Adrienne H. Brouwers

Biodistribution of 89Zr-trastuzumab and PET Imaging of HER2-Positive Lesions in Patients With Metastatic Breast Cancer

We performed a feasibility study to determine the optimal dosage and time of administration of the monoclonal antibody zirconium‐89 (89Zr)‐trastuzumab to enable positron emission tomography (PET) imaging of human epidermal growth factor receptor 2 (HER2)‐positive lesions. Fourteen patients with HER2‐positive metastatic breast cancer received 37 MBq of 89Zr‐trastuzumab at one of three doses (10 or 50 mg for those who were trastuzumab‐naive and 10 mg for those who were already on trastuzumab treatment). The patients underwent at least two PET scans between days 2 and 5. The results of the study showed that the best time for assessment of 89Zr‐trastuzumab uptake by tumors was 4–5 days after the injection. For optimal PET‐scan results, trastuzumab‐naive patients required a 50 mg dose of 89Zr‐trastuzumab, and patients already on trastuzumab treatment required a 10 mg dose. The accumulation of 89Zr‐trastuzumab in lesions allowed PET imaging of most of the known lesions and some that had been undetected earlier. The relative uptake values (RUVs) (mean ± SEM) were 12.8 ± 5.8, 4.1 ± 1.6, and 3.5 ± 4.2 in liver, bone, and brain lesions, respectively, and 5.9 ± 2.4, 2.8 ± 0.7, 4.0 ± 0.7, and 0.20 ± 0.1 in normal liver, spleen, kidneys, and brain tissue, respectively. PET scanning after administration of 89Zr‐trastuzumab at appropriate doses allows visualization and quantification of uptake in HER2‐positive lesions in patients with metastatic breast cancer.

In Vivo VEGF Imaging with Radiolabeled Bevacizumab in a Human Ovarian Tumor Xenograft

Vascular endothelial growth factor (VEGF), released by tumor cells, is an important growth factor in tumor angiogenesis. The humanized monoclonal antibody bevacizumab blocks VEGF-induced tumor angiogenesis by binding, thereby neutralizing VEGF. Our aim was to develop radiolabeled bevacizumab for noninvasive in vivo VEGF visualization and quantification with the single γ-emitting isotope 111In and the PET isotope 89Zr. Methods: Labeling, stability, and binding studies were performed. Nude mice with a human SKOV-3 ovarian tumor xenograft were injected with 89Zr-bevacizumab, 111In-bevacizumab, or human 89Zr-IgG. Human 89Zr-IgG served as an aspecific control antibody. Small-animal PET and microCT studies were obtained at 24, 72, and 168 h after injection of 89Zr-bevacizumab and 89Zr-IgG (3.5 ± 0.5 MBq, 100 ± 6 μg, 0.2 mL [mean ± SD]). Small-animal PET and microCT images were fused to calculate tumor uptake and compared with ex vivo biodistribution at 168 h after injection. 89Zr- and 111In-bevacizumab ex vivo biodistribution was compared at 24, 72, and 168 h after injection (2.0 ± 0.5 MBq each, 100 ± 4 μg in total, 0.2 mL). Results: Labeling efficiencies, radiochemical purity, stability, and binding properties were optimal for the radioimmunoconjugates. Small-animal PET showed uptake in well-perfused organs at 24 h and clear tumor localization from 72 h onward. Tumor uptake determined by quantification of small-animal PET images was higher for 89Zr-bevacizumab—namely, 7.38 ± 2.06 %ID/g compared with 3.39 ± 1.16 %ID/g (percentage injected dose per gram) for human 89Zr-IgG (P = 0.011) at 168 h and equivalent to ex vivo biodistribution studies. Tracer uptake in other organs was seen primarily in liver and spleen. 89Zr- and 111In-bevacizumab biodistribution was comparable. Conclusion: Radiolabeled bevacizumab showed higher uptake compared with radiolabeled human IgG in a human SKOV-3 ovarian tumor xenograft. Noninvasive quantitative small-animal PET was similar to invasive ex vivo biodistribution. Radiolabeled bevacizumab is a new tracer for noninvasive in vivo imaging of VEGF in the tumor microenvironment.

