Lutetium-177-labelled anti-prostate-specific membrane antigen antibody and ligands for the treatment of metastatic castrate-resistant prostate cancer: a systematic review and meta-analysis

Construction of truncated PSMA as a PET reporter gene for CAR T cell trafficking

In solid tumors, there are multiple barriers for a chimeric antigen receptor (CAR) T cell to surmount in order to reach the tumor site. For better understanding whether CAR T cells effectively infiltrate into tumor site, and simultaneously, whether there are off-target effects, real-time monitoring technologies need to be established. Cell-based positron emission tomography reporter genes have been developed to monitor engineered cells in living subjects. In this study, we reported the construction of a novel reporter gene truncated prostate-specific membrane antigen (ΔPSMA) pending for monitoring CAR T cells using 68Ga-PSMA-617 and a method for tracking the distribution of CAR T cells in vivo was developed. Data were provided to demonstrate that ΔPSMA was predominantly localized on the plasma membrane and could take up 68Ga-PSMA-617 in vitro in a time-dependent manner. And the expression of ΔPSMA did not affect CAR expression and cytolytic capacity of CAR T cells. CAR-ΔPSMA T cell xenografts in nude mice were clearly imaged by positron emission tomography 60 min after injection of 68Ga-PSMA-617. PSMA paired with 68Ga-PSMA-617 was capable of identifying approximately 1 × 104 engineered CAR T cells. The ability to image small numbers of CAR T cells in vivo would be helpful to accelerate the translation of cell-based therapies into the clinic, and it may reinforce our understanding of treatment success, failure, and toxicity.

Nuclear Medicine and Cancer Theragnostics: Basic Concepts

Cancer theragnostics is a novel approach that combines diagnostic imaging and radionuclide therapy. It is based on the use of a pair of radiopharmaceuticals, one optimized for positron emission tomography imaging through linkage to a proper radionuclide, and the other bearing an alpha- or beta-emitter isotope that can induce significant damage to cancer cells. In recent years, the use of theragnostics in nuclear medicine clinical practice has increased considerably, and thus investigation has focused on the identification of novel radionuclides that can bind to molecular targets that are typically dysregulated in different cancers. The major advantages of the theragnostic approach include the elimination of multi-step procedures, reduced adverse effects to normal tissues, early diagnosis, better predictive responses, and personalized patient care. This review aims to discuss emerging theragnostic molecules that have been investigated in a series of human malignancies, including gliomas, thyroid cancer, neuroendocrine tumors, cholangiocarcinoma, and prostate cancer, as well as potent and recently introduced molecular targets, like cell-surface receptors, kinases, and cell adhesion proteins. Furthermore, special reference has been made to copper radionuclides as theragnostic agents and their radiopharmaceutical applications since they present promising alternatives to the well-studied gallium-68 and lutetium-177.

Prognostic role of early prostate specific antigen changes after [177 Lu]Lu-PSMA radioligand therapy of metastasized prostate cancer: A meta-analysis

BACKGROUND

Approximately 10%-20% of prostate cancers progress to metastatic and castration-resistant forms (mCRPC). Radioligand (RLT) therapy with [177 Lu]Lu-prostate-specific membrane antigen (PSMA) is an emerging treatment for metastasized mCRPC and its efficacy is assessed not only but also by prostate specific antigen (PSA) measurement after 12 weeks or more after treatment. Our aim was to evaluate the role of early PSA measurement after RLT in predicting overall survival (OS) of mCRPC patients.

METHODS

A systematic search on PubMed, Web Of Science and Scopus was performed from January to December 2022. PRISMA guidelines for prognostic studies was adopted. Risk of bias was assessed using quality of prognostic studies (QUIPS).

RESULTS

Twelve studies at low-intermediate risk of bias, were included in the meta-analysis (1646 patients, mean age 70 years). About 50% of patients showed a PSA decline after 1-2 of [177 Lu]Lu-PSMA, and more than 30% reported a PSA decline ≥50%. The median OS range for patients with any PSA decline was 13-20 months, while for patients with stable or increased PSA, the median OS fell to 6-12 months. The OS rate for a PSA decline after the one-two [177 Lu]Lu-PSMA cycles was 0.39 (95% CI: 0.31-0.50), while OS for a PSA decline ≥50% was 0.69 (95% CI: 0.57-0.83).

CONCLUSIONS

A PSA decline is observed in almost 50% of mCRPC patients after 1-2 [177 Lu]Lu-PSMA cycles, with a significantly longer OS compared to stable or increased PSA levels, respectively. Accordingly, any PSA decline after 1-2 cycles of therapy should be regarded as a favourable prognostic factor for OS.

Adoption of Lutetium-177 PSMA radioligand therapy for metastatic castration resistant prostate cancer: a total population analysis in Germany from 2016 to 2020

PURPOSE

This study is to investigate the adoption and current trends of Lutetium-177 PSMA RLT for mCRPC in Germany.

METHODS

We analyzed data from the reimbursement.INFO tool based on German hospitals' quality reports for Lutetium-177 PSMA RLT from 2016 to 2020 and from the nationwide German hospital billing database (Destatis) for general therapy with open radionuclides in combination with prostate cancer from 2006 to 2020. For validation of these billing data, we included the 177Lu-PSMA RLT cycles from two participating institutions from 2016 to 2020. For detection of trends over time we applied linear regression models.

RESULTS

General therapy with open radionuclides increased from 2006 to 2020. We identified a total of 12,553 177Lu-PSMA RLT cycles. The number of 177Lu-PSMA RLTs steadily increased from a total of 1026 therapies in 2016 to 3328 therapies in 2020 (+ 576 RLT/year; p < 0.005). In 2016, 25 departments of nuclear medicine offered this treatment, which increased to 44 nuclear medicine departments in 2020. In 2016, 16% of nuclear medicine departments (4/25) performed more than 100 177Lu-PSMA RLTs, which increased to 36% (16/44) in 2020 (p < 0.005). In 2016, 88% (22/25) of 177Lu-PSMA RLTs were performed at a university hospital, which decreased to 70% (31/44) in 2020. The proportion of patients older than 65 years receiving 177Lu-PSMA RLT increased from 78% in 2016 to 81% in 2020.

CONCLUSION

Treatment of mCRPC with 177Lu-PSMA RLT has been rapidly increasing in Germany in the recent years providing an additional therapy option. This development is remarkable, because of outstanding formal EMA approval.

Response to [ 177 Lu]Lu-PSMA radioligand therapy in metastatic castration-resistant prostate cancer patients presenting with only lymph node metastases

OBJECTIVE

[ 177 Lu]Lu-PSMA radioligand therapy (PSMA-RLT) is a promising therapy for patients with metastatic castration-resistant prostate cancer (mCRPC) and offers a survival benefit particularly to patients with only lymph node metastases. We therefore sought to evaluate the clinical outcome of this therapy in such a cohort.

