Molecular Dynamics Simulations of Native Protein Charging via Proton Transfer during Electrospray Ionization with Grotthuss Diffuse H3O.

Unraveling the mechanism by which native proteins are charged through electrospray ionization (ESI) has been the focus of considerable research because observable charge states can be correlated to biophysical characteristics, such as protein folding and, thus, solution conformation. Difficulties in characterizing electrosprayed droplets have catalyzed the use of molecular dynamics (MD) to provide insights into the mechanisms by which proteins are charged and transferred to the gas phase. However, prior MD studies have utilized metal ions, primarily Na+, as charge carriers, even though proteins are primarily detected as protonated ions in the mass spectra. Here, we propose a modified MD protocol for simulating discrete Grotthuss diffuse H3O+ that is capable of dynamically altering amino-acid protonation states to model electrospray charging and gaseous ion formation of model proteins, ubiquitin, and myoglobin. Application of the protocol to the evaporation of acidic droplets enables a molecular perspective of H3O+ coordination and proton transfer to/from proteins, which is unfeasible with the metal charge carriers used in previous MD studies of ESI. Our protocol recreates experimentally observed charge-state distributions and supports the charge residue model (CRM) as the dominant mechanism of native protein ionization during ESI. Additionally, our results suggest that protonation is highly specific to individual residues and is correlated to the formation of localized hydrated regions on the protein surface as droplets desolvate. Considering the use of discrete H3O+ instead of Na+, the developed protocol is a necessary step toward developing a more comprehensive model of protein ionization during ESI.

Evidence of H/D Exchange within Metal-Adducted Carbohydrates after Ion/Ion-Dissociation Reactions.

Tandem mass spectrometry (MS/MS) using fragmentation has become one of the most effective methods for gaining sequence and structural information on biomolecules. Ion/ion reactions are competitive reactions, where either proton transfer (PT) or electron transfer (ET) can occur from interactions between multiply charged cations and singly charged anions. Utilizing ion/ion reactions with fluoranthene has offered a unique method of fragment formation for the structural elucidation of biomolecules. Fluoranthene is considered an ideal anion reagent because it selectively causes electron-transfer dissociation (ETD) and minimizes PT when interacting with peptides. However, limited investigations have sought to understand how fluoranthene─the primary, commercially available anion reagent─interacts with other biomolecules. Here, we apply deuterium labeling to investigate ion/ion reaction mechanisms between fluoranthene and divalent, metal-adducted carbohydrates (Ca2+, Mg2+, Co2+, and Ni2+). Deuterium labeling of carbohydrates allowed us to observe evidence of hydrogen/deuterium exchange (HDX) occurring after ion/ion dissociation reactions. The extent of deuterium loss is dependent on several factors, including the physical properties of the metal ion and the fragment structure. Based on the deuterium labeling data, we have proposed ETD, PTD, and intermolecular PT─also described as HDX─mechanisms. This research provides a fundamental perspective of ion/ion and ion/molecule reaction mechanisms and illustrates properties that impact ion/ion and ion/molecule reactions for carbohydrates. Together, this could improve the capability to distinguish complex and heterogeneous biomolecules, such as carbohydrates.

Gas-phase stability and thermodynamics of ligand-bound, binary complexes of chloramphenicol acetyltransferase reveal negative cooperativity.

The biological role of the bacterial chloramphenicol (Chl)-resistance enzyme, chloramphenicol acetyltransferase (CAT), has seen renewed interest due to the resurgent use of Chl against multi-drug-resistant microbes. This looming threat calls for more rationally designed antibiotic derivatives that have improved antimicrobial properties and reduced toxicity in humans. Herein, we utilize native ion mobility spectrometry-mass spectrometry (IMS-MS) to investigate the gas-phase structure and thermodynamic stability of the type I variant of CAT from Escherichia coli (EcCATI) and several EcCATI:ligand-bound complexes. EcCATI readily binds multiple Chl without incurring significant changes to its gas-phase structure or stability. A non-hydrolyzable acetyl-CoA derivative (S-ethyl-CoA, S-Et-CoA) was used to kinetically trap EcCATI and Chl in a ternary, ligand-bound state (EcCATI:S-Et-CoA:Chl). Using collision-induced unfolding (CIU)-IMS-MS, we find that Chl dissociates from EcCATI:S-Et-CoA:Chl complexes at low collision energies, while S-Et-CoA remains bound to EcCATI even as protein unfolding occurs. Gas-phase binding constants further suggest that EcCATI binds S-Et-CoA more tightly than Chl. Both ligands exhibit negative cooperativity of subsequent ligand binding in their respective binary complexes. While we observe no significant change in structure or stability to EcCATI when bound to either or both ligands, we have elucidated novel gas-phase unfolding and dissociation behavior and provided a foundation for further characterization of alternative substrates and/or inhibitors of EcCATI.

Disentangling inflammatory from fibrotic disease activity by fibroblast activation protein imaging.

