Current use of PSMA-PET in prostate cancer management. Nat Rev Urol. 2016;13:226-235. [PMID: 26902337 DOI: 10.1038/nrurol.2016.26]

Novel technetium-99m-labeled bivalent PSMA-targeting probe based on hydroxamamide chelate for diagnosis of prostate cancer

OBJECTIVE

Prostate-specific membrane antigen (PSMA) is a well-known biomarker of prostate cancer. Previously, our group reported that the succinimidyl-cystatin-urea-glutamate (SCUE) moiety has a high affinity for PSMA. In this study, we developed the novel technetium-99m-labeled PSMA-targeting probe "[99mTc]Tc-(Ham-SCUE)2" based on a hydroxamamide chelate with a bivalent SCUE and evaluated its potential as a SPECT imaging probe for the diagnosis of PSMA-expressing prostate cancer.

METHODS

Ham-SCUE was synthesized by a one-step reaction with Ham-Mal and cysteine-urea-glutamine. Then, Ham-SCUE was reacted with [99mTc]NaTcO4 for 10 min at room temperature to obtain [99mTc]Tc-(Ham-SCUE)2. [99mTc]Tc-(Ham-SCUE)2 was added to LNCaP (high PSMA expression) cells or PC3 (low PSMA expression) cells, and their radioactivity was measured 60 min after administration. The blocking study was performed by co-incubation of LNCaP cells with various concentrations of 2-PMPA (a PSMA inhibitor) for 15 min before adding [99mTc]Tc-(Ham-SCUE)2. The biodistribution of [99mTc]Tc-(Ham-SCUE)2 in LNCaP/PC3 dual xenografted C.B.-17/Icr scid/scid Jcl mice was evaluated for 120 min after intravenous injection. The blocking study was performed by pretreatment of mice with 2-PMPA (10 mg/kg weight).

RESULTS

[99mTc]Tc-(Ham-SCUE)2 was acquired at radiochemical yields of 56% with a radiochemical purity of over 95%. The cellular uptake level of [99mTc]Tc-(Ham-SCUE)2 by LNCaP cells was significantly higher than that by PC3 cells (LNCaP: 11.12 ± 0.71 vs. PC3: 1.40 ± 0.13%uptake/mg protein, p < 0.01), and the uptake was significantly suppressed by pretreatment with 2-PMPA (2.56 ± 0.37%uptake/mg protein, p < 0.05). IC50 of 2-PMPA was 245 ± 47 nM. In the in vivo study, the radioactivity of LNCaP tumor tissue was significantly higher than that of PC3 tumor tissue at 120 min after the administration of [99mTc]Tc-(Ham-SCUE)2 (LNCaP: 9.97 ± 2.79, PC3: 1.16 ± 0.23%ID/g, p < 0.01), and was suppressed by pretreatment with 2-PMPA (2.50 ± 0.45%ID/g, p < 0.01).

CONCLUSION

[99mTc]Tc-(Ham-SCUE)2 has the potential to be a SPECT imaging agent for diagnosing high PSMA-expressing prostate cancer.

PSMA and Sigma-1 receptor dual-targeted peptide mediates superior radionuclide imaging and therapy of prostate cancer

Radionuclide therapy, in particular peptide receptor radionuclide therapy (PRRT), has emerged as a valuable means to combat malignant tumors. The specific affinity of ACUPA peptide toward prostate-specific membrane antigen (PSMA) renders the successful development of PRRT for prostate cancer. The clinical outcome of PRRT is, however, generally challenged by moderate tumor uptake and off-target toxicity. Here, we report on a novel design of Sigma-1 receptor and PSMA dual-receptor targeted peptide (S1R/PSMA-P) for superior radionuclide imaging and therapy of prostate cancer. S1R/PSMA-P was acquired with good purity and could efficiently be labeled with 177Lu to yield 177Lu-S1R/PSMA-P with high specific activity and radiostability. Interestingly, 177Lu-S1R/PSMA-P revealed greatly enhanced affinity to LNCaP cells over single-targeted control 177Lu-PSMA-617. The single photon emission computed tomography (SPECT) imaging demonstrated exceptional uptake and retention of 177Lu-S1R/PSMA-P in LNCaP tumor, affording about 2-fold better tumor accumulation while largely reduced uptake by most normal tissues compared to 177Lu-PSMA-617. The selective uptake in LNCaP tumor was also visualized by positron emission tomography (PET) with 68Ga-S1R/PSMA-P. In accordance, a single and low dosage of 177Lu-S1R/PSMA-P at 11.1 MBq effectively suppressed tumor growth without causing apparent side effects. This dual-targeting strategy presents an appealing radionuclide therapy for malignant tumors.

Assessing the Heterogeneity of Response of [68Ga] Ga-PSMA-11 PET/CT Lesions in Patients With Biochemical Recurrence of Prostate Cancer

INTRODUCTION

Treatment of men with metastatic prostate cancer can be difficult due to the heterogeneity of response of lesions. [68Ga]Ga-PSMA-11 (PSMA) PET/CT assists with monitoring and directing clinical intervention; however, the impact of response heterogeneity has yet to be related to outcome measures. The aim of this study was to assess the impact of quantitative imaging information on the value of PSMA PET/CT to assess patient outcomes in response evaluation.

PATIENTS AND METHODS

Baseline and follow-up (6 months) PSMA PET/CT of 162 men with oligometastatic PC treated with standard clinical care were acquired between 2015 and 2016 for analysis. An augmentative software medical device was used to track lesions between scans and quantify lesion change to categorize them as either new, increasing, stable, decreasing, or disappeared. Quantitative imaging features describing the size, intensity, extent, change, and heterogeneity of change (based on percent change in SUVtotal) among lesions were extracted and evaluated for association with overall survival (OS) using Cox regression models. Model performance was evaluated using the c-index.

RESULTS

Forty-one (25%) of subjects demonstrated heterogeneous response at follow-up, defined as having at least 1 new or increasing lesion and at least 1 decreasing or disappeared lesion. Subjects with heterogeneous response demonstrated significantly shorter OS than subjects without (median OS = 76.6 months vs. median OS not reached, P < .05, c-index = 0.61). In univariate analyses, SUVtotal at follow-up was most strongly associated with OS (HR = 1.29 [1.19, 1.40], P < .001, c-index = 0.73). Multivariable models applied using heterogeneity of change features demonstrated higher performance (c-index = 0.79) than models without (c-index = 0.71-0.76, P < .05).

CONCLUSION

Augmentative software tools enhance the evaluation change on serial PSMA PET scans and can facilitate lesional evaluation between timepoints. This study demonstrates that a heterogeneous response at a lesional level may impact adversely on patient outcomes and supports further investigation to evaluate the role of imaging to guide individualized patient management to improve clinical outcomes.

Pattern of Failure in Patients with Biochemical Recurrence After PSMA Radioguided Surgery

Prostate-specific membrane antigen (PSMA)-targeted radioguided surgery (RGS) is evolving as a new treatment modality for patients with early biochemical recurrence of prostate cancer and disease limited to locoregional lymph nodes on PSMA-ligand PET/CT. Nevertheless, the pattern of failure (locoregional vs. systemic) after PSMA RGS remains unknown. Therefore, the aim of this retrospective analysis was to evaluate the pattern of disease using PSMA-ligand PET in patients experiencing relapse after PSMA RGS. Methods: We evaluated 100 patients with biochemical recurrence after previous PET-guided PSMA RGS who underwent PSMA-ligand PET (median prostate-specific antigen [PSA], 0.9 ng/mL; range, 0.2-14.2 ng/mL). All suspicious lesions for recurrent prostate cancer were grouped according to the molecular imaging TNM classification system. Detection rates and lesion localization were determined and stratified by PSA values and the International Society of Urological Pathology grade group. Further, lesion localization was compared before and after PSMA RGS. Results: The median time between PSMA RGS and PSMA-ligand PET for relapse was 11.4 mo (range, 5.5-25.6 mo). In total, 91 of 100 (91%) patients showed PSMA-ligand-positive findings. PSMA PET detection rates were 82.6%, 92.6%, 91.3%, and 96.3% for PSA levels of 0.2-0.49, 0.5-0.99, 1-1.99, and at least 2 ng/mL, respectively. More than half of the patients (53%; 48/91) showed local recurrence or pelvic lymph node metastases only. Extrapelvic lymph node metastases, bone metastases, and visceral metastases were present in 22% (20/91), 16% (15/91), and 9% (8/91) of the patients, respectively. With increasing International Society of Urological Pathology grade group, the percentage of patients with bone and visceral metastases increased, whereas the number of patients with only locoregional disease decreased. Conclusion: PSMA-ligand PET is a useful method to detect and localize recurrent disease in patients with biochemical failure after PSMA RGS, with more than half of the patients presenting with locoregional recurrence, offering the potential for a second local therapy (e.g., radiation therapy or repeated surgery).

Potential application of [18F]AlF-PSMA-11 PET/CT in radioiodine refractory thyroid carcinoma

BACKGROUND

Patients diagnosed with radioiodine refractory (RAI-R) thyroid carcinoma (TC) have a significantly worse prognosis than patients with radiosensitive TC. These refractory malignancies are often dedifferentiated, hindering the effectiveness of iodine-based imaging. Additionally, the role of metabolic imaging using [18F]FDG PET/CT is also limited in these cases, making adequate staging of RAI-R TC challenging. Recent case series have shown promising results regarding the role of the prostate-specific membrane antigen (PSMA) in TC. In this study we explored the value of [18F]AlF-PSMA-11 PET/CT in RAI-R TC.

METHODS

In this phase II study, lesions detected on [18F]AlF-PSMA-11 PET were compared to findings from [18F]FDG PET/CT. Additionally, the serologic soluble prostate-specific membrane antigen (sPSMA) was measured using ELISA. PSMA-expression on tumor tissue in any available resection specimens was analysed with an immunostainer.

RESULTS

Eight patients were included, with a total of 39 identified lesions based on PET imaging. [18F]AlF-PSMA-11 PET identified 30 of 39 lesions, and [18F]FDG PET identified 33 lesions, leading to a detection rate of 76.9% and 84.6%, respectively. Interestingly, while nine lesions were solely visualized on [18F]FDG, six were uniquely seen on [18F]AlF-PSMA-11 PET. While sPSMA was immeasurable in all female patients, no correlation was found between sPSMA in male patients and disease-related factors. In five out of eight patients immunohistology showed PSMA expression on the primary tumor.

CONCLUSIONS

Although not all lesions could be visualized, [18F]PSMA-11 PET identified multiple lesions imperceptible on [18F]FDG PET. These results display the potential additional diagnostic role of PSMA-targeted imaging in patients with RAI-R TC. Trial registration number No. EudraCT 2021-000456-19.

