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

Novel Therapeutic Targets on the Horizon: An Analysis of Clinical Trials on Therapies for Bone Metastasis in Prostate Cancer

In the absence of early detection and initial treatment, prostate cancer often progresses to an advanced stage, frequently spreading to the bones and significantly impacting patients' well-being and healthcare resources. Therefore, managing patients with prostate cancer that has spread to the bones often involves using bone-targeted medications like bisphosphonates and denosumab to enhance bone structure and minimize skeletal complications. Additionally, researchers are studying the tumor microenvironment and biomarkers to understand the mechanisms and potential treatment targets for bone metastases in prostate cancer. A literature search was conducted to identify clinical studies from 2013 to 2023 that focused on pain, performance status, or quality of life as primary outcomes. The analysis included details such as patient recruitment, prior palliative therapies, baseline characteristics, follow-up, and outcome reporting. The goal was to highlight the advancements and trends in bone metastasis research in prostate cancer over the past decade, with the aim of developing strategies to prevent and treat bone metastases and improve the quality of life and survival rates for prostate cancer patients.

Prostate-Specific Membrane Antigen: Gateway to Management of Advanced Prostate Cancer

Prostate-specific membrane antigen (PSMA) as a transmembrane protein is overexpressed by prostate cancer (PC) cells and is accessible for binding antibodies or low-molecular-weight radioligands due to its extracellular portion. Successful targeting of PSMA began with the development of humanized J591 antibody. Due to their faster clearance compared to antibodies, small-molecule radioligands for targeted imaging and therapy of PC have been favored in recent development efforts. PSMA positron emission tomography (PET) imaging has higher diagnostic performance than conventional imaging for initial staging of high-risk PC and biochemical recurrence detection/localization. However, it remains to be demonstrated how to integrate PSMA PET imaging for therapy response assessment and as an outcome endpoint measure in clinical trials. With the recent approval of 177Lu-PSMA-617 by the US Food and Drug Administration for metastatic castration-resistant PC progressing after chemotherapy, the high value of PSMA-targeted therapy was confirmed. Compared to standard of care, PSMA-based radioligand therapy led to a better outcome and a higher quality of life. This review, focusing on the advanced PC setting, provides an overview of different approved and nonapproved PSMA-targeted imaging and therapeutic modalities and discusses the future of PSMA-targeted theranostics, also with an outlook on non-radiopharmaceutical-based PSMA-targeted therapies.

Imaging GRPr Expression in Metastatic Castration-Resistant Prostate Cancer with [68Ga]Ga-RM2-A Head-to-Head Pilot Comparison with [68Ga]Ga-PSMA-11

BACKGROUND

The gastrin-releasing peptide receptor (GRPr) is highly overexpressed in several solid tumors, including treatment-naïve and recurrent prostate cancer. [68Ga]Ga-RM2 is a well-established radiotracer for PET imaging of GRPr, and [177Lu]Lu-RM2 has been proposed as a therapeutic alternative for patients with heterogeneous and/or low expression of PSMA. In this study, we aimed to evaluate the expression of GRPr and PSMA in a group of patients diagnosed with castration-resistant prostate cancer (mCRPC) by means of PET imaging.

METHODS

Seventeen mCRPC patients referred for radio-ligand therapy (RLT) were enrolled and underwent [68Ga]Ga-PSMA-11 and [68Ga]Ga-RM2 PET/CT imaging, 8.8 ± 8.6 days apart, to compare the biodistribution of each tracer. Uptake in healthy organs and tumor lesions was assessed by SUV values, and tumor-to-background ratios were analyzed.

RESULTS

[68Ga]Ga-PSMA-11 showed significantly higher uptake in tumor lesions in bone, lymph nodes, prostate, and soft tissues and detected 23% more lesions compared to [68Ga]Ga-RM2. In 4/17 patients (23.5%), the biodistribution of both tracers was comparable.

CONCLUSIONS

Our results show that in our cohort of mCRPC patients, PSMA expression was higher compared to GRPr. Nevertheless, RLT with [177Lu]Lu-RM2 may be an alternative treatment option for selected patients or patients in earlier disease stages, such as biochemical recurrence.

Precision strikes: PSMA-targeted radionuclide therapy in prostate cancer - a narrative review

Introduction

Radio-ligand targeted therapy is a new and promising concept of treatment Castration resistant prostate cancer (CRPC). Only a few radio-pharmaceutics were approved for usage in treating prostate cancer, among the multiple others tested. We aimed to review and summarize the literature on the therapeutic isotopes specific for PSMA.

Methods

We performed a scoping literature review of PubMed from January 1996 to December 2022.

Results

98 publications were selected for inclusion in this review. The studies contained in publications allowed to summarize the data on pharmacokinetics, therapeutic effects, side effects and the medical use of 225Ac and 177Lu radionuclides. The review also presents new research directions for specific PSMA radionuclides.

Conclusion

Radioligand targeted therapy is a new and promising concept where Lu-177-PSMA-617 have promising outcomes in treatment according to standard of care.

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.

Joint EANM/SNMMI procedure guideline for the use of 177Lu-labeled PSMA-targeted radioligand-therapy (177Lu-PSMA-RLT)

Prostate-specific membrane antigen (PSMA) is expressed by the majority of clinically significant prostate adenocarcinomas, and patients with target-positive disease can easily be identified by PSMA PET imaging. Promising results with PSMA-targeted radiopharmaceutical therapy have already been obtained in early-phase studies using various combinations of targeting molecules and radiolabels. Definitive evidence of the safety and efficacy of [177Lu]Lu-PSMA-617 in combination with standard-of-care has been demonstrated in patients with metastatic castration-resistant prostate cancer, whose disease had progressed after or during at least one taxane regimen and at least one novel androgen-axis drug. Preliminary data suggest that 177Lu-PSMA-radioligand therapy (RLT) also has high potential in additional clinical situations. Hence, the radiopharmaceuticals [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T are currently being evaluated in ongoing phase 3 trials. The purpose of this guideline is to assist nuclear medicine personnel, to select patients with highest potential to benefit from 177Lu-PSMA-RLT, to perform the procedure in accordance with current best practice, and to prepare for possible side effects and their clinical management. We also provide expert advice, to identify those clinical situations which may justify the off-label use of [177Lu]Lu-PSMA-617 or other emerging ligands on an individual patient basis.

Lutetium-177 PSMA for the treatment of metastatic castrate resistant prostate cancer: a systematic review

INTRODUCTION

Metastatic castrate resistant prostate cancer (mCPRC) remains an aggressive form of prostate cancer that no longer responds to traditional hormonal treatment alone. Despite the advent of novel anti-androgen medications, many patients continue to progress, and as a result, there is a growing need for additional treatment options.

AREAS COVERED

Lutetium-177 (177Lu) - PSMA-617 has become one of the new frontline treatment options for refractory metastatic castrate resistant prostate cancer after the failure of novel anti-androgen therapy and chemotherapy. Lu-177 has been used in real-world prospective trials and is now becoming utilized in newer phase III clinical trials. Here, we present a comprehensive overview of the current literature, covering retrospective studies, prospective studies, and clinical trials that established Lutetium-177-PSMA-617 (177Lu-PSMA-617) for the treatment of mCRPC.

EXPERT OPINION

177Lu - PSMA-617 has been approved for treatment of mCRPC based on positive phase III studies. While this treatment is tolerable and effective, biomarkers are necessary to determine which patients will benefit. In the future, radioligand treatments will likely be utilized in earlier lines of therapy and potentially in combination with other prostate cancer treatments.

Treatment of Advanced Metastatic Prostate Cancer Using Molecular-Targeted Therapy: Radioligand Lutetium-177 Prostate-Specific Membrane Antigen

This study investigates the predicting factors of the biochemical response and survival of patients with advanced metastatic prostate cancer who underwent therapy with radioligand lutetium-177 (¹⁷⁷Lu)-prostate-specific membrane antigen (PSMA), often referred to as [¹⁷⁷Lu]Lu-PSMA. This study is a review of the previous literature. This study included articles published in the last 10 years in the English language. According to the literature review, treatment with [¹⁷⁷Lu]Lu-PSMA has a positive impact on prostate-specific antigen (PSA) within the first cycle and a negative impact on lymph node metastasis. There is a plausible positive impact on PSA after multiple cycles and performance status and a negative impact on visceral metastasis. In conclusion, the reviews show that treatment with [¹⁷⁷Lu]Lu-PSMA in patients with castration-resistant prostate cancer is beneficial in reducing PSA and metastasis.

