[131I]MIBG and topotecan: a rationale for combination therapy for neuroblastoma

Reaching the target dose with one single 131 I-mIBG administration in high-risk neuroblastoma: The determinant impact of the primary tumour

BACKGROUND

131 I-metaiodobenzylguanidine (131 I-mIBG) effectiveness in children with metastasised neuroblastoma (NB) is linked to the effective dose absorbed by the target; a target of 4 Gy whole-body dose threshold has been proposed. Achieving this dose often requires administering 131 I-mIBG twice back-to-back, which may cause haematological toxicity. In this study, we tried identifying the factors predicting the achievement of 4 Gy whole-body dose with a single radiopharmaceutical administration.

MATERIALS AND METHODS

Children affected by metastatic NB and treated with a high 131 I-mIBG activity (>450 MBq (megabecquerel)/kg) were evaluated retrospectively. Kinetics measurements were carried out at multiple time points to estimate the whole-body dose, which was compared with clinical and activity-related parameters.

RESULTS

Seventeen children (12 females, median age 3 years, age range: 1.5-6.9 years) were included. Eleven of them still bore the primary tumour. The median whole-body dose was 2.88 Gy (range: 1.63-4.22 Gy). Children with a 'bulky' primary (>30 mL) received a higher whole-body dose than those with smaller or surgically removed primaries (3.42 ± 0.74 vs. 2.48 ± 0.65 Gy, respectively, p = .016). Conversely, the correlation between activity/kg and the whole-body dose was moderate (R: 0.42, p = .093). In the multivariate analysis, the volume of the primary tumour was the most relevant predictor of the whole-body dose (p = .002).

CONCLUSIONS

These data suggest that the presence of a bulky primary tumour can significantly prolong the 131 I-mIBG biological half-life, effectively increasing the absorbed whole-body dose. This information could be used to model the administered activity, allowing to attain the target dose without needing a two-step radiopharmaceutical administration.

Norepinephrine transporter analog benzylguanidine-conjugated nanoparticles for the delivery of paclitaxel in neuroblastoma

Aim: We previously synthesized a polyethylene glycol-based norepinephrine transporter-targeted agent, BG-P-TAT, which has a benzylguanidine and a triazolyl-tetrac group. This targeted conjugate showed suppression of neuroblastoma tumor progression. In this study we aimed to synthesize nanoparticles to encapsulate the chemotherapeutic agent paclitaxel for targeting neuroblastoma tumors by using benzylguanidine so that it can compete with norepinephrine for uptake by neuroendocrine cells. Methods: Biocompatible poly(lactide-co-glycolic acid)-polyethylene glycol was chosen to prepare targeted nanoparticles for safe delivery of the chemotherapy agent paclitaxel. Result: Paclitaxel concentration was 60% higher in neuroblastoma tumors of mice treated with paclitaxel encapsulated in targeted nanoparticles than with non-targeted nanoparticles. Conclusion: These findings support the targeted delivery of paclitaxel as a chemotherapeutic agent for neuroblastoma.

Paediatric Molecular Radiotherapy: Challenges and Opportunities

The common contemporary indications for paediatric molecular radiotherapy (pMRT) are differentiated thyroid cancer and neuroblastoma. It may also have value in neuroendocrine cancers, and it is being investigated in clinical trials for other diseases. pMRT is the prototypical biomarker-driven, precision therapy, with a unique mode of delivery and mechanism of action. It is safe and well tolerated, compared with other treatments. However, its full potential has not yet been achieved, and its wider use faces a number of challenges and obstacles. Paradoxically, the success of radioactive iodine as a curative treatment for metastatic thyroid cancer has led to a 'one size fits all' approach and limited academic enquiry into optimisation of the conventional treatment regimen, until very recently. Second, the specialised requirements for the delivery of pMRT are available in only a very limited number of centres. This limited capacity and geographical coverage results in reduced accessibility. With few enthusiastic advocates for this treatment modality, investment in research to improve treatments and broaden indications from both industry and national and charitable research funders has historically been suboptimal. Nonetheless, there is now an increasing interest in the opportunities offered by pMRT. Increased research funding has been allocated, and technical developments that will permit innovative approaches in pMRT are available for exploration. A new portfolio of clinical trials is being assembled. These studies should help to move at least some paediatric treatments from simply palliative use into potentially curative protocols. Therapeutic strategies require modification and optimisation to achieve this. The delivery should be personalised and tailored appropriately, with a comprehensive evaluation of tumour and organ-at-risk dosimetry, in alignment with the external beam model of radiotherapy. This article gives an overview of the current status of pMRT, indicating the barriers to progress and identifying ways in which these may be overcome.

