Differentiated expression of somatostatin receptor subtypes in experimental models and clinical neuroblastoma

Imaging of pediatric neuroblastoma: A COG Diagnostic Imaging Committee/SPR Oncology Committee White Paper

Neuroblastoma is the most common extracranial solid neoplasm in children. This manuscript provides consensus-based imaging recommendations for pediatric neuroblastoma patients at diagnosis and during follow-up.

Nanomedicines and cell-based therapies for embryonal tumors of the nervous system

Embryonal tumors of the nervous system are neoplasms predominantly affecting the pediatric population. Among the most common and aggressive ones are neuroblastoma (NB) and medulloblastoma (MB). NB is a sympathetic nervous system tumor, which is the most frequent extracranial solid pediatric cancer, usually detected in children under two. MB originates in the cerebellum and is one of the most lethal brain tumors in early childhood. Their tumorigenesis presents some similarities and both tumors often have treatment resistances and poor prognosis. High-risk (HR) patients require high dose chemotherapy cocktails associated with acute and long-term toxicities. Nanomedicine and cell therapy arise as potential solutions to improve the prognosis and quality of life of children suffering from these tumors. Indeed, nanomedicines have been demonstrated to efficiently reduce drug toxicity and improve drug efficacy. Moreover, these systems have been extensively studied in cancer research over the last few decades and an increasing number of anticancer nanocarriers for adult cancer treatment has reached the clinic. Among cell-based strategies, the clinically most advanced approach is chimeric-antigen receptor (CAR) T therapy for both pathologies, which is currently under investigation in phase I/II clinical trials. However, pediatric drug research is especially hampered due not only to ethical issues but also to the lack of efficient pre-clinical models and the inadequate design of clinical trials. This review provides an update on progress in the treatment of the main embryonal tumors of the nervous system using nanotechnology and cell-based therapies and discusses key issues behind the gap between preclinical studies and clinical trials in this specific area. Some directions to improve their translation into clinical practice and foster their development are also provided.

A Phase II Trial of a Personalized, Dose-Intense Administration Schedule of 177Lutetium-DOTATATE in Children With Primary Refractory or Relapsed High-Risk Neuroblastoma-LuDO-N

Background

Half the children with high-risk neuroblastoma die with widespread metastases. Molecular radiotherapy is an attractive systemic treatment for this relatively radiosensitive tumor. 131I-mIBG is the most widely used form in current use, but is not universally effective. Clinical trials of 177Lutetium DOTATATE have so far had disappointing results, possibly because the administered activity was too low, and the courses were spread over too long a period of time, for a rapidly proliferating tumor. We have devised an alternative administration schedule to overcome these limitations. This involves two high-activity administrations of single agent 177Lu-DOTATATE given 2 weeks apart, prescribed as a personalized whole body radiation absorbed dose, rather than a fixed administered activity. "A phase II trial of 177Lutetium-DOTATATE in children with primary refractory or relapsed high-risk neuroblastoma - LuDO-N" (EudraCT No: 2020-004445-36, ClinicalTrials.gov Identifier: NCT04903899) evaluates this new dosing schedule.

Methods

The LuDO-N trial is a phase II, open label, multi-center, single arm, two stage design clinical trial. Children aged 18 months to 18 years are eligible. The trial is conducted by the Nordic Society for Pediatric Hematology and Oncology (NOPHO) and it has been endorsed by SIOPEN (https://www.siopen.net). The Karolinska University Hospital, is the sponsor of the LuDO-N trial, which is conducted in collaboration with Advanced Accelerator Applications, a Novartis company. All Scandinavian countries, Lithuania and the Netherlands participate in the trial and the UK has voiced an interest in joining in 2022.

Results

The pediatric use of the Investigational Medicinal Product (IMP) 177Lu-DOTATATE, as well as non-IMPs SomaKit TOC® (68Ga-DOTATOC) and LysaKare® amino acid solution for renal protection, have been approved for pediatric use, within the LuDO-N Trial by the European Medicines Agency (EMA). The trial is currently recruiting. Recruitment is estimated to be finalized within 3-5 years.

