HDAC6 inhibition effectively reverses chemotherapy-induced peripheral neuropathy

Serendipitous and Systematic Chemoproteomic Discovery of MBLAC2, HINT1, and NME1-4 Inhibitors from Histone Deacetylase-Targeting Pharmacophores

Metalloenzyme inhibitors often incorporate a hydroxamic acid moiety to bind the bivalent metal ion cofactor within the enzyme's active site. Recently, inhibitors of Zn2+-dependent histone deacetylases (HDACs), including clinically advanced drugs, have been identified as potent inhibitors of the metalloenzyme MBLAC2. However, selective chemical probes for MBLAC2, which are essential for studying its inhibitory effects, have not yet been reported. To discover highly selective MBLAC2 inhibitors, we conducted chemoproteomic target deconvolution and selectivity profiling of a library of hydroxamic acid-type molecules and other metal-chelating compounds. This screen revealed MBLAC2 as a frequent off-target of supposedly selective HDAC inhibitors, including the HDAC6 inhibitor SW-100. Profiling a focused library of SW-100-related phenylhydroxamic acids led to identifying two compounds, KV-65 and KV-79, which exhibit nanomolar binding affinity for MBLAC2 and over 60-fold selectivity compared to HDACs. Interestingly, some phenylhydroxamic acids were found to bind additional off-targets. We identified KV-30 as the first drug-like inhibitor of the histidine triad nucleotide-binding protein HINT1 and confirmed its mode of inhibition through a cocrystal structure analysis. Furthermore, we report the discovery of the first inhibitors for the undrugged nucleoside diphosphate kinases NME1, NME2, NME3, and NME4. Overall, this study maps the target and off-target landscape of 53 metalloenzyme inhibitors, providing the first selective MBLAC2 inhibitors. Additionally, the discovery of pharmacophores for NME1-4 and HINT1 establishes a foundation for the future design of potent and selective inhibitors for these targets.

Contribution of S1pr1 -featured astrocyte subpopulation to cisplatin-induced neuropathic pain

Chemotherapy-induced peripheral neuropathy accompanied by neuropathic pain (CIPN) is a major neurotoxicity of cisplatin, a platinum-based drug widely used for lung, ovarian, and testicular cancer treatment. CIPN causes drug discontinuation and severely impacts life quality with no FDA-approved interventions. We previously reported that platinum-based drugs increase levels of sphingosine 1-phosphate (S1P) in the spinal cord and drive CIPN through activating the S1P receptor subtype 1 (S1PR1). However, the mechanisms engaged downstream of S1PR1 remain poorly understood. Using single cell transcriptomics on male mouse spinal cord, our findings uncovered subpopulation-specific responses to cisplatin associated with CIPN. Particularly, cisplatin increased the proportion of astrocytes with high expression levels of S1pr1 ( S1pr1 high astrocytes), specific to which a Wnt signaling pathway was identified. To this end, several genes involved in Wnt signaling, such as the fibroblast growth factor receptor 3 gene ( Fgfr3 ), were highly expressed in S1pr1 high astrocytes. The functional S1PR1 antagonist, ozanimod, prevented cisplatin-induced neuropathic pain and astrocytic upregulation of the Wnt signaling pathway genes. FGFR3 belongs to the FGF/FGFR family which often signals to activate Wnt signaling. Intrathecal injection of the FGFR3 antagonist, PD173074, prevented the development of CIPN in male mice. These data not only highlight FGFR3 as one of the astrocytic targets of S1PR1 but raise the possibility that S1PR1-induced engagement of Wnt signaling in S1pr1 high astrocytes may contribute to CIPN. Overall, our results provide a comprehensive mapping of cellular and molecular changes engaged in cisplatin-induced neuropathic pain and decipher novel S1PR1-based mechanisms of action.

Potential of histone deacetylase 6 inhibitors in alleviating chemotherapy-induced peripheral neuropathy

Background

Histone deacetylase 6 (HDAC6), belonging to class IIb of histone deacetylases, regulates the acetylation of the cytoplasmic protein α-tubulin. The overexpression of HDAC6 is linked to the development of tumors, and inhibiting HDAC6 is known to trigger apoptosis in multiple myeloma cells. In addition to its application in cancer treatment, bortezomib, a proteasome inhibitor, is widely used in managing multiple myeloma and has shown effectiveness in patients with both newly diagnosed and relapsed disease. However, the treatment regimen may be delayed or discontinued due to the risk of peripheral neuropathy, a significant non-hematologic side effect.

Methods

Animal models of peripheral neuropathy induced by various anti-cancer drugs were established, confirming the potential of HDAC6 inhibitors as a treatment for this condition. Six- to eight-week-old male Sprague Dawley rats were utilized to create these models. Mechanical allodynia and electron microscopy served as indicators of peripheral neuropathy. The HDAC6 inhibitor CKD-011 was administered at doses of 5, 10, 20, and 40 mg/kg.

Results

In an animal model of bortezomib-induced peripheral neuropathy, CKD-011, an HDAC6 inhibitor, effectively ameliorated peripheral neuropathy. Similarly, CKD-011 administration demonstrated recovery from peripheral neuropathy in models induced with oxaliplatin, paclitaxel, and cisplatin.

Conclusions

These findings suggest that HDAC6 inhibitors have the potential to mitigate peripheral neuropathy induced by chemotherapeutic agents.

HDAC6 inhibition ameliorates sensory hypersensitivity and reduces immune cell signatures in the dorsal root ganglia in murine chronic pain models

Histone deacetylase (HDAC)6 is a broadly expressed class IIb HDAC that regulates cytoskeletal dynamics and some nuclear processes. Previously research has shown that HDAC6 enzymatic inhibition has analgesic properties in models of chemotherapy-induced peripheral neuropathy. Here, we evaluated the effects of genetic and pharmacologic inhibition of HDAC6 on the development of sensory hypersensitivity in mouse models of peripheral nerve injury and peripheral inflammation. Daily administration of the peripherally restricted HDAC6 inhibitor, ACY1215 (Regenacy Pharmaceuticals, Inc), attenuated mechanical allodynia in the von Frey assay within 2 days of treatment initiation, with no signs of analgesic tolerance after 21 days of administration. We observed a similar antiallodynic effect across the implemented injury models after conditionally knocking down Hdac6 in the adult dorsal root ganglia (DRGs). Bioinformatic analysis of whole-transcriptome RNA-sequencing data predicted that ACY1215 treatment predominantly attenuated proinflammatory mechanisms, such as the suppression of immune cell infiltration into the DRG after injury. Accordingly, we demonstrated a reduction in the expression of various immune cell markers in the DRG after pharmacologic and genetic HDAC6 inhibition in both neuropathic and inflammatory pain models. We identified a direct relationship between Ccl5/Ccr5 and Hdac6 downregulation, as well as reduced hypersensitivity after hind paw CCL5 administration upon Hdac6 knockdown in the DRG. Our findings highlight that peripheral inhibition of HDAC6 ameliorates sensory hypersensitivity in models of postoperative inflammatory and neuropathic pain through mechanisms beyond reduction of tubulin deacetylation. SIGNIFICANCE STATEMENT: Recent studies highlight the role of histone deacetylase (HDAC)6 in chemotherapy-induced peripheral neuropathy, through mechanisms of action including tubulin acetylation and mitochondrial trafficking. In this study, various murine models of acute and chronic pain are applied to show that inhibition of HDAC6 activity in the periphery, using the clinically tested ACY1215 compound, and genetic inactivation of the Hdac6 gene in the dorsal root ganglia, alleviated mechanical hypersensitivity in male and in female mice through mechanisms that include targeting injury-induced inflammation.

Regulation of HDAC6 Catalytic Activity in Cancer: The Role of Post-Translational Modifications and Protein-Protein Interactions

Histone deacetylase 6 (HDAC6) is a large multidomain protein that deacetylates lysine residues on cytoplasmic proteins, influencing numerous cellular processes. Both the catalytic and noncatalytic functions of HDAC6 have been implicated in cancer development and progression. Over a decade of research on catalytic domain inhibitors has shown that these drugs are well tolerated, exhibit anticancer activity, and can alleviate chemotherapy-induced peripheral neuropathies. However, their effectiveness in treating solid tumours remains uncertain. HDAC6 activity is regulated by protein-protein interactions and post-translational modifications, which may allosterically influence its catalytic domains. As a result, effective inhibition of HDAC6 in cancer using small molecule inhibitors requires a more sophisticated understanding of its role within tumour cells, including whether its expression correlates with deacetylase activity. A comprehensive understanding of cancer-specific HDAC6 expression, functional activity, and activation states will be critical for refining the use of HDAC6 inhibitors in cancer therapy.

