Differences in Distribution and Detection Rate of the [68Ga]Ga-PSMA Ligands PSMA-617, -I&T and -11-Inter-Individual Comparison in Patients with Biochemical Relapse of Prostate Cancer

Prostate-Specific Membrane Antigen Radioligand Therapy in Non-Prostate Cancers: Where Do We Stand?

INTRODUCTION

The term theragnostic refers to the combination of a predictive imaging biomarker with a therapeutic agent. The promising application of prostate-specific membrane antigen (PSMA)-based radiopharmaceuticals in the imaging and treatment of prostate cancer (PCa) patients opens the way to investigate a possible role of PSMA-based radiopharmaceuticals in cancers beyond the prostate. Therefore, the aim of this review was to evaluate the role of 177Lu-PSMA radioligand therapy (RLT) in malignancies other than prostate cancer by evaluating preclinical, clinical studies, and ongoing clinical trials.

METHODS

An extensive literature search was performed in three different databases using different combinations of the following terms: "Lu-PSMA", "177Lu-PSMA", "preclinical", "mouse", "salivary gland cancer", "breast cancer", "glioblastoma", "solid tumour", "renal cell carcinoma", "HCC", "thyroid", "salivary", "radioligand therapy", and "lutetium-177". The search had no beginning date limit and was updated to April 2024. Only articles written in English were included in this review.

RESULTS

A total of four preclinical studies were selected (breast cancer model n = 3/4). PSMA-RLT significantly reduced cell viability and had anti-angiogenic effects, especially under hypoxic conditions, which increase PSMA binding and uptake. Considering the clinical studies (n = 8), the complexity of evaluating PSMA-RLT in cancers other than prostate cancer was clearly revealed, since in most of the presented cases a sufficient tumour radiation dose was not achieved. However, encouraging results can be found in some types of diseases, such as thyroid cancer. Some clinical trials are still ongoing, and results from prospective larger cohorts of patients are awaited.

CONCLUSIONS

The need for larger patient cohorts and more RLT cycles administered underscores the need for further comprehensive studies. Given the very preliminary results of both preclinical and clinical studies, ongoing clinical trials in the near future may provide stronger evidence of both the safety and therapeutic efficacy of PSMA-RLT in malignancies other than prostate cancer.

Dependence of Renal Uptake on Kidney Function in [68Ga]Ga-PSMA-11 PET/CT Imaging

(1) Background: PSMA ligand PET/CT is increasingly important for diagnostics of prostate cancer and other tumor diseases. In particular, the radiopharmaceutical [68Ga]Ga-PSMA-11 is widely used. Besides its tumor-specific binding, the uptake within the kidneys is dominant and seems to visualize the renal cortex specifically. Kidney diseases may alter the uptake of radiopharmaceuticals. Therefore, the correlation between renal uptake in PET/CT imaging and renal function should be investigated. (2) Methods: A group of 103 male patients were retrospectively evaluated for eGFR according to the CKD-EPI equation, tracer uptake intensity (SUVmax, SUVpeak, SUVmean), the molecular volume of the renal cortex, morphological kidney size, and total renal uptake. Manual and three different computer-assisted contouring methods (thresholds at 50% of SUVmax, 30% of SUVmax, and absolute SUV of 20) were used for measurements. Correlations between parameters were calculated using linear regression models. (3) Results: Renal SUVmax, SUVpeak, and SUVmean do not correlate with eGFR for manual or computer-assisted measurements. In contrast, molecular cortex volume shows a moderate correlation with eGFR (R2 = 0.231, p < 0.001), superior to morphological kidney size. A contouring threshold of 30% of SUVmax outperformed the other settings for renal cortex volume and total renal uptake. (4) Conclusions: Renal uptake of [68Ga]Ga-PSMA-11 cannot predict eGFR, but the functional renal cortex can be quantified by PET/CT imaging.

