Multi-modality megatherapy with [131I]meta-iodobenzylguanidine, high dose melphalan and total body irradiation with bone marrow rescue: feasibility study of a new strategy for advanced neuroblastoma

Timing and chemotherapy association for 131-I-MIBG treatment in high-risk neuroblastoma

Prognosis of high-risk neuroblastoma is dismal, despite intensive induction chemotherapy, surgery, high-dose chemotherapy, radiotherapy, and maintenance. Patients who do not achieve a complete metastatic response, with clearance of bone marrow and skeletal NB infiltration, after induction have a significantly lowersurvival rate. Thus, it's necessary to further intensifytreatment during this phase. 131-I-metaiodobenzylguanidine (131-I-MIBG) is a radioactive compound highly effective against neuroblastoma, with32% response rate in relapsed/resistant cases, and only hematological toxicity. 131-I-MIBG wasutilized at different doses in single or multiple administrations, before autologous transplant or combinedwith high-dose chemotherapy. Subsequently, it was added to consolidationin patients with advanced NB after induction, but an independent contribution against neuroblastoma and for myelotoxicity is difficult to determine. Despiteresults of a 2008 paper demonstratedefficacy and mild hematological toxicity of 131-I-MIBG at diagnosis, no center had included it with intensive chemotherapy in first-line treatment protocols. In our institution, at diagnosis, 131-I-MIBG was included in a 5-chemotherapy drug combination and administered on day-10, at doses up to 18.3 mCi/kg. Almost 87% of objective responses were observed 50 days from start with acceptable hematological toxicity. In this paper, we review the literature data regarding 131-I-MIBG treatment for neuroblastoma, and report on doses and combinations used, tumor responses and toxicity. 131-I-MIBG is very effective against neuroblastoma, in particular if given to patients at diagnosis and in combination with chemotherapy, and it should be included in all induction regimens to improve early responses rates and consequently long-term survival.

Tandem high-dose 131I-MIBG therapy supported by dosimetry in pediatric patients with relapsed-refractory high-risk neuroblastoma: the Bambino Gesu' Children's Hospital experience

OBJECTIVE

131I-meta-iodobenzylguanidine (131I-MIBG) combined with myeloablative chemotherapy represents an effective treatment in children affected by relapsed/refractory neuroblastoma (NBL) for disease palliation and in improving progression-free survival. The aim of our study is to evaluate the feasibility, safety and efficacy of tandem 131I-MIBG followed by high-dose chemotherapy with Melphalan.

METHODS

Thirteen patients (age range: 3-17 years) affected by relapsed/refractory NB, previously treated according to standard procedures, were included in the study. Each treatment cycle included two administrations of 131I-MIBG (with a dosimetric approach) followed by a single dose of Melphalan with peripheral blood stem cell rescue.

RESULTS

At the end of the treatment, ten patients experienced grade 4 neutropenia, two grade 3 and one patient grade 2, three patients presented febrile neutropenia and all needed RBC and platelets transfusions; one patient presented grade 4 mucositis, four grade 3 and one patient grade 2 mucositis. One patient showed progressive disease, eight patients showed stable disease and four patients showed partial response.

CONCLUSION

High-dose 131I-MIBG therapy combined with chemotherapy represent a well-tolerated and effective modality of treatment in heavily pretreated patients affected by relapsed/refractory NBL. However, further studies, including a wider cohort of patients, are needed.

131 I-Meta-iodobenzylguanidine followed by busulfan and melphalan and autologous stem cell rescue in high-risk neuroblastoma

INTRODUCTION

Despite the progress in current treatments, the event-free survival of high-risk neuroblastoma (HR-NB) patients does not exceed 40%-50%, and the prognosis of refractory or relapsed patients is poor, still representing a challenge for pediatric oncologist. Therapeutic Iodine-131 meta-iodobenzylguanidine (Th-¹³¹ I-MIBG) is a recognized safe and potentially effective treatment for NB.

MATERIALS

This retrospective study reports the outcomes of 28 MIBG-avid NB patients with advanced disease either refractory or relapsed, which was undertaken from 1996 to 2014. Th-¹³¹ I-MIBG was administered shortly before (median: 17 days) high-dose chemotherapy with busulfan and melphalan (HD-BuMel) and autologous stem cell rescue (ASCR) at the Gaslini Institute in Genoa, with the aim of analyzing the feasibility, safety, and efficacy of this approach.

RESULTS

Engraftment occurred in all patients after a median of 14 (11-29) and 30 days (13-80) from ASCR for neutrophils and platelets, respectively. No treatment-related deaths were observed. The main high-grade (3-4) toxicity observed was oral and gastrointestinal mucositis in 78.6% and 7.1% of patients, respectively, whereas high-grade hepatic toxicity was observed in 10.7%. Two patients developed veno-occlusive-disease (7.1%), completely responsive to defibrotide. Hypothyroidism was the main late complication that occurred in nine patients (31.1%). After Th-¹³¹ MIBG and HD-BuMel, 19 patients (67.8%) showed an improvement in disease status. Over a median follow-up of 15.9 years, the three-year and five-year overall survival (OS) probabilities were 53% (CI 0.33-0.69) and 41% (CI 0.22-0.59), and the three-year and five-year rates of cumulative risk of progression/relapse were 64% (CI 0.47-0.81) and 73% (CI 0.55-0.88), respectively. MYCN amplification emerged as the only risk factor significantly associated with OS (HR, 3.58;P = 0.041).

CONCLUSION

Th-¹³¹ I-MIBG administered shortly before HD-BuMel is a safe and effective regimen for patients with advanced MIBG-avid NB. These patients should be managed in centers with proven expertise.

Upfront consolidation treatment with 131I-mIbG followed by myeloablative chemotherapy and hematopoietic stem cell transplantation in high-risk neuroblastoma

Importance

¹³¹I‐metaiodobenzylguanidine (¹³¹I‐mIBG) has a significant targeted antitumor effect for neuroblastoma. However, currently there is a paucity of data for the use of ¹³¹I‐mIBG as a “front‐line” therapeutic agent in those patients with newly diagnosed high‐risk neuroblastoma as part of the conditioning regimen for myeloablative chemotherapy (MAC).

Objective

To evaluate the feasibility of upfront consolidation treatment with ¹³¹I‐mIBG plus MAC and hematopoietic stem cell transplantation (HSCT) in high‐risk neuroblastoma patients.

Methods

A retrospective, single‐center study was conducted from 2003–2019 on newly diagnosed high‐risk neuroblastoma patients without progressive disease (PD) after the completion of induction therapy. They received ¹³¹I‐mIBG infusion and MAC followed by HSCT.

Results

A total of 24 high‐risk neuroblastoma patients were enrolled with a median age of 3.0 years at diagnosis. After receiving this sequential consolidation treatment, 3 of 13 patients who were in partial response (PR) before ¹³¹I‐mIBG treatment achieved either complete response (CR) (n = 1) or very good partial response (VGPR) (n = 2) after HSCT. With a median follow‐up duration of 13.0 months after ¹³¹I‐mIBG therapy, the 5‐year event‐free survival and overall survival rates estimated were 29% and 38% for the entire cohort, and 53% and 67% for the patients who were in CR/VGPR at the time of ¹³¹I‐mIBG treatment.