Upregulation of delta opioid receptor by meningeal interleukin-10 prevents relapsing pain

Chronic pain often includes periods of transient amelioration and even remission that alternate with severe relapsing pain. While most research on chronic pain has focused on pain development and maintenance, there is a critical unmet need to better understand the mechanisms that underlie pain remission and relapse. We found that interleukin (IL)-10, a pain resolving cytokine, is produced by resident macrophages in the spinal meninges during remission from pain and signaled to IL-10 receptor-expressing sensory neurons. Using unbiased RNA-sequencing, we identified that IL-10 upregulated expression and antinociceptive activity of δ-opioid receptor (δOR) in the dorsal root ganglion. Genetic or pharmacological inhibition of either IL-10 signaling or δOR triggered relapsing pain. Overall, our findings, from electrophysiology, genetic manipulation, flow cytometry, pharmacology, and behavioral approaches, indicate that remission of pain is not simply a return to the naïve state. Instead, remission is an adapted homeostatic state associated with lasting pain vulnerability resulting from persisting neuroimmune interactions within the nociceptive system. Broadly, this sheds light on the elusive mechanisms underlying recurrence a common aspect across various chronic pain conditions.

Curcumin-coated iron oxide nanoparticles for photodynamic therapy of breast cancer

Breast cancer is the deadliest cancer among women and its treatment using traditional methods leads the patient to experience adverse effects. However, photodynamic therapy (PDT) is a non-invasive therapy modality that works through a photosensitizing agent, which treating activated by a suitable light source, releases reactive oxygen species capable of treating cancer. Furthermore, recent research indicates that combining PDT and nanoparticles can enhance therapeutic effects. In this way, the synthesis of IONPs (iron oxide nanoparticles) was carried out, and their subsequent coating was done with curcumin (IONPs@curcumin) so that they could act as therapeutic agents against breast cancer. Curcumin solubility tests were carried out to achieve the best results, with ethanol as a solvent, in different concentrations of ethanolic curcumin solution, with the optimal outcome observed at a concentration of 1 mM. Subsequently, the stability analysis was conducted by adjusting the pH of the medium, revealing that at pH 10, the IONPs@curcumin exhibited the best stability and dispersion conditions. Then, cytotoxicity tests of IONPs@curcumin were carried out on the MDA-MB-468 triple-negative breast cancer cell line, under experimental conditions without irradiation and subjected to PDT. The results revealed a viability greater than 70%, as it did not exhibit cytotoxicity for cells in the dark. After 1 h of incubation, the PDT associated with IONPs@curcumin showed 32% of cell viability at a concentration of 30 mg/mL.

Upregulated spinal histone deacetylases induce nociceptive sensitization by inhibiting the GABA system in chronic constriction injury-induced neuropathy in rats

Introduction

Neuropathic pain (NP) affects countless people worldwide; however, few effective treatments are currently available. Histone deacetylases (HDACs) participate in epigenetic modifications in neuropathy-induced nociceptive sensitization. Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter that can inhibit NP. The present study aimed to examine the role of spinal HDAC and its isoforms in neuropathy.

Methods

Male Wistar Rat with chronic constriction injury (CCI)-induced peripheral neuropathy and HDAC inhibitor, panobinostat, was administrated intrathecally. We performed quantitative real-time polymerase chain reaction (RT-qPCR), western blot, and immunohistochemical analysis of lumbar spinal cord dorsal horn and nociceptive behaviors (thermal hyperalgesia and mechanical allodynia) measurements.

Results

Herein, RT-qPCR analysis revealed that spinal hdac3, hdac4, and hdac6 were upregulated in CCI rats. Western blotting and immunofluorescence staining further confirmed that HDAC3, HDAC4, and HDAC6 were significantly upregulated, whereas GABA and its synthesis key enzyme glutamic acid decarboxylase (GAD) 65 were dramatically downregulated. Intrathecal panobinostat attenuated nociceptive behavior and restored the downregulated spinal GAD65 and GABA expression in CCI rats.

Conclusions

HDAC upregulation might induce nociception through GAD65 and GABA inhibition in CCI-induced neuropathy. These findings strongly suggest that HDACs negatively regulate inhibitory neurotransmitters, constituting a potential therapeutic strategy for an epigenetic approach to manage NP.

Site-specific drug release of monomethyl fumarate to treat oxidative stress disorders

Treatment of diseases of oxidative stress through activation of the antioxidant nuclear factor E2-related factor 2 (NRF2) is limited by systemic side effects. We chemically functionalize the NRF2 activator monomethyl fumarate to require Baeyer-Villiger oxidation for release of the active drug at sites of oxidative stress. This prodrug reverses chronic pain in mice with reduced side effects and could be applied to other disorders of oxidative stress.

Therapeutic indications for HDAC6 inhibitors in the peripheral and central nervous disorders

INTRODUCTION

Inhibition of the enzymatic function of HDAC6 is currently being explored in clinical trials ranging from peripheral neuropathies to cancers. Advances in selective HDAC6 inhibitor discovery allowed studying highly efficacious brain penetrant and peripheral restrictive compounds for treating PNS and CNS indications.

AREAS COVERED

This review explores the multifactorial role of HDAC6 in cells, the common pathological hallmarks of PNS and CNS disorders, and how HDAC6 modulates these mechanisms. Pharmacological inhibition of HDAC6 and genetic knockout/knockdown studies as a therapeutic strategy in PNS and CNS indications were analyzed. Furthermore, we describe the recent developments in HDAC6 PET tracers and their utility in CNS indications. Finally, we explore the advancements and challenges with HDAC6 inhibitor compounds, such as hydroxamic acid, fluoromethyl oxadiazoles, HDAC6 degraders, and thiol-based inhibitors.

EXPERT OPINION

Based on extensive preclinical evidence, pharmacological inhibition of HDAC6 is a promising approach for treating both PNS and CNS disorders, given its involvement in neurodegeneration and aging-related cellular processes. Despite the progress in the development of selective HDAC6 inhibitors, safety concerns remain regarding their chronic administration in PNS and CNS indications, and the development of novel compound classes and modalities inhibiting HDAC6 function offer a way to mitigate some of these safety concerns.

Involvement of HDAC2-mediated kcnq2/kcnq3 genes transcription repression activated by EREG/EGFR-ERK-Runx1 signaling in bone cancer pain

Bone cancer pain (BCP) represents a prevalent symptom among cancer patients with bone metastases, yet its underlying mechanisms remain elusive. This study investigated the transcriptional regulation mechanism of Kv7(KCNQ)/M potassium channels in DRG neurons and its involvement in the development of BCP in rats. We show that HDAC2-mediated transcriptional repression of kcnq2/kcnq3 genes, which encode Kv7(KCNQ)/M potassium channels in dorsal root ganglion (DRG), contributes to the sensitization of DRG neurons and the pathogenesis of BCP in rats. Also, HDAC2 requires the formation of a corepressor complex with MeCP2 and Sin3A to execute transcriptional regulation of kcnq2/kcnq3 genes. Moreover, EREG is identified as an upstream signal molecule for HDAC2-mediated kcnq2/kcnq3 genes transcription repression. Activation of EREG/EGFR-ERK-Runx1 signaling, followed by the induction of HDAC2-mediated transcriptional repression of kcnq2/kcnq3 genes in DRG neurons, leads to neuronal hyperexcitability and pain hypersensitivity in tumor-bearing rats. Consequently, the activation of EREG/EGFR-ERK-Runx1 signaling, along with the subsequent transcriptional repression of kcnq2/kcnq3 genes by HDAC2 in DRG neurons, underlies the sensitization of DRG neurons and the pathogenesis of BCP in rats. These findings uncover a potentially targetable mechanism contributing to bone metastasis-associated pain in cancer patients.

Chemotherapy-Induced Peripheral Neuropathy: A Recent Update on Pathophysiology and Treatment

Chemotherapy-induced peripheral neuropathy (CIPN) is a major long-lasting side effect of some chemotherapy drugs, which threatens cancer survival rate. CIPN mostly affects sensory neurons and occasionally motor neurons, causing numbness, tingling, discomfort, and burning pain in the upper and lower extremities. The pathophysiology of CIPN is not completely understood; however, it is believed that chemotherapies induce peripheral neuropathy via directly damaging mitochondria, impairing the function of ion channels, triggering immunological mechanisms, and disrupting microtubules. The treatment of CIPN is a medical challenge, and there are no approved pharmacological options. Currently, duloxetine and other antidepressants, antioxidant, anti-inflammatory, and ion-channel targeted therapies are commonly used in clinics to relieve the symptoms of CIPN. Several other types of drugs, such as cannabinoids, sigma-1 receptor antagonists, and nicotinamides ribose, are being evaluated in preclinical and clinical studies. This paper summarizes the information related to the physiology of CIPN and medicines that could be used for treating this condition.

