Threshold for defining PSMA-positivity prior to 177Lu-PSMA therapy: a comparison of [68Ga]Ga-PSMA-11 and [18F]F-DCFPyL in metastatic prostate cancer

Impact of interdisciplinary tumor boards (ITB) and personalized treatment on survival outcomes in metastatic castration-resistant prostate cancer

PURPOSE

Interdisciplinary tumor boards (ITB) are essential in optimizing treatment recommendations for metastatic castration-resistant prostate cancer (mCRPC) by incorporating oncology guidelines, clinical trials, and patient-specific factors to ensure individualized care. This study examines clinical parameters that influence ITB recommendations, evaluates their adherence to guidelines, and assesses their impact on patient survival.

METHODS

In a retrospective analysis, data from 187 mCRPC patients discussed at an ITB in a tertiary care center in 2018 were evaluated. Patient- and disease-specific factors were correlated with adherence to National Comprehensive Cancer Network® (NCCN®) guidelines and overall survival (OS). The impact of clinical parameters on survival outcomes was assessed through univariate and multivariate analyses.

RESULTS

The median patient age was 72.8 years, with a median prostate-specific antigen (PSA) level of 65.0 ng/ml. Guideline-compliant recommendations were given in 42.9% of cases, while 57.1% received individualized recommendations. Clinical trial eligibility was noted in 24.8% of patients. Individualized ITB recommendations were associated with significantly longer OS (38.3 vs. 21.2 months, p = 0.03). Shorter OS correlated with renal impairment (p = 0.007), symptomatic metastases (p < 0.0001), and visceral metastases (p < 0.0001). Limitations include the retrospective design, lack of follow-up on therapy adherence, and absence of progression-free survival (PFS) data.

CONCLUSION

ITB discussions improve survival in mCRPC patients, mainly due to personalized approaches and better access to clinical trials. Visceral and symptomatic metastases as well as renal impairment are risk factors for reduced OS, emphasizing the need for careful management of these high-risk patients. The results support the expanded use of ITB to improve mCRPC treatment outcomes.

Investigating the significance of SPECT/CT-SUV for monitoring 177Lu-PSMA-targeted radionuclide therapy: a systematic review

BACKGROUND

Quantitative molecular imaging via single-photon emission computed tomography-derived standardised uptake value (SPECT/CT-SUV) is used to assess the response of metastatic castration-resistant prostate cancer (mCRPC) patients to targeted radionuclide therapy (TRT) with [177Lu]Lu-PSMA. This imaging technique determines the radiopharmaceutical distribution and internal dosimetry in patients who receive TRT. However, there is limited evidence regarding the role of image quantification in monitoring changes induced by [177Lu]Lu-PSMA. This systematic examines the role of quantitative SPECT/CT-SUV during [177Lu]Lu-PSMA TRT and assesses whether SUV changes correlate with quantitative imaging and biomarkers.

METHODS

A systematic review was conducted in accordance with the PRISMA guidelines. The MEDLINE/PubMed databases were searched from January 2016 to July 2024 to identify relevant articles. The inclusion criterion was the use of quantitative SPECT/CT-SUV during [177Lu]Lu-PSMA TRT for patients with mCRPC. The records were screened to determine their eligibility. The abstracts of 62 records were screened, and 28 were excluded because they were not relevant; the full texts of 34 original papers were retrieved and assessed for eligibility.

RESULTS

A total of five studies were included in this systematic review (two prospective studies and three retrospective studies). The sample sizes of the studies ranged from 6 to 73 patients. The highest number of lesions analysed was 144. Three studies reported the SPECT/CT-SUV following cycle 1, and only one study reported the correlation with pretherapy PET/CT (r = 0.9, p = 0.005). SPECT/CT-SUV changes between the first two to three cycles were reported in one study. None of the studies reported the SPECT/CT-SUV for normal organs. One study reported correlations between SPECT/CT-derived SUV and PET/CT-derived SUV in target and nontarget tissues.

CONCLUSION

Quantitative SPECT/CT-SUV can be used to predict responses to subsequent PSMA-TRT cycles. Disease burden and tumour heterogeneity are the leading causes of TRT individualisation.

Do you know your PSMA-tracer? Variability in the biodistribution of different PSMA ligands and its potential impact on defining PSMA-positivity prior to PSMA-targeted therapy

BACKGROUND

In clinical practice, several radiopharmaceuticals are used for PSMA-PET imaging, each with distinct biodistribution patterns. This may impact treatment decisions and outcomes, as eligibility for PSMA-directed radioligand therapy is usually assessed by comparing tumoral uptake to normal liver uptake as a reference. In this study, we aimed to compare tracer uptake intraindividually in various reference regions including liver, parotid gland and spleen as well as the respective tumor-to-background ratios (TBR) of different 18F-labeled PSMA ligands to today's standard radiopharmaceutical 68Ga-PSMA-11 in a series of patients with biochemical recurrence of prostate cancer who underwent a dual PSMA-PET examination as part of an individualized diagnostic approach.

