PSMA Ligands for Radionuclide Imaging and Therapy of Prostate Cancer: Clinical Status

Adverse reactions to therapeutic radiopharmaceuticals

Radiopharmaceuticals are drugs used in treatment or diagnosis that contain a radioactive part, usually a pharmaceutical part in their structure. Adverse drug reactions are harmful and unexpected responses that occur when administered at normal doses. Although radiopharmaceuticals are regarded as safe medical products, adverse reactions should not be ignored. More serious adverse reactions such as myelosuppression, pleural effusion, and death may develop in therapeutic radiopharmaceuticals due to their use at higher doses than those used in diagnosis. Therefore, monitoring adverse reactions and reporting them to health authorities is important. This review aims to provide information about adverse reactions that may be related to radiopharmaceuticals used in treatment.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

[18F]AlF-PSMA-11 PET in diagnosing prostate cancer: a head-to-head comparison with [68Ga]Ga-PSMA-11 PET and an exploration of dual-phase scanning

PURPOSE

To evaluate the physiological distribution and tumour detection ability of [18F]AlF-PSMA-11 positron emission tomography (PET) dual-phase scans in patients with prostate cancer (PCa).

METHODS

As a retrospective study, clinical and PET data of PCa patients who underwent dual-phase [18F]AlF-PSMA-11 PET of routine scan (45-50 min) and delayed scan (120 min) from November 2020 to June 2021 were collected, and physiological and pathological regions of interest were quantified to determine the time-dependent maximum standardized uptake value (SUVmax) of [18F]AlF-PSMA-11. Part of the above subjects who underwent [68Ga]Ga-PSMA-11 PET in the following 6 months were included in a head-to-head comparison. The difference with a p-value < 0.05 was defined as statistical significance. Diagnosis accuracy of primary and metastatic lesions was measured referring to the surgical findings, pathology, and follow-up imaging.

RESULTS

[68Ga]Ga-PSMA-11 and [18F]AlF-PSMA-11 were of the comparable uptake in glands in head, but the latter was of a significant lower distribution in liver and spleen. For the 25 patients initially diagnosed with prostate cancer and 3 patients with biochemical recurrence after radical surgery, the SUVmax of the primary lesions, lacrimal glands, parotid glands and submandibular glands was higher at 120 min compared to that at 45-50 min, but not a significant difference. SUVmax of the liver, spleen and bladder decreased significantly at 120 min, but the bladder SUVmax remained higher than that of primary lesions. SUVmax of the kidneys and centrum was the same in dual-phase scans. For the 31 primary lesions detected in [18F]AlF-PSMA-11 PET, both the SUVmax of the two phases kept the positive correlation with PSA, Gleason score and initial risk stratification. For the 39 distant metastatic lesions, 94.87% accuracy of routine scan and 100% accuracy of delayed scan were acquired, and 7.14% patients (2/28) benefited from the dual-phase [18F]AlF-PSMA-11 scans that revealed novel information on metastatic lesions compared to the routine scan.

CONCLUSION

[18F]AlF-PSMA-11 PET expanded the time window and further decreased metabolic background of [68Ga]Ga-PSMA-11 PET. The dual-phase scan of [18F]AlF-PSMA-11 PET can benefit prostate cancer diagnosis via providing more PSMA-specific information.

Lutetium-177-PSMA therapy for recurrent/metastatic salivary gland cancer: a prospective pilot study

There is an urgent need for novel systemic therapies for recurrent/systemic salivary gland cancer, as current treatment options are scarce. [68Ga]Ga-PSMA-11 PET/CT revealed relevant uptake of prostate-specific membrane antigen (PSMA) in adenoid cystic carcinoma (AdCC) and salivary duct carcinoma (SDC). Therefore, we assessed the safety, feasibility, efficacy and radiation dosimetry of [177Lu]Lu-PSMA-I&T treatment in AdCC and SDC patients in a prospective pilot study. Methods: This single-center, single-arm study intended to include 10 recurrent/metastatic AdCC patients and five recurrent/metastatic SDC patients. AdCC patients could only participate in case of progressive and/or symptomatic disease. Patients required ≥ 1 lesion ≥ 1.5 cm with an SUVmax on [68Ga]Ga-PSMA-11 PET/CT above liver SUVmean. Patients were planned to receive four cycles ~ 7.4 GBq [177Lu]Lu-PSMA-I&T. In case of progressive disease per RECIST 1.1 at mid-treatment evaluation after two cycles, treatment was discontinued. Safety was the primary endpoint. Secondary endpoints included objective response rate (ORR), tumor- and organ-absorbed radiation doses and progression-free survival. Results: After screening, 10 out of 15 (67%) AdCC and two out of 10 (20%) SDC patients were eligible. Two patients (17%) demonstrated grade 3 treatment-related toxicity: lymphocytopenia (8%) and hyponatremia (8%). No dose-limiting toxicities occurred. In the AdCC cohort, six patients (60%) completed the four treatment cycles. Due to progressive disease, treatment was discontinued after two cycles in three patients (30%) and after one cycle in one patient (10%). No objective responses were observed (ORR: 0%). Three AdCC patients (30%) showed stable disease ≥ 6 months (7, 17 and 23 months). None of the two SDC patients completed the treatment: one patient deteriorated after the first cycle, while the other had progressive disease after two cycles. The high screen failure rate due to insufficient PSMA uptake resulted in premature closure of the SDC cohort. Dosimetry revealed low tumor-absorbed doses (median 0.07 Gy/GBq, range 0.001-0.63 Gy/GBq). Conclusions: [177Lu]Lu-PSMA-I&T in AdCC and SDC patients was safe and generally well-tolerated. However, efficacy was limited, likely due to low tumor-absorbed doses. For SDC, [177Lu]Lu-PSMA-I&T appears unfeasible due to insufficient PSMA uptake.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Time-efficient HPLC Validation Methodology for the Qualitative Analysis of 68Ga PSMA-11 in Routine Clinical Usage under Isocratic Method

Background

Prostate-specific membrane antigen (PSMA) has shown to be a promising agent for prostate cancer imaging under PET-CT. With the automation in radiolabeling with 68Ga, using iTG 68Ge/68Ga generator, it has helped introduce various new diagnostic agents and achieve good manufacturing practices (GMP) simultaneously. However, before any radiopharmaceutical is put into clinical usage, it should always be checked for its radiochemical purity and other quality parameters before injecting in the patient. Chromatography techniques such as Gas Chromatography (GC), High-Performance Liquid Chromatography (HPLC), and Thin-Layer Chromatography (TLC) are the most frequently utilized separation technique for purity analysis. A rapid quality control HPLC based methodology was required for radiopharmaceuticals.

Aim & Objective

In our current setting, we conducted quality control analysis and standardized and validated HPLC method for the routine quality check of 68Ga-PSMA-11.

Materials and Methods

The QC of 68Ga PSMA-11 was performed under ITLC and HPLC.

Results

Linearity, accuracy, precision and specificity were assessed and quantified in accordance with International conference on harmonisation of technical requirements for registration of pharmaceuticals for human use (Q2 (R1) ICH) guidelines, which can be implemented in resource-limited settings to check the quality.

Conclusion

The current HPLC based methodology is rapid, with a retention time of 2.24 min, rendering it a favorable analytical standard operating procedure for QC analysis of 68Ga-PSMA-11.

Development and first-in-human study of PSMA-targeted PET tracers with improved pharmacokinetic properties

PURPOSE

A series of new 68Ga-labeled tracers based on [68Ga]Ga-PSMA-617 were developed to augment the tumor-to-kidney ratio and reduce the activity accumulation in bladder, ultimately minimize radiation toxicity to the urinary system.

METHODS

We introduced quinoline group, phenylalanine and decanoic acid into different tracers to enhance their lipophilicity, strategically limiting their metabolic pathway through the urinary system. Their binding affinity onto LNCaP cells was determined through in vitro saturation assays and competition binding assays. In vivo metabolic study, PET imaging and biodistribution experiment were performed in LNCaP tumor-bearing B-NSG male mice. The most promising tracer was selected for first-in-human study.

RESULTS

Four radiotracers were synthesized with radiochemical purity (RCP) > 95% and molar activity in a range of 20.0-25.5 GBq/μmol. The binding affinities (Ki) of TWS01, TWS02 to PSMA were in the low nanomolar range (< 10 nM), while TWS03 and TWS04 exhibited binding affinities with Ki > 20 nM (59.42 nM for TWS03 and 37.14 nM for TWS04). All radiotracers exhibited high stability in vivo except [68Ga]Ga-TWS03. Micro PET/CT imaging and biodistribution analysis revealed that [68Ga]Ga-TWS02 enabled clear tumor visualization in PET images at 1.5 h post-injection, with higher tumor-to-kidney ratio (T/K, 0.93) and tumor-to-muscle ratio (T/M, 107.62) compared with [68Ga]Ga-PSMA-617 (T/K: 0.39, T/M: 15.01) and [68Ga]Ga-PSMA-11 (T/K: 0.15, T/M: 24.00). In first-in-human study, [68Ga]Ga-TWS02 effectively detected PCa-associated lesions including primary and metastatic lesions, with lower accumulation in urinary system, suggesting that [68Ga]Ga-TWS02 might be applied in the detection of bladder invasion, with minimized radiation toxicity to the urinary system.

