Prediction of response to therapy with ezatiostat in lower risk myelodysplastic syndrome

SMURF2 predisposes cancer cell toward ferroptosis in GPX4-independent manners by promoting GSTP1 degradation

Ferroptosis is a non-apoptotic form of regulated cell death. Glutathione (GSH) peroxidase 4 (GPX4) and GSH-independent ferroptosis suppressor protein 1 (FSP1) have been identified as major defenses. Here, we uncover a protective mechanism mediated by GSH S-transferase P1 (GSTP1) by monitoring proteinomic dynamics during ferroptosis. Dramatic downregulation of GSTP1 is caused by SMURF2-mediated GSTP1 ubiquitination and degradation at early stages of ferroptosis. Intriguingly, GSTP1 acts in GPX4- and FSP1-independent manners by catalyzing GSH conjugation of 4-hydroxynonenal and detoxifying lipid hydroperoxides via selenium-independent GSH peroxidase activity. Genetic modulation of the SMURF2/GSTP1 axis or the pharmacological inhibition of GSTP1's catalytic activity sensitized tumor responses to Food and Drug Administration (FDA)-approved ferroptosis-inducing drugs both in vitro and in vivo. GSTP1 expression also confers resistance to immune checkpoint inhibitors by blunting ferroptosis. Collectively, these findings demonstrate a GPX4/FSP1-independent cellular defense mechanism against ferroptosis and suggest that targeting SMURF2/GSTP1 to sensitize cancer cells to ferroptosis has potential as an anticancer therapy.

Synthesis of β-Thiolated-α-arylated Ketones Enabled by Photoredox and N-Heterocyclic Carbene-Catalyzed Radical Relay of Alkenes with Disulfides and Aldehydes

β-Thiolated-α-arylated ketones are perversive in bioactive molecules and serve as potential bidentate ligands for catalysis. Herein, a straightforward protocol to access β-thiolated ketones from aldehydes, alkenes, and disulfides enabled by the combination of photocatalysis and N-heterocyclic carbene catalysis is reported. The sequential radical addition to alkenes and subsequent radical-radical coupling cascade process simultaneously forge C-S and C-C bonds. The mild conditions allow for radical relay coupling with a broad functional group tolerance.

Development of Telintra as an Inhibitor of Glutathione S-Transferase P

Glutathione S-transferase P (GSTP) is a component of a complex series of pathways that provide cellular redox homeostasis. It is an abundant protein in certain tumors and is over-expressed in cancer drug resistance. It has diverse cellular functions that include, thiolase activities with small electrophilic agents or susceptible cysteine residues on the protein to mediate S-glutathionylation, and chaperone binding with select protein kinases. Preclinical and clinical testing of a nanomolar inhibitor of GSTP, TLK199 (Telintra; Ezatiostat) has indicated a role for the enzyme in hematopoiesis and utility for the drug in the treatment of patients with myelodysplastic syndrome.

Treatment of Lymphoid and Myeloid Malignancies by Immunomodulatory Drugs

Thalidomide and its derivatives (lenalidomide, pomalidomide, avadomide, iberdomide hydrochoride, CC-885 and CC-90009) form the family of immunomodulatory drugs (IMiDs). Lenalidomide (CC5013, Revlimid®) was approved by the US FDA and the EMA for the treatment of multiple myeloma (MM) patients, low or intermediate-1 risk transfusion-dependent myelodysplastic syndrome (MDS) with chromosome 5q deletion [del(5q)] and relapsed and/or refractory mantle cell lymphoma following bortezomib. Lenalidomide has also been studied in clinical trials and has shown promising activity in chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL). Lenalidomide has anti-inflammatory effects and inhibits angiogenesis. Pomalidomide (CC4047, Imnovid® [EU], Pomalyst® [USA]) was approved for advanced MM insensitive to bortezomib and lenalidomide. Other IMiDs are in phases 1 and 2 of clinical trials. Cereblon (CRBN) seems to have an important role in IMiDs action in both lymphoid and myeloid hematological malignancies. Cereblon acts as the substrate receptor of a cullin-4 really interesting new gene (RING) E3 ubiquitin ligase CRL4CRBN. This E3 ubiquitin ligase in the absence of lenalidomide ubiquitinates CRBN itself and the other components of CRL4CRBN complex. Presence of lenalidomide changes specificity of CRL4CRBN which ubiquitinates two transcription factors, IKZF1 (Ikaros) and IKZF3 (Aiolos), and casein kinase 1α (CK1α) and marks them for degradation in proteasomes. Both these transcription factors (IKZF1 and IKZF3) stimulate proliferation of MM cells and inhibit T cells. Low CRBN level was connected with insensitivity of MM cells to lenalidomide. Lenalidomide decreases expression of protein argonaute-2, which binds to cereblon. Argonaute-2 seems to be an important drug target against IMiDs resistance in MM cells. Lenalidomide decreases also basigin and monocarboxylate transporter 1 in MM cells. MM cells with low expression of Ikaros, Aiolos and basigin are more sensitive to lenalidomide treatment. The CK1α gene (CSNK1A1) is located on 5q32 in commonly deleted region (CDR) in del(5q) MDS. Inhibition of CK1α sensitizes del(5q) MDS cells to lenalidomide. CK1α mediates also survival of malignant plasma cells in MM. Though, inhibition of CK1α is a potential novel therapy not only in del(5q) MDS but also in MM. High level of full length CRBN mRNA in mononuclear cells of bone marrow and of peripheral blood seems to be necessary for successful therapy of del(5q) MDS with lenalidomide. While transfusion independence (TI) after lenalidomide treatment is more than 60% in MDS patients with del(5q), only 25% TI and substantially shorter duration of response with occurrence of neutropenia and thrombocytopenia were achieved in lower risk MDS patients with normal karyotype treated with lenalidomide. Shortage of the biomarkers for lenalidomide response in these MDS patients is the main problem up to now.