Interpretation

Upfront consolidation treatment with ¹³¹I‐mIBG plus MAC and HSCT is feasible and tolerable in high‐risk neuroblastoma patients, however the survival benefit of this ¹³¹I‐mIBG regimen is only observed in the patients who were in CR/VGPR at the time of ¹³¹I‐mIBG treatment.

Molecular targeting therapies for neuroblastoma: Progress and challenges

There is an urgent need to identify novel therapies for childhood cancers. Neuroblastoma is the most common pediatric solid tumor, and accounts for ~15% of childhood cancer‐related mortality. Neuroblastomas exhibit genetic, morphological and clinical heterogeneity, which limits the efficacy of existing treatment modalities. Gaining detailed knowledge of the molecular signatures and genetic variations involved in the pathogenesis of neuroblastoma is necessary to develop safer and more effective treatments for this devastating disease. Recent studies with advanced high‐throughput “omics” techniques have revealed numerous genetic/genomic alterations and dysfunctional pathways that drive the onset, growth, progression, and resistance of neuroblastoma to therapy. A variety of molecular signatures are being evaluated to better understand the disease, with many of them being used as targets to develop new treatments for neuroblastoma patients. In this review, we have summarized the contemporary understanding of the molecular pathways and genetic aberrations, such as those in MYCN, BIRC5, PHOX2B, and LIN28B, involved in the pathogenesis of neuroblastoma, and provide a comprehensive overview of the molecular targeted therapies under preclinical and clinical investigations, particularly those targeting ALK signaling, MDM2, PI3K/Akt/mTOR and RAS‐MAPK pathways, as well as epigenetic regulators. We also give insights on the use of combination therapies involving novel agents that target various pathways. Further, we discuss the future directions that would help identify novel targets and therapeutics and improve the currently available therapies, enhancing the treatment outcomes and survival of patients with neuroblastoma.

MIBG in neuroblastoma diagnosis and treatment

Neuroblastoma is a heterogenous disease, with solid tumors arising in the adrenal gland or paraspinal regions in young children. Neuroblastoma is unique, with varied presentation and prognosis based on primary location and tumor stage. Tumor behavior and response to treatment ranges from spontaneous regression to disseminated, lethal disease depending on the individual biology of a patient's tumor. Stratification of the disease has changed, with patients now placed in low, intermediate, and high-risk categories depending on age, stage, and tumor biology. Long-term survival for the high-risk subset of patients with metastatic disease is <40% despite aggressive multimodal therapy. Derived from sympathoadrenal cells of the adrenal medulla and sympathetic nervous system, both malignant neuroblastoma and differentiated tumors have specialized norepinephrine transporter (NET) receptors which are naturally occurring in the sympathetic nervous system throughout the body. Metaiodobenzylguanidine (MIBG) is a norepinephrine analog that undergoes active uptake by NET receptors resulting in accumulation in neuroblastoma as well as tissues normally expressing the NET receptor. When radioiodine labeled, MIBG can be used for both diagnosis and treatment. This article describes the history of MIBG use in neuroblastoma, including its utility as an imaging modality for diagnosis as well as the varied ways in which is it included in the multimodal treatment algorithm.

EANM practical guidance on uncertainty analysis for molecular radiotherapy absorbed dose calculations

A framework is proposed for modelling the uncertainty in the measurement processes constituting the dosimetry chain that are involved in internal absorbed dose calculations. The starting point is the basic model for absorbed dose in a site of interest as the product of the cumulated activity and a dose factor. In turn, the cumulated activity is given by the area under a time-activity curve derived from a time sequence of activity values. Each activity value is obtained in terms of a count rate, a calibration factor and a recovery coefficient (a correction for partial volume effects). The method to determine the recovery coefficient and the dose factor, both of which are dependent on the size of the volume of interest (VOI), are described. Consideration is given to propagating estimates of the quantities concerned and their associated uncertainties through the dosimetry chain to obtain an estimate of mean absorbed dose in the VOI and its associated uncertainty. This approach is demonstrated in a clinical example.

Feasibility of Busulfan Melphalan and Stem Cell Rescue After 131I-MIBG and Topotecan Therapy for Refractory or Relapsed Metastatic Neuroblastoma: The French Experience

High-risk neuroblastoma is characterized by poor long-term survival, especially for very high-risk (VHR) patients (poor response of metastases after induction therapy). The benefits of a tandem high-dose therapy and hematologic stem cell reinfusion (HSCR) have been shown in these patients. Further dose escalation will be limited by toxicity. It is thus important to evaluate the efficacy and tolerability of the addition of new agents such as I-MIBG (131Iode metaiodobenzylguanidine) to be combined with high-dose therapy in the consolidation phase. We report the feasibility of busulfan/melphalan (BuMel) after I-MIBG therapy with HSCR in patients with refractory or relapsed metastatic neuroblastoma. From November 2008 to March 2015, 9 patients received BuMel after I-MIBG therapy and topotecan. The main toxicity was digestive with only 1 patient developing grade 4 sinusoidal obstructive syndrome. Seven patients are alive at a median follow-up of 25 months. Among them, 2 are in ongoing complete remission and 1 in ongoing stable disease. These results suggest that BuMel with HSCR can be administered safely 2 months after I-MIBG therapy associated with topotecan for VHR patients. This strategy will be compared with tandem high-dose chemotherapy (thiotepa and busulfan-melphalan), followed by HSCR in the upcoming SIOPEN VHR Neuroblastoma Protocol.

Current Consensus on I-131 MIBG Therapy

Metaiodobenzylguanidine (MIBG) is structurally similar to the neurotransmitter norepinephrine and specifically targets neuroendocrine cells including some neuroendocrine tumors. Iodine-131 (I-131)-labeled MIBG (I-131 MIBG) therapy for neuroendocrine tumors has been performed for more than a quarter-century. The indications of I-131 MIBG therapy include treatment-resistant neuroblastoma (NB), unresectable or metastatic pheochromocytoma (PC) and paraganglioma (PG), unresectable or metastatic carcinoid tumors, and unresectable or metastatic medullary thyroid cancer (MTC). I-131 MIBG therapy is one of the considerable effective treatments in patients with advanced NB, PC, and PG. On the other hand, I-131 MIBG therapy is an alternative method after more effective novel therapies are used such as radiolabeled somatostatin analogs and tyrosine kinase inhibitors in patients with advanced carcinoid tumors and MTC. No-carrier-aided (NCA) I-131 MIBG has more favorable potential compared to the conventional I-131 MIBG. Astatine-211-labeled meta-astatobenzylguanidine (At-211 MABG) has massive potential in patients with neuroendocrine tumors. Further studies about the therapeutic protocols of I-131 MIBG including NCA I-131 MIBG in the clinical setting and At-211 MABG in both the preclinical and clinical settings are needed.

