Composite Prediction Score to Interpret Bone Focal Uptake in Hormone-Sensitive Prostate Cancer Patients Imaged with [18F]PSMA-1007 PET/CT.

Unspecific bone uptake (UBU) related to [18F]PSMA-1007 PET/CT imaging represents a clinical challenge. We aimed to assess whether a combination of clinical, biochemical, and imaging parameters could predict skeletal metastases in patients with [18F]PSMA-1007 bone focal uptake, aiding in result interpretation. Methods: We retrospectively analyzed [18F]PSMA-1007 PET/CT performed in hormone-sensitive prostate cancer (PCa) patients at 3 tertiary-level cancer centers. A fourth center was involved in performing an external validation. For each, a volume of interest was drawn using a threshold method to extract SUVmax, SUVmean, PSMA tumor volume, and total lesion PSMA. The same volume of interest was applied to CT images to calculate the mean Hounsfield units (HUmean) and maximum Hounsfield units. Clinical and laboratory data were collected from electronic medical records. A composite reference standard, including follow-up histopathology, biochemistry, and imaging data, was used to distinguish between PCa bone metastases and UBU. PET readers with less (n = 2) or more (n = 2) experience, masked to the reference standard, were asked to visually rate a subset of focal bone uptake (n = 178) as PCa metastases or not. Results: In total, 448 bone [18F]PSMA-1007 focal uptake specimens were identified in 267 PCa patients. Of the 448 uptake samples, 188 (41.9%) corresponded to PCa metastases. Ongoing androgen deprivation therapy at PET/CT (P < 0.001) with determination of SUVmax (P < 0.001) and HUmean (P < 0.001) independently predicted bone metastases. A composite prediction score, the bone uptake metastatic probability (BUMP) score, achieving an area under the receiver-operating-characteristic curve (AUC) of 0.87, was validated through a 10-fold internal and external validation (n = 89 bone uptake, 51% metastatic; AUC, 0.92). The BUMP score's AUC was significantly higher than that of HUmean (AUC, 0.62) and remained high among lesions with HUmean in the first tertile (AUC, 0.80). A decision-curve analysis showed a higher net benefit with the score. Compared with the visual assessment, the BUMP score provided added value in terms of specificity in less-experienced PET readers (88% vs. 54%, P < 0.001). Conclusion: The BUMP score accurately distinguished UBU from bone metastases in PCa patients with [18F]PSMA-1007 focal bone uptake at PET imaging, offering additional value compared with the simple assessment of the osteoblastic CT correlate. Its use could help clinicians interpret imaging results, particularly those with less experience, potentially reducing the risk of patient overstaging.

The Glucose-Glutamine Metabolic Interplay in MCF-7 Cells, a Hormone-Sensitive Breast Cancer Model.

BACKGROUND: Selective deprivation of glutamine has been shown to accelerate the generation of reactive oxygen species (ROS) and to impair the activity of a specific pentose phosphate pathway (PPP) located within the endoplasmic reticulum (ER). The consequent oxidative damage suggests that glucose flux through this reticular pathway might contribute to the redox stress of breast cancer cells. We thus evaluated whether this response is reproduced when the glutamine shortage is coupled with the glucose deprivation. METHODS: Cancer growth, metabolic plasticity and redox status were evaluated under saturating conditions and after 48 h starvation (glucose 2.5 mM, glutamine 0.5 mM). The Seahorse technology was used to estimate adenosine triphosphate (ATP)-linked and ATP-independent oxygen consumption rate (OCR) as well as proton efflux rate (PER). 18F-fluoro-deoxy-glucose (FDG) uptake was evaluated through the LigandTracer device. Proliferation rate was estimated by the carboxyfluorescein-diacetate-succinimidyl ester (CFSE) staining, while cell viability by the propidium iodide exclusion assay. RESULTS: Starvation reduced the proliferation rate of MCF-7 cells without affecting their viability. It also decreased lactate release and PER. Overall OCR was left unchanged although ATP-synthase dependent fraction was increased under nutrient shortage. Glutaminolysis inhibition selectively impaired the ATP-independent and the oligomycin-sensitive OCR in control and starved cultures, respectively. The combined nutrient shortage decreased the cytosolic and mitochondrial markers of redox stress. It also left unchanged the expression of the reticular unfolded protein marker GRP78. By contrast, starvation decreased the expression of hexose-6P-dehydrogenase (H6PD) thus decreasing the glucose flux through the ER-PPP as documented by the profound impairment in the uptake rate of FDG. CONCLUSIONS: When combined with glucose deprivation, glutamine shortage does not elicit the expected enhancement of ROS generation in the studied breast cancer cell line. Combined with the decreased activity of ER-PPP, this observation suggests that glutamine interferes with the reticular glucose metabolism to regulate the cell redox balance.

