P02.13 Before requiring a cure: towards preventing the outgrowth of brain metastases

Abstract

Background

Brain metastases (BM) are a devastating and frequent complication in patient with metastatic cancer. Survival is severely limited as the current treatment strategies have to conquer several obstacles in symptomatic BM including the heterogenous composition of the blood-brain barrier and the altered microenvironment characteristics. "Prevent_BM" is a collaborative effort of five research groups, both clinical and pre-clinical, to identify a treatment concept targeting the formation of early BM and preventing the outgrowth to macro-metastases. In Prevent_BM, the preclinical studies focus on tumor cell-astrocyte gap junction connections, the PI3K/mTor pathway, improving brain-tropism of T-cells and the role of the pro-metastatic perivascular niche. These targets will be validated in a clinical setting, and state-of-the-art bioinformatics platform allows integration and analysis of the results.

Material and Methods

To monitor the early steps of brain colonization in real time, we employ intravital multiphoton laser-scanning microscopy (MPLSM) through a chronic cranial window in mice. Following intracardiac injection of fluorescent tumor cells, we can study the effect of different treatments on BM growth over the period of weeks.

Results

Intravital imaging allows us to investigate the effects of PI3K/mTor inhibitors on BM growth over time, as a potential target strategy for BM prevention. While studying the role of tumor cell-astrocytes in BM formation, we observed tumor-microtube formation in a subset of tumor cells, analogue to the connections formed by glioblastoma cells. To visualize tumor cell-astrocyte connections, we can measure the transfer of gap-junction permeable dye in vivo. Here, we find that the microtube-forming metastatic cells indeed take up the SR101 dye, with similar dynamics as astrocyte cells. The intravital MPLSM approach uniquely enables studying how the tumor microenvironment and therapeutic agents affect the development of BM, and allows revealing the BM immune-surveillance and the structural organization of the blood-tumor-barrier. Importantly, the remodeling of the brain vasculature during metastatic seeding can monitored during the early steps of colonization and metastatic outgrowth. Hereto, we can correlate in vivo imaging to 3D electron microscopy to reveal the dynamic interactions between tumor cells and the neurovascular unit at high resolution.

Conclusion

Upon completion of Prevent_BM, we expect to have generated a unique database, allowing deciding how to move forward with a first-of-its-kind, randomized clinical trial to prevent the symptomatic occurrence of BM. Preventing future metastasis outgrowth with a well-tolerated, low-dose targeted systemic treatment, would fundamentally change the course of many patients suffering from metastatic cancer.