Inhibition of STAT3 by Anticancer Drug Bendamustine

An Insight into the Structure-activity Relationship of Benzimidazole and Pyrazole Derivatives as Anticancer Agents

INTRODUCTION

Cancer is a leading cause of death worldwide, driving the urgent need for new and effective treatments. Benzimidazole and pyrazole derivatives have gained attention for their potential as anticancer agents due to their diverse biological activities. The development of resistance in cancer cells, toxicity concerns, and inconsistent efficacy across different types of cancer are a few of the challenges. To overcome these challenges, optimisation of these nuclei using the structure-activity relationships is necessary.

OBJECTIVES

This review aimed to examine various benzimidazole, pyrazole, and their hybrid derivatives by focusing on their structure-activity relationships (SAR) as anticancer agents. Results of the most potent and least potent benzimidazole, pyrazole compounds, and their hybrid derivatives published by researchers were compiled.

METHODS

The findings of different researchers working on benzimidazole and pyrazole nuclei were reviewed and analysed for different targets and cell lines. Moreover, substitutions on different positions of pyrazole, benzimidazole, and their hybrid were summarised to derive an optimised pharmacophore.

RESULTS

Based on our analysis of existing studies, we anticipate that this review will guide researchers in creating potent pyrazole, benzimidazole, and hybrid derivatives crucial for combating cancer effectively.

CONCLUSION

Structure-Activity Relationship (SAR) studies can help in developing pyrazolebenzimidazole hybrids that are more powerful and selective in targeting specific aspects of cancer.

The potential efficacy and mechanism of bendamustine in entra-nodal NK/T cell lymphoma

Bendamustine has been shown to have anti-tumor activities in hematological malignancies, but the role of bendamustine in natural killer (NK)/T cell lymphoma (NKTCL) treatment is unclear. Our study has shown that bendamustine had potent growth-inhibitory and apoptosis-inducing effects on NKTCL cells. Interestingly, we noticed that the combination of either gemcitabine or etoposide results in additive or synergistic cytotoxicity. Bendamustine induced mitochondria-mediated apoptosis in concentration- and time-dependent manners in NKTCL cells, shown as down-regulation of Bcl-2 and activation of cleavage of caspases 3, 7, 9 and poly adenosinediphosphate-ribose polymerase (PARP). Bendamustine arrested NKTCL cells in G2/M phase, with downregulation of expression of cyclin B1 and upregulation of expression of p-cdc2, p-cdc25c and p-P53. Furthermore, we confirmed that bendamustine activated DNA damage response (DDR) directly or through Ataxia Telangiectasia Mutated Protein (ATM)/Chk2 and ATR/Chk1 pathway and increased the intracellular reactive oxygen species (ROS) level in NKTCL cells, which caused G2/M phase arrest and apoptosis. Bendamustine also inhibited phosphorylation of transcriptional factor STAT3, contributing to cell apoptosis and proliferation inhibition. Finally, we verified the effect of bendamustine on NKTCL cells in vivo. It showed that bendamustine dramatically inhibited the growth of the subcutaneous tumor, with no obvious impact on mice weight. These findings demonstrate that bendamustine activates DDR pathway, induces the accumulation of intracellularROS level as well as inhibition of STAT3, leading to cell apoptosis and G2/M cell cycle arrest in NKTCL cells, which indicates that bendamustine dramatically suppressed NKTCL both in vitro and in vivo and provides a potential therapeutic strategy in the treatment of NK/T lymphoma.

Recent Update on Development of Small-Molecule STAT3 Inhibitors for Cancer Therapy: From Phosphorylation Inhibition to Protein Degradation

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various biological processes, including proliferation, metastasis, angiogenesis, immune response, and chemoresistance. In normal cells, STAT3 is tightly regulated to maintain a transiently active state, while persistent STAT3 activation occurs frequently in cancers, associating with a poor prognosis and tumor progression. Targeting the STAT3 protein is a potentially promising therapeutic strategy for tumors. Although none of the STAT3 inhibitors has been marketed yet, a few of them have succeeded in entering clinical trials. This Review aims to systematically summarize the progress of the last 5 years in the discovery of directive STAT3 small-molecule inhibitors and degraders, focusing primarily on their structural features, design strategies, and bioactivities. We hope this Review will shed light on future drug design and inhibitor optimization to accelerate the discovery process of STAT3 inhibitors or degraders.

