Prostate-specific Membrane Antigen Targeting Research Articles

Development of [177Lu]Lu-LNC1003 for radioligand therapy of prostate cancer with a moderate level of PSMA expression.

Evans blue as an albumin binder has been widely used to improve pharmacokinetics and enhance tumor uptake of radioligands, including prostate-specific membrane antigen (PSMA) targeting agents. The goal of this study is to develop an optimal Evans blue-modified radiotherapeutic agent that could maximize the absolute tumor uptake and tumor absorbed dose thus the therapeutic efficacy to allow treatment of tumors even with moderate level of PSMA expression. [177Lu]Lu-LNC1003 was synthesized based on PSMA-targeting agent and Evans blue. Binding affinity and PSMA targeting specificity were verified through cell uptake and competition binding assay in 22Rv1tumor model that has moderate level of PSMA expression. SPECT/CT imaging and biodistribution studies in 22Rv1 tumor-bearing mice were performed to evaluate the preclinical pharmacokinetics. Radioligand therapy studies were conducted to systematically assess the therapeutic effect of [177Lu]Lu-LNC1003. LNC1003 showed high binding affinity (IC50 = 10.77nM) to PSMA in vitro, which was comparable with that of PSMA-617 (IC50 = 27.49nM) and EB-PSMA-617 (IC50 = 7.91nM). SPECT imaging of [177Lu]Lu-LNC1003 demonstrated significantly improved tumor uptake and retention as compared with [177Lu]Lu-EB-PSMA and [177Lu]Lu-PSMA-617, making it suitable for prostate cancer therapy. Biodistribution studies further confirmed the remarkably higher tumor uptake of [177Lu]Lu-LNC1003 (138.87 ± 26.53%ID/g) over [177Lu]Lu-EB-PSMA-617 (29.89 ± 8.86%ID/g) and [177Lu]Lu-PSMA-617 (4.28 ± 0.25%ID/g) at 24h post-injection. Targeted radioligand therapy results showed noteworthy inhibition of 22Rv1 tumor growth after administration of a single dose of 18.5MBq [177Lu]Lu-LNC1003. There was no obvious antitumor effect after [177Lu]Lu-PSMA-617 treatment under the same condition. In this study, [177Lu]Lu-LNC1003 was successfully synthesized with high radiochemical purity and stability. High binding affinity and PSMA targeting specificity were identified in vitro and in vivo. With greatly enhanced tumor uptake and retention, [177Lu]Lu-LNC1003 has the potential to improve therapeutic efficacy using significantly lower dosages and less cycles of 177Lu that promises clinical translation to treat prostate cancer with various levels of PSMA expression.

Theranostics of Primary Prostate Cancer: Beyond PSMA and GRP-R.

First, we prospectively performed neurotensin receptor-1 (NTS1) IHC in a series of patients receiving both [68Ga]Ga-PSMA-617 and [68Ga]Ga-RM2 before prostatectomy. In this series, PSMA and GRP-R IHC were also available (n = 16). Next, we aimed at confirming the PSMA/GRP-R/NTS1 expression profile by retrospective autoradiography (n = 46) using a specific radiopharmaceuticals study and also aimed to decipher the expression of less-investigated targets such as NTS2, SST2 and CXCR4. In the IHC study, all samples with negative PSMA staining (two patients with ISUP 2 and one with ISUP 3) were strongly positive for NTS1 staining. No samples were negative for all three stains-for PSMA, GRP-R or NTS1. In the autoradiography study, binding of [111In]In-PSMA-617 was high in all ISUP groups. However, some samples did not bind or bound weakly to [111In]In-PSMA-617 (9%). In these cases, binding of [111n]In-JMV 6659 and [111In]In-JMV 7488 towards NTS1 and NTS2 was high. Targeting PSMA and NTS1/NTS2 could allow for the detection of all intraprostatic lesions.

Molecular Design of 68Ga- and 89Zr-Labeled Anticalin Radioligands for PET-Imaging of PSMA-Positive Tumors.

