Recent update on discovery and development of Hsp90 inhibitors as senolytic agents

Senotherapy, cancer, and aging

INTRODUCTION

We aimed to highlight the effects of senotherapy on the prevention and treatment of cancer in older individuals. The aim of senotherapy is to eliminate senescent cells. These cells express the senescence-associated secretory phenotype (SASP). With production of inflammatory cytokines, growth factors, and different type of proteases, the SASP is responsible for aging-associated disability and diseases. All mammalian cells experience senescence. The main agents of aging include fibroblasts and adipose cells. Senescent tumor cells may undergo genomic reprogramming and re-enter cell cycle with a stem cell phenotype.

MATERIALS AND METHODS

We conducted a Medline search for the following key words: senotherapy, senolysis, senomorphic agents. We provide a narrative review of the finding.

RESULTS

Different agents may eliminate senescent cells from cell cultures and murine models. These include metformin, rapamycin, desatinib, quercitin, fisetin, ruloxitinib, and BCL2 inhibitors. A randomized controlled study of metformin in 3,000 patients aged 65-79 without glucose intolerance aiming to establish whether senotherapy may prevent or reverse disability and aging associated diseases, including cancer, is ongoing. Senotherapy prolongs the life span and decreases the incidence of cancer in experimental animal models, as well as delays and reverses disability. Senescent tumor cells are found prior to treatment and after chemotherapy and radiation. These elements may be responsible for tumor recurrence and treatment refractoriness.

DISCUSSION

Senotherapy may have substantial effects on cancer management including decreased incidence and aggressiveness of cancer, improved tolerance of antineoplastic treatment, and prevention of relapse after primary treatment. Senotherapy may ameliorate several complications of cancer chemotherapy.

Emerging roles of senolytics/senomorphics in HIV-related co-morbidities

Human immunodeficiency virus (HIV) is known to cause cellular senescence and inflammation among infected individuals. While the traditional antiretroviral therapies (ART) have allowed the once fatal infection to be managed effectively, the quality of life of HIV patients on prolonged ART use is still inferior. Most of these individuals suffer from life-threatening comorbidities like chronic obstructive pulmonary disease (COPD), pulmonary arterial hypertension (PAH), and diabetes, to name a few. Interestingly, cellular senescence is known to play a critical role in the pathophysiology of these comorbidities as well. It is therefore important to understand the role of cellular senescence in the disease progression and co-morbidity development in HIV-infected individuals. In this respect, use of senolytic/senomorphic drugs as combination therapy with ART would be beneficial for HIV patients. This review provides a critical analysis of the current literature to determine the potential and efficacy of using senolytics/senotherapeutics in managing HIV infection, latency, and associated co-morbidities in humans. The various classes of senolytics have been studied in detail to focus on their potential to combat against HIV infections and associated pathologies with advancing age.

Intervention treatment reducing cellular senescence inhibits tubulointerstitial fibrosis in diabetic mice following acute kidney injury

Senescence of kidney tubules leads to tubulointerstitial fibrosis (TIF). Proximal tubular epithelial cells undergo stress-induced senescence during diabetes and episodes of acute kidney injury (AKI), and combining these injuries promotes the progression of diabetic kidney disease (DKD). Since TIF is crucial to progression of DKD, we examined the therapeutic potential of targeting senescence with a senolytic drug (HSP90 inhibitor) and/or a senostatic drug (ASK1 inhibitor) in a model of TIF in which AKI is superimposed on diabetes. After 8 weeks of streptozotocin-induced diabetes, mice underwent bilateral clamping of renal pedicles to induce mild AKI, followed by 28 days of reperfusion. Groups of mice (n=10-12) received either vehicle, HSP90 inhibitor (alvespimycin), ASK1 inhibitor (GS-444217), or both treatments. Vehicle-treated mice displayed tubular injury at day 3 and extensive tubular cell senescence at day 10, which remained unresolved at day 28. Markers of senescence (Cdkn1a and Cdkn2a), inflammation (Cd68, Tnf, and Ccl2), and TIF (Col1a1, Col4a3, α-Sma/Acta2, and Tgfb1) were elevated at day 28, coinciding with renal function impairment. Treatment with alvespimycin alone reduced kidney senescence and levels of Col1a1, Acta2, Tgfb1, and Cd68; however, further treatment with GS-444217 also reduced Col4a3, Tnf, Ccl2, and renal function impairment. Senolytic therapy can inhibit TIF during DKD, but its effectiveness can be improved by follow-up treatment with a senostatic inhibitor, which has important implications for treating progressive DKD.