HIGH-DOSE 131I-MIBG THERAPIES IN CHILDREN: FEASIBILITY, PATIENT DOSIMETRY AND RADIATION EXPOSURE TO WORKERS AND FAMILY CAREGIVERS

The objective of the present multicentric phase II study (MIITOP) was to determine the response rate, survival and toxicity of tandem infusions of 131I-meta-iodobenzylguanidine (mIBG) and topotecan in children with relapsed/refractory neuroblastoma. High-dose 131I-mIBG therapy programme requires a deal of planning, availability of hospital resources and the commitment of individuals with training and expertise in multiple disciplines. Here in the present study, procedures and the results of patient's dosimetry, as well as family and worker's exposures, were reported for the patients treated in Lille. A total of 15 children were treated with 131I-mIBG between 2009 and 2011 according to the MIITOP protocol. High activity of 131I-mIBG (444 MBq kg-1) was administered on Day 0. In vivo dosimetry was used to calculate a second activity, to be given on Day 21, to obtain a total whole body absorbed dose of 4 Gy. Family and worker's exposures were performed too. The injected activity by treatment was from 703 to 11470 MBq. Total whole body absorbed dose by patient ranged from 2.74 to 5.2 Gy. Concerning relatives, whole body exposure ranged from 0.018 to 2.8 mSv. The mean whole body exposure of the radiopharmacist was 4.4 nSv MBq-1, and the mean exposure of fingers ranged from 0.18 to 0.24 µSv MBq-1 according to each finger. The mean whole body exposure was 33.6 and 20.2 µSv d-1 per person, for night nurses and day nurses, respectively. Exposure of doctors was less than 5 µSv d-1. Under strict radiation protection precautions, this study shows the feasibility of high-activity 131I-mIBG therapy in France.

Improved selectivity of mIBG uptake into neuroblastoma cells in vitro and in vivo by inhibition of organic cation transporter 3 uptake using clinically approved corticosteroids

INTRODUCTION

Radiolabeled meta-iodobenzylguanidine (mIBG) is used for imaging and therapy of neuroblastoma as well as pheochromocytoma. However, non-tumorous tissues also incorporate mIBG mainly by organic cation transporters (OCTs). In this study, we tested different clinically approved corticosteroids as potential inhibitors of the OCT3-mediated uptake in vitro and in vivo, to achieve a more selective mIBG tumor uptake.

METHODS

The in vitro incorporation of [(3)H]norepinephrine ([(3)H]NE), [(3)H]dopamine ([(3)H]DA) and [(123)I]mIBG in neuroblastoma cells (SK-N-SH, Kelly, IMR-32) and in HEK-293 cells transfected with human OCT3 was measured with and without supplemental corticosteroids (hydrocortisone, prednisolone, dexamethasone, corticosterone). The in vivo biodistribution of [(123)I]mIBG in absence and presence of corticosteroids was studied in non-tumor bearing NOD scid gamma mice. Retrospectively, we selected patients with and without corticosteroid treatment prior to [(123)I]mIBG scintigraphy.

RESULTS

A concentration-dependent inhibitory effect of different corticosteroids on the [(3)H]NE and [(3)H]DA uptake via OCT3 was illustrated in vitro. The highest OCT3 inhibition was observed for corticosterone, but clinically used corticosteroids, showed also promising inhibitory effects. In contrast, the uptake in neuroblastoma cells was reduced only moderately. Hydrocortisone or prednisolone had only minor effects on [(123)I]mIBG uptake of both neuroblastoma cells, but reduced uptake in OCT3 expressing cells significantly. In mice tissues, [(123)I]mIBG uptake was inhibited by corticosteroids especially in the small intestine and kidney. Finally, in one patient with hydrocortisone treatment performed prior to [(123)I]mIBG scan, heart and liver uptake was reduced compared to untreated patients.

CONCLUSIONS

The OCT3 is widely spread in many organs and responsible for non-targeted uptake of radiolabeled mIBG. In our study, clinically approved corticosteroids inhibited mIBG uptake in OCT3 expressing cells effectively, whereas tracer accumulation in NT (norepinephrine transporter) expressing neuroblastoma cells showed consistency. We conclude, that a single dose of hydrocortisone or prednisolone prior to [(123)I]mIBG scintigraphy may improve specificity and reduce radiation dose to non-target organs.

Nothing but NET: a review of norepinephrine transporter expression and efficacy of 131I-mIBG therapy

Neuroblastoma is unique amongst common pediatric cancers for its expression of the norepinephrine transporter (NET), enabling tumor-selective imaging and therapy with radioactive analogues of norepinephrine. The majority of neuroblastoma tumors are avid for (123)I-metaiodobenzaguanidine (mIBG) on imaging, yet the therapeutic response to (131) I-mIBG is only 30% in clinical trials, and off-target effects cause short- and long-term morbidity. We review the contemporary understanding of the tumor-selective uptake, retention, and efflux of meta-iodobenzylguanidine (mIBG) and strategies currently in development for improving its efficacy. Combination treatment strategies aimed at enhancing NET are likely necessary to reach the full potential of (131)I-mIBG therapy.

Promising therapeutic targets in neuroblastoma

Neuroblastoma, the most common extracranial solid tumor in children, is derived from neural crest cells. Nearly half of patients present with metastatic disease and have a 5-year event-free survival of <50%. New approaches with targeted therapy may improve efficacy without increased toxicity. In this review we evaluate 3 promising targeted therapies: (i) (131)I-metaiodobenzylguanidine (MIBG), a radiopharmaceutical that is taken up by human norepinephrine transporter (hNET), which is expressed in 90% of neuroblastomas; (ii) immunotherapy with monoclonal antibodies targeting the GD2 ganglioside, which is expressed on 98% of neuroblastoma cells; and (iii) inhibitors of anaplastic lymphoma kinase (ALK), a tyrosine kinase that is mutated or amplified in ~10% of neuroblastomas and expressed on the surface of most neuroblastoma cells. Early-phase trials have confirmed the activity of (131)I-MIBG in relapsed neuroblastoma, with response rates of ~30%, but the technical aspects of administering large amounts of radioactivity in young children and limited access to this agent have hindered its incorporation into treatment of newly diagnosed patients. Anti-GD2 antibodies have also shown activity in relapsed disease, and a recent phase III randomized trial showed a significant improvement in event-free survival for patients receiving chimeric anti-GD2 (ch14.18) combined with cytokines and isotretinoin after myeloablative consolidation therapy. A recently approved small-molecule inhibitor of ALK has shown promising preclinical activity for neuroblastoma and is currently in phase I and II trials. This is the first agent directed to a specific mutation in neuroblastoma, and marks a new step toward personalized therapy for neuroblastoma. Further clinical development of targeted treatments offers new hope for children with neuroblastoma.

