Pharmacological upregulation of prostate-specific membrane antigen (PSMA) expression in prostate cancer cells

Preclinical Efficacy of a PSMA-Targeted Actinium-225 Conjugate (225Ac-Macropa-Pelgifatamab): A Targeted Alpha Therapy for Prostate Cancer

PURPOSE

Initially, prostate cancer responds to hormone therapy, but eventually resistance develops. Beta emitter-based prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs.

EXPERIMENTAL DESIGN

The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide.

RESULTS

Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi; all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models.

CONCLUSIONS

These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase I study has been initiated (NCT06052306).

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.

Towards Improving the Efficacy of PSMA-Targeting Radionuclide Therapy for Late-Stage Prostate Cancer-Combination Strategies

PURPOSE OF REVIEW

[177Lu]Lu-PSMA-617 is a radiopharmaceutical that emits beta-minus radiation and targets prostate-specific membrane antigen (PSMA)-positive prostate cancer. Despite its clinical success, there are still patients not showing sufficient response rates. This review compiles latest studies aiming at therapy improvement in [177Lu]Lu-PSMA-617-naïve and -resistant patients by alternative or combination treatments.

RECENT FINDINGS

A variety of agents to combine with [177Lu]Lu-PSMA-617 are currently under investigation including alpha radiation-emitting pharmaceuticals, radiosensitizers, taxane chemotherapeutics, androgen receptor pathway inhibitors, immune checkpoint inhibitors, and external beam radiation. Actinium-225 (225Ac)-labeled PSMA-targeting inhibitors are the most studied pharmaceuticals for combination therapy or as an alternative for treatment after progression under [177Lu]Lu-PSMA-617 therapy. Alpha emitters seem to have a potential of achieving a response to PSMA-targeting radionuclide therapy in both initial non-responders or responders to [177Lu]Lu-PSMA-617 later developing treatment resistance. Emerging evidence for immunostimulatory effects of radiopharmaceuticals and first prospective studies support the combination of [177Lu]Lu-PSMA-617 and immune checkpoint inhibition for late-stage prostate cancer.

Improved Prostate-Specific Membrane Antigen (PSMA) Stimulation Using a Super Additive Effect of Dutasteride and Lovastatin In Vitro

Prostate-specific membrane antigen (PSMA)-based imaging improved the detection of primary, recurrent and metastatic prostate cancer. However, in certain patients, a low PSMA surface expression can be a limitation for this promising diagnostic tool. Pharmacological induction of PSMA might be useful to further improve the detection rate of PSMA-based imaging. To achieve this, we tested dutasteride (Duta)-generally used for treatment of benign prostatic enlargement-and lovastatin (Lova)-a compound used to reduce blood lipid concentrations. We aimed to compare the individual effects of Duta and Lova on cell proliferation as well as PSMA expression. In addition, we tested if a combination treatment using lower concentrations of Duta and Lova can further induce PSMA expression. Our results show that a treatment with ≤1 μM Duta and ≥1 μM Lova lead to a significant upregulation of whole and cell surface PSMA expression in LNCaP, C4-2 and VCaP cells. Lower concentrations of Duta and Lova in combination (0.5 μM Duta + 0.5 μM Lova or 0.5 μM Duta + 1 μM Lova) were further capable of enhancing PSMA protein expression compared to a single compound treatment using higher concentrations in all tested cell lines (LNCaP, C4-2 and VCaP).

Bipolar Androgen Therapy: When Excess Fuel Extinguishes the Fire

Androgen deprivation therapy (ADT) remains the cornerstone of advanced prostate cancer treatment. However, the progression towards castration-resistant prostate cancer is inevitable, as the cancer cells reactivate androgen receptor signaling and adapt to the castrate state through autoregulation of the androgen receptor. Additionally, the upfront use of novel hormonal agents such as enzalutamide and abiraterone acetate may result in long-term toxicities and may trigger the selection of AR-independent cells through "Darwinian" treatment-induced pressure. Therefore, it is crucial to develop new strategies to overcome these challenges. Bipolar androgen therapy (BAT) is one such approach that has been devised based on studies demonstrating the paradoxical inhibitory effects of supraphysiologic testosterone on prostate cancer growth, achieved through a variety of mechanisms acting in concert. BAT involves rapidly alternating testosterone levels between supraphysiological and near-castrate levels over a period of a month, achieved through monthly intramuscular injections of testosterone plus concurrent ADT. BAT is effective and well-tolerated, improving quality of life and potentially re-sensitizing patients to previous hormonal therapies after progression. By exploring the mechanisms and clinical evidence for BAT, this review seeks to shed light on its potential as a promising new approach to prostate cancer treatment.

Prostate-specific Membrane Antigen Positron Emission Tomography as a Biomarker to Assess Treatment Response in Patients with Advanced Prostate Cancer

CONTEXT

Prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) has superior accuracy for detection of metastatic lesions in patients with prostate cancer (PC). Although PSMA PET has a prominent role in primary and secondary imaging of PC, data on its role in assessing treatment response in advanced PC are limited.

OBJECTIVE

To review current data in the literature regarding the impact of antiandrogen therapy on PSMA expression of metastatic sites and the role of serial (baseline and at least 1 follow-up scan) PSMA PET to assess treatment response in patients with metastatic PC.

EVIDENCE ACQUISITION

A comprehensive literature search in the PubMed database was performed using the terms "PSMA expression prostate", "PSMA regulation", "PSMA PET response assessment", and "serial PSMA PET".

EVIDENCE SYNTHESIS

Serial PSMA PET studies (baseline and at least 1 follow-up scan) provide valuable data regarding PSMA expression changes after systemic treatment in patients with metastatic PC. PSMA PET-detected flare and upregulation of PSMA expression following hormonal intervention seem to be early events resolving after 3 mo of treatment. PSMA PET imaging is essential in selecting patients for ¹⁷⁷Lu-PSMA radioligand therapy (RLT). Growing evidence favors its use in assessing treatment responses after RLT. Preliminary evidence indicates the value of PSMA PET for assessment of the treatment response in patients receiving systemic treatment other than RLT for metastatic PC.

CONCLUSIONS

PSMA flare following antiandrogen therapy seems to be an early event and thus PET scans should be performed no earlier than 3 mo after the start of treatment. PSMA PET has a promising role in tailoring treatment according to the specific needs of individual patients and assessing responses following systemic treatment in patients with advanced PC.

PATIENT SUMMARY

This review describes how a sensitive imaging method can be used to assess the tumor response to treatment for metastatic prostate cancer.

Targeting mTORC1 Activity to Improve Efficacy of Radioligand Therapy in Cancer

Radioligand therapy (RLT) represents an effective strategy to treat malignancy by cancer-selective delivery of radioactivity following systemic application. Despite recent therapeutic successes, cancer radioresistance and insufficient delivery of the radioactive ligands, as well as cytotoxicity to healthy organs, significantly impairs clinical efficacy. To improve disease management while minimizing toxicity, in recent years, the combination of RLT with molecular targeted therapies against cancer signaling networks showed encouraging outcomes. Characterization of the key deregulated oncogenic signaling pathways revealed their convergence to activate the mammalian target of rapamycin (mTOR), in which signaling plays an essential role in the regulation of cancer growth and survival. Therapeutic interference with hyperactivated mTOR pathways was extensively studied and led to the development of mTOR inhibitors for clinical applications. In this review, we outline the regulation and oncogenic role of mTOR signaling, as well as recapitulate and discuss mTOR complex 1 (mTORC1) inhibition to improve the efficacy of RLT in cancer.