Mechanisms and therapeutic strategies for senescence-associated secretory phenotype in the intervertebral disc degeneration microenvironment

As a permanent state of cell cycle arrest, cellular senescence has become an important factor in aging and age-related diseases. As a central regulator of physiology and pathology associated with cellular senescence, the senescence associated secretory phenotype can create an inflammatory and catabolic environment through autocrine and paracrine ways, ultimately affecting tissue microstructure. As an age-related disease, the correlation between intervertebral disc degeneration and cellular senescence has been confirmed by many studies. Various pathological factors in the microenvironment of intervertebral disc degeneration promote senescent cells to produce and accumulate and express excessive senescence associated secretory phenotype. In this case, senescence associated secretory phenotype has received considerable attention as a potential target for delaying or treating disc degeneration. Therefore, we reviewed the latest research progress of senescence associated secretory phenotype, related regulatory mechanisms and intervertebral disc cell senescence treatment strategies. It is expected that further understanding of the underlying mechanism between cellular senescence pathology and intervertebral disc degeneration will help to formulate reasonable senescence regulation strategies, so as to achieve ideal therapeutic effects.

The translational potential of this article

Existing treatment strategies often fall short in addressing the challenge of repairing intervertebral disc Intervertebral disc degeneration（IVD） degeneration. The accumulation of senescent cells and the continuous release of senescence-associated secretory phenotype (SASP) perpetually impede disc homeostasis and hinder tissue regeneration. This impairment in repair capability presents a significant obstacle to the practical clinical implementation of strategies for intervertebral disc degeneration. As a result, we present a comprehensive overview of the latest advancements in research, the associated regulatory mechanisms, and strategies for treating SASP in IVD cells. This article aims to investigate effective interventions for delaying the onset and progression of age-related intervertebral disc degeneration. In an era where the aging population is becoming increasingly prominent, this endeavor holds paramount practical and translational significance.

Heat shock protein 90: biological functions, diseases, and therapeutic targets

Heat shock protein 90 (Hsp90) is a predominant member among Heat shock proteins (HSPs), playing a central role in cellular protection and maintenance by aiding in the folding, stabilization, and modification of diverse protein substrates. It collaborates with various co-chaperones to manage ATPase-driven conformational changes in its dimer during client protein processing. Hsp90 is critical in cellular function, supporting the proper operation of numerous proteins, many of which are linked to diseases such as cancer, Alzheimer's, neurodegenerative conditions, and infectious diseases. Recognizing the significance of these client proteins across diverse diseases, there is a growing interest in targeting Hsp90 and its co-chaperones for potential therapeutic strategies. This review described biological background of HSPs and the structural characteristics of HSP90. Additionally, it discusses the regulatory role of heat shock factor-1 (HSF-1) in modulating HSP90 and sheds light on the dynamic chaperone cycle of HSP90. Furthermore, the review discusses the specific contributions of HSP90 in various disease contexts, especially in cancer. It also summarizes HSP90 inhibitors for cancer treatment, offering a thoughtful analysis of their strengths and limitations. These advancements in research expand our understanding of HSP90 and open up new avenues for considering HSP90 as a promising target for therapeutic intervention in a range of diseases.

