Prolonged androgen deprivation leads to downregulation of androgen receptor and prostate-specific membrane antigen in prostate cancer cells

Prostate-Specific Membrane Antigen Biology and Pathophysiology in Prostate Carcinoma, an Update: Potential Implications for Targeted Imaging and Therapy

Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein, was shown to be expressed 100-1000 fold higher in prostate adenocarcinoma as compared to normal prostate epithelium. Given the enzymatic function of PSMA with the presence of an internalization triggering motif, various Glu-urea-Lys-based inhibitors have been developed and, amongst others, radiolabeled with positron emitters for targeted positron emission tomography imaging such as 68Ga-PSMA-HBED-CC Glu-urea-Lys(Ahx) as well as with beta and alpha-emitting radioisotopes for targeted therapy, e.g., 177Lu-PSMA-617. In this paper, we review and discuss the potential implications for targeted imaging and therapy of altered PSMA-glycosylation, of PSMA-driven activation of the P13K/Akt/mTOR, of the evolution over time and the relationship with androgen signaling and changes in DNA methylation of PSMA, and of androgen deprivation therapy (ADT) in prostate carcinoma.

Evaluating appropriateness of 18F-fluciclovine PET/CT relative to standard of care imaging guidelines and the impact of ADT on positivity: a prospective study in 62 Veterans Administration patients at a single institution

BACKGROUND

According to the National Comprehensive Cancer Network Guidelines, 18F-fluciclovine PET/CT is considered appropriate after negative standard of care (SOC) imaging.

OBJECTIVE

To prospectively compare 18F-fluciclovine to SOC imaging, investigate whether it should be done when SOC imaging is (+), and evaluate its detection rate in patients receiving androgen deprivation therapy.

METHODS

We recruited 57 prostate cancer patients with biochemical recurrence with 18F-fluciclovine PET/CT and SOC imaging within 30 days. Prostate-specific antigen (PSA) level, Gleason score (GS), history of radical prostatectomy (RP), radiation therapy (RT) or hormone therapy (HT) were reviewed.

RESULTS

The 57 patients had a median PSA of 2.6 and average GS of 7.4; 27 (47.4%) had RP, 28 (49.1%) had RT, 1 (1.75%) had HT and 1 (1.75%) observation only. 18F-fluciclovine identified disease recurrence in 45/57 patients (78.9%), including oligometastasis in 18/45 (40%). SOC imaging identified recurrent disease in 12/57 patients (21.1%) while 18F-fluciclvoine identified additional sites of disease in 11/12 (91.7%). The (+) 18F-fluciclovine studies had a median PSA 2.6 ng/ml compared to 6.0 ng/ml in the (+) SOC studies.

CONCLUSION

18F-fluciclovine was superior to SOC imaging for lesion detection, identification of oligometastasis and identification of additional sites of disease.

An objective measure of response on whole-body MRI in metastatic hormone sensitive prostate cancer treated with androgen deprivation therapy, external beam radiotherapy, and radium-223

OBJECTIVES

The aim of this study was to generate an objective method to describe MRI data to assess response in the vertebrae of patients with metastatic hormone sensitive prostate cancer (mHSPC), treated with external beam radiation therapy and systemic therapy with Radium-223 and to correlate changes with clinical outcomes.

METHODS

Three sets of whole-body MRI (WBMRI) images were utilized from 25 patients from the neo-adjuvant Androgen Deprivation Therapy pelvic Radiotherapy and RADium-223 (ADRRAD) clinical trial: MRI1 (up to 28 days before Radium-223), MRI2, and MRI3 (2 and 6 months post completion of Radium-223). Radiological response was assessed based on post baseline MRI images. Vertebrae were semi-automatically contoured in the sagittal T1-weighted (T1w) acquisitions, MRI intensity was measured, and spinal cord was used to normalize the measurements. The relationship between MRI intensity vs time to biochemical progression and radiology response was investigated. Survival curves were generated and splitting measures for survival and biochemical progression investigated.

RESULTS

Using a splitting measure of 1.8, MRI1 was found to be a reliable quantitative indicator correlating with overall survival (P = 0.023) and biochemical progression (P = 0.014). MRI (3-1) and MRI (3-2) were found to be significant indicators for patients characterized by progressive/non-progressive disease (P = 0.021, P = 0.004) and biochemical progression within/after 12 months (P = 0.007, P = 0.001).

CONCLUSIONS

We have identified a potentially useful objective measure of response on WBMRI of vertebrae containing bone metastases in mHSPC which correlates with survival/progression (prognostic) and radiology response (predictive).

ADVANCES IN KNOWLEDGE

Measurements of T1w WBMRI normalized intensity may allow identifying potentially useful response biomarkers correlating with survival, radiological response and biochemical progression.

Prostate-Specific Membrane Antigen-Targeted Therapies for Prostate Cancer: Towards Improving Therapeutic Outcomes

CONTEXT

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein overexpressed in most prostate cancers and exploited as a target for PSMA-targeted therapies. Different approaches to target PSMA-expressing cancer cells have been developed, showing promising results in clinical trials.

OBJECTIVE

To discuss the regulation of PSMA expression and the main PSMA-targeted therapeutic concepts illustrating their clinical development and rationalizing combination approaches with examples.

EVIDENCE ACQUISITION

We performed a detailed literature search using PubMed and reviewed the American Society of Clinical Oncology and European Society of Medical Oncology annual meeting abstracts up to September 2023.

EVIDENCE SYNTHESIS

We present an overarching description of the different strategies to target PSMA. The outcomes of PSMA-targeted therapies strongly rely on surface-bound PSMA expression. However, PSMA heterogeneity at different levels (interpatient and inter/intratumoral) limits the efficacy of PSMA-targeted therapies. We highlight the molecular mechanisms governing PSMA regulation, the understanding of which is crucial to designing therapeutic strategies aimed at upregulating PSMA expression. Thus far, homeobox B13 (HOXB13) and androgen receptor (AR) have emerged as critical transcription factors positively and negatively regulating PSMA expression, respectively. Furthermore, epigenetic regulation of PSMA has been also reported recently. In addition, many established therapeutic approaches harbor the potential to upregulate PSMA levels as well as potentiate DNA damage mediated by current radioligands.

CONCLUSIONS

PSMA-targeted therapies are rapidly advancing, but their efficacy is strongly limited by the heterogeneous expression of the target. A thorough comprehension of how PSMA is regulated will help improve the outcomes through increasing PSMA expression and will provide the basis for synergistic combination therapies.

PATIENT SUMMARY

Prostate-specific membrane antigen (PSMA) is overexpressed in most prostate cancers. PSMA-targeted therapies have shown promising results, but the heterogeneous expression of PSMA limits their efficacy. We propose to better elucidate the regulation of PSMA expression to increase the levels of the target and improve the therapeutic outcomes.

The efficacy of natural bioactive compounds against prostate cancer: Molecular targets and synergistic activities

Globally, prostate cancer (PCa) is regarded as a challenging health issue, and the number of PCa patients continues to rise despite the availability of effective treatments in recent decades. The current therapy with chemotherapeutic drugs has been largely ineffective due to multidrug resistance and the conventional treatment has restricted drug accessibility to malignant tissues, necessitating a higher dosage resulting in increased cytotoxicity. Plant-derived bioactive compounds have recently attracted a great deal of attention in the field of PCa treatment due to their potent effects on several molecular targets and synergistic effects with anti-PCa drugs. This review emphasizes the molecular mechanism of phytochemicals on PCa cells, the synergistic effects of compound-drug interactions, and stem cell targeting for PCa treatment. Some potential compounds, such as curcumin, phenethyl-isothiocyanate, fisetin, baicalein, berberine, lutein, and many others, exert an anti-PCa effect via inhibiting proliferation, metastasis, cell cycle progression, and normal apoptosis pathways. In addition, multiple studies have demonstrated that the isolated natural compounds: d-limonene, paeonol, lanreotide, artesunate, and bicalutamide have potential synergistic effects. Further, a significant number of natural compounds effectively target PCa stem cells. However, further high-quality studies are needed to firmly establish the clinical efficacy of these phytochemicals against PCa.