CONCLUSION

Introduction of quinoline group, phenylalanine and decanoic acid into different tracers can modulate the binding affinity and pharmacokinetics of PSMA in vivo. [68Ga]Ga-TWS02 showed high binding affinity to PSMA, excellent pharmacokinetic properties and clear imaging of PCa-associated lesions, making it a promising radiotracer for the clinical diagnosis of PCa. Moreover, TWS02 with a chelator DOTA could also label 177Lu and 225Ac, which could be used for PCa treatment without significant side effects.

TRIAL REGISTRATION

The clinical evaluation of this study was registered On October 30, 2021 at https://www.chictr.org.cn/ (No: ChiCTR2100052545).

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).

Theranostic Nuclear Medicine with Gallium-68, Lutetium-177, Copper-64/67, Actinium-225, and Lead-212/203 Radionuclides

Molecular changes in malignant tissue can lead to an increase in the expression levels of various proteins or receptors that can be used to target the disease. In oncology, diagnostic imaging and radiotherapy of tumors is possible by attaching an appropriate radionuclide to molecules that selectively bind to these target proteins. The term "theranostics" describes the use of a diagnostic tool to predict the efficacy of a therapeutic option. Molecules radiolabeled with γ-emitting or β+-emitting radionuclides can be used for diagnostic imaging using single photon emission computed tomography or positron emission tomography. Radionuclide therapy of disease sites is possible with either α-, β-, or Auger-emitting radionuclides that induce irreversible damage to DNA. This Focus Review centers on the chemistry of theranostic approaches using metal radionuclides for imaging and therapy. The use of tracers that contain β+-emitting gallium-68 and β-emitting lutetium-177 will be discussed in the context of agents in clinical use for the diagnostic imaging and therapy of neuroendocrine tumors and prostate cancer. A particular emphasis is then placed on the chemistry involved in the development of theranostic approaches that use copper-64 for imaging and copper-67 for therapy with functionalized sarcophagine cage amine ligands. Targeted therapy with radionuclides that emit α particles has potential to be of particular use in late-stage disease where there are limited options, and the role of actinium-225 and lead-212 in this area is also discussed. Finally, we highlight the challenges that impede further adoption of radiotheranostic concepts while highlighting exciting opportunities and prospects.

Synthesis, Preclinical Evaluation, and First-in-Human PET Study of [68Ga]-Labeled Biphenyl-Containing PSMA Tracers

Radioisotope-labeled prostate-specific membrane antigen (PSMA) PET tracers have gained popularity in diagnosing prostate cancer (PCa). This study aimed to improve the affinity and tumor-targeting capabilities of new PSMA tracers by increasing the number of pharmacophores that specifically bind to PSMA. Using biphenyl as a core scaffold, we investigated the relationship among spacer segments, affinity, and pharmacokinetic properties. In preclinical PET studies on mice with 22Rv1 tumors, compared with [68Ga]Ga-PSMA-11 (SUVmax = 3.37), [68Ga]Ga-PSMA-D5 (Ki = 0.15) showed higher tumor uptake (SUVmax = 3.51) and lower renal uptake (T/K = 1.84). In the first-in-human study, [68Ga]Ga-PSMA-D5 effectively detected small PCa-associated lesions and distant metastases. The advantages of [68Ga]Ga-PSMA-D5 include high tumor uptake, straightforward synthesis, and labeling, making it a promising PSMA PET tracer. Furthermore, [68Ga]Ga-PSMA-D5 contains a DOTA chelator, allowing convenient labeling with therapeutic radionuclides such as 177Lu and 225Ac, providing the potential for targeted radioligand therapy in PCa.

Multicentric 68Ga-PSMA PET radiomics for treatment response assessment of 177Lu-PSMA-617 radioligand therapy in patients with metastatic castration-resistant prostate cancer

Objective

The treatment with 177Lutetium PSMA (177Lu-PSMA) in patients with metastatic castration-resistant prostate cancer (mCRPC) has recently been approved by the FDA and EMA. Since treatment success is highly variable between patients, the prediction of treatment response and identification of short- and long-term survivors after treatment could help tailor mCRPC diagnosis and treatment accordingly. The aim of this study is to investigate the value of radiomic parameters extracted from pretreatment 68Ga-PSMA PET images for the prediction of treatment response.

Methods

A total of 45 mCRPC patients treated with 177Lu-PSMA-617 from two university hospital centers were retrospectively reviewed for this study. Radiomic features were extracted from the volumetric segmentations of metastases in the bone. A random forest model was trained and validated to predict treatment response based on age and conventionally used PET parameters, radiomic features and combinations thereof. Further, overall survival was predicted by using the identified radiomic signature and compared to a Cox regression model based on age and PET parameters.

Results

The machine learning model based on a combined radiomic signature of three features and patient age achieved an AUC of 0.82 in 5-fold cross-validation and outperformed models based on age and PET parameters or radiomic features (AUC, 0.75 and 0.76, respectively). A Cox regression model based on this radiomic signature showed the best performance to predict overall survival (C-index, 0.67).

Conclusion

Our results demonstrate that a machine learning model to predict response to 177Lu-PSMA treatment based on a combination of radiomics and patient age outperforms a model based on age and PET parameters. Moreover, the identified radiomic signature based on pretreatment 68Ga-PSMA PET images might be able to identify patients with an improved outcome and serve as a supportive tool in clinical decision making.

Comparison of the Effects of DOTA and NOTA Chelators on 64Cu-Cudotadipep and 64Cu-Cunotadipep for Prostate Cancer

BACKGROUND

This study compared the effects of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) as 64Cu-chelating agents in newly developed prostate-specific membrane antigen (PSMA) target compounds, 64Cu-cudotadipep and 64Cu-cunotadipep, on pharmacokinetics.

METHODS

The in vitro stability of the chelators was evaluated using human and mouse serum. In vitro PSMA-binding affinity and cell uptake were compared using human 22Rv1 cells. To evaluate specific PSMA-expressing tumor-targeting efficiency, micro-positron emission tomography (mcroPET)/computed tomography (CT) and biodistribution analysis were performed using PSMA+ PC3-PIP and PSMA- PC3-flu tumor xenografts.

RESULTS

The serum stability of DOTA- or NOTA-conjugated 64Cu-cudotadipep and 64Cu-cunotadipep was >97%. The Ki value of the NOTA derivative, cunotadipep, in the in vitro affinity binding analysis was higher (2.17 ± 0.25 nM) than that of the DOTA derivative, cudotadipep (6.75 ± 0.42 nM). The cunotadipep exhibited a higher cellular uptake (6.02 ± 0.05%/1 × 106 cells) compared with the cudotadipep (2.93 ± 0.06%/1 × 106 cells). In the biodistribution analysis and microPET/CT imaging, the 64Cu-labeled NOTA derivative, 64Cu-cunotadipep, demonstrated a greater tumor uptake and lower liver uptake than the DOTA derivative.

CONCLUSIONS

This study indicates that the PSMA-targeted 64Cu-cunotadipep can be applied in clinical practice owing to its high diagnostic power for prostate cancer.

Dual probe difference specimen imaging for prostate cancer margin assessment

Significance

Positive margin status due to incomplete removal of tumor tissue during radical prostatectomy for high-risk localized prostate cancer requires reoperation or adjuvant therapy, which increases morbidity and mortality. Adverse effects of prostate cancer treatments commonly include erectile dysfunction, urinary incontinence, and bowel dysfunction, making successful initial curative prostatectomy imperative.

Aim

Current intraoperative tumor margin assessment is largely limited to frozen section analysis, which is a lengthy, labor-intensive process that is obtrusive to the clinical workflow within the operating room (OR). Therefore, a rapid method for prostate cancer margin assessment in the OR could improve outcomes for patients.

Approach

Dual probe difference specimen imaging (DDSI), which uses paired antibody-based probes that are labeled with spectrally distinct fluorophores, was shown herein for prostate cancer margin assessment. The paired antibody-based probes consisted of a targeted probe to prostate-specific membrane antigen (PSMA) and an untargeted probe, which were used as a cocktail to stain resected murine tissue specimens including prostate tumor, adipose, muscle, and normal prostate. Ratiometric images (i.e., DDSI) of the difference between targeted and untargeted probe uptake were calculated and evaluated for accuracy using receiver operator characteristic curve analysis with area under the curve values used to evaluate the utility of the DDSI method to detect PSMA positive prostate cancer.

