Novel technology of molecular radio-guidance for lymph node dissection in recurrent prostate cancer by PSMA-ligands

67 Ga-PSMA I&T for Radioguided Surgery of Lymph Node Metastases in Patients With Biochemical Recurrence of Prostate Cancer

PURPOSE

Radioguided lymph node dissection in patients with prostate cancer, and suffering from biochemical recurrence has been described thoroughly during the past few years. Several prostate-specific membrane antigen (PSMA)-directed ligands labeled with 111 In, 99m Tc, and 68 Ga have been published; however, limitations regarding availability, short half-life, high costs, and unfavorable high energy might restrict frequent use. This study aims at introducing 67 Ga as a promising radionuclide for radioguided surgery.

METHODS

Retrospective analysis was performed on 6 patients with 7 PSMA-positive lymph node metastases. 67 Ga-PSMA I&T (imaging and therapy) was synthesized in-house and intravenously applied according to §13 2b of the German Medicinal Products Act. Radioguided surgery was performed 24 hours after injection of 67 Ga-PSMA I&T using a gamma probe. Patient urine samples were collected. Occupational and waste dosimetry was performed to describe hazards arising from radiation.

RESULTS

67 Ga-PSMA application was tolerated without adverse effects. Five of 7 lymph nodes were detected on 22-hour SPECT/CT in 4 of 6 patients. During surgery, all 7 lymph node metastases were identified by positive gamma probe signal. Relevant accumulation of 67 Ga was observed in lymph node metastases (32.1 ± 15.1 kBq). Histology analysis of near-field lymph node dissection revealed more lymph node metastases than PET/CT (and gamma probe measurements) identified. Waste produced during inpatient stay required decay time of up to 11 days before reaching exemption limits according to German regulations.

CONCLUSIONS

Radioguided surgery using 67 Ga-PSMA I&T is a safe and feasible option for patients suffering from biochemical recurrence of prostate cancer. 67 Ga-PSMA I&T was successfully synthesized according to Good Manufacturing Practice guidelines. Radioguided surgery with 67 Ga-PSMA I&T does not lead to relevant radiation burden to urology surgeons and represents a novel interdisciplinary approach in nuclear medicine and urology.

Synthesis and preclinical evaluation of novel 99mTc-labeled PSMA ligands for radioguided surgery of prostate cancer

BACKGROUND

Radioguided surgery (RGS) has recently emerged as a valuable new tool in the management of recurrent prostate cancer (PCa). After preoperative injection of a ^99mTc-labeled prostate-specific membrane antigen (PSMA) inhibitor, radioguided intraoperative identification and resection of lesions is facilitated by means of suitable γ-probes. First clinical experiences show the feasibility of RGS and suggest superiority over conventional lymph node dissection in recurrent PCa. However, commonly used [^99mTc]Tc-PSMA-I&S exhibits slow whole-body clearance, thus hampering optimal tumor-to-background ratios (TBR) during surgery. We therefore aimed to develop novel ^99mTc-labeled, PSMA-targeted radioligands with optimized pharmacokinetic profile to increase TBR at the time of surgery.

METHODS

Three ^99mTc-labeled N4-PSMA ligands were preclinically evaluated and compared to [^99mTc]Tc-PSMA-I&S. PSMA affinity (IC₅₀) and internalization were determined on LNCaP cells. Lipophilicity was assessed by means of the distribution coefficient logD_7.4 and an ultrafiltration method was used to determine binding to human plasma proteins. Biodistribution studies and static µSPECT/CT-imaging were performed at 6 h p.i. on LNCaP tumor-bearing CB17-SCID mice.

RESULTS

The novel N4-PSMA tracers were readily labeled with [^99mTc]TcO₄^- with RCP > 95%. Comparable and high PSMA affinity was observed for all [^99mTc]Tc-N4-PSMA-ligands. The ligands showed variable binding to human plasma and medium to low lipophilicity (logD_7.4 - 2.6 to - 3.4), both consistently decreased compared to [^99mTc]Tc-PSMA-I&S. Biodistribution studies revealed comparable tumor uptake among all [^99mTc]Tc-N4-PSMA-ligands and [^99mTc]Tc-PSMA-I&S, while clearance from most organs was superior for the novel tracers. Accordingly, increased TBR were achieved. [^99mTc]Tc-N4-PSMA-12 showed higher TBR than [^99mTc]Tc-PSMA-I&S for blood and all evaluated tissue. In addition, a procedure suitable for routine clinical production of [^99mTc]Tc-N4-PSMA-12 was established. Labeling with 553 ± 187 MBq was achieved with RCP of 98.5 ± 0.6% (n = 10).

