Diagnostic accuracy of intraoperative perfusion-weighted MRI and 5-aminolevulinic acid in relation to contrast-enhanced intraoperative MRI and 11C-methionine positron emission tomography in resection of glioblastoma: a prospective study.

The aim of our study was to compare depicted pre-, intra-, and postoperative tumor volume of met-PET, perfusion-weighed MRI (PWI), and Gd-DTPA MRI. Further, to assess their sensitivity and specificity in correlation with histopathological specimen. Inclusion criteria of the prospective study were histological confirmed glioblastoma (GB), age > 18, and eligible for gross total resection (GTR). Met-PET was performed before and after surgery. Gd-DTPA MRI and PWI were performed before, during, and after surgery. A combined 5-aminolevulinic acid (5-ALA) and iMRI-guided surgery was performed. Volumetric analysis was evaluated for all imaging modalities except for 5-ALA. A total of 59 navigated biopsies were taken. Sensitivity and specificity were calculated for Gd-DTPA MRI, PWI, met-PET, and 5-ALA according to the histology of specimen. Met-PET depicted significantly larger tumor volume before surgery (p = 0.01) compared to PWI and Gd-DTPI MRI. We found no significant difference in tumor volume between met-PET and PWI after surgery (p = 0.059). Both PWI and met-PET showed significantly larger tumor volume after surgery when compared to Gd-DTPA (p = 0.018 and p = 0.003, respectively). Intraoperative PWI reading was impaired in 33.3% due to artifacts. Met-PET showed the highest sensitivity for detection of GB with 95%. The lowest sensitivity was found with Gd-DTPA MRI (50%), while 5-ALA and intraoperative PWI showed similar results (69 and 67%). Met-Pet is the imaging modality with the highest sensitivity to detect a residual tumor in GB. Intraoperative PWI seems to have a synergistic effect to Gd-DTPA and 5-ALA. However, its value may be limited by artifacts. Both pre- and intraoperative PWI cannot substitute met-PET in tumor detection.

Detection of lymph node metastasis in patients with nodal prostate cancer relapse using (18)F/(11)C-choline positron emission tomography/computerized tomography.

PURPOSE: We evaluated the diagnostic accuracy of choline positron emission tomography/computerized tomography for nodal relapse of prostate cancer according to topographical site and tumor infiltration size in lymph nodes. MATERIALS AND METHODS: A total of 72 patients with nodal prostate cancer relapse after primary therapy underwent pelvic and/or retroperitoneal salvage lymph node dissection. Salvage was done after whole body positron emission tomography/computerized tomography with (11)C-choline or (18)F-fluoroethylcholine showed positron emission tomography positive lymph nodes but no other detectable metastasis. Diagnostic accuracy was evaluated in 160 dissected lymph node regions (pelvic left/right and retroperitoneal), 498 subregions (common, external and internal iliac, obturator, presacral, aortic bifurcation, aortal, vena caval and interaortocaval) and 2,122 lymph nodes. RESULTS: Lymph node metastasis was present in 32% of resected lymph nodes (681 of 2,122), resulting in 238 positive subregions and 111 positive regions. Positron emission tomography/computerized tomography was positive for 110 regions and 209 subregions. Sensitivity, specificity, positive and negative predictive values, and accuracy were 91.9%, 83.7%, 92.7%, 82.0% and 89.4% (region based), 80.7%, 93.5%, 91.9%, 84.1% and 87.3% (subregion based), and 57.0%, 98.4%, 94.5%, 82.6% and 84.9% (lesion based), respectively. Of 393 positive lymph node metastases detected by this method 278 (70.7%) were in lymph nodes with a less than 10 mm short axis diameter. Imaging sensitivity was 13.3%, 57.4% and 82.8% for a tumor infiltration depth of 2 or greater to less than 3 mm, 5 or greater to less than 6 mm and 10 or greater to less than 11 mm, respectively. Lymph node metastasis site and the radiotracer ((11)C-choline/(18)F-fluoroethylcholine) had no substantial impact on diagnostic accuracy. CONCLUSIONS: Choline positron emission tomography/computerized tomography detects affected lymph node regions (pelvic left/right and retroperitoneal) in patients with prostate cancer relapse with high accuracy and it seems helpful for guiding salvage lymph node dissection. Sensitivity decreases with the size of metastatic infiltration in lymph nodes. This technique detects metastasis in a significant fraction of lymph nodes that are not pathologically enlarged on computerized tomography.

