Probe-Based Confocal Laser Endomicroscopy for Imaging TRAIL-Expressing Mesenchymal Stem Cells to Monitor Colon Xenograft Tumors In Vivo

Noninvasive in vivo cell tracking using molecular imaging: A useful tool for developing mesenchymal stem cell-based cancer treatment

Mounting evidence has emphasized the potential of cell therapies in treating various diseases by restoring damaged tissues or replacing defective cells in the body. Cell therapies have become a strong therapeutic modality by applying noninvasive in vivo molecular imaging for examining complex cellular processes, understanding pathophysiological mechanisms of diseases, and evaluating the kinetics/dynamics of cell therapies. In particular, mesenchymal stem cells (MSCs) have shown promise in recent years as drug carriers for cancer treatment. They can also be labeled with different probes and tracked in vivo to assess the in vivo effect of administered cells, and to optimize therapy. The exact role of MSCs in oncologic diseases is not clear as MSCs have been shown to be involved in tumor progression and inhibition, and the exact interactions between MSCs and specific cancer microenvironments are not clear. In this review, a multitude of labeling approaches, imaging modalities, and the merits/demerits of each strategy are outlined. In addition, specific examples of the use of MSCs and in vivo imaging in cancer therapy are provided. Finally, present limitations and future outlooks in terms of the translation of different imaging approaches in clinics are discussed.

Indium-111-labeled CD166-targeted peptide as a potential nuclear imaging agent for detecting colorectal cancer stem-like cells in a xenograft mouse model

BACKGROUND

Cancer stem cells (CSCs) are involved in drug resistance, metastasis, and relapse of cancers, which can significantly affect tumor therapy. Hence, to develop specifically therapeutic target probe at CSCs for improvement of survival and quality of life of cancer patients is urgently needed. The CD166 protein has been suggested to be involved in colorectal cancer (CRC) tumorigenesis and to be considered a marker for colorectal CSCs (CRCSCs) detection. In this study, therefore, we attend to apply a nuclear imaging agent probe, Glycine₁₈-Cystine-linked CD166-targeted peptides (CD166tp-G₁₈C), to detect the changes of CD166 level in a CRC xenograft mouse model.

RESULTS

We isolated the CD166-positive cells from the HCT15 CRC cell line (CD166⁺HCT15) and evaluated their morphology and ability of clone formation, migration, protein expression, and drug resistance. The CD166-positive HCT15 cells display the CSCs characteristics. We discovered and designed a CD166-targeted peptide (CD166tp-G₁₈C) as a targeted probe of CRC stem-like cell for cell binding assay. The CD166tp-G₁₈C confirmed the CD166 protein targeting ability in CD166⁺HCT15 cells. The diethylenetriaminopentaacetic acid (DTPA)-conjugated CD166tp-G₁₈C further was labeled with indium-111 (¹¹¹In-DTPA-CD166tp-G₁₈C) as nuclear imaging agent for imaging and bio-distribution analysis in vivo. Finally, we observed that the ¹¹¹In-DTPA-CD166tp-G₁₈C was significantly enhanced in tumor tissues of CD166⁺HCT15 xenograft mice as compared to the non-CD166tp-G₁₈C control.

CONCLUSIONS

Our results indicated that the indium-111-labeled CD166tp-G₁₈C may be served as a powerful tool for colorectal CSCs nuclear imaging in the CRC patients.

Functional endoscopy techniques for tracking stem cell fate

Tracking and monitoring implanted stem cells are essential to maximize benefits and to minimize the side effects of stem cell therapy for personalized or "precision" medicine. Previously, we proposed a comprehensive biological Global Positioning System (bGPS) to track and monitor stem cells in vivo. Magnetic resonance imaging (MRI), positron emission tomography (PET), bioluminescent imaging, fluorescence imaging, and single-photon emission computerized tomography (SPECT) have been utilized to track labeled or genetically-modified cells in vivo in rats and humans. A large amount of research has been dedicated to the design of reporter genes and molecular probes for imaging and the visualization of the biodistribution of the implanted cells in high resolution. On the other hand, optical-based functional imaging, such as photoacoustic imaging (PAI), optical coherence tomography (OCT), and multiphoton microscopy (MPM), has been implemented into small endoscopes to image cells inside the body. The optical fiber allows miniaturization of the imaging probe while maintaining high resolution due to light-based imaging. Upon summarizing the recent progress in the design and application of functional endoscopy techniques for stem cell monitoring, we offer perspectives for the future development of endoscopic molecular imaging tools for in vivo tracking of spatiotemporal changes in subclonal evolution at the single cell level.

Nonimmune cells equipped with T-cell-receptor-like signaling for cancer cell ablation

The ability to engineer custom cell-contact-sensing output devices into human non-immune cells would be useful for extending the applicability of cell-based cancer therapies and avoiding risks associated with engineered immune cells. Here, we have developed a new class of synthetic T-cell receptor-like signal-transduction device that functions efficiently in human non-immune cells and triggers release of output molecules specifically upon sensing contact with a target cell. This device employs an interleukin signaling cascade, whose OFF/ON switching is controlled by biophysical segregation of a transmembrane signal-inhibitory protein from the sensor cell/target cell interface. We further showed that designer non-immune cells equipped with this device driving expression of a membrane-penetrator/prodrug-activating enzyme construct could specifically kill target cells in the presence of the prodrug, indicating its potential usefulness for target-cell-specific, cell-based enzyme-prodrug cancer therapy. Our study also contributes to advancement of synthetic biology by extending available design principles to transmit extracellular information to cells.