Dosimetry of a Novel 111Indium-Labeled Anti-P-Cadherin Monoclonal Antibody (FF-21101) in Non-Human Primates.

P-cadherin is associated with a wide range of tumor types, making it an attractive therapeutic target. FF-21101 is a human-mouse chimeric monoclonal antibody (mAb) directed against human P-cadherin, which has been radioconjugated with indium-111 (111In) utilizing a DOTA chelator. We investigated the biodistribution of FF-21101(111In) in cynomolgus macaques and extrapolated the results to estimate internal radiation doses of 111In- and yttrium-90 (90Y)-FF-21101 for targeted radioimmunotherapy in humans. Whole-body planar and SPECT imaging were performed at 0, 2, 24, 48, 72, 96, and 120 h post-injection, using a dual-head gamma camera. Volumes of interest of identifiable source organs of radioactivity were defined on aligned reference CT and serial SPECT images. Organs with the highest estimated dose values (mSv/MBq) for FF-21101(111In) were the lungs (0.840), spleen (0.816), liver (0.751), kidneys (0.629), and heart wall (0.451); and for FF-21101(90Y) dose values were: lungs (10.49), spleen (8.21), kidneys (5.92), liver (5.46), and heart wall (2.61). FF-21101(111In) exhibits favorable biodistribution in cynomolgus macaques and estimated human dosimetric characteristics. Data obtained in this study were used to support the filing of an investigational new drug application with the FDA for a Phase I clinical trial.

Current Status of Radiolabeled Monoclonal Antibodies Targeting PSMA for Imaging and Therapy.

Prostate cancer (PCa) is one of the most prevalent cancer diagnoses among men in the United States and in several other developed countries. The prostate specific membrane antigen (PSMA) has been recognized as a promising molecular target in PCa, which has led to the development of specific radionuclide-based tracers for imaging and radiopharmaceuticals for PSMA targeted therapy. These compounds range from small molecule ligands to monoclonal antibodies (mAbs). Monoclonal antibodies play a crucial role in targeting cancer cell-specific antigens with a high degree of specificity while minimizing side effects to normal cells. The same mAb can often be labeled in different ways, such as with radionuclides suitable for imaging with Positron Emission Tomography (ß+ positrons), Gamma Camera Scintigraphy (γ photons), or radiotherapy (ß- electrons, α-emitters, or Auger electrons). Accordingly, the use of radionuclide-based PSMA-targeting compounds in molecular imaging and therapeutic applications has significantly grown in recent years. In this article, we will highlight the latest developments and prospects of radiolabeled mAbs that target PSMA for the detection and treatment of prostate cancer.

The Role of Radiolabeled Monoclonal Antibodies in Cancer Imaging and ADC Treatment.

ABSTRACT: Antibody-drug conjugates (ADCs) are designed to deliver cytotoxic payloads to distinctive target-expressing cancer cells. Following internalization, the ADCs are routed to different compartments in the cells, where cleavage of the linker causes release of the cytotoxic cargo. With such a delivery system, more effective payloads can reach cancer cells, allowing for more efficient treatment and dosing schedule. The monoclonal antibody (mAb) component of ADC plays a crucial role in the effective targeting of cancer cell-specific antigens while minimizing binding to normal cells. Often, the same mAbs used in ADCs can be labeled instead with radionuclides suitable for positron emission tomography or gamma-camera scintigraphy. To achieve high sensitivity and specificity for imaging, radiolabeled mAbs must have high affinity for the antigen, favorable pharmacokinetic properties, and a low toxicity profile. The use of radiolabeled mAbs permits the noninvasive interrogation of specific target expression on tumor cells and assessment of tumor heterogeneity in vivo by a simple diagnostic imaging scan that may include the whole body in the field of view. With this approach, radiolabeled mAbs can serve as important imaging biomarkers to predict the optimal delivery of ADCs to tumors and be used to monitor therapy with follow-up scans. Moreover, the same mAb can then be radiolabeled with an analogous radionuclide for the delivery of ß-emitters, α-particles, or Auger electrons as part of a radioimmunotherapy approach. The purpose of this review is to introduce key concepts regarding radiolabeled mAbs targeting various tumor antigens (CD20, CDH3, type I insulinlike growth factor receptor, prostate-specific membrane antigen, and human epidermal growth factor receptor 2) that are being used in the clinical setting or undergoing development.

