Real-time imaging of the epithelial-mesenchymal transition using microRNA-200a sequence-based molecular beacon-conjugated magnetic nanoparticles

Visualization of epithelial-mesenchymal transition in an inflammatory microenvironment-colorectal cancer network

Epithelial-mesenchymal transition (EMT) is a biological process by which epithelial cells acquire mesenchymal characteristics. In malignant tumors, EMT is crucial for acquisition of a mesenchymal phenotype with invasive and metastatic properties, leading to tumor progression. An inflammatory microenvironment is thought to be responsible for the development and progression of colorectal cancer (CRC); however, the precise role of inflammatory microenvironments in EMT-related CRC progression remains unclear. Here, we show the spatiotemporal visualization of CRC cells undergoing EMT using a fluorescence-guided EMT imaging system in which the mesenchymal vimentin promoter drives red fluorescent protein (RFP) expression. An inflammatory microenvironment including TNF-α, IL-1β, and cytokine-secreting inflammatory macrophages induced RFP expression in association with the EMT phenotype in CRC cells. In vivo experiments further demonstrated the distribution of RFP-positive CRC cells in rectal and metastatic tumors. Our data suggest that the EMT imaging system described here is a powerful tool for monitoring EMT in inflammatory microenvironment-CRC networks.

Dendrimer-Functionalized Superparamagnetic Nanobeacons for Real-Time Detection and Depletion of HSP90α mRNA and MR Imaging

Background & Aims: The use of antisense oligonucleotide-based nanosystems for the detection and regulation of tumor-related gene expression is thought to be a promising approach for cancer diagnostics and therapies. Herein, we report that a cubic-shaped iron oxide nanoparticle (IONC) core nanobeacon is capable of delivering an HSP90α mRNA-specific molecular beacon (HSP90-MB) into living cells and enhancing T₂-weighted MR imaging in a tumor model.

Methods: The nanobeacons were built with IONC, generation 4 poly(amidoamine) dendrimer (G4 PAMAM), Pluronic P123 (P123) and HSP90-MB labeled with a quencher (BHQ1) and a fluorophore (Alexa Fluor 488).

Results: After internalization by malignant cells overexpressing HSP90α, the fluorescence of the nanobeacon was recovered, thus distinguishing cancer cells from normal cells. Meanwhile, MB-mRNA hybridization led to enzyme activity that degraded DNA/RNA hybrids and resulted in downregulation of HSP90α at both the mRNA and protein levels. Furthermore, the T₂-weighted MR imaging ability of the nanobeacons was increased after PAMAM and P123 modification, which exhibited good biocompatibility and hemocompatibility.

Conclusions: The nanobeacons show promise for applicability to tumor-related mRNA detection, regulation and multiscale imaging in the fields of cancer diagnostics and therapeutics.

EMT in cancer

Similar to embryonic development, changes in cell phenotypes defined as an epithelial to mesenchymal transition (EMT) have been shown to play a role in the tumorigenic process. Although the first description of EMT in cancer was in cell cultures, evidence for its role in vivo is now widely reported but also actively debated. Moreover, current research has exemplified just how complex this phenomenon is in cancer, leaving many exciting, open questions for researchers to answer in the future. With these points in mind, we asked four scientists for their opinions on the role of EMT in cancer and the challenges faced by scientists working in this fast-moving field.

Dual Functional Roles of Molecular Beacon as a MicroRNA Detector and Inhibitor

MicroRNAs are essential in many cellular processes. The ability to detect microRNAs is important for understanding its function and biogenesis. This study is aimed at using a molecular beacon to detect miR-430 in developing zebrafish embryos as a proof of principle. miR-430 is crucial for the clearance of maternal mRNA during maternal zygotic transition in embryonic development. Despite its known function, the temporal and spatial expression of miR-430 remains unclear. We used various imaging techniques, including laser scanning confocal microscopy, spinning disk, and lightsheet microscopy, to study the localization of miR-430 and any developmental defects possibly caused by the molecular beacon. Our results show that miR-430 is expressed early in development and is localized in distinct cytoplasmic granules where its target mRNA can be detected. We also show that the designed molecular beacon can inhibit the function of miR-430 and cause developmental defect in the brain, notochord, heart, and kidney, depending on the delivery site within the embryo, suggesting that miR-430 plays a diverse role in embryonic morphogenesis. When compared with morpholino, molecular beacon is 2 orders of magnitude more potent in inhibiting miR-430. Thus, our results reveal that in addition to being used as a valuable tool for the detection of microRNAs in vivo, molecular beacons can also be employed to inhibit microRNAs in a specific manner.