METHODS

Of all prostate cancer patients admitted to our department between September 2015 and March 2019 to receive 1-4 courses of PSMA-RLT (each course consisted of three cycles of highly standardized PSMA-RLT every 4 weeks), only 10 consecutive men were found to have nodal metastases only and were analyzed retrospectively.

RESULTS

Nine out of 10 patients responded to their first PSMA-RLT course with a mean prostate-specific antigen (PSA) decline of 71.8 ± 25.2%, seven of them demonstrated a PSA decline of ≥50%. Collectively, seven of eight patients responded to further PSMA-RLT courses with a total PSA reduction of 59.8 ± 30.0%, five of which showed a PSA reduction of ≥50%. One patient experienced complete remission. Median progression-free survival was 85 weeks (range 14-255 weeks) and median overall survival was not reached during the median observation time of 209 weeks (30-298 weeks). Univariate Cox-regression identified initial PSA decline as the only predictive parameter for progression-free survival ( P = 0.047).

CONCLUSION

mCRPC patients with only lymph node metastases showed favorable survival and excellent response to PSMA-RLT, leading to transient partial remission of the disease in most of them.

Stability matters: Radiochemical stability of therapeutic radiopharmaceutical of 177Lu-PSMA-I&T

Labelling radiopharmaceuticals and testing the quality of the labelled product before injecting it into patients are standard operating procedures in the Nuclear Medicine department. There is a different shelf life for each labelled product, which determines how long a product can maintain in-vitro stability before it needs to be discarded. Lutetium-177 (¹⁷⁷Lu) is a radioactive isotope that is increasingly being accepted into the treatment paradigm for palliation of advanced-stage tumours, including metastatic castration-resistant prostate cancer (mCRPC) and neuroendocrine tumours (NET). In our institution, synthesis of ¹⁷⁷Lu with prostate-specific membrane antigen imaging and therapy (PSMA-I & T) for palliation of mCRPC is performed on Eckert & Ziegler Eurotope's Modular-Lab Pharm Tracer® automated synthesis system. Sterile GMP-certified no-carrier-added ¹⁷⁷Lu is supplied by Australia's Nuclear Science and Technology Organization (ANSTO). Following each synthesis, the final product quality is evaluated by High-performance liquid chromatography (HPLC) and instant thin-layer chromatography (ITLC) at three different time points: 0 hours, 24 hours, and 48 hours. Between February 2020 to October 2020, the quality of 35 batches of ¹⁷⁷Lu-PSMA-I & T was evaluated. The average radiochemical purity of ITLC-SG was found to be greater than 99 percent (99.70±05%), and HPLC was greater than 98 percent (98.60±0.05%). Our findings demonstrate that automated synthesis of ¹⁷⁷Lu-PSMA-I & T with Eckert & Ziegler Eurotope's Modular-Lab Pharm Tracer® can remain stable for 48 hours post labelling.

Update of PSMA Theranostics in Prostate Cancer: Current Applications and Future Trends

There is now an increasing trend for targeting cancers to go beyond early diagnosis and actually improve Progression-Free Survival and Overall Survival. Identifying patients who might benefit from a particular targeted treatment is the main focus for Precision Medicine. Radiolabeled ligands can be used as predictive biomarkers which can confirm target expression by cancers using positron emission tomography (PET). The same ligand can subsequently be labeled with a therapeutic radionuclide for targeted radionuclide therapy. This combined approach is termed “Theranostics”. The prostate-specific membrane antigen (PSMA) has emerged as an attractive diagnostic and therapeutic target for small molecule ligands in prostate cancer. It can be labeled with either positron emitters for PET-based imaging or beta and alpha emitters for targeted radionuclide therapy. This review article summarizes the important concepts for Precision Medicine contributing to improved diagnosis and targeted therapy of patients with prostate cancer and we identify some key learning points and areas for further research.

Predictors and Real-World Use of Prostate-Specific Radioligand Therapy: PSMA and Beyond

PSMA is a transmembrane protein that is markedly overexpressed in prostate cancer, making it an excellent target for imaging and treating patients with prostate cancer. Several small molecule inhibitors and antibodies of PSMA have been radiolabeled for use as therapeutic agents and are currently under clinical investigation. PSMA-based radionuclide therapy is a promising therapeutic option for men with metastatic prostate cancer. The phase II TheraP study demonstrated superior efficacy, lower side effects, and improved patient-reported outcomes compared with cabazitaxel. The phase III VISION study demonstrated that radionuclide therapy with β-emitter ¹⁷⁷Lu-PSMA-617 can prolong survival and improve quality of life when offered in addition to standard-of-care therapy in men with PSMA-positive metastatic castration-resistant prostate cancer whose disease had progressed with conventional treatments. Nevertheless, up to 30% of patients have inherent resistance to PSMA-based radionuclide therapy, and acquired resistance is inevitable. Hence, strategies to increase the efficacy of PSMA-based radionuclide therapy have been under clinical investigation. These include better patient selection; increased radiation damage delivery via dosimetry-based administered dose or use of α-emitters instead of β-emitters; or using combinatorial approaches to overcome radioresistance mechanisms (innate or acquired), such as with novel hormonal agents, PARP inhibitors, or immunotherapy.

Targeting PSMA Revolutionizes the Role of Nuclear Medicine in Diagnosis and Treatment of Prostate Cancer

Targeting the prostate-specific membrane antigen (PSMA) protein has become of great clinical value in prostate cancer (PCa) care. PSMA positron emission tomography/computed tomography (PET/CT) is increasingly used in initial staging and restaging at biochemical recurrence in patients with PCa, where it has shown superior detection rates compared to previous imaging modalities. Apart from targeting PSMA for diagnostic purposes, there is a growing interest in developing ligands to target the PSMA-protein for radioligand therapy (RLT). PSMA-based RLT is a novel treatment that couples a PSMA-antibody to (alpha or beta-emitting) radionuclide, such as Lutetium-177 (177Lu), to deliver high radiation doses to tumor cells locally. Treatment with 177Lu-PSMA RLT has demonstrated a superior overall survival rate within randomized clinical trials as compared to routine clinical care in patients with metastatic castration-resistant prostate cancer (mCRPC). The current review provides an overview of the literature regarding recent developments in nuclear medicine related to PSMA-targeted PET imaging and Theranostics.

[Interdisciplinary expert consensus on innovations in imaging diagnostics and radionuclide-based therapies for advanced prostate cancer]

BACKGROUND

Numerous diagnostic and therapeutic innovations in the treatment of advanced prostate cancer, both in the hormone-sensitive and in the castration-resistant situation, recently led to a new orientation in the management of this tumor. However, there are potential indications beyond the ones covered by the S3 guideline on early detection, diagnosis and therapy of prostate cancer in clinical care that might be helpful for patients.

OBJECTIVES

Since July 2018, an interdisciplinary group of experts from nuclear medicine, radiologists, radio-oncologists and urologists developed a consensus paper on state-of-the-art innovations in imaging diagnostics and radionuclide-based therapies for advanced prostate cancer.