Results

Targeted and untargeted probe uptake was similar between the high and low PSMA expressing tumor due to nonspecific probe uptake after topical administration. The ratiometric DDSI approach showed substantial contrast difference between the PSMA positive tumors and their respective normal tissues (prostate, adipose, muscle). Furthermore, DDSI showed substantial contrast difference between the high PSMA expressing tumors and the minimally PSMA expressing tumors due to the ratiometric correction for the nonspecific uptake patterns in resected tissues.

Conclusions

Previous work has shown that ratiometic imaging has strong predictive value for breast cancer margin status using topical administration. Translation of the ratiometric DDSI methodology herein from breast to prostate cancers demonstrates it as a robust, ratiometric technique that provides a molecularly specific imaging modality for intraoperative margin detection. Using the validated DDSI protocol on resected prostate cancers permitted rapid and accurate assessment of PSMA status as a surrogate for prostate cancer margin status. Future studies will further evaluate the utility of this technology to quantitatively characterize prostate margin status using PSMA as a biomarker.

Synthesis, 123I-Radiolabeling Optimization, and Initial Preclinical Evaluation of Novel Urea-Based PSMA Inhibitors with a Tributylstannyl Prosthetic Group in Their Structures

Prostate-specific membrane antigen (PSMA) has been identified as a target for the development of theranostic agents. In our current work, we describe the design and synthesis of novel N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-(S)-L-lysine (DCL) urea-based PSMA inhibitors with a chlorine-substituted aromatic fragment at the lysine ε-nitrogen atom, a dipeptide including two phenylalanine residues in the L-configuration as the peptide fragment of the linker, and 3- or 4-(tributylstannyl)benzoic acid as a prosthetic group in their structures for radiolabeling. The standard compounds [127I]PSMA-m-IB and [127I]PSMA-p-IB for comparative and characterization studies were first synthesized using two alternative synthetic approaches. An important advantage of the alternative synthetic approach, in which the prosthetic group (NHS-activated esters of compounds) is first conjugated with the polypeptide sequence followed by replacement of the Sn(Bu)3 group with radioiodine, is that the radionuclide is introduced in the final step of synthesis, thereby minimizing operating time with iodine-123 during the radiolabeling process. The obtained DCL urea-based PSMA inhibitors were radiolabeled with iodine-123. The radiolabeling optimization results showed that the radiochemical yield of [123I]PSMA-p-IB was higher than that of [123I]PSMA-m-IB, which were 74.9 ± 1.0% and 49.4 ± 1.2%, respectively. The radiochemical purity of [123I]PSMA-p-IB after purification was greater than 99.50%. The initial preclinical evaluation of [123I]PSMA-p-IB demonstrated a considerable affinity and specific binding to PC-3 PIP (PSMA-expressing cells) in vitro. The in vivo biodistribution of this new radioligand [123I]PSMA-p-IB showed less accumulation than [177Lu]Lu-PSMA-617 in several normal organs (liver, kidney, and bone). These results warrant further preclinical development, including toxicology evaluation and experiments in tumor-bearing mice.

N-Alkyl Carbamoylimidazoles as Versatile Synthons for the Synthesis of Urea-Based PSMA Inhibitors

We describe N-alkyl carbamoylimidazoles as readily available and highly versatile synthons for synthesizing urea-based prostate-specific membrane antigen (PSMA) inhibitors. Urea formation proceeded in high yields (>80%) at room temperature under aqueous conditions. All novel compounds were tested for their PSMA inhibitory potency in a cell-based radiometric binding assay. Compound 17 was identified as a novel high-affinity PSMA inhibitor (IC50 = 0.013 μM) suitable for developing an 18F-labeled radioligand for PET imaging of PSMA in prostate cancer.

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

PURPOSE

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.

METHODS

[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 22Rv1 tumor 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.

RESULTS

LNC1003 showed high binding affinity (IC50 = 10.77 nM) to PSMA in vitro, which was comparable with that of PSMA-617 (IC50 = 27.49 nM) and EB-PSMA-617 (IC50 = 7.91 nM). 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 24 h post-injection. Targeted radioligand therapy results showed noteworthy inhibition of 22Rv1 tumor growth after administration of a single dose of 18.5 MBq [177Lu]Lu-LNC1003. There was no obvious antitumor effect after [177Lu]Lu-PSMA-617 treatment under the same condition.

CONCLUSION

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.

Imaging and photodynamic therapy of prostate cancer using a theranostic PSMA-targeting ligand

PURPOSE

Incomplete resection of prostate cancer (PCa) results in increased risk of disease recurrence. Combined fluorescence-guided surgery with tumor-targeted photodynamic therapy (tPDT) may help to achieve complete tumor eradication. We developed a prostate-specific membrane antigen (PSMA) ligand consisting of a DOTA chelator for 111In labeling and a fluorophore/photosensitizer IRDye700DX (PSMA-N064). We evaluated the efficacy of PSMA-tPDT using PSMA-N064 in cell viability assays, a mouse xenograft model and in an ex vivo incubation study on fresh human PCa tissue.

METHODS

In vitro, therapeutic efficacy of PSMA-N064 was evaluated using PSMA-positive LS174T cells and LS174T wild-type cells. In vivo, PSMA-N064-mediated tPDT was tested in immunodeficient BALB/c mice-bearing PSMA-positive LS174T xenografts. Tumor growth and survival were compared to control mice that received either NIR light or ligand injection only. Ex vivo tPDT efficacy was evaluated in excised fresh human PCa tissue incubated with PSMA-N064.

RESULTS

In vitro, tPDT led to a PSMA-specific light- and ligand dose-dependent loss in cell viability. In vivo, tPDT-induced tumor cell apoptosis, delayed tumor growth, and significantly improved survival (p = 0.004) of the treated PSMA-positive tumor-bearing mice compared with the controls. In fresh ex vivo human PCa tissue, apoptosis was significantly increased in PSMA-tPDT-treated samples compared to non-treated control samples (p = 0.037).

CONCLUSION

This study showed the feasibility of PSMA-N064-mediated tPDT in cell assays, a xenograft model and excised fresh human PCa tissue. This paves the way to investigate the impact of in vivo PSMA-tPDT on surgical outcome in PCa patients.

Monitoring the biodistribution of radiolabeled therapeutics in mice

Radiopharmaceutical therapy is a rapidly growing field for the treatment of cancer due to its high specificity and ability to target individual affected cells. A key component of the pre-clinical development of a new therapeutic radiopharmaceutical is the determination of its time-dependent distribution in tumors, normal tissues, and the whole body in mouse tumor models. Here, we provide an overview of the available instrumentation for the novice in radiation measurement. We also detail the methodology for assessing distribution and kinetics of a radiopharmaceutical and calculating radiation absorbed dose in mice using a gamma counter or a PET or SPECT camera.

Prostate-Specific Membrane Antigen (PSMA) Expression in The Neovasculature of High Grade Gliomas (Histopathological and Immunohistochemical Study)

BACKGROUND

Prostate-specific membrane antigen (PSMA) was first noticed in prostate cancer cells, thereafter, It has been found in the endothelial cells of neovasculature in a variety of tumors, but not in normal vascular endothelium, This specificity makes PSMA an ideal molecule for vascular targeting in Cancer theranostics (i.e., combined diagnostic and therapeutic).

OBJECTIVES

The objective of this study was to evaluate the immunohistochemical (IHC) expression of PSMA in the neovasculature (identified by CD 31) of high-grade gliomas (HGGs) and to Correlate PSMA IHC expression in HGGs with clinicopathological features, to detect its possible role in tumor angiogenesis, where PSMA can be used as a future diagnostic and therapeutic target.

MATERIALS AND METHODS

This retrospective study included a total of 69 archived, formalin-fixed, paraffin-embedded tissue blocks of HGGs, including 52 cases classified as WHO grade IV (75.4%) and 17 cases as WHO grade III (24.6%). The samples were immunohistochemically analyzed for PSMA expression (in both TMV and parenchymal tumor cells) which was assessed using the composite PSMA immunostaining score. A score (0) was considered negative while scores 1-7 were considered positive (1-4, 5-6, or 7; weak, moderate, or strong respectively).

RESULTS

PSMA is expressed specifically and significantly in endothelial cells of tumor microvessels (TMV) of HGGs, A statistically significant relationship was detected between PSMA IHC expression in both TMV and in parenchymal tumor cells (TC) and various glioma subtypes (P-value < 0.05 and <0.001 respectively).  Positive PSMA immunostaining in TMV was detected in all anaplastic ependymoma cases and in near all cases of classic GB and GB with oligodendroglial features more than other subtypes, with P-value specifically for PSMA positivity/negativity in TMV statistically significant (0.022). While for Tumor cells, Positive PSMA immunostaining was detected in all anaplastic ependymoma, most anaplastic astrocytoma and classic GB cases in contrary to other variants, with P-value statistically extremely significant (< 0.001). Comparing PSMA IHC expression in TMV and its expression in TC, it was significantly expressed in TMV of 82.7% versus TC of 51.9% of grade IV cases. Likewise, in GB with oligodendroglial features and gliosarcoma, the majority of cases showed positive staining in their TMV [8/8 (100%), 9/13 (69.2%) respectively], and, the reverse occurs in tumor cells where the majority of cases did NOT show staining in the tumor cells for PSMA (5/8 (62.5%), 11/13 (84.6%) of cases respectively), which was statistically significant (P-value ≤ 0.05) besides the significant difference in the pattern of staining according to composite PSMA scoring (P-value ≤ 0.05).