Anticalin proteins directed against the prostate-specific membrane antigen (PSMA), optionally having tailored plasma half-life using PASylation technology, show promise as radioligands for PET-imaging of xenograft tumors in mice. To investigate their suitability, the short-circulating unmodified Anticalin was labeled with 68Ga (τ1/2 = 68 min), using the NODAGA chelator, whereas the half-life extended PASylated Anticalin was labeled with 89Zr (τ1/2 = 78 h), using either the linear chelator deferoxamine (Dfo) or a cyclic derivative, fusarinine C (FsC). Different PSMA targeting Anticalin versions (optionally carrying the PASylation sequence) were produced carrying a single exposed N- or C-terminal Cys residue and site-specifically conjugated with the different radiochelators via maleimide chemistry. These protein conjugates were labeled with radioisotopes having distinct physical half-lives and, subsequently, applied for PET-imaging of subcutaneous LNCaP xenograft tumors in CB17 SCID mice. Uptake of the protein tracers into tumor versus healthy tissues was assessed by segmentation of PET data as well as biodistribution analyses. PET-imaging with both the 68Ga-labeled plain Anticalin and the 89Zr-labeled PASylated Anticalin allowed clear delineation of the xenograft tumor. The radioligand A3A5.1-PAS(200)-FsC·89Zr, having an extended plasma half-life, led to a higher tumor uptake 24 h p.i. compared to the 68Ga·NODAGA-Anticalin imaged 60 min p.i. (2.5% ID/g vs 1.2% ID/g). Pronounced demetallation was observed for the 89Zr·Dfo-labeled PASylated Anticalin, which was ∼50% lower in the case of the cyclic radiochelator FsC (p < 0.0001). Adjusting the plasma half-life of Anticalin radioligands using PASylation technology is a viable approach to increase radioisotope accumulation within the tumor. Furthermore, 89Zr-ImmunoPET-imaging using the FsC radiochelator is superior to that using Dfo. Our strategy for the half-life adjustment of a tumor-targeting Anticalin to match the physical half-life of the applied radioisotope illustrates the potential of small binding proteins as an alternative to antibodies for PET-imaging.

Comparative assessment of 18F-PSMA-1007 biodistribution at 60 and 120 minutes after administration by PET/CT in prostate cancer patients

INTRODUCTION: Positron emission tomography combined with computed tomography (PET/CT) with prostate-specific membrane antigen-targeted (PSMA) radiopharmaceuticals is a valuable method for prostate cancer (PCa) imaging. Both 68Ga- and 18F-labelled PSMA ligands are used in clinical practice now, for example, 18F-PSMA-1007. Currently there is no consensus on time interval between 18F-PSMA-1007 administration and scanning start that served as the basis for this study. OBJECTIVE: The aim of this study was to determinate the optimal time interval between 18F-PSMA-1007 administration and scanning start at PET/CT in PCa patients. MATERIALS AND METHODS: This prospective analysis included the results of 18F-PSMA-1007 PET/CT of 26 patients with PCa (mean age — 69.1±7.1 years, mean PSA value — 3.9 (0.5; 10) ng/ml), 4 patients — at primary staging, 10 patients — with therapy assessment and 12 patients — with biochemical recurrence. The PET/CT scanning was performed at 60 and 120 minutes after 18F-PSMA-1007 administration with subsequent measurement and comparison of the pathological and physiological uptake. TBR value (Tumor-to-Background Ratio) was calculated for the pathological uptake in the prostate or prostate bed and lymph nodes lesions relative to the physiological uptake in urinary bladder and abdominal aortic blood pool respectively. Statistics: Statistical analysis was carried out using the software SPSS Statistics 28 to analyse the significance of the differences in median SUVmax (for pathological 18F-PSMA-1007 uptake), SUVmean (for physiological 18F-PSMA-1007 uptake) and TBR between two stages of scanning. RESULTS: There was a significant decrease of physiological 18F-PSMA-1007 uptake from median SUVmean 1.5 (1.0; 1.73) to 0.9 (0.5; 0.9), p&lt;0.001 in the abdominal aortic blood pool, 2.6 (1.3; 3.6) to 1.7 (1.1; 2.8), p&lt;0.05 in the urinary bladder, 0.4 (0.35; 0.44) to 0.33 (0.3; 0.37), p&lt;0.05 in the right gluteus medius muscle in the second scan. Moreover, there was a significant increase of physiological 18F-PSMA-1007 uptake from median SUVmean 8.9±2.8 to 10.3±3.4, p&lt;0.001 in the liver, 7.5±3.5 to 8.3±3.8, p&lt;0,001 in the spleen, 9.8±3.7 to 11.6±4.3, p&lt;0.001 in the right parotid salivary gland. Uptake in the bone marrow remained stable with median SUVmean 1 (0.8; 1.3), p=0.917. There was a significant increase of pathological uptake from median SUVmax 4.6 (2.7; 7.7) to 5.25 (3.2; 9.0), p&lt;0.001 in 76 lesions without appearance of new lesions in the second scan at 120 minutes. Mean TBR value also significantly increased for the ratios «prostate or prostate bed/urinary bladder» from 1.7 (1.1; 4.7) to 3.6 (2.1; 9.5), p&lt;0.05 and «lymph node/aortic blood pool»: per-lesion analysis from 2.8 (2.5; 5.2) to 6.2 (5; 10.1), p&lt;0.001 and per-patient analysis from 4,6 (2.7; 5.5) to 9.8 (4.9; 12.1), p&lt;0.05. DISCUSSION: It’s not justified to use time interval in 120 minutes routinely because of the lack of new lesions in the second scan, irrational spending of the department resources and time of medical staff. However, there was an increase in the TBR values indicating the higher quality of images in the second scan at 120 minutes. CONCLUSION: Due to the lack of clinical benefits of the 120 minutes interval and the associated time cost, a 60 minutes interval between 18F-PSMA-1007 administration and the start of a PET/CT scan in PCa patients is more optimal, however, delayed scan is justified in cases of obtaining unclear results.

