Radiolabeled peptides in diagnosis and tumor imaging: clinical overview

CAR T cells for brain tumors: Lessons learned and road ahead

Malignant brain tumors, including glioblastoma, represent some of the most difficult to treat of solid tumors. Nevertheless, recent progress in immunotherapy, across a broad range of tumor types, provides hope that immunological approaches will have the potential to improve outcomes for patients with brain tumors. Chimeric antigen receptors (CAR) T cells, a promising immunotherapeutic modality, utilizes the tumor targeting specificity of any antibody or receptor ligand to redirect the cytolytic potency of T cells. The remarkable clinical response rates of CD19-targeted CAR T cells and early clinical experiences in glioblastoma demonstrating safety and evidence for disease modifying activity support the potential of further advancements ultimately providing clinical benefit for patients. The brain, however, is an immune specialized organ presenting unique and specific challenges to immune-based therapies. Remaining barriers to be overcome for achieving effective CAR T cell therapy in the central nervous system (CNS) include tumor antigenic heterogeneity, an immune-suppressive microenvironment, unique properties of the CNS that limit T cell entry, and risks of immune-based toxicities in this highly sensitive organ. This review will summarize preclinical and clinical data for CAR T cell immunotherapy in glioblastoma and other malignant brain tumors, including present obstacles to advancement.

Perforated Goblet Cell Carcinoid Tumors of the Appendix: Navigating the Management Conundrum

Appendix is the most common site of occurrence for a goblet cell carcinoid tumor. A diagnosis of an appendiceal goblet cell carcinoid is made in retrospect the majority of the time. These tumors are best treated with a right hemicolectomy and adjuvant therapies tailored according to the presence or absence of residual disease. Presentation as a perforated appendix is seen in 16% of these tumors. The natural history and the ideal management strategy in such a scenario are not well described. In those with peritoneal spread cytoreductive surgery with HIPEC (hyperthermic intraperitoneal chemotherapy) offers the best disease-free and progression-free survival. Close follow-up with cross-sectional imaging helps in identifying recurrences at the earliest. Multimodality management involving patient participation in every aspect of care accomplishes high-value care in the treatment of these tumors.

Appendiceal Goblet Cell Carcinoids: Management Considerations from a Reference Peritoneal Tumour Service Centre and ENETS Centre of Excellence

BACKGROUND

Appendix goblet cell carcinoids are known to share histological features of adenocarcinoma and neuroendocrine tumours. Due to their low incidence, quality evidence is lacking for the management of these patients.

METHODS

We performed a single-centre retrospective study of patients with a confirmed diagnosis of appendiceal goblet cell carcinoid (GCC; 1996-2014). Patients were divided into curative intent (CI) and palliative intent (PI) cohorts. Our primary end point was overall survival (OS).

RESULTS

Seventy-four patients were eligible; 76% were treated with CI [surgery only (36%), cytoreductive surgery (CRS) and hyperthermic intra-peritoneal chemotherapy (HIPEC; 36%), adjuvant chemotherapy (20%) and a combination of CRS and HIPEC followed by adjuvant chemotherapy (9%)], and 23% had advanced-stage disease amenable to palliative treatment (chemotherapy or supportive care) only. Completion right hemicolectomy, performed in 64% of the CI cohort, did not impact on the relapse rate or disease-free survival. FOLFOX chemotherapy was used in both the adjuvant and palliative settings; safety was as expected, and we observed a high rate (60%) of disease control in the palliative cohort. The estimated median OS (all patients), disease-free survival (CI patients) and progression-free survival (PI patients) were 52.1 (95% CI 29.4-90.3), 75.9 (26.6-not reached) and 5.3 (0.6-5.7) months, respectively. Age and stage were independent factors associated with OS in the multivariable analysis. Tang classification showed a trend for impact on OS. No benefit from specific adjuvant approach was identified; however, selection bias for treatment approach was observed.

CONCLUSION

Prospective trials are needed to define optimal approaches in GCC. All GCC patients should be managed by specialized centres due to their esoteric behaviour; we provide management considerations based on our experience and conclusions.

VPAC2 receptor expression in human normal and neoplastic tissues: evaluation of the novel MAB SP235

The vasoactive intestinal peptide receptor 2 (VPAC2) is widely distributed throughout the body and is also overexpressed in a variety of human neoplastic tissues. However, little is known about its precise tissue distribution, regulation and function, which is in part be due to the lack of specific monoclonal anti-VPAC2 antibodies. In this study, we extensively characterised the novel rabbit monoclonal anti-VPAC2 antibody (clone SP235) using transfected cells and mouse, rat and human tissues. SP235 was then subjected to a comparative immunohistochemical study on a series of 167 histological specimens from formalin-fixed, paraffin-embedded human tumours and adjacent normal tissues. SP235 detected a broad band migrating at a molecular weight of 50-70 kDa in western blotting analyses of various mouse tissues as well as VPAC2- but not VPAC1-transfected human embryonic kidney 293 cells. SP235 yielded an efficient immunostaining of distinct cell populations in human tissue samples with a predominance of plasma membrane staining, which was completely abolished by preadsorption with its immunising peptide. SP235 immunohistochemistry detected VPAC2 receptors in lymphocytes present in spleen, tonsils, lymph nodes and Peyer's patches, chief cells of gastric mucosa, exocrine and endocrine pancreas, kidney tubules and blood vessels. In addition, VPAC2 was observed in thyroid, gastric and lung carcinomas, pancreatic adenocarcinomas, sarcomas and neuroendocrine tumours. SP235 may prove of great value in the identification of VPAC2 receptors during routine histopathological examination. VPAC2 visualisation with this simple and rapid immunohistochemical method will facilitate identification of candidate tumours for vasoactive intestinal peptide (VIP)-based diagnostics or therapeutic interventions.