Noninvasive longitudinal PET/CT imaging of CAR T cells using PSMA reporter gene

PURPOSE

Chimeric antigen receptor (CAR) T cell therapy has achieved great success in treating hematologic malignancies. However, it is yet to prove effective in the treatment of solid tumors. Thus, it is necessary to develop appropriate methodology for the long-term, accurate, and quantitative evaluation of the distribution and activities of CAR T cells in solid tumors. In the present study, we engineered TfR ΔPSMA CAR (CAR-ΔPSMA) T cells, which targeted the transferrin receptor (TfR) expressed by tumor cells and could be tracked in vivo via a reporter gene encoding the truncated prostate specific membrane antigen (ΔPSMA). We then quantitatively monitored these CAR T cells in vitro and in vivo using [68Ga]Ga-PSMA-617 positron emission tomography (PET)/computed tomography (CT).

METHODS

The CAR-ΔPSMA T cells were genetically engineered by transducing T cells with a lentiviral vector encoding TfR41BBζ-T2A-ΔPSMA. Firstly, the target expression, activation, and cytotoxicity of CAR-ΔPSMA T cells were validated in vitro. Secondly, the minimum thresholds of CAR-ΔPSMA T cells detection for [68Ga]Ga-PSMA-617 PET/CT were also determined in vitro and in vivo respectively. Lastly, the feasibility of monitoring the biodistribution and infiltration of CAR-ΔPSMA T cells after systematic administration was evaluated in the breast cancer subcutaneous xenograft model.

RESULTS

The CAR-ΔPSMA T cells retained activation and tumor killing capacity after transduction of the ΔPSMA-encoding reporter gene. Next, the CAR-ΔPSMA T cells could be reliably tracked by [68Ga]Ga-PSMA-617 PET/CT, the detection sensitivity of which was 250 cells/mm3 in vitro and 100 cells/mm3 in vivo. Next, the sequential imaging assays revealed that [68Ga]Ga-PSMA-617 PET/CT could be used to specifically visualize ΔPSMA+ CAR T cells at the tumor site. The increase in the [68Ga]Ga-PSMA-617 signal intensity over time allowed us to effectively detect CAR T cells in vivo.

CONCLUSION

Our findings preliminarily confirmed that [68Ga]Ga-PSMA-617 PET/CT could reliably detect CAR-ΔPSMA T cells in vitro and in vivo in solid tumors, laying the foundation for the monitoring CAR T cell therapy in the future.

Evaluation of the tolerability and safety of [225Ac]Ac-PSMA-I&T in patients with metastatic prostate cancer: a phase I dose escalation study

BACKGROUND

Life expectancy of patients with metastatic castration-resistant prostate cancer (mCRPC) is still limited despite several systemic treatments. Within five years after diagnosis of primary prostate cancer, 10-20% of the patients have mCRPC and curation is not an option. Radionuclide therapy (RNT) targeted against prostate-specific membrane antigen (PSMA) emerged as a new treatment option and showed effective results in patients with mCRPC. Survival benefit after [177Lu]Lu-PSMA RNT has already been demonstrated in several clinical trials. However, [225Ac]Ac-PSMA (225Ac-PSMA) appears to be an even more promising radiopharmaceutical for the treatment of mCRPC. The use of alpha emitting radionuclides offers advantages over beta emitting radionuclides due to the high linear energy transfer effective for killing tumor cells and the limited range to reduce the radiation effects on the healthy tissue. However, these results are based on retrospective data and safety data of 225Ac-PSMA are still limited. Therefore, a prospective trial is needed to determine the optimal amount of activity that can be administered.

METHODS

The 225Ac-PSMA-Imaging & Therapy (I&T) trial is an investigator-initiated phase I, single-center, open label, repeated dose-escalation and expansion trial. Patient with PSMA-positive mCRPC after at least one line of chemotherapy and/or one line of nonsteroidal antiandrogen will be treated with 225Ac-PSMA-I&T in increasing amount of activity per cycle. Dose-escalation following an accelerated 3 + 3 design which allows to open the next dose-level cohort in the absence of dose limiting toxicity while the previous one is still ongoing. Up to 4 treatment cohorts will be explored including up to 3 dose-escalation cohorts and one expansion cohort where patients will be administered with the recommended dose. A total of up to 30 patients will be enrolled in this trial. All patients will be evaluated for safety. Additionally, dosimetry was performed for the patients in the dose-escalation cohorts after the first 225Ac-PSMA-I&T administration.