18F-Fluciclovine-Avid Reactive Axillary Lymph Nodes After COVID-19 Vaccination.

ABSTRACT: A 74-year-old man presenting with biochemical recurrent prostate cancer 9 months after robotic-assisted radical prostatectomy and pelvic lymphadenectomy underwent 18F-fluciclovine PET/CT for restaging to determine subsequent treatment strategy. Serum prostate-specific antigen was 0.7 ng/mL at the time of imaging. Images demonstrated foci of abnormal increased 18F-fluciclovine uptake corresponding to prominent round lymph nodes in the left axilla, some of which with fatty hila. Due to recent mRNA COVID-19 vaccination in the ipsilateral arm and the low likelihood of nodal metastases to the axilla from prostate cancer in this patient, the lymph nodes were considered to be benign, reactive to the vaccine.

18F-Fluciclovine Uptake in a Ureterocele.

A 60-year-old man with prostate adenocarcinoma status post radical prostatectomy and bilateral pelvic lymph node dissection referred for restaging F-fluciclovine PET/CT due to rising serum prostate-specific antigen levels (1.1 ng/mL at that time of imaging). PET/CT images were obtained from the proximal thighs to the vertex of the skull approximately 3 to 5 minutes after the IV administration of 347.8 MBq (9.4 mCi) of F-fluciclovine. PET/CT imaging demonstrated a focus of abnormally increased F-fluciclovine uptake at the right ureterovesical junction. Subsequent MRI of the pelvis revealed that this focus corresponded to a benign ureterocele.

Prostate Cancer Liver Metastases Presenting as Relatively Photopenic Lesions on 18F-Fluciclovine PET/CT.

ABSTRACT: A 66-year-old man with prostate adenocarcinoma status post radical retropubic prostatectomy and bilateral pelvic lymph node dissection, followed by salvage external beam radiation therapy to the prostate bed 1 year after surgery. Over the course of 17 years, the patient underwent multiple lines of systemic treatment for recurrent disease. He was referred for restaging 18F-fluciclovine PET/CT due to rising serum prostate-specific antigen levels. Contrast-enhanced 18F-fluciclovine PET/CT images demonstrated multiple new liver metastases, which were relatively photopenic in comparison with the physiologic radiotracer activity in the surrounding normal liver parenchyma.

Incidental 18F-Fluciclovine Uptake in a Warthin Tumor of the Parotid Gland in a Patient Undergoing PET/CT Imaging for Biochemical Recurrent Prostate Cancer.

A 67-year-old asymptomatic man with biochemical recurrent prostate cancer underwent F-fluciclovine PET/CT for restaging to determine subsequent treatment strategy. PET/CT images were obtained from the proximal thighs to the vertex of the skull, after the intravenous administration of 362.6 MBq (9.8 mCi) of F-fluciclovine. PET/CT imaging demonstrated a focus of abnormally increased F-fluciclovine uptake corresponding to a small nodularity in the left parotid gland. Subsequent ultrasound-guided fine-needle aspiration biopsy of the lesion revealed histopathology compatible with a benign Warthin tumor.

Gallium-68 in Medical Imaging.

Over the past several years, Positron Emission Tomography (PET) imaging agents labeled with ;68Gallium (68Ga) have undergone a significant increase in clinical utilization. 68Ga is conveniently produced from a germanium-68/gallium-68 (68Ge/68Ga) generator. Because of the compact size and ease of use of the generator, 68Ga labeled compounds may be more cost-effective than PET radioisotopes that are cyclotron-produced. The convenient half-life of 68Ga (T1/2=68 min) provides sufficient radioactivity for various PET imaging applications, while delivering acceptable radiation doses to patients. This chapter summarizes the emerging clinical utilization of 68Ga-based radiotracers in medical imaging.

Maternal dietary uridine causes, and deoxyuridine prevents, neural tube closure defects in a mouse model of folate-responsive neural tube defects.