Regulatory Dendritic Cells Induced by Bendamustine Are Associated With Enhanced Flt3 Expression and Alloreactive T-Cell Death

The growth factor Flt3 ligand (Flt3L) is central to dendritic cell (DC) homeostasis and development, controlling survival and expansion by binding to Flt3 receptor tyrosine kinase on the surface of DCs. In the context of hematopoietic cell transplantation, Flt3L has been found to suppress graft-versus-host disease (GvHD), specifically via host DCs. We previously reported that the pre-transplant conditioning regimen consisting of bendamustine (BEN) and total body irradiation (TBI) results in significantly reduced GvHD compared to cyclophosphamide (CY)+TBI. Pre-transplant BEN+TBI conditioning was also associated with greater Flt3 expression among host DCs and an accumulation of pre-cDC1s. Here, we demonstrate that exposure to BEN increases Flt3 expression on both murine bone marrow-derived DCs (BMDCs) and human monocyte-derived DCs (moDCs). BEN favors development of murine plasmacytoid DCs, pre-cDC1s, and cDC2s. While humans do not have an identifiable equivalent to murine pre-cDC1s, exposure to BEN resulted in decreased plasmacytoid DCs and increased cDC2s. BEN exposure and heightened Flt3 signaling are associated with a distinct regulatory phenotype, with increased PD-L1 expression and decreased ICOS-L expression. BMDCs exposed to BEN exhibit diminished pro-inflammatory cytokine response to LPS and induce robust proliferation of alloreactive T-cells. These proliferative alloreactive T-cells expressed greater levels of PD-1 and underwent increased programmed cell death as the concentration of BEN exposure increased. Alloreactive CD4⁺ T-cell death may be attributable to pre-cDC1s and provides a potential mechanism by which BEN+TBI conditioning limits GvHD and yields T-cells tolerant to host antigen.

Immunomodulatory Effects of Bendamustine in Hematopoietic Cell Transplantation

Bendamustine (BEN) is a unique alkylating agent with efficacy against a broad range of hematological malignancies, although investigations have only recently started to delve into its immunomodulatory effects. These immunomodulatory properties of BEN in the context of hematopoietic cell transplantation (HCT) are reviewed here. Pre- and post-transplant use of BEN in multiple murine models have consistently resulted in reduced GvHD and enhanced GvL, with significant changes to key immunological cell populations, including T-cells, myeloid derived suppressor cells (MDSCs), and dendritic cells (DCs). Further, in vitro studies find that BEN enhances the suppressive function of MDSCs, skews DCs toward cDC1s, enhances Flt3 expression on DCs, increases B-cell production of IL-10, inhibits STAT3 activation, and suppresses proliferation of T- and B-cells. Overall, BEN has a broad range of immunomodulatory effects that, as they are further elucidated, may be exploited to improve clinical outcomes. As such, clinical trials are currently underway investigating new potential applications of BEN in the setting of allogeneic HCT.

One-Pot Synthesis of Unsymmetrical Bis-Heterocycles: Benzimidazole-, Benzoxazole-, and Benzothiazole-Linked Thiazolidines

A one-pot, three-component synthesis of benzimidazole-linked thiazolidines from 2-cyanomethyl benzimidazole, iso-, isothio-, or isoselenocyanates and 1,2-dichloroethane is reported. Isolation of the key intermediate formed during the course of the reaction validates its mechanistic pathway. Under the same reaction conditions, benzimidazole-linked/fused thiazinanes were obtained when 1,3-dichloropropane or diiodomethane was used.

The Antipsychotic Agent Sertindole Exhibited Antiproliferative Activities by Inhibiting the STAT3 Signaling Pathway in Human Gastric Cancer Cells

Gastric cancer (GC) is the third leading cause of cancer-related death. Although the therapeutic approaches have improved, the 5-year survival rate of GC patients after surgical resection remains low due to the high rates of metastasis and recurrence. Patients with schizophrenia have significantly lower incidences of cancer after long-term drug treatment, suggesting the potential or partially ameliorate the risk of cancer development of antipsychotic drugs. The goal of this study was to explore antipsychotic drugs with an optional effective therapy against gastric cellular carcinoma. We found that sertindole, an atypical antipsychotic, exhibited anti-tumor efficacy on human GC cells in vitro and in vivo. Moreover, sertindole in combination with cisplatin dramatically enhanced apoptosis-induction in GC cells. In addition, the pro-apoptotic effect of sertindole on GC might in part, involved in inhibition of STAT3 activation and downstream signals, including Mcl1, surviving, c-Myc, cyclin D1. Collectively, these results suggested that sertindole could be a potential anticancer reagent and be an attractive therapeutic adjuvant for the treatment of human GC.

