168P - Effect of sequence treatment of chemotherapy plus radiotherapy activates innate immunity in SCLC

Background

In the past decade, radiotherapy (RT) has been widely practised for treating extensive-stage small cell lung cancer (ES-SCLC). Despite this, it has been discouraged in phase III trials of first line chemoimmunotherapy. Instead, robust rationales have emerged in favour of using RT as a booster to promote a sustained anti-tumour immune response. On basis of published data defining a subtype of SCLC patients who respond to chemotherapy (CT) classified as \"inflamed\" and expressing high innate immune genes such as the STimulator of INterferon pathway (STING) pathway and based on further preclinical data supporting STING levels as potential biomarkers of response to combined chemo- and immunotherapy, we hypothesised that innate immune activation may provide an opportunity to evaluate anti-tumour immune activity in vitro.

Methods

We explored the landscape of STING, Mitochondrial antiviral-signaling protein (MAVS), Gamma-interferon-inducible protein (IFI-16) and immune-related cytokines expression both at mRNA and protein expression levels among two SCLC cell lines, namely H82 and H524. We then tested the effect of in vivo treatment with CT and RT (4 Gy dose) on PBMC subpopulations derived from SCLC patients by LDH cytotoxicity assay.

Results

We performed sequential in vitro treatment with CT and RT (4 Gy) in selected SCLC cell lines and we investigated changes in STING pathway, as indicator of DNA damage induced by CT and RT. cGAS, STING and downstream protein p-TBK1 and p-IRF3 were upregulated by CT plus RT in both cell lines. Interestingly, these increments were accompanied by high levels of DNA damage, as suggested by increased levels of H2A.X, ATM, ATR, and DNA-PK. IFI-16 DNA sensor was also increased at both protein and mRNA levels. Moreover, inflammatory T cells recruiting the chemokines IL6, IFN-β, CXCL5, CXCL10, were also significantly increased by sequential treatment with CT and RT. The SCLC patients-derived immune cells activity patients were also significantly increased post-RT as measured by LDH cytotoxicity assay.

Conclusions

We demonstrated in cellular models of SCLC a positive modulation of innate immune pathways with CT and RT sequential treatment, suggesting a possible boost role of RT in SCLC patients treated with chemoimmunotherapy.

Legal entity responsible for the study

The authors.

Funding

AIRC.

Disclosure

All authors have declared no conflicts of interest.