BACKGROUND: Folic acid prevents neural tube closure defects (NTDs), but the causal metabolic pathways have not been established. Serine hydroxymethyltransferase 1 (SHMT1) is an essential scaffold protein in folate-dependent de novo thymidylate synthesis in the nucleus. SHMT1-deficient mice provide a model to investigate folic acid-responsive NTDs wherein disruption of de novo thymidylate synthesis impairs neural tube closure. OBJECTIVE: We examined the effects of maternal supplementation with the pyrimidine nucleosides uridine, thymidine, or deoxyuridine with and without folate deficiency on NTD incidence in the Shmt1 mouse model. DESIGN: Shmt1(+/+) and Shmt1(-/-) female mice fed folate-replete or folate-deficient diets and supplemented with uridine, thymidine, or deoxyuridine were bred, and litters (n = 10-23 per group) were examined for the presence of NTDs. Biomarkers of impaired folate status and metabolism were measured, including plasma nucleosides, hepatic uracil content, maternal plasma folate concentrations, and incorporation of nucleoside precursors into DNA. RESULTS: Shmt1(+/-) and Shmt1(-/-) embryos from dams fed the folate-deficient diet were susceptible to NTDs. No NTDs were observed in litters from dams fed the folate-deficient diet supplemented with deoxyuridine. Surprisingly, uridine supplementation increased NTD incidence, independent of embryo genotype and dietary folic acid. These dietary nucleosides did not affect maternal hepatic uracil accumulation in DNA but did affect plasma folate concentrations. CONCLUSIONS: Maternal deoxyuridine supplementation prevented NTDs in dams fed the folate-deficient diet, whereas maternal uridine supplementation increased NTD incidence, independent of folate and embryo genotype. These findings provide new insights into the metabolic impairments and mechanisms of folate-responsive NTDs resulting from decreased Shmt1 expression.

Warburg effect's manifestation in aggressive pheochromocytomas and paragangliomas: insights from a mouse cell model applied to human tumor tissue.

A glycolytic profile unifies a group of pheochromocytomas and paragangliomas (PHEOs/PGLs) with distinct underlying gene defects, including von Hippel-Lindau (VHL) and succinate dehydrogenase B (SDHB) mutations. Nevertheless, their tumor aggressiveness is distinct: PHEOs/PGLs metastasize rarely in VHL-, but frequently in SDHB-patients. To date, the molecular mechanisms causing the more aggressive phenotype in SDHB-PHEOs/PGLs remain largely unknown. Recently, however, an excellent model to study aggressive PHEOs (mouse tumor tissue (MTT) cells) has been developed from mouse PHEO cells (MPC). We employed this model for a proteomics based approach to identify changes characteristic for tumor aggressiveness, which we then explored in a homogeneous set of human SDHB- and VHL-PHEOs/PGLs. The increase of glucose transporter 1 in VHL, and of hexokinase 2 in VHL and SDHB, confirmed their glycolytic profile. In agreement with the cell model and in support of decoupling of glycolysis, the Krebs cycle and oxidative phosphorylation (OXPHOS), SDHB tumors showed increased lactate dehydrogenase levels. In SDHB-PGLs OXPHOS complex activity was increased at complex III and, as expected, decreased at complex II. Moreover, protein and mRNA expression of all tested OXPHOS-related genes were higher in SDHB- than in VHL-derived tumors. Although there was no direct evidence for increased reactive oxygen species production, elevated superoxide dismutase 2 expression may reflect elevated oxidative stress in SDHB-derived PHEOs/PGLs. For the first time, we show that despite dysfunction in complex II and evidence for a glycolytic phenotype, the Warburg effect does not seem to fully apply to SDHB-PHEOs/PGLs with respect to decreased OXPHOS. In addition, we present evidence for increased LDHA and SOD2 expression in SDHB-PHEOs/PGLs, proteins that have been proposed as promising therapeutic targets in other cancers. This study provides new insight into pathogenic mechanisms in aggressive human PHEOs/PGLs, which may lead to identifying new diagnostic and prognostic markers in the near future.

Murine models and cell lines for the investigation of pheochromocytoma: applications for future therapies?

