Therapy of neuroendocrine tumors with radiolabeled MIBG and somatostatin analogues

Advances in Radionuclide Therapies for Patients with Neuro-endocrine Tumors

PURPOSE OF REVIEW

To provide insights into the role of peptide receptor radionuclide therapy (PRRT) in patients with advanced neuroendocrine tumors (NET) and an overview of possible strategies to combine PRRT with locoregional and systemic anticancer treatments.

RECENT FINDINGS

Research on combining PRRT with other treatments encompasses a wide variety or treatments, both local (transarterial radioembolization) and systemic therapies, chemotherapy (i.e., capecitabine and temozolomide), targeted therapies (i.e., olaparib, everolimus, and sunitinib), and immunotherapies (e.g., nivolumab and pembrolizumab). Furthermore, PRRT shows promising first results as a treatment prior to surgery. There is great demand to enhance the efficacy of PRRT through combination with other anticancer treatments. While research in this area is currently limited, the field is rapidly evolving with numerous ongoing clinical trials aiming to address this need and explore novel therapeutic combinations.

Bladder Preservation for Patients With Bladder Paragangliomas: Case Series and Review of the Literature

Bladder paragangliomas are rare tumors, with no prospective studies or guidelines on the management of this disease. We present a case series of 6 patients managed with bladder preservation over a median follow-up period of 124 months. We also present a review of the recent literature on bladder paragangliomas. We aim to provide a timely synthesis of the recent evidence on bladder paragangliomas as changing paradigms necessitate individualized treatment.

Developing preclinical models of neuroblastoma: driving therapeutic testing

Despite advances in cancer therapeutics, particularly in the area of immuno-oncology, successful treatment of neuroblastoma (NB) remains a challenge. NB is the most common cancer in infants under 1 year of age, and accounts for approximately 10% of all pediatric cancers. Currently, children with high-risk NB exhibit a survival rate of 40–50%. The heterogeneous nature of NB makes development of effective therapeutic strategies challenging. Many preclinical models attempt to mimic the tumor phenotype and tumor microenvironment. In vivo mouse models, in the form of genetic, syngeneic, and xenograft mice, are advantageous as they replicated the complex tumor-stroma interactions and represent the gold standard for preclinical therapeutic testing. Traditional in vitro models, while high throughput, exhibit many limitations. The emergence of new tissue engineered models has the potential to bridge the gap between in vitro and in vivo models for therapeutic testing. Therapeutics continue to evolve from traditional cytotoxic chemotherapies to biologically targeted therapies. These therapeutics act on both the tumor cells and other cells within the tumor microenvironment, making development of preclinical models that accurately reflect tumor heterogeneity more important than ever. In this review, we will discuss current in vitro and in vivo preclinical testing models, and their potential applications to therapeutic development.

Mathematical Modeling of Preclinical Alpha-Emitter Radiopharmaceutical Therapy

Preclinical studies, in vivo, and in vitro studies, in combination with mathematical modeling can help optimize and guide the design of clinical trials. The design and optimization of alpha-particle emitter radiopharmaceutical therapy (αRPT) is especially important as αRPT has the potential for high efficacy but also high toxicity. We have developed a mathematical model that may be used to identify trial design parameters that will have the greatest impact on outcome. The model combines Gompertzian tumor growth with antibody-mediated pharmacokinetics and radiation-induced cell killing. It was validated using preclinical experimental data of antibody-mediated ²¹³Bi and ²²⁵Ac delivery in a metastatic transgenic breast cancer model. In modeling simulations, tumor cell doubling time, administered antibody, antibody specific-activity, and antigen-site density most impacted median survival. The model was also used to investigate treatment fractionation. Depending upon the time-interval between injections, increasing the number of injections increased survival time. For example, two administrations of 200 nCi, ²²⁵Ac-labeled antibody, separated by 30 days, resulted in a simulated 31% increase in median survival over a single 400 nCi administration. If the time interval was 7 days or less, however, there was no improvement in survival; a one-day interval between injections led to a 10% reduction in median survival. Further model development and validation including the incorporation of normal tissue toxicity is necessary to properly balance efficacy with toxicity. The current model is, however, useful in helping understand preclinical results and in guiding preclinical and clinical trial design towards approaches that have the greatest likelihood of success. SIGNIFICANCE: Modeling is used to optimize αRPT.

Prevention and management of carcinoid crises in patients with high-risk neuroendocrine tumours undergoing peptide receptor radionuclide therapy (PRRT): Literature review and case series from two Australian tertiary medical institutions

Peptide receptor radionuclide therapy (PRRT) is an important therapeutic option for somatostatin receptor (SSTR) positive metastatic and/or inoperable neuroendocrine tumours (NETs). However, in patients with poorly controlled carcinoid syndrome, it may lead to an acute flare of carcinoid symptoms or even carcinoid crisis. We report seven patients who received PRRT with (¹⁷⁷Lu-DOTA⁰, Tyr³) octreotate (¹⁷⁷Lu-octreotate-LuTate) across two Australian tertiary medical institutions who developed acute flare of carcinoid symptoms/carcinoid crisis during/after PRRT. Cases were identified as high-risk due to previous history of carcinoid crises, high tumour burden and markedly elevated tumour markers. We propose a protocol to prevent and manage severe carcinoid symptoms in high-risk patients treated with PRRT.

Nuclear Medicine in Thyroid Diseases in Pediatric and Adolescent Patients

Both benign and malignant diseases of the thyroid are rare in the pediatric and adolescent population, except congenital hypothyroidism. Nuclear medicine plays a major role, both in the diagnosis and therapy of thyroid pathologies. Use of radioactivity in pediatric population is strictly controlled due to possible side effects such as secondary cancers; therefore, management of pediatric patients requires detailed literature knowledge. This article aims to overview current algorithms in the management of thyroid diseases and use of radionuclide therapy in pediatric and adolescent population.

