Approach to the patient: Concept and application of targeted radiotherapy in the paraganglioma patient

Paragangliomas can metastasize, posing potential challenges in both symptomatic management and disease control. Systemic targeted radiotherapies using 131I-MIBG and 177Lu-DOTATATE are a mainstay in the treatment of metastatic paragangliomas. This clinical scenario and discussion aim to enhance physicians' knowledge of the stepwise approach to treat these patients with paraganglioma targeted radiotherapies. It comprehensively discusses current approaches to selecting paraganglioma patients for targeted radiotherapies and how to choose between the two radiotherapies based on specific patient and tumor characteristics, when either therapy is feasible, or one is superior to another one. The safety, efficacy, toxicity profiles, and optimization of these radiotherapies are also discussed, along with other therapeutic options including radiotherapies, available for patients besides these two therapies. As conclusion, perspectives in radiotherapies of paraganglioma patients are outlined since they hold near future promising approaches that can improve patient outcomes.

Diagnostic performance of [68Ga]DOTATATE PET/CT, [18F]FDG PET/CT, MRI of the spine, and whole-body diagnostic CT and MRI in the detection of spinal bone metastases associated with pheochromocytoma and paraganglioma

OBJECTIVE

To compare the diagnostic performance of [68Ga]DOTATATE PET/CT, [18F]FDG PET/CT, MRI of the spine, and whole-body CT and MRI for the detection of pheochromocytoma/paraganglioma (PPGL)-related spinal bone metastases.

MATERIALS AND METHODS

Between 2014 and 2020, PPGL participants with spinal bone metastases prospectively underwent [68Ga]DOTATATE PET/CT, [18F]FDG PET/CT, MRI of the cervical-thoracolumbar spine (MRIspine), contrast-enhanced MRI of the neck and thoraco-abdominopelvic regions (MRIWB), and contrast-enhanced CT of the neck and thoraco-abdominopelvic regions (CTWB). Per-patient and per-lesion detection rates were calculated. Counting of spinal bone metastases was limited to a maximum of one lesion per vertebrae. A composite of all functional and anatomic imaging served as an imaging comparator. The McNemar test compared detection rates between the scans. Two-sided p values were reported.

RESULTS

Forty-three consecutive participants (mean age, 41.7 ± 15.7 years; females, 22) with MRIspine were included who also underwent [68Ga]DOTATATE PET/CT (n = 43), [18F]FDG PET/CT (n = 43), MRIWB (n = 24), and CTWB (n = 33). Forty-one of 43 participants were positive for spinal bone metastases, with 382 lesions on the imaging comparator. [68Ga]DOTATATE PET/CT demonstrated a per-lesion detection rate of 377/382 (98.7%) which was superior compared to [18F]FDG (72.0%, 275/382, p < 0.001), MRIspine (80.6%, 308/382, p < 0.001), MRIWB (55.3%, 136/246, p < 0.001), and CTWB (44.8%, 132/295, p < 0.001). The per-patient detection rate of [68Ga]DOTATATE PET/CT was 41/41 (100%) which was higher compared to [18F]FDG PET/CT (90.2%, 37/41, p = 0.13), MRIspine (97.6%, 40/41, p = 1.00), MRIWB (95.7%, 22/23, p = 1.00), and CTWB (81.8%, 27/33, p = 0.03).

CONCLUSIONS

[68Ga]DOTATATE PET/CT should be the modality of choice in PPGL-related spinal bone metastases due to its superior detection rate.

CLINICAL RELEVANCE STATEMENT

In a prospective study of 43 pheochromocytoma/paraganglioma participants with spinal bone metastases, [68Ga]DOTATATE PET/CT had a superior per-lesion detection rate of 98.7% (377/382), compared to [18F]FDG PET/CT (p < 0.001), MRI of the spine (p < 0.001), whole-body CT (p < 0.001), and whole-body MRI (p < 0.001).

KEY POINTS

• Data regarding head-to-head comparison between functional and anatomic imaging modalities to detect spinal bone metastases in pheochromocytoma/paraganglioma are limited. • [68Ga]DOTATATE PET/CT had a superior per-lesion detection rate of 98.7% in the detection of spinal bone metastases associated with pheochromocytoma/paraganglioma compared to other imaging modalities: [18]F-FDG PET/CT, MRI of the spine, whole-body CT, and whole-body MRI. • [68Ga]DOTATATE PET/CT should be the modality of choice in the evaluation of spinal bone metastases associated with pheochromocytoma/paraganglioma.

Managing Catecholamine Release Syndrome During and Following Lu-177-DOTATATE in High-Risk Pheochromocytoma Patients

Pheochromocytomas and paragangliomas (PPGLs) are rare catecholamine-producing tumors that express somatostatin receptors (SSTR) that can be treated with lutetium-177 DOTATATE (Lu-177-TRT); however, treatment can be associated with life-threatening cardiovascular events. A patient case with management strategies for high-risk PPGL patients receiving Lu-177-TRT is described. The 78-year-old patient with metastatic paraganglioma was enrolled and treated under NCT03206060. Deemed to be at high risk, the patient was preemptively admitted to the intensive care unit (ICU) with central line access placed. Due to comorbidities, a reduced dose of 100 mCi x 4 cycles was used for this patient. Vital signs, blood work, and serum catecholamine levels were obtained at various time points. Despite reduced dosing, the patient still developed a severe hypertensive reaction with systolic blood pressure of 240 mmHg within minutes of Lu-177-TRT infusion, which was controlled with an intravenous nicardipine drip. The patient remained in the ICU for 24 hours post Lu-177-TRT before moving to an inpatient ward for an additional 24 hours. All subsequent infusions were performed using reduced doses with elective ICU admissions and were well-tolerated. Despite the increased risk, metastatic PPGL patients can be safely treated with proper staff training, monitoring, and preparation for intravenous medications, especially nicardipine.

Management of phaeochromocytoma and paraganglioma in patients with germline SDHB pathogenic variants: an international expert Consensus statement

Adult and paediatric patients with pathogenic variants in the gene encoding succinate dehydrogenase (SDH) subunit B (SDHB) often have locally aggressive, recurrent or metastatic phaeochromocytomas and paragangliomas (PPGLs). Furthermore, SDHB PPGLs have the highest rates of disease-specific morbidity and mortality compared with other hereditary PPGLs. PPGLs with SDHB pathogenic variants are often less differentiated and do not produce substantial amounts of catecholamines (in some patients, they produce only dopamine) compared with other hereditary subtypes, which enables these tumours to grow subclinically for a long time. In addition, SDHB pathogenic variants support tumour growth through high levels of the oncometabolite succinate and other mechanisms related to cancer initiation and progression. As a result, pseudohypoxia and upregulation of genes related to the hypoxia signalling pathway occur, promoting the growth, migration, invasiveness and metastasis of cancer cells. These factors, along with a high rate of metastasis, support early surgical intervention and total resection of PPGLs, regardless of the tumour size. The treatment of metastases is challenging and relies on either local or systemic therapies, or sometimes both. This Consensus statement should help guide clinicians in the diagnosis and management of patients with SDHB PPGLs.

Early short-term effects on catecholamine levels and pituitary function in patients with pheochromocytoma or paraganglioma treated with [177Lu]Lu-DOTA-TATE therapy

Purpose

While there are reports of treatment-related endocrine disruptions and catecholamine surges in pheochromocytoma/paraganglioma (PPGL) patients treated with [177Lu]Lu-DOTA-TATE therapy, the spectrum of these abnormalities in the immediate post-treatment period (within 48 hours) has not been previously evaluated and is likely underestimated.

