Novel thioredoxin reductase inhibitor butaselen inhibits tumorigenesis by down-regulating programmed death-ligand 1 expression.

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.

Ethaselen: a novel organoselenium anticancer agent targeting thioredoxin reductase 1 reverses cisplatin resistance in drug-resistant K562 cells by inducing apoptosis.

It has been reported that Ethaselen shows inhibitory effects on thioredoxin reductase (TrxR) activity and human tumor cell growth. In order to find an efficient way to reverse cisplatin resistance, we investigated the reversal effects of Ethaselen on cisplatin resistance in K562/cisplatin (CDDP) cells that were established by pulse-inducing human erythrocyte leukemic cell line K562, which are fivefold more resistant to cisplatin compared to K562 cells. The morphology and growth showed that the adhesion of K562/CDDP further decreased while the cell volume increased. The proliferation of K562/CDDP is strengthened. The antitumor activities in vitro were assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and combination index (CI), showing the significant synergic effects of cisplatin and Ethaselen. Focusing on apoptosis, a series of comparisons was made between K562 and K562/CDDP. Cisplatin induced higher reactive oxygen species (ROS) generation in K562 and subsequently induced the formation of mitochondrial permeability transition pores (PTPs). In addition, cisplatin increased the ratio of Bax to Bcl-2 in K562, which can influence the mitochondrial membrane permeability. PTP formation and mitochondrial membrane permeabilization eventually resulted in the release of cytochrome c and activation of the Caspase pathway. However, these effects were not clearly seen in K562/CDDP, which may be the reason for the acquired CDDP resistance. However, Ethaselen can induce a high level of ROS in K562/CDDP by TrxR activity inhibition and increased ratio of Bax to Bcl-2 in K562/CDDP by nuclear factor κB (NF-κB) suppression, which subsequently induces the release of cytochrome c in K562/CDDP. This response is partly responsible for the reversal of the cisplatin resistance in K562/CDDP cells.

Dose-biomarker-response modeling of the anticancer effect of ethaselen in a human non-small cell lung cancer xenograft mouse model.

Thioredoxin reductase (TrxR) is a component of several redox-sensitive signaling cascades that mediate important biological processes such as cell survival, maturation, growth, migration and inhibition of apoptosis. The expression levels of TrxR1 in some human carcinoma cell lines are nearly 10 times higher than those in normal cells. Ethaselen is a novel antitumor candidate that exerts potent inhibition on non-small cell lung cancer (NSCLC) by targeting TrxR. In this study we explored the relationship between the ethaselen dose and TrxR activity level and the relationship between TrxR degradation and tumor apoptosis in a human lung carcinoma A549 xenograft model. BALB/c nude mice implanted with human NSCLC cell line A54 were administered ethaselen (36, 72, 108 mg·kg-1·d-1, ig) or vehicle for 10 d. The tumor size and TrxR activity levels in tumor tissues were daily recorded and detected. Based on the experimental data, NONMEM 7.2 was used to develop an integrated dose-biomarker-response model for describing the quantitative relationship between ethaselen dose and tumor eradication effects. The time course of TrxR activity levels was modeled using an indirect response model (IDR model), in which the influence of the tumor growth rates on Kin with the linear correction factor γ1 (0.021 d/mm). The drug binding-inhibition effects on Kout was described using a sigmoidal Emax model with Smax (5.95), SC50 (136 mg/kg) and Hill's coefficient γ2 (2.29). The influence of TrxR activity inhibition on tumor eradication was characterized by an Emax model with an Emax (130 mm3/d) and EC50 (0.0676). This model was further validated using a visual predictive check (VPC) and was used to predict the efficacy of different doses. In conclusion, the properties and characteristics of ethaselen acting on TrxR degradation and subsequently resulting in tumor apoptosis are characterized by the IDR model and integrated dose-biomarker-response model with high goodness-of-fit and great predicative ability. This approach shed new light on the detailed processes and mechanism of ethaselen action and may offer a valuable reference for an appropriate dosing regimen for use in further clinical applications.