Divergent Oxidative Stress in Normal Tissues and Inflammatory Cells in Hodgkin and Non-Hodgkin Lymphoma.

BACKGROUND: Previous studies reported mitochondrial and endoplasmic reticulum redox stress in peripheral blood mononucleated cells (PBMCs) of treatment-naïve Hodgkin lymphoma (HL) patients. Here, we assessed whether this response also applies to non-HL (NHL) patients, and whether the oxidative damage is a selective feature of PBMCs or, rather, also affects tissues not directly involved in the inflammatory response. METHODS: Isolated PBMCs of 28 HL, 9 diffuse large B cell lymphoma, 8 less aggressive-NHL, and 45 controls underwent flow cytometry to evaluate redox stress and uptake of the glucose analogue 2-NBDG. This analysis was complemented with the assay of malondialdehyde (MDA) levels and enzymatic activity of glucose-6P-dehydrogenase and hexose-6P-dehydrogenase (H6PD). In all lymphoma patients, 18F-fluoro-deoxyglucose uptake was estimated in the myocardium and skeletal muscles. RESULTS: Mitochondrial reactive oxygen species generation and MDA levels were increased only in HL patients as well as H6PD activity and 2-NBDG uptake. Similarly, myocardial FDG retention was higher in HL than in other groups as opposed to a similar tracer uptake in the skeletal muscle. CONCLUSIONS: Redox stress of PBMCs is more pronounced in HL with respect to both NHL groups. This phenomenon is coherent with an increased activity of H6PD that also extends to the myocardium.

Combined forced diuresis and late acquisition on [68Ga]Ga-PSMA-11 PET/CT for biochemical recurrent prostate cancer: a clinical practice-oriented study.

OBJECTIVES: Increased detection of prostate cancer (PCa) recurrences using [68Ga]Ga-PSMA-11 PET/CT has been reported by adding forced diuresis or late-phase imaging to the standard protocol. However, the combination of these procedures in the clinical setting is still not standardized. METHODS: One hundred prospectively recruited biochemical recurrent PCa patients were restaged with dual-phase [68Ga]Ga-PSMA-11 PET/CT from September 2020 to October 2021. All patients received a standard scan (60 min), followed by diuretics (140 min) and a late-phase abdominopelvic scan (180 min). PET readers with low (n = 2), intermediate (n = 2), or high (n = 2) experience rated (i) standard and (ii) standard + forced diuresis late-phase images in a stepwise fashion according to E-PSMA guidelines, scoring their level of confidence. Study endpoints were (i) accuracy against a composite reference standard, (ii) reader's confidence level, and (iii) interobserver agreement. RESULTS: Forced diuresis late-phase imaging increased the reader's confidence category for local and nodal restaging (both p < 0.0001), and the interobserver agreement in identifying nodal recurrences (from moderate to substantial, p < 0.01). However, it significantly increased diagnostic accuracy exclusively for local uptakes rated by low-experienced readers (from 76.5 to 84%, p = 0.05) and for nodal uptakes rated as uncertain at standard imaging (from 68.1 to 78.5%, p < 0.05). In this framework, SUVmax kinetics resulted in an independent predictor of PCa recurrence compared to standard metrics, potentially guiding the dual-phase PET/CT interpretation. CONCLUSIONS: The present results do not support the systematic combination of forced diuresis and late-phase imaging in the clinical setting, but allow the identification of patients-, lesions-, and reader-based scenarios that might benefit from it. KEY POINTS: • Increased detection of prostate cancer recurrences has been reported by adding diuretics administration or an additional late abdominopelvic scan to the standard [68Ga]Ga-PSMA-11 PET/CT procedure. • We verified the added value of combined forced diuresis and delayed imaging, showing that this protocol only slightly increases the diagnostic accuracy of [68Ga]Ga-PSMA-11 PET/CT, thus not justifying its systematic use in clinics. • However, it can be helpful in specific clinical scenarios, e.g., when PET/CT is reported by low-experienced readers. Moreover, it increased the reader's confidence and the agreement among observers.

Gene's expression underpinning the divergent predictive value of [18F]F-fluorodeoxyglucose and prostate-specific membrane antigen positron emission tomography in primary prostate cancer: a bioinformatic and experimental study.