Quantitative assessment of PSMA PET response to therapy in castration-sensitive prostate cancer using an automated imaging platform for disease identification and measurement

RationaleProstate cancer treatment response may be automatically quantified using a molecular imaging analysis platform targeting prostate-specific membrane antigen (PSMA).MethodsA retrospective analysis of patients with castration-sensitive prostate cancer who underwent PSMA-targeted molecular imaging prior to and 3 months or more after treatment was conducted. Disease burden was analyzed with aPROMISE, an artificial intelligence imaging platform that automatically quantifies PSMA-positive lesions. The calculated PSMA scores for prostate/bed, nodal, and osseous disease sites were compared with prostate-specific antigen (PSA) values.ResultsOf 30 eligible patients, the median decline in prostate/bed, nodal, and osseous disease PSMA scores were 100% (range 52–100%), 100% (range − 87–100%), and 100% (range − 21–100%), respectively. PSMA score decline was significantly associated with PSA decline.ConclusionChanges in aPROMISE PSMA scores are associated with changes in PSA and may quantify treatment response.

Laser-activated nanoparticles for ultrasound/photoacoustic imaging-guided prostate cancer treatment.

Prostate cancer (PCa) is the most common malignant tumor in men. Prostate-specific membrane antigen (PSMA), which is overexpressed on the surface of Prostate cancer cells, may serve as a potential therapeutic target. Recently, image-guided and targeted therapy for prostate cancers has attracted much attention by using Prostate-specific membrane antigen targeting nanoparticle. In this study, we produced PSMA-targeted light-responsive nanosystems. These nanosystems of liquid perfluorocarbon cores and polymer shells were loaded with the photosensitizer IR780 and therapeutic drugs paclitaxel. The liquid perfluorocarbon (PFP) in nanoparticles can perform ultrasound-enhanced imaging by liquid-gas transition and promote the deliver and release of paclitaxel. IR780 can perform photothermal therapy (PTT) guided by photoacoustic (PA) imaging. Combination treatment with photothermal therapy and chemotherapy exhibited excellent inhibition of cell proliferation in vitro and a significant therapeutic effect in vivo. In conclusion, we successfully formulated PSMA-targeted nanosystems with precision targeting and ultrasound/PA dual-modality imaging for anti-tumor effects.

Development of PSMA-PET-guided CT-based radiomic signature to predict biochemical recurrence after salvage radiotherapy

PurposeTo develop a CT-based radiomic signature to predict biochemical recurrence (BCR) in prostate cancer patients after sRT guided by positron-emission tomography targeting prostate-specific membrane antigen (PSMA-PET).Material and methodsConsecutive patients, who underwent 68Ga-PSMA11-PET/CT-guided sRT from three high-volume centers in Germany, were included in this retrospective multicenter study. Patients had PET-positive local recurrences and were treated with intensity-modulated sRT. Radiomic features were extracted from volumes of interests on CT guided by focal PSMA-PET uptakes. After preprocessing, clinical, radiomics, and combined clinical-radiomic models were developed combining different feature reduction techniques and Cox proportional hazard models within a nested cross validation approach.ResultsAmong 99 patients, median interval until BCR was the radiomic models outperformed clinical models and combined clinical-radiomic models for prediction of BCR with a C-index of 0.71 compared to 0.53 and 0.63 in the test sets, respectively. In contrast to the other models, the radiomic model achieved significantly improved patient stratification in Kaplan-Meier analysis. The radiomic and clinical-radiomic model achieved a significantly better time-dependent net reclassification improvement index (0.392 and 0.762, respectively) compared to the clinical model. Decision curve analysis demonstrated a clinical net benefit for both models. Mean intensity was the most predictive radiomic feature.ConclusionThis is the first study to develop a PSMA-PET-guided CT-based radiomic model to predict BCR after sRT. The radiomic models outperformed clinical models and might contribute to guide personalized treatment decisions.