Discussion

In this paper we present the protocol of the LuDO-N Trial. The rationale and design of the trial are discussed in relation to other ongoing, or planned trials with similar objectives. Further, we discuss the rapid development of targeted radiopharmaceutical therapy and the future perspectives for developing novel therapies for high-risk neuroblastoma and other pediatric solid tumors.

p53-Mediated Radiosensitization of 177Lu-DOTATATE in Neuroblastoma Tumor Spheroids

p53 is involved in DNA damage response and is an exciting target for radiosensitization in cancer. Targeted radionuclide therapy against somatostatin receptors with 177Lu-DOTATATE is currently being explored as a treatment for neuroblastoma. The aim of this study was to investigate the novel p53-stabilizing peptide VIP116 in neuroblastoma, both as monotherapy and together with 177Lu-DOTATATE. Five neuroblastoma cell lines, including two patient-derived xenograft (PDX) lines, were characterized in monolayer cultures. Four out of five were positive for 177Lu-DOTATATE uptake. IC50 values after VIP116 treatments correlated with p53 status, ranging between 2.8-238.2 μM. IMR-32 and PDX lines LU-NB-1 and LU-NB-2 were then cultured as multicellular tumor spheroids and treated with 177Lu-DOTATATE and/or VIP116. Spheroid growth was inhibited in all spheroid models for all treatment modalities. The most pronounced effects were observed for combination treatments, mediating synergistic effects in the IMR-32 model. VIP116 and combination treatment increased p53 levels with subsequent induction of p21, Bax and cleaved caspase 3. Combination treatment resulted in a 14-fold and 1.6-fold induction of MDM2 in LU-NB-2 and IMR-32 spheroids, respectively. This, together with differential MYCN signaling, may explain the varying degree of synergy. In conclusion, VIP116 inhibited neuroblastoma cell growth, potentiated 177Lu-DOTATATE treatment and could, therefore, be a feasible treatment option for neuroblastoma.

Neuroblastoma xenograft models demonstrate the therapeutic potential of 177Lu-octreotate

BACKGROUND

Neuroblastoma (NB) is one of the most frequently diagnosed tumors in infants. NB is a neuroendocrine tumor type with various characteristics and features, and with diverse outcome. The most malignant NBs have a 5-year survival rate of only 40-50%, indicating the need for novel and improved treatment options. 177Lu-octreotate is routinely administered for treatment of neuroendocrine tumors overexpressing somatostatin receptors (SSTR). The aim of this study was to examine the biodistribution of 177Lu-octreotate in mice bearing aggressive human NB cell lines, in order to evaluate the potential usefulness of 177Lu-octreotate for treatment of NB.

METHODS

BALB/c nude mice bearing CLB-BAR, CLB-GE or IMR-32 tumor xenografts (n = 5-7/group) were i.v. injected with 0.15 MBq, 1.5 MBq or 15 MBq 177Lu-octreotate and sacrificed 1 h, 24 h, 48 h and 168 h after administration. The radioactivity concentration was determined for collected tissue samples, tumor-to-normal-tissue activity concentration ratios (T/N) and mean absorbed dose for each tissue were calculated. Immunohistochemical (IHC) staining for SSTR1-5, and Ki67 were carried out for tumor xenografts from the three cell lines.

RESULTS

High 177Lu concentration levels and T/N values were observed in all NB tumors, with the highest for CLB-GE tumor xenografts (72%IA/g 24 h p.i.; 1.5 MBq 177Lu-octreotate). The mean absorbed dose to the tumor was 6.8 Gy, 54 Gy and 29 Gy for CLB-BAR, CLB-GE and IMR-32, respectively, p.i. of 15 MBq 177Lu-octreotate. Receptor saturation was clearly observed in CLB-BAR, resulting in higher concentration levels in the tumor when lower activity levels where administered. IHC staining demonstrated highest expression of SSTR2 in CLB-GE, followed by CLB-BAR and IMR-32.

CONCLUSION

T/N values for all three human NB tumor xenograft types investigated were high relative to previously investigated neuroendocrine tumor types. The results indicate a clear potential of 177Lu-octreotate as a therapeutic alternative for metastatic NB.