CONCLUSION

High tumor accumulation and favorable clearance from blood and non-target tissue make [^99mTc]Tc-N4-PSMA-12 an attractive tracer for RGS, possibly superior to currently established [^99mTc]Tc-PSMA-I&S. Its GMP-production according to a method presented here and first clinical investigations with this novel radioligand is highly recommended.

[PSMA-PET-MRI and radio-guided surgery in cervical lymphadenectomy]

A 75-year-old male patient with suspicious cervical lymph nodes in level IV on the left side is presented. The cervical mass was detected in PSMA-PET-MRI as part of a restaging examination conducted due to an increase of PSA levels in the context of the patient's known prostate cancer. We conducted a selective cervical level IV lymphadenectomy with the aid of a gamma probe subsequent to radiolabelling with ^99mTc-PSMA. Two visibly enlarged lymph nodes with high gamma probe signals could be extracted. Histopathological examination revealed lymph node metastases of the known prostate cancer. Using an adequate tracer radio-guided surgery helps to detect pathological lymph nodes in the head and neck region allowing for supraselective resection.

A Review on the Current State and Future Perspectives of [99mTc]Tc-Housed PSMA-i in Prostate Cancer

Recently, prostate-specific membrane antigen (PSMA) has gained momentum in tumor nuclear molecular imaging as an excellent target for both the diagnosis and therapy of prostate cancer. Since 2008, after years of preclinical research efforts, a plentitude of radiolabeled compounds mainly based on low molecular weight PSMA inhibitors (PSMA-i) have been described for imaging and theranostic applications, and some of them have been transferred to the clinic. Most of these compounds include radiometals (e.g., ⁶⁸Ga, ⁶⁴Cu, ¹⁷⁷Lu) for positron emission tomography (PET) imaging or endoradiotherapy. Nowadays, although the development of new PET tracers has caused a significant drop in single-photon emission tomography (SPECT) research programs and the development of new technetium-99m (^99mTc) tracers is rare, this radionuclide remains the best atom for SPECT imaging owing to its ideal physical decay properties, convenient availability, and rich and versatile coordination chemistry. Indeed, ^99mTc still plays a relevant role in diagnostic nuclear medicine, as the number of clinical examinations based on ^99mTc outscores that of PET agents and ^99mTc-PSMA SPECT/CT may be a cost-effective alternative for ⁶⁸Ga-PSMA PET/CT. This review aims to give an overview of the specific features of the developed [^99mTc]Tc-tagged PSMA agents with particular attention to [^99mTc]Tc-PSMA-i. The chemical and pharmacological properties of the latter will be compared and discussed, highlighting the pros and cons with respect to [⁶⁸Ga]Ga-PSMA11.

How molecular imaging will enable robotic precision surgery : The role of artificial intelligence, augmented reality, and navigation

Molecular imaging is one of the pillars of precision surgery. Its applications range from early diagnostics to therapy planning, execution, and the accurate assessment of outcomes. In particular, molecular imaging solutions are in high demand in minimally invasive surgical strategies, such as the substantially increasing field of robotic surgery. This review aims at connecting the molecular imaging and nuclear medicine community to the rapidly expanding armory of surgical medical devices. Such devices entail technologies ranging from artificial intelligence and computer-aided visualization technologies (software) to innovative molecular imaging modalities and surgical navigation (hardware). We discuss technologies based on their role at different steps of the surgical workflow, i.e., from surgical decision and planning, over to target localization and excision guidance, all the way to (back table) surgical verification. This provides a glimpse of how innovations from the technology fields can realize an exciting future for the molecular imaging and surgery communities.

How accurate is 68Gallium-prostate specific membrane antigen positron emission tomography / computed tomography (68Ga-PSMA PET/CT) on primary lymph node staging before radical prostatectomy in intermediate and high risk prostate cancer? A study of patient- and lymph node- based analyses

BACKGROUND AND AIM

Gallium-68 (68Ga)-Prostate Membrane Specific Antigen Positron Emission Tomography/Computed Tomography (68Ga-PSMA PET/CT) is an emerging diagnostic modality which is gaining importance in individualized prostate cancer (PCa) management era. This study aimed to investigate the diagnostic accuracy of ⁶⁸Ga-PSMA PET/CT on primary LN staging before radical prostatectomy (RP) in intermediate and high risk PCa.