Pharmacological Optimization of PSMA-Based Radioligand Therapy

Prostate cancer (PCa) is the most common malignancy in men of middle and older age. The standard treatment strategy for PCa ranges from active surveillance in low-grade, localized PCa to radical prostatectomy, external beam radiation therapy, hormonal treatment and chemotherapy. Recently, the use of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) for metastatic castration-resistant PCa has been approved. PSMA is predominantly, but not exclusively, expressed on PCa cells. Because of its high expression in PCa, PSMA is a promising target for diagnostics and therapy. To understand the currently used RLT, knowledge about pharmacokinetics (PK) and pharmacodynamics (PD) of the PSMA ligand and the PSMA protein itself is crucial. PK and PD properties of the ligand and its target determine the duration and extent of the effect. Knowledge on the concentration-time profile, the target affinity and target abundance may help to predict the effect of RLT. Increased specific binding of radioligands to PSMA on PCa cells may be associated with better treatment response, where nonspecific binding may increase the risk of toxicity in healthy organs. Optimization of the radioligand, as well as synergistic effects of concomitant agents and an improved dosing strategy, may lead to more individualized treatment and better overall survival.

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.

Prostate-specific Membrane Antigen Biology in Lethal Prostate Cancer and its Therapeutic Implications

CONTEXT

Prostate-specific membrane antigen (PSMA) is a promising, novel theranostic target in advanced prostate cancer (PCa). Multiple PSMA-targeted therapies are currently in clinical development, with some agents showing impressive antitumour activity, although optimal patient selection and therapeutic resistance remain ongoing challenges.

OBJECTIVE

To review the biology of PSMA and recent advances in PSMA-targeted therapies in PCa, and to discuss potential strategies for patient selection and further therapeutic development.

EVIDENCE ACQUISITION

A comprehensive literature search was performed using PubMed and review of American Society of Clinical Oncology and European Society of Medical Oncology annual meeting abstracts up to April 2021.

EVIDENCE SYNTHESIS

PSMA is a largely extracellular protein that is frequently, but heterogeneously, expressed by PCa cells. PSMA expression is associated with disease progression, worse clinical outcomes and the presence of tumour defects in DNA damage repair (DDR). PSMA is also expressed by other cancer cell types and is implicated in glutamate and folate metabolism. It may confer a tumour survival advantage in conditions of cellular stress. PSMA regulation is complex, and recent studies have shed light on interactions with androgen receptor, PI3K/Akt, and DDR signalling. A phase 2 clinical trial has shown that 177Lu-PSMA-617 causes tumour shrinkage and delays disease progression in a significant subset of patients with metastatic castration-resistant PCa in comparison to second-line chemotherapy. Numerous novel PSMA-targeting immunotherapies, small molecules, and antibody therapies are currently in clinical development, including in earlier stages of PCa, with emerging evidence of antitumour activity. To date, the regulation and function of PSMA in PCa cells remain poorly understood.

CONCLUSIONS

There has been rapid recent progress in PSMA-targeted therapies for the management of advanced PCa. Dissection of PSMA biology will help to identify biomarkers for and resistance mechanisms to these therapies and facilitate further therapeutic development to improve PCa patient outcomes.

PATIENT SUMMARY

There have been major advances in the development of therapies targeting a molecule, PSMA, in PCa. Radioactive molecules targeting PSMA can cause tumour shrinkage and delay progression in some patients with lethal disease. Future studies are needed to determine which patients are most likely to respond, and how other treatments can be combined with therapies targeting PSMA so that more patients may benefit.

Prostate specific membrane antigen positron emission tomography in primary prostate cancer diagnosis: First-line imaging is afoot

Prostate specific membrane antigen positron emission tomography (PSMA PET) is an excellent molecular imaging technique for prostate cancer. Currently, PSMA PET for patients with primary prostate cancer is supplementary to conventional imaging techniques, according to guidelines. This supplementary function of PSMA PET is due to a lack of systematic review of its strengths, limitations, and potential development direction. Thus, we review PSMA ligands, detection, T, N, and M staging, treatment management, and false results of PSMA PET in clinical studies. We also discuss the strengths and challenges of PSMA PET. PSMA PET can greatly increase the detection rate of prostate cancer and accuracy of T/N/M staging, which facilitates more appropriate treatment for primary prostate cancer. Lastly, we propose that PSMA PET could become the first-line imaging modality for primary prostate cancer, and we describe its potential expanded application.

Prostate-Specific Membrane Antigen Expression and Response to DNA Damaging Agents in Prostate Cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) targeting therapies such as Lutetium-177 (177Lu)-PSMA-617 are affecting outcomes from metastatic castration-resistant prostate cancer (mCRPC). However, a significant subset of patients have prostate cancer cells lacking PSMA expression, raising concerns about treatment resistance attributable at least in part to heterogeneous PSMA expression. We have previously demonstrated an association between high PSMA expression and DNA damage repair defects in mCRPC biopsies and therefore hypothesized that DNA damage upregulates PSMA expression.

EXPERIMENTAL DESIGN

To test this relationship between PSMA and DNA damage we conducted a screen of 147 anticancer agents (NCI/NIH FDA-approved anticancer "Oncology Set") and treated tumor cells with repeated ionizing irradiation.

RESULTS

The topoisomerase-2 inhibitors, daunorubicin and mitoxantrone, were identified from the screen to upregulate PSMA protein expression in castration-resistant LNCaP95 cells; this result was validated in vitro in LNCaP, LNCaP95, and 22Rv1 cell lines and in vivo using an mCRPC patient-derived xenograft model CP286 identified to have heterogeneous PSMA expression. As double-strand DNA break induction by topoisomerase-2 inhibitors upregulated PSMA, we next studied the impact of ionizing radiation on PSMA expression; this also upregulated PSMA protein expression in a dose-dependent fashion.

CONCLUSIONS

The results presented herein are the first, to our knowledge, to demonstrate that PSMA is upregulated in response to double-strand DNA damage by anticancer treatment. These data support the study of rational combinations that maximize the antitumor activity of PSMA-targeted therapeutic strategies by upregulating PSMA.

