Preclinical evaluation and first in human study of Al18F radiolabeled ODAP-urea-based PSMA targeting ligand for PET imaging of prostate cancer

A visual whole-body tumor-burden classification based on PSMA PET/CT to predict response to novel androgen receptor signaling inhibitors for metastatic hormone-sensitive prostate cancer patients

PURPOSE

The incidence rates of metastatic hormone-sensitive prostate cancer (mHSPC) have increased rapidly. Androgen deprivation therapy (ADT) with AR signaling inhibitors (ARSIs) has been determined survival benefit for mHSPC patients in several randomized trials. However, patients do not respond uniformly. Whole-body tumor-burden schemes guided by prostate-specific membrane antigen (PSMA) PET/CT have been proven to be a useful predictive tool for PSMA-targeted radioligand therapy (RLT), while the value for hormone therapy was unclear. We hypothesized a visual whole-body tumor-burden classification based on PSMA PET/CT can enable selective patient stratification and prognostic evaluation for hormone treatment.

MATERIALS AND METHODS

Patients diagnosed with de novo mHSPC through pathological test and [18F]F-PSMA PET/CT between February 2022 and December 2023 who received ADT alone or ADT plus first-generation antiandrogens or ADT plus second-generation/novel ARSIs in our hospital were included. Only can hormone treatments (ADT or ADT plus first-generation antiandrogens or ADT plus novel ARSIs) be adopted at least six months after initial diagnosis. Prostate Cancer Multidisciplinary Team (MDT) of our hospital proposed a newly visual whole-body tumor-burden scheme based on PSMA PET/CT (MDT scheme: high vs. low): MDT high group (fulfilling any one of the three following criteria): (I) the number of metastatic lesions is more than 10 (diffused involvement of single bone is counted as 4 lesions) and PSMA uptake levels of 80% lesions are higher than that of parotid glands, (II) the presence of visceral metastases, (III) at least 4 bone metastases (≥ 1 beyond the vertebral bodies or the pelvis). In addition, other three tumor-burden classification methods (PSMA-CHAARTED, PSMA-LATITUDE, revised-vPSG schemes) were also assessed in this study. A series of other parameters including SUV-derived features of PSMA PET/CT and potential clinical and pathological factors were evaluated. SUV-derived features were determined for measurable locations and included: SUVmax, SUVpeak, SUVmean and tumor volume (TV) of prostatic primary lesions, the highest SUVmax of all lesions in whole body (wbSUVmax), primary-tumor SUVmax ratio backgrounds (including blood pool of liver/ spleen/ mediastinum/parotid glands), wbSUVmax ratio backgrounds above. Serum prostate-specific antigen (PSA) lower than 0.2 ng/ml after six-month hormone treatment was set as the primary endpoint for prediction of PSA response. PSA99 (PSA reduction ≥ 99%) was the second endpoint for survival analysis. All parameters above including the four tumor-burden classification schemes were evaluated for the predictive and prognostic value according to the endpoints using logistic and Cox proportional hazards regression analysis, respectively. All P values < 0.05 were considered significant.