PSMA PET/CT for Response Assessment and Overall Survival Prediction in Patients with Metastatic Castration-Resistant Prostate Cancer Treated with Androgen Receptor Pathway Inhibitors

We aimed to evaluate the role of prostate-specific membrane antigen (PSMA) PET/CT for response assessment and outcome prediction in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with androgen receptor pathway inhibitors (ARPIs), including abiraterone acetate or enzalutamide. Methods: We retrospectively analyzed 30 ARPI-treated mCRPC patients who underwent 68Ga-PSMA-11 PET/CT within 8 wk before (baseline) and 12 ± 4 wk after treatment initiation. Total PSMA tumor volume was calculated using the fixed threshold method (SUV ≥ 3). Patients were categorized as PSMA responders (PSMA-Rs) or PSMA nonresponders (PSMA-NRs) on the basis of both European Association of Urology/European Association of Nuclear Medicine (EAU/EANM) criteria and Response Evaluation Criteria in PSMA PET/CT (RECIP) 1.0. PSMA-R included patients with a complete response, a partial response, or stable disease, and PSMA-NR included those with progressive disease. On the basis of prostate-specific antigen (PSA), patients were classified as biochemical responders if PSA decreased by at least 50% and as nonresponders if it did not. The Φ-coefficient was used to evaluate the correlation of PSMA- and PSA-based responses. Survival analysis was performed using the Cox regression hazard model and the Kaplan-Meier method. Predictive accuracy was tested for both response criteria. Results: On the basis of PSMA PET/CT, 13 (43%) patients were PSMA-NR according to the EAU/EANM criteria and 11 (37%) patients were PSMA-NR according to RECIP 1.0. Significant correlations were observed between PSMA- and PSA-based responses for both criteria (Φ = 0.79 and 0.66, respectively). After a median follow-up of 25 mo (interquartile range, 21-43 mo), the median overall survival was significantly longer for PSMA-R than PSMA-NR (54 vs. 22 mo) for both the EAU/EANM criteria and RECIP 1.0, with hazard ratios of 6.9 (95% CI, 1.9-26; P = 0.004) and 5.6 (95% CI, 1.69-18.26, P = 0.005), respectively. No significant difference in predictive accuracy was found between the 2 criteria (C-index, 0.79 vs. 0.76, respectively, P = 0.54). Flare phenomena at the second PSMA PET study were not observed in our cohort. Conclusion: Our results demonstrate that PSMA PET/CT is a valuable imaging biomarker for response assessment and overall survival prediction when performed at 3 mo after ARPI treatment initiation in mCRPC patients. Both proposed PSMA response criteria (EAU/EANM and RECIP 1.0) seem to perform equally well. No PSMA flare was observed. Prospective validation of these findings is strongly needed.

Development of a 18F-Labeled Bicyclic Peptide Targeting EphA2 for Molecular Imaging of PSMA-Negative Prostate Cancer

Although PSMA PET/CT imaging has great potential for noninvasively detecting prostate cancer (PCa), limitations exist for patients with low PSMA expression, caused by androgen deprivation treatment or neuroendocrine differentiation. Analysis of The Cancer Genome Atlas Prostate Adenocarcinoma (TCGA-PRAD) data found that erythropoietin-producing hepatocellular receptor A2 (EphA2), a receptor overexpressed in most PCa could be a potential target for PSMA-negative PCa. A fluorescent ligand ETF and a radiolabeled ligand [18F]AlF-ETN derived from a EphA2-targeting bicyclic peptide were synthesized and investigated. ETF could selectively stain and visualize the EphA2-positive but PSMA-negative PC3 cells, in complementary to the PSMA-targeting probe. PET/CT imaging and biodistribution experiments demonstrated that [18F]AlF-ETN specifically accumulated in PC3 tumors with a high contrast (tumor-to-muscle ratio: 21.29 ± 6.55). In conclusion, we have demonstrated the potential for using EphA2 to detect PSMA-negative PCa and developed a radiolabeled ligand [18F]AlF-ETN to specifically image EphA2 expressing PCa with high contrast.

Antihormonal-Treatment Status Affects 68Ga-PSMA-HBED-CC PET Biodistribution in Patients with Prostate Cancer

Androgen deprivation therapy (ADT) is known to influence the prostate-specific membrane antigen (PSMA) expression of prostate cancer, potentially complicating the interpretation of PSMA ligand PET findings and affecting PSMA radioligand therapy. However, the impact of ADT on PSMA ligand biodistribution in nontumorous organs is not well understood. Methods: Men (n = 112) with histologically proven prostate cancer who underwent 68Ga-PSMA-HBED-CC (68Ga-PSMA-11) PET/CT between November 2015 and July 2021 at the Medical University Vienna with known ADT status were retrospectively recruited. Fifty-six patients were on gonadotropin-releasing hormone-interfering ADT at the time of imaging (ADT group), whereas 56 patients with no history of ADT served as a control group. Physiologically PSMA-expressing organs (salivary glands, kidneys, liver, and spleen) were delineated, and their uptake was compared according to their data distributions. Multivariate regression analysis assessed the relationship between renal, hepatic, splenic, and salivary gland uptake and the explanatory variables metabolic tumor volume, glomerular filtration rate, and ADT status. Results: ADT was associated with lower levels of PSMA uptake in the kidneys (SUVmean: Δ[ADT - control] = -7.89; 95% CI, -10.73 to -5.04; P < 0.001), liver (SUVpeak: Δ[ADT - control] = -2.3; 95% CI, -5.72 to -0.93; P = 0.003), spleen (SUVpeak: Δ[ADT - control] = -1.27; 95% CI, -3.61 to -0.16; P = 0.033), and salivary glands (SUVmean: Δ[ADT - control] = -1.04; 95% CI, -2.48 to -0.13; P = 0.027). In a multivariate analysis, ADT was found to be associated with lower renal (SUVmean: β = -7.95; 95% CI, -11.06 to -4.84; P < 0.0001), hepatic (SUVpeak: β = -7.85; 95% CI, -11.78 to -3.91; P < 0.0001), splenic (SUVpeak: β = -5.83; 95% CI, -9.95 to -1.7; P = 0.006), and salivary gland (SUVmean: β = -1.47; 95% CI, -2.76 to -0.17; P = 0.027) uptake. A higher glomerular filtration rate was associated with a higher renal SUVmean (β = 0.16; 95% CI, 0.05 to 0.26; P = 0.0034). Conclusion: These findings suggest that ADT systemically modulates PSMA expression, which may have implications for treatment-optimizing and side-effect-minimizing strategies for PSMA radioligand therapies, particularly those using more potent 225Ac-labeled PSMA conjugates.

Using PSMA imaging for prognostication in localized and advanced prostate cancer

The use of prostate-specific membrane antigen (PSMA)-directed applications in modern prostate cancer management has evolved rapidly over the past few years, helping to establish new treatment pathways and provide further insights into prostate cancer biology. However, the prognostic implications of PSMA-PET have not been studied systematically, owing to rapid clinical implementation without long follow-up periods to determine intermediate-term and long-term oncological outcomes. Currently available data suggest that traditional prognostic factors and survival outcomes are associated with high PSMA expression (both according to immunohistochemistry and PET uptake) in men with localized and biochemically recurrent disease. Treatment with curative intent (primary and/or salvage) often fails when PSMA-positive metastases are present; however, the sensitivity of PSMA-PET in detecting all metastases is poor. Low PSMA-PET uptake in recurrent disease is a favourable prognostic factor; however, it can be associated with poor prognosis in conjunction with high ¹⁸F-fluorodeoxyglucose uptake in metastatic castration-resistant prostate cancer. Clinical trials embedding PSMA-PET for guiding management with reliable oncological outcomes are needed to support ongoing clinical use.

PSA-Stratified Performance of [18F]DCFPyL PET/CT in Biochemically Recurrent Prostate Cancer Patients under Androgen Deprivation Therapy

Based on in vitro studies, it is known that androgen deprivation therapy (ADT) increases prostate-specific membrane antigen (PSMA) expression on prostate cancer (PCa) cells. However, ADT also has cytoreductive effects which can decrease lesion size. The present evaluation was conducted to further analyze the influence of ongoing ADT on [18F]DCFPyL positron emission tomography/computed tomography (PET/CT) performance in the setting of biochemically recurrent PCa. We retrospectively evaluated two groups of PCa patients, previously treated with radical intent, who had undergone [18F]DCFPyL PET/CT because of biochemical relapse with a minimum PSA level of 0.4 ng/mL. One group consisted of 95 patients under ADT at the time of the PET examination, and the other consisted of 445 patients not receiving ADT at the time of PET/CT. The uptake characteristics of the cardiac blood pool, liver, parotid glands, and five most active lesions were measured and compared between these two groups. The overall detection rate of [18F]DCFPyL PET/CT in patients under ADT at the time of imaging was significantly higher than patients not under ADT (91.6% vs. 80.4%, p-value = 0.007). However, the PSA-stratified differences in detection rates between patients with and without ADT did not reach statistical significance. Except for the maximal standardized uptake values corrected for lean body mass (SULmax) in the PSA range of 1 to <2 ng/mL, the intensity and volume of [18F]DCFPyL accumulation were higher in patients with ADT compared to the patients without. Statistical significance was attained for the SULmax in PSA range of 0.5 to <1 ng/mL (p-value = 0.0004) and metabolic tumor volume (MTV) in all PSA ranges (p-values of 0.0005 to 0.03). No significant difference was observed for radiotracer uptake in normal organs between the two groups with and without ADT. In this study population with biochemical recurrence of PCa and measurable PSA, ongoing ADT at the time of [18F]DCFPyL PET/CT imaging was associated with higher radiotracer uptake and overall lesion detection rate. This could be due in part to the more aggressive disease phenotype in patients with ongoing ADT.