NIR-II-triggered photothermal therapy with Au@PDA/PEG-PI for targeted downregulation of PSMA in prostate cancer.

Although positron emission tomography (PET) imaging products targeting prostate-specific membrane antigen (PSMA) have been approved for marketing, clinical challenges remain in the study of its use as a therapeutic target, such as the complex synthesis process and side effects after treatment. Here, we developed a strategy for targeted photothermal therapy (PTT) using PSMA as the target. The results of molecular docking demonstrated that the synthesized PEG modified urea-based PSMA inhibitor (small molecular PSMA inhibitor, PI) PI-PEG has a high affinity energy (binding energy=- 8.3 kcal mol-1) for the PSMA target. Therefore, modification of PI-PEG onto the surface of gold@polydopamine (Au@PDA) with NIR-II absorption could enable targeted PTT against PSMA. This work revealed that the prepared Au@PDA/PEG-PI were not only highly selective for PSMA, but also could efficiently ablate PSMA expression by targeted PTT at the maximum permissible exposure (MPE) of the NIR-II laser. Moreover, Au@PDA/PEG-PI also have potential for photoacoustic (PA) imaging and computed tomography (CT) imaging. As the first strategy to downregulate the expression of PSMA and successfully inhibit prostate cancer by targeted PTT, this study case provides a new idea for the clinical translation of PSMA as an integrated target for tumor diagnosis and anti-tumor treatment. STATEMENT OF SIGNIFICANCE: (1) Au@PDA/PEG-PI NPs were the novel PTT agent to target PSMA and successfully down-regulate PSMA expression. (2) Molecular docking results demonstrated that PI-PEG inhibitors have a high affinity energy for PSMA (binding energy=- 8.3 kcal mol-1). (3) Au@PDA/PEG-PI NPs can be targeted for efficient PTT at the MPE of the NIR-II laser. (4) Au@PDA/PEG-PI NPs also have the potential for PA and CT imaging.

Determinants of outcome following PSMA-based radioligand therapy and mechanisms of resistance in patients with metastatic castration-resistant prostate cancer.

[177Lu]Lu-PSMA has recently been approved for use in the post-taxane, post-novel hormonal-agent setting in patients with metastatic castration-resistant prostate cancer. As a beta-emitting radioligand targeting prostate-specific membrane antigen (PSMA), it delivers radiation to cells expressing PSMA on their surface. In pivotal clinical trials, patients were selected for this treatment based on positron emission tomography (PET)/CT imaging, requiring PSMA-avid disease with no evidence of discordant disease on 2-[18F]fluoro-2-deoxy-D-glucose PET/CT or contrast CT scan. Despite exhibiting an optimal imaging phenotype, the response for many patients is not durable, and a minority do not respond to [177Lu]Lu-PSMA at all. Disease progression is inevitable even for those who achieve an exceptional initial response. Reasons for both primary and acquired resistance are largely unknown; however, they are likely due to the presence of underlying PSMA-negative disease not identified on imaging, molecular factors conferring radioresistance, and inadequate delivery of lethal radiation, particularly to sites of micrometastatic disease. Biomarkers are urgently needed to optimize patient selection for treatment with [177Lu]Lu-PSMA by identifying those who are most and least likely to respond. Retrospective data support using several prognostic and predictive baseline patient- and disease-related parameters; however, robust prospective data is required before these can be translated into widespread use. Further, early on-treatment clinical parameters (in addition to serial prostate-specific antigen [PSA] levels and conventional restaging imaging) may serve as surrogates for predicting treatment response. With little known about the efficacy of treatments given after [177Lu]Lu-PSMA, optimal treatment sequencing is paramount, and biomarker-driven patient selection will hopefully improve treatment and survival outcomes.

Prostate-Specific Membrane Antigen Targeted Deep Tumor Penetration of Polymer Nanocarriers.