Pheochromocytomas (PCCs) are slow-growing neuroendocrine tumors arising from adrenal chromaffin cells. Tumors arising from extra-adrenal chromaffin cells are called paragangliomas. Metastases can occur up to approximately 60% or even more in specific subgroups of patients. There are still no well-established and clinically accepted "metastatic" markers available to determine whether a primary tumor is or will become malignant. Surgical resection is the most common treatment for non-metastatic PCCs, but no standard treatment/regimen is available for metastatic PCC. To investigate what kind of therapies are suitable for the treatment of metastatic PCC, animal models or cell lines are very useful. Over the last two decades, various mouse and rat models have been created presenting with PCC, which include models presenting tumors that are to a certain degree biochemically and/or molecularly similar to human PCC, and develop metastases. To be able to investigate which chemotherapeutic options could be useful for the treatment of metastatic PCC, cell lines such as mouse pheochromocytoma (MPC) and mouse tumor tissue (MTT) cells have been recently introduced and they both showed metastatic behavior. It appears these MPC and MTT cells are biochemically and molecularly similar to some human PCCs, are easily visualized by different imaging techniques, and respond to different therapies. These studies also indicate that some mouse models and both mouse PCC cell lines are suitable for testing new therapies for metastatic PCC.

Usefulness of [18F]-DA and [18F]-DOPA for PET imaging in a mouse model of pheochromocytoma.

PURPOSE: To evaluate the usefulness of [(18)F]-6-fluorodopamine ([(18)F]-DA) and [(18)F]-L-6-fluoro-3,4-dihydroxyphenylalanine ([(18)F]-DOPA) positron emission tomography (PET) in the detection of subcutaneous (s.c.) and metastatic pheochromocytoma in mice; to assess the expression of the norepinephrine transporter (NET) and vesicular monoamine transporters 1 and 2 (VMAT1 and VMAT2), all important for [(18)F]-DA and [(18)F]-DOPA uptake. Furthermore, to compare tumor detection by micro-computed tomography (microCT) to magnetic resonance imaging (MRI) in individual mouse. METHODS: SUV(max) values were calculated from [(18)F]-DA and [(18)F]-DOPA PET, tumor-to-liver ratios (TLR) were obtained and expression of NET, VMAT1 and VMAT2 was evaluated. RESULTS: [(18)F]-DA detected less metastatic lesions compared to [(18)F]-DOPA. TLR values for liver metastases were 2.26-2.71 for [(18)F]-DOPA and 1.83-2.83 for [(18)F]-DA. A limited uptake of [(18)F]-DA was found in s.c. tumors (TLR = 0.22-0.27) compared to [(18)F]-DOPA (TLR = 1.56-2.24). Overall, NET and VMAT2 were expressed in all organ and s.c. tumors. However, s.c. tumors lacked expression of VMAT1. We confirmed [(18)F]-DA's high affinity for the NET for its uptake and VMAT1 and VMAT2 for its storage and retention in pheochromocytoma cell vesicles. In contrast, [(18)F]-DOPA was found to utilize only VMAT2. CONCLUSION: MRI was superior in the detection of all organ tumors compared to microCT and PET. [(18)F]-DOPA had overall better sensitivity than [(18)F]-DA for the detection of metastases. Subcutaneous tumors were localized only with [(18)F]-DOPA, a finding that may reflect differences in expression of VMAT1 and VMAT2, perhaps similar to some patients with pheochromocytoma where [(18)F]-DOPA provides better visualization of lesions than [(18)F]-DA.

Pharmacologic modulation of serine/threonine phosphorylation highly sensitizes PHEO in a MPC cell and mouse model to conventional chemotherapy.

BACKGROUND: The failure of cytotoxic cancer regimens to cure the most drug-resistant, well-differentiated solid tumors has been attributed to the heterogeneity of cell types that differ in their capacities for growth, differentiation, and metastases. We investigated the effect of LB1, a small molecule inhibitor of serine/threonine protein phosphatase 2A (PP2A), on its ability to inhibit a low growth fraction and highly drug-resistant solid neuroendocrine tumor, such as metastatic pheochromocytoma (PHEO). Subsequently, we evaluated the increased efficacy of chemotherapy combined with LB1. METHODOLOGY/PRINCIPAL FINDINGS: The effect of LB1 and temozolomide (TMZ), a standard chemotherapeutic agent that alone only transiently suppressed the growth and regression of metastatic PHEO, was evaluated in vitro on a single PHEO cell line and in vivo on mouse model of metastatic PHEO. In the present study, we show that metastatic PHEO, for which there is currently no cure, can be eliminated by combining LB1, thereby inhibiting PP2A, with TMZ. This new treatment approach resulted in long term, disease-free survival of up to 40% of animals bearing multiple intrahepatic metastases, a disease state that the majority of patients die from. Inhibition of PP2A was associated with prevention of G1/S phase arrest by p53 and of mitotic arrest mediated by polo-like kinase 1 (Plk-1). CONCLUSIONS/SIGNIFICANCE: The elimination of DNA damage-induced defense mechanisms, through transient pharmacologic inhibition of PP2A, is proposed as a new approach for enhancing the efficacy of non-specific cancer chemotherapy regimens against a broad spectrum of low growth fraction tumors very commonly resistant to cytotoxic drugs.