Signal Transducer and Activator of Transcription Protein 3 (STAT3): An Update on its Direct Inhibitors as Promising Anticancer Agents

BACKGROUND

Since Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor which plays an important role in multiple aspects of cancer, including progression and migration, and it is constitutively activated in various human tumors, STAT3 inhibition has emerged as a validated strategy for the treatment of several malignancies. The aim of this review is to provide an update on the identification of new promising direct inhibitors targeting STAT3 domains, as potential anticancer agents.

METHODS

A thorough literature search focused on recently reported STAT3 direct inhibitors was undertaken. We considered the relevant developments regarding the STAT3 domains, which have been identified as potential drug targets.

RESULTS

In detail, 135 peer-reviewed papers and 7 patents were cited; the inhibitors we took into account targeted the DNA binding domain (compounds were grouped into natural derivatives, small molecules, peptides, aptamers and oligonucleotides), the SH2 binding domain (natural, semi-synthetic and synthetic compounds) and specific residues, like cysteines (natural, semi-synthetic, synthetic compounds and dual inhibitors) and tyrosine 705.

CONCLUSION

The huge number of direct STAT3 inhibitors recently identified demonstrates a strong interest in the investigation of this target, although it represents a challenging task considering that no drug targeting this enzyme is currently available for anticancer therapy. Notably, many studies on the available inhibitors evidenced that some of them possess a dual mechanism of action.

A high-throughput fluorescence polarization assay for discovering inhibitors targeting the DNA-binding domain of signal transducer and activator of transcription 3 (STAT3)

Anti-cancer drug discovery efforts to directly inhibit the signal transducer and activator of transcription 3 (STAT3) have been active for over a decade following the discovery that 70% of cancers exhibit elevated STAT3 activity. The majority of research has focused on attenuating STAT3 activity through preventing homo-dimerization by targeting the SH2 or transcriptional activation domains. Such dimerization inhibitors have not yet reached the market. However, an alternative strategy focussed on preventing STAT3 DNA-binding through targeting the DNA-binding domain (DBD) offers new drug design opportunities. Currently, only EMSA and ELISA-based methods have been implemented with suitable reliability to characterize STAT3 DBD inhibitors. Herein, we present a new orthogonal, fluorescence polarization (FP) assay suitable for high-throughput screening of molecules. This assay, using a STAT3^127-688 construct, was developed and optimized to screen molecules that attenuate the STAT3:DNA association with good reliability (Z’ value > 0.6) and a significant contrast (signal-to-noise ratio > 15.0) at equilibrium. The assay system was stable over a 48 hour period. Significantly, the assay is homogeneous and simple to implement for high-throughput screening compared to EMSA and ELISA. Overall, this FP assay offers a new way to identify and characterize novel molecules that inhibit STAT3:DNA association.

Association of Soluble Interleukin-2 Receptor and C-Reactive Protein with the Efficacy of Bendamustine Salvage Treatment for Indolent Lymphomas and Mantle Cell Lymphoma

Bendamustine has demonstrated favourable efficacy in relapsed or refractory indolent lymphoma and mantle cell lymphoma. We retrospectively evaluated the pre-treatment clinical and laboratory factors and their correlation with the clinical outcome of these lymphomas. We analysed 53 patients who had been treated with bendamustine alone (n = 6) or rituximab plus bendamustine (n = 47). The overall response rate was 81.1%, with a complete response (CR) rate of 39.6%. The CR rate was significantly low in patients who had elevated levels of soluble interleukin-2 receptor (p = 0.024) and C-reactive protein (CRP; p = 0.004). The 1-year overall survival (OS) rate was 79.3%. An elevated CRP was associated with a short OS (p = 0.056). The present findings suggest that the lymphoma microenvironment and immune response were involved in the effects of bendamustine. These findings are also important in order to understand the pathophysiology of refractory lymphoma and to find effective strategies using bendamustine.