Accurate preoperative localization of parathyroid adenomas with C-11 methionine PET/CT.

BACKGROUND: Focused unilateral or minimally invasive parathyroidectomy for primary hyperparathyroidism (pHPT) depends on the successful preoperative localization of parathyroid adenomas. The aim of this prospective study was to determine the accuracy of C-11 methionine positron emission tomography/computed tomography (Met-PET/CT), a novel localization procedure for hyperfunctional parathyroid tissue. METHODS: Preoperative Met-PET/CT scans of the neck and mediastinum of 102 patients undergoing parathyroidectomy for pHPT were preoperatively evaluated by a radiologist and a nuclear medicine physician and prospectively documented. The results of Met-PET/CT were compared with intraoperative and histopathological findings. RESULTS: pHPT was caused by a single-gland adenoma in 97 patients, whereas 5 patients had multiglandular disease. Met-PET/CT correctly located a single-gland adenoma in 83 of 97 (86%) patients with pHPT (sensitivity 91%). The positive predictive value of Met-PET/CT in localizing a single-gland adenoma was 93%. Of the 5 patients with multiglandular disease, Met-PET/CT identified 2 hyperfunctioning parathyroid glands in 1 patient, 1 gland in 3 individuals, and was negative in the fifth patient (sensitivity 80%). A highly significant correlation was observed between true-positive findings and the size (mean = 1.81 ± 0.84 cm) and weight (mean = 1.50 ± 2.56 g) of parathyroid adenoma, whereas patients with false-negative findings had significantly smaller (mean = 1.09 ± 0.41 cm) and lighter (mean = 0.37 ± 0.29 g) glands (P < 0.001 and P = 0.001, respectively). CONCLUSIONS: This study demonstrates the high accuracy of Met-PET/CT in the preoperative localization of parathyroid adenomas in a large series of patients with pHPT.

Radioimmunotherapy-based conditioning for hematopoietic cell transplantation in children with malignant and nonmalignant diseases.

Targeted irradiation of the bone marrow with radiolabeled monoclonal antibodies (radioimmunotherapy) represents a novel therapeutic approach with both myeloablative and antileukemic potential. In an open-label, single-center pilot study, 30 pediatric and adolescent patients undergoing hematopoietic cell transplantation for malignant (n = 16) and nonmalignant (n = 14) disorders received treatment with a 9°Y-labeled anti-CD66 monoclonal antibody. Patients with a high risk of relapse (n = 7) received additional treatment with standard conditioning based on either total body irradiation or busulfan to intensify the antileukemic effect. In patients with comorbidities (n = 23), radioimmunotherapy was combined with a reduced-intensity conditioning regimen to reduce systemic toxicity. Preferential irradiation of the bone marrow was achieved in all patients. Nonrelapse mortality was 4 (13%) of 30 patients. In patients with malignant diseases, the probabilities of overall and disease-free survival at 2 years were 0.69 (95% confidence interval 0.37-0.87) and 0.46 (95% confidence interval 0.19-0.70), respectively. In patients with nonmalignant diseases, the probability of both overall and disease-free survival at 2 years was 0.94 (95% confidence interval 0.63-0.99). This pilot study demonstrates that radioimmunotherapy is effective in achieving myeloablation with low additional toxicity when used in combination with standard or reduced-intensity conditioning in young patients.

Differences in predicted and actually absorbed doses in peptide receptor radionuclide therapy.