BACKGROUND: Positron Emission Tomography (PET) imaging with Prostate-Specific Membrane Antigen (PSMA) and Fluorodeoxyglucose (FDG) represent promising biomarkers for risk-stratification of Prostate Cancer (PCa). We verified whether the expression of genes encoding for PSMA and enzymes regulating FDG cellular uptake are independent and additive prognosticators in PCa. METHODS: mRNA expression of genes involved in glucose metabolism and PSMA regulation obtained from primary PCa specimens were retrieved from open-source databases and analyzed using an integrative bioinformatics approach. Machine Learning (ML) techniques were used to create predictive Progression-Free Survival (PFS) models. Cellular models of primary PCa with different aggressiveness were used to compare [18F]F-PSMA-1007 and [18F]F-FDG uptake kinetics in vitro. Confocal microscopy, immunofluorescence staining, and quantification analyses were performed to assess the intracellular and cellular membrane PSMA expression. RESULTS: ML analyses identified a predictive functional network involving four glucose metabolism-related genes: ALDOB, CTH, PARP2, and SLC2A4. By contrast, FOLH1 expression (encoding for PSMA) did not provide any additive predictive value to the model. At a cellular level, the increase in proliferation rate and migratory potential by primary PCa cells was associated with enhanced FDG uptake and decreased PSMA retention (paralleled by the preferential intracellular localization). CONCLUSIONS: The overexpression of a functional network involving four glucose metabolism-related genes identifies a higher risk of disease progression since the earliest phases of PCa, in agreement with the acknowledged prognostic value of FDG PET imaging. By contrast, the prognostic value of PSMA PET imaging is independent of the expression of its encoding gene FOLH1. Instead, it is influenced by the protein docking to the cell membrane, regulating its accessibility to tracer binding.

Oligometastatic Prostate Cancer Treated with Metastasis-Directed Therapy Guided by Positron Emission Tomography: Does the Tracer Matter?

The superior diagnostic accuracy of [68Ga]Ga-prostate-specific membrane antigen-11 (PSMA) ([68Ga]Ga-PSMA-11) compared to [18F]F-Fluorocholine Positron Emission Tomography/Computed Tomography (PET/CT) in Prostate Cancer (PCa) is established. However, it is currently unclear if the added diagnostic accuracy actually translates into improved clinical outcomes in oligometastatic PCa patients treated with [68Ga]Ga-PSMA-11 PET-guided metastasis-directed therapy (MDT). The present study aimed to assess the impact of these two imaging techniques on Progression-Free Survival (PFS) in a real-world sample of oligometastatic PCa patients submitted to PET-guided MDT. Thirty-seven oligometastatic PCa patients treated with PET-guided MDT were retrospectively enrolled. MDT was guided by [18F]F-Fluorocholine PET/CT in eleven patients and by [68Ga]Ga-PSMA-11 PET/CT in twenty-six. Progression was defined as biochemical recurrence (BR), radiological progression at subsequent PET/CT imaging, clinical progression, androgen deprivation therapy initiation, or death. Clinical and imaging parameters were assessed as predictors of PFS. [18F]F-Fluorocholine PET-guided MDT was associated with significantly lower PFS compared to the [68Ga]Ga-PSMA-11 group (median PFS, mPFS 15.47 months, 95% CI: 4.13−38.00 vs. 40.93 months, 95% CI: 40.93−40.93, respectively; p < 0.05). Coherently, the radiotracer used for PET-guided MDT resulted in predictive PFS at the univariate analysis, as well as the castration-resistant status at the time of MDT and the PSA nadir after MDT. However, in the multivariate analysis, castration resistance and PSA nadir after MDT remained the sole independent predictors of PFS. In conclusion, in the present proof-of-concept study, [68Ga]Ga-PSMA-11 provided higher PFS rates than [18F]F-Fluorocholine imaging in oligometastatic PCa patients receiving PET-guided MDT. Although preliminary, this finding suggests that enlarging the "tip of the iceberg", by detecting a major proportion of the submerged disease thanks to next-generation imaging may favourably impact the oncological outcome of oligometastatic PCa treated with MDT.

Fundamental Role of Pentose Phosphate Pathway within the Endoplasmic Reticulum in Glutamine Addiction of Triple-Negative Breast Cancer Cells.