Tumoral uptake of large-size nanoparticles is mediated by the enhanced permeability and retention (EPR) effect, with variable accumulation and heterogenous tumor tissue penetration depending on the tumor phenotype. The performance of nanocarriers via specific targeting has the potential to improve imaging contrast and therapeutic efficacy in vivo with increased deep tissue penetration. To address this hypothesis, we designed and synthesized prostate cancer-targeting starPEG nanocarriers (40 kDa, 15 nm), [89Zr]PEG-(DFB)3(ACUPA)1 and [89Zr]PEG-(DFB)1(ACUPA)3, with one or three prostate-specific membrane antigen (PSMA)-targeting ACUPA ligands. The in vitro PSMA binding affinity and in vivo pharmacokinetics of the targeted nanocarriers were compared with a nontargeted starPEG, [89Zr]PEG-(DFB)4, in PSMA+ PC3-Pip and PSMA- PC3-Flu cells, and xenografts. Increasing the number of ACUPA ligands improved the in vitro binding affinity of PEG-derived polymers to PC3-Pip cells. While both PSMA-targeted nanocarriers significantly improved tissue penetration in PC3-Pip tumors, the multivalent [89Zr]PEG-(DFB)1(ACUPA)3 showed a remarkably higher PC3-Pip/blood ratio and background clearance. In contrast, the nontargeted [89Zr]PEG-(DFB)4 showed low EPR-mediated accumulation with poor tumor tissue penetration. Overall, ACUPA conjugated targeted starPEGs significantly improve tumor retention with deep tumor tissue penetration in low EPR PC3-Pip xenografts. These data suggest that PSMA targeting with multivalent ACUPA ligands may be a generally applicable strategy to increase nanocarrier delivery to prostate cancer. These targeted multivalent nanocarriers with high tumor binding and low healthy tissue retention could be employed in imaging and therapeutic applications.

PSMA1-mediated ultrasmall gold nanoparticles facilitate tumor targeting and MR/CT/NIRF multimodal detection of early-stage prostate cancer

Prostate-specific membrane antigen (PSMA) is a prominent biomarker for prostate cancer (PCa) diagnosis. Safe contrast agents able to render the expression and distribution of PSMA would facilitate early accurate screening and prognostic prediction of PCa. However, current Gd-containing nanoparticles are often limited by nonspecific redistribution in mononuclear phagocyte system (MPS) and inadequate perfusion to target sites. Besides, intrinsic defects of magnetic resonance (MR) equipment also hamper their use for precisely depicting PSMA details. Herein, we devised a novel noninvasive MR/CT/NIRF multimodal contrast agent (AGGP) coordinated to a high-affinity PSMA ligand (PSMA1) to specifically detect and quantify PSMA expression in PCa lesions, which exhibited formidable tripe-modal signal augments, preferential PSMA targeting, effective MPS escaping and profitable renal-clearable behavior in living mice. Biocompatibility and histopathological studies substantiated high security of AGGP in vivo, opening the door to future opportunities for improving early-stage PCa detection and clinical implementation of more effective multifunctional nanotherapeutics.

Preclinical evaluation and first in human study of Al18F radiolabeled ODAP-urea-based PSMA targeting ligand for PET imaging of prostate cancer.

This study aimed to introduce a novel [18F]AlF-labeled ODAP-Urea-based Prostate-specific membrane antigen (PSMA) probe, named [18F]AlF-PSMA-137, which was derived from the successful modification of glutamate-like functional group. The preclinically physical and biological characteristics of the probe were analyzed. Polit clinical PET/CT translation was performed to analyze its feasibility in clinical diagnosis of prostate cancer. [18F]AlF-PSMA-137 was maturely labeled with the [18F]AlF2+ labeling technique. It was analyzed by radio-HPLC for radiochemical purity and stability analysis in vitro and in vivo. The PSMA specificity was investigated in PSMA-positive (LNCaP) and PSMA-negative (PC3) cells, and the binding affinity was evaluated in LNCaP cells. Micro-PET/CT imaging was performed in mice bearing LNCaP or PC3 tumors. Thirteen patients with newly diagnosed prostate cancer were included for [18F]AlF-PSMA-137 PET/CT imaging. Physiologic biodistribution and tumor burden were semi-quantitatively evaluated and the radiation dosimetry of [18F]AlF-PSMA-137 was estimated. The radiochemical yield of [18F]AlF-PSMA-137 was 54.2 ± 10.7% (n = 16) with the radiochemical purity over 99% and the specific activity of 26.36 ± 7.33 GBq/μmol. The binding affinity to PSMA was 2.11 ± 0.63 nM. [18F]AlF-PSMA-137 showed high cell/tumor uptake which can be specifically blocked by PSMA inhibitor. According to the biodistribution in patients, [18F]AlF-PSMA-137 was mainly accumulated in kidneys, lacrimal glands, parotid glands, submandibular glands and liver which was similar to the extensive Glu-Ureas based probes. A total of 81 lesions were detected in PET/CT imaging and over 91% of lesions increased between 1 h p.i. (SUVmean: 10.98 ± 18.12) and 2 h p.i. (SUVmean: 14.25 ± 21.28) (p < 0.001). Additionally, the probe showed intensive accumulation in lesions which provided excellent imaging contrast with the high tumor-to-muscle ratio of 15.57 ± 27.21 at 1 h p.i. and 25.42 ± 36.60 at 2 h p.i. (p < 0.001), respectively. The effective dose of [18F]AlF-PSMA-137 was estimated as 0.0119 ± 0.0009 mSv/MBq. An ODAP-Urea-based PSMA probe [18F]AlF-PSMA-137 was successfully prepared with high specificity and binding affinity to PSMA. Micro-PET/CT imaging study demonstrated its feasibility for prostate cancer imaging. Pilot clinical study showed its potential for delay-imaging and prostate cancer detection.