PURPOSE: An important assumption in dosimetry prior to radionuclide therapy is the equivalence of pretherapeutic and therapeutic biodistribution. In this study the authors investigate if this assumption is justified in sst2-receptor targeting peptide therapy, as unequal amounts of peptide and different peptides for pretherapeutic measurements and therapy are commonly used. METHODS: Physiologically based pharmacokinetic models were developed. Gamma camera and serum measurements of ten patients with metastasizing neuroendocrine tumors were conducted using (111)In-DTPAOC. The most suitable model was selected using the corrected Akaike information criterion. Based on that model and the estimated individual parameters, predicted and measured (90)Y-DOTATATE excretions during therapy were compared. The residence times for the pretherapeutic (measured) and therapeutic scenarios (simulated) were calculated. RESULTS: Predicted and measured therapeutic excretion differed in three patients by 10%, 31%, and 7%. The measured pretherapeutic and therapeutic excretion differed by 53%, 56%, and 52%. The simulated therapeutic residence times of kidney and tumor were 3.1 ± 0.6 and 2.5 ± 1.2 fold higher than the measured pretherapeutic ones. CONCLUSIONS: To avoid the introduction of unnecessary inaccuracy in dosimetry, using the same substance along with the same amount for pretherapeutic measurements and therapy is recommended.

New molecular markers for prostate tumor imaging: a study on 2-methylene substituted fatty acids as new AMACR inhibitors.

The development of prostate carcinoma is associated with alterations in fatty acid metabolism. α-Methylacyl-CoA racemase (AMACR) is a peroxisomal and mitochondrial enzyme that catalyses interconversion between the (S)/(R)-isomers of a range of α-methylacyl-CoA thioesters. AMACR is involved in the ß-oxidation of the dietary branched-chain fatty acids and bile acid intermediates. It is highly expressed in prostate (more than 95 %), colon (92 %), and breast cancers (44 %) but not in the respective normal or hyperplastic tissues. Thus, targeting of AMACR could be a new strategy for molecular imaging and therapy of prostate and some other cancers. Unlabeled 2-methylenacyl-CoA thioesters (12 a-c) were designed as AMACR binding ligands. The thioesters were tested for their ability to inhibit the AMACR-mediated epimerization of (25R)-THC-CoA and were found to be strong AMACR inhibitors. Radioiodinated (E)-(131) I-13-iodo-2-methylentridec-12-enoic acid ((131) I-7 c) demonstrated preferential retention in AMACR-positive prostate tumor cells (LNCaP, LNCaP C4-2wt and DU145) compared with both AMACR-knockout LNCaP C4-2 AMACR-siRNA and benign BPH1 prostate cell lines. A significant protein-bound radioactive fraction with main bands at 47 (sum of molecular weights of AMACR plus 12 c), 70, and 75 kDa was detected in LNCaP C4-2 wt cells. In contrast, only negligible amounts of protein-bound radioactivity were found in LNCaP C4-2 AMACR-siRNA cells.

Optimal preloading in radioimmunotherapy with anti-cD45 antibody.

PURPOSE: Anti-CD45 antibody is predominantly used in the treatment of acute leukemia. CD45 is stably expressed on all leukocytes and their precursors, and therefore the liver and spleen constitute major antigen sinks. Thus, as the red marrow is the target organ, in radioimmunotherapy with anti-CD45 antibody, preloading with unlabeled antibody is a method to increase the absorbed dose to the target cells. In a previous study, a method to individually determine the optimal preload for five patients with acute leukemia was developed. Here, this method is examined and improved using two pretherapeutic measurement series and a refined pharmacokinetic model. METHODS: To obtain the biodistribution of 111In-labeled anti-CD45 antibody under different saturation conditions, two measurement series one with and one without preloading were conducted in five patients. For each patient, two physiologically based pharmacokinetic models were fitted to the data and the corrected Akaike information criterion was used to identify the model, which was empirically most supported. The resultant parameter values were compared to values reported in the literature. To individually determine the optimal amount of unlabeled antibody for therapy, computer simulations for preloads ranging from 0 to 60 mg were performed based on the estimated parameters of each patient. The prediction power of the model was assessed by comparing the simulated therapeutic serum curves to the actual 90Y measurements. RESULTS: Visual inspection showed good fits and the adjusted R2 was >0.90 for all patients. All parameters were in a physiologically reasonable range. The relative deviation of the predicted area under the therapeutic serum curve and the measured curve was 15%-33%. The optimal preloading increased the marrow-over-liver selectivity up to 3.9 fold compared to the simulated biodistribution using a standard dose (0.5 mg/kg). CONCLUSIONS: The presented method can be used to individually determine the optimal preload and the corresponding residence times in radioimmunotherapy with anti-CD45 antibody.

