Expression of Prostate-Specific Membrane Antigen in Tumor-Associated Neovasculature of Renal Neoplasms

Utility of PSMA PET/CT in Staging and Restaging of Renal Cell Carcinoma: A Systematic Review and Metaanalysis

Prostate-specific membrane antigen (PSMA) is expressed in the neovasculature of multiple solid tumors, including renal cell carcinoma (RCC). Studies have demonstrated promising results on the utility of PSMA-targeted PET/CT imaging in RCC. This report aims to provide a systematic review and metaanalysis on the utility and detection rate of PSMA PET/CT imaging in staging or evaluation of primary RCC and restaging of metastatic or recurrent RCC. Methods: Searches were performed in PubMed, Embase, and abstract proceedings (last updated, August 2023). Studies that provided a lesion-level detection rate of PSMA radiotracers in staging or restaging of RCC were included in the metaanalysis. The overall pooled detection rate with a 95% CI was estimated, and subgroup analysis was performed when feasible. Results: Nine studies comprising 152 patients (133 clear cell RCC [ccRCC], 19 other RCC subtypes) were included in the metaanalysis. The pooled detection rate of PSMA PET/CT in evaluation of primary or metastatic RCC was estimated to be 0.83 (95% CI, 0.67-0.92). Subgroup analysis showed a pooled PSMA detection rate of 0.74 (95% CI, 0.57-0.86) in staging or evaluation of primary RCC lesions and 0.87 (95% CI, 0.73-0.95) in restaging of metastatic or recurrent RCC. Analysis based on the type of radiotracer showed a pooled detection rate of 0.85 (95% CI, 0.62-0.95) for 68Ga-based PSMA tracers and 0.92 (95% CI, 0.76-0.97) for 18F-DCFPyL PET/CT. Furthermore, in metastatic ccRCC, the available data support a significantly higher detection rate for 18F-DCFPyL PET/CT than for conventional imaging modalities (2 studies). Conclusion: Our preliminary results show that PSMA PET/CT could be a promising alternative imaging modality for evaluating RCC, particularly metastatic ccRCC. Large prospective studies are warranted to confirm clinical utility in the staging and restaging of RCC.

Preclinical Evaluation of Biodistribution and Toxicity of [211At]PSMA-5 in Mice and Primates for the Targeted Alpha Therapy against Prostate Cancer

Astatine (211At) is a cyclotron-produced alpha emitter with a physical half-life of 7.2 h. In our previous study, the 211At-labeled prostate-specific membrane antigen (PSMA) compound ([211At]PSMA-5) exhibited excellent tumor growth suppression in a xenograft model. We conducted preclinical biodistribution and toxicity studies for the first-in-human clinical trial. [211At]PSMA-5 was administered to both normal male ICR mice (n = 85) and cynomolgus monkeys (n = 2). The mice were divided into four groups for the toxicity study: 5 MBq/kg, 12 MBq/kg, 35 MBq/kg, and vehicle control, with follow-ups at 1 day (n = 10 per group) and 14 days (n = 5 per group). Monkeys were observed 24 h post-administration of [211At]PSMA-5 (9 MBq/kg). Blood tests and histopathological examinations were performed at the end of the observation period. Blood tests in mice indicated no significant myelosuppression or renal dysfunction. However, the monkeys displayed mild leukopenia 24 h post-administration. Despite the high accumulation in the kidneys and thyroid, histological analysis revealed no abnormalities. On day 1, dose-dependent single-cell necrosis/apoptosis was observed in the salivary glands of mice and intestinal tracts of both mice and monkeys. Additionally, tingible body macrophages in the spleen and lymph nodes indicated phagocytosis of apoptotic B lymphocytes. Cortical lymphopenia (2/10) in the thymus and a decrease in the bone marrow cells (9/10) were observed in the 35 MBq/kg group in mice. These changes were transient, with no irreversible toxicity observed in mice 14 days post-administration. This study identified no severe toxicities associated with [211At]PSMA-5, highlighting its potential as a next-generation targeted alpha therapy for prostate cancer. The sustainable production of 211At using a cyclotron supports its applicability for clinical use.

Characterization of FOLH1 Expression in Renal Cell Carcinoma

PURPOSE

Given the emergence of PSMA-targeted diagnostic agents and therapeutics, we sought to investigate patterns of FOLH1 expression in RCC and their impacts on RCC outcomes.

METHODS

We conducted a pooled multi-institutional analysis of patients with RCC having undergone DNA and RNA next-generation sequencing. FOLH1-high/low expression was defined as the ≥75th/<25th percentile of RNA transcripts per million (TPM). Angiogenic, T-effector, and myeloid expression signatures were calculated using previously defined gene sets. Kaplan-Meier estimates were calculated from the time of tissue collection or therapy start.

RESULTS

We included 1,724 patients in the analysis. FOLH1 expression was significantly higher in clear cell (71%) compared to non-clear cell RCC tumors (19.0 versus 3.3 TPM, p < 0.001) and varied by specimen site (45% primary kidney/55% metastasis, 13.6 versus 9.9 TPM, p < 0.001). FOLH1 expression was correlated with angiogenic gene expression (Spearman = 0.76, p < 0.001) and endothelial cell abundance (Spearman = 0.76, p < 0.001). While OS was similar in patients with FOLH1-high versus -low ccRCC, patients with FOLH1-high clear cell tumors experienced a longer time on cabozantinib treatment (9.7 versus 4.6 months, respectively, HR 0.57, 95% CI 0.35-0.93, p < 0.05).

CONCLUSIONS

We observed differential patterns of FOLH1 expression based on histology and tumor site in RCC. FOLH1 was correlated with angiogenic gene expression, increased OS, and a longer duration of cabozantinib treatment.

Dependence of Renal Uptake on Kidney Function in [68Ga]Ga-PSMA-11 PET/CT Imaging

(1) Background: PSMA ligand PET/CT is increasingly important for diagnostics of prostate cancer and other tumor diseases. In particular, the radiopharmaceutical [68Ga]Ga-PSMA-11 is widely used. Besides its tumor-specific binding, the uptake within the kidneys is dominant and seems to visualize the renal cortex specifically. Kidney diseases may alter the uptake of radiopharmaceuticals. Therefore, the correlation between renal uptake in PET/CT imaging and renal function should be investigated. (2) Methods: A group of 103 male patients were retrospectively evaluated for eGFR according to the CKD-EPI equation, tracer uptake intensity (SUVmax, SUVpeak, SUVmean), the molecular volume of the renal cortex, morphological kidney size, and total renal uptake. Manual and three different computer-assisted contouring methods (thresholds at 50% of SUVmax, 30% of SUVmax, and absolute SUV of 20) were used for measurements. Correlations between parameters were calculated using linear regression models. (3) Results: Renal SUVmax, SUVpeak, and SUVmean do not correlate with eGFR for manual or computer-assisted measurements. In contrast, molecular cortex volume shows a moderate correlation with eGFR (R2 = 0.231, p < 0.001), superior to morphological kidney size. A contouring threshold of 30% of SUVmax outperformed the other settings for renal cortex volume and total renal uptake. (4) Conclusions: Renal uptake of [68Ga]Ga-PSMA-11 cannot predict eGFR, but the functional renal cortex can be quantified by PET/CT imaging.

Role of PSMA-targeted PET-CT in renal cell carcinoma: a systematic review and meta-analysis

Fluoro-deoxy glucose positron emission tomography/computed tomography (PET/CT), the workhorse of nuclear medicine, has limited utility for renal cell carcinoma (RCC), particularly clear cell variant. Thus, various other tracers have been tried for evaluation of RCC. One of the most promising targets for radiotracers is prostate-specific membrane antigen (PSMA) expressed in abundance in carcinoma-associated neo-vasculature. Thus, we tried to review and analyse the role of PSMA-targeted PET/CT in evaluation of RCC. Databases like PubMed, EMBASE and SCOPUS were searched for original studies published on PSMA-targeted PET/CT in RCC till 30 September 2023. Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) checklist was used to assess the included studies. Pooled sensitivity and specificity were calculated and represented with 95% confidence intervals (95%CI). Heterogeneity in the studies was assessed by I-square index. Pooled sensitivity and specificity of PSMA-targeted PET/CT for detection of local disease estimates were 87.2% (95%CI: 77-94%) and 100% (95%CI: 92.9-100%), respectively. Pooled sensitivity and specificity for detection of local recurrent disease are 100% (95%CI: 71.5-100%) and 100% (95%CI: 89.4-100%), respectively. Pooled sensitivity and specificity for detection of metastatic disease are 92% (95%CI: 86.2-96%) and 96.9% (95%CI: 83.8-99.9%), respectively. Pooled sensitivity of PSMA-targeted PET/CT for detection of clear cell renal cell carcinoma (ccRCC) and non-ccRCC are 94.7% (95%CI: 88-98.3%) and 75% (95%CI: 35-96.8%), respectively. PSMA-targeted PET-CT demonstrated better diagnostic efficacy for the detection of recurrent RCC. Whilst for staging RCC, it had higher specificity but lower sensitivity. Thus, it can serve as a non-invasive adjuvant tool to conventional imaging in the evaluation of staging of RCC, particularly clear cell variant.

