A novel 89Zr-a-PD-1 immuno-PET-CT may improve pseudoprogression detection in a lung cancer murine model receiving immunotherapy.

Abstract

e15116 Background: Immune checkpoint inhibitors (ICIs) have revolutionized lung cancer treatment improving survival outcomes of non-small cell lung cancer (NSCLC) patients. Response assessment of patients on ICIs treatment 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 18F-FDG-PET scans do not accurately discriminate P from PP. We have recently reported the efficacy of a combined blockade of PD-1 and ID1 in NSCLC mouse model. We aimed to evaluate a novel 89Zr-labelled radiotracer for micro mPET-CT to detect PP 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 commercially available monoclonal antibody against PD-1 (a-PD-1) (RPM1-14, 300 mg, IP, on days 7, 10 and 14). Tumor growth and response to ID1-PD-1 blockade, was measured by 18F-FDG uptake. Additionally, PP was measured labelling the anti-PD-1 with 89Zr (89Zr-a-PD-1) and analyzing 89Zr uptake at day 15, 17 and 20. Tumor microenvironment was analyzed with immunohistochemistry, multiplex immunofluorescence and quantification of relative expression of interleukins by RT-PCR. Results: 18F-FDG uptake did not show significant differences between groups, underestimating the real metabolic response induced by the treatment. However, 89Zr-mPET-CT showed a significantly higher 89Zr uptake when ID1 was inhibited in both, tumor cells and tumor micro-environment and mice were treated with a-PD-1 (p = 0.0075). The analysis of the tumor tissues in those animals by immunohistochemistry and multiplex immunofluorescence disclosed an increase in immune T CD8+ cells infiltration, being responsible for the antitumor response observed and correlating with 89Zr signal. Moreover, the analysis of interleukins expression showed that tumors with ID1 inhibition in the tumor micro-environment presented an upregulation of pro-inflammatory interleukins, favoring T- cell infiltration. 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-a-PD-1 immuno-PET-CT may improve PP detection in a NSCLC murine model receiving immunotherapy.