68Ga-DOTATATE and 123I-mIBG as imaging biomarkers of disease localisation in metastatic neuroblastoma: implications for molecular radiotherapy

PURPOSE

Iodine-131-labelled meta-iodobenzylguanidine (I-mIBG) and lutetium-177-labelled DOTATATE (Lu-DOTATATE) are used for molecular radiotherapy of metastatic neuroblastoma. These are taken up by the noradrenaline transporter (NAT) and the somatostatin receptor subtype 2 (SSTR-2), respectively. Scintigraphy of iodine-123-labelled meta-iodobenzylguanidine (I-mIBG) and gallium-68 DOTATATE (Ga-DOTATATE) PET are used to select patients for therapy. These demonstrate the extent and location of tumour, and avidity of uptake by cells expressing NAT and SSTR-2, respectively. This study compared the similarities and differences in the anatomical distribution of these two imaging biomarkers in an unselected series of patients with metastatic neuroblastoma undergoing assessment for molecular radiotherapy.

METHODS

Paired whole-body planar I-mIBG views and Ga-DOTATATE maximum intensity projection PET scans of metastatic neuroblastoma patients were visually compared. The disease extent was assessed by a semiquantitative scoring method.

RESULTS

Paired scans from 42 patients were reviewed. Ga-DOTATATE scans were positive in all patients, I-mIBG scans were negative in two. In two patients, there was a mismatch, with some lesions identified only on the I-mIBG scan, and others visible only on the Ga-DOTATATE scan.

CONCLUSION

Ga-DOTATATE and I-mIBG scans yield complementary information. For a more comprehensive assessment, consideration could be given to the use of both I-mIBG and Ga-DOTATATE imaging scans. Because of the heterogeneity of distribution of molecular targets revealed by these techniques, a combination of both I-mIBG and Lu-DOTATATE molecular radiotherapy may possibly be more effective than either alone.

Feasibility and Therapeutic Potential of Combined Peptide Receptor Radionuclide Therapy With Intensive Chemotherapy for Pediatric Patients With Relapsed or Refractory Metastatic Neuroblastoma

BACKGROUND

Recent evidence has demonstrated high expression of somatostatin receptors in neuroblastoma (NB) cells. Because of this, we endeavored to evaluate the diagnostic performance and clinical efficacy of 68Ga-DOTATATE PET/CT and peptide receptor radionuclide therapy (PRRT) using 177Lu-DOTATATE combined with chemotherapy in pediatric NB patients.

PATIENTS AND METHODS

In total, 14 pediatric patients with histopathologically confirmed NB underwent 68Ga-DOTATATE PET/CT. Among them, the patients who were refractory or relapsed after therapy with 131I-MIBG and had intensive uptake of 68Ga-DOTATATE were referred for PRRT using 177Lu-DOTATATE. Treatment response based on follow-up imaging was classified into complete response, partial response, stable disease, and progressive disease. After each cycle of PRRT, laboratory tests were performed for evaluation of hematological, renal, and hepatic toxicities. The CTCAE (Common Terminology Criteria for Adverse Events; version 4.03) was used for grading adverse event. Curie score and International Society of Pediatric Oncology Europe Neuroblastoma score were used for semiquantitative analysis of scans of patients who underwent PRRT. In addition, overall survival was calculated as the time interval between the date of the first cycle and the end of follow-up or death.

RESULTS

Overall, 14 refractory NB children including 7 boys and 7 girls with a median age of 5.5 years (ranged from 4 to 9) underwent 68Ga-DOTATATE PET/CT. PET/CT was positive in 10/14 patients (71.4%), and the median number of detected lesions in positive patients was 2 (range, 1-13). Of 14 patients, 5 patients underwent PRRT, including 3 boys and 2 girls. A total of 19 PRRT cycles and 66.4 GBq 177Lu-DOTATATE were given. Among these 5 patients, 2 showed an initial complete response, which relapsed a few months later, 1 showed a partial response, and 2 showed progressive disease. According to the Kaplan-Meier test, the overall survival was estimated at 14.5 months (95% confidence interval, 8.9-20.1). In evaluation of PRRT-related toxicity according to the CTCAE, 4 patients showed grade 1, and 1 showed grade 2 leukopenia. Two patients showed grade 1, and 2 others showed grade 2 anemia. Two patients showed grade 1, and 3 patients showed grade 2 thrombocytopenia. Serum creatinine in 1 patient increased to grade 1.