The Role of Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography in Primary Staging of Selected Renal Tumours: Initial Experience in a Multicentre Cohort

BACKGROUND

Accurate primary staging of renal cancer with conventional imaging is challenging. Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) may serve to improve the accuracy of renal cancer staging.

OBJECTIVE

To determine clinicopathological and management differences for primary renal cancer staged with PSMA PET/CT in comparison to conventional imaging.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a retrospective cohort study of PSMA PET/CT scans performed for primary staging of renal cancer and incidental renal lesions at three sites in Brisbane, Australia between June 2015 and June 2020. Clinical characteristics, imaging, and histopathology were reviewed.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Clinicopathological and management differences according to staging modality (PSMA PET/CT, conventional imaging) were assessed. Descriptive statistics were used to report demographics and clinical parameters. Nonparametric methods were used for statistical analysis. Fisher's exact test was used for comparison of small-cell size categorical variables.

RESULTS AND LIMITATIONS

From a total of 120 PSMA PET/CT scans, 61 were included (52 staging, 9 incidental) for predominantly males (74%) with a mean age of 65.1 yr (standard deviation 12.0). Most primary lesions (40/51) were clear-cell renal cell carcinoma (ccRCC; 98% PSMA-avid), eight were non-ccRCC (75% PSMA-avid), and three were non-RCC (oncocytoma; 67% PSMA-avid). PSMA PET identified a greater number of presumed metastatic lesions than conventional imaging (195 vs 160). A management change was observed for 32% of patients (20% major, 12% minor). Limitations include the retrospective design and selection bias, lack of blinding to PSMA reporting, and the use of different PSMA radiotracers.

CONCLUSIONS

PSMA PET/CT detected more metastases than conventional imaging and most renal cancers were PSMA-avid, resulting in a management change for one-third of the patients.

PATIENT SUMMARY

We looked at a newer type of scan called PSMA PET/CT for first staging of kidney cancer. We found that this detects more metastasis and helps in decisions on changes in treatment for some patients. This type of imaging is a useful addition to conventional scans in tricky cases and may help in better selection of suitable treatments, but more studies are required.

Tata Memorial Centre Evidence Based Use of Nuclear medicine diagnostic and treatment modalities in cancer

ABSTRACT

PET/CT and radioisotope therapy are diagnostic and therapeutic arms of Nuclear Medicine, respectively. With the emergence of better technology, PET/CT has become an accessible modality. Diagnostic tracers exploring disease-specific targets has led the clinicians to look beyond FDG PET. Moreover, with the emergence of theranostic pairs of radiopharmaceuticals, radioisotope therapy is gradually making it's way into treatment algorithm of common cancers in India. We therefore would like to discuss in detail the updates in PET/CT imaging and radionuclide therapy and generate a consensus-driven evidence based document which would guide the practitioners of Oncology.

The evolution of PET imaging in renal, bladder, upper urinary tract urothelial, testicular and penile carcinoma - Today's impact, tomorrow's potential

INTRODUCTION

The advancement of hybrid PET/CT or PET/MRI imaging for non-prostate genitourinary cancers has not experienced the rapid progress of prostate cancer. Nevertheless, these neoplasms are aggressive and reliable imaging plays a pivotal role in enhancing patients' quality of life and prognosis.

AREAS COVERED

the main evidence regarding [18F]FDG and non-[18F]FDG PET/CT or PET/MRI in non-prostate uro-oncological malignancies are summarized and discussed. Moreover, potential future directions concerning PET imaging in these neoplasms are debated, with the aim to stimulate future research projects covering these fields.

EXPERT OPINION

In Renal Cell Carcinoma (RCC), [18F]FDG PET/CT demonstrates varying efficacy in staging, restaging, and prognostic stratification, but PSMA PET/CT is emerging as a potential game-changer, particularly in advanced, high-grade aggressive clear cell RCC. [18F]FDG PET/CT may see an increased use in N and M-staging of bladder cancer, as well as for detecting recurrence and response to neoadjuvant chemotherapy. Preliminary data regarding [68Ga]-FAPI also looks promising in this context. [18F]FDG PET/MRI could be useful for the T-staging of bladder cancer, while upper tract urothelial carcinoma still lacks of molecular imaging literature reports. In testicular and penile cancer [18F]FDG PET/CT has demonstrated its usefulness in several clinical settings, although experiences with non-[18F]FDG radiotracers are lacking.

Clinical impact of Prostate-Specific Membrane Antigen Positron Emission Tomography (PET) on intensification or deintensification of advanced renal cell carcinoma management

PURPOSE

There is an emerging role of the use of Prostate-Specific Membrane Antigen (PSMA) Positron Emission Tomography (PET) in renal cell carcinoma. Herein, we report our experience in use of PSMA PET in recurrent or metastatic renal cell carcinoma (RCC).

METHODS

A retrospective analysis of all patients who underwent PSMA PET for suspected recurrent or de-novo metastatic RCC between 2015 and 2020 at three institutions was performed. The primary outcome was change in management (intensification or de-intensification) following PSMA PET scan. Secondary outcomes included histopathological correlation of PSMA avid sites, comparison of sites of disease on PSMA PET to diagnostic CT and time to systemic treatment.

RESULTS

PSMA-Expression Is Highly Associated with Histological Subtypes of Renal Cell Carcinoma: Potential Implications for Theranostic Approaches

In renal cell carcinoma (RCC), accurate imaging methods are required for treatment planning and response assessment to therapy. In addition, there is an urgent need for new therapeutic options, especially in metastatic RCC. One way to combine diagnostics and therapy in a so-called theranostic approach is the use of radioligands directed against surface antigens. For instance, radioligands against prostate-specific membrane antigen (PSMA) have already been successfully used for diagnosis and radionuclide therapy of metastatic prostate cancer. Recent studies have demonstrated that PSMA is expressed not only in prostate cancer but also in the neovasculature of several solid tumors, which has raised hopes to use PSMA-guided theranostic approaches in other tumor entities, too. However, data on PSMA expression in different histopathological subtypes of RCC are sparse. Because a better understanding of PSMA expression in RCC is critical to assess which patients would benefit most from theranostic approaches using PSMA-targeted ligands, we investigated the expression pattern of PSMA in different subtypes of RCC on protein level. Immunohistochemical staining for PSMA was performed on formalin-fixed, paraffin-embedded archival material of major different histological subtypes of RCC (clear cell RCC (ccRCC)), papillary RCC (pRCC) and chromophobe RCC (cpRCC). The extent and intensity of PSMA staining were scored semi-quantitatively and correlated with the histological RCC subtypes. Group comparisons were calculated with the Kruskal-Wallis test. In all cases, immunoreactivity was detected only in the tumor-associated vessels and not in tumor cells. Staining intensity was the strongest in ccRCC, followed by cpRCC and pRCC. ccRCC showed the most diffuse staining pattern, followed by cpRCC and pRCC. Our results provide a rationale for PSMA-targeted theranostic approaches in ccRCC and cpRCC.

High Prognostic Value of 68Ga-PSMA PET/CT in Renal Cell Carcinoma and Association with PSMA Expression Assessed by Immunohistochemistry

In oligo-metastatic renal cell carcinoma (RCC), neither computed tomography (CT) nor bone scan is sensitive enough to detect small tumor deposits hampering early treatment and potential cure. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein expressed in the neo-vasculature of numerous malignant neoplasms, including RCC, that can be targeted by positron emission tomography (PET) using PSMA-targeting radioligands. Our aim was to investigate whether PSMA-expression patterns of renal cancer in the primary tumor or metastatic lesions on immunohistochemistry (IHC) are associated with PET/CT findings using [68Ga]-PSMA-HBED-CC (PSMA-PET/CT). We then analyzed the predictive and prognostic role of the PSMA-PET/CT signal. In this retrospective single-center study we included patients with renal cancer submitted to PSMA-PET/CT for staging or restaging, with tumor specimens available for PSMA-IHC. Clinical information (age, tumor type, and grade) and IHC results from the primary tumor or metastases were collected. The intensity of PSMA expression at IHC was scored into four categories: 0: none; 1: weak; 2: moderate; 3: strong. PSMA expression was also graded according to the proportion of vessels involved (PSMA%) into four categories: 0: none; 1: 1-25%; 2: 25-50%; 3: >50%. The intensity of PSMA expression and PSMA% were combined in a three-grade score: 0-2 absent or mildly positive, 3-4 moderately positive, and 5-6 strongly positive. PSMA scores were used for correlation with PSMA-PET/CT results. Results: IHC and PET scans were available for the analysis in 26 patients (22 ccRCC, 2 papillary RCC, 1 chromophobe, 1 "not otherwise specified" RCC). PSMA-PET/CT was positive in 17 (65%) and negative in 9 patients (35%). The mean and median SUVmax in the target lesion were 34.1 and 24.9, respectively. Reporter agreement was very high for both distant metastasis location and local recurrence (kappa 1, 100%). PSMA-PET detected more lesions than conventional imaging and revealed unknown metastases in 4 patients. Bone involvement, extension, and lesion number were greater than in the CT scan (median lesion number on PET/CT 3.5). The IHC PSMA score was concordant in primary tumors and metastases. All positive PSMA-PET/CT results (15/22 ccRCC, 1 papillary cancer type II, and 1 chromofobe type) were revealed in tumors with strong or moderate PSMA combined scores (3-4 and 5-6). In ccRCC tissue samples, PSMA expression was strong to moderate in 20/22 cases. The SUVmax values correlated to the intensity of PSMA expression which were assessed using IHC (p = 0.01), especially in the ccRCC subgroup (p = 0.009). Median survival was significantly higher in patients with negative PSMA-PET/CT (48 months) compared to patients with a positive scan (24 months, p= 0.001). SUVmax ≥ 7.4 provides discrimination of patients with a poor prognosis. Results of PSMA-PET/CT changed treatment planning. Conclusions: in renal cancer, positive PSMA-PET/CT is strongly correlated to the intensity of PSMA expression on immunohistochemistry in both ccRCC and chromophobe cancer. PSMA-PET/CT signal predicts a poor prognosis confirming its potential as an aggressiveness biomarker and providing paramount additional information influencing patient management.

