Preclinical evaluation of PSMA-targeted ultrasound contrast agents in an orthotopic model of prostate cancer in rabbits.
PSMA-targeted nanobubbles showed improved imaging characteristics in a rabbit model of prostate cancer compared to standard microbubbles, but further research is needed to confirm clinical relevance.
Where it sits
this study against the rest of the mgf (mechano growth factor) corpusSummary and findings
This study evaluated PSMA-targeted lipid-shelled perfluorocarbon nanobubbles (PSMA-NBs) in an orthotopic rabbit model of prostate cancer. The study measured peak intensities and mean transit time (MTT) of PSMA-NBs compared to microbubbles (MBs) and plain nanobubbles (Plain-NBs). Results indicated higher peak intensities and improved retention of PSMA-NBs in tumor areas.
Abstract
The localization of prostate cancer by ultrasound remains limited by the lack of B-mode conspicuity and the confinement of clinically approved microbubbles (MBs) to the vasculature. This precludes differentiating viable tumor, necrotic tissue, and margin-associated disease. We investigated prostate-specific membrane antigen (PSMA)-targeted lipid-shelled perfluorocarbon nanobubbles (PSMA-NBs) in an orthotopic rabbit model using a clinical contrast-enhanced ultrasound (CEUS) system. We implanted PSMA-positive PC3pip-GFP tumors into the prostates of immunosuppressed New Zealand White rabbits and performed transabdominal imaging with PSMA-NBs, MBs, and Plain-NBs using identical protocols. To address tumor heterogeneity and ultrasound boundary ambiguity, regions of interest were defined from baseline B-mode images and segmented into the tumor core, rim, and a peritumoral area. Pixel-wise parametric and decorrelation time (DT) maps were generated and compared with whole-slide histology (H&E) and, in an exploratory and non-specific analysis, with PSMA IHC. Compared to MBs at the doses used, PSMA-NBs exhibited higher peak intensities in the tumor core and rim (1.60-fold and 1.50-fold, respectively) and improved retention (mean transit time [MTT]: 4.20 to 5.40-fold higher) for up to 10 min in the tumor and peritumoral areas. In an exploratory analysis constrained by cohort size, PSMA-NB kinetics, notably MTT, tracked histology-defined tumor viability, and DT mapping showed spatially heterogeneous retention at the tumor periphery. Compared to Plain-NBs, PSMA-NBs also exhibited improved retention (MTT +21% overall) in the rim and peritumoral areas. This study demonstrates the potential of PSMA-NBs to characterize prostate cancer by molecularly targeted CEUS beyond that achieved with MBs at the doses used.
Background
The study addresses the limitations of ultrasound in localizing prostate cancer, particularly the difficulty in differentiating viable tumor from necrotic tissue. Previous research has shown that conventional microbubbles are confined to the vasculature, limiting their effectiveness. This study evaluates a novel approach using PSMA-targeted nanobubbles to improve imaging of prostate cancer.
Methods
The study utilized an orthotopic rabbit model with implanted PSMA-positive PC3pip-GFP tumors. New Zealand White rabbits were used, and imaging was performed using a clinical contrast-enhanced ultrasound system. The primary outcome measures included peak intensity and mean transit time (MTT) of PSMA-NBs compared to MBs and Plain-NBs.
Results
PSMA-NBs exhibited a peak intensity that was 1.60-fold higher in the tumor core and 1.50-fold higher in the tumor rim compared to MBs. The mean transit time (MTT) for PSMA-NBs was reported to be 4.20 to 5.40-fold higher in the tumor and peritumoral areas compared to MBs. Additionally, PSMA-NBs showed improved retention of +21% overall in the rim and peritumoral areas compared to Plain-NBs.
Interpretation
The findings suggest that PSMA-NBs may enhance the characterization of prostate cancer compared to traditional MBs. However, while the statistical significance of the findings is noted, the clinical relevance remains uncertain due to the small sample size and exploratory nature of the analysis. The study's limitations, including the lack of long-term follow-up and reliance on a single animal model, may affect the generalizability of the results.
Key findings
- PSMA-NBs exhibited 1.60-fold higher peak intensity in the tumor core compared to MBs.
- PSMA-NBs exhibited 1.50-fold higher peak intensity in the tumor rim compared to MBs.
- Mean transit time (MTT) for PSMA-NBs was 4.20 to 5.40-fold higher in tumor and peritumoral areas compared to MBs.
- PSMA-NBs showed +21% overall improved retention in the rim and peritumoral areas compared to Plain-NBs.
Limitations
- small cohort size limits generalizability
- exploratory analysis without robust statistical validation
- no long-term follow-up reported
- animal model may not fully represent human disease