Cancer utilization of large glutamine equivalents contributes to diverging glucose-6-P flux toward the pentose phosphate shunt (PPP) to feed the building blocks and the antioxidant responses of rapidly proliferating cells. In addition to the well-acknowledged cytosolic pathway, cancer cells also run a largely independent PPP, triggered by hexose-6P-dehydrogenase within the endoplasmic reticulum (ER), whose activity is mandatory for the integrity of ER-mitochondria networking. To verify whether this reticular metabolism is dependent on glutamine levels, we complemented the metabolomic characterization of intermediates of the glucose metabolism and tricarboxylic acid cycle with the estimation of proliferating activity, energy metabolism, redox damage, and mitochondrial function in two breast cancer cell lines. ER-PPP activity and its determinants were estimated by the ER accumulation of glucose analogs. Glutamine shortage decreased the proliferation rate despite increased ATP and NADH levels. It depleted NADPH reductive power and increased malondialdehyde content despite a marked increase in glucose-6P-dehydrogenase. This paradox was explained by the deceleration of ER-PPP favored by the decrease in hexose-6P-dehydrogenase expression coupled with the opposite response of its competitor enzyme glucose-6P-phosphatase. The decreased ER-PPP activity eventually hampered mitochondrial function and calcium exchanges. These data configure the ER-PPP as a powerful, unrecognized regulator of cancer cell metabolism and proliferation.

Changes over the years in radiopharmaceutical design.

Of the many uses of radiopharmaceuticals, developing radiotracers that contribute significantly to diagnosis and therapy of patients has been a major focus. This requires a broad spectrum of expertise including that of the attending physician who lends insight to an unmet clinical need neither addressed by other imaging techniques nor by analysis of tissue, blood, and urine for diagnostics and addressed by pharmaceuticals for therapeutic applications. The design criteria have depended on radiochemistry, on matching the radiopharmaceutical with the imaging devices, and basing the design on current pharmaceuticals. The chelates of technetium-99m were based on radiochemistry rather than clinical need yet are still used today in >70% of the clinical studies. Targeted radiotracers in neurologic and psychiatric disorders, inflammation, cardiovascular disease, and oncology have all been studied with the goal of determining the change in the density of a target protein as a function of disease or treatment or, especially in oncology, detection of the total extent of disease. In the latter approach, PET in university settings leads the way; however, the use of SPECT/CT has increased the specificity of SPECT imaging to complement the cost-effective generator and instant kits already available. Remarkable advances have been achieved in radionuclide therapy using theragnostic agents, with the exclusive domain of oncology. For this application the design of radionuclide therapy follows that used for diagnostics. The increased impact of the discipline depends on the opportunity to continue the search for the most appropriate radiopharmaceutical for each individual patient.

Concomitant Prostate Cancer and Hodgkin Lymphoma: A Differential Diagnosis Guided by a Combined 68Ga-PSMA-11 and 18F-FDG PET/CT Approach.

Here we report the case of concomitant favorable-risk prostate cancer and Hodgkin Lymphoma in a 38-year old male. 68Ga-Prostate Specific Membrane Antigen-11 Positron Emission Tomography/Computed Tomography (68Ga-PSMA-11 PET/CT) was performed for staging purposes, showing the focal PSMA prostatic uptake as well as the presence of enlarged low-PSMA expressing mediastinal lymphadenopathies, thus raising the suspicion of another malignancy. A subsequent 18F-Fluorodeoxyglucose (18F-FDG) PET/CT demonstrated a high FDG-avidity by mediastinal lymphadenopathies as opposed to the low prostate cancer FDG uptake. Of note, both tumor entities were clearly detected by the two scans. However, different ranges in terms of Maximum Standardized Uptake Value (SUVmax) uptake allowed the discrimination between the two tumor entities. At the subsequent mediastinal lymph nodal biopsy, the coexistence of Hodgkin lymphoma was documented. The present case suggests that even if specific for prostate cancer, 68Ga-PSMA-11 PET/CT may raise the suspicion of other concurrent malignancies thanks to its non-receptor bounding mechanism. Further, it shows that in certain cases, the combination of 18F-FDG and 68Ga-PSMA PET/CT imaging may non-invasively guide the clinical management, optimizing the diagnostic process and the subsequent therapeutic interventions.

Toward the Discovery and Development of PSMA Targeted Inhibitors for Nuclear Medicine Applications.