Vascular Expression of Prostate-specific Membrane Antigen (PSMA) in MiTF Family Translocation Renal Cell Carcinoma and Related Neoplasms

Multiple studies have demonstrated prostate-specific membrane antigen (PSMA) expression in the neo-vasculature of non-prostate tumors including clear cell renal cell carcinoma (ccRCC). However, PSMA expression in rare renal tumors including MiTF family translocation renal cell carcinoma has not been previously characterized. We examined PSMA expression by immunohistochemistry in a series of MiTF family translocation renal cell carcinomas as well as in several genetically related tumors including alveolar soft part sarcoma and PEComas with TFE3 rearrangements. PSMA expression was also studied in several cases of ccRCC and papillary RCC. Overall, PSMA immunohistochemistry was performed in 61 samples from 58 patients. Vascular PSMA expression was seen with the highest frequency in ccRCC [88% (14/16)] (38% focal, 50% diffuse). Translocation RCC (tRCC) demonstrated the second highest frequency of PSMA expression [71% (22/28)] (57% focal, 14% diffuse), followed by alveolar soft part sarcoma [50% (4/8)] (38% focal, 12% diffuse). No PSMA expression was seen in PEComas with TFE3 rearrangement (0/3) or papillary RCC (0/6). PSMA expression was only present in tumor-associated neo-vasculature. A patient with oligometastatic tRCC underwent 68 Ga-PSMA-11 PET imaging which detected multiple putative metastatic lesions not detected on conventional computed tomography imaging performed 2 weeks prior, supporting the potential utility of PSMA imaging in tRCC. These findings have potential implications for the utility of PSMA guided diagnostic and therapeutic agents in both common and uncommon renal cell carcinoma subtypes as well as genetically related mesenchymal neoplasms.

Vascularized tumor on a microfluidic chip to study mechanisms promoting tumor neovascularization and vascular targeted therapies

The cascade of events leading to tumor formation includes induction of a tumor supporting neovasculature as a primary hallmark of cancer. Developing vasculature is difficult to evaluate in vivo but can be captured using microfluidic chip technology and patient derived cells. Herein, we established an on chip approach to investigate the mechanisms promoting tumor vascularization and vascular targeted therapies via co-culture of metastatic renal cell carcinoma spheroids and endothelial cells in a 3D environment. Our model permitted real-time, high-resolution observation and assessment of tumor-induced angiogenesis, where endothelial cells sprout towards the tumor and mimic a vascular network. Bevacizumab, an angiogenic inhibitor, disrupted interactions between vessels and tumors, destroying the vascular network. The on chip approach enabled assessment of endothelial cell biology, vessel's functionality, drug delivery, and molecular expression of PSMA. Finally, observations in the vascularized tumor on chip permitted direct and conclusive quantification of this therapy in weeks as opposed to months in a comparable animal model.

Teaser

Vascularized tumor on microfluidic chip provides opportunity to study targeted therapies and improves preclinical drug discovery.

Rationale for Prostate-Specific-Membrane-Antigen-Targeted Radionuclide Theranostic Applied to Metastatic Clear Cell Renal Carcinoma

Prostate-specific membrane antigen (PSMA), whose high expression has been demonstrated in metastatic aggressive prostate adenocarcinoma, is also highly expressed in the neovessels of various solid tumors, including clear cell renal cell carcinoma (ccRCC). In the VISION phase III clinical trial, PSMA-targeted radioligand therapy (PRLT) with lutetium 177 demonstrated a 4-month overall survival OS benefit compared to the best standard of care in heavily pretreated metastatic prostate cancer. Despite the improvement in the management of metastatic clear cell renal cell carcinoma (mccRCC) with antiangiogenic tyrosine kinase inhibitor (TKI) and immunotherapy, there is still a need for new treatments for patients who progress despite these drugs. In this study, we discuss the rationale of PRLT applied to the treavtment of mccRCC.

[177Lu]Lu-PSMA-617 theranostic probe for hepatocellular carcinoma imaging and therapy

PURPOSE

This study aimed to explore the feasibility of using [177Lu]Lu-prostate-specific membrane antigen (PSMA)-617 and [177Lu]Lu-Evans blue (EB)-PSMA-617 for in vivo radioligand therapy by single-dose administration in a PSMA-positive hepatocellular carcinoma (HCC) xenograft mouse model.

METHODS

[177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 were prepared, and labelling efficiency and radiochemical purity were determined. A HepG2 human HCC subcutaneous xenograft mouse model was established. After intravenous injection of [177Lu]Lu-PSMA-617 or [177Lu]Lu-EB-PSMA-617 (37 MBq) into the mouse model, single-photon emission computed tomography/computed tomography (SPECT/CT) was performed. Biodistribution studies were conducted to verify targeting specificity and pharmacokinetics. In the radioligand therapy study, mice were randomized into 4 groups: 37 MBq [177Lu]Lu-PSMA-617, 18.5 MBq [177Lu]Lu-PSMA-617, 7.4 MBq [177Lu]Lu-EB-PSMA-617, and saline (control). A single-dose administration was applied at the beginning of therapy studies. Tumor volume, body weight, and survival were monitored every 2 days. After the end of therapy, mice were euthanized. Tumors were then weighed, and systemic toxicity was evaluated via blood testing and histological examination of healthy organs.

RESULTS

[177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 were successfully prepared with high purity and stability. SPECT/CT and biodistribution showed that tumor uptake was higher and persisted longer for [177Lu]Lu-EB-PSMA-617 compared with [177Lu]Lu-PSMA-617. [177Lu]Lu-PSMA-617 was rapidly cleared from the blood, while [177Lu]Lu-EB-PSMA-617 persisted for significantly longer. In radioligand therapy studies, tumor growth was significantly suppressed in the 37 MBq [177Lu]Lu-PSMA-617, 18.5 MBq [177Lu]Lu-PSMA-617, and 7.4 MBq [177Lu]Lu-EB-PSMA-617 groups compared to the saline group. Median survival was 40, 44, 43, and 30 days, respectively. No healthy organ toxicity was observed in safety and tolerability evaluation.

CONCLUSIONS

Radioligand therapy using [177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 significantly suppressed tumor growth and prolonged survival time in PSMA-positive HCC xenograft mice without obvious toxicity. These radioligands appear promising for clinical use in humans, and future studies are warranted.

α-SMA positive vascular mural cells suppress cyst formation in hemangioblastoma

Approximately 60% of hemangioblastomas (HBs) have peritumoral cysts adjacent to the tumor, which can cause neurological deficits due to the mass effect, and the management of cyst formation is a clinical challenge. Vascular mural cells surrounding endothelial cells consist of vascular smooth muscle cells (vSMCs) and pericytes, which are essential elements that support blood vessels and regulate permeability. This study investigated the involvement of mural cells in cyst formation. We analyzed the expression of α-smooth muscle actin (α-SMA), platelet-derived growth factor receptor-beta (PDGFRB), and CD31 in 39 consecutive human cerebellar HBs, 20 of cystic and 19 of solid type. Solid type HBs showed stronger diffuse expression of α-SMA in precapillary arterioles and capillaries within the tumor than cystic type HBs (p = 0.001), whereas there was no difference in PDGFRB and CD31 expression. Detailed observation with immunofluorescence demonstrated that α-SMA was expressed in vascular mural cells surrounding capillaries in the solid rather than in the cystic type. Multivariate analysis including various clinical and pathological factors showed that lower α-SMA expression was significantly correlated with cyst formation (p < 0.001). Our data suggested that vascular mural cells from precapillary arterioles to capillaries expressing α-SMA may be pericytes and play a crucial role in HB cystogenesis.

Exploration of 68Ga-labelled prostate-specific membrane antigen-11 PET/CT parameters for identifying PBRM1 status in primary clear cell renal cell carcinoma

AIM

To investigate the predictive value of ⁶⁸Ga-labelled prostate-specific membrane antigen-11 (⁶⁸Ga-PSMA-11) integrated positron-emission tomography (PET)/computed tomography (CT) in PBRM1-deficient clear cell renal cell carcinoma (ccRCC).

MATERIALS AND METHODS

A total of 41 patients with ccRCC, were enrolled retrospectively and underwent ⁶⁸Ga-PSMA-11 PET/CT preoperatively. Radiological parameters, including CT attenuation value and maximum standard uptake value (SUVmax), were derived. Immunohistochemical and multiple immunofluorescences staining were performed to evaluate the PBRM1 status and immune response. The predictive value of imaging factors was analysed using a receiver operator characteristic curve analysis. Univariate and multivariate logistic regression analyses were used to investigate the relationship between clinical and radiological variables and PBRM1 status.

