Predictors of Response to Radioligand Therapy of Metastatic Castrate-Resistant Prostate Cancer with 177Lu-PSMA-617

Explorative analysis of a score predicting the therapy response of patients with metastatic, castration resistant prostate cancer undergoing radioligand therapy with 177Lu-labeled prostate-specific membrane antigen

OBJECTIVE

Up to 60% of patients with metastatic, castration-resistant prostate cancer (mCRPC) treated with 177Lu prostate-specific membrane antigen (PSMA) radioligand therapy (RLT) achieves a partial biochemical response with a decrease of > 50% in prostate-specific antigen (PSA) levels. The remaining fractions, however, do not respond to RLT. The aim of this explorative analysis was to identify pre-therapeutic factors for the prediction of response.

METHODS

46 patients [age = 68 years (50-87)] with mCRPC who consecutively underwent RLT with 177Lu PSMA [median applied activity = 6 GBq (2.9-6.2)] were included and analysed retrospectively. The association of different clinical and laboratory factors and parameters from pre-therapeutic 68Ga PSMA positron emission tomography (PET) with the outcome of RLT was tested (Fisher's test). Outcome was defined as PSA changes 8 weeks after second RLT [partial response (PR), PSA decrease > 50%; progressive disease (PD), PSA increase ≥ 25%; stable disease (SD), others]. Significant predictive factors were combined in a predictive score.

RESULTS

30% showed a post-treatment PR (median 73% PSA decrease), 35% SD (median 17% PSA decrease) and 35% PD (median 42% PSA increase). Significant predictors for PD were alkaline phosphatase (ALP) > 135 U/l (p = 0.002), PSA > 200 ng/ml (p = 0.036), and maximum standardized uptake value (SUVmax) of the "hottest lesion" in pre-therapeutic PET < 45 (p = 0.005). The predictive score including PSA, ALP and SUVmax could separate 2 distinct groups of patients: ≤ 2 predictive factors (19% PD) and 3 predictive factors (90% PD).

CONCLUSION

The presented predictive score allowed a pre-therapeutic estimate of the expected response to 2 cycles of RLT. As our study was retrospective, prospective trials are needed for validation.

Estimating the Potential of Radiomics Features and Radiomics Signature from Pretherapeutic PSMA-PET-CT Scans and Clinical Data for Prediction of Overall Survival When Treated with 177Lu-PSMA

Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PSMA-PET/CT) scans can facilitate diagnosis and treatment of prostate disease. Radiomics signature (RS) is widely used for the analysis of overall survival (OS) in cancer diseases. This study aims at investigating the role of radiomics features (RFs) and RS from pretherapeutic gallium-68 (⁶⁸Ga)-PSMA-PET/CT findings and patient-specific clinical parameters to analyze overall survival of prostate cancer (PC) patients when treated with lutethium-177 (¹⁷⁷Lu)-PSMA. A cohort of 83 patients with advanced PC was retrospectively analyzed. Average values of 73 RFs of 2070 malignant hotspots as well as 22 clinical parameters were analyzed for each patient. From the Cox proportional hazard model, the least absolute shrinkage and selection operator (LASSO) regularization method is used to select most relevant features (standardized uptake value (SUV)_Min and kurtosis with the coefficients of 0.984 and −0.118, respectively) and to calculate the RS from the RFs. Kaplan–Meier (KM) estimator was used to analyze the potential of RFs and conventional clinical parameters, such as metabolic tumor volume (MTV) and standardized uptake value (SUV) for the prediction of survival. As a result, SUV_Min, kurtosis, the calculated RS, SUV_Mean, as well as Hemoglobin (Hb)1, C-reactive protein (CRP)1, and ECOG1 (clinical parameters) achieved p-values less than 0.05, which suggest the potential of findings from ⁶⁸Ga-PSMA-PET/CT scans as well as patient-specific clinical parameters for the prediction of OS for patients with advanced PC treated with ¹⁷⁷Lu-PSMA therapy.

Prostate-specific Membrane Antigen-based Imaging of Castration-resistant Prostate Cancer

CONTEXT

Positron emission tomography (PET) targeting prostate-specific membrane antigen (PSMA) has unprecedented accuracy for localization of initial or recurrent prostate cancer (PC). There is now growing evidence regarding the value of PSMA-PET in patients with advanced PC.

OBJECTIVE

To review the value of PSMA-PET/computed tomography (CT) in the context of castration-resistant PC (CRPC).

EVIDENCE ACQUISITION

A search of the PubMed database using the terms "PSMA PET castration resistant prostate cancer" (years 2011-2020) was performed. Reviews, case reports/series, non-English articles, preclinical studies, access-restricted studies, and studies on PSMA radioligand therapy without further analysis of PSMA-PET parameters were subsequently excluded.

EVIDENCE SYNTHESIS

Compared to conventional imaging, PSMA-PET better identifies the true extent of CRPC, especially nonmetastatic CRPC. The clinical benefit of this stage migration is still unclear and needs to be evaluated in further studies. High accuracy of PSMA-PET holds promise for better, PET-guided metastasis-directed treatment in patients with oligometastatic CRPC. PSMA-PET is an essential eligibility criterion for [¹⁷⁷Lu]-PSMA theranostic applications. Preliminary evidence indicates the value of PSMA-PET for the assessment of treatment responses.

CONCLUSIONS

Among other applications, PSMA-PET offers more precise staging for nonmetastatic CRPC. In particular, target localization for metastasis-directed therapy and target expression assessment for PSMA radioligand therapy also hold promise. Potential translation of this diagnostic tool into an oncologic benefit needs to be defined in future trials.

PATIENT SUMMARY

This review describes how prostate-specific membrane antigen positron emission tomography (PSMA-PET), a new sensitive imaging tool for prostate cancer, might help to guide clinicians in making treatment decisions for advanced prostate cancer.

Visceral Metastases as Predictors of Response and Survival Outcomes in Patients of Castration-Resistant Prostate Cancer Treated With 177Lu-Labeled Prostate-Specific Membrane Antigen Radioligand Therapy: A Systematic Review and Meta-analysis

BACKGROUND

The presence of visceral metastases is associated with poor prognosis in patients of metastatic castration-resistant prostate cancer (mCRPC) treated with hormonal therapy and chemotherapy. However, studies evaluating its impact on treatment outcomes with Lu-labeled prostate-specific membrane antigen (PSMA) radioligand therapy (RLT) are currently limited and show inconsistent results. This systematic review was conducted to precisely evaluate the impact of visceral metastases on biochemical response and survival outcomes in patients of mCRPC treated with Lu-PSMA RLT.

METHODS

This systematic review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. Searches in PubMed, Scopus, and EMBASE were made using relevant keywords, and articles up to May 2020 were included. Univariate and multivariate odds ratios and hazard ratios (HRs) were extracted from the individual articles, and pooled estimates were generated using meta-analysis.

RESULTS

Twelve articles comprising 1504 patients were included in this review. Presence of visceral metastases not only predicted low biochemical response rate (pooled univariate odds ratio: 0.38, 95% confidence interval [CI], 0.22-0.66) but was also a significant prognosticator of worse progression-free survival (pooled univariate HR, 1.85; 95% CI, 1.39-2.46; and pooled multivariate HR, 1.48; 95% CI, 1.15-1.92) and overall survival (pooled univariate HR, 1.77; 95% CI, 1.29-2.44; and pooled multivariate HR, 2.22; 95% CI, 1.82-2.70). There was no evidence of publication bias.

CONCLUSIONS

Presence of visceral metastases was associated with poor response and survival outcomes in patients of mCRPC treated with Lu-PSMA RLT. The results are clinically significant for pretreatment risk stratification of such patients and to guide optimal treatment strategies.