OBJECTIVES: To date, there is no valuable tool to assess fibrotic disease activity in humans in vivo in a non-invasive way. This study aims to uncouple inflammatory from fibrotic disease activity in fibroinflammatory diseases such as IgG4-related disease. METHODS: In this cross-sectional clinical study, 27 patients with inflammatory, fibrotic and overlapping manifestations of IgG4-related disease underwent positron emission tomography (PET) scanning with tracers specific for fibroblast activation protein (FAP; 68Ga-FAP inhibitor (FAPI)-04), 18F-fluorodeoxyglucose (FDG), MRI and histopathological assessment. In a longitudinal approach, 18F-FDG and 68Ga-FAPI-04 PET/CT data were evaluated before and after immunosuppressive treatment and correlated to clinical and MRI data. RESULTS: Using combination of 68Ga-FAPI-04 and 18F-FDG-PET, we demonstrate that non-invasive functional tracking of IgG4-related disease evolution from inflammatory towards a fibrotic outcome becomes feasible. 18F-FDG-PET positive lesions showed dense lymphoplasmacytic infiltration of IgG4+ cells in histology, while 68Ga-FAPI-04 PET positive lesions showed abundant activated fibroblasts expressing FAP according to results from RNA-sequencing of activated fibroblasts. The responsiveness of fibrotic lesions to anti-inflammatory treatment was far less pronounced than that of inflammatory lesions. CONCLUSION: FAP-specific PET/CT permits the discrimination between inflammatory and fibrotic activity in IgG4-related disease. This finding may profoundly change the management of certain forms of immune-mediated disease, such as IgG4-related disease, as subtypes dominated by fibrosis may require different approaches to control disease progression, for example, specific antifibrotic agents rather than broad spectrum anti-inflammatory treatments such as glucocorticoids.

Correction to: Assessment of treatment responses in children and adolescents with Ewing sarcoma with metabolic tumor parameters derived from 18F-FDG-PET/CT and circulating tumor DNA.

The author names and family names of the originally published article was inversed. Correct presentation is presented here.

Assessment of treatment responses in children and adolescents with Ewing sarcoma with metabolic tumor parameters derived from 18F-FDG-PET/CT and circulating tumor DNA.

PURPOSE: The purpose of this study was to perform a prospective integrated analysis of 18F-fluorodeoxyglucose (18F-FDG)-positron emission tomography (PET)/computed tomography (CT) and circulating tumor DNA (ctDNA) to assess responses to multimodal chemotherapy in children and adolescents suffering from Ewing sarcoma (EwS). METHODS: A total of 20 patients with histologically confirmed EwS underwent multiple 18F-FDG-PET/CT, performed at the time of each patient's initial diagnosis and after the second and fifth induction chemotherapy block (EWING2008 treatment protocol, NCT00987636). Additional PET examinations were performed as clinically indicated in some patients, e.g., in patients suspected of having progressive or relapsing disease. All 263 18F-FDG-positive lesions in the field of view suggestive of tumor tissue were assessed quantitatively to calculate PET-derived parameters, including whole-body metabolic tumor volume (wb-MTV) and whole-body total lesion glycolysis (wb-TLG), as well as the following data: standardized uptake value (SUV)max and SUVmean. Tumor-specific ctDNA in patient plasma samples was quantified using digital droplet PCR (ddPCR), and the correlations between ctDNA levels and PET-derived parameters were analyzed. Metabolic responses to multimodal chemotherapy as assessed with PET-parameters were compared to biochemical responses as assessed with changes in ctDNA levels. RESULTS: Twenty patients underwent a total of 87 18F-FDG-PET/CT scans, which detected 263 FDG-positive tumor lesions. Significant correlations between SUVmax, SUVmean, wb-MTV and wb-TLG values, and ctDNA levels were observed (all p < 0.0001). All patients suffering from EwS, with histology serving as gold standard, also presented with a positive corresponding ctDNA sample and a positive 18F-FDG-PET/CT examination before initiation of therapy. There were no false-negative results. Evaluation of treatment response after the fifth block of induction chemotherapy showed that the agreement between the metabolic response and biochemical response was 90%, which was statistically significant (Cohen κ = 0.62; p < 0.05). Non-detectable ctDNA after the second block of induction chemotherapy was associated with complete biochemical and metabolic responses after the fifth block of induction chemotherapy in 16/17 patients (94%). During a median follow-up period of 36 months (range: 8-104 months), four patients had tumor relapses, which, in all cases, were accompanied by an increase in plasma ctDNA levels and a positive 18F-FDG-PET/CT. No false-negative results were observed in the study cohort. Complete biochemical and metabolic responses after the fifth block of induction chemotherapy had a high positive predictive value for disease remission during the follow-up period; specifically, the positive predictive value was 88%. CONCLUSION: The combination of 18F-FDG-PET/CT and ctDNA quantification is a very promising noninvasive tool for assessing treatment responses and detecting tumor relapses in children and young adolescents suffering from EwS who are undergoing multimodal chemotherapy.