Preclinical assessment of strategies for enhancement of metaiodobenzylguanidine therapy of neuroendocrine tumors

By virtue of its high affinity for the norepinephrine transporter (NET), [(131)I]metaiodobenzylguanidine ([(131)I]MIBG) has been used for the therapy of tumors of neuroectodermal origin for more than 25 years. Although not yet universally adopted, [(131)I]MIBG targeted radiotherapy remains a highly promising means of management of neuroblastoma, pheochromocytoma, and carcinoids. Appreciation of the mode of conveyance of [(131)I]MIBG into malignant cells and of factors that influence the activity of the uptake mechanism has indicated a variety of means of increasing the effectiveness of this type of treatment. Studies in model systems revealed that radiolabeling of MIBG to high specific activity reduced the amount of cold competitor, thereby increasing tumor dose and minimizing pressor effects. Increased radiotoxicity to targeted tumors might also be achieved by the use of the α-particle emitter [(211)At]astatine rather than (131)I as radiolabel. Recently it has been demonstrated that potent cytotoxic bystander effects were induced by [(131)I]MIBG, [(123)I]MIBG, and [(211)At]meta-astatobenzylguanidine. Discovery of the structure of bystander factors could increase the therapeutic ratio achievable by MIBG targeted radiotherapy. [(131)I]MIBG combined with topotecan produced supra-additive cytotoxicity in vitro and tumor growth delay in vivo. The enhanced antitumor effect was consistent with a failure to repair DNA damage. Initial findings suggest that further enhancement of efficacy might be achieved by triple combination therapy with drugs that disrupt alternative tumor-specific pathways and synergize not only with [(131)I]MIBG abut also with topotecan. With these ploys, it is expected that advances will be made toward the optimization of [(131)I]MIBG therapy of neuroectodermal tumors.

[Radio iodized metaiodobenzylguanidine (MIBG) in the treatment of neuroblastoma: modalities and indications]

Neuroblastoma is the most common pediatric extracranial solid cancer. Patients with metastatic disease at initial diagnosis who are greater than 18  months of age and patients with MycN amplified locoregional tumors are treated with intensive multimodal therapy. While this intensive approach has been shown to improve outcome, patients with high-risk disease frequently relapse and fewer than 50% of these patients will be long-term survivors necessitating new approaches for therapy. Derived from the sympathetic nervous system, this tumor typically expresses the norepinephrine transporter. This transporter mediates active intracellular uptake of metaiodobenzylguanidine (MIBG) an analogue of norepinephrine in approximately 90% of patients allowing the use of radiolabeled (metaiodobenzylguanidine) MIBG, for targeted radiotherapy. This article will review the clinical experience of using MIBG as targeted radiotherapy in neuroblastoma. The administration guidelines, toxicity, response and survival are discussed. Recent studies have evaluated combinations of (131)I-MIBG with myeloablative regimens such as chemotherapy agents with radiation sensitizing properties, or with biologic agents. Most of them report a response rate of 30-40% with (131)I-MIBG in patients with relapsed or refractory neuroblastoma. Due to this high response rates and low non-hematologic toxicity, (131)I-MIBG seems to be an interesting agent for incorporation into the upfront management of newly diagnosed patients with high-risk neuroblastoma.

Autologous and allogeneic cellular therapies for high-risk pediatric solid tumors

Since the 1950s, the overall survival of children with cancer has gone from almost zero to approaching 80%. Although there have been notable successes in treating solid tumors such as Wilms tumor, some childhood solid tumors have continued to elude effective therapy. With the use of megatherapy techniques such as tandem transplantation, dose escalation has been pushed to the edge of dose-limiting toxicities, and any further improvements in event-free survival will have to be achieved through novel therapeutic approaches. This article reviews the status of autologous and allogeneic hematopoietic stem cell transplantation (HSCT) for many pediatric solid tumor types. Most of the clinical experience in transplant for pediatric solid tumors is in the autologous setting, so some general principles of autologous HSCT are reviewed. The article then examines HSCT for diseases such as Hodgkin disease, Ewing sarcoma, and neuroblastoma, and the future of cell-based therapies by considering some experimental approaches to cell therapies.

Radiolabeled metaiodobenzylguanidine for the treatment of neuroblastoma

INTRODUCTION

Neuroblastoma is the most common pediatric extracranial solid cancer. This tumor is characterized by metaiodobenzylguanidine (MIBG) avidity in 90% of cases, prompting the use of radiolabeled MIBG for targeted radiotherapy in these tumors.

METHODS

The available English language literature was reviewed for original research investigating in vitro, in vivo and clinical applications of radiolabeled MIBG for neuroblastoma.

RESULTS

MIBG is actively transported into neuroblastoma cells by the norepinephrine transporter. Preclinical studies demonstrate substantial activity of radiolabeled MIBG in neuroblastoma models, with (131)I-MIBG showing enhanced activity in larger tumors compared to (125)I-MIBG. Clinical studies of (131)I-MIBG in patients with relapsed or refractory neuroblastoma have identified myelosuppression as the main dose-limiting toxicity, necessitating stem cell reinfusion at higher doses. Most studies report a response rate of 30-40% with (131)I-MIBG in this population. More recent studies have focused on the use of (131)I-MIBG in combination with chemotherapy or myeloablative regimens.

CONCLUSIONS

(131)I-MIBG is an active agent for the treatment of patients with neuroblastoma. Future studies will need to define the optimal role of this targeted radiopharmaceutical in the therapy of this disease.

28 years of high-dose therapy and SCT for neuroblastoma in Europe: lessons from more than 4000 procedures

Between 1978 and 2006, the European Group for Blood and Marrow Transplantation registered 4098 high-dose therapy (HDT) procedures followed by stem cell rescue (SCR) (3974 autologous/124 allogeneic) in patients with neuroblastoma. The 5-year rates for overall (OS) and event-free survival are 37 and 32%, respectively. The median age at diagnosis is 3.9 years (0.3-62 years) with 76 patients older than 18 years. Patients above 10 years carry a 2.5-fold higher risk. Younger patients cure significantly (<0.001) better with OS rates of 40 and 30% for age groups 2-4 years and 4-10 years, respectively. Their risks are about twofold higher than that of patients below 2 years with OS rates of 60%. The better the quality of remission status before HDT/SCT the better are the observed OS rates: 43% in CR1 (1199 patients) and 42% for CR2 (140 patients), and 36% for those in very good partial or partial remission (1413 patients) and 21% for those with sensitive relapse (134 patients). Patients reported with stable disease in first remission still had an OS rate of 30%. Multivariate analysis shows significantly better OS in the age group of less than 2 years (<0.0001), as well as a better quality of remission status before HDT/SCT (P<0.0001), with the use of peripheral stem cells (P=0.014), autologous SCT (P=0.031) and busulphan/melphalan HDT (P<0.001). Busulphan/melphalan HDT/SCT in first remission achieves an OS of 48%, while it is only 35% with other regimens (P<0.001), including melphalan alone, other melphalan-containing regimens, a variety of other drugs given as a single HDT as well as the addition of TBI or sequential HDT/SCT procedures. Further progress in the field may only be expected from large-scale international randomized trials.