Clinical Applications of PSMA PET Examination in Patients with Prostate Cancer

Simple Summary

The prostate specific membrane antigens, abbreviated as PSMAs, are type II membrane proteins that are highly ex-pressed on the surface of malignant prostate tissue in prostate cancer (PCa), particularly in aggressive, andro-gen-deprived, metastatic, and hormone-refractory PCa. Today, radionuclides that bind to these PSMA peptides are widely available for diagnostic and therapeutic purposes to specifically image and target prostate tumor cells at molec-ular level. In this descriptive review, we aimed to emphasize the usefulness of PSMA positron emission tomography (PET) examination in the management of patients with various stages of PCa. In addition, we outlined the main pitfalls and limitations of this scan to avoid misinterpretation of the results and to improve the decision making process in rela-tion to the patient’s further treatment. We concluded that PSMA PET examination in primary PCa patients has an es-sential role in the high-risk group. It is the new imaging standard in patients with in biochemical recurrence PCa and plays an important role in treatment decision. Furthermore, PSMA PET scan is a gold standard for the evaluation of PSMA targeted therapies in patients having progress of the disease. Future prospective studies, particularly on the im-pact of PSMA PET on therapy stratification, may further strengthen the role of PSMA in the treatment of PCa patients.

Abstract

With the progressive aging of the population in industrially developed countries, as well as advances in diagnostic and biopsy techniques and improvements in patient awareness, the incidence of prostate cancer (PCa) is continuously increasing worldwide. Therefore, PCa is currently considered as the second leading cause of tumor-related death. Early detection of the tumor and its metastasis is essential, as the rate of disease recurrence is high and occurs in 27% to 53% of all patients who underwent curative therapy with radical prostatectomy or local radiotherapy. In this regard, the prostate specific membrane antigens, abbreviated as PSMAs, are type II membrane proteins that are highly expressed on the surface of malignant prostate tissue in PCa, particularly in aggressive, androgen-deprived, metastatic, and hormone-refractory PCa, and they are inversely associated with the androgen level. Up to 95% of adenocarcinomas of the prostate express PSMA receptors on their surface. Today, radionuclides that bind to these PSMA peptides are widely accepted for diagnostic and therapeutic purposes to specifically image and target prostate tumor cells at the molecular level, a process referred to as targeted theranostics. Numerous studies have demonstrated that the integration of these peptides into diagnostic and therapeutic procedures plays a critical role in the primary staging and treatment decisions of especially high-risk PCa, expands therapeutic options for patients with advanced stage of prostate tumor, and prolongs patients’ survival rate. In this review article, we intend to briefly spotlight the latest clinical utilization of the PSMA-targeted radioligand PET imaging modality in patients with different stages of PCa. Furthermore, limitations and pitfalls of this diagnostic technique are presented.

Androgen receptor genomic alterations and treatment resistance in metastatic prostate cancer

BACKGROUND

Genomic alterations to the androgen receptor (AR) are common in metastatic castration-resistant prostate cancer (mCRPC). AR copy number amplifications, ligand-binding domain missense mutations, and intronic structural rearrangements can all drive resistance to approved AR pathway inhibitors and their detection via tissue or liquid biopsy is linked to clinical outcomes. With an increasingly crowded treatment landscape, there is hope that AR genomic alterations can act as prognostic and/or predictive biomarkers to guide patient management.

METHODS

In this review, we evaluate the current evidence for AR genomic alterations as clinical biomarkers in mCRPC, focusing on correlative studies that have used plasma circulating tumor DNA to characterize AR genotype.

RESULTS

We highlight data that demonstrates the complexity of AR genotype within individual patients, and suggest that future studies should account for cancer clonal heterogeneity and variable tumor content in liquid biopsy samples. Given the potential for cooccurrence of multiple AR genomic alterations in the same or competing subclones of a patient, it is distinctly challenging to attribute blanket clinical significance to any individual alteration. This challenge is further complicated by the varied treatment exposures in contemporary patients, and the fact that AR genotype continues to evolve in the mCRPC setting across sequential lines of systemic therapy.

CONCLUSIONS

As treatment access and liquid biopsy technology continues to improve, we posit that real-time measures of AR biology are likely to play a key role in emerging precision oncology strategies for metastatic prostate cancer.

Chemotherapy and Physical Therapeutics Modulate Antigens on Cancer Cells

Cancer cells possess specific properties, such as multidrug resistance or unlimited proliferation potential, due to the presence of specific proteins on their cell membranes. The release of proliferation-related proteins from the membrane can evoke a loss of adaptive ability in cancer cells and thus enhance the effects of anticancer therapy. The upregulation of cancer-specific membrane antigens results in a better outcome of immunotherapy. Moreover, cytotoxic T-cells may also become more effective when stimulated ex-vivo toward the anticancer response. Therefore, the modulation of membrane proteins may serve as an interesting attempt in anticancer therapy. The presence of membrane antigens relies on various physical factors such as temperature, exposure to radiation, or drugs. Therefore, changing the tumor microenvironment conditions may lead to cancer cells becoming sensitized to subsequent therapy. This paper focuses on the therapeutic approaches modulating membrane antigens and enzymes in anticancer therapy. It aims to analyze the possible methods for modulating the antigens, such as pharmacological treatment, electric field treatment, photodynamic reaction, treatment with magnetic field or X-ray radiation. Besides, an overview of the effects of chemotherapy and immunotherapy on the immunophenotype of cancer cells is presented. Finally, the authors review the clinical trials that involved the modulation of cell immunophenotype in anticancer therapy.

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

Simple Summary

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

Abstract

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

Molecular Imaging Assessment of Androgen Deprivation Therapy in Prostate Cancer

Hormonal therapy has long been recognized as a mainstay treatment for prostate cancer. New generation imaging agents have provided unprecedented opportunities at all phases along the natural history of prostate cancer. We review the literature on the effect of androgens and androgen deprivation therapy on prostate tumor at its various biological phases using the new generation molecular imaging agents in conjunction with positron emission tomography.

Small interfering RNA targeting N-cadherin regulates cell proliferation and migration in enzalutamide-resistant prostate cancer

Enzalutamide is one of the options for treating patients with castration-resistant or metastatic prostate cancer. However, a substantial proportion of patients become resistant to enzalutamide after a period of treatment. Cells in these tumors typically exhibit increased proliferative and migratory capabilities, in which N-cadherin (CDH2) appear to serve an important role. In the present study, by up- and downregulating the expression of CDH2, the possible effects of CDH2 on the prostate cancer cell line LNCaP were investigated. Male sex hormone-sensitive LNCaP cells treated with 10 µM enzalutamide were named LNCaP enzalutamide-resistant (EnzaR) cells. Reverse transcription-PCR, western blotting and immunofluorescence staining were used to measure CDH2, E-cadherin, α-SMA, Snail and Slug expression. Transfection with the pCMV-CDH2 plasmid was performed for CDH2 upregulation, whilst transfection with small interfering RNA (siRNA)-CDH2 was performed for CDH2 downregulation. MTT and Cell Counting Kit-4 assays were used to evaluate the proportion of viable cancer cells. Subsequently, gap closure assay was performed to evaluate the migratory capability of both LNCaP and LNCaP EnzaR cell lines. CDH2 expression was found to be increased in LNCaP EnzaR cells compared with that in LNCaP cells. CDH2 overexpression increased cell viability and migration in both LNCaP and LNCaP EnzaR cell lines. By contrast, the opposite trend was observed after CDH2 expression was knocked down. CDH2 expression also showed a high association with that of four epithelial-mesenchymal transition markers, which was confirmed by western blotting. Based on these results, it was concluded that knocking down CDH2 expression using siRNA transfection mediated significant influence on LNCaP EnzaR cell physiology, which may be a potential therapeutic option for prostate cancer treatment.

Evaluation of 18F-PSMA-1007 PET/CT in prostate cancer patients with biochemical recurrence after radical prostatectomy

PURPOSE

Prostate-specific membrane antigen (PSMA) ligands targeting has shown promising results in staging of prostate cancer (PCa). The aim of present study was to evaluate the value of ¹⁸F-PSMA-1007 PET/CT in PCa patients with biochemical recurrence.

METHODS

71 patients with PCa after radical prostatectomy (RP) were included in the present study. Median prostate-specific antigen (PSA) level was 1.27 ng/mL (range 0.01-67.40 ng/mL, n = 69). All patients underwent whole-body PET/CT imaging after injection of 333±38 MBq ¹⁸F-PSMA-1007. The distribution of PSMA-positive lesions was assessed. The influence of PSA level, androgen deprivation therapy and primary Gleason score on PSMA-positive finding and uptake of ¹⁸F-PSMA-1007 were evaluated.

RESULTS

56 (79%) patients showed at least one pathological finding on ¹⁸F-PSMA-1007 PET/CT. The rates of positive scans were 50%, 80%, 100%, 100% among patients with PSA levels ≤0.5, 0.51-1.0, 1.1-2.0 and >2.0 ng/mL, respectively. The median Gleason score was 8 (range 7-10), and higher Gleason score (≤7 vs. ≥8) leads to higher detection rates (58.3% (14/24) vs. 88.9% (32/36), P = 0.006). The median SUVmax of positive findings in patients with PSA levels ≤0.5, 0.51-1.0, 1.1-2.0 and >2.0 ng/mL were 4.51, 4.27, 11.50 and 14.08, respectively. The median SUVmax in patients with PSA level >2.0 ng/mL was significantly higher than that in patients with PSA ≤2.0 ng/mL (14.08 vs. 6.13, P<0.001).

