Circulating tumor cells (CTCs) are considered as the “seeds” which disseminate from the solid tumors, circulate within the vasculature and colonize the distant organs (“soil”). CTCs level in peripheral blood has been used for diagnosis, staging, prognosis of cancer, as well as treatment evaluation. Currently, the ex vivo CTC isolation methods (e.g. CellSearch system) are limited to several milliliters of blood and do not take into account the temporal distribution of CTCs in the peripheral blood, However, few studies were conducted to investigate whether CTCs were released into the blood vessel erratically and whether the distribution of CTCs in the blood is uniform. A reliable research tool that can provide sufficient quantity of CTCs, as well as the temporal information of each CTC is necessary to study the temporal distribution of CTCs. In vivo flow cytometry (IVFC) has been demonstrated to be a powerful tool for real-time and continuous monitoring of circulating cells. The time points of each CTC events are recorded with IVFC detection. Here, we established an orthotopic mouse model of prostate cancer by using GFP labeled PC3 cell lines and monitored the variation of CTCs in mouse ear arteries during 24-h of a day with IVFC. Our results suggested that the temporal distribution of CTCs was not even in the orthotopic mouse model of prostate cancer and CTC release may be regulated by circadian rhythm. Our work is thus hopeful to provide a guideline on the time of blood sampling and gain insight into the shedding process of CTCs.
Melanoma, developing from melanocytes, is the deadliest type of malignant skin tumors in the world. Due to high light absorption of melanin, rare circulating melanoma cells, as an endogenous marker for metastasis at the early stage, can be quantitatively detected in small superficial vessels of mouse ears by in vivo photoacoustic flow cytometry (PAFC). Before clinical application, the capability of promising PAFC platform should be verified and optimized by mouse vessels, which are similar in size and depth to human vessels. In the current study, compared with optical resolution PAFC (OR-PAFC), we build acoustic resolution PAFC (AR-PAFC) using focused ultrasonic transducer and 1064 nm laser with lower pulse rate, leading to higher detection depth and lower laser power density in mouse models. Besides, based on laser frequency doubling and high absorption coefficient of hemoglobin at 532nm wavelength, the blood vessels can be positioned by lowcost navigation system rather than the expensive system of two coupled lasers or charged coupled device with depth limitation. We confirm that AR-PAFC can be applied to noninvasive label-free counting of circulating melanoma cells in mouse tail veins, and validated by in vitro assays using phantom models, which simulates the scattering and absorption coefficients of living tissue. These results show that AR-PAFC platform has great potential for preoperative diagnosis and postoperative evaluation of melanoma patients.
Prostate cancer has already become the biggest threat among all cancer types for male people and many people died because of its bone metastases. Circulating tumor cells (CTCs) can be used as early metastasis marker so that the detection of CTCs in blood is meaningful for early diagnosis and treatment. However, the relationship between these therapies and metastasis has not been fully clarified yet. Hence, we built PC3 subcutaneous tumor model and developed in vivo flow cytometer (IVFC) platform to record the dynamics of CTC before and after tumor resection. We found out that tumor resection can reduce CTC quantities instantaneously while having a good control of metastasis. CTC re-occurred 7 days after surgery, which might be correlated with early disseminated and deposited tumors. In conclusion, in vivo flow cytometry (IVFC) is capable of detecting CTC dynamics in prostate subcutaneous tumor model and this method could facilitate further research about relationship between other cancer therapies and circulating tumor cells.
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