Radiation Dosimetry of Theragnostic Pairs for Isotopes of Iodine in IAZA

Theragnostic pairs of isotopes are used to infer radiation dosimetry for a therapeutic radiopharmaceutical from a diagnostic imaging study with the same tracer molecule labelled with an isotope better suited for the imaging task. We describe the transfer of radiation dosimetry from the diagnostic radioiodine isotope ¹²³I, labelled for the hypoxia tracer molecule iodoazomycin arabinoside ([¹²³I]IAZA), to isotopes ¹³¹I (therapeutic) and ¹²⁴I (PET imaging). Uncertainties introduced by the dissimilar isotope half-lives are discussed in detail. Radioisotope dosimetries for [¹²³I]IAZA were obtained previously. These data are used here to calculate residence times for ¹³¹I and ¹²⁴I and their uncertainties. We distinguish two cases when extrapolating to infinity: purely physical decay (case A) and physical decay plus biological washout (case B). Organ doses were calculated using the MIRD schema with the OLIDNA/EXM code. Significant increases in some organ doses (in mSv per injected activity) were found for ¹³¹I and ¹²⁴I. The most affected organs were the intestinal walls, thyroid, and urinary bladder wall. Uncertainty remained similar to ¹²³I for case A but considerably greater for case B, especially for long biological half-lives (GI tract). Normal tissue dosimetries for IAZA must be considered carefully when substituting isotope species. A long biological half-life can significantly increase dosimetric uncertainties. These findings are relevant when considering PET imaging studies with [¹²⁴I]IAZA or therapeutic administration of [¹³¹I]IAZA.

Rapid Standardized CT-Based Method to Determine Lean Body Mass SUV for PET—A Significant Improvement Over Prediction Equations

In 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) studies, maximum standardized uptake value (SUVmax) is the parameter commonly used to provide a measurement of the metabolic activity of a tumor. SUV normalized by body mass is affected by the proportions of body fat and lean tissue, which present high variability in patients with cancer. SUV corrected by lean body mass (LBM), denoted as SUL, is recommended to provide more accurate, consistent, and reproducible SUV results; however, LBM is frequently estimated rather than measured. Given the increasing importance of a quantitative PET parameter, especially when comparing PET studies over time to evaluate disease response clinically, and its use in oncological clinical trials, we set out to evaluate the commonly used equations originally derived by James (1976) and Janmahasatian et al. (2005) against computerized tomography (CT)-derived measures of LBM.

Methods

Whole-body 18F-FDG PET images of 195 adult patients with cancer were analyzed retrospectively. Representative liver SUVmean was normalized by total body mass. SUL was calculated using a quantitative determination of LBM based on the CT component of the PET/CT study (LBMCT) and compared against the equation-estimated SUL. Bland and Altman plots were generated for SUV-SUL differences.

Results

This consecutive sample of patients undergoing usual care (men, n = 96; women, n = 99) varied in body mass (38–127 kg) and in Body Mass Index (BMI) (14.7–47.2 kg/m2). LBMCT weakly correlated with body mass (men, r2 = 0.32; women, r2 = 0.22), and thus SUV and SULCT were also weakly correlated (men, r2 = 0.24; women, r2 = 0.11). Equations proved inadequate for the assessment of LBM. LBM estimated by James’ equation showed a mean bias (overestimation of LBM compared with LBMCT) in men (+6.13 kg; 95% CI 4.61–7.65) and in women (+6.32 kg; 95% CI 5.26–7.39). Janmahasatian’s equation provided similarly poor performance.

Conclusions

CT-based LBM determinations incorporate the patient’s current body composition at the time of a PET/CT study, and the information garnered can provide care teams with information with which to more accurately determine FDG uptake values, allowing comparability over multiple scans and treatment courses and will provide a robust basis for the use of PET Response Criteria in Solid Tumors (PERCIST) in clinical trials.

Prolonged Response to Regorafenib in a Patient with Iodine Refractory Thyroid Cancer

Thyroid cancer is the most common type of endocrine malignancy. Cornerstones of thyroid cancer treatment include surgery, radioactive iodine ablation, and thyroid stimulating hormone suppression. The National Comprehensive Cancer Network guidelines recommend two tyrosine kinase inhibitors for thyroid cancer patients who are non-responsive to iodine: sorafenib and lenvatinib. Another oral kinase inhibitor, regorafenib, is not considered standard of care treatment for differentiated thyroid cancer. The chemical structures of regorafenib and sorafenib differ by a single fluorine atom. Given the significant improvement in progression-free survival (PFS) of sorafenib compared to placebo demonstrated in the phase 3 DECISION trial, we report on a patient with iodine-refractory follicular thyroid cancer treated with regorafenib as part of a phase 1 clinical trial. A 75 year old woman was diagnosed with follicular thyroid carcinoma in 2006 and initiated on treatment with regorafenib in 2011. She has completed 76 cycles with stable disease and pulmonary metastases 34% smaller than baseline.

Pharmacokinetics and Scintigraphic Imaging of the Hypoxia-Imaging Agent [123I]IAZA in Healthy Adults Following Exercise-Based Cardiac Stress †