A phase IIa trial of molecular radiotherapy with 177-lutetium DOTATATE in children with primary refractory or relapsed high-risk neuroblastoma

PURPOSE

The objective of this phase IIa, open-label, single-centre, single-arm, two-stage clinical trial was to evaluate the safety and activity of 177-lutetium DOTATATE (LuDO) molecular radiotherapy in neuroblastoma.

METHODS

Children with relapsed or refractory metastatic high-risk neuroblastoma were treated with up to four courses of LuDO. The administered activity was 75 to 100 MBq kg-1 per course, spaced at 8- to 12-week intervals. Outcomes were assessed by the International Neuroblastoma Response Criteria (primary outcome), progression-free survival (PFS), and overall survival (OS).

RESULTS

The trial recruited 21 patients; eight received the planned four courses. There was dose-limiting haematologic toxicity in one case, but no other significant haematologic or renal toxicities. None of 14 evaluable patients had an objective response at 1 month after completion of treatment (Wilson 90% CI 0.0, 0.16; and 95% CI is 0.0, 0.22). The trial did not therefore proceed to the second stage. The median PFS was 2.96 months (95% CI 1.71, 7.66), and the median OS was 13.0 months (95% CI 2.99, 21.52).

CONCLUSION

In the absence of any objective responses, the use of LuDO as a single agent at the dose schedule used in this study is not recommended for the treatment of neuroblastoma. There are several reasons why this treatment schedule may not have resulted in objective responses, and as other studies do show benefit, the treatment should not be regarded as being of no value. Further trials designed to overcome this schedule's limitations are required.

TRIAL REGISTRATION

ISRCTN98918118; URL: https://www.isrctn.com/search?q=98918118.

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.

Preliminary evaluation of prostate-targeted radiotherapy using (131) I-MIP-1095 in combination with radiosensitising chemotherapeutic drugs

Objectives

Despite recent advances in the treatment of metastatic prostate cancer, survival rates are low and treatment options are limited to chemotherapy and hormonal therapy. ¹³¹I‐MIP‐1095 is a recently developed prostate‐specific membrane antigen (PSMA)‐targeting, small molecular weight radiopharmaceutical which has anti‐tumour activity as a single agent. Our purpose was to determine in vitro the potential benefit to be gained by combining ¹³¹I‐MIP‐1095 with cytotoxic drug treatments.

Methods

Various cytotoxic agents were evaluated in combination with ¹³¹I‐MIP‐1095 for their capacity to delay the growth of LNCaP cells cultured as multicellular tumour spheroids. Two end‐points were used to assess treatment efficacy: (i) the time required for doubling of spheroid volume and (ii) the area under the volume–time growth curves.

Key findings

The PARP‐1 inhibitor olaparib, the topoisomerase I inhibitor topotecan, the proteasome inhibitor bortezomib, the inhibitor of the P53–MDM2 interaction nutlin‐3 and the copper‐chelated form of the oxidising agent disulfiram (DSF:Cu) all significantly enhanced the inhibition of the growth of spheroids induced by ¹³¹I‐MIP‐1095. However, the Chk1 inhibitor AZD7762 failed to potentiate the effect of ¹³¹I‐MIP‐1095.

Conclusions

These results indicate that targeted radiotherapy of prostate cancer may be optimised by combining its administration with chemotherapy.