Iodine-131-metaiodobenzylguanidine as initial induction therapy in stage 4 neuroblastoma patients over 1 year of age

PURPOSE

To determine the response to radionuclide targeted therapy with I-131-metaiodobenzylguanidine ((131)I-MIBG) as induction therapy in high-risk neuroblastoma patients.

PATIENTS AND METHODS

The protocol dictated at least two cycles of (131)I-MIBG with a fixed dose of 7.4 and 3.7 GBq, respectively, followed by surgery, if feasible, or followed by neoadjuvant chemotherapy and surgery. This was followed by consolidation with four courses of chemotherapy myeloablative chemotherapy and autologous stem-cell transplantation (ASCT). Consolidation therapy with 13-cis-retinoic acid was given for 6 months.

RESULTS

Of 44 consecutive patients, 41 were evaluable after two courses of (131)I-MIBG. The objective response rate at this point was 66%. In 24 patients, (131)I-MIBG was continued as pre-operative induction treatment. Seventeen patients required additional chemotherapy before surgery. After pre-operative therapy and surgery, the overall response rate was 73%.

CONCLUSION

First line (131)I-MIBG-targeted therapy is a valuable tool in the treatment of MIBG-positive high-risk neuroblastoma patients.

The radiation burden of radiological investigations

The harmful effects of ionising radiation are widely acknowledged. It has been reported that young children, particularly girls, have a higher sensitivity to radiation than adults. However, the exact detrimental effects of radiation, particularly at the low doses used in routine diagnostic radiography, are unknown and the subject of much controversy. Computed tomography (CT) accounts for about 9% of all radiological examinations but is responsible for 47% of medical radiation dose. Approximately 11% of CT examinations performed are in the paediatric population, but the long-term hazards of CT are unknown.

Phase I dose escalation of iodine-131-metaiodobenzylguanidine with myeloablative chemotherapy and autologous stem-cell transplantation in refractory neuroblastoma: a new approaches to Neuroblastoma Therapy Consortium Study

PURPOSE

To determine the maximum-tolerated dose (MTD) and toxicity of iodine-131-metaiodobenzylguanidine ((131)I-MIBG) with carboplatin, etoposide, melphalan (CEM) and autologous stem-cell transplantation (ASCT) in refractory neuroblastoma.

PATIENTS AND METHODS

Twenty-four children with primary refractory neuroblastoma and no prior ASCT were entered; 22 were assessable for toxicity and response. (131)I-MIBG was administered on day -21, CEM was administered on days -7 to -4, and ASCT was performed on day 0, followed by 13-cis-retinoic acid. (131)I-MIBG was escalated in groups of three to six patients, stratified by corrected glomerular filtration rate (GFR).

RESULTS

The MTD for patients with normal GFR (> or = 100 mL/min/1.73 m2) was 131I-MIBG 12 mCi/kg, carboplatin 1,500 mg/m2, etoposide 1,200 mg/m2, and melphalan 210 mg/m2. In the low-GFR cohort, at the initial dose level using 12 mCi/kg of 131I-MIBG and reduced chemotherapy, one in six patients had dose limiting toxicity (DLT), including veno-occlusive disease (VOD). Three more patients in this group had grade 3 or 4 hepatotoxicity, and two had VOD, without meeting DLT criteria. There was only one death as a result of toxicity among all 24 patients. All assessable patients engrafted, with median time for neutrophils > or = 500/microL of 10 days and median time for platelets > or = 20,000/microL of 26 days. Six of 22 assessable patients had complete or partial response, and 15 patients had mixed response or stable disease. The estimated probability of event-free survival and survival from the day of MIBG infusion for all patients at 3 years was 0.31 +/- 0.10 and 0.58 +/- 0.10, respectively.

CONCLUSION

131I-MIBG with myeloablative chemotherapy is feasible and effective for patients with neuroblastoma exhibiting de novo resistance to chemotherapy.

Feasibility of Dosimetry-Based High-Dose 131I-Meta-Iodobenzylguanidine with Topotecan as a Radiosensitizer in Children with Metastatic Neuroblastoma

INTRODUCTION

(131)I-meta iodobenzylguanidine ((131)I-mIBG) therapy is established palliation for relapsed neuroblastoma. The topoisomerase-1 inhibitor, topotecan, has direct activity against neuroblastoma and acts as a radiation sensitiser. These 2 treatments are synergistic in laboratory studies. Theoretically, the benefit of (131)I-mIBG treatment could be enhanced by dose escalation and combination with topotecan. Haematological support would be necessary to overcome the myelosuppression, which is the dose-limiting toxicity.

AIMS

Firstly, one aim of this study was to establish whether in vivo dosimetry could be used to guide the delivery of a precise total whole-body radiation-absorbed dose of 4 Gy accurately from 2 (131)I-mIBG treatments. Secondly, the other aim of this study was to determine whether it is feasible to combine this treatment with the topotecan in children with metastatic neuroblastoma.

MATERIAL AND METHODS

An activity of (131)I-mIBG (12 mCi/kg, 444 MBq/kg), estimated to give a whole-body absorbed-radiation dose of approximately 2 Gy, was administered on day 1, with topotecan 0.7 mg/m(2) administered daily from days 1-5. In vivo dosimetry was used to calculate a 2nd activity of (131)I-mIBG, to be given on day 15 which would give a total whole-body dose of 4 Gy. A further 5 doses of topotecan were given from days 15-19. The myeloablative effect of this regimen was circumvented by peripheral blood stem cell or bone marrow support.

RESULTS

Eight children with relapsed stage IV neuroblastoma were treated. The treatment was delivered according to protocol in all patients. There were no unanticipated side-effects. Satisfactory haematological reconstitution occurred in all patients. The measured total whole-body radiation-absorbed dose ranged from 3.7 Gy to 4.7 Gy (mean, 4.2 Gy).

CONCLUSIONS

In vivo dosimetry allows for a specified total whole-body radiation dose to be delivered accurately. This schedule of intensification of (131)I-mIBG therapy by dose escalation and radiosensitization with topotecan with a haemopoietic autograft is safe and practicable. This approach should now be tested for efficacy in a phase II clinical trial.

Biodistribution of post-therapeutic versus diagnostic (131)I-MIBG scans in children with neuroblastoma

BACKGROUND

To evaluate the biodistribution of therapeutic (131)I-metaiodobenzylguanidine (MIBG) and assess the sensitivity of diagnostic versus therapeutic (131)I-MIBG scans to detect metastatic disease.

PROCEDURE

This retrospective study included 44 diagnostic and post-therapy scans (PTS) in 18 children with neuroblastoma treated with (131)I-MIBG (2.0-33.1 GBq). The findings of diagnostic scans (DS) (2.6-44.4 MBq) were compared to those of corresponding PTS.

