Imaging early steps of sindbis virus infection by total internal reflection fluorescence microscopy.

Sindbis virus (SINV) is an alphavirus that has a broad host range and has been widely used as a vector for recombinant gene transduction, DNA-based vaccine production, and oncolytic cancer therapy. The mechanism of SINV entry into host cells has yet to be fully understood. In this paper, we used single virus tracking under total internal reflection fluorescence microscopy (TIRFM) to investigate SINV attachment to cell surface. Biotinylated viral particles were labeled with quantum dots, which retained viral viability and infectivity. By time-lapse imaging, we showed that the SINV exhibited a heterogeneous dynamics on the surface of the host cells. Analysis of SINV motility demonstrated a two-step attachment reaction. Moreover, dual color TIRFM of GFP-Rab5 and SINV suggested that the virus was targeted to the early endosomes after endocytosis. These findings demonstrate the utility of quantum dot labeling in studying the early steps and behavior of SINV infection.

Susceptibility of colorectal cancer cells to Sindbis virus infection.

Sindbis virus (SIN), a member of the Togaviridae family, infects a broad range of cells and has been shown to be an effective anti-tumor agent. The infection efficiency of the virus, however, varies greatly among target cells. In this report, we compared the ability of SIN to infect colorectal cancer cells and cells of other cancer origin. While tumor cells from breast, leukemia, and prostate cancers were largely resistant to SIN infection, nine of the ten colorectal cancer cell lines tested were sensitive to SIN infection. Moreover, SIN susceptibility correlated with the metastatic potential of the colorectal cancer cells. Two highly aggressive and invasive cell lines, SW620 and COLO-320DM were the most sensitive to SIN infection. Similarly, SIN preferentially targeted metastatic tumor cells in a mouse xenograft model for colon cancer progression. The higher infection rate was not due to increased expression of the 67kD laminin receptor, a specific receptor for SIN infection, although viral attachment and entry were markedly enhanced in SW620 cells. These results suggest that SIN may employ a novel cell attachment/entry mechanism during infection, allowing selective targeting of colorectal cancer cells.