Methods

The study population included patients (≥18 years) enrolled in a phase 2 trial for treatment of somatostatin receptor (SSTR)-2+ inoperable/metastatic pheochromocytoma/paraganglioma with [177Lu]Lu-DOTA-TATE (7.4 GBq per cycle for 1 - 4 cycles). Hormonal measurements [adrenocorticotropic hormone (ACTH), cortisol, thyroid stimulating hormone (TSH), free thyroxine (FT4), follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, estradiol, growth hormone, prolactin], catecholamines, and metanephrines were obtained on days-1, 2, 3, 30, and 60 per cycle as per trial protocol, and were retrospectively analyzed.

Results

Among the 27 patients (age: 54 ± 12.7 years, 48.1% females) who underwent hormonal evaluation, hypoprolactinemia (14.1%), elevated FSH (13.1%), and elevated LH (12.5%) were the most frequent hormonal abnormalities across all 4 cycles combined. On longitudinal follow-up, significant reductions were noted in i. ACTH without corresponding changes in cortisol, ii. TSH, and FT4, and iii. prolactin at or before day-30 of [177Lu]Lu-DOTA-TATE. No significant changes were observed in the gonadotropic axis and GH levels. Levels of all hormones on day-60 were not significantly different from day-1 values, suggesting the transient nature of these changes. However, two patients developed clinical, persistent endocrinopathies (primary hypothyroidism: n=1 male; early menopause: n=1 female). Compared to day-1, a significant % increase in norepinephrine, dopamine, and normetanephrine levels were noted at 24 hours following [177Lu]Lu-DOTA-TATE dose and peaked within 48 hours.

Conclusions

[177Lu]Lu-DOTA-TATE therapy is associated with alterations in endocrine function likely from radiation exposure to SSTR2+ endocrine tissues. However, these changes may sometimes manifest as clinically significant endocrinopathies. It is therefore important to periodically assess endocrine function during [177Lu]Lu-DOTA-TATE therapy, especially among symptomatic patients.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT03206060?term=NCT03206060&draw=2&rank=1, identifier NCT03206060.

225Ac-Macropatate: A Novel Alpha Particle Peptide Receptor Radionuclide Therapy for Neuroendocrine Tumors

Neuroendocrine tumors (NETs) express somatostatin receptors (SSTRs) 2 and 5. Modified variants of somatostatin, the cognate ligand for SSTR2 and SSTR5, are used in treatment for metastatic and locoregional disease. Peptide receptor radionuclide therapy with ¹⁷⁷Lu-DOTATATE (DOTA-octreotate), a β-particle-emitting somatostatin derivative, has demonstrated survival benefit in patients with SSTR-positive NETs. Despite excellent results, a subset of patients has tumors that are resistant to treatment, and alternative agents are needed. Targeted α-particle therapy has been shown to kill tumors that are resistant to targeted β-particle therapy, suggesting that targeted α-particle therapy may offer a promising treatment option for patients with ¹⁷⁷Lu-DOTATATE-resistant disease. Although DOTATATE can chelate the clinically relevant α-particle-emitting radionuclide ²²⁵Ac, the labeling reaction requires high temperatures, and the resulting radioconjugate has suboptimal stability. Methods: We designed and synthesized MACROPATATE (MACROPA-octreotate), a novel radioconjugate capable of chelating ²²⁵Ac at room temperature, and assessed its in vitro and in vivo performance. Results: MACROPATATE demonstrated comparable affinity to DOTATATE (dissociation constant, 21 nM) in U2-OS-SSTR2, a SSTR2-positive transfected cell line. ²²⁵Ac-MACROPATATE demonstrated superior serum stability at 37°C over time compared with ²²⁵Ac-DOTATATE. Biodistribution studies demonstrated higher tumor uptake of ²²⁵Ac-MACROPATATE than of ²²⁵Ac-DOTATATE in mice engrafted with subcutaneous H69 NETs. Therapy studies showed that ²²⁵Ac-MACROPATATE exhibits significant antitumor and survival benefit compared with saline control in mice engrafted with SSTR-positive tumors. However, the increased accumulation of ²²⁵Ac-MACROPATATE in liver and kidneys and subsequent toxicity to these organs decreased its therapeutic index compared with ²²⁵Ac-DOTATATE. Conclusion: ²²⁵Ac-MACROPATATE and ²²⁵Ac-DOTATATE exhibit favorable therapeutic efficacy in animal models. Because of elevated liver and kidney accumulation and lower administered activity for dose-limiting toxicity of ²²⁵Ac-MACROPATATE, ²²⁵Ac-DOTATATE was deemed the superior agent for targeted α-particle peptide receptor radionuclide therapy.

Performances of Functional and Anatomic Imaging Modalities in Succinate Dehydrogenase A-Related Metastatic Pheochromocytoma and Paraganglioma

Simple Summary

Pheochromocytoma and paraganglioma (PPGL) are rare neuroendocrine cancers which carry the risk of metastatic disease. Pathogenic variants in the succinate dehydrogenase subunit A gene (SDHA) have been shown to cause metastatic disease, occurring in various regions of the body. Imaging is an early and vital step in the diagnosis and clinical care of these patients. The study here identifies which imaging modality among positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI) performs better in localizing metastatic PPGL lesions related to SDHA. The study identified that ⁶⁸Ga-DOTATATE PET/CT performed best at overall lesion detection; however, ¹⁸F-FDG PET/CT performed better in certain anatomic regions of the body. A combined approach with ⁶⁸Ga-DOTATATE and ¹⁸F-FDG would optimize care and guide clinicians in selecting the appropriate interventions and therapies.

Abstract

The study identifies the importance of positron emission tomographic (PET) and anatomic imaging modalities and their individual performances in detecting succinate dehydrogenase A (SDHA)-related metastatic pheochromocytoma and paraganglioma (PPGL). The detection rates of PET modalities—⁶⁸Ga-DOTATATE, ¹⁸F-FDG, and ¹⁸F-FDOPA—along with the combination of computed tomography (CT) and magnetic resonance imaging (MRI) are compared in a cohort of 11 patients with metastatic PPGL in the setting of a germline SDHA mutation. The imaging detection performances were evaluated at three levels: overall lesions, anatomic regions, and a patient-by-patient basis. ⁶⁸Ga-DOTATATE PET demonstrated a lesion-based detection rate of 88.6% [95% confidence interval (CI), 84.3–92.5%], while ¹⁸F-FDG, ¹⁸F-FDOPA, and CT/MRI showed detection rates of 82.9% (CI, 78.0–87.1%), 39.8% (CI, 30.2–50.2%), and 58.2% (CI, 52.0–64.1%), respectively. The study found that ⁶⁸Ga-DOTATATE best detects lesions in a subset of patients with SDHA-related metastatic PPGL. However, ¹⁸F-FDG did detect more lesions in the liver, mediastinum, and abdomen/pelvis anatomic regions, showing the importance of a combined approach using both PET modalities in evaluating SDHA-related PPGL.