RESULTS

In terms of biodistribution, the PTS identified (131)I-MIBG activity in one or more patients in the following regions not detected on the DS: nasal mucosa, cerebellum, central brain, adrenals, spleen, kidneys, thyroid, salivary glands, lower halves of the lungs, bladder, bowel, and an incisional scar. Conversely, the DS identified activity in the thorax, heart, kidneys, and bladder each in one patient without being visualized on the PTS. In terms of sensitivity to detect metastatic disease, 210 lesions were seen on the PTS compared to 151 on the DS. The PTS demonstrated sites of disease not evident in the DS in 16 cases.

CONCLUSIONS

The biodistribution of (131)I-MIBG is different using therapeutic doses as compared to pre-therapy doses. (131)I-MIBG imaging following high therapeutic doses often reveals sites of occult metastatic disease that may be clinically relevant.

Second malignancies in children with neuroblastoma after combined treatment with 131I-metaiodobenzylguanidine

BACKGROUND

(131)I-metaiodobenzylguanidine ((131)I-MIBG) is selectively taken up by cells of neural crest origin, allowing targeted radiotherapy of tumors such as neuroblastoma (NB) and pheochromocytoma. Radiotherapy may provide additional benefits in the treatment of NB, with moderate side effects such as hematologic and thyroid toxicity. However, with longer follow-up, other complications might occur. We describe our experience with second cancers occurring in children treated with (131)I-MIBG and chemotherapy.

METHODS

The clinical records of 119 consecutive NB cases treated with (131)I-MIBG at a single institution between 1984 and 2001 were reviewed for the occurrence of a second malignant neoplasm (SMN).

RESULTS

Overall, five cases of SMN occurred in the study patients. In particular, two cases of myeloid leukemia, one of angiomatous fibrous histiocytoma, one of malignant schwannoma, and one case of rhabdomyosarcoma were detected. The schwannoma and the rhabdomyosarcoma developed within the residual neuroblastic mass after first-line therapy.

CONCLUSIONS

Should (131)I-MIBG treatment become more broadly employed in the therapeutic strategy for neuroblastoma, the risk of second cancer will have to be taken into consideration. The organization of an international registry of subjects treated with (131)I-MIBG might better define the frequency and features of second malignancies following this radiometabolic approach.

Pilot study of iodine-131-metaiodobenzylguanidine in combination with myeloablative chemotherapy and autologous stem-cell support for the treatment of neuroblastoma

PURPOSE

The survival for children with relapsed or metastatic neuroblastoma remains poor. More effective regimens with acceptable toxicity are required to improve prognosis. Iodine-131-metaiodobenzylguanidine ((131)I-MIBG) selectively targets radiation to catecholamine-producing cells, including neuroblastoma cells. A pilot study was performed to examine the feasibility of a novel regimen combining (131)I-MIBG and myeloablative chemotherapy with autologous stem-cell rescue.

PATIENTS AND METHODS

Twelve patients with neuroblastoma were treated after relapse (five patients) or after induction therapy (seven patients). Eight patients had metastatic and four had localized disease at the time of therapy. All patients received (131)I-MIBG 12 mCi/kg on day -21, followed by carboplatin (1,500 mg/m(2)), etoposide (800 mg/m(2)), and melphalan (210 mg/m(2)) administered from day -7 to day -4. Autologous peripheral-blood stem cells or bone marrow were infused on day 0. Engraftment, toxicity, and response rates were evaluated.

RESULTS

The (131)I-MIBG infusion and myeloablative chemotherapy were both well tolerated. Grade 2 to 3 oral mucositis was the predominant nonhematopoietic toxicity, occurring in all patients. The median times to neutrophil (> or = 0.5 x 10(3)/microL) and platelet (> or = 20 x 10(3)/microL) engraftment were 10 and 28 days, respectively. For the eight patients treated with metastatic disease, three achieved complete response and two had partial responses by day 100 after transplantation.

CONCLUSION

Treatment with (131)I-MIBG in combination with myeloablative chemotherapy and hematopoietic stem-cell rescue is feasible with acceptable toxicity. Future study is warranted to examine the efficacy of this novel therapy.

Megatherapy combining I(131) metaiodobenzylguanidine and high-dose chemotherapy with haematopoietic progenitor cell rescue for neuroblastoma

Despite the use of aggressive chemotherapy, stage 4 high risk neuroblastoma still has very poor prognosis which is estimated at 25%. Metabolic radiotherapy with I(131) MIBG appears a feasible option to enhance the effects of chemotherapy. Seventeen patients having MIBG-positive residual disease received 4.1-11.1 mCi/kg of I(131) MIBG 7-10 days before initiating the high-dose chemotherapy cycle consisting of busulphan 16 mg/kg and melphalan 140 mg/m(2) followed by PBSC infusion. We compared the toxicity in these patients to that seen in 15 control subjects with neuroblastoma who underwent a PBSC transplant without MIBG therapy. We observed greater toxic involvement of the gastrointestinal system in children treated with I(131) MIBG: grade 2 or 3 mucositis developed in 13/17 patients treated with I(131) MIBG and in 9/15 treated without it. Grade 1-2 gastrointestinal toxicity occurred in 12/17 children given MIBG and in 5/15 of the controls. One child receiving I(131) MIBG developed transient interstitial pneumonia. Another child who also received I(131) MIBG after PBSC rescue developed fatal pneumonia after the third course of metabolic radiotherapy. Our experience indicates that MIBG can be included in the high-dose chemotherapy regimens followed by PBSC rescue for children with residual neuroblastoma taking up MIBG. Attention should be paid to avoiding lung complications. Prospective studies are needed to demonstrate the real efficacy of this treatment.

Radiation physics and genetic targeting: new directions for radiotherapy. The Douglas Lea Lecture 1999

Radiation as a cancer treatment modality is of high physical precision but limited biological specificity. Targeted radiotherapy, the delivery of radiation to cancer cells by radioisotopes conjugated to tumour-seeking targeting agents, is a biologically attractive option but is currently effective for just a few tumour types (neuroblastoma, lymphoma) for which efficacious targeting agents are available. Radiobiological modelling and radiation microdosimetry have provided useful guidelines in choosing treatment strategies for targeted radiotherapy. These considerations generally favour the incorporation of targeted radiotherapy as one component of a multimodal treatment regimen. Very recently, gene therapy techniques have been developed which should enhance the clinical efficacy of both external beam radiation and targeted radiotherapy. Typically, non-harmful viruses are modified to incorporate therapeutic genes which cause altered cellular radiosensitivity or which facilitate the cellular uptake of targeting agents. To achieve specificity, therapeutic genes would be co-transfected with tissue-specific promoter genes causing the therapeutic genes to be expressed in cells of particular types. In laboratory models, our research group are exploring the transfection-mediated uptake of the targeting agents MIBG and sodium iodide. These approaches do not require transfection of every cell in order to cure a tumour-cells which have escaped transfection may be sterilized by radiation cross-fire from transfected neighbours. A new task for radiation microdosimetry is to quantify the cross-fire effect and to compute the efficacies of gene transfection which will be required for tumour cure. In the spirit of Douglas Lea, the analytic approach of physics can be used to illuminate and enhance developments in genetics, to the benefit of medicine.

