidates for further development for clinical studies.

Analgesic activity of a non-peptide imidazolidinedione somatostatin agonist: in vitro and in vivo studies in rat

Several lines of evidence support an important role for somatostatin receptors (SSTRs) in pain modulation. The therapeutic use of established SSTR peptide agonists for this indication is limited by their broad range of effects, need for intrathecal delivery, and short half-life. Therefore, the goal of the present study was to investigate the analgesic effect of SCR007, a new, highly selective SSTR2 non-peptide agonist. Behavioral studies demonstrated that paw withdrawal latencies to heat were significantly increased following intraplantar SCR007. Furthermore, both intraperitoneal and intraplantar injection of SCR007 significantly reduced formalin- and capsaicin-induced flinching and lifting/licking nociceptive behaviors. Recordings from nociceptors using an in vitro glabrous skin-nerve preparation showed that SCR007 reduced heat responses in a dose-dependent fashion, bradykinin-induced excitation, heat sensitization and capsaicin-induced excitation. In both the behavioral and single fiber studies, the SCR007 effects were reversed by the SSTR antagonist cyclo-somatostatin, demonstrating receptor specificity. In the single fiber studies, the opioid antagonist naloxone did not reverse SCR007-induced anti-nociception suggesting that SCR007 did not exert its effects through activation of opioid receptors. Analysis of cAMP/protein kinase A (PKA) involvement demonstrated that SCR007 prevented forskolin- and Sp-8-Br-cAMPS (a PKA activator)-induced heat sensitization, supporting the hypothesis that SCR007-induced inhibition could involve a down-regulation of the cAMP/PKA pathway. These data provide several lines of evidence that the non-peptide imidazolidinedione SSTR2 agonist SCR007 is a promising anti-nociceptive and analgesic agent for the treatment of pain of peripheral and/or central origin.

Cellular detection of sst2A receptors in human gastrointestinal tissue

BACKGROUND AND AIMS

Many neuroendocrine gastrointestinal tumours express receptors for the regulatory peptide somatostatin. Among the five existing somatostatin receptor (sst) subtypes, sst2A is the most frequently expressed in these tumours. However, little information is available about the cellular location of sst2A in corresponding non-neoplastic epithelial tissues.

METHODS

We searched for sst2A immunoreactive cells in non-neoplastic gastrointestinal tissues, and evaluated their number and immunohistochemical characteristics with neuroendocrine markers.

RESULTS

The gastric antrum showed numerous sst2A cells, situated in the epithelium, corresponding to gastrin containing neuroendocrine cells, while the gastric corpus was largely devoid of sst2A cells, including enterochromaffin-like cells. The remaining foregut, namely the duodenum and proximal jejunum, also contained a large number of sst2A cells, all being neuroendocrine cells and many of them characterised as gastrin cells. Sst2A cells were also detected in the midgut, in low numbers in the epithelium of the distal jejunum and ileum, but not in the appendix vermiformis, the caecum, or the hindgut, despite the large number of neuroendocrine cells present in this area. In addition, sst2A cells were found in the whole gastrointestinal tract in the myenteric and submucosal plexus.

CONCLUSIONS

While sst2A receptors on antral gastrin cells presumably mediate somatostatin inhibition of gastrin secretion, the effects of somatostatin on motility and ion transport in the lower gastrointestinal tract may be mediated by sst2A receptors in the neural plexus. These data provide a molecular basis for the physiological actions of somatostatin in human gastrointestinal tissue.

Immunohistochemical Localization of Somatostatin Receptor sst2A in Human Gut and Lung Tissue: Possible Implications for Physiology and Carcinogenesis

Many neuroendocrine gastrointestinal and lung tumors express sst2A somatostatin receptors. Because the cellular location of sst2A in the corresponding non-neoplastic tissue is unknown, we searched for sst2A immuno-reactive cells and characterized their type in these tissues using a highly specific sst2A antibody (R2-88). Epithelial sst2A cells, identified as neuroendocrine, gastrin-producing cells, were found in large numbers in the antrum and the duodenum, but not in the gastric corpus. They were also present in the proximal jejunum, rarely noted in the distal jejunum and ileum, and absent in the large intestine and the appendix vermiformis. Moreover, sst2A cells were found abundantly in the neural plexus. sst2A receptors on antral gastrin cells could mediate somatostatin inhibition on gastrin secretion, whereas those in the neural plexus could mediate somatostatin effects on motility and ion transport in the lower gastrointestinal tract. Rare sst2A cells in bronchi and bronchioles located basally and parabasally in the gastrointestinal epithelium were detected that could represent stem/progenitor cells. It is currently not clear whether and which of the identified sst2A cells are at the origin of sst2A-positive neuroendocrine gut or lung tumors.

Radiolabeled neurotensin analog, 99mTc-NT-XI, evaluated in ductal pancreatic adenocarcinoma patients

The study aim was to assess the safety, biodistribution, tissue kinetics, and tumor uptake of the (99m)Tc-labeled neurotensin (NT) analog NT-XI.

METHODS

Four patients presenting ductal pancreatic adenocarcinoma were studied with (99m)Tc-NT-XI. Patients were followed by scintigraphy up to 4 h and by continued blood and urinary sampling until surgery 18-22 h after injection. Surgical tissue samples were analyzed for radioactivity uptake and NT receptor expression.

RESULTS

No side effects were observed on injection of (99m)Tc-NT-XI. Blood biologic half-lives alpha and beta were 35 min (range, 17-62 min) and 230 min (range, 107-383 min), respectively. Repeated whole-body scintigraphy performed in 2 patients showed a single exponential decrease of whole-body activity with half-lives of 101 and 232 min. Tracer elimination was mainly renal, with 92% and 98% of activity counted in urine in the first 20 h. Kidney, liver, spleen, and bone marrow activity uptake was observed in all patients. Tumor was not visualized in the first 3 patients but could be localized by tomoscintigraphy in the pancreas head region of patient 4. In vitro tissue analysis showed high expression of NT receptor in the tumor of patient 4, correlated with the highest tumor radioactivity uptake and the highest tumor-to-fat radioactivity ratio. In vitro receptor expression was also positive in a second patient having a tumor characterized by very low cellularity; however, the remaining 2 tumors lacked NT receptor expression.

CONCLUSION

Injection of (99m)Tc-NT-XI was well tolerated. The in vivo tumor uptake appeared specific as it was observed in the 1 patient with a pancreatic tumor that expressed high amounts of NT receptor. The results are compatible with preclinical animal results and in favor of further development of radiolabeled NT analogs for diagnosis or therapy of cancer.

Stabilised 111In-labelled DTPA- and DOTA-conjugated neurotensin analogues for imaging and therapy of exocrine pancreatic cancer

Neurotensin (NT) receptors are overexpressed in exocrine pancreatic cancer and Ewing's sarcoma. The potential utility of native NT in cancer diagnosis and therapy is, however, limited by its rapid degradation in vivo. Therefore, NT analogues were synthesised with modified lysine and arginine derivatives to enhance stability and coupled either to DTPA, to enable high specific activity labelling with indium-111 for imaging, or to DOTA, to enable high specific activity labelling with beta-emitting radionuclides, such as lutetium-177 and yttrium-90. Based on serum stability (4 h incubation at 37 degrees C in human serum) and receptor binding affinity, the five most promising analogues were selected and further evaluated in in vitro internalisation studies in human colorectal adenocarcinoma HT29 cells, which overexpress NT receptors. All five NT analogues bound with high affinity to NT receptors on human exocrine pancreatic tumour sections. The analogues could be labelled with (111)In to a high specific activity. The (111)In-labelled compounds were found to be very stable in serum. Incubation of HT29 cells with the (111)In-labelled analogues at 37 degrees C showed rapid receptor-mediated uptake and internalisation. The most promising analogue, peptide 2530 [DTPA-(Pip)Gly-Pro-(PipAm)Gly-Arg-Pro-Tyr-tBuGly-Leu-OH] was further tested in vivo in a biodistribution study using HT29 tumour-bearing nude mice. The results of this study showed low percentages of injected dose per gram tissue of this (111)In-labelled 2530 analogue in receptor-negative organs like blood, spleen, pancreas, liver, muscle and femur. Good uptake was found in the receptor-positive HT29 tumour and high uptake was present in the kidneys. Co-injection of excess unlabelled NT significantly reduced tumour uptake, showing that tumour uptake is a receptor-mediated process. With their enhanced stability, maintained high receptor affinity and rapid receptor-mediated internalisation, the (111)In-labelled DTPA- and DOTA-conjugated NT analogues are excellent candidates for imaging and therapy of exocrine pancreatic cancer, peptide 2530 being the most promising analogue.

