Flare on Serial Prostate-Specific Membrane Antigen-Targeted 18F-DCFPyL PET/CT Examinations in Castration-Resistant Prostate Cancer: First Observations

Pluvicto-Induced 18 F-PSMA PET Bone Flare

ABSTRACT

A 79-year-old man with a history of metastatic prostate cancer was initially treated with Eligard and switched to relugolix in 2021. The 2022 bone scan presented superscan and extensive osseous metastatic lesions; some had intense PSMA uptake on the initial PSMA PET scan without nodal or visceral metastatic lesions. We treated him with Pluvicto and relugolix. The intermediate PSMA scan demonstrated prominent bone marrow PSMA uptake. However, PSA decreased 58.5%. We hypothesized that the patient might have a bone flare. The final PSMA scan confirmed our hypothesis. Based on our knowledge, this is the first case of Pluvicto-induced bone flare.

Altered Glucose Metabolism Postchemotherapy Precedes PSMA Expression in Poorly Differentiated Prostate Cancer

ABSTRACT

A 73-year-old man presented with gastric lesion on upper endoscopy, biopsy-proven as poorly differentiated carcinoma. Staging FDG PET/CT scan showed gastric, intraprostatic, nodal, and extensive osseous lesions. Prostate-specific antigen levels were greater than 1000. The patient was treated as metastatic poorly differentiated prostate cancer with chemotherapy. Posttherapy 18 F-PSMA-1007 and FDG PET/CT scans were obtained. PSMA PET/CT scan revealed extensive disease similar in appearance as staging FDG PET/CT scan, indicating no apparent treatment response. FDG PET/CT scan showed partial metabolic response, correlating with improved prostate-specific antigen levels. This case indicates that chemotherapy-induced changes in glucose metabolism likely precede change in PSMA expression in poorly differentiated prostate cancer.

Bone and Lymph Node Flare to Androgen Deprivation Therapy in Metastatic Hormone-Sensitive Prostate Cancer on 18F-Prostate-Specific Membrane Antigen PET/CT With Decreasing Prostate-Specific Antigen of 0.7 ng/mL

ABSTRACT

A 72-year-old man with prostate cancer was found to have prostate-specific membrane antigen (PSMA)-avid oligometastasis on initial staging with 18F-DCFPyL PET/CT. Meanwhile, his prostate-specific antigen was 10.0 ng/mL, and testosterone level was 381 ng/dL. Six weeks after initiation of treatment on androgen deprivation therapy plus abiraterone, his restaging 18F-DCFPyL PET/CT showed decreased PSMA uptake in primary prostate lesion, but increased uptake in bone and lymph node metastases, whereas his prostate-specific antigen decreased to 0.7 ng/mL, and testosterone level was <3 ng/dL. This case illustrates hormone-sensitive metastatic bone and lymph node flare on 18F-PSMA PET/CT.

Prospective, Single-Arm Trial Evaluating Changes in Uptake Patterns on Prostate-Specific Membrane Antigen-Targeted 18F-DCFPyL PET/CT in Patients with Castration-Resistant Prostate Cancer Starting Abiraterone or Enzalutamide