Evaluation of the prostate cancer and its metastases in the [68Ga]Ga-PSMA PET/CT images: deep learning method vs. conventional PET/CT processing

PURPOSE

This study demonstrates the feasibility and benefits of using a deep learning-based approach for attenuation correction in [68Ga]Ga-PSMA PET scans.

METHODS

A dataset of 700 prostate cancer patients (mean age: 67.6 ± 5.9 years, range: 45-85 years) who underwent [68Ga]Ga-PSMA PET/computed tomography was collected. A deep learning model was trained to perform attenuation correction on these images. Quantitative accuracy was assessed using clinical data from 92 patients, comparing the deep learning-based attenuation correction (DLAC) to computed tomography-based PET attenuation correction (PET-CTAC) using mean error, mean absolute error, and root mean square error based on standard uptake value. Clinical evaluation was conducted by three specialists who performed a blinded assessment of lesion detectability and overall image quality in a subset of 50 subjects, comparing DLAC and PET-CTAC images.

RESULTS

The DLAC model yielded mean error, mean absolute error, and root mean square error values of -0.007 ± 0.032, 0.08 ± 0.033, and 0.252 ± 125 standard uptake value, respectively. Regarding lesion detection and image quality, DLAC showed superior performance in 16 of the 50 cases, while in 56% of the cases, the images generated by DLAC and PET-CTAC were found to have closely comparable quality and lesion detectability.

CONCLUSION

This study highlights significant improvements in image quality and lesion detection capabilities through the integration of DLAC in [68Ga]Ga-PSMA PET imaging. This innovative approach not only addresses challenges such as bladder radioactivity but also represents a promising method to minimize patient radiation exposure by integrating low-dose computed tomography and DLAC, ultimately improving diagnostic accuracy and patient outcomes.

Leptomeningeal metastases in prostate cancer: A review of the current literature

Leptomeningeal metastasis/leptomeningeal carcinomatosis (LMC; terms used interchangeably) is an inflammatory complication of primary tumors that involves the spread of the disease to the meninges (specifically the arachnoid and pia maters) and spinal cord. In the United States, approximately 110,000 new cases are diagnosed each year, and the prognosis is usually poor. Complications of LMC include cognitive impairment, cranial nerve dysfunction, ischemic stroke, and mortality. The survival times of untreated and treated LMC are approximately 4-6 weeks and 2-4 months, respectively. Leptomeningeal carcinomatoses are usually metastatic cancers that spread to the central nervous system. Although lung and breast cancers have a clearly defined relationship with LMC, it remains unclear whether prostate cancer (PC) is also directly associated with LMC. To determine whether such association exists, we conducted a PubMed review of the literature on patients with PC with coexisting LMCs. Our search yielded 23 case reports of patients with preexisting PC who developed LMC. In addition, 2 retrospective cohort studies were examined. Various findings were identified in the revised cases and studies. The first 3 findings were related to the progression of the disease: patients presenting with neurological disease symptoms were in remission from PC for 7 years on average, LMCs tended to occur after other cancer diagnoses, and the disease had already rapidly progressed by the time the symptoms were present. Regarding diagnosis, the major finding was that most LMCs were detected by magnetic resonance imaging (which does not detect early dissemination), and it was suggested that single-photon emission computed tomography or positron emission tomography imaging could be used for earlier detection. Finally, in terms of treatment, the main finding was that treatment was palliative rather than curative and that prognosis remained poor despite treatment. On the basis of these results, we recommend for individuals with risk factors, such as high-grade PC and hormonal PC, to be evaluated on a case-by-case basis for increased surveillance of LMC development.

One-Step Synthesis of [18F]Aromatic Electrophile Prosthetic Groups via Organic Photoredox Catalysis

To avoid the harsh conditions that are oftentimes adopted in direct radiofluorination reactions, conjugation of bioactive ligands with 18F-labeled prosthetic groups has become an important strategy to construct novel PET agents under mild conditions when the ligands are structurally sensitive. Prosthetic groups with [18F]fluoroarene motifs are especially appealing because of their stability in physiological environments. However, their preparation can be intricate, often requiring multistep radiosynthesis with functional group conversions to prevent the decomposition of unprotected reactive prosthetic groups during the harsh radiofluorination. Here, we report a general and simple method to generate a variety of highly reactive 18F-labeled electrophiles via one-step organophotoredox-mediated radiofluorination. The method benefits from high step-economy, reaction efficiency, functional group tolerance, and easily accessible precursors. The obtained prosthetic groups have been successfully applied in PET agent construction and subsequent imaging studies, thereby demonstrating the feasibility of this synthetic method in promoting imaging and biomedical research.

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Prostate-specific membrane antigen-radioguided surgery salvage lymph node dissection: experience with fifty oligorecurrent prostate cancer patients

PURPOSE

The higher detection efficacy of PSMA PET for oligometastatic recurrence of prostate cancer has promoted new loco-regional treatment options. PSMA-targeted radioguided surgery (PSMA-RGS) was introduced to facilitate salvage surgery of small tumor deposits. The objectives of this retrospective analysis are to describe an independent single-center consecutive cohort of patients undergoing PSMA-RGS and to evaluate its clinical and oncological outcomes.

METHOD

Between 2018 and 2022, 53 patients were treated with PSMA-RGS and 50 patients were available for final analyses. All patients were initially treated with radical prostatectomy (RP) and presented with biochemical recurrence (BCR) with at least one positive lesion on PSMA-PET imaging. After preparation of 99mTc-PSMA-I&S and intravenous injection, surgery was performed by using a gamma-probe intraoperatively.

RESULTS

Median age was 70 years (IQR 65-73) and the median PSA at salvage surgery was 1.2 ng/mL (IQR 0.6-3.0). In all patients pathologically positive lesions could be removed during PSMA-RGS. 29 (58%) patients had one pathologically positive lesion, 14 (28%) had two and 7 (14%) had three or more, respectively. The overall complication rate was 26% with 4 (8%), 1 (2%), and 8 (16%) having Clavien-Dindo (CD) type I, II, and IIIb complications, respectively. During the follow-up period 31 (62%) patients experienced BCR and 29 (58%) received further therapy.

CONCLUSIONS

PSMA-RGS is a promising treatment option to enhance salvage surgery in early biochemical recurrence. However, only 42% of the patients treated with PSMA RGS remain without a biochemical recurrence. Further research is mandatory to identify patients, who profit from PSMA-RGS.

Diagnostic efficacy of [99mTc]Tc-PSMA SPECT/CT for prostate cancer: a meta-analysis

BACKGROUND

Prompt and accurate diagnosis of prostate cancer (PCa) is of paramount importance for effective treatment planning. While Gallium-68 labeled prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) has proven efficacy in detecting PCa, limited availability poses challenges. As a potential alternative, [99mTc]Tc-PSMA single photon emission computed tomography (SPECT)/computed tomography (CT) holds promise. This systematic review and meta-analysis aimed to evaluate the diagnostic value of [99mTc]Tc-PSMA SPECT/CT for prostate cancer.

METHODS

A comprehensive search of PubMed, Cochrane, EMBASE, Scopus, Ovid, and Web of Science databases was conducted until July 2024. Sensitivity and specificity data were extracted to assess the diagnostic accuracy of [99mTc]Tc-PSMA SPECT/CT, while the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool was used to evaluate study quality. Statistical analyses were performed using STATA 18, with MetaDisc 1.4 employed to detect threshold effects. Diagnostic accuracy indicators, including sensitivity, specificity, diagnostic odds ratio (DOR), negative likelihood ratio (LR-), and positive likelihood ratio (LR+), were pooled. The area under the curve (AUC) of the combined model was calculated using summary receiver-operating characteristic (SROC) curves.

RESULTS

Seven studies meeting the inclusion criteria were identified from an initial pool of 1467 articles, with no publication bias observed. The pooled sensitivity, specificity, and AUC of [99mTc]Tc-PSMA SPECT/CT were found to be 0.89 (95% CI, 0.84-0.93), 0.92 (95% CI, 0.67-0.99), and 0.93 (95% CI, 0.90-0.95), respectively. Additionally, the comprehensive diagnostic odds ratio, diagnostic score, positive likelihood ratio, and negative likelihood ratio were calculated as 95.24 (95% CI, 17.30-524.41), 4.56 (95% CI, 2.85-6.26), 11.35 (95% CI, 2.31-55.71), and 0.12 (95% CI, 0.08-0.18), respectively.

CONCLUSIONS

In conclusion, our findings demonstrate that [99mTc]Tc-PSMA SPECT/CT exhibits favorable diagnostic performance for prostate cancer and can provide valuable supplementary information, particularly in regions and settings where [68Ga]Ga-PSMA PET/CT availability is limited, such as remote areas. These results highlight the potential of [99mTc]Tc-PSMA SPECT/CT as a valuable tool in the diagnosis and management of prostate cancer, warranting further investigation and validation in larger patient cohorts.

From foes to friends: rethinking the role of lymph nodes in prostate cancer

Clinically localized prostate cancer is often treated with radical prostatectomy combined with pelvic lymph node dissection. Data suggest that lymph node dissection does improve disease staging, but its therapeutic value has often been debated, with few studies showing that lymph node removal directly improves oncological outcomes; however, lymph nodes are an important first site of antigen recognition and immune system activation and the success of many currently used immunological therapies hinges on this dogma. Evidence, particularly in the preclinical setting, has demonstrated that the success of immune checkpoint inhibitors is dampened by the removal of tumour-draining lymph nodes. Thus, whether lymph nodes are truly 'foes' or whether they are actually 'friends' in oncological care is an important idea to discuss.

Biological determinants of PSMA expression, regulation and heterogeneity in prostate cancer

Prostate-specific membrane antigen (PSMA) is an important cell-surface imaging biomarker and therapeutic target in prostate cancer. The PSMA-targeted theranostic 177Lu-PSMA-617 was approved in 2022 for men with PSMA-PET-positive metastatic castration-resistant prostate cancer. However, not all patients respond to PSMA-radioligand therapy, in part owing to the heterogeneity of PSMA expression in the tumour. The PSMA regulatory network is composed of a PSMA transcription complex, an upstream enhancer that loops to the FOLH1 (PSMA) gene promoter, intergenic enhancers and differentially methylated regions. Our understanding of the PSMA regulatory network and the mechanisms underlying PSMA suppression is evolving. Clinically, molecular imaging provides a unique window into PSMA dynamics that occur on therapy and with disease progression, although challenges arise owing to the limited resolution of PET. PSMA regulation and heterogeneity - including intertumoural and inter-patient heterogeneity, temporal changes, lineage dynamics and the tumour microenvironment - affect PSMA theranostics. PSMA response and resistance to radioligand therapy are mediated by a number of potential mechanisms, and complementary biomarkers beyond PSMA are under development. Understanding the biological determinants of cell surface target regulation and heterogeneity can inform precision medicine approaches to PSMA theranostics as well as other emerging therapies.