CONCLUSIONS

Combination of 177Lu-DOTATATE with chemotherapeutic agents might achieve worthwhile responses with low toxicity, encouraging survival in NB patients who have relapsed or are refractory to conventional therapy, including 131I-MIBG therapy. Imaging with 68Ga-DOTATATE PET/CT in such patients has a relatively high detection efficacy, demonstrating its potential use as an alternative imaging tool to conventional modalities such as 123I/131I-MIBG. However, further well-designed trials are highly warranted.

On the mechanism of tumor cell entry of aloe-emodin, a natural compound endowed with anticancer activity

Aloe‐emodin (1,8‐dihydroxy‐3‐[hydroxymethyl]‐anthraquinone), AE, is one of the active constituents of a number of plant species used in traditional medicine. We have previously identified, for the first time, AE as a new antitumor agent and shown that its selective in vitro and in vivo killing of neuroblastoma cells was promoted by a cell‐specific drug uptake process. However, the molecular mechanism underlying the cell entry of AE has remained elusive as yet. In this report, we show that AE enters tumor cells via two of the five somatostatin receptors: SSTR2 and SSTR5. This observation was suggested by gene silencing, receptor competition, imaging and molecular modeling experiments. Furthermore, SSTR2 was expressed in all surgical neuroblastoma specimens we analyzed by immunohistochemistry. The above findings have strong implications for the clinical adoption of this natural anthraquinone molecule as an antitumor agent.

Nuclear Medicine Imaging in Neuroblastoma: Current Status and New Developments

Neuroblastoma is the most common extracranial solid malignancy in children. At diagnosis, approximately 50% of patients present with metastatic disease. These patients are at high risk for refractory or recurrent disease, which conveys a very poor prognosis. During the past decades, nuclear medicine has been essential for the staging and response assessment of neuroblastoma. Currently, the standard nuclear imaging technique is meta-[¹²³I]iodobenzylguanidine ([¹²³I]mIBG) whole-body scintigraphy, usually combined with single-photon emission computed tomography with computed tomography (SPECT-CT). Nevertheless, 10% of neuroblastomas are mIBG non-avid and [¹²³I]mIBG imaging has relatively low spatial resolution, resulting in limited sensitivity for smaller lesions. More accurate methods to assess full disease extent are needed in order to optimize treatment strategies. Advances in nuclear medicine have led to the introduction of radiotracers compatible for positron emission tomography (PET) imaging in neuroblastoma, such as [¹²⁴I]mIBG, [¹⁸F]mFBG, [¹⁸F]FDG, [⁶⁸Ga]Ga-DOTA peptides, [¹⁸F]F-DOPA, and [¹¹C]mHED. PET has multiple advantages over SPECT, including a superior resolution and whole-body tomographic range. This article reviews the use, characteristics, diagnostic accuracy, advantages, and limitations of current and new tracers for nuclear medicine imaging in neuroblastoma.

Detection and therapy of neuroblastoma minimal residual disease using [64/67Cu]Cu-SARTATE in a preclinical model of hepatic metastases

Background

A major challenge to the long-term success of neuroblastoma therapy is widespread metastases that survive initial therapy as minimal residual disease (MRD). The SSTR2 receptor is expressed by most neuroblastoma tumors making it an attractive target for molecularly targeted radionuclide therapy. SARTATE consists of octreotate, which targets the SSTR2 receptor, conjugated to MeCOSar, a bifunctional chelator with high affinity for copper. Cu-SARTATE offers the potential to both detect and treat neuroblastoma MRD by using [⁶⁴Cu]Cu-SARTATE to detect and monitor the disease and [⁶⁷Cu]Cu-SARTATE as the companion therapeutic agent. In the present study, we tested this theranostic pair in a preclinical model of neuroblastoma MRD. An intrahepatic model of metastatic neuroblastoma was established using IMR32 cells in nude mice. The biodistribution of [⁶⁴Cu]Cu-SARTATE was measured using small-animal PET and ex vivo tissue analysis. Survival studies were carried out using the same model: mice (6–8 mice/group) were given single doses of saline, or 9.25 MBq (250 µCi), or 18.5 MBq (500 µCi) of [⁶⁷Cu]Cu-SARTATE at either 2 or 4 weeks after tumor cell inoculation.