PET with small molecules targeting prostate-specific membrane antigen (PSMA) is being adopted as a clinical standard for prostate cancer imaging. In this study, we evaluated changes in uptake on PSMA-targeted PET in men starting abiraterone or enzalutamide. Methods: This prospective, single-arm, 2-center, exploratory clinical trial enrolled men with metastatic castration-resistant prostate cancer initiating abiraterone or enzalutamide. Each patient was imaged with 18F-DCFPyL at baseline and within 2-4 mo after starting therapy. Patients were followed for up to 48 mo from enrollment. A central review evaluated baseline and follow-up PET scans, recording change in SUVmax at all disease sites and classifying the pattern of change. Two parameters were derived: the δ-percent SUVmax (DPSM) of all lesions and the δ-absolute SUVmax (DASM) of all lesions. Kaplan-Meier curves were used to estimate time to therapy change (TTTC) and overall survival (OS). Results: Sixteen evaluable patients were accrued to the study. Median TTTC was 9.6 mo (95% CI, 6.9-14.2), and median OS was 28.6 mo (95% CI, 18.3-not available [NA]). Patients with a mixed-but-predominantly-increased pattern of radiotracer uptake had a shorter TTTC and OS. Men with a low DPSM had a median TTTC of 12.2 mo (95% CI, 11.3-NA) and a median OS of 37.2 mo (95% CI, 28.9-NA), whereas those with a high DPSM had a median TTTC of 6.5 mo (95% CI, 4.6-NA, P = 0.0001) and a median OS of 17.8 mo (95% CI, 13.9-NA, P = 0.02). Men with a low DASM had a median TTTC of 12.2 mo (95% CI, 11.3-NA) and a median OS of NA (95% CI, 37.2 mo-NA), whereas those with a high DASM had a median TTTC of 6.9 mo (95% CI, 6.1-NA, P = 0.003) and a median OS of 17.8 mo (95% CI, 13.9-NA, P = 0.002). Conclusion: Findings on PSMA-targeted PET 2-4 mo after initiation of abiraterone or enzalutamide are associated with TTTC and OS. Development of new lesions or increasing intensity of radiotracer uptake at sites of baseline disease are poor prognostic findings suggesting shorter TTTC and OS.

More Than Meets the Eye: Scientific Rationale behind Molecular Imaging and Therapeutic Targeting of Prostate-Specific Membrane Antigen (PSMA) in Metastatic Prostate Cancer and Beyond

Simple Summary

Prostate-specific membrane antigen (PSMA) is a transmembrane protein that is overexpressed in prostate cancer and correlates with the aggressiveness of the disease. PSMA is a promising target for imaging and therapeutics in prostate cancer patients validated in prospective trials. However, the role of PSMA in prostate cancer progression is poorly understood. In this review, we discuss the biology and scientific rationale behind the use of PSMA and other targets in the detection and theranostics of metastatic prostate cancer.

Abstract

Prostate cancer is the second most common cancer type in men globally. Although the prognosis for localized prostate cancer is good, no curative treatments are available for metastatic disease. Better diagnostic methods could help target therapies and improve the outcome. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed on malignant prostate tumor cells and correlates with the aggressiveness of the disease. PSMA is a clinically validated target for positron emission tomography (PET) imaging-based diagnostics in prostate cancer, and during recent years several therapeutics have been developed based on PSMA expression and activity. The expression of PSMA in prostate cancer can be very heterogeneous and some metastases are negative for PSMA. Determinants that dictate clinical responses to PSMA-targeting therapeutics are not well known. Moreover, it is not clear how to manipulate PSMA expression for therapeutic purposes and develop rational treatment combinations. A deeper understanding of the biology behind the use of PSMA would help the development of theranostics with radiolabeled compounds and other PSMA-based therapeutic approaches. Along with PSMA several other targets have also been evaluated or are currently under investigation in preclinical or clinical settings in prostate cancer. Here we critically elaborate the biology and scientific rationale behind the use of PSMA and other targets in the detection and therapeutic targeting of metastatic prostate cancer.

Consensus statements on PSMA PET/CT response assessment criteria in prostate cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) is used for (re)staging prostate cancer (PCa) and as a biomarker for evaluating response to therapy, but lacks established response criteria. A panel of PCa experts in nuclear medicine, radiology, and/or urology met on February 21, 2020, in Amsterdam, The Netherlands, to formulate criteria for PSMA PET/CT-based response in patients treated for metastatic PCa and optimal timing to use it.

METHODS

Panelists received thematic topics and relevant literature prior to the meeting. Statements on how to interpret response and progression on therapy in PCa with PSMA PET/CT and when to use it were developed. Panelists voted anonymously on a nine-point scale, ranging from strongly disagree (1) to strongly agree (9). Median scores described agreement and consensus.

