Landscape of prostate-specific membrane antigen heterogeneity and regulation in AR-positive and AR-negative metastatic prostate cancer

Tumor expression of prostate-specific membrane antigen (PSMA) is lost in 15-20% of men with castration-resistant prostate cancer (CRPC), yet the underlying mechanisms remain poorly defined. In androgen receptor (AR)-positive CRPC, we observed lower PSMA expression in liver lesions versus other sites, suggesting a role of the microenvironment in modulating PSMA. PSMA suppression was associated with promoter histone 3 lysine 27 methylation and higher levels of neutral amino acid transporters, correlating with 18F-fluciclovine uptake on positron emission tomography imaging. While PSMA is regulated by AR, we identified a subset of AR-negative CRPC with high PSMA. HOXB13 and AR co-occupancy at the PSMA enhancer and knockout models point to HOXB13 as an upstream regulator of PSMA in AR-positive and AR-negative prostate cancer. These data demonstrate how PSMA expression is differentially regulated across metastatic lesions and in the context of the AR, which may inform selection for PSMA-targeted therapies and development of complementary biomarkers.

P15.10.B A multicenter phase 3 trial in progress: diagnostic performance of18F-fluciclovine PET for the detection of recurrent brain metastases after radiation therapy (REVELATE)

Background

Following treatment of brain metastases, which can affect up to 40% of patients with cancer, patients will typically be closely monitored with serial brain magnetic resonance imaging (MRI) owing to the high likelihood of recurrence. The recommended follow-up modalities (CE-T1-weighted and FLAIR/T2-weighted MRI) have poor specificity, meaning that differentiation of true disease from treatment-related changes such as radiation necrosis can be difficult. Recent pilot studies have reported amino acid PET radiopharmaceutical, 18F-fluciclovine, to be potentially useful in discriminating brain tumor recurrence from treatment-related changes. This may potentially help physicians to make confident diagnoses and inform subsequent treatment plans.

Material and Methods

REVELATE (NCT04410133) will evaluate the diagnostic performance of 18F-fluciclovine PET (read with conventional MRI for anatomical reference) for the detection of recurrent brain metastases in patients for whom MRI is equivocal. This multicenter, phase 3, prospective, open-label trial aims to enroll approximately 150 subjects from across 19 US sites with solid tumor brain metastases who have undergone radiation therapy, if they have a lesion considered equivocal on MRI that requires further confirmatory diagnostic procedures (either biopsy/neurosurgical intervention or clinical follow-up). Patients will undergo 18F-fluciclovine PET <42 days after the equivocal MRI and 1-21 days pre-biopsy/neurosurgical intervention. Clinical follow-up will occur for 6m post-18F-fluciclovine PET.

Results

The primary endpoint of REVELATE is the subject-level 18F-fluciclovine negative and positive percent agreement (equivalent to specificity and sensitivity, respectively) for detection of recurrent brain metastases. Further objectives include evaluation of the lesion-level diagnostic performance, inter-reader and intra-reader agreement, and safety evaluations.

Conclusion

This ongoing phase 3 study will provide efficacy and safety data for the use of 18F-fluciclovine for the detection of recurrent brain metastases. Enrolment began in October 2020 and the trial is active but not recruiting at the time of submission.

NEIM-03 A MULTICENTER PHASE 3 TRIAL IN PROGRESS: DIAGNOSTIC PERFORMANCE OF18F-FLUCICLOVINE PET FOR THE DETECTION OF RECURRENT BRAIN METASTASES AFTER RADIATION THERAPY (REVELATE)

INTRODUCTION

Following treatment of brain metastases, which can affect up to 40% of patients with cancer, patients will typically be closely monitored with serial brain magnetic resonance imaging (MRI) owing to the high likelihood of recurrence. The recommended follow-up modalities (CE-T1-weighted and FLAIR/T2-weighted MRI) have poor specificity, meaning that differentiation of true disease from treatment-related changes such as radiation necrosis can be difficult. Recent pilot studies have reported amino acid PET radiopharmaceutical, ¹⁸F-fluciclovine, to be potentially useful in discriminating tumor recurrence from treatment-related changes. This may potentially aid physicians in making confident diagnoses and inform subsequent treatment plans.