Increased uptake of [¹²³I]meta-iodobenzylguanidine, [¹8F]fluorodopamine, and [³H]norepinephrine in mouse pheochromocytoma cells and tumors after treatment with the histone deacetylase inhibitors.

[¹³¹I]meta-iodobenzylguanidine ([¹³¹I]MIBG) is the most commonly used treatment for metastatic pheochromocytoma and paraganglioma. It enters the chromaffin cells via the membrane norepinephrine transporter; however, its success has been modest. We studied the ability of histone deacetylase (HDAC) inhibitors to enhance [¹²³I]MIBG uptake by tumors in a mouse metastatic pheochromocytoma model. HDAC inhibitors are known to arrest growth, induce differentiation and apoptosis in various cancer cells, and further inhibit tumor growth. We report the in vitro and in vivo effects of two HDAC inhibitors, romidepsin and trichostatin A, on the uptake of [(3)H]norepinephrine, [¹²³I]MIBG, and [(18)F]fluorodopamine in a mouse model of metastatic pheochromocytoma. The effects of both inhibitors on norepinephrine transporter activity were assessed in mouse pheochromocytoma (MPC) cells by using the transporter-blocking agent desipramine and the vesicular-blocking agent reserpine. HDAC inhibitors increased [(3)H]norepinephrine, [¹²³I]MIBG, and [(18)F]fluorodopamine uptake through the norepinephrine transporter in MPC cells. In vivo, inhibitor treatment resulted in significantly increased uptake of [(18)F]fluorodopamine positron emission tomography (PET) in pheochromocytoma liver metastases (19.1 ± 3.2% injected dose per gram of tumor (%ID/g) compared to liver metastases in pretreatment scans 5.9 ± 0.6%; P<0.001). Biodistribution analysis after inhibitors treatment confirmed the PET results. The uptake of [(123)I]MIBG was significantly increased in liver metastases 9.5 ± 1.1% compared to 3.19 ± 0.4% in untreated control liver metastases (P<0.05). We found that HDAC inhibitors caused an increase in the amount of norepinephrine transporter expressed in tumors. HDAC inhibitors may enhance the therapeutic efficacy of [(131)I]MIBG treatment in patients with advanced malignant pheochromocytoma and paraganglioma.

In vivo micro-CT imaging of liver lesions in small animal models.

Three-dimensional micro computed tomography (microCT) offers the opportunity to capture images liver structures and lesions in mice with a high spatial resolution. Non-invasive microCT allows for accurate calculation of vessel tortuosity and density, as well as liver lesion volume and distribution. Longitudinal monitoring of liver lesions is also possible. However, distinguishing liver lesions from variations within a normal liver is impossible by microCT without the use of liver- or tumor-specific contrast-enhancing agents. The combination of microCT for morphologic imaging with functional imaging, such as positron emission tomography (PET) or single photon emission tomography (SPECT), offers the opportunity for better abdominal imaging and assessment of structure discrepancies visible by functional imaging. This paper describes methods of current microCT imaging options for imaging of liver lesions compared to other imaging techniques in small animals.

Comparison of 18F-fluoro-L-DOPA, 18F-fluoro-deoxyglucose, and 18F-fluorodopamine PET and 123I-MIBG scintigraphy in the localization of pheochromocytoma and paraganglioma.