[Radioguided surgery in neuroendocrine tumors. A review of the literature]

Radioguided surgery can be a useful technique in the localization of neuroendocrine tumors. It detects more and smaller lesions compared to pre-surgical imaging and intraoperative digital palpation by the surgeon. It detects residual lesions and also indicates the shortest access route to the lesion. Nevertheless, its use has not become widespread because of technical difficulties. There is a limited number of published series, a lack of standardized protocol because of the great variability regarding type of radiopharmaceutical, dose of radiotracer, timing between injection and surgery. In this paper, we review these issues, describing the experience of different authors in diverse tumors.

Goblet cell carcinoids of the appendix

Goblet cell carcinoid (GCC) tumors are a rare subgroup of neuroendocrine tumors almost exclusively originating in the appendix. The tumor most often presents in the fifth or sixth decade with a clinical picture of appendicitis or in advanced cases an abdominal mass associated with abdominal pain. Histologically tumors are most often positive for chromogranin A and synaptophysin, however, less homogenous than for classic appendix carcinoids. The malignant potential is higher than that for the classic appendix carcinoids due to local spread and distant metastases at diagnosis and the proliferation markers (Ki67 index) may determine prognosis. Octreotide receptor scintigraphy is usually negative while CT/MRI scans may be useful. Chromogranin A is usually negative and other biomarkers related to the mucinous component or the tumor (CEA, CA-19-9, and CA-125) may be used. Surgery is the main treatment with appendectomy and right hemicolectomy while patients with disseminated disease should be treated with chemotherapy. Overall 5-year survival is approximately 75%. The diagnosis and treatment of GCC tumorss should be restricted to high volume NET centers in order to accumulate knowledge and improve survival in GCC NET patients. The aim of this paper is to update on epidemiology, clinical presentation, and diagnostic markers including Ki67 index, treatment, and survival.

Flexible or fixed: a comparative review of linear and cyclic cancer-targeting peptides

Peptides can serve as versatile cancer-targeting ligands and have been used for clinically relevant applications such as cancer imaging and therapy. A current and long-standing focus within peptide research is the creation of structurally constrained peptides generated through cyclization. Cyclization is envisioned to enhance the selective binding, uptake, potency and stability of linear precursors. This review compares closely related linear and cyclic peptides in these respects. Peptide cyclization generally improves the selective binding and stability of linear precursors; however, not all cyclization strategies and constrained geometries enhance these properties to the same extent. In some instances, linear analogues actually have better cancer-targeting properties compared with their cyclic counterparts. Although cyclization does not necessarily improve the cancer-targeting properties of linear analogues, cyclic peptides may obtain properties that allow them to be used for additional applications. This review aims to convey the advantages and limitations of cyclic cancer-targeting peptides.

Review of the pathogenesis, diagnosis, and management of type I gastric carcinoid tumor

Gastric carcinoid tumors comprise 7% of all gastrointestinal carcinoids and have significantly increased in incidence over the past few decades. Seventy to 80% of gastric carcinoids are type I, which usually are clinically asymptomatic and found incidentally at endoscopic evaluation for abdominal pain or anemia. In this review, advances in understanding the pathophysiology of type I gastric carcinoid are highlighted. In addition, various current diagnostic and treatment options are discussed. Although type I carcinoids generally hold a benign course, rigorous investigation is needed to ensure accurate diagnosis and optimal treatment. This includes appropriate diagnostic procedures and imaging and accurate staging of tumor. Tumor size, depth of invasion, presence of metastasis, and the tumor's gastrin dependency dictate treatment options. Appropriate treatments can consist of endoscopic resection, antrectomy, medical management, or frequent follow-up. This article provides a systematic method of evaluating and treating type I gastric carcinoid.

111In-pentetreotide scintigraphy: procedure guidelines for tumour imaging

This document provides general information about somatostatin receptor scintigraphy with (111)In-pentetreotide. This guideline should not be regarded as the only approach to visualise tumours expressing somatostatin receptors or as exclusive of other nuclear medicine procedures useful to obtain comparable results. The aim of this guideline is to assist nuclear medicine physicians in recommending, performing, reporting and interpreting the results of (111)In-pentetreotide scintigraphy.