CONCLUSIONS

Provided by the working group are suggestions and strategies to improve the implementation of new imaging techniques such as multiparametric magnetic resonance imaging (mpMRI), PSMA-PET/CT (prostate-specific membrane antigen-positron emission tomography/computed tomography) and innovative therapeutic options (radium-223 dichloride, lutetium-177-PSMA) in the complex treatment of metastatic castration-resistant prostate cancer (mCRPC).

Should Lutetium-prostate specific membrane antigen radioligand therapy for metastatic prostate cancer be used earlier in men with lymph node only metastatic prostate cancer?

PURPOSE

Lutetium labelled prostate-specific membrane antigen radioligand therapy (Lu-PSMA RLT) has shown pleasing early results in management of high-volume metastatic castration resistant prostate cancer (mCRPC), but its role in the early treatment of men with only lymph node metastasis (LNM) is unknown. The aim was to assess the outcome of Lu-PSMA RLT earlier in the treatment of men with only LNM.

MATERIALS AND METHODS

Single institution retrospective review of men with only LNM on staging Ga-PSMA PET PSMA who proceeded with Lu-PSMA RLT.

RESULTS

There were 17 men with only LNM, including 13 with mCRPC and 3 who were both hormone and chemotherapy naïve. The median PSA was 3.7 (0.46-120 ng/mL). A PSA decline of ≥50% occurred in 10/17 (58.8%), decreasing to <0.2 ng/mL in 35.3% (6/17). The PSA continues to decline or remain stable in 10/17 (58.8%) with a median follow-up of 13 months, and 8/17 (47.1%) have not reached their pre-treatment levels. There were no significant side effects. There was a better PSA response in men without prior chemotherapy (p=0.05). The prostate cancer specific and overall survival is 82.4% (14/17).

CONCLUSIONS

Our results identify improved PSA response to Lu-PSMA RLT in men with only LNM, especially in the chemotherapy naïve cohort, compared to previous series with more advanced mCRPC. These findings provide important proof of principle to aid with planning of future prospective randomized trials evaluating the role of Lu-PSMA RLT earlier in the management of node metastatic prostate cancer, including men naïve of ADT and chemotherapy.

Evaluation of [68Ga]Ga-PSMA PET/CT for therapy response assessment of [177Lu]Lu-PSMA radioligand therapy in metastasized castration refractory prostate cancer and correlation with survival

PURPOSE

The aim of this retrospective study was to evaluate the use of [68Ga]Ga-PSMA PET/CT in therapy response assessment (TRA) of mCRPC patients treated with [177Lu]Lu-PSMA-617 and its correlation with overall survival (OS).

METHODS

Thirty-nine patients were included in the study. Patient-/lesion-based early and late response assessment (ERA/LRA) was defined as PET2 (after two therapy cycles) vs. PET1 (before the first cycle) (n = 29) and end of treatment PET vs. PET1 (n = 17), respectively. PET-based response (PET parameters; modified (m) PERCIST/EORTC), biochemical response (ΔPSA; category-based) and category-based clinical response (CRA) was tested for correlation/agreement. PET-based TRA was correlated with OS.

RESULTS

A significant correlation/agreement was shown between PET parameters and CRA as well as biochemical response in LRA of all lesions and between mPERCIST-based and category-based PSA response assessment in LRA (bone lesion-based, P = 0.045, κ = 0.184). At ERA, OS was significantly higher in CR/PR/SD compared to progressive disease applying mPERCIST/EORTC criteria (P = 0.0024).

CONCLUSION

In [177Lu]Lu-PSMA-617-treated mCRPC patients OS of the group of CR/PR/SD was significantly higher compared to the progressive disease group (mPERCIST/EORTC) in ERA. Therefore, [68Ga]Ga-PSMA PET might serve as a complementary diagnostic tool for TRA offering prognostic value regarding OS.

Radioimmunotherapy for solid tumors: spotlight on Glypican-1 as a radioimmunotherapy target

Radioimmunotherapy (i.e., the use of radiolabeled tumor targeting antibodies) is an emerging approach for the diagnosis, therapy, and monitoring of solid tumors. Often using paired agents, each targeting the same tumor molecule, but labelled with an imaging or therapeutic isotope, radioimmunotherapy has achieved promising clinical results in relatively radio-resistant solid tumors such as prostate. Several approaches to optimize therapeutic efficacy, such as dose fractionation and personalized dosimetry, have seen clinical success. The clinical use and optimization of a radioimmunotherapy approach is, in part, influenced by the targeted tumor antigen, several of which have been proposed for different solid tumors. Glypican-1 (GPC-1) is a heparan sulfate proteoglycan that is expressed in a variety of solid tumors, but whose expression is restricted in normal adult tissue. Here, we discuss the preclinical and clinical evidence for the potential of GPC-1 as a radioimmunotherapy target. We describe the current treatment paradigm for several solid tumors expressing GPC-1 and suggest the potential clinical utility of a GPC-1 directed radioimmunotherapy for these tumors.

177Lu-PSMA Radioligand Therapy Is Favorable as Third-Line Treatment of Patients with Metastatic Castration-Resistant Prostate Cancer. A Systematic Review and Network Meta-Analysis of Randomized Controlled Trials

In this systematic review and network meta-analysis (NMA), we aimed to assess the benefits and harms of third-line (L3) treatments in randomized controlled trials (RCTs) of patients with metastatic castration-resistant prostate cancer (mCRPC). Two reviewers searched for publications from 1 January 2006 to 30 June 2021. The review analyzed seven RCTs that included 3958 patients and eight treatments. Treatment with prostate-specific membrane antigen (PSMA)-based radioligand therapy (PRLT) resulted in a 1.3-times-higher rate of median PSA decline ≥50% than treatment with abiraterone, enzalutamide, mitoxantrone, or cabazitaxel (p = 0.00001). The likelihood was 97.6% for PRLT to bring about the best PSA response, out of the examined treatments. PRLT resulted in a 1.1-times-higher six-month rate of median radiographic progression-free survival. Treatment with PRLT in the VISION trial resulted in 1.05-times-higher twelve-month median overall survival than L3 treatment with cabazitaxel in other RCTs. PRLT more often resulted in severe thrombocytopenia and less often in severe leukopenia than did cabazitaxel. In conclusion, for patients with mCRPC, L3 treatment with PRLT is highly effective and safe.