HDAC inhibitors as a potential therapy for chemotherapy-induced neuropathic pain

Cancer, a chronic disease characterized by uncontrolled cell development, kills millions of people globally. The WHO reported over 10 million cancer deaths in 2020. Anticancer medications destroy healthy and malignant cells. Cancer treatment induces neuropathy. Anticancer drugs cause harm to spinal cord, brain, and peripheral nerve somatosensory neurons, causing chemotherapy-induced neuropathic pain. The chemotherapy-induced mechanisms underlying neuropathic pain are not fully understood. However, neuroinflammation has been identified as one of the various pathways associated with the onset of chemotherapy-induced neuropathic pain. The neuroinflammatory processes may exhibit varying characteristics based on the specific type of anticancer treatment delivered. Neuroinflammatory characteristics have been observed in the spinal cord, where microglia and astrocytes have a significant impact on the development of chemotherapy-induced peripheral neuropathy. The patient's quality of life might be affected by sensory deprivation, loss of consciousness, paralysis, and severe disability. High cancer rates and ineffective treatments are associated with this disease. Recently, histone deacetylases have become a novel treatment target for chemotherapy-induced neuropathic pain. Chemotherapy-induced neuropathic pain may be treated with histone deacetylase inhibitors. Histone deacetylase inhibitors may be a promising therapeutic treatment for chemotherapy-induced neuropathic pain. Common chemotherapeutic drugs, mechanisms, therapeutic treatments for neuropathic pain, and histone deacetylase and its inhibitors in chemotherapy-induced neuropathic pain are covered in this paper. We propose that histone deacetylase inhibitors may treat several aspects of chemotherapy-induced neuropathic pain, and identifying these inhibitors as potentially unique treatments is crucial to the development of various chemotherapeutic combination treatments.

Dependence on mitochondrial respiration of malignant T cells reveals a new therapeutic target for angioimmunoblastic T-cell lymphoma

Cancer metabolic reprogramming has been recognized as one of the cancer hallmarks that promote cell proliferation, survival, as well as therapeutic resistance. Up-to-date regulation of metabolism in T-cell lymphoma is poorly understood. In particular, for human angioimmunoblastic T-cell lymphoma (AITL) the metabolic profile is not known. Metabolic intervention could help identify new treatment options for this cancer with very poor outcomes and no effective medication. Transcriptomic analysis of AITL tumor cells, identified that these cells use preferentially mitochondrial metabolism. By using our preclinical AITL mouse model, mimicking closely human AITL features, we confirmed that T follicular helper (Tfh) tumor cells exhibit a strong enrichment of mitochondrial metabolic signatures. Consistent with these results, disruption of mitochondrial metabolism using metformin or a mitochondrial complex I inhibitor such as IACS improved the survival of AITL lymphoma-bearing mice. Additionally, we confirmed a selective elimination of the malignant human AITL T cells in patient biopsies upon mitochondrial respiration inhibition. Moreover, we confirmed that diabetic patients suffering from T-cell lymphoma, treated with metformin survived longer as compared to patients receiving alternative treatments. Taking together, our findings suggest that targeting the mitochondrial metabolic pathway could be a clinically efficient approach to inhibit aggressive cancers such as peripheral T-cell lymphoma.

Ketamine impairs growth cone and synaptogenesis in human GABAergic projection neurons via GSK-3β and HDAC6 signaling

The growth cone guides the axon or dendrite of striatal GABAergic projection neurons that protrude into the midbrain and cortex and form complex neuronal circuits and synaptic networks in a developing brain, aberrant projections and synaptic connections in the striatum related to multiple brain disorders. Previously, we showed that ketamine, an anesthetic, reduced dendritic growth, dendritic branches, and spine density in human striatal GABAergic neurons. However, whether ketamine affects the growth cone, the synaptic connection of growing striatal GABAergic neurons has not been tested. Using human GABAergic projection neurons derived from human inducible pluripotent stem cells (hiPSCs) and embryonic stem cells (ES) in vitro, we tested ketamine effects on the growth cones and synapses in developing GABAergic neurons by assessing the morphometry and the glycogen synthase kinase-3 (GSK-3) and histone deacetylase 6 (HDAC6) pathway. Ketamine exposure impairs growth cone formation, synaptogenesis, dendritic development, and maturation via ketamine-mediated activation of GSK-3 pathways and inhibiting HDAC6, an essential stabilizing protein for dendritic morphogenesis and synapse maturation. Our findings identified a novel ketamine neurotoxic pathway that depends on GSK-3β and HDAC6 signaling, suggesting that microtubule acetylation is a potential target for reducing ketamine's toxic effect on GABAergic projection neuronal development.

Mechanistic and Structural Insights on Difluoromethyl-1,3,4-oxadiazole Inhibitors of HDAC6

Histone deacetylase 6 (HDAC6) is increasingly recognized for its potential in targeted disease therapy. This study delves into the mechanistic and structural nuances of HDAC6 inhibition by difluoromethyl-1,3,4-oxadiazole (DFMO) derivatives, a class of non-hydroxamic inhibitors with remarkable selectivity and potency. Employing a combination of nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectrometry (LC-MS) kinetic experiments, comprehensive enzymatic characterizations, and X-ray crystallography, we dissect the intricate details of the DFMO-HDAC6 interaction dynamics. More specifically, we find that the chemical structure of a DMFO and the binding mode of its difluoroacetylhydrazide derivative are crucial in determining the predominant hydrolysis mechanism. Our findings provide additional insights into two different mechanisms of DFMO hydrolysis, thus contributing to a better understanding of the HDAC6 inhibition by oxadiazoles in disease modulation and therapeutic intervention.

Histone deacetylase as emerging pharmacological therapeutic target for neuropathic pain: From epigenetic to selective drugs

BACKGROUND

Neuropathic pain remains a formidable challenge for modern medicine. The first-line pharmacological therapies exhibit limited efficacy and unfavorable side effect profiles, highlighting an unmet need for effective therapeutic medications. The past decades have witnessed an explosion in efforts to translate epigenetic concepts into pain therapy and shed light on epigenetics as a promising avenue for pain research. Recently, the aberrant activity of histone deacetylase (HDAC) has emerged as a key mechanism contributing to the development and maintenance of neuropathic pain.

AIMS

In this review, we highlight the distinctive role of specific HDAC subtypes in a cell-specific manner in pain nociception, and outline the recent experimental evidence supporting the therapeutic potential of HDACi in neuropathic pain.

METHODS

We have summarized studies of HDAC in neuropathic pain in Pubmed.

RESULTS

HDACs, widely distributed in the neuronal and non-neuronal cells of the dorsal root ganglion and spinal cord, regulate gene expression by deacetylation of histone or non-histone proteins and involving in increased neuronal excitability and neuroinflammation, thus promoting peripheral and central sensitization. Importantly, pharmacological manipulation of aberrant acetylation using HDAC-targeted inhibitors (HDACi) has shown promising pain-relieving properties in various preclinical models of neuropathic pain. Yet, many of which exhibit low-specificity that may induce off-target toxicities, underscoring the necessity for the development of isoform-selective HDACi in pain management.

CONCLUSIONS

Abnormally elevated HDACs promote neuronal excitability and neuroinflammation by epigenetically modulating pivotal gene expression in neuronal and immune cells, contributing to peripheral and central sensitization in the progression of neuropathic pain, and HDACi showed significant efficacy and great potential for alleviating neuropathic pain.

Design, synthesis and neuroprotective biological evaluation of novel HDAC6 inhibitors incorporating benzothiadiazinyl systems as cap groups

Histone deacetylase 6 (HDAC6), as the key regulatory enzyme, plays an important role in the development of the nervous system. More and more studies indicate that HDAC6 has become a promising therapeutic target for CNS diseases. Herein we designed and synthesized a series of novel HDAC6 inhibitors with benzothiadiazinyl systems as cap groups and evaluated their activity in vitro and in vivo. Among them, compound 3 exhibited superior selective inhibitory activity against HDAC6 (IC50 = 5.1 nM, about 30-fold selectivity over HDAC1). The results of docking showed that compound 3 can interact well with the key amino acid residues of HDAC6. Compound 3 showed lower cytotoxicity (20 μM to SH-SY5Y cells, inhibition rate = 25.75%) and better neuroprotective activity against L-glutamate-induced SH-SY5Y cell injury model in vitro. Meanwhile, compound 3 exhibited weak cardiotoxicity (10 μM hERG inhibition rate = 17.35%) and possess good druggability properties. Especially, compound 3 could significantly reduce cerebral infarction from 49.87% to 32.18%, and similar with butylphthalide in MCAO model, indicating potential clinical application prospects for alleviating ischemic stroke-induced brain infarction.