Reducing False-Positives Due to Urinary Stagnation in the Prostatic Urethra on 18 F-DCFPyL PSMA PET/CT With MRI

PURPOSE

Prostate-specific membrane antigen (PSMA)-targeting PET radiotracers reveal physiologic uptake in the urinary system, potentially misrepresenting activity in the prostatic urethra as an intraprostatic lesion. This study examined the correlation between midline 18 F-DCFPyL activity in the prostate and hyperintensity on T2-weighted (T2W) MRI as an indication of retained urine in the prostatic urethra.

PATIENTS AND METHODS

Eighty-five patients who underwent both 18 F-DCFPyL PSMA PET/CT and prostate MRI between July 2017 and September 2023 were retrospectively analyzed for midline radiotracer activity and retained urine on postvoid T2W MRIs. Fisher's exact tests and unpaired t tests were used to compare residual urine presence and prostatic urethra measurements between patients with and without midline radiotracer activity. The influence of anatomical factors including prostate volume and urethral curvature on urinary stagnation was also explored.

RESULTS

Midline activity on PSMA PET imaging was seen in 14 patients included in the case group, whereas the remaining 71 with no midline activity constituted the control group. A total of 71.4% (10/14) and 29.6% (21/71) of patients in the case and control groups had urethral hyperintensity on T2W MRI, respectively ( P < 0.01). Patients in the case group had significantly larger mean urethral dimensions, larger prostate volumes, and higher incidence of severe urethral curvature compared with the controls.

CONCLUSIONS

Stagnated urine within the prostatic urethra is a potential confounding factor on PSMA PET scans. Integrating PET imaging with T2W MRI can mitigate false-positive calls, especially as PSMA PET/CT continues to gain traction in diagnosing localized prostate cancer.

Comparison of digital and analog [68Ga]Ga-PSMA-11 PET/CT for detecting post-prostatectomy biochemical recurrence in prostate cancer patients: a prospective study

Digital positron emission tomography/computed tomography (PET/CT) has shown enhanced sensitivity and spatial resolution compared with analog PET/CT. The present study compared the diagnostic performance of digital and analog PET/CT with [68Ga]Ga-PSMA-11 in prostate cancer patients who experienced biochemical recurrence (BCR) after prostatectomy. Forty prostate cancer patients who experienced BCR, defined as serum prostate-specific antigen (PSA) concentrations exceeding 0.2 ng/mL after prostatectomy, were prospectively recruited. These patients were stratified into three groups based on their serum PSA levels. [68Ga]Ga-PSMA-11 was injected into each patient, and images were acquired using both analog and digital PET/CT scanners. Analog and digital PET/CT showed comparable lesion detection rate (71.8% vs. 74.4%), sensitivity (85.0% vs. 90.0%), and positive predictive value (PPV, 100.0% vs. 100.0%). However, digital PET/CT detected more lesions (139 vs. 111) and had higher maximum standardized uptake values (SUVmax, 14.3 vs. 10.3) and higher kappa index (0.657 vs. 0.502) than analog PET/CT, regardless of serum PSA levels. On both analog and digital PET/CT, lesion detection rates and interrater agreement increased with increasing serum PSA levels. Compared with analog PET/CT, digital PET/CT detected more lesions with a higher SUVmax and better interrater agreement in prostate cancer patients who experienced BCR after prostatectomy.

Diagnostic Accuracy of Molecular Imaging Techniques for Detecting Prostate Cancer: A Systematic Review

Molecular imaging modalities show valuable non-invasive techniques capable of precisely and selectively addressing molecular markers associated with prostate cancer (PCa). This systematic review provides an overview of imaging markers utilized in positron emission tomography (PET) methods, specifically focusing on the pathways and mediators involved in PCa. This systematic review aims to evaluate and analyse existing literature on the diagnostic accuracy of molecular imaging techniques for detecting PCa. The PubMed, EBSCO, ScienceDirect, and Web of Science databases were searched, identifying 32 studies that reported molecular imaging modalities for detecting PCa. Numerous imaging modalities and radiotracers were used to detect PCa, including 68Ga-prostate-specific membrane antigen (PSMA) PET/computed tomography (CT), 68Ga-PSMA-11 PET/magnetic resonance imaging (MRI), 18F-PSMA-1007 PET/CT, 18F-DCFPyL PET/MRI, 18F-choline PET/MRI, and 18F-fluoroethylcholine PET/MRI. Across 11 studies, radiolabelled 68Ga-PSMA PET/CT imaging had a pooled sensitivity of 80 (95% confidence interval [CI]: 35-93), specificity of 90 (95% CI: 71-98), and accuracy of 86 (95% CI: 64-96). The PSMA-ligand 68Ga-PET/CT showed good diagnostic performance and appears promising for detecting and staging PCa.

Development of the quantitative PET prostate phantom (Q3P) for improved quality assurance of 18F-PSMA PET imaging in metastatic prostate cancer

BACKGROUND

Phantoms are commonly used to evaluate and compare the performance of imaging systems given the known ground truth. Positron emission tomography (PET) scanners are routinely validated using the NEMA image quality phantom, in which lesions are modeled using 10 to 37 mm fillable spheres. The NEMA phantom neglects, however, to model focal (3-10-mm), high-uptake lesions that are increasingly observed in prostate-specific membrane antigen (PSMA) PET images. PSMA-targeting radiopharmaceuticals allow for enhanced detection of metastatic prostate cancers. As such, there is significant need to develop an updated phantom which considers both the quantitative and lesion detectability of this new paradigm in oncological PET imaging.

PURPOSE

In this work, we present the Quantitative PET Prostate Phantom (Q3P); a portable and modular phantom that can be used to improve and harmonize imaging protocols for 18F-PSMA PET scans.

METHODS

A one-piece cylindrical phantom was designed effectively in two halves, which we call modules. Module 1 was designed to mimic lesions in the presence of background, and Module 2 mimicked very high contrast conditions (i.e., very low background) that can be observed in 18F-PSMA PET scans. Shell-less radioactive spheres (3-16-mm) were cast using epoxy resin mixed with sodium-22 (22Na), a long half-life positron emitter with positron range similar to 18F. To establish realistic lesion contrast, the 22Na spheres were mounted in a cylindrical chamber that can be filled with an 18F background (module 1). Thirteen exchangeable spherical cavity inserts (3-37-mm) were machined in two parts and solvent welded together, and filled with 18F (50 kBq/mL) to model lesions with very high contrast (module 2). Five 2.5-min PET scans were acquired on a 5-ring GE Discovery MI PET/CT scanner (General Electric, USA). Lesions were segmented using 41% of SUVmax fixed thresholding (41% FT) and recovery coefficients (RCs) were computed from 5 noise realizations.

RESULTS

The manufactured phantom is portable (5.7 kg) and scan preparation takes less than 40 min. The total 22Na activity is 250 kBq, allowing it to be shipped as an exempt package under International Atomic Energy Agency (IAEA) regulations. Recovery coefficients, computed using PSF modeling and no post-reconstruction smoothing, were 130.3% (16 mm), 147.1% (10 mm), 87.2% (6 mm), and 7.0% (3 mm) for RCmax, which decreased to 91.1% (16 mm), 90.6% (10 mm), 53.2% (6 mm), and 3.6% (3 mm) for RCmean in the 22Na spheres. Comparatively, 18F sphere recovery was 110.7% (17 mm), 123.6% (10 mm), 106.5% (7 mm), and 23.3% (3 mm) for RCmax, which was reduced to 76.7% (17 mm), 77.7% (10 mm), 66.8% (7 mm), and 13.5% (3 mm), for RCmean.

CONCLUSIONS

A standardized imaging phantom was developed for lesion quantification assessment in 18F-PSMA PET images. The phantom is configurable, providing users with the opportunity to modify background activity levels or sphere sizes according to clinical demands. Distributed to the community, the Q3P phantom has the potential to enable better assessment of lesion quantification and harmonization of 18F-PSMA PET imaging, which may lead to more robust predictive metrics and better outcome prediction in metastatic prostate cancer.

Head-to-head comparison of prostate-specific membrane antigen PET and multiparametric MRI in the diagnosis of pretreatment patients with prostate cancer: a meta-analysis

OBJECTIVES

To compare prostate-specific membrane antigen (PSMA) PET with multiparametric MRI (mpMRI) in the diagnosis of pretreatment prostate cancer (PCa).

METHODS

Pubmed, Embase, Medline, Web of Science, and Cochrane Library were searched for eligible studies published before June 22, 2022. We assessed risk of bias and applicability by using QUADAS-2 tool. Data synthesis was performed with Stata 17.0 software, using the "midas" and "meqrlogit" packages.

RESULTS

We included 29 articles focusing on primary cancer detection, 18 articles about primary staging, and two articles containing them both. For PSMA PET versus mpMRI in primary PCa detection, sensitivities and specificities in the per-patient analysis were 0.90 and 0.84 (p<0.0001), and 0.66 and 0.60 (p <0.0001), and in the per-lesion analysis they were 0.79 and 0.78 (p <0.0001), and 0.84 and 0.82 (p <0.0001). For the per-patient analysis of PSMA PET versus mpMRI in primary staging, sensitivities and specificities in extracapsular extension detection were 0.59 and 0.66 (p =0.005), and 0.79 and 0.76 (p =0.0074), and in seminal vesicle infiltration (SVI) detection they were 0.51 and 0.60 (p =0.0008), and 0.93 and 0.96 (p =0.0092). For PSMA PET versus mpMRI in lymph node metastasis (LNM) detection, sensitivities and specificities in the per-patient analysis were 0.68 and 0.46 (p <0.0001), and 0.91 and 0.90 (p =0.81), and in the per-lesion analysis they were 0.67 and 0.36 (p <0.0001), and 0.99 and 0.99 (p =0.18).

CONCLUSION

PSMA PET has higher diagnostic value than mpMRI in the detection of primary PCa. Regarding the primary staging, mpMRI has potential advantages in SVI detection, while PSMA PET has relative advantages in LNM detection.

CLINICAL RELEVANCE STATEMENT

The integration of prostate-specific membrane antigen (PSMA) PET into the diagnostic pathway may be helpful for improving the accuracy of prostate cancer detection. However, further studies are needed to address the cost implications and evaluate its utility in specific patient populations or clinical scenarios. Moreover, we recommend the combination of PSMA PET and mpMRI for cancer staging.

KEY POINTS

• Prostate-specific membrane antigen PET has higher sensitivity and specificity for primary tumor detection in prostate cancer compared to multiparametric MRI. • Prostate-specific membrane antigen PET also has significantly better sensitivity and specificity for lymph node metastases of prostate cancer compared to multiparametric MRI. • Multiparametric MRI has better accuracy for extracapsular extension and seminal vesicle infiltration compared to ate-specific membrane antigen PET.