Neutron-activated theranostic radionuclides for nuclear medicine

Theranostics in nuclear medicine refers to personalized patient management that involves targeted therapy and diagnostic imaging using a single or combination of radionuclide (s). The radionuclides emit both alpha (α) or beta (β-) particles and gamma (γ) rays which possess therapeutic and diagnostic capabilities, respectively. However, the production of these radionuclides often faces difficulties due to high cost, complexity of preparation methods and that the products are often sourced far from the healthcare facilities, hence losing activity due to radioactive decay during transportation. Subject to the availability of a nuclear reactor within an accessible distance from healthcare facilities, neutron activation is the most practical and cost-effective route to produce radionuclides suitable for theranostic purposes. Holmium-166 (166Ho), Lutetium-177 (177Lu), Rhenium-186 (186Re), Rhenium-188 (188Re) and Samarium-153 (153Sm) are some of the most promising neutron-activated radionuclides that are currently in clinical practice and undergoing clinical research for theranostic applications. The aim of this paper is to review the physical characteristics, current clinical applications and future prospects of these neutron activated radionuclides in theranostics. The production, physical properties, validated clinical applications and clinical studies for each neutron-activated radionuclide suitable for theranostic use in nuclear medicine are reviewed in this paper.

Prediction of response and survival after standardized treatment with 7400 MBq 177Lu-PSMA-617 every 4 weeks in patients with metastatic castration-resistant prostate cancer

BACKGROUND AND AIMS

[¹⁷⁷Lu]Lu-PSMA-617 radioligand therapy (PSMA-RLT) is a new therapy for patients with metastatic castration-resistant prostate cancer (mCRPC). However, identification of reliable prognostic factors is hampered by heterogeneous treatment regimens applied in previous studies. Hence, we sought clinical factors able to predict response and survival to PSMA-RLT in a homogenous group of patients, all receiving 7400 MBq every 4 weeks.

PATIENTS AND METHODS

Data of 61 patients (mean age 71.6 ± 6.9 years, median basal PSA 70.7 [range 1.0-4890 μg/L]), pretreated with abiraterone/enzalutamide (75.4%) and docetaxel/cabazitaxel (68.9%), received three cycles of PSMA-RLT (mean 7321 ± 592 MBq) at four weekly intervals and were analyzed retrospectively. General medical conditions and laboratory parameters of every patients were regularly assessed. Response to therapy was based on PSA levels 1 month after the 3rd cycle. Binary logistic regression test and Kaplan-Meier estimates were used to evaluate predictors and overall survival (OS).

RESULTS

Forty-nine (80.3%) patients demonstrated a therapy response in terms of any PSA decline, while 21 (19.7%) patients showed increase or no changes in their PSA levels. Baseline hemoglobin (Hb) significantly predicted PSA reductions of ≥ 50% 4 weeks after receiving the 3rd PSMA-RLT (P = 0.01, 95% CI: 1.09-2.09) with an AUC of 0.68 (95% CI: 0.54-0.81). The levels of basal Hb and basal PSA were able to predict survival of patients, both P < 0.05 (relative risk 1.51 and 0.79, 95% CI: 1.09-2.09 and 0.43-1.46), respectively. In comparison to patients with reduced basal Hb, patients with normal basal Hb levels lived significantly longer (median survival not reached vs. 89 weeks, P = 0.016). Also, patients with basal PSA levels ≤ 650 μg/L had a significantly longer survival than patients with basal PSA levels > 650 μg/L (median survival not reached vs. 97 weeks, P = 0.031). Neither pretreatments with abiraterone/enzalutamide or docetaxel/cabazitaxel nor distribution of metastasis affected survival and rate of response to PSMA-RLT.

CONCLUSION

Basal Hb level is an independent predictor for therapy response and survival in patients receiving PSMA-RLT every 4 weeks. Both baseline PSA ≤ 650 μg/L and normal Hb levels were associated with longer survival.

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.

Clinical impact of PET imaging in prostate cancer management

PURPOSE OF REVIEW

Imaging of prostate cancer has been a rapidly evolving field in recent years with the introduction of multiple new PET tracer agents. Introduction of novel imaging techniques into clinical practice requires careful evaluation, with the ultimate aims of improved patient outcomes, better sequencing of treatments, and cost effectiveness. The increased sensitivity and specificity of these new PET agents present both challenges and opportunities. We know they frequently change management, but are these effective management changes, and is it always in the best interests of the patients?

RECENT FINDINGS

This review will focus on recent publications that provide high-level evidence for the use of PET in prostate cancer. It will discuss studies that have evaluated the clinical impact of PET imaging in prostate cancer and will review a number of trials that demonstrate the potential of PET to change current standard of care, from diagnosis, to prognostic capabilities in men with metastatic prostate cancer.

SUMMARY

Evidence for the use of PET in prostate cancer is building with studies evaluating diagnostic accuracy of PET at all stages of prostate cancer. We review the evidence available, focusing on prospective trials that are measuring the impact of new technology on patient outcomes.

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.

Review of 177Lu-PSMA-617 in Patients With Metastatic Castration-Resistant Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a cell membrane glycoprotein that is selectively expressed in prostate cells, with expression levels increasing dramatically in prostatic adenocarcinoma. PSMA-based radioligand therapy (RLT) has emerged as a viable therapeutic modality for the treatment of progressive metastatic prostate cancer. One commonly employed combination involves lutetium-177 conjugated to the ligand PSMA-617 (¹⁷⁷Lu-PSMA-617). In this meta-analysis, we examine therapeutic responses in patients with metastatic disease who have received ¹⁷⁷Lu-PSMA-617 therapy. We conducted a literature search with the following inclusion criteria: clinical trials involving more than 10 patients and solely utilizing ¹⁷⁷Lu-PSMA-617. Seventeen studies were included in the final analysis. Variables documented included the number of patients, the total therapeutic dose administered, the percentage of any prostate-specific antigen (PSA) decline, the percentage with PSA decline exceeding 50% baseline, and toxicities. Overall, a majority of patients responded to therapy, and in the prospective studies, survival was found to be upwards of one year. Significant toxicities included cytopenias, which were infrequent. Patients who had PSA declines in response to therapy had longer survival. Performance status and tumor grade were also key predictors of outcome.

Analysis of PSMA expression and outcome in patients with advanced Prostate Cancer receiving 177Lu-PSMA-617 Radioligand Therapy

Rationale: PSMA-PET-CT enables measuring molecular expression of prostate-specific membrane antigen (PSMA) in vivo, which is the target molecule of ¹⁷⁷Lu-PSMA-617 (Lu-PSMA) therapy. However, the correlation of PSMA expression and overall survival (OS) in patients treated with Lu-PSMA therapy is currently unclear; especially with regard to coexistence of high and low PSMA expressing metastases. To this end, this retrospective single arm study elucidates the correlation of PSMA expression and overall survival in patients treated with Lu-PSMA therapy. Additionally, PET based criteria to define low PSMA expression were explored. Methods: Eighty-five patients referred to Lu-PSMA therapy were included in the analysis. Pretherapeutic ⁶⁸Ga-PSMA-PET-CT scans were available for all patients. SUV_max of the highest PSMA expressing metastasis (PSMA_max), SUV_max of the lowest PSMA expressing metastasis (PSMA_min), and average SUV_max of all metastases (PSMA_average) amongst other PET parameters were measured for each patient. A log-rank cutoff-finder was used to determine low (lowPSMA_average) and high (highPSMA_average) average PSMA expression as well as low (lowPSMA_min) and high (highPSMA_min) minimal PSMA expression. Results: PSMA_average was a significant prognosticator of overall survival in contrast to PSMA_max (HR: 0.959; p = 0.047 vs. HR: 0.992; p = 0.231). Optimal log rank cut-offs were: PSMA_average = 14.3; PSMA_min = 10.2. Patients with low average PSMA expression (lowPSMA_average) had significantly shorter survival compared to those with high average expression (highPSMA_average) (5.3 vs. 15.1 months; p < 0.001; HR: 3.738, 95%CI = 1.953-7.154; p < 0.001). Patients with low PSMA expressing metastases (lowPSMA_min) had shorter survival compared to those without a low PSMA expressing metastasis (highPSMA_min) (p = 0.003; 7.9 months vs. 21.3; HR: 4.303, 95%CI = 1.521-12.178; p = 0.006). Patients that were classified as highPSMA_average but with lowPSMA_min had an intermediate overall survival (11.4 months; longer compared to lowPSMA_average, 5.3 months, p = 0.002; but shorter compared to highPSMA_min, 21.3 months, p = 0.02). Conclusion: Low average PSMA expression is a negative prognosticator of overall survival. Absence of low PSMA expressing metastases is associated with best overall survival and the maximum PSMA expression seems not suited to prognosticate overall survival. Low PSMA expression might therefore be a negative prognosticator for the outcome of patients treated with Lu-PSMA therapy. Future studies are warranted to elucidate the degree of low PSMA expression tolerable for Lu-PSMA therapy.

