Cerenkov luminescence imaging is an effective preclinical tool for assessing colorectal cancer PD-L1 levels in vivo

Background: Preclinical and clinical studies have demonstrated that immunotherapy has effectively delayed tumor progression, and the clinical outcomes of anti-PD-1/PD-L1 therapy were related to PD-L1 expression level in the tumors. A ¹³¹I-labeled anti-PD-L1 monoclonal antibody tracer, ¹³¹I-PD-L1-Mab, was developed to study the target ability of noninvasive Cerenkov luminescence imaging in colorectal Cancer xenograft mice.

Method: Anti-PD-L1 monoclonal antibody labeled with ¹³¹I (¹³¹I-PD-L1-Mab), and in vitro binding assays were used to evaluate the affinity of ¹³¹I-PD-L1-Mab to PD-L1 and their binding level to different colorectal Cancer cells, and compared with flow cytometry, Western blot analysis, and immunofluorescence staining. The clinical application value of ¹³¹I-PD-L1-Mab was evaluated through biodistribution and Cerenkov luminescence imaging, and different tumor-bearing models expressing PD-L1 were evaluated.

Results: ¹³¹I-PD-L1-Mab showed high affinity to PD-L1, and the equilibrium dissociation constant was 1.069 × 10^-9 M. The competitive inhibition assay further confirmed the specific binding ability of ¹³¹I-PD-L1-Mab. In four different tumor-bearing models with different PD-L1 expression, the biodistribution and Cerenkov luminescence imaging showed that the RKO tumors demonstrated the highest uptake of the tracer ¹³¹I-PD-L1-Mab, with a maximum uptake of 1.613 ± 0.738% IA/g at 48 h.

Conclusions: There is a great potential for ¹³¹I-PD-L1-Mab noninvasive Cerenkov luminescence imaging to assess the status of tumor PD-L1 expression and select patients for anti-PD-L1 targeted therapy.