BACKGROUND: The rising incidence rate of prostate cancer (PCa) has promoted the development of new diagnostic and therapeutic radiopharmaceuticals during the last decades. Promising improvements have been achieved in clinical practice using prostate specific membrane antigen (PSMA) labeled agents, including specific antibodies and small molecular weight inhibitors. Focusing on molecular docking studies, this review aims to highlight the progress in the design of PSMA targeted agents for a potential use in nuclear medicine. RESULTS: Although the first development of radiopharmaceuticals able to specifically recognize PSMA was exclusively oriented to macromolecule protein structure such as radiolabeled monoclonal antibodies and derivatives, the isolation of the crystal structure of PSMA served as the trigger for the synthesis and the further evaluation of a variety of low molecular weight inhibitors. Among the nuclear imaging probes and radiotherapeutics that have been developed and tested till today, labeled Glutamate-ureido inhibitors are the most prevalent PSMA-targeting agents for nuclear medicine applications. CONCLUSION: PSMA represents for researchers the most attractive target for the detection and treatment of patients affected by PCa using nuclear medicine modalities. [99mTc]MIP-1404 is considered the tracer of choice for SPECT imaging and [68Ga]PSMA-11 is the leading diagnostic for PET imaging by general consensus. [18F]DCFPyL and [18F]PSMA-1007 are clearly the emerging PET PSMA candidates for their great potential for a widespread commercial distribution. After paving the way with new imaging tools, academic and industrial R&Ds are now focusing on the development of PSMA inhibitors labeled with alpha or beta minus emitters for a theragnostic application.

11C-choline PET/CT predicts survival in prostate cancer patients with PSA < 1 NG/ml.

PURPOSE: The main drawback of 11C-choline PET/CT for restaging prostate cancer (PCa) patients with biochemical failure is the relatively low positive detection rate for prostate specific antigen (PSA) < 1 ng/ml. This study assessed whether 11C-choline PET/CT predicts survival in PCa patients with PSA < 1 ng/ml. METHODS: This retrospective study included 210 PCa patients treated with radical prostatectomy who underwent 11C-choline PET/CT from December 1, 2004 to July 31, 2007 due to biochemical failure. PCa-specific survival was estimated using Kaplan-Meier curves. Cox regression analysis was used to evaluate the association between clinicopathologic variables and PCa-specific survival. PCa-specific survival was computed as the interval from radical prostatectomy to PCa-specific death. RESULTS: Median follow-up after radical prostatectomy was 6.9 years (95% confidence interval, CI, 2.0-14.5 years). 11C-choline PET/CT was positive in 20.5% of patients. Median PCa-specific survival was 13.4 years (95% CI, 9.9-16.8 years) in patients with positive 11C-choline PET/CT, and it was not achieved in patients with negative 11C-choline PET/CT (log-rank, chi-square = 15.0, P < 0.001). Ten-year survival probabilities for patients with negative 11C-choline PET/CT and for patients with positive 11C-choline PET/CT were 86.0% (95% CI: 80.7%-91.3%) and 63.6% (95% CI: 54.5-72.7%). At multivariate analysis, only 11C-choline PET/CT significantly predicted PCa-specific survival (hazard ratio = 2.54, 95% CI, 1.05-6.13, P = 0.038). Patients with pathological 11C-choline uptake in the prostatic bed or in pelvic lymph nodes had longer PCa-specific survival in comparison to patients with pathological tracer uptake in the skeleton (log-rank: chi-square = 27.4, P < 0.001). CONCLUSION: Despite the relatively low positive detection rate for PSA < 1 ng/ml, positive 11C-choline PET/CT predicts PCa-specific survival in this low PSA range. As long as more sensitive radiotracers, such as 68Ga-PSMA-11, do not become more widely available, these results might support a broader use of radiolabeled choline in restaging PCa for PSA < 1 ng/ml.

Sensitivity of fluorine-18-fluoromethylcholine PET/CT to prostate-specific antigen over different plasma levels: a retrospective study in a cohort of 192 patients with prostate cancer.

PURPOSE: Several factors have been identified that predict positive fluorine-18-fluoromethylcholine (F-FCH) PET/CT result in patients with prostate cancer undergoing PET/CT for biochemical failure. Among these factors, prostate-specific antigen (PSA) is the single factor most consistently associated with the prediction of positive F-FCH PET/CT. In this study, we wished to confirm this finding and expand it in a large series of patients. PATIENTS AND METHODS: We retrospectively analyzed 192 patients with prostate cancer who were recruited from the Nuclear Medicine Department of the Sant'Andrea Hospital of La Spezia, Italy, from March 2013 to March 2018 and who underwent F-FCH PET/CT owing to biochemical failure after radical prostatectomy. RESULTS: Median trigger PSA was 2.57 ng/ml. The overall positive detection rate of F-FCH PET/CT was 60.9%. The percent of positive scans was 30.5% for PSA less than 1 ng/ml, 59.4% (38/64) for PSA between 1 and 5 ng/ml, and 88.4% for PSA greater than 5 ng/ml (P<0.001). On univariate regression analysis, high PSA levels, biochemical failure during antiandrogenic therapy at the time of PET/CT, and older age significantly (P<0.05) predicted positive F-FCH PET/CT result. On multivariate regression analysis, only high PSA levels and biochemical failure during antiandrogenic therapy maintained the statistical significance (P<0.05). However, when the analysis was restricted to patients with PSA less than 1 ng/ml, PSA lost the statistical significance. Receiver operating characteristic analysis revealed an area under the curve of 0.795. The PSA cutoff value that best distinguished PET/CT-positive from PET/CT-negative patients was 2.57 ng/ml. Sensitivity and specificity at this PSA value were 66.7 and 76.0%, respectively. CONCLUSION: This study confirms that PSA robustly predicts positive PET/CT result with radiolabeled choline. Unfortunately, this study also confirms the limited sensitivity of F-FCH PET/CT for PSA less than 1 ng/ml, which currently represents the weakest point of the technique.