Prostate Cancer Theranostics - An Overview

Metastatic prostate cancer is incurable, and novel methods to detect the disease earlier and to direct definitive treatment are needed. Molecularly specific tools to localize diagnostic and cytotoxic radionuclide payloads to cancer cells and the surrounding microenvironment are recognized as a critical component of new approaches to combat this disease. The implementation of theranostic approaches to characterize and personalize patient management is beginning to be realized for prostate cancer patients. This review article summarized clinically translated approaches to detect, characterize, and treat disease in this rapidly expanding field.

Response and outcome of liver metastases in patients with metastatic castration-resistant prostate cancer (mCRPC) undergoing 177Lu-PSMA-617 radioligand therapy

PURPOSE

Little is known about the efficacy of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) against liver metastases of metastatic castration-resistant prostate cancer (mCRPC). We retrospectively analyzed efficacy-related outcomes of ¹⁷⁷Lu-PSMA-617 RLT in this setting and potential predictors of those outcomes.

METHODS

Twenty-eight consecutive mCRPC patients with liver metastases given ¹⁷⁷Lu-PSMA-617 RLT were analyzed retrospectively. Their planned regimen was 4-6 cycles at 6 ± 2-week intervals; the mean activity/cycle was 6.5 ± 0.5 GBq. Hepatic response was determined by modified positron emission tomography response criteria in solid tumors; association of such response with overall survival (OS) was tested, as were relationships of the selected patient, disease, and treatment characteristics with hepatic progression-free survival (PFS_hep) and OS. Survival analyses used Kaplan-Meier curves, log-rank test at p < 0.05 significance, and Cox proportional-hazards modeling.

RESULTS

Median (minimum-maximum) follow-up was 37.5 (2.3-50.6) months. In liver metastases, complete or partial response was observed in 6 patients (21%) each, and stable disease in 1 (4%), for hepatic disease control in 46%. Overall, median (95% confidence interval) PFS_hep was 5.7 (2.2-9.2) months, and OS, 11.7 (3.0-20.4) months. Patients with hepatic disease control did not reach the median OS, while those with hepatic progressive disease had median OS (95% confidence interval) of 6.4 (1.6-11.1) months. In multivariate analysis, hepatic disease control by ¹⁷⁷Lu-PSMA-617 RLT was significantly independently associated with OS, as was a prostate-specific antigen decline of ≥ 50% after 2 RLT cycles, and good baseline performance status (Eastern Cooperative Oncology Group 0-1). Hepatic tumor burden (≤ 25% vs. > 25% of liver volume) had no apparent relationship with hepatic tumor response, PFS_hep, or OS.

CONCLUSION

¹⁷⁷Lu-PSMA-617 RLT frequently controlled liver metastases, resulting in long PFS_hep and significantly improved OS. Hepatic tumor burden appeared to lack any relationship with treatment efficacy, supporting ¹⁷⁷Lu-PSMA-617 RLT of late-stage/end-stage mCRPC with liver metastases.

Clinical Variables Associated with PSA Response to Lutetium-177-PSMA ([177Lu]-PSMA-617) Radionuclide Treatment in Men with Metastatic Castration-Resistant Prostate Cancer

Lutetium-177-PSMA ([177Lu]-PSMA-617), a radiolabeled small molecule, binds with high affinity to prostate-specific membrane antigen (PSMA), enabling targeted radiation therapy to metastatic prostate lesions. Our objective was to retrospectively analyze the activity of [177Lu]-PSMA-617 given off-trial to men with metastatic castration resistant prostate cancer (mCRPC) and identify clinical factors associated with PSA response. Electronic medical records of all men treated with [177Lu]-PSMA-617 were reviewed and analyzed. Overall survival was calculated using the Kaplan-Meier method. The association between potential variables and PSA response was analyzed by univariate analysis, using either logistic regression or χ²/Fisher's exact test. Multivariable analysis was carried out using logistic regression on all categorical variables with a P-value of <0.1 on univariate analysis. Variables found to be statistically significant were then used to define a categorical score. A total of 52 patients received at least one cycle of [177Lu]-PSMA-617. Clinical benefit was observed in 28 patients (52%). PSA decline ≥20% and ≥50% was observed in 26 (50%) and 18 patients (35%), respectively. Achievement of any PSA decline at first measurement was significantly associated with survival. There was a negative association between the number of previous chemotherapy lines and PSA decline above 20%. Univariate analysis followed by multivariable analysis showed that older age and higher hemoglobin were significantly associated with a PSA decline >20%. A score combining these two parameters was significantly associated with PSA response. In summary, [177Lu]-PSMA-617 is active in the 'real-life' setting of heavily pretreated men with mCRPC.

Theranostic approaches in nuclear medicine: current status and future prospects

Introduction: Theranostics is an emerging field in which diagnosis and specific targeted therapy are combined to achieve a personalized treatment approach to the patient. In nuclear medicine clinical practice, theranostics is often performed utilizing the same molecule labeled with two different radionuclides, one radionuclide for imaging and another for therapy.Areas covered: The authors review the clinical applications of different radiopharmaceuticals in the field of interest, including the well-established use of radioactive iodine in differentiated thyroid cancer, radiolabeled metaiodobenzylguanidine (MIBG) in neuroblastoma and the clinical impact of peptide radionuclide receptorial therapy (PRRT) in the management of neuroendocrine tumors. Furthermore, the more cutting-edge and recently introduced theranostic approaches will be reviewed, such as the radioligand therapy with ¹⁷⁷Lu-prostate specific membrane antigen (PSMA) and targeted alpha therapy in castration-resistant prostate cancer. Finally, the main applications of PET for the imaging of biomarkers suitable for the non-radionuclide targeted therapy will be covered.Expert opinion: Theranostics is envisaging a revolutionary clinical approach which is deeply connected with the concept of personalized medicine and ruled by a 'patient-centered' vision. In this perspective, the theranostic applications will need well-trained specialists, capable to manage not only the technological aspects of the discipline, but also to deal with the more innovative oncological therapies in a multidisciplinary setting.

Neuroendocrine Differentiation and Response to PSMA-Targeted Radioligand Therapy in Advanced Metastatic Castration-Resistant Prostate Cancer: A Single-Center Retrospective Study

Neuroendocrine differentiation is associated with treatment failure and poor outcome in metastatic castration-resistant prostate cancer. We investigated the effect of circulating neuroendocrine biomarkers on the efficacy of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT). Methods: Neuroendocrine biomarker profiles (progastrin-releasing peptide, neuron-specific enolase, and chromogranin-A) were analyzed in 50 patients commencing ¹⁷⁷Lu-PSMA-617 RLT. The primary endpoint was a prostate-specific antigen response in relation to baseline neuroendocrine marker profiles. An additional endpoint was progression-free survival. Tumor uptake on posttherapeutic scans, a known predictive marker for response, was used as a control variable. Results: Neuroendocrine biomarker profiles were abnormal in most patients. Neuroendocrine biomarker levels did not predict treatment failure or early progression (P ≥ 0.13). By contrast, intense PSMA-ligand uptake in metastases predicted both treatment response (P = 0.0030) and reduced risk of early progression (P = 0.0111). Conclusion: Neuroendocrine marker profiles do not predict an adverse outcome from RLT. By contrast, high ligand uptake was confirmed to be crucial for achieving a tumor response.