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

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

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

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

Streamlined Schemes for Dosimetry of 177Lu-Labeled PSMA Targeting Radioligands in Therapy of Prostate Cancer

Simple Summary

In patients with progressive metastasized castration-resistance prostate cancer PSMA radioligand therapies have shown promising results regarding clinical safety and efficacy. Dosimetry is mandatory due to legal regulations and also required for the estimation of doses to organs at risk allowing for individual tailoring of treatment in PSMA-RLT. Due to those factors and the often poor health status of patients which restricts intense dosimetric imaging protocols, there is a clear need for simplified dosimetric approaches in mCRPC patients treated with [¹⁷⁷Lu]Lu-PSMA-617. In this study, we evaluated different dosimetric methodologies and found that a streamlined dosimetric approach is feasible and valid. This approach is based on single time-point imaging at 48 h p.i. in cycle 2 to 6 taking into account kinetic results of a full dosimetric scheme performed only in cycle1. These results might have a relevant impact on patients handling regarding dosimetry during [¹⁷⁷Lu]Lu-PSMA-617 radioligand therapy.

Abstract

(Background) Aim of this retrospective analysis was to investigate in mCRPC patients treated with [¹⁷⁷Lu]Lu-PSMA-617 whether the absorbed dose (AD) in organs at risk (OAR, i.e., kidneys and parotid glands) can be calculated using simplified methodologies with sufficient accuracy. For this calculation, results and kinetics of the first therapy cycle were used. (Methods) 46 patients treated with 2 to 6 cycles of [¹⁷⁷Lu]Lu-PSMA-617 were included. As reference (current clinical standard) full dosimetry of the OAR based on quantitative imaging (whole body scintigraphy and quantitative SPECT/CT at 2, 24, 48 and 72 h p.i.) for every cycle was used. Alternatively, two dosimetry schemes, simplified in terms of image acquisition and dose calculation, were established, both assuming nearly unchanged kinetics of the radiopharmaceutical for subsequent cycles. (Results) In general, for both OAR the simplified methods provided results that were consistent with the dosimetric reference method, both per cycle and in terms of cumulative AD. Best results were obtained when imaging was performed at 48 h p.i. in each of the subsequent cycles. However, both simplified methods tended to underestimate the cumulative AD. (Conclusion) Simplified dosimetry schemes are feasible to tailor multi-cycle [¹⁷⁷Lu]Lu-PSMA-targeted therapies.

Theranostics in Nuclear Medicine: Emerging and Re-emerging Integrated Imaging and Therapies in the Era of Precision Oncology

Theranostics refers to the pairing of diagnostic biomarkers with therapeutic agents that share a specific target in diseased cells or tissues. Nuclear medicine, particularly with regard to applications in oncology, is currently one of the greatest components of the theranostic concept in clinical and research scenarios. Theranostics in nuclear medicine, or nuclear theranostics, refers to the use of radioactive compounds to image biologic phenomena by means of expression of specific disease targets such as cell surface receptors or membrane transporters, and then to use specifically designed agents to deliver ionizing radiation to the tissues that express these targets. The nuclear theranostic approach has sparked increasing interest and gained importance in parallel to the growth in molecular imaging and personalized medicine, helping to provide customized management for various diseases; improving patient selection, prediction of response and toxicity, and determination of prognosis; and avoiding futile and costly diagnostic examinations and treatment of many diseases. The authors provide an overview of theranostic approaches in nuclear medicine, starting with a review of the main concepts and unique features of nuclear theranostics and aided by a retrospective discussion of the progress of theranostic agents since early applications, with illustrative cases emphasizing the imaging features. Advanced concepts regarding the role of fluorine 18-fluorodeoxyglucose PET in theranostics, as well as developments in and future directions of theranostics, are discussed. ^©RSNA, 2020 See discussion on this article by Greenspan and Jadvar.

A Systematic Review and Meta-analysis of the Effectiveness and Toxicities of Lutetium-177-labeled Prostate-specific Membrane Antigen-targeted Radioligand Therapy in Metastatic Castration-Resistant Prostate Cancer

CONTEXT

Castration-resistant prostate cancer (CRPC) treatment is an evolving challenge. Prostate-specific membrane antigen (PSMA)-targeted endoradiotherapy/radioligand therapy (PRLT) with small-molecule, urea-based agents labeled with the β-particle-emitting radionuclide lutetium-177 (177Lu) is a promising new approach.

OBJECTIVE

In this systematic review and meta-analysis, we evaluated the efficacy and toxicity of PRLT.

EVIDENCE ACQUISITION

A systematic search was performed in PubMed/Medline (last updated February 18, 2019). A total of 250 studies were reviewed, and 24 studies with 1192 patients were included in the analysis. Proportions of patients with ≥50% serum prostate-specific antigen (PSA) decrease, any PSA decrease, and any PSA increase were extracted. Proportions of patients showing any grade toxicity and those with grade 3/4 toxicities based on Common Terminology Criteria for Adverse Events (CTCAE) grading were extracted from manuscripts. Overall survival and progression-free survival were evaluated. A meta-analysis of single proportions was carried out. Furthermore, we compared the two most common PRLT agents, 177Lu-PSMA with 177Lu-PSMA-I&T, for effectiveness and toxicity.

EVIDENCE SYNTHESIS

Among the 24 included studies, 20 included data on 177Lu-PSMA-617, three included data on 177Lu-PSMA-I&T, and one study had aggregated data for 177Lu-PSMA-617 and 177Lu-PSMA-I&T. The estimated proportion of 177Lu-PSMA-617-treated patients who showed a serum PSA decrease of ≥50% with at least an 8-wk interval between therapy and PSA measurement was 0.44 (0.39; 0.50). Therapy with 177Lu-PSMA-I&T demonstrated an estimated proportion of patients with ≥50% PSA reduction to be 0.36 (0.26; 0.47). The aggregate results for men treated with more than one cycle of any kind of PRLT showed an estimated proportion of 0.46 (0.41; 0.51) for PSA response ≥50%. Regarding aggregate data from all of the PRLT agents, we found that grade 3 and 4 toxicities were uncommon, with estimated proportions from 0.01 (0.00;0.04) for nausea, fatigue, diarrhea, and elevated aspartate transaminase up to 0.08 (0.05; 0.12) for anemia. There was considerable heterogeneity among the studies in the "any-grade toxicity" groups. Meta-regression showed that more than one cycle of PRLT is associated with a greater proportion of patients with ≥50% PSA reduction. Overall survival according to pooled hazard ratios (HRs) for any PSA decline was 0.29 (0.18; 0.46), and for >50% PSA reduction was 0.67 (0.43; 1.07). Progression-free survival according to a pooled HR of >50% PSA reduction was 0.53 (0.32; 0.86).

CONCLUSIONS

The relatively high number of PSA responders alongside the low rate of severe toxicity reflects the potentially promising role of PRLT in treating CRPC. The ultimate utility of this treatment modality will become clearer as multiple prospective studies continue to accrue. In the interim, this systematic review and meta-analysis can serve as a compendium of effectiveness and adverse events associated with PRLT for treating clinicians.

PATIENT SUMMARY

Prostate-specific membrane antigen-targeted endoradiotherapy/radioligand therapy (PRLT) is associated with ≥50% reduction in prostate-specific antigen level in a large number of patients and a low rate of toxicity, reflecting its potential in treating castration-resistant prostate cancer. This systematic review and meta-analysis presents as a compendium of the effectiveness and adverse events related to PRLT for treating clinicians.