Brain metastasis: An insight into novel molecular targets for theranostic approaches

Brain metastases (BrM) are common malignant lesions in the central nervous system, and pose a significant threat in advanced-stage malignancies due to delayed diagnosis and limited therapeutic options. Their distinct genomic profiles underscore the need for molecular profiling to tailor effective treatments. Recent advances in cancer biology have uncovered molecular drivers underlying tumor initiation, progression, and metastasis. This, coupled with the advances in molecular imaging technology and radiotracer synthesis, has paved the way for the development of innovative radiopharmaceuticals with enhanced specificity and affinity for BrM specific targets. Despite the challenges posed by the blood-brain barrier to effective drug delivery, several radiolabeled compounds have shown promise in detecting and targeting BrM. This manuscript provides an overview of the recent advances in molecular biomarkers used in nuclear imaging and targeted radionuclide therapy in both clinical and preclinical settings. Additionally, it explores potential theranostic applications addressing the unique challenges posed by BrM.

Multimodal, PSMA-Targeted, PAMAM Dendrimer-Drug Conjugates for Treatment of Prostate Cancer: Preclinical Evaluation

Introduction

Prostate cancer (PC) is the second most common cancer and the fifth most frequent cause of cancer death among men. Prostate-specific membrane antigen (PSMA) expression is associated with aggressive PC, with expression in over 90% of patients with metastatic disease. Those characteristics have led to its use for PC diagnosis and therapies with radiopharmaceuticals, antibody-drug conjugates, and nanoparticles. Despite these advancements, none of the current therapeutics are curative and show some degree of toxicity. Here we present the synthesis and preclinical evaluation of a multimodal, PSMA-targeted dendrimer-drug conjugate (PT-DDC), synthesized using poly(amidoamine) (PAMAM) dendrimers. PT-DDC was designed to enable imaging of drug delivery, providing valuable insights to understand and enhance therapeutic response.

Methods

The PT-DDC was synthesized through consecutive conjugation of generation-4 PAMAM dendrimers with maytansinoid-1 (DM1) a highly potent antimitotic agent, Cy5 infrared dye for optical imaging, 2,2',2"-(1,4,7-triazacyclononane-1,4,7-triyl)triacetic acid (NOTA) chelator for radiolabeling with copper-64 and positron emission tomography tomography/computed tomography (PET/CT), lysine-urea-glutamate (KEU) PSMA-targeting moiety and the remaining terminal primary amines were capped with butane-1,2-diol. Non-targeted control dendrimer-drug conjugate (Ctrl-DDC) was formulated without conjugation of KEU. PT-DDC and Ctrl-DDC were characterized using high-performance liquid chromatography, matrix assisted laser desorption ionization mass spectrometry and dynamic light scattering. In vitro and in vivo evaluation of PT-DDC and Ctrl-DDC were carried out in isogenic human prostate cancer PSMA+ PC3 PIP and PSMA- PC3 flu cell lines, and in mice bearing the corresponding xenografts.

Results

PT-DDC was stable in 1×PBS and human blood plasma and required glutathione for DM1 release. Optical, PET/CT and biodistribution studies confirmed the in vivo PSMA-specificity of PT-DDC. PT-DDC demonstrated dose-dependent accumulation and cytotoxicity in PSMA+ PC3 PIP cells, and also showed growth inhibition of the corresponding tumors. PT-DDC did not accumulate in PSMA- PC3 flu tumors and did not inhibit their growth. Ctrl-DDC did not show PSMA specificity.

Conclusion

In this study, we synthesized a multimodal theranostic agent capable of delivering DM1 and a radionuclide to PSMA+ tumors. This approach holds promise for enhancing image-guided treatment of aggressive, metastatic subtypes of prostate cancer.

Reasons for Discordance between 68Ga-PSMA-PET and Magnetic Resonance Imaging in Men with Metastatic Prostate Cancer

BACKGROUND

PSMA PET has emerged as a "gold standard" imaging modality for assessing prostate cancer metastases. However, it is not universally available, and this limits its impact. In contrast, whole-body MRI is much more widely available but misses more lesions. This study aims to improve the interpretation of whole-body MRI by comparing false negative scans retrospectively to PSMA PET.

METHODS

This study was a retrospective sub-analysis of a prospectively collected database of patients who participated in a clinical trial of PSMA PET/MRI comparing PSMA PET and whole-body MRI from 2018-2021. Subjects whose separately read PSMA PET and MRI diagnostic reports showed discrepancies ("false negative" MRI cases) were selected for sub-analysis. The cases were reviewed by the same attending radiologist who originally read the scans. The radiologist noted specific features on MRI indicating metastatic disease that were initially missed.

RESULTS

Of 263 cases, 38 (14%) met the inclusion criteria and were reviewed. Six classes of mpMRI false negatives were identified: anatomically normal (18, 47%), atypical MRI appearance (6, 16%), mischaracterization (1, 3%), undercall (6, 16%), obscured (4, 11%), and no abnormality on MRI (3, 8%). Considering that the atypical and undercalled cases could have been adjusted in retrospect, and that 4 additional cases had positive lesions to the same extent and 11 further cases had disease confined to the pelvis, only 11 (4%) of the original 263 would have had disease outside of a conventional radiation treatment plan.

CONCLUSION

Notably, almost 50% of the cases, including most lymph node metastases, were anatomically normal using standard criteria. This suggests that current anatomic criteria for evaluating prostate cancer lymph node metastases are not ideal, and there is a need for improved criteria. In addition, 32% of cases involved some element of human interpretive error, and, therefore, improving reader training may lead to more accurate results.

Design, synthesis and evaluation of novel prostate-specific membrane antigen-targeted aryl [18F]fluorosulfate PET tracers

The expression of prostate-specific membrane antigen (PSMA) in prostate cancer is 100-1000 times higher than that in normal tissues, and it has shown great advantages in the diagnosis and treatment of prostate cancer. The combination of PSMA and PET imaging technology based on the principle of metabolic imaging can achieve high sensitivity and high specificity for diagnosis. Due to its suitable half-life (109 min) and good positron abundance (97%), as well as its cyclotron accelerated generation, 18F has the potential to be commercialize, which has attracted much attention. In this article, we synthesized a series of fluorosulfate PET tracers targeting PSMA. All four analogues have shown high affinity to PSMA (IC50 = 1.85-5.15 nM). After the radioisotope exchange labeling, [18F]L9 and [18F]L10 have PSMA specific cellular uptake (0.65 ± 0.04% AD and 1.19 ± 0.03% AD) and effectively accumulated in 22Rv1 xenograft mice model. This study demonstrates that PSMA-1007-based PSMA-targeted aryl [18F]fluorosulfate novel tracers have the potential for PET imaging in tumor tissues.

Cancer Cell-Selective PD-L1 Inhibition via a DNA Safety Catch to Enhance Immunotherapy Specificity

Immune checkpoint protein blockade (ICB) has emerged as a powerful immunotherapy approach, but suppressing immune-related adverse events (irAEs) for noncancerous cells and normal tissues remains challenging. Activatable ICB has been developed with tumor microenvironment highly-expressed molecules as stimuli, but they still lack precision and efficiency considering the diffusion of stimuli molecules in whole tumor tissue. Here we assemble PD-L1 with a duplex DNA strand, termed as "safety catch", to regulate its accessibility for ICB. The safety catch remains at "on" status for noncancerous cells to prevent ICB binding to PD-L1. Cancer cell membrane protein c-Met acts as a trigger protein to react with safety catch, which selectively exposes its hybridization region for ICB reagent. The ICB reagent is a retractable DNA nanostring with repeating hairpin-structural units, whose contraction drives PD-L1 clustering with endocytosis-guided degradation. The safety catch, even remained at "safety on" status, is removed from the cell membrane via a DNA strand displacement reaction to minimize its influence on noncancerous cells. This strategy demonstrates selective and potent immunotherapeutic capabilities only against cancer cells both in vitro and in vivo, and shows effective suppression of irAEs in normal tissues, therefore would become a promising approach for precise immunotherapy in mice.

Biochemical Response of <0.1 ng/ml Predicts Therapy-free Survival of Prostate Cancer Patients following Prostate-specific Membrane Antigen-targeted Salvage Surgery

BACKGROUND

In a subset of patients with oligorecurrent prostate cancer (PCa), salvage surgery with prostate-specific membrane antigen (PSMA) radioguided surgery (PSMA-RGS) seems to be of value.

OBJECTIVE

To evaluate whether a lower level of postoperative prostate-specific antigen (PSA; <0.1 ng/ml) is predictive of therapy-free survival (TFS) following salvage PSMA-RGS.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study evaluated patients with biochemical recurrence after radical prostatectomy and oligorecurrent PCa on PSMA positron emission tomography treated with PSMA-RGS in three tertiary care centers (2014-2022).

INTERVENTION

PSMA-RGS.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Postsalvage surgery PSA response was categorized as <0.1, 0.1-<0.2, or >0.2 ng/ml. Kaplan-Meier and multivariable Cox regression models evaluated TFS according to PSA response.

RESULTS AND LIMITATIONS

Among 553 patients assessed, 522 (94%) had metastatic soft tissue lesions removed during PSMA-RGS. At 2-16 wk after PSMA-RGS, 192, 62, and 190 patients achieved PSA levels of <0.1, 0.1-<0.2, and >0.2 ng/ml, respectively. At 2 yr of follow-up, TFS rate was 81.1% versus 56.1% versus 43.1% (p < 0.001) for patients with PSA <0.1 versus 0.1-<0.2 versus >0.2 ng/ml. In multivariable analyses, PSA levels of 0.1-0.2 ng/ml (hazard ratio [HR]: 1.9, confidence interval [CI]: 1.1-3.1) and ≥0.2 ng/ml (HR: 3.2, CI: 2.2-4.6, p < 0.001) independently predicted the need for additional therapy after PSMA-RGS. The main limitation is the lack of a control group.

CONCLUSIONS

For patients after salvage PSMA-RGS, a lower biochemical response (PSA <0.1 ng/ml) seems to predict longer TFS. This insight may help in counseling patients postoperatively as well as guiding the timely selection of additional therapy.

PATIENT SUMMARY

We studied what happened to prostate cancer patients in three European centers who had salvage surgery using a special method called prostate-specific membrane antigen-targeted radioguidance. We found that patients who had low prostate-specific antigen levels soon after surgery were less likely to need further treatment for a longer time.

A prospective study on the early evaluation of response to androgen receptor-targeted agents with 11C-Choline, 68Ga-PSMA, and 18F-FACBC PET in metastatic castration-resistant prostate cancer: a single-center experience

BACKGROUND

The early identification of responsive and resistant patients to androgen receptor-targeting agents (ARTA) in metastatic castration-resistant prostate cancer (mCRPC) is not completely possible with prostate-specific antigen (PSA) assessment and conventional imaging. Considering its ability to determine metabolic activity of lesions, positron emission tomography (PET) assessment might be a promising tool.