PET imaging of somatostatin receptors: design, synthesis and preclinical evaluation of a novel 18F-labelled, carbohydrated analogue of octreotide

Because of the excellent nuclear properties of fluorine-18 and the growing interest in somatostatin receptor (sst) scintigraphy with PET, a novel carbohydrated (18)F-labelled sst ligand was developed and preclinically evaluated. Synthesis of N(alpha)-(1-deoxy- D-fructosyl)- N(epsilon)-(2-[(18)F]fluoropropionyl)-Lys(0)-Tyr(3)-octreotate ([(18)F]FP-Gluc-TOCA) was completed in approximately 3 h (20%-30% yield). [(19)F]FP-Gluc-TOCA showed no affinity to hsst1 and hsst3, moderate affinity to hsst4 (IC(50): 437+/-84 n M) and hsst5 (IC(50): 123+/-8.8 n M) and very high affinity to hsst2 (IC(50): 2.8+/-0.4 n M). As a result of carbohydration, lipophilicity of [(18)F]FP-Gluc-TOCA was found to be low (lg P(OW)=-1.70+/-0.02). In mice, the tracer was rapidly cleared via renal excretion (kidneys: 8.69%+/-1.09%ID/g) and showed low uptake in liver (0.72%+/-0.14%ID/g) and intestine (1.88%+/-0.52%ID/g) and high tumour uptake (13.54%+/-1.47%ID/g) (all data at 1 h p.i.). Tumour to non-tumour ratios at 60 min p.i. reached 25, 19, 7, 1.6 and 56 for blood, liver, intestine, kidney and muscle, respectively. A similar biodistribution pattern was observed in pancreatic tumour-bearing rats. Tumour uptake in rats was reduced to 36% and 18% of control (30 and 60 min) by co-injection of 500 microg Tyr(3)-octreotide, demonstrating sst-specific uptake. In a first [(18)F]FP-Gluc-TOCA-PET study of a patient with a metastatic carcinoid in the liver the tracer showed superior pharmacokinetics, e.g. rapid urinary excretion and low uptake in liver, kidney and spleen. Multiple liver lesions (SUVs ranging from 21.4 to 38.0) and previously unknown focal uptake in the abdomen (SUV 10.0) were clearly visible. This is the first report on PET imaging using an (18)F-labelled sst binding peptide; it indicates that [(18)F]FP-Gluc-TOCA offers excellent imaging characteristics and allows sst imaging with high tumour to non-tumour contrast.

Potent and long-acting corticotropin releasing factor (CRF) receptor 2 selective peptide competitive antagonists

We present evidence that members of the corticotropin releasing factor (CRF) family assume distinct structures when interacting with the CRF(1) and CRF(2) receptors. Predictive methods, physicochemical measurements, and structure-activity relationship studies have suggested that CRF, its family members, and competitive antagonists such as astressin [cyclo(30-33)[DPhe(12),Nle(21),Glu(30),Lys(33),Nle(38)]hCRF((12-41))] assume an alpha-helical conformation when interacting with their receptors. We had shown that alpha-helical CRF((9-41)) and sauvagine showed some selectivity for CRF receptors other than that responsible for ACTH secretion(1) and later for CRF2.(2) More recently, we suggested the possibility of a helix-turn-helix motif around a turn encompassing residues 30-33(3) that would confer high affinity for both CRF(1) and CRF(2)(2,4) in agonists and antagonists of all members of the CRF family.(3) On the other hand, the substitutions that conferred ca. 100-fold CRF(2) selectivity to the antagonist antisauvagine-30 [[DPhe(11),His(12)]sauvagine((11-40))] did not confer such property to the corresponding N-terminally extended agonists. We find here that a Glu(32)-Lys(35) side chain to side chain covalent lactam constraint in hCRF and the corresponding Glu(31)-Lys(34) side chain to side chain covalent lactam constraint in sauvagine yield potent ligands that are selective for CRF(2). Additionally, we introduced deletions and substitutions known to increase duration of action to yield antagonists such as cyclo(31-34)[DPhe(11),His(12),C(alpha)MeLeu(13,39),Nle(17),Glu(31),Lys(34)]Ac-sauvagine((8-40)) (astressin(2)-B) with CRF(2) selectivities greater than 100-fold. CRF receptor autoradiography was performed in rat tissue known to express CRF(2) and CRF(1) in order to confirm that astressin(2)-B could indeed bind to established CRF(2) but not CRF(1) receptor-expressing tissues. Extended duration of action of astressin(2)-B vs that of antisauvagine-30 is demonstrated in the CRF(2)-mediated animal model whereby the inhibition of gastric emptying of a solid meal in mice by urocortin administered intraperitoneally at time zero is antagonized by the administration of astressin(2)-B but not by antisauvagine-30 at times -3 and -6 h while both peptides are effective when given 10 min before urocortin.

Octreotide and octreotate derivatives radiolabeled with yttrium: pharmacokinetics in rats

Distribution profiles and elimination pathways in rats of two new octreotate derivatives radiolabeled with yttrium, namely Y-DOTAGA-tate and Y-DOTA-t-GA-tate, were compared with those of Y-DOTA-octreotide and Y-DOTA-Tyr(3)-octreotide. All synthetic somatostatin analogues under study were rapidly cleared from the blood and most organs of rats. The main elimination pathway for all peptides under study was urine excretion. High and long-term uptakes of radioactivity in the kidneys and also in organs with high density of somatostatin receptors (the adrenals and pancreas) were found. Radioactivity concentrations in these somatostatin receptor-rich organs were substantially higher for octreotate derivatives in comparison with octreotide analogues; the highest values for Y-DOTAGA-tate were determined. The octreotate derivatives under study appear to be specific ligands for treatment of somatostatin receptor-positive tumors if some mechanism to decrease their kidney retention is provided.

Comparison of somatostatin receptor expression in human gliomas and medulloblastomas

The expression of the five somatostatin receptor subtypes, sst1-5 was compared on tissue containing glial tumours (glioblastomas or oligodendrogliomas), medulloblastomas, and on normal human cortex. By semiquantitative reverse transcription coupled to polymerase chain reaction, the receptor expression profiles were high in cortex and in tissue containing oligodendrogliomas. It was moderate in medulloblastomas. Tissue containing glioblastomas displayed lower expression of somatostatin receptor subtypes, sst1 and sst3 being mostly expressed. By 125I-Tyr0DTrp8 somatostatin-14 or 125I-Leu8DTrp22 Tyr25 somatostatin-28 autoradiography combined with synaptophysin immunohistochemistry, it was possible to differentiate between isolated tumoral cell component infiltrating the cerebral parenchyma (cortex or white matter) and tumoral tissue (without residual parenchyma) in glioblastomas or oligodendrogliomas. Glial tumoral tissue per se presented few somatostatin receptors. By contrast, medulloblastoma tumoral cells exhibited numerous octreotide sensitive somatostatin receptors. sst2 immunocytochemistry demonstrated immunostaining of neuronal cells and neuropile; sst2 and sst3 immunostaining was identified on glioblastoma proliferating vessels endothelial cells and on medulloblastomas tumoral cells. Faint sst2 immunostaining among glial tumoral cells was due to microglia, while glioma cells did not significantly stain. In summary, medulloblastoma tumoral cells express sst2/sst3 receptors at a high level while glioma cells do not. In gliomas, sst expression is restricted to endothelial cells on proliferating vessels (displaying both sst2 and sst3 receptors), including parenchyma and reactive microglia (only sst2). The differential expression of sst2/sst3 receptors on gliomas and medulloblastomas has implications for the therapy of these tumours.

