Safety, pharmacokinetics, and pharmacodynamics of oral omaveloxolone (RTA 408), a synthetic triterpenoid, in a first-in-human trial of patients with advanced solid tumors

Myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment and their targeting in cancer therapy

The advent of immunotherapy represents a significant breakthrough in cancer treatment, with immune checkpoint inhibitors (ICIs) targeting PD-1 and CTLA-4 demonstrating remarkable therapeutic efficacy. However, patient responses to immunotherapy vary significantly, with immunosuppression within the tumor microenvironment (TME) being a critical factor influencing this variability. Immunosuppression plays a pivotal role in regulating cancer progression, metastasis, and reducing the success rates of immunotherapy. Myeloid-derived suppressor cells (MDSCs), due to their potent immunosuppressive capabilities, emerged as major negative regulators within the TME, facilitating tumor immune evasion by modulating various immune cells. In addition to their immunosuppressive functions, MDSCs also promote tumor growth and metastasis through non-immunological mechanisms, such as angiogenesis and the formation of pre-metastatic niches. Consequently, MDSCs in the TME are key regulators of cancer immune responses and potential therapeutic targets in cancer treatment. This review describes the origins and phenotypes of MDSCs, their biological roles in tumor progression, and regulatory mechanisms, with a focus on current therapeutic approaches targeting tumor-associated MDSCs. Furthermore, the synergistic effects of targeting MDSCs in combination with immunotherapy are explored, aiming to provide new insights and directions for cancer therapy.

Naturally-derived modulators of the Nrf2 pathway and their roles in the intervention of diseases

Cumulative evidence has verified that persistent oxidative stress is involved in the development of various chronic diseases, including pulmonary, neurodegenerative, kidney, cardiovascular, and liver diseases, as well as cancers. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a pivotal role in regulating cellular oxidative stress and inflammatory reactions, making it a focal point for disease prevention and treatment strategies. Natural products are essential resources for discovering leading molecules for new drug research and development. In this review, we comprehensively outlined the progression of the knowledge on the Nrf2 pathway, Nrf2 activators in clinical trials, the naturally-derived Nrf2 modulators (particularly from 2014-present), as well as their effects on the pathogenesis of chronic diseases.

The importance of synthetic pharmacotherapy for recessive cerebellar ataxias

INTRODUCTION

The last decade has witnessed major breakthroughs in identifying novel genetic causes of hereditary ataxias, deepening our understanding of disease mechanisms, and developing therapies for these debilitating disorders.

AREAS COVERED

This article reviews the currently approved and most promising candidate pharmacotherapies in relation to the known disease mechanisms of the most prevalent autosomal recessive ataxias. Omaveloxolone is an Nrf2 activator that increases antioxidant defense and was recently approved for treatment of Friedreich ataxia. Its therapeutic effect is modest, and further research is needed to find synergistic treatments that would halt or reverse disease progression. Promising approaches include upregulation of frataxin expression by epigenetic mechanisms, direct protein replacement, and gene replacement therapy. For ataxia-telangiectasia, promising approaches include splice-switching antisense oligonucleotides and small molecules targeting oxidative stress, inflammation, and mitochondrial function. Rare recessive ataxias for which disease-modifying therapies exist are also reviewed, emphasizing recently approved therapies. Evidence supporting the use of riluzole and acetyl-leucine in recessive ataxias is discussed.

EXPERT OPINION

Advances in genetic therapies for other neurogenetic conditions have paved the way to implement feasible approaches with potential dramatic benefits. Particularly, as we develop effective treatments for these conditions, we may need to combine therapies, consider newborn testing for pre-symptomatic treatment, and optimize non-pharmacological approaches.

Principal Bioactive Properties of Oleanolic Acid, Its Derivatives, and Analogues

Natural products have always played an important role in pharmacotherapy, helping to control pathophysiological processes associated with human disease. Thus, natural products such as oleanolic acid (OA), a pentacyclic triterpene that has demonstrated important activities in several disease models, are in high demand. The relevant properties of this compound have motivated re-searchers to search for new analogues and derivatives using the OA as a scaffold to which new functional groups have been added or modifications have been realized. OA and its derivatives have been shown to be effective in the treatment of inflammatory processes, triggered by chronic diseases or bacterial and viral infections. OA and its derivatives have also been found to be effective in diabetic disorders, a group of common endocrine diseases characterized by hyperglycemia that can affect several organs, including the liver and brain. This group of compounds has been reported to exhibit significant bioactivity against cancer processes in vitro and in vivo. In this review, we summarize the bioactive properties of OA and its derivatives as anti-inflammatory, anti-bacterial, antiviral, anti-diabetic, hepatoprotective, neuroprotective, and anticancer agents.

Biomarkers of NRF2 signalling: Current status and future challenges

The cytoprotective transcription factor NRF2 regulates the expression of several hundred genes in mammalian cells and is a promising therapeutic target in a number of diseases associated with oxidative stress and inflammation. Hence, an ability to monitor basal and inducible NRF2 signalling is vital for mechanistic understanding in translational studies. Due to some caveats related to the direct measurement of NRF2 levels, the modulation of NRF2 activity is typically determined by measuring changes in the expression of one or more of its target genes and/or the associated protein products. However, there is a lack of consensus regarding the most relevant set of these genes/proteins that best represents NRF2 activity across cell types and species. We present the findings of a comprehensive literature search that according to stringent criteria identifies GCLC, GCLM, HMOX1, NQO1, SRXN1 and TXNRD1 as a robust panel of markers that are directly regulated by NRF2 in multiple cell and tissue types. We assess the relevance of these markers in clinically accessible biofluids and highlight future challenges in the development and use of NRF2 biomarkers in humans.