Chemical Versatility in Catalysis and Inhibition of the Class IIb Histone Deacetylases

The zinc-dependent histone deacetylases (HDACs 1-11) belong to the arginase-deacetylase superfamily of proteins, members of which share a common α/β fold and catalytic metal binding site. While several HDACs play a role in epigenetic regulation by catalyzing acetyllysine hydrolysis in histone proteins, the biological activities of HDACs extend far beyond histones. HDACs also deacetylate nonhistone proteins in the nucleus as well as the cytosol to regulate myriad cellular processes. The substrate pool is even more diverse in that certain HDACs can hydrolyze other covalent modifications. For example, HDAC6 is also a lysine decrotonylase, and HDAC11 is a lysine-fatty acid deacylase. Surprisingly, HDAC10 is not a lysine deacetylase but instead is a polyamine deacetylase. Thus, the HDACs are biologically and chemically versatile catalysts as they regulate the function of diverse protein and nonprotein substrates throughout the cell.Owing to their critical regulatory functions, HDACs serve as prominent targets for drug design. At present, four HDAC inhibitors are FDA-approved for cancer chemotherapy. However, these inhibitors are active against multiple HDAC isozymes, and a lack of selectivity is thought to contribute to undesirable side effects. Current medicinal chemistry campaigns focus on the development of isozyme-selective inhibitors, and many such studies largely focus on HDAC6 and HDAC10. HDAC6 is a target for therapeutic intervention due to its cellular role as a tubulin deacetylase and tau deacetylase, and selective inhibitors are being studied in cancer chemotherapy and the treatment of peripheral neuropathy. Crystal structures of enzyme-inhibitor complexes reveal how various features of inhibitor design, such as zinc-coordinating groups, bifurcated capping groups, and aromatic fluorination patterns, contribute to affinity and isozyme selectivity. The polyamine deacetylase HDAC10 is also an emerging target for cancer chemotherapy. Crystal structures of intact substrates trapped in the HDAC10 active site reveal the molecular basis of strikingly narrow substrate specificity for N8-acetylspermidine hydrolysis. Active site features responsible for substrate specificity have been successfully exploited in the design of potent and selective inhibitors.In this Account, I review the structural chemistry and inhibition of HDACs, highlighting recent X-ray crystallographic and functional studies of HDAC6 and HDAC10 in my laboratory. These studies have yielded fascinating snapshots of catalysis as well as novel chemical transformations involving bound inhibitors. The zinc-bound water molecule in the HDAC active site is the catalytic nucleophile in the deacetylation reaction, but this activated water molecule can also react with inhibitor C═O or C═N groups to yield unanticipated reaction products that bind exceptionally tightly. Versatile active site chemistry unleashes the full inhibitory potential of such compounds, and X-ray crystallography allows us to view this chemistry in action.

Design and Synthesis of Dual-Targeting Inhibitors of sEH and HDAC6 for the Treatment of Neuropathic Pain and Lipopolysaccharide-Induced Mortality

Epoxyeicosatrienoic acids with anti-inflammatory effects are inactivated by soluble epoxide hydrolase (sEH). Both sEH and histone deacetylase 6 (HDAC6) inhibitors are being developed as neuropathic pain relieving agents. Based on the structural similarity, we designed a new group of compounds with inhibition of both HDAC6 and sEH and obtained compound M9. M9 exhibits selective inhibition of HDAC6 over class I HDACs in cells. M9 shows good microsomal stability, moderate plasma protein binding rate, and oral bioavailability. M9 exhibited a strong analgesic effect in vivo, and its analgesic tolerance was better than gabapentin. M9 improved the survival time of mice treated with lipopolysaccharide (LPS) and reversed the levels of inflammatory factors induced by LPS in mouse plasma. M9 represents the first sEH/HDAC6 dual inhibitors with in vivo antineuropathic pain and anti-inflammation.

Epigenetic HDAC5 Inhibitor Reverses Craniofacial Neuropathic Pain in Mice

Identifying and resolving molecular complexities underlying chronic neuropathic pain is a significant challenge. Among the numerous classes of histone deacetylases, Class I (HDAC 1-3) and Class III (sirtuins) have been best studied in experimental pain models where inhibitor pre-treatments but not post-treatments abrogate the development of pain-related behaviors. Post-treatment here in week 3 with less well-studied Class IIa HDAC4/5 selective inhibitor LMK235 diminishes the trigeminal ganglia increases of HDAC5 RNA and protein in two chronic orofacial neuropathic pain models to levels measured in naïve mice at week 10 post-model induction. HDAC4 RNA reported in lower limb inflammatory pain models is not evident in the trigeminal models. Many other gene alterations persisting at week 10 in the trigeminal ganglia (TG) are restored to naïve levels in mice treated with LMK235. Important pain-related upregulated genes Hoxc8,b9,d8; P2rx4, Cckbr, growth hormone (Gh), and schlafen (Slfn4) are greatly reduced in LMK235-treated mice. Fold increase in axon regeneration/repair genes Sostdc1, TTr, and Folr1 after injury are doubled by LMK235 treatment. LMK235 reduces the excitability of trigeminal ganglia neurons in culture isolated from nerve injured mice compared to vehicle-treated controls, with no effect on neurons from naïve mice. Electrophysiological characterization profile includes a shift where ∼20% of the small neurons recorded under LMK235-treated conditions are high threshold, whereas none of the neurons under control conditions have high thresholds. LMK235 reverses long-standing mechanical and cold hypersensitivity in chronic trigeminal neuropathic pain models in males and females (5,10 mg/kg), preventing development of anxiety- and depression-like behaviors. PERSPECTIVE: Data here support HDAC5 as key epigenetic factor in chronic trigeminal neuropathic pain persistence, validated with the study of RNA alterations, TG neuronal excitability, and pain-related behaviors. HDAC5 inhibitor given in week 3 restores RNA balance at 10 weeks, while upregulation remains for response to wound healing and chronic inflammation RNAs.

Monoclonal Antibody Targeting CGRP Relieves Cisplatin-Induced Neuropathic Pain by Attenuating Neuroinflammation

Chemotherapy-induced neuropathic pain (CIPN) is a common side effect of antitumor chemotherapeutic agents. It describes a pathological state of pain related to the cumulative dosage of the drug, significantly limiting the efficacy of antitumor treatment. Sofas strategies alleviating CIPN still lack. Calcitonin gene-related peptide (CGRP) is a neuropeptide involved in many pathologic pains. In this study, we explored the effects of CGRP blocking on CIPN and potential mechanisms. Total dose of 20.7 mg/kg cisplatin was used to establish a CIPN mouse model. Mechanical and thermal hypersensitivity was measured using von Frey hairs and tail flick test. Western blot and immunofluorescence were utilized to evaluate the levels of CGRP and activated astrocytes in mouse spinal cord, respectively. In addition, real-time quantitative PCR (RT-qPCR) was used to detect the level of inflammatory cytokines such as IL-6, IL-1β, and NLRP3 in vitro and in vivo. There are markedly increased CGRP expression and astrocyte activation in the spinal cord of mice following cisplatin treatment. Pretreatment with a monoclonal antibody targeting CGRP (ZR8 mAb) effectively reduced cisplatin-induced mechanical hypersensitivity and thermal nociceptive sensitization and attenuated neuroinflammation as marked by downregulated expression of IL-6, IL-1β, and NLRP3 in the mice spinal cord and spleen. Lastly, ZR8 mAb does not interfere with the antitumor effects of cisplatin in tumor-bearing mice. Our findings indicate that neutralizing CGRP with monoclonal antibody could effectively alleviate CIPN by attenuating neuroinflammation. CGRP is a promising therapeutic target for CIPN.

Applications of Cannabinoids in Neuropathic Pain: An Updated Review

Neuropathic pain is experienced due to injury to the nerves, underlying disease conditions or toxicity induced by chemotherapeutics. Multiple factors can contribute to neuropathic pain such as central nervous system (CNS)-related autoimmune and metabolic disorders, nerve injury, multiple sclerosis and diabetes. Hence, development of pharmacological interventions to reduce the drawbacks of existing chemotherapeutics and counter neuropathic pain is an urgent unmet clinical need. Cannabinoid treatment has been reported to be beneficial for several disease conditions including neuropathic pain. Cannabinoids act by inhibiting the release of neurotransmitters from presynaptic nerve endings, modulating the excitation of postsynaptic neurons, activating descending inhibitory pain pathways, reducing neural inflammation and oxidative stress and also correcting autophagy defects. This review provides insights on the various preclinical and clinical therapeutic applications of cannabidiol (CBD), cannabigerol (CBG), and cannabinol (CBN) in various diseases and the ongoing clinical trials for the treatment of chronic and acute pain with cannabinoids. Pharmacological and genetic experimental strategies have well demonstrated the potential neuroprotective effects of cannabinoids and also elaborated their mechanism of action for the therapy of neuropathic pain.

