Abstract 4514: Intravital imaging at single-cell resolution reveals, for the first time, the mechanism of cancer cell dissemination and metastasis
Authors: Borriello Lucia , Coste Anouchka , Wang Yarong , Oktay Maja , Entenberg David , Condeelis John 
Published: August 2019

Abstract
Metastatic dissemination is the major cause of cancer mortality and is responsible for over 1/2 million deaths each year in the U.S. alone. Over the past decades, metastasis has been speculated to be an inefficient process, as the majority of disseminated tumor cells (DTCs) are not believed to complete all the steps of the metastatic cascade. This conclusion has been reached by studies in which TCs are intravenously injected in mice - a process called experimental metastasis (EM) - and then attempt to quantify the number of disseminated cells in the lung over time using low resolution and indirect methods. To date, very little is known about the efficiency of each step in metastatic cascade due to the inability to track metastatic cancer cells in an intact organ over time.
Using a new cutting-edge technology, the Window for High Resolution Imaging of the Lung1, we are able for the first time to (1) track in real-time the fate of each DTC and (2) quantitatively assess the efficiency of each step of the metastatic cascade in the lung, from DTC arrival and retention in the lung vasculature, extravasation, interaction with the host microenvironment, survival, dormancy, to growth into micro-metastases. All steps are studied at single-cell resolution, longitudinally, in the same animal, and using the EM model as well as a more clinically relevant model called Spontaneous Metastasis (SM) in which tumor cells spontaneously disseminate from an orthotopic primary tumor.
A comparative analysis of the two models (EM vs. SM) demonstrated that DTCs in SM have a drastically increased metastatic efficiency compared to DTCs in EM. In particular, we found that DTCs are retained in the lung 10-times more efficiently compared to EM (62% vs. 6%). We further observe that in SM, DTCs extravasate in the lung very rapidly compared to EM (8 hrs vs. 24 hrs) and that the vast majority of DTCs after extravasation died in EM compared to SM where DTCs are dormant and express a stem-like phenotype. These data indicate that dissemination is indeed a very efficient process, but that growth at the secondary site is a rate-limiting step in the SM model.
In conclusion, the ability to observe both spontaneous and experimental metastasis, with single cell resolution, and longitudinally, has provided new insight into the efficiency of each step of the metastatic cascade in the lung. This approach additionally gives the ability to investigate the molecular mechanisms underlying seeding and dormancy of metastatic tumor cells, in the presence of the full tumor microenvironment, as well as to directly evaluate the response of disseminated tumor cells to therapeutic treatment in real time in a live mouse.
(1). Entenberg D, et al., (2017). A permanent window for the murine lung enables high-resolution imaging of cancer metastasis. Nat Methods. 15(1):73-80.
Citation Format: Lucia Borriello, Anouchka Coste, Yarong Wang, Maja Oktay, David Entenberg, John Condeelis. Intravital imaging at single-cell resolution reveals, for the first time, the mechanism of cancer cell dissemination and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4514.