Abstract
IntroductionThe detection of circulating tumor cells (CTCs) is very important for cancer diagnosis. CTCs can travel from primary tumors through the circulation to form secondary tumor colonies via bloodstream extravasation. The number of CTCs has been used as an indicator of cancer progress. However, the population of CTCs is very heterogeneous. It is very challenging to identify CTC subpopulations such as cancer stem cells (CSCs) with high metastatic potential, which are very important for cancer diagnostic management.ResultsWe report a study of real-time CTC and CSC imaging in the bloodstreams of living animals using multi-photon microscopy and antibody conjugated quantum dots. We have developed a cancer model for noninvasive imaging wherein pancreatic cancer cells expressing fluorescent proteins were subcutaneously injected into the earlobes of mice and then formed solid tumors. When the cancer cells broke away from the solid tumor, CTCs with fluorescent proteins in the bloodstream at different stages of development could be monitored noninvasively in real time. The number of CTCs observed in the blood vessels could be correlated to the tumor size in the first month and reached a maximum value of approximately 100 CTCs/min after 5 weeks of tumor inoculation. To observe CTC subpopulations, conjugated quantum dots were used. It was found that cluster of differentiation (CD)24+ CTCs can move along the blood vessel walls and migrate to peripheral tissues. CD24+ cell accumulation on the solid tumors’ sides was observed, which may provide valuable insight for designing new drugs to target cancer subpopulations with high metastatic potential. We also demonstrated that our system is capable of imaging a minor population of cancer stem cells, CD133+ CTCs, which are found in 0.7% of pancreatic cancer cells and 1%–3% of solid tumors in patients.ConclusionsWith the help of quantum dots, CTCs with higher metastatic potential, such as CD24+ and CD133+ CTCs, have been identified in living animals. Using our approach, it may be possible to investigate detailed metastatic mechanism such as tumor cell extravasation to the blood vessels. In addition, the number of observed CTCs in the blood stream could be correlated with tumor stage in the early stage of cancer.
Highlights
The detection of circulating tumor cells (CTCs) is very important for cancer diagnosis
We report a study of real-time CTC and cancer stem cells (CSCs) imaging in the bloodstreams of living animals using multi-pho‐ ton microscopy and antibody conjugated quantum dots
We have developed a cancer model for noninvasive imag‐ ing wherein pancreatic cancer cells expressing fluorescent proteins were subcutaneously injected into the earlobes of mice and formed solid tumors
Summary
The detection of circulating tumor cells (CTCs) is very important for cancer diagnosis. CTCs can travel from primary tumors through the circulation to form secondary tumor colonies via bloodstream extravasation. It is very challenging to identify CTC subpopulations such as cancer stem cells (CSCs) with high metastatic potential, which are very important for cancer diagnostic management. It is commonly believed that some tumor cells disseminated from primary tumors could invade the blood vessels, circulate in. It was found that the observation of CTC clusters in the blood could increase metastatic potential in both animals and patients [9, 10]. It is very difficult to determine whether the CTCs isolated from peripheral blood are from the primary tumor trying to form metastatic sites or from the established metastatic sites. To use CTCs as a prognostic biomarker, it is very important to study the spatiotemporal behavior of CTCs and identify a specific CTC subpopulation in the bloodstream
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