Biodistribution and dosimetry for combined [177Lu]Lu-PSMA-I&T/[225Ac]Ac-PSMA-I&T therapy using multi-isotope quantitative SPECT imaging

PURPOSE

Quantitative SPECT for patient-specific dosimetry is a valuable tool in the scope of radionuclide therapy, although its clinical application for ²²⁵Ac-based treatments may be limited due to low therapeutic activities. Therefore, the aim of this study was to demonstrate the feasibility of clinical quantitative low-count SPECT imaging during [¹⁷⁷Lu]Lu-PSMA-I&T/[²²⁵Ac]Ac-PSMA-I&T treatment.

METHODS

Eight prostate cancer patients (1000 MBq/8 MBq [¹⁷⁷Lu]Lu-PSMA-I&T/[²²⁵Ac]Ac-PSMA-I&T) received a single-bed quantitative ¹⁷⁷Lu/²²⁵Ac SPECT/CT acquisition (1 h) at 24 h post treatment (high-energy collimator, 16 projections p. head à 3.5 min, 128 × 128 pixel). The gamma peak at 440 keV (width: 10%) of the progeny ²¹³Bi was imaged along with the peak at 208 keV (width: 15%) of ¹⁷⁷Lu. Quantification included CT-based attenuation and window-based scatter correction plus resolution modelling. Gaussian post-filtering with a full-width-half-maximum of 30 mm and 40-45 mm was employed to match the signal-to-noise ratio of ²²⁵Ac and ¹⁷⁷Lu, respectively.

RESULTS

Kidney (r = 0.96, p < 0.01) and lesion (r = 0.94, p < 0.01) SUV for [¹⁷⁷Lu]Lu-PSMA-I&T and [²²⁵Ac]Ac-PSMA-I&T showed a strong and significant correlation. Kidney SUV were significantly higher (p < 0.01) for [²²⁵Ac]Ac-PSMA-I&T (2.5 ± 0.8 vs. 2.1 ± 0.9), while for [¹⁷⁷Lu]Lu-PSMA-I&T lesion SUV were significantly higher (p = 0.03; 1.8 ± 1.1 vs. 2.1 ± 1.5). For absorbed dose estimates, significant differences regarding the kidneys remained, while no significant differences for lesion dosimetry were found.

CONCLUSION

Quantitative low-count SPECT imaging of the peak at 440 keV during [²²⁵Ac]Ac-PSMA-I&T therapy is feasible. Multi-isotope imaging for [¹⁷⁷Lu]Lu-PSMA-I&T/[²²⁵Ac]Ac-PSMA-I&T therapy indicates accumulation of free ²¹³Bi in the kidneys.

Current and upcoming radionuclide therapies in the direction of precision oncology: A narrative review

As new molecular tracers are identified to target specific receptors, tissue, and tumor types, opportunities arise for the development of both diagnostic tracers and their therapeutic counterparts, termed "theranostics." While diagnostic tracers utilize positron emitters or gamma-emitting radionuclides, their theranostic counterparts are typically bound to beta and alpha emitters, which can deliver specific and localized radiation to targets with minimal collateral damage to uninvolved surrounding structures. This is an exciting time in molecular imaging and therapy and a step towards personalized and precise medicine in which patients who were either without treatment options or not candidates for other therapies now have expanded options, with tangible data showing improved outcomes. This manuscript explores the current state of theranostics, providing background, treatment specifics, and toxicities, and discusses future potential trends.

Single Center Experience with a 4-Week 177Lu-PSMA-617 Treatment Interval in Patients with Metastatic Castration-Resistant Prostate Cancer

Background: 177Lu-PSMA-617 is a promising theragnostic treatment for metastatic castration-resistant prostate cancer (mCRPC). However, both the optimal treatment dose and interval in mCRPC and the rate of identification of responders from non-responders among possible treatment candidates are unknown. Methods: 62 men with mCRPC who were treated with 177Lu-PSMA-617 during 1/2017−2/2019 were included in the study. Treatment responses, overall survival (OS) and progression free survival (PFS) were determined. The median follow-up time was 1.4 years (IQR 0.5−2.2). Tumor volume of metastases (MTV), SUVmax and tumor lesion activity (TLA) were quantitated from pre-treatment PSMA PET/CT images together with pre-treatment PSA. Results: An average of three treatment cycles (2−5) were given within a four-week interval. PFS was 4.9 months (2.4−9.6) and OS was 17.2 months (6−26.4). There were no major adverse events reported. A significant PSA response of >50% was found in 58.7% of patients, which was significantly associated with longer OS, p < 0.004. PSA response was not associated with staging PSMA-derived parameters. Conclusions: 177Lu-PSMA-617 treatment in four-week intervals was safe and effective. Almost 60% of patients had a significant PSA response, which was associated with better OS. Pre-treatment PSA kinetics or staging PSMA PET/CT-derived parameters were not helpful in identifying treatment responders from non-responders; better biomarkers are needed to aid in patient selection.

Predictive and prognostic potential of pretreatment 68Ga-PSMA PET tumor heterogeneity index in patients with metastatic castration-resistant prostate cancer treated with 177Lu-PSMA

Introduction

This study was conducted to evaluate the predictive values of volumetric parameters and radiomic features (RFs) extracted from pretreatment 68Ga-PSMA PET and baseline clinical parameters in response to 177Lu-PSMA therapy.

Materials and methods

In this retrospective multicenter study, mCRPC patients undergoing 177Lu-PSMA therapy were enrolled. According to the outcome of therapy, the patients were classified into two groups including positive biochemical response (BCR) (≥ 50% reduction in the serum PSA value) and negative BCR (< 50%). Sixty-five RFs, eight volumetric parameters, and also seventeen clinical parameters were evaluated for the prediction of BCR. In addition, the impact of such parameters on overall survival (OS) was evaluated.

Results

33 prostate cancer patients with a median age of 69 years (range: 49-89) were enrolled. BCR was observed in 22 cases (66%), and 16 cases (48.5%) died during the follow-up time. The results of Spearman correlation test indicated a significant relationship between BCR and treatment cycle, administered dose, HISTO energy, GLCM entropy, and GLZLM LZLGE (p<0.05). In addition, according to the Mann-Whitney U test, age, cycle, dose, GLCM entropy, and GLZLM LZLGE were significantly different between BCR and non BCR patients (p<0.05). According to the ROC curve analysis for feature selection for prediction of BCR, GLCM entropy, age, treatment cycle, and administered dose showed acceptable results (p<0.05). According to SVM for assessing the best model for prediction of response to therapy, GLCM entropy alone showed the highest predictive performance in treatment planning. For the entire cohort, the Kaplan-Meier test revealed a median OS of 21 months (95% CI: 12.12-29.88). The median OS was estimated at 26 months (95% CI: 17.43-34.56) for BCR patients and 13 months (95% CI: 9.18-16.81) for non BCR patients. Among all variables included in the Kaplan Meier, the only response to therapy was statistically significant (p=0.01).

Conclusion

This exploratory study showed that the heterogeneity parameter of pretreatment 68Ga-PSMA PET images might be a potential predictive value for response to 177Lu-PSMA therapy in mCRPC; however, further prospective studies need to be carried out to verify these findings.