Spinal cord compression after radiolabeled metaiodobenzylguanidine analogue therapy in advanced malignant insulinoma

Malignant insulinomas are frequently diagnosed at a late stage. Medical management is necessary to slow progression of the disease and control of hypoglycemic symptoms when cure by surgical treatment is not possible. Multimodal treatment, in these cases, has been used with variable clinical response. We describe a 68-yr-old woman who presented response failure to usual treatment and was alternatively treated with radiolabeled metaiodobenzylguanidine ([131I]-MIBG) analogue therapy with development of neurologic complications. We also present a review of the current role of [131I]-MIBG treatment in insulinomas.

PPARgamma in Neuroblastoma

Neuroblastoma (NB) is the most common extracranial tumor in children and accounts for around 15% of all paediatric oncology deaths. The treatment of NB includes surgery, chemotherapy, and radiotherapy. Unfortunately, most children with NB present with advanced disease, and more than 60% of patients with high-risk features will have a poor prognosis despite intensive therapy. Agonists of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) have been shown to have pleiotropic effects, including antineoplastic effects. The studies that addressed the role and the possible mechanism(s) of action of PPARgamma in NB cells are reviewed.

Therapy of aggressive pituitary tumors

INTRODUCTION

Aggressive tumors of the pituitary gland are classically defined as pituitary tumors with a massive invasion of the surrounding anatomical structures and rapid growth. They are notoriously difficult to manage and are associated with poor prognosis because the therapeutic options are limited and the tumors are generally unresponsive to therapy.

AREAS COVERED

This review focuses on treatment options for aggressive pituitary tumors, including surgery, radiotherapy and medical treatment, as well as focusing on the promising therapeutic options for aggressive pituitary tumors, evaluating the literature of the last 15 years. With the exception of prolactinomas, surgery is the first-line option, but most aggressive pituitary tumors often require repeated surgery. Pharmacotherapies are useful when surgery is unlikely to improve symptoms, or as an adjunct therapy to surgery. In prolactinomas, dopamine agonists are the first-line treatment and normalize prolactin levels in most patients, even those with macroprolactinomas. Somatostatin analogs are effective agents for primary therapy, pre-operatively or post-operatively to control tumor re-expansion of pituitary adenomas. However, dopamine agonists and somatostatin analogs are not as effective as they are for the treatment of non-aggressive adenomas. When surgery and pharmacotherapy fail, radiotherapy is a useful third-line strategy. Conventional chemotherapy is poorly effective but recent case reports with the temozolomide, an alkylating agent, have provided better results in the short term.

EXPERT OPINION

Aggressive pituitary tumors are associated with poor prognosis as therapeutic options are limited. Moreover, they tend to recur quickly after initial treatment, are generally unresponsive to therapy, and are difficult to manage. To improve the overall response rate, the early application of current therapeutic approaches with the incorporation of new therapeutic developments is mandatory.

Neuroendocrine Tumors — Laboratory Diagnosis

Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms originating from endocrine cells, which are characterized by the presence of secretory granules as well as the ability to produce biogenic amines and polypeptide hormones. These tumors originate from endocrine glands such as the adrenal medulla, the pituitary, and the parathyroids, as well as endocrine islets within the thyroid or the pancreas, and dispersed endocrine cells in the respiratory and gastrointestinal tract. The clinical behavior of NETs is extremely variable; they may be functioning or not functioning, ranging from very slow-growing tumors (well-differentiated NETs), which are the majority, to highly aggressive and very malignant tumors (poorly differentiated NETs). Classically, NETs of the gastrointestinal tract are classified into 2 main groups: (1) carcinoids and (2) endocrine pancreatic tumors (EPTs). Most neuroendocrine tumors produce and secrete a multitude of peptide hormones and amines. Some of these substances cause a specific clinical syndrome: carcinoid, Zollinger-Ellison, hyperglycemic, glucagonoma and WDHA syndrome. Specific markers for these syndromes are basal and/or stimulated levels of urinary 5-HIAA, serum or plasma gastrin, insulin, glucagon and vasoactive intestinal polypeptide, respectively. Some carcinoid tumors and about one third of endocrine pancreatic tumors do not present any clinical symptoms and are called ‘nonfunctioning’ tumors. Therefore, general tumor markers such as chromogranin A, pancreatic polypeptide, serum neuron-specific enolase and subunits of glycoprotein hormones have been used for screening purposes in patients without distinct clinical hormone-related symptoms. Among these general tumor markers chromogranin A, although its precise function is not yet established, has been shown to be a very sensitive and specific serum marker for various types of neuroendocrine tumors. This is because it may also be elevated in many cases of less well-differentiated tumors of neuroendocrine origin that do not secrete known hormones. At the moment, chromogranin A is considered the best general neuroendocrine serum or plasma marker available both for diagnosis and therapeutic evaluation, and is increased in 50-100% of patients with various neuroendocrine tumors. Chromogranin A serum or plasma levels reflect tumor load, and it may be an independent marker of prognosis in patients with midgut carcinoids.

