Urokinase exerts antimetastatic effects by dissociating clusters of circulating tumor cells.

Jin Woo Choi,Kwon-Ha Yoon,Yun Jung Yang,Seok Hyun Yun,Jun Ki Kim,Pilhan Kim

doi:10.1158/0008-5472.can-15-0684

Abstract

Clusters of circulating tumor cells (CTC) exhibit more robust metastatic properties than single CTC. Thus, understanding the distinct behaviors of CTC clusters and how CTC clustering is regulated may offer new insights into how to limit metastasis. In this study, we utilized an in vivo confocal system to observe the clustering behavior of CTC in real time, finding that the number of clusters increased proportionally with the growth of the primary tumor. Our experiments also indicated that the flow rate of the CTC clusters in blood vessels was relatively slower than single CTC due to increased vessel wall adhesion. Depending on disease stage, 5% to 10% of total CTC in circulation were in clusters, with this proportion increasing to >24% within lung metastases examined. Notably, in the 4T1 mouse model of breast cancer metastasis, we found that injecting host animals with urokinase-type plasminogen activator, a clinical thrombolytic agent, was effective at preventing the assembly of CTC clusters and prolonging overall host survival by approximately 20% relative to control animals. Our results suggest a tractable approach to limit metastasis by suppressing the formation or stability of CTC clusters circulating in the blood of cancer patients.

Highlights

In primary tumors, the capacity of the majority of cells means that they cannot metastasize into other organs
By analyzing the characteristics of circulating tumor cells (CTC) clusters, we confirmed a hypothesis about the crucial involvement of CTC clusters in metastasis; we investigated the inhibitory effect of urokinase on fibrin in the CTC clusters, thereby uncovering potential pharmacologic routes for the suppression of CTC clustering
To visualize CTCs in blood vessels and evaluate the meaning of the number of CTCs in peritumoral regions, GFP-expressing B16 and B16F10 cells were injected into both flanks of each of the test mice; the latter line is a more metastatic subline derived from B16

Summary

Introduction

The capacity of the majority of cells means that they cannot metastasize into other organs. A limited number of primary tumor cells become the circulating tumor cells (CTC) that subsequently invade a patient's blood vessels, leading to the ultimate dissemination of such cells into the secondary organs. An increase of the number of CTCs generally means a greater likelihood of a poor survival outcome. For this reason, CTC detection has emerged as a useful practice to predict the emergence of cancer metastases and describe the progression of. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). The presence of CTC clusters as well as single CTCs in the bloodstream has been frequently reported, while it has been confirmed that CTCs form clusters in circulatory areas [4], and around primary tumors [5]

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Results

Conclusion