Distinct genomic landscapes of gastroesophageal adenocarcinoma depending on PD-L1 expression identify mutations in RAS-MAPK pathway and TP53 as potential predictors of immunotherapy efficacy.

BACKGROUND: The impact of molecular alterations on programmed death-ligand 1 (PD-L1) combined positive score (CPS) is not well studied in gastroesophageal adenocarcinomas (GEAs). We aimed to characterize genomic features of tumors with different CPSs in GEAs. PATIENTS AND METHODS: Genomic alterations of 2518 GEAs were compared in three groups (PD-L1 CPS ≥ 10, high; CPS = 1-9, intermediate; CPS < 1, low) using next-generation sequencing. We assessed the impact of gene mutations on the efficacy of immune checkpoint inhibitors (ICIs) and tumor immune environment based on the Memorial Sloan Kettering Cancer Center and The Cancer Genome Atlas databases. RESULTS: High, intermediate, and low CPSs were seen in 18%, 54% and 28% of GEAs, respectively. PD-L1 positivity was less prevalent in women and in tissues derived from metastatic sites. PD-L1 CPS was positively associated with mismatch repair deficiency/microsatellite instability-high, but independent of tumor mutation burden distribution. Tumors with mutations in KRAS, TP53, and RAS-mitogen-activated protein kinase (MAPK) pathway were associated with higher PD-L1 CPSs in the mismatch repair proficiency and microsatellite stability (pMMR&MSS) subgroup. Patients with RAS-MAPK pathway alterations had longer overall survival (OS) from ICIs compared to wildtype (WT) patients [27 versus 13 months, hazard ratio (HR) = 0.36, 95% confidence interval (CI): 0.19-0.7, P = 0.016] and a similar trend was observed in the MSS subgroup (P = 0.11). In contrast, patients with TP53 mutations had worse OS from ICIs compared to TP53-WT patients in the MSS subgroup (5 versus 21 months, HR = 2.39, 95% CI: 1.24-4.61, P = 0.016). CONCLUSIONS: This is the largest study to investigate the distinct genomic landscapes of GEAs with different PD-L1 CPSs. Our data may provide novel insights for patient selection using mutations in TP53 and RAS-MAPK pathway and for the development of rational combination immunotherapies in GEAs.

Polymorphic electrophile response elements in the mouse glutathione S-transferase GSTa1 gene that confer increased induction.

Induced transcription of a battery of stress response genes in mammals, including several phase I and phase II drug-metabolizing enzymes, is regulated by the electrophile responsive element (EpRE). Because previous directed mutagenesis of nucleotide motifs within the large, composite EpRE were shown to affect transcription factor binding and associated induced expression of dependent genes, we hypothesized that naturally-occurring variation or polymorphism in the EpRE sequence, if found, could affect the induced expression of important protective genes like glutathione S-transferases, and that this could be an important determinant of cancer risk in humans and other mammals. To determine whether this occurred in nature, 32 strains and species of inbred mice were screened to examine the EpRE sequence present in the mGSTa1 promoter. Two species, Mus caroli and Mus spretus, showed TGAC-->TGGC mutations in the tandem TGAC motif. Inducibility (15-fold) of the variant Mus spretus EpRE sequence in a reporter gene construct in HepG2 cells was significantly increased versus the wild-type EpRE sequence (8-fold). A comparison of mGSTa1-induced expression in the livers of Mus spretus, Mus caroli, and BALB/cJ mice showed the highest level of mGSTa1 mRNA in livers from the Mus spretus and Mus carolimice. This naturally-occurring polymorphism within the EpRE domain is the first mutation with an associated phenotype to be reported within a promoter regulatory element of a drug metabolizing gene.

Immunogold analysis of antioxidant enzymes in human renal cell carcinoma.

Analysis of activities of the antioxidant enzyme manganese superoxide dismutase in human renal cell carcinomas often showed greatly altered enzyme levels (either elevated or depressed) compared to the cell of origin, the kidney proximal tubule. In order to better understand the variability observed, immunogold studies were performed on human renal cell carcinomas using a polyclonal antibody to human kidney manganese superoxide dismutase. For comparison, studies were also performed using antibodies to other antioxidant enzymes. For histologic studies, renal cell carcinomas were subclassified on the basis of light microscopy and ultrastructural analysis into clear cell, granular cell, or mixed clear and granular cell variants. In all three types of tumor, immunogold studies showed little staining using antibodies to copper, zinc superoxide dismutase or glutathione-dependent enzymes. However, intensity of labeling for manganese superoxide dismutase and catalase depended on the cell type(s) in the tumor. Clear cell variants demonstrated trace staining for manganese superoxide dismutase and catalase, while granular cell variants exhibited heavy staining for both of these enzymes. Mixed types of tumors showed clear cells with trace staining for all antioxidant enzymes examined, while granular cells again showed intense labeling for manganese superoxide dismutase and catalase. Using normal kidney proximal tubule as a comparison, immunogold ultrastructural analysis using antibody to manganese superoxide dismutase demonstrated infrequent small lightly labeled mitochondria in clear cell variants, while granular cell variants exhibited numerous medium-sized heavily labeled mitochondria. These data suggest that: 1) the variability in activity values for manganese superoxide dismutase may be due to heterogeneity of cell types in these tumors and 2) manganese superoxide dismutase immunoreactive protein was elevated in granular cells both because of an increase in number of mitochondria and because the labeling density in mitochondria was increased compared to mitochondria in clear cell types or in normal proximal tubular cells.