Results

PET imaging and ex vivo biodistribution confirmed tumor uptake of [⁶⁴Cu]Cu-SARTATE and rapid clearance from other tissues. The major clearance tissues were the kidneys (15.6 ± 5.8% IA/g at 24 h post-injection, 11.5 ± 2.8% IA/g at 48 h, n = 3/4). Autoradiography and histological analysis confirmed [⁶⁴Cu]Cu-SARTATE uptake in viable, SSTR2-positive tumor regions with mean tumor uptakes of 14.1–25.0% IA/g at 24 h. [⁶⁷Cu]Cu-SARTATE therapy was effective when started 2 weeks after tumor cell inoculation, extending survival by an average of 13 days (30%) compared with the untreated group (mean survival of control group 43.0 ± 8.1 days vs. 55.6 ± 9.1 days for the treated group; p = 0.012). No significant therapeutic effect was observed when [⁶⁷Cu]Cu-SARTATE was started 4 weeks after tumor cell inoculation, when the tumors would have been larger (control group 14.6 ± 8.5 days; 9.25 MBq group 9.5 ± 1.6 days; 18.5 MBq group 15.6 ± 4.1 days; p = 0.064).

Conclusions

Clinical experiences of peptide-receptor radionuclide therapy for metastatic disease have been encouraging. This study demonstrates the potential for a theranostic approach using [^64/67Cu]Cu-SARTATE for the detection and treatment of SSTR2-positive neuroblastoma MRD.

Prevalence and Clinical Correlations of Somatostatin Receptor-2 (SSTR2) Expression in Neuroblastoma

Alternative radiolabeled, targeted agents are being investigated for children with relapsed neuroblastoma (NB) who do not respond to I-metaiodobenzylguanidine (MIBG) therapy. (DOTA-Tyr)-octreotate targets somatostatin receptors (SSTRs), particularly SSTR2, which are expressed on NB cells. We investigated SSTR2 expression in NB tumors (36 high-risk [HR]; 33 non-HR patients) and correlated SSTR2 levels with clinical features, norepinephrine transporter (NET) expression, and MIBG avidity. SSTR2 and NET immunohistochemistry scores (0 to 3) were calculated on biopsies using digital image analysis based on staining intensity and distribution. Clinical data were correlated with SSTR2 expression. Median SSTR2 score for 69 patients was 1.31 (0.26 to 2.55). Non-HR NB was associated with a higher SSTR2 score (P=0.032). The SSTR2 expression did not correlate with age, International Neuroblastoma Staging System (INSS) stage, MYCN amplification and histology. Higher SSTR2 scores were observed in MIBG-avid versus MIBG-nonavid NB. SSTR2 score was not significantly associated with NET score (r=-0.062, P=0.62). Twenty-six patients who relapsed or progressed had a median SSTR2 score of 1.33 (0.26 to 2.55). Patients with NB including relapsed or progressive disease showed SSTR2 expression at diagnosis, suggesting they could be candidates for radiolabeled-DOTA-conjugated peptide imaging or therapy.

Current management of neuroblastoma and future direction

Neuroblastoma is the most common solid extracranial tumor in pediatrics and can regress spontaneously or grow and metastasize with resistance to multiple therapeutic approaches. The prognosis and approach to treatment depends on the tumor presentation and whether it expresses certain drivers such as MYCN, ALK, and TrkB. Expression or mutation of these genes and kinases correlates with high-risk and poor prognosis. Multiple therapeutic approaches are being used to target MYCN, ALK, and TrkB, as well as GD2, a surface antigen present on the surface of neuroblastoma tumor cells. This review discusses the nature of these targets and several current therapies for neuroblastoma. A focus is placed on recent therapeutic developments including targeted delivery of chemotherapy, novel radiation therapy, and immunotherapy.

Guidelines on nuclear medicine imaging in neuroblastoma

Nuclear medicine has a central role in the diagnosis, staging, response assessment and long-term follow-up of neuroblastoma, the most common solid extracranial tumour in children. These EANM guidelines include updated information on ¹²³I-mIBG, the most common study in nuclear medicine for the evaluation of neuroblastoma, and on PET/CT imaging with ¹⁸F-FDG, ¹⁸F-DOPA and ⁶⁸Ga-DOTA peptides. These PET/CT studies are increasingly employed in clinical practice. Indications, advantages and limitations are presented along with recommendations on study protocols, interpretation of findings and reporting results.