[68Ga]-Dota Peptide PET/CT in Neuroendocrine Tumors: Main Clinical Applications.

OBJECTIVE: Neuroendocrine Neoplasms (NENs) are generally defined as rare and heterogeneous tumors. The gastrointestinal system is the most frequent site of NENs localization, however they can be found in other anatomical regions, such as pancreas, lungs, ovaries, thyroid, pituitary, and adrenal glands. Neuroendocrine neoplasms have significant clinical manifestations depending on the production of active peptide. METHODS: Imaging modalities play a fundamental role in initial diagnosis as well as in staging and treatment monitoring of NENs, in particular they vastly enhance the understanding of the physiopathology and diagnosis of NENs through the use of somatostatin analogue tracers labeled with appropriate radioisotopes. Additionally, the use of somatostatin analogues provides the ability to in-vivo measure the expression of somatostatin receptors on NEN cells, a process that might have important therapeutic implications. RESULTS: A large body of evidences showed improved accuracy of molecular imaging based on PET/CT radiotracer with SST analogues (e.g. [68Ga]-DOTA peptide) for the detection of NEN lesions in comparison to morphological imaging modalities. So far, the role of imaging technologies in assessing treatment response is still under debate. CONCLUSION: This review offers the systems of classification and grading of NENs and summarizes the more useful recommendations based on data recently published for the management of patients with NENs, with special focus on the role of imaging modalities based on SST targeting with PET / CT radiotracers.

PET/CT With 68Ga-PSMA in Prostate Cancer: Radiopharmaceutical Background and Clinical Implications.

BACKGROUND AND OBJECTIVE: In the last twenty years, positron emission tomography / computed tomography (PET/CT) with radiolabeled choline, represented the most powerful imaging modality for prostate cancer (PCa). However, the low positive detection rate of the technique for PSA < 1 ng/ml prompted the development of other tracers for imaging PCa. METHODS: We performed a critical review of 68Ga-PSMA, a receptor ligand tracer, which has been identified as the most promising radiopharmaceutical for imaging PCa. RESULTS: The most promising feature of this radiopharmaceutical is the high positive detection rate for prostate specific antigen (PSA) levels < 1 ng/ml or less (i.e., PSA < 0.5 ng/ml). 68Ga-PSMA detection rate is also sensitive to PSA kinetics, expressed either as PSA doubling time or PSA velocity. There are initial results indicating that 68Ga-PSMA may significantly affect the clinical management of PCa patients, even though the additional advantages in comparison to radiolabeled choline need to be further supported in future perspective studies. Other clinical implications, such as whether 68Ga-PSMA PET/CT predicts PCa-specific survival, have not yet been investigated. Numerous clinical studies have been published, some of them with histopathological verification so that despite the recent introduction in the clinical field reliable estimation of sensitivity and specificity of 68Ga-PSMA PET/CT have been obtained through meta-analyses. Most clinical studies with PET/CT with 68Ga-PSMA are retrospective, single-institutional studies and in many cases include heterogeneous patient cohorts. Thus, multidisciplinary, well-throughout prospective trials are needed to better define the clinical implications of 68Ga- PSMA PET/CT in PCa patients. The increasing availability of positron emission tomography / magnetic resonance (PET/MR) hybrid devices promotes the use of this radiopharmaceutical especially at initial staging when identification of tumor localization and of extra-prostatic disease represent clinically relevant questions. PSMA cold ligands can also be labeled with beta emitters with good chemical stability so that 68Ga-PSMA PET/CT can be used to guide radiometabolic therapy of advanced metastatic PCa patients through 177Lu-labeled PSMA ligands. CONCLUSION: PSMA labeled ligands appear very promising for diagnosis and treatment of PCa.

PET/MR Tomographs: A Review with Technical, Radiochemical and Clinical Perspectives.

