Matthew Garrett

 Introduction. Gastric cardia adenocarcinoma (GCA) is one of the most prevalent cancers in the world and is steadily on the rise in developed and undeveloped nations alike.¹ Two of the most common risk factors for GCA include Helicobacter pylori and Epstein-Barr Virus.^2-3 The rates of metastasis and post-operative recurrence measure between 40%-65%, likely due to Multi-Drug Resistance mutations.^1,4 The Programmed cell death protein-1 (PD-1)/Programmed death-ligand 1 (PD-L1) interaction has become a target for multi-drug resistant (MDR) cancers as it serves as an immune checkpoint regulator, effectively inactivating cytotoxic T-cells.⁵ Epigenetic modulation of PD-L1 expression on cancer cells increases MDR mutations leading to greater T-cell evasion.⁶  Current Anti-PD-1 therapy targets the PD-1/PD-L1 interaction which has been shown to downregulate PD-L1 expression.¹  GCA is particularly interesting in that is has been shown to resist anti-PD-1 therapy.¹ Methods.  A mouse xenograft model was used to study the effect of hypomethylating agents with pembrolizumab.¹ miR-152 and miR-200b were predicted to be effective miRNA targets through TargetScan and PicTar algorithms.² Luciferase assays were conducted to determine 3’ UTR activity in the B7-H1 transcript and quantitative PCR was used to find correlation between miRNA levels and B7-H1 (PD-L1) levels in gastric cancer cells.² Luciferase assays were conducted to determine PD-L1 expression on EBV associated Gastric Cell (EBVaGC) lines: NCC24, SNU719, YCCEL1.³  These cell lines were then treated with inhibitors of PI3K, JAK2, and mTor prior to exposure to IFN-γ.³ Results. PD-L1 was shown to be epigenetically controlled through promoter methylation and miRNAs.¹  Azacytidine(AZA) sensitized GCA to pembrolizumab and increased PD-L1 gene transcripts.¹ Combination therapy of AZA and pembrolizumab showed synergistic effects.¹  Gastric cancer cells with HP infection demonstrated high B7-H1 expression over uninfected cells through miRNA suppression.²  MiR-152 and miR-200b showed negative correlation with B7-H1 expression.² EBVaGC, which are known to increase PI3k, JAK2, and mTor, increased PD-L1 production when exposed to IFN-γ.³  When treated with various inhibitors, PI3k, JAK2, and mTor were downregulated in EBVaGCs after being previously exposed to IFN-γ.³ Conclusions. Combination therapy of anti-PD-1 drugs and hypomethylating drugs have clinical potential in addressing MDR GCA.¹ In addition, microRNAs hold potential to be targets in treating anti-PD-1 resistant cells.^1-2 EBV increases PI3k, JAK2, and mTor which poses as a possible therapeutic target in EBVaGC; however, more research needs to conducted to evaluate plausibility.³ IFN-γ may serve as a biomarker for anti-PD-1 resistant gastric cancers.³

1. Zhu T, Hu Z, Wang Z, et al. Epigenetically silenced PD-L1 confers drug resistance to anti-PD1 therapy in gastric cardia adenocarcinoma. International Immunopharmacology. 2020;82:106245. http://www.sciencedirect.com/science/article/pii/S1567576919328255. doi: https://doi.org/10.1016/j.intimp.2020.106245.
2. Xie G, Li W, Li R, et al. Helicobacter pylori promote B7-H1 expression by suppressing miR-152 and miR-200b in gastric cancer cells. PloS one. 2017;12(1):e0168822. https://www.ncbi.nlm.nih.gov/pubmed/28056089. doi: 10.1371/journal.pone.0168822.
3. Sasaki S, Sasaki S, Nishikawa J, et al. EBV-associated gastric cancer evades T-cell immunity by PD-1/PD-L1 interactions. Gastric Cancer. 2019;22(3):486-496. https://www.ncbi.nlm.nih.gov/pubmed/30264329. doi: 10.1007/s10120-018-0880-4.
4. Dallavalle S, Dobričić V, Lazzarato L, et al. Improvement of conventional anti-cancer drugs as new tools against multidrug resistant tumors. Drug Resistance Updates. 2020;50:100682. http://www.sciencedirect.com/science/article/pii/S1368764620300091. doi: https://doi.org/10.1016/j.drup.2020.100682.
5. Zhuang Y, Liu C, Liu J, Li G. Resistance mechanism of PD-1/PD-L1 blockade in the cancer-immunity cycle. OncoTargets and therapy. 2020;13:83-94. https://www.ncbi.nlm.nih.gov/pubmed/32021257. doi: 10.2147/OTT.S239398.
6. Lingling Z, Jiewei L, Li W, et al. Molecular regulatory network of PD-1/PD-L1 in non-small cell lung cancer. Pathology – Research and Practice. 2020:152852. http://www.sciencedirect.com/science/article/pii/S0344033819327542. doi: https://doi.org/10.1016/j.prp.2020.152852.