Omaveloxolone for the treatment of Friedreich ataxia: clinical trial results and practical considerations

INTRODUCTION

Omavaloxolone, an NRF2 activator, recently became the first drug approved specifically for the treatment of Friedreich ataxia (FRDA). This landmark achievement provides a background for a review of the detailed data leading to the approval.

AREAS COVERED

The authors review the data from the 4 major articles on FRDA in the context of the authors' considerable (>1000 patients) experience in treating individuals with FRDA. The data is presented in the context not only of its scientific meaning but also in the practical context of therapy in FRDA.

EXPERT OPINION

Omaveloxolone provides a significant advance in the treatment of FRDA that is likely to be beneficial in a majority of the FRDA population. The data suggesting a benefit is consistent, and adverse issues are relatively modest. The major remaining questions are the subgroups that are most responsive and how long the beneficial effects will remain significant in FRDA patients.

Recent progress and applications of small molecule inhibitors of Keap1-Nrf2 axis for neurodegenerative diseases

The Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) pathway serves as a crucial regulator against oxidative stress (OS) damage in various cells and organs. It has garnered significant attention as a potential therapeutic target for neurodegenerative diseases (NDD). Although progress has been achieved in strategies to regulate the Keap1-Nrf2 pathway, the availability of Nrf2 activators applicable to NDD is currently limited. Currently, the FDA has approved the Nrf2 activators dimethyl fumarate (DMF) and Omaveloxolone (Omav) as novel first-line oral drugs for the treatment of patients with relapsing forms of multiple sclerosis and Friedreich's ataxia. A promising alternative approach involves the direct inhibition of Keap1-Nrf2 protein-protein interactions (PPI), which offers numerous advantages over the use of electrophilic Nrf2 activators, primarily in avoiding off-target effects. This review examines the compelling evidence supporting the beneficial role of Nrf2 in NDD and explores the potential of Keap1 inhibitors and Keap1-Nrf2 PPI inhibitors as therapeutic agents, with the aim to provide further insights into the development of inhibitors targeting this pathway for the treatment of NDD.

Application of a Human Blood Brain Barrier Organ-on-a-Chip Model to Evaluate Small Molecule Effectiveness against Venezuelan Equine Encephalitis Virus

The blood brain barrier (BBB) is a multicellular microenvironment that plays an important role in regulating bidirectional transport to and from the central nervous system (CNS). Infections by many acutely infectious viruses such as alphaviruses and flaviviruses are known to impact the integrity of the endothelial lining of the BBB. Infection by Venezuelan Equine Encephalitis Virus (VEEV) through the aerosol route causes significant damage to the integrity of the BBB, which contributes to long-term neurological sequelae. An effective therapeutic intervention strategy should ideally not only control viral load in the host, but also prevent and/or reverse deleterious events at the BBB. Two dimensional monocultures, including trans-well models that use endothelial cells, do not recapitulate the intricate multicellular environment of the BBB. Complex in vitro organ-on-a-chip models (OOC) provide a great opportunity to introduce human-like experimental models to understand the mechanistic underpinnings of the disease state and evaluate the effectiveness of therapeutic candidates in a highly relevant manner. Here we demonstrate the utility of a neurovascular unit (NVU) in analyzing the dynamics of infection and proinflammatory response following VEEV infection and therapeutic effectiveness of omaveloxolone to preserve BBB integrity and decrease viral and inflammatory load.

Omaveloxolone inhibits IL-1β-induced chondrocyte apoptosis through the Nrf2/ARE and NF-κB signalling pathways in vitro and attenuates osteoarthritis in vivo

Osteoarthritis (OA) is a common degenerative joint disease. Effective drugs that can halt or decelerate osteoarthritis progression are still lacking. Omaveloxolone is a semisynthetic oleanane triterpenoid exerting antioxidative and anti-inflammatory effects. The present study aims to determine whether omaveloxolone has a therapeutic effect on OA. Chondrocytes were treated with interleukin (IL)-1β to establish an OA cell model in vitro. Indicators of cell viability, oxidative stress, inflammation, cell apoptosis and extracellular matrix (ECM) degradation were investigated. Proteins related to the Nuclear factor erythroid derived-2-related factor 2 (Nrf2)/antioxidant response element (ARE) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signalling pathways were assessed using Western blotting. A destabilized medial meniscus surgery-induced OA rat model was used in vivo. Gait analysis, microcomputed tomography analysis, and histopathological and immunohistochemical analyses were performed to determine the therapeutic effect of omaveloxolone on attenuating osteoarthritis in vivo. The results showed that omaveloxolone exerts antioxidative, anti-inflammatory, antiapoptotic and anti-ECM degradation effects via activation of the Nrf2/ARE signalling pathway and inhibition of the NF-κB signalling pathway in chondrocytes in vitro and attenuates OA progression in vivo, suggesting that omaveloxolone may be a potential therapeutic agent for OA.