An evaluation in vitro of the efficacy of nutlin-3 and topotecan in combination with 177Lu-DOTATATE for the treatment of neuroblastoma

Targeted radiotherapy of metastatic neuroblastoma using the somatostatin receptor (SSTR)-targeted octreotide analogue DOTATATE radiolabelled with lutetium-177 (¹⁷⁷Lu-DOTATATE) is a promising strategy. This study evaluates whether its effectiveness may be enhanced by combination with radiosensitising drugs. The growth rate of multicellular tumour spheroids, derived from the neuroblastoma cell lines SK-N-BE(2c), CHLA-15 and CHLA-20, was evaluated following treatment with ¹⁷⁷Lu-DOTATATE, nutlin-3 and topotecan alone or in combination. Immunoblotting, immunostaining and flow cytometric analyses were used to determine activation of p53 signalling and cell death. Exposure to ¹⁷⁷Lu-DOTATATE resulted in a significant growth delay in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Nutlin-3 enhanced the spheroid growth delay induced by topotecan in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Importantly, the combination of nutlin-3 with topotecan enhanced the spheroid growth delay induced by X-irradiation or by exposure to ¹⁷⁷Lu-DOTATATE. The efficacy of the combination treatments was p53-dependent. These results indicate that targeted radiotherapy of high risk neuroblastoma with ¹⁷⁷Lu-DOTATATE may be improved by combination with the radiosensitising drugs nutlin-3 and topotecan.

Immunohistochemical evaluation of molecular radiotherapy target expression in neuroblastoma tissue

PURPOSE

Neuroblastoma may be treated with molecular radiotherapy, 131I meta-Iodobenzylguanidine and 177Lu Lutetium DOTATATE, directed at distinct molecular targets: Noradrenaline Transporter Molecule (NAT) and Somatostatin Receptor (SSTR2), respectively. This study used immunohistochemistry to evaluate target expression in archival neuroblastoma tissue, to determine whether it might facilitate clinical use of molecular radiotherapy.

METHODS

Tissue bank samples of formalin fixed paraffin embedded neuroblastoma tissue from patients for whom clinical outcome data were available were sectioned and stained with haematoxylin and eosin, and monoclonal antibodies directed against NAT and SSTR2. Sections were examined blinded to clinical information and scored for the percentage and intensity of tumour cells stained. These data were analysed in conjunction with clinical data.

RESULTS

Tissue from 75 patients was examined. Target expression scores varied widely between patients: NAT median 45%, inter-quartile range 25% - 65%; and SSTR2 median 55%, interquartile range 30% - 80%; and in some cases heterogeneity of expression between different parts of a tumour was observed. A weak positive correlation was observed between the expression scores of the different targets: correlation coefficient = 0.23, p = 0.05. MYCN amplified tumours had lower SSTR2 scores: mean difference 23% confidence interval 8% - 39%, p < 0.01. Survival did not differ by scores.

CONCLUSIONS

As expression of both targets is variable and heterogeneous, imaging assessment of both may yield more clinical information than either alone. The clinical value of immunohistochemical assessment of target expression requires prospective evaluation. Variable target expression within a patient may contribute to treatment failure.

Correlation of Somatostatin Receptor-2 Expression with Gallium-68-DOTA-TATE Uptake in Neuroblastoma Xenograft Models

Peptide-receptor imaging and therapy with radiolabeled somatostatin analogs such as ⁶⁸Ga-DOTA-TATE and ¹⁷⁷Lu-DOTA-TATE have become an effective treatment option for SSTR-positive neuroendocrine tumors. The purpose of this study was to evaluate the correlation of somatostatin receptor-2 (SSTR2) expression with ⁶⁸Ga-DOTA-TATE uptake and ¹⁷⁷Lu-DOTA-TATE therapy in neuroblastoma (NB) xenograft models. We demonstrated variable SSTR2 expression profiles in eight NB cell lines. From micro-PET imaging and autoradiography, a higher uptake of ⁶⁸Ga-DOTA-TATE was observed in SSTR2 high-expressing NB xenografts (CHLA-15) compared to SSTR2 low-expressing NB xenografts (SK-N-BE(2)). Combined autoradiography-immunohistochemistry revealed histological colocalization of SSTR2 and ⁶⁸Ga-DOTA-TATE uptake in CHLA-15 tumors. With a low dose of ¹⁷⁷Lu-DOTA-TATE (20 MBq/animal), tumor growth inhibition was achieved in the CHLA-15 high SSTR2 expressing xenograft model. Although, in vitro, NB cells showed variable expression levels of norepinephrine transporter (NET), a molecular target for ¹³¹I-MIBG therapy, low ¹²³I-MIBG uptake was observed in all selected NB xenografts. In conclusion, SSTR2 expression levels are associated with ⁶⁸Ga-DOTA-TATE uptake and antitumor efficacy of ¹⁷⁷Lu-DOTA-TATE. ⁶⁸Ga-DOTA-TATE PET is superior to ¹²³I-MIBG SPECT imaging in detecting NB tumors in our model. Radiolabeled DOTA-TATE can be used as an agent for NB tumor imaging to potentially discriminate tumors eligible for ¹⁷⁷Lu-DOTA-TATE therapy.