RESULTS

Differences in background activity among different PSMA-PET tracers lead to variations in tumor-to-background ratios (TBR). In [18F]F-DCFPyL-PET, TBR with the liver as the reference organ (TBRliver) was comparable to [68Ga]Ga-PSMA-11-PET, while [18F]F-PSMA-1007-PET and [18F]F-JK-PSMA-7-PET showed significantly lower values. Using the parotid gland as the reference (TBRparotidgland), [18F]F-DCFPyL-PET exhibited significantly higher values, whereas [18F]F-PSMA-1007-PET and [18F]F-JK-PSMA-7-PET were comparable. For the spleen (TBRspleen), [18F]F-JK-PSMA-7-PET was comparable, but [18F]F-DCFPyL-PET and [18F]F-PSMA-1007-PET showed significantly higher and lower values, respectively. An additional Bland-Altman analyses revealed low bias for [18F]F-DCFPyL-PET in TBRparotidgland, whereas significant differences in TBRliver and TBRspleen for the other tracers resulted in higher bias.

CONCLUSION

Different PSMA-PET tracers exhibit distinct biodistribution patterns, leading to variations in tumor-to-background ratios (TBR) in reference organs such as the liver, parotid gland, and spleen. Patient selection for PSMA-directed radioligand therapy is currently based on a semiquantitative approach using the liver as a reference region in [68Ga]Ga-PSMA-11-PET. Thus, the use of alternative [18F]-labeled tracers may result in under- or overestimation of a patient's suitability for therapy. This highlights the importance of a comprehensive understanding of the differences in tracer-specific uptake behavior for accurate decisions regarding PSMA-expression levels. However, as the patient cohort in this study is at earlier disease stages, the generalizability of these findings to later-stage patients remains unclear and requires further investigation.

PSMA Radiotheranostics in Prostate Cancer: Principles, Practice, and Future Prospects

Prostate cancer is a leading cause of cancer-related mortality in men, with metastatic castration-resistant prostate cancer presenting a substantial treatment challenge. The authors focuse on prostate-specific membrane antigen (PSMA) radiotheranostics, particularly lutetium 177 (177Lu)-PSMA radioligand therapy, as an emerging treatment modality for metastatic castration-resistant prostate cancer. The U.S. Food and Drug Administration approval of 177Lu-PSMA-617 marked a substantial advancement in the treatment paradigm of metastatic castration-resistant prostate cancer, based on the VISION trial that showed improved overall survival and quality of life compared with those for standard care. PSMA expression, assessed via PSMA PET, is crucial for patient selection and assessment of treatment eligibility. The authors discuss current practices, including therapy administration, dosing, and side effects, with a particular focus on eligibility criteria and the added value of posttherapy imaging. Response assessment criteria using PSMA PET are discussed, although these require further validation. The discussion of future directions highlights ongoing trials investigating PSMA targeting agents, the extension of radioligand therapy to earlier stages of prostate cancer, and combination therapies. This review underscores the role of PSMA radioligand therapy in the evolving landscape of prostate cancer treatment and its promise for improving patient outcomes. ©RSNA, 2024 Supplemental material is available for this article.

Normal-organ distribution of PSMA-targeting PET radiopharmaceutical 18F-flotufolastat: a post hoc analysis of the LIGHTHOUSE and SPOTLIGHT studies

BACKGROUND

High-affinity radiohybrid PSMA-targeting radiopharmaceutical 18F-flotufolastat (18F-rhPSMA-7.3) is newly approved for diagnostic imaging of prostate cancer. Here, we conduct a post hoc analysis of two phase 3 studies to quantify 18F-flotufolastat uptake in a range of normal organs.

METHODS

All 718 evaluable 18F-flotufolastat scans from LIGHTHOUSE and SPOTLIGHT were re-evaluated. Additionally, patients' medical records were reviewed and any patients with high tumor burden (PSA>20 ng/mL), altered biodistribution (e.g., chronic kidney disease), major anatomical changes to normal organs (e.g., nephrectomy), or any other history of cancer were excluded. A medical physicist defined volumes of interest over specific organs for evaluation of SUVmean and SUVpeak per PERCIST 1.0 criteria. Normally distributed data are reported as mean (SD) and non-normally distributed data as median (IQR). The co-efficient of variation (CoV; calculated as SD/mean for normally distributed data and IQR/median for non-normally distributed data) was used to quantify variability of SUV metrics.

RESULTS

In total, scans from 546 patients (244 primary, 302 recurrent) were eligible for this analysis. All organs were considered to be normally distributed except for the bladder and spleen. In the liver, the mean SUVmean was 6.7 (SD 1.7), CoV 26%, while the bladder median SUVmean was 10.6 (IQR 11.9), CoV 112%. The mean SUVpeak in the liver was 8.2 (SD 2.1), CoV 26% and median SUVpeak in the bladder was 16.0 (IQR 18.5), CoV 116%.

CONCLUSIONS

Physiological 18F-flotufolastat uptake in normal organs was broadly consistent with other renally-cleared radiopharmaceuticals, which may have clinically significant implications when considering patient selection for radioligand therapy. Additionally, the bladder median SUVpeak for 18F-flotufolastat was lower than that previously reported for 68Ga-PSMA-11 and 18F-DCFPyL.