Evaluation of bone marrow microenvironment could change how myelodysplastic syndromes are diagnosed and treated

Myelodysplastic syndromes are a heterogeneous group of clonal hematopoietic disorders. However, the therapies used against the hematopoietic stem cells clones have limited efficacy; they slow the evolution toward acute myeloid leukemia rather than stop clonal evolution and eradicate the disease. The progress made in recent years regarding the role of the bone marrow microenvironment in disease evolution may contribute to progress in this area. This review presents the recent updates on the role of the bone marrow microenvironment in myelodysplastic syndromes pathogenesis and tries to find answers regarding how this information could improve myelodysplastic syndromes diagnosis and therapy.

Hypomethylating agents (HMA) treatment for myelodysplastic syndromes: alternatives in the frontline and relapse settings

INTRODUCTION

Hypomethylating agents (HMA) have played a pivotal role for treating myelodysplastic syndromes (MDS) over the past decade, inducing sustained hematological responses and delaying progression to leukemia. However, a vast majority of patients will experience treatment failure within 2 years, with poor prognoses and limited options, and management of this growing patient population remains unclear. Areas covered: With the introduction of new agents in the MDS field, a better understanding of the biology of MDS, and updated information on standard of care options (including allogeneic transplantation), we re-evaluate the global treatment strategy in MDS via novel agents, focusing in particular on investigational approaches for patients who fail to respond to HMA when applicable. This review aims to address two questions: what are reasonable alternatives to HMA in MDS, and what strategies can be used for patients experiencing HMA failure. Expert opinion/commentary: HMA therapy remains a mainstay of treatment, even if additional research is still warranted to maximize its benefits for the different groups of patients. The outcome of patients experiencing HMA failure remains grim, without standard of care, but several new approaches seem promising, as there is an increasing focus on studying treatments for patients refractory to HMA treatment.

Ezatiostat hydrochloride for the treatment of myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes (MDSs) are associated with significant morbidity due to ineffective hematopoiesis. Given the limited number of drugs approved by the FDA, there is a need for new therapeutic options. Ezatiostat is a novel agent targeting oxidative stress via inhibition of glutathione S-transferase 1.

AREAS COVERED

Herein, the authors summarize the standard of care in order to build the framework for therapeutic advancements. The purpose of this paper is to review the body of preclinical and clinical research literature on the investigational agent ezatiostat hydrochloride (TLK199) for the treatment of MDSs. The article includes details of the pathophysiology, pharmacology, toxicity and efficacy of ezatiostat hydrochloride from controlled studies in patients with myelodysplasia.

EXPERT OPINION

MDS clonal heterogeneity and clonal architecture complexity has presented a significant technical challenge in developing effective therapies. Ezatiostat offers a unique and specific mechanism to improve the transfusion burden associated with myelodysplasia. Since it is tolerable as a monotherapy, combining ezatiostat with agents such as lenalidomide may have the most potential benefit.

Pleiotropic functions of glutathione S-transferase P

Glutathione S-transferase P (GSTP) is one member of the GST superfamily that is prevalently expressed in mammals. Known to possess catalytic activity through deprotonating glutathione allowing formation of thioether bonds with electrophilic substrates, more recent discoveries have broadened our understanding of the biological roles of this protein. In addition to catalytic detoxification, other properties so far ascribed to GSTP include chaperone functions, regulation of nitric oxide pathways, regulation of a variety of kinase signaling pathways, and participation in the forward reaction of protein S-glutathionylation. The expression of GSTP has been linked with cancer and other human pathologies and more recently even with drug addiction. With respect to human health, polymorphic variants of GSTP may determine individual susceptibility to oxidative stress and/or be critical in the design and development of drugs that have used redox pathways as a discovery platform.

Oxidative stress, redox regulation and diseases of cellular differentiation

BACKGROUND

Within cells, there is a narrow concentration threshold that governs whether reactive oxygen species (ROS) induce toxicity or act as second messengers.

SCOPE OF REVIEW

We discuss current understanding of how ROS arise, facilitate cell signaling, cause toxicities and disease related to abnormal cell differentiation and those (primarily) sulfur based pathways that provide nucleophilicity to offset these effects.