PATIENTS AND METHODS

We carried out a monocentric prospective study in patients with mCRPC treated with ARTA to evaluate the role of different PET radiotracers: 49 patients were randomized to receive 11C-Choline, Fluorine 18 fluciclovine (anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid - FACBC) (18F-FACBC), or Gallium-68-prostate-specific-membrane-antigen (68Ga-PSMA) PET, one scan before therapy and one 2 months later. The primary aim was to investigate the performance of three novel PET radiotracers for the early evaluation of response to ARTA in metastatic CRPC patients; the outcome evaluated was biochemical response (PSA reduction ≥50%). The secondary aim was to investigate the prognostic role of several semiquantitative PET parameters and their variations with the different radiotracers in terms of biochemical progression-free survival (bPFS) and overall survival (OS). The study was promoted by the Italian Department of Health (code RF-2016-02364809).

RESULTS

Regarding the primary endpoint, at log-rank test a statistically significant correlation was found between metabolic tumor volume (MTV) (P = 0.018) and total lesion activity (TLA) (P = 0.025) percentage variation among the two scans with 68Ga-PSMA PET and biochemical response. As for the secondary endpoints, significant correlations with bPFS were found for 68Ga-PSMA total MTV and TLA at the first scan (P = 0.001 and P = 0.025, respectively), and MTV percentage variation (P = 0.031). For OS, statistically significant correlations were found for different 68Ga-PSMA and 18F-FACBC parameters and for major maximum standardized uptake value at the first 11C-Choline PET scan.

CONCLUSIONS

Our study highlighted that 11C-Choline, 68Ga-PSMA, and 18F-FACBC semiquantitative PET parameters and their variations present a prognostic value in terms of OS and bPFS, and MTV and TLA variations with 68Ga-PSMA PET a correlation with biochemical response, which could help to assess the response to ARTA.

Limited prognostic role of routine serum markers (AP, CEA, LDH and NSE) in oligorecurrent prostate cancer patients undergoing PSMA-radioguided surgery

INTRODUCTION

We evaluated the prognostic role of pre-salvage prostate-specific membrane antigen-radioguided surgery (PSMA-RGS) serum levels of alkaline phosphatase (AP), carcinoembryonic antigen (CEA), lactate dehydrogenase (LDH), and neuron-specific enolase (NSE).

MATERIALS AND METHODS

Patients who consecutively underwent PSMA-RGS for prostate cancer (PCa) oligorecurrence between January 2019 and January 2022 were selected. Biomarkers were assessed one day before surgery. Cox regression and logistic regression models tested the relationship between biochemical recurrence-free survival (BFS), 6- and 12-month biochemical recurrence (BCR), and several independent variables, including biomarkers.

RESULTS

153 consecutive patients were analyzed. In the univariable Cox regression analysis, none of the biomarkers achieved predictor status (AP: hazard ratio [HR] = 1.03, 95% CI 0.99, 1.01; p = 0.19; CEA: HR = 1.73, 95% CI 0.94, 1.21; p = 0.34; LDH: HR = 1.01, 95% CI 1.00, 1.01; p = 0.05; NSE: HR = 1.02, 95% CI 0.98, 1.06; p = 0.39). The only independent predictor of BFS was the number of positive lesions on PSMA PET (HR = 1.17, 95% CI 1.02, 1.30; p = 0.03). The number of positive lesions was confirmed as independent predictor for BCR within 6 and 12 months (BCR < 6 months: odds ratio [OR] = 1.1, 95% CI 1.0, 1.3; p = 0.04; BCR < 12 months: OR = 1.1, 95% CI 1.0, 1.3; p = 0.04).

CONCLUSION

The assessment of AP, CEA, LDH, and NSE before salvage PSMA-RGS showed no prognostic impact. Further studies are needed to identify possible predictors that will optimize patient selection for salvage PSMA-RGS.

Human ABC and SLC Transporters: The Culprit Responsible for Unspecific PSMA-617 Uptake?

[177Lu]Lu-PSMA-617 has recently been successfully approved by the FDA, the MHRA, Health Canada and the EMA as Pluvicto®. However, salivary gland (SG) and kidney toxicities account for its main dose-limiting side-effects, while its corresponding uptake and retention mechanisms still remain elusive. Recently, the presence of different ATP-binding cassette (ABC) transporters, such as human breast cancer resistance proteins (BCRP), multidrug resistance proteins (MDR1), multidrug-resistance-related proteins (MRP1, MRP4) and solute cassette (SLC) transporters, such as multidrug and toxin extrusion proteins (MATE1, MATE2-K), organic anion transporters (OAT1, OAT2v1, OAT3, OAT4) and peptide transporters (PEPT2), has been verified at different abundances in human SGs and kidneys. Therefore, our aim was to assess whether [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are substrates of these ABC and SLC transporters. For in vitro studies, the novel isotopologue ([α,β-3H]Nal)Lu-PSMA-617 was used in cell lines or vesicles expressing the aforementioned human ABC and SLC transporters for inhibition and uptake studies, respectively. The corresponding probe substrates and reference inhibitors were used as controls. Our results indicate that [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 are neither inhibitors nor substrates of the examined transporters. Therefore, our results show that human ABC and SLC transporters play no central role in the uptake and retention of [177Lu]Lu-PSMA-617 and [225Ac]Ac-PSMA-617 in the SGs and kidneys nor in the observed toxicities.

Targeting solid tumor antigens with chimeric receptors: cancer biology meets synthetic immunology

Chimeric antigen receptor (CAR) T cell therapy is a medical breakthrough in the treatment of B cell malignancies. There is intensive focus on developing solid tumor-targeted CAR-T cell therapies. Although clinically approved CAR-T cell therapies target B cell lineage antigens, solid tumor targets include neoantigens and tumor-associated antigens (TAAs) with diverse roles in tumor biology. Multiple early-stage clinical trials now report encouraging signs of efficacy for CAR-T cell therapies that target solid tumors. We review the landscape of solid tumor target antigens from the perspective of cancer biology and gene regulation, together with emerging clinical data for CAR-T cells targeting these antigens. We then discuss emerging synthetic biology strategies and their application in the clinical development of novel cellular immunotherapies.

A Prospective Study Assessing the Efficacy and Toxicity of Stereotactic Body Radiation Therapy for Oligometastatic Bone Metastases

Purpose

Stereotactic body radiation therapy (SBRT) is a promising treatment for oligometastatic disease in bone because of its delivery of high dose to target tissue and minimal dose to surrounding tissue. The purpose of this study is to assess the efficacy and toxicity of this treatment in patients with previously unirradiated oligometastatic bony disease.

Methods and Materials

In this prospective phase II trial, patients with oligometastatic bone disease, defined as ≤3 active sites of disease, were treated with SBRT at Brigham and Women's Hospital/Dana Farber Cancer Center and Beth Israel Deaconess Medical Center between December 2016 and May 2019. SBRT dose and fractionation regimen were not protocol mandated. Local progression-free survival, progression-free survival, prostatic specific antigen progression, and overall survival were reported. Treatment-related toxicity was also reported.

Results

A total of 98 patients and 126 lesions arising from various tumor histologies were included in this study. The median age of patients enrolled was 72.8 years (80.6% male, 19.4% female). Median follow-up was 26.7 months. The most common histology was prostate cancer (68.4%, 67/98). The most common dose prescriptions were 27/30 Gy in 3 fractions (27.0%, 34/126), 30 Gy in 5 fractions (16.7%, 21/126), or 30/35 Gy in 5 fractions (16.7%, 21/126). Multiple doses per treatment regimen reflect dose painting employing the lower dose to the clinical target volume and higher dose to the gross tumor volume. Four patients (4.1%, 4/98) experienced local progression at 1 site for each patient (3.2%, 4/126). Among the entire cohort, 2-year local progression-free survival (including death without local progression) was 84.8%, 2-year progression-free survival (including deaths as well as local, distant, and prostatic specific antigen progression) was 47.5%, and 2-year overall survival was 87.3%. Twenty-six patients (26.5%, 26/98) developed treatment-related toxicities.

Conclusions

Our study supports existing literature in showing that SBRT is effective and tolerable in patients with oligometastatic bone disease. Larger phase III trials are necessary and reasonable to determine long-term efficacy and toxicities.

Diagnostic Accuracy of a Combination of Preoperative 68-Ga Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography and Multiparametric Magnetic Resonance Imaging in Localized Prostate Cancer

INTRODUCTION

Prostate cancer (PCa) is a common and leading course of cancer-related death in men. Although there are studies on multiparametric magnetic resonance imaging (MpMRI) with good diagnostic results in detecting clinically significant PCa, new methods have been investigated due to the low positive predictive values. In this context, prostate-specific membrane antigen positron emission tomography (PSMA PET) emerges as an alternative imaging method to MpMRI. This study aimed to compare 68Ga PSMA I&T-PET/CT and MpMRI in determining tumor location.

METHODS

Preoperative MpMRI and 68Ga PSMA I&T-PET/CT scans and pathology specimens of patients who underwent radical prostatectomy for PCa at our clinic between 2018 and 2021 were retrospectively evaluated. PSMA I&T-PET/CT, MpMRI, combined imaging were compared for tumor localization according to histopathological data.

RESULTS

In terms of tumor localization, MpMRI demonstrated overall accuracy rates of 75.9% (p kappa [κ] 0.0001* [0.525]). 68Ga PSMA I&T-PET/CT showed 71.5% (p κ 0.0001* [0.438]). For the combined imaging approach, the overall accuracy rate was calculated as 79.2% (p κ 0.0001* [0.576]). Additionally, high diagnostic accuracy was achieved for the combined imaging approach, particularly in the intermediate ISUP group. Moreover, SUVmax was calculated as 6.37.

CONCLUSION

The combined use of 68Ga PSMA I&T-PET/CT and MpMRI has high diagnostic rates. However, the high cost is a significant disadvantage that limits their routine combined use.

Deep learning-based whole-body characterization of prostate cancer lesions on [68Ga]Ga-PSMA-11 PET/CT in patients with post-prostatectomy recurrence

PURPOSE

The automatic segmentation and detection of prostate cancer (PC) lesions throughout the body are extremely challenging due to the lesions' complexity and variability in appearance, shape, and location. In this study, we investigated the performance of a three-dimensional (3D) convolutional neural network (CNN) to automatically characterize metastatic lesions throughout the body in a dataset of PC patients with recurrence after radical prostatectomy.