Predictors of 18F-DCFPyL PET/CT Positivity in Patients with Biochemical Recurrence of Prostate Cancer After Local Therapy

Our objective was to investigate the factors predicting scan positivity and disease location in patients with biochemical recurrence (BCR) of prostate cancer (PCa) after primary local therapy using prostate-specific membrane antigen-targeted ¹⁸F-DCFPyL PET/CT. Methods: This was a 2-institution study including 245 BCR PCa patients after primary local therapy and negative results on conventional imaging. The patients underwent ¹⁸F-DCFPyL PET/CT. We tested for correlations of lesion detection rate and disease location with tumor characteristics, time from initial therapy, prostate-specific antigen (PSA) level, and PSA doubling time (PSAdt). Multivariate logistic regression analyses were used to determine predictors of a positive scan. Regression-based coefficients were used to develop nomograms predicting scan positivity and extrapelvic disease. Results: Overall, 79.2% (194/245) of patients had a positive ¹⁸F-DCFPyL PET/CT result, with detection rates of 48.2% (27/56), 74.3% (26/35), 84% (37/44), 96.7% (59/61), and 91.8% (45/49) for PSAs of <0.5, 0.5 to <1.0, 1.0 to <2.0, 2.0 to <5.0, and ≥5.0 ng/mL, respectively. Patients with lesions confined to the pelvis had lower PSAs than those with distant sites (1.6 ± 3.5 vs. 3.0 ± 6.3 ng/mL, P < 0.001). In patients treated with prostatectomy (n = 195), 24.1% (47/195) had a negative scan result, 46.1% (90/195) showed intrapelvic disease, and 29.7% (58/195) showed extrapelvic disease. In the postradiation subgroup (n = 50), ¹⁸F-DCFPyL PET/CT was always negative at a PSA lower than 1.0 ng/mL and extrapelvic disease was seen only when PSA was greater than 2.0 ng/mL. At multivariate analysis, PSA and PSAdt were independent predictive factors of scan positivity and the presence of extrapelvic disease in postsurgical patients, with area under the curve of 78% and 76%, respectively. PSA and PSAdt were independent predictors of the presence of extrapelvic disease in the postradiation cohort, with area under the curve of 85%. Time from treatment to scan was significantly longer for prostatectomy-bed-only recurrences than for those with bone or visceral disease (6.2 ± 6.4 vs. 2.4 ± 1.3 y, P < 0.001). Conclusion:¹⁸F-DCFPyL PET/CT offers high detection rates in BCR PCa patients. PSA and PSAdt are able to predict scan positivity and disease location. Furthermore, the presence of bone or visceral lesions is associated with shorter intervals from treatment than are prostate-bed-only recurrences. These tools might guide clinicians to select the most suitable candidates for ¹⁸F-DCFPyL PET/CT imaging.

Monitoring PSMA Responses to ADT in Prostate Cancer Patient-Derived Xenograft Mouse Models Using [18F]DCFPyL PET Imaging

PURPOSE

PSMA overexpression has been associated with aggressive prostate cancer (PCa). However, PSMA PET imaging has revealed highly variable changes in PSMA expression in response to ADT treatment ranging from increases to moderate decreases. To better understand these PSMA responses and potential relationship to progressive PCa, the PET imaging agent, [¹⁸F]DCFPyL, was used to assess changes in PSMA expression in response to ADT using genomically characterized LuCaP patient-derived xenograft mouse models (LuCaP-PDXs) which were found to be sensitive to ADT (LuCaP73 and LuCaP136;CS) or resistant (LuCaP167;CR).

METHODS

[¹⁸F]DCFPyL (2-(3-{1-carboxy-5-[(6-[¹⁸F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid) was used to assess PSMA in vitro (saturation assays) in LuCaP tumor membrane homogenates and in vivo (imaging/biodistribution) in LuCaP-PDXs. Control and ADT-treated LuCaPs were imaged before ADT (0 days) and 2-, 7-, 14-, and 21-days post-ADT from which tumor:muscle ratios (T:Ms) were determined and concurrently tumor volumes were measured (caliper). After the 21-day imaging, biodistributions and histologic/genomic (PSMA, AR) analysis were done.

RESULTS

[¹⁸F]DCFPyL exhibited high affinity for PSMA and distinguished different levels of PSMA in LuCaP tumors. Post-ADT CS LuCaP73 and LuCaP136 tumor volumes significantly decreased at day 7 or 14 respectively vs controls, whereas the CR LuCaP167 tumor volumes were minimally changed. [¹⁸F]DCFPyL imaging T:Ms were increased 3-5-fold in treated LuCaP73 tumors vs controls, while treated LuCaP136 T:Ms remained unchanged which was confirmed by day 21 biodistribution results. For treated LuCaP167, T:Ms were decreased (~ 45 %) vs controls but due to low T:M values (<2) may not be indicative of PSMA level changes. LuCaP73 tumor PSMA histologic/genomic results were comparable to imaging/biodistribution results, whereas the results for other tumor types varied.

CONCLUSION

Tumor responses to ADT varied from sensitive to resistant among these LuCaP PDXs, while only the high PSMA expressing LuCaP model exhibited an increase in PSMA levels in response to ADT. These models may be useful in understanding the clinical relevance of PSMA PET responses to ADT and potentially the relationship to disease progression as it may relate to the genomic signature.

A comparison of 18F-DCFPyL, 18F-NaF and 18F-FDG PET/CT in a prospective cohort of men with metastatic prostate cancer

Introduction: ¹⁸F-DCFPyL, ¹⁸F-NaF and ¹⁸F-FDG PET/CT were compared in a prospective cohort of men with metastatic prostate cancer (PCa). Materials and Methods: 67 men (Group 1) with documented metastatic PCa underwent ¹⁸F-DCFPyL and ¹⁸F-NaF PET/CT and a subgroup of 30 men (Group 2) underwent additional imaging with ¹⁸F-FDG PET/CT. The tracers were compared for their detection rates, imaging concordance, associations with Prostate Specific Antigen (PSA), treatment at the time of imaging and castration status. Results: Overall, 61 men had metastatic disease detected on one or more scans, while 6 men were negative. In Group 1, ¹⁸F-NaF detected significantly more metastatic lesions than ¹⁸F-DCFPyL (median of 3 lesions versus 2, P = 0.001) even after eliminating benign causes of ¹⁸F-NaF uptake. This difference was particularly clear for men receiving treatment (P = 0.005) or who were castrate resistant (P = 0.014). The median percentage of bone lesions that were concordant on ¹⁸F-DCFPyL and ¹⁸F-NaF was 50%. In Group 2, ¹⁸F-DCFPyL detected more lesions than ¹⁸F-FDG (median of 5 lesions versus 2, P = 0.0003), regardless of PSA level, castration status or treatment. The median percentage of lesions that were concordant on ¹⁸F-DCFPyL and ¹⁸F-FDG was 22.2%. This percentage was slightly higher for castrate-resistant than castrate-sensitive men (P = 0.048). Conclusion: ¹⁸F-DCFPyL PET/CT is the most versatile of the three PET agents for metastatic PCa however, ¹⁸F-NaF detects more bone metastases. Imaging reveals substantial tumor heterogeneity with only 50% concordance between ¹⁸F-DCFPyL and ¹⁸F-NaF and 22% concordance for ¹⁸F-DCFPyL and ¹⁸F-FDG. This indicates considerable phenotypic differences among metastatic lesions.

Systemic Radiopharmaceutical Therapy of Pheochromocytoma and Paraganglioma

Whereas benign pheochromocytomas and paragangliomas are often successfully cured by surgical resection, treatment of metastatic disease can be challenging in terms of both disease control and symptom control. Fortunately, several options are available, including chemotherapy, radiation therapy, and surgical debulking. Radiolabeled metaiodobenzylguanidine (MIBG) and somatostatin receptor imaging have laid the groundwork for use of these radiopharmaceuticals as theranostic agents. ¹³¹I-MIBG therapy of neuroendocrine tumors has a long history, and the recent approval of high-specific-activity ¹³¹I-MIBG for metastatic or inoperable pheochromocytoma or paraganglioma by the U.S. Food and Drug Administration has resulted in general availability of, and renewed interest in, this treatment. Although reports of peptide receptor radionuclide therapy of pheochromocytoma and paraganglioma with ⁹⁰Y- or ¹⁷⁷Lu-DOTA conjugated somatostatin analogs have appeared in the literature, the approval of ¹⁷⁷Lu-DOTATATE in the United States and Europe, together with National Comprehensive Cancer Network guidelines suggesting its use in patients with metastatic or inoperable pheochromocytoma and paraganglioma, has resulted in renewed interest. These agents have shown evidence of efficacy as palliative treatments in patients with metastatic or inoperable pheochromocytoma or paraganglioma. In this continuing medical education article, we discuss the therapy of pheochromocytoma and paraganglioma with ¹³¹I-MIBG and ⁹⁰Y- or ¹⁷⁷Lu-DOTA-somatostatin analogs.