The objective of this work is to evaluate the potential effect of cardiac stress exercise on the accumulation of [¹²³I]IAZA, a radiopharmaceutical used to image focal tissue hypoxia, in otherwise normal myocardium in healthy volunteers, and to determine the impact of exercise on [¹²³I]IAZA pharmacokinetics. The underlying goal is to establish a rational basis and a baseline for studies of focal myocardial hypoxia in cardiac patients using [¹²³I]IAZA. Three healthy male volunteers ran the ‘Bruce’ treadmill protocol, a clinically-accepted protocol designed to expose myocardial ischemia in patients. The ‘Bruce’ criterion heart rate is 85% of [220–age]. Approximately one minute before reaching this level, [¹²³I]IAZA (5.0 mCi/0.85 mg) was administered as a slow (1–3 min) single intravenous (i.v.) injection via an indwelling venous catheter. The volunteer continued running for an additional 1 min before being transferred to a gamma camera. Serum samples were collected from the arm contralateral to the administration site at pre-determined intervals from 1 min to 45 h post injection and were analyzed by radio HPLC. Pharmacokinetic (PK) parameters were derived for [¹²³I]IAZA and total radioactivity (total[¹²³I]) using compartmental and noncompartmental analyses. Whole-body planar scintigraphic images were acquired from 0.75 to 24 h after dosing. PK data and scintigraphic images were compared to previously published [¹²³I]IAZA data from healthy volunteers rest. Following exercise stress, both [¹²³I]IAZA and total[¹²³I] exhibited bi-exponential decline profiles, with rapid distribution phases [half-lives (t_1/2α) of 1.2 and 1.4 min, respectively], followed by slower elimination phases [t_1/2β of 195 and 290 min, respectively]. Total body clearance (CL_TB) and the steady state volume of distribution (V_ss) were 0.647 L/kg and 185 mL/min, respectively, for [¹²³I]IAZA and 0.785 L/kg and 135 mL/min, respectively, for total[¹²³I]. The t_1/2β, CL_TB and V_ss values were comparable to those reported previously for rested volunteers. The t_1/2α was approximately 4-fold shorter for [¹²³I]IAZA and approximately 3-fold shorter for total[¹²³I] under exercise relative to rested subjects. The heart region was visualized in early whole body scintigraphic images, but later images showed no accumulated radioactivity in this region, and no differences from images reported for rested volunteers were apparent. Minimal uptake of radiotracer in myocardium and skeletal muscle was consistent with uptake in non-stressed myocardium. Whole-body scintigrams for [¹²³I]IAZA in exercise-stressed healthy volunteers were indistinguishable from images of non-exercised volunteers. There was no evidence of hypoxia-dependent binding in exercised but otherwise healthy myocardium, supporting the conclusion that exercise stress at Bruce protocol intensity does not induce measurable myocardial hypoxia. Effects of exercise on PK parameters were minimal; specifically, the t_1/2α was shortened, reflecting increased cardiac output associated with exercise. It is concluded that because [¹²³I]IAZA was not metabolically bound in exercise-stressed myocardium, a stress test will not create elevated myocardial background that would mask regions of myocardial perfusion deficiency. [¹²³I]IAZA would therefore be suitable for the detection of viable, hypoxic myocardium in patients undergoing stress-test-based diagnosis.

Comparison of 30 mCi and 50 mCi I-131 doses for ablation of thyroid remnant in papillary thyroid cancer patients

PURPOSE OF THE STUDY

To compare efficacy of thyroid remnant ablation using 30 mCi or 50 mCi 131-I in papillary thyroid cancer patients.

MATERIALS AND METHODS

Five hundred and fifteen consecutive patients with Tumor-Node-Metastasis (TNM) stages T1-T3 N1/N0/NX receiving either 30 mCi or 50 mCi I-131 were analyzed for the effectiveness of remnant ablation using rhTSH-stimulated serum thyroglobulin. One hundred and five consecutive patients receiving 100 mCi I-131 were analyzed for the incidence of radiation thyroiditis and sialadenitis.

RESULTS AND CONCLUSIONS

Doses of 30 mCi and 50 mCi were equally effective for low- and moderate-risk disease but 30 mCi was less effective for T1T2NX disease, and 50 mCi was less effective for T3 compared to T1T2 disease. Low dose radiation hypersensitivity or unknown more extensive disease may have accounted for observed differences. Radiation thyroiditis and sialadenitis were more common in a comparison series of 100 mCi dose compared to 30 mCi, but not more common than in 50 mCi doses.

123I-mIBG scintigraphy in neuroblastoma: development of a SIOPEN semi-quantitative reporting ,method by an international panel

Purpose

A robust method is required to standardise objective reporting of diagnostic ¹²³I-mIBG images in neuroblastoma. Prerequisites for an appropriate system are low inter- and intra-observer error and reproducibility across a broad disease spectrum. We present a new reporting method, developed and tested for SIOPEN by an international expert panel.

Method

Patterns of abnormal skeletal ¹²³I-mIBG uptake were defined and assigned numerical scores [0–6] based on disease extent within 12 body segments. Uptake intensity was excluded from the analysis. Data sets from 82 patients were scored independently by six experienced specialists as unblinded pairs (pre- and post-induction chemotherapy) and in random order as a blinded study. Response was defined as ≥50 % reduction in post induction score compared with baseline.

Results

In total, 1968 image sets were reviewed individually. Response rates of 88 % and 82 % were recorded for patients with baseline skeletal scores ≤23 and 24-48 respectively, compared with 44 % response in patients with skeletal scores >48 (p = 0.02). Reducing the number of segments or extension scale had a small but statistically negative impact upon the number of responses detected. Intraclass correlation coefficients [ICCs] calculated for the unblinded and blinded study were 0.95 at diagnosis and 0.98 and 0.99 post-induction chemotherapy, respectively.

Conclusions

The SIOPEN mIBG score method is reproducible across the full spectrum of disease in high risk neuroblastoma. Numerical assessment of skeletal disease extent avoids subjective evaluation of uptake intensity. This robust approach provides a reliable means with which to examine the role of 123I mIBG scintigraphy as a prognostic indicator in neuroblastoma.

Separation of [(99m)Tc]pertechnetate and molybdate using polyethylene glycol coated C18 and C30 resins

Hydrophobic adsorbents such as C18 and C30 were coated with PEG and subsequently used for the separation of Mo/Tc. The most effective resin for adsorbing PEG was the C18-U resin, which demonstrated a coating capacity of 97.6±2.8mg PEG per g of resin. The ability to adsorb pertechnetate was proportional to the amount of PEG coated on the hydrophobic resin. The [(99m)Tc]pertechnetate recovery during the separation of cyclotron produced (99m)Tc from (100)Mo was 91.8±0.3% (n=2). The resultant product met relevant USP monograph specifications.

The Challenges of Treating Paraganglioma Patients with (177)Lu-DOTATATE PRRT: Catecholamine Crises, Tumor Lysis Syndrome and the Need for Modification of Treatment Protocols

PURPOSE

A high percentage of paragangliomas express somatostatin receptors that can be utilized for targeted radioisotope therapy. The aim of this study was to describe and discuss the challenges of treating these tumors with (177)Lu-[DOTA(0),Tyr(3)]octreotate (DOTATATE) radioisotope therapy using established protocols.