Synthesis and in vitro proof-of-concept studies on bispecific iron oxide magnetic nanoparticles targeting PSMA and GRP receptors for PET/MR imaging of prostate cancer

Prostate cancer (PCa) is the most common malignancy worldwide in men. This is a proof-of-concept study describing the development of ⁶⁸Ga-magnetic iron oxide nanoparticles (mNP) targeting prostate specific membrane antigen (PSMA) and gastrin releasing peptide (GRPR) receptors as potential tools for diagnosis of PCa with PET/MRI. Two pharmacophores targeting PSMA, 1, and GRPR, 2, were coupled to mNPs carrying -SH (mNP-S1/2) or -NH₂ (mNP-N1/2) groups. The mNP-S1/2 and mNP-N1/2 were characterized for their size, zeta potential, structure, and efficiency of functionalization using dynamic light scattering (DLS), FT-IR and RP-HPLC. A direct ⁶⁸Ga-labelling procedure was followed, where ⁶⁸Ga-mNP-N1/2 proved superior to ⁶⁸Ga-mNP-S1/2 regarding radiolabelling efficiency, and thus were further evaluated in vitro. Toxicity studies in PCa cells (LNCaP, PC-3) showed low toxicity, and minimal hemolysis of red blood cells. In vitro assays in cells expressing PSMA (LNCaP), and GRPR (PC-3), showed specific time-dependent binding (40 min to plateau), high avidity (PC-3: K_d = 28.27 nM, LNCaP: K_d = 11.49 nM) and high internalization rates for ⁶⁸Ga-mNP-N1/2 in both cell lines.

Addition of Standard Enzalutamide Medication Shows Synergistic Effects on Response to [177Lu]Lu-PSMA-617 Radioligand Therapy in mCRPC Patients with Imminent Treatment Failure-Preliminary Evidence of Pilot Experience

Simple Summary

In this study, we investigated co-medication with enzalutamide, a well-established newer androgen axis drug, as a potential re-sensitizer for prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) in n = 10 patients with imminent treatment failure on standard ¹⁷⁷Lu-based PSMA-RLT. After the introduction of enzalutamide medication, all patients showed a PSA decrease (7/10 patients with partial remission). This pilot experience suggests the synergistic potential of adding enzalutamide to PSMA-RLT derived from the intra-individual comparison of ¹⁷⁷Lu-based PSMA-RLT ± enzalutamide.

Abstract

Well-received strong efficacy of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) does not prevent patients from either early or eventual disease progression under this treatment. In this study, we investigated co-medication with enzalutamide as a potential re-sensitizer for PSMA-RLT in patients with imminent treatment failure on standard ¹⁷⁷Lu-based PSMA-RLT. Ten mCRPC patients who exhibited an insufficient response to conventional [¹⁷⁷Lu]Lu-PSMA-617 RLT received oral medication of enzalutamide 160 mg/d as an adjunct to continued PSMA-RLT. Prostate-specific antigen (PSA) and standard toxicity screening lab work-up were performed to assess the treatment efficacy and safety in these individuals. The mean PSA increase under PSMA-RLT before starting the re-sensitizing procedure was 22.4 ± 26.5%. After the introduction of enzalutamide medication, all patients experienced a PSA decrease, –43.4 ± 20.0% and –48.2 ± 39.0%, after one and two cycles of enzalutamide-augmented PSMA-RLT, respectively. A total of 70% of patients (7/10) experienced partial remission, with a median best PSA response of –62%. Moreover, 5/6 enzalutamide-naïve patients and 2/4 patients who had previously failed enzalutamide exhibited a partial remission. There was no relevant enzalutamide-induced toxicity observed in this small cohort. This pilot experience suggests the synergistic potential of adding enzalutamide to PSMA-RLT derived from the intra-individual comparison of ¹⁷⁷Lu-based PSMA-RLT ± enzalutamide.

Investigation of Tumor Cells and Receptor-Ligand Simulation Models for the Development of PET Imaging Probes Targeting PSMA and GRPR and a Possible Crosstalk between the Two Receptors

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have both been used in nuclear medicine as targets for molecular imaging and therapy of prostate (PCa) and breast cancer (BCa). Three bioconjugate probes, the PSMA specific: [⁶⁸Ga]Ga-1, ((HBED-CC)-Ahx-Lys-NH-CO-NH Glu or PSMA-11), the GRPR specific: [⁶⁸Ga]Ga-2, ((HBED-CC)-4-amino-1-carboxymethyl piperidine-[D-Phe⁶, Sta¹³]BN(6-14), a bombesin (BN) analogue), and 3 (the BN analogue: 4-amino-1-carboxymethyl piperidine-[(R)-Phe⁶, Sta¹³]BN(6-14) connected with the fluorescent dye, BDP-FL), were synthesized and tested in vitro with PCa and BCa cell lines, more specifically, with PCa cells, PC-3 and LNCaP, with BCa cells, T47D, MDA-MB-231, and with the in-house created PSMA-overexpressing PC-3^(PSMA), T47D^(PSMA), and MDA-MB-231^(PSMA). In addition, biomolecular simulations were conducted on the association of 1 and 2 with PSMA and GRPR. The PSMA overexpression resulted in an increase of cell-bound radioligand [⁶⁸Ga]Ga-1 (PSMA) for PCa and BCa cells and also of [⁶⁸Ga]Ga-2 (GRPR), especially in those cell lines already expressing GRPR. The results were confirmed by fluorescence-activated cell sorting with a PE-labeled PSMA-specific antibody and the fluorescence tracer 3. The docking calculations and molecular dynamics simulations showed how 1 enters the PSMA funnel region and how pharmacophore Glu-urea-Lys interacts with the arginine patch, the S1', and S1 subpockets by forming hydrogen and van der Waals bonds. The chelating moiety of 1, that is, HBED-CC, forms additional stabilizing hydrogen bonding and van der Waals interactions in the arene-binding site. Ligand 2 is diving into the GRPR transmembrane (TM) helical cavity, thereby forming hydrogen bonds through its amidated end, water-mediated hydrogen bonds, and π-π interactions. Our results provide valuable information regarding the molecular mechanisms involved in the interactions of 1 and 2 with PSMA and GRPR, which might be useful for the diagnostic imaging and therapy of PCa and BCa.

Upregulation of PSMA Expression by Enzalutamide in Patients with Advanced mCRPC

In this study, we investigated upregulation of prostate-specific membrane antigen (PSMA) by enzalutamide in a cohort (n = 30) of patients with advanced metastatic castration-resistant prostate cancer (mCRPC). Patients were examined by [68Ga]Ga-PSMA-11 PET/CT pre- and post-enzalutamide medication (mean 13 ± 7 days). Imaging results were compared based on quantification of whole-body PSMA tumor burden: total lesion PSMA (TLP) and normalized TLP values to liver (TLP-LR) and to parotid gland (TLP-PR). In addition, lesion-based analyses were performed. The median (mean) increases in TLP, TLP-LR and TLP-PR after enzalutamide medication were 10.1% (20.2%), 29.5% (34.8%) and 27.6% (24.4%), respectively. These increases were statistically significant (p = 0.002, p < 0.001, and p < 0.001), while prostate-specific antigen (PSA) serum values did not change significantly (p = 0.483). The increase was independent of prior patient exposure to enzalutamide. SUVmax increased substantially (>10%) in 49.6% of target lesions. The relative change was significantly higher in the subgroup of lesions with SUVmax < 10 (p < 0.001). In conclusion, short-term enzalutamide medication significantly increases PSMA expression in patients with mCRPC, irrespective of prior enzalutamide exposure. The relative PSMA upregulation effect seems to be more pronounced in lesions with only moderate baseline PSMA expression. Enzalutamide may provide a potential enhancer medication for PSMA-targeted radioligand therapy.