RESULTS

A total of 165 patients were included. The average age was 69.30 ± 8.12 years. In univariate logistic regression analysis, MDT, PSMA-CHAARTED, revised-vPSG tumor-burden classifications, type of hormone treatment and primary-tumor TV were significantly related to PSA response, and PSMA-LATITUDE scheme wasn't relevant to PSA response. The results of further multivariate logistic regression revealed MDT scheme (MDT high group vs. low group: OR = 5.34, 95%CI: 2.40-11.87, P < 0.001), type of hormone treatment (ADT + second-generation ARSIs vs. ADT alone or ADT + first-generation antiandrogens: OR = 0.21, 95%CI: 0.08-0.53, P = 0.001), and primary-tumor TV (≥ 12.49 cm3 vs. < 12.49 cm3: OR = 2.93, 95%CI: 1.25-6.89, P = 0.014) were proven to be independent significant predictors for mHSPC patients. Subgroups analysis of patients treated with ADT + second-generation ARSIs (N = 133) showed MDT, PSMA-CHAARTED, PSMA-LATITUDE, revised-vPSG tumor-burden classifications and primary-tumor TV were significantly associated with PSA response through univariate analysis, and in multivariate regression MDT scheme (MDT high group vs. low group: OR = 5.73, 95%CI: 2.47-13.30, P < 0.001) and primary-tumor TV (≥ 12.49 cm3 vs. < 12.49 cm3: OR = 2.75, 95%CI: 1.09-6.96, P = 0.032) were independent significant predictors for PSA response of novel ARSIs. The AUC of three-predictors model of 165 mHSPC patients was 0.740 (95% CI: 0.664-0.816, P < 0.001). The AUC of two-predictors model of 133 mHSPC patients treated with ADT + novel ARSIs was 0.751 (95% CI: 0.666-0.836, P < 0.001). Univariate survival analysis revealed that patients treated with ADT + second-generation ARSIs were prone to obtaining PSA remission in shorter period (P < 0.001). In multivariate Cox regression, MDT scheme (MDT high group vs. low group: HR = 0.52, 95%CI: 0.36-0.74, P < 0.001) and type of hormone treatment (ADT + second-generation ARSIs vs. ADT alone or ADT + first-generation antiandrogens: HR = 3.34, 95%CI: 2.02-5.54, P < 0.001) were demonstrated to be independent significant prognostic indicators of patients with mHSPC. The survival analysis of patients treated with ADT + second-generation ARSIs (N = 133), patients with low burden of MDT (P < 0.001) or PSMA-CHAARTED (P = 0.029) or PSMA-LATITUDE (P = 0.009) could achieve PSA 99% reduction faster, and the low and high group patients based on revised-vPGS weren't displayed the significant difference in PSA99. Through the multivariate Cox survival regression, only MDT scheme (MDT high group vs. low group: HR = 0.47, 95%CI: 0.33-0.69, P < 0.001) was selected as the independent significant prognostic biomarker for mHSPC patients treated with ADT + second-generation ARSIs.

CONCLUSION

The visual whole-body tumor-burden classification based on PSMA PET/CT should be an effective stratification strategy for mHSPC patients treated with ADT + ARSIs, especially with ADT + second-generation ARSIs. PSA99 (PSA reduction ≥ 99%) could be a superior endpoint for patients with HSPC. This classification scheme could be a promising method for stratifying mHSPC patients. These findings need to be confirmed and validated through a longer follow-up, prospective and clinical data.

First-in-human Study of a Dual-modality Prostate-specific Membrane Antigen-targeted Probe for Preoperative Positron Emission Tomography/Computed Tomography Imaging and Intraoperative Fluorescence Imaging in Prostate Cancer

BACKGROUND AND OBJECTIVE

Accurately distinguishing between cancerous and noncancerous tissues during robot-assisted radical prostatectomy (RARP) is a challenge that can increase the risk of residual disease. This study aimed to evaluate the safety, optimal dose and accuracy of a dual-modality prostate-specific membrane antigen (PSMA)-targeted probe (68Ga-P3) for preoperative positron emission tomography (PET)/computed tomography (CT) imaging and intraoperative fluorescence imaging in prostate cancer.

METHODS AND SURGICAL PROCEDURE

Each participant received an intravenous chemical dose of 68Ga-P3 (10, 20, and 40 μg/kg), with radioactivity of 3.7 MBq/kg. PET/CT imaging was conducted 30, 60, and 120 min after injection to evaluate its biodistribution and dosimetry. RARP was performed at 24 ± 6 h after injection, in the sensitive mode of Firefly fluorescence imaging.

KEY FINDINGS AND LIMITATIONS

Between May 2024 and July 2024, a total of 16 patients were included; 68Ga-P3 was well tolerated without any adverse events related to 68Ga-P3 administration or fluorescence imaging. At 2 h after administration, the median tumor maximum standardized uptake value was 5.3 (4.1-8.1). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 68Ga-P3 PET/CT for tumor localization were 79.1%, 90.4%, 81.5%, and 89.0%, respectively. The overall NPV, PPV, and accuracy of intraoperative fluorescence imaging were 100%, 43.8%, and 90.9%, respectively. Of overall false-positive sites, 88.9% (8/9) were confirmed as tumor adjacent to the surgical margin. A dose of 40 μg/kg resulted in the highest accuracy of 92.3%.

CONCLUSIONS AND CLINICAL IMPLICATIONS

In PSMA-targeted PET imaging and fluorescence-guided surgery, 68Ga-P3 is safe and feasible for use, offering a novel tool for the surgical management of prostate cancer.