METHODS AND RESULTS

Three paraganglioma patients were treated with 4-5 cycles of (177)Lu-DOTATATE and were evaluated for side effects and response to therapy. Two of the three patients developed severe adverse reactions following their first (177)Lu-DOTATATE treatment. One patient developed a catecholamine crisis and tumor lysis syndrome within hours of treatment, requiring intensive care unit (ICU) support, and another developed a catecholamine crisis 3 days after treatment, requiring hospitalization. The treatment protocols at our institution were subsequently modified by increasing the radioisotope infusion time from 15 to 30 min, as recommended in the literature, to 2-4 h and by reducing the administered dose of (177)Lu-DOTATATE. Subsequent (177)Lu-DOTATATE treatments utilizing the modified protocols were well tolerated, and response to therapy was achieved in all three patients, resulting in significantly improved quality of life.

CONCLUSION

(177)Lu-DOTATATE is an exciting new therapeutic option in the management of paragangliomas; however, current treatment protocols described in the literature may need to be modified by lengthening the infusion time and/or lowering the initial treatment dose to prevent or reduce the severity of adverse reactions.

Role for (11)C-choline PET in active surveillance of prostate cancer

INTRODUCTION

Active surveillance (AS) is an increasingly popular management strategy for men diagnosed with low-risk indolent prostate cancer. Current tests (prostate-specific antigen [PSA], clinical staging, and prostate biopsies) to monitor indolent disease lack accuracy. (11)C-choline positron emission tomography (PET) has excellent detection rates in local and distant recurrence of prostate cancer. We examine (11)C-choline PET for identifying aggressive prostate cancer warranting treatment in the AS setting.

METHODS

In total, 24 patients on AS had clinical assessment and PSA testing every 6 months and (11)C-choline PET and prostate biopsies annually. The sensitivity and specificity to identify prostate cancer and progressive disease (PD) were calculated for each (11)C-choline PET scan.

RESULTS

In total, 62 biopsy-paired, serial (11)C-choline PET scans were analyzed using a series of standard uptake value-maximum (SUVmax) cut-off thresholds. During follow-up (mean 25.3 months), 11 of the 24 low-risk prostate cancer patients developed PD and received definitive treatment. The prostate cancer detection rate with (11)C-choline PET had moderate sensitivity (72.1%), but low specificity (45.0%). PD prediction from baseline (11)C-choline PET had satisfactory sensitivity (81.8%), but low specificity (38.5%). The addition of clinical parameters to the baseline (11)C-choline PET improved specificity (69.2%), with a slight reduction in sensitivity (72.7%) for PD prediction.

CONCLUSIONS

Addition of (11)C-choline PET imaging during AS may help to identify aggressive disease earlier than traditional methods. However, (11)C-choline PET alone has low specificity due to overlap of SUV values with benign pathologies. Triaging low-risk prostate cancer patients into AS versus therapy will require further optimization of PET protocols or consideration of alternative strategies (i.e., magnetic resonance imaging, biomarkers).

A phase I open-labeled, single-arm, dose-escalation, study of dichloroacetate (DCA) in patients with advanced solid tumors

Purpose Preclinical evidence suggests dichloroacetate (DCA) can reverse the Warburg effect and inhibit growth in cancer models. This phase 1 study was undertaken to assess the safety, recommended phase 2 dose (RP2D), and pharmacokinetic (PK) profile of oral DCA in patients with advanced solid tumors. Patients and Methods Twenty-four patients with advanced solid malignancies were enrolled using a standard 3 + 3 protocol at a starting dose of 6.25 mg/kg twice daily (BID). Treatment on 28 days cycles was continued until progression, toxicity, or consent withdrawal. PK samples were collected on days 1 and 15 of cycle 1, and day 1 of subsequent cycles. PET imaging ((18) F-FDG uptake) was investigated as a potential biomarker of response. Results Twenty-three evaluable patients were treated with DCA at two doses: 6.25 mg/kg and 12.5 mg/kg BID (median of 2 cycles each). No DLTs occurred in the 6.25 mg/kg BID cohort so the dose was escalated. Three of seven patients had DLTs (fatigue, vomiting, diarrhea) at 12.5 mg/kg BID. Thirteen additional patients were treated at 6.25 mg/kg BID. Most toxicities were grade 1-2 with the most common being fatigue, neuropathy and nausea. No responses were observed and eight patients had stable disease. The DCA PK profile in cancer patients was consistent with previously published data. There was high variability in PK values and neuropathy among patients. Progressive increase in DCA trough levels and a trend towards decreased (18) F-FDG uptake with length of DCA therapy was observed. Conclusions The RP2D of oral DCA is 6.25 mg/kg BID. Toxicities will require careful monitoring in future trials.

Low but measurable stimulated serum thyroglobulin levels <2 µg/L frequently predict incomplete response in differentiated thyroid cancer patients

INTRODUCTION

The study was aimed to determine the response and predictive risk factors of differentiated thyroid cancer (DTC) with measurable (0.4-2.0 µg/L) stimulated serum thyroglobulin (sTg) during the 10-24 months after radioiodine remnant ablation (RRA) and their long-term outcomes.

METHODS

Out of 839 retrospectively reviewed patients, 95 eligible DTC patients were included. Patients were classified as having incomplete response or no evidence of disease (NED). The sTg cut-off values with highest predicted accuracy for incomplete response at 10-24 months were calculated with receiver operator characteristics curve analysis.

RESULTS AND CONCLUSION

At 10-24 months after RRA, incomplete response was identified in 54 patients (57%) and 38/54 (70.4%) patients were found with structural evidence of disease. The remaining 16 patients (29.6%) had biochemical evidence of disease without structural evidence of disease. Forty-one patients (43%) were classified as having NED at 10-24 months after RRA and 27 patients (66%) did not receive further radioactive iodine (RAI) therapy and remained disease free at median follow-up of 6.5 years. Fourteen patients received second RAI treatment after 6 months and before the 10-24 months assessment time point. Of these, 2 had persistent tumor 6 years later. The sTg >0.6 µg/L at 6-10 months after RRA had optimal sensitivity (83.3%), specificity (56%) and negative predictive value (72%) of detecting incomplete response at 10-24 months after RRA. A total of 23/43 patients in the American Thyroid Association low-risk category had incomplete response after first RRA and 5/23 (21.7%) had recurrent/persistent disease at long-term follow-up.