PSMA: a game changer in the diagnosis and treatment of advanced prostate cancer

Although management of advanced prostate cancer is evolving, a lot of work remains to be done for patients who have exhausted all options. Molecular targeting of prostate specific membrane antigen (PSMA) is valuable not only for diagnostic but also for therapeutic reasons. PSMA is thus considered to be useful in a theranostic approach. PSMA scans are upcoming diagnostic modalities which detect metastatic lesions that are missed by conventional imaging modalities. PSMA ligand therapy is also an upcoming treatment modality that has been proven to be beneficial with minimal toxicity in patients with advanced prostate cancer that have progressed on prior therapy. In this review article, we summarize the current knowledge regarding PSMA diagnostics and PSMA ligand therapies and discuss their implication in the treatment of advanced prostate cancer.

General Concepts in Theranostics

Theranostics describes the pairing of diagnostic biomarkers and therapeutic agents with common specific targets. Nuclear medicine is the greatest theranostics protagonist, relying on radioactive tracers for imaging biologic phenomena and delivering ionizing radiation to the tissues that take up those tracers. The concept has gained importance with the growth of personalized medicine, allowing customized management for diseases, refining patient selection, better predicting responses, reducing toxicity, and estimating prognosis. This work provides an overview of the general concepts of the theranostics approach in nuclear medicine discussing its background, features, and future directions in imaging and therapy.

177Lu-PSMA Therapy in Metastatic Castration-Resistant Prostate Cancer

The aim of this narrative review is to evaluate the current status of 177Lu-PSMA (prostate specific membrane antigen) therapy for metastatic castration-resistant prostate cancer (mCRPC) in the light of the current literature. We also addressed patient preparation, therapy administration and side effect profiles. 177Lu-PSMA therapy efficacy was assessed by using prospective trials, meta-analyses and major retrospective trials. Predictors of efficacy were also mentioned. Although there are some different approaches regarding the use of 177Lu-PSMA therapy in different countries, this type of therapy is generally safe, with a low toxicity profile. From the oncological point of view, a PSA (prostate specific antigen) decline of ≥50% was seen in 10.6-69% of patients with mCRPC; whereas progression-free survival (PFS) was reported to be 3-13.7 months in different studies. Consequently, 177Lu-PSMA therapy is a promising treatment in patients with mCRPC, with good clinical efficacy, even in heavily pretreated patients with multiple lines of systemic therapy. Currently, there are ongoing clinical trials in the United States, including a phase III multicenter FDA registration trial.

Identification, Characterization, and Suppression of Side Products Formed during the Synthesis of [177Lu]Lu-PSMA-617

In recent years, radiolabeled tracers targeting prostate-specific membrane antigen (PSMA) have had a tremendous impact on prostate cancer management. Here, we report on the formation of radioactive impurities formed during the clinical production of ¹⁷⁷Lu-labeled PSMA-617. We provide compelling evidence that these impurities are the result of a spontaneous, thermally mediated condensation reaction of the Glu-CO-Lys moiety resulting in the formation of three different five-membered ring systems. Density functional theory (DFT) calculations show that the condensation and cyclization of the Glu-CO-Lys moiety is thermodynamically spontaneous. In cell experiments, no affinity of these cyclized compounds toward PSMA was observed. HPLC analyses of urine samples from patient studies showed rapid renal excretion of these radioactive cyclized species. Radiolabeling conditions were identified that significantly reduced the formation of cyclized side products yielding ¹⁷⁷Lu-labeled PSMA-617 in high radiochemical yield and purity in concordance with current good manufacturing practice (cGMP) requirements.

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.

Adenoid cystic carcinoma: a review of clinical features, treatment targets and advances in improving the immune response to monoclonal antibody therapy

The natural history of adenoid cystic carcinoma (ACC) is relentless, defined by treatment failure heralded by locoregional recurrence and distant metastatic disease. In this review, we present an update of clinical features, molecular classification, current targeted therapies, immune landscapes and novel treatment targets with their respective clinical trials. The presented results are defined by a lack of overall response rate and limited progression free survival, with restriction to stable disease. In addition, ACC is resistant to immune checkpoint inhibition due to low tumour immunogenicity and lack of PD-L1 expression. Here we present a new prospective research paradigm for ACC, including the potential to target prostate specific membrane antigen (PSMA) and the potential for manipulation of target receptors in the clinic. The presentation of this review aims to promote future research to improve response rates and outcomes for therapeutics undergoing clinical trial in ACC.

Evaluation of [131I]I- and [177Lu]Lu-DTPA-A11 Minibody for Radioimmunotherapy in a Preclinical Model of PSCA-Expressing Prostate Cancer

PURPOSE

Radioimmunotherapy uses tumor-specific antibodies to deliver therapeutic radionuclides, but hematological toxicity due to the long serum half-life of intact antibodies remains a challenge. We evaluated a smaller antibody fragment, the minibody, with faster kinetics and a potentially improved therapeutic index.

PROCEDURES

The anti-prostate stem cell antigen (PSCA) minibody (A11 Mb) was radiolabeled with iodine-124 ([124I]I-A11 Mb) or conjugated with deferoxamine (DFO) and labeled with zirconium-89 ([89Zr]Zr-DFO-A11 Mb) for surrogate immunoPET to profile pharmacokinetics in a human prostate cancer xenograft model. Subsequently, minibodies labeled with two therapeutic beta emitters, directly iodinated [131I]I-A11 Mb (non-residualizing) and 177Lu chelated using DTPA ([177Lu]Lu-DTPA-A11 Mb) (residualizing), were compared for in vitro antigen-specific cytotoxicity. Full biodistribution studies (in 22Rv1-PSCA tumor bearing and hPSCA knock-in mice) were conducted for dosimetry calculations. Finally, the lead candidate [131I]I-A11 Mb was evaluated in a radioimmunotherapy experiment. Escalating single doses (3.7, 11, or 37 MBq) and saline control were administered to 22Rv1-PSCA tumor bearing mice and anti-tumor effects (tumor volume) and toxicity (body weight) were monitored.

RESULTS

Minibodies radiolabeled with therapeutic beta emitters [131I]I-A11 Mb and [177Lu]Lu-DTPA-A11 Mb exhibited comparable tumor cell growth inhibition in vitro. In vivo surrogate immunoPET imaging using [89Zr]Zr-DFO-A11 Mb showed activity retention in liver and kidney up to 72 h, while [124I]I-A11 Mb cleared from liver, kidney, and blood by 48 h. Based on full biodistribution and dosimetry calculations, administering 37 MBq [131I]I-A11 Mb was predicted to deliver a favorable dose to the tumor (35 Gy), with a therapeutic index of 22 (tumor:bone marrow). For [177Lu]Lu-DTPA-A11 Mb, the kidneys would be dose-limiting, and the maximum tolerated activity (7.4 MBq) was not predicted to deliver an effective radiation dose to tumor. Radioimmunotherapy with a single dose of [131I]I-A11 Mb showed dose-dependent tumor inhibition with minimal off-target toxicity and improved median survival (19 and 24 days, P < 0.001) compared with untreated mice (12 days).