The 68Ga/177Lu-theragnostic concept in PSMA-targeting of metastatic castration-resistant prostate cancer: impact of post-therapeutic whole-body scintigraphy in the follow-up

INTRODUCTION

A new therapeutic option for metastatic castration-resistant prostate cancer (mCRPC) of heavily pre-treated patients lies in ¹⁷⁷Lu-PSMA-617 radioligand therapy.

METHODS

On the basis of PSMA-targeted ⁶⁸Ga-PSMA-11 PET/CT, 32 consecutive mCRPC patients were selected for ¹⁷⁷Lu-PSMA-617 therapy (6 GBq/cycle, 2 to 6 cycles, 6-10 weeks apart) and followed until death. Post-therapy whole-body (WB) dosimetry and ⁶⁸Ga-PSMA-11 PET/CT data were compared and related to progression free and overall survival.

RESULTS

¹⁷⁷Lu-PSMA-617 dosimetry after the first cycle indicated high tumor doses for skeletal (4.01 ± 2.64; range 1.10-13.00 Gy/GBq), lymph node (3.12 ± 2.07; range 0.70-8.70 Gy/GBq), and liver (2.97 ± 1.38; range 0.76-5.00 Gy/GBq) metastases whereas the dose for tissues/organs was acceptable in all patients for an intention-to-treat activity of 24 GBq. Any PSA decrease after the first cycle was found in 23/32 (72%), after the second cycle in 22/32 (69%), after the third cycle in 16/28 (57%), and after the fourth cycle in 8/18 (44%) patients. Post-therapy 24 h WB scintigraphy showed decreased tumor-to-background ratios in 24/32 (75%) after the first therapy cycle, after the second cycle in 17/29 (59%), and after the third cycle in 13/21 (62%) patients. The median PFS was 7 months and the median OS 12 months. In the group of PSA responders (n = 22) the median OS was 17 months versus 11 months in the group of non-responders (n = 10), p < 0.05. Decreasing SUV_max values were found for parotid (15.93 ± 6.23 versus 12.33 ± 4.07) and submandibular glands (17.65 ± 7.34 versus 13.12 ± 4.62) following treatment, along with transient (n = 6) or permanent (n = 2) xerostomia in 8/32 (25%) patients. In 3/32 patients, nephrotoxicity changed from Grade 2 to 3, whereas neither Grade 4 nephrotoxicity nor hematotoxicity was found. In most patients a good agreement was observed for the visual interpretation of the tracer accumulation between 24 h WB and PET/CT scans. However, no significance could be calculated for baseline-absorbed tumor doses and SUV_max values of tumor lesions. 5/32 (16%) patients showed a mixed response pattern, which resulted in disease progression over time.

CONCLUSION

Serial PSA measurements and post-therapy 24 h WB scintigraphy seems to allow a sufficiently accurate follow-up of ¹⁷⁷Lu-PSMA-617-treated mCRPC patients whereas ⁶⁸Ga-PSMA-11 PET/CT should be performed for patient selection and final response assessment.

Lutetium-177 prostate-specific membrane antigen (PSMA) theranostics: practical nuances and intricacies

Theranostic principles utilize a molecular biomarker specific for a tumor target, initially for imaging to assess target expression and, if deemed suitable, for targeted therapy. This presents an exciting opportunity for a highly personalized treatment strategy in the era of precision medicine. Prostate-specific membrane antigen (PSMA) theranostics has attracted increasing attention as a promising targeted treatment in metastatic prostate cancer (PC). ¹⁷⁷Lu-DOTA-PSMA-617 (¹⁷⁷Lu-PSMA-617) is a PSMA-targeted small molecule with favorable properties and is the most extensively investigated PSMA radioligand for radionuclide therapy (RNT) in PC. Since 2014 multiple retrospective studies and more recently a phase II prospective study demonstrated safety and impressive efficacy of ¹⁷⁷Lu-PSMA RNT. The evidence generated by these trials led to two currently underway randomized trials in metastatic castrate-resistant PC: TheraP (NCT03392428) and VISION (NCT03511664). While we wait for these pivotal trials to read out, nuclear medicine physicians, medical oncologists, radiation oncologists, and urologists are facing a steep learning curve to master the intricacies and nuances of this novel therapeutic strategy. This review article aims to share and discuss the evolving experience in practical aspects of PSMA theranostics.

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.

Radioligand therapy using [177Lu]Lu-PSMA-617 in mCRPC: a pre-VISION single-center analysis

Background

Radioligand therapy with [¹⁷⁷Lu]Lu-PSMA-617 is efficacious for the treatment of patients with metastasized castration-resistant prostate cancer (mCRPC). Various studies have evaluated the efficacy and safety of [¹⁷⁷Lu]Lu-PSMA-617 using a dose of 6.0 GBq and an 8-week therapy interval. However, the first prospective phase III trial (VISION) plans to use an elevated cumulative dose by applying 7.5 GBq in a 6-week interval. The aim of the present study was to compare safety and efficacy of the two aforementioned [¹⁷⁷Lu]Lu-PSMA-617 therapy regimes (7.5 GBq every 6 weeks vs. 6.0 GBq every 8 weeks).

Methods

A total number of 78 consecutive patients with mCRPC and a history of first-line chemotherapy were included in this retrospective analysis. The outcome of patients treated with 6.0 GBq [¹⁷⁷Lu]Lu-PSMA-617 per cycle (n = 37) were compared with those treated with 7.5 GBq (n = 41) per cycle. The median therapy intervals were 8.4 weeks (6.0 GBq group) vs. 6.5 (7.5 GBq group). PSA response, PSA progression-free survival (PSA-PFS), overall survival, and adverse events were evaluated and compared between both groups. Chi-squared test, Kaplan Meier estimates, Cox regression, and log-rank test were used. The highest decline from pretherapeutic PSA levels was measured as percentage (best PSA response) and compared between groups by Wilcoxon test.

Results

There was no significant difference comparing the rate of > 50% PSA decline or best PSA response between the 6.0 GBq and 7.5 GBq group (35% vs. 54%, p = 0.065; and − 40.2% vs. − 57.8%, p = 0.329). The median estimated survival and PSA-PFS did not significantly differ between the 6.0 GBq and 7.5 GBq groups as well (11.3 vs. 12.7 months, p = 0.384; and 9.5 vs. 12.3 months, p = 0.258). There was no significant difference regarding the change of kidney, liver, and blood cell parameters under therapy between the treatment groups.

Conclusion

Higher cumulated doses of [¹⁷⁷Lu]Lu-PSMA-617 were well tolerated and caused no significantly increased rate of adverse reactions. Moreover, 7.5 GBq of [¹⁷⁷Lu]Lu-PSMA-617 every 6 weeks causes slightly higher, though not statistically significant, response rates and seems therefore to be the preferable treatment regime. However, future studies are needed to elucidate the dose-related efficacy of [¹⁷⁷Lu]Lu-PSMA-617 as a way to personalized medicine.

The value of tumor markers in men with metastatic prostate cancer undergoing [177 Lu]Lu-PSMA therapy

BACKGROUND

Currently, prostate-specific membrane antigen-radioligand therapy (PSMA-RLT) is considered a last-line treatment option in advanced castration-resistant prostate cancer. Despite these patients' poor prognosis, accurate estimation of their overall survival (OS) is essential to determine whether benefits exist from the treatment and whether the loss of valuable time and unnecessary side effects can be avoided. The aim of the present study is to evaluate whether various biochemical markers can predict OS in men undergoing PSMA-RLT and whether the changes assessed after PSMA-RLT correlate with the OS.