Glu-Urea-Lys Scaffold Functionalized Superparamagnetic Iron Oxide Nanoparticles Targeting PSMA for In Vivo Molecular MRI of Prostate Cancer.

The prostate specific membrane antigen (PSMA), extensively overexpressed on prostate cancer (PCa) cell surface, has been validated as a diagnostic biomarker for PCa. However, insufficient attention has been paid to the development of PSMA-specific probes loaded with small chemical molecules for the in vivo molecular imaging of PCa. In this study, we innovatively labelled superparamagnetic iron oxide nanoparticles with a PSMA-targeting Glu-Urea-Lys scaffold. An optimized synthetic route was developed to offer a physiochemically stable probe. The probe demonstrated high binding affinity (0.38 ± 0.08 μg(Fe)/mL) and binding specificity to PSMA expressed on prostate cancer cell surface in vitro. In a xenograft PCa mouse model, significant negative contrast of the implanted prostate cancer xenograft could be specifically observed by MRI 6 h after tail vein injection of the tracer (Fe, 20 mg/kg), exhibiting its potential to exclusively enhance magnetic resonance detection of PCa.

A convenient total synthesis of PSMA-617: A prostate specific membrane antigen (PSMA) ligand for prostate cancer endotherapeutic applications

The treatment of metastatic Castration Resistant Prostate Cancer (mCRPC) by targeting Prostate Specific Membrane Antigen (PSMA), that is ubiquitously expressed on malicious cells, using177Lu-PSMA-617, has been showing great potential. Considering the promising results from Radioligand Therapy (RLT) studies conducted at multiple centres, 177Lu-PSMA-617, is being considered for FDA approval. The organic ligand, PSMA-617, is therefore in great demand, but it is also an expensive pharmaceutical precursor. We demonstrate here a convenient synthetic protocol for PSMA-617, using a solution phase method. Both, linear and convergent synthetic strategies were explored to affirm that the later approach furnished the target in better yield. The protocol presented here involves the use of commercially and economically viable reagents together with flow reactor based metal catalyzed hydrogenation as vital step. Using the method portrayed, PSMA-617 with purity >99.5% was achieved, while, radiolabelling with 177Lu afforded, 177Lu-PSMA-617 with radiochemical purity >98%, which is adequate for therapeutic applications. 177Lu-PSMA-617 prepared using the synthesized ligand showed parity in purity against that made from commercial equivalent.

Current Status of PSMA-Targeted Radioligand Therapy in the Era of Radiopharmaceutical Therapy Acquiring Marketing Authorization.

Prostate-specific membrane antigen (PSMA) is highly expressed in PCa, which gradually increases in high-grade tumors, metastatic tumors, and tumors nonresponsive to androgen deprivation therapy. PSMA has been a topic of interest during the past decade for both diagnostic and therapeutic targets. Radioligand therapy (RLT) utilizes the delivery of radioactive nuclides to tumors and tumor-associated targets, and it has shown better efficacy with minimal toxicity compared to other systemic cancer therapies. Nuclear medicine has faced a new turning point claiming theranosis as the core of academic identity, since new RLTs have been introduced to clinics through the official new drug development processes for approval from the Food and Drug Administration (FDA) or European Medical Agency. Recently, PSMA targeting RLT was approved by the US FDA in March 2022. This review introduces PSMA RLT focusing on ongoing clinical trials to enhance our understanding of nuclear medicine theranosis and strive for the development of new radiopharmaceuticals.