Therapeutic strategies for gastric cancer targeting immune cells: Future directions

Gastric cancer (GC) is a malignancy with a high incidence and mortality, and the emergence of immunotherapy has brought survival benefits to GC patients. Compared with traditional therapy, immunotherapy has the advantages of durable response, long-term survival benefits, and lower toxicity. Therefore, targeted immune cells are the most promising therapeutic strategy in the field of oncology. In this review, we introduce the role and significance of each immune cell in the tumor microenvironment of GC and summarize the current landscape of immunotherapy in GC, which includes immune checkpoint inhibitors, adoptive cell therapy (ACT), dendritic cell (DC) vaccines, reduction of M2 tumor-associated macrophages (M2 TAMs), N2 tumor-associated neutrophils (N2 TANs), myeloid-derived suppressor cells (MDSCs), effector regulatory T cells (eT_regs), and regulatory B cells (B_regs) in the tumor microenvironment and reprogram TAMs and TANs into tumor killer cells. The most widely used immunotherapy strategies are the immune checkpoint inhibitor programmed cell death 1/programmed death-ligand 1 (PD-1/PD-L1) antibody, cytotoxic T lymphocyte–associated protein 4 (CTLA-4) antibody, and chimeric antigen receptor T (CAR-T) in ACT, and these therapeutic strategies have significant anti-tumor efficacy in solid tumors and hematological tumors. Targeting other immune cells provides a new direction for the immunotherapy of GC despite the relatively weak clinical data, which have been confirmed to restore or enhance anti-tumor immune function in preclinical studies and some treatment strategies have entered the clinical trial stage, and it is expected that more and more effective immune cell–based therapeutic methods will be developed and applied.

Variable effects of omaveloxolone (RTA408) on primary fibroblasts with mitochondrial defects

Omaveloxolone (RTA408) is a second-generation oleanane triterpenoid Nrf2 inducer with antioxidant and anti-inflammatory properties and was reported to improve mitochondrial bioenergetics. It is currently being tested in medical trials for Friedrich ataxia, a genetic, multi-organ disease involving mitochondrial dysfunction. Thus, omaveloxolone could potentially be beneficial for additional disorders involving mitochondrial dysfunction. To this end, we investigated its effect on primary fibroblasts derived from patients with mitochondrial complex I deficiency, mitochondrial cytochrome oxidase deficiency, and two recessive forms of Parkinson’s disease. Patients and control cells were incubated in the presence or absence of 50 nM omaveloxolone for 72 h prior to measurements. Generally, growth on galactose medium and ATP production were unaltered. Mitochondrial membrane potential was slightly but significantly decreased, while reactive oxygen species (ROS) production was variably decreased. Mitochondrial mass and mitochondrial DNA (mtDNA) contents were significantly increased in the patient’s cells. These results were partially confirmed by the results of oxygen consumption studies which disclosed increased maximal oxygen consumption rates in most cells and increased energy status in all treated cells. Further investigation is required to explore the precise effect of omaveloxolone on mitochondrial function in disease.

The Novel Nrf2 Activator Omaveloxolone Regulates Microglia Phenotype and Ameliorates Secondary Brain Injury after Intracerebral Hemorrhage in Mice

The polarization of microglia is recognized as a crucial factor in reducing neuroinflammation and promoting hematoma clearance after intracerebral hemorrhage (ICH). Previous studies have revealed that redox components participate in the regulation of microglial polarization. Recently, the novel Nrf2 activator omaveloxolone (Omav) has been validated to improve neurological function in patients with neurodegenerative disorders by regulating antioxidant responses. In this study, we examined the efficacy of Omav in ICH. Omav significantly promoted Nrf2 nuclear accumulation and the expression of HO-1 and NQO1 in BV2 cells. In addition, both in vitro and in vivo experiments showed that Omav treatment inhibited M1-like activation and promoted the activation of the M2-like microglial phenotype. Omav inhibited OxyHb-induced ROS generation and preserved the function of mitochondria in BV2 cells. Intraperitoneal administration of Omav improved sensorimotor function in the ICH mouse model. Importantly, these effects were blocked by pretreatment with ML385, a selective inhibitor of Nrf2. Collectively, Omav modulated microglial polarization by activating Nrf2 and inhibiting ROS generation in ICH models, suggesting that it might be a promising drug candidate for the treatment of ICH.

HO-1 in Bone Biology: Potential Therapeutic Strategies for Osteoporosis

Osteoporosis is a prevalent bone disorder characterized by bone mass reduction and deterioration of bone microarchitecture leading to bone fragility and fracture risk. In recent decades, knowledge regarding the etiological mechanisms emphasizes that inflammation, oxidative stress and senescence of bone cells contribute to the development of osteoporosis. Studies have demonstrated that heme oxygenase 1 (HO-1), an inducible enzyme catalyzing heme degradation, exhibits anti-inflammatory, anti-oxidative stress and anti-apoptosis properties. Emerging evidence has revealed that HO-1 is critical in the maintenance of bone homeostasis, making HO-1 a potential target for osteoporosis treatment. In this Review, we aim to provide an introduction to current knowledge of HO-1 biology and its regulation, focusing specifically on its roles in bone homeostasis and osteoporosis. We also examine the potential of HO-1-based pharmacological therapeutics for osteoporosis and issues faced during clinical translation.