METHODS

The tested tumor markers in this retrospective analysis were alkaline phosphatase (ALP), bone-specific alkaline phosphatase (BAP), prostate-specific antigen (PSA), lactate dehydrogenase (LDH), chromogranin A, and pro-gastrin-releasing peptide (pro-GRP). For the evaluation, we performed blood tests before each PSMA-RLT cycle and during follow-up visits (which were 2-3 months apart). All patients were followed up until their deaths. To test the correlations between the tumor markers and survival, we conducted the logrank tests and the multivariate Cox proportional-hazards regression model. The significance level was set at P < .05.

RESULTS

The study included 137 patients who received a total of 487 PSMA-RLT cycles between January 2015 and November 2017. Of the tested biochemical tumor markers, baseline ALP (120 U/L cut-off), LDH (248 U/L cut-off), and PSA (first quartile cut-off) correlated significantly with survival post-PSMA-RLT (P < .001 for ALP and LDH, and P = .007 for PSA). Stable and/or decreased values in most of the initially abnormal parameters were associated with significantly better OS; these parameters were ALP (P = .009), LDH (P = .005), PSA (P < .001), and pro-GRP (P = .013). The BAP and ALP responses also correlated significantly with survival in patients with bone metastases (P = .002 and P < .001, respectively). Furthermore, there was a strong correlation of the kinetic patterns of PSA, ALP, BAP, and LDH with the survival, showing that patients with steadily increasing markers had the shortest OS.

CONCLUSION

Along with the established tumor marker PSA, ALP, LDH, BAP, and pro-GRP were correlated with the OS post-PSMA-RLT in the univariate and multivariate analyses.

Clinical outcome of standardized 177Lu-PSMA-617 therapy in metastatic prostate cancer patients receiving 7400 MBq every 4 weeks

Purpose

[¹⁷⁷Lu]Lu-PSMA-617 radio-ligand therapy (PSMA-RLT) is emerging in patients with an advanced metastatic castration-resistant prostate cancer (mCRPC). Here, we aimed to estimate the results of PSMA-RLT in terms of response, progression-free survival (PFS), and overall survival (OS) in patients receiving a highly standardized treatment regimen due to mCRPC. The toxicity of PSMA-RLT has also been evaluated.

Patients and methods

Fifty-four patients (mean age 72 ± 7 years, median PSA at time of initial therapy 66 [range 1.0–4890 μg/L]), receiving three PSMA-RLT cycles (mean 7315 ± 573 MBq) at four weekly intervals, were included in this retrospective analysis. Hematological and biochemical parameters were regularly determined in every patient. Kaplan-Meier estimates were used to assess PFS and OS and a Cox proportional hazard model was used to analyze significant associations. Treatment response was based on PSA measurements 4 weeks after the 3rd treatment.

Results

The majority of patients were previously treated with abiraterone/enzalutamide (69%) and docetaxel/cabazitaxel (67%). In total, 79% of the patients showed a decrease in PSA (median PSA decrease from 66 to 19.8, range 0.7–4563 μg/L, P < 0.001) 1 month after the 3rd therapy cycle. Among them, 58% and 35% demonstrated a PSA-decline of > 50% and > 80%, respectively. Median OS was 119 weeks; median PFS was 25 weeks. Patients presenting with a PSA decline had significantly longer PFS (27 vs. 15 weeks, P < 0.0001) and OS (median survival not reached vs. 52 weeks, P < 0.001) than patients with no PSA reduction. Moreover, patients with reduction in PSA levels ≥ 50% (median survival not reached vs. 52 weeks, P < 0.0001) and ≥ 80% (median survival not reached vs. 87 weeks, P = 0.008) lived significantly longer. While hemoglobin did not change during treatment, levels of platelets (236 ± 71 g/L vs. 193 ± 67 g/L) and leucocytes (6.5, range 2.9–13.7 g/L vs. 4.8, range 1.5–12.3 g/L) decreased significantly, both P < 0.001. Two grade 3 leukocytopenia and one grade 3 anemia were observed.

Conclusion

Intense PSMA-RLT regime with four weekly intervals between the cycles is well-tolerated and offers favorable response rates, PFS, and survival rates for patients with mCRPC.

Response Prediction of 177Lu-PSMA-617 Radioligand Therapy Using Prostate-Specific Antigen, Chromogranin A, and Lactate Dehydrogenase

Neuroendocrinelike transdifferentiation of prostate cancer adenocarcinomas correlates with serum levels of chromogranin A (CgA) and drives treatment resistance. The aim of this work was to evaluate whether CgA can serve as a response predictor for ¹⁷⁷Lu-prostate-specific membrane antigen 617 (PSMA) radioligand therapy (RLT) in comparison with the established tumor markers. Methods: One hundred consecutive patients with metastasized castration-resistant prostate cancer scheduled for PSMA RLT were evaluated for prostate-specific antigen (PSA), lactate dehydrogenase (LDH), and CgA at baseline and in follow-up of PSMA RLT. Tumor uptake of PSMA ligand, a known predictive marker for response, was assessed as a control variable. Results: From the 100 evaluated patients, 35 had partial remission, 16 stable disease, 15 mixed response, and 36 progression of disease. Tumor uptake above salivary gland uptake translated into partial remission, with an odds ratio (OR) of 60.265 (95% confidence interval [CI], 5.038-720.922). Elevated LDH implied a reduced chance for partial remission, with an OR of 0.094 (95% CI, 0.017-0.518), but increased the frequency of progressive disease (OR, 2.717; 95% CI, 1.391-5.304). All patients who achieved partial remission had a normal baseline LDH. Factor-2 elevation of CgA increased the risk for progression, with an OR of 3.089 (95% CI, 1.302-7.332). Baseline PSA had no prognostic value for response prediction. Conclusion: In our cohort, baseline PSA had no prognostic value for response prediction. LDH was the marker with the strongest prognostic value, and elevated LDH increased the risk for progression of disease under PSMA RLT. Elevated CgA demonstrated a moderate impact as a negative prognostic marker in general but was explicitly related to the presence of liver metastases. Well in line with the literature, sufficient tumor uptake is a prerequisite to achieve tumor response.

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.

Preclinical Evaluation of 203/212Pb-Labeled Low-Molecular-Weight Compounds for Targeted Radiopharmaceutical Therapy of Prostate Cancer