Imaging of Pheochromocytoma and Paraganglioma

Imaging plays a critical role in the management of pheochromocytomas and paragangliomas and often guides treatment. The discovery of susceptibility genes associated with these tumors has led to better understanding of clinical and imaging phenotypes. Functional imaging is of prime importance because of its sensitivity and specificity in subtypes of pheochromocytoma and paraganglioma. Several radiopharmaceuticals have been developed to target specific receptors and metabolic processes seen in pheochromocytomas and paragangliomas, including ¹³¹I/¹²³I-metaiodobenzylguanidine, 6-¹⁸F-fluoro-l-3,4-dihydroxyphenylalanine, ¹⁸F-FDG, and ⁶⁸Ga-DOTA-somatostatin analogs. Two of these have consequently been adapted for therapy. This educational review focuses on the current imaging approaches used in pheochromocytomas and paragangliomas, which vary among clinical and genotypic presentations.

Competitive blocking of salivary gland [18F]DCFPyL uptake via localized, retrograde ductal injection of non-radioactive DCFPyL: a preclinical study

Background

PSMA-targeted radionuclide therapy (TRT) is a promising treatment for prostate cancer (PCa), but dose-limiting xerostomia can severely limit its clinical adaptation, especially when using alpha-emitting radionuclides. With [¹⁸F]DCFPyL as a surrogate for PSMA-TRT, we report a novel method to selectively reduce salivary gland (SG) uptake of systemically administered [¹⁸F]DCFPyL by immediate prior infusion of non-radioactive standard of [¹⁸F]DCFPyL (DCFPyL) directly into the SG via retrograde cannulation.

Methods

A dose-finding cohort using athymic nude mice demonstrated proof of principle that SG uptake can be selectively blocked by DCFPyL administered either locally via cannulation (CAN group) or systemically (SYS group). The experiments were repeated in a validation cohort of 22RV1 tumor-bearing mice. Submandibular glands (SMG) of CAN mice were locally blocked with either saline or DCFPyL (dose range: 0.01× to 1000× molar equivalent of the radioactive [18F]DCFPyL dose). The radioactive dose of [18F]DCFPyL was administered systemically 10 min later and the mice euthanized after 1 h for biodistribution studies. Toxicity studies were done at up to 1000× dose.

Results

In the dose-finding cohort, the SYS group showed a dose-dependent 12–40% decrease in both the SMG T/B and the kidney (tumor surrogate). Mild blocking was observed at 0.01× , with maximal blocking reached at 1× with no additional blocking up to 1000× . In the CAN group, blocking at the 0.1× and 1× dose levels resulted in a similar 42–53% decrease, but without the corresponding decrease in kidney uptake as seen in the SYS group. Some evidence of “leakage” of DCFPyL from the salivary gland into the systemic circulation was observed. However, experiments in 22RV1 tumor-bearing mice at the 0.1× and 1× dose levels confirm that, at the appropriate blocking dose, SG uptake of [18F]DCFPyL can be selectively reduced without affecting tumor uptake and with no toxicity.

Conclusion

Our results suggest that direct retrograde instillation of DCFPyL into the SG could predictably and selectively decrease salivary uptake of systemically administered [¹⁸F]DCFPyL without altering tumor uptake, if given at the appropriate dose. This novel approach is easily translatable to clinical practice and has the potential to mitigate xerostomia, without compromising the therapeutic efficacy of the PSMA-TRT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00803-9.

Lutetium-177 DOTATATE Therapy Is Associated With Biochemical Endocrine Abnormalities in the Immediate Post-Treatment Period

Introduction: Lutetium-177(177Lu) DOTATATE is a form of peptide receptor radionuclide therapy (PRRT) targeting somatostatin receptor-2 (SSTR2), that is utilized in the treatment of neuroendocrine tumors. As various endocrine glands express SSTR2, 177Lu-DOTATATE can potentially disrupt endocrine function. The immediate post-treatment effects of 177Lu-DOTATATE on endocrine function are not known. Methods: We performed a retrospective analysis of data obtained from patients (≥18 years) enrolled under the 177Lu-DOTATATE trial (NCT03206060) for treatment of SSTR2 positive inoperable/metastatic pheochromocytoma/paraganglioma. 177Lu-DOTATATE (200 mCi) was administered intravenously every 8 weeks, for a total of 4 cycles. Endocrine evaluation was performed on blood samples obtained through an indwelling intravenous catheter during each cycle of PRRT on day 1 (pre-PRRT), day 2 (post-PRRT day 1), day 3 (post-PRRT day 2), day 30 (post-PRRT day 29), and day 60 (day 1 of the next cycle). Hormonal evaluation included ACTH, cortisol, TSH, free T4, GH, FSH, LH, testosterone, estradiol, and prolactin. Baseline abnormal hormonal values, and gonadotrophs in premenopausal women were excluded. Results: Data from 27 subjects (age: 54 ± 12.7 years; 13 female, 14 male) were analyzed. Three out of 27 patients (11.1%) developed clinically significant persistent endocrinopathies - secondary adrenal insufficiency (AI): (n=1 male), primary hypothyroidism: (n=1 male) and hypergonadotropic hypogonadism: (n=1 female). Compared to day 1, there were significant reductions in 1) ACTH (pg/mL) levels on day 2 (36.8 ± 34.1 vs. 23.1 ± 21; p&lt;0.0001), day 3 (36.8 ± 34.1 vs. 24.3 ± 19.4; p&lt;0.0001), and day 30 (36.8 ± 34.1 vs. 27.7 ± 19.1; p=0.01), without significant changes in average cortisol level, apart from 1 patient with undetectable cortisol, who developed secondary AI after 2nd cycle 2) LH (IU/L) levels on day 3 (16.4 ± 13.5 vs. 15.4 ± 13.5; p=0.014), 3) prolactin (ng/mL) on day 2 (9.9 ± 7.0 vs. 7.1 ± 5.7; p&lt;0.0001), day 3 (9.9 ± 7.0 vs. 7.1 ± 5.4; p&lt;0.0001), and day 30 (9.9 ± 7.0 vs. 7.6 ± 5.7; p=0.005), without significant changes in average estrogen and testosterone levels, apart from 1 woman with low estrogens developing hypergonadotropic hypogonadism after 3rd cycle 4) TSH (microIU/L) on day 2 (2.2 ± 1.4 vs. 1.4 ± 0.9; p&lt;0.0001), and day 3 (2.2 ± 1.4 vs. 1.7 ± 1.3; p=0.001), and 5) free T4 (ng/dL) on day 2 (1.1 ± 0.2 vs. 1 ± 0.2; p=0.002). Hormonal values on day 60 were not significantly different from those on day 1, suggesting that majority of these changes were transient. Conclusions:177Lu-DOTATATE can be associated with transient endocrine disruption in the immediate post-treatment period. However, some of these changes may lead to persistent endocrinopathies which are likely associated with radiation exposure to the tissues expressing SSTR2. It is therefore important to periodically assess endocrine function during PRRT.

In Vitro and In Vivo Comparison of 3,2-HOPO Versus Deferoxamine-Based Chelation of Zirconium-89 to the Antimesothelin Antibody Anetumab

Introduction: [²²⁷Th]Th-3,2-HOPO-MSLN-mAb, a mesothelin (MSLN)-targeted thorium-227 therapeutic conjugate, is currently in phase I clinical trial; however, direct PET imaging using this conjugate is technically challenging. Thus, using the same MSLN antibody, we synthesized 3,2-HOPO and deferoxamine (DFO)-based zirconium-89 antibody conjugates, [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb and [⁸⁹Zr]Zr-DFO-MSLN-mAb, respectively, and compared them in vitro and in vivo.