Growth rates of malignant and benign thyroid nodules in an ultrasound follow-up study: a retrospective cohort study.

BACKGROUND: Thyroid nodules are frequently detected by cervical ultrasound examinations. In follow-up studies, malignant as well as benign nodules may exhibit an increase in size. The objective of our investigation was to test whether histologically determined malignant and benign thyroid nodules show differences in growth rates above a defined significance level. METHODS: A retrospective ultrasound cohort follow-up study from 4 to 132 months included 26 patients with differentiated carcinomas and 26 patients with adenomas of the thyroid gland. Significance levels were determined by intra- and interobserver variations of volumetric measurements in 25 individuals. RESULTS: Intra- and interobserver volumetric measurements were highly correlated (r = 0.99 and r = 0.98, respectively), with variations of 28 and 40%, respectively. The growth rates of malignant and benign nodules did not show differences with respect to two sonographic measurements (d = - 0.04, 95%CI(P): 0.41-0.85, P = 0.83). Using shorter increments and multiple measurements, growth rates of malignant nodules revealed significantly higher values (d = 0.16, 95%CI(P): 0.02-0.04, P = 0.039). CONCLUSIONS: The growth rates of benign and malignant thyroid nodules do not appear to differ using two sonographic volumetric measurements. However, due to temporal changes in cellular proliferation and arrest, malignant nodules may exhibit higher growth rates with multiple assessments and shorter increments.

68Ga-PSMA-11 PET/CT-derived metabolic parameters for determination of whole-body tumor burden and treatment response in prostate cancer.

PURPOSE: We aimed at evaluating the role of 68Ga-PSMA-11 PET/CT-derived metabolic parameters for assessment of whole-body tumor burden and its capability to determine therapeutic response in patients with prostate cancer. METHODS: A total of 142 patients with biochemical recurrence of prostate cancer underwent PET/CT with [68Ga]Ga-PSMA-HBED-CC (68Ga-PSMA-11). Quantitative assessment of all 641 68Ga-PSMA-11-positive lesions in the field of view was performed to calculate PSMA-derived parameters, including whole-body PSMA tumor volume (PSMA-TV) and whole-body total lesion PSMA (TL-PSMA), as well as the established SUVmax and SUVmean values. All PET-derived parameters were tested for correlation with serum PSA levels and for association with Gleason scores. In 23 patients who underwent 68Ga-PSMA-11 PET/CT before and after therapy with either external beam radiation, androgen deprivation, or docetaxel chemotherapy, SUVmax and TL-PSMA were compared to radiographic response assessment of CT images based on RECIST 1.1 criteria and to biochemical response determined by changes of serum PSA levels. RESULTS: PSMA-TV and TL-PSMA demonstrated a significant correlation with serum PSA levels (P < 0.0001) and TL-PSMA was significantly different for different Gleason scores. The agreement rate between TL-PSMA derived from PET and biochemical response was 87% (95% confidence interval, 0.66-0.97; Cohen's κ = 0.78; P < 0.01) and, thus, higher than for SUVmax, which was 74% (95% CI, 0.52-0.90; κ = 0.55; P < 0.01). Furthermore, agreement with PSA was higher for TL-PSMA and SUVmax than for CT-based response evaluation. Discordant findings between PET and CT were most likely due to limitations of CT and RECIST in rating small lymph nodes as metastases, as well as bone involvement, which was sometimes not detectable in CT. CONCLUSION: 68Ga-PSMA-11 PET/CT-derived metabolic tumor parameters showed promising results for evaluation of treatment response. Especially, TL-PSMA demonstrated higher agreement rates with biochemical response compared to SUVmax. Larger, ideally prospective trials are needed to help to reveal the full potential of metabolic parameters derived from PET imaging with 68Ga-PSMA-11.

MIBI scintigraphy of parathyroid adenomas: correlation with biochemical and histological markers.

PURPOSE: In this study, we tested the hypothesis that MIBI-positive and MIBI-negative adenomas of parathyroid glands (APGs) have distinct biochemical and histological markers that could help differentiate MIBI-positive from MIBI-negative APGs. PATIENTS AND METHODS: 40 patients with 41 APGs were included in the study. Patients were enrolled in the study after MIBI scintigraphy examinations had been carried out. Biochemical analyses included serum levels of calcium (Ca), intact parathyroid hormone (iPTH), and 25-hydroxyvitamin D3 (25-OH-D3). All patients had neck ultrasound and MIBI examinations. After surgical resection the APGs were examined histologically. RESULTS: In each of 39 patients one APG could be confirmed by histology, and in one patient, two contralateral APGs were identified. MIBI studies were positive in 73 % and negative in 27 % of the APGs. False-positive cases were not observed. MIBI-negative APGs were only present in patients with iPTH values below 150 pg/ml. In 82 % of MIBI negative studies oxyphilic cells were absent, and this cell type was present in only 18 % of MIBI negative cases (p < 0.001). Regarding cysts within the APGs, no differences were demonstrated between MIBI positive or negative studies (p = 0.32). Fat cells were seen in none of the MIBI -negative studies and in only 3 % of MIBI positive studies (p = 0.08). CONCLUSIONS: For APGs, MIBI positivity correlates with serum iPTH concentration. The absence of oxyphilic cells with large numbers of mitochondria in APGs contributes to MIBI negativity, probably because of the reduced binding sites for the radiotracer.