Functional nuclear medicine imaging of medullary thyroid cancer

Medullary thyroid cancer (MTC) originates from parafollicular C cells of the thyroid and accounts for 3-12% of all thyroid cancers. As opposed to other types of dedifferentiated thyroid tumours, MTC cells are highly functional, producing and secreting high amounts of calcitonin and carcinoembryonic antigen. As parafollicular C cells are of neural crest origin, MTC acts as a neuroendocrine tumour also and expresses somatostatin receptors. Although conventional radiological methods such as ultrasonography, computed tomography and magnetic resonance imaging are widely used in the primary diagnosis and staging, they often fail to localize the residual or recurrent disease because the majority of MTC recurrence presents as occult disease. Thus, owing to functional characteristics of MTC, functional imaging modalities of nuclear medicine play a major role in the diagnostic and therapeutic strategies for MTC. Among nuclear medicine modalities, Tc(V) -dimercaptosuccinic acid, In-octreotide and I/I-meta-iodobenzylguanidine are commonly used in the diagnostic and even more in postoperative work-up of MTC. Alternatively, F-fluorodeoxyglucose and other positron emission tomography radiopharmaceuticals such as F-fluorodopa or F-fluorodopamine as well as radiolabelled antibodies such as Tc/I/I anticarcinoembryonic antigen, antigastrin, and anticholecystokinin-B have promising results. Functional imaging has a great advantage for nuclear medicine techniques in the routine work-up of MTC patients and also has a wide use in experimental studies.

A radioiodinated MIBG-octreotate conjugate exhibiting enhanced uptake and retention in SSTR2-expressing tumor cells

Several neuroendocrine tumors are known to express both the somatostatin receptor subtype 2 (SSTR2) and the norepinephrine transporter (NET), and radiopharmaceuticals directed toward both these targets such as MIBG and octreotide derivatives are routinely used in the clinic. To investigate the possibility of targeting both NET and SSTR2 conjointly, a conjugate of radioiodinated MIBG and octreotate was synthesized. Attempts to synthesize the radioiodinated target compound (MIBG-octreotate; [ (131)I] 12a) from a tin precursor were futile; however, it could be accomplished from a bromo precursor by exchange radioiodination in 3-36% ( n = 10) radiochemical yields. The total uptake of [ (131)I] 12a in SK-N-SH human neuroblastoma cells transfected to express SSTR2 (SK-N-SHsst2) was similar to that for [ (125)I]MIBG at all time points (34.9 +/- 2.4% vs 43.8 +/- 1.2% at 4 h; p < 0.05), while it was substantially lower (5.4 +/- 0.3% vs 35.9 +/- 1.2%) in the SH-SY5Y cell line, a subclone of SK-N-SH line that is known to express SSTR2. The NET blocker desipramine reduced the uptake of [ (131)I] 12a only to a small extent, further suggesting a limited role of NET in its binding and accumulation. Uptake of [ (131)I] 12a in SK-N-SHsst2 cells was 8-10-fold higher ( p < 0.05) than that of [ (125)I]I-Gluc-TOCA, an octreotide analogue, at all time points over a 4 h period and was reduced to about 20% by 10 muM octreotide demonstrating that the uptake of [ (131)I] 12a in this cell line is predominantly mediated by SSTR2. The intracellularly trapped radioactivity in SK-N-SHsst2 cells was substantially higher for [ (131)I] 12a compared to that for [ (125)I]OIBG-octreotate, an isomeric congener of 12a. Because MIBG has more specific NET-mediated uptake than OIBG, this suggests at least a partial role for NET-mediated uptake of [ (131)I] 12a in this cell line. While further refinement in the structure of the conjugate-probably interposition of a flexible and/or cleavable linker between the MIBG and octreotate moieties-may be necessary to make it a substrate/ligand for both NET and SSTR2, this conjugate is demonstrated to be much superior than I-Gluc-TOCA with respect to the uptake in SSTR2-expressing cells.

Radiation and inhibition of angiogenesis by canstatin synergize to induce HIF-1alpha-mediated tumor apoptotic switch

Tumor radioresponsiveness depends on endothelial cell death, which leads in turn to tumor hypoxia. Radiation-induced hypoxia was recently shown to trigger tumor radioresistance by activating angiogenesis through hypoxia-inducible factor 1-regulated (HIF-1-regulated) cytokines. We show here that combining targeted radioiodide therapy with angiogenic inhibitors, such as canstatin, enhances direct tumor cell apoptosis, thereby overcoming radio-induced HIF-1-dependent tumor survival pathways in vitro and in vivo. We found that following dual therapy, HIF-1alpha increases the activity of the canstatin-induced alpha(v)beta(5) signaling tumor apoptotic pathway and concomitantly abrogates mitotic checkpoint and tetraploidy triggered by radiation. Apoptosis in conjunction with mitotic catastrophe leads to lethal tumor damage. We discovered that HIF-1 displays a radiosensitizing activity that is highly dependent on treatment modalities by regulating key apoptotic molecular pathways. Our findings therefore support a crucial role for angiogenesis inhibitors in shifting the fate of radiation-induced HIF-1alpha activity from hypoxia-induced tumor radioresistance to hypoxia-induced tumor apoptosis. This study provides a basis for developing new biology-based clinically relevant strategies to improve the efficacy of radiation oncology, using HIF-1 as an ally for cancer therapy.

Nuclear medicine procedures in the diagnosis and therapy of medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor originating in the parafollicular cells (C cells) of the thyroid and secretes both calcitonin and carcino-embryonic antigen (CEA). Genetic and biochemical testing allow early pre-clinical identification of familial forms. Sporadic MTC usually presents as a solitary thyroid nodule; the diagnosis can be made preoperatively by fine-needle aspiration or by calcitonin assay, though it is usually established at the time of surgery. In the diagnostic assessment of MTC, nuclear medicine imaging provides its contribution mainly in the post-operative work-up to detect residual/recurrent tumor. For such purpose a number of radiopharmaceuticals, which take advantage of the specific expression of receptors (the somatostatin analogue (111)In-octreotide), hormone transporters (radiolabelled MIBG) or molecular targets (radiolabelled anti-CEA monoclonal antibodies) by MTC lesions are available; these tracers may be used also for the palliative treatment of advanced MTC. Interesting perspectives for MTC imaging are offered by PET radiopharmaceuticals.