RESULTS

A total of 41 patients were included in this study, with 14 patients having PBRM1-deficient status. The tumour diameter on imaging and SUVmax differed significantly in patients with different PBRM1 expression statuses and no difference in CT attenuation was identified. Univariate and multivariate logistic regression analyses showed SUVmax was an obvious predictor for identification of PBRM1-deficient tumours. In addition, PBRM1-deficient tumours tended to be accompanied by greater cytotoxic T-cell infiltration, although most of them were in an exhausted state.

CONCLUSIONS

⁶⁸Ga-PSMA-11 PET/CT could be used to discriminate invasive PBRM1-deficient ccRCC.

Special issue "The advance of solid tumor research in China": 68Ga-PSMA-11 PET/CT for evaluating primary and metastatic lesions in different histological subtypes of renal cell carcinoma

Conventional imaging examinations are not sensitive enough for the early detection of recurrent or metastatic lesions in renal cell carcinoma (RCC) patients. We aimed to explore the role of ⁶⁸ Ga-prostate specific membrane antigen (PSMA)-11 positron emission tomography (PET)/computed tomography (CT) in the detection of primary and metastatic lesions in such patients. We retrospectively analyzed 50 RCC patients who underwent ⁶⁸ Ga-PSMA-11 PET/CT from November 2017 to December 2020. We observed a higher median accuracy and tumor-to-background maximum standard uptake value (SUV_max ) ratio (TBR) of ⁶⁸ Ga-PSMA-11 PET/CT in clear cell RCC (ccRCC; 96.57% and 6.00, respectively) than in non-clear cell RCC (ncRCC; 82.05% and 2.99, respectively). The accuracies in detecting lesions in the renal region, bone, lymph nodes and lungs in ccRCC were 100.00%, 95.00%, 98.08% and 75.00%, respectively, and those in the renal region, bone and lymph nodes in ncRCC were 100.00%, 86.67% and 36.36%, respectively. The median TBRs of the lesions from the above locations were 0.38, 10.96, 6.69 and 13.71, respectively, in ccRCC and 0.13, 4.02 and 0.73, respectively, in ncRCC. The PSMA score evaluated with immunohistochemistry was correlated with the SUV_max (P = .046) in RCC. Higher PSMA scores were observed in ccRCC than in ncRCC (P = .031). ⁶⁸ Ga-PSMA-11 PET/CT resulted in changes in clinical management in 12.9% (4/31) of cases because of the discovery of new metastases not detected with conventional imaging. These results indicate that ⁶⁸ Ga-PSMA-11 PET/CT is a promising method for the detection of metastatic lesions in ccRCC, especially for those in the bone and lymph nodes.

A Novel PSMA-Targeted Probe for NIRF-Guided Surgery and Photodynamic Therapy: Synthesis and Preclinical Validation

A total of 20% to 50% of prostate cancer (PCa) patients leave the surgery room with positive tumour margins. The intraoperative combination of fluorescence guided surgery (FGS) and photodynamic therapy (PDT) may be very helpful for improving tumour margin delineation and cancer therapy. PSMA is a transmembrane protein overexpressed in 90−100% of PCa cells. The goal of this work is the development of a PSMA-targeted Near InfraRed Fluorescent probe to offer the surgeon a valuable intraoperative tool for allowing a complete tumour removal, implemented with the possibility of using PDT to kill the eventual not resected cancer cells. PSMA-617 binding motif was conjugated to IRDye700DX-NHS and the conjugation did not affect the photophysical characteristics of the fluorophore. The affinity of IRDye700DX-PSMA-617 towards PCa cells followed the order of their PSMA expression, i.e., PC3-PIP > LNCaP > PC3, PC3-FLU. NIRF imaging showed a significant PC3-PIP tumour uptake after the injection of 1 or 5 nmol with a maximum tumour-to-muscle ratio (ca. 60) observed for both doses 24 h post-injection. Importantly, urine, healthy prostate, and the bladder were not fluorescent at 24 h post-injection. Flow cytometry and confocal images highlighted a co-localization of PSMA+ cells with IRDye700DX-PSMA uptake. Very interestingly, ex vivo analysis on a tumour specimen highlighted a significant PSMA expression by tumour-associated macrophages, likely attributable to extracellular vesicles secreted by the PSMA(+) tumour cells. FGS proved that IRDye700DX-PSMA was able to easily delineate tumour margins. PDT experiments showed a concentration-dependent decrease in cell viability (from 75% at 10 nM to 12% at 500 nM), whereas controls did not show any cytotoxicity. PC3-PIP tumour-bearing mice subjected to photodynamic therapy showed a delayed tumour growth. In conclusion, a novel PSMA-targeted NIRF dye with dual imaging-PDT capabilities was synthesized and displayed superior specificity compared to other small PSMA targeted molecules.

Impact of Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography in the Management of Oligometastatic Renal Cell Carcinoma

Background

Prostate-specific membrane antigen (PSMA) is overexpressed in the neovasculature of renal cell carcinoma (RCC). However, there remains limited evidence regarding the use of PSMA positron emission tomography/computed tomography (PET/CT) in RCC.

Objective

To assess the impact of PSMA PET/CT in the management of metastatic RCC.

Design, setting, and participants

This was a retrospective review of patients who underwent PSMA PET/CT from 2014 to 2020 for restaging or suspected metastatic RCC in a tertiary academic setting.

Outcome measurements and statistical analysis

Management plans before and after PSMA PET/CT were recorded. Impact was classified as high (change of treatment intent, modality, or site), medium (change in treatment method), or low. Secondary outcomes included the patient-level detection rate, PSMA PET/CT parameters, sensitivity, and comparison to CT and, if available, fluorodeoxyglucose (FDG) PET/CT.

Results and limitations

Sixty-one patients met the inclusion criteria, of whom 54 (89%) had clear cell RCC. PSMA-positive disease was detected in 51 patients (84%). For 30 patients (49%) there was a change in management due to PSMA PET/CT (high impact, 29 patients, 48%). In 15 patients (25%), more metastases were detected on PSMA PET/CT than on CT. The sensitivity of combined PSMA PET/CT and diagnostic CT was 91% (95% confidence interval 77–98%). In a subcohort of 40 patients, the detection rate was 88% for PSMA and 75% for FDG PET/CT (p = 0.17). The maximum standardised uptake value (SUV_max) was higher for PSMA than for FDG PET/CT (15.2 vs 8.0; p = 0.02). Limitations include selection bias due to the retrospective design, and a lack of corresponding histopathology for all patients.

Conclusions

PSMA PET/CT is a promising imaging modality in metastatic RCC and led to a change in management in 49% of patients. PSMA PET/CT detected additional metastases compared to CT in 25% of patients and registered a significantly higher SUV_max than FDG PET/CT. Prospective studies are required to further define its role.

Patient summary

We report on a group of patients undergoing a new type of imaging for suspected advanced kidney cancer, called PSMA PET/CT. This imaging changed the management plan in 49% of the patients. PSMA PET/CT detected metastases in 84% of our patients and detected more metastases than computed tomography imaging in 25%.

PET imaging of hepatocellular carcinoma by targeting tumor-associated endothelium using [68Ga]Ga-PSMA-617

OBJECTIVE

Hepatocellular carcinoma (HCC) is a malignant tumor associated with high morbidity and mortality rates. In many non-prostate solid tumors such as HCC, prostate-specific membrane antigens (PSMA) are overexpressed in tumor-associated endothelial cells. Therefore, the aim of this study was to evaluate the performance of [68Ga]Ga-PSMA-617 PET imaging on HCC with different animal models, including cell line-derived xenografts (CDX) and patient-derived xenografts (PDX), and to explore its mechanisms of function.

METHODS

[68Ga]Ga-PSMA-617 was prepared. The expression level of PSMA in two human hepatocellular cancer cells (HepG2 and HuH-7) was evaluated, and the cellular uptakes of [68Ga]Ga-PSMA-617 were assayed. HepG2 and HuH-7 subcutaneous xenograft models, HepG2 orthotopic xenograft models, and four different groups of PDX models were prepared. Preclinical pharmacokinetics and performance of [68Ga]Ga-PSMA-617 were evaluated in different types of HCC xenografts models using small animal PET and biodistribution studies.

RESULTS

Low PSMA expression level of HepG2 and HuH-7 cells was observed, and the cellular uptake and blocking study confirmed the non-specificity of the PSMA-targeted probe binding to HepG2 and HuH-7 cells. In the subcutaneous xenograft models, the tumor uptakes at 0.5 h were 0.76 ± 0.12%ID/g (HepG2 tumors) and 0.78 ± 0.08%ID/g (HuH-7 tumors), respectively, which were significantly higher than those of the blocking groups (0.23 ± 0.04%ID/g and 0.20 ± 0.04%ID/g, respectively). In the orthotopic xenograft models, PET images clearly displayed the tumor locations based on the preferential accumulation of [68Ga]Ga-PSMA-617 in tumor tissue versus normal liver tissue, suggesting the possibility of using [68Ga]Ga-PSMA-617 PET imaging to detect primary HCC lesions in deep tissue. In the four different groups of HCC PDX models, PET imaging with [68Ga]Ga-PSMA-617 provided clear tumor uptakes with prominent tumor-to-background contrast, further demonstrating its potential for the clinical imaging of PSMA-positive HCC lesions. The staining of tumor tissue sections with CD31- and PSMA-specific antibodies visualized the tumor-associated blood vessels and PSMA expression on endothelial cells in subcutaneous, orthotopic tissues, and PDX tissues, confirming the imaging with [68Ga]Ga-PSMA-617 might be mediated by targeting tumor associated endothelium.

