Tumor cell extravasation is a key step during cancer metastasis, yet the precise mechanisms that regulate this dynamic process are unclear. We utilized a high-resolution time-lapse intravital imaging approach to visualize the dynamics of cancer cell extravasation in vivo. During intravascular migration, cancer cells form protrusive structures identified as invadopodia by their enrichment of MT1-MMP, cortactin, Tks4, and importantly Tks5, which localizes exclusively to invadopodia. Cancer cells extend invadopodia through the endothelium into the extravascular stroma prior to their extravasation at endothelial junctions. Genetic or pharmacological inhibition of invadopodia initiation (cortactin), maturation (Tks5), or function (Tks4) resulted in an abrogation of cancer cell extravasation and metastatic colony formation in an experimental mouse lung metastasis model. This provides direct evidence of a functional role for invadopodia during cancer cell extravasation and distant metastasis and reveals an opportunity for therapeutic intervention in this clinically important process.

Nanomaterials with elongated architectures have been shown to possess differential tumor homing properties compared to their spherical counterparts. Here, we investigate whether this phenomenon is mirrored by plant viral nanoparticles that are filamentous (Potato virus X) or spherical (Cowpea mosaic virus). Our studies demonstrate that Potato virus X (PVX) and Cowpea mosaic virus (CPMV) show distinct biodistribution profiles and differ in their tumor homing and penetration efficiency. Analogous to what is seen with inorganic nanomaterials, PVX shows enhanced tumor homing and tissue penetration. Human tumor xenografts exhibit higher uptake of PEGylated filamentous PVX compared to CPMV, particularly in the core of the tumor. This is supported by immunohistochemical analysis of the tumor sections, which indicates greater penetration and accumulation of PVX within the tumor tissues. The enhanced tumor homing and retention properties of PVX along with its higher payload carrying capacity makes it a potentially superior platform for applications in cancer drug delivery and imaging applications.

Aims Vimentin, a type III intermediate filament, is upregulated during epithelial–mesenchymal transition and tumor progression. Vimentin is surface-expressed on cells involved in inflammation; the function remains unknown. We investigated the expression of surface vimentin on cancer cells and evaluated targeting nanoparticles to tumors exploiting vimentin. Materials & methods Cowpea mosaic virus nanoparticles that interact with surface vimentin were used as probes. Tumor homing was tested using the chick chorioallantoic membrane model with human tumor xenografts. Results & discussion Surface vimentin levels varied during cell cycle and among the cell lines tested. Surface vimentin expression correlated with cowpea mosaic virus uptake, underscoring the utility of cowpea mosaic virus to detect invasive cancer cells. Targeting to tumor xenografts was observed; homing was based on the enhanced permeability and retention effect. Our data provide novel insights into the role of surface vimentin in cancer and targeting nanoparticles in vivo.

Viral nanoparticles are a novel class of biomolecular agents that take advantage of the natural circulatory and targeting properties of viruses to allow the development of therapeutics, vaccines and imaging tools. We have developed a multivalent nanoparticle platform based on the cowpea mosaic virus (CPMV) that facilitates particle labeling at high density with fluorescent dyes and other functional groups. Compared with other technologies, CPMV-based viral nanoparticles are particularly suited for long-term intravital vascular imaging because of their biocompatibility and retention in the endothelium with minimal side effects. The stable, long-term labeling of the endothelium allows the identification of vasculature undergoing active remodeling in real time. In this study, we describe the synthesis, purification and fluorescent labeling of cpMV nanoparticles, along with their use for imaging of vascular structure and for intravital vascular mapping in developmental and tumor angiogenesis models. Dye-labeled viral nanoparticles can be synthesized and purified in a single day, and imaging studies can be conducted over hours, days or weeks, depending on the application.

Multivalent nanoparticles have several key advantages in terms of solubility, binding avidity, and uptake, making them particularly well suited to molecular imaging applications. Herein is reported the stepwise synthesis and characterization of NIR viral nanoparticles targeted to gastrin-releasing peptide receptors that are over-expressed in human prostate cancers. The pan-bombesin analogue, [β-Ala11, Phe13, Nle14]bombesin-(7–14), is conjugated to cowpea mosaic virus particles functionalized with an NIR dye (Alexa Fluor 647) and polyethylene glycol (PEG) using the copper(I)-catalyzed azide-alkyne cycloaddition reaction. Targeting and uptake in human PC-3 prostate cells is demonstrated in vitro. Tumor homing is observed using human prostate tumor xenografts on the chicken chorioallantoic membrane model using intravital imaging. Further development of this viral nanoparticle platform may open the door to potential clinical noninvasive molecular imaging strategies.