The thioredoxin system plays a role in a variety of physiological functions, including cell growth, differentiation, apoptosis, tumorigenesis, and immunity. We previously confirmed that butaselen (BS), a novel thioredoxin reductase inhibitor, can inhibit the growth of various human cancer cell lines, yet the underlying mechanism remains elusive. In this study, we investigated the anti-tumor effect of BS in vivo through regulating the immune system of KM mice. We found that BS inhibits tumor proliferation by promoting the activation of splenic lymphocytes in mice. BS can elevate the percentage of CD₄^-CD₈⁺ T lymphocytes and the secretion of downstream cytokines in mice via down-regulating the expression of programmed death-ligand 1 (PD-L1) on the tumor cells' surface in vivo. Further study in HepG2 and BEL-7402 cells showed that decrease of PD-L1 level after BS treatment was achieved by inhibiting signal transducer and activator of transcription 3 (STAT3) phosphorylation. Taken together, our results suggest that BS has a role in promoting the immune response by reducing PD-L1 expression via the STAT3 pathway, and subsequently suppresses tumorigenesis.
Animals ; Antineoplastic Agents/pharmacology* ; B7-H1 Antigen/antagonists & inhibitors* ; Benzene Derivatives/therapeutic use* ; CD8-Positive T-Lymphocytes/drug effects* ; Hep G2 Cells ; Humans ; Liver Neoplasms/pathology* ; Male ; Mice ; Organoselenium Compounds/therapeutic use* ; STAT3 Transcription Factor/physiology* ; Thioredoxin-Disulfide Reductase/antagonists & inhibitors* ; Tumor Burden/drug effects*

Human thioredoxin reductase (TrxR) system is associated with cancer cell growth and anti-apoptosis process. Effects of 1,2-[bis(1,2-benzisoselenazolone-3(2H)-ketone)]ethane (BBSKE), a novel TrxR inhibitor, were investigated on human leukemia cell lines HL-60 and K562. BBSKE treatment induced cell growth inhibition and apoptosis in both cell lines. Apoptosis induced by BBSKE is through Bcl-2/Bax and caspase-3 pathways. Ehrlich's ascites carcinoma-bearing mice were used to investigate the anti-tumor effect of BBSKE in vivo. Tumor-bearing mice treated with BBSKE showed an increase of life span with a comparable effect to cyclophosphamide (CTX). These results suggest a potential usage of BBSKE as a therapeutic agent against non-solid tumors.
Apoptosis ; drug effects ; Bridged Bicyclo Compounds, Heterocyclic ; pharmacology ; Cell Proliferation ; drug effects ; Enzyme Inhibitors ; pharmacology ; HL-60 Cells ; Humans ; K562 Cells ; Organoselenium Compounds ; pharmacology ; Proto-Oncogene Proteins c-bcl-2 ; physiology ; Thioredoxin-Disulfide Reductase ; antagonists & inhibitors ; bcl-2-Associated X Protein ; physiology