Emodin inhibits HDAC6 mediated NLRP3 signaling and relieves chronic inflammatory pain in mice

Chronic pain reduces the quality of life and ability to function of individuals suffering from it, making it a common public health problem. Neuroinflammation which is mediated by the Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in the spinal cord participates and modulates chronic pain. A chronic inflammatory pain mouse model was created in the current study by intraplantar injection of complete Freund's adjuvant (CFA) into C57BL/6J left foot of mice. Following CFA injection, the mice had enhanced pain sensitivities, decreased motor function, increased spinal inflammation and activated spinal astrocytes. Emodin (10 mg/kg) was administered intraperitoneally into the mice for 3 days. As a result, there were fewer spontaneous flinches, higher mechanical threshold values and greater latency to fall. Additionally, in the spinal cord, emodin administration reduced leukocyte infiltration level, downregulated protein level of IL-1β, lowered histone deacetylase (HDAC)6 and NLRP3 inflammasome activity and suppressed astrocytic activation. Emodin also binds to HDAC6 via four electrovalent bonds. In summary, emodin treatment blocked the HDAC6/NLRP3 inflammasome signaling, suppresses spinal inflammation and alleviates chronic inflammatory pain.

Gadolinium Presence in Rat Skin: Assessment of Histopathologic Changes Associated with Small Fiber Neuropathy

Background The presence of gadolinium traces in the skin after administration of gadolinium-based contrast agents (GBCAs) raised safety concerns regarding a potential association with small fiber neuropathy (SFN). Purpose To investigate signs of SFN in rat foot pads by quantification of the intraepidermal nerve fiber density (IENFD) after multiple GBCA administrations and to evaluate gadolinium concentration, chemical species, and clearance. Materials and Methods Fifty rats received eight intravenous injections of either gadodiamide, gadobutrol, gadoterate, gadoteridol (8 × 0.6 mmol per kilogram of body weight), or saline (1.2 mL per kilogram of body weight), within 2 weeks and were sacrificed 5 days or 5 weeks after the last injection. IENFD was determined with protein gene product (PGP) 9.5 immunofluorescent staining and blinded and automated image analysis. The gadolinium and GBCA concentrations were measured with inductively coupled plasma mass spectrometry (ICP-MS), laser ablation ICP-MS, and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI). P values were calculated using linear contrasts of model analysis. Results The IENFD (measured as geometric mean [SD] and in number of nerve fibers per millimeter of epidermis) was not significantly altered after 5 days (saline, 8.4 [1.1]; gadobutrol, 9.7 [1.2]; gadoterate, 9.2 [1.2]; gadoteridol, 9.9 [1.3]; gadodiamide, 10.5 [1.2]) or 5 weeks (saline, 19.7 [1.4]; gadobutrol, 16.4 [1.6]; gadoterate, 14.3 [1.6]; gadoteridol, 22.2 [1.8]; gadodiamide, 17.9 [1.4]). Gadolinium skin concentrations were highest for gadodiamide after 5 days (16.0 nmol/g [1.1]) and 5 weeks (10.6 nmol/g [1.2], -33%). Macrocyclic agents were lower at 5 days (gadoteridol, 2.6 nmol/g [1.2]; gadobutrol, 2.7 nmol/g [1.1]; and gadoterate, 2.3 nmol/g [1.2]) and efficiently cleared after 5 weeks (gadoteridol, -95%; gadobutrol and gadoterate, -96%). The distribution of gadolinium and IENF did not visually overlap. For macrocyclic agents, gadolinium was found in sweat glands and confirmed to be intact chelate. Conclusion There were no signs of SFN in rat foot pads using multiple dosing regimens at two time points after administration of GBCAs. Macrocyclic GBCAs exhibited lower levels of gadolinium in the skin and were effectively eliminated within 5 weeks compared with linear gadodiamide, and intact macrocyclic GBCA was detected in sweat glands. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Clement in this issue.

Inhibition of HDAC6 alleviates cancer‑induced bone pain by reducing the activation of NLRP3 inflammasome

Cancer‑induced bone pain (CIBP) is characterized as moderate to severe pain that negatively affects the daily functional status and quality of life of patients. When cancer cells metastasize and grow in bone marrow, this activates neuroinflammation in the spinal cord, which plays a vital role in the generation and persistence of chronic pain. In the present study, a model of CIBP was constructed by inoculating of MRMT‑1 rat breast carcinoma cells into the medullary cavity of the tibia in male Sprague‑Dawley rats. Following two weeks of surgery, CIBP rats exhibited damaged bone structure, increased pain sensitivity and impaired motor coordination. Neuroinflammation was activated in the spinal cords of CIBP rats, presenting with extensive leukocyte filtration, upregulated cytokine levels and activated astrocytes. Histone deacetylase 6 (HDAC6) works as a therapeutic target for chronic pain. The intrathecal injection of the HDAC6 inhibitor tubastatin A (TSA) in the lumbar spinal cord resulted in decreased spinal inflammatory cytokine production, suppressed spinal astrocytes activation and reduced NOD‑like receptor pyrin domain containing 3 (NLRP3) inflammasome activity. Consequently, this effect alleviated spontaneous pain and mechanical hyperalgesia and recovered motor coordination in CIBP rats. It was demonstrated by immunoprecipitation assay that TSA treatment reduced the interaction between HDAC6 and NLRP3. Cell research on C6 rat glioma cells served to verify that TSA treatment reduced HDAC6 and NLRP3 expression. In summary, the findings of present study indicated that TSA treatment alleviated cancer‑induced bone pain through the inhibition of HDAC6/NLRP3 inflammasome signaling in the spinal cord.

A randomized, double-blind, placebo-controlled study of histone deacetylase type 6 inhibition for the treatment of painful diabetic peripheral neuropathy

Introduction

Current treatments for painful diabetic peripheral neuropathy (DPN) are insufficiently effective for many individuals and do not treat nonpain signs and symptoms. The enzyme histone deacetylase type 6 (HDAC6) may play a role in the pathophysiology of painful DPN, and inhibition of HDAC6 has been proposed as a potential treatment.

Objectives

To assess the efficacy and safety of the novel HDAC6 inhibitor ricolinostat for the treatment of painful diabetic peripheral neuropathy.

Methods

We conducted a 12-week randomized, double-blind, placebo-controlled phase 2 study of the efficacy of ricolinostat, a novel selective HDAC6 inhibitor, in 282 individuals with painful DPN. The primary outcome was the change in the patient-reported pain using a daily diary, and a key secondary outcome was severity of nonpain neuropathic signs using the Utah Early Neuropathy Scale (UENS) score.

Results

At the 12-week assessment, changes in average daily pain and UENS scores were not different between the ricolinostat and placebo groups.

Conclusion

These results do not support the use of the HDAC6 inhibitor ricolinostat as a treatment for neuropathic pain in DPN for periods up to 12 weeks.

A Novel Therapy for Cisplatin-Induced Allodynia and Dysfunctional and Emotional Impairments in Male and Female Mice

Patients undergoing chemotherapy with cisplatin (CIS) develop neuropathy in addition to other symptoms such as, anxiety, depression, muscle wasting and body weight loss. This symptomatology greatly weakens patients and may even lead to adjournment of chemotherapy. The protecting actions of molecular hydrogen in many neurological illnesses have been described, but its effect on the functional and emotional deficiencies caused by CIS has not been assessed. In C57BL/6J male and female mice injected with CIS, we examined the impact of the prophylactic treatment with hydrogen-rich water (HRW) on: (i) the tactile and cold allodynia, (ii) the deficits of grip strength and weight loss, (iii) the anxiodepressive-like behaviors and (iv) the inflammatory and oxidative reactions incited by CIS in the dorsal root ganglia (DRG) and prefrontal cortex (PFC). The results demonstrate that the mechanical allodynia and the anxiodepressive-like comportment provoked by CIS were similarly manifested in both sexes, whereas the cold allodynia, grip strength deficits and body weight loss produced by this chemotherapeutic agent were greater in female mice. Nonetheless, the prophylactic treatment with HRW prevented the allodynia and the functional and emotional impairments resulting from CIS in both sexes. This treatment also inhibited the inflammatory and oxidative responses activated by CIS in the DRG and PFC in both sexes, which might explain the therapeutic actions of HRW in male and female mice. In conclusion, this study revealed the plausible use of HRW as a new therapy for the allodynia and physical and mental impairments linked with CIS and its possible mechanism of action.