CONTEXT: Besides (123)I-metaiodobenzylguanidine (MIBG), positron emission tomography (PET) agents are available for the localization of paraganglioma (PGL), including (18)F-3,4-dihydroxyphenylalanine (DOPA), (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG), and (18)F-fluorodopamine ((18)F-FDA). OBJECTIVE: The objective of the study was to establish the optimal approach to the functional imaging of PGL and examine the link between genotype-specific tumor biology and imaging. DESIGN: This was a prospective observational study. INTERVENTION: There were no interventions. PATIENTS: Fifty-two patients (28 males, 24 females, aged 46.8 +/- 14.2 yr): 20 with nonmetastatic PGL (11 adrenal), 28 with metastatic PGL (13 adrenal), and four in whom PGL was ruled out; 22 PGLs were of the succinate dehydrogenase subunit B (SDHB) genotype. MAIN OUTCOME MEASURES: Sensitivity of (18)F-DOPA, (18)F-FDG, and (18)F-FDA PET, (123)I-MIBG scintigraphy, computed tomography (CT), and magnetic resonance imaging (MRI) for the localization of PGL were measured. RESULTS: Sensitivities for localizing nonmetastatic PGL were 100% for CT and/or MRI, 81% for (18)F-DOPA PET, 88% for (18)F-FDG PET/CT, 78% for (18)F-FDA PET/CT, and 78% for (123)I-MIBG scintigraphy. For metastatic PGL, sensitivity in reference to CT/MRI was 45% for (18)F-DOPA PET, 74% for (18)F-FDG PET/CT, 76% for (18)F-FDA PET/CT, and 57% for (123)I-MIBG scintigraphy. In patients with SDHB metastatic PGL, (18)F-FDA and (18)F-FDG have a higher sensitivity (82 and 83%) than (123)I-MIBG (57%) and (18)F-DOPA (20%). CONCLUSIONS: (18)F-FDA PET/CT is the preferred technique for the localization of the primary PGL and to rule out metastases. Second best, equal alternatives are (18)F-DOPA PET and (123)I-MIBG scintigraphy. For patients with known metastatic PGL, we recommend (18)F-FDA PET in patients with an unknown genotype, (18)F-FDG or (18)F-FDA PET in SDHB mutation carriers, and (18)F-DOPA or (18)F-FDA PET in non-SDHB patients.

Overexpression of interleukin-13 receptor-alpha2 in neuroendocrine malignant pheochromocytoma: a novel target for receptor directed anti-cancer therapy.

CONTEXT: Pheochromocytomas and paragangliomas are rare catecholamine-secreting neuroendocrine tumors arising from the adrenal medulla and sympathetic tissues. When complete surgical resection is not an option, the treatment of pheochromocytoma is limited. OBJECTIVE: The objective of the study was to identify and characterize overexpression of IL-13 receptor-alpha2 (IL-13Ralpha2) gene expression in human and murine tumors and verify xenograft mouse pheochromocytoma cell (MPC)-derived tumor's response to a selective cytotoxin. DESIGN/SETTING/PATIENTS: Expression of IL-13Ralpha2 was evaluated in a panel of 25 human pheochromocytoma clinical samples by RT-PCR and eight MPC tumors by indirect immunofluorescence assay and RT-PCR. INTERVENTION: The function of IL-13Ralpha2 in these tumor cells was examined by evaluating tumor sensitivity to a recombinant IL-13-Pseudomonas exotoxin (IL-13PE). Subcutaneous small and large MPC tumors in athymic nude mice (n = 10) were treated intratumorally with IL-13PE (100 m icrog/kg). MAIN OUTCOME MEASURES: IC(50) and tumor size were measured. RESULTS: IL-13PE immunotoxin was highly cytotoxic to IL-13Ralpha2-overexpressing MPC cells (IC(50) <2.5 ng/ml) in vitro. Furthermore, IL-13PE was highly cytotoxic to sc tumors. Our results showed a statistically significant decrease in tumor size as early as 3 d after initial treatment and further suppressed growth of MPC tumors. All tumors displayed a histological evidence of necrosis in response to IL-13 immunotoxin without any adverse effects in host at this dose. CONCLUSIONS: Human and murine neuroendocrine pheochromocytoma overexpress the IL-13Ralpha2 chain, and an IL-13PE-based receptor-directed anticancer approach may prove useful in treatment for metastatic pheochromocytoma patients.

Noninvasive monitoring of a murine model of metastatic pheochromocytoma: a comparison of contrast-enhanced microCT and nonenhanced MRI.