MATERIALS AND METHODS

The retrospectively documented 49 patients with intermediate and high risk non-metastatic PCa who had ⁶⁸Ga-PSMA PET/CT before RP were enrolled into this study. The histopathology of dissected LNs was used as reference standard to evaluate the accuracy of ⁶⁸Ga-PSMA PET/CT on primary LN staging, both in per-patient (n = 49) and in per-node (n = 454) analyses. The diagnostic accuracy was investigated using sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV), and by area under the curve (AUC) provided using receiver operating curve (ROC) analysis.

RESULTS

Median age was 64 (48-79) years and, median and mean PSA values were 10 (1.31-138) ng/ml and 16.2 (±19.8) ng/ml, respectively. 22 (44.9%) and 27 (55.1%) of patients had intermediate and high risk PCa, respectively. A total of 5 (10.2%) patients had histopathologically proven LN metastasis and 3 (60%) of them was detected in ⁶⁸Ga-PSMA PET/CT. In per patient analysis, the sensitivity, specifity, PPV and NPV of ⁶⁸Ga-PSMA PET/CT on primary LN staging were 0.60, 0.96, 0.60 and 0.96, respectively. Among overall 454 LNs, 16 (3.5 %) of them were reported as metastatic in histopathology and, 13 (2.9%) of these metastatic LNs were detected in ⁶⁸Ga-PSMA PET/CT. In per-node analysis, the sensitivity, specificity, PPV and NPV of ⁶⁸Ga-PSMA PET/CT on primary LN staging were 0.82, 0.99, 0.87 and 0.99, respectively. The ROC analyses found AUCs for primary LN staging as 0.777 (95%CI:0.508-1.0) in per patient analysis and, as 0.904 (95%CI:0.790 - 1.0) in per node analysis, respectively.

CONCLUSION

The use of ⁶⁸Ga-PSMA PET/CT has promising diagnostic accuracy on primary LN staging before RP in intermediate and high risk PCa. However, the efforts should be taken to increase sensitivity of ⁶⁸Ga-PSMA PET/CT in individualized treatment era.

Indocyanine green guidance improves the efficiency of extended pelvic lymph node dissection during laparoscopic radical prostatectomy

OBJECTIVES

To evaluate whether indocyanine green guidance can improve the quality of extended pelvic lymph node dissection in patients undergoing radical prostatectomy.

METHODS

A total of 214 patients underwent laparoscopic radical prostatectomy with indocyanine green-guided lymph node dissection plus extended pelvic lymph node dissection. These patients (group A) were matched 1:1 for clinical risk groups according to the National Comprehensive Cancer Network classification with patients who underwent the same procedure without fluorescence guidance (group B). Biochemical recurrence was defined as two consecutive prostate-specific antigen rises of at least 0.2 ng/mL. The Kaplan-Meier method and Cox regression models were used to identify predictors of biochemical recurrence.

RESULTS

The median number of retrieved nodes was significantly higher in group A (22 vs 14, P < 0.001). The rate of lymph node metastases was higher in group A (65.9% vs 34.1%, P = 0.01). Increasing the yield of lymph node dissection was independently and negatively correlated with the biochemical recurrence risk in both overall and pN-positive patients (hazard ratio 0.97, P = 0.03; and hazard ratio 0.95, P = 0.02). The 5-year biochemical recurrence-free survival rates were (75.8% vs 65.9, P = 0.09) and (54.1% vs 24.9%, P = 0.023) for group A and group B in the overall cohort and pN-positive cohort, respectively.

CONCLUSION

Indocyanine green-guided lymph node dissection plus extended pelvic lymph node dissection improves identification of lymphatic drainage, resulting in a higher number of lymph nodes and retrieved lymph node metastases, and allowing a more accurate local staging and a prolonged biochemical recurrence-free survival.

99mTc-labelled PSMA ligand for radio-guided surgery in nodal metastatic prostate cancer: proof of principle

Purpose

Intraoperative identification of prostate cancer (PCa) lymph node (LN) metastases (LNM) detected by preoperative PSMA PET/CT may be facilitated by PSMA radio-guided surgery (RGS) with use of a γ-probe. Earlier we demonstrated excellent performance of the ¹¹¹In-labelled PSMA ligand DKFZ-617 ([¹¹¹In]In-PSMA-617) in RGS for ex situ distinction of LN vs LNM at lymphadenectomy (LA) at a single LN level. In comparison with indium-111, technetium-99m has better physical properties for γ-probe measurements, better availability and lower radiation exposure for patients and medical personnel. Against this background, we evaluated the uptake of ^99mTc-PSMA-I&S ligand at the level of single LN and its power to discriminate between unaffected LN and LNM.

