Non-invasive PD-L1 quantification using [ 18 F]DK222-PET imaging in cancer immunotherapy.

Background: Combination therapies that aim to improve the clinical efficacy to immune checkpoint inhibitors have led to the need for non-invasive and early pharmacodynamic biomarkers. Positron emission tomography (PET) is a promising non-invasive approach to monitoring target dynamics, and programmed death-ligand 1 (PD-L1) expression is a central component in cancer immunotherapy strategies. [ ¹⁸ F]DK222, a peptide-based PD-L1 imaging agent, was investigated in this study using humanized mouse models to explore the relationship between PD-L1 expression and therapy-induced changes in cancer.
Methods: Cell lines and xenografts derived from three non-small cell lung cancers (NSCLCs) and three urothelial carcinomas (UCs) were used to validate the specificity of [ ¹⁸ F]DK222 for PD-L1. PET was used to quantify anti-programmed cell death protein-1 (PD-1) therapy-induced changes in PD-L1 expression in tumors with and without microsatellite instability (MSI) in humanized mice. Furthermore, [ ¹⁸ F]DK222-PET was used to validate PD-L1 pharmacodynamics in the context of monotherapy and combination immunotherapy in humanized mice bearing A375 melanoma xenografts. PET measures of PD-L1 expression were used to establish a relationship between pathological and immunological changes. Lastly, spatial distribution analysis of [ ¹⁸ F]DK222-PET was developed to assess the effects of different immunotherapy regimens on tumor heterogeneity.
Results: [ ¹⁸ F]DK222-PET and biodistribution studies in mice with NSCLC and UC xenografts revealed high but variable tumor uptake at 60 min that correlated with PD-L1 expression. In MSI tumors treated with anti-PD-1, [ ¹⁸ F]DK222 uptake was higher than in control tumors. Moreover, [ ¹⁸ F]DK222 uptake was higher in A375 tumors treated with combination therapy compared with monotherapy, and negatively correlated with final tumor volumes. In addition, a higher number of PD-L1+ cells and higher CD8 ⁺ -to-CD4 ⁺ cell ratio was observed with combination therapy compared with monotherapy, and positively correlated with PET. Furthermore, spatial distribution analysis showed higher [ ¹⁸ F]DK222 uptake towards the core of the tumors in combination therapy, indicating a more robust and distinct pattern of immune cell infiltration.
Conclusion: [ ¹⁸ F]DK222-PET has potential as a non-invasive tool for monitoring the effects of immunotherapy on tumors. It was able to detect variable PD-L1 expression in tumors of different cancer types and quantify therapy-induced changes in tumors. Moreover, [ ¹⁸ F]DK222-PET was able to differentiate the impact of different therapies on tumors.
Competing Interests: Competing interests: SN, MGP and DK are co-inventors on pending patents covering [18F]DK222, and as such are entitled to a portion of any licensing fees and royalties generated by this technology. This arrangement was reviewed and approved by Johns Hopkins University in accordance with its conflict-of-interest policies. SN, MGP and SPR received funding and were consultants for Precision Molecular, Inc., the licensee of [18F]DK222. SN, MGP and SPR have equity in D&D Pharmatech, the parent company of Precision Molecular, Inc. All other authors declare no conflicts pertaining to the described work.
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