Inflammation-induced mitochondrial and metabolic disturbances in sensory neurons control the switch from acute to chronic pain

Pain often persists in patients with an inflammatory disease, even when inflammation has subsided. The molecular mechanisms leading to this failure in pain resolution and the transition to chronic pain are poorly understood. Mitochondrial dysfunction in sensory neurons links to chronic pain, but its role in resolution of inflammatory pain is unclear. Transient inflammation causes neuronal plasticity, called hyperalgesic priming, which impairs resolution of pain induced by a subsequent inflammatory stimulus. We identify that hyperalgesic priming in mice increases the expression of a mitochondrial protein (ATPSc-KMT) and causes mitochondrial and metabolic disturbances in sensory neurons. Inhibition of mitochondrial respiration, knockdown of ATPSCKMT expression, or supplementation of the affected metabolite is sufficient to restore resolution of inflammatory pain and prevents chronic pain development. Thus, inflammation-induced mitochondrial-dependent disturbances in sensory neurons predispose to a failure in resolution of inflammatory pain and development of chronic pain.

Lysophosphatidic acid exerts protective effects on HEI-OC1 cells against cytotoxicity of cisplatin by decreasing apoptosis, excessive autophagy, and accumulation of ROS

Lysophosphatidic acid (LPA) is an active phospholipid signaling molecule that binds to six specific G protein-coupled receptors (LPA1-6) on the cell surface and exerts a variety of biological functions, including cell migration and proliferation, morphological changes, and anti-apoptosis. The earliest study from our group demonstrated that LPA treatment could restore cochlear F-actin depolymerization induced by noise exposure, reduce hair cell death, and thus protect hearing. However, whether LPA could protect against cisplatin-induced ototoxicity and which receptors play the major role remain unclear. To this end, we integrated the HEI-OC1 mouse cochlear hair cell line and zebrafish model, and found that cisplatin exposure induced a large amount of reactive oxygen species accumulation in HEI-OC1 cells, accompanied by mitochondrial damage, leading to apoptosis and autophagy. LPA treatment significantly attenuated autophagy and apoptosis in HEI-OC1 cells after cisplatin exposure. Further investigation revealed that all LPA receptors except LPA3 were expressed in HEI-OC1 cells, and the mRNA expression level of LPA1 receptor was significantly higher than that of other receptors. When LPA1 receptor was silenced, the protective effect of LPA was reduced and the proportion of apoptosis cells was increased, indicating that LPA-LPA1 plays an important role in protecting HEI-OC1 cells from cisplatin-induced apoptosis. In addition, the behavioral trajectory and in vivo fluorescence imaging results showed that cisplatin exposure caused zebrafish to move more actively, and the movement speed and distance were higher than those of the control and LPA groups, while LPA treatment reduced the movement behavior. Cisplatin caused hair cell death and loss in zebrafish lateral line, and LPA treatment significantly protected against hair cell death and loss. LPA has a protective effect on hair cells in vitro and in vivo against the cytotoxicity of cisplatin, and its mechanism may be related to reducing apoptosis, excessive autophagy and ROS accumulation.

Interleukin-10-producing monocytes contribute to sex differences in pain resolution in mice and humans

Pain is closely associated with the immune system, which exhibits sexual dimorphism. For these reasons, neuro-immune interactions are suggested to drive sex differences in pain pathophysiology. However, our understanding of peripheral neuro-immune interactions on sex differences in pain resolution remains limited. Here, we have shown, in both a mouse model of inflammatory pain and in humans following traumatic pain, that males had higher levels of interleukin (IL)-10 than females, which were correlated with faster pain resolution. Following injury, we identified monocytes (CD11b+ Ly6C+ Ly6G-F4/80 mid ) as the primary source of IL-10, with IL-10-producing monocytes being more abundant in males than females. In a mouse model, neutralizing IL-10 signaling through antibodies, genetically ablating IL-10R1 in sensory neurons, or depleting monocytes with clodronate all impaired the resolution of pain hypersensitivity in both sexes. Furthermore, manipulating androgen levels in mice reversed the sexual dimorphism of pain resolution and the levels of IL-10-producing monocytes. These results highlight a novel role for androgen-driven peripheral IL-10-producing monocytes in the sexual dimorphism of pain resolution. These findings add to the growing concept that immune cells play a critical role in resolving pain and preventing the transition into chronic pain.

Graphical abstract

Harnessing pyrimidine as a building block for histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are well-established multifaceted bioactive agents against tumors and neurodegenerative disorders. Pyrimidine and its fused and substituted derivatives were employed as a surface recognition moiety of HDAC inhibitors. De facto, the literature was loaded with different success stories of pyrimidine-based HDAC inhibitors that garnered much interest. Provoked by our continuous interest in HDAC inhibitors, we summarized and elaborated on the successful harnessing of the pyrimidine scaffold in this regard. Furthermore, we dissect our perspective that may guide medicinal chemists for an effective future design of more active chemotherapeutic agents with potential clinical applications.

Acetylated α-Tubulin and α-Synuclein: Physiological Interplay and Contribution to α-Synuclein Oligomerization

Emerging evidence supports that altered α-tubulin acetylation occurs in Parkinson's disease (PD), a neurodegenerative disorder characterized by the deposition of α-synuclein fibrillary aggregates within Lewy bodies and nigrostriatal neuron degeneration. Nevertheless, studies addressing the interplay between α-tubulin acetylation and α-synuclein are lacking. Here, we investigated the relationship between α-synuclein and microtubules in primary midbrain murine neurons and the substantia nigra of post-mortem human brains. Taking advantage of immunofluorescence and Proximity Ligation Assay (PLA), a method allowing us to visualize protein-protein interactions in situ, combined with confocal and super-resolution microscopy, we found that α-synuclein and acetylated α-tubulin colocalized and were in close proximity. Next, we employed an α-synuclein overexpressing cellular model and tested the role of α-tubulin acetylation in α-synuclein oligomer formation. We used the α-tubulin deacetylase HDAC6 inhibitor Tubacin to modulate α-tubulin acetylation, and we evaluated the presence of α-synuclein oligomers by PLA. We found that the increase in acetylated α-tubulin significantly induced α-synuclein oligomerization. In conclusion, we unraveled the link between acetylated α-tubulin and α-synuclein and demonstrated that α-tubulin acetylation could trigger the early step of α-synuclein aggregation. These data suggest that the proper regulation of α-tubulin acetylation might be considered a therapeutic strategy to take on PD.

Oxidative phosphorylation is a metabolic vulnerability of endocrine therapy and palbociclib resistant metastatic breast cancers

Resistance to endocrine treatments and CDK4/6 inhibitors is considered a near-inevitability in most patients with estrogen receptor positive breast cancers (ER + BC). By genomic and metabolomics analyses of patients' tumours, metastasis-derived patient-derived xenografts (PDX) and isogenic cell lines we demonstrate that a fraction of metastatic ER + BC is highly reliant on oxidative phosphorylation (OXPHOS). Treatment by the OXPHOS inhibitor IACS-010759 strongly inhibits tumour growth in multiple endocrine and palbociclib resistant PDX. Mutations in the PIK3CA/AKT1 genes are significantly associated with response to IACS-010759. At the metabolic level, in vivo response to IACS-010759 is associated with decreased levels of metabolites of the glutathione, glycogen and pentose phosphate pathways in treated tumours. In vitro, endocrine and palbociclib resistant cells show increased OXPHOS dependency and increased ROS levels upon IACS-010759 treatment. Finally, in ER + BC patients, high expression of OXPHOS associated genes predict poor prognosis. In conclusion, these results identify OXPHOS as a promising target for treatment resistant ER + BC patients.

Discovery of IACS-52825, a Potent and Selective DLK Inhibitor for Treatment of Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major unmet medical need with limited treatment options. Despite different mechanisms of action, diverse chemotherapeutics can cause CIPN through a converged pathway─an active axon degeneration program that engages the dual leucine zipper kinase (DLK). DLK is a neuronally enriched kinase upstream in the MAPK-JNK cascade, and while it is dormant under physiological conditions, DLK mediates a core mechanism for neuronal injury response under stress conditions, making it an attractive target for treatment of neuronal injury and neurodegenerative diseases. We have developed potent, selective, brain penetrant DLK inhibitors with excellent PK and activity in mouse models of CIPN. Lead compound IACS-52825 (22) showed strongly effective reversal of mechanical allodynia in a mouse model of CIPN and was advanced into preclinical development.

