Abstract 2477: PD-L1 PET quantifies the pharmacodynamic effects of immunotherapy
Authors: Mishra Akhilesh , Kumar Dhiraj , Gupta Kuldeep , Forde Patrick M. , Gabrielson Edward , Nimmagadda Sridhar 
Published: June 2022

Introduction: Immune checkpoint protein targeted therapeutics have transformed cancer treatment but only a subset of patients derive benefit. To improve efficacy, a variety of combination therapies are being studied. Programmed death ligand-1 (PD-L1) immunohistochemistry (IHC) is used as a biomarker to guide many of those therapies. Non-invasive evaluation of therapy induced changes in PD-L1 levels in the whole body could provide insights to guide those therapies. Here, we investigated the potential of [18F]DK222, a novel PD-L1 binding positron emission tomography (PET) imaging agent, to quantify PD-L1 levels and pharmacodynamics in humanized mouse modes.

Methods: Non-small cell lung cancer (NSCLC), urothelial carcinoma (UC) and melanoma cell lines were screened by flow cytometry (FC) for PD-L1 expression and density. In vitro cell uptake assays, in vivo PET imaging and ex vivo biodistribution studies were used to evaluate the specificity of [18F]DK222 to bind PD-L1 (n=5-6/tumor). To quantify immunotherapy induced changes in PD-L1, A375 melanoma xenografts were inoculated in NSG mice humanized with CD34+ cells. Mice were treated with either 5 mg/kg anti- PD-1; (pembrolizumab) or 5 mg/kg of anti-PD-1 + 4 mg/kg of anti- CTLA-4 (ipilimumab) (n=5) and [18F]DK222 PET was acquired before and 7 days after start of treatment. Tumor growth was monitored. FC of tumors was performed to measure changes in TME and immune cell infiltrates.

Results: In vitro uptake of [18F]DK222 in NSCLC (H244 &gt; H226 &gt; A549) and UC (BFTC909 &gt; T24 &gt; SCaBER) correlated with PD-L1 density (R2=0.96). [18F]DK222 PET and biodistribution studies in mice with NSCLC and UC xenografts revealed high and variable tumor uptake at 60 min, which was in agreement with PD-L1 levels detected by IHC. These data established sensitivity of [18F]DK222 PET to quantify variable PD-L1 levels in vivo. We next sought to quantify therapy induced changes in PD-L1 levels. We observed higher [18F]DK222 uptake in tumors of mice treated with combination therapy compared to monotherapy (1.83 vs 0.47 %ID/cc). A significant delay in tumor growth was observed with combination therapy compared to monotherapy. Two out of five mice with highest increase in [18F]DK222 uptake in combination therapy group exhibited least tumor growth. Also, final tumor volumes negatively correlated with [18F]DK222 uptake (R2=0.33) irrespective of treatment regimen. FC analysis showed higher immune infiltrates (1320 vs 230 per milligram of tumor), PD-L1+ cells (6005 vs 2739/mg) and ratio of CD8+ to CD4+ cells (1.94 vs 0.47) in tumors treated with combination therapy compared with monotherapy. These observations confirmed that immunotherapy induced changes in PD-L1 levels in tumors can be quantified using [18F]DK222 PET.

Conclusion: [18F]DK222 PET can effectively quantify variable PD-L1 levels in tumors. Moreover, [18F]DK222 PET exhibits the sensitivity to quantify PD-L1 pharmacodynamics to inform on tumor response to therapy.

Citation Format: Akhilesh Mishra, Dhiraj Kumar, Kuldeep Gupta, Patrick M. Forde, Edward Gabrielson, Sridhar Nimmagadda. PD-L1 PET quantifies the pharmacodynamic effects of immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2477.