Beyond immunosuppressive effects: dual roles of myeloid-derived suppressor cells in bone-related diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells (IMCs) with immunosuppressive functions, whereas IMCs originally differentiate into granulocytes, macrophages, and dendritic cells (DCs) to participate in innate immunity under steady-state conditions. At present, difficulties remain in identifying MDSCs due to lacking of specific biomarkers. To make identification of MDSCs accurately, it also needs to be determined whether having immunosuppressive functions. MDSCs play crucial roles in anti-tumor, angiogenesis, and metastasis. Meanwhile, MDSCs could make close interaction with osteoclasts, osteoblasts, chondrocytes, and other stromal cells within microenvironment of bone and joint, and thereby contributing to poor prognosis of bone-related diseases such as cancer-related bone metastasis, osteosarcoma (OS), rheumatoid arthritis (RA), osteoarthritis (OA), and orthopedic trauma. In addition, MDSCs have been shown to participate in the procedure of bone repair. In this review, we have summarized the function of MDSCs in cancer-related bone metastasis, the interaction with stromal cells within the bone microenvironment as well as joint microenvironment, and the critical role of MDSCs in bone repair. Besides, the promising value of MDSCs in the treatment for bone-related diseases is also well discussed.

Synthetic Triterpenoid RTA-408: Limits Radiation Damage to Normal Tissue

OBJECTIVES/HYPOTHESIS

To assess the efficacy and mechanism of action of a novel approach to mitigate acute and chronic radiation toxicity in a validated animal model.

STUDY DESIGN

Randomized, prospective study using an in vivo rat model.

METHODS

Experimental animal study utilizing Sprague-Dawley rats divided into three cohorts: 1) radiation + dimethyl sulfoxide (DMSO) (inert vehicle); 2) radiation + RTA-408 (therapeutic drug); and 3) no radiation + DMSO. All animals in the radiation cohorts underwent 40 Gy of radiation with subsequent inferior epigastric axial rotational flap 30 days later in all cohorts with percentage of flap necrosis and vascular density calculated by blinded observers. In a second experiment, an additional three cohorts, underwent serial punch biopsies of the abdominal skin before, during, and after radiation and drug/vehicle control treatment. Transcriptome analysis utilizing gene set enrichment analysis and digital polymerase chain reaction were performed at various time points.

RESULTS

The first experiment revealed average flap necrosis of 20% (95% confidence interval [CI] 16-45) in the radiation control group, 3% (95% CI 0-11) in the nonirradiated control, and 3% (95% CI 0.2-10) in the radiation group treated with RTA-408. Vascular density was preserved in the treatment group as compared to the radiated control. Nine rats were included in the second experiment, and transcriptome analyses in the treatment group revealed robust activation of antioxidant pathways with induced expression of genes associated with hypoxia and adipogenesis/angiogenesis.

CONCLUSIONS

Administration of RTA-408 during radiation treatment in a rat model resulted in transcriptome changes which appear to mitigate the toxic effects of radiation, preserving capillary networks and improving flap survival and tissue healing after subsequent surgery.

LEVEL OF EVIDENCE

Foundational Evidence, Animal Research Laryngoscope, 2021.

Nrf2 Activation Attenuates Chronic Constriction Injury-Induced Neuropathic Pain via Induction of PGC-1α-Mediated Mitochondrial Biogenesis in the Spinal Cord

BACKGROUND

Neuropathic pain is a debilitating disease with few effective treatments. Emerging evidence indicates the involvement of mitochondrial dysfunction and oxidative stress in neuropathic pain. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a potent regulator of the antioxidant response system. In this study, we investigated whether RTA-408 (RTA, a novel synthetic triterpenoid under clinical investigation) could activate Nrf2 and promote mitochondrial biogenesis (MB) to reverse neuropathic pain and the underlying mechanisms.

METHODS

Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve. Pain behaviors were measured via the von Frey test and Hargreaves plantar test. The L4-6 spinal cord was collected to examine the activation of Nrf2 and MB.

RESULTS

RTA-408 treatment significantly reversed mechanical allodynia and thermal hyperalgesia in CCI mice in a dose-dependent manner. Furthermore, RTA-408 increased the activity of Nrf2 and significantly restored MB that was impaired in CCI mice in an Nrf2-dependent manner. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1α) is the key regulator of MB. We found that the PGC-1α activator also induced a potent analgesic effect in CCI mice. Moreover, the antinociceptive effect of RTA-408 was reversed by the preinjection of the PGC-1α inhibitor.

CONCLUSIONS

Nrf2 activation attenuates chronic constriction injury-induced neuropathic pain via induction of PGC-1α-mediated mitochondrial biogenesis in the spinal cord. Our results indicate that Nrf2 may be a potential therapeutic strategy to ameliorate neuropathic pain and many other disorders with oxidative stress and mitochondrial dysfunction.

The medicinal chemistry of mitochondrial dysfunction: a critical overview of efforts to modulate mitochondrial health

Mitochondria are subcellular organelles that perform a variety of critical biological functions, including ATP production and acting as hubs of immune and apoptotic signalling. Mitochondrial dysfunction has been extensively linked to the pathology of multiple neurodegenerative disorders, resulting in significant investment from the drug discovery community. Despite extensive efforts, there remains no disease modifying therapies for neurodegenerative disorders. This manuscript aims to review the compounds historically used to modulate the mitochondrial network through the lens of modern medicinal chemistry, and to offer a perspective on the evidence that relevant exposure was achieved in a representative model and that exposure was likely to result in target binding and engagement of pharmacology. We hope this manuscript will aid the community in identifying those targets and mechanisms which have been convincingly (in)validated with high quality chemical matter, and those for which an opportunity exists to explore in greater depth.