Methods

Six patients with PCa with the suspicion of LNM on preoperative PSMA-PET/CT underwent [^99mTc]Tc-PSMA-I&S RGS (4 salvage LA, 2 primary LA) with intravenous injection of [^99mTc]Tc-PSMA-I&S 24 h prior to surgery. Resected samples were isolated manually aiming at the level of single LN. Uptake measurements were done ex situ with a high-purity germanium detector. Receiver operating characteristic (ROC) analysis was performed based on [^99mTc]Tc-PSMA-I&S uptake expressed as lean body mass standard uptake value (SUL).

Results

Separation of the tissue samples from 73 subregions resulted in 498 single samples. After final histopathology 356 LN, 160 LNM und 11 non-nodal PCa samples were identified. Median SUL of tumor-free samples (0.26) and samples with cancer (3.5) was significantly different (p < 0.0001). ROC analysis revealed an area under the curve (AUC) of 0.917 (95% CI 0.89–0.95). Using a SUL cutoff of 1.1, sensitivity, specificity, positive predictive value, and negative predictive values were 76.6%, 94.4%, 89.4% and 86.9%.

Conclusion

Ex situ analysis of [^99mTc]Tc-PSMA-I&S uptake at single LN level showed good diagnostic performance for the ex situ distinction of tumor-bearing vs tumor-free LN during RGS.

Interventional nuclear medicine: a focus on radioguided intervention and surgery

Within interventional nuclear medicine (iNM) a prominent role is allocated for the sub-discipline of radioguided surgery. Unique for this discipline is the fact that an increasing number of clinical indications (e.g. lymphatic mapping, local tumor demarcation and/or tumor receptor targeted applications) have been adopted into routine care. The clinical integration is further strengthened by technical innovations in chemistry and engineering that enhance the translational potential of radioguided procedures in iNM. Together, these features not only ensure ongoing expansion of iNM but also warrant a lasting clinical impact for the sub-discipline of radioguided surgery.

Where to next prostate-specific membrane antigen PET imaging frontiers?

PURPOSE OF REVIEW

Technical improvements in imaging equipment and availability of radiotracers, such as PSMA-ligands have increased the synergy between Urology and Nuclear Medicine. Meanwhile artificial intelligence is introduced in Nuclear Imaging. This review will give an overview of recent technical and clinical developments and an outlook on application of these in the near future.

RECENT FINDINGS

Digital PET/CT has shown gradual improvement in lesion detection and demarcation over conventional PET/CT, but total-body PET/CT holds promise for a magnitude of improvement in scan duration and quality, quantification, and dose optimization. PET-guided decision-making with the application of PSMA-ligands has been shown useful in demonstrating and biopting primary prostate cancer (PCa) lesions, guiding radiotherapy, guiding surgical resection of recurrent PCa, and assessing therapy response in PCa. Artificial intelligence made its way into Nuclear Imaging just recently, but encouraging progress promises clinical application with unprecedented possibilities.

SUMMARY

Evidence is growing on clinical usefulness of PET-guided decision-making with the still relatively new PSMA ligands as a prime example. Rapid evolution of PET instrumentation and clinical introduction of artificial intelligence will be the gamechangers of nuclear imaging in the near future, though its powers should still be mastered and incorporated in clinical practice.

Targeted Nanobubbles Carrying Indocyanine Green for Ultrasound, Photoacoustic and Fluorescence Imaging of Prostate Cancer

Objective

To construct prostate-specific membrane antigen (PSMA)-targeting, indocyanine green (ICG)-loaded nanobubbles (NBs) for multimodal (ultrasound, photoacoustic and fluorescence) imaging of prostate cancer.

Methods

The mechanical oscillation method was used to prepare ICG-loaded photoacoustic NBs (ICG NBs). Then, PSMA-binding peptides were connected to the surface of ICG NBs using the biotin–avidin method to make targeted photoacoustic NBs, namely, PSMAP/ICG NBs. Their particle sizes, zeta potentials, and in vitro ultrasound, photoacoustic and fluorescence imaging were examined. Confocal laser scanning microscopy and flow cytometry were used to detect the binding ability of the PSMAP/ICG NBs to PSMA-positive LNCaP cells, C4-2 cells, and PSMA-negative PC-3 cells. The multimodal imaging effects of PSMAP/ICG NBs and ICG NBs were compared in nude mouse tumor xenografts.