Neuroblastoma

The clinical hallmark of neuroblastoma is heterogeneity, with the likelihood of cure varying widely according to age at diagnosis, extent of disease, and tumour biology. A subset of tumours will undergo spontaneous regression while others show relentless progression. Around half of all cases are currently classified as high-risk for disease relapse, with overall survival rates less than 40% despite intensive multimodal therapy. This Seminar focuses on recent advances in our understanding of the biology of this complex paediatric solid tumour. We outline plans for the development of a uniform International Neuroblastoma Risk Group (INRG) classification system, and summarise strategies for risk-based therapies. We also update readers on new discoveries related to the underlying molecular pathogenesis of this tumour, with special emphasis on advances that are translatable to the clinic. Finally, we discuss new approaches to treatment, including recently discovered molecular targets that might provide more effective treatment strategies with the potential for less toxicity.

Les phéochromocytomes malins : à propos de trois observations

The authors report three cases of malignant pheochromocytomas. Metastases occurred in the liver in two cases whereas malignancy was suspected in the third case because of recurrence and local invasion. One case was pregnant at diagnosis of pheochromocytoma. Pheochromocytoma was associated to papillary thyroïd carcinoma in another case. The treatment considered was surgery in all cases.

Therapeutic options for gastrointestinal carcinoids

Although wide surgical resection is the optimal curative therapy for carcinoid tumors, in most patients the presence of metastatic disease at diagnosis usually renders excision a palliative procedure. This nevertheless decreases tumor burden, facilitates symptom control, and prevents complications caused by bleeding, perforation, or bowel obstruction resulting from fibrosis. In the stomach (types I and II) and rectum endoscopic excision may be adequate provided the lesion(s) are local. Long-term therapy is focused on symptom alleviation and improvement of quality of life using somatostatin analogues, particularly in a subcutaneous depot formulation. In some instances interferons may have a role but their usage often is associated with substantial adverse events. Conventional chemotherapy and external radiotherapy either alone or in a variety of permutations are of minimal efficacy and should be balanced against the decrease in quality of life often engendered by such agents. Hepatic metastases may be amenable to surgery, radiofrequency ablation, or embolization either alone or in combination with chemotherapeutic agents or isotopically loaded microspheres. Rarely hepatic transplantation may be of benefit although controversy exists as to its actual use. Peptide-receptor-targeted radiotherapy for advanced disease using radiolabeled octapeptide analogs (111In/90Yt/177Lu-octreotide) appear promising but data are limited and its status remains investigational. A variety of antiangiogenesis and growth factor-targeted agents have been evaluated, but as yet have shown little promise. The keystone of current therapy remains the long-acting somatostatin analogues that alleviate symptomatology and substantially improve quality of life with minimal adverse effects.

[Radiation therapy with 131I-MIBG is still relevant for metastatic carcinoid tumors]

We report different treatment options (currently used and on trial) for a patient with a gastrointestinal carcinoid tumor and metastases in the liver, and discuss the advantages of using internal radiotherapy with 131I-MIBG rather than other treatments. According to the literature, this pathology has a poor prognosis, and considering the significant efficacy of this radiopharmaceutical treatment on symptoms, tumor reduction, and biochemical parameters, it seems to be under used. There are currently no standard treatment options. We present a management strategy for gastrointestinal carcinoid tumors with 131I-MIBG.

Targeted therapy with a cytotoxic somatostatin analog, AN-238, inhibits growth of human experimental endometrial carcinomas expressing multidrug resistance protein MDR-1

BACKGROUND

Chemoresistance mediated by membrane transporters such as multidrug resistance (MDR-1) glycoprotein remains a challenge in the chemotherapy treatment of advanced or recurrent endometrial carcinoma. Targeted chemotherapy might overcome this resistance. The cytotoxic somatostatin (SST) analog, AN-238, consists of a superactive derivative of doxorubicin (DOX), 2-pyrrolino-DOX (AN-201), linked to the SST analog carrier, RC-121. This conjugate binds strongly to SST receptor subtypes (sst) 2a (sst2(a)) and 5 (sst(5)) and can be targeted to tumors that express these receptors.

METHODS

The presence of sst2(a) and sst(5) was determined in 3 human endometrial carcinoma cell lines (HEC-1A, RL-95-2, and AN3CA). Nude mice bearing xenografts of these cancers were treated with AN-238 and its radical, AN-201. The antitumor effects and toxicity were compared. The authors studied the effects of AN-238 and AN-201 on the expression levels of MDR-1, multidrug resistance related protein (MRP-1), and breast carcinoma resistance protein (BCRP) by real-time polymerase chain reaction.

RESULTS

The authors demonstrated the presence of mRNA and receptor protein for sst(2a) and sst(5) on HEC-1A, RL-95-2, and AN3CA tumors. AN-238 significantly (P < 0.05) inhibited the growth of these tumors, whereas AN-201 had no effect. Blockade of SST receptors nullified the effects of AN-238. In all 3 endometrial carcinoma lines, AN-238 caused a weaker induction of MDR-1 than AN-201. No major induction of MRP-1 and BCRP occurred after treatment with AN-238 or AN-201.

CONCLUSIONS

Targeted chemotherapy with the cytotoxic SST analog, AN-238, inhibited powerfully the growth of endometrial carcinoma, which express SST receptors, regardless of their expression level of MDR-1.

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.

The palliative role of 131I-MIBG and 111In-octreotide therapy in patients with metastatic progressive neuroendocrine neoplasms

BACKGROUND

Radiolabeled octreotide and metaiodobenzylguanidine (MIBG) have demonstrated limited antitumor effect on neuroendocrine neoplasms (NENs). The purpose of this study was to assess the palliative benefit of radionuclide therapy (RNT) in NENs.

METHODS

Since April 2001, RNT for progressive, nonsurgically resectable NENs was utilized. NENs that were MIBG positive received 131 I-MIBG therapy, whereas octreotide-only-positive neoplasms received 111 In-octreotide therapy. Symptomatic, quality of life (QoL), biochemical, and radiographic responses to RNT were evaluated.