The Potential Application of Pentacyclic Triterpenoids in the Prevention and Treatment of Retinal Diseases

Retinal diseases are a leading cause of impaired vision and blindness but some lack effective treatments. New therapies are required urgently to better manage retinal diseases. Natural pentacyclic triterpenoids and their derivatives have a wide range of activities, including antioxidative, anti-inflammatory, cytoprotective, neuroprotective, and antiangiogenic properties. Pentacyclic triterpenoids have great potential in preventing and/or treating retinal pathologies. The pharmacological effects of pentacyclic triterpenoids are often mediated through the modulation of signalling pathways, including nuclear factor erythroid-2 related factor 2, high-mobility group box protein 1, 11β-hydroxysteroid dehydrogenase type 1, and Src homology region 2 domain-containing phosphatase-1. This review summarizes recent in vitro and in vivo evidence for the pharmacological potential of pentacyclic triterpenoids in the prevention and treatment of retinal diseases. The present literature supports the further development of pentacyclic triterpenoids. Future research should now attempt to improve the efficacy and pharmacokinetic behaviour of the agents, possibly by the use of medicinal chemistry and targeted drug delivery strategies.

Standard of care versus new-wave corticosteroids in the treatment of Duchenne muscular dystrophy: Can we do better?

BACKGROUND

Pharmacological corticosteroid therapy is the standard of care in Duchenne Muscular Dystrophy (DMD) that aims to control symptoms and slow disease progression through potent anti-inflammatory action. However, a major concern is the significant adverse effects associated with long term-use. MAIN: This review discusses the pros and cons of standard of care treatment for DMD and compares it to novel data generated with the new-wave dissociative corticosteroid, vamorolone. The current status of experimental anti-inflammatory pharmaceuticals is also reviewed, with insights regarding alternative drugs that could provide therapeutic advantage.

CONCLUSIONS

Although novel dissociative steroids may be superior substitutes to corticosteroids, other potential therapeutics should be explored. Repurposing or developing novel pharmacological therapies capable of addressing the many pathogenic features of DMD in addition to anti-inflammation could elicit greater therapeutic advantages.

Targeted de-repression of neuronal Nrf2 inhibits α-synuclein accumulation

Many neurodegenerative diseases are associated with neuronal misfolded protein accumulation, indicating a need for proteostasis-promoting strategies. Here we show that de-repressing the transcription factor Nrf2, epigenetically shut-off in early neuronal development, can prevent protein aggregate accumulation. Using a paradigm of α-synuclein accumulation and clearance, we find that the classical electrophilic Nrf2 activator tBHQ promotes endogenous Nrf2-dependent α-synuclein clearance in astrocytes, but not cortical neurons, which mount no Nrf2-dependent transcriptional response. Moreover, due to neuronal Nrf2 shut-off and consequent weak antioxidant defences, electrophilic tBHQ actually induces oxidative neurotoxicity, via Nrf2-independent Jun induction. However, we find that epigenetic de-repression of neuronal Nrf2 enables them to respond to Nrf2 activators to drive α-synuclein clearance. Moreover, activation of neuronal Nrf2 expression using gRNA-targeted dCas9-based transcriptional activation complexes is sufficient to trigger Nrf2-dependent α-synuclein clearance. Thus, targeting reversal of the developmental shut-off of Nrf2 in forebrain neurons may alter neurodegenerative disease trajectory by boosting proteostasis.

A decision process for drug discovery in retinoblastoma

Intraocular retinoblastoma treatment has changed radically over the last decade, leading to a notable improvement in ocular survival. However, eyes that relapse remain difficult to treat, as few alternative active drugs are available. More challenging is the scenario of central nervous system (CNS) metastasis, in which almost no advancements have been made. Both clinical scenarios represent an urgent need for new drugs. Using an integrated multidisciplinary approach, we developed a decision process for prioritizing drug selection for local (intravitreal [IVi], intrathecal/intraventricular [IT/IVt]), systemic, or intra-arterial chemotherapy (IAC) treatment by means of high-throughput pharmacological screening of primary cells from two patients with intraocular tumor and CNS metastasis and a thorough database search to identify clinical and biopharmaceutical data. This process identified 169 compounds to be cytotoxic; only 8 are FDA-approved, lack serious toxicities and available for IVi administration. Four of these agents could also be delivered by IT/IVt. Twelve FDA-approved drugs were identified for systemic delivery as they are able to cross the blood-brain barrier and lack serious adverse events; four drugs are of oral usage and six compounds that lack vesicant or neurotoxicity could be delivered by IAC. We also identified promising compounds in preliminary phases of drug development including inhibitors of survivin, antiapoptotic Bcl-2 family proteins, methyltransferase, and kinesin proteins. This systematic approach may be applied more broadly to prioritize drugs to be repurposed or to identify novel hits for use in retinoblastoma treatment.

