962P - SBRT improves the efficacy of immuno-checkpoint inhibitors for hepatocellular carcinoma through the activation of IL-6/JAK1-STAT3/PD-L1 axis mediated by MBD3 degradation

Background

Stereotactic radiotherapy (SBRT) has shown promising for unresectable hepatocellular carcinoma (HCC) due to its ability to modulate the tumor immune microenvironment. Methyl-CpG binding domain protein 3 (MBD3) is highly expressed in HCC and negatively correlated with prognosis. However, the role of MBD3 in the radioimmunology of SBRT in HCC remains unclear.

Methods

The expression and correlation of MBD3 and programmed cell death ligand 1 (PD-L1) were analyzed in HCC tissues before and after SBRT by immunohistochemistry (IHC). The mechanic regulations of MBD3 in the radioimmunology of SBRT in HCC were investigated both in vitro and in vivo studies.

Results

We observed a significant increase of PD-L1 in HCC after SBRT, which was associated with decreased MBD3 expression. As the radiation dose increased, MBD3 gradually degraded, while PD-L1 gradually upregulated in human and murine liver cancer cells. Through RNA sequencing, KEGG enrichment analysis and in vitro experiments, we identified that IL-6 was massively activated and released, leading to the activation of the JAK1/STAT3 signaling pathway, and ultimately resulted in the upregulation of PD-L1, which were induced by MBD3 degradation in liver cancer cells by irradiation. In vivo experiments showed that the combination of SBRT and PD-L1 blockade significantly enhanced the antitumor efficacy in the murine orthotopic model of HCC, partly dependent on the increased infiltration of IFNγ⁺CD8⁺T cells in the tumor. We also found that SBRT reactivated proteinase-activated receptor 2 (PAR2) to promote the release of IL-6, activating the JAK1/STAT3 signaling pathway, leading to the upregulation of PD-L1 through relieving the inhibition of F2RL1 (encoding PAR2) mediated by the deacetylation of the MBD3/NuRD complex. Our findings were further confirmed by IHC analysis of the above proteins in HCC tissues before and after SBRT.

Conclusions

Our study suggests that SBRT can reprogram the tumor immune microenvironment by activating the PAR2/IL-6/JAK1/STAT3 axis through MBD3 degradation, leading to PD-L1 upregulation, which may help develop new therapeutic strategies targeting PD-L1 to improve the efficacy of SBRT in HCC.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.