[131I]IAZA as a molecular radiotherapeutic (MRT) drug: wash-out with cold IAZA accelerates clearance in a murine tumor model

Based on animal model studies, [131I]IAZA may be useful as an adjunct radiotherapeutic (MRT) drug for the treatment of tumor hypoxia. However, radioactivity in the blood of patients and healthy volunteers dosed with [123I]IAZA has a protracted terminal elimination phase in which clearance is influenced by free [123I]IAZA and possibly by unidentified metabolites. The current work reports that about 40% of the radioactivity in human serum is associated with the serum protein fraction, and that the free:bound ratio is constant at about 60:40 for at least the first 135 min after injection, as determined by radio-HPLC analyses. In order to modulate the clearance of bound and free radioactive IAZA, nonradioactive (cold) IAZA was administered i.v. 1 h following injection of high specific activity [125I][IAZA in the Balb/C EMT-6 murine tumor model. This 'wash out' procedure reduced the concentrations of radioactivity by at least 40% in all tissues, with greatest effect in kidney and liver, and least in tumor. As a result, the tumor:blood ratio increased from 5.8 to 8.5 at 4 h post-injection. This effect would be advantageous for the use of [131I]IAZA as an MRT drug. Optimization of intervals between radioactive and wash out dose, and confirmation of the self-irradiation dose to all tissues, remain to be undertaken before [131I]IAZA can be tested as a low-dose-rate MRT supplement to external beam x-ray radiotherapy.

Analysis of intraprostatic therapeutic effects in prostate cancer patients using [(11)C]-choline pet/ct after external-beam radiation therapy

PURPOSE

The objective of the present study was to analyze, with relatively high sensitivity and specificity, uptake properties of [(11)C]-choline in prostate cancer patients by means of positron-emission tomography (pet)/computed tomography (ct) imaging using objectively defined pet parameters to test for statistically significant changes before, during, and after external-beam radiation therapy (ebrt) and to identify the time points at which the changes occur.

METHODS

The study enrolled 11 patients with intermediate-risk prostate cancer treated with ebrt, who were followed for up to 12 months after ebrt. The [(11)C]-choline pet scans were performed before treatment (baseline); at weeks 4 and 8 of ebrt; and at 1, 2, 3, 6, and 12 months after ebrt.

RESULTS

Analysis of [(11)C]-choline uptake in prostate tissue before treatment resulted in a maximum standardized uptake value (suvmax) of 4.0 ± 0.4 (n = 11) at 40 minutes after injection. During week 8 of ebrt, the suvmax declined to 2.9 ± 0.1 (n = 10, p < 0.05). At 2 and 12 months after ebrt, suvmax values were 2.3 ± 0.3 (n = 10, p < 0.01) and 2.2 ± 0.2 (n = 11, p < 0.001) respectively, indicating that, after ebrt, maximum radiotracer uptake in the prostate was significantly reduced. Similar effects were observed when analyzing the tumour:muscle ratio (tmr). The tmr declined from 7.4 ± 0.6 (n = 11) before ebrt to 6.1 ± 0.4 (n = 11, nonsignificant) during week 8 of ebrt, to 5.6 ± 0.03 (n = 11, p < 0.05) at 2 months after ebrt, and to 4.4 ± 0.4 (n = 11, p < 0.001) at 12 months after ebrt.

CONCLUSIONS

Our study demonstrated that intraprostatic [(11)C]-choline uptake in the 11 analyzed prostate cancer patients significantly declined during and after ebrt. The pet parameters SUVmax and tmr also declined significantly. These effects can be detected during radiation therapy and up to 1 year after therapy. The prognostic value of these early and statistically significant changes in intraprostatic [(11)C]-choline pet avidity during and after ebrt are not yet established. Future studies are indicated to correlate changes in [(11)C]-choline uptake parameters with long-term biochemical recurrence to further evaluate [(11)C]-choline pet changes as a possible, but currently unproven, biomarker of response.

A phase II study of submandibular gland transfer prior to radiation for prevention of radiation-induced xerostomia in head-and-neck cancer (RTOG 0244)

PURPOSE

We report the results of a phase II study to determine the reproducibility of a submandibular salivary gland transfer (SGT) surgical technique for prevention of radiation (XRT)-induced xerostomia in a multi-institutional setting and to assess severity of xerostomia.

METHODS AND MATERIALS

Eligible patients had surgery for primary, neck dissection, and SGT, followed by XRT, during which the transferred salivary gland was shielded. Intensity modulated radiation therapy, amifostine, and pilocarpine were not allowed, but postoperative chemotherapy was allowed. Each operation was reviewed by 2 reviewers and radiation by 1 reviewer. If 13 or more (of 43) were "not per protocol," then the technique would be considered not reproducible as per study design. The secondary endpoint was the rate of acute xerostomia, grade 2 or higher, and a rate of ≤ 51% was acceptable.

RESULTS

Forty-four of the total 49 patients were analyzable: male (81.8%), oropharynx (63.6%), stage IV (61.4%), median age 56.5 years. SGT was "per protocol" or within acceptable variation in 34 patients (77.3%) and XRT in 79.5%. Nine patients (20.9%) developed grade 2 acute xerostomia; 2 had grade 0-1 xerostomia (4.7%) but started on amifostine/pilocarpine. Treatment for these 11 patients (25.6%) was considered a failure for the xerostomia endpoint. Thirteen patients died; median follow-up for 31 surviving patients was 2.9 years. Two-year overall and disease-free survival rates were 76.4% and 71.7%, respectively.

CONCLUSIONS

The technique of submandibular SGT is reproducible in a multicenter setting. Seventy-four percent of patients were prevented from XRT-induced acute xerostomia.