Results

The particle size of the PSMAP/ICG NBs was approximately 457.7 nm, and the zeta potential was approximately −23.5 mV. Both confocal laser scanning microscopy and flow cytometry confirmed that the PSMAP/ICG NBs could specifically bind to both LNCaP and C4-2 cells, but they rarely bound to PC-3 cells. The ultrasound, photoacoustic and fluorescence imaging intensities of the PSMAP/ICG NBs in vitro positively correlated with their concentrations. The ultrasound and photoacoustic imaging effects of the PSMAP/ICG NBs in LNCaP and C4-2 tumor xenografts were significantly enhanced compared with those in PC-3 tumor xenografts, which were characterized by a significantly increased duration of ultrasound enhancement and heightened photoacoustic signal intensity (P < 0.05). Fluorescence imaging showed that PSMAP/ICG NBs could accumulate in LNCaP and C4-2 tumor xenografts for a relatively long period.

Conclusion

The targeted photoacoustic nanobubbles prepared in this study can specifically bind to PSMA-positive prostate cancer cells and have the ability to enhance ultrasound, photoacoustic and fluorescence imaging of PSMA-positive tumor xenografts. Photoacoustic imaging could visually display the intensity of the red photoacoustic signal in the tumor region, providing a more intuitive imaging modality for targeted molecular imaging. This study presents a potential multimodal contrast agent for the accurate diagnosis and assessment of prostate cancer.

Radioguided Surgery for Meckel Diverticulum: Nuclear Medicine Aspects

We present the case of a 13-year-old boy with bleeding complications from a Meckel diverticulum (MD), which was scintigraphically confirmed. A first exploratory laparoscopy was unsuccessful in identifying the diverticulum. A new Tc-pertechnetate scintigraphy (including SPECT/CT), 3 years later, suggested the anatomical location and was helpful during the surgical exploration for the MD by radioguided surgery. Radioguidance is helpful in pathologies characterized by small size or variable anatomical location. A MD with ectopic gastric mucosa can be distinguished from the rest of the small bowel based on selective Tc-pertechnetate uptake in the gastric mucosa, with limited background activity.

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

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

Navigating systemic therapy for metastatic castration-naïve prostate cancer

INTRODUCTION

The last decade has seen a remarkable shift in the treatment landscape of advanced prostate cancer, none more so than in the management of metastatic castration-naïve disease.

METHODS

This narrative review will examine existing and emerging evidence supporting systemic therapy use for metastatic castration-naïve prostate cancer (mCNPC) and provide guidance on the selection of these agents with respect to optimising patient outcomes.

RESULTS

The addition of either docetaxel (chemohormonal approach) or an AR pathway inhibitor (abiraterone, enzalutamide or apalutamide) is a reasonable standard of care option for men commencing long-term ADT for mCNPC. While the issue of disease volume as a predictive biomarker for docetaxel benefit has previously been debated, recent data support consideration of upfront docetaxel in all patients, regardless of metastatic burden. Decisions regarding systemic treatment for men with mCNPC should be based on comprehensive consideration of disease, patient and logistical factors. Multiple novel therapeutics for mCNPC are currently under active investigation.

CONCLUSION

The introduction of potent systemic therapy earlier in the mCNPC disease course has resulted in dramatic improvements in clinical outcomes for patients. As the management of mCNPC continues to evolve, the future remains promising, with the expectation of ongoing improvements to patient outcomes and quality of life.

PSMA-targeting agents for radio- and fluorescence-guided prostate cancer surgery

Despite recent improvements in imaging and therapy, prostate cancer (PCa) still causes substantial morbidity and mortality. In surgical treatment, incomplete resection of PCa and understaging of possible undetected metastases may lead to disease recurrence and consequently poor patient outcome. To increase the chance of accurate staging and subsequently complete removal of all cancerous tissue, prostate specific membrane antigen (PSMA) targeting agents may provide the surgeon an aid for the intraoperative detection and resection of PCa lesions. Two modalities suitable for this purpose are radionuclide detection, which allows sensitive intraoperative localization of tumor lesions with a gamma probe, and fluorescence imaging, allowing tumor visualization and delineation. Next to fluorescence, use of photosensitizers may enable intraoperative targeted photodynamic therapy to eradicate remaining tumor lesions. Since radiodetection and optical imaging techniques each have their own strengths and weaknesses, a combination of both modalities could be of additional value. Here, we provide an overview of recent preclinical and clinical advances in PSMA-targeted radio- and fluorescence-guided surgery of PCa.

