A novel GM-CSF-encoding oncolytic adenovirus induces profound autophagy and promotes viral replication to enhance anti-tumor efficacy.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) acts as a double-edged sword in cancer by enhancing both anti- and pro-tumorigenic immune cells. In this study, two oncolytic adenoviruses were engineered to modulate GM-CSF expression using different strategies: one with the CMV promoter (oAd-CMV-GM-CSF) and the other using the endogenous viral E3 promoter (oAd-GM-CSF). The impacts of these modifications on transgene expression, cytotoxicity, viral replication, and apoptosis were assessed both in vitro and in vivo. The results demonstrated that oAd-CMV-GM-CSF produced significantly lower GM-CSF levels than oAd-GM-CSF, interestingly oAd-CMV-GM-CSF exhibited increased cytotoxicity and apoptosis compared to oAd-GM-CSF and control groups. The further study showed oAd-CMV-GM-CSF induced profound autophagy through the activation of the Janus kinase 2/Signal Transducer and Activator of Transcription 2 (JAK2/STAT2) signaling pathway. The use of autophagy and JAK-2 inhibitors, Chloroquine (CQ) and AG-490, respectively, significantly mitigated the apoptosis induced by oAd-CMV-GM-CSF. In addition, oAd-CMV-GM-CSF presented a faster viral replication and production of more active progeny virus than oAd-GM-CSF, which could be inhibited by CQ. oAd-CMV-GM-CSF augments propagation of the progeny viruses and induces immunogenic cell death(ICD) in A549 and PANC-1 cells. In vivo oAd-CMV-GM-CSF had stronger anti-tumor effect than oAd-GM-CSF in immunodeficient model and immune-competent model. Our findings indicate that oAd-CMV-GM-CSF induces more profound autophagy and promoting viral replication to enhance the anti-tumor efficacy.