Improved Staging of Patients With Carcinoid and Islet Cell Tumors With 18F-Dihydroxy-Phenyl-Alanine and 11C-5-Hydroxy-Tryptophan Positron Emission Tomography

PURPOSE To evaluate and compare diagnostic sensitivity of positron emission tomography (PET) scanning in carcinoid and islet cell tumor patients with a serotonin and a catecholamine precursor as tracers. PATIENTS AND METHODS Carcinoid (n = 24) or pancreatic islet cell tumor (n = 23) patients with at least one lesion on conventional imaging including somatostatin receptor scintigraphy (SRS) and computed tomography (CT) scan underwent (11)C-5-hydroxytryptophan ((11)C-5-HTP) PET and 6-[F-18]fluoro-L-dihydroxy-phenylalanine ((18)F-DOPA) PET. PET findings were compared with a composite reference standard derived from all available imaging along with clinical and cytologic/histologic information. RESULTS In carcinoid tumor patients, per-patient analysis showed sensitivities for (11)C-5-HTP PET, (18)F-DOPA PET, SRS, and CT of 100%, 96%, 86%, 96%, respectively, and in islet cell tumors of 100%, 89%, 78%, 87%, respectively. In carcinoid patients, per-lesion analysis revealed sensitivities for (11)C-5-HTP PET, (11)C-5-HTP PET/CT, (18)F-DOPA PET, (18)F-DOPA PET/CT, SRS, SRS/CT, and CT alone of, respectively, 78%, 89%, 87%, 98%, 49%, 73%, and 63% and in islet cell tumors of 67%, 96%, 41%, 80%, 46%, 77%, and 68%, respectively. In all carcinoid patients (18)F-DOPA PET and (11)C-5-HTP PET detected more lesions than SRS (P < .001). (11)C-5-HTP PET was superior to (18)F-DOPA PET in islet cell tumors (P < .0001). In all cases, CT improved the sensitivity of the nuclear scans. CONCLUSION (18)F-DOPA PET/CT is the optimal imaging modality for staging in carcinoid patients and (11)C-5-HTP PET/CT in islet cell tumor patients.

6-L-18F-fluorodihydroxyphenylalanine PET in neuroendocrine tumors: basic aspects and emerging clinical applications.

In recent years, 6-l-18F-fluorodihydroxyphenylalanine (18F-DOPA) PET has emerged as a new diagnostic tool for the imaging of neuroendocrine tumors. This application is based on the unique property of neuroendocrine tumors to produce and secrete various substances, a process that requires the uptake of metabolic precursors, which leads to the uptake of 18F-DOPA. This nonsystematic review first describes basic aspects of 18F-DOPA imaging, including radiosynthesis, factors involved in tracer uptake, and various aspects of metabolism and imaging. Subsequently, this review provides an overview of current clinical applications in neuroendocrine tumors, including carcinoid tumors, pancreatic islet cell tumors, pheochromocytoma, paraganglioma, medullary thyroid cancer, hyperinsulinism, and various other clinical entities. The application of PET/CT in carcinoid tumors has unsurpassed sensitivity. In medullary thyroid cancer, pheochromocytoma, and hyperinsulinism, results are also excellent and contribute significantly to clinical management. In the remaining conditions, the initial experience with 18F-DOPA PET indicates that it seems to be less valuable, but further study is required.