Radionuclide Therapy in Prostate Cancer: from standalone to combination PSMA theranostics

Despite significant advances in prostate cancer therapeutic development over the last two decades, metastatic prostate cancer remains a lethal disease. Prostate-specific membrane antigen (PSMA), which is markedly overexpressed by prostate cancer cells, including at metastatic sites, but have low normal tissue expression, has emerged as an important theranostic target for these diseases. Both beta-emitting and alpha-emitting PSMA-targeted radionuclide therapy (RNT) are in clinical development. Several of these agents have already shown promising activity, however, a significant subset of patients have primary resistant disease and secondary resistance invariably occurs. Further, the effect of these therapies on healthy organs limit their therapeutic window. Elucidating the biology of PSMA as well as characterising the pharmacokinetic and pharmacodynamic properties of PSMA-targeted RNT will facilitate therapeutic approaches aimed at improving efficacy and safety. In this review, we provide an overview of existing PSMA-targeting RNT and an update on novel combinatorial approaches.

Darolutamide Potentiates the Antitumor Efficacy of a PSMA-targeted Thorium-227 Conjugate by a Dual Mode of Action in Prostate Cancer Models

PURPOSE

Androgen receptor (AR) inhibitors are well established in the treatment of castration-resistant prostate cancer and have recently shown efficacy also in castration-sensitive prostate cancer. Although most patients respond well to initial therapy, resistance eventually develops, and thus, more effective therapeutic approaches are needed. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and presents an attractive target for radionuclide therapy. Here, we evaluated the efficacy and explored the mode of action of the PSMA-targeted thorium-227 conjugate (PSMA-TTC) BAY 2315497, an antibody-based targeted alpha-therapy, in combination with the AR inhibitor darolutamide.

EXPERIMENTAL DESIGN

The in vitro and in vivo antitumor efficacy and mode of action of the combination treatment were investigated in preclinical cell line-derived and patient-derived prostate cancer xenograft models with different levels of PSMA expression.

RESULTS

Darolutamide induced the expression of PSMA in androgen-sensitive VCaP and LNCaP cells in vitro, and the efficacy of darolutamide in combination with PSMA-TTC was synergistic in these cells. In vivo, the combination treatment showed synergistic antitumor efficacy in the low PSMA-expressing VCaP and in the high PSMA-expressing ST1273 prostate cancer models, and enhanced efficacy in the enzalutamide-resistant KUCaP-1 model. The treatments were well tolerated. Mode-of-action studies revealed that darolutamide induced PSMA expression, resulting in higher tumor uptake of PSMA-TTC, and consequently, higher antitumor efficacy, and impaired PSMA-TTC-mediated induction of DNA damage repair genes, potentially contributing to increased DNA damage.

CONCLUSIONS

These results provide a strong rationale to investigate PSMA-TTC in combination with AR inhibitors in patients with prostate cancer.

Prostate Cancer Theranostics: From Target Description to Imaging

Prostate-specific membrane antigen-PET/computed tomography (PSMA-PET/CT) is the investigation of choice for imaging prostate cancer. Demonstrating high diagnostic accuracy, PSMA-PET/CT detects disease at very early stages of recurrence, where the chances of a definitive cure may be at their greatest. A number of PSMA-radioligands are in established clinical routine, and there are currently only limited data and no single tracer can clearly be advocated over the others at present. Further clinical trial data, comparing and contrasting radiotracers and reporting outcome-based data are necessary to further increase the implementation of this very promising imaging modality.

68Ga-PSMA-11 PET imaging in patients with ongoing androgen deprivation therapy for advanced prostate cancer

Purpose

Prostate-specific membrane antigen (PSMA) targeted positron emission tomography (PET) imaging significantly improved the detection of recurrent prostate cancer (PCa). However, the value of PSMA PET imaging in patients with advanced hormone-sensitive or hormone-resistant PCa is still largely unknown. The aim of this study was to analyze the detection rate and distribution of lesions using PSMA PET imaging in patients with advanced PCa and ongoing androgen deprivation therapy (ADT).

Methods

A total of 84 patients diagnosed with hormone-sensitive or hormone-resistant PCa who underwent ⁶⁸Ga-PSMA-11 PET/magnetic resonance imaging (MRI) or computer tomography (CT) under ongoing ADT were retrospectively analyzed. We assessed the detection of PSMA-positive lesions overall and for three PSA subgroups (0 to < 1 ng/mL, 1 to < 20 ng/mL and > 20 ng/mL). In addition, PSMA-positive findings were stratified by localization (prostatic fossa, pelvic, para-aortic, mediastinal/supraclavicular and axillary lymph nodes, bone lesions and visceral lesions) and hormone status (hormone-sensitive vs. hormone-resistant). Furthermore, we assessed how many patients would be classified as having oligometastatic disease (≤ 3 lesions) and theoretically qualify for metastasis-directed radiotherapy (MDRT) in a personalized patient management.

Results

We detected PSMA-positive lesions in 94.0% (79 of 84) of all patients. In the three PSA subgroups detection rates of 85.2% (0 to < 1 ng/mL, n = 27), 97.3% (1 to < 20 ng/mL, n = 37) and 100% (> 20 ng/mL, n = 20) were observed, respectively. PSMA-positive visceral metastases were observed only in patients with a PSA > 1 ng/mL. Detection of PSMA-positive lesions did not significantly differ between patients with hormone-sensitive and hormone-resistant PCa. Oligometastatic PCa was detected in 19 of 84 patients (22.6%). Almost all patients, 94.7% (n = 18) would have been eligible for MDRT.

Conclusions

In this study, we observed an overall very high detection rate of 94% using PSMA PET imaging in patients with advanced PCa and ongoing ADT. Even in a majority of patients with very low PSA values < 1 ng/ml PSMA-positive lesions were found.

177Lu-PSMA-RLT of metastatic castration-resistant prostate cancer: limitations and improvements

The prevalence of metastatic castration-resistant prostate cancer (mCRPC) is increasing, and its prognosis is often poor. As a highly expressed target in mCRPC, prostate-specific membrane antigen (PSMA) is very attractive for its diagnosis and treatment. When the efficacy of chemical therapy is limited, radioligand therapy (RLT)-based on Lutetium-177 (¹⁷⁷Lu)-PSMA has received more research as an emerging treatment. To date, most published related studies have proven this method is effective and safe. However, about 1/3 of mCRPC patients have not benefited from ¹⁷⁷Lu-PSMA-RLT. The underlying mechanism of this phenomenon remains unclear. So based on the comprehensive research in recent years, this article proposes the possible reasons, including tumor lesions, PSMA heterogeneity, differences in DNA repair defects, and accelerated repopulation. Combining with the existing experience to give suggestions to improve the treatment efficacy, benefit more mCRPC patients.

Impact of short-term Dutasteride treatment on prostate-specific membrane antigen expression in a mouse xenograft model

Background

Dutasteride has been shown to increase expression of the prostate‐specific membrane antigen (PSMA) in prostate cancer cells in previous in vitro studies. This 5‐alpha‐reductase inhibitor is commonly used for the treatment of symptomatic benign prostatic enlargement. The modulation of PSMA expression might affect PSMA‐based prostate cancer imaging and therapy.