131I/123I-metaiodobenzylguanidine (mIBG) scintigraphy: procedure guidelines for tumour imaging.

The aim of this document is to provide general information about mIBG scintigraphy in cancer patients. The guidelines describe the mIBG scintigraphy protocol currently used in clinical routine, but do not include all existing procedures for neuroendocrine tumours. The guidelines should therefore not be taken as exclusive of other nuclear medicine modalities that can be used to obtain comparable results. It is important to remember that the resources and facilities available for patient care may vary from one country to another and from one medical institution to another. The present guidelines have been prepared for nuclear medicine physicians and intend to offer assistance in optimizing the diagnostic information that can currently be obtained from mIBG scintigraphy. The corresponding guidelines of the Society of Nuclear Medicine (SNM) and the Dosimetry, Therapy and Paediatric Committee of the EANM have been taken into consideration, and partially integrated into this text. The same has been done with the most relevant literature on this topic, and the final result has been discussed within a group of distinguished experts.

Clinical value of 18F-fluorodihydroxyphenylalanine positron emission tomography/computed tomography (18F-DOPA PET/CT) for detecting pheochromocytoma.

PURPOSE: In detecting pheochromocytoma (PHEO), positron emission tomography (PET) with the radiolabelled amine precursor (18)F-fluorodihydroxyphenylalanine ((18)F-DOPA) offers excellent specificity, while computed tomography (CT) provides high sensitivity and ability to localize lesions; therefore, the combination of these modalities could be advantageous in this setting. The aim of this study was to investigate whether combined (18)F-DOPA PET/CT more accurately detects and localizes PHEO lesions than does each modality alone. METHODS: (18)F-DOPA PET, CT and (18)F-DOPA PET/CT images of 25 consecutive patients undergoing diagnostic scanning of suspected sporadic or multiple endocrine neoplasia type 2 syndrome-associated PHEO were reviewed retrospectively in randomized sequence. Two blinded observers scored the images regarding the likelihood of PHEO being present and localizable. Results were correlated with subsequent clinical history and, when available, histology. RESULTS: Of the 19 lesions detected by all three modalities, PET identified each as positive for PHEO, but was unable to definitively localize 15 of 19 (79%). CT could definitively localize all 19 lesions, but could not definitively diagnose or exclude PHEO in 18 of 19 (95%) lesions. Furthermore, CT falsely identified as negative for PHEO one lesion which was judged to be positive for this tumor by both PET and PET/CT. Only in PET/CT scans were all 19 lesions accurately characterized and localized. On a per-patient basis, the sensitivity of (18)F-DOPA PET/CT for PHEO was 100% and the specificity 88%, with a 100% positive predictive value and an 88% negative predictive value. CONCLUSION: (18)F-DOPA PET/CT more accurately diagnoses and localizes adrenal and extra-adrenal masses suspicious for PHEO than do (18)F-DOPA PET or CT alone.

Integrated FDG-PET-CT: its role in the assessment of bone and soft tissue tumors.

PURPOSE: The purpose of this study was to evaluate prospectively, whether integrated 2-deoxy-2-[(18)F]fluoro-D: -glucose positron emission tomography-computed tomography (FDG-PET-CT) is more accurate for determination musculoskeletal tumors compared with separate interpretation of CT and FDG-PET, because most of the current clinical data come from patients studied with PET. METHODS: Eighty patients with newly diagnosed musculoskeletal tumors underwent FDG-PET-CT. CT, FDG-PET, and FDG-PET-CT were interpreted separately to determine the performance of each imaging modality. RESULTS: Assuming that equivocal lesions are benign, performance of diagnostic tests was as follows: sensitivity, specificity and accuracy for CT alone was 81, 84, 83%, for PET 71, 82, 76, and for PET-CT 80, 83 and 86%. Assuming that equivocal lesions are malignant, sensitivity, specificity, and accuracy for CT was 61, 100, 70%, for PET 69, 100, 79, and for PET-CT 69, 100 and 79%. CONCLUSIONS: Combined FDG-PET-CT reliably differentiates soft tissue and bone tumors from benign lesions. The value of the information provided by FDG-PET-CT for planning surgical procedures must be evaluated in further studies.