Cyclotron production of ⁹⁹mTc: recycling of enriched ¹⁰⁰Mo metal targets

There is growing interest in the large scale cyclotron production of (99m)Tc via the (100)Mo(p,2n)(99m)Tc reaction. While the use and recycling of cyclotron-irradiated enriched molybdenum targets has been reported previously in the context of (94m)Tc production, to the best of our knowledge, previous recycling studies have been limited to the use of oxide targets. To facilitate reuse of high-power enriched (100)Mo targets, this work presents and evaluates a strategy for recycling of enriched metallic molybdenum. For the irradiated (100)Mo targets in this study, an overall metal to metal recovery of 87% is reported. Evaluation of "new" and "recycled" (100)Mo revealed no changes in the molybdenum isotopic composition (as measured via ICP-MS). For similar irradiation conditions of "new" and "recycled" (100)Mo, (i.e. target thicknesses, irradiation time, and energy), comparable levels of (94g)Tc, (95g)Tc, and (96g)Tc contaminants were observed. Comparable QC specifications (i.e. aluminum ion concentration, pH, and radiochemical purity) were also reported. We finally note that [(99m)Tc]-MDP images obtained by comparing MDP labelled with generator-based (99m)Tc vs. (99m)Tc obtained following the irradiation of recycled (100)Mo demonstrated comparable biodistribution. With the goal of producing large quantities of (99m)Tc, the proposed methodology demonstrates that efficient recycling of enriched metallic (100)Mo targets is feasible and effective.

A conjugate of gemcitabine with bisphosphonate (Gem/BP) shows potential as a targeted bone-specific therapeutic agent in an animal model of human breast cancer bone metastases

Bone metastases in advanced breast cancer patients remains a significant treatment challenge. Bisphosphonates are now a routine first line treatment for prevention and treatment of skeletal damage caused by malignancies and, moreover, have shown an ability to transport therapeutic drugs to the bone. Here, we describe the effect of a conjugate between the potent anticancer drug gemcitabine and a bisphosphonate molecule (Gem/BP) in an animal model of breast cancer metastases. We have previously demonstrated the targeting of this compound to bone in normal mice using an analog labeled with the radionuclide 99mTc. Using a bone metastasis model in nude mice produced by intracardiac injection of the human breast cancer cell line MDA-MB-231BO, we examined the effect of Gem/BP and gemcitabine in reducing the frequency and severity of osteolytic bone lesions. High-resolution radiographs and microPET images showed that Gem/ BP reduced the number and size of bone metastases relative to the gemcitabine-treated and the untreated control groups. Histological examination of the humeri and femurs of the control and gemcitabine groups revealed large metastatic cancer lesions in the outer and inner cortices and the medullary cavities. In contrast, Gem/BP-treated mice showed occasional small wedge-shaped metastases under the periosteum of the outer cortex and very occasionally in the medulla. These findings suggest that Gem/BP should be further evaluated for use in the treatment of bone metastases in breast cancer.

Radiopharmacological evaluation of 6-deoxy-6-[18F]fluoro-D-fructose as a radiotracer for PET imaging of GLUT5 in breast cancer

INTRODUCTION

Several clinical studies have shown low or no expression of GLUT1 in breast cancer patients, which may account for the low clinical specificity and sensitivity of 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) used in positron emission tomography (PET). Therefore, it has been proposed that other tumor characteristics such as the high expression of GLUT2 and GLUT5 in many breast tumors could be used to develop alternative strategies to detect breast cancer. Here we have studied the in vitro and in vivo radiopharmacological profile of 6-deoxy-6-[(18)F]fluoro-D-fructose (6-[(18)F]FDF) as a potential PET radiotracer to image GLUT5 expression in breast cancers.

METHODS

Uptake of 6-[(18)F]FDF was studied in murine EMT-6 and human MCF-7 breast cancer cells over 60 min and compared to [(18)F]FDG. Biodistribution of 6-[(18)F]FDF was determined in BALB/c mice. Tumor uptake was studied with dynamic small animal PET in EMT-6 tumor-bearing BALB/c mice and human xenograft MCF-7 tumor-bearing NIH-III mice in comparison to [(18)F]FDG. 6-[(18)F]FDF metabolism was investigated in mouse blood and urine.

RESULTS

6-[(18)F]FDF is taken up by EMT-6 and MCF-7 breast tumor cells independent of extracellular glucose levels but dependent on the extracellular concentration of fructose. After 60 min, 30±4% (n=9) and 12±1% (n=7) ID/mg protein 6-[(18)F]FDF was found in EMT-6 and MCF-7 cells, respectively. 6-deoxy-6-fluoro-d-fructose had a 10-fold higher potency than fructose to inhibit 6-[(18)F]FDF uptake into EMT-6 cells. Biodistribution in normal mice revealed radioactivity uptake in bone and brain. Radioactivity was accumulated in EMT-6 tumors reaching 3.65±0.30% ID/g (n=3) at 5 min post injection and decreasing to 1.75±0.03% ID/g (n=3) at 120 min post injection. Dynamic small animal PET showed significantly lower radioactivity uptake after 15 min post injection in MCF-7 tumors [standard uptake value (SUV)=0.76±0.05; n=3] compared to EMT-6 tumors (SUV=1.23±0.09; n=3). Interestingly, [(18)F]FDG uptake was significantly different in MCF-7 tumors (SUV(15 min) 0.74±0.12 to SUV(120 min) 0.80±0.15; n=3) versus EMT-6 tumors (SUV(15 min) 1.01±0.33 to SUV(120 min) 1.80±0.25; n=3). 6-[(18)F]FDF was shown to be a substrate for recombinant human ketohexokinase, and it was metabolized rapidly in vivo.

CONCLUSION

Based on the GLUT5 specific transport and phosphorylation by ketohexokinase, 6-[(18)F]FDF may represent a novel radiotracer for PET imaging of GLUT5 and ketohexokinase-expressing tumors.