CONCLUSION

¹⁸F-PSMA-1007 PET/CT demonstrated a high detection rate for patients with a raised PSA level after radical prostatectomy even in patients with extremely low PSA level (eg. PSA level ≤0.5 ng/mL), which was essential for further clinical management for PCa patients.

Bone Metastases Are Measurable: The Role of Whole-Body MRI and Positron Emission Tomography

Metastatic tumor deposits in bone marrow elicit differential bone responses that vary with the type of malignancy. This results in either sclerotic, lytic, or mixed bone lesions, which can change in morphology due to treatment effects and/or secondary bone remodeling. Hence, morphological imaging is regarded unsuitable for response assessment of bone metastases and in the current Response Evaluation Criteria In Solid Tumors 1.1 (RECIST1.1) guideline bone metastases are deemed unmeasurable. Nevertheless, the advent of functional and molecular imaging modalities such as whole-body magnetic resonance imaging (WB-MRI) and positron emission tomography (PET) has improved the ability for follow-up of bone metastases, regardless of their morphology. Both these modalities not only have improved sensitivity for visual detection of bone lesions, but also allow for objective measurements of bone lesion characteristics. WB-MRI provides a global assessment of skeletal metastases and for a one-step "all-organ" approach of metastatic disease. Novel MRI techniques include diffusion-weighted imaging (DWI) targeting highly cellular lesions, dynamic contrast-enhanced MRI (DCE-MRI) for quantitative assessment of bone lesion vascularization, and multiparametric MRI (mpMRI) combining anatomical and functional sequences. Recommendations for a homogenization of MRI image acquisitions and generalizable response criteria have been developed. For PET, many metabolic and molecular radiotracers are available, some targeting tumor characteristics not confined to cancer type (e.g. 18F-FDG) while other targeted radiotracers target specific molecular characteristics, such as prostate specific membrane antigen (PSMA) ligands for prostate cancer. Supporting data on quantitative PET analysis regarding repeatability, reproducibility, and harmonization of PET/CT system performance is available. Bone metastases detected on PET and MRI can be quantitatively assessed using validated methodologies, both on a whole-body and individual lesion basis. Both have the advantage of covering not only bone lesions but visceral and nodal lesions as well. Hybrid imaging, combining PET with MRI, may provide complementary parameters on the morphologic, functional, metabolic and molecular level of bone metastases in one examination. For clinical implementation of measuring bone metastases in response assessment using WB-MRI and PET, current RECIST1.1 guidelines need to be adapted. This review summarizes available data and insights into imaging of bone metastases using MRI and PET.

More Than Meets the Eye: Scientific Rationale behind Molecular Imaging and Therapeutic Targeting of Prostate-Specific Membrane Antigen (PSMA) in Metastatic Prostate Cancer and Beyond

Simple Summary

Prostate-specific membrane antigen (PSMA) is a transmembrane protein that is overexpressed in prostate cancer and correlates with the aggressiveness of the disease. PSMA is a promising target for imaging and therapeutics in prostate cancer patients validated in prospective trials. However, the role of PSMA in prostate cancer progression is poorly understood. In this review, we discuss the biology and scientific rationale behind the use of PSMA and other targets in the detection and theranostics of metastatic prostate cancer.

Abstract

Prostate cancer is the second most common cancer type in men globally. Although the prognosis for localized prostate cancer is good, no curative treatments are available for metastatic disease. Better diagnostic methods could help target therapies and improve the outcome. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed on malignant prostate tumor cells and correlates with the aggressiveness of the disease. PSMA is a clinically validated target for positron emission tomography (PET) imaging-based diagnostics in prostate cancer, and during recent years several therapeutics have been developed based on PSMA expression and activity. The expression of PSMA in prostate cancer can be very heterogeneous and some metastases are negative for PSMA. Determinants that dictate clinical responses to PSMA-targeting therapeutics are not well known. Moreover, it is not clear how to manipulate PSMA expression for therapeutic purposes and develop rational treatment combinations. A deeper understanding of the biology behind the use of PSMA would help the development of theranostics with radiolabeled compounds and other PSMA-based therapeutic approaches. Along with PSMA several other targets have also been evaluated or are currently under investigation in preclinical or clinical settings in prostate cancer. Here we critically elaborate the biology and scientific rationale behind the use of PSMA and other targets in the detection and therapeutic targeting of metastatic prostate cancer.

Phosphodiesterase Type-5 Inhibitor Tadalafil Modulates Steroid Hormones Signaling in a Prostate Cancer Cell Line

Background: The androgen receptor (AR) plays a key role in normal prostate homeostasis and in prostate cancer (PCa) development, while the role of aromatase (Cyp19a1) is still unclear. We evaluated the effects of a treatment with Tadalafil (TAD) on both these proteins. Methods: Androgen-sensitive human PCa cell line (LnCAP) was incubated with/without TAD (10⁻⁶ M) and bicalutamide (BCT) (10⁻⁴ M) to evaluate a potential modulation on cell proliferation, protein and mRNA expression of Cyp19a, AR and estrogen receptor-β (ERβ), respectively. Results: TAD increased early AR nuclear translocation (p < 0.05, after 15 min of exposure), and increased AR transcriptional activity (p < 0.05) and protein expression (p < 0.05) after 24 h. Moreover, after 24 h this treatment upregulated Cyp19a1 and ERβ mRNA (p < 0.05 and p < 0.005 respectively) and led to an increase in protein expression of both after 48 h (p < 0.05). Interestingly, TAD counteracted Cyp19a1 stimulation induced by BCT (p < 0.05) but did not alter the effect induced by BCT on the AR protein expression. Conclusion: We demonstrate for the first time that TAD can significantly modulate AR expression and activity, Cyp19a1 and ERβ expression in PCa cells, suggesting a specific effect of these proteins. In addition, TAD potentiates the antiproliferative activity of BCT, opening a new clinical scenario in the treatment of PCa.

[18F]-JK-PSMA-7 and [18F]-FDG tumour PET uptake in treated xenograft human prostate cancer model in mice

PURPOSE

This preclinical study aims to evaluate the extent to which a change in prostate-specific membrane antigen (PSMA) expression of castration-resistant prostate cancer (CRPC) following standard treatment is reflected in [¹⁸F]JK-PSMA-7 PET/CT.

METHODS

Castrated mice supplemented with testosterone implant were xenografted with human LNCaP CRPC. After appropriate tumour growth, androgen deprivation therapy (ADT) was carried out by the removal of the implant followed by a single injection of docetaxel (400 μg/20-g mouse) 2 weeks later. [¹⁸F]JK-PSMA-7 PET/CT were performed before ADT, then before and at days 12, 26, 47 and 69 after docetaxel administration. The [¹⁸F]JK-PSMA-7 PET data were compared to corresponding unspecific metabolic [¹⁸F]FDG PET/CT and ex vivo quantification of PSMA expression estimated by flow cytometry on repeated tumour biopsies.

RESULTS

ADT alone had no early effect on LNCaP tumours that pursued their progression. Until day 12 post-docetaxel, the [¹⁸F]JK-PSMA7 uptake was significantly higher than that of [¹⁸F]FDG, indicating the persistence of PSMA expression at those time points. From day 26 onwards when the tumours were rapidly expanding, both [¹⁸F]JK-PSMA7 and [¹⁸F]FDG uptake continuously decreased although the decrease in [¹⁸F]JK-PSMA uptake was markedly faster. The fraction of PSMA-positive cells in tumour biopsies decreased similarly over time to reach a non-specific level after the same time period.

CONCLUSION

Applying PSMA-based imaging for therapy monitoring in patients with CRPC should be considered with caution since a reduction in [¹⁸F]JK-PSMA-7 PET uptake after successive ADT and chemotherapy may be related to downregulation of PSMA expression in dedifferentiated and rapidly proliferating tumour cells.

[68Ga]Ga-PSMA-11 PET before and after initial long-term androgen deprivation in patients with newly diagnosed prostate cancer: a retrospective single-center study

Purpose

The study aimed to evaluate the effect of androgen deprivation therapy (ADT) on PSMA imaging and its correlation to the PSA concentration by comparing qualitative and quantitative parameters: SUV_max, SUV_mean, PSMA-derived tumor volume (PSMA-TV), total lesion PSMA (TL-PSMA) and molecular imaging (mi)PSMA score.

Methods

Retrospective analysis of 21 therapy-naïve patients with oligometastatic prostate cancer (median age 70 years) who underwent either [⁶⁸Ga]Ga-PSMA-11-PET/CT or -PET/MRI before initiation of (T1) as well as during ADT (T2). The median duration of ADT was 155 days (range 61–289 days). All lesions were analyzed using several qualitative and quantitative PET parameters.

Results

A total of 109 PSMA-positive lesions (24 intraprostatic, 56 lymphonodal and 29 osseous) were visually detected at any of the examinations, while at T2, two new bone lesions were detected in one patient. During ADT, all patients experienced a decrease in their PSA level (median: 29.1 before vs. 0.71 after; p < 0.001). During long-term ADT, a relevant decrease in lesion count occurred, especially in patients with a T2 PSA value < 1 ng/ml (median: 4 vs. 0.9; p = 0.007) and PSMA expression, which resulted in miN- and/or miM-downstaging in 11 patients (52.7%).

