Multi-technique imaging of bone metastases: spotlight on PET-CT

Preparation, Optimisation, and In Vitro Evaluation of [18F]AlF-NOTA-Pamidronic Acid for Bone Imaging PET

[¹⁸F]sodium fluoride ([¹⁸F]NaF) is recognised to be superior to [⁹⁹mTc]-methyl diphosphate ([^99mTc]Tc-MDP) and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in bone imaging. However, there is concern that [¹⁸F]NaF uptake is not cancer-specific, leading to a higher number of false-positive interpretations. Therefore, in this work, [¹⁸F]AlF-NOTA-pamidronic acid was prepared, optimised, and tested for its in vitro uptake. NOTA-pamidronic acid was prepared by an N-Hydroxysuccinimide (NHS) ester strategy and validated by liquid chromatography-mass spectrometry analysis (LC-MS/MS). Radiolabeling of [¹⁸F]AlF-NOTA-pamidronic acid was optimised, and it was ensured that all quality control analysis requirements for the radiopharmaceuticals were met prior to the in vitro cell uptake studies. NOTA-pamidronic acid was successfully prepared and radiolabeled with ¹⁸F. The radiolabel was prepared in a 1:1 molar ratio of aluminium chloride (AlCl₃) to NOTA-pamidronic acid and heated at 100 °C for 15 min in the presence of 50% ethanol (v/v), which proved to be optimal. The preliminary in vitro results of the binding of the hydroxyapatite showed that [¹⁸F]AlF-NOTA-pamidronic acid was as sensitive as [¹⁸F]sodium fluoride ([¹⁸F]NaF). Normal human osteoblast cell lines (hFOB 1.19) and human osteosarcoma cell lines (Saos-2) were used for the in vitro cellular uptake studies. It was found that [¹⁸F]NaF was higher in both cell lines, but [¹⁸F]AlF-NOTA-pamidronic acid showed promising cellular uptake in Saos-2. The preliminary results suggest that further preclinical studies of [¹⁸F]AlF-NOTA-pamidronic acid are needed before it is transferred to clinical research.

Review of imaging techniques for evaluating morphological and functional responses to the treatment of bone metastases in prostate and breast cancer

Bone metastases are very common complications associated with certain types of cancers that frequently negatively impact the quality of life and functional status of patients; thus, early detection is necessary for the implementation of immediate therapeutic measures to reduce the risk of skeletal complications and improve survival and quality of life. There is no consensus or universal standard approach for the detection of bone metastases in cancer patients based on imaging. Endorsed by the Spanish Society of Medical Oncology (SEOM), the Spanish Society of Medical Radiology (SERAM), and the Spanish Society of Nuclear Medicine and Molecular Imaging (SEMNIM) a group of experts met to discuss and provide an up-to-date review of our current understanding of the biological mechanisms through which tumors spread to the bone and describe the imaging methods available to diagnose bone metastasis and monitor their response to oncological treatment, focusing on patients with breast and prostate cancer. According to current available data, the use of next-generation imaging techniques, including whole-body diffusion-weighted MRI, PET/CT, and PET/MRI with novel radiopharmaceuticals, is recommended instead of the classical combination of CT and bone scan in detection, staging and response assessment of bone metastases from prostate and breast cancer.Clinical trial registration: Not applicable.

18F-labeled bisphosphonate as an alternative candidate to the gold standard [18F]sodium fluoride ([18F]NaF) for PET bone imaging

Bone metastases are a common source of malignancy in the skeleton and occur much more often than primary bone cancer. Several works were ongoing to identify early markers for bone metastasis and novel drug targets to improve patients' quality of life. As some concerns exist with the [¹⁸F]sodium fluoride in positron emission tomography (PET) bone imaging, there has been an increase in the number of targeted radiopharmaceutical markers for bone metastases imaging in its competitor, ⁶⁸Ga. Since ¹⁸F properties are superior to those of ⁶⁸Ga, there is a distinct motivation for developing 18F radiopharmaceuticals for bone metastases imaging.