Adverse events unlikely after fine-needle aspiration biopsies of thyroid nodules in patients on low-dose aspirin: a prospective controlled systematic single center analysis.

AIM: Our aim was to test the assertion that in terms of rate or severity level, adverse events (AEs) after fine-needle aspiration biopsies (FNABs) of thyroid nodules are unfazed by daily low-dose (100 mg) aspirin (acetylsalicylic acid, ASA) intake. METHODS: We selected 268 patients for study, grouped as ASA-treated (PASA, n=78) or control (PCtrl, n=190) subjects. Controls received no antithrombotic medication. AE rates and severities were then analyzed based on patient- and nodule-related factors. We also compared group rates of non-diagnostic cytology results. RESULTS: AEs arising after FNABs (PASA, 5%; PCtrl, 8%) did not differ significantly by group in rate (p=0.4873) or severity level (p=0.3399). All were classifiable as minor incidents, none warranting any intervention. CONCLUSIONS: The data from the present study suggest, AEs after FNABs of thyroid nodules seldom occur and qualify as minor incidents. Such procedures may be safely conducted in patients taking daily low-dose ASA. There is no evidence to support preemptive therapeutic withdrawal.

Ultrasound characteristics of follicular and parafollicular thyroid neoplasms: diagnostic performance of artificial neural network.

BACKGROUND: Ultrasound is the first-line imaging modality for detection and classification of thyroid nodules. Certain features observable by ultrasound have recently been equated with potential malignancy. This retrospective cohort study was conducted to test the hypothesis that radiomics of the four categorical divisions (medullary [MTC], papillary [PTC], or follicular [FTC] carcinoma and follicular thyroid adenoma [FTA]) demonstrate distinctive sonographic characteristics. Using an artificial neural network model for proof of concept, these sonographic features served as input. METHODS: A total of 148 patients were enrolled for study, all with confirmed thyroid pathology in one of the four named categories. Preoperative ultrasound profiles were obtained via standardized protocols. The neural network consisted of seven input neurons; three hidden layers with 50, 250, and 100 neurons, respectively; and one output layer. RESULTS: Radiomics of contour, structure, and calcifications differed significantly according to nodule type (p = 0.025, p = 0.032, and p = 0.0002, respectively). Levels of accuracy shown by artificial neural network analysis in discriminating among categories ranged from 0.59 to 0.98 (95% confidence interval [CI]: 0.57-0.99), with positive and negative predictive ranges of 0.41-0.99 and 0.78-0.97, respectively. CONCLUSIONS: Our data indicate that some MTCs, PTCs, FTCs, and FTAs have distinctive sonographic characteristics. However, a significant overlap of these characteristics may impede an explicit classification. Further prospective investigations involving larger patient and nodule numbers and multicenter access should be pursued to determine if neural networks of this sort are beneficial, helping to classify neoplasms of the thyroid gland.

Fibroblast Activation Protein Inhibitor Imaging in Nonmalignant Diseases: A New Perspective for Molecular Imaging.

Fibroblast activation protein-α (FAP-α) is a type II transmembrane glycoprotein that is overexpressed in activated fibroblasts such as those in the stroma of tumors or in the fibrotic processes accompanying various benign diseases. The recent development and clinical implementation of radiolabeled quinolone-based tracers suitable for PET that act as FAP inhibitors (FAPIs) have opened a new perspective in molecular imaging. Although multiple studies have investigated the use of FAPI imaging in cancer, evidence concerning its use in nonmalignant diseases is still scarce. Herein, we provide a comprehensive review of FAPI imaging in nonmalignant diseases to clarify the current and potential role of this class of molecules in nuclear medicine.

Ultrasound Imaging of Cervical Anatomic Variants.

Embryologic developmental variants of the thyroid and parathyroid glands may cause cervical anomalies that are detectable in ultrasound examinations of the neck. For some of these developmental variants, molecular genetic factors have been identified. Ultrasound, as the first-line imaging procedure, has proven useful in detecting clinically relevant anatomic variants. The aim of this article was to systematically summarize the ultrasound characteristics of developmental variants of the thyroid and parathyroid glands as well as ectopic thymus and neck cysts. Quantitative measures were developed based on our findings and the respective literature. Developmental anomalies frequently manifest as cysts that can be detected by cervical ultrasound examinations. Median neck cysts are the most common congenital cervical cystic lesions, with a reported prevalence of 7% in the general population. Besides cystic malformations, developmental anomalies may appear as ectopic or dystopic tissue. Ectopic thyroid tissue is observed in the midline of the neck in most patients and has a prevalence of 1/100,000 to 1/300,000. Lingual thyroid accounts for 90% of cases of ectopic thyroid tissue. Zuckerkandl tubercles (ZTs) have been detected in 55% of all thyroid lobes. Prominent ZTs are frequently observed in thyroid lobes affected by autoimmune thyroiditis compared with normal lobes or nodular lobes (P = 0.006). The correct interpretation of the ultrasound characteristics of these variants is essential to establish the clinical diagnosis. In the preoperative assessment, the identification of these cervical anomalies via ultrasound examination is indispensable.