Molecular imaging in neuroendocrine tumors: molecular uptake mechanisms and clinical results

Neuroendocrine tumors can originate almost everywhere in the body and consist of a great variety of subtypes. This paper focuses on molecular imaging methods using nuclear medicine techniques in neuroendocrine tumors, coupling molecular uptake mechanisms of radiotracers with clinical results. A non-systematic review is presented on receptor based and metabolic imaging methods. Receptor-based imaging covers the molecular backgrounds of somatostatin, vaso-intestinal peptide (VIP), bombesin and cholecystokinin (CCK) receptors and their link with nuclear imaging. Imaging methods based on specific metabolic properties include meta-iodo-benzylguanide (MIBG) and dimercapto-sulphuric acid (DMSA-V) scintigraphy as well as more modern positron emission tomography (PET)-based methods using radio-labeled analogues of amino acids, glucose, dihydroxyphenylalanine (DOPA), dopamine and tryptophan. Diagnostic sensitivities are presented for each imaging method and for each neuroendocrine tumor subtype. Finally, a Forest plot analysis of diagnostic performance is presented for each tumor type in order to provide a comprehensive overview for clinical use.

Circulating markers for endocrine tumours of the gastroenteropancreatic tract

The diffuse endocrine system (DES) includes a wide range of secretory cells that may be the source of tumours. Gastroenteropancreatic endocrine (GEP) tumours arising within the DES secrete a variety of peptides and amines that are found in the circulation and are responsible for the syndromes associated with these tumours. In this review, the most common tumours of the GEP tract are outlined and the circulating products of these tumours identified. Where differential diagnosis is difficult these points are addressed. The peptides most commonly secreted by GEP neuroendocrine tumours are identified and described and their biological activities are discussed. Current methods available for measurement of these peptides are described. Attention is drawn towards molecular specificity where appropriate, as many pancreatic and gut peptides fall within families which show considerable homology, such as the tachykinin family or the glucagon family. Other peptides such as gastrin circulate in multiple molecular forms. This homology and diversity may cause difficulty in the interpretation of peptide measurements in the clinical situation if assays are not specific.

A “false positive” octreoscan in ileal Crohn’s disease

We present a case report of a patient with a suspicious ileal carcinoid tumour. Clinical examination as well as computer tomography (CT) scan suggested a tumour. Octeotride scan showed uptake in the same bowel loop reported as pathological in CT. The patient underwent surgery and biopsy which reported Crohn’s disease (CD). The interest in the case is due to the fact that this is, to the best of our knowledge, the second report of Crohn’s disease as a cause of false positive octeotride scan. Unfortunately, no somatostatin receptors could be found in the sample, so further studies should be performed.

Insulinoma in a third-trimester pregnant woman combined with pre-eclampsia: a case report and review of the diagnostic strategies

Insulinomas are rare neuroendocrine tumors with an incidence of 4 per 1,000,000 person-years, being even rarer during pregnancy. During pregnancy most cases are recognized or become symptomatic during the first trimester. A 29-year-old woman, primigravida, was hospitalized in the 38th gestational week due to slurred speech, weakness and slow reaction patterns. An electroencephalogram and computed tomography scan of the brain and blood samples were normal. Blood pressure was 170-145/110-95 mmHg, albuminuria was moderate and there was moderate edema of the ankles. Labor started spontaneously the third day, 62 h after of hospitalization, and the patient gave birth to a healthy girl with no neonatal problems. Fourteen hours after delivery, the patient became comatose and developed universal clonic seizures. At the same time plasma glucose was <1.1 mmol/l and the patient responded immediately to intravenous glucose. The patient was managed with frequent small meals and continuous intravenous glucose. Postpartum testing was consistent with insulinoma and diazoxide treatment was initiated. Endoscopic ultrasound with biopsy showed an insulinoma in the head of the pancreas. During surgical exploration, four separate insulinomas were removed from the head of the pancreas. The hypoglycemic episodes resolved and the glucose levels normalized. Following biochemical diagnosis of insulinoma, diagnostic imaging procedures encountered include endoscopic ultrasonography, magnetic resonance imaging and digital subtraction angiography. Of isotopic procedures, somatostatin receptor scintigraphy (Octreoscan) and newer receptor binding ligands can be used in non-pregnant women. Intraoperative ultrasonography seems mandatory. The present case demonstrates that seizure disorders in non-diabetic pregnant women may be caused by hyperinsulinemia-induced hypoglycemia due to insulinoma.

Occult sporadic insulinoma: Localization and surgical strategy

Insulinomas continue to pose a diagnostic challenge to physicians, surgeons and radiologists alike. Most are intrapancreatic, benign and solitary. Biochemical diagnosis is obtained and imaging techniques to localize lesions continue to evolve. Surgical resection is the treatment of choice. Despite all efforts, an occult insulinoma (occult insulinoma refers to a biochemically proven tumor with indeterminate anatomical site before operation) may still be encountered. New localization preoperative techniques decreases occult cases and the knowledge of the site of the mass before surgery allows to determine whether enucleation of the tumor or pancreatic resection is likely to be required and whether the tumor is amenable to removal via a laparoscopic approach. In absence of preoperative localization and intraoperative detection of an insulinoma, blind pancreatic resection is not recommended.

OctreoScan positive Crohn's disease mimicking an ileal carcinoid tumor

Somatostatin receptors have been identified in many tissues throughout the human body. Alterations in the expression of somatostatin receptors have been reported in many disease states including both tumorous and nontumorous conditions. Somatostatin receptor scintigraphy utilizing OctreoScan (Mallinckrodt Medical, Inc., St. Louis, MO), a radiolabled form of octreotide, has been reported to be a highly sensitive imaging technique for identifying pathology, such as neuroendocrine tumors, that are somatostatin receptor dense. Unfortunately, many conditions cause an increase in the quantity of somatostatin receptors and therefore may cause false positive Octreoscans. In this report, we discuss the alterations in somatostatin receptors that occur with Crohn's disease and describe a case of an OctreoScan-positive inflammatory mass mimicking a carcinoid tumor.