METHODS

We retrospectively collected [68 Ga]Ga-PSMA-11 PET/CT images from 116 patients with metastatic PC at two centers: center 1 provided the data for fivefold cross validation (n = 78) and internal testing (n = 19), and center 2 provided the data for external testing (n = 19). PET and CT data were jointly input into a 3D U-Net to achieve whole-body segmentation and detection of PC lesions. The performance in both the segmentation and the detection of lesions throughout the body was evaluated using established metrics, including the Dice similarity coefficient (DSC) for segmentation and the recall, precision, and F1-score for detection. The correlation and consistency between tumor burdens (PSMA-TV and TL-PSMA) calculated from automatic segmentation and artificial ground truth were assessed by linear regression and Bland‒Altman plots.

RESULTS

On the internal test set, the DSC, precision, recall, and F1-score values were 0.631, 0.961, 0.721, and 0.824, respectively. On the external test set, the corresponding values were 0.596, 0.888, 0.792, and 0.837, respectively. Our approach outperformed previous studies in segmenting and detecting metastatic lesions throughout the body. Tumor burden indicators derived from deep learning and ground truth showed strong correlation (R2 ≥ 0.991, all P < 0.05) and consistency.

CONCLUSION

Our 3D CNN accurately characterizes whole-body tumors in relapsed PC patients; its results are highly consistent with those of manual contouring. This automatic method is expected to improve work efficiency and to aid in the assessment of tumor burden.

Automated segmentation of lesions and organs at risk on [68Ga]Ga-PSMA-11 PET/CT images using self-supervised learning with Swin UNETR

BACKGROUND

Prostate-specific membrane antigen (PSMA) PET/CT imaging is widely used for quantitative image analysis, especially in radioligand therapy (RLT) for metastatic castration-resistant prostate cancer (mCRPC). Unknown features influencing PSMA biodistribution can be explored by analyzing segmented organs at risk (OAR) and lesions. Manual segmentation is time-consuming and labor-intensive, so automated segmentation methods are desirable. Training deep-learning segmentation models is challenging due to the scarcity of high-quality annotated images. Addressing this, we developed shifted windows UNEt TRansformers (Swin UNETR) for fully automated segmentation. Within a self-supervised framework, the model's encoder was pre-trained on unlabeled data. The entire model was fine-tuned, including its decoder, using labeled data.

METHODS

In this work, 752 whole-body [68Ga]Ga-PSMA-11 PET/CT images were collected from two centers. For self-supervised model pre-training, 652 unlabeled images were employed. The remaining 100 images were manually labeled for supervised training. In the supervised training phase, 5-fold cross-validation was used with 64 images for model training and 16 for validation, from one center. For testing, 20 hold-out images, evenly distributed between two centers, were used. Image segmentation and quantification metrics were evaluated on the test set compared to the ground-truth segmentation conducted by a nuclear medicine physician.

RESULTS

The model generates high-quality OARs and lesion segmentation in lesion-positive cases, including mCRPC. The results show that self-supervised pre-training significantly improved the average dice similarity coefficient (DSC) for all classes by about 3%. Compared to nnU-Net, a well-established model in medical image segmentation, our approach outperformed with a 5% higher DSC. This improvement was attributed to our model's combined use of self-supervised pre-training and supervised fine-tuning, specifically when applied to PET/CT input. Our best model had the lowest DSC for lesions at 0.68 and the highest for liver at 0.95.

CONCLUSIONS

We developed a state-of-the-art neural network using self-supervised pre-training on whole-body [68Ga]Ga-PSMA-11 PET/CT images, followed by fine-tuning on a limited set of annotated images. The model generates high-quality OARs and lesion segmentation for PSMA image analysis. The generalizable model holds potential for various clinical applications, including enhanced RLT and patient-specific internal dosimetry.

Developing Folate-Conjugated miR-34a Therapeutic for Prostate Cancer: Challenges and Promises

Prostate cancer (PCa) remains a common cancer with high mortality in men due to its heterogeneity and the emergence of drug resistance. A critical factor contributing to its lethality is the presence of prostate cancer stem cells (PCSCs), which can self-renew, long-term propagate tumors, and mediate treatment resistance. MicroRNA-34a (miR-34a) has shown promise as an anti-PCSC therapeutic by targeting critical molecules involved in cancer stem cell (CSC) survival and functions. Despite extensive efforts, the development of miR-34a therapeutics still faces challenges, including non-specific delivery and delivery-associated toxicity. One emerging delivery approach is ligand-mediated conjugation, aiming to achieve specific delivery of miR-34a to cancer cells, thereby enhancing efficacy while minimizing toxicity. Folate-conjugated miR-34a (folate-miR-34a) has demonstrated promising anti-tumor efficacy in breast and lung cancers by targeting folate receptor α (FOLR1). Here, we first show that miR-34a, a TP53 transcriptional target, is reduced in PCa that harbors TP53 loss or mutations and that miR-34a mimic, when transfected into PCa cells, downregulated multiple miR-34a targets and inhibited cell growth. When exploring the therapeutic potential of folate-miR-34a, we found that folate-miR-34a exhibited impressive inhibitory effects on breast, ovarian, and cervical cancer cells but showed minimal effects on and targeted delivery to PCa cells due to a lack of appreciable expression of FOLR1 in PCa cells. Folate-miR-34a also did not display any apparent effect on PCa cells expressing prostate-specific membrane antigen (PMSA) despite the reported folate's binding capability to PSMA. These results highlight challenges in the specific delivery of folate-miR-34a to PCa due to a lack of target (receptor) expression. Our study offers novel insights into the challenges and promises within the field and casts light on the development of ligand-conjugated miR-34a therapeutics for PCa.

Exploring the impact of PEGylation on pharmacokinetics: a size-dependent effect of polyethylene glycol on prostate-specific membrane antigen inhibitors

BACKGROUND

Prostate cancer is the second most frequent cancer and the fifth leading cause of cancer-related deaths in men. Prostate-specific membrane antigen (PSMA) as a target has gained increasing attention. This research aims to investigate and understand how altering size of PEG impacts the in vitro and in vivo behavior and performance of PSMA inhibitors, with a specific focus on their pharmacokinetic characteristics and targeting properties.

RESULTS

Two 68Ga-labeled PSMA-targeted radiotracers were developed, namely [68Ga]Ga-PP4-WD and [68Ga]Ga-PP8-WD, with varying sizes of polyethylene glycol (PEG). [68Ga]Ga-PP4-WD and [68Ga]Ga-PP8-WD had excellent affinity for PSMA with IC50 being 8.06 ± 0.91, 6.13 ± 0.79 nM, respectively. Both tracers enabled clear visualization of LNCaP tumors in PET images with excellent tumor-to-background contrast. They also revealed highly efficient uptake and internalization into LNCaP cells, increasing over time. The biodistribution studies demonstrated that both radioligands exhibited significant and specific uptake into LNCaP tumors. Furthermore, they were rapidly cleared through the renal pathway, as evidenced by [68Ga]Ga-PP4-WD and [68Ga]Ga-PP8-WD showing a tenfold and a fivefold less in renal uptake, respectively, compared to [68Ga]Ga-Flu-1 in 30 min. Both in vitro and in vivo experiments demonstrated that PEG size significantly impacted tumor-targeting and pharmacokinetic properties.

CONCLUSIONS

These radiotracers have demonstrated their effectiveness in significantly reducing kidney uptake while maintaining the absorbed dose in tumors. Both radiotracers exhibited strong binding and internalization characteristics in vitro, displayed high specificity and affinity for PSMA in vivo.

Detection Rate of PSMA PET Using Different Ligands in Men with Biochemical Recurrent Prostate Cancer Following Radical Treatment: A Systematic Review and Meta-analysis of Prospective Studies

BACKGROUND

Despite the acknowledged diagnostic detection rate of prostate-specific membrane antigen (PSMA) positron emission tomography (PET) imaging in prostate cancer, little is known about the quality of evidence, particularly focusing on prospective studies. Most systematic reviews are based on retrospective reports.

RATIONALE AND OBJECTIVES

To conduct systematic review and meta-analysis of prospective studies reporting the diagnostic detection rate of PSMA PET (computed tomography (CT) and MR) for the detection of biochemically recurrent metastatic prostate cancer.

MATERIALS AND METHODS

We systematically searched PubMed, MEDLINE, Embase, and Scopus, from database until March 1, 2023 for randomized controlled trials and prospective studies using PSMA PET imaging in prostate cancer. The primary endpoint was to assess diagnostic detection rate of PSMA PET imaging in the detection of recurrent prostate cancer in men with biochemical relapse following radical treatment. We calculated the pooled overall diagnostic detection rate with 95% CI using a random-effects model and assessed the heterogeneity between the studies including risk of biases estimation.

RESULTS

A total of 6800 patients from 32 articles were included in this study. The overall detection rate of PSMA PET for prostate cancer was 0.67 (95% CI, 0.63, 0.71). For histologically confirmed lymph nodes, the PPV from 13 prospective studies containing 1496 patients was 0.96 (95% CI, 0.93, 0.99). We performed a subgroup analysis of PSMA PET detection rates according to categorically grouped Prostate Specific Antigen (PSA) values of 0-0.5, 0.5-1.0, 1.0-2.0, and >2.0 ng/ml and obtained detection rates of 0.44, 0.63, 0.82, and 0.94, respectively. The detection rate of 18F PSMA was better in men with a PSA between 1 ng/ml and 2 ng/ml in comparison to 68Ga PSMA (0.91 with 95% CI 0.81-0.99 vs. 0.79 with 95% CI 0.73, 0.85).

CONCLUSION

PSMA PET imaging provides a good detection rate for the metastatic recurrence of prostate cancer in men with biochemical relapse following radical treatment. The detection rate improves significantly above a serum PSA value of 1 ng/ml. The diagnostic detection rate of 18F-PSMA is best at PSA values between 1 and 2 ng/ml, in comparison to 68Ga PSMA. This conclusion is heavily biased, further research needs to focus on better methodology to minimize the risk of biases.

Dosimetric Analysis of a Phase I Study of PSMA-Targeting Radiopharmaceutical Therapy With [177Lu]Ludotadipep in Patients With Metastatic Castration-Resistant Prostate Cancer

OBJECTIVE

177Lutetium [Lu] Ludotadipep is a novel prostate-specific membrane antigen targeting therapeutic agent with an albumin motif added to increase uptake in the tumors. We assessed the biodistribution and dosimetry of [177Lu]Ludotadipep in patients with metastatic castration-resistant prostate cancer (mCRPC).

MATERIALS AND METHODS

Data from 25 patients (median age, 73 years; range, 60-90) with mCRPC from a phase I study with activity escalation design of single administration of [177Lu]Ludotadipep (1.85, 2.78, 3.70, 4.63, and 5.55 GBq) were assessed. Activity in the salivary glands, lungs, liver, kidneys, and spleen was estimated from whole-body scan and abdominal SPECT/CT images acquired at 2, 24, 48, 72, and 168 h after administration of [177Lu]Ludotadipep. Red marrow activity was calculated from blood samples obtained at 3, 10, 30, 60, and 180 min, and at 24, 48, and 72 h after administration. Organ- and tumor-based absorbed dose calculations were performed using IDAC-Dose 2.1.