Methods: [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb and [⁸⁹Zr]Zr-DFO-MSLN-mAb were evaluated in vitro to determine binding affinity and immunoreactivity in HT29-MSLN and PDX (NCI-Meso16, NCI-Meso21) cells. For both the zirconium-89 conjugates, in vivo studies (biodistribution/imaging) were performed at days 1, 3, and 6, from which tissue uptake was determined.

Results: Both the conjugates demonstrated a low nanomolar binding affinity for MSLN and >95% immunoreactivity. In all the three tumor types, biodistribution of [⁸⁹Zr]Zr-DFO-MSLN-mAb resulted in higher tumor uptake(15.88-28-33%ID/g) at all time points compared with [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb(7–13.07%ID/g). [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb femur uptake was always higher than [⁸⁹Zr]Zr-DFO-MSLN-mAb, and imaging results concurred with the biodistribution studies.

Conclusions: Even though the conjugates exhibited a high binding affinity for MSLN, [⁸⁹Zr]Zr-DFO-MSLN-mAb showed a higher tumor and lower femur uptake than [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb. Nevertheless, [⁸⁹Zr]Zr-3,2-HOPO-MSLN-mAb could be used to study organ distribution and lesion uptake with the caveat of detecting MSLN-positive bone lesions. Clinical trial (NCT03507452).

High-Specific-Activity-131I-MIBG versus 177Lu-DOTATATE Targeted Radionuclide Therapy for Metastatic Pheochromocytoma and Paraganglioma

Targeted radionuclide therapies (TRT) using ¹³¹I-metaiodobenzylguanidine (¹³¹I-MIBG) and peptide receptor radionuclide therapy (¹⁷⁷Lu or ⁹⁰Y) represent several of the therapeutic options in the management of metastatic/inoperable pheochromocytoma/paraganglioma. Recently, high-specific-activity-¹³¹I-MIBG therapy was approved by the FDA and both ¹⁷⁷Lu-DOTATATE and ¹³¹I-MIBG therapy were recommended by the National Comprehensive Cancer Network guidelines for the treatment of metastatic pheochromocytoma/paraganglioma. However, a clinical dilemma often arises in the selection of TRT, especially when a patient can be treated with either type of therapy based on eligibility by MIBG and somatostatin receptor imaging. To address this problem, we assembled a group of international experts, including oncologists, endocrinologists, and nuclear medicine physicians, with substantial experience in treating neuroendocrine tumors with TRTs to develop consensus and provide expert recommendations and perspectives on how to select between these two therapeutic options for metastatic/inoperable pheochromocytoma/paraganglioma. This article aims to summarize the survival outcomes of the available TRTs; discuss personalized treatment strategies based on functional imaging scans; address practical issues, including regulatory approvals; and compare toxicities and risk factors across treatments. Furthermore, it discusses the emerging TRTs.

Phase 1 study of Z-endoxifen in patients with advanced gynecologic, desmoid, and hormone receptor-positive solid tumors

Background: Differential responses to tamoxifen may be due to inter-patient variability in tamoxifen metabolism into pharmacologically active Z-endoxifen. Z-endoxifen administration was anticipated to bypass these variations, increasing active drug levels, and potentially benefitting patients responding sub-optimally to tamoxifen.

Materials and Methods: Patients with treatment-refractory gynecologic malignancies, desmoid tumors, or hormone receptor-positive solid tumors took oral Z-endoxifen daily with a 3+3 phase 1 dose escalation format over 8 dose levels (DLs). Safety, pharmacokinetics/pharmacodynamics, and clinical outcomes were evaluated.

Results: Thirty-four of 40 patients were evaluable. No maximum tolerated dose was established. DL8, 360 mg/day, was used for the expansion phase and is higher than doses administered in any previous study; it also yielded higher plasma Z-endoxifen concentrations. Three patients had partial responses and 8 had prolonged stable disease (≥ 6 cycles); 44.4% (8/18) of patients at dose levels 6–8 achieved one of these outcomes. Six patients who progressed after tamoxifen therapy experienced partial response or stable disease for ≥ 6 cycles with Z-endoxifen; one with desmoid tumor remains on study after 62 cycles (nearly 5 years).

Conclusions: Evidence of antitumor activity and prolonged stable disease are achieved with Z-endoxifen despite prior tamoxifen therapy, supporting further study of Z-endoxifen, particularly in patients with desmoid tumors.

Meeting report from the Prostate Cancer Foundation PSMA theranostics state of the science meeting

INTRODUCTION

The Prostate Cancer Foundation (PCF) convened a PCF prostate-specific membrane antigen (PSMA) Theranostics State of the Science Meeting on 18 November 2019, at Weill Cornell Medicine, New York, NY.

METHODS

The meeting was attended by 22 basic, translational, and clinical researchers from around the globe, with expertise in PSMA biology, development and use of PSMA theranostics agents, and clinical trials. The goal of this meeting was to discuss the current state of knowledge, the most important biological and clinical questions, and critical next steps for the clinical development of PSMA positron emission tomography (PET) imaging agents and PSMA-targeted radionuclide agents for patients with prostate cancer.

RESULTS

Several major topic areas were discussed including the biology of PSMA, the role of PSMA-targeted PET imaging in prostate cancer, the physics and performance of different PSMA-targeted PET imaging agents, the current state of clinical development of PSMA-targeted radionuclide therapy (RNT) agents, the role of dosimetry in PSMA RNT treatment planning, barriers and challenges in PSMA RNT clinical development, optimization of patient selection for PSMA RNT trials, and promising combination treatment approaches with PSMA RNT.

DISCUSSION

This article summarizes the presentations from the meeting for the purpose of globally disseminating this knowledge to advance the use of PSMA-targeted theranostic agents for imaging and treatment of patients with prostate cancer.

MON-214 Biochemical Abnormalities in Endocrine Function Associated with Lutetium 177-DOTATATE Therapy in Metastatic Pheochromocytoma and Paraganglioma