CCK receptors in human neuroendocrine tumors: clinical implications

Receptors for gastrin and cholecystokinin have been shown to be expressed in several types of human cancers. CCK-B receptors for instance have been identified in several types of neuroendocrine tumors. One of the highest incidences of CCK-B receptors has been reported in medullary thyroid cancers at the protein and at the mRNA level using in vitro receptor autoradiography and RT-PCR. It is likely that these receptors mediate the stimulation of calcitonin secretion from neoplastic C-cells by pentagastrin, a well established clinical test to detect occult medullary thyroid cancers. In order to target these tumors in vivo in patients, several peptide radiopharmaceuticals such as DTPA-linked minigastrins or non-sulfated CCK-8 analogs radiolabeled with 111Indium or 90Yttrium have recently been developed. As a proof of concept, it could be demonstrated that a majority of medullary thyroid cancer primary tumors and metastases are visualized in vivo with CCK-B receptor scintigraphy using these radioligands. More recently, radiotherapy of CCK-B receptor expressing medullary thyroid cancers with radiolabeled minigastrin has been successfully reported in a small number of patients, giving support to the proposal that CCK-B receptors overexpressed in tumors represent a useful target for clinical application.

Successful diffusible brachytherapy (dBT) of a progressive low-grade astrocytoma using the locally injected peptidic vector and somatostatin analogue [90Y]-DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC)

We present the therapeutic effect of diffusible brachytherapy (dBT), an innovative approach for the management of symptomatic low grade gliomas [1]. This protocol uses a radiolabelled small diffusible peptidic vector which is a somatostatin analogue to target somatostatin type 2 (sst-2) receptors. The stable radioconjugate [90Y]-DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC) is repeatedly injected via catheters placed into the resection cavity or into tumour nodules. We report on the four year follow-up after initiation of dBT to treat progressive disease in a patient with a complex eleven year history of fibrillary low-grade astrocytoma. The radiopharmakon was not only locally injected into the resection cavity following debulking surgery, but also administered by slow infusion technique to target recurrent and infiltrative tumour zones in the subventricular region around the inferior and posterior horns. In conclusion, peptidic vector based dBT was found to be safe, of mild and transitory toxicity, and effective in long-term tumour control.

Successful diffusible brachytherapy (dBT) of a progressive low-grade astrocytoma using the locally injected peptidic vector and somatostatin analogue [90Y]-DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC)

We present the therapeutic effect of diffusible brachytherapy (dBT), an innovative approach for the management of symptomatic low grade gliomas [1]. This protocol uses a radiolabelled small diffusible peptidic vector which is a somatostatin analogue to target somatostatin type 2 (sst-2) receptors. The stable radioconjugate [90Y]-DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC) is repeatedly injected via catheters placed into the resection cavity or into tumour nodules. We report on the four year follow-up after initiation of dBT to treat progressive disease in a patient with a complex eleven year history of fibrillary low-grade astrocytoma. The radiopharmakon was not only locally injected into the resection cavity following debulking surgery, but also administered by slow infusion technique to target recurrent and infiltrative tumour zones in the subventricular region around the inferior and posterior horns. In conclusion, peptidic vector based dBT was found to be safe, of mild and transitory toxicity, and effective in long-term tumour control.

Localization and characterization of neuropeptide receptors in human colon

Information about the expression of neuropeptide receptors is limited in human peripheral tissues, such as the gastrointestinal tract, as compared to the brain. A detailed evaluation of binding sites for gastrin-releasing peptide (GRP), neuropeptide Y, vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase-activating polypeptide (PACAP), gastrin/cholecystokinin, neurotensin, substance P and somatostatin was therefore undertaken in human colon using in vitro receptor autoradiography and subtype characterization with receptor-selective ligands. GRP receptors, Y2 receptors, PACAP type1-receptors, cholecystokinin-A receptors, neurotensinl and sst2 receptors were abundantly expressed in the myenteric plexus. Y2, neurotensinl and sst2 receptors were also strongly expressed in the submucosal plexus. Furthermore, expression of GRP receptors, neurokinin (NK)1 receptors, VIP type2-receptors and sst2 receptors was found in the mucosa-directed margin of the circular smooth muscle where the interstitial cells of Cajal are located. A variable and complementary expression of GRP receptors, VIP/PACAP receptors, Y2 neurotensinl, NK1 and somatostatin receptors was found in the circular and longitudinal smooth muscle. NK1 and Y1 receptors were often detected in arteries and veins, while VIP/PACAP and sst2 receptors were found in lymphoid follicles. Y2, VIP type, and sst2 receptors were present in the colonic mucosa. Y2 was strongly expressed in the muscularis mucosae. This study shows that neuropeptide receptors are expressed in high amounts and in highly specific patterns in distinct targets in the human colon, suggesting a major physiological role for these peptides. The data represent the molecular basis to investigate the regulation by neuropeptides of colonic functions and to develop neuropeptide drugs aimed at interacting with these receptors in colonic diseases, such as Hirschsprung's and Crohn's diseases.

Lack of evidence for cross-competition between vasoactive intestinal peptide and somatostatin at their respective receptors

A possible cross-competition between vasoactive intestinal peptide (VIP) and somatostatin (somatotropin release inhibiting factor; SRIF) and their respective receptors, was investigated at native or recombinant SRIF and VIP/pituitary adenylate cyclase-activating polypeptide (PACAP) receptors. The activity of VIP was examined in radioligand binding assays at mouse sst(1-5), rat sst(1-2) and human sst(1-5) receptors; or at human tumours preferentially expressing each of the five SRIF receptors. Moreover, SRIF was investigated at human tumoral tissues known to exclusively express specific VIP/PACAP receptor(s). VIP had no significant effect on any of the radioligand binding sites of the SRIF receptor family of rat, mouse or human origin tested. Conversely, SRIF did not interfere with the human VIP/PACAP binding sites tested. Taken together, the results cast reservation on the claimed cross-competition between VIP and SRIF at, specifically human sst(3) receptors, or any of the cloned SRIF or VIP/PACAP receptors recognised to date.

Somatostatin receptor sst1-sst5 expression in normal and neoplastic human tissues using receptor autoradiography with subtype-selective ligands

Somatostatin receptors are known to be expressed in a large number of human tumours and represent the basis for in vivo tumour targeting. Stable somatostatin derivatives such as octreotide or lanreotide are the most frequently used radiopharmaceuticals acting through specific binding to somatostatin receptors; however, they do not bind with high affinity to all five receptor subtypes. Whereas the mRNAs for most receptor subtypes have been detected in tumours, it is in most cases unclear which of the receptor subtype proteins are expressed. Since in vitro receptor binding methods are close correlates and predictors of in vivo peptide receptor targeting, we took advantage of the recently developed subtype-selective analogues and evaluated approximately 200 tumours for their receptor subtype protein expression in specific binding assays using autoradiography with 125I-[Leu8, D-Trp22, Tyr25]-somatostatin-28 and displacement by subtype-selective analogues. The majority of the tested neuroblastomas, meningiomas, medulloblastomas, breast carcinomas, lymphomas, renal cell carcinomas, paragangliomas, small cell lung carcinomas and hepatocellular carcinomas predominantly expressed sst2. The prostate carcinomas and sarcomas preferentially expressed sstl, while a majority of inactive pituitary adenomas displayed sst3 and, to a lesser extent, sst2. Growth hormone-secreting pituitary adenomas preferentially expressed sst2 and sst5; gastroenteropancreatic tumours and phaeochromocytomas frequently displayed sst2 and/or sstl. Non-neoplastic human tissues such as vessels, nerve plexus, pancreatic islets, prostatic stroma, adrenal medulla, spleen and germinal centres of the lymphoid tissues preferentially expressed sst2. However, the human gastric mucosa predominantly expressed sst1 while colonic mucosa displayed sst2. Interestingly, a minority of tumours showed a strong 125I-[Leu8, D-Trp22, Tyr25]-somatostatin-28 binding, of which less than 50% could be displaced by the sum of the five subtype-selective analogues. This observation suggests the existence of an as yet unknown subtype in selected tumours. This study is the first report to analyse the somatostatin receptor subtype expression in tumours with binding methods. We conclude that sst2, with high affinity for current radiopharmaceuticals such as Octreoscan, is predominantly expressed in a majority of tumours. Fewer tumour types (sarcomas, prostate cancers, inactive pituitary adenomas) preferentially express another subtype. This information is of importance with regard to the clinical applications and development of somatostatin analogues with distinct receptor subtype selectivities.