CONCLUSION

In this study, in vivo PET on different types of HCC xenograft models illustrated high uptake within tumors, which confirmed that [68Ga]Ga-PSMA-617 PET may be a promising imaging modality for HCC by targeting tumor associated endothelium.

Urothelial Carcinoma and Prostate-specific Membrane Antigen: Cellular, Imaging, and Prognostic Implications

CONTEXT

Staging, restaging, and surveillance of urothelial carcinoma (UC) is challenging due to suboptimal accuracy of standard of care imaging modalities. Prostate-specific membrane antigen (PSMA) imaging may serve to improve characterisation of UC.

OBJECTIVE

To appraise available literature regarding cellular, imaging, and prognostic implications of PSMA for UC.

EVIDENCE ACQUISITION

A systematic review was performed considering all available literature (including conference abstracts) published from 1990 to 2020 and reported according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines following registration in PROSPERO (CRD42020186744). All relevant texts relating to immunohistochemical analysis and PSMA-based imaging in UC were included and collated. Additionally, FOLH1 (gene encoding PSMA) expression according to The Cancer Genome Atlas (TCGA) database was analysed as well as according to consensus and TCGA molecular classification subtypes and subsequently compared with clinical outcomes.

EVIDENCE SYNTHESIS

PSMA expression across UC tumour tissue was heterogeneous (0-100%) but appeared to decrease with increased grade and stage. The TCGA analysis demonstrated loss of FOLH1 expression with increasing T stage (p = 0.0180) and N stage (p = 0.0269), and reduced FOLH1 expression was associated with worse disease-free survival. PSMA expression in UC neovasculature was variable but mostly increased (44-100%). Eleven reports of PSMA-based imaging for UC were identified, reporting on 18 patients. PSMA positron emission tomography (PET) imaging was positive in 17 out of 18 patients. The included literature review data were limited by mostly low-quality, retrospective studies.

CONCLUSIONS

Tissue PSMA, or FOLH1 expression, may inversely be associated with pathological and survival outcomes in localised UC. PSMA PET imaging may improve detection of metastatic disease and response to systemic therapy due to PSMA expression in neovasculature. Available evidence is limited; thus, larger, prospective studies are required to confirm early results and define populations that benefit most.

PATIENT SUMMARY

In this systematic review, we assess the potential role of prostate-specific membrane antigen in urothelial cancer. We found that its utility is in expression of blood vessels surrounding metastasis. We conclude that it may be beneficial in detecting metastasis and response to systemic therapies.

PSMA Radioligand Uptake as a Biomarker of Neoangiogenesis in Solid Tumours: Diagnostic or Theragnostic Factor?

Due to its overexpression on the surface of prostate cancer cells, prostate-specific membrane antigen (PSMA) is a relatively novel effective target for molecular imaging and radioligand therapy (RLT) in prostate cancer. Recent studies reported that PSMA is expressed in the neovasculature of various types of cancer and regulates tumour cell invasion as well as tumour angiogenesis. Several authors explored the role of diagnostic and therapeutic PSMA radioligands in various malignancies. In this narrative review, we describe the current status of the literature on PSMA radioligands' application in solid tumours other than prostate cancer to explore their potential role as diagnostic or therapeutic agents, with particular regard to the relevance of PSMA radioligand uptake as neoangiogenetic biomarker. Hence, a comprehensive review of the literature was performed to find relevant articles on the applications of PSMA radioligands in non-prostate solid tumours. Data on the general, methodological and clinical aspects of all included studies were collected. Forty full-text papers were selected for final review, 8 of which explored PSMA radioligand PET/CT performances in gliomas, 3 in salivary gland malignancies, 6 in thyroid cancer, 2 in breast cancer, 16 in renal cell carcinoma and 5 in hepatocellular carcinoma. In the included studies, PSMA radioligand PET showed promising performance in patients with non-prostate solid tumours. Further studies are needed to better define its potential role in oncological patients management, especially in those undergoing antineoangiogenic therapies, and to assess the efficacy of PSMA-RLT in this clinical context.

The Role of PSMA PET/CT in the Primary Diagnosis and Follow-Up of Prostate Cancer-A Practical Clinical Review

Simple Summary

The combination of positron emission tomography (PET)-diagnostics with ligands binding to the prostate-specific membrane antigen (PSMA) has been a diagnostic milestone in the situation of biochemical recurrence of prostate cancer and is gaining importance in primary diagnostics, providing a highly specific and sensitive diagnostic method in various clinical situations. However, the clinical application of this method requires a comprehensive knowledge of its advantages and disadvantages, potential pitfalls and influencing factors. This review aims to provide a practical clinical review of the currently available background data on PSMA PET/CT, as well as the clinical implications. Although a large amount of data already exist, a thorough analysis is complicated by study heterogeneity, showing the need for future systematic and prospective research.

Abstract

The importance of PSMA PET/CT in both primary diagnostics and prostate cancer recurrence has grown steadily since its introduction more than a decade ago. Over the past years, a vast amount of data have been published on the diagnostic accuracy and the impact of PSMA PET/CT on patient management. Nevertheless, a large heterogeneity between studies has made reaching a consensus difficult; this review aims to provide a comprehensive clinical review of the available scientific literature, covering the currently known data on physiological and pathological PSMA expression, influencing factors, the differences and pitfalls of various tracers, as well as the clinical implications in initial TNM-staging and in the situation of biochemical recurrence. This review has the objective of providing a practical clinical overview of the advantages and disadvantages of the examination in various clinical situations and the body of knowledge available, as well as open questions still requiring further research.

Cancers and Benign Processes on 68Ga PSMA PET-CT Imaging Other than Prostate Cancer

Background  Imaging plays an important role in the evaluation of prostate cancer patients. In recent years, much attention has been focused on gallium 68 prostate-specific membrane antigen positron emission tomography-computed tomography ( ⁶⁸ Ga PSMA PET-CT) in prostate cancer patients and has been widely used for staging, restaging, and therapy response for these patients. The aim of this study was to report ⁶⁸ Ga PSMA PET-CT in other cancers and benign processes incidentally detected on ⁶⁸ Ga PSMA PET-CT in patients with prostate cancer.

Materials and Methods  A total of 600 ⁶⁸ Ga PSMA PET-CT scans were performed for initial staging, restaging, detection of suspected recurrence, and therapy response in prostate cancer patients between December 2018 and June 2020. A total of 38 patients with histopathologically proven prostate cancer were included in the current study with other malignancies and benign processes. Mainly histopathology in most of cases and clinical and radiological follow-up in few cases after PET/CT scanning served as the standard of reference.

Results  A total of 38 patients (age range: 52–85 years; mean age: 68.6) with prostate cancer final histopathology results were included in the study. A total of 51 lesion sites were evaluated in 38 patients. Forty-one lesion regions of these 51 regions were based on histopathological diagnosis, whereas 10 of them were based on clinical follow-up and conventional radiological follow-up as differential criteria. Thirty of 51 lesion regions were evaluated as malignant and 21 were benign lesions. The most common ⁶⁸ Ga PSMA ligand avid malignancy was lung adenocarcinoma (6/38).

Conclusions  Prostate-specific membrane antigen (PSMA) is a cell surface glycoprotein and mainly expressed in prostate epithelium. ⁶⁸ Ga PSMA PET-CT imaging is very sensitive and specific imaging modality in prostate cancer patients. However, other malignancies and some benign processes may also have ⁶⁸ Ga PSMA ligand avidity and some prostate cancer metastases may imitate other malignancies.

Advances in PSMA theranostics

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PSMA is an appealing target for theranostic because it is a transmembrane protein with a known substrate that is overexpessed on prostate cancer cells and internalizes upon ligand binding.

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There are a number of PSMA theranostic ligands in clinical evaluation, clinical trial, or clinically approved.

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PSMA theranostic ligands increase progression-free survival, overall survival, and pain in patients with metastatic castration resistant prostate cancer.

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A major obstacle to PSMA-targeted radioligand therapy is off-target toxicity in salivary glands.

The validation of prostate specific membrane antigen (PSMA) as a molecular target in metastatic castration-resistant prostate cancer has stimulated the development of multiple classes of theranostic ligands that specifically target PSMA. Theranostic ligands are used to image disease or selectively deliver cytotoxic radioactivity to cells expressing PSMA according to the radioisotope conjugated to the ligand. PSMA theranostics is a rapidly advancing field that is now integrating into clinical management of prostate cancer patients. In this review we summarize published research describing the biological role(s) and activity of PSMA, highlight the most clinically advanced PSMA targeting molecules and biomacromolecules, and identify next generation PSMA ligands that aim to further improve treatment efficacy. The goal of this review is to provide a comprehensive assessment of the current state-of-play and a roadmap to achieving further advances in PSMA theranostics.