BACKGROUND AND OBJECTIVE: In the last decade, an increasing number of positron emission tomography / magnetic resonance (PET/MR) tomographs were installed and many clinical studies were performed in the neurological field. METHODS: Although PET/MR has many favorable properties to support the application in brain imaging, attenuation correction, and therefore accurate quantification, is a problem that still requires optimal solution. RESULTS: In this review we have summarized the three main methods that are currently used to correct attenuation in PET/MR, namely atlas- or template-based methods, segmentation-based methods, and reconstruction-based methods. There is currently active ongoing research to refine available methods and improvements are reasonably expected in the next years. Clinical studies using PET/MR focused mainly on neurodegenerative and neurooncological disorders. PET/MR hybrids tomographs provided promising scientific results and were logistically more convenient for patients. Additionally, in order to explore all potential clinical benefits of this hybrid technology, the design and development of multimodal contrast agents has constantly increased the attention of radiochemists. Many PET/MR dual probes have been already devised, particularly in the nanotechnology field, sometimes preceding the identification of a clear diagnostic application in medicine. CONCLUSION: In the near future, we predict more clinical studies as the availability of PET/MR will further increase and new tracers for neurodegenerative disorders will accept broader clinical acceptance.

PET and PET/CT with radiolabeled choline in prostate cancer: a critical reappraisal of 20 years of clinical studies.

We here aim to provide a comprehensive and critical review of the literature concerning the clinical applications of positron emission tomography/computed tomography (PET/CT) with radiolabeled choline in patients with prostate cancer (PCa). We will initially briefly summarize the historical context that brought to the synthesis of [11C]choline, which occurred exactly 20 years ago. We have arbitrarily grouped the clinical studies in three different periods, according to the year in which they were published and according to their relation with their applications in urology, radiotherapy and oncology. Studies at initial staging and, more extensively, studies in patients with biochemical failure, as well as factors predicting positive PET/CT will be reviewed. The capability of PET/CT with radiolabeled choline to provide prognostic information on PCa-specific survival will also be examined. The last sections will be devoted to the use of radiolabeled choline for monitoring the response to androgen deprivation therapy, radiotherapy, and chemotherapy. The accuracy and the limits of the technique will be discussed according to the information available from standard validation processes, including biopsy or histology. The clinical impact of the technique will be discussed on the basis of changes induced in the management of patients and in the evaluation of the response to therapy. Current indications to PET/CT, as officially endorsed by guidelines, or as routinely performed in the clinical practice will be illustrated. Emphasis will be made on methodological factors that might have influenced the results of the studies or their interpretation. Finally, we will briefly highlight the potential role of positron emission tomography/magnetic resonance and of new radiotracers for PCa imaging.

Radiopharmaceuticals for the Diagnosis and Therapy of Neuroendocrine Differentiated Prostate Cancer.

Neuroendocrine differentiation of prostate cancer (PCa) is a relatively frequent event, generally understudied, that carries important prognostic information. It is the most frequently observed during the advanced stages of disease, when PCa has lost its sensitivity to androgen deprivation therapy or to chemotherapy, moderate to diffuse bone metastatic spread dominates the imaging scenario and it is responsible for painful clinical symptomatology. However, evidences indicate that neuroendocrine differentiation is a progressive phenomenon that starts at the very early part of the pathogenesis of cancer transformation contributing to it. Neuroendocrine tumor phenotypes have reduced capability to secrete the prostate specific antigen (PSA) and therefore PSA does not represent a reliable marker to follow-up neuroendocrine differentiation. Tumor progression may be monitored by measuring plasma concentration of neuroendocrine tumor markers, primarily chromogranin A and neuron-specific enolase. Several nuclear medicine tracers are available for studying different biochemical properties of tumor cells with neuroendocrine differentiation. Single photon computed emission tomography (SPECT) with [111In-diethylenetriaminepentaacetic acid] ([111In-DTPA0])- octreotide (Octreoscan) has been extensively used in the past. However, the development of the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), which in comparison to DTPA allows higher affinity bindings for beta-emitting radionuclides and for somatostatin (SST) analogues, and the increased availability of the Germanium-68/Gallium-68 (68Ge/68Ga)-generator, which enables positron emission tomography/computed tomography (PET/CT) imaging, have allowed the synthesis of several PET tracers for different SST receptors. The receptor of the bombesin/ gastrin releasing peptide (GRP), which is overexpressed in PCa with neuroendocrine differentiation, also represents an innovative research field with diagnostic and therapeutic applications through, respectively, positron and beta emitters. At the moment, however, we observe some discrepancy between the high number of preclinical studies and the small number of clinical studies, most likely related to competing and, at the moment, more effective radiopharmaceuticals for imaging and for radiometabolic therapy, such PET/CT with radiolabeled choline and prostate-specific membrane antigene (PSMA)-ligands, the latter being labeled either with 68Ga for imaging or with Lutetium-177 for therapy. Radium-223 dichloride has also been recently successfully introduced for palliative therapy of bone metastases in PCa. For these reasons, while the development of radiopharmaceuticals for diagnosis and therapy (theranostics concept) of neuroendocrine differentiated PCa is scientifically stimulating, the ultimate clinical impact remains presently difficult to predict. Similar effectiveness in comparison to other forms of diagnostic and radiometabolic radiopharmaceuticals that have already gained convincing acceptance among referring clinicians needs to be demonstrated.