All analyzed PET parameters correlated strongly with each other. The PSA level at T2 correlated modestly with the decrease in PSMA expression and its derived volumes.

Conclusion

Post-ADT scans detected, especially in patients with a residual PSA < 1 ng/ml, fewer PSMA-positive lesions with overall lower PSMA expression, regardless of primary tumor site or metastatic sites. None of the PET parameters has proven to be superior, as they all correlated modestly with the PSA value at T2. Thus, the simply acquirable miPSMA score seems to be the most suitable for evaluating the effect of ADT on PSMA expression.

Does bone scintigraphy still have a role in the era of 68 Ga-PSMA PET/CT in prostate cancer?

OBJECTION

We aimed to evaluate the role of bone scintigraphy (BS) which has long been the imaging modality of choice in prostate cancer (PCa) and performed a head-to-head comparison between BS, BS + SPECT/CT and 68 Ga-PSMA-PET/CT, for the detection of bone metastasis of PCa.

METHODS

We evaluated 138 PCa patients who underwent BS and 68 Ga-PSMA PET/CT and SPECT/CT of 102 of 138 patients. Images were interpreted retrospectively and areas of abnormally increased tracer uptake related to PCa were documented as benign, metastatic or equivocal. Equivocal uptakes were finally diagnosed based on a consensus review of correlative imaging. Patient- and lesion-based analysis was performed. Patients with superscan images were excluded from lesion-based analysis.

RESULTS

At least one metastatic or equivocal uptake in skeleton was defined in 76 of 138 (55%) BS, in 33 of 102 (32.3%) SPECT/CT, and in 49 of 138 (35.5%) 68 Ga-PSMA PET/CT. 23 (16.7%) patients had also superscan findings on BS and 68 Ga-PSMA PET/CT. For patient-based analysis, sensitivity, specificity, accuracy, PPV, and NPV were calculated as 91.1%, 64.5%, 73.1%, 55.4% and 93.7% for BS; 95.5%, 82.7%, 86.9%, 72.8% and 96.2% for BS + SPECT/CT; 97.7%, 95.7%, 95.6%, 91.6% and 98.8% for 68 Ga-PSMA PET/CT. For lesion-based analysis, sensitivity, specificity, accuracy, PPV, and NPV were 53%, 63.9%, 60.1%, 42.8% and 71.8% for BS; 59.2%, 87.6%, 77.7%, 62.6% and 80% for BS + SPECT/CT; 96.4%, 98.1%, 97.5%, 96.4% and 98.1% for 68 Ga-PSMA PET/CT.

CONCLUSION

This study has shown that 68 Ga-PSMA PET/CT overcomes the limitations of BS and proves superiority in detecting bone metastases, even in patients with SPECT/CT. Our findings present important implications that 68 Ga-PSMA PET/CT can replace BS in future practice.

Missing Selectivity of Targeted 4β-Phorbol Prodrugs Expected to be Potential Chemotherapeutics

Targeting cytotoxic 4β-phorbol esters toward cancer tissue was attempted by conjugating a 4β-pborbol derivative with substrates for the proteases prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) expressed in cancer tissue. The hydrophilic peptide moiety was hypothesized to prevent penetration of the prodrugs into cells and prevent interaction with PKC. Cleavage of the peptide in cancer tumors was envisioned to release lipophilic cytotoxins, which subsequently penetrate into cancer cells. The 4β-phorbol esters were prepared from 4β-phorbol isolated from Croton tiglium seeds, while the peptides were prepared by solid-phase synthesis. Cellular assays revealed activation of PKC by the prodrugs and efficient killing of both peptidase positive as well as peptidase negative cells. Consequently no selectivity for enzyme expressing cells was found.

The Future of PSMA-Targeted Radionuclide Therapy: An Overview of Recent Preclinical Research

Prostate specific membrane antigen (PSMA) has become a major focus point in the research and development of prostate cancer (PCa) imaging and therapeutic strategies using radiolabeled tracers. PSMA has shown to be an excellent target for PCa theranostics because of its high expression on the membrane of PCa cells and the increase in expression during disease progression. Therefore, numerous PSMA-targeting tracers have been developed and (pre)clinically studied with promising results. However, many of these PSMA-targeting tracers show uptake in healthy organs such as the salivary glands, causing radiotoxicity. Furthermore, not all patients respond to PSMA-targeted radionuclide therapy (TRT). This created the necessity of additional preclinical research studies in which existing tracers are reevaluated and new tracers are developed in order to improve PSMA-TRT by protecting the (PSMA-expressing) healthy organs and improving tumor uptake. In this review we will give an overview of the recent preclinical research projects regarding PCa-TRT using PSMA-specific radiotracers, which will give an indication of where the PSMA-TRT research movement is going and what we can expect in future clinical trials.

Finasteride-Induced Inhibition of 5α-Reductase Type 2 Could Lead to Kidney Damage-Animal, Experimental Study

In the pharmacological treatment of prostate cancer, benign prostatic hyperplasia and androgenetic alopecia finasteride is commonly used. This drug inhibits 5α-reductase type 2, which is why finasteride affects androgen homeostasis, since testosterone (T) cannot be reduced to dihydrotestosterone (DHT). As studies on sex-related renal injuries suggest a high probability of androgen-induced renal dysfunction, the aim of this study was to determine the potential harmful effects of finasteride on the kidneys of rats. The study was performed on sexually mature male Wistar rats given finasteride. Histological sections of the kidneys were used for immunohistochemical visualization of the androgen receptor (AR), junctional proteins (occluding (Occ); E-cad, N-cad, E-/N-cadherin; β-cat, β-catenin; connexin 43 (Cx43)), proliferating cell nuclear antigen (PCNA), IL-6, and lymphocyte markers (CD3 for T cell, CD19 for B cell). The TUNEL method was used for cell apoptosis identification, and picro sirius red staining was used to assess collagen fibers thickness. The levels of T, DHT and estradiol (E2) were determined in blood serum. It was shown that finasteride treatment affected steroid hormone homeostasis, altered the expression of AR and intracellular junction proteins, changed the ratio between cell apoptosis and proliferation, and caused lymphocyte infiltration and an increase of IL-6. The thickening of collagen fibers was observed as tubular fibrosis and glomerulosclerosis. Summarizing, finasteride-induced hormonal imbalance impaired the morphology (i.e., dysplastic glomeruli, swollen proximal convoluted tubules) and physiology (changed level of detected proteins/markers expression) of the kidneys. Therefore, it is suggested that patients with renal dysfunction or following renal transplantation, with androgen or antiandrogen supplementation, should be under special control and covered by extended diagnostics, because the adverse negative effect of DHT deficiency on the progression of kidney disease cannot be ignored.

Neuroendocrine differentiation of prostate cancer leads to PSMA suppression

Prostate-specific membrane antigen (PSMA) is overexpressed in most prostate adenocarcinoma (AdPC) cells and acts as a target for molecular imaging. However, some case reports indicate that PSMA-targeted imaging could be ineffectual for delineation of neuroendocrine (NE) prostate cancer (NEPC) lesions due to the suppression of the PSMA gene (FOLH1). These same reports suggest that targeting somatostatin receptor type 2 (SSTR2) could be an alternative diagnostic target for NEPC patients. This study evaluates the correlation between expression of FOLH1, NEPC marker genes and SSTR2. We evaluated the transcript abundance for FOLH1 and SSTR2 genes as well as NE markers across 909 tumors. A significant suppression of FOLH1 in NEPC patient samples and AdPC samples with high expression of NE marker genes was observed. We also investigated protein alterations of PSMA and SSTR2 in an NE-induced cell line derived by hormone depletion and lineage plasticity by loss of p53. PSMA is suppressed following NE induction and cellular plasticity in p53-deficient NEPC model. The PSMA-suppressed cells have more colony formation ability and resistance to enzalutamide treatment. Conversely, SSTR2 was only elevated following hormone depletion. In 18 NEPC patient-derived xenograft (PDX) models we find a significant suppression of FOLH1 and amplification of SSTR2 expression. Due to the observed FOLH1-supressed signature of NEPC, this study cautions on the reliability of using PMSA as a target for molecular imaging of NEPC. The observed elevation of SSTR2 in NEPC supports the possible ability of SSTR2-targeted imaging for follow-up imaging of low PSMA patients and monitoring for NEPC development.

Impact of long-term androgen deprivation therapy on PSMA ligand PET/CT in patients with castration-sensitive prostate cancer

Purpose

Since the introduction of PSMA PET/CT with ⁶⁸Ga-PSMA-11, this modality for imaging prostate cancer (PC) has spread worldwide. Preclinical studies have demonstrated that short-term androgen deprivation therapy (ADT) can significantly increase PSMA expression on PC cells. Additionally, retrospective clinical data in large patient cohorts suggest a positive association between ongoing ADT and a pathological PSMA PET/CT scan. The present evaluation was conducted to further analyse the influence of long-term ADT on PSMA PET/CT findings.