CONCLUSION

PSMA has a possible role in tumor angiogenesis, therefore it might be considered a potential promising endothelial target for Cancer theranostics with PSMA-based agents, in addition, PSMA was expressed significantly in TC of HGGs, thus, it appears to be involved in biologic behavior, carcinogenesis and tumor progression.

Lutetium-177 Prostate Specific Membrane Antigen Therapy in a Patient With Double Malignancy and Single Functioning Kidney: A Case Report

Lutetium-177 labeled with 617 types of Prostate Specific Membrane Antigen (¹⁷⁷Lu PSMA-617) Radio-ligand Therapy (RLT) is an emerging modality of choice for the treatment of metastatic castration-resistant prostate carcinoma (mCRPC). After it is administered intravenously, it is excreted primarily through the kidneys. Physiological excretion and concomitant expression of PSMA receptors on renal tissues are associated with potential renal toxicity, a matter of concern while treating patients with multiple doses of RLT. There are published articles that have demonstrated the safe use of ¹⁷⁷Lu PSMA-617 in patients with bilateral fair-functioning kidneys; however, only a single study has been published that has evaluated its safety in patients with solitary-functioning kidneys. The uniqueness of this case report lies in the fact that we have documented the renal safety profile of ¹⁷⁷Lu PSMA-617 therapy after multiple doses in a patient who presented with double malignancy (metastatic castration-resistant prostate carcinoma and left renal cell carcinoma) and had a single-functioning right kidney.

Improve the Biodistribution with Bulky and Lipophilic Modification Strategies on Lys-Urea-Glu-Based PSMA-Targeting Radiotracers

Since prostate-specific membrane antigen (PSMA) is upregulated in nearly all stages of prostate cancer (PCa), PSMA can be considered a viable diagnostic biomarker and treatment target in PCa. In this study, we have developed five ⁶⁸Ga-labeled PSMA-targeted tracers, ⁶⁸Ga-Flu-1, ⁶⁸Ga-Flu-2, ⁶⁸Ga-9-Ant, ⁶⁸Ga-1-Nal, and ⁶⁸Ga-1-Noi, to investigate the effect of lipophilic bulky groups on the pharmacokinetics of PSMA inhibitors compared to ⁶⁸Ga-PSMA-11 and then explore their in vitro and in vivo properties. ⁶⁸Ga-labeled PSMA inhibitors were obtained in 88.53-99.98% radiochemical purity and at the highest specific activity of up to 20 MBq/μg. These compounds revealed a highly efficient uptake and internalization into LNCaP cells and increased over time. PET imaging and biodistribution studies were performed in mice bearing PSMA expressing LNCaP prostate cancer xenografts. All tracers enabled clear visualization of tumors in PET images with excellent tumor-to-background contrast. The biodistribution studies showed that all these radioligands were excreted mainly via the renal pathway. The in vivo biodistribution of ⁶⁸Ga-Flu-1 revealed higher tumor uptake (40.11 ± 9.24 %ID/g at 2 h p.i.) compared to ⁶⁸Ga-PSMA-11 (28.10 ± 5.96 %ID/g at 2 h p.i.). Both in vitro and in vivo experiments showed that chemical modification of the lysine fragment significantly impacts tumor-targeting and pharmacokinetic properties. Great potential to serve as new PET tracers for prostate cancer has been revealed with these radiotracers─⁶⁸Ga-Flu-1 in particular.

The Impact of Peptide Amount on Tumor Uptake to Assess PSMA Receptor Saturation on 68Ga-PSMA-11 PET/CT in Patients with Primary Prostate Cancer

⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA) is often produced on-site, where usually a fixed amount of peptide is conjugated to the generator eluate. However, fluctuations in specific activity might influence tracer distribution and tumor accumulation. Therefore, our aim was to investigate the potential effect of varying the administered peptide amount on ⁶⁸Ga-PSMA-11 uptake in tumors using PET/CT in patients with primary prostate cancer (PCa). Additionally, the impact of tumor volume on this potential effect and on accumulation in reference organs was assessed. Methods: The imaging data of 362 men with primary PCa who underwent ⁶⁸Ga-PSMA-11 PET/CT were retrospectively included. Scans were quantified for normal tissue and primary tumors. Patients were divided into 3 groups based on their tumor volume. Correlation and multivariable linear regression analyses were performed. Results: The median index lesion volume was 9.50 cm³ (range, 0.064-174 cm³). Groups were based on quartiles of prostatic lesion volume: ≤4.11 cm³ (group 1), 4.11-20.6 cm³ (group 2), and ≥20.6 cm³ (group 3). No correlation was found between administered peptide amount and tumor uptake (SUV_mean or SUV_peak) for any group, except for a significant correlation for SUV_mean in the first group (P = 0.008). Linear regression analysis supported these findings. Conclusion: The amount of administered peptide had no evident effect on ⁶⁸Ga-PSMA-11 uptake in tumors, except for a significant positive correlation between administered peptide amount and tumor SUV_mean for group 1. The findings imply that no receptor saturation occurs in men with primary PCa at peptide levels of about 2.5 μg.

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.

PSMA Expression in Solid Tumors beyond the Prostate Gland: Ready for Theranostic Applications?

In the past decades, the expanding use of prostate-specific membrane antigen (PSMA) imaging for prostate cancer has led to the incidental detection of a lot of extra-prostatic malignancies showing an increased uptake of PSMA. Due to these incidental findings, the increasing amount of immunohistochemistry studies and the deeper knowledge of the mechanisms of expression of this antigen, it is now clear that “PSMA” is a misnomer, since it is not specific to the prostate gland. Nevertheless, this lack of specificity could represent an interesting opportunity to bring new insights on the biology of PSMA and its sites of expression to image and treat new conditions, particularly several cancers. In this review, we will describe the main extra-prostatic cancers that exhibit PSMA expression and that can be studied with PSMA-based positron emission tomography–computed tomography (PET/CT) as an additional or alternative tool to conventional imaging. In particular, we will focus on cancers in which a radioligand therapy with ¹⁷⁷lutetium has been attempted, aiming to provide an overview of the possible future theragnostic applications of PSMA.

Value of 68Ga-labeled bombesin antagonist (RM2) in the detection of primary prostate cancer comparing with [18F]fluoromethylcholine PET-CT and multiparametric MRI-a phase I/II study

OBJECTIVES

The bombesin derivative RM2 is a GRPr antagonist with strong binding affinity to prostate cancer (PCa). In this study, the impact of [⁶⁸Ga]Ga-RM2 positron emission tomography-computed tomography (PET-CT) for the detection of primary PCa was compared with that of [¹⁸F]FCH PET-CT and multiparametric magnetic resonance imaging (mpMRI).

METHODS

This phase I/II study was conducted in 30 biopsy-positive PCa subjects. The patients were stratified into high (10 patients), intermediate (10 patients), and low risk (10 patients) for extraglandular metastases as defined by National Comprehensive Cancer Network (NCCN) criteria (NCCN Clinical Practice Guidelines in Oncology, 2016). The prostate gland was classified in 12 anatomic segments for data analysis of the imaging modalities as well as histopathologic findings. The segment with the highest radiotracer uptake was defined as the "index lesion." All cases were scheduled to undergo prostatectomy with pelvic lymph node (LN) dissection in intermediate- and high-risk patients. Intraprostatic and pelvic nodal [⁶⁸Ga]Ga-RM2 and [¹⁸F]FCH PET-CT findings were correlated with mpMRI and histopathologic results.

RESULTS

Of the 312 analyzed regions, 120 regions (4 to 8 lesions per patient) showed abnormal findings in the prostate gland. In a region-based analysis, overall sensitivity and specificity of [⁶⁸Ga]Ga-RM2 PET-CT in the detection of primary tumor were 74% and 90%, respectively, while it was 60% and 80% for [¹⁸F]FCH PET-CT and 72% and 89% for mpMRI. Although the overall sensitivity of [⁶⁸Ga]Ga-RM2 PET-CT was higher compared to that of [¹⁸F]FCH PET-CT and mpMRI, the statistical analysis showed only significant difference between [⁶⁸Ga]Ga-RM2 PET-CT and [¹⁸F]FCH PET-CT in the intermediate-risk group (p = 0.01) and [⁶⁸Ga]Ga-RM2 PET-CT and mpMRT in the high-risk group (p = 0.03). In the lesion-based analysis, there was no significant difference between SUVmax of [⁶⁸Ga]Ga-RM2 and [¹⁸F]FCH PET-CT in the intraprostatic malignant lesions ([⁶⁸Ga]Ga-RM2: mean SUVmax: 5.98 ± 4.13, median: 4.75; [¹⁸F]FCH: mean SUVmax: 6.08 ± 2.74, median: 5.5; p = 0.13).