Radioiodinated metaiodobenzylguanidine treatment of neuroendocrine tumors in adults

Metaiodobenzylguanidine (MIBG), radioiodinated with (131)I, has been available for 25 years. Its role in the United States is limited to diagnostic imaging, whereas its therapeutic application in patients with neuroendocrine tumors for whom surgical treatment would not lead to a cure, has been approved in Europe. (131)I-MIBG treatments can be a valuable addition to the current gamut of treatment options for patients with metastatic neuroendocrine tumors, especially given the limited role for other systemic treatments, such as chemotherapy. There are basically two treatment strategies: one or two high-dose treatments or continuous low-dose treatments. (131)I-MIBG could induce symptomatic relief in the vast majority of patients treated, both following high-dose treatment and low-dose maintenance treatment. Biochemical responses can be observed in about half of the patients, whereas radiographic responses are described in roughly one third of the patients. Several articles suggested a survival benefit to patients treated with (131)I-MIBG. Side-effects of the treatment mainly consist of myelotoxicity, nausea, and hypothyroidism. Future developments are focused on the use of high-specific-activity (131)I-MIBG in high doses. The role of (131)I-MIBG in relation to other treatments remains to be established, although treatment (131)I-MIBG seems to be at least as effective as other systemic treatments, with limited side-effects.

Synthesis and biodistribution of 8-iodo-11-(4-methylpiperazino)-5H-dibenzo[b,e][1,4]-diazepine: Iozapine

8-Iodo-11-(4-methylpiperazino)-5H-dibenzo[b,e][1,4]-diazepine: Iozapine, a potential D(4)-receptor ligand was synthesized using oxidative iodo-destannylation reaction. The preliminary biodistribution studies of radioiodinated iozapine have shown that the compound is taken up in the brains of mice and rabbits.

Clinical production, stability studies and PET imaging with 16-alpha-[18F]fluoroestradiol ([18F]FES) in ER positive breast cancer patients

PURPOSE

18F-Fluoroestradiol [18F]FES has emerged as a valuable PET tracer to predict the response to hormone therapy in recurrent or metastatic breast cancer patients. A clinically acceptable product requires a rapid reliable synthesis and must be demonstrated to maintain chemical stability and receptor specific uptake during patient studies. [18F]FES then becomes a dependable tracer for the evaluation and management of breast cancer patients.

METHODS

An improved automated radiosynthesis of [18F]FES was developed. Stability studies of the injectible form of [18F]FES were performed up to 24 h after dose formulation under normal storage conditions. A comparative FES/FDG PET imaging in ER+ breast cancer patients is reported.

RESULTS

The improved synthesis procedure utilizes fewer hydrolysis steps and a single high performance liquid column chromatography (HPLC) purification of the labeled mixture affording [18F]FES in good yield with high radiochemical purity (>99%). Stability studies with purified [18F]FES in saline/ethanol (85:15 v/v) indicated no radiolytic or chemical degradation of this radiopharmaceutical when stored for 24 h at 20-24 degrees C. Positron Emission Tomography (PET) studies with [18F]FES and [18F]FDG in estrogen receptor positive (ER+) breast cancer patients indicated that while FDG accumulation was seen in all metabolically hyperactive sites, the uptake of FES clearly delineated the ER+ tissues regions.

CONCLUSIONS

An improved automated synthesis of [18F]FES has been developed and the integrity of this product has been validated by long term stability studies and clinical PET imaging studies in ER+ breast cancer patients. A lack of concordance between FES and FDG uptake in a patient with metastatic breast cancer suggests specificity of the FES for tumors expressing estrogen receptors.

A one-pot synthesis of 1-alpha- and 1-beta-D-arabinofuranosyl-2-nitroimidazoles: synthons to the markers of tumor hypoxia

1-alpha- and 1-beta-D-Arabinofuranosyl-2-nitroimidazole (alpha-AZA and beta-AZ A) are synthons for a number of potential markers of tissue hypoxia. A one pot synthesis in which 2-nitroimidazole is coupled with a mixture of alpha- and beta-1-O-acetyl-2,3,5-tri-O-benzoyl-D-arabinofuranose in the presence of stannic chloride, followed by deprotection using ammonia/methanol, is described Previously reported conditions for coupling 2-nitroimidazole to 1-alpha-bromoarabinofuranose protected by base-hydrolyzable groups afforded alpha-AZA almost exclusively.

A human osteosarcoma cell line expressing herpes simplex type-1 thymidine kinase: studies with radiolabeled (E)-5-(2-iodovinyl)-2'-fluoro-2'-deoxyuridine

INTRODUCTION

(E)-5-(2-Iodovinyl)-2'-fluoro-2'-deoxyuridine (IVFRU) is a pyrimidine nucleoside analogue that accumulates selectively in murine cells expressing herpes simplex type-1 thymidine kinase (HSV-1 TK). The uptake of [(125)I]IVFRU in human 143B osteosarcoma cells transduced with a retroviral vector bearing the HSV-1 TK gene (143B-LTK cells) is now reported.

METHODS

HSV-1 TK gene expression in 143B-LTK cells was confirmed by Western blotting and reverse transcriptase (RT)-PCR. Cell and subcellular uptake of [(125)I]IVFRU was determined in cell culture, and whole body biodistribution after intravenous injection of [(125)I]IVFRU was determined using nude mice bearing implanted 143B or 143B-LTK tumors.

RESULTS

Although IVFRU was less toxic to the human cell line expressing HSV-1 TK (143B-LTK) than ganciclovir, both IVFRU and ganciclovir were not toxic to the cell line not expressing HSV-1 TK (143B). When cells were exposed to [(125)I]IVFRU in vitro, only the 143B-LTK cells accumulated radioactivity. The acid-soluble fraction from 143B-LTK cell lysates contained 8-fold greater activity than the acid-insoluble fraction after an 8-h exposure to [(125)I]IVFRU. Biodistribution of [(125)I]IVFRU in nude mice bearing subcutaneous 143B and 143B-LTK tumors revealed widespread distribution of the nucleoside in vivo but with specific localization in 143B-LTK tumors.

CONCLUSION

The underlying biochemical process of metabolic entrapment of IVFRU in human osteosarcoma cells expressing HSV-1 TK is responsible for selective localization in these cells. The differences in subcellular distribution into the nucleic acid fraction, and in cytotoxicity, reflect the importance of cell type and lineage as determinants of the performance of gene imaging radiopharmaceuticals.