Potent somatostatin undecapeptide agonists selective for somatostatin receptor 1 (sst1)

A family of analogues of des-AA(1,2,5)-[DTrp(8)/D2Nal(8)]-SRIF that contain a 4-(N-isopropyl)-aminomethylphenylalanine (IAmp) at position 9 was identified that has high affinity and selectivity for human somatostatin receptor subtype 1 (sst1). The binding affinities of des-AA(1,2,5)-[DTrp(8),IAmp(9)]-SRIF (c[H-Cys-Lys-Phe-Phe-DTrp-IAmp-Thr-Phe-Thr-Ser-Cys-OH], CH-275) (7), des-AA(1,5)-[Tyr(2),DTrp(8),IAmp(9)]-SRIF (CH-288) (16), des-AA(1,2,5)-[Tyr(7),DTrp(8),IAmp(9)]-SRIF (23), and des-AA(1,2,5)-[DTrp(8),IAmp(9),Tyr(11)]-SRIF (25) are about (1)/(7), (1)/(4), (1)/(125), and (1)/(4) that of SRIF-28 (1) to sst1, respectively, about (1)/(65), (1)/(130), <(1)/(1000), and <(1)/(150) that of 1 to sst3, respectively, and about or less than (1)/(1000) that of 1 to the other three human SRIF receptor subtypes. A substitution of DTrp(8) by D2Nal(8) in 7 to yield des-AA(1,2,5)-[D2Nal(8),IAmp(9)]-SRIF (13) and in 16 to yield des-AA(1,5)-[Tyr(2),D2Nal(8),IAmp(9)]-SRIF (17) was intended to increase chemical stability, selectivity, and affinity and resulted in two analogues that were less potent or equipotent with similar selectivity, respectively. Carbamoylation of the N-terminus as in des-AA(1,2,5)-[DTrp(8),IAmp(9),Tyr(11)]-Cbm-SRIF (27) increased affinity slightly as well as improved selectivity. Monoiodination of 25 to yield 26 and of 27 to yield 28 resulted in an additional 4-fold increase in affinity at sst1. Desamination of the N-terminus of 17 to yield 18, on the other hand, resulted in significant loss of affinity. Attempts at reducing the size of the ring with maintenance of selectivity failed in that des-AA(1,4,5,13)-[Tyr(2),DTrp(8),IAmp(9)]-SRIF (33) and des-AA(1,4,5,6,12,13)-[Tyr(2),DTrp(8),IAmp(9)]-SRIF (34) progressively lost affinity for all receptors. Both des-AA(1,2,5)-[DTrp(8),IAmp(9),Tyr(11)]-Cbm-SRIF (27) and des-AA(1,2,5)-[DCys(3),DTrp(8),IAmp(9),Tyr(11)]-Cbm-SRIF (29) show agonistic activity in a cAMP assay; therefore, the structural basis for the agonist property of this family of analogues is not contingent upon the chirality of the Cys residue at position 3 as shown to be the case in 18-membered ring SRIF octapeptides. None of the high affinity structures described here showed receptor antagonism. We have prepared the radiolabeled des-AA(1,2,5)-[DTrp(8),IAmp(9),(125)ITyr(11)]-SRIF ((125)I-25) and des-AA(1,2,5)-[DTrp(8),IAmp(9), (125)ITyr(11)]-Cbm-SRIF ((125)I-27), used them as in vitro tracers, and found them to be superior to des-AA(1,5)-[(125)ITyr(2),DTrp(8),IAmp(9)]-SRIF ((125)I-16) for the detection of sst1 tumors in receptor autoradiography studies.

Y(1)-mediated effect of neuropeptide Y in cancer: breast carcinomas as targets

Overexpression of selected peptide receptors in human tumors has been shown to represent clinically relevant targets for cancer diagnosis and therapy. Neuropeptide Y (NPY) is a peptide neurotransmitter mediating feeding behavior and vasoconstriction. It has never been shown to be involved in human cancer. We show here, using in vitro receptor autoradiography, a NPY receptor incidence of 85% in primary human breast carcinomas (n = 95) and of 100% in lymph node metastases of receptor-positive primaries (n = 27), predominantly as Y(1) subtype, whereas non-neoplastic human breast expressed Y(2) preferentially. Y(1) mRNA was detected in Y(1)-expressing tumors by in situ hybridization, whereas Y(2) mRNA was found in normal breast tissue. The strong predominance of Y(1) in breast carcinomas compared with Y(2) in normal breast suggests that neoplastic transformation can switch the NPY receptor expression from Y(2) to Y(1) subtype. Moreover, in Y(1)-expressing human SK-N-MC tumor cells, an NPY-induced, dose-dependent inhibition of tumor cell growth of >40% was observed, suggesting a functional role of NPY in cancer, mediated by Y(1). NPY should therefore be added to the list of small regulatory peptides related to cancer. The high incidence of Y(1) in in situ, invasive, and metastatic breast cancers allows for the possibility to target them for diagnosis and therapy with NPY analogues.

In vitro evaluation of VIP/PACAP receptors in healthy and diseased human tissues. Clinical implications

The evaluation of peptide receptors in man is relevant to identifying the physiological target tissues of a given peptide and to selecting diseases with a sufficient receptor overexpression for diagnostic or therapeutic intervention. VIP/PACAP receptors have been evaluated in normal and diseased human non-neuronal tissues by using in vitro receptor autoradiography with 125I-VIP or 125I-PACAP in tissue sections. As assessed by subtype-selective VIP analogs, VIP receptors of the VPAC1 subtype are found in a wide variety of tissues including liver, breast, kidney, prostate, ureter, bladder, pancreatic ducts, gastrointestinal mucosa, lung, thyroid, adipose, and lymphoid tissues. VPAC2 receptors are predominantly found in vessels and smooth muscles, whereas PAC1 receptors are present in the adrenal medulla. VIP/PACAP receptors are expressed in the majority of the most frequently occurring human tumors, including breast, prostate, pancreas, lung, colon, stomach, liver, and bladder carcinomas, as well as lymphomas and meningiomas, predominantly as VPAC1 receptors, as do their tissues of origin. Although leiomyomas predominantly express VPAC2 receptors, glial tumors, pituitary adenomas, neuroblastomas, paragangliomas, pheochromocytomas, and endometrial carcinomas preferentially express PAC1 receptors. The very wide distribution of VIP/PACAP receptors in the normal human body is indicative of the key role of these peptides in human physiology and pathophysiology. Moreover, the receptor expression in tumors is the molecular basis for clinical applications of VIP/PACAP such as in vivo scintigraphy and radiotherapy of tumors as well as VIP/PACAP analog treatment for tumor growth inhibition.

SST3-selective potent peptidic somatostatin receptor antagonists

A family of octapeptide derivatives of somatostatin cyclized via a disulfide bridge (des-AA(1,2,4,5,12,13)[d-2Nal(8)]-somatostatin-14, ODN-8) was identified that has high affinity and selectivity for the human sst(3) somatostatin receptor subtype transfected in CCL39 cells. The binding affinity of carbamoyl-des-AA(1,2,4,5,12, 13)[d-Cys(3),Tyr(7),d-Agl(8)(Me,2-naphthoyl)]-somatostatin-14 (sst(3)-ODN-8) is equal to that of somatostatin-28 for sst(3) and less than one-thousandth that for the other four somatostatin receptor subtypes. Compound sst(3)-ODN-8 potently reverses the somatostatin-28-induced inhibition of forskolin-stimulated cAMP production (pK(B) = 9.07) and reverses the somatostatin-28-induced stimulation of phospholipase C activity (pK(i) = 9.22) in sst(3)-transfected CCL39 cells. [(125)I-Tyr(7)]sst(3)-ODN-8 selectively labels sst(3)-expressing cells with subnanomolar binding affinity (K(D) = 0.27 nM). With the use of this radioligand, sst(3)-expressing human tumors, particularly inactive pituitary adenomas, can be identified with receptor autoradiography; moreover, areas of the human lymphoreticular system express sst(3) binding sites selectively displaced by nanomolar concentrations of sst(3)-ODN-8. Based on the structure-activity relationship of selected analogs substituted at positions 3, 7, and 8, we hypothesize that the basis for sst(3) selectivity, high affinity, and possibly antagonism resides in the ring size of the analog and the unique conformational and structural character of the N-methylated amino-2-naphthoyl side chain of aminoglycine at position 8 and not in the Tyr(7) substitution or in the d-configuration at position 3. The family of labeled and unlabeled sst(3)-ODN-8 analogs represents highly innovative, potent, and specific sst(3)-selective antagonist tools for the study of sst(3)-mediated physiological and pathophysiological conditions that may suggest novel clinical applications.