Background: Lutetium-177 (¹⁷⁷Lu) DOTATATE (Lutathera ®) is a form of peptide receptor radionuclide therapy (PRRT) that has shown efficacy in the treatment of neuroendocrine tumors through its action on somatostatin receptor 2. The effects of Lutathera on endocrine function in metastatic pheochromocytoma and paraganglioma (PPGL) has not been evaluated. Methods: We performed a prospective analysis on 21 patients (10 female, 11 male) with metastatic PPGL receiving ¹⁷⁷Lu DOTATATE (NCT03206060) at our center from July 2017 to August 2019. Hormonal evaluation was obtained 24 and 48 hours after each ¹⁷⁷Lu DOTATATE administration and 4 weeks ± 1 week after each cycle to assess for biochemical endocrine abnormalities (BEAs). Blood samples were obtained after 30 minutes of resting with an in-dwelling intravenous catheter. We excluded BEAs that were present either prior to the initiation of ¹⁷⁷Lu DOTATATE or due to a pre-existing endocrine disorder. Results: We observed BEAs in 18 of 21 (85.7%, 7 female, 11 male) patients. BEAs most commonly involved the pituitary-adrenal axis [ACTH (N: 5-46 pg/mL): 6/21 (28.5%, 5 high, 1 low); serum cortisol (N: 5-25 mcg/dL): 5/21 (23.8%, 2 high, 3 low)], followed by pituitary-thyroid axis [TSH (N: 0.27-4.2 IU/mL): 6/21 (28.5%, 4 high, 2 low); free thyroxine (N: 0.9-1.7 ng/dL): 2/21 (9%, 0 high, 2 low)], pituitary-gonadal axis [FSH (N: 1-11 U/L): 2/21 (9%, 1 high, 1 low); LH (1-8 U/L): 1/21 (5%, 0 high, 1 low); total testosterone (N: 262-1593 ng/dL): 4/21 (19%, 0 high, 4 low)]; and growth hormone [3/21 (N: 0 - 3 ng/mL): (14.3%, 3 high, 0 low)]. Of the 28 observed BEAs, 17/28 (61%) were initially noted during cycle 1, 7/28 (25%) during cycle 2, and 4/28 (14%) during cycle 3, and 16/28 (57%) were noted within 48 hours of ¹⁷⁷Lu DOTATATE injection. There was no significant association between the standardized uptake values of adrenals (p=0.28), pituitary (p=0.75), and thyroid gland (p=0.61) on the baseline diagnostic ⁶⁸Ga DOTATATE scan and their respective BEAs. One patient developed overt hypothyroidism and was started on levothyroxine, and another patient developed central adrenal insufficiency likely from immunotherapy started after ¹⁷⁷Lu DOTATATE therapy. In all other patients, BEAs were transient and spontaneously resolved. Limitations included the observational nature of the study, lack of data on levels of IGF-1, parathyroid hormone, or hemoglobin A1C. Conclusion:¹⁷⁷Lu DOTATATE therapy for metastatic PPGL is associated with biochemical abnormalities in endocrine function. Although mostly transient, there is a potential risk for BEAs to be permanent and to manifest clinically. Therefore, serial monitoring of abnormal hormonal values is necessary and treatment should be considered when appropriate. Studies on larger populations with long-term follow-up are necessary to further investigate the incidence of endocrine abnormalities with ¹⁷⁷Lu DOTATATE therapy.

SAT-502 Clinical Hypothyroidism Associated with Lutetium 177-DOTATATE Therapy for Metastatic Paraganglioma: A Novel Adverse Effect of Peptide Receptor Radionuclide Therapy

Background: Peptide receptor radionuclide therapy (PRRT) is a relatively novel, emerging therapy for the treatment of metastatic pheochromocytoma and paraganglioma (PPGL). Lutetium 177 (¹⁷⁷Lu)-DOTATATE (Lutathera ®) is a form of PRRT that is currently being evaluated for its treatment efficacy in metastatic PPGL. It acts by binding to somatostatin receptors 2 (SSTR2) which are present on PPGL and other tissues of neuroendocrine origin. Although subclinical thyroid dysfunction has been previously noted, development of clinical hypothyroidism post ¹⁷⁷Lu-DOTATATE therapy has not been reported to date. Case: A 29-year-old male with Beckwith-Weidemann syndrome and metastatic, succinate dehydrogenase subunit B (SDHB) germline mutation-positive paraganglioma with normal metanephrines was enrolled at our center under the ¹⁷⁷Lu-DOTATATE trial for the treatment of inoperable, metastatic PPGL (ClinicalTrials.gov NCT03206060). Prior to the first cycle of therapy, the patient underwent endocrine evaluation per protocol. He was noted to have suppressed thyroid stimulating hormone (TSH) of <0.01 mcIU/mL (normal: 0.27 - 4.2 mcIU/mL), and a normal free thyroxine (FT4) of 1.3 ng/dL (0.9 - 1.7 ng/dL), indicating subclinical hyperthyroidism. Thyroid auto-antibodies were not measured at that time point. The patient denied symptoms of hyper- or hypothyroidism. On physical examination, there was no thyromegaly or cervical lymphadenopathy. Serial monitoring of thyroid function tests (TFTs) was pursued. One month after the first cycle of ¹⁷⁷Lu-DOTATATE therapy, the patient complained of new onset fatigue and weight gain. The TSH had markedly increased (73.04 mcIU/mL), along with a reduction in FT4 levels (0.3 mg/dL). Mass spectrometry measures revealed a low total T4 (1.3 ng/dL; 4.9 - 10.5 ng/dL), and a low total T3 (57 ng/dL; 87 - 169 ng/dL). Thyroid peroxidase antibodies were >1000 IU/mL (0.0 - 34.9 IU/mL), and anti-thyroglobulin antibodies were 668 IU/mL (0.0-40.0 IU/mL). Weight-based levothyroxine therapy was initiated and the follow-up TFTs normalized. The baseline diagnostic Gallium 68-DOTATATE scan performed prior to PRRT demonstrated an increased diffuse uptake in the entire thyroid gland (maximum standardized uptake value: 14.3) and post-treatment SPECT-CT scan revealed similar increased, diffuse ¹⁷⁷Lu-DOTATATE uptake in the thyroid gland. The patient currently has stable metastatic disease and continues to be under ¹⁷⁷Lu-DOTATATE therapy. Conclusion: We report the first known case of clinical hypothyroidism post ¹⁷⁷Lu-DOTATATE therapy in a patient who likely had subclinical hyperthyroidism prior to treatment. The possible mechanism was development of thyroiditis. Further studies are necessary to evaluate the mechanisms of PRRT-induced endocrine abnormalities and their clinical implications.

Comparison of Prostate-Specific Membrane Antigen Expression Levels in Human Salivary Glands to Non-Human Primates and Rodents

Background: Prostate-specific membrane antigen (PSMA) has emerged as a promising target for developing radionuclide therapy (RNT) in prostate cancer; however, accumulation of PSMA-RNT in salivary glands can result in irreversible xerostomia. Methods to prevent PSMA-RNT-related xerostomia could be clinically useful; however, little is known about PSMA expression in salivary glands of preclinical animal models. Using [¹⁸F]DCFPyL autoradiography/biodistribution, PSMA expression levels were determined in salivary glands of various preclinical monkey and rodent species and compared with humans. Methods: Binding affinities (K_d) and PSMA levels (B_max) were determined by in vitro [¹⁸F]DCFPyL autoradiography studies. In vivo rodent tissue uptakes (%ID/g) were determined from [¹⁸F]DCFPyL biodistributions. Results: [¹⁸F]DCFPyL exhibited low nanomolar K_d for submandibular gland (SMG) PSMA across all the species. PSMA levels in human SMG (B_max = 60.91 nM) were approximately two-fold lower compared with baboon SMG but were two- to three-fold higher than SMG PSMA levels of cynomolgus and rhesus. Rodents had the lowest SMG PSMA levels, with the mouse being 10-fold higher than the rat. In vivo rodent biodistribution studies confirmed these results. Conclusions: SMG of monkeys exhibited comparable PSMA expression to human SMG whereas rodents were lower. However, the results suggest that mice are relatively a better small animal preclinical model than rats for PSMA salivary gland studies.

Beyond Correlations, Sensitivities, and Specificities: A Roadmap for Demonstrating Utility of Advanced Imaging in Oncology Treatment and Clinical Trial Design

Despite the widespread belief that advanced imaging should be very helpful in guiding oncology treatment decision and improving efficiency and success rates in treatment clinical trials, its acceptance has been slow. Part of this is likely attributable to gaps in study design and statistical methodology for these imaging studies. Also, results supporting the performance of the imaging in these roles have largely been insufficient to justify their use within the design of a clinical trial or in treatment decision making. Statistically significant correlations between the imaging results and clinical outcomes are often incorrectly taken as evidence of adequate performance. Assessments of whether the imaging can outperform standard techniques or meaningfully supplement them are also frequently neglected. This paper provides guidance on study designs and statistical analyses for evaluating the performance of advanced imaging in the various roles in treatment decision guidance and clinical trial conduct. Relevant methodology from the imaging literature is reviewed; gaps in the literature are addressed using related concepts from the more extensive genomic and in vitro biomarker literature.