Aim

The purpose of this work was to further analyze concentration‐dependent effects of Dutasteride on PSMA expression in a mouse xenograft model.

Methods and results

Four groups of mice bearing LNCaP xenografts were treated for 14 days with daily intraperitoneal injections of either vehicle control or different concentrations of Dutasteride (0.1, 1, 10 mg/kg). Total expression of PSMA, androgen receptor (AR), and caspase‐3 protein was analyzed using immunoblotting (WES). In addition, PSMA, cleaved caspase‐3 and Ki‐67 expression was assessed and quantified by immunohistochemistry. Tumor size was measured by caliper on day 7 and 14, tumor weight was assessed following tissue harvesting.

The mean PSMA protein expression in mice increased significantly after treatment with 1 mg/kg (10‐fold) or 10 mg/kg (sixfold) of Dutasteride compared to vehicle control. The mean fluorescence intensity significantly increased by daily injections of 0.1 mg/kg Dutasteride (1.6‐fold) as well as 1 and 10 mg/kg Dutasteride (twofold). While the reduction in tumor volume following treatment with high concentrations of 10 mg/kg Dutasteride was nonsignificant, no changes in AR, caspase‐3, cleaved caspase‐3, and Ki‐67 expression were observed.

Conclusion

Short‐term Dutasteride treatments with concentrations of 1 and 10 mg/kg significantly increase the total PSMA protein expression in a mouse LNCaP xenograft model. PSMA fluorescence intensity increases significantly even using lower daily concentrations of 0.1 mg/kg Dutasteride. Further investigations are needed to elucidate the impact of Dutasteride treatment on PSMA expression in patients.

PSMA conjugated combinatorial liposomal formulation encapsulating genistein and plumbagin to induce apoptosis in prostate cancer cells

Although the biomedical sciences have achieved tremendous success in developing novel approaches to managing prostate cancer, this disease remains one of the major health concerns among men worldwide. Liposomal formulations of single drugs have shown promising results in cancer treatment; however, the use of multi drugs has shown a better therapeutic index than individual drugs. The identification of cancer-specific receptors has added value to design targeted drug delivering nanocarriers. We have developed genistein and plumbagin co-encapsulating liposomes (∼120 nm) with PSMA specific antibodies to target prostate cancer cells selectively in this work. These liposomes showed >90 % decrease in PSMA expressing prostate cancer cell proliferation without any appreciable toxicity to healthy cells and human red blood cells. Release of plumbagin and genistein was found to decrease the expression of PI3/AKT3 signaling proteins and Glut-1 receptors (inhibited glucose uptake and metabolism), respectively. The decrease in migration potential of cells and induced apoptosis established the observed anti-proliferative effect in prostate cancer cell lines. The discussed strategy of developing novel, non-toxic, and PSMA specific antibody conjugated liposomes carrying genistein and plumbagin drugs may also be used for encapsulating other drugs and inhibit the growth of different types of cancers.

Antihormone treatment differentially regulates PSA secretion, PSMA expression and 68Ga-PSMA uptake in LNCaP cells

Background

In recent years, a variety of innovative therapeutics for castration-resistant prostate cancer have been developed, including novel anti-androgenic drugs, such as abiraterone or VPC-13566. Therapeutic monitoring of these pharmaceuticals is performed either by measuring PSA levels in serum or by imaging. PET using PSMA ligands labeled with Fluor-18 or Gallium-68 is the most sensitive and specific imaging modality for detection of metastases in advanced prostate cancer. To date, it remains unclear how PSMA expression is modulated by anti-hormonal treatment and how it correlates with PSA secretion.

Methods

We analyzed modulation of PSMA-mRNA and protein expression, ⁶⁸Ga–PSMA uptake and regulation of PSA secretion by abiraterone or VPC-13566 in LNCaP cells in vitro.

Results

We found that abiraterone and VPC-13566 upregulate PSMA protein and mRNA expression but block PSA secretion in LNCaP cells. Both anti-androgens also enhanced ⁶⁸Ga–PSMA uptake normalized by the number of cells, whereas abiraterone and VPC-13566 reduced ⁶⁸Ga–PSMA uptake in total LNCaP monolayers treated due to cell death.

Conclusion

Our data indicate that PSA secretion and PSMA expression are differentially regulated upon anti-androgen treatment. This finding might be important for the interpretation of ⁶⁸Ga–PSMA PET images in monitoring therapies with abiraterone and VPC-13566 in prostate cancer patients, but needs to be validated in vivo.

The Effect of Metformin on Male Reproductive Function and Prostate: An Updated Review

Metformin is the first-line oral antidiabetic drug that shows multiple pleiotropic effects of anti-inflamation, anti-cancer, anti-aging, anti-microbia, anti-atherosclerosis, and immune modulation. Metformin's effects on men's related health are reviewed here, focusing on reproductive health under subtitles of erectile dysfunction (ED), steroidogenesis and spermatogenesis; and on prostate-related health under subtitles of prostate specific antigen (PSA), prostatitis, benign prostate hyperplasia (BPH), and prostate cancer (PCa). Updated literature suggests a potential role of metformin on arteriogenic ED but controversial and contradictory effects (either protective or harmful) on testicular functions of testosterone synthesis and spermatogenesis. With regards to prostate-related health, metformin use may be associated with lower levels of PSA in humans, but its clinical implications require more research. Although there is a lack of research on metform's effect on prostatitis, it may have potential benefits through its anti-microbial and anti-inflammatory properties. Metformin may reduce the risk of BPH by inhibiting the insulin-like growth factor 1 pathway and some but not all studies suggest a protective role of metformin on the risk of PCa. Many clinical trials are being conducted to investigate the use of metformin as an adjuvant therapy for PCa but results currently available are not conclusive. While some trials suggest a benefit in reducing the metastasis and recurrence of PCa, others do not show any benefit. More research works are warranted to illuminate the potential usefulness of metformin in the promotion of men's health.

Prostate-specific Membrane Antigen PET: Therapy Response Assessment in Metastatic Prostate Cancer

Therapy response assessment is a critical step in cancer management, leading clinicians to optimize the use of therapeutic options during the course of the disease. Imaging is a pivotal biomarker for therapy response evaluation in oncology and has gained wider use through the development of reproducible data-based guidelines, of which the Response Evaluation Criteria in Solid Tumors is the most successful example. Disease-specific criteria have also been proposed, and the Prostate Cancer Working Group 3 criteria are the mainstay for prostate cancer (PC). However, conventional imaging evaluation in metastatic PC has several limitations, including (a) the inability to detect small-volume disease, (b) the high prevalence of bone (nonmeasurable) lesions at imaging, and (c) the established role of serum prostate-specific antigen (PSA) levels as the biomarker of choice for response assessment and disease progression. In addition, there are an increasing number of newer treatment options with various effects on imaging features. Prostate-specific membrane antigen (PSMA) PET has improved patient selection for newer treatments, such as metastasis-directed therapy (MDT) or radionuclide therapy. The role of PSMA PET in response assessment for many metastatic PC therapeutic options (MDT, androgen deprivation therapy, chemotherapy, radionuclide therapy, and immunotherapy) is an evolving issue, with emerging data showing good correlation with PSA levels and clinical outcome. However, there are specific implications of each therapy (especially androgen deprivation therapy and immunotherapy) on PSMA expression by PC cells, leading to potential pitfalls and inaccuracies that must be known by radiologists. Despite some limitations, PSMA PET is addressing gaps left by conventional imaging methods (eg, CT and bone scanning) and nonimaging biomarkers (PSA levels) in metastatic PC therapy response assessment, a role that can be improved with advances like refinement of interpretation criteria and whole-body tumor burden quantification.^© RSNA, 2020See discussion on this article by Barwick and Castellucci.

