The study of multi-targets PET tracer on early monitoring ICI curative effect of lung cancer

Introduction: Immune checkpoint inhibitors (ICI) are considered one of the most promising new anti-cancer drugs. However, the efficacy of ICI varies greatly in different patients because of the complex immune microenvironment, in which the neutrophil/lymphocyte ratio may play a key role. Here, we hypothesized that imaging of granzyme B (GZB) with and myeloperoxidase (MPO) with ⁶⁸Ga-NOTA-bis-5HT could predict the ICI responders of lung cancer, which are the effective protein of CD8+ T cell and the core protein of neutrophil trapping net (NETs), respectively.

Methods: and radiochemical purity of ⁶⁸Ga-DOTA-grazytracer and ⁶⁸Ga-NOTA-bis-5HT were analyzed by HPLC. The stability in physiological saline and serum were evaluated and the Log P was determined to make sure the biological characteristics. Then, the LLC tumor-bearing mice were treated with PD-L1 mAb (200μg) every three days intraperitoneally. Then, the uptake before and after treatment were evaluated by double PET probes with micro-PET/CT. Meanwhile, the immunotherapy effect was analyzed by determining the volumes of tumor and the weight changes every 3 days.

Results: The radioactive labeling yield ofand ⁶⁸Ga-NOTA-bis-5HT were 63% and 40%, and the radiochemical purity were＞95% and＞90%. They kept stability in salt and serum at 37℃within 4h. The lipid/water partition coefficient of the two tracers were -0.22±0.05 and -0.49±0.05, respectively, which showed the good hydrophilicity. The results of ⁶⁸Ga-DOTA-grazytracer PET imaging showed that the PET signal value of tumor was increased after treatment (P＜0.05 ), indicating that PD-L1 stimulated the release of GZB and activated immune system cytotoxicity. Meanwhile, the PET signal of ⁶⁸Ga-NOTA-bis-5HT was correlated with tumor volume after PD-L1 treatment (r=0.94), which suggesting the potential of ⁶⁸Ga-NOTA-bis-5HT to predict the tumor immunotherapy response. In addition, by monitoring the dynamic PET signal changes of GZB and MPO, it was found that the secretion of GZB and MPO were reached maximum value within 4h after the last treatment, and declined gradually, which provided new ideas for further combination therapy and clinical research.

Conclusions: GZB expression in tumor was increased by PD-L1 stimulation and the change of MPO had the potential to predict the immunotherapy response of lung cancer. The GZB and MPO expression were limited by time. Molecular imaging of ⁶⁸Ga-DOTA-grazytracer and ⁶⁸Ga-NOTA-bis-5HT may help to predict the immune efficacy early and perfect the novel therapies.