Upfront treatment of high-risk neuroblastoma with a combination of 131I-MIBG and topotecan

BACKGROUND

(131)I-metaiodobenzylguanidine ((131) I-MIBG) has a significant anti-tumor effect against neuroblastoma (NBL). Topotecan (TPT) can act as a radio-sensitizer and can up-regulate (131) I-MIBG uptake in vitro in NBL.

AIM

Determine the efficacy of the combination of (131) I-MIBG with topotecan in newly diagnosed high-risk (HR) NBL patients.

METHODS

In a prospective, window phase II study, patients with newly diagnosed high-risk neuroblastoma were treated at diagnosis with two courses of (131) I-MIBG directly followed by topotecan (0.7 mg/m(2) for 5 days). After these two courses, standard induction treatment (four courses of VECI), surgery and myeloablative therapy (MAT) with autologous stem cell transplantation (ASCT) was given. Response was measured after two courses of (131) I-MIBG-topotecan and post MAT and ASCT. Hematologic toxicity and harvesting of stem cells were analysed. Topoisomerase-1 activity levels were analysed in primary tumor material.

RESULTS

Sixteen patients were included in the study; median age was 2.8 years. MIBG administered activity (AA) (median and range) of the first course was 0.5 (0.4-0.6) GBq/kg (giga Becquerel/kilogram) and of the second course 0.4 (0.3-0.5) GBq/kg. The overall objective response rate (ORR) after 2 × MIBG/TPT was 57%, the primary tumor RR was 94%, and bone marrow RR was 43%. The ORR post MAT and ASCT was 57%. Hematologic grade four toxicity: after first and second (131) I-MIBG (platelets 25/33%, neutrophils 13/33%, and hemoglobin 25/7%). Topoisomerase-1 activity levels were increased in 10/10 (100%) measured tumors.

CONCLUSIONS

Combination therapy with MIBG-topotecan is an effective window treatment in newly diagnosed high-risk neuroblastoma patients.

Inhibition of poly(ADP-Ribose) polymerase enhances the toxicity of 131I-metaiodobenzylguanidine/topotecan combination therapy to cells and xenografts that express the noradrenaline transporter

Targeted radiotherapy using (131)I-metaiodobenzylguanidine ((131)I-MIBG) has produced remissions in some neuroblastoma patients. We previously reported that combining (131)I-MIBG with the topoisomerase I inhibitor topotecan induced long-term DNA damage and supraadditive toxicity to noradrenaline transporter (NAT)-expressing cells and xenografts. This combination treatment is undergoing clinical evaluation. This present study investigated the potential of poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP-1) inhibition, in vitro and in vivo, to further enhance (131)I-MIBG/topotecan efficacy.

METHODS

Combinations of topotecan and the PARP-1 inhibitor PJ34 were assessed for synergism in vitro by combination-index analysis in SK-N-BE(2c) (neuroblastoma) and UVW/NAT (NAT-transfected glioma) cells. Three treatment schedules were evaluated: topotecan administered 24 h before, 24 h after, or simultaneously with PJ34. Combinations of PJ34 and (131)I-MIBG and of PJ34 and (131)I-MIBG/topotecan were also assessed using similar scheduling. In vivo efficacy was measured by growth delay of tumor xenografts. We also assessed DNA damage by γH2A.X assay, cell cycle progression by fluorescence-activated cell sorting analysis, and PARP-1 activity in treated cells.

RESULTS

In vitro, only simultaneous administration of topotecan and PJ34 or PJ34 and (131)I-MIBG induced supraadditive toxicity in both cell lines. All scheduled combinations of PJ34 and (131)I-MIBG/topotecan induced supraadditive toxicity and increased DNA damage in SK-N-BE(2c) cells, but only simultaneous administration induced enhanced efficacy in UVW/NAT cells. The PJ34 and (131)I-MIBG/topotecan combination treatment induced G(2) arrest in all cell lines, regardless of the schedule of delivery. In vivo, simultaneous administration of PJ34 and (131)I-MIBG/topotecan significantly delayed the growth of SK-N-BE(2c) and UVW/NAT xenografts, compared with (131)I-MIBG/topotecan therapy.