Improving anti-CD45 antibody radioimmunotherapy using a physiologically based pharmacokinetic model.

UNLABELLED: Radioimmunotherapy is a method to selectively deliver radioactivity to cancer cells via specific antibodies. A strategy to enhance the efficacy of radioimmunotherapy is the prior application of unlabeled antibody, resulting in an increase in the dose to the target tissue and a decrease in the burden to other organs. It was suggested that optimizing this approach might considerably improve radioimmunotherapy with anti-CD45 antibody. The present work develops a physiologically based pharmacokinetic model to individually determine the optimal preload for radioimmunotherapy with the YAML568 anti-CD45 antibody for each patient. METHODS: A physiologically based pharmacokinetic model was developed to describe the biodistribution of anti-CD45 antibody. The transport of antibody to the organs of interest via blood flow, competitive binding of unlabeled and labeled antibody, degradation and excretion of antibody, and physical decay were included in the model. The model was fitted to the biokinetics data of 5 patients with acute myeloid leukemia. On the basis of the estimated parameters, simulations for a 0- to 534-nmol preload of unlabeled antibody were conducted and the organ residence times were calculated. RESULTS: The measured data could be adequately described by the constructed model. The estimated numbers of accessible antigens in the respective organ, in nanomoles, were 97+/-33 for red marrow, 49+/-24 for liver, 34+/-18 for spleen, 38+/-31 for lymph nodes, and 0.9+/-0.4 for blood. These ranges indicate high interpatient variability. The optimal amount of unlabeled antibody identified by simulations would improve the ratio of residence time in red marrow to residence time in liver by a factor of 1.6-2.4. CONCLUSION: The efficacy of radioimmunotherapy using anti-CD45 antibody can be considerably increased with the presented model. A more selective delivery of radioactivity to the target organ and a reduction in the toxicity to normal tissue are achieved by determining the optimal preload. Furthermore, the adverse effects of radioimmunotherapy might be drastically reduced while saving antibody expenses. The validation of the model is ongoing. The model is easily extendible and therefore most probably applicable to radioimmunotherapy of other hematologic malignancies, such as antibodies targeted to CD20, CD33, or CD66.

Detection of bone metastases in patients with lung cancer: 99mTc-MDP planar bone scintigraphy, 18F-fluoride PET or 18F-FDG PET/CT.

PURPOSE: The aim of the study was to compare the diagnostic accuracy of (18)F-fluorodeoxyglucose (FDG) PET/CT versus standard planar bone scintigraphy (BS) and (18)F-labelled NaF ((18)F) PET for the detection of bone metastases (BM) in non-small cell lung cancer (NSCLC). METHODS: (18)F-FDG PET/CT was performed in 126 patients with NSCLC. Within 7 days BS (n = 58) or (18)F PET (n = 68) was performed. (18)F-FDG PET/CT, BS and (18)F PET were evaluated by two experienced readers. Lesions were graded on a scale from 1 (definite BM) to 5 (degenerative lesion), and equivocal lesions were determined as indifferent (grade 3). RESULTS: A total of 92 patients showed degenerative lesions (grade 4/5) on PET/CT, BS or (18)F PET. In 34 patients (27%) BM lesions were diagnosed (grades 1 and 2). In 13 of 18 patients BM were concordantly diagnosed with PET/CT and (18)F PET. PET/CT showed more BM compared to (18)F PET (53 vs 40). In one patient one osteolytic BM was false-negative on (18)F PET. However, (18)F PET identified four patients with BM compared to negative findings on PET/CT. Of 16 patients, 11 had concordant findings of BM on PET/CT and BS. In three patients BS was false-negative and in two patients BM were diagnosed as indifferent. CONCLUSION: Integrated (18)F-FDG PET/CT is superior to BS in the detection of osteolytic BM in NSCLC. Thus, PET/CT may obviate the need to perform additional BS or (18)F PET in the staging of NSCLC, which significantly reduces costs.