Targeting Myeloid-Derived Suppressor Cells in Cancer Immunotherapy

Simple Summary

Myeloid-Derived Suppressor Cells (MDSCs) have been regarded as the main promoters of cancer development in recent years. They can protect tumor cells from being eliminated by neutralizing the anti-tumor response mediated by T cells, macrophages and dendritic cells (DCs). Therefore, different treatment methods targeting MDSCs, including chemotherapy, radiotherapy and immunotherapy, have been developed and proven to effectively inhibit tumor expansion. Herein, we summarize the immunosuppressive role of MDSCs in the tumor microenvironment and some effective treatments targeting MDSCs, and discuss the differences between different therapies.

Abstract

Myeloid-derived suppressor cells (MDSCs), which are activated under pathological conditions, are a group of heterogeneous immature myeloid cells. MDSCs have potent capacities to support tumor growth via inhibition of the antitumoral immune response and/or the induction of immunosuppressive cells. In addition, multiple studies have demonstrated that MDSCs provide potential therapeutic targets for the elimination of immunosuppressive functions and the inhibition of tumor growth. The combination of targeting MDSCs and other therapeutic approaches has also demonstrated powerful antitumor effects. In this review, we summarize the characteristics of MDSCs in the tumor microenvironment (TME) and current strategies of cancer treatment by targeting MDSCs.

The New Era of Cancer Immunotherapy: Targeting Myeloid-Derived Suppressor Cells to Overcome Immune Evasion

Suppression of antitumor immune responses is one of the main mechanisms by which tumor cells escape from destruction by the immune system. Myeloid-derived suppressor cells (MDSCs) represent the main immunosuppressive cells present in the tumor microenvironment (TME) that sustain cancer progression. MDSCs are a heterogeneous group of immature myeloid cells with a potent activity against T-cell. Studies in mice have demonstrated that MDSCs accumulate in several types of cancer where they promote invasion, angiogenesis, and metastasis formation and inhibit antitumor immunity. In addition, different clinical studies have shown that MDSCs levels in the peripheral blood of cancer patients correlates with tumor burden, stage and with poor prognosis in multiple malignancies. Thus, MDSCs are the major obstacle to many cancer immunotherapies and their targeting may be a beneficial strategy for improvement the efficiency of immunotherapeutic interventions. However, the great heterogeneity of these cells makes their identification in human cancer very challenging. Since both the phenotype and mechanisms of action of MDSCs appear to be tumor-dependent, it is important to accurately characterized the precise MDSC subsets that have clinical relevance in each tumor environment to more efficiently target them. In this review we summarize the phenotype and the suppressive mechanisms of MDSCs populations expanded within different tumor contexts. Further, we discuss about their clinical relevance for cancer diagnosis and therapy.

KEAP1, a cysteine-based sensor and a drug target for the prevention and treatment of chronic disease

Redox imbalance and persistent inflammation are the underlying causes of most chronic diseases. Mammalian cells have evolved elaborate mechanisms for restoring redox homeostasis and resolving acute inflammatory responses. One prominent mechanism is that of inducing the expression of antioxidant, anti-inflammatory and other cytoprotective proteins, while also suppressing the production of pro-inflammatory mediators, through the activation of transcription factor nuclear factor-erythroid 2 p45-related factor 2 (NRF2). At homeostatic conditions, NRF2 is a short-lived protein, which avidly binds to Kelch-like ECH-associated protein 1 (KEAP1). KEAP1 functions as (i) a substrate adaptor for a Cullin 3 (CUL3)-based E3 ubiquitin ligase that targets NRF2 for ubiquitination and proteasomal degradation, and (ii) a cysteine-based sensor for a myriad of physiological and pharmacological NRF2 activators. Here, we review the intricate molecular mechanisms by which KEAP1 senses electrophiles and oxidants. Chemical modification of specific cysteine sensors of KEAP1 results in loss of NRF2-repressor function and alterations in the expression of NRF2-target genes that encode large networks of diverse proteins, which collectively restore redox balance and resolve inflammation, thus ensuring a comprehensive cytoprotection. We focus on the cyclic cyanoenones, the most potent NRF2 activators, some of which are currently in clinical trials for various pathologies characterized by redox imbalance and inflammation.

Potential Applications of NRF2 Modulators in Cancer Therapy

The nuclear factor erythroid 2-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 (KEAP1) regulatory pathway plays an essential role in protecting cells and tissues from oxidative, electrophilic, and xenobiotic stress. By controlling the transactivation of over 500 cytoprotective genes, the NRF2 transcription factor has been implicated in the physiopathology of several human diseases, including cancer. In this respect, accumulating evidence indicates that NRF2 can act as a double-edged sword, being able to mediate tumor suppressive or pro-oncogenic functions, depending on the specific biological context of its activation. Thus, a better understanding of the mechanisms that control NRF2 functions and the most appropriate context of its activation is a prerequisite for the development of effective therapeutic strategies based on NRF2 modulation. In line of principle, the controlled activation of NRF2 might reduce the risk of cancer initiation and development in normal cells by scavenging reactive-oxygen species (ROS) and by preventing genomic instability through decreased DNA damage. In contrast however, already transformed cells with constitutive or prolonged activation of NRF2 signaling might represent a major clinical hurdle and exhibit an aggressive phenotype characterized by therapy resistance and unfavorable prognosis, requiring the use of NRF2 inhibitors. In this review, we will focus on the dual roles of the NRF2-KEAP1 pathway in cancer promotion and inhibition, describing the mechanisms of its activation and potential therapeutic strategies based on the use of context-specific modulation of NRF2.