¹8F-NaF Uptake by Atherosclerotic Plaque on PET/CT Imaging: Inverse Correlation Between Calcification Density and Mineral Metabolic Activity.

UNLABELLED: Several studies have highlighted the role of vascular (18)F-NaF uptake as a marker of ongoing calcium deposition. However, accumulation of (18)F-NaF is often inconsistent with localization of arterial plaque. Calcification activity and thus (18)F-NaF uptake might prevail in the earlier plaque stages. To test this hypothesis, we evaluated (18)F-NaF uptake in plaque of 3 different densities, using density as a marker of calcification progression. We also tested whether attenuation-weighted image reconstruction affects (18)F-NaF uptake in the different plaque stages. METHODS: Sixty-four oncologic patients (14 men and 50 women; mean age, 65.3 ± 8.2 y; range, 26-81 y) underwent (18)F-NaF PET/CT. A volume of interest was drawn on each plaque within the infrarenal aorta to assess mean standardized uptake value and attenuation (in Hounsfield units [HU]). Plaque was then categorized as light (<210 HU), medium (211-510 HU), or heavy (>510 HU). Standardized uptake value was normalized for blood (18)F-NaF activity to obtain the plaque target-to-background ratio (TBR). During this process, several focal, noncalcified areas of (18)F-NaF were identified (hot spots). The TBR of the hot spots was computed after isocontour thresholding. The TBR of a noncalcified control region was also calculated. In 35 patients, the TBR of non-attenuation-corrected images was calculated. RESULTS: The average TBR was highest in light plaque (2.21 ± 0.88), significantly lower in medium plaque (1.59 ± 0.63, P < 0.001), and lower still in heavy plaque (1.14 ± 0.37, P < 0.0001 with respect to both light and medium plaque). The TBR of the control region was not significantly different from that of heavy plaque but was significantly lower than that of light and medium plaque (P < 0.01). Hot spots had the highest absolute TBR (3.89 ± 1.87, P < 0.0001 vs. light plaque). TBRs originating from non-attenuation-corrected images did not significantly differ from those originating from attenuation-corrected images. CONCLUSION: Our results support the concept that (18)F-NaF is a feasible option in imaging molecular calcium deposition in the early stages of plaque formation, when active uptake mechanisms are the main determinants of calcium presence, but that retention of (18)F-NaF progressively decreases with increasing calcium deposition in the arterial wall. Our data suggest that non-attenuation-corrected reconstruction does not significantly affect evaluation of plaque of any thickness.

Use of the uteroglobin platform for the expression of a bivalent antibody against oncofetal fibronectin in Escherichia coli.

Escherichia coli is a robust, economic and rapid expression system for the production of recombinant therapeutic proteins. However, the expression in bacterial systems of complex molecules such as antibodies and fusion proteins is still affected by several drawbacks. We have previously described a procedure based on uteroglobin (UG) for the engineering of very soluble and stable polyvalent and polyspecific fusion proteins in mammalian cells (Ventura et al. 2009. J. Biol. Chem. 284∶26646-26654.) Here, we applied the UG platform to achieve the expression in E. coli of a bivalent human recombinant antibody (L19) toward the oncofetal fibronectin (B-FN), a pan-tumor target. Purified bacterial L19-UG was highly soluble, stable, and, in all molecules, the L19 moiety maintained its immunoreactivity. About 50-70% of the molecules were covalent homodimer, however after refolding with the redox couple reduced-glutathione/oxidized-glutathione (GSH/GSSG), 100% of molecules were covalent dimers. Mass spectrometry studies showed that the proteins produced by E. coli and mammalian cells have an identical molecular mass and that both proteins are not glycosylated. L19-UG from bacteria can be freeze-dried without any loss of protein and immunoreactivity. In vivo, in tumor-bearing mice, radio-iodinated L19-UG selectively accumulated in neoplastic tissues showing the same performance of L19-UG from mammalian cells. The UG-platform may represent a general procedure for production of various biological therapeutics in E. coli.