METHODS

REVELATE (NCT04410133) will evaluate the diagnostic performance of ¹⁸F-fluciclovine PET (read with conventional MRI for anatomical reference) for the detection of recurrent brain metastases in patients for whom MRI is equivocal. This multicenter, phase 3, prospective, open-label trial aims to enroll approximately 150 subjects from across 19 US sites with solid tumor brain metastases who have undergone radiation therapy, if they have a lesion considered equivocal on MRI that requires further confirmatory diagnostic procedures (either biopsy/neurosurgical intervention or clinical follow-up). Patients will undergo ¹⁸F-fluciclovine PET <42 days after the equivocal MRI and 1–21 days pre-biopsy/neurosurgical intervention. Clinical follow-up will occur for 6m post-¹⁸F-fluciclovine PET. Secondary objectives include evaluation of subject- and lesion-level ¹⁸F-fluciclovine negative and positive percent agreement (equivalent to specificity and sensitivity, respectively) for recurrent brain metastases, inter-reader and intra-reader agreement, and safety evaluations. Enrolment began in October 2020 and the trial is active but not recruiting at the time of submission.

NEIM-02. TRIAL IN PROGRESS: A MULTICENTER PHASE 3 STUDY TO ESTABLISH THE DIAGNOSTIC PERFORMANCE OF 18F-FLUCICLOVINE PET IN DETECTING RECURRENT BRAIN METASTASES AFTER RADIATION THERAPY (REVELATE)

BACKGROUND

Brain metastases occur in up to 40% of patients with cancer and are associated with poor prognosis and considerable levels of recurrence. Consequently, close follow-up with serial brain MRI is performed post-treatment to monitor for recurrent disease. Although conventional MRI (CE-T1-weighted and FLAIR/T2-weighted) is the recommended follow-up modality, it has poor specificity with limited ability to differentiate between true disease recurrence and treatment-related changes such as radiation necrosis. Therefore, alternative imaging options are sought in order to help physicians confidently diagnose treatment-related changes and thus reliably stratify the risk of continuation of a therapeutic regimen, especially given the morbidity associated with current treatments. Amino acid PET imaging agent, 18F-fluciclovine, has increased uptake in brain tumors relative to normal tissue and may be useful for detecting recurrent brain metastases.

METHODS

NCT04410133 is a prospective, open-label, single-arm, single-dose (185 MBq ±20%) study with a primary objective to confirm the diagnostic performance of 18F-fluciclovine PET (read with conventional MRI for anatomical reference) for detection of recurrent brain metastases where MRI is equivocal. Approximately 150 subjects with solid tumor brain metastases who have undergone radiation therapy will be enrolled in this multicenter trial (~18 US sites) if they have a lesion considered equivocal on MRI that requires further confirmatory diagnostic procedures such as biopsy/neurosurgical intervention or clinical follow-up. Subjects will undergo 18F-fluciclovine PET &lt;42 days after the equivocal MRI and 1–21 days pre-biopsy/neurosurgical intervention. Clinical follow-up will occur for 6m post-18F-fluciclovine PET. Secondary objectives include evaluation of subject- and lesion-level 18F-fluciclovine negative and positive percent agreement (equivalent to specificity and sensitivity, respectively) for recurrent brain metastases, inter-reader and intra-reader agreement, and safety evaluations. Enrolment began in October 2020 and the trial is open at the time of submission.

CLRM-02. TRIAL IN PROGRESS: A PROSPECTIVE, MULTICENTER PHASE 2B STUDY TO ESTABLISH IMAGE INTERPRETATION CRITERIA FOR 18F-FLUCICLOVINE PET IN DETECTING RECURRENT BRAIN METASTASES AFTER RADIATION THERAPY (PURSUE)

BACKGROUND

Brain metastases represent the most common intracranial tumor in adults, occurring in 10-40% of cancer patients. Most patients undergo multimodal treatment approaches and post-treatment follow-up with conventional MRI (CE-T1-weighted and FLAIR/T2-weighted) of the brain is performed to monitor for disease recurrence. However, owing to the similar appearance of treatment-related changes like radiation necrosis with that of true recurrence, conventional MRI alone suffers from low specificity. Given the high mortality of patients with brain metastases and the considerable treatment-associated morbidity, a need remains for an imaging modality that accurately differentiates recurrence from treatment-related changes. Accurate imaging is key to preventing unnecessary surgery or changes in effective therapy in patients mistaken for disease progression as well as prevent continuation of ineffective therapy if radiation necrosis is incorrectly diagnosed. To this end, 18F-fluciclovine is a synthetic amino acid-based PET imaging agent that has potential to evaluate primary and metastatic brain cancers owing to its low normal background uptake in the brain and increased uptake in brain tumors.