Rational design of peptide inhibitors targeting HSP90-CDC37 protein-protein interaction

Background: Specifically blocking HSP90-CDC37 interaction is emerging as a prospective strategy for cancer therapy. Aim: Applying a kinase pseudopeptide rationale to the discovery of HSP90-CDC37 protein-protein interaction (PPI) inhibitors. Methods: Pseudosubstrates were identified through sequence alignment and evaluated by biolayer interferometry assay, co-immunoprecipitation assay and antiproliferation assay. Results: TAT-DDO-59120 was identified to disrupt HSP90-CDC37 PPI through directly binding to HSP90, both extracellularly and intracellularly. In addition, the identified peptide showed ideal antiproliferative activity against the colorectal cancer cell HCT116 (IC50 = 12.82 μM). Conclusion: Compared with the traditional method of screening a large compound library to identify PPI inhibitors, this method is rapid and efficient with strong purpose, which provides a novel strategy for designing HSP90-CDC37 PPI inhibitors.

The Cross Talk between Cellular Senescence and Melanoma: From Molecular Pathogenesis to Target Therapies

Melanoma is a malignant skin tumor that originates from melanocytes. The pathogenesis of melanoma involves a complex interaction that occurs between environmental factors, ultraviolet (UV)-light damage, and genetic alterations. UV light is the primary driver of the skin aging process and development of melanoma, which can induce reactive oxygen species (ROS) production and the presence of DNA damage in the cells, and results in cell senescence. As cellular senescence plays an important role in the relationship that exists between the skin aging process and the development of melanoma, the present study provides insight into the literature concerning the topic at present and discusses the relationship between skin aging and melanoma, including the mechanisms of cellular senescence that drive melanoma progression, the microenvironment in relation to skin aging and melanoma factors, and the therapeutics concerning melanoma. This review focuses on defining the role of cellular senescence in the process of melanoma carcinogenesis and discusses the targeting of senescent cells through therapeutic approaches, highlighting the areas that require more extensive research in the field.

Heat-Shock Proteins

Heat-shock proteins (HSPs), or stress proteins, are abundant and highly conserved, present in all organisms and in all cells. Selected HSPs, also known as chaperones, play crucial roles in folding and unfolding of proteins, assembly of multiprotein complexes, transport and sorting of proteins into correct subcellular compartments, cell-cycle control and signaling, and protection of cells against stress and apoptosis. More recently, HSPs have been shown to be key players in immune responses: during antigen presentation as well as cross-priming, they chaperone and transfer antigenic peptides to class I and class II molecules of the major histocompatibility complexes. In addition, extracellular HSPs can stimulate and cause maturation of professional antigen-presenting cells of the immune system, such as macrophages and dendritic cells. They also chaperone several toll-like receptors, which play a central role in innate immune responses. HSPs constitute a large family of proteins that are often classified based on their molecular weight as Hsp10, Hsp40, Hsp60, Hsp70, Hsp90, etc. This unit contains a table that lists common HSPs and summarizes their characteristics including (a) name, (b) subcellular localization, (c) known function, (d) chromosome assignment, (e) brief comments, and (f) references. © 2022 Wiley Periodicals LLC.

Heterocyclic Compounds as Hsp90 Inhibitors: A Perspective on Anticancer Applications

Heat shock proteins (Hsps) have garnered special attention in cancer therapy as molecular chaperones with regulatory/mediatory effects on folding, maintenance/stability, maturation, and conformation of proteins as well as their effects on prevention of protein aggregation. Hsp90 ensures the stability of various client proteins needed for the growth of cells or the survival of tumor cells; therefore, they are overexpressed in tumor cells and play key roles in carcinogenesis. Accordingly, Hsp90 inhibitors are recognized as attractive therapeutic agents for investigations pertaining to tumor suppression. Natural Hsp90 inhibitors comprising geldanamycin (GM), reclaimed analogs of GM including 17-AAG and DMAG, and radicicol, a natural macrocyclic antifungal, are among the first potent Hsp90 inhibitors. Herein, recently synthesized heterocyclic compounds recognized as potent Hsp90 inhibitors are reviewed along with the anticancer effects of heterocyclic compounds, comprising purine, pyrazole, triazine, quinolines, coumarin, and isoxazoles molecules.

