Imaging of Prostate Cancer Using Urokinase-Type Plasminogen Activator Receptor PET

Prognostic Value of Urokinase-Type Plasminogen Activator Receptor PET/CT in Head and Neck Squamous Cell Carcinomas and Comparison with 18F-FDG PET/CT: A Single-Center Prospective Study

The aim of this phase II clinical trial (NCT02965001) was to evaluate the prognostic value of urokinase-type plasminogen activator receptor (uPAR) PET/CT with the novel ligand ⁶⁸Ga-NOTA-AE105 in head and neck cancer and compare it with ¹⁸F-FDG. Methods: Patients with head and neck squamous cell carcinoma referred for curatively intended radiotherapy were eligible and prospectively included in this study. ⁶⁸Ga-uPAR and ¹⁸F-FDG PET/CT were performed before initiation of curatively intended radiotherapy, and the SUV_max of the primary tumor was measured on both PET/CT studies by 2 independent readers. Relapse-free survival (RFS) and overall survival (OS) were calculated, and optimal cutoffs were established for ⁶⁸Ga-uPAR and ¹⁸F-FDG PET independently and compared using log rank and Kaplan-Meier statistics, as well as univariate and multivariate analysis in a Cox proportional-hazards model. Results: In total, 57 patients were included and followed for a median of 33.8 mo (range, 2.30-47.2, mo). The median SUV_max of the primary tumors was 2.98 (range, 1.94-5.24) for ⁶⁸Ga-uPAR and 15.7 (range, 4.24-45.5) for ¹⁸F-FDG. The optimal cutoffs for ⁶⁸Ga-NOTA-AE105 SUV_max in the primary tumor were 2.63 for RFS and 2.66 for OS. A high uptake of ⁶⁸Ga-NOTA-AE105 (SUV_max above cutoff) was significantly associated with poor RFS and OS (log-rank P = 0.012 and P = 0.022). ⁶⁸Ga-NOTA-AE105 uptake in the primary tumor was significantly associated with poor RFS in univariate analysis (hazard ratio [HR], 8.53 [95% CI, 1.12-64.7]; P = 0.038), and borderline-associated with OS (HR, 7.44 [95% CI, 0.98-56.4]; P = 0.052). For ¹⁸F-FDG PET, the optimal cutoffs were 22.7 for RFS and 22.9 for OS. An ¹⁸F-FDG SUV_max above the cutoff was significantly associated with reduced RFS (log-rank P = 0.012) and OS (log-rank P = 0.000). ¹⁸F-FDG uptake was significantly associated with reduced RFS (HR, 3.27 [95% CI, 1.237-8.66]; P = 0.017) and OS (HR, 7.10 [95% CI, 2.60-19.4]; P < 0.001) in univariate analysis. In a multivariate analysis including ⁶⁸Ga-uPAR SUV_max, ¹⁸F-FDG SUV_max, TNM stage, and p16 status, only ⁶⁸Ga-uPAR SUV_max remained significant (HR, 8.51 [95% CI, 1.08-66.9]; P = 0.042) for RFS. For OS, only TNM stage and ¹⁸F-FDG remained significant. Conclusion: The current trial showed promising results for the use of ⁶⁸Ga-uPAR PET SUV_max in the primary tumor to predict RFS in head and neck squamous cell carcinoma patients referred for curatively intended radiotherapy when compared with ¹⁸F-FDG PET, TNM stage, and p16 status. ⁶⁸Ga-uPAR PET could potentially become valuable for identification of patients suited for deescalation of treatment and risk-stratified follow-up schemes.