PSMA PET/CT in Renal Cell Carcinoma: An Overview of Current Literature

Although the vast majority of prostate-specific membrane antigen (PSMA) positron emission tomography (PET) imaging occurs in the field of prostate cancer, PSMA is also highly expressed on the cell surface of the microvasculature of several other solid tumors, including renal cell carcinoma (RCC). This makes it a potentially interesting imaging target for the staging and monitoring of RCC. The objective of this review is to provide an overview of the current evidence regarding the use of PSMA PET/Computed Tomography in RCC patients.

Role of PSMA-ligands imaging in Renal Cell Carcinoma management: current status and future perspectives

Background

Renal masses detection is continually increasing worldwide, with Renal Cell Carcinoma (RCC) accounting for approximately 90% of all renal cancers and remaining one of the most aggressive urological malignancies. Despite improvements in cancer management, accurate diagnosis and treatment strategy of RCC by computed tomography (CT) and magnetic resonance imaging (MRI) are still challenging. Prostate-Specific Membrane Antigen (PSMA) is known to be highly expressed on the endothelial cells of the neovasculature of several solid tumors other than prostate cancer, including RCC. In this context, recent preliminary studies reported a promising role for positron emission tomography (PET)/CT with radiolabeled molecules targeting PSMA, in alternative to fluorodeoxyglucose (FDG) in RCC patients.

Purpose

The aim of our review is to provide an updated overview of current evidences and major limitations regarding the use of PSMA PET/CT in RCC.

Methods

A literature search, up to 31 December 2021, was performed using the following electronic databases: PubMed, SCOPUS, Web of Science, and Google Scholar.

Results

The findings of this review suggest that PSMA PET/CT could represent a valid imaging option for diagnosis, staging, and therapy response evaluation in RCC, particularly in clear cell RCC.

Conclusions

Further studies are needed for this “relatively” new imaging modality to consolidate its indications, timing, and practical procedures.

Prognostic Value of Vascular-Expressed PSMA and CD248 in Urothelial Carcinoma of the Bladder

Background

Urothelial carcinoma of the bladder (UCB) is a common cancer of the urinary system. Despite substantial improvements in available treatment options, the survival outcome of patients with advanced UCB is unsatisfactory. Therefore, it is necessary to identify new prognostic biomarkers for monitoring and therapy guidance of UCB. In recent years, prostate-specific membrane antigen (PSMA) and CD248 have been identified promising candidate bio7markers.

Methods

In this study, we first examined PSMA and CD248 expression in tissues from 124 patients with UCB using immunohistochemical and immunofluorescent staining. We then analyzed the association between the expression of the two biomarkers and other clinicopathological features and prognosis. Finally, we performed bioinformatic analysis of CD248 and FOLH 1 (PSMA) using the TCGA-BLCA dataset to explore the underlying mechanism of PSMA and CD248 in the progression of UCB.

Results

Among the 124 cases, PSMA and CD248 were confirmed to be expressed in tumor-associated vessels. Vascular PSMA and CD248 expression levels were associated significantly with several deteriorated clinicopathological features. Furthermore, using univariate and multivariate Cox analyses, high vascular PSMA and CD248 expression levels were observed to be associated significantly with poor prognosis in patients with UCB. As risk factors, both PSMA and CD248 expression showed good performance to predict prognosis. Furthermore, combining these vascular molecules with other clinical risk factors generated a risk score that could promote predictive performance. Bioinformatic analysis showed that both PSMA and CD248 might contribute to angiogenesis and promote further progression of UCB.

Conclusion

Both PSMA and CD248 are specifically expressed in the tumor-associated vasculature of UCB. These two molecules might be used as novel prognostic biomarkers and vascular therapeutic targets for UCB.

PSMA-targeted low-molecular double conjugates for diagnostics and therapy

This review presents data on dual conjugates of therapeutic and diagnostic action for targeted delivery to prostate cancer cells. The works of the last ten years on this topic were analyzed. The mail attention focuses on low-molecular-weight conjugates directed to the prostate-specific membrane antigen (PSMA); the comparison of high and low molecular weight PSMA-targeted conjugates was made. The considered conjugates were divided in the review into two main classes: diagnostic bimodal conjugates (which are containing two fragments for different types of diagnostics), theranostic conjugates (containing both therapeutic and diagnostic agents); also bimodal high molecular weight therapeutic conjugates containing two therapeutic agents are briefly discussed. The data of in vitro and in vivo studies for PSMA-targeted double conjugates available by the beginning of 2021 have been analyzed.

[Imaging of oligometastatic disease in selected urologic cancers]

BACKGROUND

Local treatment of the primary or metastatic sites in urologic malignancies is promising when compared to systemic therapy alone, leading to the definition of a potentially curative oligometastatic state.

OBJECTIVES

Comparison of imaging modalities regarding local and metastatic tumor sites in urologic cancers.

METHODS

Review of comparative trials addressing quality criteria of imaging modalities.

RESULTS

Depending on primary tumor and metastatic site, conventional imaging modalities such as computer tomography (CT) and bone scintigraphy still represent the standard of care in Germany. Due to superior quality criteria, hybrid-imaging techniques were widely adopted for oncological staging and particular due to the new PSMA-ligand (PSMA-PET/CT) in prostate cancer imaging. The development of new radioisotopes as well as their clinical application remains a focus of current research.

CONCLUSIONS

High-quality diagnostic imaging modalities lay the groundwork for a precise definition of an oligometastatic state. By enabling treatment of the entire tumor burden, a delay of systemic therapy, longer progression-free survival, or even curative treatment may become achievable.

Nephrotoxicity after radionuclide therapies

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Nuclear medicine theranostics have demonstrated success with a favourable safety and efficacy profile in several malignancies.

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Kidneys being the primary excretory organ for most therapeutic radiopharmaceuticals are at risk of increased radiation exposure.

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Recognition of the mechanisms of radiation induced nephropathy and associated risk factors can help in the development of appropriate interventions to prevent and limit renal toxicity.

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Developments in reducing chronic radiation nephropathy following radionuclide therapies will help in avoiding the related morbidities, preserving the overall quality of life.

Radioligand therapies have opened new treatment avenues for cancer patients. They offer precise tumor targeting with a favorable efficacy-to-toxicity profile. Specifically, the kidneys, once regarded as the critical organ for radiation toxicity, also show excellent tolerance to radiation doses as high as 50–60 Gy in selected cases. However, the number of nephrons that form the structural and functional units of the kidney is determined before birth and is fixed. Thus, loss of nephrons secondary to any injury may lead to an irreversible decline in renal function over time. Our primary understanding of radiation-induced nephropathy is derived from the effects of external beam radiation on the renal tissue. With the growing adoption of radionuclide therapies, considerable evidence has been gained with regard to the occurrence of renal toxicity and its associated risk factors. In this review, we discuss the radionuclide therapies associated with the risk of nephrotoxicity, the present understanding of the factors and mechanisms that contribute to renal injury, and the current and potential methods for preventing, identifying, and managing nephrotoxicity, specifically acute onset nephropathies.

Blending of Designer Synthetic Polymers to a Dual Targeted Nanoformulation for SARS-CoV-2 Associated Kidney Damage

As the COVID-19 pandemic has continued to spread, studies have shown that hospitalized COVID-19 patients are at significant risk for developing acute kidney injury (AKI), which can cause increased morbidity, the need for dialysis treatment, chronic kidney diseases, and even death. In this paper, we present a proof-of-concept study for the utilization of combination therapeutic-loaded dual-targeted biodegradable nanoparticles (NPs) to treat concurrent AKI and COVID-19 in patients by delivering the therapeutics across the gut epithelial barrier and to the kidney, in order to lower the viral load as well as reduce the symptoms of AKI. Despite recent vaccination efforts and the end of the COVID-19 pandemic in sight, problems related to the long-term effects of COVID-19 will continue to persist, including impacts on patients suffering from AKI and other chronic renal conditions. Therefore, the dual-targeted blended polymeric NP developed in this study to treat concurrent COVID-19 infection and AKI is a useful proof-of-concept nanoplatform for future treatments of these complications.

18F-FDG and 68GA-Prostate-Specific Membrane Antigen PET/CT Perform Better Than CT Alone in Restaging Papillary Renal Cell Carcinoma Recurrence

ABSTRACT

Renal cell carcinoma (RCC) shows variable FDG uptake; recently, PET/CT with prostate-specific membrane antigen (PSMA)-target radiotracers was demonstrated to be a promising tool in staging and restaging of RCC patients. We describe the case of a 77-year-old man with a lung metastasis of papillary RCC missed by CT scan who successfully underwent [18F]FDG PET/CT restaging. Targeted therapy with sunitinib was administered. A [68Ga]PSMA PET/CT performed during follow-up demonstrated, among the already known lesions, also a bone marrow metastasis, missed by previous CT scans. This case demonstrates that PET/CT molecular imaging with [18F]FDG and [68Ga]PSMA is superior to conventional imaging in RCC restaging and in assessing therapy response.

