Myeloid-derived suppressor cells (MDSCs) are one of the key players that contribute to immune evasion. The purpose of the present study was to investigate whether MDSCs could be a novel target for the treatment of cisplatin-resistant bladder cancer. We established cisplatin-resistant bladder cancer cell lines (MB49R, MBT-2R, and T24R) and evaluated chemokine expression and MDSC expansion. We also assessed the antitumor effect by depleting MDSCs with or without a α-PD-L1 antibody using MB49R xenograft models. The chemokine expression of CXCL1, CXCL2, and CCL2 increased in cisplatin-resistant cells compared to those in their parent strains. Monocytic MDSCs (Mo-MDSCs) were observed more frequently compared to polymorphonuclear MDSCs (PMN-MDSCs) in MB49R tumors. The immunosuppressive genes arginase 1 and iNOS were comparably expressed in each MDSC subtype. In vivo, combination therapy targeting both PMN- and Mo-MDSCs using α-Gr1 and α-Ly6C antibodies significantly reduced tumor volume with increased infiltration of CD8 T cells in the tumor. Finally, co-targeting pan-MDSCs and PD-L1 remarkably reduced the tumor growth. These findings suggest that targeting MDSCs might enhance the therapeutic effect of immune checkpoint inhibitors in cisplatin-resistant bladder cancers.

Immunotherapy based on blockade of the programmed death‐1 (PD‐1)/programmed death‐ligand 1 (PD‐L1) axis has shown promising clinical activity for renal cell carcinoma (RCC) patients; however, the most effective use of these agents in combination with conventional targeted therapy remains to be resolved. Here we evaluated the therapeutic efficacy of the combination of the mTOR inhibitor everolimus (EVE) and anti‐PD‐L1 using an immunocompetent mouse model of RCC. We first assessed the in vitro effect of EVE on PD‐L1 expression in the human 786‐O and mouse RENCA RCC cell lines and found that EVE upregulated PD‐L1 expression in these RCC cell lines. We then treated RENCA tumor‐bearing mice with EVE and found that PD‐L1 expression was also increased in tumor cells after EVE treatment. To determine the antitumor effects of EVE alone, anti‐PD‐L1 alone, and EVE in combination with anti‐PD‐L1, we evaluated their antitumor effects on RENCA tumor‐bearing mice. A significant decrease in the tumor burden was observed in the EVE alone but not in the anti‐PD‐L1 alone treatment group compared with the control group. Importantly, the combination of EVE with anti‐PD‐L1 significantly reduced tumor burden compared with the EVE alone treatment, increasing tumor infiltrating lymphocytes (TILs) and the ratio of cytotoxic CD8⁺ T cells to TILs. The results of the present study demonstrated that anti‐PD‐L1 treatment enhanced the antitumor effect of EVE in a mouse model, supporting a direct translation of this combination strategy to the clinic for the treatment of RCC.

In the present study, protein lysates from microdissected glutathione S-transferase placental-form–positive (GST-P⁺) foci and hepatocellular carcinomas from livers of rats treated with N-diethylnitrosamine followed by phenobarbital at doses of 0 and 500 ppm in the diet for 10 and 33 weeks were analyzed using QSTAR Elite liquid chromatography with tandem mass spectrometry and iTRAQ technology. Among 75 proteins, a total of 27 and 50 proteins displaying significant quantitative changes comparing with adjacent normal-appearing liver tissue were identified in GST-P⁺ foci of initiation control and promotion groups, respectively, which are related to transcription, protein folding, cytoskeleton filaments reorganization, cell cycle control, nuclear factor (erythroid-derived 2)-like 2 (NRF2)–mediated oxidative stress responses, lipid metabolism, glutathione metabolism, oxidative phosphorylation, and signal transduction. Furthermore, Ingenuity Pathway and bioinformatic analyses revealed that expression changes of genes encoding proteins with altered expression detected in GST-P⁺ foci are likely to be controlled by c-myc, NRF2, aryl hydrocarbon receptor, nuclear factor kappa B, and hepatocyte nuclear factor 4 transcriptional factors. Coordinated overexpression of mitochondrial chaperons prohibitin (PHB) and prohibitin 2 (PHB2), septin 9 (SEPT9), neurabin 1, and other cytoskeletal and functional proteins in areas of GST-P⁺ foci during initiation and/or promotion stages of rat hepatocarcinogenesis was associated with induction of cell proliferation and might be responsible for the neoplastic transformation of rat liver preneoplastic lesions. Newly discovered elevation of PHB, PHB2, and SEPT9 in GST-P⁺ foci and tumors, imply that they might play important role in the onset of liver cancer and be of potential values in the studies of hepatocarcinogenesis.

This review highlights several in vivo studies utilizing non-genotoxic and genotoxic chemical carcinogens, and the mechanisms of their high and low dose carcinogenicities with respect to formation of oxidative stress. Here, we survey the examples and discuss possible mechanisms of hormetic effects with cytochrome P₄₅₀ inducers, such as phenobarbital, a-benzene hexachloride and 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane. Epigenetic processes differentially can be affected by agents that impinge on oxidative DNA damage, repair, apoptosis, cell proliferation, intracellular communication and cell signaling. Non-genotoxic carcinogens may target nuclear receptors and induce post-translational modifications at the protein level, thereby impacting on the stability or activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. We further discuss role of oxidative stress focusing on the low dose carcinogenicities of several genotoxic carcinogens such as a hepatocarcinogen contained in seared fish and meat, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, arsenic and its metabolites, and the kidney carcinogen potassium bromate.

This study investigated whether the expression of CD44 variant 9 (CD44v9) might be a functional marker of tumor‐initiating stem‐like cells in primary hepatocellular carcinomas (HCCs) of hepatitis C virus (HCV)⁺ patients and provide an indicator of patient survival, as well as associated mechanisms. A total of 90 HCV⁺ HCC patients who underwent surgery from 2006 to 2011 were enrolled and monitored for 2–8 years. Expression of CD44v9 was validated immunohistochemically in all HCCs, followed by comparative proteome, survival, and clinicopathological analyses. CD44 variant 8–‐10 was further evaluated in diethylnitrosamine‐induced HCCs of C57Bl/6J mice. Focally localized CD44v⁺ cells with a membranous staining pattern were detected in human HCV⁺ and mouse HCCs. CD44v9⁺ cells of HCCs were predominantly negative for Ki67 and P‐p38, indicating decrease of cell proliferation in the CD44v9⁺ tumor cell population, likely to be related to suppression of intracellular oxidative stress due to activation of Nrf2‐mediated signaling, DNA repair, and inhibition of xenobiotic metabolism. CD44v9 IHC evaluation in 90 HCV⁺ HCC cases revealed that positive expression was significantly associated with poor overall and recurrence‐free survival, a younger age, poor histological differentiation of HCCs, and high alkaline phosphatase levels compared with patients with negative expression. CD44v9 is concluded to be a potential biomarker of tumor‐initiating stem‐like cells and a prognostic marker in HCV⁺ HCC patients associated with Nrf2‐mediated resistance to oxidative stress.