TMOD-12. AN ONCOLYTIC MEASLES VIRUS SENSITIVE GROUP 3 MEDULLOBLASTOMA MODEL IN IMMUNE-COMPETENT MICE

Abstract

Modified measles virus (MV) has demonstrated oncolytic efficacy in xenograft models of multiple tumor types using human cells in immune-deficient mice. However, MV does not grow in murine cells, thus, no murine tumor cell line that is oncogenic, grows in immune-competent mice, and is infectable by MV exists. The lack of such a model prevents an examination of the effect of anti-MV immunity and other possible effects of the immune system on MV oncotherapy. We have developed a murine Group 3 medulloblastoma cell line that allows replication of, and is killed by, MV in-vivo. Cerebellar stem cells isolated from P6 human CD46-transgenic immune-competent mice were transduced to express Sendai virus C-protein, c-Myc-Td tomato and GFI1B-GFP proteins. The cell line stably expresses higher levels of C-myc and GFI1B proteins but identical levels of N-myc and p53 when compared to unmodified cerebellar stem cells. Measles virus infects and replicates in the cell line, and cells are killed in a dose and time dependent manner with 55%, 85% and 92% cell death at MOI of 0.1, 1 and 10 respectively after 96h of MV infection. The cells express stem cell makers and NPR3, an established marker for the group 3 subtype of medulloblastoma. This cell line is highly tumorigenic when orthotopically implanted into the brain of syngeneic immune-competent mice. A single intratumoral injection of MV results in significant prolongation of median survival compared to mice injected with heat-killed virus (P=0.0027). Sixty percent of MV-treated mice did not die during the period of study and showed no evidence of tumor at autopsy. Autopsy of brains from inactivated virus treated animals revealed tumors resembling group 3 medulloblastoma in all mice. This is the first cell line and tumor model of any type available for testing the effect of an intact immune system on MV therapy.