Bioluminescence imaging of invasive intracranial xenografts: implications for translational research and targeted therapeutics of brain tumors

Non-invasive Bioluminescence Monitoring of Hepatocellular Carcinoma Therapy in an HCR Mouse Model

Animal models play crucial roles in the development of anticancer therapeutics. The ability to quickly assess the localized primary hepatocellular carcinoma (HCC) status in a non-invasive manner would significantly improve the effectiveness of anti-HCC therapeutic studies. However, to date, animal models with this advantage are extremely scarce. In this study, we developed a novel animal model for the fast assessment of drug efficacy against primary HCC in vivo. HCC was induced in immunocompetent hepatocarcinogenesis reporter (HCR) mice by diethylnitrosamine (DEN) injection and confirmed by histopathological staining. Using the bioluminescence imaging (BLI) technique, HCC progression was longitudinally visualized and monitored in a non-invasive way. Tests of two clinical drugs showed that both sorafenib and oxaliplatin significantly inhibited the BLI signal in mouse liver in a dose-dependent manner. The in vivo intensity of BLI signals was highly consistent with the final tumor burden status in mouse liver after drug treatment. The inhibitory effect of anti-HCC drugs was accurately evaluated through in vivo BLI intensity detection. Our study successfully established a bioluminescence mouse model for non-invasive real-time monitoring of HCC therapy, and this HCR mouse model would be a useful tool for potential anti-HCC drug screening and new therapeutic strategy development.

Integrating in vitro experiments with in silico approaches for Glioblastoma invasion: the role of cell-to-cell adhesion heterogeneity

Glioblastoma cells adopt migration strategies to invade into the brain parenchyma ranging from individual to collective mechanisms, whose role and dynamics are not yet fully understood. In this work, we explore Glioblastoma heterogeneity and recapitulate its invasive patterns both in vitro, by utilizing primary cells along with the U87MG cell line, and in silico, by adopting discrete, individual cell-based mathematics. Glioblastoma cells are cultured three-dimensionally in an ECM-like substrate. The primary Glioblastoma spheroids adopt a novel cohesive pattern, mimicking perivascular invasion in the brain, while the U87MG adopt a typical, starburst invasive pattern under the same experimental setup. Mathematically, we focus on the role of the intrinsic heterogeneity with respect to cell-to-cell adhesion. Our proposed mathematical approach mimics the invasive morphologies observed in vitro and predicts the dynamics of tumour expansion. The role of the proliferation and migration is also explored showing that their effect on tumour morphology is different per cell type. The proposed model suggests that allowing cell-to-cell adhesive heterogeneity within the tumour population is sufficient for variable invasive morphologies to emerge which remain originally undetectable by conventional imaging, indicating that exploration in pathological samples is needed to improve our understanding and reveal potential patient-specific therapeutic targets.

Targeting Orthotopic Glioma in Mice with Genetically Engineered Salmonella typhimurium

Objective

With the growing interests of bacteria as a targeting vector for cancer treatment, diverse genetically engineered Salmonella has been reported to be capable of targeting primary or metastatic tumor regions after intravenous injection into mouse tumor models. The purpose of this study was to investigate the capability of the genetically engineered Salmonella typhimurium (S. typhimurium) to access the glioma xenograft, which was monitored in mouse brain tumor models using optical bioluminescence imaging technique.

Methods

U87 malignant glioma cells (U87-MG) stably transfected with firefly luciferase (Fluc) were implanted into BALB/cAnN nude mice by stereotactic injection into the striatum. After tumor formation, attenuated S. typhimurium expressing bacterial luciferase (Lux) was injected into the tail vein. Bioluminescence signals from transfected cells or bacteria were monitored using a cooled charge-coupled device camera to identify the tumor location or to trace the bacterial migration. Immunofluorescence staining was also performed in frozen sections of mouse glioma xenograft.

Results

The injected S. typhimurium exclusively localized in the glioma xenograft region of U87-MG-bearing mouse. Immunofluorescence staining also demonstrated the accumulation of S. typhimurium in the brain tumors.

Conclusion

The present study demonstrated that S. typhimurium can target glioma xenograft, and may provide a potentially therapeutic probe for glioma.

Multimodal imaging enables early detection and characterization of changes in tumor permeability of brain metastases

Our goal was to develop strategies to quantify the accumulation of model therapeutics in small brain metastases using multimodal imaging, in order to enhance the potential for successful treatment. Human melanoma cells were injected into the left cardiac ventricle of immunodeficient mice. Bioluminescent, MR and PET imaging were applied to evaluate the limits of detection and potential for contrast agent extravasation in small brain metastases. A pharmacokinetic model was applied to estimate vascular permeability. Bioluminescent imaging after injecting d-luciferin (molecular weight (MW) 320 D) suggested that tumor cell extravasation had already occurred at week 1, which was confirmed by histology. 7T T1w MRI at week 4 was able to detect non-leaky 100 μm sized lesions and leaky tumors with diameters down to 200 μm after contrast injection at week 5. PET imaging showed that (18)F-FLT (MW 244 Da) accumulated in the brain at week 4. Gadolinium-based MRI tracers (MW 559 Da and 2.066 kDa) extravasated after 5 weeks (tumor diameter 600 μm), and the lower MW agent cleared more rapidly from the tumor (mean apparent permeabilities 2.27 × 10(-5)cm/s versus 1.12 × 10(-5)cm/s). PET imaging further demonstrated tumor permeability to (64)Cu-BSA (MW 65.55 kDa) at week 6 (tumor diameter 700 μm). In conclusion, high field T1w MRI without contrast may improve the detection limit of small brain metastases, allowing for earlier diagnosis of patients, although the smallest lesions detected with T1w MRI were permeable only to d-luciferin and the amphipathic small molecule (18)F-FLT. Different-sized MR and PET contrast agents demonstrated the gradual increase in leakiness of the blood tumor barrier during metastatic progression, which could guide clinicians in choosing tailored treatment strategies.