CONCLUSIONS

[⁶⁸Ga]Ga-RM2 showed promising PET tracer for the detection of intraprostatic PCa in a cohort of patients with different risk stratifications. However, significant differences were only found between [⁶⁸Ga]Ga-RM2 PET-CT and [¹⁸F]FCH PET-CT in the intermediate-risk group and [⁶⁸Ga]Ga-RM2 PET-CT and mpMRT in the high-risk group. In addition, GRP-R-based imaging seems to play a complementary role to choline-based imaging for full characterization of PCa extent and biopsy guidance in low- and intermediate-metastatic-risk PCa patients and has the potential to discriminate them from those at higher risks.

KEY POINTS

• [⁶⁸Ga]Ga-RM2 is a promising PET tracer with a high detection rate for intraprostatic PCa especially in intermediate-risk prostate cancer patients. • GRPr-based imaging seems to play a complementary role to choline-based or PSMA-based PET/CT imaging in selected low- and intermediate-risk PCa patients for better characterization and eventually biopsy guidance of prostate cancer disease.

Theranostic PSMA ligands with optimized backbones for intraoperative multimodal imaging and photodynamic therapy of prostate cancer

INTRODUCTION

The first generation ligands for prostate-specific membrane antigen (PSMA)-targeted radio- and fluorescence-guided surgery followed by adjuvant photodynamic therapy (PDT) have already shown the potential of this approach. Here, we developed three new photosensitizer-based dual-labeled PSMA ligands by crucial modification of existing PSMA ligand backbone structures (PSMA-1007/PSMA-617) for multimodal imaging and targeted PDT of PCa.

METHODS

Various new PSMA ligands were synthesized using solid-phase chemistry and provided with a DOTA chelator for 111In labeling and the fluorophore/photosensitizer IRDye700DX. The performance of three new dual-labeled ligands was compared with a previously published first-generation ligand (PSMA-N064) and a control ligand with an incomplete PSMA-binding motif. PSMA specificity, affinity, and PDT efficacy of these ligands were determined in LS174T-PSMA cells and control LS174T wildtype cells. Tumor targeting properties were evaluated in BALB/c nude mice with subcutaneous LS174T-PSMA and LS174T wildtype tumors using µSPECT/CT imaging, fluorescence imaging, and biodistribution studies after dissection.

RESULTS

In order to synthesize the new dual-labeled ligands, we modified the PSMA peptide linker by substitution of a glutamic acid into a lysine residue, providing a handle for conjugation of multiple functional moieties. Ligand optimization showed that the new backbone structure leads to high-affinity PSMA ligands (all IC50 < 50 nM). Moreover, ligand-mediated PDT led to a PSMA-specific decrease in cell viability in vitro (P < 0.001). Linker modification significantly improved tumor targeting compared to the previously developed PSMA-N064 ligand (≥ 20 ± 3%ID/g vs 14 ± 2%ID/g, P < 0.01) and enabled specific visualization of PMSA-positive tumors using both radionuclide and fluorescence imaging in mice.

CONCLUSION

The new high-affinity dual-labeled PSMA-targeting ligands with optimized backbone compositions showed increased tumor targeting and enabled multimodal image-guided PCa surgery combined with targeted photodynamic therapy.

Pretherapeutic Comparative Dosimetry of 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T in Patients with Metastatic Castration-Resistant Prostate Cancer

Radiohybrid prostate-specific membrane antigen (rhPSMA) ligands allow for labeling with 18F and radiometals for endoradiotherapy. rhPSMA-7.3 has been designated as a lead compound with promising preclinical data for 177Lu-rhPSMA-7.3, which has shown higher tumor uptake than 177Lu-PSMA I&T. In this retrospective analysis, we compared pretherapeutic clinical dosimetry data of both PSMA ligands. Methods: Six patients with metastatic castration-resistant prostate cancer underwent both 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T pretherapeutic dosimetry. Whole-body scintigraphy was performed at 1 h, 4 h, 24 h, 48 h, and 7 d after injection. Regions of interest covering the whole body, organs, bone marrow, and tumor lesions were drawn for each patient. Absorbed doses for individual patients and pretherapeutic applications were calculated using OLINDA/EXM. To facilitate the comparison of both ligands, we introduced the therapeutic index (TI), defined as the ratio of mean pretherapeutic doses to tumor lesions over relevant organs at risk. Results: Mean whole-body pretherapeutic effective doses for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T were 0.12 ± 0.07 and 0.05 ± 0.03 Sv/GBq, respectively. Mean absorbed organ doses for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T were, for example, 1.65 ± 0.28 and 0.73 ± 0.18 Gy/GBq for the kidneys, 0.19 ± 0.09 and 0.07 ± 0.03 Gy/GBq for the liver, 2.35 ± 0.78 and 0.80 ± 0.41 Gy/GBq for the parotid gland, and 0.67 ± 0.62 and 0.30 ± 0.27 Gy/GBq for the bone marrow, respectively. Tumor lesions received mean absorbed doses of 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T of 6.44 ± 6.44 and 2.64 ± 2.24 Gy/GBq, respectively. The mean TIs for the kidneys were 3.7 ± 2.2 and 3.6 ± 2.2 for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T, respectively, and those for the bone marrow were 15.2 ± 10.2 and 15.1 ± 10.2 for 177Lu-rhPSMA-7.3 and 177Lu-PSMA I&T, respectively. Conclusion: Pretherapeutic clinical dosimetry confirmed preclinical results of mean absorbed doses for tumors that were 2-3 times higher for 177Lu-rhPSMA-7.3 than for 177Lu-PSMA I&T. Absorbed doses to normal organs also tended to be higher for 177Lu-rhPSMA-7.3, resulting overall in similar average TIs for both radiopharmaceuticals with considerable interpatient variability. 177Lu-rhPSMA-7.3 has promise for a therapeutic efficacy similar to that of 177Lu-PSMA I&T at smaller amounts of injected activity, simplifying radiation safety measurements (especially for large patient numbers or dose escalation regimens).

PSMA-Targeting Imaging and Theranostic Agents-Current Status and Future Perspective

In the past two decades, extensive efforts have been made to develop agents targeting prostate-specific membrane antigen (PSMA) for prostate cancer imaging and therapy. To date, represented by two recent approvals of [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]F-DCFPyL by the United States Food and Drug Administration (US-FDA) for positron emission tomography (PET) imaging to identify suspected metastases or recurrence in patients with prostate cancer, PSMA-targeting imaging and theranostic agents derived from small molecule PSMA inhibitors have advanced to clinical practice and trials of prostate cancer. The focus of current development of new PSMA-targeting agents has thus shifted to the improvement of in vivo pharmacokinetics and higher specific binding affinity with the aims to further increase the detection sensitivity and specificity and minimize the toxicity to non-target tissues, particularly the kidneys. The main strategies involve systematic chemical modifications of the linkage between the targeting moiety and imaging/therapy payloads. In addition to a summary of the development history of PSMA-targeting agents, this review provides an overview of current advances and future promise of PSMA-targeted imaging and theranostics with focuses on the structural determinants of the chemical modification towards the next generation of PSMA-targeting agents.

Evaluation of Predictors of Biochemical Recurrence in Prostate Cancer Patients, as Detected by 68Ga-PSMA PET/CT

Objectives: To explore the existence of new predictors of the ⁶⁸Ga-Prostate-Specific Membrane Antigen (PSMA) PET/CT detection rate at biochemical recurrence (BCR) and to determine the detection rate of ⁶⁸Ga-PSMA PET/CT dependent of prostate-specific antigen (PSA) levels. Materials and methods: In total, 189 PCa patients scanned with ⁶⁸Ga-PSMA PET/CT for detection of BCR after curatively intended treatment with either radical prostatectomy (n = 153) or radiotherapy (n = 36) were included. Clinicopathological information at the time of diagnosis (PSA, clinical tumor-stage, International Society of Urological Pathology Grade Group and whether ⁶⁸Ga-PSMA PET/CT was used for primary staging), treatment (RT/RP and histopathology of the prostatectomies), and pre-PET PSA were collected from medical records. Results: Of the 189 ⁶⁸Ga-PSMA PET/CT scans, 103 (54.5%) were positive for BCR of PCa. No significant coherency was observed between detection rate and any clinicopathological variables at diagnosis. Detection rates significantly increased with rising PSA: <0.5 ng/mL = 28%, 0.5 ≤ 1 ng/mL = 39%, 1 ≤ 2 ng/mL = 64%, 2 ≤ 5 ng/mL = 87.5% and ≥5 ng/mL = 97%. Conclusions: The detection rate of PCa recurrence was strongly dependent of pre-PET PSA levels. None of the additional clinical variables acquired during primary staging, prostatectomy pathology reports, nor primary staging imaging modality affected the detection rate.