Advanced thyroid carcinomas: neural network analysis of ultrasonographic characteristics.

BACKGROUND: Ultrasound is the first-line imaging modality for detection and classification of thyroid nodules. Certain characteristics observable by ultrasound have recently been identified that may indicate malignancy. This retrospective cohort study was conducted to test the hypothesis that advanced thyroid carcinomas show distinctive clinical and sonographic characteristics. Using a neural network model as proof of concept, nine clinical/sonographic features served as input. METHODS: All 96 study enrollees had histologically confirmed thyroid carcinomas, categorized (n = 32, each) as follows: group 1, advanced carcinoma (ADV) marked by local invasion or distant metastasis; group 2, non-advanced papillary carcinoma (PTC); or group 3, non-advanced follicular carcinoma (FTC). Preoperative ultrasound profiles were obtained via standardized protocols. The neural network had nine input neurons and one hidden layer. RESULTS: Mean age and the number of male patients in group 1 were significantly higher compared with groups 2 (p = 0.005) or 3 (p <  0.001). On ultrasound, tumors of larger volume and irregular shape were observed significantly more often in group 1 compared with groups 2 (p <  0.001) or 3 (p ≤ 0.01). Network accuracy in discriminating advanced vs. non-advanced tumors was 84.4% (95% confidence interval [CI]: 75.5-91), with positive and negative predictive values of 87.1% (95% CI: 70.2-96.4) and 92.3% (95% CI: 83.0-97.5), respectively. CONCLUSIONS: Our study has shown some evidence that advanced thyroid tumors demonstrate distinctive clinical and sonographic characteristics. Further prospective investigations with larger numbers of patients and multicenter design should be carried out to show whether a neural network incorporating these features may be an asset, helping to classify malignancies of the thyroid gland.

68Ga-FAPI-04 PET-CT for molecular assessment of fibroblast activation and risk evaluation in systemic sclerosis-associated interstitial lung disease: a single-centre, pilot study.

BACKGROUND: Interstitial lung disease (ILD) is the most common cause of death in systemic sclerosis. To date, the progression of systemic sclerosis-associated ILD is judged by the accrual of lung damage on CT and pulmonary function tests. However, diagnostic tools to assess disease activity are not available. Here, we tested the hypothesis that quantification of fibroblast activation by PET-CT using a 68Ga-labelled selective inhibitor of prolyl endopeptidase FAP (68Ga-FAPI-04) would correlate with ILD activity and disease progression in patients with systemic sclerosis-associated ILD. METHODS: Between Sept 10, 2018, and April 8, 2020, 21 patients with systemic sclerosis-associated ILD confirmed by high-resolution CT (HRCT) within 12 months of inclusion and with onset of systemic sclerosis-associated ILD within 5 years or signs of progressive ILD and 21 controls without ILD were consecutively enrolled. All participants underwent 68Ga-FAPI-04 PET-CT imaging and standard-of-care procedures, including HRCT and pulmonary function tests at baseline. Patients with systemic sclerosis-associated ILD were followed for 6 months with HRCT and pulmonary function tests. We compared baseline 68Ga-FAPI-04 PET-CT uptake with standard diagnostic tools and predictors of ILD progression. The association of 68Ga-FAPI-04 uptake with changes in forced vital capacity was analysed using mixed-effects models. Follow-up 68Ga-FAPI-04 PET-CT scans were obtained in a subset of patients treated with nintedanib (follow-up between 6-10 months) to assess change over time. FINDINGS: 68Ga-FAPI-04 accumulated in fibrotic areas of the lungs in patients with systemic sclerosis-associated ILD compared with controls, with a median standardised uptake value (SUV) mean over the whole lung of 0·80 (IQR 0·60-2·10) in the systemic sclerosis-ILD group and 0·50 (0·40-0·50) in the control group (p<0·0001) and a mean whole lung maximal SUV of 4·40 (range 3·05-5·20) in the systemic sclerosis-ILD group compared with 0·70 (0·65-0·70) in the control group (p<0·0001). Whole-lung FAPI metabolic active volume (wlFAPI-MAV) and whole-lung total lesion FAPI (wlTL-FAPI) were not measurable in control participants, because no 68Ga-FAPI-04 uptake above background level was observed. In the systemic sclerosis-ILD group the median wlFAPI-MAV was 254·00 cm3 (IQR 163·40-442·30), and the median wlTL-FAPI was 183·60 cm3 (98·04-960·70). 68Ga-FAPI-04 uptake was higher in patients with extensive disease, with previous ILD progression, or high EUSTAR activity scores than in those with with limited disease, previously stable ILD, or low EUSTAR activity scores. Increased 68Ga-FAPI-04 uptake at baseline was associated with progression of ILD independently of extent of involvement on HRCT scan and the forced vital capacity at baseline. In consecutive 68Ga-FAPI-04 PET-CTs, changes in 68Ga-FAPI-04 uptake was concordant with the observed response to the fibroblast-targeting antifibrotic drug nintedanib. INTERPRETATION: Our study presents the first in-human evidence that fibroblast activation correlates with fibrotic activity and disease progression in the lungs of patients with systemic sclerosis-associated ILD and that 68Ga-FAPI-04 PET-CT might improve risk assessment of systemic sclerosis-associated ILD. FUNDING: German Research Foundation, Erlangen Anschubs-und Nachwuchsfinanzierung, Interdisziplinäres Zentrum für Klinische Forschung Erlangen, Bundesministerium für Bildung und Forschung, Deutsche Stiftung Systemische Sklerose, Wilhelm-Sander-Foundation, Else-Kröner-Fresenius-Foundation, European Research Council, Ernst-Jung-Foundation, and Clinician Scientist Program Erlangen.