DISCUSSION

This trial will assess the safety and tolerability of 225Ac-PSMA-I&T in patients with mCRPC to recommend the optimal dose for the phase II trial.

TRIAL REGISTRATION

ClinicalTrials.gov, (NCT05902247). Retrospectively registered 13 June 2023.

Head-to-Head Comparison of 68Ga-PSMA-11 with 68Ga-P137 in Patients with Suspected Prostate Cancer

P137 is a novel oxalyldiaminopropionic acid-urea-based prostate-specific membrane antigen (PSMA) targeting agent. This study compared the uptake patterns of 68Ga-P137 and the FDA-approved PET tracer 68Ga-PSMA-11 for diagnosing prostate cancer (PCa). Sixteen patients suspected of PCa were scanned by 68Ga-PSMA-11 and 68Ga-P137 PET/CT, respectively, followed by prospective analysis. The tumor-to-background ratio was calculated using normal prostate tissue, blood pool, muscle, and urine as backgrounds. Pathology or follow-up results were used to analyze uptake patterns of benign/malignant lesions and various organs. Thirteen patients were diagnosed with PCa and three with benign prostate diseases (BPD). The number and location of primary lesions, lymph node metastasis (LNM) (n = 25), bone metastasis (n = 30), and liver metastasis (n = 3) detected by the two tracers were identical. Maximum standardized uptake value (SUVmax), tumor/normal prostate ratio, as well as semiquantitative miPSMA-ES and PRIMARY diagnostic scores (P all >0.05) showed similar uptake levels of primary lesions between 68Ga-P137 and 68Ga-PSMA-11. Compared to 68Ga-P137, the SUVmax of 68Ga-PSMA-11 was significantly higher for bone metastasis, LNM, and liver metastasis (14.9 ± 7.2 vs 9.1 ± 4.4, 14.4 ± 5.0 vs 7.5 ± 2.4, 13.9 ± 2.0 vs 8.8 ± 2.4, P all <0.05). One-hour postinjection, SUVmax of the duodenum (9.4 ± 2.1 vs 16.2 ± 6.1), kidney (19.4 ± 4.3 vs 45.6 ± 20.9), and urine (14.1 ± 7.1 vs 42.1 ± 25.9) were significantly lower for 68Ga-P137 than for 68Ga-PSMA-11 (P all <0.05), whereas the radioactivity accumulation of blood pool and muscle (3.9 ± 0.5 vs 1.6 ± 0.4, 1.0 ± 0.1 vs 0.6 ± 0.1, P all <0.05) of 68Ga-P137 was significantly higher than 68Ga-PSMA-11. The uptake level of 68Ga-P137 has no significant difference from that of 68Ga-PSMA-11 in prostate primary lesions, and their imaging performances are visually equivalent for both primary and metastatic lesions, despite a higher blood pool and muscle background and a lower uptake in metastatic lesions. Due to the lower urine excretion of 68Ga-P137, primary prostate lesions near the urine can potentially be displayed clearer than 68Ga-PSMA-11.

68Ga-PSMA-11 PET/CT versus 68Ga-PSMA-11 PET/MRI for the detection of biochemically recurrent prostate cancer: a systematic review and meta-analysis

Purpose

Our aim was to conduct a meta-analysis and systematic review in order to compare the diagnostic efficacy of 68Ga-PSMA-11 PET/CT and 68Ga-PSMA-11 PET/MRI in patients with biochemically recurrent after radical prostatectomy and biochemically recurrent prostate cancers (BCR) after hybrid RT and RP.