Recent advances in nuclear and hybrid detection modalities for image-guided surgery

Introduction: Radioguided surgery is an ever-evolving part of nuclear medicine. In fact, this nuclear medicine sub-discipline actively bridges non-invasive molecular imaging with surgical care. Next to relying on the availability of radio- and bimodal-tracers, the success of radioguided surgery is for a large part dependent on the imaging modalities and imaging concepts available for the surgical setting. With this review, we have aimed to provide a comprehensive update of the most recent advances in the field. Areas covered: We have made an attempt to cover all aspects of radioguided surgery: 1) the use of radioisotopes that emit γ, β⁺, and/or β^- radiation, 2) hardware developments ranging from probes to 2D cameras and even the use of advanced 3D interventional imaging solutions, and 3) multiplexing solutions such as dual-isotope detection or combined radionuclear and optical detection. Expert opinion: Technical refinements in the field of radioguided surgery should continue to focus on supporting its implementation in the increasingly complex minimally invasive surgical setting, e.g. by accommodating robot-assisted laparoscopic surgery. In addition, hybrid concepts that integrate the use of radioisotopes with other image-guided surgery modalities such as fluorescence or ultrasound are likely to expand in the future.

Dual-time-point 64 Cu-PSMA-617-PET/CT in patients suffering from prostate cancer

Regardless of its high positron energy, ⁶⁸ Ga-labeled PSMA ligands have become standard of care in metabolic prostate cancer imaging. ⁶⁴ Cu, a radionuclide with a much longer half-life (12.7 h), is available for PSMA labeling allowing imaging much later than ⁶⁸ Ga. In this study, the diagnostic performance of ⁶⁴ Cu-labeled PSMA was compared between early and late scans. Sixteen men (median age: 70 y) with prostate cancer in different stages underwent ⁶⁴ Cu-PSMA-617-PET/CT 2 and 22 hours post tracer injection. Pathologic and physiologic uptakes were analyzed for both points of time. Pathologic tracer accumulations occurred in 12 patients. Five patients presented with pathologic uptake in 17 different lymph nodes, two patients showed pathologic bone uptake in nine lesions, and seven patients had pathologic PSMA uptake in eight prostatic lesions. Physiologic uptake of the renal parenchyma, urine bladder, and salivary glands decreased over time, while the physiologic uptake of liver and bowel increased. In the present study, ⁶⁴ Cu-PSMA-617-PET demonstrated to be feasible for imaging prostate cancer for both the primary tumor site and metastases. Later imaging showed no additional, clinically relevant benefit compared with the early scans. At least the investigated time points we chose did not vindicate the additional expenditure.

PSMA-Targeted Radiopharmaceuticals for Imaging and Therapy

As described in more detail in other contributions in this issue of Seminars in Nuclear Medicine, prostate-specific membrane antigen (PSMA) has become one of the most promising molecular targets in nuclear medicine. Due to its overexpression on prostate cancer cells in proportion to the stage and grade of tumour progression, especially in androgen-independent, advanced and metastatic disease, various tracers for the detection and treatment of prostate cancer by means of radioligand imaging, radioligand therapy or radioguided surgery have been developed and transferred to clinical applications. Even though monoclonal antibodies were investigated and introduced as first PSMA-targeted probes, the inherent advantage of fast tumour uptake and rapid excretion of small molecules has shifted the research focus during the last decade to low molecular weight inhibitors with high affinity to PSMA, such as [¹⁸F]FDCFPyL, [¹⁸F]PSMA-1007, [⁶⁸Ga]PSMA-HBED, [¹⁷⁷Lu]PSMA-617, [¹⁷⁷Lu]PSMA-I&T, [^99mTc]MIP-1404 or [^99mTc]PSMA I&S, to mention only a few. Due to the plethora of such PSMA probes described during the last years, this review aims to give an overview over the specific characteristics of those radiopharmaceuticals that have already found widespread clinical application. In addition, recently introduced concepts such as PSMA-tracers with increased plasma protein binding, are discussed.

177Lu-PSMA radioligand therapy of predominant lymph node metastatic prostate cancer