Marginal cost of operating a positron emission tomography center in a regulatory environment

Objectives: Cost studies of positron emission tomography (PET) imaging are important for resource and operational planning; the most relevant cost analysis in this regard is the marginal cost. Operating within a regulatory environment can add considerably to the costs of providing PET services. Previously published research has not examined the marginal cost structure of PET nor have they described the implications of regulatory compliance to operational costs. The purpose of this study was to conduct a comprehensive cost estimation of PET imaging with 18F-fluorodeoxyglucose (18F-FDG) to better identify the fixed and variable cost components, the marginal cost structure, and the added costs of satisfying regulatory requirements.

Methods: Financial data on capital and operating expenses were collected for the PET center at the Cross Cancer Institute in Edmonton, Alberta, Canada.

Results: The total per-service cost for clinical operations ranged between $7,869 (400 annual scans) and $1,231 (3,200 annual scans). The marginal cost for the center remained steady as volume increased up to the throughput capacity.

Conclusions: Results indicate that economies from increased volumes did not arise. Regulatory requirements added significant costs to operating an 18F-FDG-PET center.

[131I]Iodoazomycin arabinoside for low-dose-rate isotope radiotherapy: radiolabeling, stability, long-term whole-body clearance and radiation dosimetry estimates in mice

BACKGROUND

The preliminary characterization of [(131)I]iodoazomycin arabinoside ([(131)I]IAZA) as a potential radiotherapeutic radiopharmaceutical is described.

METHODS

High-specific-activity [(131)I]IAZA was prepared in therapeutic doses (up to 3 GBq per batch) by isotope exchange in pivalic acid melt and was purified on Sep-Pak cartridges. Stability in 15% ethanol in saline at 4 degrees C was determined by high-performance liquid chromatography. IAZA cytotoxicity (IC(50), approximately 0.1 mM) against both murine (EMT-6) and human (143B, 143B-LTK) tumor cells determined by MTT test was in the range previously reported for EMT-6 cells using a clonogenic assay. Tissue radioactivity levels were measured in a murine tumor model for the 24- to 168-h postinjection period. Radiation dose estimates obtained from the tissue activity levels for this period were calculated from pharmacokinetic (WinNonlin) and dosimetry (MIRD and RAdiation Dose Assessment Resource) parameters.

RESULTS

The radioiodination efficiency was >90%, but with systematic losses during Sep-Pak purification, the recovered yields of [(131)I]IAZA were approximately 75%. The product (specific activity, 4.6-6.4 GBq/micromol) was stable for at least 2 weeks, with only approximately 6% degradation over this storage period. Extended biodistribution studies in Balb/c mice bearing implanted EMT-6 tumors showed that the highest tumor/blood radioactivity ratio (T/B; 4.8) occurred 24 h after dosing; the T/B ratio was approximately 1.5 at the end of the 7-day study. The 24- to 168-h tissue radioactivity data fit a one-compartment model except for liver data, which best fit a two-compartment model. Dosimetry estimates showed a tumor self-dose of 7.4 mGy/MBq, which is several-fold higher than for the liver or the kidney.

CONCLUSIONS

[(131)I]IAZA can be efficiently radiolabeled at high specific activity, purified by a simple Sep-Pak technique and stored with little radiolysis or chemical decomposition at these specific activities. Based on measured radioactivity burdens during the week following injection and on published animal ([(125)I]IAZA) and clinical ([(123)I]IAZA) dosimetry data, the current dose estimates point to selective tumor irradiation at low dose rates.

The palliative role of 131I-MIBG and 111In-octreotide therapy in patients with metastatic progressive neuroendocrine neoplasms

BACKGROUND

Radiolabeled octreotide and metaiodobenzylguanidine (MIBG) have demonstrated limited antitumor effect on neuroendocrine neoplasms (NENs). The purpose of this study was to assess the palliative benefit of radionuclide therapy (RNT) in NENs.

METHODS

Since April 2001, RNT for progressive, nonsurgically resectable NENs was utilized. NENs that were MIBG positive received 131 I-MIBG therapy, whereas octreotide-only-positive neoplasms received 111 In-octreotide therapy. Symptomatic, quality of life (QoL), biochemical, and radiographic responses to RNT were evaluated.

RESULTS

Twenty-four patients had either MIBG or octreotide avid NENs. A mean (range) of 4 (1-7) 131 I-MIBG treatments were given to 13 patients over a duration of 18 months (6-42). The group consisted of 2 medullary thyroid cancer (MTC), and 2 foregut and 9 small-bowel carcinoids; 12 patients (92%) had symptomatic improvement. Stability of tumor size was confirmed in 6, regression in 2, and progression in 5. Biochemical responses were demonstrated in 2. Five (2-16) treatments of 111 In-octreotide was given to 11 patients over 17 months (6-40). There were 1 MTC, 1 insulinoma, 2 gastrinomas, and 3 small-bowel and 4 foregut carcinoids. Symptomatic benefit was seen in 6 (55%), biochemical response in 3. Tumor regression was seen in 1, stability in 5, and progression in 5.

CONCLUSIONS

Radionuclide therapy appears to offer good palliation to patients with progressive NENs.

Hypoxia-specific tumor imaging with 18F-fluoroazomycin arabinoside

The study was performed to compare the (18)F-labeled nitroimidazole compound fluoroazomycin arabinoside ((18)F-FAZA) with the standard hypoxia tracer fluoromisonidazole ((18)F-FMISO) in detection of tumor tissue hypoxia and to verify the oxygenation dependency of (18)F-FAZA uptake.

METHODS

Biodistribution of (18)F-FAZA was studied at various time points in EMT6 tumor-bearing BALB/c mice and in AR42J and A431 tumor-bearing nude mice and compared with that of (18)F-FMISO. The presence of tumor tissue hypoxia was verified in 5 EMT6 and 5 AR42J tumors using an oxygen-sensing needle electrode system. To evaluate the oxygenation dependency of (18)F-FAZA uptake, using the Munich prototype animal PET scanner, 2 serial PET scans were performed in 13 A431 tumor-bearing nude mice breathing pure oxygen or room air on 1 d and then selecting the other oxygen breathing condition on the following day. In addition, digital autoradiography was performed with EMT6 tumor-bearing (18)F-FAZA-dosed, nude mice breathing either room air (n = 8) or carbogen (n = 9).