Estimation of [177Lu]PSMA-617 tumor uptake based on voxel-wise 3D Monte Carlo tumor dosimetry in patients with metastasized castration resistant prostate cancer.

OBJECTIVE: Patients with advanced prostate cancer are suitable candidates for [177Lu]PSMA-617 therapy. Integrated SPECT/CT systems have the potential to improve the accuracy of patient-specific tumor dosimetry. We present a novel patient-specific Monte Carlo based voxel-wise dosimetry approach to determine organ and total tumor doses (TTD). METHODS: 13 patients with histologically confirmed metastasized castration-resistant prostate cancer were treated with a total of 18 cycles of [177Lu]PSMA-617 therapy. In each patient, dosimetry was performed after the first cycle of [177Lu]PSMA-617 therapy. Regions of interest were defined manually on the SPECT/CT images for the kidneys, spleen and all 295 PSMA-positive tumor lesions in the field of view. The absorbed dose to normal organs and to all tumor lesions were calculated by a three dimensional dosimetry method based on Monte Carlo Simulations. RESULTS: The average dose values yielded the following results: 2.59 ±â€Š0.63 Gy (1.67-3.92 Gy) for the kidneys, 0.79 ± 0.46 Gy (0.31-1.90 Gy) for the spleen and 11.00 ±â€Š11.97 Gy (1.28-49.10 Gy) for all tracer-positive tumor lesions. A trend towards higher TTD was observed in patients with Gleason Scores > 8 compared to Gleason Scores ≤ 8 and in lymph node metastases compared to bone metastases. A significant correlation was determined between the serum-PSA level before RLT and the TTD (r = -0.57, p < 0.05), as well as between the TTD with the percentage change of serum-PSA levels before and after therapy was observed (r = -0.57, p < 0.05). Patients with higher total tumor volumes of PSMA-positive lesions demonstrated significantly lower kidney average dose values (r = -0.58, p < 0.05). CONCLUSION: The presented novel Monte Carlo based voxel-wise dosimetry calculates a patient specific whole-body dose distribution, thus taking into account individual anatomies and tissue compositions showing promising results for the estimation of radiation doses of normal organs and PSMA-positive tumor lesions.

99mTc-MIP-1404 SPECT/CT for Assessment of Whole-Body Tumor Burden and Treatment Response in Patients With Biochemical Recurrence of Prostate Cancer.