Extracellular HSP90α promotes cellular senescence by modulating TGF-β signaling in pulmonary fibrosis

Recent findings suggest that extracellular heat shock protein 90α (eHSP90α) promotes pulmonary fibrosis, but the underlying mechanisms are not well understood. Aging, especially cellular senescence, is a critical risk factor for idiopathic pulmonary fibrosis (IPF). Here, we aim to investigate the role of eHSP90α on cellular senescence in IPF. Our results found that eHSP90α was upregulated in bleomycin (BLM)-induced mice, which correlated with the expression of senescence markers. This increase in eHSP90α mediated fibroblast senescence and facilitated mitochondrial dysfunction. eHSP90α activated TGF-β signaling through the phosphorylation of the SMAD complex. The SMAD complex binding to p53 and p21 promoters triggered their transcription. In vivo, the blockade of eHSP90α with 1G6-D7, a specific eHSP90α antibody, in old mice attenuated the BLM-induced lung fibrosis. Our findings elucidate a crucial mechanism underlying eHSP90α-induced cellular senescence, providing a framework for aging-related fibrosis interventions.

Senotherapeutics in Cancer and HIV

Cellular senescence is a stress-response mechanism that contributes to homeostasis maintenance, playing a beneficial role during embryogenesis and in normal adult organisms. In contrast, chronic senescence activation may be responsible for other events such as age-related disorders, HIV and cancer development. Cellular senescence activation can be triggered by different insults. Regardless of the inducer, there are several phenotypes generally shared among senescent cells: cell division arrest, an aberrant shape, increased size, high granularity because of increased numbers of lysosomes and vacuoles, apoptosis resistance, defective metabolism and some chromatin alterations. Senescent cells constitute an important area for research due to their contributions to the pathogenesis of different diseases such as frailty, sarcopenia and aging-related diseases, including cancer and HIV infection, which show an accelerated aging. Hence, a new pharmacological category of treatments called senotherapeutics is under development. This group includes senolytic drugs that selectively attack senescent cells and senostatic drugs that suppress SASP factor delivery, inhibiting senescent cell development. These new drugs can have positive therapeutic effects on aging-related disorders and act in cancer as antitumor drugs, avoiding the undesired effects of senescent cells such as those from SASP. Here, we review senotherapeutics and how they might affect cancer and HIV disease, two very different aging-related diseases, and review some compounds acting as senolytics in clinical trials.

Senolytics: Eliminating Senescent Cells and Alleviating Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the main cause of cervical and lumbar spondylosis. Over the past few years, the relevance between cellular senescence and IVDD has been widely studied, and the senescence-associated secretory phenotype (SASP) produced by senescent cells is found to remodel extracellular matrix (ECM) metabolism and destruct homeostasis. Elimination of senescent cells by senolytics and suppression of SASP production by senomorphics/senostatics are effective strategies to alleviate degenerative diseases including IVDD. Here, we review the involvement of senescence in the process of IVDD; we also discuss the potential of senolytics on eliminating senescent disc cells and alleviating IVDD; finally, we provide a table listing senolytic drugs and small molecules, aiming to propose potential drugs for IVDD therapy in the future.

AHSA1 is a promising therapeutic target for cellular proliferation and proteasome inhibitor resistance in multiple myeloma

BACKGROUND

Currently, multiple myeloma (MM) is still an incurable plasma cell malignancy in urgent need of novel therapeutic targets and drugs.

METHODS

Bufalin was known as a highly toxic but effective anti-cancer compound. We used Bufalin as a probe to screen its potential targets by proteome microarray, in which AHSA1 was the unique target of Bufalin. The effects of AHSA1 on cellular proliferation and drug resistance were determined by MTT, western blot, flow cytometry, immunohistochemistry staining and xenograft model in vivo. The potential mechanisms of Bufalin and KU-177 in AHSA1/HSP90 were verified by co-immunoprecipitation, mass spectrometry, site mutation and microscale thermophoresis assay.