Pharmacological Optimization of PSMA-Based Radioligand Therapy

Prostate cancer (PCa) is the most common malignancy in men of middle and older age. The standard treatment strategy for PCa ranges from active surveillance in low-grade, localized PCa to radical prostatectomy, external beam radiation therapy, hormonal treatment and chemotherapy. Recently, the use of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) for metastatic castration-resistant PCa has been approved. PSMA is predominantly, but not exclusively, expressed on PCa cells. Because of its high expression in PCa, PSMA is a promising target for diagnostics and therapy. To understand the currently used RLT, knowledge about pharmacokinetics (PK) and pharmacodynamics (PD) of the PSMA ligand and the PSMA protein itself is crucial. PK and PD properties of the ligand and its target determine the duration and extent of the effect. Knowledge on the concentration-time profile, the target affinity and target abundance may help to predict the effect of RLT. Increased specific binding of radioligands to PSMA on PCa cells may be associated with better treatment response, where nonspecific binding may increase the risk of toxicity in healthy organs. Optimization of the radioligand, as well as synergistic effects of concomitant agents and an improved dosing strategy, may lead to more individualized treatment and better overall survival.

Any decline in prostate-specific antigen levels identifies survivors scheduled for prostate-specific membrane antigen-directed radioligand therapy

BACKGROUND

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) is increasingly incorporated in the therapeutic algorithm of patients with metastatic castration-resistant prostate cancer (mCRPC). We aimed to elucidate the predictive performance of early biochemical response for overall survival (OS).

MATERIALS AND METHODS

In this bicentric analysis, we included 184 mCRPC patients treated with ¹⁷⁷ Lu-PSMA RLT. Response to treatment was defined as decrease in prostate-specific antigen (PSA) levels 8 weeks after the first cycle of RLT (any decline or >50% according to Prostate Cancer Working Group 3). OS of responders and nonresponders was then compared using Kaplan-Meier curves and log-rank comparison.

RESULTS

A total of 114/184 patients (62.0%) showed any PSA decline (PSA response >50%, 55/184 [29.9%]). For individuals exhibiting a PSA decline >50%, OS of 19 months was significantly longer relative to nonresponders (13 months; hazard ratio of death [HR] = 0.64, 95% confidence interval [95% CI] = 0.44-0.93; p = 0.02). However, the difference was even more pronounced for any PSA decline, with an OS of 19 months in responders, but only 8 months in nonresponders (HR = 0.39, 95% CI = 0.25-0.60; p < 0.001).

CONCLUSIONS

In mCRPC patients scheduled for RLT, early biochemical response was tightly linked to prolonged survival, irrespective of the magnitude of PSA decline. As such, even in patients with PSA decrease of less than 50%, RLT should be continued.

Outcome of 177 Lu-PSMA Radionuclide Treatment in Advanced Prostate Cancer and Its Association With Clinical Parameters : A Single-Center Experience

PURPOSE

This study was set out to analyze the efficacy and safety of 177 Lu-PSMA-617 (LuPSMA) treatment in metastatic castration-resistant prostate cancer (mCRPC) patients.

PATIENTS AND METHODS

Progressive mCRPC patients who received at least 1 cycle of LuPSMA therapy were evaluated retrospectively. Demographic, clinic, and histopathological data were documented. Treatment efficacy was determined based on biochemical response criteria (Prostate Cancer Clinical Trial Working Group 3), and toxicity rates were defined based on CTCAE v4.03. The prognostic significance of laboratory/clinical data and 68 Ga-PSMA PET/CT quantitative results were analyzed using SPSS Version 24.0.

RESULTS

One hundred patients (median prostate-specific antigen [PSA] level, 75.7 ng/mL) who met the eligibility criteria were identified. The median number of cycles received per patient was 3 (range, 1-9). After the first cycles of LuPSMA, biochemical partial response, biochemical stable disease, and biochemical progressive disease were observed in 31%, 36%, and 33% of patients, respectively. Any PSA decline was determined in 60% of patients. After the fourth cycle of treatment, biochemical partial response, biochemical stable disease, and biochemical progressive disease were defined in 48%, 26%, and 26% of patients, respectively. The median overall survival (OS) from the first cycle of LuPSMA was 14 months. Patients who had any PSA response after the first cycle had significantly longer OS than nonresponders (median OS: 17 vs 9 months; P ≤ 0.001). Total PSMA-derived tumor volume ( P = 0.004), total PSMA activity per lesion ( P = 0.01), PSA ( P = 0.007), alkaline phosphatase ( P = 0.002), lactate dehydrogenase ( P < 0.001), and hemoglobin ( P < 0.001) were significant prognostic factors for OS in univariate Cox regression analysis.

CONCLUSIONS

LuPSMA therapy is a favorable treatment for mCRPC with remarkable therapeutic efficacy and low toxicity rates, even in progressive disease under standard therapies. Baseline PSMA-based tumor burden, PSA, alkaline phosphatase, lactate dehydrogenase, and hemoglobin were significant predictors of OS and can be useful for selection of the best candidate for LuPSMA therapy.

mCRPC patients with PSA fluctuations under radioligand therapy have comparable survival benefits relative to patients with sustained PSA decrease

Introduction

In men with metastatic castration-resistant prostate cancer (mCRPC) scheduled for prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT), biochemical response is assessed based on repeated measurements of prostate-specific antigen (PSA) levels. We aimed to determine overall survival (OS) in patients experiencing sustained PSA increase, decrease, or fluctuations during therapy.

Materials and methods

In this bicentric study, we included 176 mCRPC patients treated with PSMA-directed RLT. PSA levels were determined using blood samples prior to the first RLT and on the admission days for the following cycles. We calculated relative changes in PSA levels compared to baseline. Kaplan–Meier curves as well as log-rank test were used to compare OS of different subgroups, including patients with sustained PSA increase, decrease, or fluctuations (defined as change after initial decrease or increase after the first cycle).

Results

Sixty-one out of one hundred seventy-six (34.7%) patients showed a sustained increase and 86/176 (48.8%) a sustained decrease in PSA levels. PSA fluctuations were observed in the remaining 29/176 (16.5%). In this subgroup, 22/29 experienced initial PSA decrease followed by an increase (7/29, initial increase followed by a decrease). Median OS of patients with sustained decrease in PSA levels was significantly longer when compared to patients with sustained increase of PSA levels (19 vs. 8 months; HR 0.35, 95% CI 0.22–0.56; P < 0.001). Patients with PSA fluctuations showed a significantly longer median OS compared to patients with sustained increase of PSA levels (18 vs. 8 months; HR 0.49, 95% CI 0.30–0.80; P < 0.01), but no significant difference relative to men with sustained PSA decrease (18 vs. 19 months; HR 1.4, 95% CI 0.78–2.49; P = 0.20). In addition, in men experiencing PSA fluctuations, median OS did not differ significantly between patients with initial decrease or initial increase of tumor marker levels (16 vs. 18 months; HR 1.2, 95% CI 0.38–4.05; P = 0.68).

Conclusion

Initial increase or decrease of PSA levels is sustained in the majority of patients undergoing RLT. Sustained PSA decrease was linked to prolonged survival and men with PSA fluctuations under treatment experienced comparable survival benefits. As such, transient tumor marker oscillations under RLT should rather not lead to treatment discontinuation, especially in the absence of radiological progression.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05910-w.

Pre- and intratherapeutic predictors of overall survival in patients with advanced metastasized castration-resistant prostate cancer receiving Lu-177-PSMA-617 radioligand therapy

BACKGROUND

Systemic Lutetium-177 prostate-specific membrane antigen-617 radioligand therapy (Lu-177-PSMA-617-RLT) is a novel treatment approach in patients suffering from metastasized castration-resistant prostate cancer. Nonetheless, a therapeutic response may fail to appear in a proportion of patients. This study aims to identify routinely obtainable pre- and intratherapeutic parameters to allow a prediction of overall survival in patients receiving Lu-177-PSMA-617 radioligand therapy.

METHODS

Between January 2015 and December 2020 52 patients treated with a total of 146 cycles Lu-177-PSMA-617-RLT were retrospectively analysed in a single-center trial. The median overall survival time (OS) was compared to pre-therapeutic serological parameters, the extend of metastatic spread and previously performed therapies using Kaplan-Meier estimators and multivariate Cox-regression. Bonferroni-Holm correction was performed on all statistical tests.