CONCLUSION

The antitumor efficacy of topotecan, (131)I-MIBG, and (131)I-MIBG/topotecan combination treatment was increased by PARP-1 inhibition in vitro and in vivo.

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.

Preclinical evaluation of an 131I-labeled benzamide for targeted radiotherapy of metastatic melanoma

Radiolabeled benzamides are attractive candidates for targeted radiotherapy of metastatic melanoma as they bind melanin and exhibit high tumor uptake and retention. One such benzamide, N-(2-diethylamino-ethyl)-4-(4-fluoro-benzamido)-5-iodo-2-methoxy-benzamide (MIP-1145), was evaluated for its ability to distinguish melanin-expressing from amelanotic human melanoma cells, and to specifically localize to melanin-containing tumor xenografts. The binding of [(131)I]MIP-1145 to melanoma cells in vitro was melanin dependent, increased over time, and insensitive to mild acid treatment, indicating that it was retained within cells. Cold carrier MIP-1145 did not reduce the binding, consistent with the high capacity of melanin binding of benzamides. In human melanoma xenografts, [(131)I]MIP-1145 exhibited diffuse tissue distribution and washout from all tissues except melanin-expressing tumors. Tumor uptake of 8.82% injected dose per gram (ID/g) was seen at 4 hours postinjection and remained at 5.91% ID/g at 24 hours, with tumor/blood ratios of 25.2 and 197, respectively. Single photon emission computed tomography imaging was consistent with tissue distribution results. The administration of [(131)I]MIP-1145 at 25 MBq or 2.5 GBq/m(2) in single or multiple doses significantly reduced SK-MEL-3 tumor growth, with multiple doses resulting in tumor regression and a durable response for over 125 days. To estimate human dosimetry, gamma camera imaging and pharmacokinetic analysis was performed in cynomolgus monkeys. The melanin-specific binding of [(131)I]MIP-1145 combined with prolonged tumor retention, the ability to significantly inhibit tumor growth, and acceptable projected human dosimetry suggest that it may be effective as a radiotherapeutic pharmaceutical for treating patients with metastatic malignant melanoma.

The role of 131I-MIBG in high-risk neuroblastoma treatment

Despite aggressive research and treatment, high-risk neuroblastoma continues to have a devastating mortality rate of more than 40%. Research conducted over the past 2 decades has shown that the radioisotope (131)I-MIBG (metaiodobenzylguanidine) is effective in the treatment of this difficult patient population. The purpose of this article is to review the diagnosis, staging, and conventional treatment of neuroblastoma and to understand the mechanism of action of MIBG and ( 131)I-MIBG. This article also reviews treatments for high-risk neuroblastoma patients and analyzes recent research studies that used (131)I-MIBG to better define the role of this treatment in high-risk neuroblastoma patients. In addition, this article explores the role of the advanced practice nurse to serve at the forefront in the implementation of a multidisciplinary ( 131)I-MIBG treatment program.

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.

The norepinephrine transporter and pheochromocytoma

Pheochromocytomas are rare neuroendocrine tumors of chromaffin cell origin that synthesize and secrete excess quantities of catecholamines and other vasoactive peptides. Pheochromocytomas also express the norepinephrine transporter (NET), a molecule that is used clinically as a means of incorporating radiolabelled substrates such as 131I-MIBG (iodo-metaiodobenzylguanidine) into pheochromocytoma tumor cells. This allows the diagnostic localization of these tumors and, more recently, 131I-MIBG has been used in trials in the treatment of pheochromocytoma, potentially giving rise to NET as a therapeutic target. However, because of varying levels or activities of the transporter, the ability of 131I-MIBG to be consistently incorporated into tumor cells is limited, and therefore various strategies to increase NET functional activity are being investigated, including the use of traditional chemotherapeutic agents such as cisplatin or doxorubicin. Other aspects of NET discussed in this short review include the regulation of the transporter and how novel protein-protein interactions between NET and structures such as syntaxin 1A may hold the key to innovative ways to increase the therapeutic value of 131I-MIBG.