Methods

A retrospective analysis was performed of all 1,704 patients who underwent a ⁶⁸Ga-PSMA-11 PET/CT scan at our institution from 2011 to 2017 to detect PC. Of 306 patients scanned at least twice, 10 had started and continued ADT with a continuous clinical response between the two PSMA PET/CT scans. These ten patients were included in the current analysis which compared the tracer uptake intensity and volume of PC lesions on PSMA PET/CT before and during ongoing ADT.

Results

Overall, 31 PC lesions were visible in all ten patients before initiation of ADT. However, during ongoing ADT (duration 42–369 days, median 230 days), only 14 lesions were visible in eight of the ten patients. The average tracer uptake values decreased in 71% and increased in 12.9% of the PC lesions. Of all lesions, 33.3% were still visible in six patients with a complete PSA response (≤0.1 ng/ml).

Conclusion

Continuous long-term ADT significantly reduces the visibility of castration-sensitive PC on PSMA PET/CT. If the objective is visualization of the maximum possible extent of disease, we recommend referring patients for PSMA PET/CT before starting ADT.

Inducible expression of cancer-testis antigens in human prostate cancer

Immune tolerance to self-antigens can limit robust anti-tumor immune responses in the use of tumor vaccines. Expression of novel tumor associated antigens can improve immune recognition and lysis of tumor cells. The cancer-testis antigen (CTA) family of proteins has been hypothesized to be an ideal class of antigens due to tumor-restricted expression, a subset of which have been found to induce antibody responses in patients with prostate disease. We demonstrate that CTA expression is highly inducible in five different Prostate Cancer (PC) cell lines using a hypomethylating agent 5-Aza-2′-deoxycytidine (5AZA) and/or a histone deacetylase inhibitor LBH589. These CTAs include NY-ESO1, multiple members of the MAGE and SSX families and NY-SAR35. A subset of CTAs is synergistically induced by the combination of 5AZA and LBH589. We developed an ex vivo organ culture using human PC biopsies for ex vivo drug treatments to evaluate these agents in clinical samples. These assays found significant induction of SSX2 in 9/9 distinct patient samples and NY-SAR35 in 7/9 samples. Further, we identify expression of SSX2 in circulating tumor cells (CTC) from patients with advanced PC. These results indicate that epigenetic modifying agents can induce expression of a broad range of neoantigens in human PC and may serve as a useful adjunctive therapy with novel tumor vaccines and checkpoint inhibitors.

Detection level and pattern of positive lesions using PSMA PET/CT for staging prior to radiation therapy

Background

To determine the potential role of ⁶⁸Ga-PSMA positron emission tomography/computed tomography (PET/CT) in radiotherapy (RT) planning for prostate cancer (PCa).

Methods

One hundred twenty-nine patients (pts) with ⁶⁸Ga-PSMA PET/CT were retrospectively analysed. Potentially influencing factors (androgen deprivation therapy, amount of ⁶⁸Ga-PSMA-HBED-CC, PSA doubling time ≤/> 10 months, PSA before PET/CT, T−/N-category and Gleason score) were evaluated by logistic regression analysis. The detection rate of PSMA PET/CT was compared to contrast enhanced CT and its impact on RT management analysed.

Results

One hundred twenty-nine patients (pts) (20 at initial diagnosis, 49 with PSA relapse and 60 with PSA persistence after radical prostatectomy) received PSMA PET/CT prior to RT. The majority of pts. (71.3%) had PET-positive findings (55.1% of pts. with PSA recurrence, 75% of pts. with PSA persistence and 100% of newly diagnosed pts). Median PSA before PET/CT in pts. with pathological findings (n = 92) was 1.90 ng/ml and without (n = 37) 0.30 ng/ml. PSA level at time of PET/CT was the only factor associated with PET-positivity. In pts. with a PSA ≤ 0.2 ng/ml, the detection rate of any lesion was 33.3%, with a PSA of 0.21–0.5 ng/ml 41.2% and with a PSA of 0.51–1.0 ng/ml 69.2%, respectively. Regarding the anatomic distribution of lesions, 42.2% and 14.7% of pts. with relapse or persistence had pelvic lymph node and distant metastases. In pts. at initial diagnosis the detection rate of pelvic lymph nodes and distant metastases was 20% and 10%. ⁶⁸Ga-PSMA PET/CT had a high detection rate of PCa recurrence outside the prostatic fossa in pts. being considered for salvage RT (22.4% PET-positive pelvic lymph nodes and 4.1% distant metastases). Compared to CT, PSMA PET/CT had a significantly higher sensitivity in diagnosing rates of local recurrence/primary tumour (10.1% vs. 38%), lymph nodes (15.5% vs. 38.8%) and distant metastases (5.4% vs. 14.0%). This resulted in a modification of RT treatment in 56.6% of pts.

Conclusions

The detection of PCa is strongly associated with PSA level at time of ⁶⁸Ga-PSMA PET/CT. PSMA PET/CT differentiates between local, regional and distant metastatic disease with implications for disease management. PSMA PET/CT allows for tumour detection in post-prostatectomy pts. with PSA ≤ 0.5 ng/ml considered for salvage RT.

A triad of telomerase, androgen receptor and early growth response 1 in prostate cancer cells

Telomerase activation is one of the key mechanisms that allow cells to bypass replicative senescence. Telomerase activity is primarily regulated at the level of transcription of its catalytic unit- hTERT. Prostate cancer (PCa), akin to other cancers, is characterized by high telomerase activity. Existing data suggest that hTERT expression and telomerase activity are positively regulated by androgenic stimuli in androgen-dependent prostate cancer (ADPC) cells. A part of the present study reaffirmed this by demonstrating a decline in the hTERT expression and telomerase activity on "loss of AR" in ADPC cells. The study further addressed 2 unresolved queries, i) whether AR-mediated signaling is of any relevance to hTERT expression in castration-resistant prostate cancer (CRPC) and ii) whether this signaling involves EGR1. Our data suggest that AR-mediated signaling negatively regulates hTERT expression in CRPC cells. Incidental support for the possibility of EGR1 being a regulator of hTERT expression in PCa was provided by i) immunolocalization of hTERT and EGR1 proteins in the same cell type (secretory epithelium) of PCa and BPH tissues; ii) significantly (p< 0.001) higher levels of both these proteins in CRPC (PC3 and DU145), compared with ADPC (LNCaP) cells. A direct evidence for the role of EGR1 in hTERT expression was evident by a significant (p<0.0001) decrease in the hTERT transcript levels in the EGR1-silenced CRPC cells. Further, "gain of AR" led to a significant reduction in the levels of hTERT and EGR1 in CRPC cells. However, restoration of EGR1 levels prevented the decline in the hTERT transcript levels in these cells. Taken together, our data indicate that AR regulates the expression of EGR1, which in turn acts as a positive regulator of hTERT expression in CRPC cells. Thus, AR exerts an inhibitory effect on hTERT expression and telomerase activity by modulating EGR1 levels in CRPC cells.

PSMA Ligands for PET Imaging of Prostate Cancer

Targeting the prostate-specific membrane antigen (PSMA) with ⁶⁸Ga-labeled and ¹⁸F-labeled PET agents has become increasingly important in recent years. Imaging of biochemically recurrent prostate cancer has been established as a widely accepted clinical indication for PSMA ligand PET/CT in many parts of the world because of the results of multiple, primarily retrospective, studies that indicate superior detection efficacy compared with standard-of-care imaging. For high-risk primary prostate cancer, evidence is growing that this modality significantly aids in the detection of otherwise occult nodal and bone metastases. For both clinical indications in recurrent as well as in primary prostate cancer, preliminary data demonstrate a substantial impact on clinical management. Emerging data imply that intraprostatic tumor localization, therapy stratification, and treatment monitoring of advanced disease in specific clinical situations might become future indications. Current criteria for image reporting of PSMA ligand PET are evolving given the expanding body of literature on physiologic and pathologic uptake patterns and pitfalls. This article intends to give an educational overview on the current status of PSMA ligand PET imaging, including imaging procedure and interpretation, clinical indications, diagnostic potential, and impact on treatment planning.

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

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

Diagnostic performance of 68Ga-PSMA-11 (HBED-CC) PET/CT in patients with recurrent prostate cancer: evaluation in 1007 patients

Purpose

Since the clinical introduction of ⁶⁸Ga-PSMA-11 PET/CT, this imaging method has rapidly spread and is now regarded as a significant step forward in the diagnosis of recurrent prostate cancer (PCa). The aim of this study was to analyse the influence of several variables with possible influence on PSMA ligand uptake in a large cohort.

Methods

We performed a retrospective analysis of 1007 consecutive patients who were scanned with ⁶⁸Ga-PSMA-11 PET/CT (1 h after injection) from January 2014 to January 2017 to detect recurrent disease. Patients with untreated primary PCa or patients referred for PSMA radioligand therapy were excluded. The possible effects of different variables including PSA level and PSA doubling time (PSA_DT), PSA velocity (PSA_Vel), Gleason score (GSC, including separate analysis of GSC 7a and 7b), ongoing androgen deprivation therapy (ADT), patient age and amount of injected activity were evaluated.