Glycoforms of human prostate-specific membrane antigen (PSMA) in human cells and prostate tissue

INTRODUCTION

N-glycosylation is a ubiquitous and variable posttranslational modification that regulates physiological functions of secretory and membrane-associated proteins and the dysregulation of glycosylation pathways is often associated with cancer growth and metastasis. Prostate-specific membrane antigen (PSMA) is an established biomarker for prostate cancer imaging and therapy.

METHODS

Mass spectrometry was used to analyze the distribution of the site-specific glycoforms of PSMA in insect, human embryonic kidney, and prostate cancer cells, and in prostate tissue upon immunoaffinity enrichment.

RESULTS

While recombinant PSMA expressed in insect cells was decorated mainly by paucimannose and high mannose glycans, complex, hybrid, and high mannose glycans were detected in samples from human cells and tissue. We noted an interesting spatial distribution of the glycoforms on the PSMA surface-high mannose glycans were the dominant glycoforms at the N459, N476, and N638 sequons facing the plasma membrane, while the N121, N195, and N336 sites, located at the exposed apical PSMA domain, carried primarily complex glycans. The presence of high mannose glycoforms at the former sequons likely results from the limited access of enzymes of the glycosynthetic pathway required for the synthesis of the complex structures. In line with the limited accessibility of membrane-proximal sites, no glycosylation was observed at the N51 site positioned closest to the membrane.

CONCLUSIONS

Our study presents initial descriptive analysis of the glycoforms of PSMA observed in cell lines and in prostate tissue. It will hopefully stimulate further research into PSMA glycoforms in the context of tumor staging, noninvasive detection of prostate tumors, and the impact of glycoforms on physicochemical and enzymatic characteristics of PSMA in a tissue-specific manner.

Radiomics in prostate cancer: an up-to-date review

Prostate cancer (PCa) is the most common worldwide diagnosed malignancy in male population. The diagnosis, the identification of aggressive disease, and the post-treatment follow-up needs a more comprehensive and holistic approach. Radiomics is the extraction and interpretation of images phenotypes in a quantitative manner. Radiomics may give an advantage through advancements in imaging modalities and through the potential power of artificial intelligence techniques by translating those features into clinical outcome prediction. This article gives an overview on the current evidence of methodology and reviews the available literature on radiomics in PCa patients, highlighting its potential for personalized treatment and future applications.

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

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

Overview and Future Perspectives on Tumor-Targeted Positron Emission Tomography and Fluorescence Imaging of Pancreatic Cancer in the Era of Neoadjuvant Therapy

BACKGROUND

Despite recent advances in the multimodal treatment of pancreatic ductal adenocarcinoma (PDAC), overall survival remains poor with a 5-year cumulative survival of approximately 10%. Neoadjuvant (chemo- and/or radio-) therapy is increasingly incorporated in treatment strategies for patients with (borderline) resectable and locally advanced disease. Neoadjuvant therapy aims to improve radical resection rates by reducing tumor mass and (partial) encasement of important vascular structures, as well as eradicating occult micrometastases. Results from recent multicenter clinical trials evaluating this approach demonstrate prolonged survival and increased complete surgical resection rates (R0). Currently, tumor response to neoadjuvant therapy is monitored using computed tomography (CT) following the RECIST 1.1 criteria. Accurate assessment of neoadjuvant treatment response and tumor resectability is considered a major challenge, as current conventional imaging modalities provide limited accuracy and specificity for discrimination between necrosis, fibrosis, and remaining vital tumor tissue. As a consequence, resections with tumor-positive margins and subsequent early locoregional tumor recurrences are observed in a substantial number of patients following surgical resection with curative intent. Of these patients, up to 80% are diagnosed with recurrent disease after a median disease-free interval of merely 8 months. These numbers underline the urgent need to improve imaging modalities for more accurate assessment of therapy response and subsequent re-staging of disease, thereby aiming to optimize individual patient's treatment strategy. In cases of curative intent resection, additional intra-operative real-time guidance could aid surgeons during complex procedures and potentially reduce the rate of incomplete resections and early (locoregional) tumor recurrences. In recent years intraoperative imaging in cancer has made a shift towards tumor-specific molecular targeting. Several important molecular targets have been identified that show overexpression in PDAC, for example: CA19.9, CEA, EGFR, VEGFR/VEGF-A, uPA/uPAR, and various integrins. Tumor-targeted PET/CT combined with intraoperative fluorescence imaging, could provide valuable information for tumor detection and staging, therapy response evaluation with re-staging of disease and intraoperative guidance during surgical resection of PDAC.

METHODS

A literature search in the PubMed database and (inter)national trial registers was conducted, focusing on studies published over the last 15 years. Data and information of eligible articles regarding PET/CT as well as fluorescence imaging in PDAC were reviewed. Areas covered: This review covers the current strategies, obstacles, challenges, and developments in targeted tumor imaging, focusing on the feasibility and value of PET/CT and fluorescence imaging for integration in the work-up and treatment of PDAC. An overview is given of identified targets and their characteristics, as well as the available literature of conducted and ongoing clinical and preclinical trials evaluating PDAC-targeted nuclear and fluorescent tracers.

Single-Center Comparison of [64Cu]-DOTAGA-PSMA and [18F]-PSMA PET-CT for Imaging Prostate Cancer

Introduction: the diagnostic performance of [⁶⁴Cu]-DOTAGA-PSMA PET–CT imaging was compared retrospectively to [¹⁸F]-PSMA PET–CT in prostate cancer patients with recurrent disease and in the primary staging of selected patients with advanced local and possible metastatic disease. Methods: We retrospectively selected a total of 100 patients, who were consecutively examined in our department, with biochemical recurrence after radical prostatectomy or who had progressive local and possible metastatic disease in the last 3 months prior to this investigation. All patients were examined with a dedicated PET–CT scanner (Biograph; Siemens Healthineers). A total of 250 MBq (3.5 MBq per kg bodyweight, range 230–290 MBq) of [⁶⁴Cu]-DOTAGA-PSMA or [¹⁸-F]-PSMA was applied intravenously. PET images were performed 1 h post-injection (skull base to mid-thigh). The maximum standardized uptake values (SUVmax) of PSMA-positive lesions and the mean standardized uptake value (SUVmean) of the right liver lobe were measured. Results: All but 9/50 of the patients (18%; PSA range: 0.01–0.7 µg/L) studied with [⁶⁴Cu]-DOTAGA-PSMA and 6/50 of the ones (12%; PSA range: 0.01–4.2) studied with [¹⁸F]-PSMA had at least one positive PSMA lesion shown by PET–CT. The total number of lesions was higher with [⁶⁴Cu]-DOTAGA-PSMA (209 vs. 191); however, the median number of lesions was one for [⁶⁴Cu]-DOTAGA-PSMA and two for [¹⁸F]-PSMA. Interestingly, the median SUVmean of the right liver lobe was slightly higher for [¹⁸F]-PSMA (11.8 vs. 8.9). Conclusions: [⁶⁴Cu]-DOTAGA-PSMA and [¹⁸F]-PSMA have comparable detection rates for the assessment of residual disease in patients with recurrent or primary progressive prostate cancer. The uptake in the liver is moderately different, and therefore at least the SUVs of the lesions in both studies would not be comparable.

A PSMA-targeted bispecific antibody for prostate cancer driven by a small-molecule targeting ligand

Despite the development of next-generation antiandrogens, metastatic castration-resistant prostate cancer (mCRPC) remains incurable. Here, we describe a unique semisynthetic bispecific antibody that uses site-specific unnatural amino acid conjugation to combine the potency of a T cell-recruiting anti-CD3 antibody with the specificity of an imaging ligand (DUPA) for prostate-specific membrane antigen. This format enabled optimization of structure and function to produce a candidate (CCW702) with specific, potent in vitro cytotoxicity and improved stability compared with a bispecific single-chain variable fragment format. In vivo, CCW702 eliminated C4-2 xenografts with as few as three weekly subcutaneous doses and prevented growth of PCSD1 patient-derived xenograft tumors in mice. In cynomolgus monkeys, CCW702 was well tolerated up to 34.1 mg/kg per dose, with near-complete subcutaneous bioavailability and a PK profile supporting testing of a weekly dosing regimen in patients. CCW702 is being evaluated in a first in-human clinical trial for men with mCRPC who had progressed on prior therapies (NCT04077021).