The Nrf2 activator RTA-408 attenuates osteoclastogenesis by inhibiting STING dependent NF-κb signaling

The dysregulation of ROS production and osteoclastogenesis is involved in the progress of osteoporosis. To identify novel and effective targets to treat this disease, it is important to explore the underlying mechanisms. In our study, we firstly tested the effect of the Nrf2 activator RTA-408, a novel synthetic triterpenoid under clinical investigation for many diseases, on osteoclastogenesis. We found that it could inhibit osteoclast differentiation and bone resorption in a time- and dose-dependent manner. Further, RTA-408 enhanced the expression and activity of Nrf2 and significantly suppressed RANKL-induced reactive oxygen species (ROS) production. Nrf2 regulates the STING expression and STING induces the production of IFN-β. Here, we found that RTA-408 could suppress STING expression, but that it does not affect Ifnb1 expression. RANKL-induced degradation of IκBα and the nuclear translocation of P65 was suppressed by RTA-408. Although this compound was not found to influence STING-IFN-β signaling, it suppressed the RANKL-induced K63-ubiquitination of STING via inhibiting the interaction between STING and the E3 ubiquitin ligase TRAF6. Further, adenovirus-mediated STING overexpression rescued the suppressive effect of RTA-408 on NF-κB signaling and osteoclastogenesis. In vivo experiments showed that this compound could effectively attenuate ovariectomy (OVX)-induced bone loss in C57BL/6 mice by inhibiting osteoclastogenesis. Collectively, we show that RTA-408 inhibits NF-κB signaling by suppressing the recruitment of TRAF6 to STING, in addition to attenuating osteoclastogenesis and OVX-induced bone loss in vivo, suggesting that it could be a promising candidate for treating osteoporosis in the future.

Drug Development for the Therapy of Mitochondrial Diseases

Mitochondrial diseases are a heterogeneous group of inherited or acquired devastating disorders that affect the energy metabolism of the body. Many strategies have been investigated, but currently there is no FDA-approved drug that can alleviate disease symptoms or slow disease progression. This review analyzes to what extent growing knowledge over the past two decades about the etiology and pathogenesis of mitochondrial diseases is reflected in the design and development of new experimental drugs for the therapy of these disorders. All currently registered clinical trials involving new experimental drug entities are reviewed to evaluate how far away we are from the first FDA-approved drug therapy for mitochondrial disease.

The CCAAT/Enhancer-Binding Protein Family: Its Roles in MDSC Expansion and Function

Immunosuppressive cells have been highlighted in research due to their roles in tumor progression and treatment failure. Myeloid-derived suppressor cells (MDSCs) are among the major immunosuppressive cell populations in the tumor microenvironment, and transcription factors (TFs) are likely involved in MDSC expansion and activation. As key regulatory TFs, members of the CCAAT/enhancer-binding protein (C/EBP) family possibly modulate many biological processes, including cell growth, differentiation, metabolism, and death. Current evidence suggests that C/EBPs maintain critical regulation of MDSCs and are involved in the differentiation and function of MDSCs within the tumor microenvironment. To better understand the MDSC-associated transcriptional network and identify new therapy targets, we herein review recent findings about the C/EBP family regarding their participation in the expansion and function of MDSCs.

Pharmacokinetics and pharmacodynamics of the novel Nrf2 activator omaveloxolone in primates

Background

Omaveloxolone is a synthetic oleanane triterpenoid that pharmacologically activates Nrf2, a master transcription factor that regulates genes with antioxidative, anti-inflammatory, and mitochondrial bioenergetic properties, and is being evaluated in patients with Friedreich’s ataxia.

Methods

The present study evaluated the pharmacokinetics (PK) and tissue distribution of omaveloxolone in monkeys after single and multiple oral doses, and then compared these data to initial results in Friedreich’s ataxia patients. Pharmacodynamic (PD) evaluations in monkeys consisted of Nrf2 target gene mRNA expression in peripheral blood mononuclear cells (PBMCs), liver, lung, and brain. A PK/PD model was generated with the monkey data, and used to further evaluate the Friedreich’s ataxia patient PK profile.

Results

Oral administration of omaveloxolone to monkeys was associated with dose-linear plasma PK and readily measureable and dose-proportional concentrations in liver, lung, and brain. Dose-dependent induction of Nrf2 target genes in PBMCs and tissues was also observed. Clinically, oral administration of omaveloxolone to Friedreich’s ataxia patients at incremental doses from 2.5 to 300 mg produced dose-proportional systemic exposures. Clinical doses of at least 80 mg were associated with meaningful improvements in neurological function in patients and generated plasma omaveloxolone concentrations consistent with those significantly inducing Nrf2 target genes in monkeys, as shown with the monkey PK/PD model.

Conclusion

Overall, the monkey data demonstrate a well-characterized and dose-proportional PK and tissue distribution profile after oral administration of omaveloxolone, which was associated with Nrf2 activation. Further, systemic exposures to omaveloxolone that produce Nrf2 activation in monkeys were readily achievable in Friedreich’s ataxia patients after oral administration.

