PET/CT Imaging with an 18F-Labeled Galactodendritic Unit in a Galectin-1-Overexpressing Orthotopic Bladder Cancer Model

Non-Invasive Imaging Modalities in Intravesical Murine Models of Bladder Cancer

Bladder cancer (BCa) is the sixth most prevalent cancer in men and seventeenth most prevalent cancer in women worldwide. Current treatment paradigms have limited therapeutic impact, suggesting an urgent need for the investigation of novel therapies. To best emulate the progression of human BCa, a pre-clinical intravesical murine model is required in conjunction with existing non-invasive imaging modalities to detect and evaluate cancer progression. Non-invasive imaging modalities reduce the number of required experimental models while allowing for longitudinal studies of novel therapies to investigate long-term efficacy. In this review, we discuss the individual and multi-modal use of non-invasive imaging modalities; bioluminescence imaging (BLI), micro-ultrasound imaging (MUI), magnetic resonance imaging (MRI), and positron emission tomography (PET) in BCa evaluation. We also provide an update on the potential and the future directions of imaging modalities in relation to intravesical murine models of BCa.

EGFR-Targeted ImmunoPET of UMUC3 Orthotopic Bladder Tumors

PURPOSE

Immuno-positron emission tomography (immunoPET) combines the specificity of an antibody with the sensitivity of PET to image dysregulated pathways in cancer. This study examines the performance of immunoPET using the radioimmunoconjugate [⁸⁹Zr]Zr-DFO-Panitumumab to detect epidermal growth factor receptor (EGFR) expression in an orthotopic model of bladder cancer (BCa).

PROCEDURES

Expression and quantification of EGFR receptors were confirmed in four different BCa cell lines. Binding assays validated [⁸⁹Zr]Zr-DFO-Panitumumab specificity for EGFR-expressing UMUC3 BCa cells. Subcutaneous and orthotopic UMUC3 xenografts were then used for PET imaging and ex vivo biodistribution of the radioimmunoconjugate. Control cohorts included non-tumor mice, ⁸⁹Zr-labeled non-specific IgG, and blocking experiments.

RESULTS

[⁸⁹Zr]Zr-DFO-Panitumumab binds specifically to EGFR-expressing UMUC3 cells with a B_max value of 5.9 × 10⁴ EGFRs/cell in vitro. ImmunoPET/CT images show localization of the antibody in subcutaneous UMUC3 xenografts and murine bladder tumors. In the orthotopic model, the immunoPET signal correlates with the respective tumor volume. Ex vivo biodistribution analysis further confirmed imaging results.

CONCLUSION

The preclinical data presents a proof of concept for utilizing EGFR-targeted immunoPET to image BCa with altered EGFR protein levels.

Galectin expression detected by 68Ga-galectracer PET as a predictive biomarker of radiotherapy resistance

PURPOSE

Hypoxia is a hallmark of solid tumors that is related to radiotherapy resistance. As galectin members, such as galectin-1 and galectin-3, are associated with tumor hypoxia, herein we aimed to investigate whether positron emission tomography (PET) imaging of galectin expression can be employed to effectively pinpoint tumor hypoxia, and to predict radiotherapy resistance.

METHODS

We synthesized a galectin-targeting radiotracer, designated ⁶⁸Ga-galectracer, by radiolabeling a thiodigalactoside derivative. The properties of ⁶⁸Ga-galectracer for PET imaging of tumor hypoxia were characterized in three tumor hypoxia mouse models. Additionally, preliminary PET/CT was performed in two patients with lung cancer to investigate the potential application of ⁶⁸Ga-galectracer for clinical imaging.

RESULTS

High-contrast imaging was achieved in the murine acute hypoxia tumor model, A549 natural hypoxia model, and sorafenib treatment-induced hypoxic 4T1 tumor model by PET using ⁶⁸Ga-galectracer. In fact, ⁶⁸Ga-galectracer exhibited superior hypoxia detection to that of ¹⁸F-misonidazole in the 4T1 tumors. Moreover, tumors with high galectin expression levels, as detected by ⁶⁸Ga-galectracer PET, exhibited significantly lower responses to subsequent radiotherapy compared to those with low galectin expression levels. In patients with lung cancer, PET imaging using ⁶⁸Ga-galectracer provided data that were complementary to that of the glucose metabolic PET radiotracer ¹⁸F-fluorodeoxyglucose.

CONCLUSION

⁶⁸Ga-galectracer is a promising radiotracer for PET-based imaging of tumor hypoxia in vivo. Thus, hypoxia PET with ⁶⁸Ga-galectracer could provide a noninvasive approach to proactively predict radiotherapy efficacy.

TRIAL REGISTRATION

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