Bombesin receptors in distinct tissue compartments of human pancreatic diseases

Overexpression of receptors for regulatory peptides in various human diseases is reportedly of clinical interest. Among these peptides, bombesin and gastrin-releasing peptide (GRP) have been shown to play a physiological and pathophysiological role in pancreatic tissues. Our aim has been to localize bombesin receptors in the human diseased pancreas to identify potential clinical applications of bombesin analogs in this tissue. The presence of bombesin receptor subtypes has been evaluated in specimens of human pancreatic tissues with chronic pancreatitis (n = 23) and ductal pancreatic carcinoma (n = 29) with in vitro receptor autoradiography on tissue sections incubated with 125I-[Tyr4]-bombesin or the universal ligand 125I-[D-Tyr6, beta-Ala11, Phe13, Nle14]-bombesin(6-14) as radioligands and displaced by subtype-selective bombesin receptor agonists and antagonists. GRP receptors were identified in the pancreatic exocrine parenchyma in 17 of 20 cases with chronic pancreatitis. No measurable bombesin receptors were found in the tumor tissue of ductal pancreatic carcinomas, however, GRP receptors were detected in a subset of peritumoral small veins in 19 of 29 samples. Moreover, residual pancreatic islets in these tissues were shown to express the BB3 receptor subtype. These data demonstrate the presence of bombesin receptors in three distinct tissue compartments of the pancreas, namely GRP receptors in the exocrine parenchyma in chronic pancreatitis and in peritumoral vessels around ductal pancreatic carcinomas, and BB3 receptors in residual pancreatic islets. Such a selective expression of bombesin receptor subtypes in pancreatic tissues may not only be of pathophysiological significance but may represent the basis for potential diagnostic and therapeutic clinical applications of bombesin analogs, including GRP receptor scintigraphy to differentiate chronic pancreatitis from ductal pancreatic carcinoma.

Vasoactive intestinal peptide receptor scintigraphy in patients with pancreatic adenocarcinomas or neuroendocrine tumours

Human adenocarcinomas of the gastroenteropancreatic system overexpress vasoactive intestinal peptide (VIP) receptors and therefore represent logical diagnostic targets for receptor scintigraphy. Using iodine-123 labelled VIP, the newly employed diagnostic procedure termed VIP receptor scintigraphy (VIP-RS) appears to detect tumour tissue, especially pancreatic metastatic tumours, in almost all cases. So far, however, only a single centre has demonstrated convincing positive results. The aim of this study was to compare the sensitivity and specificity of VIP-RS with those of computer tomography (CT) and transabdominal ultrasound in patients with extensive pancreatic metastatic adenocarcinomas and neuroendocrine tumours. VIP was radiolabelled with carrier-free 123I using the chloramine T-method and preparative high-performance liquid chromatography for purification. Patients with metastatic pancreatic (n=12) and colorectal (n=3) carcinomas (adenocarcinoma: n=13, neuroendocrine tumour: n=2) were studied by VIP-RS, CT, ultrasound and, in one case, also by radioligand receptor autoradiography. Carrier-free radioiodinated VIP of maximum specific radioactivity maintained a high biological activity as determined by cAMP formation in receptor-expressing tumour cell lines. Intravenous injection of 123I-VIP did not cause any side-effects. Biodistribution, determined over 24 h, was high in the lungs and low in abdominal organs. Although all patients had extensive metastatic disease as evidenced by CT and ultrasound, VIP-RS was unable to detect either primaries or metastases in these patients. Only in two patients could a significant uptake of radiolabel be detected in organs directly infiltrated by the primary. To exclude false-negative findings, tumour tissue in one patient with a large primary, undetectable by VIP-RS, was analysed by radioligand receptor autoradiography and shown to be receptor positive. Moreover, in vitro receptor determinations showed that pancreatic carcinomas usually have fewer VIP receptors than the normal tissues to which they metastasize, like the liver. It is concluded that VIP can be radioactively labelled with maximum specific radioactivity while maintaining biological activity. Intravenous administration leads to a biodistribution almost identical to that reported previously. However, in contrast to these reports, very low sensitivity and specificity were observed for the detection of pancreatic cancers. In retrospect, these findings are not surprising since VIP receptor expression was observed to be higher in normal tissues than in neoplastic ones.

Cholecystokinin-B/gastrin receptors enhance wound healing in the rat gastric mucosa

Although physiological functions of the CCK-B/gastrin receptor are well explored, little is known about its role during healing. Here, we evaluated the role of this receptor in the rat oxyntic mucosa following the introduction of a cryoulcer. In this model, we located and quantified CCK-B/gastrin receptors by reverse transcriptase PCR and receptor autoradiography. Rats with cryoulcers were treated with placebo, omeprazole, the CCK-B/gastrin receptor antagonist YF-476, omeprazole plus YF-476, gastrin-17, and gastrin 17 plus YF-476. During wound healing, CCK-B/gastrin receptors were specifically expressed and localized to the regenerative mucosal ulcer margin. This high expression was limited in time, and the pattern of expression of CCK-B/gastrin receptors correlated closely with the proliferative activity of the regenerative mucosa. Functionally, omeprazole and gastrin-17 caused profound hypergastrinemia, increased cell proliferation in the mucosal ulcer margin and accelerated the late ulcer healing phase. These effects were completely reversed by cotherapy with YF-476. These in vivo and vitro data suggest that CCK-B/gastrin receptors in regenerative rat gastric oxyntic mucosa enhance trophic effects during wound healing.

Subcellular distribution of somatostatin sst2A receptors in human tumors of the nervous and neuroendocrine systems: membranous versus intracellular location

The distribution of the sst2A receptor was investigated, using immunohistochemistry, with the specific antipeptide antibody R2-88, in a total of 120 tumors of the nervous and the neuroendocrine systems, including small-cell lung carcinomas, medulloblastomas, neuroblastomas, pheochromocytomas, and paragangliomas. The great majority of the tumor samples, frozen or formalin-fixed, showed a positive immunohistochemical staining with R2-88, and an excellent correlation with receptor autoradiography using 125I[Tyr3]-octreotide. Whereas small-cell lung carcinomas and medulloblastomas had a predominantly plasma membrane staining, pheochromocytomas and neuroblastomas had variable ratios of cell surface and intracellular staining. Strikingly, a preferentially cytoplasmic staining was seen in tumors with a high level of somatostatin gene expression, whereas a more plasma membranous staining was seen in tumors lacking somatostatin messenger RNA. Specificity of both the plasma membrane and the cytoplasmic staining pattern was confirmed in immunoblots, which showed the immunoreactive receptor migrating as a characteristic 70-kDa broad band. In both immunohistochemical and immunoblotting experiments, staining was abolished by antibody blockade with 100 nM antigen peptide. These results describe, for the first time, the localization of the sst2A receptor protein in human small-cell lung carcinomas, medulloblastomas, neuroblastomas, and paragangliomas. Moreover, it is the first report investigating possible causes for distinct subcellular localizations of sst2A in human tissues. We show that the subcellular distribution of the receptor may be dependent on the surrounding somatostatin concentration, consistent with both the known effect of somatostatin to cause sst2A receptor internalization and an autocrine regulation of tumors by the peptide they produce. Moreover, our demonstration that the sst2A receptor can be identified in this group of tumors using simple immunohistochemical methods in formalin-fixed, paraffin-embedded material opens numerous diagnostic, therapeutic, and prognostic opportunities.

Cholecystokinin receptor imaging using an octapeptide DTPA-CCK analogue in patients with medullary thyroid carcinoma

Cholecystokinin (CCK)-B receptors have been demonstrated on a high percentage of medullary thyroid carcinomas (MTC) in vitro. After encouraging results both in vitro and in animal studies, we studied the efficacy of an octapeptide [111In-DTPA]-CCK analogue in seven patients with MTC. In four of five patients in whom serum calcitonin levels were monitored, a significant rise was found following the injection, indicating retained biological activity of the radiopeptide. In all patients there was visualization of the CCK-B receptor-positive stomach. In one of two patients with known MTC lesions, some of the lesions were visualized; in addition some lesions were visualized in one of the five other patients who had elevated serum tumour markers but negative localizing studies. Radioactivity in the presumed tumour sites was still present at 48 h p.i. The uptake in the presumed tumour sites and stomach was low. Background radioactivity dropped rapidly owing to urinary excretion. After 1 h, breakdown products of the labelled analogue predominated both in urine and in serum, and virtually no intact peptide was present.

