METHODS: Cisplatin-resistant cell line (MCF7-CR) was developed from the MCF7 human breast adenocarcinoma cell line by performing a seven-cyclic exposure to cisplatin. Following NDV infection, fluorescence-activated cell sorting (FACS) analysis and immunoblotting were used to measure cell viability and viral protein expression, respectively. Production of virus progeny was then assessed by using the plaque assay technique.

RESULTS: Infection of a mass population of the MCF7-CR with NDV resulted in 50% killing in the first 12 hours post-infection (hpi), comparable to the parental MCF7. From 12 hpi onwards, the remaining MCF7-CR became less susceptible to NDV killing. This reduced susceptibility led to increased viral protein synthesis and virus progeny production. The reduction was also associated with a prolonged cell survival via stabilization of the survivin protein.