Radio-guided surgery in neuroendocrine tumors

The majority of Neuroendocrine tumors (NET) express somatostatin (SS) receptors, and thus can be successfully targeted with radiolabeled SS analogs in vivo. Somatostatin receptor scintigraphy (SRS) with (111)In-DTPA Octreotide is the main imaging technique for evaluation of NETs. Radio-guided surgery for NETs, therefore, primarily utilizes (111)In-DTPA Octreotide tumor localization mechanism and kinetics. Somatostatin analog radiopharmacy continues to evolve to include the development of more selective and higher affinity analogs and PET tracers. These changes are expected to open new venues for radio-guided surgery technology.

Radio-guided surgery with the use of [99mTc-EDDA/HYNIC]octreotate in intra-operative detection of neuroendocrine tumours of the gastrointestinal tract

PURPOSE

Radio-guided surgery (RGS) is an intra-operative localising technique which enables identification of tissue "marked" by a specific radiotracer injected before surgery. It is mainly used for sentinel node mapping and for detection of parathyroid adenomas and other tumours, including neuroendocrine tumours of the gastrointestinal tract (GEP-NET). The aim of this study was to determine whether intra-operative radio-detection with the use of [(99m)Tc-EDDA/HYNIC]octreotate, a new somatostatin analogue, is able to reveal an unknown primary and secondary sites, thereby improving surgical treatment and the final outcome of GEP-NET.

METHODS

The study group included nine patients with suspected GEP-NET (four carcinoids, five pancreatic NET) localised with somatostatin receptor scintigraphy (with [(99m)Tc-EDDA/HYNIC]octreotate), who had negative results on other pre-operative imaging tests. At surgery, suspected tumours were measured in situ and ex vivo and precise exploration of the abdominal cavity was performed with the intra-operative scintillation detector (Navigator).

RESULTS

Intra-operative gamma counting localised three carcinoids. In one patient SRS was false positive (owing to inflammatory infiltration). Compared with SRS, RGS revealed additional lymph node metastases in one case. RGS resulted in successful localisation of all pancreatic NET (the smallest lesion was 8 mm in diameter).

CONCLUSION

[(99m)Tc-EDDA/HYNIC]octreotate SRS followed by RGS is a promising technique to improve the rate of detection and efficacy of treatment of GEP-NET, especially in the presence of occult endocrine tumours. The imaging properties of [(99m)Tc-EDDA/HYNIC]octreotate and the 1-day imaging protocol offer opportunities for more widespread application of this tracer followed by RGS in oncology.

Integrating noninvasive molecular imaging into molecular medicine: an evolving paradigm

Molecular imaging is a rapidly emerging field, providing noninvasive visual quantitative representations of fundamental biological processes in intact living subjects. Fundamental biomedical research stands to benefit considerably from advances in molecular imaging, with improved molecular target selection, probe development and imaging instrumentation. The noninvasiveness of molecular imaging technologies will also provide benefit through improved patient care. Molecular imaging endpoints can be quantified, and therefore are particularly useful for translational research. Integration of the two disciplines of molecular imaging and molecular medicine, combined with systems-biology approaches to understanding disease complexity, promises to provide predictive, preventative and personalized medicine that will transform healthcare.

Pre-clinical evaluation of 2,3-dimercaptosuccinic acid as a radiation nephrotoxicity protective agent during radiopeptide therapy of neuroendocrine malignancy

AIM

To determine if dimercaptosuccinic acid (DMSA), an agent originally developed as a safe non-toxic antidote for heavy metal poisoning, would be useful as a kidney radiation dose reduction agent in patients undergoing radiopeptide therapy for cancer.

METHODS

Thirty-six adult male Wistar rats were injected via the penile vein with 10 MBq of 177Lu-DOTA-tyr(3)-octreotate. At 30 min after the radiopeptide injection, 18 of the animals (intervention group) were injected with 0.15 mg x g(-1) of DMSA (i.p.). Samples were collected for gamma counting at 24 (n=12), 48 (n=12) and 72 h (n=12) after administration of the radiopeptide. At each time point, the percentage injected dose per gram of tissue in each sample of the six control animals was compared with that of the six animals from the DMSA injection regimen.

RESULTS

The i.p. injection of 0.15 mg x g(-1) of DMSA 30 min following the administration of the 177Lu-DOTATATE reduced the mean (95% CI) kidney retention of radiopeptide by 15.6% (2.6-24.6) at 72 h while not significantly affecting uptake in other organs. Statistical testing of the difference between the two groups of animals (DMSA versus controls) at 72 h post-administration of the radiopeptide indicated only a 3% chance that the magnitude of the reduction in kidney radiopeptide retention observed would be expected due to natural variation (i.e., if there was no difference between the groups).

CONCLUSION

This study has indicated that DMSA has the potential to selectively reduce radiopeptide kidney retention. Further work is necessary to determine the most effective dose of DMSA and the most effective timing regimen, and to examine the clinical efficacy of several other chelating agents.