¹⁷⁷Lu-PSMA radioligand therapy (LuPRLT) is mainly used for patients with metastatic castration-resistant prostate cancer who are resistant to established drugs. This study describes LuPRLT, either LuPSMA I&T or LuPSMA RLT-617, for 45 patients with predominant lymph node metastatic prostate cancer (LNM PC). Thirty-five patients had LNM and ten patients had LNM and one or two bone metastases. Before LuPRLT, the patients had prostate specific antigen (PSA) of median 18 µg/l (interquartile range (IQR): 3.3–39). LuPRLT was given with a cumulative injected ¹⁷⁷Lu activity of median 14.5 GBq (IQR: 12.2–20.4). Maximum percentage decline of PSA was median 92% (IQR: 70–99). Thirty-five patients with only LNM had a better overall survival (OS) than ten patients with LNM and one or two bone metastases. Thirty-three docetaxel-naïve patients had a longer PSMA PET/CT progression-free survival than twelve patients who were resistant to docetaxel. Twenty-two patients who received LuPRLT with a cumulative injected ¹⁷⁷Lu activity ≥ 14.8 GBq had a better PSMA PET/CT progression-free survival than 23 patients who received LuPRLT with a lower cumulative injected ¹⁷⁷Lu activity. Seventeen patients with relapse after LuPRLT who received rechallenge LuPRLT or ActPRLT had a better OS than five patients who received other forms for relapse treatment. LuPRLT gave mild and transitory adverse effects. The findings of the present study suggest that LuPRLT of patients with LNM may be effective and safe. The promising results motivate randomized phase II trials to further quantify the impact of LuPRLT as treatment of patients with LNM.

Precision prostate cancer surgery: an overview of new technologies and techniques

Over the past few years several new technologies have become available for the management of PCa. The implementation of robotic surgery allowed an unprecedented refinement of surgical techniques, and the RARP procedure is constantly evolving. Nowadays research is mainly focused towards a "tailored" case-specific surgical approach that might allow to achieve PCa control while preserving urinary continence and erectile function. Therefore, in contemporary urology era, several new tools have been introduced to optimize surgical planning, to aid surgical navigation, and to refine surgical execution. In this non-systematic review emerges that a better imaging technique in the preoperative setting can facilitate surgical planning. Moreover, in the intraoperative setting, new tools for image-guided surgical navigation are promising and will allow real time understanding of surgical anatomy. In the next future, a more personalized approach for the minimally invasive surgical treatment of PCa will be available, and the achievement of the best oncological and functional outcomes will be obtained.

Updates in Urologic Robot Assisted Surgery

Modern robotics is an advanced minimally invasive technology with the advantages of wristed capability, three-dimensional optics, and tremor filtration compared with conventional laparoscopy. Urologists have been early adopters of robotic surgical technology: robotics have been used in urologic oncology for more than 20 years and there has been an increasing trend for utilization in benign urologic pathology in the last couple of years. The continuing development and interest in robotics are aimed at surgical efficiency as well as patient outcomes. However, despite its advantages, improvements in haptics, system size, and cost are still desired. This article explores the current use of robotics in urology as well as future improvements on the horizon.

Synthesis and Preclinical Characterization of the PSMA-Targeted Hybrid Tracer PSMA-I&F for Nuclear and Fluorescence Imaging of Prostate Cancer

The prostate-specific membrane antigen (PSMA)–targeted radiotracers ⁶⁸Ga/¹⁷⁷Lu-PSMA-I&T and ^99mTc-PSMA-I&S (for imaging and surgery) are currently successfully used for clinical PET imaging, radionuclide therapy, and radioguided surgery of metastatic prostate cancer. To additionally exploit the high sensitivity and spatial resolution of fluorescence imaging for improved surgical guidance, a PSMA-I&T–based hybrid tracer, PSMA-I&F (DOTAGA-k(Sulfo-Cy5)-y-nal-k-Sub-KuE), has been developed and evaluated. Methods: The in vitro PSMA-targeting efficiency of PSMA-I&F, the reference PSMA-I&T, and their corresponding ^natGa-/⁶⁸Ga- and ^natLu/¹⁷⁷Lu counterparts was determined in LNCaP cells via competitive binding assays (IC₅₀) and dual-tracer radioligand and fluorescence internalization studies. Biodistribution and small-animal PET imaging studies were performed in CB17 SCID and LNCaP xenograft–bearing SHO mice, respectively, and complemented by intraoperative far-red fluorescence imaging using a clinical laparoscope. Additionally, fully automated serial cryosectioning and fluorescence imaging of 1 tumor-bearing animal as well as PSMA immunohistochemistry and fluorescence microscopy of organ cryosections (tumor, kidney, spleen) were also performed. Results: Compared with the parent PSMA-I&T analogs, the PSMA affinities of PSMA-I&F and its ^natGa-/^natLu-complexes remained high and unaffected by dye conjugation (7.9 < IC₅₀ < 10.5 nM for all ligands). The same was observed for the internalization of ⁶⁸Ga- and ¹⁷⁷Lu-PSMA-I&F. In vivo, blood clearance of ⁶⁸Ga- and ¹⁷⁷Lu-PSMA-I&F was only slightly delayed by high plasma protein binding (94%–95%), and very low accumulation in nontarget organs was observed already at 1 h after injection. Dynamic PET imaging confirmed PSMA-specific (as demonstrated by coinjection of 2-PMPA) uptake into the LNCaP xenograft (4.5% ± 1.8 percentage injected dose per gram) and the kidneys (106% ± 23 percentage injected dose per gram). Tumor-to-background ratios of 2.1, 5.2, 9.6, and 9.6 for blood, liver, intestines, and muscle, respectively, at 1 h after injection led to excellent imaging contrast in ⁶⁸Ga-PSMA-I&F PET and in intraoperative fluorescence imaging. Furthermore, fluorescence imaging of tissue cryosections allowed high-resolution visualization of intraorgan PSMA-I&F distribution in vivo and its correlation with PSMA expression as determined by immunohistochemistry. Conclusion: Thus, with its high PSMA-targeting efficiency and favorable pharmacokinetic profile, ⁶⁸Ga/¹⁷⁷Lu-PSMA-I&F serves as an excellent proof-of-concept compound for the general feasibility of PSMA-I&T–based hybrid imaging. The PSMA-I&T scaffold represents a versatile PSMA-targeted lead structure, allowing relatively straightforward adaptation to the different structural requirements of dedicated nuclear or hybrid imaging agents.