CONCLUSIONS

These findings show the potential of the anti-PSCA minibody for targeted radioimmunotherapy with minimal toxicity, and the application of immunoPET and dosimetry for personalized treatment.

Improving quality of life in patients with metastatic prostate cancer following one cycle of 177Lu-PSMA-617 radioligand therapy: a pilot study

INTRODUCTION

 To evaluate the clinical therapeutic response of PSMA targeted radioligand therapy with ¹⁷⁷Lu-PSMA-617 in patients with metastatic castration-resistant prostate cancer. The current study analyzed disease-related quality of life (QoL) in patients undergoing PSMA therapy with a special focus on the association with simultaneous PSA response.

METHODS

 Thirty patients (age range 50-87 years, median 73.5 years) undergoing ¹⁷⁷Lu-PSMA-617 therapy from 2014 to 2016 at our institution were included in this pilot study. Health-related QoL was assessed by EORTC QLQ-C30 questionnaire filled in at baseline and two months after initializing the PSMA-therapy. The treatment response was evaluated under three categories with regard to changes in (a) global health status and other functional scales, (b) disease-related symptoms, and (c) effects of PSA values.

RESULTS

 Most patients underwent three treatment cycles (n = 12); at least 2 cycles (n = 6) or at most 8 cycles (n = 1) were performed. Out of 30 cases, PSA response after the first cycle was observed in 73 % (n = 22). Compared to baseline, QoL was significantly improved at 2-month follow-up revealing increase in global health status (p = 0.025), role functioning (p = 0.017) and emotional functioning (0.010), and decrease in pain (p = 0.033). Global health status variation can be explained up to 20.5 % by response in PSA (p = 0.012), this improved with PSA reduction.

CONCLUSION

 PSMA radioligand therapy seems to be an effective treatment option of metastatic castration-resistant prostate cancer patients as it improves their QoL in terms of increasing global health and mitigation of disease-related pain.

Prostate-specific membrane antigen theranostics in advanced prostate cancer: an evolving option

OBJECTIVES

To review current data for the role of prostate specific membrane antigen (PSMA) radioligand therapy (RLT) for patients with advanced prostate cancer. This review provides an update for multidisciplinary teams on the current and potential future applications of theranostics in prostate cancer.

METHODS

Narrative review focussing on PSMA as a target for RLT, and data using RESULTS: RLT with PSMA is an exciting therapeutic alternative to the existing management options already in use for patients with metastatic castrate-resistant prostate cancer (mCRPC). To date, most evidence exists regarding small-molecule PSMA inhibitors bound to beta-emitting radioisotopes such as 177Lu (Lu-PSMA). Prospective phase II data supports the safety and efficacy of Lu-PSMA in men with heavily pre-treated progressive mCRPC, and several late-phase randomised trials of Lu-PSMA are underway, with many more in the pipeline. Early results are encouraging, indicating that the theranostic approach may play a vital role in management of advanced prostate cancer and perhaps even in much earlier disease states.

CONCLUSIONS

PSMA RLT is a promising new treatment option for men with mCPRC, and may also have utility in less advanced prostate cancer.

Changing the Goal Posts: Prostate-specific Membrane Antigen Targeted Theranostics in Prostate Cancer

OBJECTIVE

Prostate-specific membrane antigen (PSMA) theranostics is changing the face of prostate cancer diagnosis and therapy. PSMA, a transmembrane protein over-expressed in many prostate cancers, is a promising target for theranostics. Theranostics is the concept of small molecule proteins that are labelled to different radionuclides and can be used for either diagnosis or therapy, dependent on whether they are labelled with an imaging or therapy radionuclide. By directly targeting the cancer cells with imaging and then for therapy, this approach embodies the philosophy of precision medicine - right drug, right time, right dose. The question is how to best utilise these new imaging and therapy agents in clinical practice. This review will evaluate the importance of PSMA in prostate cancer, its role in diagnostic imaging, and its potential as a therapy of advanced prostate cancer.

DATA SOURCES

Electronic databases including MEDLINE, Scopus, professional websites were searched.

CONCLUSION

PSMA-directed theranostics has an expanding role in prostate cancer because of its utility as a sensitive diagnostic tool that can be coupled with efficacious and low-toxicity therapeutic options. Ongoing research is required to determine how to use this effective tool for best patient care.

IMPLICATIONS FOR NURSING PRACTICE

PSMA theranostics is rapidly being incorporated into the routine care of men with prostate cancer. Understanding its strengths, its limitations, and where it may be valuable in clinical care is important in undertaking best patient practice.

[Algorithms for systemic therapy of prostate cancer, transitional cell carcinoma and renal cell carcinoma]

Systemic therapy in uro-oncology is currently undergoing major changes. In the past, drug therapies only showed good treatment results in metastasized testicular tumors. New developments indicate that an improved understanding of tumor biology will lead to targeted treatment strategies for metastatic prostate, urothelial and renal cell carcinoma. In the following article, we summarize the practice-relevant innovations in systemic therapy in the guidelines on prostate cancer, transitional cell carcinoma of the bladder and renal cell carcinoma.

[PSMA-based theranostics for prostate cancer : From imaging to treatment]

BACKGROUND

In recent years nuclear medicine theranostics using radiolabeled prostate-specific membrane antigen (PSMA) ligands have gained increasing importance in the management of prostate cancer.

AIM

The aim of this work is to highlight the value of theranostic concepts using radiolabeled PSMA ligands for both the diagnostic work-up and treatment of advanced prostate cancer.

MATERIAL AND METHODS

The currently available knowledge in the literature is summarized and presented.

RESULTS

The use of PSMA in positron emission tomography-computed tomography (PET/CT) shows a high sensitivity and specificity for prostate cancer imaging, particularly in patients with biochemical recurrences. Furthermore, promising results are also reported for staging of primary prostate cancer and treatment monitoring. In addition, radioligand therapy using alpha and beta emitters is a promising third line treatment option in intensively pretreated patients with metastases. The reduction of side effects and optimization of the treatment sequence of radioligand therapy is of increasing importance.

CONCLUSION

Nuclear medicine theranostics have an increasing clinical impact on the diagnostics and treatment of prostate cancer.

PSMA Theranostics: Review of the Current Status of PSMA-Targeted Imaging and Radioligand Therapy

Prostate-specific membrane antigen (PSMA) has been the subject of extensive investigation in the past two decades as a promising molecular target for prostate cancer (PCa). Its appealing molecular features have enabled the development of a novel diagnostic and therapeutic-thus "theranostic"-approach to PCa. There is now substantial evidence of the high sensitivity of PSMA-targeted imaging for PCa lesions and growing evidence of the therapeutic efficacy of PSMA radioligand therapy for metastatic castration-resistant prostate cancer. This article presents a broad overview of the current status of PSMA theranostics, including current evidence, potential clinical impact, and active areas of research.