RESULTS

The median OS of all patients was 55.6 weeks. Multivariate Cox-regression revealed significant lower survival for decreased pretherapeutic hemoglobin levels (HR 0.698 per g/dl; 95%-CI 0.560-0.872; p = 0.001), increased lactate dehydrogenase (LDH) levels (HR 1.073 per 25 U/l; 95%-CI 1.024-1.125; p = 0.003) and the presence of hepatic metastasis (HR 6.981; 95%-CI 2.583-18.863; p < 0.001). Increased pretherapeutic c-reactive protein (CRP), alkaline phosphatase (ALP) and gamma-glutamyltransferase (GGT) levels were also associated with a shorter survival. A prostate-specific antigen decline after one therapy cycle did not significantly correlate with an increased survival. No significant relations were observed between overall survival time and other serological parameters or previously performed therapies.

CONCLUSION

Pre-therapeutic hemoglobin and LDH levels, as well as the presence of hepatic metastasis are independent predictors of overall survival in patients receiving Lu-177-PSMA-617-RLT. CRP, ALP and GGT levels cloud be utilized as additional decision aids when a Lu-177-PSMA-617-RLT is intended. Trial Registration Not applicable (retrospective observational study).

177 Lu-PSMA radioligand therapy effectiveness in metastatic castration-resistant prostate cancer: An updated systematic review and meta-analysis

BACKGROUND

An updated systematic review and meta-analysis of relevant studies to evaluate the effectiveness of prostate-specific membrane antigen (PSMA)-targeted endoradiotherapy/radioligand therapy (PRLT) in castration resistant prostate cancer (CRPC).

METHODS

A systematic search was performed in July 2020 using PubMed/Medline database to update our prior systematic review. The search was limited to papers published from 2019 to June 2020. A total of 472 papers were reviewed. The studied parameters included pooled proportion of patients showing any or ≥50% prostate-specific antigen (PSA) decline after PRLT. Survival effects of PRLT were assessed based on pooled hazard ratios (HRs) of the overall survival (OS) according to any PSA as well as ≥50% PSA decline after PRLT. Response to therapy based on ≥50% PSA decrease after PRLT versus controls was evaluated using Mantel-Haenszel random effect meta-analysis. All p values < 0.05 were considered as statistically significant.

RESULTS

A total of 45 publications were added to the prior 24 studies. 69 papers with total of 4157 patients were included for meta-analysis. Meta-analysis of the two recent randomized controlled trials showed that patients treated with ¹⁷⁷ Lu-PSMA 617 had a significantly higher response to therapy compared to controls based on ≥50% PSA decrease. Meta-analysis of the HRs of OS according to any PSA decline and ≥50% PSA decline showed survival prolongation after PRLT.

CONCLUSIONS

PRLT results in higher proportion of patients responding to therapy based on ≥50% PSA decline compared to controls. Any PSA decline and ≥50% PSA decline showed survival prolongation after PRLT.

ADVANCES IN KNOWLEDGE

This is the first meta-analysis to aggregate the recent randomized controlled trials of PRLT which shows CRPC patients had a higher response to therapy after PRLT compared to controls.

Advances in PSMA-targeted therapy for prostate cancer

Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein located on the cell membrane, is specifically and highly expressed in prostate cancer (PCa). Besides, its expression level is related to tumor invasiveness. As a molecular target of PCa, PSMA has been extensively studied in the past two decades. Currently, a great deal of evidence suggests that significant progresses have been made in the PSMA-targeted therapy of PCa. Herein, different PSMA-targeted therapies for PCa are reviewed, including radioligand therapy (¹⁷⁷Lu-PSMA-RLT, ²²⁵Ac-PSMA-RLT), antibody-drug conjugates (MLN2704, PSMA-MMAE, MEDI3726), cellular immunotherapy (CAR-T, CAR/NK-92, PSMA-targeted BiTE), photodynamic therapy, imaging-guided surgery (radionuclide-guided surgery, fluorescence-guided surgery, multimodal imaging-guided surgery), and ultrasound-mediated nanobubble destruction.

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

Simple Summary

Imaging plays a crucial role in the accurate staging of prostate cancer. Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer cells, and targeting the PSMA protein for diagnostic purposes has become of great clinical value. Another valuable feature of PSMA is its opportunity to serve as a target for delivering radionuclide therapy to cancer cells. PSMA-ligands can be labeled with various radionuclides, such as alpha and beta-emitters. This review offers an overview of the literature on recent developments in nuclear medicine regarding PSMA in prostate cancer diagnostics and targeted radionuclide therapy.

Abstract

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.

Early PSA Change after [177Lu]PSMA-617 Radioligand Therapy as a Predicator of Biochemical Response and Overall Survival

Simple Summary

Radioligand therapy with [¹⁷⁷Lu]PSMA-617 (PSMA-RLT) is a promising therapeutic option for metastatic castration-resistant prostate cancers (mCRPC), as its clinical relevance has recently been confirmed in the phase III VISION-trial. As prostate-specific antigen (PSA) plays an important role in the response evaluation of this therapy, and the aim of this study was to prospectively assess the prognostic value of early PSA measurements. We found PSA changes as early as four weeks after the first administration of PSMA-RLT to be predictive of both long-term biochemical and PET imaging response, as well as overall survival. We then evaluated relevant predictive thresholds in PSA change at that time point, as the early detection of long-term (non-)response to PSMA-RLT can be of great benefit in the clinical management of terminally ill mCRPC-patients.

Abstract

Purpose: Radioligand therapy with [¹⁷⁷Lu]PSMA-617 (PSMA-RLT) is a promising therapeutic option for metastatic castration-resistant prostate cancer (mCPRP). This study assessed the prognostic value of early PSA measurements during PSMA-RLT. Methods: 27 patients with mCRPC scheduled for PSMA-RLT were prospectively enrolled for a serial short-interval PSA-assessment. Change in PSA (∆%PSA) during two treatment cycles was correlated with biochemical response (BR) and change in tumor volume on PET (TV) after 16 weeks (w16), as well as overall survival (OS). PCWG3 criteria and the recently recommended threshold of ∆%PSA ≤ −30% were assessed for their predictive value. Results: ∆%PSA first correlated with BR, TV and OS after 4 weeks (c1w4). At c1w4, ∆%PSA ≤ −30% was associated with the biochemical response at w16 (p = 0.003) and a longer median OS (p = 0.025), whereas the PCWG3-derived threshold of ∆%PSA ≤ −50% showed no such correlation. In contrast, ∆%PSA ≥ 25% at c1w4 was associated with biochemical progression at w16 (p = 0.003) and a shorter median OS (p < 0.001). Conclusion: PSA changes as early as four weeks after PSMA-RLT allow a significant prediction of later biochemical and PET-based imaging response, as well as OS. At this early time point, a more lenient threshold for a PSA decrease of at least 30% appears better-suited for the prediction of a positive biochemical response and longer OS. In contrast, the PCWG3-derived threshold for PSA increase (+25%) reliably anticipates biochemical progression and shorter OS.

Preparation of 177Lu-PSMA-617 in Hospital Radiopharmacy: Convenient Formulation of a Clinical Dose Using a Single-Vial Freeze-Dried PSMA-617 Kit Developed In-House

Objective

In the recent time, endoradionuclide therapy for metastatic castration-resistant prostate carcinoma employing ¹⁷⁷Lu-PSMA-617 has yielded encouraging results and several clinical trials with the agent are currently ongoing. Routine preparation of ¹⁷⁷Lu-PSMA-617 patient doses can be made simpler and convenient, if the ingredients essential for radiolabeling are made available in a ready-to-use lyophilized form.

Methods

PSMA-617 freeze-dried kit was formulated and used for the preparation of ¹⁷⁷Lu-PSMA-617 clinical dose with high radiochemical purity using low/medium specific activity ¹⁷⁷Lu. Detailed radiochemical studies were performed to determine the maximum activity and volume of ¹⁷⁷LuCl₃, which can be added in the kit for the formulation of ¹⁷⁷Lu-PSMA-617. Studies were also performed to determine the shelf life of the kit to ensure its long-term usage. Studies were performed in buffer as well as human serum medium to determine the stability of the ¹⁷⁷Lu-PSMA-617 complex after storing in respective media up to 7 days postpreparation. About ten patient doses of ¹⁷⁷Lu-PSMA-617 were administered, and posttherapy scans were acquired.