OBJECTIVE: This study aims to investigate the value of Tc-MIP-1404 SPECT/CT for assessment of whole-body tumor burden and treatment response in patients with biochemical recurrence of prostate cancer who undergo androgen deprivation therapy (ADT) or external beam radiation therapy (EBRT). METHODS: A total of 125 patients with biochemical recurrence of prostate cancer underwent Tc-MIP-1404 SPECT/CT. All 364 prostate-specific membrane antigen (PSMA)-positive lesions in the field of view were assessed quantitatively to calculate PSMA-derived metabolic tumor parameters, including whole-body PSMA tumor volume and whole-body total lesion PSMA. These metrics were correlated with serum prostate-specific antigen (PSA) levels and Gleason scores. In a subset of 50 patients who underwent Tc-MIP-1404 SPECT/CT before the initiation of ADT or EBRT, TL-PSMA and SUVmax were compared with radiographic response assessment by CT based on RECIST 1.1 and to biochemical response (BR) determined by changes in serum PSA levels. RESULTS: Serum PSA levels correlated with SUVmax, whole-body PSMA tumor volume, and whole-body total lesion PSMA in patients with 1 and in those with more than 1 PSMA-positive lesion (P < 0.05). The correlations were significant for both well-differentiated (Gleason score ≤7) and poorly differentiated tumors (Gleason score ≥8) (P < 0.05). The agreement between TL-PSMA derived from SPECT and BR in patients who underwent Tc-MIP-1404 SPECT/CT before and after initiation of ADT was 80% (95% confidence interval [CI], 0.43-0.91; Cohen κ = 0.68; P < 0.05); in these patients, the agreement between TL-PSMA and CT was 60% (95% CI, 0.20-0.72; Cohen κ = 0.46; P < 0.05) and the agreement between BR and CT was 52% (0.07-0.61; Cohen κ = 0.34; P < 0.05). Comparable results were found for patients who underwent SPECT/CT before and after initiation of EBRT, with the strongest agreement between TL-PSMA and BR (80%; 95% CI, 0.38-0.93; Cohen κ = 0.66; P < 0.05) compared with the agreement between TL-PSMA and CT (60%; 95% CI, 0.13-0.69; Cohen κ = 0.69; P < 0.05) and between BR and CT (48%; 95% CI, 0-0.54; Cohen κ = 0.26; P = 0.11). Discordant findings between SPECT and CT were most likely due to limitations in the assessment of small lymph node metastases and bone involvement, which were detectable on SPECT but not on CT. CONCLUSIONS: The results of our study show that Tc-MIP-1404 SPECT/CT is a promising method for the evaluation of treatment response in patients with biochemical recurrence of prostate cancer who undergo either ADT or EBRT. TL-PSMA for assessment of treatment response has the strongest correlation with serum PSA levels, superior to SUVmax-based evaluation and response assessment based on CT data and RECIST 1.1.

99mTc-MIP-1404 SPECT/CT for Patients With Metastatic Prostate Cancer: Interobserver and Intraobserver Variability in Treatment-Related Longitudinal Tracer Uptake Assessments of Prostate-Specific Membrane Antigen-Positive Lesions.

BACKGROUND: Tc-MIP-1404 is a SPECT-suitable prostate-specific membrane antigen (PSMA) ligand for detection of prostate cancer. In patients with metastatic prostate cancer, there are no data as yet on interobserver and intraobserver variability when assessing PSMA-positive lesions for longitudinal changes of tracer uptake. METHODS: Tc-MIP-1404 SPECT/CT scans of 22 patients with metastatic prostate cancer were analyzed, and each subject was imaged at 2 separate points in time, before and after treatment. Mean interval between scans was 10 months. Three independent observers visually assessed a total of 96 PSMA-positive metastases (bone, 69; lymph node, 22; viscera, 3) or local recurrences (n = 2) for longitudinal changes in tracer uptake on planar scintigraphy and SPECT/CT. All lesions were categorized as regressive, stable, or progressive based on visual findings and on peak SUV (SUVpeak) of quantitative SPECT/CT (progressive, >30% SUVpeak increase; regressive, <30% SUVpeak decrease; or stable, all others). RESULTS: Quantitative analysis of PSMA-positive lesions yielded significantly higher interobserver agreement (90.6%; 95% confidence interval [CI], 0.83%-0.96%) than visual assessments by either SPECT/CT (76.0%; 95% CI, 0.66%-0.84%) or planar scintigraphy (56.3%; 95% CI, 0.46%-0.66%). Intermethod comparison of aggregated results yielded significantly higher agreement between quantitative and visual SPECT/CT (85.1%; 95% CI, 0.80%-0.89%), as opposed to quantitative SPECT/CT and planar scintigraphy (53.1%; 95% CI, 0.47%-0.59%) or visual SPECT/CT and planar scintigraphy (54.9%; 95% CI, 0.49%-0.61%). In visual and quantitative analysis of 96 PSMA-positive lesions, the number of discrepancies ranged from 9 (9.4%) for quantitative SPECT/CT to 42 (43.8%) for planar scintigraphy. Overall reader confidence was higher for SPECT/CT than for planar scintigraphy (P < 0.001). Intraobserver agreement was near-perfect for all methods, whether SPECT/CT (visual, all κ = 0.94-0.97; quantitative κ = 0.94-0.98) or planar scintigraphy (all κ = 0.90-0.94). CONCLUSIONS: Quantitative evaluation of longitudinal change in tracer uptake by PSMA-positive lesions measured via SPECT/CT is superior to visual interpretation of images by planar scintigraphy or SPECT/CT. Compared with visual evaluation, quantitative SPECT/CT is highly reproducible, showing near-perfect agreement among observers and higher reader confidence.

PSMA SPECT/CT with 99mTc-MIP-1404 in biochemical recurrence of prostate cancer: predictive factors and efficacy for the detection of PSMA-positive lesions at low and very-low PSA levels.