RESULTS

AHSA1 expression was increased in MM samples compared to normal controls, which was significantly associated with MM relapse and poor outcomes. Furthermore, AHSA1 promoted MM cell proliferation and proteasome inhibitor (PI) resistance in vitro and in vivo. Mechanism exploration indicated that AHSA1 acted as a co-chaperone of HSP90A to activate CDK6 and PSMD2, which were key regulators of MM proliferation and PI resistance respectively. Additionally, we identified AHSA1-K137 as the specific binding site of Bufalin on AHSA1, mutation of which decreased the interaction of AHSA1 with HSP90A and suppressed the function of AHSA1 on mediating CDK6 and PSMD2. Intriguingly, we discovered KU-177, an AHSA1 selective inhibitor, and found KU-177 targeting the same site as Bufalin. Bufalin and KU-177 treatments hampered the proliferation of flow MRD-positive cells in both primary MM and recurrent MM patient samples. Moreover, KU-177 abrogated the cellular proliferation and PI resistance induced by elevated AHSA1, and decreased the expression of CDK6 and PSMD2.

CONCLUSIONS

We demonstrate that AHSA1 may serve as a promising therapeutic target for cellular proliferation and proteasome inhibitor resistance in multiple myeloma.

Cellular Senescence: Mechanisms and Therapeutic Potential

Cellular senescence is a complex and multistep biological process which cells can undergo in response to different stresses. Referring to a highly stable cell cycle arrest, cellular senescence can influence a multitude of biological processes-both physiologically and pathologically. While phenotypically diverse, characteristics of senescence include the expression of the senescence-associated secretory phenotype, cell cycle arrest factors, senescence-associated β-galactosidase, morphogenesis, and chromatin remodelling. Persistent senescence is associated with pathologies such as aging, while transient senescence is associated with beneficial programmes, such as limb patterning. With these implications, senescence-based translational studies, namely senotherapy and pro-senescence therapy, are well underway to find the cure to complicated diseases such as cancer and atherosclerosis. Being a subject of major interest only in the recent decades, much remains to be studied, such as regarding the identification of unique biomarkers of senescent cells. This review attempts to provide a comprehensive understanding of the diverse literature on senescence, and discuss the knowledge we have on senescence thus far.

Recent advances in the discovery of senolytics

The demonstration in model organisms that cellular senescence drives aging and age-related diseases has led to widespread efforts to identify compounds able to selectively kill senescent cells, termed senolytics. Approaches used to identify senolytics include bioinformatic analysis of senescent cell anti-apoptotic pathways (SCAPs) for drug development and screening of drugs libraries on different senescent cell types in culture. Alternatively, cytotoxic compounds can be made specific to senescent cells through a prodrug strategy such as linking the compound to a galactose moiety where toxicity is activated by lysosomal β-galactosidase. Identified senolytics can then be optimized through medicinal chemistry or linking to E3 targeting moieties to facilitate proteolysis of their targets. This review will provide an overview of approaches to identify senolytics and an update of the classes of senolytics identified to date.

A Review of Progress in Histone Deacetylase 6 Inhibitors Research: Structural Specificity and Functional Diversity

Histone deacetylases (HDACs) are essential for maintaining homeostasis by catalyzing histone deacetylation. Aberrant expression of HDACs is associated with various human diseases. Although HDAC inhibitors are used as effective chemotherapeutic agents in clinical practice, their applications remain limited due to associated side effects induced by weak isoform selectivity. HDAC6 displays unique structure and cellular localization as well as diverse substrates and exhibits a wider range of biological functions than other isoforms. HDAC6 inhibitors have been effectively used to treat cancers, neurodegenerative diseases, and autoimmune disorders without exerting significant toxic effects. Progress has been made in defining the crystal structures of HDAC6 catalytic domains which has influenced the structure-based drug design of HDAC6 inhibitors. This review summarizes recent literature on HDAC6 inhibitors with particular reference to structural specificity and functional diversity. It may provide up-to-date guidance for the development of HDAC6 inhibitors and perspectives for optimization of therapeutic applications.