The Utilization of Microfluidic and Optical Sensing Technologies for the Detection of Clinical Circulating Tumor Cells (CTCs)---The Lactic Acid Metabolism-Based Method for Low-Cost CTCs Detections

Cancer metastasis is a leading cause of cancer-derived death. During cancer progression, circulating tumor cells (CTCs), the rare cell species present in blood, have been found in the peripheral blood not only during metastasis but also at the early stage of cancer development. CTCs are considered to mainly contribute to cancer metastasis or relapse. Thus, the detection of CTCs is regarded as an essential clinical tool to detect early metastatic disease. In addition, CTC detection is also a promising tool in the management of cancer care because it can (1) evaluate tumor progression in real-time, (2) monitor disease recurrence, (3) estimate long-term prognosis, (4) monitor disease recurrence, and (5) assess the response of anti-cancer therapy. Nevertheless, most of the current methods for CTC detection have their shortcomings mainly related to the detection biases due to their neglect of the heterogeneity and complexity of surface antigens on CTCs, and the high cost. These can hinder the widespread applications of CTC detection for the diagnosis of early metastatic disease, or for the management of cancer care. In order to detect the all possible CTCs in blood without biases relevant to the heterogeneity of CTCs, and to perform CTC detection in an affordable cost for the cancer patients, the proposed project aims to develop an indirect approch to detect CTCs. The detection is primarily based on the metabolic characteristics of CTCs to produce lactic acid in vitro whereas the leukocytes do not adopt the metabolic route. This phenomenon has been found in our pilot study. We hypothesize that the quantitative detection of CTCs can be simply achieved through the measurement of lactic acid production of CTCs without the need for costly immunological approaches for CTC isolation and identification. Due to the rarity of CTCs in a blood sample, however, the amount of lactic acid produced by the CTCs is low. Therefore, it is technically demanding to detect through the conventional lactate assays. To tackle the technical hurdle, a high-density blood cell suspension with lactate reagent added is uniformly segmented to multiple micro-droplets. Due to their tiny volume, the resultant lactic acid concentration in the micro-droplets is technically feasible for detection. Borrowing from the advantageous features of microfluidic technology, a microfluidic chip capable of continuously generating uniform micro-droplets in a microchannel will be developed in the first year project. In the design, a tunable pulsed airflow is used to segment a continuous blood cell suspension flow to form micro-droplets in a microchannel. After an appropriate incubation in the microchannel, the CTCs in the micro-droplets can produce an adequate amount of lactic acid for the subsequent on-chip biosensing. In the first year project, moreover, an optical fiber-based sensing mechanism will be developed and integrated in the proposed microfluidic chip for on-line lactate detection, based on our previous experiences. In the hardware development process, the operation conditions including the pressure and frequency of pulsed airflow injected, the size of micro-droplets for the optical-based lactic acid detection, and the cell density and incubation time of cell-containing micro-droplets will be optimized for the CTC detections. In the second year project, furthermore, the quantitative links between the lactic acid production of CTCs and the corresponding CTC number in the blood samples of metastatic oral cancer patients will be established so as to evaluate the clinical utility of the presented method. Overall, we ultimately hope that the proposed method can provide a useful clinical tool for CTC detection in the future clinical cancer care.

Project ID:PB10301-0506
External Project ID:NSC102-2221-E182-019-MY2