Role of pH Regulatory Proteins and Dysregulation of pH in Prostate Cancer

Prostate cancer is the fourth most commonly diagnosed cancer, and although it is often a slow-growing malignancy, it is the second leading cause of cancer-associated deaths in men and the first in Europe and North America. In many forms of cancer, when the disease is a solid tumor confined to one organ, it is often readily treated. However, when the cancer becomes an invasive metastatic carcinoma, it is more often fatal. It is therefore of great interest to identify mechanisms that contribute to the invasion of cells to identify possible targets for therapy. During prostate cancer progression, the epithelial cells undergo epithelial-mesenchymal transition that is characterized by morphological changes, a loss of cell-cell adhesion, and invasiveness. Dysregulation of pH has emerged as a hallmark of cancer with a reversed pH gradient and with a constitutively increased intracellular pH that is elevated above the extracellular pH. This phenomenon has been referred to as "a perfect storm" for cancer progression. Acid-extruding ion transporters include the Na⁺/H⁺ exchanger NHE1 (SLC9A1), the Na⁺HCO₃^- cotransporter NBCn1 (SLC4A7), anion exchangers, vacuolar-type adenosine triphosphatases, and the lactate-H⁺ cotransporters of the monocarboxylate family (MCT1 and MCT4 (SLC16A1 and 3)). Additionally, carbonic anhydrases contribute to acid transport. Of these, several have been shown to be upregulated in different human cancers including the NBCn1, MCTs, and NHE1. Here the role and contribution of acid-extruding transporters in prostate cancer growth and metastasis were examined. These proteins make significant contributions to prostate cancer progression.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

A Comprehensive Review of Non-Covalent Radiofluorination Approaches Using Aluminum [18F]fluoride: Will [18F]AlF Replace 68Ga for Metal Chelate Labeling?

Due to its ideal physical properties, fluorine-18 turns out to be a key radionuclide for positron emission tomography (PET) imaging, for both preclinical and clinical applications. However, usual biomolecules radiofluorination procedures require the formation of covalent bonds with fluorinated prosthetic groups. This drawback makes radiofluorination impractical for routine radiolabeling, gallium-68 appearing to be much more convenient for the labeling of chelator-bearing PET probes. In response to this limitation, a recent expansion of the 18F chemical toolbox gave aluminum [18F]fluoride chemistry a real prominence since the late 2000s. This approach is based on the formation of an [18F][AlF]2+ cation, complexed with a 9-membered cyclic chelator such as NOTA, NODA or their analogs. Allowing a one-step radiofluorination in an aqueous medium, this technique combines fluorine-18 and non-covalent radiolabeling with the advantage of being very easy to implement. Since its first reports, [18F]AlF radiolabeling approach has been applied to a wide variety of potential PET imaging vectors, whether of peptidic, proteic, or small molecule structure. Most of these [18F]AlF-labeled tracers showed promising preclinical results and have reached the clinical evaluation stage for some of them. The aim of this report is to provide a comprehensive overview of [18F]AlF labeling applications through a description of the various [18F]AlF-labeled conjugates, from their radiosynthesis to their evaluation as PET imaging agents.

Surface Modification of Liposomes by a Lipopolymer Targeting Prostate Specific Membrane Antigen for Theranostic Delivery in Prostate Cancer

Prostate specific membrane antigen (PSMA) is a marker for diagnosis and targeted delivery of therapeutics to advanced/metastasized prostate cancer. We report a liposome-based system for theranostic delivery to PSMA-expressing (PSMA⁺) LNCaP cells. A lipopolymer (P³) comprising of PSMA ligand (PSMAL), polyethylene glycol (PEG₂₀₀₀), and palmitate was synthesized and post-inserted into the surface of preformed liposomes. These P³-liposomes were loaded with doxorubicin and radiolabeled with ^99mTc radionuclide to study their theranostic characteristics. Differential expression of PSMA on LNCaP and PC3 cells was confirmed by immunoblotting as well as by uptake of PSMAL labeled with ¹⁸F radionuclide. We found that the uptake of ^99mTc-labeled P³-liposomes by LNCaP cells was >3-fold higher than ^99mTc-labeled Plain-liposomes; the amount of doxorubicin delivered to LNCaP cells was also found to be >3-fold higher by P³-liposomes. Cell-based cytotoxicity assay results showed that doxorubicin-loaded P³-liposomes were significantly more toxic to LNCaP cells (p < 0.05), but not to PSMA-negative PC3 cells. Compared to doxorubicin-loaded Plain-liposomes, the IC₅₀ value of doxorubicin-loaded P³-liposomes was reduced by ~5-fold in LNCaP cells. Together, these results suggest that surface functionalization of liposomes with small PSMA-binding motifs, such as PSMAL, can provide a viable platform for specific delivery of theranostics to PSMA⁺ prostate cancer.