IN CONCLUSION

(1) the CCK-B receptor-positive gastric mucosa and presumed MTC lesions could be visualized in patients using an octapeptide [111In-DTPA]-CCK analogue that is probably internalized, proving the feasibility of CCK-B receptor imaging in vivo; (2) there was a relatively low uptake of the CCK analogue in the strongly CCK receptor positive stomach, and rapid degradation of the peptide in serum.

Vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor subtypes in human tumors and their tissues of origin

The evaluation of peptide receptors in man is needed not only to discover the physiological target tissues of a given peptide but also to identify diseases with a sufficient receptor overexpression for diagnostic or therapeutic interventions. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) receptors have been evaluated in human tumors and in their tissues of origin using in vitro receptor autoradiography with 125I-VIP or 125I-acetyl-PACAP-27 in tissue sections. The VIP/PACAP receptor subtypes VPAC1, VPAC2, and PAC1 were evaluated in these tissues by determining the rank order of potencies of VIP and PACAP as well as VPAC1- and VPAC2-selective analogues. The VIP/PACAP receptors expressed in the great majority of the most frequently occurring human tumors, including breast (100% receptor incidence), prostate (100%), pancreas (65%), lung (58%), colon (96%), stomach (54%), liver (49%), and urinary bladder (100%) carcinomas as well as lymphomas (58%) and meningiomas (100%), are predominantly of the VPAC1 type. Their cells or tissues of origin, i.e., hepatocytes, breast lobules and ducts, urothelium, prostate glands, pancreatic ducts, lung acini, gastrointestinal mucosa, and lymphocytes, also predominantly express VPAC1. Leiomyomas predominantly express VPAC2 receptors, whereas paragangliomas, pheochromocytomas, and endometrial carcinomas preferentially express PAC1 receptors. Conversely, VPAC2 receptors are found mainly in smooth muscle (i.e., stomach), in vessels, and in stroma (e.g., of the prostate), whereas PAC1 receptors are present in the adrenal medulla and in some uterine glands. Whereas the very wide distribution of VIP/PACAP receptors in the normal human body is indicative of a key role of these peptides in human physiology, the high VIP/PACAP receptor expression in tumors may represent the molecular basis for clinical applications of VIP/PACAP such as in vivo scintigraphy and radiotherapy of tumors as well as VIP/PACAP analogue treatment for tumor growth inhibition.

Somatostatin receptor in breast cancer and axillary nodes: study with scintigraphy, histopathology and receptor autoradiography

We conducted a prospective analysis of somatostatin receptor scintigraphy using (111)In radiolabeled pentetreotide, a somatostatin analog, in patients with breast cancer in the aim to visualize the primary tumor and axillary or parasternal metastatic extension because some malignant breast tumors express somatostatin receptors (SS-R) in 50%, approximately. An analysis of SS-R was performed by autoradiography.

PATIENTS AND METHODS

Thirteen patients with clinically suspected breast tumors (T1, T2), and at least one palpable axillary node (N1) were included. In vivo planar scintigrams were acquired 1, 4, and 24 h after subcutaneous, then after intravenous injections (24 h delay between injections). Improved (111)In-pentetreotide uptake in invaded nodes after subcutaneous injection was hypothesized. Ex vivo scintigrams of surgical specimens were also acquired immediately after tumor resection and axillary dissection. Pathological examination and receptor autoradiography were performed on all surgical specimens.

RESULTS

Among 11 pathologically proven malignant tumors (9 ductal and 2 lobular carcinomas), only four were scintigraphically visible although six expressed SS-R receptors in vitro. Among six pathologically proven malignant nodes, four expressed SS-R, including two visualized scintigraphically. Scintigrams acquired after subcutaneous injections were less sensitive than after intravenous injections. There were no false positive. False negatives occurred in cases with small tumors with low-density or heterogeneously distributed SS-R. There was no significant difference by histological type or prognostic factors.

CONCLUSION

Somatostatin receptor scintigraphy does not appear to be sensitive enough to evaluate axillary node extension of breast cancer or even to confirm the presence of tumoral tissue, and this whatever the administration route for (111)In-pentetreotide.

Affinity profiles for human somatostatin receptor subtypes SST1-SST5 of somatostatin radiotracers selected for scintigraphic and radiotherapeutic use

In vivo somatostatin receptor scintigraphy using Octreoscan is a valuable method for the visualisation of human endocrine tumours and their metastases. Recently, several new, alternative somatostatin radioligands have been synthesised for diagnostic and radiotherapeutic use in vivo. Since human tumours are known to express various somatostatin receptor subtypes, it is mandatory to assess the receptor subtype affinity profile of such somatostatin radiotracers. Using cell lines transfected with somatostatin receptor subtypes sst1, sst2, sst3, sst4 and sst5, we have evaluated the in vitro binding characteristics of labelled (indium, yttrium, gallium) and unlabelled DOTA-[Tyr3]-octreotide, DOTA-octreotide, DOTA-lanreotide, DOTA-vapreotide, DTPA-[Tyr3]-octreotate and DOTA-[Tyr3]-octreotate. Small structural modifications, chelator substitution or metal replacement were shown to considerably affect the binding affinity. A marked improvement of sst2 affinity was found for Ga-DOTA-[Tyr3]-octreotide (IC50 2.5 nM) compared with the Y-labelled compound and Octreoscan. An excellent binding affinity for sst2 in the same range was also found for In-DTPA-[Tyr3]-octreotate (IC50 1.3 nM) and for Y-DOTA-[Tyr3]-octreotate (IC50 1.6 nM). Remarkably, Ga-DOTA-[Tyr3]-octreotate bound at sst2 with a considerably higher affinity (IC50 0.2 nM). An up to 30-fold improvement in sst3 affinity was observed for unlabelled or Y-labelled DOTA-octreotide compared with their Tyr3-containing analogue, suggesting that replacement of Tyr3 by Phe is crucial for high sst3 affinity. Substitution in the octreotide molecule of the DTPA by DOTA improved the sst3 binding affinity 14-fold. Whereas Y-DOTA-lanreotide had only low affinity for sst3 and sst4, it had the highest affinity for sst5 among the tested compounds (IC50 16 nM). Increased binding affinity for sst3 and sst5 was observed for DOTA-[Tyr3]-octreotide, DOTA-lanreotide and DOTA-vapreotide when they were labelled with yttrium. These marked changes in subtype affinity profiles are due not only to the different chemical structures but also to the different charges and hydrophilicity of these compounds. Interestingly, even the coordination geometry of the radiometal complex remote from the pharmacophoric amino acids has a significant influence on affinity profiles as shown with Y-DOTA versus Ga-DOTA in either [Tyr3]-octreotide or [Tyr3]-octreotate. Such changes in sst affinity profiles must be identified in newly designed radiotracers used for somatostatin receptor scintigraphy in order to correctly interpret in vivo scintigraphic data. These observations may represent basic principles relevant to the development of other peptide radioligands.

Neurotensin receptor-1 mRNA analysis in normal pancreas and pancreatic disease

By autoradiography, neurotensin (NT) binding is specifically detectable in pancreatic cancer, but not in the normal pancreas, chronic pancreatitis (CP), or other pancreatic disorders. In the present study, we investigated whether this is due to NT receptor-1 (NTR-1) mRNA up-regulation and whether NTR-1 mRNA could also be used as a specific diagnostic marker and treatment target in pancreatic cancer. Fifteen normal pancreas tissue samples, 20 CP samples, and 30 pancreatic cancer samples were studied. Expression and localization of NTR-1 mRNA was investigated by Northern blot analysis and in situ hybridization. Furthermore, consecutive tissue sections were analyzed for NTR-1 mRNA expression and NT binding. By Northern blot analysis, NTR-1 mRNA expression was 4.4-fold (P < 0.01) and 3.0-fold (P < 0.01) higher in pancreatic cancer and CP tissue samples, respectively, compared with normal controls. There was no difference in NTR-1 mRNA levels between CP and cancer samples (P > 0.05). In pancreatic cancer, the NTR-1 mRNA levels were higher in advanced tumor stage (stages III and IV) than early tumor stage (stages I and II; P < 0.05), but no difference was found between well/moderately differentiated (grades 1 and 2) and poorly differentiated/undifferentiated cancers (grades 3 and 4; P > 0.05). By in situ hybridization, NTR-1 mRNA signals were weakly present in the cytoplasm of acinar and ductal cells of the normal pancreas. Moderate to intense NTR-1 mRNA signals were present in the cytoplasm of acinar cells dedifferentiating into tubular complexes and degenerating acinar cells of CP samples. In the cancer samples, NTR-1 mRNA was moderately to intensely expressed in the cytoplasm of cancer cells. When on consecutive tissue sections NTR-1 mRNA expression was compared with the presence of NTR-1, measured by receptor autoradiography, a correlation was found in carcinomas but not in CP samples, in which no receptors were detectable by autoradiography. The enhanced expression of NTR-1 mRNA in pancreatic cancer cells further suggests that neuroendocrine hormones might modulate pancreas cancer cell behavior. However, its relatively high levels in CP excludes NTR-1 mRNA as a specific parameter for pancreatic cancer and for the differentiation of pancreatic cancer from CP.