Preclinical Evaluation of an Al18F-Radiolabeled Bicyclic Peptide Targeting Nectin-4

Precisely assessing nectin-4 expression in tumors is important in identifying patients who may benefit from nectin-4-targeted therapies. In our previous work, we developed a bicyclic peptide-based nectin-4-targeting radiotracer 68Ga-N188 and validated its nectin-4 detection efficacy. However, the relatively short half-life and low positron emission rate of 68Ga limit its further application. In this study, we constructed three novel nectin-4-targeting ligands N230-232 based on a bicyclic peptide structure and labeled with radionuclide 18F, which has a longer half-life and a higher positron emission rate, for PET imaging. Micro-PET/CT imaging-based screening showed that Al18F-N231 had the best imaging contrast with a tumor-to-muscle ratio of 10.97 ± 2.39. Further characterization demonstrated that ligand N231 had a high affinity to nectin-4 with a Kd of 4.29 nM, and Al18F-N231 had a good stability and safety profile in vivo. Biodistribution studies validated the specific binding of Al18F-N231 to nectin-4 in vivo, with tumor uptake in the nectin-4+ SW780 tumor group being 1.45- and 3.75-fold higher than that in the nectin-4- 5637 tumor group and blocking group, respectively. Based on the results of this work, Al18F-N231 has promising capability for noninvasive nectin-4 detection in vivo.

Inspired by novel radiopharmaceuticals: Rush hour of nuclear medicine

Nuclear medicine plays an irreplaceable role in the diagnosis and treatment of tumors. Radiopharmaceuticals are important components of nuclear medicine. Among the radiopharmaceuticals approved by the Food and Drug Administration (FDA), radio-tracers targeting prostate-specific membrane antigen (PSMA) and somatostatin receptor (SSTR) have held essential positions in the diagnosis and treatment of prostate cancers and neuroendocrine neoplasms, respectively. In recent years, FDA-approved serials of immune-therapy and targeted therapy drugs targeting programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1), human epidermal growth factor receptor 2 (HER2), and nectin cell adhesion molecule 4 (Nectin 4). How to screen patients suitable for these treatments and monitor the therapy? Nuclear medicine with specific radiopharmaceuticals can visualize the expression level of those targets in systemic lesions and evaluate the efficacy of treatment. In addition to radiopharmaceuticals, imaging equipment is also a key step for nuclear medicine. Advanced equipment including total-body positron emission tomography/computed tomography (PET/CT) and positron emission tomography/magnetic resonance imaging (PET/MRI) has been developed, which contribute to the diagnosis and treatment of tumors, as well as the development of new radiopharmaceuticals. Here, we conclude most recently advances of radiopharmaceuticals in nuclear medicine, and they substantially increase the "arsenal" of clinicians for tumor therapy.

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Imageological/Structural Study regarding the Improved Pharmacokinetics by 68Ga-Labeled PEGylated PSMA Multimer in Prostate Cancer

PMSA (prostate-specific membrane antigen) is currently the most significant target for diagnosing and treating PCa (prostate cancer). Herein, we reported a series ⁶⁸Ga/¹⁷⁷Lu-labeled multimer PSMA tracer conjugating with PEG chain, including [⁶⁸Ga]Ga-DOTA-(1P-PEG₄), [⁶⁸Ga]Ga-DOTA-(2P-PEG₀), [⁶⁸Ga]Ga-DOTA-(2P-PEG₄), and [⁶⁸Ga]Ga/[¹⁷⁷Lu]Lu-DOTA-(2P-PEG₄)₂, which showed an advantage of a multivalent effect and PEGylation to achieve higher tumor accumulation and faster kidney clearance. To figure out how structural optimizations based on a PSMA multimer and PEGylation influence the probe's tumor-targeting ability, biodistribution, and metabolism, we examined PSMA molecular probes' affinities to PC-3 PIP (PSMA-highly-expressed PC-3 cell line), and conducted pharmacokinetics analysis, biodistribution detection, small animal PET/CT, and SPECT/CT imaging. The results showed that PEG₄ and PSMA dimer optimizations enhanced the probes' tumor-targeting ability in PC-3 PIP tumor-bearing mice models. Compared with the PSMA monomer, the PEGylated PSMA dimer reduced the elimination half-life in the blood and increased uptake in the tumor, and the biodistribution results were consistent with PET/CT imaging results. [⁶⁸Ga]Ga-DOTA-(2P-PEG₄)₂ exhibited higher tumor-to-organ ratios. When labeled by lutetium-177, relatively high accumulation of DOTA-(2P-PEG₄)₂ was still detected in PC-3 PIP tumor-bearing mice models after 48 h, indicating its prolonged tumor retention time. Given the superiority in imaging, simple synthetic processes, and structural stability, DOTA-(2P-PEG₄)₂ is expected to be a promising tumor-targeting diagnostic molecular probe in future clinical practice.