6-[F-18]Fluoro-l-Dihydroxyphenylalanine Positron Emission Tomography Is Superior to Conventional Imaging with 123I-Metaiodobenzylguanidine Scintigraphy, Computer Tomography, and Magnetic Resonance Imaging in Localizing Tumors Causing Catecholamine Excess

CONTEXT Catecholamine excess is rare, but symptoms may be life threatening. OBJECTIVE The objective of the study was to investigate the sensitivity of 6-[F-18]fluoro-l-dihydroxyphenylalanine positron emission tomography ((18)F-DOPA PET), compared with (123)I-metaiodobenzylguanidine ((123)I-MIBG) scintigraphy and computer tomography (CT)/magnetic resonance imaging (MRI) for tumor localization in patients with catecholamine excess. DESIGN AND SETTING All consecutive patients with catecholamine excess visiting the University Medical Center Groningen, Groningen, The Netherlands, between March 2003 and January 2008 were eligible. PATIENTS Forty-eight patients were included. The final diagnosis was pheochromocytoma in 40, adrenal hyperplasia in two, paraganglioma in two, ganglioneuroma in one, and unknown in three. MAIN OUTCOME MEASURES Sensitivities and discordancy between (18)F-DOPA PET, (123)I-MIBG, and CT or MRI were analyzed for individual patients and lesions. Metanephrines and 3-methoxytyramine in plasma and urine and uptake of (18)F-DOPA with PET were measured to determine the whole-body metabolic burden and correlated with biochemical tumor activity. The gold standard was a composite reference standard. RESULTS (18)F-DOPA PET showed lesions in 43 patients, (123)I-MIBG in 31, and CT/MRI in 32. Patient-based sensitivity for (18)F-DOPA PET, (123)I-MIBG, and CT/MRI was 90, 65, and 67% (P < 0.01 for (18)F-DOPA PET vs. both (123)I-MIBG and CT/MRI, P = 1.0 (123)I-MIBG vs. CT/MRI). Lesion-based sensitivities were 73, 48, and 44% (P < 0.001 for (18)F-DOPA PET vs. both (123)I-MIBG and CT/MRI, P = 0.51 (123)I-MIBG vs. CT/MRI). The combination of (18)F-DOPA PET with CT/MRI was superior to (123)I-MIBG with CT/MRI (93 vs. 76%, P < 0.001). Whole-body metabolic burden measured with (18)F-DOPA PET correlated with plasma normetanephrine (r = 0.82), urinary normetanephrine (r = 0.84), and metanephrine (r = 0.57). CONCLUSION To localize tumors causing catecholamine excess, (18)F-DOPA PET is superior to (123)I-MIBG scintigraphy and CT/MRI.

VEGF-PET Imaging Is a Noninvasive Biomarker Showing Differential Changes in the Tumor during Sunitinib Treatment

Non-invasive imaging of angiogenesis could ease the optimization of antiangiogenesis treatments for cancer. In this study, we evaluated the role of VEGF-PET as a biomarker of dynamic angiogenic changes in tumors following treatment with the kinase inhibitor sunitinib. The effects of sunitinib treatment and withdrawal on the tumor was investigated using the new VEGF-PET tracer (89)Zr-ranibizumab as well as (18)F-FDG PET, and (15)O-water PET in mouse xenograft models of human cancer. The obtained imaging results were compared with tumor growth, VEGF plasma levels and immunohistologic analyzes. In contrast to (18)F-FDG and (15)O-water PET, VEGF-PET demonstrated dynamic changes during sunitinib treatment within the tumor with a strong decline in signal in the tumor center and only minimal reduction in tumor rim, with a pronounced rebound after sunitinib discontinuation. VEGF-PET results corresponded with tumor growth and immunohistochemical vascular- and tumor- markers. Our findings highlight the strengths of VEGF-PET imaging to allow serial analysis of angiogenic changes in different areas within a tumor.