Predictors of Prostate-specific Membrane Antigen (PSMA/FOLH1) Expression in a Genomic Database

OBJECTIVE

To assess predictors of prostate-specific membrane antigen (PSMA) expression in a genomic database; positron emission tomography with PSMA-targeted radiopharmaceuticals is increasingly being utilized.

METHODS

The de-identified Decipher Biosciences database, which includes expression for more than 46,000 coding and noncoding genes per patient, was queried for expression of FOLH1 (PSMA). Prostate cancer patients who underwent radical prostatectomy and received the Decipher Test were included in the analysis. PSMA expression was compared to the Gleason Grade Group, Decipher risk category (a validated 22 biomarker genomic score), basal versus luminal molecular subtype, and androgen receptor activity. Multivariable regression analyses were performed.

RESULTS

The Decipher de-identified Decipher Biosciences database contained 16,807 men who underwent prostatectomy with the average age being 65-year old and most being Gleason Grade Group 2 (35%) or 3 (27%). Higher Grade Group was associated with higher PSMA expression except in Grade Group 5 [Grade group: 1 (0.66), 2 (0.84), 3 (0.99), 4 (1.07), 5 (0.99), P <.001]. Luminal subtype was found to have much higher PSMA expression when compared to basal (1.01 vs 0.68, P <.001). The androgen receptor activity signature demonstrated a dramatic difference between basal (0.19) and luminal (0.62) subtypes (P <.001). In the multivariable model, luminal patients, high androgen receptor activity scores, and high Grade Groups were significantly associated with higher FOLH1 percentile rank (P <.001).

CONCLUSION

High PSMA expression (FOLH1) was associated with high androgen receptor activity and luminal subtype. Genomic tests could aid in predicting, interpreting, and/or directing PSMA theranostics.

Molecular analysis of circulating tumor cells of metastatic castration-resistant Prostate Cancer Patients receiving 177Lu-PSMA-617 Radioligand Therapy

Rationale: Lu-177-PSMA-617 radioligand therapy (RLT) is currently under approval for treatment of metastatic castration resistant prostate cancer (mCRPC) patients with late stage disease. However, previous studies demonstrated both heterogeneity of prostate specific membrane antigen (PSMA) expression, as well as response to PSMA treatment among mCRPC patients. Thus, there is an unmet need for identifying predictive parametres prior or under PSMA-RLT treatment. We therefore aimed to correlate several clinical and molecular parameters with response to PSMA treatment in a cohort of mCRPC patients undergoing PSMA RLT followed by a detailed analysis of promising candidates.

Methods: Nineteen patients, median age 68.8 years (range: 56.9 - 83.3) with mCRPC were included in this study. We performed baseline analysis of clinical parameters based on PSMA PET/CT, (metabolic tumor volume (MTV), total tumor volume (TTV)), serum PSA, ALP, LDH and gene expression analysis of circulating tumor cells (expression of AR full length (AR-FL), AR splice variant 7 (AR-V7), PSA and PSMA) as well as common markers for neuroendocrine differentiation (NED).

Results: Patients presented with bone, lymph node, and visceral metastases (89%, 68%, and 21%, respectively). All patients were pretreated with docetaxel, either abiraterone or enzalutamide, or both. Biochemical response in terms of PSA decline ≥50 or ≥30% was observed in 42% and 63%, respectively. There were significant correlations between PSA and PSMA mRNA expression, as well as tumor volumes (both MTV and TTV), AR-FL and AR-V7 mRNA expression. However, there was no correlation with response to PSMA treatment. Furthermore, none of these parameters was significantly correlated with baseline serum PSA values. Common NED markers were shown to be specifically high expressed and revealed impact on OS independent from AR-V7 gene expression.

Conclusion: We demonstrate that AR-FL and its splice variant AR-V7 might serve as prognostic biomarkers displaying high tumor burden in mCRPC patient prior to PSMA-RLT. Contrary, PSMA, which has been discussed as a biomarker for PSMA targeted treatment, does not display strong prognostic ability - at least on the mRNA level. Surprisingly, none of these parameters correlates to response to PSMA treatment. In contrast, commom NED markers such as SYP and ENO2 as well as FOXA1 expression level seem to predict OS, but not PFS, more reliably. We admit that a limitation of our study is the focus on mRNA expression of potential biomarkers only. Further investigations analyzing the potential role of protein expression of these markers are therefore warranted.

Immunohistochemical PSMA expression patterns of primary prostate cancer tissue are associated with the detection rate of biochemical recurrence with 68Ga-PSMA-11-PET

Prostate-specific membrane antigen (PSMA) targeted PET has a high detection rate for biochemical recurrence (BCR) of prostate cancer (PCa). Nevertheless, even at high prostate-specific antigen (PSA) levels (> 3 ng/ml), a relevant number of PSMA-PET scans are negative, mainly due to PSMA-negative PCa. Our objective was to investigate whether PSMA-expression patterns of the primary tumour on immunohistochemistry (IHC) are associated with PSMA-PET detection rate of recurrent PCa. Methods: Retrospective institutional review board approved single-centre analysis of patients who had undergone ⁶⁸Ga-PSMA-11-PET for BCR after radical prostatectomy (RPE) between 04/2016 and 07/2019, with tumour specimens available for PSMA-IHC. Clinical information (age, PSA-level, ongoing androgen deprivation therapy (ADT), Gleason score) and PSMA-IHC of the primary tumour were collected and their relationship to results from PSMA-PET (positive/negative) was investigated using a multiple logistic regression analysis. Results: 120 PSMA-PET scans in 74 patients were available for this analysis. Overall detection rate was 62% (74/120 scans), with a mean PSA value at scan time of 0.99 ng/ml (IQR 0.32-4.27). Of the clinical factors, only PSA-level and ADT were associated with PSMA-PET positivity. The percentage of PSMA-negative tumour area on IHC (PSMA_%neg) had a significant association to PSMA-PET negativity (OR = 2.88, p < 0.001), while membranous PSMA-expression showed no association (p = 0.73). The positive predictive value of PSMA_%neg ≥ 50% for a negative PSMA-PET was 85% (13/11) and for a PSMA_%neg of 80% or more, 100% (9/9). Conclusions: PSMA-negative tumour area on IHC exhibited the strongest association with negative PSMA-PET scans, beside PSA-level and ADT. Even at very high PSA levels, PSMA-PET scans were negative in most of the patients with PSMA_%neg ≥ 50%.