Preclinical and initial clinical evaluation of 111In-labeled nonsulfated CCK8 analog: a peptide for CCK-B receptor-targeted scintigraphy and radionuclide therapy

The presence of cholecystokinin (CCK)-B (gastrin) receptors has been shown in more than 90% of medullary thyroid cancers (MTCs) and in a high percentage of small cell lung cancers, stromal ovarium cancers and several other tumor types.

METHODS

The aim of this study was to evaluate in vitro and in vivo whether 111In-labeled CCK-B receptor-specific CCK8 analog [D-Asp26,Nle28,31]CCK26-33 (D-Asp-Tyr-Nle-Gly-Trp-Nle-Asp-Phe-NH2) is suitable for CCK-B receptor scintigraphy based on the finding that unlabeled nonsulfated diethylenetriamine pentaacidic acid [DTPA0]CCK8 and tetraazacyclododecanetetraacetic acid [DOTA0]CCK8 analogs show high and specific binding for CCK-B receptors in human tumors. Fifty percent inhibitory concentrations were in the low nanomolar range.

RESULTS

In vitro, [111In-DOTA0]CCK8 showed specific internalization in CCK-B receptor-positive rat pancreatic tumor cells AR42J. Internalization of the analog appeared to be time and temperature dependent and receptor specific. From the data obtained with [111In-DOTA0]CCK8 and (125I)I-gastrin, the latter being a specific ligand for the CCK-B receptor, the rat pancreatic cell line CA20948 also appeared to be CCK-B receptor positive. This provides an in vitro and in vivo rat tumor model because this cell line can be grown to solid tumors in Lewis rats. In vivo biodistribution experiments in CA20948 tumor-bearing Lewis rats showed rapid clearance of [111In-DOTA0]CCK8, and specific uptake was found in the CCK-B receptor-expressing stomach and tumor. Furthermore, comparing [111In-DOTA0]CCK8 with the radioiodinated nonsulfated CCK10 analog (D-Tyr-Gly-Asp-Tyr-Nle-Gly-Trp-Nle-Asp-Phe-NH2), both ligands having high affinity for the CCK-B receptor, tumor-to-blood ratios were significantly higher for [111In-DOTA0]CCK8 than for 125I-CCK10, analogous to the findings with radioiodinated and 111In-labeled octreotide. The study in humans with [111In-DTPA0]CCK8 showed receptor-specific uptake in the CCK-B receptor-positive stomach and in metastases in the neck region up to 48 h after injection.

CONCLUSION

[111In-DOTA0]CCK8 is most promising for scintigraphy and, after coupling to therapeutic radionuclides, for radionuclide therapy of human CCK-B receptor-positive tumors such as MTC and small cell lung cancer.

Gastrin-releasing peptide receptors in non-neoplastic and neoplastic human breast

The regulatory peptide gastrin-releasing peptide (GRP) may play a role in human cancer as a stimulatory growth factor. To understand the potential role of GRP in human breast cancer, we have evaluated GRP receptor expression in human non-neoplastic and neoplastic breast tissues and in axillary lymph node metastases, using in vitro receptor autoradiography on tissue sections with [(125)I]Tyr(4)-bombesin and with [(125)I]D-Tyr(6), beta Ala(11), Phe(13), Nle(14)-bombesin(6-14) as radioligands. GRP receptors were detected, often in high density, in neoplastic epithelial mammary cells in 29 of 46 invasive ductal carcinomas, in 11 of 17 ductal carcinomas in situ, in 1 of 4 invasive lobular carcinomas, in 1 of 2 lobular carcinomas in situ, and in 1 mucinous and 1 tubular carcinoma. A heterogeneous GRP receptor distribution was found in the neoplastic tissue samples in 32 of 52 cases with invasive carcinoma and 12 of 19 cases with carcinoma in situ. The lymph node metastases (n = 33) from those primary carcinomas expressing GRP receptors were all positive, whereas surrounding lymphoreticular tissue was negative. GRP receptors were also present in high density but with heterogeneous distribution in ducts and lobules from all available breast tissue samples (n = 23). All of the receptors corresponded to the GRP receptor subtype of bombesin receptors, having high affinity for GRP and bombesin and lower affinity for neuromedin B. All tissues expressing GRP receptors were identified similarly with both radioligands. These data describe not only a high percentage of GRP receptor-positive neoplastic breast tissues but also for the first time a ubiquitous GRP receptor expression in nonneoplastic human breast tissue. Apart from suggesting a role of GRP in breast physiology, these data represent the molecular basis for potential clinical applications of GRP analogs such as GRP receptor scintigraphy, radiotherapy, or chemotherapy.

Regulatory peptide receptors in human hepatocellular carcinomas

BACKGROUND

Overexpression of regulatory peptide receptors in selected human tumours is of diagnostic and therapeutic relevance.

AIMS

To evaluate the expression of somatostatin, vasoactive intestinal peptide (VIP), substance P, cholecystokinin (CCK) A and B, and neurotensin receptors in hepatocellular carcinoma (HCC).

METHODS

In vitro receptor autoradiography for the various peptide receptors using selective iodinated radioligands on tissue sections in 59 cases of HCC.

RESULTS

41% of HCC expressed somatostatin receptors; 47% expressed VIP receptors. VIP receptors were always identified in non-neoplastic liver tissue. Substance P receptors were only identified in 5% of HCC but in the majority of their peritumorous and intratumorous vessels. CCK-A and -B and neurotensin receptors were not detected in HCC. The somatostatin receptors showed high affinity for somatostatin and octreotide. The VIP receptors had high affinity for VIP, pituitary adenylate cyclase activating peptide (PACAP) 27, and a VIP1 selective analogue, suggesting the presence of VIP1/PACAP II type receptors. PACAP I receptors were identified in two cases. Substance P receptors were all of the NK1 subtype. The density of somatostatin receptors in HCC was low compared with the density found in liver metastases of neuroendocrine tumours. The VIP receptor density was always lower in HCC than in adjacent liver tissue.

CONCLUSIONS

Somatostatin, VIP, and substance P may have a receptor mediated role in HCC. Substance P receptors may be involved in regulation of tumour associated blood flow; somatostatin receptors and VIP receptors may mediate tumour growth. Diagnostic and therapeutic evaluation of somatostatin and VIP analogues may be of interest in receptor positive HCC.

Immunohistochemical detection of somatostatin sst2a receptors in the lymphatic, smooth muscular, and peripheral nervous systems of the human gastrointestinal tract: facts and artifacts

The cellular distribution of the somatostatin sst2A receptor protein was investigated in the lymphatic, smooth muscular, and nervous components of the human gastrointestinal tract using subtype-specific antibody R2-88 for immunohistochemical staining of cryostat and formalin-fixed, paraffin-embedded tissue sections. Germinal centers of intestinal lymphatic follicles were immunostained, exhibiting a predominantly plasma membrane localization of the receptor. Similarly, nerve fibers and cells in the submucosal and myenteric plexus were stained for sst2A. Antibody preabsorption with 100 nmol/L antigen peptide abolished staining in all of these tissues, and immunohistochemical staining correlated with the labeling observed after receptor autoradiography using the sst2-preferring radioligand 125I-[Tyr3]octreotide. Cytoplasmic immunostaining was detected in gastrointestinal smooth muscle cells and was inhibited by antibody pre-absorption with antigen peptide. However, 125I-[Tyr3]octreotide autoradiography was negative, and Western blots showed no band at the usual 70-90 kDa location for sst2A. Instead, a band was observed at 205 kDa. This band comigrated with the rabbit myosin standard, which was also stained with R2-88, although antibody sensitivity for myosin was less than 0.002% of that for the sst2A receptor. Rigorous computer-based sequence analysis demonstrated the peptide sequence chosen for antibody production was unique. Moreover, standard sequence alignment protocols were unable to identify the sequences in myosin responsible for the observed reactivity with the R2-88 antiserum. The observed cross-reactivity emphasizes the need for extensive controls to prove the specificity of immunostaining for such low abundance proteins as receptors even when the peptide sequence chosen for antibody production is unique. This study demonstrates for the first time the presence of specific sst2A receptor protein by immunohistochemistry in the human gastrointestinal lymphatic and nervous components, but not in gastrointestinal circular and longitudinal smooth muscle.