Results

In 79.5% of patients at least one lesion with characteristics suggestive of recurrent PCa was detected. A pathological (positive) PET/CT scan was associated with PSA level and ADT. GSC, amount of injected activity, patient age, PSA_DT and PSA_Vel were not associated with a positive PET/CT scan in multivariate analysis.

Conclusion

⁶⁸Ga-PSMA-11 PET/CT detects tumour lesions in a high percentage of patients with recurrent PCa. Tumour detection is clearly associated with PSA level and ADT. Only a tendency for an association without statistical significance was found between higher GSC and a higher probability of a pathological PET/CT scan. No associations were found between a pathological ⁶⁸Ga-PSMA-11 PET/CT scan and patient age, amount of injected activity, PSA_DT or PSA_Vel.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-017-3711-7) contains supplementary material, which is available to authorized users.

Current Status of Prostate-Specific Membrane Antigen Targeting in Nuclear Medicine: Clinical Translation of Chelator Containing Prostate-Specific Membrane Antigen Ligands Into Diagnostics and Therapy for Prostate Cancer

The prostate-specific membrane antigen (PSMA) is expressed by approximately 90% of prostate carcinomas. The expression correlates with unfavorable prognostic factors, such as a high Gleason score, infiltrative growth, metastasis, and hormone-independence. The high specificity, especially in the undifferentiated stage, makes it an excellent target for diagnosis and therapy. Therefore, antibodies and small molecule inhibitors have been developed for imaging and therapy. In 2011 PSMA-11, a ligand that consists of the Glu-urea-motif and the chelator HBED-CC, which can be exclusively radiolabeled with (68)Ga for PET imaging, presented the clinical breakthrough for prostate cancer diagnostics. In two large diagnostic studies (n = 319 and n = 248) PET/CT with PSMA-11 successfully localized the recurrent tumor in approximately 90% of patients with biochemical relapse. Integrating PSMA-PET/CT into the planning phase of radiotherapy, the treatment concept is changed in 30%-50% of the patients. The combination of the Glu-urea-motif with DOTA, which can be labeled with several diagnostic and therapeutic radionuclides, opened new avenues for therapeutic usage of the small-molecule PSMA ligands. In the beginning of 2016, there are four confirmative reports (n = 19, n = 24, n = 30, and n = 56) from four different centers reporting a PSA response in approximately 70% of patients treated with (177)Lu-labeled PSMA ligands. In conclusion, the data available up to now indicate a widespread use of PSMA ligands for diagnostic applications with respect to staging, detection of recurrence, or metastases in patients with rising tumor markers and for therapy in case of failure of guideline-compliant treatment.

The Rise of PSMA Ligands for Diagnosis and Therapy of Prostate Cancer

The prostate-specific membrane antigen (PSMA) has received increased consideration during the past few years as an excellent target for both imaging and therapy of prostate cancer. After many years of outstanding preclinical research, the first significant step forward in clinical use was achieved in 2008 with the first human experience with the small-molecule PSMA inhibitors ¹²³I-MIP-1972 and ¹²³I-MIP-1095. A clinical breakthrough followed in 2011 with ⁶⁸Ga-PSMA-11 for PET imaging and ¹³¹I-MIP-1095 for endoradiotherapy of metastatic prostate cancer. Since then, PET/CT with ⁶⁸Ga-PSMA-11 has rapidly spread worldwide, and endoradiotherapy with PSMA ligands has been conducted at increasing numbers of centers. ⁶⁸Ga-PSMA-11 is currently the subject of multicenter studies in different countries. Since 2013, ¹³¹I-related PSMA therapy has been replaced by ¹⁷⁷Lu-labeled ligands, such as PSMA-617, which is also the subject of multicenter studies. Alternative PSMA ligands for both imaging and therapy are available. Among them is ^99mTc-MIP-1404, which has recently entered a phase 3 clinical trial. This article focuses on the highlights of the development and clinical application of PSMA ligands.

Rationale for Modernising Imaging in Advanced Prostate Cancer

CONTEXT

To effectively manage patients with advanced prostate cancer (APC), it is essential to have accurate, reproducible, and validated methods for detecting and quantifying the burden of bone and soft tissue metastases and for assessing their response to therapy. Current standard of care imaging with bone and computed tomography (CT) scans have significant limitations for the assessment of bone metastases in particular.

OBJECTIVE

We aimed to undertake a critical comparative review of imaging methods used for diagnosis and disease monitoring of metastatic APC from the perspective of their availability and ability to assess disease presence, extent, and response of bone and soft tissue disease.

EVIDENCE ACQUISITION

An expert panel of radiologists, nuclear medicine physicians, and medical physicists with the greatest experience of imaging in advanced prostate cancer prepared a review of the practicalities, performance, merits, and limitations of currently available imaging methods.

EVIDENCE SYNTHESIS

Meta-analyses showed that positron emission tomography (PET)/CT with different radiotracers and whole-body magnetic resonance imaging (WB-MRI) are more accurate for bone lesion detection than CT and bone scans (BSs). At a patient level, the pooled sensitivities for bone disease by using choline (CH)-PET/CT, WB-MRI, and BS were 91% (95% confidence interval [CI], 83-96%), 97% (95% CI, 91-99%), and 79% (95% CI, 73-83%), respectively. The pooled specificities for bone metastases detection using CH-PET/CT, WB-MRI, and BS were 99% (95% CI, 93-100%), 95% (95% CI, 90-97%), and 82% (95% CI, 78-85%), respectively. The ability of PET/CT and WB-MRI to assess therapeutic benefits is promising but has not been comprehensively evaluated. There is variability in the cost, availability, and quality of PET/CT and WB-MRI.

CONCLUSIONS

Standardisation of acquisition, interpretation, and reporting of WB-MRI and PET/CT scans is required to assess the performance of these techniques in clinical trials of treatment approaches in APC.

PATIENT SUMMARY

PET/CT and whole-body MRI scans have the potential to improve detection and to assess response to treatment of all states of advanced prostate cancer. Consensus recommendations on quality standards, interpretation, and reporting are needed but will require validation in clinical trials of established and new treatment approaches.

Prostate-specific membrane antigen positron emission tomography in prostate cancer: a step toward personalized medicine

PURPOSE OF REVIEW

Increasing attention is being given to personalized medicine in oncology, where therapies are tailored to the particular characteristics of the individual cancer patient. In recent years, there has been greater focus on prostate-specific membrane antigen (PSMA) in prostate cancer (PCa) as a target for imaging and therapy with radionuclides. This review highlights the recent advancements in PSMA positron emission tomography (PET) in PCa during the past year.

RECENT FINDINGS

Several reports on PSMA PET/computed tomography (CT) in PCa patients are demonstrating promising results, especially for detection of biochemical recurrence. F-PSMA PET/CT may be superior to Ga-PSMA PET/CT. The detection rate of PSMA PET is influenced by prostate-specific antigen level. PSMA PET/CT may have a higher detection rate than choline PET/CT. Only a few reports have been published on PSMA PET/magnetic resonance imaging (MRI), and this modality remains to be elucidated further.

SUMMARY

Molecular imaging with PSMA PET is paving the way for personalized medicine in PCa. However, large prospective clinical studies are needed to further evaluate the role of PSMA PET/CT and PET/MRI in the clinical workflow of PCa. PSMA is an excellent target for imaging and therapy with radionuclides, and the 'image and treat' strategy has the potential to become a milestone in the management of PCa patients.

PSMA PET/CT with Glu-urea-Lys-(Ahx)-[⁶⁸Ga(HBED-CC)] versus 3D CT volumetric lymph node assessment in recurrent prostate cancer

Purpose

PET/CT with the PSMA ligand is a powerful new method for the early detection of nodal metastases in patients with biochemical relapse. The purpose of this retrospective investigation was to evaluate the volume and dimensions of nodes identified by Glu-urea-Lys-(Ahx)-[⁶⁸Ga(HBED-CC)] (⁶⁸Ga-PSMA-11) in the setting of recurrent prostate cancer.

Methods

All PET/CT images were acquired 60 ± 10 min after intravenous injection of ⁶⁸Ga-PSMA-11 (mean dose 176 MBq). In 21 patients with recurrent prostate cancer and rising PSA, 49 PSMA-positive lymph nodes were identified. Using semiautomated lymph node segmentation software, node volume and short-axis and long-axis dimensions were measured and compared with the maximum standardized uptake values (SUVmax). Round nodes greater than or equal to 8 mm were considered positive by morphological criteria alone. The percentage of nodes identified by elevated SUVmax but not by conventional morphological criteria was determined.

Results

The mean volume of ⁶⁸Ga-PSMA-11-positive nodes was 0.5 ml (range 0.2 – 2.3 ml), and the mean short-axis diameter was 5.8 mm (range 2.4 – 13.3 mm). In 7 patients (33.3 %) with 31 PSMA-positive nodes only 11 (36 %) were morphologically positive based on diameters >8 mm on CT. In the remaining 14 patients (66.7 %), 18 (37 %) of PSMA positive lymph nodes had short-axis diameters <8 mm with a mean short-axis diameter of 5.0 mm (range 2.4 – 7.9 mm). Thus, in this population, ⁶⁸Ga-PSMA-11 PET/CT detected nodal recurrence in two-thirds of patients who would have been missed using conventional morphological criteria.