Goblet cell carcinoid tumors (adenocarcinoid) of the appendix

PURPOSE

Goblet cell appendiceal carcinoids represent rare tumors that exhibit histologic features of both adenocarcinomas and neuroendocrine tumors. We present the long-term results of a series of 15 patients, focusing on clinical manifestations, diagnosis, and management.

METHODS

Eight male and seven female patients (median age, 52.8 years) were included. Final diagnosis was confirmed by histology. Patients were evaluated clinically, biochemically, and radiologically every four months. Median follow-up was 30 months.

RESULTS

The majority of patients (7/15) presented with symptoms compatible with acute appendicitis. Right hemicolectomy was performed in all except one, who subsequently developed metastases. Three patients had metastases at previous diagnosis. Plasma chromogranin-A was slightly elevated in two of them, while urinary 5-hydroxy-indol-acetic acid was normal. (111)Indium-labeled octreotide scintigraphy was positive only in two of the four patients with metastases. Ki67 index was greater than 20 percent in all of them, while in only one with local tumor. Combination chemotherapy with either cisplatin plus etoposide or with 5-fluorouracil, cisplatin, and streptozotocin was administered to all patients with metastases resulting in temporary stabilization of disease. Twelve patients are alive, while three died of their disease 9, 13, and 14 months after diagnosis.

CONCLUSIONS

The diagnostic value of chromogranin-A, urinary 5-hydroxy-indol-acetic acid, and (111)Indium-labeled octreotide scintigraphy seems to be limited in these tumors. Ki67 index appears to predict tumor behavior. Right hemicolectomy may reduce the risk of developing metastases. Chemotherapy may have efficacy in metastatic disease, however, more data are required to determine this and the optimal regimen.

Imaging of neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare neoplasms, which are characterized by the presence of neuroamine uptake mechanisms and/or peptide receptors at the cell membrane and these features constitute the basis of the clinical use of specific radiolabeled ligands, both for imaging and therapy. Radiolabeled metaiodobenzylguanidine (MIBG) was the first radiopharmaceutical used to specifically depict and localize catecholamine-secreting tumors (pheochromocytomas, paragangliomas, and neuroblastomas) and is still regarded as a first-choice imaging technique for diagnosis and follow-up; in patients with malignant disease, MIBG scintigraphy is an essential step to select patients for (131)I-MIBG therapy. Scintigraphy with (111)In- or (99m)Tc-labeled somatostatin analogs has become the main imaging technique for NETs, particularly those expressing a high density of somatostatin receptors, such as gastroenteropancreatic tumors; this procedure is used routinely for localizing the primary tumor, evaluating disease extension, monitoring the effect of treatment and for selecting patients for radioreceptor therapy. Since the recent development of hybrid machines, it has been possible to obtain images that simultaneously hold both anatomic (computed tomography [CT]) and functional (single-photon emission computed tomography [SPECT] or positron emission tomography [PET]) information, with great impact on diagnostic accuracy. Significant improvements have been made during the past few years with the development of highly specific radiopharmaceuticals for PET studies that reflect the different metabolic pathways of NETs, such as glucose metabolism ((18)F-fluorodeoxyglucose), the uptake of hormone precursors ((11)C-5-hydroxytryptophan, (11)C- or (18)F-dihydroxyphenylalanine, (18)F-fluorodopamine), the expression of receptors ((68)Ga-labeled somatostatin analogs), as well as the synthesis, storage, and release of hormones ((11)C-hydroxyephedrine and others). Among these radiopharmaceuticals, (68)Ga-labeled somatostatin analogs are increasingly used in specialized centers in Europe for PET and PET/CT imaging and show very promising results with high diagnostic sensitivity. New somatostatin analogs with different receptor affinity as well as other peptides are currently under investigation and will further improve our diagnostic and therapeutic capabilities in the future.

The management of insulinoma

BACKGROUND

Insulinomas are rare tumours. Their clinical presentation, localization techniques and operative management were reviewed.

METHODS

An electronic search of the Medline, Embase and Cochrane databases was undertaken for articles published between January 1966 and June 2005 on the history, presentation, clinical evaluation, use of imaging techniques for tumour localization and operative management of insulinoma.

RESULTS AND CONCLUSION

Most insulinomas are intrapancreatic, benign and solitary. Biochemical diagnosis is obtained during a supervised 72-h fast. Non-invasive preoperative imaging techniques to localize lesions continue to evolve. Intraoperative ultrasonography can be combined with other preoperative imaging modalities to improve tumour detection. Surgical resection is the treatment of choice. In the absence of preoperative localization and intraoperative detection of an insulinoma, blind pancreatic resection is not recommended.

The progress and promise of molecular imaging probes in oncologic drug development

As addressed by the recent Food and Drug Administration Critical Path Initiative, tools are urgently needed to increase the speed, efficiency, and cost-effectiveness of drug development for cancer and other diseases. Molecular imaging probes developed based on recent scientific advances have great potential as oncologic drug development tools. Basic science studies using molecular imaging probes can help to identify and characterize disease-specific targets for oncologic drug therapy. Imaging end points, based on these disease-specific biomarkers, hold great promise to better define, stratify, and enrich study groups and to provide direct biological measures of response. Imaging-based biomarkers also have promise for speeding drug evaluation by supplementing or replacing preclinical and clinical pharmacokinetic and pharmacodynamic evaluations, including target interaction and modulation. Such analyses may be particularly valuable in early comparative studies among candidates designed to interact with the same molecular target. Finally, as response biomarkers, imaging end points that characterize tumor vitality, growth, or apoptosis can also serve as early surrogates of therapy success. This article outlines the scientific basis of oncology imaging probes and presents examples of probes that could facilitate progress. The current regulatory opportunities for new and existing probe development and testing are also reviewed, with a focus on recent Food and Drug Administration guidance to facilitate early clinical development of promising probes.

