1. Small molecule inhibitors targeting the PD-1/PD-L1 signaling pathway
Si-Cheng Li, Qian Wu, Bo Yang, Ji Cao, Li Jiang, Qiao-Jun He Acta Pharmacol Sin . 2021 Jan;42(1):1-9. doi: 10.1038/s41401-020-0366-x.
Tumor cells form immune escape and subsequently obtain unlimited proliferation ability due to the abnormal immune surveillance mediated by immune checkpoints. Among this class of immune checkpoints, PD-1/PD-L1 was recognized as an anticancer drug target for many years, and so far, several monoclonal antibodies have achieved encouraging outcome in cancer treatment by targeting the PD-1/PD-L1 signaling pathway. Due to the inherent limitations of antibodies, the development of small molecule inhibitors based on PD-1/PD-L1 signaling pathway is gradually reviving in decades. In this review, we summarized a number of small molecule inhibitors based on three different therapeutic approaches interfering PD-1/PD-L1 signaling pathway: (1) blocking direct interaction between PD-1 and PD-L1; (2) inhibiting transcription and translation of PD-L1; and (3) promoting degradation of PD-L1 protein. The development of these small molecule inhibitors opens a new avenue for tumor immunotherapy based on PD-1/PD-L1 signaling pathway.
2. Cyclin D-CDK4 kinase destabilizes PD-L1 via cullin 3-SPOP to control cancer immune surveillance
Jinfang Zhang, Xia Bu, Naoe Taira Nihira, Yasheng Zhu, Xiangpeng Dai, Shancheng Ren, Yinghao Sun, Gordon J Freeman, Wenyi Wei, Yanpeng Ci, Caoqi Fan, Yan Geng, Jianping Guo, Yuyong Tan, Fei Wu, Yu-Han Huang, Piotr Sicinski, Haizhen Wang Nature . 2018 Jan 4;553(7686):91-95. doi: 10.1038/nature25015.
Treatments that target immune checkpoints, such as the one mediated by programmed cell death protein 1 (PD-1) and its ligand PD-L1, have been approved for treating human cancers with durable clinical benefit. However, many patients with cancer fail to respond to compounds that target the PD-1 and PD-L1 interaction, and the underlying mechanism(s) is not well understood. Recent studies revealed that response to PD-1-PD-L1 blockade might correlate with PD-L1 expression levels in tumour cells. Hence, it is important to understand the mechanistic pathways that control PD-L1 protein expression and stability, which can offer a molecular basis to improve the clinical response rate and efficacy of PD-1-PD-L1 blockade in patients with cancer. Here we show that PD-L1 protein abundance is regulated by cyclin D-CDK4 and the cullin 3-SPOP E3 ligase via proteasome-mediated degradation. Inhibition of CDK4 and CDK6 (hereafter CDK4/6) in vivo increases PD-L1 protein levels by impeding cyclin D-CDK4-mediated phosphorylation of speckle-type POZ protein (SPOP) and thereby promoting SPOP degradation by the anaphase-promoting complex activator FZR1. Loss-of-function mutations in SPOP compromise ubiquitination-mediated PD-L1 degradation, leading to increased PD-L1 levels and reduced numbers of tumour-infiltrating lymphocytes in mouse tumours and in primary human prostate cancer specimens. Notably, combining CDK4/6 inhibitor treatment with anti-PD-1 immunotherapy enhances tumour regression and markedly improves overall survival rates in mouse tumour models. Our study uncovers a novel molecular mechanism for regulating PD-L1 protein stability by a cell cycle kinase and reveals the potential for using combination treatment with CDK4/6 inhibitors and PD-1-PD-L1 immune checkpoint blockade to enhance therapeutic efficacy for human cancers.
3. Safety and Efficacy of PD-1/PD-L1 inhibitors combined with radiotherapy in patients with non-small-cell lung cancer: a systematic review and meta-analysis
Zhen Yang, Chengcheng Li, Shuangwu Feng, Qiuning Zhang, Zheng Li, Xiaohu Wang, Hongtao Luo, Lina Wang, Bing Lu, Yichao Geng, Xueshan Zhao, Ruifeng Liu Cancer Med . 2021 Feb;10(4):1222-1239. doi: 10.1002/cam4.3718.
Background:A combination of programmed cell death protein-1 (PD-1)/programmed cell death ligand-1 (PD-L1) inhibitors and radiotherapy (RT) is increasingly being used to treat non-small-cell lung cancer (NSCLC). However, the safety and efficacy of this approach remains controversial. We performed a systematic review and meta-analysis to summarize the related research.Methods:We searched the China Biology Medicine, EMBASE, Cochrane Library, and PubMed databases for all the relevant studies. The Stata software, version 12.0 was used for the meta-analysis.Results:The study included 20 clinical trials that enrolled 2027 patients with NSCLC. Compared with non-combination therapy, combination therapy using PD-1/PD-L1 inhibitors and RT was associated with prolonged overall survival (OS) (1-year OS: odds ratio [OR] 1.77, 95% confidence interval [CI] 1.35-2.33, p = 0.000; 2-year OS: OR 1.77, 95% CI 1.35-2.33, p = 0.000) and progression-free survival (PFS) (0.5-year PFS: OR 1.83, 95% CI 1.13-2.98, p = 0.014; 1-year PFS: OR 2.09, 95% CI 1.29-3.38, p = 0.003; 2-year PFS: OR 2.47, 95% CI 1.13-5.37, p = 0.023). Combination therapy also improved the objective response rate (OR 2.76, 95% CI 1.06-7.19, p = 0.038) and disease control rate (OR 1.80, 95% CI 1.21-2.68, p = 0.004). This meta-analysis showed that compared with non-combination therapy, combination therapy using PD-1/PD-L1 inhibitors and RT did not increase the serious adverse event rates (≥grade 3); however, this approach increased the rate of grade 1-2 immune-related or radiation pneumonitis. Subgroup analyses revealed that the sequence of PD-1/PD-L1 inhibitors followed RT outperformed in which concurrent PD-1/PD-L1 inhibitor and RT followed PD-1/PD-L1 inhibitor. Combination of stereotactic body RT or stereotactic radiosurgery with PD-1/PD-L1 inhibitors may be more effective than a combination of conventional RT with PD-1/PD-L1 inhibitors in patients with advanced NSCLC.Conclusion:Combination therapy using PD-1/PD-L1 inhibitors and RT may improve OS, PFS, and tumor response rates without an increase in serious adverse events in patients with advanced NSCLC. However, combination therapy was shown to increase the incidence of mild pneumonitis.