Initial Experience With Gallium-68 DOTA-Octreotate PET/CT and Peptide Receptor Radionuclide Therapy for Pediatric Patients With Refractory Metastatic Neuroblastoma

RATIONALE

Pediatric patients with refractory neuroblastoma have limited therapeutic options. Neuroblastoma may express somatostatin receptors (SSTRs) allowing imaging with 68Ga-DOTA-Octreotate (GaTATE) positron emission tomography/computed tomography (PET/CT) and peptide receptor radionuclide therapy (PRRT). We reviewed our experience with this theranostic combination.

MATERIALS AND METHODS

GaTATE studies (8 patients; 2 to 9 years old) were reviewed and compared with 123I-MIBG or posttreatment 131I-MIBG studies. Immunohistochemistry (IHC) for SSTR subtype 2 was performed in 5 patients. Four patients received PRRT.

RESULTS

GaTATE PET showed additional disease in 38% (3/8 patients), and upstaged 1 patient by detecting marrow involvement. IHC detected SSTR 2 in all patients assessed. Six patients were deemed suitable for PRRT on imaging. Four patients received 17 cycles of palliative PRRT (10 111In-DOTATATE; 5 177Lu-DOTATATE; 1 combined 111In and 177Lu-DOTATATE; 1 combined 177Lu and 90Y-DOTATATE) with no significant toxicity attributed to PRRT. All had objective responses. Two survivors are now 40 and 56 months from PRRT commencement.

CONCLUSIONS

GaTATE PET was positive in a high proportion of patients with refractory neuroblastoma, correlating with SSTR 2 on IHC, with additional disease identified compared with MIBG imaging. PRRT seems safe, feasible, with responses observed in patients with progression despite multimodality treatment. These data support ongoing clinical trials in such patients.

Expressions of Somatostatin Receptor Subtypes (SSTR-1, 2, 3, 4 and 5) in Neuroblastic Tumors; Special Reference to Clinicopathological Correlations with International Neuroblastoma Pathology Classification and Outcomes

Somatostatin receptor (SSTR) expressions in neuroblastomas (NBs) have been confirmed employing various methods. High SSTR-2 expression was suggested to be a favorable prognostic marker, though little is known about the relationships between the expressions of SSTR subtypes, other than SSTR-2, and prognosis. We investigated the expressions of all five known SSTR subtypes in 63 neuroblastic tumors (NTs), employing immunohistochemistry, and also conducted quantitative real-time RT-PCR in 37 of these tumors. We evaluated correlations between the expressions of SSTR subtypes and prognosis, based on the International Neuroblastoma Pathology Classification and patient outcomes. More than 90% of cases expressed, at a minimum, SSTR-1 and/or 2. Ganglioneuromas and ganglioneuroblastomas expressed more than two SSTR subtypes. Among NBs, the favorable histology group showed higher SSTR subtype expressions than the unfavorable histology group. The same tendency was observed when surviving and deceased cases were compared, though SSTR-2 expression was well preserved in some of the deceased cases. In conclusion, NTs highly expressed SSTR-1 and/or 2, and expressions of SSTR generally indicate a good prognosis. However, even those in the unfavorable histology group with NBs expressing SSTR are good candidates for molecular targeting therapy using somatostatin analogues.