Efficacy and Safety of 177Lu-PSMA-617 Radioligand Therapy in Metastatic Castration-Resistant Prostate Cancer Patients

PURPOSE

The aim of this study was to evaluate the efficacy and safety of Lu-PSMA-617 radioligand therapy in metastatic castration-resistant prostate cancer (mCRPC).

METHODS

In this prospective, single-arm, single-institutional study, 90 mCRPC patients with progressive disease (PD) on second-line hormonal therapy and/or docetaxel chemotherapy were recruited for the study. All patients underwent diagnostic Ga-PSMA-HBED-CC PET/CT, prior to inclusion for therapy. Included patients underwent Lu-PSMA-617 therapy at 8- to 12-weekly intervals. The primary end point was to assess the overall survival. The secondary and cosecondary end points included biochemical response assessment as per the Prostate Cancer Working Group 3 criteria, progression-free survival, radiological and molecular response criteria, clinical response, safety profile, and disease control rates. All the outcome parameters were evaluated in 90 patients except for the radiographic and molecular response, which was evaluated in 69 patients.

RESULTS

The median age of patients was 66.5 years (range, 30-88 years). The median activity administered per cycle was 3.7 to 8 GBq ranging from 1 to 7 cycles, and patients were followed up over a median duration of 28 months. At 2- to 3-month interval after the first therapy and the end of the assessment, greater than 50% decline in prostate-specific antigen was observed in 32.2% and 45.5%, respectively. Univariate analysis did not reveal any variables such as prior therapies, laboratory parameters, concomitant hormonal therapy, and SUV patient parameters associated with prostate-specific antigen decline. Radiographic response by diagnostic CT revealed partial remission in 23% (16/69), stable disease in 54% (37/69), and PD in 23% (16/69) of patients. Molecular tumor response by PET Response Criteria in Solid Tumor 1 criteria revealed 19 (27.5%) of 69 patients with partial remission, 30 (43.5%) of 69 with stable disease, and 20 (29%) of 69 with PD. The disease control rates according to the radiographic and molecular response were 77% and 71%, respectively. The median overall survival and median progression-free survivals were 14 and 11.8 months, respectively. Toxicities related to radioligand therapy were low and transient with no serious adverse effects.

CONCLUSIONS

Lu-PSMA-617 radionuclide therapy is a safe and effective approach to the treatment of mCRPC patients.

Safety Profile and Therapeutic Efficacy of One Cycle of Lu177-PSMA in End-Stage Metastatic Castration-Resistant Prostate Cancer Patients with Low Performance Status

Purpose

The aim of this study was to evaluate safety and therapeutic efficacy of lutetium 177 prostate-specific membrane antigen (Lu-177-PSMA) in metastatic castration-resistant prostate cancer (mCRPC) patients with low performance status.

Methods

Twenty-two patients already treated with anti-androgens and docetaxel were enrolled for one cycle of Lu-177-PSMA therapy. Haemoglobin, total leukocyte counts, platelets and serum creatinine for toxicity profile while prostate specific antigen (PSA), Eastern Cooperative Oncology Group (ECOG) performance status, visual analogue scale (VAS) and analgesic quantification scale (AQS) for therapeutic efficacy were recorded pre and 8 weeks post therapy. Wilcoxon signed-rank and ANOVA tests were used for statistical analysis.

Results

Partial response (PR), stable disease (SD) and progressive disease (PD) for PSA were seen in 5 (22.7%), 13 (59.1%) and 4 (18.2%) patients respectively treated with mean 6.88 GBq dose of Lu-177-PSMA. 8/22 (36.4%) patients showed ≥ 30% drop in PSA. Grade 3 haemoglobin toxicity was seen in 5/22 (22.7%) patients. No patient developed grade 4 haemoglobin toxicity. No patients had grade 3 or 4 leukocytopenia or thrombocytopenia. Wilcoxon signed-rank test showed statistical significant (P < 0.05) difference in pre and post treatment ECOG, VAS, and AQS scores. The ANOVA test showed statistically significant difference in mean doses of Lu-177-PSMA used in three PSA response groups while difference was non-significant for other variables.

Conclusion

We concluded that Lu-177-PSMA therapy has adequate pain palliation in end-stage mCRPC patients with low performance status and it has a potential to become effective therapeutic option in properly selected patients.

EANM procedure guidelines for radionuclide therapy with 177Lu-labelled PSMA-ligands (177Lu-PSMA-RLT)

Prostate-specific membrane antigen (PSMA) is expressed in most prostate cancers and can be identified by PSMA-ligand imaging, which has already become clinically accepted in several countries in- and outside Europe. PSMA-directed radioligand therapy (PSMA-RLT) with Lutetium-177 (¹⁷⁷Lu-PSMA) is currently undergoing clinical validation. Retrospective observational data have documented favourable safety and striking clinical responses. Recent results from a prospective clinical trial (phase II) have been published confirming high response rates, low toxicity and reduction of pain in metastatic castration-resistant prostate cancer (mCRPC) patients who had progressed after conventional treatments. Such patients typically survive for periods less than 1.5 years. This has led some facilities to adopt compassionate or unproven use of this therapy, even in the absence of validation within a randomised-controlled trial. As a result, a consistent body of evidence exists to support efficacy and safety data of this treatment. The purpose of this guideline is to assist nuclear medicine specialists to deliver PSMA-RLT as an "unproven intervention in clinical practice", in accordance with the best currently available knowledge.

Prostate-specific membrane antigen theranostics: therapy with lutetium-177

PURPOSE OF REVIEW

Prostate-specific membrane antigen (PSMA) theranostics offers a new approach for a personalized and targeted treatment for metastatic prostate cancer. Lutetium-177-labelled PSMA-ligands (Lu-PSMA) is a radionuclide therapy that is directed to PSMA expressing prostate cancer. Clinical experience with Lu-PSMA in men with advanced prostate cancer is growing. The purpose of this review is to outline the mechanism of action of this therapy, summarize recent efficacy and toxicity data and highlight future direction and challenges in establishing Lu-PSMA treatment as part of routine clinical practice.

RECENT FINDINGS

The first reports on safety and efficacy of Lu-PSMA have been retrospective series of men with advanced prostate cancer who previously failed conventional therapies and received Lu-PSMA on compassionate basis. These studies highlight promising efficacy, favourable toxicity profile and quality of life improvements. Limitation stem from the retroospective nature of these data with short follow-up.

SUMMARY

Several studies suggest that radionuclide therapy with Lu-PSMA has high activity and is well tolerated. Crucial to establishing this treatment in routine clinical management will be the generation of high-level evidence from prospective trials that can confirm the encouraging patient outcomes reported to date.