METHODS

NCT04410367 is a prospective, open-label, single-arm, single-dose (185 MBq ± 20%) study with a primary objective to establish visual image interpretation criteria for 18F-fluciclovine PET studies of recurrent brain metastases. Forty subjects with solid tumor brain metastases who have undergone radiation therapy will be enrolled across ~8 US sites if they have a reference lesion considered equivocal on MRI for recurrent disease and are planned for craniotomy. Subjects will undergo 18F-fluciclovine PET &lt;42 days after the MRI and 1–21 days before planned craniotomy. Outcome measures comprise the diagnostic performance of 18F-fluciclovine PET at different thresholds of 18F-fluciclovine uptake compared with histopathology, subject- and lesion-level diagnostic performance based on established image interpretation criteria, and safety evaluations. Enrolment began in August 2020 and the trial is open at the time of submission.

TRLS-02. Trial in Progress: A Multicenter Phase 3 Study to Establish the Diagnostic Performance of 18F-Fluciclovine PET in Detecting Recurrent Brain Metastases after Radiation Therapy (REVELATE)

Background

Brain metastases occur in up to 40% of patients with cancer and are associated with poor prognosis and considerable levels of recurrence. Consequently, close follow-up with serial brain MRI is performed post-treatment to monitor for recurrent disease. Although conventional MRI (CE-T1-weighted and FLAIR/T2-weighted) is the recommended follow-up modality, it has poor specificity with limited ability to differentiate between true disease recurrence and treatment-related changes such as radiation necrosis. Therefore, alternative imaging options are sought in order to help physicians confidently diagnose treatment-related changes and thus reliably stratify the risk of continuation of a therapeutic regimen, especially given the morbidity associated with current treatments. Amino acid PET imaging agent, 18F-fluciclovine, has increased uptake in brain tumors relative to normal tissue and may be useful for detecting recurrent brain metastases.

Methods

NCT04410133 is a prospective, open-label, single-arm, single-dose (185 MBq ±20%) study with a primary objective to confirm the diagnostic performance of 18F-fluciclovine PET (read with conventional MRI for anatomical reference) for detection of recurrent brain metastases where MRI is equivocal.

Approximately 150 subjects with solid tumor brain metastases who have undergone radiation therapy will be enrolled in this multicenter trial (~18 US sites) if they have a lesion considered equivocal on MRI that requires further confirmatory diagnostic procedures such as biopsy/neurosurgical intervention or clinical follow-up. Subjects will undergo 18F-fluciclovine PET &lt;28 days after the equivocal MRI and 2–21 days pre-biopsy/neurosurgical intervention. Clinical follow-up will occur for 6m post-18F-fluciclovine PET. Secondary objectives include evaluation of subject- and lesion-level 18F-fluciclovine negative and positive percent agreement (equivalent to specificity and sensitivity respectively) for recurrent brain metastases, inter-reader and intra-reader agreement, and safety evaluations. Enrolment began in October 2020 and the trial is open at the time of submission.

TRLS-01. Trial in Progress: A Prospective, Multicenter Phase 2b Study to Establish Image Interpretation Criteria for 18F-Fluciclovine PET in Detecting Recurrent Brain Metastases after Radiation Therapy (PURSUE)

Background

Brain metastases are the most common intracranial tumor in adults, occurring in 10–40% of patients with cancer. Despite multimodal treatment approaches, the prognosis remains poor and post-treatment follow-up with conventional MRI (CE-T1-weighted and FLAIR/T2-weighted) of the brain is recommended to monitor for disease recurrence. However, owing to the similar appearance of treatment-related changes like radiation necrosis with that of true recurrence, conventional MRI has low specificity.

Given the high mortality of patients with brain metastases and the considerable treatment-associated morbidity, a need remains for an imaging modality that accurately differentiates recurrence from treatment-related changes. Accurate imaging could help physicians identify patients for whom non-effective or unneeded treatments can be ceased in order to minimize treatment-associated morbidity, and to avoid erroneous premature cessation of potentially effective therapy.

¹⁸F-Fluciclovine is a synthetic amino acid-based PET imaging agent that has potential to evaluate primary and metastatic brain cancers owing to its low normal background uptake in the brain and increased uptake in brain tumors.

Methods

NCT04410367 is a prospective, open-label, single-arm, single-dose (185 MBq ± 20%) study with a primary objective to establish visual image interpretation criteria for 18F-fluciclovine PET studies of recurrent brain metastases. Forty subjects with solid tumor brain metastases who have undergone radiation therapy will be enrolled across 8 US sites if they have a reference lesion considered equivocal on MRI for recurrent brain metastasis and are planned for craniotomy. Subjects will undergo 18F-fluciclovine PET <28 days after the equivocal MRI and 2–21 days before planned craniotomy. Outcome measures comprise diagnostic performance of 18F-fluciclovine PET at different thresholds of 18F-fluciclovine uptake compared with histopathology, subject- and lesion-level diagnostic performance based on application of the established image interpretation criteria, and safety evaluations. Enrolment began in August 2020 and the trial is open at the time of submission.