RESULTS

Twenty-four patients had either MIBG or octreotide avid NENs. A mean (range) of 4 (1-7) 131 I-MIBG treatments were given to 13 patients over a duration of 18 months (6-42). The group consisted of 2 medullary thyroid cancer (MTC), and 2 foregut and 9 small-bowel carcinoids; 12 patients (92%) had symptomatic improvement. Stability of tumor size was confirmed in 6, regression in 2, and progression in 5. Biochemical responses were demonstrated in 2. Five (2-16) treatments of 111 In-octreotide was given to 11 patients over 17 months (6-40). There were 1 MTC, 1 insulinoma, 2 gastrinomas, and 3 small-bowel and 4 foregut carcinoids. Symptomatic benefit was seen in 6 (55%), biochemical response in 3. Tumor regression was seen in 1, stability in 5, and progression in 5.

CONCLUSIONS

Radionuclide therapy appears to offer good palliation to patients with progressive NENs.

Growth inhibition of experimental non-Hodgkin's lymphomas with the targeted cytotoxic somatostatin analogue AN-238

The cytotoxic analogue of somatostatin, AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201), a superactive derivative of doxorubicin (DOX), linked to somatostatin analogue carrier RC-121 binds with high affinity to receptors for somatostatin and can be targeted to tumors that express these receptors. Because somatostatin receptors are found in a high percentage of human non-Hodgkin's lymphomas (NHLs), we evaluated the antitumor effect of AN-238 in 2 human NHL cell lines in vivo. Nude mice bearing xenografts of RL and HT human NHL were treated with AN-238 or its components at equimolar doses, and antitumor effects were determined. Expression of mRNA for somatostatin receptor subtypes was measured by RT-PCR, and the presence of somatostatin receptors was determined by radioligand binding. Toxicity was evaluated by following white blood cell count (WBC) and body weight. AN-238 significantly (p < 0.05) inhibited growth of RL and HT xenografts and prolonged the tumor doubling time. Cytotoxic radical AN-201, the unconjugated mixture of somatostatin analogue RC-121 and AN-201 or RC-121 alone had no significant effects. Blockade of somatostatin receptors by excess RC-121 abolished the effect of AN-238, demonstrating targeting. Expression of somatostatin receptors was not changed after repeated treatment with AN-238. AN-201, but not AN-238, significantly lowered the WBC and caused a greater decrease in body weight than AN-238. Our findings demonstrate that targeted chemotherapy with AN-238 can strongly inhibit the growth of NHL cells, which express somatostatin receptors. AN-238 could be considered for the treatment for patients with NHL.

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

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

The diagnosis and medical management of advanced neuroendocrine tumors

Neuroendocrine tumors (NETs) constitute a heterogeneous group of neoplasms that originate from endocrine glands such as the pituitary, the parathyroids, and the (neuroendocrine) adrenal, as well as endocrine islets within glandular tissue (thyroid or pancreatic) and cells dispersed between exocrine cells, such as endocrine cells of the digestive (gastroenteropancreatic) and respiratory tracts. Conventionally, NETs may present with a wide variety of functional or nonfunctional endocrine syndromes and may be familial and have other associated tumors. Assessment of specific or general tumor markers offers high sensitivity in establishing the diagnosis and can also have prognostic significance. Imaging modalities include endoscopic ultrasonography, computed tomography and magnetic resonance imaging, and particularly, scintigraphy with somatostatin analogs and metaiodobenzylguanidine. Successful treatment of disseminated NETs requires a multimodal approach; radical tumor surgery may be curative but is rarely possible. Well-differentiated and slow-growing gastroenteropancreatic tumors should be treated with somatostatin analogs or alpha-interferon, with chemotherapy being reserved for poorly differentiated and progressive tumors. Therapy with radionuclides may be used for tumors exhibiting uptake to a diagnostic scan, either after surgery to eradicate microscopic residual disease or later if conventional treatment or biotherapy fails. Maintenance of the quality of life should be a priority, particularly because patients with disseminated disease may experience prolonged survival.

Vertebral metastatic chemodectoma: imaging and therapeutic octreotide. Case report

The authors report on the use of external-beam radiotherapy and octreotide in a 32-year-old woman who presented with spinal cord compression secondary to metastatic chemodectoma. Scintigraphy studies were used to confirm the presence of somatostatin receptors. Magnetic resonance imaging, and in particular spinal angiography, were performed to define the extent of spinal metastatic disease. The literature on current investigation and management of vertebral metastatic chemodectoma is reviewed.

Radioisotope diagnosis and therapy of malignant pheochromocytoma

The availability of radiopharmaceuticals to depict primary malignant pheochromocytoma and its metastases has markedly changed the approach to these unusual cancers. Whole body screening afforded by scintigraphy allows remote tumor involvement to be identified and provides staging information necessary to guide subsequent therapy. The avid accumulation by malignant pheochromocytoma of some radiopharmaceuticals used for scanning has shown promise in therapeutic trials. In this paper, we discuss radiopharmaceuticals presently employed in malignant pheochromocytoma for both diagnostic and therapeutic uses and potential future compounds that may find their way into clinical practice in the approach to these and other related neoplasms.

Dosimetric comparison of radionuclides for therapy of somatostatin receptor-expressing tumors

PURPOSE

Therapy of tumors expressing somatostatin receptors, sstr, has recently been clinically tested using somatostatin analogues labeled with (111)In and (90)Y. Several other radionuclides, i.e., (131)I, (161)Tb, (64)Cu, (188)Re, (177)Lu, and (67)Ga, have also been proposed for this type of therapy. The aim of this work was to investigate the usefulness of the above-mentioned radionuclides bound to somatostatin analogues for tumor therapy.