Results

The formulated freeze-dried kit of PSMA-617 could be radiolabeled with an average percentage radiochemical purity > 98.53 ± 0.38. The freeze-dried kit was found suitable for tolerating up to 0.5 mL of ¹⁷⁷LuCl₃ (in 0.01 N HCl) and specific activity of 555 MBq/μg (15 mCi/μg) for the preparation of the patient dose of ¹⁷⁷Lu-PSMA-617. The ¹⁷⁷Lu-PSMA-617 complex prepared using the freeze-dried kit of PSMA-617 was observed to maintain % radiochemical purity (RCP) of 96.74 ± 0.87 and 94.81 ± 2.66, respectively, even after storing up to 7 days in buffer and human serum, respectively. ¹⁷⁷Lu-PSMA-617 prepared using the in-house formulated freeze-dried kit of PSMA-617 exhibited accumulation in metastatic lesions picked up in a pretherapy PET scan. Reduction in number as well as size of lesions was observed in posttherapy scans acquired after two months of administering the first therapeutic dose of ¹⁷⁷Lu-PSMA-617.

Conclusions

The freeze-dried kit of PSMA-617 could be used for the preparation of ¹⁷⁷Lu-PSMA-617 with high radiochemical purity (>98%) in a reproducible manner. ¹⁷⁷Lu-PSMA-617 prepared using the developed kit was successfully evaluated in patients suffering from metastatic prostate cancer.

177Lu-PSMA-617 versus docetaxel in chemotherapy-naïve metastatic castration-resistant prostate cancer: a randomized, controlled, phase 2 non-inferiority trial

Purpose

Lutetium-177 prostate-specific membrane antigen-617 (¹⁷⁷Lu-PSMA-617) in end-stage metastatic castration-resistant prostate cancer (mCRPC) has reported favourable outcomes. In this study, we aimed to prospectively compare the efficacy and safety of ¹⁷⁷Lu-PSMA-617 and docetaxel in chemotherapy-naïve mCRPC patients.

Methods

This was a randomized, parallel-group, open-label, phase 2, and non-inferiority trial. Chemotherapy-naïve patients with mCRPC and high PSMA-expressing lesions on ⁶⁸ Ga-PSMA-11 PET/CT were randomly assigned in 1:1 ratio to ¹⁷⁷Lu-PSMA-617 (6.0–7.4 GBq/cycle, every 8 weeks, up to 4 cycles) or docetaxel (75 mg/m²/cycle, every 3 weeks, up to 10 cycles). The primary end-point was best prostate-specific antigen response rate (PSA-RR), defined according to Prostate Cancer Clinical Trials Working Group-3 as proportion of patients achieving ≥ 50% decline in PSA from baseline. Non-inferiority margin of − 15% was pre-specified for PSA-RR.

Results

Between December 2019 and March 2021, 40 of the 45 patients assessed for eligibility underwent randomization. Fifteen of 20 patients in ¹⁷⁷Lu-PSMA-617 arm and 20/20 patients in docetaxel arm received treatment per protocol. Of these, best PSA-RR in the ¹⁷⁷Lu-PSMA-617 arm was 60% (9/15) versus 40% (8/20) in the docetaxel arm. The difference in the PSA-RRs between the two arms was 20% (95% confidence interval, CI: − 12–47, P = 0.25), meeting the pre-specified criterion for non-inferiority in per-protocol analysis. Further, progression-free survival rates at 6 months were 30% and 20% in the ¹⁷⁷Lu-PSMA-617 and docetaxel arms respectively (difference 10%, 95% CI: − 18–38, P = 0.50). Overall, treatment-emergent grade ≥ 3 adverse events occurred less frequently with ¹⁷⁷Lu-PSMA-617 than with docetaxel (6/20, 30% versus 10/20, 50%, respectively, P = 0.20). Quality-of-life outcomes improved significantly in ¹⁷⁷Lu-PSMA-617 arm compared to docetaxel arm (P < 0.01).

Conclusion

¹⁷⁷Lu-PSMA-617 was demonstrated to be safe and non-inferior to docetaxel in the treatment of mCRPC and could, thus, be potentially employed earlier in the disease course rather than being solely reserved for advanced end-stage disease.

Clinical trial registration

Clinical Trials Registry-India, CTRI/2019/12/022282.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05618-3.

Update on radioligand therapy with 177Lu-PSMA for metastatic castration-resistant prostate cancer: clinical aspects and survival effects

OBJECTIVE

To give an updated overview on clinical aspects and survival effects of lutetium-177-prostate-specific membrane antigen (PSMA) (¹⁷⁷Lu-PSMA) radioligand therapy (RLT), a novel treatment option for patients with metastatic castration-resistant prostate cancer (mCRPC).

METHODS

PubMed/MEDLINE database was searched for relevant articles published up to March 2021. The search was restricted to English-language articles.

RESULTS

Current evidence from the literature consistently demonstrated the efficacy, safety, and survival benefit of ¹⁷⁷Lu-PSMA RLT in mCRPC. However, current data rely predominantly on retrospective analyses, showing heterogeneity of patient population and treatment protocols. More recently, results from the first randomized phase II study (TheraP) demonstrated that ¹⁷⁷Lu-PMSA therapy significantly improved prostate-specific antigen response rate (66% vs 37%) and had fewer grade 3/4 adverse events when compared to cabazitaxel in patients with docetaxel-pretreated, progressive mCRPC. This review is intended to provide an updated overview of treatment protocols and responses, toxicity profile, and survival effects of ¹⁷⁷Lu-PSMA RLT.

CONCLUSIONS

¹⁷⁷Lu-PSMA RLT has emerged as a promising targeted treatment in mCRPC. It is currently applied in compassionate use programs and following exhaustion of approved therapies. Crucial for establishing this treatment in routine clinical management will be the results of the phase III VISION trial, which may confirm the encouraging patient outcomes reported to date.

PSMA-Targeting Radiopharmaceuticals for Prostate Cancer Therapy: Recent Developments and Future Perspectives

Simple Summary

One of the most frequently diagnosed cancer in men is adenocarcinoma of the prostate. Once the disease is metastatic, only very limited treatment options are available, resulting in a very short median survival time of 13 months; however, this reality is gradually changing due to the discovery of prostate-specific membrane antigen (PSMA), a protein that is present in cancerous prostate tissue. Researchers have developed pharmaceuticals specific for PSMA, ranging from antibodies (mAb) to low-molecular weight molecules coupled to beta minus and alpha-emitting radionuclides for their use in targeted radionuclide therapy (TRT). TRT offers the possibility of selectively removing cancer tissue via the emission of radiation or radioactive particles within the tumour. In this article, the major milestones in PSMA ligand research and the therapeutic developments are summarised, together with a future perspective on the enhancement of current therapeutic approaches.

Abstract

Prostate cancer (PC) is the second most common cancer among men, with 1.3 million yearly cases worldwide. Among those cancer-afflicted men, 30% will develop metastases and some will progress into metastatic castration-resistant prostate cancer (mCRPC), which is associated with a poor prognosis and median survival time that ranges from nine to 13 months. Nevertheless, the discovery of prostate specific membrane antigen (PSMA), a marker overexpressed in the majority of prostatic cancerous tissue, revolutionised PC care. Ever since, PSMA-targeted radionuclide therapy has gained remarkable international visibility in translational oncology. Furthermore, on first clinical application, it has shown significant influence on therapeutic management and patient care in metastatic and hormone-refractory prostate cancer, a disease that previously had remained immedicable. In this article, we provide a general overview of the main milestones in the development of ligands for PSMA-targeted radionuclide therapy, ranging from the firstly developed monoclonal antibodies to the current state-of-the-art low molecular weight entities conjugated with various radionuclides, as well as potential future efforts related to PSMA-targeted radionuclide therapy.