Contribution of Nrf2 Modulation to the Mechanism of Action of Analgesic and Anti-inflammatory Drugs in Pre-clinical and Clinical Stages

Despite the progress that has occurred in recent years in the development of therapies to treat painful and inflammatory diseases, there is still a need for effective and potent analgesics and anti-inflammatory drugs. It has long been known that several types of antioxidants also possess analgesic and anti-inflammatory properties, indicating a strong relationship between inflammation and oxidative stress. Understanding the underlying mechanisms of action of anti-inflammatory and analgesic drugs, as well as essential targets in disease physiopathology, is essential to the development of novel therapeutic strategies. The Nuclear factor-2 erythroid related factor-2 (Nrf2) is a transcription factor that regulates cellular redox status through endogenous antioxidant systems with simultaneous anti-inflammatory activity. This review summarizes the molecular mechanisms and pharmacological actions screened that link analgesic, anti-inflammatory, natural products, and other therapies to Nrf2 as a regulatory system based on emerging evidences from experimental disease models and new clinical trial data.

Recent Advances in Targeting Human Mitochondrial AAA+ Proteases to Develop Novel Cancer Therapeutics

The mitochondrion is a vital organelle that performs diverse cellular functions. In this regard, the cell has evolved various mechanisms dedicated to the maintenance of the mitochondrial proteome. Among them, AAA+ ATPase-associated proteases (AAA+ proteases) such as the Lon protease (LonP1), ClpXP complex, and the membrane-bound i-AAA, m-AAA and paraplegin facilitate the clearance of misfolded mitochondrial proteins to prevent the accumulation of cytotoxic protein aggregates. Furthermore, these proteases have additional regulatory functions in multiple biological processes that include amino acid metabolism, mitochondria DNA transcription, metabolite and cofactor biosynthesis, maturation and turnover of specific respiratory and metabolic proteins, and modulation of apoptosis, among others. In cancer cells, the increase in intracellular ROS levels promotes tumorigenic phenotypes and increases the frequency of protein oxidation and misfolding, which is compensated by the increased expression of specific AAA+ proteases as part of the adaptation mechanism. The targeting of AAA+ proteases has led to the discovery and development of novel anti-cancer compounds. Here, we provide an overview of the molecular characteristics and functions of the major mitochondrial AAA+ proteases and summarize recent research efforts in the development of compounds that target these proteases.

Design and development of Nrf2 modulators for cancer chemoprevention and therapy: a review

A major cell defense mechanism against oxidative and xenobiotic stress is mediated by the Nrf2/Keap1 signaling pathway. The Nrf2/Keap1 pathway regulates gene expression of many cytoprotective and detoxifying enzymes, thus playing a pivotal role in maintaining redox cellular homeostasis. Many diseases including cancer have been closely related to impaired Nrf2 activity. Targeting Nrf2 and modulating its activity represents a novel modern strategy for cancer chemoprevention and therapy. In this review, different design strategies used for the development of Nrf2 modulators are described in detail. Moreover, the main focus is on important and recently developed Nrf2 activators and inhibitors, their in vitro and in vivo studies, and their potential use as chemopreventive agents and/or cancer therapeutics.

Novel Nrf2-Inducer Prevents Mitochondrial Defects and Oxidative Stress in Friedreich's Ataxia Models

Friedreich’s Ataxia (FRDA) is an autosomal recessive neurodegenerative disorder, affecting dorsal root ganglia (DRG), cerebellar dentate nuclei and heart. It is caused by a GAA repeat expansion mutation within the frataxin gene (FXN). This impedes FXN transcription resulting in a progressive decrease of the mitochondrial protein, frataxin. Increased oxidative stress leading to a chronic depletion of endogenous antioxidants affects the survival of the cells and causes neurodegeneration. In particular, cerebellar granule neurons (CGNs) show a significant increase of reactive oxygen species (ROS), lipid peroxidation and lower level of reduced glutathione (GSH). In FRDA, one of the major pathways of oxidant scavengers, the Nrf2 antioxidant pathway, is defective. Previous studies on FRDA-like CGNs showed that the reduced level of frataxin and the oxidative stress induce mitochondrial impairments. By triggering the Nrf2 endogenous pathway pharmacologically we determined whether this could promote mitochondrial fitness and counteract oxidative stress. In this work, we sought to investigate the beneficial effect of a promising Nrf2-inducer, omaveloxolone (omav), in CGNs from two FRDA mouse models, KIKO and YG8R, and human fibroblasts from patients. We found that CGNs from both KIKO and YG8R presented Complex I deficiency and that omav was able to restore substrate availability and Complex I activity. This was also confirmed in human primary fibroblasts from FRDA patients. Although fibroblasts are not the major tissue affected, we found that they show significant differences recapitulating the disease; this is therefore an important tool to investigate patients’ pathophysiology. Interestingly, we found that patient fibroblasts had an increased level of endogenous lipid peroxidation and mitochondrial ROS (mROS), and lower GSH at rest. Omav was able to reverse this phenotype, protecting the cells against oxidative stress. By stimulating the cells with hydrogen peroxide (H₂O₂) and looking for potential mitochondrial pathophysiology, we found that fibroblasts could not maintain their mitochondrial membrane potential (ΔΨ_m). Remarkably, omav was protective to mitochondrial depolarization, promoting mitochondrial respiration and preventing cell death. Our results show that omav promotes Complex I activity and protect cells from oxidative stress. Omav could, therefore, be used as a novel therapeutic drug to ameliorate the pathophysiology of FRDA.