The maximum standardized uptake value in patients with recurrent or persistent prostate cancer after radical prostatectomy and PSMA-PET-guided salvage radiotherapy—a multicenter retrospective analysis

PurposeThis study aims to evaluate the association of the maximum standardized uptake value (SUVmax) in positron-emission tomography targeting prostate-specific membrane antigen (PSMA-PET) prior to salvage radiotherapy (sRT) on biochemical recurrence free survival (BRFS) in a large multicenter cohort.MethodsPatients who underwent 68 Ga-PSMA11-PET prior to sRT were enrolled in four high-volume centers in this retrospective multicenter study. Only patients with PET-positive local recurrence (LR) and/or nodal recurrence (NR) within the pelvis were included. Patients were treated with intensity-modulated-sRT to the prostatic fossa and elective lymphatics in case of nodal disease. Dose escalation was delivered to PET-positive LR and NR. Androgen deprivation therapy was administered at the discretion of the treating physician. LR and NR were manually delineated and SUVmax was extracted for LR and NR. Cox-regression was performed to analyze the impact of clinical parameters and the SUVmax-derived values on BRFS.ResultsTwo hundred thirty-five patients with a median follow-up (FU) of 24 months were included in the final cohort. Two-year and 4-year BRFS for all patients were 68% and 56%. The presence of LR was associated with favorable BRFS (p = 0.016). Presence of NR was associated with unfavorable BRFS (p = 0.007). While there was a trend for SUVmax values ≥ median (p = 0.071), SUVmax values ≥ 75% quartile in LR were significantly associated with unfavorable BRFS (p = 0.022, HR: 2.1, 95%CI 1.1–4.6). SUVmax value in NR was not significantly associated with BRFS. SUVmax in LR stayed significant in multivariate analysis (p = 0.030). Sensitivity analysis with patients for who had a FU of > 12 months (n = 197) confirmed these results.ConclusionThe non-invasive biomarker SUVmax can prognosticate outcome in patients undergoing sRT and recurrence confined to the prostatic fossa in PSMA-PET. Its addition might contribute to improve risk stratification of patients with recurrent PCa and to guide personalized treatment decisions in terms of treatment intensification or de-intensification.This article is part of the Topical Collection on Oncology—Genitourinary.

Hetero-bivalent agents targeting FAP and PSMA.

We developed a theranostic radiopharmaceutical that engages two key cell surface proteases, fibroblast activation protein alpha (FAP) and prostate-specific membrane antigen (PSMA), each frequently overexpressed within the tumor microenvironment (TME). The latter is also expressed in most prostate tumor epithelium. To engage a broader spectrum of cancers for imaging and therapy, we conjugated small-molecule FAP and PSMA-targeting moieties using an optimized linker to provide 64Cu-labeled compounds. We synthesized FP-L1 and FP-L2 using two linker constructs attaching the FAP and PSMA-binding pharmacophores. We determined in vitro inhibition constants (Ki) for FAP and PSMA. Cell uptake assays and flow cytometry were conducted in human glioma (U87), melanoma (SK-MEL-24), prostate cancer (PSMA + PC3 PIP and PSMA - PC3 flu), and clear cell renal cell carcinoma lines (PSMA + /PSMA - 786-O). Quantitative positron emission tomography/computed tomography (PET/CT) and tissue biodistribution studies were performed using U87, SK-MEL-24, PSMA + PC3 PIP, and PSMA + 786-O experimental xenograft models and the KPC genetically engineered mouse model of pancreatic cancer. 64Cu-FP-L1 and 64Cu-FP-L2 were produced in high radiochemical yields (> 98%) and molar activities (> 19MBq/nmol). Ki values were in the nanomolar range for both FAP and PSMA. PET imaging and biodistribution studies revealed high and specific targeting of 64Cu-FP-L1 and 64Cu-FP-L2 for FAP and PSMA. 64Cu-FP-L1 displayed more favorable pharmacokinetics than 64Cu-FP-L2. In the U87 tumor model at 2h post-injection, tumor uptake of 64Cu-FP-L1 (10.83 ± 1.02%ID/g) was comparable to 64Cu-FAPI-04 (9.53 ± 2.55%ID/g). 64Cu-FP-L1 demonstrated high retention 5.34 ± 0.29%ID/g at 48h in U87 tumor. Additionally, 64Cu-FP-L1 showed high retention in PSMA + PC3 PIP tumor (12.06 ± 0.78%ID/g at 2h and 10.51 ± 1.82%ID/g at 24h). 64Cu-FP-L1 demonstrated high and specific tumor targeting of FAP and PSMA. This compound should enable imaging of lesions expressing FAP, PSMA, or both on the tumor cell surface or within the TME. FP-L1 can readily be converted into a theranostic for the management of heterogeneous tumors.