Functional Imaging Signature of Patients Presenting with Polycythemia/Paraganglioma Syndromes

Pheochromocytoma/paraganglioma (PPGL) syndromes associated with polycythemia have previously been described in association with mutations in the von Hippel-Lindau gene. Recently, mutations in the prolyl hydroxylase gene (PHD) 1 and 2 and in the hypoxia-inducible factor 2 α (HIF2A) were also found to be associated with multiple and recurrent PPGL. Such patients also presented with PPGL and polycythemia, and later on, some presented with duodenal somatostatinoma. In additional patients presenting with PPGL and polycythemia, no further mutations have been discovered. Because the functional imaging signature of patients with PPGL-polycythemia syndromes is still unknown, and because these tumors (in most patients) are multiple, recurrent, and metastatic, the goal of our study was to assess the optimal imaging approach using 4 different PET radiopharmaceuticals and CT/MRI in these patients. Methods: Fourteen patients (10 women, 4 men) with confirmed PPGL and polycythemia prospectively underwent ⁶⁸Ga-DOTATATE (13 patients), ¹⁸F-FDG (13 patients), ¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-FDOPA) (14 patients), ¹⁸F-fluorodopamine (¹⁸F-FDA) (11 patients), and CT/MRI (14 patients). Detection rates of PPGL lesions were compared between all imaging studies and stratified between the underlying mutations. Results:¹⁸F-FDOPA and ¹⁸F-FDA PET/CT showed similar combined lesion-based detection rates of 98.7% (95% confidence interval [CI], 92.7%-99.8%) and 98.3% (95% CI, 90.9%-99.7%), respectively. The detection rates for ⁶⁸Ga-DOTATATE (35.3%; 95% CI, 25.0%-47.2%), ¹⁸F-FDG (42.3; 95% CI, 29.9%-55.8%), and CT/MRI (60.3%; 95% CI, 48.8%-70.7%) were significantly lower (P < 0.01), irrespective of the mutation status. Conclusion:¹⁸F-FDOPA and ¹⁸F-FDA are superior to ¹⁸F-FDG, ⁶⁸Ga-DOTATATE, and CT/MRI and should be the radiopharmaceuticals of choice in this rare group of patients.

Utility of 18F-fluoroestradiol (18F-FES) PET/CT imaging as a pharmacodynamic marker in patients with refractory estrogen receptor-positive solid tumors receiving Z-endoxifen therapy

BACKGROUND

Z-endoxifen is the most potent of the metabolites of tamoxifen, and has the potential to be more effective than tamoxifen because it bypasses potential drug resistance mechanisms attributable to patient variability in the expression of the hepatic microsomal enzyme CYP2D6. ¹⁸F-FES is a positron emission tomography (PET) imaging agent which selectively binds to estrogen receptor alpha (ER-α) and has been used for non-invasive in vivo assessment of ER activity in tumors. This study utilizes ¹⁸F-FES PET imaging as a pharmacodynamic biomarker in patients with ER+ tumors treated with Z-endoxifen.

METHODS

Fifteen patients were recruited from a parent therapeutic trial of Z-endoxifen and underwent imaging with ¹⁸F-FES PET at baseline. Eight had positive lesions on the baseline scan and underwent follow-up imaging with ¹⁸F-FES 1-5 days post administration of Z-endoxifen.

RESULTS

Statistically significant changes (p = 0.0078) in standard uptake value (SUV)-Max were observed between the baseline and follow-up scans as early as 1 day post drug administration.

CONCLUSION

F-FES PET imaging could serve as a pharmacodynamic biomarker for patients treated with ER-directed therapy.

Brown Adipose Reporting Criteria in Imaging STudies (BARCIST 1.0): Recommendations for Standardized FDG-PET/CT Experiments in Humans

Human brown adipose tissue (BAT) presence, metabolic activity, and estimated mass are typically measured by imaging [18F]fluorodeoxyglucose (FDG) uptake in response to cold exposure in regions of the body expected to contain BAT, using positron emission tomography combined with X-ray computed tomography (FDG-PET/CT). Efforts to describe the epidemiology and biology of human BAT are hampered by diverse experimental practices, making it difficult to directly compare results among laboratories. An expert panel was assembled by the National Institute of Diabetes and Digestive and Kidney Diseases on November 4, 2014 to discuss minimal requirements for conducting FDG-PET/CT experiments of human BAT, data analysis, and publication of results. This resulted in Brown Adipose Reporting Criteria in Imaging STudies (BARCIST 1.0). Since there are no fully validated best practices at this time, panel recommendations are meant to enhance comparability across experiments, but not to constrain experimental design or the questions that can be asked.

PET/CT comparing (68)Ga-DOTATATE and other radiopharmaceuticals and in comparison with CT/MRI for the localization of sporadic metastatic pheochromocytoma and paraganglioma

PURPOSE

Pheochromocytomas/paragangliomas (PPGLs) and their metastases are tumors that predominantly express somatostatin receptor 2 (SSR2). (68)Ga-DOTA(0)-Tyr(3)-octreotate ((68)Ga-DOTATATE) is a PET radiopharmaceutical with both high and selective affinity for SSRs. The purpose of this study was to evaluate the utility of (68)Ga-DOTATATE in comparison with other specific and nonspecific radiopharmaceuticals recommended in the current guidelines for the localization of metastatic sporadic PPGL by PET/CT.

METHODS

This prospective study included 22 patients (15 men, 7 women; aged 50.0 ± 13.9 years) with confirmed metastatic PPGL, a negative family history for PPGL, and negative genetic testing, who underwent (68)Ga-DOTATATE, (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG) PET/CT, and CT/MRI. Only 12 patients underwent an additional (18)F-fluorodihydroxyphenylalanine ((18)F-FDOPA) PET/CT scan and only 11 patients underwent an additional (18)F-fluorodopamine ((18)F-FDA) PET/CT scan. The rates of detection of metastatic lesions were compared among all the imaging studies. A composite of all functional and anatomical imaging studies served as the imaging comparator.

RESULTS

(68)Ga-DOTATATE PET/CT showed a lesion-based detection rate of 97.6 % (95 % confidence interval, CI, 95.8 - 98.7 %). (18)F-FDG PET/CT, (18)F-FDOPA PET/CT, (18)F-FDA PET/CT, and CT/MRI showed detection rates of 49.2 % (CI 44.5 - 53.6 %; p < 0.01), 74.8 % (CI 69.0 - 79.9 %); p < 0.01), 77.7 % (CI 71.5 - 82.8 %; p < 0.01), and 81.6 % (CI 77.8 - 84.8 %; p < 0.01), respectively.

CONCLUSION

The results of this study demonstrate the superiority of (68)Ga-DOTATATE PET/CT in the localization of sporadic metastatic PPGLs compared to all other functional and anatomical imaging modalities, and suggest modification of future guidelines towards this new imaging modality.

PET/CT imaging of renal cell carcinoma with (18)F-VM4-037: a phase II pilot study

BACKGROUND

Carbonic anhydrase IX (CA-IX) is a potential imaging biomarker of clear cell renal cell carcinoma (ccRCC). Here, we report the results of a phase II clinical trial of a small molecule radiotracer targeting CA-IX ((18)F-VM4-037) in ccRCC.

METHODS

Between October 2012 and May 2013, 11 patients with kidney masses underwent (18)F-VM4-037 PET/CT prior to surgery. Dynamic imaging was performed for the first 45 min post injection and whole-body imaging was obtained at 60 min post injection. Tumors were surgically excised or biopsied within 4 weeks of imaging.