[(11)C]choline PET/CT in prostate cancer patients with biochemical recurrence after radical prostatectomy.

OBJECTIVE: To evaluate [(11)C]choline positron emission tomography/computed tomography ([(11)C]choline PET/CT) for the detection of a biochemical recurrence of prostate cancer after radical prostatectomy. METHODS: Retrospective analysis of [(11)C]choline PET/CT performed in 41 consecutive prostate cancer patients with a rising PSA. The mean time to biochemical relapse was 24 months. PSA levels were determined at time of examination, and patients received either a targeted biopsy or surgery. Histopathology reports served as reference for the evaluation of the [(11)C]choline PET/CT findings. RESULTS: Mean PSA in [(11)C]choline PET/CT positive patients was 3.1 ng/ml (median 2.2 ng/ml, range 0.5-11.6 ng/ml) and 0.86 ng/ml in [(11)C]choline PET/CT negative patients (median 0.83 ng/ml, range 0.41-1.40 ng/ml). Six of 12 patients with PSA < 1.5 ng/ml [(11)C]choline PET/CT revealed a pathological uptake. Histopathology was positive in 6/12 patients in this group. At PSA levels ranging from 1.5 to 2.5 ng/ml all [(11)C]choline PET/CT were positive (n = 16), a positive histology was found in 12/16 patients (75%) and at PSA 2.5-5 ng/ml [(11)C]choline PET/CT was positive in 8/8 patients, confirmed by histology in 7/8 patients. Finally, at PSA higher than 5 ng/ml [(11)C]choline PET/CT identified 5/5 patients positive all confirmed by histology. The sensitivity of [(11)C]choline PET/CT for the detection of recurrence at PSA < 2.5 ng/ml was 89% with a positive predictive value of 72%. CONCLUSION: [(11)C]choline PET/CT is useful for re-staging of prostate cancer in patients with rising PSA even at levels below 1.5 ng/ml. Our study confirms results from other published studies on [(11)C]choline PET/CT in prostate cancer relapse.

Towards to hENT1-nucleoside transporter selective imaging agents. Synthesis and in vitro evaluation of the radiolabeled SAENTA analogues.

Three new potential hENT(1) inhibitors suitable for labeling with PET/SPECT radioisotopes were prepared from an advanced intermediate 4. They were tested for their capability to inhibit binding of SAENTA-fluorescein to HL60 leukemia cells in flow cytometry assay and SAENTA-I (5) was determined to be the most active compound. (131)I-5 showed high hENT(1)-specific binding (up to 54% ID) to 6 from 7 tested tumor cell lines and was chosen for further in vivo study.

Pro-apoptosis and anti-proliferation effects of a recombinant dominant-negative survivin-T34A in human cancer cells.

BACKGROUND: Survivin is an attractive target for anti-cancer drug development; however targeting it by small molecules or antibodies is difficult, as survivin is neither a kinase nor a cell surface protein. Protein transduction domain (PTD)-mediated macromolecular therapeutics provides an alternative avenue for targeting survivin. MATERIALS AND METHODS: A plasmid expressing a dominant-negative survivin-T34A fused with the immunodeficiency virus protein transduction domain TAT was constructed. The fusion protein was expressed and purified from E. coli. The inhibition of proliferation and induction of apoptosis was tested in human lung carcinoma cell line A549 by directly adding survivin-T34A to the cell culture medium. RESULTS: Recombinant survivin-T34A was efficiently expressed and purified by affinity chromatography. It induced cell apoptosis as demonstrated by induction of caspase 3 activation and higher percentage of Annexin V staining, and inhibited cell proliferation as determined by cell number counting. CONCLUSION: This functional recombinant protein is promising for development of macromolecular therapeutics targeting survivin.

Preferential tumor targeting and selective tumor cell cytotoxicity of 5-[131/125I]iodo-4'-thio-2'-deoxyuridine.

