Drugging the "undruggable" DNA-binding domain of STAT3

Advances in RNA therapeutics for modulation of 'undruggable' targets

Over the past decades, drug discovery utilizing small pharmacological compounds, fragment-based therapeutics, and antibody therapy have significantly advanced treatment options for many human diseases. However, a major bottleneck has been that>70% of human proteins/genomic regions are 'undruggable' by the above-mentioned approaches. Many of these proteins constitute essential drug targets against complex multifactorial diseases like cancer, immunological disorders, and neurological diseases. Therefore, alternative approaches are required to target these proteins or genomic regions in human cells. RNA therapeutics is a promising approach for many of the traditionally 'undruggable' targets by utilizing methods such as antisense oligonucleotides, RNA interference, CRISPR/Cas-based genome editing, aptamers, and the development of mRNA therapeutics. In the following chapter, we will put emphasis on recent advancements utilizing these approaches against challenging drug targets, such as intranuclear proteins, intrinsically disordered proteins, untranslated genomic regions, and targets expressed in inaccessible tissues.

Artificial Base-Directed In Vivo Assembly of an Albumin-siRNA Complex for Tumor-Targeting Delivery

RNA interference (RNAi) mediated by short interfering RNA (siRNA) is a promising method for cancer treatment, but the clinical application is hampered by several limitations, including metabolic instability, lack of tumor specificity, and poor cellular uptake. To meet these challenges, we have explored the possibility of structure modification of siRNA with artificial bases for property optimization. A series of siRNAs functionalized with different numbers of hydrophobic base F are prepared for screening. The interactions of plasma proteins with F-base-modified siRNA (F-siRNA) are investigated, and it is identified that the interaction with serum albumin is dominant. Experiments revealed that the introduction of F bases conferred modified siRNA with improved tumor-specific accumulation, prolonged circulatory retention time, and better tissue permeability. Mechanistic studies indicated that the F base induces the formulation of a stable siRNA-albumin complex, which transports siRNA to tumor tissues selectively owing to an enhanced permeability and retention (EPR) effect of albumin. The F base also facilitates the binding of siRNA to transport-associated proteins on the cell membrane, enabling its cellular internalization. Together, these data demonstrate that F base modification confers siRNA-enhanced cellular uptake and biostability and specific accumulation in tumor tissue, which provides a new approach for the development of siRNA-based cancer therapeutics.

The multifaceted role of STAT3 pathway and its implication as a potential therapeutic target in oral cancer

Oral cancer is one of the leading causes of cancer-related deaths, and it has become a matter of serious concern due to the alarming rise in its incidence rate worldwide. Despite recent advancements in oral cancer treatment strategies, there are no significant improvements in patient's survival rate. Among the numerous cell signaling pathways involved in oral cancer development and progression, STAT3 is known to play a multifaceted oncogenic role in shaping the tumor pathophysiology. STAT3 hyperactivation in oral cancer contributes to survival, proliferation, invasion, epithelial to mesenchymal transition, metastasis, immunosuppression, chemoresistance, and poor prognosis. A plethora of pre-clinical and clinical studies have documented the role of STAT3 in the initiation and development of oral cancer and showed that STAT3 inhibition holds significant potential in the prevention and treatment of this cancer. However, to date, targeting STAT3 activation mainly involves inhibiting the upstream signaling molecules such as JAK and IL-6 receptors. The major challenge in targeting STAT3 lies in the complexity of its phosphorylation- and dimerization-independent functions, which are not affected by disrupting the upstream regulators. The present review delineates the significance of the STAT3 pathway in regulating various hallmarks of oral cancer. In addition, it highlights the STAT3 inhibitors identified to date through various preclinical and clinical studies that can be employed for the therapeutic intervention in oral cancer treatment.

