Measuring kinetics and metastatic propensity of CTCs by blood exchange between mice

Current methods for acquiring dissemination kinetics of rare circulating tumor cells (CTCs) that form metastases have several limitations. Here, the authors show an approach for measuring endogenous CTC kinetics by continuously exchanging CTC-containing blood between un-anesthetized, tumor-bearing mice and healthy, tumor-free counterparts. Existing preclinical methods for acquiring dissemination kinetics of rare circulating tumor cells (CTCs) en route to forming metastases have not been capable of providing a direct measure of CTC intravasation rate and subsequent half-life in the circulation. Here, we demonstrate an approach for measuring endogenous CTC kinetics by continuously exchanging CTC-containing blood over several hours between un-anesthetized, tumor-bearing mice and healthy, tumor-free counterparts. By tracking CTC transfer rates, we extrapolated half-life times in the circulation of between 40 and 260 s and intravasation rates between 60 and 107,000 CTCs/hour in mouse models of small-cell lung cancer (SCLC), pancreatic ductal adenocarcinoma (PDAC), and non-small cell lung cancer (NSCLC). Additionally, direct transfer of only 1-2% of daily-shed CTCs using our blood-exchange technique from late-stage, SCLC-bearing mice generated macrometastases in healthy recipient mice. We envision that our technique will help further elucidate the role of CTCs and the rate-limiting steps in metastasis.

Automated summary

This study presents a new method for measuring endogenous CTC kinetics by continuously exchanging blood between tumor-bearing and tumor-free mice. The research found varying half-life times of CTCs in circulation in different cancer models, and demonstrated the ability to generate distant metastases by transferring only 1-2% of shed CTCs. This technique is expected to further elucidate the role of CTCs and the rate-limiting steps in metastasis.