PURPOSE: Auger electron emitting radiopharmaceuticals are attractive for targeted nanoirradiation therapy, provided that DNA of malignant cells is selectively addressed. Here, we examine 5-[123/125/131I]iodo-4'-thio-2'-deoxyuridine (ITdU) for targeting DNA in tumor cells in a HL60 xenograft severe combined immunodeficient mouse model. EXPERIMENTAL DESIGN: Thymidine kinase and phosphorylase assays were done to determine phosphorylation and glycosidic bond cleavage of ITdU, respectively. The biodistribution and DNA incorporation of ITdU were determined in severe combined immunodeficient mice bearing HL60 xenografts receiving pretreatment with 5-fluoro-2'-deoxyuridine (FdUrd). Organ tissues were dissected 0.5, 4, and 24 h after radioinjection and uptake of [131I]ITdU (%ID/g tissue) was determined. Cellular distribution of [125I]ITdU was imaged by microautoradiography. Apoptosis and expression of the proliferation marker Ki-67 were determined by immunohistologic staining using corresponding paraffin tissue sections. RESULTS: ITdU is phosphorylated by thymidine kinase 1 and stable toward thymidylate phosphatase-mediated glycosidic bond cleavage. Thymidylate synthase-mediated deiodination of [123/125/131I]ITdU was inhibited with FdUrd. Pretreatment with FdUrd increased preferentially tumor uptake of ITdU resulting in favorable tumor-to-normal tissue ratios and tumor selectivity. ITdU was exclusively localized within the nucleus and incorporated into DNA. In FdUrd-pretreated animals, we found in more than 90% of tumor cells apoptosis induction 24 h postinjection of ITdU, indicating a highly radiotoxic effect in tumor cells but not in cells of major proliferating tissues. CONCLUSION: ITdU preferentially targets DNA in proliferating tumor cells and leads to apoptosis provided that the thymidylate synthase is inhibited.

Imaging bone and soft tissue tumors with the proliferation marker [18F]fluorodeoxythymidine.

PURPOSE: We have determined the ability of positron emission tomography (PET) with the thymidine analogue 3'-deoxy-3'[18F]fluorothymidine (FLT) to detect manifestation sites of bone and soft tissue tumors, to assess tumor grading, and to differentiate malignant from benign tumors. MATERIALS AND METHODS: In this prospective bicenter trial, FLT-PET was done in 22 patients with established or suspected soft or bone tissue lesions. Routine diagnostic procedures included incisional biopsy, magnetic resonance imaging, and/or contrast-enhanced spiral computed tomography in all patients and [18F]fluorodeoxyglucose (FDG)-PET in 15 patients. Forty-five to 60 minutes after i.v. injection of 350 to 425 MBq FLT, emission and transmission scanning was done. Tracer uptake in the tumor was evaluated semiquantitatively by calculation of mean and maximum standardized uptake values (FLT-SUV) and compared with respective values of FDG. Results were correlated to histopathology and tumor grading. RESULTS: FLT-PET detected all malignant bone or soft tissue tumors (17 of 17). Mean FLT-SUV in benign lesions was 0.7 (range, 0.3-1.3), and 1.3 in low-grade sarcoma (grade 1; range, 1.0-1.6), 4.1 (range, 2.2-6.0; P = 0.002) and 6.1 (range, 2.5-8.3; P = 0.001) in grade 2 and grade 3 tumors, respectively. FLT but not FDG uptake correlated significantly with tumor grading (r = 0.71 versus r = 0.01), and a cutoff value of 2.0 for FLT-SUV discriminated between low- and high-grade tumors. CONCLUSION: In this clinical study, the proliferation marker FLT was suitable for imaging malignant bone or soft tissue tumors. FLT but not FDG uptake correlated significantly with the tumor grade, suggesting FLT as superior PET tracer for noninvasive grading of sarcomas.

Breaking chemoresistance and radioresistance with [213Bi]anti-CD45 antibodies in leukemia cells.