Antibodies targeting Prostate-Specific Membrane Antigen positive prostate cancer: from diagnostic imaging to theranostics

PURPOSE OF REVIEW

Targeting Prostate-Specific Membrane Antigen (PSMA) has paved the way for personalized medicine in prostate cancer (PCa) patients. This review aims to highlight the role of PSMA targeting antibodies in PCa, for diagnostic and therapeutic purposes.

RECENT FINDINGS

PSMA Positron Emission Tomography/Computed Tomography has been a game changer in the diagnosis of PCa in the recent decade. Two anti-PSMA monoclonal antibodies have been studied in PCa: 7E11-C35 (limited use) and J591. J591 antibody was used for diagnostic purposes coupled with different radionuclides. Most importantly, it was combined to numerous therapeutic radionuclides such as Lutetium-177 (177Lu), Yttrium-90 (90Y), Indium-111 (111In), and Actinium-225 (225Ac). It was also conjugated to drugs forming antibody-drug conjugates (e.g. MLN2704 and PSMA-ADC). These compounds were tested in recent phase I/II clinical trials.

SUMMARY

PSMA targeting antibodies are very promising for further clinical investigation and continue to be a momentous research area, for both imaging and therapeutic settings. Although some clinical trials resulted in unfavorably safety profiles for some antibodies, they validated PSMA as a crucial immunoconjugate target.

Assessing the correlation between 68Ga-PSMA-11 renal PET parameters and renal function tests

Aim: ⁶⁸Ga -PSMA ligands are used for prostate cancer but also show high renal cortical uptake. In this study, we aimed to assess if there is any correlation between renal PSMA PET parameters and renal function tests using the images of prostate cancer patients. Methods: ⁶⁸Ga-PSMA-11 PET/CT images of the patients with prostate cancer were retrospectively evaluated. The following PET parameters were obtained: SUV_max, SUVmean, SULmax, SULmean, volume, TLGSUL and counts of both kidneys as well as SUVmean of liver, blood pool and spleen. Total TLGSUL, total volume, kidney to liver and kidney to blood pool ratios were calculated. Patient's creatinine values were obtained and GFR was calculated using the MDRD formula. Statistical analysis was performed to understand if there is a correlation between above parameters and renal function tests. Results: Twenty five patients were included in this study. GFR was significantly/positively correlated and creatinine was significantly/negatively correlated with renal SUV/liver SUV and renal SUV/blood pool SUV ratios. GFR was marginally positively correlated with renal SULmean and creatinine was marginally negatively correlated with total TLGSUL. Total renal parenchymal volume was significantly and directly (positively) associated with GFR and significantly and inversely (negatively) associated with creatinine. Conclusion: Renal ⁶⁸Ga-PSMA uptake appears to be correlated with renal function tests. Our method of measuring approximate renal parenchymal volume on PET image appears to be reliable.

Renal Cortical Scarring: 68Ga-PSMA-11 PET versus 99mTc-DMSA Scan in a Case with Pyelonephritis

We previously reported ⁶⁸Ga-prostate‑specific membrane antigen (PSMA)-11 and ^99mTcdimercaptosuccinic acid (DMSA) images of the 1st case of our prospective research comparing renal PSMA PET to DMSA scan in adult patients with pyelonephritis. Here, we present renal cortical PSMA PET and DMSA images of our 2nd patient with chronic recurring pyelonephritis which demonstrated renal parenchymal defects secondary to scarring in the kidney.

SUV95th as a Reliable Alternative to SUVmax for Determining Renal Uptake in [68Ga] PSMA PET/CT

PURPOSE

Widely used in clinical practice, the maximum standardized uptake value (SUV_max) is a statistical index highly prone to physical and biological variations, which can lead to unpredictable errors. This study has a methodological aim: to identify a more robust SUV-based index representing the tracer accumulation. In particular, the new metric was tested to confirm the potential of mannitol to reduce renal uptake Ga-68 prostate-specific membrane antigen ([₆₈Ga]PSMA).

PROCEDURES

To this aim, our previously published work, proving the efficacy of mannitol, was considered as a background study. Renal SUV_max was calculated in nine patients undergoing [⁶⁸Ga]PSMA positron emission tomography (PET)/X-ray computed tomography (CT) at baseline (b-PET/CT) and at follow-up after intravenous infusion of 500 ml of 10 % mannitol (m-PET/CT). SUV values of kidney volumes were extracted by a new 3D segmentation method. A new parameter, the median computed on the upper 10% of the SUV distribution (SUV_95th), was introduced to better characterize the tracer accumulation. A comparison between SUV_max and SUV_95th was also performed. Kruskal-Wallis test was used to assess the statistical significance of the differences in SUV_95th between b-PET/CT and m-PET/CT.

RESULTS

SUV_95th not only confirmed the efficacy of mannitol as demonstrated in the previous study but improved the separability of b-PET/CT and m-PET/CT examinations, overturning SUV_max findings in two cases. The outcomes of the Kruskal-Wallis test computed for each kidney proved that differences between b-PET/CT and m-PET/CT SUV_95th values were significant (p value < 0.001).

CONCLUSIONS

Our findings indicate that SUV_95th is a more robust index to assess high uptake level, representing a reliable alternative to SUV_max. Independently from the segmentation method, the superiority of SUV_95th and its easy computation could make its clinical impact decisive. The results obtained with SUV_95th, more representative of tracer uptake than those with SUV_max suggest, in our opinion, that mannitol infusion could be used to reduce the adsorbed dose to the kidneys during [⁶⁸Ga]PSMA PET/CT and Lu-177 or Ac-225 therapy. Our future goal will be confirming this effect in a larger cohort of patients, also verifying the role of SUV_95th in the evaluation of tumor response to therapy.

PET/CT limitations and pitfalls in urogenital cancers

Hybrid FDG PET/CT plays a vital role in oncologic imaging and has been widely adopted for the staging and restaging of a variety of malignancies. Its diagnostic value in urogenital malignancies is less well-known, not at least because of the variable FDG avidity of these tumor entities, the sites of these tumors, and technical challenges associated with sequential imaging of CT and PET. PET/CT interpretation thus can be especially challenging and is associated with many pitfalls, which can lead to both false-positive and false-negative diagnoses as well as incorrect assessment of metabolic change following therapy. Currently, FDG PET/CT is not the standard of care for the initial diagnosis or staging of early-stage or low-risk urogenital cancers; however, it can help evaluate distant metastatic disease, response to therapy, and disease recurrence in high-risk patients. Knowledge of imaging features of tumor metabolic avidity and pitfalls is essential for accurate interpretation.

PSMA-PET/CT in Patients with Recurrent Clear Cell Renal Cell Carcinoma: Histopathological Correlations of Imaging Findings

PET/CT with prostate-specific membrane antigen (PSMA)-targeted tracers has been used in the diagnosis and staging of patients with clear cell renal cell carcinoma (ccRCC). For ccRCC primary tumors, PET parameters were shown to predict histologic grade and features. The aim of this study was to correlate PSMA PET/CT with histopathological findings in patients with metastatic recurrence of ccRCC. Patients with ccRCC who underwent PSMA-targeted PET/CT and subsequent histopathological evaluation of suspicious lesions were included. Specimens underwent immunohistochemical marking. Lesion diameter, volume and tracer uptake were correlated with the extent and intensity of molecular PSMA expression and with clinical findings. Twelve PET-positive lesions of nine patients were evaluated. Eleven ccRCC metastases and one prostate carcinoma were detected histopathologically. Molecular PSMA expression was detected in all lesions, which intensity and distribution did not correlate with PET parameters. PSMA-targeted PET/CT is a feasible tool for the evaluation of patients with ccRCC but cannot reliably predict histologic features of metastases. PSMA may also be expressed in malignant lesions other than ccRCC, leading to incidental detection of these tumors.

PSMA radioligand therapy for solid tumors other than prostate cancer: background, opportunities, challenges, and first clinical reports

In the past decade, a growing body of literature has reported promising results for prostate-specific membrane antigen (PSMA)-targeted radionuclide imaging and therapy in prostate cancer. First clinical studies evaluating the efficacy of [¹⁷⁷Lu]Lu-PSMA radioligand therapy (PSMA-RLT) demonstrated favorable results in prostate cancer patients. [¹⁷⁷Lu]Lu-PSMA is generally well tolerated due to its limited side effects. While PSMA is highly overexpressed in prostate cancer cells, varying degrees of PSMA expression have been reported in other malignancies as well, particularly in the tumor-associated neovasculature. Hence, it is anticipated that PSMA-RLT could be explored for other solid cancers. Here, we describe the current knowledge of PSMA expression in other solid cancers and define a perspective towards broader clinical implementation of PSMA-RLT. This review focuses specifically on salivary gland cancer, glioblastoma, thyroid cancer, renal cell carcinoma, hepatocellular carcinoma, lung cancer, and breast cancer. An overview of the (pre)clinical data on PSMA immunohistochemistry and PSMA PET/CT imaging is provided and summarized. Furthermore, the first clinical reports of non-prostate cancer patients treated with PSMA-RLT are described.