Kinin B2 Receptor Mediates Cisplatin-Induced Painful Peripheral Neuropathy by Intracellular Kinase Pathways and TRPA1 Channel Sensitisation

Chemotherapy-induced peripheral neuropathy is a severe clinical problem frequently associated with cisplatin use. Although its pathophysiology is poorly understood, it is known that kinin receptors and the transient receptor potential ankyrin 1 (TRPA1) channel play a significant role in the peripheral neuropathy induced by cisplatin in rodents. However, the role of signalling pathways downstream from B₂ kinin receptors activation and sensitisation of the TRPA1 channel remains unknown in this model. The cisplatin-induced neuropathy model caused mechanical and cold allodynia in male Swiss mice. Antagonists for kinin B₂ and B₁ receptors and the TRPA1 channel attenuated the painful parameters. Local sub-nociceptive doses of kinin B₂ receptor (bradykinin) and TRPA1 channel (allyl isothiocyanate; AITC) agonists enhanced the painful parameters in cisplatin-treated mice, which their respective antagonists attenuated. Furthermore, we demonstrated the interaction between the kinin B₂ receptor and the TRPA1 channel in cisplatin-induced peripheral neuropathy since phospholipase C (PLC) and protein kinase C epsilon (PKCε) inhibitors attenuated the increase in mechanical and cold allodynia evoked by bradykinin and AITC in cisplatin-treated mice. Therefore, regulating the activation of signalling pathways downstream from the kinin B₂ receptors activation and TRPA1 channel sensitisation can mitigate the painful peripheral neuropathy decurrent of the oncology treatment with cisplatin.

Spinal HDAC6 mediates nociceptive behaviors induced by chronic constriction injury via neuronal activation and neuroinflammation

Neuropathic pain (NP) is often accompanied by psychiatric comorbidities and currently lacks effective treatment. Prior research has shown that HDAC6 plays a crucial role in pain sensitization, but the specific mechanisms remain unclear. HDAC6 inhibitors have been found to alleviate mechanical allodynia caused by inflammation and peripheral nerve damage. In this study, we investigated the cellular mechanisms of HDAC6 in the development and maintenance of neuropathic pain. Our findings indicate that HDAC6 expression in the spinal cord (SC) is upregulated in a time-dependent manner following chronic constriction injury (CCI). HDAC6 is primarily expressed in neurons and microglia in the spinal cord. CCI-induced HDAC6 production was abolished by intrathecal injection of a microglia inhibitor. ACY-1215, a specific HDAC6 inhibitor, significantly reduced CCI-induced mechanical allodynia, but not thermal hyperalgesia. ACY-1215 also inhibited neuron activation and suppressed CCI-induced pyroptosis and neuroinflammatory responses. In summary, our results suggest that HDAC6 contributes to the development and maintenance of NP through neuronal activation and neuroinflammation. HDAC6 may be a promising target for treating NP.

Complex I inhibitor of oxidative phosphorylation in advanced solid tumors and acute myeloid leukemia: phase I trials

Although targeting oxidative phosphorylation (OXPHOS) is a rational anticancer strategy, clinical benefit with OXPHOS inhibitors has yet to be achieved. Here we advanced IACS-010759, a highly potent and selective small-molecule complex I inhibitor, into two dose-escalation phase I trials in patients with relapsed/refractory acute myeloid leukemia (NCT02882321, n = 17) and advanced solid tumors (NCT03291938, n = 23). The primary endpoints were safety, tolerability, maximum tolerated dose and recommended phase 2 dose (RP2D) of IACS-010759. The PK, PD, and preliminary antitumor activities of IACS-010759 in patients were also evaluated as secondary endpoints in both clinical trials. IACS-010759 had a narrow therapeutic index with emergent dose-limiting toxicities, including elevated blood lactate and neurotoxicity, which obstructed efforts to maintain target exposure. Consequently no RP2D was established, only modest target inhibition and limited antitumor activity were observed at tolerated doses, and both trials were discontinued. Reverse translational studies in mice demonstrated that IACS-010759 induced behavioral and physiological changes indicative of peripheral neuropathy, which were minimized with the coadministration of a histone deacetylase 6 inhibitor. Additional studies are needed to elucidate the association between OXPHOS inhibition and neurotoxicity, and caution is warranted in the continued development of complex I inhibitors as antitumor agents.

A mechanistic understanding of the relationship between skin innervation and chemotherapy-induced neuropathic pain

Neuropathic pain is a frequent complication of chemotherapy-induced peripheral neurotoxicity (CIPN). Chemotherapy-induced peripheral neuropathies may serve as a model to study mechanisms of neuropathic pain, since several other common causes of peripheral neuropathy like painful diabetic neuropathy may be due to both neuropathic and non-neuropathic pain mechanisms like ischemia and inflammation. Experimental studies are ideally suited to study changes in morphology, phenotype and electrophysiologic characteristics of primary afferent neurons that are affected by chemotherapy and to correlate these changes to behaviors reflective of evoked pain, mainly hyperalgesia and allodynia. However, hyperalgesia and allodynia may only represent one aspect of human pain, i.e., the sensory-discriminative component, while patients with CIPN often describe their pain using words like annoying, tiring and dreadful, which are affective-emotional descriptors that cannot be tested in experimental animals. To understand why some patients with CIPN develop neuropathic pain and others not, and which are the components of neuropathic pain that they are experiencing, experimental and clinical pain research should be combined. Emerging evidence suggests that changes in subsets of primary afferent nerve fibers may contribute to specific aspects of neuropathic pain in both preclinical models and in patients with CIPN. In addition, the role of cutaneous neuroimmune interactions is considered. Since obtaining dorsal root ganglia and peripheral nerves in patients is problematic, analyses performed on skin biopsies from preclinical models as well as patients provide an opportunity to study changes in primary afferent nerve fibers and to associate these changes to human pain. In addition, other biomarkers of small fiber damage in CIPN, like corneal confocal microscope and quantitative sensory testing, may be considered.

Discovery of 1-Benzhydryl-Piperazine-Based HDAC Inhibitors with Anti-Breast Cancer Activity: Synthesis, Molecular Modeling, In Vitro and In Vivo Biological Evaluation

Isoform-selective histone deacetylase (HDAC) inhibition is promoted as a rational strategy to develop safer anti-cancer drugs compared to non-selective HDAC inhibitors. Despite this presumed benefit, considerably more non-selective HDAC inhibitors have undergone clinical trials. In this report, we detail the design and discovery of potent HDAC inhibitors, with 1-benzhydryl piperazine as a surface recognition group, that differ in hydrocarbon linker. In vitro HDAC screening identified two selective HDAC6 inhibitors with nanomolar IC₅₀ values, as well as two non-selective nanomolar HDAC inhibitors. Structure-based molecular modeling was employed to study the influence of linker chemistry of synthesized inhibitors on HDAC6 potency. The breast cancer cell lines (MDA-MB-231 and MCF-7) were used to evaluate compound-mediated in vitro anti-cancer, anti-migratory, and anti-invasive activities. Experiments on the zebrafish MDA-MB-231 xenograft model revealed that a novel non-selective HDAC inhibitor with a seven-carbon-atom linker exhibits potent anti-tumor, anti-metastatic, and anti-angiogenic effects when tested at low micromolar concentrations.

Istradefylline protects from cisplatin-induced nephrotoxicity and peripheral neuropathy while preserving cisplatin antitumor effects

Cisplatin is a potent chemotherapeutic drug that is widely used in the treatment of various solid cancers. However, its clinical effectiveness is strongly limited by frequent severe adverse effects, in particular nephrotoxicity and chemotherapy-induced peripheral neuropathy. Thus, there is an urgent medical need to identify novel strategies that limit cisplatin-induced toxicity. In the present study, we show that the FDA-approved adenosine A2A receptor antagonist istradefylline (KW6002) protected from cisplatin-induced nephrotoxicity and neuropathic pain in mice with or without tumors. Moreover, we also demonstrate that the antitumoral properties of cisplatin were not altered by istradefylline in tumor-bearing mice and could even be potentiated. Altogether, our results support the use of istradefylline as a valuable preventive approach for the clinical management of patients undergoing cisplatin treatment.