Theranostics in Brain Tumors

Theranostic nuclear oncology, mainly in neuro-oncology (neurotheranostics), aims to combine cancer imaging and therapy using the same targeting molecule. This approach tries to identify patients who are most likely to benefit from tumor molecular radionuclide therapy. The ability of radioneurotheranostic agents to interact with cancer cells at the molecular level with high specificity can significantly improve the effectiveness of cancer therapy. A variety of biologic targets are under investigation for treating brain tumors. PET-based precision imaging can substantially improve the therapeutic efficacy of radiotheranostic approach in brain tumors.

Immunoconjugates for Cancer Targeting: A Review of Antibody-Drug Conjugates and Antibody-Functionalized Nanoparticles

Targeted therapy has been recently highlighted due to the reduction of side effects and improvement in overall efficacy and survival from different types of cancers. Considering the approval of many monoclonal antibodies in the last twenty years, cancer treatment can be accomplished by the combination of monoclonal antibodies and small molecule chemotherapeutics. Thus, strategies to combine both drugs in a single administration system are relevant in the clinic. In this context, two strategies are possible and will be further discussed in this review: antibody-drug conjugates (ADCs) and antibody-functionalized nanoparticles. First, it is important to better understand the possible molecular targets for cancer therapy, addressing different antigens that can selectively bind to antibodies. After selecting the best target, ADCs can be prepared by attaching a cytotoxic drug to an antibody able to target a cancer cell antigen. Briefly, an ADC will be formed by a monoclonal antibody (MAb), a cytotoxic molecule (cytotoxin) and a chemical linker. Usually, surface-exposed lysine or the thiol group of cysteine residues are used as anchor sites for linker-drug molecules. Another strategy that should be considered is antibody-functionalized nanoparticles. Basically, liposomes, polymeric and inorganic nanoparticles can be attached to specific antibodies for targeted therapy. Different conjugation strategies can be used, but nanoparticles coupling between maleimide and thiolated antibodies or activation with the addition of ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/ N-hydroxysuccinimide (NHS) (1:5) and further addition of the antibody are some of the most used strategies. Herein, molecular targets and conjugation strategies will be presented and discussed to better understand the in vitro and in vivo applications presented. Also, the clinical development of ADCs and antibody-conjugated nanoparticles are addressed in the clinical development section. Finally, due to the innovation related to the targeted therapy, it is convenient to analyze the impact on patenting and technology. Information related to the temporal evolution of the number of patents, distribution of patent holders and also the number of patents related to cancer types are presented and discussed. Thus, our aim is to provide an overview of the recent developments in immunoconjugates for cancer targeting and highlight the most important aspects for clinical relevance and innovation.

Performance of 18F-DCFPyL PET/CT Imaging in Early Detection of Biochemically Recurrent Prostate Cancer: A Systematic Review and Meta-Analysis

Background: Prostate-specific membrane antigen (PSMA)-targeted 2-(3-{1-carboxy-5-[(6-[18F] fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (18F-DCFPyL) positron emission tomography/computed tomography (PET/CT) has shown advantages in primary staging, restaging, and metastasis detection of prostate cancer (PCa). However, little is known about the role of 18F-DCFPyL PET/CT in biochemically recurrent prostate cancer (BRPCa). Hence, we performed a systematic review and meta-analysis to evaluate 18F-DCFPyL PET/CT as first-line imaging modality in early detection of BRPCa. Methods: A comprehensive literature search of PubMed, Web of Science, Embase, and Cochrane Library was conducted until December 2020. The pooled detection rate on a per-person basis and together with 95% confidence interval (CI) was calculated. Furthermore, a prostate-specific antigen (PSA)-stratified performance of detection positivity was obtained to assess the sensitivity of 18F-DCFPyL PET/CT in BRPCa with different PSA levels. Results: A total of nine eligible studies (844 patients) were included in this meta-analysis. The pooled detection rate (DR) of 18F-DCFPyL PET/CT in BRPCa was 81% (95% CI: 76.9-85.1%). The pooled DR was 88.8% for PSA ≥ 0.5 ng/ml (95% CI: 86.2-91.3%) and 47.2% for PSA < 0.5 ng/ml (95% CI: 32.6-61.8%). We also noticed that the regional lymph node was the most common site with local recurrence compared with other sites (45.8%, 95% CI: 42.1-49.6%). Statistical heterogeneity and publication bias were found. Conclusion: The results suggest that 18F-DCFPyL PET/CT has a relatively high detection rate in BRPCa. The results also indicate that imaging with 18F-DCFPyL may exhibit improved sensitivity in BRPCa with increased PSA levels. Considering the publication bias, further large-scale multicenter studies are warranted for validation.

Standardization of the [68Ga]Ga-PSMA-11 Radiolabeling Protocol in an Automatic Synthesis Module: Assessments for PET Imaging of Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a glycoprotein present in the prostate, that is overexpressed in prostate cancer (PCa). Recently, PSMA-directed radiopharmaceuticals have been developed, allowing the pinpointing of tumors with the Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) imaging techniques. The aim of the present work was to standardize and validate an automatic synthesis module-based radiolabeling protocol for [⁶⁸Ga]Ga-PSMA-11, as well as to produce a radiopharmaceutical for PET imaging of PCa malignancies. [⁶⁸Ga]Ga-PSMA-11 was evaluated to determine the radiochemical purity (RCP), stability in saline solution and serum, lipophilicity, affinity to serum proteins, binding and internalization to lymph node carcinoma of the prostate (LNCaP) cells, and ex vivo biodistribution in mice. The radiopharmaceutical was produced with an RCP of 99.06 ± 0.10%, which was assessed with reversed-phase high-performance liquid chromatography (RP-HPLC). The product was stable in saline solution for up to 4 h (RCP > 98%) and in serum for up to 1 h (RCP > 95%). The lipophilicity was determined as -3.80 ± 0.15, while the serum protein binding (SPB) was <17%. The percentages of binding to LNCaP cells were 4.07 ± 0.51% (30 min) and 4.56 ± 0.46% (60 min), while 19.22 ± 2.73% (30 min) and 16.85 ± 1.34% (60 min) of bound material was internalized. High accumulation of [⁶⁸Ga]Ga-PSMA-11 was observed in the kidneys, spleen, and tumor, with a tumor-to-contralateral-muscle ratio of >8.5 and a tumor-to-blood ratio of >3.5. In conclusion, an automatic synthesis module-based radiolabeling protocol for [⁶⁸Ga]Ga-PSMA-11 was standardized and the product was evaluated, thus verifying its characteristics for PET imaging of PCa tumors in a clinical environment.

Contemporary update of SPECT tracers and novelties in radioguided surgery: a perspective based on urology

Recent technical advances and implementation of novel radiotracers have further increased the potential of radioguided surgery for a broad variety of malignancies. Indeed, the possibilities for future applications of novel radiotracers in diverse oncological strategies has become more promising than ever. This literature review aims to provide a contemporary update on a selected group of radiotracers and evaluates the usability of radioguided surgery and sentinel node procedures, focusing on most promising advances. For example, the impact of targeted radiotracers on prostate specific membrane antigen (PSMA), CD206 receptor-targeted agents (^99mTc-tilmanocept), and hybrid tracers adding fluorescence to radioguidance (ICG-^99mTc-nanocolloid) as well as targeting hypoxia-induced carbonic anhydrase IX (CAIX) will be covered. Furthermore, future outlooks on the implementation of gold nanoparticles (AuNP's), but also technical advances in improved radiotracer detection by hybrid gamma devices will be discussed.

Real-World Data Analysis of Efficacy and Survival After Lutetium-177 Labelled PSMA Ligand Therapy in Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

Lutetium-177 prostate-specific membrane antigen (¹⁷⁷Lu-PSMA) radioligand therapy is emerging as a promising treatment for metastatic castration-resistant prostate cancer refractory to established therapies. While there is an increasing body of survival and other data from retrospective analyses and prospective trials, there is no clear understanding of how best to predict therapy response and survival outcomes.

OBJECTIVE

In this retrospective cohort analysis, we aimed to identify features that are associated with response to radioligand therapy and greater survival based on analysis of real-world data.

PATIENTS AND METHODS

191 patients aged 70 ± 8 years with metastatic castration-resistant prostate cancer treated with radioligand therapy from November 2015 to February 2019 were included for analysis. Eligible patients had PSMA-expressing metastatic castration-resistant prostate cancer (confirmed by a ⁶⁸Ga-PSMA-ligand positron emission tomography (PET)/computed tomography (CT) scan), an Eastern Cooperative Oncology Group performance status score ≤ 2 and no significant kidney, liver or bone marrow dysfunction (as characterised by kidney and liver function tests and a full blood count). Patients received one to five cycles of intravenous ¹⁷⁷Lu-PSMA-ligand therapy. Endpoints included biochemical [prostate-specific antigen (PSA)] and radiologic (PSMA PET/CT) response, progression-free survival and overall survival, defined according to the Prostate Cancer Working Group 3 guidelines. Survival analysis was conducted by Kaplan-Meier estimation.