Methods

Up until February 2023, we searched PubMed, Embase, and Web of Science for pertinent papers. Studies examining the utility of 68Ga-PSMA-11 PET/CT or PET/MRI as a screening tool for biochemically recurrent prostate cancer were included. To measure heterogeneity, we employed the I2 statistic. In cases of substantial heterogeneity (I2 > 50%), we used the random effect model to produce a forest plot. In other cases, we utilized the fixed model. Furthermore, we assessed the quality of the studies included using the Quality Assessment of Diagnostic Performance Studies (QUADAS-2) method.

Results

In total, 37 studies involving 8409 patients were examined. For 68Ga-PSMA-11 PET/CT and 68Ga-PSMA-11 PET/MRI, the combined total detection rate was 0.70 (95% CI: 0.65-0.75) and 0.71 (95% CI:0.67-0.75), respectively. 68Ga-PSMA-11 PET/CT and 68Ga-PSMA-11 PET/MRI did not substantially differ in terms of the overall detection rate for BCR (P = 0.58). The detection rate was unaffected by the PSA values (all P > 0.05).

Conclusion

The diagnostic efficacy of 68Ga-PSMA-11 PET/CT appears to be equivalent to that of 68Ga-PSMA-11 PET/MRI in detecting biochemically recurrent prostate cancer. Nonetheless, it should be noted that not all studies have used pathological biopsies as the gold standard. Therefore, additional larger prospective studies are needed to address this issue.

Systematic review registration

identifier CRD42023410039.

Detection efficacy of [89Zr]Zr-PSMA-617 PET/CT in [68Ga]Ga-PSMA-11 PET/CT-negative biochemical recurrence of prostate cancer

RATIONALE

In patients with biochemical recurrence of prostate cancer (BCR), preliminary data suggest that prostate-specific membrane antigen (PSMA) ligand radiotracers labeled with zirconium-89 (89Zr; half-life ~ 78.41 h), which allow imaging ≥ 24 h post-injection, detect suspicious lesions that are missed when using tracers incorporating short-lived radionuclides.

MATERIALS AND METHODS

To confirm [89Zr]Zr-PSMA-617 positron emission tomography/computed tomography (PET/CT) detection efficacy regarding such lesions, and compare quality of 1-h, 24-h, and 48-h [89Zr]Zr-PSMA-617 scans, we retrospectively analyzed visual findings and PET variables reflecting lesional [89Zr]Zr-PSMA-617 uptake and lesion-to-background ratio. The cohort comprised 23 men with BCR post-prostatectomy, median (minimum-maximum) prostate-specific antigen (PSA) 0.54 (0.11-2.50) ng/mL, and negative [68Ga]Ga-PSMA-11 scans 40 ± 28 d earlier. Primary endpoints were percentages of patients with, and classifications of, suspicious lesions.

RESULTS

Altogether, 18/23 patients (78%) had 36 suspicious lesions (minimum-maximum per patient: 1-4) on both 24-h and 48-h scans (n = 33 lesions) or only 48-h scans (n = 3 lesions). Only one lesion appeared on a 1-h scan. Lesions putatively represented local recurrence in 11 cases, and nodal or bone metastasis in 21 or 4 cases, respectively; 1/1 lesion was histologically confirmed as a nodal metastasis. In all 15 patients given radiotherapy based on [89Zr]Zr-PSMA-617 PET/CT, PSA values decreased after this treatment. Comparison of PET variables in 24-h vs 48-h scans suggested no clear superiority of either regarding radiotracer uptake, but improved lesion-to-background ratio at 48 h.

CONCLUSIONS

In men with BCR and low PSA, [89Zr]Zr-PSMA-617 PET/CT seems effective in finding prostate malignancy not seen on [68Ga]Ga-PSMA-11 PET/CT. The higher detection rates and lesion-to-background ratios of 48-h scans versus 24-h scans suggest that imaging at the later time may be preferable. Prospective study of [89Zr]Zr-PSMA-617 PET/CT is warranted.