Synergic effect of PD-1 blockade and endostar on the PI3K/AKT/mTOR-mediated autophagy and angiogenesis in Lewis lung carcinoma mouse model

Background: Immunotherapy has been shown to be effective as a first-line treatment option for non-small cell lung cancer (NSCLC) patients. Unfortunately, it has failed to acquire an anticipant anti-tumour effect for relatively lower clinical benefit rates. It is therefore important to identify novel strategies for improving immunotherapy. Endostar is a novel recombinant human endostatin that exerts its anti-angiogenic effects via vascular endothelial growth factor (VEGF)-related signalling pathways. Anti-programmed death receptor 1 (PD-1) antibody is an immune checkpoint inhibitor that was developed to stimulate the immune system. In this study, the synergy of PD-1 blockade and endostar was assessed in a lung carcinoma mouse model. Methods: Lewis lung carcinoma (LLC)-bearing mice were randomly assigned into three groups: controls, anti-PD-1 and anti-PD-1+endostar. The levels of cytokines such as interleukin (IL)-17, transforming growth factor-β1 (TGF-β1) and interferon-γ (IFN-γ) were measured with enzyme-linked immune sorbent assay (ELISA). The expression of VEGF, CD34 and CD31 was assessed with immunohistochemistry (IHC). The proportion of mature dendritic cells (mDC) and myeloid-derived suppressor cells (MDSC) was analysed with flow cytometry. The major proteins in PI3K/AKT/mTOR and autophagy were quantified with Western blot. Results: Anti-PD-1 combined with endostar dramatically suppressed tumour growth in LLC mouse models. This synergistic effect resulted in decreased pro-inflammatory cytokine IL-17 and immunosuppressive factor TGF-β1 levels, increased IFN-γ secretion, reduced myeloid-derived suppressor cell (MDSC) accumulation, and reversed CD8 + T cell suppression. The expression of VEGF, CD34 and CD31 was significantly down-regulated, while tumour cell apoptosis and PI3K/AKT/mTOR-mediated autophagy was up-regulated. Conclusion: The combination of anti-PD-1 and endostar has a remarkably synergic effect on LLC tumour growth by means of improving the tumour microenvironment and activating autophagy.