111Indium Pentetreotide Imaging in the Evaluation of Head and Neck Tumors

OBJECTIVES/HYPOTHESIS

Peptide receptor imaging with Indium pentetreotide is useful in the diagnosis of diffuse neuroendocrine system tumors (DNEST) of the head and neck. Uses of Indium pentetreotide scintigraphy include tumor and metastases detection, familial tumor screening, and surveillance for recurrence. Using target to background ratios (TBR) could generate a comparative scale for these tumors.

STUDY DESIGN

A retrospective study evaluated the size, TBR, conventional imaging, and outcomes of patients imaged with Indium pentetreotide scintigraphy for suspected head and neck DNEST.

METHODS

Patients with head and neck tumors imaged by Indium pentetreotide scintigraphy during a nine-year period were reviewed. Data analyzed were age, sex, scintigraphy, pathology, and conventional radiology. Tumor data included dimension, multiplicity, metastases, and tumor and brain counts.

RESULTS

Fifty-three patients underwent 58 scans. The sensitivity and specificity were 93% and 92%. Several different DNEST were successfully evaluated, including familial paragangliomas and multiple paragangliomas. TBRs were variable depending on type of DNEST.

CONCLUSIONS

Indium pentetreotide scintigraphy is accurate in determining the presence of paragangliomas, carcinoid tumors, esthesioneuroblastomas, small cell neuroendocrine tumors, andmetastases. It is an excellent surveillance tool. Screening patients for familial paragangliomas can be accomplished. No reliable comparative scale to distinguish amongst the various DNEST could be developed using TBR.

Immunocytochemical identification of VPAC1, VPAC2, and PAC1 receptors in normal and neoplastic human tissues with subtype-specific antibodies

Human tumors frequently overexpress receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP). However, none of the VIP/PACAP receptor proteins has been visualized individually in human tumors. Here, we developed and characterized a panel of antipeptide antibodies to the carboxyl-terminal regions of the VIP/PACAP receptor subtypes vasoactive intestinal peptide receptor (VPAC)1, VPAC2, and pituitary adenylate cyclase-activating peptide receptor (PAC)1. Specificity of the antisera was shown by the following: (1) detection of broad bands migrating at Mr 50,000 to 70,000 in Western blots of membranes from receptor-expressing tumors and receptor-transfected cells; (2) cell surface staining of VIP/PACAP receptor-transfected cells; (3) translocation of VIP/PACAP receptor immunostaining in transfected cells after agonist exposure; and (4) abolition of tissue immunostaining by preadsorbtion of the antibodies with their immunizing peptides. The distribution of VIP/PACAP receptors was investigated in 98 human tumors and their tissues of origin. VPAC1, VPAC2, and PAC1 receptors were clearly located at the plasma membrane of the tumor cells in a variety of human neoplasms. In the gastrointestinal tract, VPAC1 receptor immunoreactivity was abundant in the mucosa and myenteric neurons; VPAC2 receptor immunoreactivity was detected in neuroendocrine cells, blood vessels, and smooth muscle; and PAC1 receptor immunoreactivity was found in myenteric neurons. This is the first localization of all of the VIP/PACAP receptor subtypes in human formalin-fixed, paraffin-embedded tissues. VIP/PACAP receptor visualization with this simple and rapid immunohistochemical method will facilitate identification of tumors with a sufficient receptor overexpression for diagnostic or therapeutic intervention.

Weaving single photon imaging into new drug development

The specific aim of this review is to assess the potential contribution of single photon emitting radiopharmaceutical technologies to new drug development. For each phase of therapeutic drug development, published literature was sought that shows single photon emitters can add value by quantifying pharmacokinetics, visualizing mechanisms of drug action, estimating therapeutic safety indices, or measuring dose-dependent pharmacodynamic effects. Not any published reports were found that describe using nuclear medicine techniques to help manage the progress of a new drug development program. As a consequence, most of the case in favor of weaving single photon imaging into the process had to be built on extrapolations from studies that showed feasibility post hoc. The strongest evidence of potential value was found for drug candidates that hope to influence diseases characterized by cell proliferation or cell death, particularly in the fields of oncology, cardiology, nephrology, and inflammation. Receptor occupancy studies were observed to occasionally offer unique advantages over analogous studies with positron emission tomography (PET). Enough hard data sets were found to justify the costs of using single photon imaging in a variety of new drug development paradigms.