PURPOSE: To compare contrast-enhanced micro-computed tomography (microCT) and nonenhanced respiratory-triggered magnetic resonance imaging (MRI) in an animal model of metastatic pheochromocytoma. Animal models are becoming important in the study of cancer treatment and imaging is useful in minimizing the number of animals needed and reducing costs associated with autopsies. However, the choice of imaging modality is still evolving. MATERIALS AND METHODS: Adult female nude mice were injected by tail vein with a mouse pheochromocytoma (MPC) cell line (MPC 4/30PRR) to create a metastatic model. After optimizing imaging techniques, eight mice were imaged with both respiratory triggered MRI and microCT and the findings were verified histologically. RESULTS: MicroCT and MRI were approximately equal in their ability to detect hepatic metastases at a size threshold of 350 microm. In the lungs, MRI was more sensitive than microCT, detecting lesions 0.6 mm in diameter versus 1 mm for microCT. Additionally, MRI was more sensitive for lesions in the kidneys, bone, ovaries, and adrenal glands. MRI demonstrated a higher contrast-to-noise ratio (CNR) than microCT. CONCLUSION: In addition to the advantage of not exposing the animal to ionizing radiation, MRI provided a more complete assessment of the extent of metastases in this model compared to microCT.

Characterization of an animal model of aggressive metastatic pheochromocytoma linked to a specific gene signature.

Pheochromocytomas are chromaffin cell-derived neuroendocrine tumors. There is presently no cure for metastatic pheochromocytoma and no reliable way to distinguish malignant from benign tumors before the development of metastases. In order to successfully manage pheochromocytoma, it is necessary to better understand the biological determinants of tumor behavior. For this purpose, we have recently established a mouse model of metastatic pheochromocytoma using tail vein injection of mouse pheochromocytoma (MPC) cells. We optimized this model modifying the number of cells injected, length of trypsin pre-treatment, and incubation temperature and duration for the MPC cells before injection, and by serial passage and re-selection of tumors exhibiting the metastatic phenotype. We evaluated the effect of these modifications on tumor growth using serial in vivo Magnetic Resonance Imaging studies. These results show that number of cells injected, the pre-injection incubation temperature, and duration of trypsin treatment are important factors to produce faster growing, more aggressive tumors that yielded secondary metastatic lesions. Serial harvest, culture and re-selection of metastatic liver lesions produced even more aggressive pheochromocytoma cells that retained their biochemical phenotype. Microarray gene expression comparison and quantitative real-time PCR of these more aggressive cells to the MPC-parental cell line identified genes that may be important for the metastatic process.

[18F]FBEM-Z(HER2:342)-Affibody molecule-a new molecular tracer for in vivo monitoring of HER2 expression by positron emission tomography.

PURPOSE: The expression of human epidermal growth factor receptor-2 (HER2) receptors in cancers is correlated with a poor prognosis. If assessed in vivo, it could be used for selection of appropriate therapy for individual patients and for monitoring of the tumor response to targeted therapies. We have radiolabeled a HER2-binding Affibody molecule with fluorine-18 for in vivo monitoring of the HER2 expression by positron emission tomography (PET). MATERIALS AND METHODS: The HER2-binding Z(HER2:342)-Cys Affibody molecule was conjugated with N-2-(4-[18F]fluorobenzamido)ethyl]maleimide ([18F]FBEM). The in vitro binding of the resulting radioconjugate was characterized by receptor saturation and competition assays. For in vivo studies, the radioconjugate was injected into the tail vein of mice bearing subcutaneous HER2-positive or HER2-negative tumors. Some of the mice were pre-treated with non-labeled Z(HER2:342)-Cys. The animals were sacrificed at different times post-injection, and the radioactivity in selected tissues was measured. PET images were obtained using an animal PET scanner. RESULTS: In vitro experiments indicated specific, high-affinity binding to HER2. PET imaging revealed a high accumulation of the radioactivity in the tumor as early as 20 min after injection, with a plateau being reached after 60 min. These results were confirmed by biodistribution studies demonstrating that, as early as 1 h post-injection, the tumor to blood concentration ratio was 7.5 and increased to 27 at 4 h. Pre-saturation of the receptors with unlabeled Z(HER2:342)-Cys lowered the accumulation of radioactivity in HER2-positive tumors to the levels observed in HER2-negative ones. CONCLUSION: Our results suggest that the [18F]FBEM-Z(HER2:342) radioconjugate can be used to assess HER2 expression in vivo.