Circulating androgen receptor gene amplification and resistance to 177Lu-PSMA-617 in metastatic castration-resistant prostate cancer: results of a Phase 2 trial

BACKGROUND

In a Phase 2 clinical trial, we aimed to determine the lutetium-177 [¹⁷⁷Lu]-PSMA-617 activity and the clinical utility of levels of plasma androgen receptor (AR) gene in patients with heavily pretreated metastatic castration-resistant prostate cancer (mCRPC).

METHODS

We determined AR copy number in pretreatment plasma samples. We used logistic regression to estimate the odds ratio (OR) and 95% confidence intervals (95% CIs) in order to evaluate the independent relevance of AR status and to evaluate patients with early progressive disease (PD) defined as treatment interruption occurring within 4 months after the start of ¹⁷⁷Lu-PSMA-617.

RESULTS

Twelve of the 15 (80%) with AR gene gain and 5 of the 25 (20%) patients with no gain of AR had early PD (p = 0.0002). The OR for patients without PSA response having AR gain was 3.69 (95% CI 0.83-16.36, p = 0.085). The OR for patients with early PD having AR gain was 16.00, (95% CI 3.23-79.27, p = 0.0007). Overall, median PFS and OS were 7.5 and 12.4 months, respectively. AR-gained had a significant shorter OS compared to AR-normal patients (7.4 vs 19.1 months, p = 0.020). No treatment interruptions due to adverse effects were reported.

DISCUSSION

Plasma AR status helped to indicate mCRPC with early resistance to ¹⁷⁷Lu-PSMA-617.

TRIAL REGISTRATION

NCT03454750.

Evaluation of 68Ga-PSMA-11 PET-MRI in Patients with Advanced Prostate Cancer Receiving 177Lu-PSMA-617 Therapy: A Radiomics Analysis

¹⁷⁷Lutetium PSMA-617 (Lu-PSMA) therapy in patients with metastatic castration resistant prostate cancer (mCRPC) has gained visibility through the ongoing phase III trial. The data on prediction of therapy outcome and survival out of pretherapeutic imaging parameters is still sparse. In this study, the predictive and prognostic value of radiomic features from ⁶⁸Ga-PSMA-11 PET-MRI are analyzed. In total, 21 patients with mCRPC underwent ⁶⁸Ga-PSMA-11 PET-MRI before Lu-PSMA therapy. The PET-positive tumor volume was defined and transferred to whole-body T2-, T1- and contrast-enhanced T1-weighted MRI-sequences. The radiomic features from PET and MRI sequences were extracted by using a freely available software package. For selecting features that allow differentiation of biochemical response (PSA decrease > 50%), a stepwise dimension reduction was performed. Logistic regression models were fitted, and selected features were tested for their prognostic value (overall survival) in all patients. Eight patients achieved biochemical response after Lu-PSMA therapy. Ten independent radiomic features differentiated well between responders and non-responders. The logistic regression model, including the feature interquartile range from T2-weighted images, revealed the highest accuracy (AUC = 0.83) for the prediction of biochemical response after Lu-PSMA therapy. Within the final model, patients with a biochemical response (p = 0.003) and higher T2 interquartile range values in pre-therapeutic imaging (p = 0.038) survived significantly longer. This proof-of-concept study provides first evidence on a potential predictive and prognostic value of radiomic analysis of pretherapeutic ⁶⁸Ga-PSMA-11 PET-MRI before Lu-PSMA therapy.

Theranostics in oncology: What radiologists want to know

Combination of radioligand imaging and therapy, so called radiotheranostics, is a novel tool of precision oncology with proven clinical value. In-depth knowledge of functional imaging nuances is critically needed for precise prognostication and guidance of management. Here, we review theranostic applications with up to Phase III type evidence for outcome improvement: Imaging and therapy of neuroendocrine neoplasms (NEN) exploiting high levels of somatostatin receptor (SSTR) expression and radiotheranostics of prostate cancer targeting the prostate specific membrane antigen (PSMA). This narrative review focusses on these two applications and elucidates patient selection and response assessment by radioligand scintigraphy and/or positron emission tomography. Furthermore, we provide a brief outlook on future applications for novel targets outside of NEN and prostate cancer.

Response Assessment and Prediction of Progression-Free Survival by 68Ga-PSMA-11 PET/CT Based on Tumor-to-Liver Ratio (TLR) in Patients with mCRPC Undergoing 177Lu-PSMA-617 Radioligand Therapy

At present, little is known about the molecular imaging-based response assessment of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy with ¹⁷⁷Lutetium (¹⁷⁷Lu-PSMA-617 RLT) in metastatic castration-resistant prostate cancer (mCRPC). Our study evaluated the response to RLT using both molecular imaging and biochemical response assessments, and their potential prediction of progression-free survival (PFS). Fifty-one consecutive patients given two cycles of RLT at 6-week intervals were analyzed retrospectively. ⁶⁸Ga-PSMA-11 PET/CT was obtained about 2 weeks prior to the first and 4–6 weeks after the second cycle. Molecular imaging-based response using SUV_peak and tumor-to-liver ratio (TLR) was determined by modified PERCIST criteria. ∆TLR and ∆SUV were significantly correlated with ∆PSA (p < 0.001, each). After a median follow-up of 49 months, the median PFS (95% CI) was 8.0 (5.9–10.1) months. In univariate analysis, responders showing partial remission (PR_PSA and PR_TLR) had significantly (p < 0.001, each) longer PFS (median: 10.5 and 9.3 months) than non-responders showing either stable or progressive disease (median: 4.0 and 3.5 months). Response assessment using SUV_peak failed to predict survival. In multivariable analysis, response assessment using TLR was independently associated with PFS (p < 0.001), as was good performance status (p = 0.002). Molecular imaging-based response assessment with ⁶⁸Ga-PSMA-11 PET/CT using normalization of the total lesion PSMA over healthy liver tissue uptake (TLR) could be an appropriate biomarker to monitor RLT in mCRPC patients and to predict progression-free survival (PFS) of this treatment modality.

Lutetium-177 Labelled PSMA Targeted Therapy in Advanced Prostate Cancer: Current Status and Future Perspectives

Patients suffering from metastatic castration-resistant prostate cancer (mCRPC) have a poor prognosis. As a further treatment option ¹⁷⁷Lutetium (Lu) prostate-specific membrane antigen (PSMA) radioligand therapy gained a significant interest of many investigators. Several publications showed great response and prolonged survival with limited adverse events. However, to this point, it still remains unclear which patients benefit the most from ¹⁷⁷Lu-PSMA therapy, and how to improve the treatment regimen to achieve best outcome while minimizing potential adverse events. The efficacy for mCRPC patients is a given fact, and with the newly published results of the VISION trial its approval is only a matter of time. Recently, investigators started to focus on treating prostate cancer patients in earlier disease stages and in combination with other compounds. This review gives a brief overview of the current state and the future perspectives of ¹⁷⁷Lu labelled PSMA radioligand therapy.

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.

An Impressive Approach in Nuclear Medicine: Theranostics

Radiometal-based theranostics or theragnostics, first used in the early 2000s, is the combined application of diagnostic and therapeutic agents that target the same molecule, and represents a considerable advancement in nuclear medicine. One of the promising fields related to theranostics is radioligand therapy. For instance, the concepts of targeting the prostate-specific membrane antigen (PSMA) for imaging and therapy in prostate cancer, or somatostatin receptor targeted imaging and therapy in neuroendocrine tumors (NETs) are part of the field of theranostics. Combining targeted imaging and therapy can improve prognostication, therapeutic decision-making, and monitoring of the therapy.

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.

Biomarkers in Prostate-Specific Membrane Antigen Theranostics

Theranostics of prostate cancer (PC) represents a growing area of development of imaging agents and targeted radionuclide therapeutics against a major target, prostate specific membrane antigen (PSMA). In view of the encouraging efficacy from the use of ¹⁷⁷Lu and other radionuclides in metastatic castration-resistant prostate cancer (mCRPC), it is becoming increasingly important to identify surrogate markers that can help predict which patients are more likely to respond and experience improved survival. This review discusses potential predictors of efficacy of PSMA-targeted radionuclide therapies (TRT) segregated in three major categories: imaging, clinical and molecular.