Enteroendocrine tumors other than carcinoid: a review of clinically significant advances

Only relatively recently has there been an increased clinical recognition and characterization of the heterogeneous group of rare gastroenteropancreatic neuroendocrine neoplasms. Most have endocrine function and exhibit varying degrees of malignancy. This review summarizes the derivation of these tumors and the advances in their diagnosis and treatment over the past decade and a half. They are varied in their biological behavior and clinical courses and, depending on their cell type, can produce different hormones causing distinct clinical endocrine syndromes (insulinoma [hypoglycemia], gastrinoma [Zollinger-Ellison syndrome (ZES)], vasoactive intestinal peptideoma [VIPoma], watery diarrhea, hypokalemia-achlorhydria [WDHA], glucagonoma [glucagonoma syndrome], and so forth). In addition to surgery for cure or palliation (by excision and a variety of other cytoreductive techniques), they each are treated with anti-hormonal agents or drugs targeted to each tumor's specific product or its effects. The majority have benefited from the gut hormone-inhibiting action of somatostatin analogs. Because of their usual slow rate of growth it is recommended that, even when they are advanced and incurable, unlike in patients with common and more malignant cancers, patients with neuroendocrine tumors often can be palliated and appear to survive longer when managed with an active approach using sequential multimodality treatment. Advances in these various therapies are reviewed and the beneficial emergence of global self-help patient support groups is noted.

Preclinical Evaluation of New and Highly Potent Analogues of Octreotide for Predictive Imaging and Targeted Radiotherapy

Purpose: Molecular imaging and targeted radiotherapy are emerging fields in nuclear oncology. Five human somatostatin receptors (hsstr1-hsstr5) are known to be overexpressed to some degree on various tumors, sstr2 being the most important one. Clinically used somatostatin based radiopeptides target exclusively sstr2. The aim of this study was to develop novel analogues with a broader sstr profile for diagnostic (positron emission tomography and single-photon emission computed tomography) and radiotherapeutic applications.

Experimental Design: The following promising structures emerged from a parallel synthetic approach: [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA0),1-Nal3,Thr8]-octreotide (1, DOTA-NOC-ATE) and [DOTA0,BzThi3,Thr8]-octreotide (2, DOTA-BOC-ATE). The conjugates were labeled with cold and radioactive 111In. Pharmacologic properties were compared with [111In-DOTA,Tyr3]-octreotide ([111In-DOTA]-TOC).

Results: The receptor affinity profile showed high affinity of both peptides to hsstr2, hsstr3, and hsstr5 and some intermediate affinity to hsstr4, whereas [111In-DOTA]-TOC shows affinity only to sstr2. The internalization is fast in sstr2 expressing AR4-2J and in transfected sstr3 expressing human embryonic kidney 293 cells. Both radiopeptides internalize much more efficiently than [111In-DOTA]-TOC. Animal biodistribution studies showed very high and specific uptake of [111In]-1 and [111In]-2 in s.c. implanted AR4-2J tumors (Lewis rats) and in somatostatin receptor expressing normal tissues. The uptake was at least 2-fold higher in these tissues and in the tumor compared with [111In-DOTA]-TOC. In addition, the kidney uptake was significantly lower for both radiopeptides.

Conclusions: These data suggest that the novel radiopeptides are superior to [111In/90Y-DOTA]-TOC and show great promise for the clinical application in the imaging of somatostatin receptor–positive tumors and their targeted radiotherapy.

Clinical usefulness of 99mTc-EDDA/HYNIC-TOC scintigraphy in oncological diagnostics: a pilot study

The clinical usefulness of a new 99mTc-labeled somatostatin analogue has been studied from the standpoint of oncological diagnostics. The group of patients studied included 40 individuals with diagnosed malignant neoplasms (32 primary and 8 metastatic). Among the primary tumors were 7 pituitary adenomas (5 hormonally active and 2 inactive), 1 liposarcoma, 2 carcinoids, 1 breast carcinoma, and 21 cases of lung cancer (2 small cell and 19 non-small cell) were represented. The metastatic tumors consisted of: 3 malignant melanomas, 1 pheochromocytoma, 1 prostatic cancer, 1 leiomyosarcoma, 1 pancreatic carcinoma ectopically secreting ACTH, and 1 carcinoid of the thymus. The radiopharmaceutical, 99mTc-EDDA/HYNIC-octreotide, was i.v. administered at the activity of 740-925 MBq. The imaging was comprized of a whole-body scan and single photon emission computed tomography. Positive scintigrams were obtained in 4 of 5 hormonally active pituitary adenomas, in 1 of 2 cases of carcinoid, in liposarcoma, breast cancer, and all cases of small cell (SCLC) and non-small cell lung cancer (NSCLC). The neoplastic metastases were visualized in 2 of 3 cases of melanoma and in patients with pheochromocytoma, pancreatic carcinoma secreting ACTH, and thymic carcinoid. Scintigrams were negative in both hormonally inactive pituitary adenomas, in one case of metastatic malignant melanoma, leiomyosarcoma, and in cases of metastasis from the prostatic carcinomas. The results of this pilot study indicated that 99mTc-EDDA/HYNIC-TOC is a potentially useful radiopharmaceutical for the imaging of a wide range of primary and metastatic tumors. More detailed indications for the clinical usefulness of the new tracer for the imaging of selected tumor types require studies on much larger groups of patients. Special attention should be paid to the successful imaging of all cases of NSCLC.