METHODS

Biokinetic data of (111)In-labeled octreotide in mice and man were used, primarily from our studies but sometimes from the literature. Dosimetric calculations were performed with the assumption that biokinetics were similar for all radionuclides bound to somatostatin analogues. The cumulated tumor:normal-tissue activity concentration, TNC was calculated for the various physical half-lives of the radionuclides. Using mathematical models, the tumor:normal-tissue mean absorbed dose rate ratio, TN D and tumor:normal-tissue mean absorbed dose ratio, TND, were calculated for various tumor sizes in mice and humans.

RESULTS

TNC of radionuclide-labeled octreotide increased with physical half-life for most organs, both in mice and in humans. TN D showed that radionuclides emitting electrons with too high energy are not suitable for therapy of small tumors. Furthermore, radionuclides with a higher frequency of photon emissions relative to electron emissions will yield lower TN D and are thus less suitable for therapy than radionuclides with a lower frequency of photon emissions. The TND was highest for (161)Tb in both mice and humans.

CONCLUSIONS

The results demonstrate that long-lived radionuclides, which emit electrons with rather low energy and which have low frequency of photon emissions, should be the preferred therapy for disseminated small sstr-expressing tumors.

Inhibition of the UCI-107 human ovarian carcinoma cell line by a targeted cytotoxic analog of somatostatin, AN-238

BACKGROUND

Cytotoxic analogs of somatostatin (SST), such as AN-238, which consists of 2-pyrrolinodoxorubicin (AN-201) linked to the SST carrier RC-121, can be targeted to tumors that express SST receptors. Because SST receptors are present in ovarian carcinoma cells, the authors evaluated the effect of AN-238 on the UCI-107 ovarian carcinoma cell line.

METHODS

An analysis of microsatellite alleles in cocultured SST receptor positive and receptor negative cells was used for the demonstration of in vitro targeting. The toxicity and antitumor effects of AN-238 in nude mice bearing UCI-107 human ovarian tumors were investigated with or without pharmacologic inhibition of serum carboxylesterases (CE). The expression of SST receptor subtypes was determined by reverse transcriptase-polymerase chain reaction analysis, and the binding affinity of AN-238 to SST receptors was determined by radioligand assays.

RESULTS

The proliferation of SST receptor positive UCI-107 cells in vitro was inhibited preferentially by AN-238. AN-238 showed high-affinity binding to UCI-107 tumor membranes at a 50% inhibition concentration of 3.39 nM +/- 0.74 nM. In vivo, the volume and weights of UCI-107 tumors treated with AN-238 were decreased by more than 60% (P < 0.05) compared with controls. Cytotoxic radical AN-201 or the unconjugated mixture of AN-201 with carrier RC-121 had no significant effects on tumors and were toxic. In mice with inhibited serum CE activity, AN-201 at 400 nmol/kg was lethal, whereas AN-238 at a total dose of 800 nmol/kg caused only 22% mortality and reduced tumor weight by 69% and volume by 70% (P < 0.05 vs. control).

CONCLUSIONS

Targeted chemotherapy with the SST conjugate AN-238 inhibits SST receptor positive experimental ovarian tumors. AN-238 may provide a new treatment modality for patients with advanced ovarian carcinoma.

Current approaches and perspectives in the therapy of medullary thyroid carcinoma

BACKGROUND

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor derived from parafollicular cells. At present, surgery is the most important treatment for MTC.

METHODS

We describe the current approaches of MTC treatment (surgery, chemotherapy, radiation therapy, and biologic therapy).

RESULTS

MTC is currently approached surgically in the main part through total thyroidectomy and compartment-oriented microdissection of cervicomediastinal lymph nodes. Substitutive l-thyroxine administration together with close clinical monitoring and the measurement of basal and stimulated serum calcitonin are subsequently performed. Radiotherapy and chemotherapy play a marginal role in advanced MTC. Recently, it has been found that somatostatin analogs and type I interferon are able to control the neuroendocrine symptoms induced by advanced MTC and that they provide clinical benefit by improving the lifestyle of these patients.

CONCLUSION

Although these agents are poorly active in inducing a shrinkage in tumor mass, the combined use of different biologic agents and cytotoxic drugs needs to be explored in advanced MTC. However, at present, surgery is the only curative treatment for MTC.

Radiotherapeutic efficacy of (153)Sm-CMDTPA-Tyr(3)-octreotate in tumor-bearing rats

A number of radiolabeled somatostatin analogs have been evaluated in animal tumor models for radiotherapeutic efficacy. The majority of the agents tested have used either high-energy beta-emitters, such as Y-90 or Re-188, or the Auger electron-emitting radionuclide, In-111. Because a medium-energy beta-emitter might have equivalent efficacy compared to high-energy emitters, and lower toxicity to non-target tissues, we have evaluated the therapeutic potential of the beta-emitting nuclide, Sm-153, chelated to the somatostatin analog, CMDTPA-Tyr(3)-octreotate. Using an in vitro binding assay, this octreotate derivative was shown to have high affinity for the somatostatin subtype-2 receptor (IC(50) = 2.7 nM). Biodistribution studies in CA20948 tumor-bearing Lewis rats demonstrate that the Sm-153 labeled compound has high uptake and retention in tumor tissue (1.7% injected dose/g tissue, 4 hrs post injection) and has rapid overall clearance properties from non-target tissue. Radiotherapy studies were carried out using (153)Sm-CMDTPA-Tyr(3)-octreotate and CA20948 tumor bearing Lewis rats at 7 days post implant. Dose regimens consisting of single and multiple i.v. injections of 5.0 mCi/rat (185 MBq) were employed over a time span of 7 days. Suppression of tumor growth rate was observed in all treated animals compared to untreated controls. Greater inhibition of tumor growth was observed in animals that received multiple doses. These studies indicate that medium-energy beta-emitting isotopes have considerable potential for the treatment of somatostatin receptor-positive tumors.