131I-metaiodobenzylguanidine (131I-MIBG) therapy for residual neuroblastoma: a mono-institutional experience with 43 patients

Incomplete response to therapy may compromise the outcome of children with advanced neuroblastoma. In an attempt to improve tumour response we incorporated 131I-metaiodobenzylguanidine (131I-MIBG) in the treatment regimens of selected stage 3 and stage 4 patients. Between 1986 and 1997, 43 neuroblastoma patients older than 1 year at diagnosis, 13 with stage 3 (group A) and 30 with stage 4 disease (group B) who had completed the first-line protocol without achieving complete response entered in this study. 131I-MIBG dose/course ranged from 2.5 to 5.5 Gbq (median, 3.7). The number of courses ranged from 1 to 5 (median 3) depending on the tumour response and toxicity. The most common acute side-effect was thrombocytopenia. Later side-effects included severe interstitial pneumonia in one patient, acute myeloid leukaemia in two, reduced thyroid reserve in 21. Complete response was documented in one stage 4 patient, partial response in 12 (two stage 3, 10 stage 4), mixed or no response in 25 (ten stage 3, 15 stage 4) and disease progression in five (one stage 3, four stage 4) Twenty-four patients (12/13 stage 3, 12/30 stage 4) are alive at 22-153 months (median, 59) from diagnosis. 131I-MIBG therapy may increase the cure rate of stage 3 and improve the response of stage 4 neuroblastoma patients with residual disease after first-line therapy. A larger number of patients should be treated to confirm these results but logistic problems hamper prospective and coordinated studies. Long-term toxicity can be severe.

Influence of cisplatin and doxorubicin on 125I-meta-iodobenzylguanidine uptake in human neuroblastoma cell lines

The combination of 131I-meta-iodobenzylguanidine (MIBG) with chemotherapy has recently been employed in the treatment of advanced stage neuroblastoma with encouraging results. However, the mechanisms underlying the interaction between these two different modalities of treatment have not yet been explored. In this study, human neuroblastoma cell lines pretreatment with cisplatin and doxorubicin increased cellular 125I-MIBG accumulation in a dose-dependent manner. Cell cycle analysis showed that increased 125I-MIBG accumulation correlated with the drug-induced G2/M phase block. Northern blot analysis demonstrated an increase in gene expression of the noradrenaline transporter induced by doxorubicin, but not by cisplatin treatment. Increased 125I-MIBG accumulation was also observed in murine xenografts of the human neuroblastoma cell line SK-N-DZ or BE(2)M17 treated intraperitoneally (i.p.) with cisplatin or doxorubicin, respectively. These results suggest that the combination of 131I-MIBG and these drugs could selectively increase radiation doses delivered to neuroblastomas.

131I MIBG therapy in neuroblastoma: mechanisms, rationale, and current status

131I MIBG has been used as palliative treatment of neuroblastoma patients with recurrent or persistent disease who failed other modalities of treatment. Since the results were promising, the concept arose of using it in conjunction with other modalities, either as an up-front treatment or as combination therapy. This article reviews the principle of 131I MIBG treatment, in conjunction with other modalities currently used for the treatment of neuroblastoma, in an attempt to improve the final outcome.

Neuroblastoma

The neuroblastic tumours originate from primordial neural crest cells that normally develop into sympathetic nervous system, including the adrenal medulla. Neuroblastoma is the most intriguing pediatric neoplasm displaying diverse clinical and biologic characteristics and natural history. It has the highest rate of spontaneous regression of all human cancers, yet exhibits extremely malignant behaviour in older children with regional and disseminated disease. In the last 30 years, only a nominal improvement has occurred in the outlook of older children with metastatic disease at diagnosis. Tremendous gains in understanding of the biology of neuroblastoma in recent years have led to development of risk-related therapy based on age, stage and biological characteristics of neuroblastoma.

Treatment of neuroblastoma stage 4 with 131I-meta-iodo-benzylguanidine, high-dose chemotherapy and immunotherapy. A pilot study

Disseminated neuroblastoma after infancy has a prognosis of approximately 10-20% with conventional therapy. We investigated the role of high-dose chemotherapy (HDCT) with peripheral blood stem cell (PBSC) rescue in combination with 131I-metaiodobenzylguanidine ([131I-m]IBG). 11 children with neuroblastoma stage 4 were pretreated within the German Neuroblastoma Trial NB90 and included in a high-dose concept for consolidation. Remission was documented by ultrasound, CT, NMR, or [123I-m]IBG scanning. HDCT was a combination of melphalan (180 mg/m2), carboplatin (1,500 mg/m2) and etoposide (40 mg/kg). All children were treated by [131I-m]IBG (0.58 GBq/kg) prior to high-dose treatment. All 11 children were additionally treated with antiGD2 murine- or chimeric-antibody (ch14.18). 4 children had no change to their remission status but three achieved a complete response (from a partial response to first line) and one a partial response (from no response to first line). The other 3 children progressed, 2 dying of their disease. Using Kaplan-Meier analysis, the probability of progression-free survival was 0.70 +/- 0.15 with a median observation time of 19 months. 9/11 children are alive, 8 without progression or relapse, whilst 2 have died of their disease. The combination of mIBG plus high-dose chemotherapy with PBSC support supplemented by immunotherapy with antiGD2 antibody appears to be a feasible and effective treatment regimen for disseminated neuroblastoma in this limited series. Larger numbers of patients should be treated to confirm these results.

Role of 131I-metaiodobenzylguanidine in the treatment of neuroblastoma

BACKGROUND

Standard chemo-radiotherapy methods for the treatment of children with advanced neuroblastoma (NBL) including bone marrow transplant approaches have been disappointing. These poor results can be ascribed to the evolution of residual drug-resistant cell populations. Curative attempts should therefore be directed to their elimination during induction treatment. This can best be accomplished through the use of multiple, non-cross-resistant agents early in therapy. 131I-Metaiodobenzylguanidine (131I-MIBG) provides a mechanism for the delivery of high doses of radiation to NBL lesions. Experience reported from several institutions indicates an approximate 50% response rate in previously treated children with advanced NBL.

CONCLUSIONS

A better strategy is to employ 131I-MIBG together with intensive chemotherapy at the time of diagnosis. A pilot study adopting these principles and supported by laboratory data has been designed and is underway.

Engraftment after myeloablative doses of 131I-metaiodobenzylguanidine followed by autologous bone marrow transplantation for treatment of refractory neuroblastoma

BACKGROUND

Metaiodobenzylguanidine (MIBG) labeled with 131I has been used for targeted radiotherapy of neural crest tumors, with bone marrow suppression being the primary dose-limiting toxicity. The purpose of this study was to examine the engraftment and toxicity of higher myeloablative doses of 131I-MIBG with autologous bone marrow support.

