2241P - A novel 89Zr-anti-PD-1 immuno-PET-CT may predict response to PD-1 inhibitors and improve response assessment in a lung cancer murine model receiving immunotherapy

Background

Immune checkpoint inhibitors (ICIs) have revolutionized lung cancer treatment improving survival outcomes of NSCLC patients. Response assessment of patients on immunotherapy represents a challenge since an increase in tumor size or the appearance of new lesions might not reflect true disease progression (P) but pseudoprogression (PP), which has been reported in a range of 3-6% in NSCLC. Conventional FDG-PET scans does not accurately discriminate P from PP. We have recently reported the efficacy of a combined blockade of PD-1 and Id1 in a NSCLC mouse model. We aimed to evaluate a novel ⁸⁹Zr-anti-PD-1 immuno-PET-CT to better assess response in a NSCLC murine model.

Methods

Syngeneic subcutaneous tumors were generated using LLC cells (with constitutive expression of Id1 or Id1-silenced) in C57BL6J and in Id1-deficient mice, treated with PBS or with a monoclonal antibody against PD-1. Tumor growth and response, was measured by FDG uptake. Additionally, tumor lymphocyte infiltration was measured analyzing ⁸⁹Zr uptake. Tumor microenvironment was explored with immunohistochemistry, multiplex immunofluorescence and quantification of relative expression of interleukins by RT-PCR.

Results

FDG uptake did not show significant differences between groups, underestimating the real metabolic response induced by the treatment. However, ⁸⁹Zr-PET-CT showed a significantly higher ⁸⁹Zruptake when Id1 was inhibited in both, tumor cells and tumor micro-environment and mice were treated with anti-PD-1 (p=0.0075). The tumor tissues analysis in those animals by immunohistochemistry and multiplex immunofluorescence disclosed an increase in immune CD8⁺ T cells infiltration, being responsible for the antitumor response observed and correlating with ⁸⁹Zr signal. Moreover, the analysis of interleukins expression showed an upregulation of tumor pro-inflammatory interleukins.

Conclusions

Id1 inhibition in tumor cells and in tumor micro-environment combined with PD-1 blockade enhanced immune cell infiltration through pro-inflammatory interleukins upregulation. ⁸⁹Zr-anti-PD-1 immuno-PET-CT may improve tumor response assessment in a NSCLC murine model receiving immunotherapy.

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.