The role of nuclear medicine in the evaluation of pancreatic disease

F-18 FDG PET in patients with nonendocrine pancreatic cancer and somatostatin receptor imaging in patients with endocrine pancreatic cancer have an important role in detecting or confirming the presence of a mass in the pancreas--a crucial step in the management of these patients. Both agents also have an important role in staging and in defining which patients are good candidates for resection surgery. Somatostatin receptor imaging also has a crucial role in selecting from the various systemic therapeutic options available. I-131 MIBG therapy can be of value therapeutically, mostly palliative, in patients who demonstrate a markedly elevated concentration of tumor radioactivity.

Somatostatin receptor imaging, therapy and new strategies in patients with neuroendocrine tumours

BACKGROUND

Somatostatin receptors have been found on a variety of neuroendocrine tumours, such as carcinoids and paragangliomas, as well as on most pancreatic endocrine and breast tumours. Somatostatin receptor scintigraphy with a radionuclide-labelled somatostatin analogue, [111Indium- diethylenetriaminopenta-acetic acid]octreotide, is a sensitive and specific technique for visualizing in vivo the presence of somatostatin receptors on various tumours.

METHODS

Material was identified from previous review articles, references cited in original papers and a Medline search of the literature. Additional material was obtained from recently published abstracts of meetings.

RESULTS AND CONCLUSION

Somatostatin receptor imaging of neuroendocrine tumours is essential in the diagnostic evaluation of most of these tumours. The expression of somatostatin receptors in vivo not only predicts the outcome of somatostatin analogue treatment but also opens the possibility of new therapeutic strategies. Because better information about spread of the disease can be obtained, more justifiable options for therapy can be proposed.

In vivo inhibition of PC-3 human androgen-independent prostate cancer by a targeted cytotoxic bombesin analogue, AN-215

The effectiveness of chemotherapy targeted to bombesin (BN) receptors was evaluated in nude mice bearing PC-3 human androgen-independent prostate cancers. Cytotoxic BN analogue AN-215, consisting of 2-pyrrolinodoxorubicin (AN-201) linked to BN-like carrier peptide RC-3094, was injected i.v. at 150 nmol/kg on days 1, 11 and 21. After treatment with AN-215, tumor volume was 69% (p < 0.01) smaller than that in controls and tumor doubling time was extended from 8.5 +/- 0.7 days to 20.3 +/- 3.5 days (p < 0.05). Cytotoxic radical AN-201, carrier RC-3094 and their unconjugated mixture administered at the same dosage were ineffective. The mortality rate was 12.5% in the AN-201 group and 16.7% in the group treated with the mixture, but no deaths occurred in mice receiving AN-215. Because the ester bond linking AN-201 to the carrier molecule is hydrolyzed much faster in mouse serum than in human serum, in the second experiment we investigated the tolerance to AN-215 and its effect in nude mice bearing PC-3 tumors after pharmacological inhibition of serum carboxylesterases. Two applications of AN-201 at 200 nmol/kg were lethal, whereas no mortality was observed after 4 injections of AN-215 at the same dose. Administration of 200 nmol/kg AN-215 on days 1, 7, 17 and 26 again produced 69% tumor inhibition. BN receptors on membranes of PC-3 tumors were detected by (125)I-[Tyr(4)]BN binding, and expression of mRNA for BRS-3 and GRP-R subtypes was also found. AN-215 showed a high affinity to PC-3 tumors, displacing the radioligand at an IC(50) of 12.95 +/- 0.35 nM. Because BN receptors are present on primary and metastatic prostate cancer, targeted chemotherapy with AN-215 might benefit patients with advanced prostatic carcinoma who relapsed androgen ablation.

High expression of somatostatin receptors and messenger ribonucleic acid for its receptor subtypes in organ-confined and locally advanced human prostate cancers

To evaluate the potential application of somatostatin (SST) analogs as an adjuvant treatment for prostate cancer, we characterized the binding sites for SST octapeptide analogs on prostate cancers in patients treated with radical prostatectomy. The affinity and density of binding sites for SST analog RC-160 on 80 surgical specimens of prostate cancers were determined by ligand competition assays. The expression of messenger ribonucleic acid (mRNA) for SST receptor subtype 1 (SSTR1), subtype 2 (SSTR2), and subtype 5 (SSTR5) was also investigated in 22 samples by RT-PCR. Fifty-two of 80 specimens (65%), showed a single class of specific binding sites for RC-160 with a mean dissociation constant (K(d)) of 9.44 nmol/L and a mean maximal binding capacity of 754.8 fmol/mg membrane protein. The mRNA for SSTR1 was detected in 86% of samples, whereas the incidences of mRNA for SSTR2 and SSTR5 were 14% and 64%, respectively. The expression of SSTR2 and/or SSTR5 was 100%, consistent with the presence of RC-160 binding. In patients at high risk of cancer recurrence (stage pT3 and/or Gleason score of 8-10), the incidence of RC-160 binding (65.7%) was similar to that observed in the low risk group (64.3%). The demonstration of the high incidence of octapeptide-preferring SSTRs in organ-confined and locally advanced prostate cancers supports the merit of further investigations of the application of SST analogs and their radionuclide and cytotoxic derivatives for adjuvant treatment of patients at high risk of cancer recurrence after radical prostatectomy. Such approaches could be also considered for patients with advanced prostate cancer at the time of relapse.