RESULTS

Most individuals (89.5%) previously underwent first- and second-line systematic therapy. Of the 191 men treated with 452 cycles with mean injected activity of 6.1 ± 1.0 GBq per cycle, 159 patients were assessed for a biochemical response defined as a PSA decline ≥ 50% from baseline. A ≥ 50% PSA decline was observed in 89 (56%) patients, while any PSA decline occurred in 120 (75%) men. For the entire cohort, median values (interquartile range) of overall survival [n = 191], PSA progression-free survival [n = 132] and PET/CT progression-free survival were 12 (5-18), 4 (3-8) and 6 (3-10) months, respectively. Survival analysis confirmed better outcomes in individuals who had demonstrated therapy response. Predominantly lymph node metastatic disease and chemotherapy-naïve status were significant pre-therapy factors associated with longer survival. Baseline PSA was significantly linked to survival outcomes: lower levels predicted a lower risk of death and disease progression. Treatment-related adverse events included grade 3 or 4 haematological (12%), grade 1 or 2 renal (4.5%), and grade 3 or 4 clinical events (5.7%).

CONCLUSIONS

Our findings suggest that ¹⁷⁷Lu-PSMA radioligand therapy provides a significant response rate with a low toxicity profile. The evidence promotes greater efficacy of radioligand therapy in predominantly lymph node metastatic castration-resistant prostate cancer, and in individuals with chemotherapy-naïve status and lower levels of baseline PSA.

Preclinical and Clinical Status of PSMA-Targeted Alpha Therapy for Metastatic Castration-Resistant Prostate Cancer

Bone, lymph node, and visceral metastases are frequent in castrate-resistant prostate cancer patients. Since such patients have only a few months' survival benefit from standard therapies, there is an urgent need for new personalized therapies. The prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer and is a molecular target for imaging diagnostics and targeted radionuclide therapy (theragnostics). PSMA-targeted α therapies (PSMA-TAT) may deliver potent and local radiation more selectively to cancer cells than PSMA-targeted β- therapies. In this review, we summarize both the recent preclinical and clinical advances made in the development of PSMA-TAT, as well as the availability of therapeutic α-emitting radionuclides, the development of small molecules and antibodies targeting PSMA. Lastly, we discuss the potentials, limitations, and future perspectives of PSMA-TAT.

Radiomics and Prostate MRI: Current Role and Future Applications

Multiparametric prostate magnetic resonance imaging (mpMRI) is widely used as a triage test for men at a risk of prostate cancer. However, the traditional role of mpMRI was confined to prostate cancer staging. Radiomics is the quantitative extraction and analysis of minable data from medical images; it is emerging as a promising tool to detect and categorize prostate lesions. In this paper we review the role of radiomics applied to prostate mpMRI in detection and localization of prostate cancer, prediction of Gleason score and PI-RADS classification, prediction of extracapsular extension and of biochemical recurrence. We also provide a future perspective of artificial intelligence (machine learning and deep learning) applied to the field of prostate cancer.

Early differences in dynamic uptake of 68Ga-PSMA-11 in primary prostate cancer: A test-retest study

INTRODUCTION

Dynamic PET/CT allows visualization of pharmacokinetics over the time, in contrast to static whole body PET/CT. The objective of this study was to assess 68Ga-PSMA-11 uptake in pathological lesions and benign tissue, within 30 minutes after injection in primary prostate cancer (PCa) patients in test-retest setting.

MATERIALS AND METHODS

Five patients, with biopsy proven PCa, were scanned dynamically in list mode for 30 minutes on a digital PET/CT-scanner directly after an intravenous bolus injection of 100 MBq 68Ga-PSMA-11. Approximately 45 minutes after injection a static whole body scan was acquired, followed by a one bed position scan of the pelvic region. The scans were repeated approximately four weeks later, without any intervention in between. Semi-quantitative assessment was performed using regions-of-interest in the prostate tumor, bladder, gluteal muscle and iliac artery. Time-activity curves were extracted from the counts in these regions and the intra-patient variability between both scans was assessed.

RESULTS

The uptake of the iliac artery and gluteal muscle reached a plateau after 5 and 3 minutes, respectively. The population fell apart in two groups with respect to tumor uptake: in some patients the tumor uptake reached a plateau after 5 minutes, whereas in other patients the uptake kept increasing, which correlated with larger tumor volumes on PET/CT scan. Median intra-patient variation between both scans was 12.2% for artery, 9.7% for tumor, 32.7% for the bladder and 14.1% for the gluteal muscle.

CONCLUSION

Dynamic 68Ga-PSMA-11 PET/CT scans, with a time interval of four weeks, are reproducible with a 10% variation in uptake in the primary prostate tumor. An uptake plateau was reached for the iliac artery and gluteal muscle within 5 minutes post-injection. A larger tumor volume seems to be related to continued tumor uptake. This information might be relevant for both response monitoring and PSMA-based radionuclide therapies.

SOX2-dependent expression of dihydroorotate dehydrogenase regulates oral squamous cell carcinoma cell proliferation

Oral squamous cell carcinoma (OSCC) become a heavy burden of public health, with approximately 300 000 newly diagnosed cases and 145 000 deaths worldwide per year. Nucleotide metabolism fuel DNA replication and RNA synthesis, which is indispensable for cell proliferation. But how tumor cells orchestrate nucleotide metabolic enzymes to support their rapid growth is largely unknown. Here we show that expression of pyrimidine metabolic enzyme dihydroorotate dehydrogenase (DHODH) is upregulated in OSCC tissues, compared to non-cancerous adjacent tissues. Enhanced expression of DHODH is correlated with a shortened patient survival time. Inhibition of DHODH by either shRNA or selective inhibitors impairs proliferation of OSCC cells and growth of tumor xenograft. Further, loss of functional DHODH imped de novo pyrimidine synthesis, and disrupt mitochondrial respiration probably through destabilizing the MICOS complex. Mechanistic study shows that transcriptional factor SOX2 plays an important role in the upregulation of DHODH in OSCC. Our findings add to the knowledge of how cancer cells co-opt nucleotide metabolism to support their rapid growth, and thereby highlight DHODH as a potential prognostic and therapeutic target for OSCC treatment.

PSMA-targeted melanin-like nanoparticles as a multifunctional nanoplatform for prostate cancer theranostics

Prostate-specific membrane antigen (PSMA) is highly expressed on the surface of most prostate tumor cells and is considered a promising target for prostate cancer imaging and treatment. It is possible to establish a PSMA-targeted theranostic probe to achieve early diagnosis and treatment of this cancer type. In this contribution, we prepared a multifunctional melanin-like polydopamine (PDA) nanocarrier decorated with a small-molecule PSMA inhibitor, N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-(S)-l-lysine (DCL). PDA-DCL was then functionalized with perfluoropentane (PFP) and loaded with the photosensitizer chlorin e6 (Ce6) to give Ce6@PDA-DCL-PFP, which was successfully used for ultrasound-guided combined photodynamic/photothermal therapy (PDT/PTT) of prostate cancer. Compared with the corresponding non-targeted probe (Ce6@PDA-PEG-PFP), our targeted probe induced higher cellular uptake in vitro (6.5-fold) and more tumor accumulation in vivo (4.6-fold), suggesting strong active targeting capacity. Meanwhile, this new nanoplatform significantly enhanced the ultrasound contrast signal at the tumor site in vivo, thus facilitating precise and real-time detection of the tumor. In addition, this Ce6-loaded PDA nanoplatform produced a synergistic effect of PDT and PTT under 660 nm and 808 nm irradiation, inducing a more efficient killing effect compared with the individual therapy in vitro and in vivo. Furthermore, the tumor in the targeted group was more effectively suppressed than that in the non-targeted group under the same irradiation condition. This multifunctional probe may hold great potential for precise and early theranostics of prostate cancer.

Photosensitizer-based multimodal PSMA-targeting ligands for intraoperative detection of prostate cancer

Incomplete resection of prostate cancer (PCa) occurs in 15%-50% of PCa patients. Disease recurrence negatively impacts oncological outcome. The use of radio-, fluorescent-, or photosensitizer-labeled ligands to target the prostate-specific membrane antigen (PSMA) has become a well-established method for the detection and treatment of PCa. Methods: Here, we developed and characterized multimodal [¹¹¹In]In-DOTA(GA)-IRDye700DX-PSMA ligands, varying in their molecular composition, for use in intraoperative radiodetection, fluorescence imaging and targeted photodynamic therapy of PCa lesions. PSMA-specificity of these ligands was determined in xenograft tumor models and on fresh human PCa biopsies. Results: Ligand structure optimization showed that addition of the photosensitizer (IRDye700DX) and additional negative charges significantly increased ligand uptake in PSMA-expressing tumors. Moreover, an ex vivo incubation study on human tumor biopsies confirmed the PSMA-specificity of these ligands on human samples, bridging the gap to the clinical situation. Conclusion: We developed a novel PSMA-targeting ligand, optimized for multimodal image-guided PCa surgery combined with targeted photodynamic therapy.