89Zr-Bevacizumab PET Imaging in Primary Breast Cancer

Vascular endothelial growth factor (VEGF)-A is overexpressed in most malignant and premalignant breast lesions. VEGF-A can be visualized noninvasively with PET imaging and using the tracer 89Zr-labeled bevacizumab. In this clinical feasibility study, we assessed whether VEGF-A in primary breast cancer can be visualized by 89Zr-bevacizumab PET. Methods: Before surgery, breast cancer patients underwent a PET/CT scan of the breasts and axillary regions 4 d after intravenous administration of 37 MBq of 89Zr-bevacizumab per 5 mg. PET images were compared with standard imaging modalities. 89Zr-bevacizumab uptake was quantified as the maximum standardized uptake value (SUVmax). VEGF-A levels in tumor and normal breast tissues were assessed with enzyme-linked immunosorbent assay. Data are presented as mean ± SD. Results: Twenty-five of 26 breast tumors (mean size ± SD, 25.1 ± 19.8 mm; range, 4–80 mm) in 23 patients were visualized. SUVmax was higher in tumors (1.85 ± 1.22; range, 0.52–5.64) than in normal breasts (0.59 ± 0.37; range, 0.27–1.69; P < 0.001). The only tumor not detected on PET was 10 mm in diameter. Lymph node metastases were present in 10 axillary regions; 4 could be detected with PET (SUVmax, 2.66 ± 2.03; range, 1.32–5.68). VEGF-A levels in the 17 assessable tumors were higher than in normal breast tissue in all cases (VEGF-A/mg protein, 184 ± 169 pg vs. 10 ± 21 pg; P = 0.001), whereas 89Zr-bevacizumab tumor uptake correlated with VEGF-A tumor levels (r = 0.49). Conclusion: VEGF-A in primary breast cancer can be visualized by means of 89Zr-bevacizumab PET.

Lack of Efficacy of Two Consecutive Treatments of Radioimmunotherapy With 131I-cG250 in Patients With Metastasized Clear Cell Renal Cell Carcinoma

PURPOSE A previous activity dose-escalation study using 131I-labeled chimeric monoclonal antibody cG250 in patients with progressive metastatic renal cell carcinoma (RCC) resulted in occasional therapeutic responses. The present study was designed to determine the safety and therapeutic efficacy of two sequential high-dose treatments with 131I-cG250. PATIENTS AND METHODS Patients (n = 29) with progressive metastatic RCC received a low dose of (131)I-cG250 for assessment of preferential targeting of metastatic lesions, followed by the first radioimmunotherapy (RIT) with 2220 MBq/m2 131I-cG250 (n = 27) 1 week later. If no grade 4 hematologic toxicity was observed, a second low-dose 131I-cG250 (n = 20) was given 3 months later. When blood clearance was not accelerated, a second RIT of 131I-cG250 was administered at an activity-dose of 1110 MBq/m2 (n = 3) or 1665 MBq/m2 (n = 16). Patients were monitored weekly for toxicity, and tumor size was evaluated by computed tomography once every 3 months intervals. RESULTS The maximum-tolerated dose (MTD) of the second RIT was 1,665 MBq/m2 because of dose-limiting hematological toxicity. Based on an intention-to-treat analysis, after two RIT treatments, the disease stabilized in five of 29 patients, whereas it remained progressive in 14 of 29 patients. Two patients received no RIT, and eight of 29 received only one 131I-cG250 RIT because of grade 4 hematologic toxicity, formation of human antichimeric antibodies, or disease progression. CONCLUSION In patients with progressive end-stage RCC, the MTD of the second treatment was 75% of the MTD of the first RIT. In the majority of patients, two cycles of 131I-cG250 could be safely administered without severe toxicity. No objective responses were observed, but occasionally two RIT doses resulted in stabilization of previously progressive disease.

Prospective Comparison of [18F]Fluorodeoxyglucose Positron Emission Tomography and Computed Tomography in Patients With Melanoma With Palpable Lymph Node Metastases: Diagnostic Accuracy and Impact on Treatment