Functional imaging of endocrine tumors: role of positron emission tomography

This article provides an update on functional imaging approaches for diagnostic localization of endocrine tumors, with emphasis on positron emission tomography (PET). [18F]Fluorodeoxyglucose PET scanning is now a widely accepted imaging approach in clinical oncology. Benefits include improved patient outcome facilitated by staging and monitoring of disease and better treatment planning. [18F]Fluorodeoxyglucose PET is also useful in some endocrine tumors, particularly in recurrent or metastatic thyroid cancer where the degree of accumulation of the radionuclide has prognostic value. However, this imaging approach does not take full advantage of the unique characteristics of endocrine tumors. Endocrine tumor cells take up hormone precursors, express receptors and transporters, and synthesize, store, and release hormones. These characteristics offer highly specific targets for PET. Radiopharmaceuticals developed for such approaches include 6-[18F]fluorodopamine, and [11C]hydroxyephedrine for localization of pheochromocytomas, [11C]5-hydroxytryptophan and [11C]L-dihydroxyphenylalanine for carcinoid tumors, and [11C]metomidate for adrenocortical tumors. These functional imaging approaches are not meant to supplant conventional imaging modalities but should be used conjointly to better identify specific characteristics of endocrine tumors. This represents a relatively new and evolving approach to imaging that promises to answer specific questions about the behavior and growth of endocrine tumors, their malignant potential, and responsiveness to different treatment modalities.

Scintigraphy with [111In]octreotide and 201Tl in a Hürthle cell thyroid carcinoma without detectable radio-iodine uptake. Report of a case and review of the literature

AIM

To describe the visualization of recurrent disease by [111In]octreotide and 201Tl scintigraphy in a patient with Hürthle cell thyroid carcinoma, increased thyroglobulin levels, and a negative radio-iodine total-body scan.

METHODS

Scintigraphy with [111In]octreotide and 201Tl was performed, and a local recurrence in the thyroid bed was detected which was excised by surgery.

RESULTS

On histology, the tumour proved to be a Hürthle cell carcinoma, and within the tumour somatostatin receptors were detected by RT-PCR.

CONCLUSION

Scintigraphy with [111In]octreotide and 201Tl is an alternative imaging method for the detection of residual disease in patients with a differentiated thyroid carcinoma having increased thyroglobulin levels and a negative radio-iodine total-body scan.

Imaging and therapy of tumors induced to express somatostatin receptor by gene transfer using radiolabeled peptides and single chain antibody constructs

The fields of radioimmunodetection and radioimmunotherapy began with an initial paradigm that a targeting molecule (eg, antibody) carrying a radioisotope had the potential of selectively imaging and delivering a therapeutic dose of radiation to tumor sites. A second paradigm was developed in which injection of the targeting molecule was separated from injection of a short-lived radioisotope-labeled ligand (so-called "pretargeting strategy"). This strategy has improved radioisotope delivery to tumors in animal models, enhanced radioimmune imaging in man, and therapeutic trials are in an early phase. We proposed a third paradigm to achieve radioisotopic localization at tumor sites by inducing tumor cells to synthesize a membrane expressed receptor with a high affinity for infused radiolabeled ligands. The use of gene transfer technology to induce expression of high affinity membrane receptors can enhance the specificity of radioligand localization, while the use of radioisotopes with the ability to deliver radiation damage across several cell diameters will compensate for less than perfect transduction efficiency. This approach was termed "Genetic Radioisotope Targeting Strategy." Using this strategy, induction of high levels of gastrin releasing peptide receptor or human somatostatin receptor subtype 2 expression and selective tumor uptake of radiolabeled peptides was achieved. The advantages of the genetic transduction approach are (1) constitutive expression of a tumor-associated antigen/receptor is not required; (2) tumor cells are altered to express a new target receptor or increased quantities of an existing receptor at levels that may significantly improve tumor targeting of radiolabeled ligands compared with normal tissues; (3) gene transfer can be achieved by intratumoral or regional injection of gene vectors; (4) it is feasible to target adenovirus vectors to receptors overexpressed on tumor cells by modifying adenoviral tropism (binding) so that the virus will be targeted specifically to the desired tumor; and (5) it is possible to coexpress the receptor gene and a therapeutic gene, such as cytosine deaminase, for molecular prodrug therapy to produce an enhanced therapeutic effect.

Molecular imaging: an old and new field connecting basic science and clinical medicine

Combination of recent progress in imaging technology and molecular biology/gene technology has evolved a new field named "molecular imaging". It includes wide range of imaging technique from basic research to clinical practice. For basic researchers, we focused on the part of in vivo imaging in human, and introduce the recent progress of modern biomedical imaging, as a crossing point of basic science and clinical medicine.

Positron emission tomography in cancer research and treatment

Positron emission tomography (PET), the imaging of pharmaceuticals labeled with positron-emitting radionuclides, is a rapidly growing modality for the diagnosis and management of cancer. PET yields high-quality images characterizing substrate metabolism, cellular proliferation, receptor density, and other parameters that can be used to identify cancer and evaluate its response to therapies. The technique mainly utilized in cancer management is FDG-PET, which exploits the abnormal glucose metabolism of cancer cells first characterized by Warburg. We discuss the principles of PET, the currently available instrumentation and radiopharmaceuticals, the efficacy of FDG-PET in the management of cancer, and the prospects for near-term advances in cancer using PET.