PRIMARY CONCLUSIONS

Cellular redox homeostasis mediates a plethora of cellular pathways that determine life and death events. For example, ROS intersect with GSH based enzyme pathways to influence cell differentiation, a process integral to normal hematopoiesis, but also affecting a number of diverse cell differentiation related human diseases. Recent attempts to manage such pathologies have focused on intervening in some of these pathways, with the consequence that differentiation therapy targeting redox homeostasis has provided a platform for drug discovery and development.

GENERAL SIGNIFICANCE

The balance between electrophilic oxidative stress and protective biomolecular nucleophiles predisposes the evolution of modern life forms. Imbalances of the two can produce aberrant redox homeostasis with resultant pathologies. Understanding the pathways involved provides opportunities to consider interventional strategies. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

GSTpi protects against angiotensin II-induced proliferation and migration of vascular smooth muscle cells by preventing signal transducer and activator of transcription 3 activation

Angiotensin II (Ang II)-elicited excessive proliferation, hypertrophy and migration of vascular smooth muscle cells (VSMCs) are vital to the pathogenesis of atheroclerosis. Glutathione S-transferase pi (GSTpi) exists extensively in various kinds of cells and protects cells against different stresses. However, knowledge remains limited about what GSTpi acts in VSMCs. We investigated the effect of GSTpi on Ang II-induced VSMC proliferation, hypertrophy and migration and its latent mechanism. Overexpression and RNAi experiments demonstrated that GSTpi inhibited Ang II-induced proliferation, hypertrophy and migration of VSMCs and arrested progression of cell cycle from G0/G1 to S phase. Immunoprecipitation, mass spectrometry and confocal microscopy analyses showed that GSTpi directly associated with signal transducer and activator of transcription 3 (STAT3) to prevent Ang II-triggered binding of Src to STAT3 and thus suppressed Ang II-stimulated phosphorylation and nuclear translocation of STAT3, as well as cyclin D1 expression. In contrast, GSTpi didn't affect Ang II-activated extracellular signal-regulated kinase (ERK1/2). GSTpi acts as a negative regulator to prevent Ang II-triggered proliferative signaling in VSMCs, suggesting that it may protect vessels against the stresses associated with atherosclerosis formation.

Signal transduction inhibitors in treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of hematologic disorders characterized by ineffective hematopoiesis that results in reduced blood counts. Although MDS can transform into leukemia, most of the morbidity experienced by these patients is due to chronically low blood counts. Conventional cytotoxic agents used to treat MDS have yielded some encouraging results but are characterized by many adverse effects in the predominantly elderly patient population. Targeted interventions aimed at reversing the bone marrow failure and increasing the peripheral blood counts would be advantageous in this cohort of patients. Studies have demonstrated over-activated signaling of myelo-suppressive cytokines such as TGF-β, TNF-α and Interferons in MDS hematopoietic stem cells. Targeting these signaling cascades could be potentially therapeutic in MDS. The p38 MAP kinase pathway, which is constitutively activated in MDS, is an example of cytokine stimulated kinase that promotes aberrant apoptosis of stem and progenitor cells in MDS. ARRY-614 and SCIO-469 are p38 MAPK inhibitors that have been used in clinical trials and have shown activity in a subset of MDS patients. TGF-β signaling has been therapeutically targeted by small molecule inhibitor of the TGF-β receptor kinase, LY-2157299, with encouraging preclinical results. Apart from TGF-β receptor kinase inhibition, members of TGF-β super family and BMP ligands have also been targeted by ligand trap compounds like Sotatercept (ACE-011) and ACE-536. The multikinase inhibitor, ON-01910.Na (Rigosertib) has demonstrated early signs of efficacy in reducing the percentage of leukemic blasts and is in advanced stages of clinical testing. Temsirolimus, Deforolimus and other mTOR inhibitors are being tested in clinical trials and have shown preclinical efficacy in CMML. EGF receptor inhibitors, Erlotinib and Gefitinib have shown efficacy in small trials that may be related to off target effects. Cell cycle regulator inhibitors such as Farnesyl transferase inhibitors (Tipifarnib, Lonafarnib) and MEK inhibitor (GSK1120212) have shown acceptable toxicity profiles in small studies and efforts are underway to select mutational subgroups of MDS and AML that may benefit from these inhibitors. Altogether, these studies show that targeting various signal transduction pathways that regulate hematopoiesis offers promising therapeutic potential in this disease. Future studies in combination with high resolution correlative studies will clarify the subgroup specific efficacies of these agents.

The genetic basis of phenotypic heterogeneity in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are malignant clonal disorders of haematopoietic stem cells and their microenvironment, affecting older individuals (median age ∼70 years). Unique features that are associated with MDS - but which are not necessarily present in every patient with MDS - include excessive apoptosis in maturing clonal cells, a pro-inflammatory bone marrow microenvironment, specific chromosomal abnormalities, abnormal ribosomal protein biogenesis, the presence of uniparental disomy, and mutations affecting genes involved in proliferation, methylation and epigenetic modifications. Although emerging insights establish an association between molecular abnormalities and the phenotypic heterogeneity of MDS, their origin and progression remain enigmatic.