Performance of 111In-labelled PSMA ligand in patients with nodal metastatic prostate cancer: correlation between tracer uptake and histopathology from lymphadenectomy

PURPOSE

Intraoperative identification of lymph node (LN) metastases (LNM) detected on preoperative PSMA PET/CT may be facilitated by PSMA radioguided surgery with the use of a gamma probe. We evaluated the uptake of ¹¹¹In-labelled PSMA ligand DKFZ-617 (referred to as ¹¹¹In-PSMA-617) in unaffected LN and LNM at the level of single LN.

METHODS

Six patients with prostate cancer (PCa) with suspicion of LNM on preoperative PSMA PET/CT underwent ¹¹¹In-PSMA-617-guided lymphadenectomy (LA; four salvage LA and two primary LA). ¹¹¹In-PSMA-617 (109 ± 5 MBq). was injected Intravenously 48 h prior to surgery Template LAs were performed in small subregions: common, external, obturator and internal iliac vessels, and presacral and retroperitoneal subregions (n = 4). Samples from each subregion were isolated aiming at the level of single LN. Uptake was measured ex situ using a germanium detector. Receiver operating characteristic (ROC) analysis was performed based on ¹¹¹In-PSMA-617 uptake expressed as standardized uptake values normalized to lean body mass (SUL).

RESULTS

Overall 310 LN (mean 52 ± 19.7) were removed from 74 subregions (mean 12 ± 3.7). Of the 310 LN, 35 turned out to be LNM on histopathology. Separation of the samples from all subregions resulted in 318 single specimens: 182 PCa-negative LN samples with 275 LN, 35 single LNM samples, 3 non-nodal PCa tissue samples and 98 fibrofatty tissue samples. The median SULs of nonaffected LN (0.16) and affected LN (13.2) were significantly different (p < 0.0001). Based on 38 tumour-containing and 182 tumour-free specimens, ROC analysis revealed an area under the curve of 0.976 (95% CI 0.95-1.00, p < 0.0001). Using a SUL cut-off value of 1.136, sensitivity, specificity, positive predictive value, negative predictive value and accuracy in discriminating affected from nonaffected LN were 92.1% (35/38), 98.9% (180/182), 94.6% (35/37), 98.4% (180/183) and 97.7% (215/220), respectively.

CONCLUSION

Ex situ analysis at the level of single LN showed that ¹¹¹In-PSMA-617 had excellent ability to discriminate between affected and nonaffected LN in our patients with PCa. This tracer characteristic is a prerequisite for in vivo real-time measurements during surgery.

PSMA-PET guided hook-wire localization of nodal metastases in prostate cancer: a targeted approach

Prostate Specific Membrane Antigen Positron Emission Tomography/Computed Tomography (PSMA-PET/CT) has increased the sensitivity and specificity of imaging to identify metastatic prostate cancer in the group of patients with early biochemical recurrence when compared to conventional imaging. In patients who develop biochemical recurrence of prostate cancer following surgical resection, salvage lymph node dissection may reduce prostate specific antigen (PSA) levels and delay the time for commencement of systemic therapies. However, PLND may be an anatomically and technically difficult procedure, particularly with small metastatic diseases which can be problematic for intra-operative identification. We describe the technique using PSMA-PET imaging to pre-operatively localise areas of low-volume nodal metastatic disease with hookwire to allow targeted lymph node dissection with direct visualisation and palpation to ensure adequate clearance of involved nodes.