Conclusion

⁶⁸Ga-PSMA-11 PET/CT is more sensitive than CT based 3D volumetric lymph node evaluation in determining the node status of patients with recurrent prostate cancer, and is a promising method of restaging prostate cancers in this setting.

A high-affinity [(18)F]-labeled phosphoramidate peptidomimetic PSMA-targeted inhibitor for PET imaging of prostate cancer

INTRODUCTION

In this study, a structurally modified phosphoramidate scaffold, with improved prostate-specific membrane antigen (PSMA) avidity, stability and in vivo characteristics, as a PET imaging agent for prostate cancer (PCa), was prepared and evaluated.

METHODS

p-Fluorobenzoyl-aminohexanoate and 2-(3-hydroxypropyl)glycine were introduced into the PSMA-targeting scaffold yielding phosphoramidate 5. X-ray crystallography was performed on the PSMA/5 complex. [(18)F]5 was synthesized, and cell uptake and internalization studies were conducted in PSMA(+) LNCaP and CWR22Rv1 cells and PSMA(-) PC-3 cells. In vivo PET imaging and biodistribution studies were performed at 1 and 4 h post injection in mice bearing CWR22Rv1 tumor, with or without blocking agent.

RESULTS

The crystallographic data showed interaction of the p-fluorobenzoyl group with an arene-binding cleft on the PSMA surface. In vitro studies revealed elevated uptake of [(18)F]5 in PSMA(+) cells (2.2% in CWR22Rv1 and 12.1% in LNCaP) compared to PSMA(-) cells (0.08%) at 4 h. In vivo tumor uptake of 2.33% ID/g and tumor-to-blood ratio of 265:1 was observed at 4 h.

CONCLUSIONS

We have successfully synthesized, radiolabeled and evaluated a new PSMA-targeted PET agent. The crystal structure of the PSMA/5 complex highlighted the interactions within the arene-binding cleft contributing to the overall complex stability. The high target uptake and rapid non-target clearance exhibited by [(18)F]5 in PSMA(+) xenografts substantiates its potential use for PET imaging of PCa.

ADVANCES IN KNOWLEDGE

The only FDA-approved imaging agent for PCa, Prostascint®, targets PSMA but suffers from inherent shortcomings. The data acquired in this manuscript confirmed that our new generation of [(18)F]-labeled PSMA inhibitor exhibited promising in vivo performance as a PET imaging agent for PCa and is well-positioned for subsequent clinical trials. Implications for Patient Care Our preliminary data demonstrate that this tracer possesses the required imaging characteristics to be sensitive and specific for PCa imaging in patients at all stages of the disease.

The diagnostic value of PET/CT imaging with the (68)Ga-labelled PSMA ligand HBED-CC in the diagnosis of recurrent prostate cancer

Purpose

Since the introduction of positron emission tomography (PET) imaging with ⁶⁸Ga-PSMA-HBED-CC (=⁶⁸Ga-DKFZ-PSMA-11), this method has been regarded as a significant step forward in the diagnosis of recurrent prostate cancer (PCa). However, published data exist for small patient cohorts only. The aim of this evaluation was to analyse the diagnostic value of ⁶⁸Ga-PSMA-ligand PET/CT in a large cohort and the influence of several possibly interacting variables.

Methods

We performed a retrospective analysis in 319 patients who underwent ⁶⁸Ga-PSMA-ligand PET/CT from 2011 to 2014. Potential influences of several factors such as prostate-specific antigen (PSA) level and doubling time (DT), Gleason score (GSC), androgen deprivation therapy (ADT), age and amount of injected tracer were evaluated. Histological verification was performed in 42 patients after the ⁶⁸Ga-PSMA-ligand PET/CT. Tracer uptake was measured in 901 representative tumour lesions.

Results

In 82.8 % of the patients at least one lesion indicative of PCa was detected. Tumor-detection was positively associated with PSA level and ADT. GSC and PSA-DT were not associated with tumor-detection. The average maximum standardized uptake value (SUV_max) of tumour lesions was 13.3 ± 14.6 (0.7–122.5). Amongst lesions investigated by histology, 30 were false-negative in 4 different patients, and all other lesions (n = 416) were true-positive or true-negative. A lesion-based analysis of sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) revealed values of 76.6 %, 100 %, 91.4 % and 100 %. A patient-based analysis revealed a sensitivity of 88.1 %. Of 116 patients available for follow-up, 50 received local therapy after ⁶⁸Ga-PSMA-ligand PET/CT.

Conclusion

⁶⁸Ga-PSMA-ligand PET/CT can detect recurrent PCa in a high number of patients. In addition, the radiotracer is highly specific for PCa. Tumour detection is positively associated with PSA and ADT. ⁶⁸Ga-PSMA-ligand PET/CT can help delay systemic therapy of PCa.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-014-2949-6) contains supplementary material, which is available to authorized users.

Monitoring of prostate cancer growth and metastasis using a PSA luciferase report plasmid in a mouse model

OBJECTIVE

To construct a PSA luciferase report plasmid and monitor the growth and metastasis of prostate cancer after emasculation in SCID mice.

METHODS

PSA promoter sequence and luciferase gene were amplified by PCR and subsequently inserted into pZsGreen1-1 vector to construct pPSA-FL-Luc vector. LNCaP cells that were stably transfected with pPSA-FL-Luc were used to establish a SCID mouse xenograft model. Then, the growth and metastasis of prostate cancer were monitored via living imaging.

RESULTS

We successfully constructed a PSA luciferase plasmid, pPSA-FL-Luc. DHT enhanced luciferase activity in a concentration-dependent manner in 293T cells with pPSA-FL-Luc transfection. Prostate cancer SCID mouse model was established with pPSA-FL-Luc transfected LNCaP cells. In tumor bearing mice with or without emasculation, pPSA-FL-Luc plasmid was applied to monitored tumor growth and metastasis based on bioluminescence imaging.

CONCLUSIONS

We construct a pPSA-FL-Luc plasmid, which stably expresses luciferase and can be applied to monitor tumor development in a prostate SCID mouse model.

Androgen receptor as a regulator of ZEB2 expression and its implications in epithelial-to-mesenchymal transition in prostate cancer

Zinc finger E-box-binding protein 2 (ZEB2) is known to help mediate the epithelial-to-mesenchymal transition, and thereby it facilitates cancer metastasis. This study was initiated to explore whether ZEB2 expression differs in prostate cancer (PCa, n=7) and benign prostatic hyperplasia (BPH, n=7) tissues. In PCa tissues, the levels of both immunoreactive ZEB2 and androgen receptor (AR) were found to be significantly higher (P<0.05) when compared with BPH tissues. Co-regulation of AR and ZEB2 prompted us to investigate the role of androgenic stimuli in ZEB2 expression. ZEB2 expression was found to be significantly (P<0.05) upregulated after androgen stimulation and downregulated following AR silencing in LNCaP cells, an androgen-dependent PCa cell line. This finding suggested AR as a positive regulator of ZEB2 expression in androgen-dependent cells. Paradoxically, androgen-independent (AI) cell lines PC3 and DU145, known to possess low AR levels, showed significantly (P<0.05) higher expression of ZEB2 compared with LNCaP cells. Furthermore, forced expression of AR in PC3 (PC3-AR) and DU145 (DU-AR) cells led to reductions in ZEB2 expression, invasiveness, and migration. These cells also exhibited an increase in the levels of E-cadherin (a transcriptional target of ZEB2). Co-transfection of AR and ZEB2 cDNA constructs prevented the decline in invasiveness and migration to a significant extent. Additionally, ZEB2 downregulation was associated with an increase in miR200a/miR200b levels in PC3-AR cells and with a decrease in miR200a/miR200b levels in AR-silenced LNCaP cells. Thus, AR acts as a positive regulator of ZEB2 expression in androgen-dependent cells and as a negative regulator in AI PCa cells.

Functional prostate-specific membrane antigen is enriched in exosomes from prostate cancer cells

Developing simple and effective approaches to detect tumor markers will be critical for early diagnosis or prognostic evaluation of prostate cancer treatment. Prostate-specific membrane antigen (PSMA) has been validated as an important tumor marker for prostate cancer progression including angiogenesis and metastasis. As a type II membrane protein, PSMA can be constitutively internalized from the cell surface into endosomes. Early endosomes can fuse with multivesicular bodies (MVB) to form and secrete exosomes (40–100 nm) into the extracellular environment. Herein, we tested whether some of the endosomal PSMA could be transferred to exosomes as an extracellular resource for PSMA. Using PSMA-positive LNCaP cells, the secreted exosomes were collected and isolated from the cultured media. The vesicular structures of exosomes were identified by electron microscopy, and exosomal marker protein CD9 and tumor susceptibility gene (TSG 101) were confirmed by western blot analysis. Our present data demonstrate that PSMA can be enriched in exosomes, exhibiting a higher content of glycosylation and partial proteolysis in comparison to cellular PSMA. An in vitro enzyme assay further confirmed that exosomal PSMA retains functional enzymatic activity. Therefore, our data may suggest a new role for PSMA in prostate cancer progression, and provide opportunities for developing non-invasive approaches for diagnosis or prognosis of prostate cancer.