Comparison of in vitro and in vivo approaches to studying brain colonization by breast cancer cells

Abstract

Brain metastases occur in 20 to 40% of patients with metastatic breast cancer. The process is complex and depends on successful cancer cell evasion from the primary tumor, distribution and survival within the blood stream and cerebral microvasculature, penetration of the blood brain barrier and proliferation within the brain microenvironment. The initial steps of brain colonization are difficult to study in vivo. Therefore, in vitro assays have been developed to mimic this process. Most commonly, in vitro studies of brain colonization focus on tumor cell adhesion to brain endothelial cells and transendothelial migration. We previously investigated breast cancer brain colonization from the blood stream in vivo and defined the time and process of brain entry for five different cancer cell lines in a mouse model. We now investigated if in vitro approaches can reliably emulate the initial steps that determine successful brain colonization in vivo. To this end, we optimized an in vitro model of the vascular blood brain barrier and compared the brain invasion properties of the in vivo characterized cell models with their ability to interact with and penetrate the blood brain barrier model in vitro. Our results show that the in vitro findings correlate only poorly with the vivo results. The limitations of the in vitro approaches are discussed in light of the in vivo processes. We conclude that investigation of mechanisms supporting the earliest steps of breast cancer brain metastasis from the blood stream will depend on in vivo analyses.

Adapting coculture in vitro models of the blood–brain barrier for use in cancer research: maintaining an appropriate endothelial monolayer for the assessment of transendothelial migration

“…However, as described previously, 12 large pores may allow ECs to migrate and grow on the lower face of the inserts. Hence, the presence of a multilayered endothelium means that the final cellular structure is no longer representative of the monolayer situation in vivo.…”

“…24,25 Unfortunately, when this original model was transposed to 3-μm-pore inserts, the ECs crossed the porous membrane to form a second layer on the lower face. 12 In vivo, circulating prometastatic cancer cells pass through a single layer of ECs when they transmigrate through brain microvessels. Hence, the migration of ECs through 3-μm-pore inserts prevents the model from being used to investigate this process in vitro.…”

The prognostic significance of serum and cerebrospinal fluid MMP-9, CCL2 and sVCAM-1 in leukemia CNS metastasis

“…There may be different mechanisms involved in CNS metastasis from non-CNS metastatic sites. Previous studies have demonstrated that metastatic extravasation into the brain takes significantly longer than it does in other organs [44]. In solid tumors, the adhesion of circulating tumor cells (CTCs) to the vascular endothelium becomes a crucial starting point of metastasis that precedes the invasion and extravasation of CTCs, and the formation of micrometastasis foci.…”

Development of a Preclinical Therapeutic Model of Human Brain Metastasis with Chemoradiotherapy

“…The survival of arrested cancer cells within brain capillaries may be a rate-limiting step in metastatic progression, since cancer cell penetration of the vessel wall in the brain is much slower than in progression and impacts the success of tumor cells to survive and grow within the brain [35–37]. …”