Expanding the role of small-molecule PSMA ligands beyond PET staging of prostate cancer

Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) is rapidly being established as arguably the leading contemporary imaging modality in the management of prostate cancer. Outside of its conventional use in the de novo staging of localized disease and detection of biochemical recurrence, additional applications for the use of PSMA PET are emerging. Uptake of PSMA tracers in other genitourinary malignancies, particularly renal cell carcinoma, has led to new fields of investigation. Therapeutic delivery of radiolabelled PSMA small molecules has shown considerable promise in advanced prostate cancer. The ability to use the same molecule for imaging and therapy - theranostics - enables a highly personalized approach. PSMA PET can also have a considerable influence in the selection and guidance of radiotherapy fields for high-risk and recurrent disease. Intriguingly, changes in intensity of PSMA uptake during systemic therapy might provide early response assessment or novel insight into the biological responses of genitourinary malignancies to treatment. An evolving range of radiolabelled PSMA radiopharmaceuticals is emerging in the multiple facets of modern clinical practice.

Investigating PSMA-Targeted Radioligand Therapy Efficacy as a Function of Cellular PSMA Levels and Intratumoral PSMA Heterogeneity

PURPOSE

Prostate-specific membrane antigen (PSMA) targeting radioligands deliver radiation to PSMA-expressing cells. However, the relationship between PSMA levels and intralesion heterogeneity of PSMA expression, and cytotoxic radiation by radioligand therapy (RLT) is unknown. Here we investigate RLT efficacy as function of PSMA levels/cell, and the fraction of PSMA⁺ cells in a tumor.

EXPERIMENTAL DESIGN

RM1 cells expressing different levels of PSMA (PSMA^-, PSMA⁺, PSMA⁺⁺, PSMA⁺⁺⁺; study 1) or a mix of PSMA⁺ and PSMA^- RM1 (study 2, 4) or PC-3/PC-3-PIP (study 3) cells at various ratios were injected into mice. Mice received ¹⁷⁷Lu- (studies 1-3) or ²²⁵Ac- (study 4) PSMA617. Tumor growth was monitored. Two days post-RLT, tumors were resected in a subset of mice. Radioligand uptake and DNA damage were quantified.

RESULTS

¹⁷⁷Lu-PSMA617 efficacy increased with increasing PSMA levels (study 1) and fractions of PSMA positive cells (studies 2, 3) in both, the RM1 and PC-3-PIP models. In tumors resected 2 days post-RLT, PSMA expression correlated with ¹⁷⁷Lu-PSMA617 uptake and the degree of DNA damage. Compared with ¹⁷⁷Lu-PSMA617, ²²⁵Ac-PSMA617 improved overall antitumor effectiveness and tended to enhance the differences in therapeutic efficacy between experimental groups.

CONCLUSIONS

In the current models, both the degree of PSMA expression and the fraction of PSMA⁺ cells correlate with ¹⁷⁷Lu-/²²⁵Ac-PSMA617 tumor uptake and DNA damage, and thus, RLT efficacy. Low or heterogeneous PSMA expression represents a resistance mechanism to RLT.See related commentary by Ravi Kumar and Hofman, p. 2774.

Prospective study on the effect of short-term androgen deprivation therapy on PSMA uptake evaluated with 68Ga-PSMA-11 PET/MRI in men with treatment-naïve prostate cancer

PURPOSE

Based on in vitro studies, it is known that androgen deprivation therapy (ADT) increases prostate-specific membrane antigen (PSMA) expression. Therefore, we hypothesised that ADT improves the performance of PSMA-PET imaging in primary staging of prostate cancer. The purpose of the study was to demonstrate the time course effect of ADT on PSMA uptake in different types of metastatic lesions evaluated with ⁶⁸Ga-PSMA-11 PET/MRI.

METHODS

Nine men with treatment-naïve prostate cancer were enrolled to a prospective, registered (NCT03313726) clinical trial. A ⁶⁸Ga-PSMA-11 PET/MRI was performed once before and 3 times post-ADT (degarelix, Firmagon). Change of maximum standardised uptake values (SUVmax) in prostate, lymph nodes, bone metastases, and physiologically PSMA-avid organs were evaluated in a time frame of 1-8 weeks.

RESULTS

All patients reached castration levels within 10 days, and 50% decrease in prostate-specific antigen (PSA) concentration was observed 14 days post-ADT. A heterogeneous increase in PSMA uptake was observed 3 to 4 weeks post-ADT. This phenomenon was definitively more evident in bone metastases: 13 (57%) of the metastasis, with a mean (range) SUVmax increase of 77% (8-238%). In one patient, already having bone metastases at baseline, three new bone metastases were observed post-ADT. Of lesions with reduced SUVmax, none disappeared.

CONCLUSIONS

Both in patient and region level, increase in PSMA uptake post-ADT is heterogenous and is seen most evidently in bone metastases. Preliminary results on a small cohort of patients suggest the clinical impact of ADT on improving the performance of ⁶⁸Ga-PSMA PET in staging seems to be minor. However, the optimal imaging time point might be 3 to 4 weeks post-ADT. Since none of the metastases with decreasing SUVmax disappeared, it seems that short-term usage of ADT does not interfere with the interpretation of ⁶⁸Ga-PSMA PET.

TRIAL REGISTRATION

NCT03313726, registered 18 October 2017; EUDRA-CT, 2017-002345-29.

Use of gallium-68 prostate-specific membrane antigen positron-emission tomography for detecting lymph node metastases in primary and recurrent prostate cancer and location of recurrence after radical prostatectomy: an overview of the current literature

Objectives

To review the literature to determine the sensitivity and specificity of gallium‐68 prostate‐specific membrane antigen (⁶⁸Ga‐PSMA) positron‐emission tomography (PET) for detecting pelvic lymph node metastases in patients with primary prostate cancer (PCa), and the positive predictive value in patients with biochemical recurrence (BCR) after initial curative treatment, and, in addition, to determine the detection rate and management impact of ⁶⁸Ga‐PSMA PET in patients with BCR after radical prostatectomy (RP).

Materials and Methods

We performed a comprehensive literature search. Search terms used in MEDLINE, EMBASE and Science Direct were ‘(PSMA, ⁶⁸Ga‐PSMA, ⁶⁸Gallium‐PSMA, Ga‐68‐PSMA or prostate‐specific membrane antigen)’ and ‘(histology, lymph node, staging, sensitivity, specificity, positive predictive value, recurrence, recurrent or detection)’. Relevant abstracts were reviewed and full‐text articles obtained where possible. References to and from obtained articles were searched to identify further relevant articles.

Results

Nine retrospective and two prospective studies described the sensitivity and specificity of ⁶⁸Ga‐PSMA PET for detecting pelvic lymph node metastases before initial treatment, which ranged from 33.3% to 100% and 80% to 100%, respectively. In eight retrospective studies, the positive predictive value of ⁶⁸Ga‐PSMA PET in patients with BCR before salvage lymph node dissection ranged from 70% to 100%. The detection rate of ⁶⁸Ga‐PSMA PET in patients with BCR after RP in the PSA subgroups <0.2 ng/mL, 0.2–0.49 ng/mL and 0.5 to <1.0 ng/mL ranged from 11.3% to 50.0%, 20.0% to 72.7% and 25.0% to 87.5%, respectively.