Ga-68 DOTATATE positron emission tomography/computer tomography in initial staging and therapy response evaluation in a rare case of primary neuroblastoma in neck

Gallium-68 (Ga-68) DOTA-peptide positron emission tomography/computer tomography (PET/CT) has higher sensitivity and improved spatial resolution for the detection of somatostatin receptor expressing tumors than conventional somatostatin receptor scintigraphy. We present the findings of Ga-68 DOTATATE PET/CT in a rare case of primary neuroblastoma of the neck in a 12-year-old female child and its role in the evaluation of the treatment response.

Nuclear medicine and multimodality imaging of pediatric neuroblastoma

Neuroblastoma is an embryonic tumor of the peripheral sympathetic nervous system and is metastatic or high risk for relapse in nearly 50% of cases. Therefore, exact staging with radiological and nuclear medicine imaging methods is crucial for defining the adequate therapeutic choice. Tumor cells express the norepinephrine transporter, which makes metaiodobenzylguanidine (MIBG), an analogue of norepinephrine, an ideal tumor specific agent for imaging. MIBG imaging has several disadvantages, such as limited spatial resolution, limited sensitivity in small lesions and the need for two or even more acquisition sessions. Most of these limitations can be overcome with positron emission tomography (PET) using [F-18]2-fluoro-2-deoxyglucose [FDG]. Furthermore, new tracers, such as fluorodopa or somatostatin receptor agonists, have been tested for imaging neuroblastoma recently. However, MIBG scintigraphy and PET alone are not sufficient for operative or biopsy planning. In this regard, a combination with morphological imaging is indispensable. This article will discuss strategies for primary and follow-up diagnosis in neuroblastoma using different nuclear medicine and radiological imaging methods as well as multimodality imaging.

Virotherapy of neuroendocrine tumors

Most patients with small intestinal neuroendocrine tumors (SI-NETs), also referred to as midgut carcinoids, present with systemic disease at the time of diagnosis with metastases primarily found in regional lymph nodes and the liver. Curative treatment is not available for these patients and there is a need for novel and specific therapies. Engineered oncolytic viruses may meet the need and play an important role in the future management of SI-NET liver metastases. This review focuses on adenovirus as the oncolytic anti-cancer agent and its potential curative role for SI-NET liver metastases, but it also summarizes the use of oncolytic viruses for NETs in general. It discusses how specific features of neuroendocrine cell biology can be used to engineer viruses to become selective for infection of NET cells and/or replication within NET cells. In addition, it points out the advantages and shortcomings of using replicating viruses in the treatment of cancer and addresses research fields that can increase the efficacy of virus-based therapy.

177Lu-DOTATATE molecular radiotherapy for childhood neuroblastoma

This study tested the principle that (68)Ga-DOTATATE PET/CT may be used to select children with primary refractory or relapsed high-risk neuroblastoma for treatment with (177)Lu-DOTATATE and evaluated whether this is a viable therapeutic option for those children.

METHODS

Between 2008 and 2010, 8 children with relapsed or refractory high-risk neuroblastoma were studied with (68)Ga-DOTATATE PET/CT. The criterion of eligibility for (177)Lu-DOTATATE therapy was uptake on the diagnostic scan equal to or higher than that of the liver.

RESULTS

Of the 8 children imaged, 6 had abnormally high uptake on the (68)Ga-DOTATATE PET/CT scan and proceeded to treatment. Patients received 2 or 3 administrations of (177)Lu-DOTATATE at a median interval of 9 wk and a median administered activity of 7.3 GBq. Of the 6 children treated, 5 had stable disease by the response evaluation criteria in solid tumors (RECIST). Of these 5 children, 2 had an initial metabolic response and reduction in the size of their lesions, and 1 patient had a persistent partial metabolic response and reduction in size of the lesions on CT, although the disease was stable by RECIST. One had progressive disease. Three children had grade 3 and 1 child had grade 4 thrombocytopenia. No significant renal toxicity has been seen.

CONCLUSION

(68)Ga-DOTATATE can be used to image children with neuroblastoma and identify those suitable for molecular radiotherapy with (177)Lu-DOTATATE. We have shown, for what is to our knowledge the first time, that treatment with (177)Lu-DOTATATE is safe and feasible in children with relapsed or primary refractory high-risk neuroblastoma. We plan to evaluate this approach formally in a phase I-II clinical trial.