RESULTS

All patients tolerated the radiotracer well with no adverse events. Ten of the 11 patients had histologically confirmed malignancy. One patient had a Bosniak Type 3 cyst with no tumor found at surgery. Two patients had extrarenal disease and 9 had tumors only in the kidney. Primary ccRCC lesions were difficult to visualize on PET alone due to high uptake of the tracer in the adjacent normal kidney parenchyma, however when viewed in conjunction with CT, the tumors were easily localized. Metastatic lesions were clearly visible on PET. Mean SUV for primary kidney lesions was 2.55 in all patients; in patients with histologically confirmed ccRCC, the mean SUV was 3.16. The time-activity curves (TAC) are consistent with reversible ligand binding with peak activity concentration at 8 min post injection followed by washout. Distribution Volume Ratio (DVR) of the lesions was measured using the Logan graphical analysis method. The mean DVR value across the 9 kidney lesions was 5.2 ± 2.8, (range 0.68-10.34).

CONCLUSION

18F-VM4-037 is a well-tolerated PET agent that allows same day imaging of CA-IX expression. The agent demonstrated moderate signal uptake in primary tumors and excellent visualization of CA-IX positive metastases. While the evaluation of primary ccRCC lesions is challenging due to high background activity in the normal kidney parenchyma, 18F-VM4-037 may be most useful in the evaluation of metastatic ccRCC lesions.

Preclinical efficacy of the anti-hepatocyte growth factor antibody ficlatuzumab in a mouse brain orthotopic glioma model evaluated by bioluminescence, PET, and MRI

PURPOSE

Ficlatuzumab is a novel therapeutic agent targeting the hepatocyte growth factor (HGF)/c-MET pathway. We summarize extensive preclinical work using this agent in a mouse brain orthotopic model of glioblastoma.

EXPERIMENTAL DESIGN

Sequential experiments were done using eight- to nine-week-old nude mice injected with 3 × 10(5) U87 MG (glioblastoma) cells into the brain. Evaluation of ficlatuzumab dose response for this brain tumor model and comparison of its response to ficlatuzumab and to temozolamide were conducted first. Subsequently, various small-animal imaging modalities, including bioluminescence imaging (BLI), positron emission tomography (PET), and MRI, were used with a U87 MG-Luc 2 stable cell line, with and without the use of ficlatuzumab, to evaluate the ability to noninvasively assess tumor growth and response to therapy. ANOVA was conducted to evaluate for significant differences in the response.

RESULTS

There was a survival benefit with ficlatuzumab alone or in combination with temozolamide. BLI was more sensitive than PET in detecting tumor cells. Fluoro-D-thymidine (FLT) PET provided a better signal-to-background ratio than 2[(18)F]fluoro-2-deoxy-d-glucose (FDG) PET. In addition, both BLI and FLT PET showed significant changes over time in the control group as well as with response to therapy. MRI does not disclose any time-dependent change. Also, the MRI results showed a temporal delay in comparison to the BLI and FLT PET findings, showing similar results one drug cycle later.

CONCLUSIONS

Targeting the HGF/c-MET pathway with the novel agent ficlatuzumab appears promising for the treatment of glioblastoma. Various clinically applicable imaging modalities including FLT, PET, and MRI provide reliable ways of assessing tumor growth and response to therapy. Given the clinical applicability of these findings, future studies on patients with glioblastoma may be appropriate.

The fate and toxicity of Raman-active silica-gold nanoparticles in mice

Raman spectroscopy is an optical imaging method that is based on the Raman effect, the inelastic scattering of a photon when energy is absorbed from light by a surface. Although Raman spectroscopy is widely used for chemical and molecular analysis, its clinical application has been hindered by the inherently weak nature of the Raman effect. Raman-silica-gold-nanoparticles (R-Si-Au-NPs) overcome this limitation by producing larger Raman signals through surface-enhanced Raman scattering. Because we are developing these particles for use as targeted molecular imaging agents, we examined the acute toxicity and biodistribution of core polyethylene glycol (PEG)-ylated R-Si-Au-NPs after different routes of administration in mice. After intravenous administration, PEG-R-Si-Au-NPs were removed from the circulation by macrophages in the liver and spleen (that is, the reticuloendothelial system). At 24 hours, PEG-R-Si-Au-NPs elicited a mild inflammatory response and an increase in oxidative stress in the liver, which subsided by 2 weeks after administration. No evidence of significant toxicity was observed by measuring clinical, histological, biochemical, or cardiovascular parameters for 2 weeks. Because we are designing targeted PEG-R-Si-Au-NPs (for example, PEG-R-Si-Au-NPs labeled with an affibody that binds specifically to the epidermal growth factor receptor) to detect colorectal cancer after administration into the bowel lumen, we tested the toxicity of the core nanoparticle after administration per rectum. We observed no significant bowel or systemic toxicity, and no PEG-R-Si-Au-NPs were detected systemically. Although additional studies are required to investigate the long-term effects of PEG-R-Si-Au-NPs and their toxicity when carrying the targeting moiety, the results presented here support the idea that PEG-R-Si-Au-NPs can be safely used in living subjects, especially when administered rectally.

Current concepts and future directions in radioimmunotherapy

Radioimmunotherapy relies on the principles of immunotherapy, but expands the cytotoxic effects of the antibody by complexing it with a radiation-emitting particle. If we consider radioimmunotherapy as a step beyond immunotherapy of cancer, the step was prompted by the (relative) failure of the latter. The conventional way to explain the failure is a lack of intrinsic killing effect and a lack of penetration into poorly vascularized tumor masses. The addition of a radioactive label (usually a β-emitter) to the antibody would improve both. Radiation is lethal and the type of radiation used (beta rays) has a sufficient range to overcome the lack of antibody penetration. At present, the most successful (and FDA approved) radioimmunotherapy agents for lymphomas are anti-CD20 monoclonal antibodies. Rituximab (Rituxan(®)) is a chimeric antibody, used as a non-radioactive antibody and to pre-load the patient when Zevalin(®) is used. Zevalin(®) is the Yttrium-90 ((90)Y) or Indium-111 ((111)In) labeled form of Ibritumomab Tiuxetan. Bexxar(®) is the Iodine-131 ((131)I) labeled form of Tositumomab. Ibritumomab Tiuxetan and Tositumomab are murine anti-CD20 monoclonal antibodies, not chimeric antibodies. Promising research is being done to utilize radioimmunotherapy earlier in the treatment algorithm for lymphoma, including as initial, consolidation, and salvage therapies. However, despite more than 8 years since initial regulatory approval, radioimmunotherapy still has not achieved widespread use due to a combination of medical, scientific, logistic, and financial barriers. Other experimental uses for radioimmunotherapy include other solid tumors to treat infections. Optimization can potentially be done with pre-targeting and bi-specific antibodies. Alpha particle and Auger electron emitters show promise as future radioimmunotherapy agents but are mostly still in pre-clinical stages.

Merlin differs from moesin in binding to F-actin and in its intra- and intermolecular interactions

The neurofibromatosis type 2 (NF2) tumor suppressor gene encodes merlin, a protein with homology to the cell membrane/F-actin linking proteins, moesin, ezrin and radixin. Unlike these closely related proteins, merlin lacks a C-terminal F-actin binding site detectable by actin blot overlays, and the GFP-tagged merlin C-terminal domain co-distributes with neither stress fibers nor cortical actin in NIH3T3 cells. Merlin also differs from the other three proteins in its inter- and intramolecular domain interactions, as shown by in vitro binding and yeast two-hybrid assays. As is true for ezrin, moesin and radixin, the N- and C-terminal domains of merlin type 1 bind to each other. However, full-length merlin and its N- and C-terminal domains, as well as the C-terminal domain of ezrin, interact with other full-length merlin type 1 molecules, and its C-terminal domain interacts with itself. Merlin 1 function in cells may thus depend on intra- and intermolecular interactions and their modulation, which include interactions with other members of this protein family.