Abstract 968: Invadopodia formation and microparticle release are required for cancer cell extravasation in vivo

Abstract

Abstract During the metastatic process, cancer cells must undergo trans-endothelial migration from the vessel lumen into underlying tissue in a process known as extravasation. Little is known about the dynamic mechanical aspects of this process. To address this, we performed real-time, sub-cellular resolution intravital imaging of human cancer cells during arrest, intravascular migration and extravasation using a shell-less avian embryo xenograft model. We find that extravasation occurs at endothelial junctions and that the majority of extravasation events occurred during the 12 hours subsequent to the intravenous injection of cancer cells. In the majority of extravasation events, long cytoplasmic extensions identified as invadopodia were observed prior to extravasation which breached underlying endothelium. We observed the release of microparticles during these invadopodial extension events prior to extravasation, and this resulted in a ∼40% reduction in cell volume post-extravasation. Based on this, we hypothesized that invadopodia are required for extravasation, and that cancer cell extravasation could be abrogated by inhibiting factors required for invadopodia function. We found that treatment with Src kinase inhibitors significantly reduced invadopodia formation in vivo and resulted in a ∼60% decrease in extravasation events when compared to vehicle treated controls. Furthermore, a higher proportion of cells in the Src kinase inhibitor-treated animals remained intravascular compared to vehicle control. In conclusion, we determined that 1) extravasation occurs at junctions between adjacent endothelial cells, 2) cancer cells form invadopodia that breach the endothelial layer prior to successful extravasation and 3) cancer cells undergoing extravasation release cancer microparticles into both the vessel lumen and tissue interstitium with a corresponding decrease in cell volume. Pharmacological inhibition of invadopodia by Src kinase inhibitors (Bosutinib, Dasatinib) reduces cancer cell extravasation, revealing a novel and potentially important mechanism of action against metastatic cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 968. doi:10.1158/1538-7445.AM2011-968