Automatic radiosynthesis and preclinical evaluation of 18F-AlF-PSMA-NF as a potential PET probe for prostate cancer imaging

Facile automatic production is important for the application of prostate-specific membrane antigen (PSMA) tracers in clinical practice. We developed a new ¹⁸F-AlF-labelled PSMA probe-¹⁸F-AlF-PSMA-NF-and explore its automated production method and potential value in clinical settings. ¹⁸F-AlF-PSMA-NF was prepared using an automated method with dimethylformamide (DMF) as the solvent in a positron emission tomography (PET)-MF-2 V-IT-I synthesizer. Tracer characteristics were examined both in vitro and in vivo. Micro-PET/computed tomography (CT) was performed to investigate the utility of ¹⁸F-AlF-PSMA-NF for imaging PSMA-positive tumours in vivo. ¹⁸F-AlF-PSMA-NF was prepared automatically within 35 min with a non-attenuation correction yield of 37.9 ± 11.2%. The tracer was hydrophilic, had a high affinity for PSMA (Kd = 2.58 ± 0.81 nM), and showed stability in both in vitro and in vivo conditions. In the cellular experiments, ¹⁸F-AlF-PSMA-NF uptake in PSMA-positive LNCaP cells was significantly higher than that in PSMA-negative PC-3 cells (P < 0.001), and could be blocked by excess ZJ-43-a PSMA inhibitor (P < 0.001). LNCaP tumours were clearly visualized by ¹⁸F-AlF-PSMA-NF on micro-PET/CT, with a high level of uptake (13.72 ± 2.01 percent injected dose per gram of tissue [%ID/g]) and high tumour/muscle ratio (close to 50:1). The PSMA-positive LNCaP tumours had a significantly higher uptake than PSMA-negative PC-3 tumours (13.72 ± 2.01%ID/g vs. 1.07 ± 0.48%ID/g, t = 10.382, P < 0.001), and could be blocked by ZJ-43 (13.72 ± 2.01%ID/g vs. 2.77 ± 1.44%ID/g, t = 8.14, P < 0.001). A new ¹⁸F-AlF-labelled PSMA probe-¹⁸F-AlF-PSMA-NF-was successfully developed and can be prepared automatically. It has the biological characteristics resembling that of a PSMA-based probe and can potentially be used in clinical settings.

Radiolabeling Optimization and Preclinical Evaluation of the New PSMA Imaging Agent [18F]AlF-P16-093

Prostate-specific membrane antigen (PSMA)-targeted radioligands have played an increasing role in the diagnosis of prostate cancer. [⁶⁸Ga]Ga-P16-093 is a PSMA-targeting agent for positron emission tomography imaging, currently under a Phase 2 clinical trial. In the present study, P16-093 was labeled with ¹⁸F via [¹⁸F]AlF²⁺ complex formation, and the biological properties of [¹⁸F]AlF-P16-093 were evaluated. Optimization of radiolabeling efficiency was performed by testing a series of parameters, including the amount of free ligand; the amount of Al³⁺; and the influence of solvent, pH, temperature, reaction time, and reaction volume. Optimal labeling results were achieved at pH 5 by reacting at 60 °C for 15 min in a vial containing 74-370 MBq of [¹⁸F]fluoride, 46 nmol of P16-093, 40 nmol of AlCl₃·6 H₂O, and 50% EtOH. [¹⁸F]AlF-P16-093 was prepared with a non-decay-corrected radiochemical yield of 54.4 ± 4.4% (n = 9) within 30 min (final radiochemical purity ≥95%). In vitro, [¹⁸F]AlF-P16-093 showed PSMA-specific high uptakes in PIP-PC3 cells. The binding affinity of [¹⁸F]AlF-P16-093 to PSMA was determined as K_d of 12.4 ± 2.0 nM. The tumor uptake in mice with a xenografted PSMA-expressing PIP-PC3 tumor was high (18.8 ± 5.14% ID/g at 1 h postinjection) and retained without washout for 2 h. In addition, tumor uptake was almost completely blocked by coinjecting a PSMA inhibitor, 2-PMPA. The bone activity at 1 h post injection was higher with [¹⁸F]AlF-P16-093 (2.83 ± 0.49% ID/g) in comparison to that of [⁶⁸Ga]Ga-P16-093 (0.26 ± 0.07% ID/g). In summary, an efficient and simple radiosynthesis of [¹⁸F]AlF-P16-093 was achieved. [¹⁸F]AlF-P16-093 showed desirable in vivo pharmacokinetics and excellent PSMA-targeting properties for imaging PSMA expression in prostate cancer.

Modulation of the Pharmacokinetics of a Radioligand Targeting Carbonic Anhydrase-IX with Albumin-Binding Moieties

The expression of carbonic anhydrase-IX (CA-IX) in tumors can lead to a poor prognosis; thus, CA-IX has attracted much attention as a target molecule for cancer diagnosis and treatment. An ¹¹¹In-labeled imidazothiadiazole sulfonamide (IS) derivative, [¹¹¹In]In-DO3A-IS1, exhibited marked tumor accumulation but also marked renal accumulation, raising concerns about it producing a low signal/background ratio and a high radiation burden on the kidneys. In this study, four ¹¹¹In-labeled IS derivatives, IS-[¹¹¹In]In-DO2A-ALB1-4, which contained four different kinds of albumin binder (ALB) moieties, were designed and synthesized with the aim of improving the pharmacokinetics of [¹¹¹In]In-DO3A-IS1. Their utility for imaging tumors that strongly express CA-IX was evaluated in mice. An in vitro binding assay of cells that strongly expressed CA-IX (HT-29 cells) was performed using acetazolamide as a competitor against CA-IX, and IS-[¹¹¹In]In-DO2A-ALB1-4 did not exhibit reduced binding to HT-29 cells compared with [¹¹¹In]In-DO3A-IS1. In contrast, IS-[¹¹¹In]In-DO2A-ALB1-4 showed a greater ability to bind to human serum albumin than [¹¹¹In]In-DO3A-IS1 in vitro. In an in vivo biodistribution study, the introduction of an ALB moiety into the ¹¹¹In-labeled IS derivative markedly decreased renal accumulation and increased HT-29 tumor accumulation and blood retention. The pharmacokinetics of the IS derivatives varied depending on the substituted group within the ALB moiety. Single-photon emission computed tomography imaging with IS-[¹¹¹In]In-DO2A-ALB1, which showed the highest tumor/kidney ratio in the biodistribution study, facilitated clear HT-29 tumor imaging, and no strong signals were observed in the normal organs. These results indicate that IS-[¹¹¹In]In-DO2A-ALB1 may be an effective CA-IX imaging probe and that the introduction of ALB moieties may improve the pharmacokinetics of CA-IX ligands.

18F-PSMA-1007 PET/CT for Initial Staging of Renal Cell Carcinoma in an End-Stage Renal Disease Patient

A 46-year-old man with end-stage renal disease and renal cell carcinoma underwent F-FDG PET/CT for initial staging followed by F-PSMA-1007 PET/CT. Unlike F-FDG, which undergoes renal clearance, F-PSMA-1007 undergoes hepatobiliary clearance and thus generates superior quality images. F-PSMA-1007 PET/CT showed intense tracer-avid left renal mass lesion (FDG nonavid); lytic bone lesions (FDG avid) and single liver lesion (FDG nonavid). This case highlights the superiority of F-PSMA-1007 over F-FDG PET/CT in identifying primary lesion as well as metastatic sites in case of renal cell carcinoma even in the presence of end-stage renal disease.

Incremental Value of Post Diuretic 68Ga-PSMA-11 PET-CT in Characterization of Indeterminate lLesions in Prostate Cancer

Objective:

The aim of current study is to evaluate the role of diuretic assisted ⁶⁸Ga-PSMA PET-CT, on image quality and clinical interpretation of indeterminate/equivocal lesions in pre-Lasix imaging of Prostate cancer.

Materials and Methods:

Forty-five patients underwent baseline ⁶⁸Ga-PSMA-11 scan 45-60 minutes post tracer injection followed by post Lasix study after ±15 minutes. The contrast to noise ratios (CNR), noise and SUVmax were determined for the focal uptakes in both pre and post Lasix images. All continuous variables were expressed as mean ± SD. Images were assessed by two experienced physicians in order to evaluate lesion detectability and delineations that have an impact on clinical interpretation.

Results:

Of total 45 patients, 12/45 (27%) showed unremarkable scan along with 33/45 (73%) showing metastases. Sixteen out of 45 (36%) of the metastatic scans showed indeterminate/equivocal lesions. In these cases, post Lasix study showed false negative findings in 7/45 (16%), better delineation of lesions 10/45 (22%), better confidence towards reporting lesions as abnormal in 5/45 (11%) with an overall 11/45 (24%) of the cases who showed increase in the number of the lesions after the Lasix study. The overall CNR was evaluated using Wilcoxon Rank test (p-value = 0.02) which suggested significant improved ratios in the post-Lasix imaging by 49.6%±24.5. There was a substantial agreement (k =0.76) between the physicians when comparing the lesion clarity and delineation in post Lasix images. The average score for physician one and two being 2.4 ±0.71 and 2.53±0.52 respectively.

Conclusion:

Post diuretic ⁶⁸Ga-PSMA imaging at ± 15 minutes clears the unwanted activity in the urinary tract which in turn improves the contrast to noise ratios. Thus leading to decline in false positive findings, improved diagnostic certainty of physician and better detection of indeterminate lesions in ⁶⁸Ga-PSMA imaging.