Imaging with radiolabelled bisphosphonates

Radiolabeled bisphosphonates were developed in the 1970s for scintigraphic functional imaging of the skeleton in benign and malignant disease. Tracers such as 99mTc-methylene diphosphonate, that map focal or global changes in mineralization in the skeleton qualitatively and quantitatively, have been the backbone of nuclear medicine imaging for decades. While competing technologies are evolving, new indications and improvements in scanner hardware, in particular hybrid imaging (e.g. single photon emission computed tomography combined with computed tomography), have allowed improved diagnostic accuracy and a continued role for radiolabeled bisphosphonate imaging in current practice.

Preparation, Characterization, and Radiolabeling of [68Ga]Ga-NODAGA-Pamidronic Acid: A Potential PET Bone Imaging Agent

Early diagnosis of bone metastases is crucial to prevent skeletal-related events, and for that, the non-invasive techniques to diagnose bone metastases that make use of image-guided radiopharmaceuticals are being employed as an alternative to traditional biopsies. Hence, in the present work, we tested the efficacy of a gallium-68 (⁶⁸Ga)-based compound as a radiopharmaceutical agent towards the bone imaging in positron emitting tomography (PET). For that, we prepared, thoroughly characterized, and radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid radiopharmaceutical, a ⁶⁸Ga precursor for PET bone cancer imaging applications. The preparation of NODAGA-pamidronic acid was performed via the N-Hydroxysuccinimide (NHS) ester strategy and was characterized using liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MSⁿ). The unreacted NODAGA chelator was separated using the ion-suppression reverse phase-high performance liquid chromatography (RP-HPLC) method, and the freeze-dried NODAGA-pamidronic acid was radiolabeled with ⁶⁸Ga. The radiolabeling condition was found to be most optimum at a pH ranging from 4 to 4.5 and a temperature of above 60 °C. From previous work, we found that the pamidronic acid itself has a good bone binding affinity. Moreover, from the analysis of the results, the ionic structure of radiolabeled [⁶⁸Ga]Ga-NODAGA-pamidronic acid has the ability to improve the blood clearance and may exert good renal excretion, enhance the bone-to-background ratio, and consequently the final image quality. This was reflected by both the in vitro bone binding assay and in vivo animal biodistribution presented in this research.

Is interim 18F-fluoride PET/CT a predictor of outcomes after radium-223 therapy?

Objective

To determine whether an interim ¹⁸F-fluoride positron-emission tomography/computed tomography (PET/CT) study performed after the third cycle of radium-223 dichloride (²²³RaCl₂) therapy is able to identify patients that will not respond to treatment.

Materials and Methods

We retrospectively reviewed 34 histologically confirmed cases of hormone-refractory prostate cancer with bone metastasis in patients submitted to ²²³RaCl₂ therapy. All of the patients underwent baseline and interim ¹⁸F-fluoride PET/CT studies. The interim study was performed immediately prior to the fourth cycle of ²²³RaCl₂. The skeletal tumor burden-expressed as the total lesion fluoride uptake above a maximum standardized uptake value of 10 (TLF₁₀)-was calculated for the baseline and the interim studies. The percent change in TLF₁₀ between the baseline and interim studies (%TFL₁₀) was calculated as follows: %TFL₁₀ = interim TLF₁₀ - baseline TLF₁₀ / baseline TLF₁₀. End points were overall survival, progression-free survival, and skeletal-related events.

Results

The mean age of the patients was 72.4 ± 10.2 years (range, 43.3-88.8 years). The %TLF₁₀ was not able to predict overall survival (p = 0.6320; hazard ratio [HR] = 0.753; 95% confidence interval [CI]: 0.236-2.401), progression-free survival (p = 0.5908; HR = 1.248; 95% CI: 0.557-2.797) nor time to a bone event (p = 0.5114; HR = 1.588; 95% CI: 0.399-6.312).

Conclusion

The skeletal tumor burden on an interim ¹⁸F-fluoride PET/CT, performed after three cycles of ²²³RaCl₂, is not able to predict overall survival, progression-free survival, or time to bone event, and should not be performed to monitor response at this time.

18F-FDG PET Response of Skeletal (Bone Marrow and Bone) Involvement After Induction Chemotherapy in Pediatric Hodgkin Lymphoma: Are Specific Response Criteria Required?