PROCEDURE

Twelve patients with refractory neuroblastoma were given infusions of their autologous, cryopreserved bone marrow following 1-4 doses of 131I-MIBG. The median cumulative administered activity per kilogram of 131I-MIBG was 18.0 mCi/kg (range 14.1-50.2 mCi/kg), the median total activity was 594 mCi (range 195-1,353 mCi), and the median cumulative whole body irradiation from 131I-MIBG was 426 cGy (range 256-800 cGy). A median of 2.5 x 10(8) viable cells/kg (range 0.9-4.7 x 10(8) cells/kg) was given in the bone marrow infusion.

RESULTS

All 12 patients achieved an absolute neutrophil count > 500/microliter with a median of 19 days, but only 5/11 evaluable patients achieved red cell transfusion independence, in a median of 44 days; and 4/11 evaluable patients achieved platelet count > 20,000/microliter without transfusion, in a median of 27 days.

CONCLUSIONS

Autologous bone marrow transplantation may allow complete hematopoietic reconstitution following ablative 131I-MIBG radiotherapy in patients with neuroblastoma. Risk factors for lack of red cell or platelet recovery include extensive prior chemotherapy, progressive disease at the time of transplant, especially in the bone marrow, and a history of prior myeloablative therapy with stem cell support.

Toxicity to neuroblastoma cells and spheroids of benzylguanidine conjugated to radionuclides with short-range emissions

Radiolabelled meta-iodobenzylguanidine (MIBG) is selectively taken up by tumours of neuroendocrine origin, where its cellular localization is believed to be cytoplasmic. The radiopharmaceutical [131I]MIBG is now widely used in the treatment of neuroblastoma, but other radioconjugates of benzylguanidine have been little studied. We have investigated the cytotoxic efficacy of beta, alpha and Auger electron-emitting radioconjugates in treating neuroblastoma cells grown in monolayer or spheroid culture. Using a no-carrier-added synthesis route, we produced 123I-, 125I-, 131I- and 211At-labelled benzylguanidines and compared their in vitro toxicity to the neuroblastoma cell line SK-N-BE(2c) grown in monolayer and spheroid culture. The Auger electron-emitting conjugates ([123I]MIBG and [125I]MIBG) and the alpha-emitting conjugate ([211At]MABG) were highly toxic to monolayers and small spheroids, whereas the beta-emitting conjugate [131I]MIBG was relatively ineffective. The Auger emitters were more effective than expected if the cellular localization of MIBG is cytoplasmic. As dosimetrically predicted however, [211At]MABG was found to be extremely potent in terms of both concentration of radioactivity and number of atoms ml(-1) administered. In contrast, the Auger electron emitters were ineffective in the treatment of larger spheroids, while the beta emitter showed greater efficacy. These findings suggest that short-range emitters would be well suited to the treatment of circulating tumour cells or small clumps, whereas beta emitters would be superior in the treatment of subclinical metastases or macroscopic tumours. These experimental results provide support for a clinical strategy of combinations ('cocktails') of radioconjugates in targeted radiotherapy.

The radiobiological basis of total body irradiation

Total body irradiation (TBI) is an all-pervasive systemic treatment modality which is well suited to the sterilization of small numbers of widely dispersed radiosensitive cells. This makes it attractive for the treatment of leukaemia or lymphoma in remission. It is unlikely that hypoxia or repopulation will be a problem in TBI treatment of leukaemia, and clonal resistance to radiation occurs less readily than to drugs. Leukaemic cells are often radiosensitive with poor repair capacities but considerable variation is seen in laboratory studies and leukaemias may be highly individual. It is possible that programmed cell death (apoptosis) contributes to leukaemic cell killing and variability of apoptosis may give rise to biological individuality. Molecular methodologies may now be used to monitor leukaemic cell populations and may enable semi-quantitative predictive assays of radiosensitivity. When the malignant cell population is not uniformly distributed throughout the body, as in lymphoma, non-uniform TBI is appropriate, e.g. by addition of local boosts or by the combination of TBI with radiolabelled antibody treatment. Major side-effects mostly relate to critical organs with late-responding characteristics (low alpha/beta ratio, high sensitivity to fraction size or dose rate). The radiobiological basis of developmental effects in children is not well understood. In future, improved selectivity of TBI may come from molecular biological strategies to sensitize malignant cells and to protect normal tissues.

Radionuclide developments

This review considers a number of recent important developments in nuclear medicine, and possible future introductions, priority being given to those products which are most likely to find a place in clinical practice. This includes both novel radiopharmaceuticals and progress with new types of imaging equipment. Three areas are chosen as being of particular importance: brain imaging, heart imaging, and diagnosis and therapy of cancer. In the brain, the clinical value of imaging regional cerebral blood flow and certain aspects of the neuroreceptor/neurotransmitter system are discussed. Cardiac imaging is considered in the light of recent work on diagnosis and risk assessment, investigating the hibernating myocardium, and the possible place of fatty acid imaging. Both diagnosis and therapy of cancer are increasingly important, and the use of radionuclides in these areas in considered.

Biology and treatment of neuroblastoma

Neuroblastoma is an enigmatic tumor that has the highest rate of spontaneous regression of all human malignant neoplasms, yet has one of the poorest outcomes when occurring as disseminated disease in children. The emergence of neuroblastoma tumor biology, coupled with age and stage of diagnosis, has allowed more accurate routing of patients to risk-related therapy and refining of such therapy to minimize treatment for those with low risk for recurrent disease and searching out new treatment strategies for patients with high-risk disease. Continued assessment of tumor biologic features in all patients will provide new insights into tumorigenesis, cell differentiation, and death pathways, resulting in the potential for developing newer therapies for patients with high-risk disease.

Neuroblastoma

The neuroblastic tumours, derived from primordial neural crest cells which ultimately populate the sympathetic ganglia, adrenal medulla and other sites, (Brodeur GM and Castleberry RP. Neuroblastoma. In Pizzo PA, Poplack DG, eds, Principles and Practice of Pediatric Oncology. Philadelphia, J. B. Lippincott Co., 1997, 761-797) are an enigmatic group of neoplasms which have the highest rate of spontaneous regression of all human malignant neoplasms yet one of the poorest outcomes when occurring as disseminated disease in children. Significant advances in understanding and predicting the natural history of neuroblastoma have resulted from translational studies coupling tumour biology and clinical features to form prognostic strata and allowing more accurate routeing of patients to risk-related management. While this strategy has clarified the management for lower risk tumours, little improvement in survival for higher risk disease has been realised. Ironically, this latter patient subset, for which the most innovative therapeutic strategies are needed, is also the one from which the least tumour biology is gleaned owing to inadequate tissue sampling. This update will summarise the evolving biology of neuroblastoma and its relationship to current risk-related therapy and future management strategies. Throughout this report, prognostic grouping by age will be infants (< 1 year) versus children (> or = 1 year) since the change of risk according to age seems most distinct at this cut-off point.