Conclusion

The review results showed that ⁶⁸Ga‐PSMA PET had a high specificity for the detection of pelvic lymph node metastases in primary PCa. Furthermore, ⁶⁸Ga‐PSMA PET had a very high positive predictive value in detecting lymph node metastases in patients with BCR. By contrast, sensitivity was only moderate; therefore, based on the currently available literature, ⁶⁸Ga‐PSMA PET cannot yet replace pelvic lymph node dissection to exclude lymph node metastases. In the salvage phase, ⁶⁸Ga‐PSMA PET had both a high detection rate and impact on radiotherapy planning in early BCR after RP.

Concentration-dependent effects of dutasteride on prostate-specific membrane antigen (PSMA) expression and uptake of 177 Lu-PSMA-617 in LNCaP cells

BACKGROUND

Prostate-specific membrane antigen (PSMA)-based imaging and therapy are increasingly used in the management of prostate cancer. However, low PSMA surface expression in certain patients is a limitation for PSMA-based technologies. We have previously shown that high doses of dutasteride, a 5α-reductase inhibitor generally used for the treatment of benign prostatic enlargement, increase the PSMA expression in vitro. We now further analyzed the concentration- and time-dependent effects of dutasteride in LNCaP cells.

METHODS

Androgen receptor (AR) expressing prostate cancer cells (LNCaP) were treated for 7 to 14 days with vehicle control (0.1% dimethyl sulfoxide) or different concentrations of dutasteride (0.25 , 0.5 , 1 , and 5  μM). In addition to cell proliferation, PSMA surface expression was assessed using flow cytometry (FACS) and immunocytochemistry. Total PSMA and AR expression was analyzed by capillary western immunoassay (WES). In addition, tumor cell uptake and internalization assays of ¹⁷⁷ Lu-PSMA-617 were performed.

RESULTS

Dutasteride treatment resulted in a significant upregulation of PSMA surface expression compared to vehicle control after 7 days in all tested concentrations. After 14 days a further, concentration-dependent increase of PSMA surface expression was detectable. Total PSMA protein expression significantly increased after treatment of cells with high concentrations of dutasteride using 5  μM for 7 or 14 days. However, when lower concentrations were used total PSMA expression was not significantly altered compared to vehicle control. Further testing revealed a dose-dependent increase in uptake and internalization of ^177Lu -PSMA-617 after 7 and 14 days. Though, a significantly increased uptake was only observed using a 5  μM dutasteride concentration for 7 days as well as 1  and 5  μM for 14 days.

CONCLUSION

Our investigations revealed a concentration- and time-dependent effect of dutasteride on PSMA expression and uptake of ^177Lu -PSMA-617 in LNCaP cells. A short-term treatment of patients with high doses of dutasteride might increase the detection rate of PSMA-based imaging and increase the effect of ^177Lu -PSMA-617 therapy via upregulation of PSMA expression.

Increased PSMA Expression in Castration-Resistant Prostate Cancer Metastases 3 Months After Initiation of Enzalutamide Indicated by 18F-DCFPyL PET/CT

Radioisotope-labeled prostate-specific membrane antigen PET/CT is increasingly used for detection of prostate cancer most often in the setting of biochemical recurrence or in primary staging. This report shows increased PSMA expression in lymph node metastases 3 months after initiation of enzalutamide for castration-resistant prostate cancer, whereas lymph node volume and serum prostate-specific antigen decreases over time. This case demonstrates that increasing F-DCFPyL uptake after initiation of androgen deprivation therapy should not be confused with disease progression.

Detection Rate and Localization of Prostate Cancer Recurrence Using 68Ga-PSMA-11 PET/MRI in Patients with Low PSA Values ≤ 0.5 ng/mL

A first analysis of simultaneous ⁶⁸Ga-prostate-specific membrane antigen (PSMA)-11 PET/MRI showed some improvement in the detection of recurrent disease at low serum prostate specific antigen (PSA) values below 0.5 ng/mL compared with the already high detection rate of ⁶⁸Ga-PSMA-11 PET/CT. We therefore focused on all patients with biochemical recurrence and PSA values no higher than 0.5 ng/mL to assess the detection rate for ⁶⁸Ga-PSMA-11 PET/MRI. Methods: We retrospectively analyzed a cohort of 66 consecutive patients who underwent ⁶⁸Ga-PSMA-11 PET/MRI for biochemical recurrence with a PSA value no higher than 0.5 ng/mL at our institution. Median PSA level was 0.23 ng/mL (range, 0.03-0.5 ng/mL). Detection of PSMA-positive lesions within the prostate fossa, local and distant lymph nodes, bones, or visceral organs was recorded. In addition, all scans with ⁶⁸Ga-PSMA-11 PET/MRI-positive lesions were retrospectively assessed to analyze if lesions were detected inside or outside a standard salvage radiotherapy volume. Results: Overall, in 36 of 66 patients (54.5%) PSMA-positive lesions were detected; in 26 of 40 (65%) patients with a PSA level between 0.2 and 0.5 ng/mL and in 10 of 26 (38.5%) patients with a PSA level less than 0.2 ng/mL. Even at those low PSA values, only 8 of 66 (12.1%) patients had exclusive local recurrence. Lymph nodes were detected in 23 patients and bone metastases in 5 on ⁶⁸Ga-PSMA-11 PET/MRI. In 26 of 66 patients (39.4%), PSMA-positive lesions were located outside a standard salvage radiotherapy volume. Conclusion: Our data confirm that ⁶⁸Ga-PSMA-11 PET/MRI has a high detection rate for recurrent prostate cancer, even at low PSA levels no higher than 0.5 ng/mL. In addition, we show that ⁶⁸Ga-PSMA-11 PET/MRI detected PSMA-positive lesions outside a standard salvage radiotherapy volume in 39.4% of all patients.

Current and potential future role of PSMA-PET in patients with castration-resistant prostate cancer

PURPOSE

To review the current literature and discuss potential future roles of the novel positron emission tomography (PET) tracers targeting the prostate-specific membrane antigen (PSMA) in patients with castration-resistant prostate cancer (CRPC).

METHODS

A literature search on February 19th 2018 was conducted using the Medline database and www.clinicaltrials.gov . Additionally, illustrative cases of CRPC patients from our own institution who were restaged and treated based on PSMA-PET scan results are provided.

RESULTS

11 Studies met the inclusion criteria. PSMA-PET detected more metastatic lesions compared to conventional bone scan. Several patients were up-staged from non-metastatic CRPC (nmCRPC) to metastatic CRPC (mCRPC). Currently, no clear consensus exists regarding treatment response assessment in PSMA-PET scans for mCRPC patients undergoing treatment. Also, the role of PSMA-PET as a gatekeeper for systemic therapy or radioligands is currently undefined. PSMA-guided metastasis-directed radiotherapy may not only alleviate local symptoms but has the potential to defer systemic treatment in patients with oligoprogressive CRPC.

CONCLUSION

Compared to bone scan, PSMA-PET is more sensitive and specific to detect metastases but the therapeutic consequences of PSMA-PET results in the setting of CRPC remain unclear. Until future studies define the role of PSMA-PET in patients with CRPC, the current standard for imaging remains bone scan and computerized tomography.