To determine whether the current ¹⁸F-FDG PET response criterion for skeletal involvement in Hodgkin lymphoma (HL) is suitable, we performed a systematic evaluation of the different types of skeletal involvement and their response on PET after 2 cycles of chemotherapy (PET-2). A secondary objective was to observe the influence of the initial uptake intensity (measured as qPET) and initial metabolic tumor volume (MTV) of skeletal lesions on the PET-2 response. Methods: The initial PET scans of 1,068 pediatric HL patients from the EuroNet-PHL-C1 trial were evaluated for skeletal involvement by central review. Three types of skeletal lesions were distinguished: PET-only lesions (those detected on PET only), bone marrow (BM) lesions (as confirmed by MRI or BM biopsy), and bone lesions. qPET and MTV were calculated for each skeletal lesion. All PET-2 scans were assessed for residual tumor activity. The rates of complete metabolic response for skeletal and nodal involvement on PET-2 were compared. Results: Of the 1,068 patients, 139 (13%) showed skeletal involvement (44 PET-only, 32 BM, and 63 bone). Of the 139 patients with skeletal involvement, 101 (73%) became PET-2-negative in the skeleton and 94 (68%) became PET-2-negative in the lymph nodes. The highest number of PET-2-negative scans in the skeleton was 42 (95%) in the 44 PET-only patients, followed by 22 skeletal lesions (69%) in the 32 BM patients and 37 (59%) in the 63 bone patients. Lesions that became PET-2-negative showed a lower initial median qPET (2.74) and MTV (2 cm³) than lesions that remained PET-2-positive (3.84 and 7 cm³, respectively). Conclusion: In this study with pediatric HL patients, the complete response rate for skeletal involvement on PET-2 was similar to that for nodal involvement. Bone flare seemed to be irrelevant. Overall, the current skeletal PET response criterion-comparison with the local skeletal background-is well suited. The initial qPET and MTV of skeletal lesions were predictive of the PET-2 result. Higher values for both parameters were associated with a worse PET-2 response.

Positron emission tomography (PET) in primary prostate cancer staging and risk assessment

Prostate cancer (PCa) is one of the few neoplasms that are not well served by 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET). As a result, a number of PET tracers have been developed to target particular biological features of PCa. Such agents can be used for diagnosis, staging, identification of biochemical recurrence (BCR) and evaluation of metastatic disease. Here, we focus on primary disease and local staging. To date, magnetic resonance imaging (MRI) has proven superior to PET in the imaging of primary PCa. However, some PET agents have shown remarkable promise in staging high-risk PCa (defined as any combination of a clinical T3, a PSA score >20 ng/mL, or a Gleason score of 8–10), as well as biochemical relapse after definitive therapy and metastatic PCa. PET agents can be divided into those that interrogate tumor metabolism (¹⁸F-FDG, ¹¹C-Choline, ¹⁸F-Choline, ¹¹C-Acetate, 18F-FACBC), hormone receptors (18F-FDHT), and other targets such as prostate specific membrane antigen (PSMA) (⁶⁸Ga-PSMA, ¹⁸F-DCFBC, ¹⁸F-DCFPyl) or gastric releasing peptide (¹⁸F-GRP or ¹⁸F-Bombesin). In this review, we compare the available PCa targeted PET tracers utilized in staging of high risk tumors.

PET Tracer 18F-Fluciclovine Can Detect Histologically Proven Bone Metastatic Lesions: A Preclinical Study in Rat Osteolytic and Osteoblastic Bone Metastasis Models