In Vivo Visualization and Characterization of Epithelial-Mesenchymal Transition in Breast Tumors

The activation of the epithelial-to-mesenchymal transition (EMT) program is a critical step in cancer progression and metastasis, but visualization of this process at the single-cell level, especially in vivo, remains challenging. We established an in vivo approach to track the fate of tumor cells based on a novel EMT-driven fluorescent color switching breast cancer mouse model and intravital two-photon laser scanning microscopy. Specifically, the MMTV-PyMT, Rosa26-RFP-GFP, and Fsp1-Cre triple transgenic mouse model was used to monitor the conversion of RFP-positive epithelial cells to GFP-positive mesenchymal cells in mammary tumors under the control of the Fsp1 (ATL1) promoter, a gate-keeper of EMT initiation. RFP-positive cells were isolated from the tumors, sorted, and transplanted into mammary fat pads of SCID mice to monitor EMT during breast tumor formation. We found that the conversion from RFP- to GFP-positive and spindle-shaped cells was a gradual process, and that GFP-positive cells preferentially localized close to blood vessels, independent of tumor size. Furthermore, cells undergoing EMT expressed high levels of the HGF receptor, c-Met, and treatment of RFP-positive cells with the c-Met inhibitor, cabozantinib, suppressed the RFP-to-GFP conversion in vitro Moreover, administration of cabozantinib to mice with palpable RFP-positive tumors resulted in a silent EMT phenotype whereby GFP-positive cells exhibited reduced motility, leading to suppressed tumor growth. In conclusion, our imaging technique provides a novel opportunity for visualizing tumor EMT at the single-cell level and may help to reveal the intricacies underlying tumor dynamics and treatment responses. Cancer Res; 76(8); 2094-104. ©2016 AACR.

Molecular mechanisms of microRNAs in regulating epithelial-mesenchymal transitions in human cancers

The epithelial-mesenchymal transition (EMT) provides a strong driving force in the progression of various human cancers and the development of chemoresistance. Recently, numbers of studies have demonstrated that microRNAs (miRNAs), by post-transcriptionally silencing EMT-related molecules, can promote or inhibit the EMT process and play pivotal roles in effectively manipulating the occurrence, development, invasion, and metastasis of cancers. MiRNAs can also control the EMT or be controlled by genetic modification and mutual regulation, especially negative feedback. Therefore, miRNAs can be viewed as either oncogenes or tumor suppressor genes to facilitate or retard the EMT, resulting in far-reaching impact on tumor metastasis and effective diagnosis, treatment, and prognosis.

Monitoring the spatiotemporal activities of miRNAs in small animal models using molecular imaging modalities

MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression by binding mRNA targets via sequence complementary inducing translational repression and/or mRNA degradation. A current challenge in the field of miRNA biology is to understand the functionality of miRNAs under physiopathological conditions. Recent evidence indicates that miRNA expression is more complex than simple regulation at the transcriptional level. MiRNAs undergo complex post-transcriptional regulations such miRNA processing, editing, accumulation and re-cycling within P-bodies. They are dynamically regulated and have a well-orchestrated spatiotemporal localization pattern. Real-time and spatio-temporal analyses of miRNA expression are difficult to evaluate and often underestimated. Therefore, important information connecting miRNA expression and function can be lost. Conventional miRNA profiling methods such as Northern blot, real-time PCR, microarray, in situ hybridization and deep sequencing continue to contribute to our knowledge of miRNA biology. However, these methods can seldom shed light on the spatiotemporal organization and function of miRNAs in real-time. Non-invasive molecular imaging methods have the potential to address these issues and are thus attracting increasing attention. This paper reviews the state-of-the-art of methods used to detect miRNAs and discusses their contribution in the emerging field of miRNA biology and therapy.

Chitosan combined with molecular beacon for mir-155 detection and imaging in lung cancer

Lung cancer is the major cause of cancer-related deaths worldwide, thus developing effective methods for its early diagnosis is urgently needed. In recent years, microRNAs (miRNAs, miR) have been reported to play important roles in carcinogenesis and have become potential biomarkers for cancer diagnosis and treatment. Molecular beacon (MB) technology is a universal technology to detect DNA/RNA expression in living cells. As a natural polymers, chitosan (CS) nanoparticles could be used as a carrier for safe delivery of nucleic acid. In this study, we developed a probe using nanoparticles of miR-155 MB self assembled with CS (CS-miR-155 MB) to image the expression of miR-155 in cancer cells. Hybridization assay showed that the locked nucleic acid (LAN) modified miR-155 MB could target miR-155 effectively and sensitively. The miR-155 MB self-assembly with CS nanoparticles formed stable complexes at the proper weight ratio. The CS nanoparticles showed higher fluorescence intensity and transfection efficiency than the lipid-based formulation transfection agent by confocal microscopy and flow cytometry analysis. The CS-MB complexes were found to be easily synthesized and exhibited strong enzymatic stability, efficient cellular uptake, high target selectivity and biocompatibility. The CS-MB complexes can also be applied in other cancers just by simply changing for a targeted miRNA highly expressed in those cancer cells. Therefore, it is a promising vehicle used for detecting miRNA expression in living cells.