177Lu-PSMA-617 Radioligand Therapy in Metastatic Castration-Resistant Prostate Cancer Patients with a Single Functioning Kidney

The aim of this study was to assess the safety, tolerability, and effects on renal function as well as therapeutic efficacy of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (PRLT) using ¹⁷⁷Lu-labeled PSMA-617 in patients with metastatic castration-resistant prostate cancer and a single functioning kidney before PRLT. Methods: Sixteen patients (aged 53-78 y; mean age, 64.7 ± 6.5 y) with a single functioning kidney received PRLT with ¹⁷⁷Lu-PSMA-617 between March 2015 and October 2018. All parameters of renal function (serum creatinine, blood urea nitrogen, and electrolytes) were prospectively documented in a structured database and analyzed before each PRLT cycle and in follow-up. Renal function was further quantified by measuring tubular extraction rate (TER) using ^99mTc-mercaptoacetyltriglycine renal scintigraphy. Treatment-related adverse events were graded according to the Common Terminology Criteria for Adverse Events (CTCAE), version 5.0. Kaplan-Meier analysis was performed to obtain the progression-free survival and overall survival. Results: The median administered activity was 22.1 GBq (range, 15.4-33.8 GBq). The calculated absorbed radiation dose to the kidney per cycle was 5.3 ± 2.1 Gy (0.81 ± 0.32 Gy/GBq). Renal function was already impaired at baseline in 43.7% of patients, including CTCAE grade 1 renal impairment in 25.0% and CTCAE grade 2 in 18.8%. Grade 1 and 2 renal impairment, respectively, were present in 37.5% and 6.3% of the patients after the first PRLT cycle and in 31.3% and 12.5% after the second cycle. No CTCAE grade 3 or 4 nephrotoxicity was observed during or after treatment. There was no significant change in either TER or the ratio of TER to lower-limit TER after the last cycle of treatment (P > 0.05). The median PFS was 8.1 mo based on both the criteria of the European Organization for Research and Treatment of Cancer and RECIST. The median overall survival has yet to be reached with a median follow-up time of 19.3 mo (range, 5.8-45.3 mo). Conclusion: In patients with a single functioning kidney, ¹⁷⁷Lu-PSMA-617 PRLT is feasible, seems to be effective, and is well tolerated, without any signs of acute or subacute nephrotoxicity during a mean follow-up of nearly 2 y (and up to 45.3 mo). Further long-term follow-up of this special patient group is warranted.

Knowledge Synthesis in Evidence-Based Medicine

Systematic reviews are the most common form of knowledge synthesis and remain a cornerstone of the practice of evidence-based medicine. They offer enhanced rigor and validity relative to traditional narrative review articles by reducing bias and increasing objectivity. In answering focused research questions, systematic reviews are directly applicable to clinical practice as well as the development of clinical guidelines and the identification of knowledge gaps, which may drive future primary research directions. Typically, such a rigorous process necessarily requires substantive time to carefully and systematically identify, screen, and synthesize all relevant available primary research on a topic. Further, other knowledge synthesis methods have emerged to address the varying needs of decision makers with respect to condensed timelines and more diverse research questions, as well as to allow incorporation of already synthesized evidence into reviews. These alternative methods include rapid reviews, scoping reviews, and overviews of systematic reviews, which are being used with increasing frequency by clinicians, decision-makers, and researchers. We encourage clinicians and researchers in nuclear medicine and other imaging sciences to acquire a greater familiarity with these methods and to consider them in clinical decision making, the development of clinical guidelines, and the planning of future research activities.

Theranostics for Advanced Prostate Cancer: Current Indications and Future Developments

CONTEXT

Advanced prostate cancer (PCa) is a prominent cause of cancer death in men; positron emission tomography (PET) imaging may play a relevant role in detecting metastases and thus allowing a more tailored therapy in these patients. Radioligand therapy (RLT) may also gain relevance as a treatment strategy in advanced disease.

OBJECTIVE

The aim of this review is to highlight how the recently developed theranostic processes may become a part of both the available diagnostic and the therapy arsenal in advanced PCa patients.

EVIDENCE ACQUISITION

An expert panel of nuclear medicine physicians and a urologist, highly experienced in the fields of radionuclide imaging and RLT in advanced PCa, performed a nonsystematic review of the current indications, performance, limitations, and potential future developments of the currently available options in PCa theranostics.

EVIDENCE SYNTHESIS

Among PET radiotracers, prostate-specific membrane antigen (PSMA)-based compounds in advanced PCa are the focus of a continuously growing interest, mostly due to their potential relevance as theranostic agents. The impact of PSMA-based PET/computed tomography imaging on treatment strategies and prognosis is promising, but still not unquestionably clear. Potential applications may include a role as a gatekeeper to PSMA-directed RLT, as well as monitoring the spread of systemic disease. Currently, initial results seem to substantiate the role of PSMA-directed RLT in terms of feasibility and efficacy.

CONCLUSIONS

PSMA is a promising molecule for both imaging and therapy in advanced PCa patients; nevertheless, further studies are needed to investigate its role and to determine the impact of its side effects and its overall strategy outcome.

PATIENT SUMMARY

Prostate-specific membrane antigen (PSMA), a protein, is highly expressed on prostate cancer cells. The possibility to perform diagnostic imaging and subsequently administer therapies by the means of the same molecule is called "theranostics". In patients with advanced prostate cancer, PSMA might have a role in detecting disease spread through both positron emission tomography and single-photon emission computed tomography imaging, while treating prostate cancer systemic localizations with radioligand therapy. Further studies are needed to better determine patients' risks and benefits of these therapeutic approaches.

Prostate-specific membrane antigen radioligand therapy of prostate cancer

Defining an optimal therapeutic approach in metastatic castration-resistance prostate cancer (mCRPC) patients in advanced stages is still challenging in routine clinical practice. Prostate-specific membrane antigen (PSMA) targeted radionuclide therapy with β- or α-emitters such as 177-Lutethium (177Lu) or 225-Actinium (225A) has been a main focus at multiple academic research centers in the last few years. This review article provides an overview of PSMA characteristics, clinical performance, safety and toxicity of PSMA targeted β- or α-radiation therapy.

PSMA PET applications in the prostate cancer journey: from diagnosis to theranostics

The heterogeneity of prostate cancer has made imaging modalities of crucial importance in this disease. Accurate diagnosis and staging of the volume and extent of disease, especially in advanced and metastatic prostate cancer, can help to tailor the timing and modalities of treatment. While MRI has been effective in the detection of significant prostate cancer, its use in the identification and quantification of extraprostatic disease is limited. This gap is now being filled by PSMA PET. PSMA PET scans have now been shown to have a role in all stages in the prostate cancer journey. Emerging evidence has shown its promise in primary staging, restaging and theranostics. In this paper, we review the evidence for the use of PSMA PET in the various stages of prostate cancer, from initial diagnosis to advanced metastatic disease where other systemic treatments have failed.