RESULTS

Absorbed dose coefficient (mean ± standard deviation) of normal organs was 1.17 ± 0.81 Gy/GBq for salivary glands, 0.05 ± 0.02 Gy/GBq for lungs, 0.14 ± 0.06 Gy/GBq for liver, 0.77 ± 0.28 Gy/GBq for kidneys, 0.12 ± 0.06 Gy/GBq for spleen, and 0.07 ± 0.02 Gy/GBq for red marrow. The absorbed dose coefficient of the tumors was 10.43 ± 7.77 Gy/GBq.

CONCLUSION

[177Lu]Ludotadipep is expected to be safe at the dose of 3.7 GBq times 6 cycles planned for a phase II clinical trial with kidneys and bone marrow being the critical organs, and shows a high tumor absorbed dose.

Uncovering the essential roles of glutamate carboxypeptidase 2 orthologs in Caenorhabditis elegans

Human glutamate carboxypeptidase 2 (GCP2) from the M28B metalloprotease group is an important target for therapy in neurological disorders and an established tumor marker. However, its physiological functions remain unclear. To better understand general roles, we used the model organism Caenorhabditis elegans to genetically manipulate its three existing orthologous genes and evaluate the impact on worm physiology. The results of gene knockout studies showed that C. elegans GCP2 orthologs affect the pharyngeal physiology, reproduction, and structural integrity of the organism. Promoter-driven GFP expression revealed distinct localization for each of the three gene paralogs, with gcp-2.1 being most abundant in muscles, intestine, and pharyngeal interneurons, gcp-2.2 restricted to the phasmid neurons, and gcp-2.3 located in the excretory cell. The present study provides new insight into the unique phenotypic effects of GCP2 gene knockouts in C. elegans, and the specific tissue localizations. We believe that elucidation of particular roles in a non-mammalian organism can help to explain important questions linked to physiology of this protease group and in extension to human GCP2 involvement in pathophysiological processes.

Current status of PSMA-targeted imaging and therapy

Currently, the incidence of prostate cancer is increasing, and it has become a great threat to men's health. The detection, staging, and follow-up of prostate cancer patients are inseparable from morphology or magnetic resonance imaging (MRI). However, these do not fully meet the needs of diagnosis and patient management. In particular, owing to the late diagnosis, metastatic castration-resistant prostate cancer (mCRPC) patients usually have poor survival and few options for further effective treatment. Prostate-specific membrane antigen (PSMA), because of its overexpression on prostate cancer cells, has gained interest due to its application in the imaging and theranostics field. Several PSMA radioligands have been developed for imaging and treating prostate cancer. Many clinical trials have assessed the efficacy and safety profiles of these radionuclide agents and show promise in patients who have exhausted other standard treatment options. To date, several small compounds for targeting PSMA have been developed, and 68Ga-PSMA-11 and 18F-DCFPyL have been approved by the United States (US) Food and Drug Administration (FDA) for imaging of prostate cancer. 111In- or 99mTc-labeled PSMA-ligand can guide surgeons searching for radioactive metastatic lymph nodes, and 177Lu- or 225Ac-labeled PSMA-ligand can be used for internal radiotherapy. Moreover, some molecules for therapeutic application are undergoing different stages of clinical trials. In this review, we present current perspectives on the use of PSMA-targeted imaging and theranostics in prostate cancer. As PSMA-targeted imaging and therapeutics are becoming the standard of care for prostate cancer patients, we emphasize the importance of integrating nuclear medicine physicians into multidisciplinary oncology teams.

Total-body PET/CT with half-dose [68 Ga]Ga-PSMA-11 for biochemical recurrent prostate cancer: comparable diagnostic value to short axial field-of-view PET/CT with full-dose [68 Ga]Ga-PSMA-11

PURPOSE

The objective of this study was to evaluate the diagnostic performance and image quality of total-body positron emission tomography/computed tomography (PET/CT) imaging using a half-dose of [68 Ga]Ga-prostate specific membrane antigen ([68 Ga]Ga-PSMA) radiotracer, compared to conventional short axial field-of-view PET/CT imaging using a full dose of [68 Ga]Ga-PSMA.

METHODS

This retrospective study enrolled 52 patients with biochemical recurrent (BCR) prostate cancer after radical prostatectomy who underwent total-body PET/CT with a half-dose (0.9-1.1 MBq/kg) of [68 Ga]Ga-PSMA. These patients were matched by baseline characteristics to another 52 BCR patients after prostatectomy who underwent conventional PET/CT with a full dose (1.8-2.2 MBq/kg) of [68 Ga]Ga-PSMA. The half-dose group was further divided into 5-min (G5) and 2-min (G2) acquisition subgroups. Image quality was assessed through subjective analysis using a 5-point scale and objective measurements of standard uptake value maximum (SUVmax), standard uptake value mean (SUVmean), background variation (BV) of the liver, blood pool, and parotid glands. Additionally, SUVmax and tumor-to-background ratio (TBR) were calculated for lesions.

RESULTS

No significant difference in subjective image quality was found between the G2 and full-dose groups (p > 0.05). PET/CT image quality was significantly higher for the G5 versus G2 (p < 0.001) and full-dose groups (p < 0.001). TBR did not differ between the G2 and full-dose groups (4.23 ± 5.21 vs 4.22 ± 3.97, p = 0.99). Liver BV was significantly lower for G2 versus full-dose groups (0.16 ± 0.03 vs 0.20 ± 0.05, p < 0.001).

CONCLUSIONS

Total-body PET/CT with a half-dose [68 Ga]Ga-PSMA yields image quality superior or comparable to that of conventional PET/CT. The utilization of total-body [68 Ga]Ga-PSMA PET/CT meets the diagnostic demands of BCR patients, particularly those who exhibit reduced tolerance to prolonged horizontal positioning and scan durations, while simultaneously reducing radiation exposure for the subjects.

Clinical and functional outcomes for risk-appropriate treatments for prostate cancer

Objectives

To describe real-world clinical and functional outcomes in an Australian cohort of men with localised prostate cancer according to treatment type and risk category.

Subjects and methods

Men diagnosed from 2008 to 2018 who were enrolled in South Australian Prostate Cancer Clinical Outcomes Collaborative registry-a multi-institutional prospective clinical registry-were studied. The main outcome measures were overall survival, cancer-specific survival, decline in functional outcomes, biochemical recurrence and transition to active treatment following active surveillance. Multivariable adjusted models were applied to estimate outcomes.

Results

Of the 8513 eligible men, majority of men (46%) underwent radical prostatectomy (RP) followed by external beam radiation therapy with or without androgen deprivation therapy (EBRT +/- ADT) in 22% of the cohort. Five-year overall survival was above 91%, and 5-year prostate cancer-specific survival was above 97% in the low- and intermediate-risk categories across all treatments. Five-year prostate cancer-specific survival in the active surveillance group was 100%. About 37% of men with high-risk disease treated with RP and 17% of men treated with EBRT +/- ADT experienced biochemical recurrence within 5 years of treatment. Of men on active surveillance, 15% of those with low risk and 20% with intermediate risk converted to active treatment within 2 years. The decline in urinary continence and sexual function 12 months after treatment was greatest among men who underwent RP while the decline in bowel function was greatest for men who received EBRT +/- ADT.

Conclusion

This contemporary real-world evidence on risk-appropriate treatment outcomes helps inform treatment decision-making for clinicians and patients.

De-Escalation of Therapy for Prostate Cancer

Prostate cancer (PCa) is the second most commonly diagnosed cancer in men with around 1.4 million new cases every year. In patients with localized disease, management options include active surveillance (AS), radical prostatectomy (RP; with or without pelvic lymph node dissection), or radiotherapy to the prostate (with or without pelvic irradiation) with or without hormonotherapy. In advanced disease, treatment options include systemic treatment(s) and/or treatment to primary tumour and/or metastasis-directed therapies (MDTs). Specifically, in advanced stage, the current trend is earlier intensification of treatment such as dual or triple combination systemic treatments or adding treatment to primary and MDT to systemic treatment. However, earlier treatment intensification comes with the cost of increased morbidity and mortality resulting from drug-/treatment-related side effects. The main goal is and should be to provide the best possible care and oncologic outcomes with minimum possible side effects. This chapter will explore emerging possibilities to de-escalate treatment in PCa driven by enhanced insights into disease biology and the natural course of PCa such as AS in intermediate-risk disease or salvage versus adjuvant radiotherapy in post-RP patients. Considerations arising from advancements in PCa imaging and technological advancements in surgical and radiation therapy techniques including omitting pelvic lymph node dissection in the era of prostate-specific membrane antigen positron emitting tomography, the potential of MDT to delay/omit systemic treatment in metachronous oligorecurrence, and the efficacy of hypofractionation schemes compared with conventional fractionated radiotherapy will be discussed.

A Critical Analysis of the Robustness of Radiomics to Variations in Segmentation Methods in 18F-PSMA-1007 PET Images of Patients Affected by Prostate Cancer

BACKGROUND

Radiomics shows promising results in supporting the clinical decision process, and much effort has been put into its standardization, thus leading to the Imaging Biomarker Standardization Initiative (IBSI), that established how radiomics features should be computed. However, radiomics still lacks standardization and many factors, such as segmentation methods, limit study reproducibility and robustness.

AIM

We investigated the impact that three different segmentation methods (manual, thresholding and region growing) have on radiomics features extracted from 18F-PSMA-1007 Positron Emission Tomography (PET) images of 78 patients (43 Low Risk, 35 High Risk). Segmentation was repeated for each patient, thus leading to three datasets of segmentations. Then, feature extraction was performed for each dataset, and 1781 features (107 original, 930 Laplacian of Gaussian (LoG) features, 744 wavelet features) were extracted. Feature robustness and reproducibility were assessed through the intra class correlation coefficient (ICC) to measure agreement between the three segmentation methods. To assess the impact that the three methods had on machine learning models, feature selection was performed through a hybrid descriptive-inferential method, and selected features were given as input to three classifiers, K-Nearest Neighbors (KNN), Support Vector Machines (SVM), Linear Discriminant Analysis (LDA), Random Forest (RF), AdaBoost and Neural Networks (NN), whose performance in discriminating between low-risk and high-risk patients have been validated through 30 times repeated five-fold cross validation.