¹⁸F-Fluciclovine (trans-1-amino-3-¹⁸F-fluorocyclobutanecarboxylic acid; anti-¹⁸F-FACBC) is a positron emission tomography (PET) tracer for diagnosing cancers (e.g., prostate and breast cancer). The most frequent metastatic organ of these cancers is bone. Fluciclovine-PET can visualize bony lesions in clinical practice; however, such lesions have not been described histologically. Methods: We investigated the potential of ¹⁴C-fluciclovine in aiding the visualization of osteolytic and osteoblastic bone metastases (with histological analyses), compared with ³H-2-deoxy-2-fluoro-D-glucose (³H-FDG), ³H-choline chloride (³H-choline), and ^99mTc-hydroxymethylene diphosphonate (^99mTc-HMDP) by using triple-tracer autoradiography in rat breast cancer osteolytic (on day 12 ± 1 postinjection of MRMT-1) and prostate cancer osteoblastic (on day 20 ± 3 postinjection of AT6.1) metastatic models. Results: The distribution patterns of ¹⁴C-fluciclovine, ³H-FDG, and ³H-choline, but not ^99mTc-HMDP, were similar in both models, and the lesions where these tracers accumulated were, histologically, typical osteolytic and osteoblastic lesions. ^99mTc-HMDP accumulated mostly in osteoblastic lesions. ¹⁴C-fluciclovine could visualize the osteolytic lesions as early as day 6 postinjection of MRMT-1. However, differential distributions in ¹⁴C-fluciclovine and ³H-FDG existed, based on histological differences: low ¹⁴C-fluciclovine and high ³H-FDG accumulation in osteolytic lesions with inflammation. In the osteoblastic metastatic model, visualization of osteoblastic lesions with ¹⁴C-fluciclovine was not clear, yet clearer than with ³H-FDG. Although half of the osteoblastic lesions with ¹⁴C-fluciclovine accumulation showed negligible ³H-choline accumulation in comparison, they were histologically similar to lesions with marked ¹⁴C-fluciclovine and ³H-choline accumulation. Conclusion: These results suggest that fluciclovine-PET can visualize true osteolytic and osteoblastic bone metastatic lesions.

PET imaging of recurrent and metastatic prostate cancer with novel tracers

Early detection of recurrent prostate cancer (PCa) is of paramount importance to deliver prompt and accurate therapy reducing the chance of progression to metastatic disease. However, current imaging modalities such as conventional computed tomography, MRI and PET scanning do not provide sufficient sensitivity, especially at lower prostate-specific antigen values. Moreover, biological characterization of PCa has become increasingly important to provide patient-specific therapy and current imaging poorly characterizes disease aggressiveness. The current uprise of novel PET tracers in recurrent and metastatic PCa shows promising, yet variable sensitivities and specificities in detection, indicating the need for further studies. In this review, we highlight current and new PET tracers that have been developed to improve the detection of recurrent and metastatic PCa.

Biochemical and Pathophysiological Premises to Positron Emission Tomography With Choline Radiotracers

Choline is a quaternary ammonium base that represents an essential component of phospholipids and cell membranes. Malignant transformation is associated with an abnormal choline metabolism at a higher levels with respect to those exclusively due to cell multiplication. The use of Positron Emission Tomography/Computed Tomography (PET/CT) with radiocholine (RCH), labeled with ¹¹ C or ¹⁸ F, is widely diffuse in oncology, with main reference to restaging of patients with prostate cancer. The enhanced concentration in neoplasm is based not only on the increasing growing rate, but also on more specific issues, such as the augmented uptake in malignant cells due to the up-regulation of choline kinase. Furthermore the role of hypoxia in decreasing choline's uptake determine an in vivo concentration only in well oxygenated tumors, with a lower uptake when malignancy increases, that is, in tumors positive at ¹⁸ F-Fluoro-deoxyglucose. In this paper we have analyzed the most important issues related to the possible utilization of RCH in diagnostic imaging of human cancer. J. Cell. Physiol. 232: 270-275, 2017. © 2016 Wiley Periodicals, Inc.

Evaluation of Bone Metastases by 18F-Choline PET/CT in a Patient with Castration-Resistant Prostate Cancer Treated with Radium-223

Background

To date, bone metastases remain the main cause of morbidity and mortality in patients with metastatic castration-resistant prostate cancer (mCRPC). Therefore, the combination of accurate early detection of bony disease and effective treatment of these lesions is crucial in the management of mCRPC patients, but clinical trials specifically designed to test novel approaches are currently lacking.

Case Description

This report describes the case of a 74-year-old male with bone mCRPC and symptomatic and biochemical progression, who underwent radium-223 therapy, following previous treatment failure. 18F-choline positron emission tomography (PET)/computed tomography (CT) was used to assess changes in skeletal tumor activity before and after radium-223. Changes in prostate-specific antigen and alkaline phosphatase were also determined. 18F-choline PET/CT showed that treatment with radium-223 was able to effectively reduce bone metastatic disease, and this was accompanied by an excellent metabolic response.

Conclusions

In clinical practice, metabolic assessment of lesions by 18F-choline PET/CT following radium-223 seems a valid approach to monitor treatment response. Until results from clinical trials become available, reporting of single cases relating to data on the use of this technique remains paramount.