RESULTS

Tissue partial pressure of oxygen (Po(2)) electrode measurements revealed that tumor hypoxia was present under room air breathing in EMT6 (tissue Po(2) = 2.9 +/- 2.6) and AR42J tumors (tissue Po(2) = 0.4 +/- 0.2), which was significantly lower compared with that of reference tissue (tissue Po(2) = 25.8 +/- 6.7 and tissue Po(2) = 29.0 +/- 3.0 [mean +/- SD], respectively; P < 0.01). In all tumor models, (18)F-FAZA displayed significantly higher tumor-to-muscle and tumor-to-blood ratios compared with (18)F-FMISO, indicating a faster clearance of (18)F-FAZA from normal tissues. In AR42J tumors, (18)F-FAZA tumor-to-normal ratios were found to increase over time. Serial animal (18)F-FAZA PET studies showed that the tumor-to-background ratio was significantly higher in animals breathing room air compared with that of animals breathing pure oxygen (7.3 +/- 2.3 vs. 4.2 +/- 1.2, respectively; P < 0.001). Similarly, autoradiography showed significantly higher tumor-to-muscle ratios in mice breathing room air compared with those of animals breathing carbogen (5.3 +/- 0.8 vs. 2.2 +/- 0.8; respectively; P < 0.02).

CONCLUSION

(18)F-FAZA shows superior biokinetics and is, thus, a promising PET tracer for the visualization of tumor hypoxia. This study also verified a hypoxia-specific uptake mechanism for (18)F-FAZA in murine tumor models.

Cytotoxicity and cellular uptake of pyrimidine nucleosides for imaging herpes simplex type-1 thymidine kinase (HSV-1 TK) expression in mammalian cells

In vivo transfer of the herpes simplex virus type-1 thymidine kinase (HSV-1 TK) gene, with subsequent administration of antiviral drugs such as ganciclovir, has emerged as a promising gene therapy protocol for treating proliferative disorders. The in vitro cytotoxicities (IC(50)) for two series of 5-iodo- and (E)-5-(2-iodovinyl)-substituted 2'-deoxy- and 2'-deoxy-2'-fluoro-pyrimidine nucleosides ranged from millimolar to low nanomolar concentrations in mammalian tumor cell lines (KBALB; R-970-5; 143B; EMT-6) and their counterparts engineered to express HSV-1 TK (KBALB-STK; 143B-LTK). Their HSV-1 TK selectivity indices ranged from one (nonselective) to one million (highly selective) based on cytotoxicity, with FIRU being the least toxic to all cell lines, and FIAU being most toxic. HSV-1 TK selectivity, based on uptake, ranged from 10 to 140, with IVDU being most selective for HSV-1 TK expressing cells, followed by IVFRU, FIRU, FIAU, IVFAU and finally IUDR. Phosphorylation of [(125)I]FIAU led to incorporation of the radiolabel into nucleic acids, whereas IVFRU and FIRU radioactivity was trapped primarily in the nucleotide pool. These data indicate that cytotoxicity does not depend on initial metabolic trapping (e.g., phosphorylation), but on elaboration of the mononucleotides to more cytotoxic anabolites. Lipophilicities and nucleoside transport rates of the six nucleosides tested were within narrow ranges. This supports the premise that cellular biochemistry, and not cellular bioavailability, is responsible for the observed broad range of cytotoxicity and trapping. In vivo biodistribution studies with 5-[(125)I]iodo-2'-fluoro-2'-deoxyribouridine (FIRU), 5-[(125)I]iodo-2'-fluoro-2'-deoxyarabinouridine (FIAU) and (E)-5-(2-[(125)I]iodovinyl)-2'-fluoro-2'-deoxyuridine (IVFRU) demonstrate selective accumulation of all three radiotracers in HSV-1 TK-expressing KBABK-STK tumors, compared to their very low accumulation in the non-HSV-1 TK-expressing KBALB tumors, in Balb/c mice. In summary, these nucleosides are unpredictably cytotoxic to the various cell lines studied, and this unpredictability extends across the HSV-1 TK expression characteristic; their uptake by cells engineered to express HSV-1 TK is also dependent on the molecular construction of the gene cassette carrying the viral TK gene.

[99mTc]Technetium labelled PnAo-azomycin glucuronides: a novel class of imaging markers of tissue hypoxia

Azomycin glucuronate was coupled to a PnAO ligand to create azomycin-based ligands that would form water-soluble 99mTc-azomycin complexes for imaging hypoxic tissue. 1-beta-D-(2-Nitroimidazolyl)glucuronic acid, (see structure in text), was synthesized by coupling 2-nitroimidazole with 1-alpha-bromo-2,3,4-tri-O-acetyl-6-methyl glucuronate, followed by deprotection. Reaction of (see structure in text) with 6-methyl-6-methylamino-HMPnAO (Pn-44) in the presence of BOP reagent in anhydrous dimethyl sulfoxide afforded the PnAO-glucuronides (see structure in text) and (see structure in text). Compound (see structure in text) was isolated in three rotomeric forms. Biological evaluation of (see structure in text) (99mTc-5) indicated selective binding to hypoxic EMT-6 cells, and cytotoxicity to fibroblasts and HeLa, sk24, sk23, and g361 cancer cell lines, at an IC20 <2.5 microgram/ml. In vivo biodistribution of two formulations of (see structure in text) in Balb/c mice with EMT-6 tumor produced diverse results, with one formulation showing no tumor preference, and the other providing a tumor/blood ratio of 2.3 at 4 h post-injection. The latter formulation delineated tumor, large intestine and liver in scintigraphic images.

Microwave-assisted (radio)halogenation of nitroimidazole-based hypoxia markers

Microwave-assisted radiohalogenation for the production of short-lived radiopharmaceuticals has now been applied to the synthesis and radiolabelling of azomycin nucleosides. (Radio)halogens were incorporated either by nucleophilic substitution of a leaving group or by halogen-halogen exchange, in the synthesis of IAZA, IAZP and FAZA. A comparison of conventional labelling and microwave-assisted labelling procedures reflects a clear advantage of the microwave technique.