Targeted radiopharmaceutical therapy (TRT) using α-particle radiation is a promising approach for treating both large and micrometastatic lesions. We developed prostate-specific membrane antigen (PSMA)-targeted low-molecular-weight agents for ²¹²Pb-based TRT of patients with prostate cancer (PC) by evaluating the matching γ-emitting surrogate, ²⁰³Pb. Methods: Five rationally designed low-molecular-weight ligands (L1-L5) were synthesized using the lysine-urea-glutamate scaffold, and PSMA inhibition constants were determined. Tissue biodistribution and SPECT/CT imaging of ²⁰³Pb-L1-²⁰³Pb-L5 were performed on mice bearing PSMA(+) PC3 PIP and PSMA(-) PC3 flu flank xenografts. The absorbed radiation dose of the corresponding ²¹²Pb-labeled analogs was determined using the biodistribution data. Antitumor efficacy of ²¹²Pb-L2 was evaluated in PSMA(+) PC3 PIP and PSMA(-) PC3 flu tumor models and in the PSMA(+) luciferase-expressing micrometastatic model. ²¹²Pb-L2 was also evaluated for dose-escalated, long-term toxicity. Results: All new ligands were obtained in high yield and purity. PSMA inhibitory activities ranged from 0.10 to 17 nM. ²⁰³Pb-L1-²⁰³Pb-L5 were synthesized in high radiochemical yield and specific activity. Whole-body clearance of ²⁰³Pb-L1-²⁰³Pb-L5 was fast. The absorbed dose coefficients (mGy/kBq) of the tumor and kidneys were highest for ²⁰³Pb-L5 (31.0, 15.2) and lowest for ²⁰³Pb-L2 (8.0, 4.2). The tumor-to-kidney absorbed dose ratio was higher for ²⁰³Pb-L3 (3.2) and ²⁰³Pb-L4 (3.6) than for the other agents, but with lower tumor-to-blood ratios. PSMA(+) tumor lesions were visualized through SPECT/CT as early as 0.5 h after injection. A proof-of-concept therapy study with a single administration of ²¹²Pb-L2 demonstrated dose-dependent inhibition of tumor growth in the PSMA(+) flank tumor model. ²¹²Pb-L2 also demonstrated an increased survival benefit in the micrometastatic model compared with ¹⁷⁷Lu-PSMA-617. Long-term toxicity studies in healthy, immunocompetent CD-1 mice revealed kidney as the dose-limiting organ. Conclusion: ²⁰³Pb-L1-²⁰³Pb-L5 demonstrated favorable pharmacokinetics for ²¹²Pb-based TRT. The antitumor efficacy of ²¹²Pb-L2 supports the corresponding ²⁰³Pb/²¹²Pb theranostic pair for PSMA-based α-particle TRT in advanced PC.

Imaging Diagnosis and Follow-up of Advanced Prostate Cancer: Clinical Perspectives and State of the Art

The management of advanced prostate cancer has changed substantially with the availability of multiple effective novel treatments, which has led to improved disease survival. In the era of personalized cancer treatments, more precise imaging may help physicians deliver better care. More accurate local staging and earlier detection of metastatic disease, accurate identification of oligometastatic disease, and optimal assessment of treatment response are areas where modern imaging is rapidly evolving and expanding. Next-generation imaging modalities, including whole-body MRI and molecular imaging with combined PET and CT and combined PET and MRI using novel radiopharmaceuticals, create new opportunities for imaging to support and refine management pathways in patients with advanced prostate cancer. This article demonstrates the potential and challenges of applying next-generation imaging to deliver the clinical promise of treatment breakthroughs.

Excellent Response to Lower Dose of 177Lu-PSMA-617 in a Metastatic Castration-Resistant Prostate Cancer Patient With a Transplanted Kidney

A 68-year-old man with metastatic castration-resistant prostate cancer and widespread bone metastases as well as a history of kidney transplant, underwent 5 cycles of Lu-prostate-specific membrane antigen 617 therapies in our department. Being more cautious of the radiation burden imposed on the transplanted kidney, a lower average dose of 4 GBq per cycle was administered (instead of the more routine 6.0-7.4 GBq per cycle). However, excellent response was noted and serum creatinine level of 0.8 mg/dL remained stable.

Targeted Radionuclide Therapy: New Advances for Improvement of Patient Management and Response

Compared to external beam radiotherapy, targeted radionuclide therapy (TRT) allows for systemic radiation treatment of metastatic lesions. Published work on recent strategies to improve patient management and response to TRT through individualising patient treatment, modifying treatment pharmacokinetics and increasing anticancer potency are discussed in this review, with a special focus on the application of clinically evaluated radiolabelled ligands and peptides in the treatment of neuroendocrine and prostate cancers.

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.

Albumin-Binding PSMA Ligands: Implications for Expanding the Therapeutic Window

Despite significant gains in the treatment of metastatic castration-resistant prostate cancer by radioligands targeting prostate-specific membrane antigen (PSMA), 30% of patients never respond to therapy. One possible explanation is insufficient dose delivery to the tumor because of suboptimal pharmacokinetics. We have recently described RPS-063, a trifunctional ligand targeting PSMA with high uptake in LNCaP xenograft tumors but also in kidneys. We aimed to use structural modifications to increase the tumor-to-kidney ratio through increased albumin binding and tumor uptake and reduction of kidney activity. Methods: Four structurally related trifunctional PSMA-targeting small molecules were prepared by either varying the albumin-binding group or inserting a polyethylene glycol 8 linker into a common structure. The compounds were ranked by PSMA affinity and albumin affinity and were radiolabeled with ⁶⁸Ga and ¹⁷⁷Lu. Tissue kinetics were determined in male BALB/C nu/nu mice bearing LNCaP xenograft tumors. Results: Each of the compounds binds PSMA with a half-maximal inhibitory concentration of no more than 10 nM. The albumin-binding group had a minimal effect on PSMA affinity but changed albumin affinity by an order of magnitude. However, the addition of a polyethylene glycol 8 spacer weakened affinity for albumin in each case. Increased affinity for albumin corresponded with delayed blood clearance and modified uptake kinetics in the tumor and kidney. Uptake of ¹⁷⁷Lu-RPS-072 (34.9 ± 2.4 %ID/g) and ¹⁷⁷Lu-RPS-077 (27.4 ± 0.6 %ID/g) increased up to 24 h after injection, and washout by 96 h was not significant. As a result, the area under the curve (AUC) in the tumor was in the following order: ¹⁷⁷Lu-RPS-072 > ¹⁷⁷Lu-RPS-077 > ¹⁷⁷Lu-RPS-063 > ¹⁷⁷Lu-RPS-071. Increased linker length corresponded to more rapid clearance from kidneys. Consequently, the ratio of tumor AUC and kidney AUC was 4.7 ± 0.3 for ¹⁷⁷Lu-RPS-072. Conclusion: The tumor AUC and tumor-to-kidney ratio of ¹⁷⁷Lu-RPS-072 are significantly enhanced compared with any small molecule investigated in a LNCaP xenograft model to date. In comparison to other PSMA-targeting radioligands that have been evaluated in a PC3-PIP model, activity in kidneys is reduced and activity in tumors compares favorably when the different PSMA expression levels in LNCaP and PC3-PIP cells are considered. RPS-072 therefore exhibits an increased therapeutic index, shows the potential to increase the dose delivered to tumors, and is a highly promising candidate for targeted radioligand therapy.

225Ac-PSMA-617 in chemotherapy-naive patients with advanced prostate cancer: a pilot study

Background

A remarkable therapeutic efficacy has been demonstrated with ²²⁵Ac-prostate-specific membrane antigen (PSMA)-617 in heavily pre-treated metastatic castration-resistant prostate cancer (mCRPC) patients. We report our experience with ²²⁵Ac-PSMA-617 therapy in chemotherapy-naïve patients with advanced metastatic prostate carcinoma.

Methods

Seventeen patients with advanced prostate cancer were selected for treatment with ²²⁵Ac-PSMA-617 in 2-month intervals, with initial activity of 8 MBq, then de-escalation to 7 MBq, 6 MBq or 4 MBq in cases of good response. In one patient, activity was escalated to 13 MBq in the third cycle. Fourteen patients had three treatment cycles administered, while in three patients treatment was discontinued after two cycles due to good response. Six out of 17 patients received additional treatments after the third cycle. Prostate-specific antigen (PSA) was measured every 4 weeks for PSA response assessment. ⁶⁸Ga-PSMA-PET/CT was used for functional response assessment before each subsequent treatment cycle. Serial full blood count, renal function test, and liver function were obtained to determine treatment-related side effects.

Results

Good antitumor activity assessed by serum PSA level and ⁶⁸Ga-PSMA-PET/CT was seen in 16/17 patients. In 14/17 patients, PSA decline ≥90% was seen after treatment, including seven patients with undetectable serum PSA following two (2/7) or three cycles (5/7) cycles of ²²⁵Ac-PSMA-617. Fifteen of 17 patients had a > 50% decline in lesions avidity for tracer on ⁶⁸Ga-PSMA-PET/CT including 11 patients with complete resolution (PET-negative and either stable sclerosis on CT for bone or resolution of lymph node metastases) of all metastatic lesions. Grade 1/2 xerostomia was seen in all patients, and none was severe enough to lead to discontinuation of treatment. One patient had with extensive bone marrow metastases and a background anemia developed a grade 3 anemia while another patient with solitary kidney and pre-treatment grade 3 renal failure developed grade 4 renal toxicity following treatment. The group presented with significant palliation of bone pain and reduced toxicity to salivary glands due to de-escalation.

