Kinetics of metastatic breast cancer cell trafficking in bone
Authors: Karen M. Bussard, Pushkar A. Phadke, Robyn R. Mercer, John F. Harms, Yijiang Jia, John C. Kappes, Andra R. Frost, Jennifer L. Jewell, Shakira Nelson, Cynthia Moore, Danny R. Welch, Andrea M. Mastro
Journal: Cancer Research (2006)

Proc Amer Assoc Cancer Res, Volume 47, 2006

3980 

Breast cancer has a high propensity for bone colonization. When present in the bone microenvironment, metastatic breast cancer cells induce osteolysis by increasing bone resorbing osteoclast activity and decreasing bone depositing osteoblast activity. Most in-vivo studies have focused on the later stages of bone metastasis, where breast cancer cells characteristically colonize the ends of long bones in humans. While this localization is of significant clinical importance, little is understood about early bone metastastic events including cell arrival, localization, and initial cancer cell colonization, which may be of importance in therapeutic intervention. MDA-MB-435 human breast cancer cells engineered to contain green fluorescent protein were injected into the left ventricle of female athymic mice, thereby minimizing first-pass filtration through pulmonary capillaries and allowing a maximal number of cells to reach the bone. Mice were then euthanized at times from 1 hr to 6 wks, and femurs isolated and analyzed by fluorescent microscopy, immunohistochemistry, real-time polymerase chain reaction, flow cytometry, and histomorphometry. As early as 1 hr post-injection, single tumor cells could be detected throughout the bone, with the majority (∼90%) found in the distal metaphyses as opposed to the diaphysis. Tumor cells remained in a single cell state in bone ends for up to 72 hrs indicating a lack of tumor cell proliferation. Solitary cells in the diaphysis were rarely detected beyond 24 hrs. Numerous foci (2-10 cells) were observed at 1 wk, and by 2 wks, fewer but larger foci (≥50 cells) were seen. By 4 wks, most bones had a single large mass (either originating from a single colony or coalescing foci) which extended into the diaphysis by 4-6 wks. While little change (<20%) was seen in osteoblast or osteoclast number at 2 wks, by 4-6 wks, the number of osteoblasts was drastically reduced (to 8% of control), with osteoclast numbers being modestly reduced (to ∼60% of control). These data confirm previous in-vitro evidence that suggest breast cancer cells induce osteoblast apoptosis and impede osteoblast replacement. This is the first in vivo study to describe the kinetics of breast cancer cells at the earliest time after arrival in the femur (a common site of metastatic breast cancer cell colonization). It also supports in vivo our recent in vitro studies that indicated osteoblasts, in the presence of breast cancer cells, undergo increased apoptosis and are prevented from differentiating. Since skeletal structural integrity is integral to survival and quality of life, comprehensive treatment of bone metastases must restore bone matrix deposition as well as limit osteolysis. Supported by the U.S. Army Medical Research and Materiel Command (DAMD-17-02-1-0541, DAMD-17-03-01-0584, and DAMD-17-02-1-0358), the University of Alabama Breast SPORE (P50-CA89019), and the National Foundation for Cancer Research and the PA Dept. of Health (CA87728).