BACKGROUND: The in vivo expression of the prostate-specific membrane antigen (PSMA) can be investigated using the SPECT-suitable tracer 99mTc-MIP-1404. We investigated the performance of 99mTc-MIP-1404 PSMA SPECT/CT in the detection of PSMA-positive tumor lesions in patients suffering from biochemical recurrence of prostate cancer presenting with serum levels of the prostate-specific antigen (PSA) below 1 ng/mL. METHODS: We retrospectively analyzed 99mTc-MIP-1404-SPECT/CT scans of 50 patients (25 with low PSA levels between > 0.5 and 1 ng/mL and 25 with very low PSA levels between 0.2 and 0.5 ng/mL) that had undergone whole-body planar scintigraphy and SPECT/CT of the thorax, abdomen and pelvis 3-4 h p.i. of 691 ± 72 MBq 99mTc-MIP-1404. All datasets were evaluated for the presence and location of PSMA-positive tumor lesions, in which maximal standardized uptake values (SUVmax) were also measured. Based on the results of the quantitative evaluation as well as on biochemical and histological parameters, predictive factors for a positive 99mTc-MIP-1404 scan result were determined. The influence of 99mTc-MIP-1404 PSMA SPECT/CT on further therapy planning was assessed, based on the decision-making of the interdisciplinary tumor board. RESULTS: Pathological 99mTc-MIP-1404 uptake was detected in a total of 25 patients (50%). In the very low PSA subgroup, detection rates of PSMA-positive lesions suggestive of tumor recurrence were 44%, in the low-PSA subgroup 56%. Gleason scores ≥ 8 and the presence of antiandrogen deprivation therapy were further significant predictors of pathological 99mTc-MIP-1404 uptake. This was paralleled by significantly higher lesional SUVmax patients with PSA levels > 0.5 ng/mL and Gleason scores ≥ 8 compared to those without these two features. Changes in therapeutic strategy following MIP-1404 imaging were recommended by the interdisciplinary tumor board in 25/50 of patients. CONCLUSION: 99mTc-MIP-1404 PSMA-SPECT/CT demonstrated a high performance in detecting PSMA-positive lesions suggestive of tumor recurrence in patients with biochemical recurrence of prostate cancer and low and very low serum PSA levels. Results from MIP-1404 PSMA SPECT/CT have therapeutic impact in one-half of the patients examined by this technology.

68Ga-PSMA-11 PET/CT derived quantitative volumetric tumor parameters for classification and evaluation of therapeutic response of bone metastases in prostate cancer patients.

BACKGROUND: To evaluate the role of 68Gallium prostate-specific membrane antigen-positron emission tomography/computed tomography (68Ga-PSMA-11 PET/CT) derived quantitative volumetric tumor parameters in comparison with fully diagnostic conventional CT and serum-PSA levels for classification and evaluation of therapeutic response of bone metastases in patients with metastasized prostate cancer (PC). METHODS: A total of 177 men with biochemical recurrence of prostate cancer suffering from bone metastases underwent PET/CT with [68Ga] Ga-PSMA-HBED-CC (68Ga-PSMA-11). To calculate 68Ga-PSMA-11 PET quantitative volumetric tumor parameters including whole-body total-lesion PSMA (TL-PSMA), whole-body PSMA-tumor volume (PSMA-TV), as well as the established maximum standard uptake values (SUVmax) and mean standard uptake values (SUVmean), all 443 68Ga-PSMA-11-positive bone lesions in the field of view were assessed quantitatively. Quantitative volumetric tumor parameters were correlated with CT-derived volume and bone density measurements of metastatic bone lesions, serum prostate-specific antigen (PSA) levels, and Gleason Scores. In the 20 patients suffering from bone metastases who underwent 68Ga-PSMA-11 PET/CT before and after therapy, CT-derived volume and bone density measurements of metastatic lesions were compared to biochemical response determined by serum-PSA levels. RESULTS: In 177 patients, a total of 443 68Ga-PSMA-11 PET-positive bone lesions were detected. Of these, 50 lesions (11%) were only detectable on PET but not on conventional CT. PET-positive/CT-negative bone metastases demonstrated a significantly lower PSMA uptake compared to PET-positive/CT-positive bone lesions (p < 0.05). SUVmax, SUVmean, PSMA-TV, and TL-PSMA of bone metastases were significantly higher (p < 0.05) in patients with Gleason Scores > 7 compared to those with Gleason Scores ≤ 7. In the linear regression analysis, an association was determined between SUVmean, Gleason Scores, lesion classification, and serum-PSA levels but not for CT-derived bone density measurements. No significant correlation could be found between changes of bone density and CT-derived volume measurements of metastatic bone lesions and changes of serum-PSA levels (p > 0.05) before and after therapy, while a highly significant correlation was observed for changes of PSMA-TV, TL-PSMA, and serum-PSA levels (p < 0.001). CONCLUSION: Our results suggest that 68Ga-PSMA-11 PET/CT might be a valuable tool for the detection and follow-up of bone metastases in patients with metastasized prostate cancer. 68Ga-PSMA-11 PET-derived quantitative volumetric parameters demonstrated a highly significant correlation with changes of serum-PSA levels during the course of therapy. No such correlation could be determined for bone density measurements of metastatic bone lesions. Compared to the fully diagnostic CT scan, a significantly higher proportion of bone metastases was detected on 68Ga-PSMA-11 PET.