Conclusions

²²⁵Ac-PSMA-617 RLT of chemotherapy-naïve patients with advanced metastatic prostate carcinoma led to a ≥ 90% decline in serum PSA in 82% of patients including 41% of patients with undetectable serum PSA who remained in remission 12 months after therapy. The remarkable therapeutic efficacy reported in this study could be achieved with reduced toxicity to salivary glands due to de-escalation of administered activities in subsequent treatment cycles. This necessitates further exploration for informing clinical practice and clinical trial design.

Role of textural heterogeneity parameters in patient selection for 177Lu-PSMA therapy via response prediction

Purpose

Prostate cancer is most common tumor in men causing significant patient mortality and morbidity. In newer diagnostic/therapeutic agents PSMA linked ones are specifically important. Analysis of textural heterogeneity parameters is associated with determination of innately aggressive and therapy resistant cell lines thus emphasizing their importance in therapy planning. The objective of current study was to assess predictive ability of tumor textural heterogeneity parameters from baseline ⁶⁸Ga-PSMA PET prior to ¹⁷⁷Lu-PSMA therapy.

Results

Entropy showed a negative correlation (r_s = −0.327, p = 0.006, AUC = 0.695) and homogeneity showed a positive correlation (r_s = 0.315, p = 0.008, AUC = 0.683) with change in pre and post therapy PSA levels.

Conclusions

Study showed potential for response prediction through baseline PET scan using textural features. It suggested that increase in heterogeneity of PSMA expression seems to be associated with an increased response to PSMA radionuclide therapy.

Materials and Methods

Retrospective analysis of 70 patients was performed. All patients had metastatic prostate cancer and were planned to undergo ¹⁷⁷Lu-PSMA therapy. Pre-therapeutic ⁶⁸Ga- PSMA PET scans were used for analysis. 3D volumes (VOIs) of 3 lesions each in bones and lymph nodes were manually delineated in static PET images. Five PET based textural heterogeneity parameters (COV, entropy, homogeneity, contrast, size variation) were determined. Results obtained were then compared with clinical parameters including pre and post therapy PSA, alkaline phosphate, bone specific alkaline phosphate levels and ECOG criteria. Spearman correlation was used to determine statistical dependence among variables. ROC analysis was performed to estimate the optimal cutoff value and AUC.

Prostate specific membrane antigen: the role in salvage lymph node dissection and radio-ligand therapy

INTRODUCTION

Prostate-specific membrane antigen (PSMA) is a receptor highly expressed on the membranes of prostate cancer (PCa) cells and provides a new opportunity for imaging and targeted therapy in metastatic prostate cancer. The use of radio-labelled peptides with high affinity for PSMA-receptor allows for localization of oligo-metastasis to guide salvage lymph node (LN) dissection, and effective delivery of radionuclide therapy to PCa cells. This review discusses the current statistics of PSMA-guided salvage lymph-node dissection.

EVIDENCE ACQUISITION

A non-systematic literature search of the Medline, Embase, and Scopus databases was performed in December 2017 using medical subject headings and free-text protocol.

EVIDENCE SYNTHESIS

The properties of PSMA has enabled the timely detection of oligometastatic disease, potentially altering oncological outcomes of men with PCa. The utility of PSMA in directing sLND has been proven to have an impact in achieving modest biochemical response which is generally not durable.

CONCLUSIONS

Larger randomized controlled trials are needed to validate the current findings, determine treatment protocols, and weigh up its benefits and determine its standing amongst the current management strategies for PCa.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Radioligand therapy of metastatic castration-resistant prostate cancer: current approaches

Prostate Cancer is the forth most common type of cancer. Prostate-specific membrane antigen (PSMA) is anchored in the cell membrane of prostate epithelial cells. PSMA is highly expressed on prostate epithelial cells and strongly up-regulated in prostate cancer. Therefore it is an appropriate target for diagnostic and therapy of prostate cancer and its metastases. This article discusses several articles on radionuclide treatments in prostate cancer and the results on PSMA therapy with either beta or alpha emitters as a salvage therapy.

[Lutetium-177-PSMA radioligand therapy : Consensus within the framework of GKV-funded care between the university hospitals in Aachen, Bonn, Düsseldorf, Essen, and Cologne and the MDK Nordrhein]

In the last 3 years, Lutetium-177 prostate-specific membrane antigen radioligand therapy (Lu-177-PSMA-RLT) has received increasing attention in nuclear medicine as a new form of treatment for castration-resistant metastatic prostate cancer. This therapy combines the radionuclide Lutetium-177, which has been therapeutically used in nuclear medicine for many years, with a molecular target of the transmembrane prostate-specific membrane antigen expressed by prostate cancer cells. Since there are no prospective randomized studies on Lu-177-PSMA-RLT and the question of reimbursement has repeatedly been the subject of review by the MDK Nordrhein (Medischenische Dienst der Krankenversicherung), there was a desire because of the increasing number of patients being treated to clarify under which circumstances Lu-177-PSMA-RLT can be reimbursed by German statutory health insurance. The goals of this article are to help treating physicians understand how this new therapy option works, to integrate it in the overall therapy concept for castration-resistant metastatic prostate cancer, and, above all, to use Lu-177-PSMA-RLT-based on the current data-at the right place in the therapy sequence of castration-resistant metastatic prostate cancer.

Predictors of overall survival in metastatic castration-resistant prostate cancer patients receiving [177Lu]Lu-PSMA-617 radioligand therapy

Prostate-specific membrane antigen (PSMA) is a promising target for the diagnosis of and therapy for metastatic castration-resistant prostate cancer (mCRPC). The aim of this study was to measure overall-survival (OS) in mCRPC patients who received either abiraterone or enzalutamide prior to PSMA therapy. The second aim of this study was to analyse the predictors of OS according to different pre-therapeutic parameters and also the responses to the first cycle of radioligand therapy (RLT) base on PSA level. Patients with mCRPC and a history of therapy with either abiraterone or enzalutamide or both, were included in this study. Different laboratory tests and pre-therapeutic parameters have been included into the analysis. One-hundred patients received a total of 347 cycles of Lu-PSMA (median: three cycles). 69 patients showed a decline in PSA two months after the first cycle, and 38 of those patients showed a PSA decline of = > 50%. The median OS was 60 weeks. In the multivariate analysis, the level of albumin, AST and haemoglobin, existence of liver metastases and a decline of > 14% in PSA level had a significant impact on overall-survival. The median OS is significantly longer in patients without hepatic involvement, with high levels of albumin and Hb and low levels of AST. A decline in PSA levels of more than 14% was the most important response parameter with regard to overall survival.

Theranostics in nuclear medicine practice

The importance of personalized medicine has been growing, mainly due to a more urgent need to avoid unnecessary and expensive treatments. In nuclear medicine, the theranostic approach is an established tool for specific molecular targeting, both for diagnostics and therapy. The visualization of potential targets can help predict if a patient will benefit from a particular treatment. Thanks to the quick development of radiopharmaceuticals and diagnostic techniques, the use of theranostic agents has been continually increasing. In this article, important milestones of nuclear therapies and diagnostics in the context of theranostics are highlighted. It begins with a well-known radioiodine therapy in patients with thyroid cancer and then progresses through various approaches for the treatment of advanced cancer with targeted therapies. The aim of this review was to provide a summary of background knowledge and current applications, and to identify the advantages of targeted therapies and imaging in nuclear medicine practices.

