Thioredxin reductase inhibitor ethaselen increases the drug sensitivity of the colon cancer cell line LoVo towards cisplatin via regulation of G1 phase and reversal of G2/M phase arrest

Novel selenadiazole derivatives as selective antitumor and radical scavenging agents

Twenty-seven novel benzo[c][1,2,5]selenadiazole-5-carboxylic acid (BSCA) derivatives were designed and synthesized. Anti-proliferative activity of these structures was tested in vitro against a panel of five human cancer cell lines, including prostate (PC-3), colon (HT-29), leukemia (CCRF-CEM), lung (HTB-54) and breast (MCF-7). Four compounds (5, 6, 7 and 19) showed potent inhibitory activity with GI₅₀ values below 10 μM in at least one of the cancer cell lines. The selectivity of these compounds was further examined in two non-malignant cell lines derived from breast (184B5) and lung (BEAS-2B). Compound 7 exhibited promising anti-proliferative activity (GI₅₀ = 3.7 μM) in MCF-7 cells, together with high selectivity index (SI > 27.1). The induction of cell death by compound 7 was independent of the apoptotic process and it did not affect cell cycle progression either. Likewise, radical scavenging properties of the new selenadiazole derivatives were confirmed by testing their ability to scavenge DPPH radicals. Four compounds (1, 2, 8 and 9) showed potent radical scavenging activity, compound 9 being the most effective. Overall, while compound 7 was identified as the most cell growth inhibitory agent and selectively toxic to cancer cells, compound 9 proved to be the most potent antioxidant among the selenadiazole derivatives synthesized. This series of compounds can serve as an excellent scaffold to achieve new and potent antioxidant compounds useful for several diseases, i.e. cancer, neurodegenerative, heart diseases and leishmaniasis, considering the high radical scavenging activity and low toxicity showed by most of the compounds.

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 K_in with the linear correction factor γ1 (0.021 d/mm). The drug binding-inhibition effects on K_out was described using a sigmoidal E_max model with S_max (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 E_max model with an E_max (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.

Role of thioredoxin reductase 1 in dysplastic transformation of human breast epithelial cells triggered by chronic oxidative stress

Thioredoxin reductase 1 (TrxR1) is a pivotal intracellular redox sensor and antioxidant enzyme. On the other hand, overexpression of TrxR1 is closely correlated with the initiation of various tumors including breast cancer, though the detailed mechanism remains unclear. Here we investigated the role of TrxR1 in dysplastic transformation of human breast epithelial cell line MCF-10A induced by chronic oxidative stress. Not surprisingly, sustained exposure to H₂O₂ significantly augmented the expression and activity of TrxR1 in MCF-10A cells. The dysplastically transformed MCF-10A (MCF-10AT) cells undergoing 8-week H₂O₂ treatment exhibited a certain degree of malignancy in tumorigenicity evaluation. Moreover, TrxR1 inhibitor ethaselen (BBSKE) could partially reverse some malignant phenotypes including epithelial to mesenchymal transition (EMT) of MCF-10AT as well as MCF-7 cells. Collectively, our results supported the considerable involvement of TrxR1 in the onset of breast cancer and BBSKE may be a promising agent against breast cancer.

Auranofin induces mesothelioma cell death through oxidative stress and GSH depletion

Mesothelioma is an aggressive tumor associated with asbestos exposure. Auranofin as an inhibitor of thioredoxin reductase (TrxR) affects many biological processes such as inflammation and proliferation. In the present study, we investigated the cellular effects of auranofin on patient-derived mesothelioma cells in relation to reactive oxygen species (ROS) and glutathione (GSH) levels. Basal TrxR1 levels have no difference between mesothelial cells and certain mesothelioma cells. In particular, ADA, CON and Hmeso mesothelioma cells showed lower levels of TrxR1 expression. Auranofin inhibited the proliferation of mesothelioma cells in a dose-dependent manner. Among mesothelioma cells were ADA and CON cells sensitive to auranofin. This agent also induced caspase-independent apoptosis and necrosis in ADA cells. In addition, auranofin increased ROS levels including O2(•-) and induced GSH depletion in mesothelioma cells. While N-acetyl cysteine (NAC) prevented cell death and decreased ROS levels in auranofin-treated mesothelioma cells, L-buthionine sulfoximine (BSO) intensified apoptosis and GSH depletion in these cells. In conclusion, auranofin induced mesothelioma cell death through oxidative stress and the death was regulated by the status of GSH content.

Andrographolide sensitizes the cytotoxicity of human colorectal carcinoma cells toward cisplatin via enhancing apoptosis pathways in vitro and in vivo

Andrographolide (Andro), a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, has been shown to suppress the growth and invasion of human colorectal carcinoma (CRC) Lovo cells, and trigger apoptosis in vitro. The potential of Andro as a chemotherapeutic agent in CRC was evaluated by investigating its cytotoxic effects as a single agent or in coadministration with cisplatin (CDDP). Andro potentiated the cytotoxic effect of CDDP in Lovo cells through apoptosis. The molecular mechanism for these favorable cellular response was further investigated by analyzing the apoptotic profiles, protein levels, and mRNA expression patterns of several key genes after treatments of Andro or/and CDDP. Molecular results indicated that the effect of Andro alone might be mediated via both intrinsic and extrinsic apoptotic pathways in Lovo cells. The addition of Andro to CDDP induced synergistic apoptosis, which could be corroborated to the changes in protein and mRNA levels of Bax and Bcl-2, and the increased Fas/FasL association in these cells, resulting in increased release of cytochrome c, and activation of caspases. Pretreatment of Nok-1 monoclonal antibody, a Fas signaling inhibitor, or Bax inhibitor peptide V5 repressed the Andro-induced cleavage of procaspase and the sensitization to CDDP-induced apoptosis. Finally, the combination therapy of Andro with CDDP was evidenced by its synergistic inhibition on the growth of Lovo cells in xenograft tumor studies. The results indicate that Andro, in combination with chemotherapeutics, is likely to represent a potential therapeutic strategy for CRC.