PURPOSE Patients with melanoma with potentially resectable lymph node metastases require accurate staging to prevent unnecessary surgery. [(18)F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) is attractive for this because melanoma typically is FDG avid. The aim of this prospective multicenter study was to perform a head-to-head comparison of FDG-PET and computed tomography (CT) in staging of patients with melanoma with palpable lymph node metastases in terms of diagnostic accuracy and impact on treatment. PATIENTS AND METHODS All consecutive patients with palpable, proven lymph node metastases of melanoma between mid 2003 and 2007 were prospectively included. The number/site of distant metastases detected with FDG-PET and CT were recorded. Histology/cytology or 6 months follow-up were the reference standard. Intended and performed treatment was recorded. RESULTS Distant metastases were suspected by FDG-PET in 32% of the 251 patients and by CT in 29% (P = .26). Upstaging was correct in 27% by FDG-PET and in 24% by CT (P = .18). FDG-PET detected more metastatic sites (133 v 112, P = .03), detecting significantly more bone and subcutaneous metastases. Treatment changed in 19% of patients; in 79% as a result of both scans, in 17% exclusively by FDG-PET, and in 4% exclusively by CT. In 34 patients (14%), FDG-PET had an additional value over spiral CT, and in 23 patients (9%), CT had additional value over FDG-PET. CONCLUSION As a result of FDG-PET and CT, 27% of patients were upstaged, and treatment changed in one of five patients. FDG-PET and CT are equivalent in upstaging; however, FDG-PET detected more metastatic sites, especially bone and subcutaneous. FDG-PET and/or CT are indicated in the staging of patients with melanoma with palpable lymph node metastases.

PET radioimmunoscintigraphy of renal cell cancer using 89Zr-labeled cG250 monoclonal antibody in nude rats

INTRODUCTION With the introduction of positron-emitting radionuclides with half-lifes in days, such as 89Zr and 124I, radioimmunoscintigraphy (RIS) with positron-emitter-labeled monoclonal antibodies (moAbs) becomes feasible. RIS, using positron emission tomography (immuno-PET), combines the specific localization of an antibody with the high resolution of a PET camera. In the present study, scintigraphic tumor imaging using chimeric moAb G250 labeled with 89Zr (immuno-PET) or 111In (RIS), and [18F]FDG-(PET) was explored in rats with s.c. renal cell carcinoma (RCC) tumors. METHODS Nude rats (6-8 rats per group) with s.c. SK-RC-52 tumors were i.v. injected with 4 MBq 111InDTPA-cG250, 20 MBq 89Zr-Df-cG250 or 4 MBq [18F]FDG. Planar 111In-DTPA-cG250 images were obtained 5 minutes, and 24, 48, and 72 hours postinjection (p.i.). 3D PET imaging was performed 5 minutes, and 24, 48, and 72 hours after a 89Zr-Df-cG250 injection and 1 hour after a [18F]FDG injection using a Siemens ECAT EXACT PET camera. Rats were killed after the last imaging session, and the uptake of the radiolabel in the dissected tissues was determined. RESULTS Both radiolabeled antibody preparations were stable during 4 days of incubation in serum at 37 degrees C, and the immunoreactivity was preserved. Two (2) days after injection, s.c. tumors (100 mg) were clearly visualized, both with 89Zr-Df-cG250 and 111In-DTPA-cG250. Tumors were not visualized with [18F]FDG (uptake in tumor of 0.5 +/- 0.1 %ID/g, 1 hour p.i.). The biodistribution experiments showed an identical uptake in the tumor for both 89Zr-Df-cG250 and 111In-DTPA-cG250 at 3 days p.i. (5.0 +/- 2.4 and 4.9 +/- 2.9 %ID/g, respectively). Blood levels at 3 days p.i. were also identical (1.4 +/- 0.4 versus 1.7 +/- 0.7 %ID/g), and no significant differences were found in the biodistribution of normal tissues between the two radiolabeled cG250 preparations. CONCLUSION The cG250 antibody can be stably labeled with the positron-emitter 89Zr, while preserving the immunoreactivity of the moAb. In this rat model, the in vivo biodistribution of 89Zr-Df-cG250 was identical to that of 111In-DTPA-cG250. Immuno-PET of RCC is feasible with 89Zr-cG250, and relatively small tumors could be visualized, even without a dedicated PET camera for small animals.