Oncolytic newcastle disease virus triggers cell death of lung cancer spheroids and is enhanced by pharmacological inhibition of autophagy.

Lung cancer stem cells (CSCs) have recently been isolated from lung cancer patient samples and have been reported to be responsible for tumor initiation, treatment resistance and tumor recurrence. We have previously shown that oncolytic Newcastle disease virus (NDV), strain FMW (NDV/FMW) induces apoptosis in drug-resistant lung cancer cells. However, how NDV exerts its oncolytic effect on lung CSCs remains to be investigated. Here we show that NDV/FMW replicates in, and lyses CSC-enriched lung cancer spheroids and inhibits the 3D growth potential of lung cancer spheroid and agar colonies. We demonstrate that NDV/FMW triggers caspase-dependent apoptosis in lung cancer spheroids as shown by increased caspase-3 processing and Poly (ADP-ribose) polymerase (PARP) cleavage. Notably, NDV/FMW infection results in the degradation of microtubule-associated protein 1 light chain 3 (LC3) II and P62, two hallmarks of autophagy maturation, indicating that NDV/FMW promotes autophagy flux in lung cancer cell spheroids. This was further confirmed by the appearance of an increased number of double-membrane vesicles as detected by transmission electron microscopy. We also show that NDV/FMW promotes autophagy degradation in lung cancer spheroids via inhibition of the AKT/mTOR pathway. In addition, treatment of spheroids with the autophagy inhibitor, chloroquine increases NDV/FMW-induced cytotoxicity. Collectively, our data show that oncolytic NDV/FMW may be a potential strategy in targeting lung CSCs.