Inhibition of growth of MX-1, MCF-7-MIII and MDA-MB-231 human breast cancer xenografts after administration of a targeted cytotoxic analog of somatostatin, AN-238

Since somatostatin (sst) receptors are expressed in a high percentage of human breast cancers, we studied the effects of a targeted cytotoxic somatostatin analog (AN-238) formed by linking the highly active doxorubicin (DOX) derivative 2-pyrrolino-DOX (AN-201) to octapeptide RC-121 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH(2)) in 3 human breast cancer models. The models included estrogen-independent MDA-MB-231 and MX-1 and estrogen-sensitive MCF-7-MIII tumors. Nude mice bearing xenografts of these cancers were injected i.v. with 250 nmol/kg doses of cytotoxic radical AN-201, cytotoxic analog AN-238 or the unconjugated mixture of AN-201 and sst analog RC-121. Significant inhibition of growth of MDA-MB-231, MX-1 and MCF-7-MIII tumors was observed 1 week after injection of a single dose of cytotoxic analog AN-238. The volume of MDA-MB-231 tumors remained significantly decreased 3 weeks after treatment. The volumes and weights of MCF-7-MIII tumors continued to be significantly reduced 60 days after therapy with AN-238. AN-238 also caused complete regression of MX-1 tumors in 5 of 10 animals, which remained tumor-free 60 days after treatment. In contrast, after treatment with cytotoxic radical AN-201, MDA-MB-231 and MCF-7-MIII tumors grew steadily and the regression of MX-1 tumors was only transitory in most animals. Toxicity of AN-201 was much greater than that of AN-238, as measured by animal deaths, loss of body weight and leukopenia. High-affinity sst receptors and mRNA for both sst(2) and sst(5) subtypes were found in all 3 tumor lines. Expression of sst receptors was not significantly affected by treatment with AN-238. Our results indicate that the cytotoxic somatostatin analog AN-238 efficaciously inhibits growth of human breast cancers expressing sst receptor subtypes 2 and 5.

Anti-proliferative effect of radiolabelled octreotide in a metastases model in rat liver

Most neuroendocrine tumours and several other tumours, such as breast carcinoma and malignant lymphoma, express somatostatin receptors (SS-Rs). Lesions expressing these receptors can be visualised by receptor scintigraphy using a low radioactive dose of the radiolabelled SS analogue [111In-DTPA0]octreotide. This radioligand is internalised and transported to the lysosomes with a long residence time of 111In. The aim of this experimental study in rats was to investigate whether the same agent, given in a high radioactive dose, can be used for therapy of hepatic metastases of different tumour cell lines. The development of hepatic metastases was determined 21 days after direct injection of SS-R-positive or -negative tumour cells into the vena porta in rats. On day 1 and/or 8, animals were treated with 370 MBq (0.5 microg) [111In-DTPA0]octreotide. In one experiment, using SS-R-positive tumour cells, animals were pre-treated with a high dose of cold octreotide to block the SS-R by saturation. The number of SS-R-positive liver metastases was significantly decreased after treatment with [111In-DTPA0]octreotide. Blocking the SS-R by octreotide substantially decreased the efficacy of treatment with [111In-DTPA0]octreotide, suggesting that the presence of SS-R is mandatory. This was confirmed by the finding that the number of SS-R-negative liver metastases was not affected by treatment with [111In-DTPA0]octreotide. Therefore, we conclude that (i) high radioactive doses of [111In-DTPA0]octreotide for PRRT (peptide receptor radionuclide therapy) can inhibit the growth of SS-R-positive liver metastases in an animal model, (ii) PRRT is effective only if SS-Rs are present on the tumours, (iii) the effect of PRRT with [111In-DTPA0]octreotide can be reduced by pre-treatment with cold octreotide, which indicates that receptor binding is essential for PRRT. Our data suggest that PRRT with radiolabelled octreotide might be a new promising treatment modality for SS-R-positive tumours.

Carcinoid tumours presenting as breast cancer: the utility of radionuclide imaging with 123I-MIBG and 111In-DTPA pentetreotide

Secondary tumours of any type in the breast are rare. A review of the literature demonstrated only 23 cases of carcinoid tumours with associated breast metastasis, as distinct from primary carcinoid tumours of the breast. Distant metastases from carcinoid tumours are correlated with poor prognosis and survival. Although both primary and metastatic mammary carcinoid tumours are uncommon, the recognition of the true origin of the tumours may be of importance owing to the different clinical management and prognosis of the two conditions. Recently, radionuclide-labelled imaging techniques have been applied to the localization of such lesions, based on isotope uptake by receptors present in these neuroendocrine tumours. We report two new cases of carcinoid tumours with breast metastases, the primaries being in the ileocaecal valve and the bronchus, respectively. The diagnosis of a carcinoid tumour was based on the clinical, biochemical, histopathological and immunostaining features. Furthermore, these patients had both 123I-MIBG and 111In pentetreotide scintigraphy performed. These radionuclides play a useful role in the localization and potentially in the management of carcinoid tumours and their distant metastases.

Imaging of olfactory neuroblastoma--an analysis of 17 cases

A total of 17 histologically confirmed olfactory neuroblastomas treated at Helsinki University Central Hospital between 1962 and 1996 were reviewed retrospectively. The tumors displayed a variety of imaging characteristics and aggressiveness. Imaging evolved from plain X-rays at the beginning of the study period to CT and MRI during the latter part of the study. CT provided the best information about the tumor and its local invasion especially into surrounding bony structures. MRI allowed an estimate of tumor spread into surrounding soft-tissue areas, such as the anterior cranial fossa and the retromaxillary space. However, signal intensity characteristics were not specific for olfactory neuroblastomas. Bone scintigraphy and MIBG scan allowed us to detect distant metastases. Olfactory neuroblastoma is an aggressive malignancy and the prognosis is poor in most cases, as shown by the short survival rates (average 45.3 months) in our study group. The tumor can be detected, delineated and its characteristics suspected by modern radiology. Definite diagnosis is based on histopathology. This study proposes general imaging strategies for detecting this disease.