AI-Based Protein Structure Prediction in Drug Discovery: Impacts and Challenges

Proteins are the molecular machinery of the human body, and their malfunctioning is often responsible for diseases, making them crucial targets for drug discovery. The three-dimensional structure of a protein determines its biological function, its conformational state determines substrates, cofactors, and protein binding. Rational drug discovery employs engineered small molecules to selectively interact with proteins to modulate their function. To selectively target a protein and to design small molecules, knowing the protein structure with all its specific conformation is critical. Unfortunately, for a large number of proteins relevant for drug discovery, the three-dimensional structure has not yet been experimentally solved. Therefore, accurately predicting their structure based on their amino acid sequence is one of the grant challenges in biology. Recently, AlphaFold2, a machine learning application based on a deep neural network, was able to predict unknown structures of proteins with an unprecedented accuracy. Despite the impressive progress made by AlphaFold2, nature still challenges the field of structure prediction. In this Perspective, we explore how AlphaFold2 and related methods help make drug design more efficient. Furthermore, we discuss the roles of predicting domain-domain orientations, all relevant conformational states, the influence of posttranslational modifications, and conformational changes due to protein binding partners. We highlight where further improvements are needed for advanced machine learning methods to be successfully and frequently used in the pharmaceutical industry.

The IL6-like Cytokine Family: Role and Biomarker Potential in Breast Cancer

IL6-like cytokines are a family of regulators with a complex, pleiotropic role in both the healthy organism, where they regulate immunity and homeostasis, and in different diseases, including cancer. Here we summarise how these cytokines exert their effect through the shared signal transducer IL6ST (gp130) and we review the extensive evidence on the role that different members of this family play in breast cancer. Additionally, we discuss how the different cytokines, their related receptors and downstream effectors, as well as specific polymorphisms in these molecules, can serve as predictive or prognostic biomarkers with the potential for clinical application in breast cancer. Lastly, we also discuss how our increasing understanding of this complex signalling axis presents promising opportunities for the development or repurposing of therapeutic strategies against cancer and, specifically, breast neoplasms.

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.

Targeting STAT3 signaling in kidney disease

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway is a multifaceted transduction system that regulates cellular responses to incoming signaling ligands. STAT3 is a central member of the JAK/STAT signaling cascade and has long been recognized for its increased transcriptional activity in cancers and autoimmune disorders but has only recently been in the spotlight for its role in the progression of kidney disease. Although genetic knockout and manipulation studies have demonstrated the salutary benefits of inhibiting STAT3 activity in several kidney disease models, pharmacological inhibition has yet to make it to the clinical forefront. In recent years, significant effort has been aimed at suppressing STAT3 activation for treatment of cancers, which has led to the development of a wide variety of STAT3 inhibitors, but only a handful have been tested in kidney disease models. Here, we review the detrimental role of dysregulated STAT3 activation in a variety of kidney diseases and the current progress in the treatment of kidney diseases with pharmacological inhibition of STAT3 activity.

ATAD2 in cancer: a pharmacologically challenging but tractable target

INTRODUCTION

ATAD2 protein is an emerging oncogene that has strongly been linked to the etiology of multiple advanced human cancers. Therapeutically, despite the fact that genetic suppression/knockdown studies have validated it as a compelling drug target for future therapeutic development, recent druggability assessment data suggest that direct targeting of ATAD2's bromodomain (BRD) may be a very challenging task. ATAD2's BRD has been predicted as a 'difficult to drug' or 'least druggable' target due to the concern that its binding pocket, and the areas around it, seem to be unfeasible for ligand binding. Areas covered: In this review, after shedding light on the multifaceted roles of ATAD2 in normal physiology as well as in cancer-etiology, we discuss technical challenges rendered by ATAD2's BRD active site and the recent drug discovery efforts to find small molecule inhibitors against it. Expert opinion: The identification of a novel low-nanomolar semi-permeable chemical probe against ATAD2's BRD by recent drug discovery campaign has demonstrated it to be a pharmacologically tractable target. Nevertheless, the development of high quality bioavailable inhibitors against ATAD2 is still a pending task. Moreover, ATAD2 may also potentially be utilized as a promising target for future development of RNAi-based therapy to treat cancers.