Investigating cellular remodelling events induced by the oncolytic Seneca Valley Virus

Abstract

Cancer is a worldwide problem affecting millions of people. Typical cancer treatments are often very toxic and have a range of negative side effects. A new field of cancer research that may provide new cancer therapies is using oncolytic viruses, viruses that selectively infect cancer cells and destroy them by cell lysis. One such virus is Seneca Valley Virus (SVV). SVV has undergone multiple phase 2 clinical trials in humans, but details about the effects of SVV on infected cells are lacking. We sought to understand in detail how SVV changes the cell morphology of a permissible human derived small cell lung cancer (SCLC) cell line; H446 wild-type (WT). Similar studies have been done using related Enteroviruses such as Poliovirus and Coxsackievirus B3 (CVB3), while none have been done with SVV. We used cryo-fixation and electron microscopy (EM) to visualize H446 WT cells at different time points post infection over a 14-hour time course. Using high-pressure freezing (HPF) and freeze substitution (FS) allowed us to get a genuine picture of the SVV induced changes occurring in the H446 WT cells over the course of infection. Thick 250 nm sections of HPF FS samples were used in electron tomography (ET) to generate 3D models from a stack of 2D images. This gave us an awareness of how the cell organelles and structures were spatially arranged. We discovered that SVV infection results in the formation of a unique structure, termed electron dense bodies (EDBs). These are comprised of an outer single membrane and a dense inner RNA replication core. To investigate the inner core we used immunogold labelling and 3D modelling from tomograms. Furthermore, we looked at the viral RNA levels and number of infectious particles over 24 hours. This research contributes to the knowledge about this promising oncolytic virus and may provide insights into key steps of SVV’s lifecycle, including how it enters cells, exits cells, and what host cellular organelles it manipulates for its replication cycle. Any new knowledge gained from this research may help further SVV as a new oncolytic virotherapy for cancer patients.