Developing In Vivo Photoacoustic Flow Cytometry Technique For Detection Of Circulating Melanoma Cells

Cancer is one of the most threatening diseases for human health.Most of the cancer death attributes to metastasis.As a conventional model of metastasis,the “seed and soil” theory suggests that some tumor cells shed from the primary tumor in the early stage.And a small portion of tumor cells enter the circulatory system,then infiltrate into the distant tissue and eventually form metastasis.Cells that shed from the primary tumor and disseminate in the blood or lymphatic system are called circulating tumor cells(CTCs).CTCs are considered as the important marker of tumor metastasis.Thus,the quantitative detection of CTCs is of great significance for early diagnosis and prognosis evaluation of tumors.Most of in vitro CTC detection assays are based on the antigen-antibody recognition and specific physical properties of tumor cells.The accuracy of in vitro detection assays is limited due to the finite volume of blood samples.Based on the photoacoustic effect of biological tissue,we built the in vivo photoacoustic flow cytometry(PAFC).PAFC allows for label-free detection of circulating melanoma cells based on the great light absorption contrast of melanin in the near infrared range.After calibration and verification of PAFC system,we constructed subcutaneous tumor models and monitored circulating melanoma cells at the detection window(the artery of mouse ear)to study the relationship between CTC counts and tumor progression.In addition,we constructed subcutaneous tumor models at the ears of mice and detected circulating melanoma cells in the neighboring and distant vessels of melanoma-bearing mice respectively.We explored the difference in the number of detectable CTCs between neighboring and distant vessels relative to the primary tumor.That aims to demonstrate the impact of detection window on sensitivity of detection.Based on the existing benchtop PAFC,we used a cage system to miniaturize the PAFC system.In addition to the original 1064 nm excitation beam(NIR range),532 nm excitation beam(visible range)was added for vascular navigation.At present,this system has been verified in vitro with great prospects for clinical translation.