Flavins and flavoproteins: applications in medicine

The potential of flavoproteins as targets of pharmacological treatments is immense. In this review we present an overview of the current research progress on medical interventions based on flavoproteins with a special emphasis on cancer, infectious diseases, and neurological disorders.

Ethaselen: a potent mammalian thioredoxin reductase 1 inhibitor and novel organoselenium anticancer agent

Mammalian thioredoxin reductase 1 (TrxR1) is considered to be an important anticancer drug target and to be involved in both carcinogenesis and cancer progression. Here, we report that ethaselen, a novel organoselenium compound with anticancer activity, specifically binds to the unique selenocysteine-cysteine redox pair in the C-terminal active site of mammalian TrxR1. Ethaselen was found to be a potent inhibitor rather than an efficient substrate of mammalian TrxR1. It effectively inhibits wild-type mammalian TrxR1 at submicromolar concentrations with an initial mixed-type inhibition pattern. By using recombinant human TrxR1 variants and human glutathione reductase, we prove that ethaselen specifically targets the C-terminal but not the N-terminal active site of mammalian TrxR1. In A549 human lung cancer cells, ethaselen significantly suppresses cell viability in parallel with direct inhibition of TrxR1 activity. It does not, however, alter either the disulfide-reduction capability of thioredoxin or the activity of glutathione reductase. As a downstream effect of TrxR1 inactivation, ethaselen causes a dose-dependent thioredoxin oxidation and enhances the levels of cellular reactive oxygen species in A549 cells. Thus, we propose ethaselen as the first selenium-containing inhibitor of mammalian TrxR1 and provide evidence that selenium compounds can act as anticancer agents based on mammalian TrxR1 inhibition.

A phase I trial of PX-12, a small-molecule inhibitor of thioredoxin-1, administered as a 72-hour infusion every 21 days in patients with advanced cancers refractory to standard therapy

PURPOSE

This phase I trial assessed the safety, dose limiting toxicity (DLT) and pharmacodynamics of PX-12 in adult patients with advanced refractory cancers.

METHODS

PX-12 was administered to sequential cohorts as a 72-h infusion utilizing a portable infusion pump on days 1, 2, and 3 of a 21-day cycle at a starting dose level of 300 mg/m(2)/day and escalating dose levels till DLT was observed. Plasma thioredoxin (Trx-1), vascular endothelial growth factor (VEGF) and FGF-2 (fibroblast growth factor) levels were measured predose and during infusion of PX-12.

RESULTS

Patients (n = 14) were enrolled to the following dose cohorts, 300 mg/m(2) (n = 3), 400 mg/m(2) (n = 10) and 500 mg/m(2) (n = 1). Common grade 1/2 toxicities included fatigue, taste alteration and odor caused by expired drug metabolite. DLTs were one episode each of grade 3 hypoxia at the 400 mg/m(2) and grade 3 reversible pneumonitis at the 500 mg/m(2) dose levels. Best response was stable disease in a patient with rectal cancer. Predose Trx-1 levels (n = 12) ranged from 5.1 to 30.0 ng/mL (median 12.6 ng/mL).

CONCLUSION

PX-12 administered at 400 mg/m(2)/day by 72-hour infusion appears safe and tolerable. Inhibition of thioredoxin is a strategy worth evaluation with next generation of inhibitors.

A randomized phase II study of PX-12, an inhibitor of thioredoxin in patients with advanced cancer of the pancreas following progression after a gemcitabine-containing combination

PURPOSE

This study evaluated PX-12, a novel small molecule inhibitor of the proto-oncogene (Trx-1), in patients with previously treated advanced pancreatic cancer (APC).

METHODS

PX-12 (54 or 128 mg/m²) was administered by 3-hour IV infusion daily × 5 days every 21 days (n = 17). Patients were randomized to either 54 or 128 mg/m² and then stratified based on CA 19-9 level (≥ 1,000 vs. < 1,000 U/ml) and SUV values on PET scans (≥ 7.0 vs. <7.0). The primary endpoint was based on a progression-free survival (PFS) at 4 months in ≥ 40% of patients, and required 40 patients in each arm. An amendment required elevated Trx-1 levels (> 18 ng/ml) as an entry criteria after the first 17 patients were accrued.

RESULTS

Plasma Trx-1 levels were elevated in 3/28 (11%) patients screened for study. The grade of the expired metabolite odor was higher in the 128 mg/m² arm. Therapy was well tolerated, and Grade ≥ 3 adverse events were uncommon. The best response was stable disease in 2 patients. There was no consistent decrease in SUV, Trx-1 levels or CA 19-9 levels with therapy. No patients had a PFS of >4 months. Median PFS and survival were 0.9 months (95% CI 0.5-1.2) and 3.2 months (95% CI 2.4-4.2), respectively.

CONCLUSIONS

Due to the lack of significant antitumor activity and unexpectedly low baseline Trx-1 levels, the study was terminated early. PX-12 does not appear to be active in unselected patients with previously treated APC.