The impact of the extent of the bone involvement on overall survival and toxicity in mCRPC patients receiving [177Lu]Lu-PSMA-617: a WARMTH multicentre study

INTRODUCTION

Prostate-specific membrane antigen (PSMA)-based radioligand therapy (RLT) showed in a multicentre WARMTH (World Association of Radiopharmaceutical and Molecular Therapy) study that the presence of bone metastases is a negative prognosticator for the survival. The current multicentre retrospective analysis aims to evaluate the response rate to RLT, the overall survival (OS) of patients and the safety of the treatment according to the extent of bone involvement.

METHODS

The study included patients with progressive metastatic castration-resistant prostate cancer (mCRPC), who underwent RLT with [¹⁷⁷Lu]Lu-PSMA-617 and a follow-up of at least 6 months. Tumour burden in the bone was classified prior to RLT as follows: less than 6 lesions, 6-20 lesions, more than 20 lesions and diffuse involvement. The response rate was evaluated using changes of the prostate-specific antigen (PSA) after the first treatment cycle. Overall survival was calculated from the date of the first treatment. Haematological adverse events were classified according to Common Terminology Criteria for Adverse Events (CTCAE), version 5.0.

RESULTS

A total of 319 males were included in the analysis. The extent of bone metastases and PSA response did not correlate significantly. Any PSA decline was observed in 73% patients; 44% showed a decline of ≥50%. The median OS of patient in the different subgroups was 18 months (less than 6 lesions), 13 months (6-20 lesions), 11 months (more than 20 lesions) and 8 months (diffuse involvement), respectively (p < 0.0001). Patients with prior Ra-223-therapy showed longer OS in all subgroups, especially in the subgroups with 6-20 lesions (OS: 16 vs. 12 months; p = 0.038) as well as diffuse involvement (OS: 11 vs. 7 months; p = 0.034). Significant negative prognosticators of OS were the existence of liver metastases in all subgroups and prior chemotherapy in patients with <6 bone lesions. Anaemia and thrombocytopenia correlated positively with the extent of bone metastases: p < 0.0001 and 0.005, respectively. No patient showed a high grade leukopenia.

CONCLUSION

The extent of bone involvement correlated negatively with the OS after RLT; however, it showed no relevant correlation with the PSA response rate. Prior therapy with Ra-223 may have a positive impact on OS. Haematotoxicity was higher in patients with more than 20 bone lesions; nevertheless, the majority of these patients did not show a relevant haematotoxicity.

Development of [225Ac]Ac-PSMA-I&T for Targeted Alpha Therapy According to GMP Guidelines for Treatment of mCRPC

Recently, promising results of the antitumor effects were observed in patients with metastatic castration-resistant prostate cancer treated with ¹⁷⁷Lu-labeled PSMA-ligands. Radionuclide therapy efficacy may even be improved by using the alpha emitter Ac-225. Higher efficacy is claimed due to high linear energy transfer specifically towards PSMA positive cells, causing more double-strand breaks. This study aims to manufacture [²²⁵Ac]Ac-PSMA-I&T according to good manufacturing practice guidelines for the translation of [²²⁵Ac]Ac-PSMA-I&T into a clinical phase 1 dose escalation study. Quencher addition during labeling was investigated. Quality control of [²²⁵Ac]Ac-PSMA-I&T was based on measurement of Fr-221 (218 keV), in equilibrium with Ac-225 in approximately six half-lives of Fr-221 (T½ = 4.8 min). Radio-(i)TLC methods were utilized for identification of the different radiochemical forms, gamma counter for concentration determination, and HPGe-detector for the detection of the radiochemical yield. Radiochemical purity was determined by HPLC. The final patient dose was prepared and diluted with an optimized concentration of quenchers as during labeling, with an activity of 8–12 MBq (±5%), pH > 5.5, 100 ± 20 μg/dose, PSMA-I&T, radiochemical yield >95%, radiochemical purity >90% (up to 3 h), endotoxin levels of <5 EU/mL, osmolarity of 2100 mOsmol, and is produced according to current guidelines. The start of the phase I dose escalation study is planned in the near future.

Long-term outcome of 177Lu-PSMA-617 radioligand therapy in heavily pre-treated metastatic castration-resistant prostate cancer patients

Objective

Investigators have extensively explored the short-term safety and efficacy data on ¹⁷⁷Lu-PSMA-617 radioligand therapy (RLT) in mCRPC patients. However, scarce literature is reported on the long-term outcome of these patients. The current goal of this study is focused on the long-term outcome of mCRPC patients treated with ¹⁷⁷Lu-PSMA-617 RLT.

Methods

Among 135 patients, 121 mCRPC patients fulfilled the eligibility criteria and were included in the final analysis. Patients received a median of 3 cycles of ¹⁷⁷Lu-PSMA-617 RLT at 6 to 12-week intervals. Primary endpoint included overall survival (OS) and secondary endpoints involved progression-free survival (PFS), predictive factors of OS and PFS, PSA response rate, molecular response, clinical response, and toxicity assessment.

Results

The median administered cumulative activity was 20 GBq (3.7–37 GBq). The median follow-up duration was 36 months (6–72 months). The estimated median PFS and OS were 12 months (mo) (95% CI: 10.3–13 mo) and 16 mo (95% CI: 13–17 mo), respectively. Any PSA decline and PSA decline >50% was achieved in 73% and 61% of the patients, respectively. Multivariate analysis revealed only failure to achieve >50% PSA decline as a significant factor associated with a poor PFS. Prognostic factors associated with reduced OS included, failure to experience >50% PSA decline, heavily pre-treated patient cohort who received >2 lines of prior treatment options, and patient sub-group treated with ≥2 lines of chemotherapy. Patients re-treated with additional treatment options after attaining ¹⁷⁷Lu-PSMA refractory disease showed a remarkably prolonged OS. A significant clinical benefit was achieved post ¹⁷⁷Lu-PSMA-617 RLT. The most common toxicities observed were fatigue (34.7%), followed by nausea (33%), and dry mouth (24.7%).

Conclusion

The current study supports the short-term safety and efficacy results of high response rates, prolonged PFS and OS, improved quality of life, and low treatment-related toxicities in patients treated with ¹⁷⁷Lu-PSMA-617 radioligand therapy.

Decision-support for treatment with 177Lu-PSMA: machine learning predicts response with high accuracy based on PSMA-PET/CT and clinical parameters

Background

Treatment with radiolabeled ligands to prostate-specific membrane antigen (PSMA) is gaining importance in the treatment of patients with advanced prostate carcinoma. Previous imaging with positron emission tomography/computed tomography (PET/CT) is mandatory. The aim of this study was to investigate the role of radiomics features in PSMA-PET/CT scans and clinical parameters to predict response to ¹⁷⁷Lu-PSMA treatment given just baseline PSMA scans using state-of-the-art machine learning (ML) methods.

Methods

A total of 2,070 pathological hotspots annotated in 83 prostate cancer patients undergoing PSMA therapy were analyzed. Two main tasks are performed: (I) analyzing correlation of averaged (per patient) values of radiomics features of individual hotspots and clinical parameters with difference in prostate specific antigen levels (ΔPSA) in pre- and post-therapy as a therapy response indicator. (II) ML-based classification of patients into responders and non-responders based on averaged features values and clinical parameters. To achieve this, machine learning (ML) algorithms and linear regression tests are applied. Grid search, cross validation (CV) and permutation test were performed to assure that the results were significant.

Results

Radiomics features (PET_Min, PET_Correlation, CT_Min, CT_Busyness and CT_Coarseness) and clinical parameters such as Alp1 and Gleason score showed best correlations with ΔPSA. For the treatment response prediction task, 80% area under the curve (AUC), 75% sensitivity (SE), and 75% specificity (SP) were obtained, applying ML support vector machine (SVM) classifier with radial basis function (RBF) kernel on a selection of radiomics features and clinical parameters with strong correlations with ΔPSA.