Repeated 177Lu-Labeled PSMA-617 Radioligand Therapy Using Treatment Activities of Up to 9.3 GBq

Current treatment protocols for ¹⁷⁷Lu-labeled PSMA-617 therapies were cautiously derived from dosimetry data, but their practical appropriateness has not yet been proven clinically. We retrospectively report our clinical observations using 4 different treatment activities. Methods: Forty patients with advanced prostate cancer and positive uptake in prostate-specific membrane antigen (PSMA) imaging were treated with 4 GBq of ¹⁷⁷Lu activity/80 nmol of precursor, 6 GBq of ¹⁷⁷Lu activity/120 nmol of precursor, 7.4 GBq of ¹⁷⁷Lu activity/150 nmol of precursor, or 9.3 GBq of ¹⁷⁷Lu activity/150 nmol of precursor (10 patients per group) every 2 mo. Safety was checked every 2 wk by laboratory tests, the prostate-specific antigen response was checked every 4 wk, and other effects were assessed by anamnesis. Results: The initial prostate-specific antigen response showed no correlation with treatment activity. However, 2 of 10, 4 of 10, 4 of 10, and 7 of 10 patients receiving doses of 4, 6, 7.4, and 9.3 GBq, respectively, were in partial remission 8 wk after completing all 3 cycles. This finding would be in line with but-because of low patient numbers-would not prove a positive dose-response relationship. Acute hematologic toxicity was also not correlated with treatment activity, and no more than 1 patient per group had grade 3/4 toxicity. Nevertheless, in contrast to the findings for the other groups, the mean platelet count in the 9.3-GBq group decreased chronically over time. Conclusion: If patients with diffuse red marrow infiltration and extensive chemotherapeutic pretreatments are excluded, then treatment activities of up to 3 injections of 9.3 GBq of ¹⁷⁷Lu-PSMA-617 every 2 mo are tolerated well. Further dose escalation should be conducted with care, as the highest dose seems to be close to the maximum tolerable dose.

Repeated PSMA-targeting radioligand therapy of metastatic prostate cancer with 131I-MIP-1095

PURPOSE

Prostate-specific membrane antigen (PSMA)-targeting radioligand therapy (RLT) was introduced in 2011. The first report described the antitumor and side effects of a single dose. The aim of this analysis was to evaluate toxicity and antitumor activity after single and repetitive therapies.

METHODS

Thirty-four men with metastatic castration-resistant prostate cancer received PSMA-RLT with 131I-MIP-1095. Twenty-three patients received a second, and three patients a third dose, timed at PSA progression after an initial response to the preceding therapy. The applied doses were separated in three groups: <3.5, 3.5-5.0 and >5.0 GBq. Antitumor and side-effects were analyzed by blood samples and other clinical data. Follow-up was conducted for up to 5 years.

RESULTS

The best therapeutic effect was achieved by the first therapy. A PSA decline of ≥50% was achieved in 70.6% of the patients. The second and third therapies were significantly less effective. There was neither an association between the applied activity and PSA response or the time-to-progression. Hematologic toxicities were less prevalent but presented in a higher percentage of patients with increasing number of therapies. After hematologic toxicities, xerostomia was the second most frequent side effect and presented more often and with higher intensity after the second or third therapy.

CONCLUSION

The first dose of RLT with 131I-MIP-1095 presented with low side effects and could significantly reduce the tumor burden in a majority of patients. The second and third therapies were less effective and presented with more frequent and more intense side effects, especially hematologic toxicities and xerostomia.

Overall survival and response pattern of castration-resistant metastatic prostate cancer to multiple cycles of radioligand therapy using [177Lu]Lu-PSMA-617

PURPOSE

Up to 30% of patients with castration-resistant prostate cancer (CRPC) do not show any response to the first cycle of radioligand therapy (RLT) with [¹⁷⁷Lu]Lu-PSMA-617 (Lu-PSMA). We evaluated patient response to the second and third cycles of RLT in patients that underwent at least three cycles. The second aim of this study was to calculate the median overall survival (OS) of responders and non-responders after the first cycle and after all three cycles of RLT.

METHODS

CRPC patients were treated with Lu-PSMA, with a median interval of 8 weeks between each cycle. The tumour marker prostate-specific antigen (PSA) was used as the marker for response evaluation.

RESULTS

Fifty-two patients underwent a total of 190 cycles of RLT (3-6 cycles per patient). Of these, 80.8% showed a decline in PSA 2 months after the first cycle, with 44.2% showing a PSA decline of ≥50%. When compared to baseline PSA, 73.1% showed a PSA decline after the third cycle. 50% of patients that did not show any response to the first cycle also did not respond to the second and third cycles. The median OS was 60 weeks in all patients. The median OS was significantly longer for patients that showed any PSA decline after the first cycle compared to patients without PSA decline (68 vs. 33 weeks). There was a significant difference in median OS between responders and non-responders for a change in PSA after the third cycle compared to baseline PSA.

CONCLUSION

Patients with a positive response to RLT, regardless of the rate of decline, had a significantly longer median OS. Of the patients that did not show any response to the first cycle, 50% responded to the second or third cycles.

The impact of repeated cycles of radioligand therapy using [177Lu]Lu-PSMA-617 on renal function in patients with hormone refractory metastatic prostate cancer

BACKGROUND

[¹⁷⁷Lu]Lu-PSMA-617 is a well-tolerated therapy for the treatment of metastatic prostate cancer. However, because of the mainly renal excretion of the tracer, the kidneys are one of the most limiting organs. The purpose of this study was to examine the post-therapeutic changes in renal function over time and to identify risk factors for developing renal toxicity. We also tested the reliability of markers for renal function monitoring.

METHODS

Fifty-five patients with castrate-resistant metastatic prostate cancer treated with at least three cycles of [¹⁷⁷Lu]Lu-PSMA-617 were investigated. Renal function was assessed through laboratory tests (creatinine, GFR, cystatin C) and Tc-99 m-MAG3 measurements. Adverse events were classified according to the Common Terminology Criteria for Adverse Events (CTCAE) v4.0. To identify risk factors for renal toxicity, we used Pearson's correlation coefficient and the corresponding p values.

RESULTS

None of the 55 patients experienced severe nephrotoxicity (grade 3/4). In 14 patients (25%), we observed increased creatinine levels of CTC 1° or 2°. There were 16 cases of increased GFR (grade 1/2). At the baseline, only 14 patients had elevated cystatin C. However, post-therapeutic cystatin C was elevated in 32 patients (58%). A significant effect on renal function was found for age (p = 0.049), hypertension (p = 0.001) and pre-existing kidney disease (p = 0.001). The most reliable predictive markers of nephrotoxicity were TER-MAG3 and cystatin C.

CONCLUSION

Renal toxicity in patients treated with [¹⁷⁷Lu]Lu-PSMA-617 was low. There was no (sub)acute grade 3 or 4 nephrotoxicity.

Lutetium 177 PSMA radionuclide therapy for men with prostate cancer: a review of the current literature and discussion of practical aspects of therapy

Prostate-specific membrane antigen (PSMA) is a receptor on the surface of prostate cancer cells that is revolutionising the way we image and treat men with prostate cancer. New small molecule peptides with high-binding affinity for the PSMA receptor have allowed high quality, highly specific PET imaging, in addition to the development of targeted radionuclide therapy for men with prostate cancer. This targeted therapy for prostate cancer has, to date, predominately used Lutetium 177 (Lu) labelled PSMA peptides. Early clinical studies evaluating the safety and efficacy of Lu PSMA therapy have demonstrated promising results with a significant proportion of men with metastatic prostate cancer, who have already failed other therapies, responding clinically to Lu PSMA. This review discusses the practical issues of administering Lu PSMA, and gives an overview of the findings from currently published trials in regards to treatment response rates, expected toxicities and safety.