Chemoresistance and radioresistance are considered one of the primary reasons for therapeutic failure in leukemias and solid tumors. Targeted radiotherapy using monoclonal antibodies radiolabeled with alpha-particles is a promising treatment approach for high-risk leukemia. We found that targeted radiotherapy using monoclonal CD45 antibodies radiolabeled with the alpha-emitter (213)Bi ([(213)Bi]anti-CD45) induces apoptosis, activates apoptosis pathways, and breaks beta-irradiation-, gamma-irradiation-, doxorubicin-, and apoptosis-resistance in leukemia cells. In contrast to beta-irradiation-, gamma-irradiation-, and doxorubicin-mediated apoptosis and DNA damage, [(213)Bi]anti-CD45-induced DNA damage was not repaired, and apoptosis was not inhibited by the nonhomologous end-joining DNA repair mechanism. Depending on the activation of caspase-3, caspase-8, and caspase-9, [(213)Bi]anti-CD45 activated apoptosis pathways in leukemia cells through the mitochondrial pathway but independent of CD95 receptor/CD95 ligand interaction. Furthermore, [(213)Bi]anti-CD45 reversed deficient activation of caspase-3, caspase-8, and caspase-9, deficient cleavage of poly(ADP-ribose) polymerase, and deficient activation of mitochondria in chemoresistant and in radioresistant and apoptosis-resistant leukemia cells. These findings show that [(213)Bi]anti-CD45 is a promising therapeutic agent to break chemoresistance and radioresistance by overcoming DNA repair mechanisms in leukemia cells and provide the foundation for discovery of novel anticancer compounds.

Chromosome instability and tumor lethality suppression in carcinogenesis.

The maintenance and survival of each organism depends on its genome integrity. Alterations of essential genes, or aberrant chromosome number and structure lead to cell death. Paradoxically, cancer cells, especially in solid tumors, contain somatic gene mutations and are chromosome instability (CIN), suggesting a mechanism that cancer cells have acquired to suppress the lethal mutations and/or CIN. Herein we will discuss a tumor lethality suppression concept based on the studies of yeast genetic interactions and transgenic mice. During the early stages of the multistep process of tumorigenesis, incipient cancer cells probably have adopted genetic and epigenetic alterations to tolerate the lethal mutations of other genes that ensue, and to a larger extent CIN. In turn, CIN mediated massive gain and loss of genes provides a wider buffer for further genetic reshuffling, resulting in cancer cell heterogeneity, drug resistance and evasion of oncogene addiction, thus CIN may be both the effector and inducer of tumorigenesis. Accordingly, interfering with tumor lethality suppression could lead to cancer cell death or growth defects. Further validation of the tumor lethality suppression concept would help to elucidate the role of CIN in tumorigenesis, the relationship between CIN and somatic gene mutations, and would impact the design of anticancer drug development.

First demonstration of leukemia imaging with the proliferation marker 18F-fluorodeoxythymidine.

UNLABELLED: Acute myeloid leukemia (AML) is a neoplasm of hematopoietic stem cells with partial or complete loss of the ability to differentiate but with preserved proliferation capacity. The aim of our study was to evaluate if the in vivo proliferation marker 3'-deoxy-3'-18F-fluorothymidine (FLT) is suitable for visualizing leukemia manifestation sites and if 18F-FLT is a surrogate marker for disease activity. METHODS: In this pilot study, 10 patients with AML underwent pretherapeutic imaging with 18F-FLT PET or 18F-FLT PET/CT. The biodistribution of 18F-FLT was assessed 60 min after intravenous injection of the radiotracer. Standardized uptake values were calculated for reference segments of bone marrow, spleen, and normal organs. 18F-FLT PET in 10 patients with benign pulmonary nodules and the absence of malignant or inflammatory disease served as controls. RESULTS: Retention of 18F-FLT was observed predominantly in bone marrow and spleen and was significantly higher in AML patients than in controls (mean 18F-FLT SUV in bone marrow, 11.5 and 6.6, P < 0.05; mean 18F-FLT SUV in spleen, 6.1 and 1.8, P < 0.05). Outside bone marrow, focal 18F-FLT uptake showed extramedullary manifestation sites of leukemia in 4 patients (meningeal disease, pericardial, abdominal, testicular, and lymph node), proven by other diagnostic procedures. CONCLUSION: This pilot study indicated that PET using 18F-FLT is able to visualize extramedullary manifestation sites of AML and reflects disease activity. Because 18F-FLT uptake in bone marrow is caused by a combination of both neoplastic and normal hematopoietic cells, the correlation of 18F-FLT uptake in bone marrow and leukemic blast infiltration did not reach statistical significance.