HDAC6 Inhibition Reverses Cisplatin-Induced Mechanical Hypersensitivity via Tonic Delta Opioid Receptor Signaling

Peripheral neuropathic pain induced by the chemotherapeutic cisplatin can persist for months to years after treatment. Histone deacetylase 6 (HDAC6) inhibitors have therapeutic potential for cisplatin-induced neuropathic pain since they persistently reverse mechanical hypersensitivity and spontaneous pain in rodent models. Here, we investigated the mechanisms underlying reversal of mechanical hypersensitivity in male and female mice by a 2 week treatment with an HDAC6 inhibitor, administered 3 d after the last dose of cisplatin. Mechanical hypersensitivity in animals of both sexes treated with the HDAC6 inhibitor was temporarily reinstated by a single injection of the neutral opioid receptor antagonist 6β-naltrexol or the peripherally restricted opioid receptor antagonist naloxone methiodide. These results suggest that tonic peripheral opioid ligand-receptor signaling mediates reversal of cisplatin-induced mechanical hypersensitivity after treatment with an HDAC6 inhibitor. Pointing to a specific role for δ opioid receptors (DORs), Oprd1 expression was decreased in DRG neurons following cisplatin administration, but normalized after treatment with an HDAC6 inhibitor. Mechanical hypersensitivity was temporarily reinstated in both sexes by a single injection of the DOR antagonist naltrindole. Consistently, HDAC6 inhibition failed to reverse cisplatin-induced hypersensitivity when DORs were genetically deleted from advillin+ neurons. Mechanical hypersensitivity was also temporarily reinstated in both sexes by a single injection of a neutralizing antibody against the DOR ligand met-enkephalin. In conclusion, we reveal that treatment with an HDAC6 inhibitor induces tonic enkephalin-DOR signaling in peripheral sensory neurons to suppress mechanical hypersensitivity.SIGNIFICANCE STATEMENT Over one-fourth of cancer survivors suffer from intractable painful chemotherapy-induced peripheral neuropathy (CIPN), which can last for months to years after treatment ends. HDAC6 inhibition is a novel strategy to reverse CIPN without negatively interfering with tumor growth, but the mechanisms responsible for persistent reversal are not well understood. We built on evidence that the endogenous opioid system contributes to the spontaneous, apparent resolution of pain caused by nerve damage or inflammation, referred to as latent sensitization. We show that blocking the δ opioid receptor or its ligand enkephalin unmasks CIPN in mice treated with an HDAC6 inhibitor (latent sensitization). Our work provides insight into the mechanisms by which treatment with an HDAC6 inhibitor apparently reverses CIPN.

Mitochondria and sensory processing in inflammatory and neuropathic pain

Rheumatic diseases, such as osteoarthritis and rheumatoid arthritis, affect over 750 million people worldwide and contribute to approximately 40% of chronic pain cases. Inflammation and tissue damage contribute to pain in rheumatic diseases, but pain often persists even when inflammation/damage is resolved. Mechanisms that cause this persistent pain are still unclear. Mitochondria are essential for a myriad of cellular processes and regulate neuronal functions. Mitochondrial dysfunction has been implicated in multiple neurological disorders, but its role in sensory processing and pain in rheumatic diseases is relatively unexplored. This review provides a comprehensive understanding of how mitochondrial dysfunction connects inflammation and damage-associated pathways to neuronal sensitization and persistent pain. To provide an overall framework on how mitochondria control pain, we explored recent evidence in inflammatory and neuropathic pain conditions. Mitochondria have intrinsic quality control mechanisms to prevent functional deficits and cellular damage. We will discuss the link between neuronal activity, mitochondrial dysfunction and chronic pain. Lastly, pharmacological strategies aimed at reestablishing mitochondrial functions or boosting mitochondrial dynamics as therapeutic interventions for chronic pain are discussed. The evidence presented in this review shows that mitochondria dysfunction may play a role in rheumatic pain. The dysfunction is not restricted to neuronal cells in the peripheral and central nervous system, but also includes blood cells and cells at the joint level that may affect pain pathways indirectly. Pre-clinical and clinical data suggest that modulation of mitochondrial functions can be used to attenuate or eliminate pain, which could be beneficial for multiple rheumatic diseases.

HDAC6 inhibitor ACY-1083 shows lung epithelial protective features in COPD

Airway epithelial damage is a common feature in respiratory diseases such as COPD and has been suggested to drive inflammation and progression of disease. These features manifest as remodeling and destruction of lung epithelial characteristics including loss of small airways which contributes to chronic airway inflammation. Histone deacetylase 6 (HDAC6) has been shown to play a role in epithelial function and dysregulation, such as in cilia disassembly, epithelial to mesenchymal transition (EMT) and oxidative stress responses, and has been implicated in several diseases. We thus used ACY-1083, an inhibitor with high selectivity for HDAC6, and characterized its effects on epithelial function including epithelial disruption, cytokine production, remodeling, mucociliary clearance and cell characteristics. Primary lung epithelial air-liquid interface cultures from COPD patients were used and the impacts of TNF, TGF-β, cigarette smoke and bacterial challenges on epithelial function in the presence and absence of ACY-1083 were tested. Each challenge increased the permeability of the epithelial barrier whilst ACY-1083 blocked this effect and even decreased permeability in the absence of challenge. TNF was also shown to increase production of cytokines and mucins, with ACY-1083 reducing the effect. We observed that COPD-relevant stimulations created damage to the epithelium as seen on immunohistochemistry sections and that treatment with ACY-1083 maintained an intact cell layer and preserved mucociliary function. Interestingly, there was no direct effect on ciliary beat frequency or tight junction proteins indicating other mechanisms for the protected epithelium. In summary, ACY-1083 shows protection of the respiratory epithelium during COPD-relevant challenges which indicates a future potential to restore epithelial structure and function to halt disease progression in clinical practice.

Sensory neuron dysfunction in orthotopic mouse models of colon cancer

Reports of neurological sequelae related to colon cancer are largely restricted to rare instances of paraneoplastic syndromes, due to autoimmune reactions. Systemic inflammation associated with tumor development influences sensory neuron function in other disease models, though the extent to which this occurs in colorectal cancer is unknown. We induced orthotopic colorectal cancer via orthotopic injection of two colorectal cancer cell lines (MC38 and CT26) in two different mouse strains (C57BL/6 and Balb/c, respectively). Behavioral tests of pain sensitivity and activity did not detect significant alterations in sensory sensitivity or diminished well-being throughout tumor development. However, immunohistochemistry revealed widespread reductions in intraepidermal nerve fiber density in the skin of tumor-bearing mice. Though loss of nerve fiber density was not associated with increased expression of cell injury markers in dorsal root ganglia, lumbar dorsal root ganglia neurons of tumor-bearing animals showed deficits in mitochondrial function. These neurons also had reduced cytosolic calcium levels in live-cell imaging and reduced spontaneous activity in multi-electrode array analysis. Bulk RNA sequencing of DRGs from tumor-bearing mice detected activation of gene expression pathways associated with elevated cytokine and chemokine signaling, including CXCL10. This is consistent with the detection of CXCL10 (and numerous other cytokines, chemokines and growth factors) in MC38 and CT26 cell-conditioned media, and the serum of tumor-bearing mice. Our study demonstrates in a pre-clinical setting that colon cancer is associated with latent sensory neuron dysfunction and implicates cytokine/chemokine signaling in this process. These findings may have implications for determining risk factors and treatment responsiveness related to neuropathy in colorectal cancer.

Role of Selective Histone Deacetylase 6 Inhibitor ACY-1215 in Cancer and Other Human Diseases

The deacetylation process regulated by histone deacetylases (HDACs) plays an important role in human health and diseases. HDAC6 belongs to the Class IIb of HDACs family, which mainly modifies non-histone proteins located in the cytoplasm. HDAC6 plays a key role in tumors, neurological diseases, and inflammatory diseases. Therefore, targeting HDAC6 has become a promising treatment strategy in recent years. ACY-1215 is the first orally available highly selective HDAC6 inhibitor, and its efficacy and therapeutic effects are being continuously verified. This review summarizes the research progress of ACY-1215 in cancer and other human diseases, as well as the underlying mechanism, in order to guide the future clinical trials of ACY-1215 and more in-depth mechanism researches.

The Epigenetic Mechanisms Involved in Chronic Pain in Rodents: A Mini- Review

Chronic pain is a common distressing neurological disorder and about 30% of the global population suffers from it. In addition to being highly prevalent, chronic pain causes a heavy economic and social burden. Although substantial progress has been achieved to dissect the underlying mechanism of chronic pain in the past few decades, the incidence and treatment of this neurological illness is yet not properly managed in clinical practice. While nerve injury-, chemotherapy- or inflammation-induced functional regulation of gene expression in the dorsal root ganglion and spinal cord are extensively reported to be involved in the pathogenic process of chronic pain, the specific mechanism of these altered transcriptional profile still remains unclear. Recent studies have shown that epigenetic mechanisms, including DNA/RNA methylation, histone modification and circular RNAs regulation, are involved in the occurrence and development of chronic pain. In this review, we provide a description of research on the role of epigenetic mechanism in chronic pain, summarize the latest clinical and preclinical advance in this field, and propose the potential directions for further research to elucidate the molecular mechanism underlying the pathogenesis of chronic pain.