RESULTS

PSMA PET/CT consensus statements concerned utility, best timing for performing, criteria for evaluation of response, patients who could benefit, and handling of radiolabeled PSMA PET tracers. Consensus was reached on all statements. PSMA PET/CT can be used before and after any local and systemic treatment in patients with metastatic disease to evaluate response to treatment. Ideally, PSMA PET/CT imaging criteria should categorize patients as responders, patients with stable disease, partial response, and complete response, or as non-responders. Specific clinical scenarios such as oligometastatic or polymetastatic disease deserve special consideration.

CONCLUSIONS

Adoption of PSMA PET/CT should be supported by indication for appropriate use and precise criteria for interpretation. PSMA PET/CT criteria should categorize patients as responders or non-responders. Specific clinical scenarios deserve special consideration.

Prostate Cancer Lymphangitic Pulmonary Carcinomatosis: Appearance on 18F-FDG PET/CT and 18F-DCFPyL PET/CT

A 51-year-old man diagnosed with high-grade, high-volume metastatic castration-sensitive prostate adenocarcinoma received pelvic radiation, androgen deprivation therapy, and intravenous docetaxel. Serum prostate-specific antigen became undetectable following treatment. Within a year, his cancer progressed to castration-resistant disease, and he was treated with oral abiraterone acetate 1000 mg and prednisone 10 mg daily. Despite this, the serum prostate-specific antigen rose from 0.03 to 1.39 μg/L, and F-DCFPyL and F-FDG PET/CT showed progression. While F-DCFPyL uptake may be seen in aggressive disease, F-FDG portends poor prognosis. Despite intravenous platinum-based chemotherapy, the patient died of respiratory failure 20 months after his initial diagnosis.

Prospective study on the effect of short-term androgen deprivation therapy on PSMA uptake evaluated with 68Ga-PSMA-11 PET/MRI in men with treatment-naïve prostate cancer

PURPOSE

Based on in vitro studies, it is known that androgen deprivation therapy (ADT) increases prostate-specific membrane antigen (PSMA) expression. Therefore, we hypothesised that ADT improves the performance of PSMA-PET imaging in primary staging of prostate cancer. The purpose of the study was to demonstrate the time course effect of ADT on PSMA uptake in different types of metastatic lesions evaluated with ⁶⁸Ga-PSMA-11 PET/MRI.

METHODS

Nine men with treatment-naïve prostate cancer were enrolled to a prospective, registered (NCT03313726) clinical trial. A ⁶⁸Ga-PSMA-11 PET/MRI was performed once before and 3 times post-ADT (degarelix, Firmagon). Change of maximum standardised uptake values (SUVmax) in prostate, lymph nodes, bone metastases, and physiologically PSMA-avid organs were evaluated in a time frame of 1-8 weeks.

RESULTS

All patients reached castration levels within 10 days, and 50% decrease in prostate-specific antigen (PSA) concentration was observed 14 days post-ADT. A heterogeneous increase in PSMA uptake was observed 3 to 4 weeks post-ADT. This phenomenon was definitively more evident in bone metastases: 13 (57%) of the metastasis, with a mean (range) SUVmax increase of 77% (8-238%). In one patient, already having bone metastases at baseline, three new bone metastases were observed post-ADT. Of lesions with reduced SUVmax, none disappeared.

CONCLUSIONS

Both in patient and region level, increase in PSMA uptake post-ADT is heterogenous and is seen most evidently in bone metastases. Preliminary results on a small cohort of patients suggest the clinical impact of ADT on improving the performance of ⁶⁸Ga-PSMA PET in staging seems to be minor. However, the optimal imaging time point might be 3 to 4 weeks post-ADT. Since none of the metastases with decreasing SUVmax disappeared, it seems that short-term usage of ADT does not interfere with the interpretation of ⁶⁸Ga-PSMA PET.

TRIAL REGISTRATION

NCT03313726, registered 18 October 2017; EUDRA-CT, 2017-002345-29.

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

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