Conclusions

Machine learning based on ⁶⁸Ga-PSMA PET/CT radiomics features holds promise for the prediction of response to ¹⁷⁷Lu-PSMA treatment, given only base-line ⁶⁸Ga-PSMA scan. In addition, it was shown that, the best correlating set of radiomics features with ΔPSA are superior to clinical parameters for this therapy response prediction task using ML classifiers.

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.

Clinical Perspectives of Theranostics

Theranostics is a precision medicine which integrates diagnostic nuclear medicine and radionuclide therapy for various cancers throughout body using suitable tracers and treatment that target specific biological pathways or receptors. This review covers traditional theranostics for thyroid cancer and pheochromocytoma with radioiodine compounds. In addition, recent theranostics of radioimmunotherapy for non-Hodgkin lymphoma, and treatment of bone metastasis using bone seeking radiopharmaceuticals are described. Furthermore, new radiopharmaceuticals for prostatic cancer and pancreatic cancer have been added. Of particular, F-18 Fluoro-2-Deoxyglucose (FDG) Positron Emission Tomography (PET) is often used for treatment monitoring and estimating patient outcome. A recent clinical study highlighted the ability of alpha-radiotherapy with high linear energy transfer (LET) to overcome treatment resistance to beta--particle therapy. Theranostics will become an ever-increasing part of clinical nuclear medicine.

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.

Antihormone treatment differentially regulates PSA secretion, PSMA expression and 68Ga-PSMA uptake in LNCaP cells

Background

In recent years, a variety of innovative therapeutics for castration-resistant prostate cancer have been developed, including novel anti-androgenic drugs, such as abiraterone or VPC-13566. Therapeutic monitoring of these pharmaceuticals is performed either by measuring PSA levels in serum or by imaging. PET using PSMA ligands labeled with Fluor-18 or Gallium-68 is the most sensitive and specific imaging modality for detection of metastases in advanced prostate cancer. To date, it remains unclear how PSMA expression is modulated by anti-hormonal treatment and how it correlates with PSA secretion.

Methods

We analyzed modulation of PSMA-mRNA and protein expression, ⁶⁸Ga–PSMA uptake and regulation of PSA secretion by abiraterone or VPC-13566 in LNCaP cells in vitro.

Results

We found that abiraterone and VPC-13566 upregulate PSMA protein and mRNA expression but block PSA secretion in LNCaP cells. Both anti-androgens also enhanced ⁶⁸Ga–PSMA uptake normalized by the number of cells, whereas abiraterone and VPC-13566 reduced ⁶⁸Ga–PSMA uptake in total LNCaP monolayers treated due to cell death.

Conclusion

Our data indicate that PSA secretion and PSMA expression are differentially regulated upon anti-androgen treatment. This finding might be important for the interpretation of ⁶⁸Ga–PSMA PET images in monitoring therapies with abiraterone and VPC-13566 in prostate cancer patients, but needs to be validated in vivo.

Role of PSMA PET/CT imaging in the diagnosis, staging and restaging of prostate cancer

Prostate-specific membrane antigen (PSMA) PET/CT is a novel imaging technique for the detection and staging of either primary or recurrent prostate cancer. Early studies demonstrated its improved sensitivity and specificity over and in combination with other currently employed imaging techniques, such as multiparametric MRI, bone scan, PET and CT. However, the lack of strength and confidence in these studies has meant incorporation of PSMA PET/CT into clinical guidelines and practice has been limited to date. In response, a number of high-quality prospective studies have recently emerged and reflect exciting results seen in preceding publications. Here we recount some of the key earlier publications, report results from the latest studies and look to the future discussing some of the eagerly awaited ongoing clinical trials.

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.

Factors predicting biochemical response and survival benefits following radioligand therapy with [177Lu]Lu-PSMA in metastatic castrate-resistant prostate cancer: a review

Background

Prostate cancer (PC) is one of the most common cancers in men. Although the overall prognosis is favorable, the management of metastatic castration-resistant prostate cancer (mCRPC) patients is challenging. Usually, mCRPC patients with progressive disease are considered for radioligand therapy (RLT) after exhaustion of other standard treatments. The prostate-specific membrane antigen (PSMA) labeled with Lutetium-177 ([¹⁷⁷Lu]Lu-PSMA) has been widely used, showing favorable and successful results in reducing prostate-specific antigen (PSA) levels, increasing quality of life, and decreasing pain, in a multitude of studies. Nevertheless, approximately thirty percent of patients do not respond to [¹⁷⁷Lu]Lu-PSMA RLT. Here, we only reviewed and reported the evaluated factors and their impact on survival or biochemical response to treatment to have an overview of the potentialprognostic parameters in [¹⁷⁷Lu]Lu-PSMA RLT.

Methods

Studies were retrieved by searching MEDLINE/PubMed and GoogleScholar. The search keywords were as follows: {(“177Lu-PSMA”) AND (“radioligand”) AND (“prognosis”) OR (“predict”)}. Studies discussing one or more factors which may be prognostic or predictive of response to [¹⁷⁷Lu]Lu-PSMA RLT, that is PSA response and survival parameters, were included.

Results

Several demographic, histological, biochemical, and imaging factors have been assessed as predictive parameters for the response to thistreatment; however, the evaluated factors were diverse, and the results mostly were divergent, except for the PSA level reduction after treatment, which unanimously predicted prolonged survival.

Conclusion

Several studies have investigated a multitude of factors to detect those predicting response to [¹⁷⁷Lu]Lu-PSMA RLT. The results wereinconsistent regarding some factors, and some were evaluated in only a few studies. Future prospective randomized trials are required to detect theindependent prognostic factors, and to further determine the clinical and survival benefits of [¹⁷⁷Lu]Lu-PSMA RLT.

Metastatic Spread in Prostate Cancer Patients Influencing Radiotherapy Response

Radiotherapy and surgery are curative treatment options for localized prostate cancer (PCa) with a 5-year survival rate of nearly 100%. Once PCa cells spread into distant organs, such as bone, the overall survival rate of patients drops dramatically. The metastatic cascade and organotropism of PCa cells are regulated by different cellular subtypes, organ microenvironment, and their interactions. This cross-talk leads to pre-metastatic niche formation that releases chemo-attractive factors enforcing the formation of distant metastasis. Biological characteristics of PCa metastasis impacting on metastatic sites, burden, and latency is of clinical relevance. Therefore, the implementation of modern hybrid imaging technologies into clinical routine increased the sensitivity to detect metastases at earlier stages. This enlarged the number of PCa patients diagnosed with a limited number of metastases, summarized as oligometastatic disease. These patients can be treated with androgen deprivation in combination with local-ablative radiotherapy or radiopharmaceuticals directed to metastatic sites. Unfortunately, the number of patients with disease recurrence is high due to the enormous heterogeneity within the oligometastatic patient population and the lack of available biomarkers with predictive potential for metastasis-directed radiotherapy. Another, so far unmet clinical need is the diagnosis of minimal residual disease before onset of clinical manifestation and/or early relapse after initial therapy. Here, monitoring of circulating and disseminating tumor cells in PCa patients during the course of radiotherapy may give us novel insight into how metastatic spread is influenced by radiotherapy and vice versa. In summary, this review critically compares current clinical concepts for metastatic PCa patients and discuss the implementation of recent preclinical findings improving our understanding of metastatic dissemination and radiotherapy resistance into standard of care.

Systemic Radiotherapy of Bone Metastases With Radionuclides

Treatments of bone metastases using radionuclides are now well established in oncology. It is also a field that continues to develop. This article reviews the evidence base that led to the approval of strontium-89 and samarium-153 ethylenediaminetetramethylene phophanate (EDTMP) for the palliation of pain from bone metastases, as well as the evidence for the use of radium-223 in metastatic castrate-resistant prostate cancer. Efforts to optimise treatments and improve response rates, either by safely increasing the radiation dose to bone metastases or by combining treatment with non-radiation-based therapies, are discussed. In addition, the development of both alpha- and beta-particle-emitting radiopharmaceuticals designed to target prostate-specific membrane antigen are reviewed.