PSMA-targeted NIR probes for image-guided detection of prostate cancer

Tumour-targeted near-infrared (NIR) optical imaging is an emerging tool for the detection of malignant tissues. This modality can be useful in both diagnosis and intraoperative visualisation, to help defining tumour margins and allow a more precise removal of all the cancerous mass during surgery. In this context, we have developed a series of NIR fluorescent probes that target the prostate-specific membrane antigen (PSMA), an established biomarker overexpressed in prostate cancer. Four new NIR imaging agents were prepared by conjugating the well-known urea-based PSMA targeting module to the NIR fluorophore Cy7.5, with linkers of 7, 10, 17 and 24 atoms. The affinity of each probe for PSMA was assessed through competitive binding and IC50 measurement in prostate cancer cells, using a previously reported PSMA-targeted NIR probe (i.e. PSMA-IRDye800CW) as reference. The NIR probe PSMA-Cy7.5_2 demonstrated a high affinity for PSMA (i.e. IC50 = 58.8 nM) and was further studied in mouse xenograft models of prostate cancer, to assess its ability to image PSMA positive tumour tissues. While PSMA-Cy7.5_2 out-performed PSMA-IRDye800CW in vitro, its tumour accumulation in vivo was not as evident. Further micellar aggregation studies indicated that the relatively higher hydrophobic property of PSMA-Cy7.5_2 may lower its bioavailability and tissue distribution following systemic injection, limiting its ability of targeting PSMA tumour in vivo. Nevertheless, the excellent binding capability of PSMA-Cy7.5_2 renders this probe a valid lead for further structural optimisation to develop imaging analogues with high affinity and specificity for PSMA, as required for effective NIR fluorescence-guided applications pre-clinically and clinically.

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: Kd = 28.27 nM, LNCaP: Kd = 11.49 nM) and high internalization rates for 68Ga-mNP-N1/2 in both cell lines.

DOTA Conjugate of Bisphosphonate and PSMA-Inhibitor: A Promising Combination for Therapy of Prostate Cancer Related Bone Metastases.

Prostate cancer (PCa) is one of the most common cancer types worldwide. 90% of men with late stage PCa will develop bone metastases. Since the expression level of PSMA (prostate-specific membrane antigen) in bone metastases can vary significantly, a compound is being searched for which accumulates in bone metastases independently of PSMA level. With DOTA-L-Lys(SA.Pam)-PSMA-617, we present a compound that, in addition to a PSMA inhibitor as a target vector, also contains a bisphosphonate that is established as a bone tracer and thus combines the advantages of PSMA targeting and bone targeting. This is a class of small molecules combining targeting of two different targets with the potential advantages for treatment of biologically heterogeneous bone metastasis from prostate cancer. The molecule can be labeled with lutetium-177 and used for the therapy of PCa-related bone metastases. DOTA-L-Lys(SA.Pam)-PSMA-617 was synthesized and radiolabelled in 1 M ammonium acetate buffer pH 5.5 at 95°C. Different amounts of precursor were evaluated. Complex stability was evaluated in three different media. LogD7.4 value was evaluated via the determination of the equilibrium distribution in a PBS/n-octanol mixture. A hydroxyapatite binding assay was used to evaluate the potential binding to bone metastases. In vitro affinity was determined and Ki value was evaluated. To evaluate the binding potential in mice, ex vivo biodistribution studies were carried out in LNCaP tumor-bearing Balb/c mice. [177Lu]Lu-labeling of DOTA-L-Lys(SA.Pam)-PSMA-617 showed quantitative RCY within 10 min and high complex stability over 14 days. The lipophilicity of the labeled compound was similar to the lipophilicity of the reference compound [177Lu]Lu-PSMA-617 and showed an excellent and selective HAP binding of 98.2 ± 0.11%. With a Ki of 42.3 ± 7.7 nM PSMA binding affinity is lower in comparison to [177Lu]Lu-PSMA-617. First ex vivo biodistribution studies with LNCaP tumor-bearing Balb/c mice showed a PSMA dependent tumor accumulation of 4.2 ± 0.7%ID/g and a femur accumulation of 3.4 ± 0.4%ID/g. [177Lu]Lu-DOTA-L-Lys(SA.Pam)-PSMA-617 is a promising compound for therapy of PCa related bone and tissue metastases. Accumulation on the bone metastases via two mechanisms also enables the treatment of bone metastases that show little or no PSMA expression.