PSMA-based therapeutics for prostate cancer

INTRODUCTION

The prostate cancer (PCa) consists the most frequently diagnosed malignancy of urogenital system in males. Traditionally, treatment of localized PCa was based on surgery or radiotherapy while hormonotherapy was used in more advanced stages. However, the implementation of radiolabels has revolutionized the landscape of prostate cancer. Specifically, prostate-specific membrane antigen (PSMA) has been investigated in different aspects of PCa therapeutic era.

AREAS COVERED

A literature review is presented about the implications of PSMA radiolabels on prostate cancer treatment. PSMA tracers were initially used as an imaging technique. Afterwards, PSMA labeled with isotopes presenting cytotoxic abilities, such as lutetium-117 and actinium-225, while reports exist about the use of radioligand immunotherapy. Meanwhile, ongoing trials examine the development of novel radionuclides as well as the evolution of the PSMA-targeted ligands.

EXPERT OPINION

Currently, PSMA radioligand treatment of prostate cancer is approved in the metastatic stage of the disease. Meanwhile, a variety of trials exist about its possible role in less advanced stages. However, plenty of parameters should be addressed before these implementations, such as PSMA dosage, dosimetry issues, and its safety profile. A future well-designed study with proper patient selection is mandatory to further explore PSMA radioligand theranostics perspectives.

Comparison of 18F-DCFPyL and 68Ga-PSMA-11 for 177Lu-PSMA-617 therapy patient selection

Purpose

68Ga-PSMA-11 is recommended for the selection of patients for treatment in the package insert for 177Lu-PSMA-617. We aimed to compare imaging properties and post-treatment outcomes from radioligand therapy (RLT) of patients selected with 68Ga-PSMA-11 and 18F-DCFPyL.

Methods

We retrospectively evaluated 80 patients undergoing PSMA RLT, who had pretreatment imaging using either 68Ga-PSMA-11 or 18F-DCFPyL. For both groups, we compared the biodistribution and lesion uptake and the PSA response to treatment.

Results

Both agents had comparable biodistribution. Patients initially imaged with 18F-DCFPyL had a higher PSA response (66% vs. 42%), and more patients had a PSA50 response (72% vs. 43%) compared to patients imaged with 68Ga-PSMA-11.

Conclusion

18F-DCFPyL and 68Ga-PSMA-11 had comparable biodistribution and lesion uptake. Patients imaged with 18F-DCFPyL demonstrated clinical benefit to PSMA RLT comparable to those imaged with 68Ga-PSMA-11, and either agent can be used for screening patients.

Optimization and scale up of production of the PSMA imaging agent [18F]AlF-P16-093 on a custom automated radiosynthesis platform

BACKGROUND

Recent advancements in positron emission tomograph (PET) using prostate specific membrane antigen (PSMA)-targeted radiopharmaceuticals have changed the standard of care for prostate cancer patients by providing more accurate information during staging of primary and recurrent disease. [68Ga]Ga-P16-093 is a new PSMA-PET radiopharmaceutical that demonstrated superior imaging performance in recent head-to-head studies with [68Ga]Ga-PSMA-11. To improve the availability of this new PSMA PET imaging agent, [18F]AlF-P16-093 was developed. The 18F-analog [18F]AlF-P16-093 has been synthesized manually at low activity levels using [18F]AlF2+ and validated in pre-clinical models. This work reports the optimization of the production of > 15 GBq of [18F]AlF-P16-093 using a custom automated synthesis platform.

RESULTS

The sensitivity of the radiochemical yield of [18F]AlF-P16-093 to reaction parameters of time, temperature and reagent amounts was investigated using a custom automated system. The automated system is a low-cost, cassette-based system designed for 1-pot syntheses with flow-controlled solid phase extraction (SPE) workup and is based on the Raspberry Pi Zero 2 microcomputer/Python3 ecosystem. The optimized none-decay-corrected yield was 52 ± 4% (N = 3; 17.5 ± 2.2 GBq) with a molar activity of 109 ± 14 GBq/µmole and a radiochemical purity of 98.6 ± 0.6%. Run time was 30 min. A two-step sequence was used: SPE-purified [18F]F- was reacted with 80 nmoles of freeze-dried AlCl3·6H2O at 65 °C for 5 min followed by reaction with 160 nmoles of P16-093 ligand at 40 °C for 4 min in a 1:1 mixture of ethanol:0.5 M pH 4.5 NaOAc buffer. The mixture was purified by SPE (> 97% recovery). The final product formulation (5 mM pH 7 phosphate buffer with saline) exhibited a rate of decline in radiochemical purity of ~ 1.4%/h which was slowed to ~ 0.4%/h when stored at 4 °C.

CONCLUSION

The optimized method using a custom automated system enabled the efficient (> 50% none-decay-corrected yield) production of [18F]AlF-P16-093 with high radiochemical purity (> 95%). The method and automation system are simple and robust, facilitating further clinical studies with [18F]AlF-P16-093.