In vivoimaging of orthotopic prostate cancer with far-red gene reporter fluorescence tomography andin vivoandex vivovalidation

Abstract

Abstract. Fluorescence gene reporters have recently become available for excitation at far-red wavelengths, enabling opportunities for small animal in vivo gene reporter fluorescence tomography (GRFT). We employed multiple projections of the far-red fluorescence gene reporters IFP1.4 and iRFP, excited by a point source in transillumination geometry in order to reconstruct the location of orthotopically implanted human prostate cancer (PC3), which stably expresses the reporter. Reconstruction was performed using a linear radiative-transfer-based regularization-free tomographic method. Positron emission tomography (PET) imaging of a radiolabeled antibody-based agent that targeted epithelial cell adhesion molecule overexpressed on PC3 cells was used to confirm in vivo GRFT results. Validation of GRFT results was also conducted from ex vivo fluorescence imaging of resected prostate tumor. In addition, in mice with large primary prostate tumors, a combination of GRFT and PET showed that the radiolabeled antibody did not penetrate the tumor, consistent with known tumor transport limitations of large (∼150 kDa) molecules. These results represent the first tomography of a living animal using far-red gene reporters.

Near-infrared fluorescent proteins engineered from bacterial phytochromes

“…Proteins of the iRFP series enabled visualization of small tumors at early stages, monitoring tumor growth and tracking metastases [13, 31]. In particular, iRFP713 protein performed well as a fluorescent marker in tumors located in deep organs, such as liver and prostate, and intrabone tumors, such as intracranial glioblastoma and intratibial osteosarcoma (Figure 2a) [32].…”

“…Using various imaging modalities (Figure 3) iRFP713 enabled imaging progression of inflammatory breast cancer and its metastases in lymph nodes [33] and detection metastatic targets of melanoma in whole body (Figure 3b) [32]. iRFP713 also allowed to monitor tumor growth and metastases in an orthotopic prostate cancer model (Figure 3f) [31, 34]. Single circulating metastatic cells labelled with iRFP713 were detected in blood vessels of a mouse [35].…”

“…This can be achieved by using either the multiple source-detector pairs, a scanning excitation source or a rotary gantry-based system [31] (Figure 3e). Furthermore, a combination of fluorescence tomography with anatomical imaging modalities, such as a magnetic resonance imaging (MRI) and an X-ray computed tomography (XCT), provides additional information.…”

FLIM-FRET for Cancer Applications

“…Lu et al utilized far-red fluorescence gene reporters to image deep-seated orthotopic primary human prostate cancer in a mouse model. Human prostate cancer cells were genetically constructed to stably express far-red fluorescence gene reporters IFP1.4 and iRFP, and orthotopically implanted in mice [108]. In vivo gene reporter fluorescence tomography (GRFT) and positron emission tomography (PET) imaging was able to reconstruct the location of the prostate cancer, but the image reconstruction in this study was prepared with assumption of a homogeneous optical distribution and it will be useful to improve reconstruction quality by using precise anatomical information.…”

Emerging lymphatic imaging technologies for mouse and man

“…In contrast to the visibly excited fluorescent gene reporters, newer, far-red-shifted fluorescent gene reporters (85,86) can be imaged non-invasively and longitudinally in whole animals (our unpublished observations and ref. 87), suggesting they may extend fluorescent gene reporter imaging beyond intravital imaging and facilitate non-invasive, longitudinal imaging of lymphatic remodeling. To date, these far-red fluorescent gene reporters have not been employed in any transgenic animal models, but could dramatically affect future preclinical study of the lymphatics.…”