Preclinical Study of a Fully Human Anti-PD-L1 Antibody as a Theranostic Agent for Cancer Immunotherapy

Recently, inhibiting the PD-1/PD-L1 checkpoint pathway utilizing anti-PD-1 or anti-PD-L1 antibodies has achieved great clinical success in cancer treatment. However, anti-PD-1 immunotherapy cannot be applied to all cancer patients, no more than 25% showed a positive response. Immunohistochemistry (IHC) is the gold standard to determine the PD-L1 expression level in malignant lesions, but a noninvasive imaging-meditated strategy is urgently required for clinical diagnosis to cover the shortcomings of invasive techniques. MX001, which is an anti-PD-L1 antibody, was labeled with Cu-64 (t(1/2) = 12.7 h) and purified by PD-10 chromatography. Comprehensive studies including positron emission tomography (PET), ex vivo biodistribution, IHC, and immunotherapy have been performed in mice bearing MC38 (PD-L1 positive (+)) and 4T1 (PD-L1 negative (-)) xenografts. PET imaging of [F-18]FDG was taken before and after therapy to monitor the therapeutic efficacy. [(64) Cu] Cu-NOTA-MX001 exhibited 2.3 +/- 1.2, 5.6 +/- 2.1, 5.6 +/- 1.2, 6.1 +/- 1.1, 6.1 +/- 0.5, and 10.2 +/- 1.7% ID/g uptake in MC38 xenografts at 0.5, 12, 24, 36, 48, and 62 h post -injection (p.i.), respectively. Meanwhile, the uptake in the liver and muscle at corresponding time points was 17.5 +/- 2.2, 8.4 +/- 2.4, 11.3 +/- 3.2, 7.2 +/- 2.1, 7.9.1 +/- 3.5, and 3.8 +/- 1.8%ID/g, and 1.2 +/- 0.5, 1.3 +/- 0.4, 1.5 +/- 0.5, 0.7 +/- 0.1, 0.6 +/- 0.2, and 0.2 +/- 0.1%ID/g, respectively. The uptake of [F-18]FDG in MC38 and 4T1 xenografts at 1-h p.i. was 5.3 +/- 0.4 and 6.4 +/- 0.6%ID/g, while the uptake of [Cu-64]Cu-NOTA-MX001 was 5.6 +/- 0.3 and 1.3 +/- 0.4%ID/g at 12-h p.i. IHC analysis confirmed that the MC38 tumor exhibited high PD -L1 expression, and the 4T1 tumor, liver, and muscle exhibited low PD -L1 expression. In addition, MC38 xenografts were suppressed by MX001 about 88% in the immunotherapy study. MX001 was successfully developed as a fully human anti-PD-L1 antibody with a high binding affinity in mouse, monkey, and human. The in vivo pharmacokinetics of MX001 was evaluated with PET imaging after being radiolabeled with Cu-64. The uptake of [64Cu]Cu-NOTA-MX001 was clearly correlated to the PD -L1 expression on various types of cancer. Subsequent immunotherapy studies demonstrated that MX001 could effectively suppress tumor growth with positive PD -L1 expression, but had poor antitumor efficacy on tumors which exhibited low PD-L1 expression. Together with the above results, MX001 has the potential to be further developed as an antibody theranostic agent for both PET imaging and immunotherapy of cancers in clinics.