Neurotensin receptors in human neoplasms: high incidence in Ewing's sarcomas

Receptors for regulatory peptides, such as somatostatin or vasoactive intestinal peptide (VIP), expressed at high density by neoplastic cells, can be instrumental for tumor diagnosis and therapy. Little is known about the expression of neurotensin receptors in human tumors. In the present study, 464 human neoplasms of various types were investigated for their neurotensin receptor content by in vitro receptor autoradiography on tissue sections using 125I-[Tyr3]-neurotensin as radioligand. Neurotensin receptors were identified and localized in tumor cells of 11/17 Ewing's sarcomas, 21/40 meningiomas, 10/23 astrocytomas, 5/13 medulloblastomas, 7/24 medullary thyroid cancers and 2/8 small cell lung cancers. They were rarely found in non-small cell lung cancers and breast carcinomas; they were absent in prostate, ovarian, renal cell and hepatocellular carcinomas, neuroendocrine gut tumors, pituitary adenomas, schwannomas, neuroblastomas and lymphomas. When present, the receptors bound with nanomolar affinity neurotensin and acetyl-neurotensin-(8-13), with lower affinity neuromedin N, diethylenetriamine penta-acetic acidneurotensin-(8-13) and SR 48692, but not neurotensin-(1-11). They were all of the NT1 type, without high affinity for levocabastine. Further, in 2 receptor-positive Ewing's sarcomas, neurotensin mRNA was detected by in situ hybridization techniques. Since neurotensin is known to stimulate cell proliferation, the presence of neurotensin receptors in human neoplasia may be of biological relevance, possibly as an integrative part of an autocrine feedback mechanism of tumor growth stimulation.

Receptor autoradiographic evaluation of cholecystokinin, neurotensin, somatostatin and vasoactive intestinal peptide receptors in gastro-intestinal adenocarcinoma samples: where are they really located?

Receptors for cholecystokinin (CCK), gastrin, neurotensin, somatostatin and vasoactive intestinal peptide (VIP) are over-expressed in several human tumors, where they have diagnostic and therapeutic implications. Since reports on the expression of these peptide receptors in primary gastric and colonic adenocarcinomas are either non-existent or conflicting, a detailed evaluation with particular emphasis on the tissue localization was undertaken. CCK-A, CCK-B, neurotensin, somatostatin and VIP receptors were localized by in vitro receptor autoradiography with iodinated radioligands on histological sections of surgical samples of 27 gastric and 25 colonic adenocarcinomas. CCK-A, CCK-B and neurotensin-1 receptors were found in a minority of both tumor types. Somatostatin receptors were found in 18/27 gastric and 2/25 colonic cancers. VIP receptors were found in 14/26 gastric and 23/25 colonic cancers; subtype characterization suggests VIP1 receptors. In addition, resected tumor samples contained non-malignant tissues (mucosa, smooth muscle, nerves or vessels) with high amounts of the various peptide receptors. Therefore, regulatory peptide receptors are expressed differentially in gastric and colonic cancers but also very frequently in "contaminating" non-malignant tissues. Since results using morphological techniques are superior to those using homogenates, we recommend that localization of these receptors to the tissues should always be attempted, to minimize receptor over-estimation in tumors and to prevent spurious results.

High expression of somatostatin receptor subtype 2 (sst2) in medulloblastoma: implications for diagnosis and therapy

Medulloblastoma is a pediatric malignancy, which arises in cerebellum. The neuropeptide somatostatin (SS-14) is a neuromodulator and growth regulator in the developing cerebellum. SS-14 has previously been demonstrated in medulloblastomas with immunohistochemical techniques, but somatostatin receptor (sst) expression is less well understood. We analyzed somatostatin and sst subtype expression (sst1-5) in central primitive neuroectodermal tumors (cPNET), including 23 medulloblastomas, 6 supratentorial PNET, and 10 cPNET cell lines. The expression of SS-14 and sst genes in cPNET was compared with expression of these genes in 17 tumors of the Ewing's sarcoma family of tumors using reverse transcriptase-PCR, Southern hybridization, quantitative in vitro receptor autoradiography, and competitive membrane binding assays. The sst1 subtype was expressed in similar frequency in cPNET (83%) and Ewing's sarcoma family of tumors (71%). Nine of the 10 cell lines and 76% of the cPNET expressed mRNA for sst2 compared with 35% of the Ewing's sarcoma family of tumors. High-affinity binding of SS-14 was demonstrated in cPNET by quantitative autoradiography as well as by competitive binding assays. The cPNET cell line D283 Med bound SS-14 and octreotide with high affinity; SS-14 inhibited proliferation of D283 Med cells as measured by a decrease in [3H]thymidine uptake. We conclude that both sst1 and sst2 are highly expressed in cPNET and suggest that somatostatin may regulate proliferation and differentiation in these developmental tumors.

Locoregional regulatory peptide receptor targeting with the diffusible somatostatin analogue 90Y-labeled DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC): a pilot study in human gliomas

Human gliomas, especially of low-grade type, have been shown to express high-affinity somatostatin receptor type 2 (J-C. Reubi et al., Am. J. Pathol, 134: 337-344, 1989). We enrolled seven low-grade and four anaplastic glioma patients in a pilot study using the diffusible peptidic vector 90Y-labeled DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC) for receptor targeting. The radiopharmakon was locoregionally injected into a stereotactically inserted Port-a-cath. DOTATOC competes specifically with somatostatin binding to somatostatin receptor type 2 in the low nanomolar range as shown by a displacement curve of 125I-[Tyr3]-octreotide in tumor tissue sections. Diagnostic (111)In-labeled DOTATOC-scintigraphy following local injection displayed homogeneous to nodular intratumoral vector distribution. The cumulative activity of regionally injected peptide-bound 90Y amounted to 370-3300 MBq, which is equivalent to an effective dose range between 60 +/- 15 and 550 +/- 110 Gy. Activity was injected in one to four fractions according to tumor volumes; 1110 MBq of 90Y-labeled DOTATOC was the maximum activity per single injection. We obtained six disease stabilizations and shrinking of a cystic low-grade astrocytoma component. The only toxicity observed was secondary perifocal edema. The activity:dose ratio (MBq:Gy) represents a measure for the stability of peptide retention in receptor-positive tissue and might predict the clinical course. We conclude that SR-positive human gliomas, especially of low-grade type, can be successfully targeted by intratumoral injection of the metabolically stable small regulatory peptide DOTATOC.

Vasoactive intestinal peptide (VIP) and VIP receptors: gene expression and growth modulation in medulloblastoma and other central primitive neuroectodermal tumors of childhood

Vasoactive intestinal peptide (VIP) is a neuromodulator and growth regulator in the developing nervous system. We analyzed 10 primitive neuroectodermal tumor (PNET) cell lines, 29 central PNET (cPNET) and 17 tumors of the Ewing's sarcoma/peripheral PNET family (ESFT) using reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern hybridization. Each of the 10 cell lines and 86.2% of cPNET expressed mRNA for VIP receptor 1 (VIPR1) compared to 52.9% of ESFT. VIPR2 was expressed in 75.8% of cPNET, in 28.6% of ESFT and in all 10 cell lines. cPNET demonstrated high-affinity binding of 125I-VIP on quantitative autoradiography and in competitive binding assays. VIP inhibited tumor cell proliferation in a dose-dependent manner in 5 of 7 PNET cell lines. We conclude that VIPR1 and VIPR2 are highly expressed in cPNET and demonstrate that VIP is a growth modulator in these tumors.