CONCLUSIONS

Our study showed that segmentation methods influence radiomics features and that Shape features were the least reproducible (average ICC: 0.27), while GLCM features the most reproducible. Moreover, feature reproducibility changed depending on segmentation type, resulting in 51.18% of LoG features exhibiting excellent reproducibility (range average ICC: 0.68-0.87) and 47.85% of wavelet features exhibiting poor reproducibility that varied between wavelet sub-bands (range average ICC: 0.34-0.80) and resulted in the LLL band showing the highest average ICC (0.80). Finally, model performance showed that region growing led to the highest accuracy (74.49%), improved sensitivity (84.38%) and AUC (79.20%) in contrast with manual segmentation.

Prevalence of bilateral loco-regional spread in unilateral pelvic PSMA PET positive recurrent prostate cancer

BACKGROUND

Defining the best surgical template for salvage lymph node dissection (SLND) in patients exhibiting unilateral prostate cancer (PCa) recurrence in pelvic lymph nodes (LNs) is an unmet need. We assessed the risk of missing contralateral nodal recurrence in patients with unilateral positive PSMA-PET who were treated with bilateral PSMA-radioguided (RGS) SLND.

METHODS

Patients who consecutively underwent bilateral PSMA-radioguided SLND for PCa recurrence between April 2014 and January 2023 were identified. We compared PSMA PET findings with the number and the location of PCa LN metastases of the final pathological report. Univariable logistic regression models to try to predict contralateral missed disease were performed.

RESULTS

Sixty patients were identified. At PSMA-RGS, the median PSA level was 0.71 ng/mL (IQR: 0.38-2.28). At PSMA-PET pre-SLND, 49 (82%) patients had unilateral exclusively pelvic lesions, 2 (3%) had unilateral positive nodes at the level of the common iliac arteries, and 9 (15%) had unilateral positive nodes in both levels. Final pathology revealed unilateral LN involvement in 43 (72%), a negative report in 3 (5%), and bilateral positive lesions in 14 (23%) patients. In the univariable logistic regression models, none of the tested factors showed influence on missing contralateral lesions. Four patients out of 35 (11%) with one positive LN at PSMA-PET had bilateral PCa recurrence.

CONCLUSIONS

Patients with one-sided positive LNs on PSMA PET can be considered for a unilateral PSMA-radioguided SLND template with the caveat that about a quarter of patients ultimately have bilateral positive LNs. Larger prospective randomized trials are needed to confirm our findings.

Protocol for SNOTOB study: radical prostatectomy without prostate biopsy following 18F-PSMA-1007 PET/CT based on a diagnostic model: a single-centre, single-arm, open-label study

INTRODUCTION

Nowadays, invasive prostate biopsy is the standard diagnostic test for patients with suspected prostate cancer (PCa). However, it has some shortcomings such as perioperative complications, economic and psychological burden on patients, and some patients may undergo repeated prostate biopsy. In this study protocol, our aim is to provide a non-invasive diagnostic strategy we call the 'prostate-specific membrane antigen (PSMA) combined model' for the diagnosis of PCa. If patients are diagnosed with PCa using PSMA combined model, we want to prove these patients can receive radical prostatectomy directly without prior prostate biopsies.

METHODS

The SNOTOB trial adopts a prospective, single-centre, single-arm, open-label study design. The PSMA combined model consists of a diagnostic model based on what we previously reported and 18F-PSMA-1007 positron emission tomography/CT (18F-PSMA-1007 PET/CT) examinations in series. First, patients use the diagnostic model (online address: https://ustcprostatecancerprediction.shinyapps.io/dynnomapp/) to calculate the risk probability of clinically significant PCa (csPCa). When the risk probability of csPCa is equal or greater than 0.60, 18F-PSMA-1007 PET/CT will be applied for further diagnosis. If patients are still considered as csPCa after 18F-PSMA-1007 PET/CT examinations, we define this condition as positive results of PSMA combined model. Subsequently, we will recommend these patients to accept radical prostatectomy without prostate biopsy directly. Finally, the diagnostic performance of PSMA combined model will be verified with the pathological results. Totally, 57 patients need to be enrolled in this clinical trial.

ETHICS AND DISSEMINATION

This study was approved by the ethics committee of The First Affiliated Hospital of USTC (No. 2022KY-142). The results of this study will be published in peer-reviewed journals and reported at academic conferences.

TRIAL REGISTRATION NUMBER

NCT05587192.

Heterogeneity of prostate-specific membrane antigen (PSMA) and PSMA-ligand uptake detection combining autoradiography and postoperative pathology in primary prostate cancer

BACKGROUND

Targeting prostate-specific membrane antigen (PSMA) has been highly successful for imaging and treatment of prostate cancer. However, heterogeneity in immunohistochemistry indicates limitations in the effect of imaging and radionuclide therapy of multifocal disease. 99mTc-PSMA-I&S is a γ-emitting probe, which can be used for intraoperative lesion detection and postsurgical autoradiography (ARG). We aimed to study its intraprostatic distribution and compared it with (immuno)-histopathology.

RESULTS

Seventeen patients who underwent RGS between 11/2018 and 01/2020 with a total of 4660 grids were included in the preliminary analysis. Marked intratumor and intra-patient heterogeneity of PSMA expression was detected, and PSMA negative foci were observed in all samples (100%). Heterogeneous intra-patient PSMA-ligand uptake was observed, and no significant correlation was present between the degree of heterogeneity of PSMA expression and PSMA-ligand uptake. Higher PSMA-ligand uptake was observed in GS ≥ 8 than GS < 8 (p < 0.001). The appearance of Gleason Pattern (GP) 4 was strongly associated with higher uptake (coefficient: 0.43, p < 0.001), while GP 5 also affected the uptake (coefficient: 0.07, p < 0.001).

CONCLUSION

PSMA expression and PSMA-ligand uptake show marked heterogeneity. Prostate carcinoma with GP 4 showed significantly higher uptake compared with non-neoplastic prostate tissue. Our analyses extend the scope of applications of radiolabeled PSMA-ligands to ARG for identifying high-grade disease and using its signal as a noninvasive biomarker in prostate cancer.

Pulmonary tumor embolism in renal cell carcinoma detected by hybrid CT and F18-PSMA PET

We present the case of a 75-year-old female in which a pulmonary tumor embolism was detected incidentally on a prostate-specific membrane antigen positron emission tomography-computed tomography restaging scan. This occurred on the background of renal cell carcinoma in remission with pazopanib systemic therapy and a right nephrectomy 4 years prior. An avidity to prostate-specific membrane antigen in the superior lingula of the left upper lobe of the lung coupled with contrast-enhanced computed tomography findings found the lesion to be a tumor thrombus. This case serves to highlight the effectiveness of incorporating contrast-enhanced computed tomography with prostate-specific membrane antigen positron emission tomography and to consider the rare diagnosis of a pulmonary tumor embolism.

The role of nuclear medicine tracers for prostate cancer surgery: from preoperative to intraoperative setting

PURPOSE OF REVIEW

There has been a growing interest in the use of novel molecular imaging modalities for the management of prostate cancer (PCa), spanning from diagnostic to therapeutic settings. The aim of this review is to provide a comprehensive overview of recently published studies investigating the use of novel nuclear medicine tracers across different stages of PCa management.

RECENT FINDINGS

Emerging evidence supports the use of molecular imaging for preoperative staging of PCa, where prostate-specific membrane antigen (PSMA) PET has shown superior accuracy compared to conventional imaging for the detection of nodal and distant metastases, which needs to be translated to new risk stratification. A role for PSMA PET has been proposed for PCa diagnosis, with local activity associated with histology. Surgical guidance, using either visual feedback or gamma-ray detectors to identify tissues with accumulated radio-labeled tracers, may improve the ability to resect locoregional diseases and thus maximize oncological control. PSMA targeted therapy (Lu-PSMA) has been mainly investigated in the castration-resistant setting, but might have a role in earlier settings such as neoadjuvant treatment.

SUMMARY

Novel molecular imaging using PSMA-based tracers could significantly improve PCa management in the diagnosis, staging, and intraoperative guidance settings, potentially leading to personalized and effective treatment decisions.

From FDG and beyond: the evolving potential of nuclear medicine

The radiopharmaceutical 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) has been dominantly used in positron emission tomography (PET) scans for over 20 years, and due to its vast utility its applications have expanded and are continuing to expand into oncology, neurology, cardiology, and infectious/inflammatory diseases. More recently, the addition of artificial intelligence (AI) has enhanced nuclear medicine diagnosis and imaging with FDG-PET, and new radiopharmaceuticals such as prostate-specific membrane antigen (PSMA) and fibroblast activation protein inhibitor (FAPI) have emerged. Nuclear medicine therapy using agents such as [177Lu]-dotatate surpasses conventional treatments in terms of efficacy and side effects. This article reviews recently established evidence of FDG and non-FDG drugs and anticipates the future trajectory of nuclear medicine.

Radiochemical and biological assessments of a PSMA-I&S cold kit for fast and inexpensive 99mTc-labeling for SPECT imaging and radioguided surgery in prostate cancer

The expression of prostate-specific membrane antigen (PSMA) is upregulated in prostate cancer (PCa) cells and PSMA-ligands have been radiolabeled and used as radiopharmaceuticals for targeted radionuclide therapy (TRT), single photon emission computed tomography (SPECT) or positron emission tomography (PET) molecular imaging, and radioguided surgery in PCa patients. Herein, we aimed at radiolabeling the PSMA-I&S cold kit with 99mTc, resulting in a radiopharmaceutical with high radiochemical yield (RCY) and stability for SPECT imaging and radioguided surgery in PCa malignancies. Various pre-clinical assays were conducted to evaluate the [99mTc]Tc-PSMA-I&S obtained by the cold kit. These assays included assessments of RCY, radiochemical stability in saline, lipophilicity, serum protein binding (SPB), affinity for LNCaP-PCa cells (binding and internalization studies), and ex vivo biodistribution profile in naive and LNCaP-PCa-bearing mice. The radiopharmaceutical was obtained with good RCY (92.05% ± 2.20%) and remained stable for 6 h. The lipophilicity was determined to be -2.41 ± 0.06, while the SPB was ∼97%. The binding percentages to LNCaP cells were 9.41% ± 0.57% (1 h) and 10.45% ± 0.45% (4 h), with 63.12 ± 0.93 (1 h) and 65.72% ± 1.28% (4 h) of the bound material being internalized. Blocking assays, employing an excess of unlabeled PSMA-I&S, resulted in a reduction in the binding percentage by 2.6 times. The ex vivo biodistribution profile confirmed high accumulation of [99mTc]Tc-PSMA-I&S in the tumor and the tumor-to-contralateral muscle ratio was ∼6.5. In conclusion, [99mTc]Tc-PSMA-I&S was successfully obtained by radiolabeling the cold kit using freshly eluted [99mTc]NaTcO4, exhibiting good RCY and radiochemical stability. The preclinical assays demonstrated that the radiopharmaceutical shows favorable characteristics for SPECT imaging and radioguided surgery in PCa patients.