Activin Receptor II Ligand Traps: New Treatment Paradigm for Low-Risk MDS

Oncofetal reprogramming in tumor development and progression: novel insights into cancer therapy

Emerging evidence indicates that cancer cells can mimic characteristics of embryonic development, promoting their development and progression. Cancer cells share features with embryonic development, characterized by robust proliferation and differentiation regulated by signaling pathways such as Wnt, Notch, hedgehog, and Hippo signaling. In certain phase, these cells also mimic embryonic diapause and fertilized egg implantation to evade treatments or immune elimination and promote metastasis. Additionally, the upregulation of ATP-binding cassette (ABC) transporters, including multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 1 (MRP1), and breast cancer-resistant protein (BCRP), in drug-resistant cancer cells, analogous to their role in placental development, may facilitate chemotherapy efflux, further resulting in treatment resistance. In this review, we concentrate on the underlying mechanisms that contribute to tumor development and progression from the perspective of embryonic development, encompassing the dysregulation of developmental signaling pathways, the emergence of dormant cancer cells, immune microenvironment remodeling, and the hyperactivation of ABC transporters. Furthermore, we synthesize and emphasize the connections between cancer hallmarks and embryonic development, offering novel insights for the development of innovative cancer treatment strategies.

Emerging biologics for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare pulmonary vascular disorder, wherein mean systemic arterial pressure (mPAP) becomes abnormally high because of aberrant changes in various proliferative and inflammatory signalling pathways of pulmonary arterial cells. Currently used anti-PAH drugs chiefly target the vasodilatory and vasoconstrictive pathways. However, an imbalance between bone morphogenetic protein receptor type II (BMPRII) and transforming growth factor beta (TGF-β) pathways is also implicated in PAH predisposition and pathogenesis. Compared to currently used PAH drugs, various biologics have shown promise as PAH therapeutics that elicit their therapeutic actions akin to endogenous proteins. Biologics that have thus far been explored as PAH therapeutics include monoclonal antibodies, recombinant proteins, engineered cells, and nucleic acids. Because of their similarity with naturally occurring proteins and high binding affinity, biologics are more potent and effective and produce fewer side effects when compared with small molecule drugs. However, biologics also suffer from the limitations of producing immunogenic adverse effects. This review describes various emerging and promising biologics targeting the proliferative/apoptotic and vasodilatory pathways involved in PAH pathogenesis. Here, we have discussed sotatercept, a TGF-β ligand trap, which is reported to reverse vascular remodelling and reduce PVR with an improved 6-minute walk distance (6-MWDT). We also elaborated on other biologics including BMP9 ligand and anti-gremlin1 antibody, anti-OPG antibody, and getagozumab monoclonal antibody and cell-based therapies. Overall, recent literature suggests that biologics hold excellent promise as a safe and effective alternative to currently used PAH therapeutics.

New Approaches to Myelodysplastic Syndrome Treatment

OPINION STATEMENT

The treatment of myelodysplastic syndromes (MDS) begins with risk stratification using a validated tool such as the International Prognostic Scoring System (IPSS) or its revised version (IPSS-R). This divides patients into lower- and higher- risk categories. Although treatment objectives in lower-risk MDS (LR-MDS) have traditionally been directed at improving cytopenias (usually anemia) as well as quality of life, recent data supports a potential role for early intervention in delaying transfusion dependency. In addition, careful individualized risk stratification incorporating clinical, cytogenetic, and mutational data might help identify patients at higher-than-expected risk for progression. Given the need for supportive care with red blood cell (RBC) transfusions leading to iron overload, iron chelation should be considered for patients with heavy transfusion requirements at risk for end-organ complications. For patients with LR-MDS and isolated anemia, no high-risk features, and endogenous erythropoietin (EPO) levels below 500 U/L, erythropoiesis-stimulating agents (ESAs) can be attempted to improve anemia. Some LR-MDS patient subgroups may also benefit from specific therapies including luspatercept (MDS with ring sideroblasts), lenalidomide (MDS with deletion 5q), or immunosuppressive therapy (hypocellular MDS). LR-MDS patients failing the above options, or those with multiple cytopenias and/or higher-risk features, can be considered for oral low-dose hypomethylating agent (HMA) therapy. Alternatively, these patients may be enrolled on a clinical trial with promising agents targeting the transforming-growth factor beta (TGF-β) pathway, the hypoxia-inducible factor (HIF) pathway, telomerase activity, inflammatory signaling, or the splicing machinery. In higher-risk MDS (HR-MDS), therapy seeks to modify the natural history of the disease and prolong survival. Eligible patients should be considered for curative allogeneic hematopoietic stem cell transplantation (aHSCT). Despite promising novel combinations, the HMAs azacitidine (AZA) or decitabine (DAC) are still the standard of care for these patients, with intensive chemotherapy-based approaches being a potential option in a small subset of patients. Individuals who fail to respond or progress after HMA experience dismal outcomes and represent a major unmet clinical need. Such patients should be treated as part of a clinical trial if possible. Experimental agents to consider include venetoclax, myeloid cell leukemia 1 (MCL-1) inhibitors, eprenetapopt, CPX-351, immunotherapies (directed towards CD47, TIM3, or CD70), interleukin-1 receptor-associated kinase 4 (IRAK4) inhibitors, pevonedistat, seclidemstat, and eltanexor. In this review, we extensively discuss the current landscape of experimental therapies for both LR- and HR-MDS.

Myelodysplastic Syndromes: A New Decade

Myelodysplastic syndromes (MDS) are a group of heterogeneous clonal hematopoietic stem cell disorders. The 2020 Surveillance, Epidemiology, and End Results data demonstrates the incidence rate of MDS increases with age especially in those greater than 70 years of age. Risk stratification that impact prognosis, survival, and rate of acute myeloid leukemia (AML) transformation in MDS is largely dependent on revised International Prognostic Scoring System along with molecular genetic testing as a supplement. Low risk MDS typically have a more indolent disease course in which treatment is only initiated to ameliorate symptoms of cytopenias. In many, anemia is the most common cytopenia requiring treatment and erythroid stimulating agents, are considered first line. In contrast, high risk MDS tend to behave more aggressively for which treatment should be initiated rapidly with Hypomethylating Agents (HMA) being in the frontline. In those with high risk MDS and eligible, evaluation for allogeneic stem cell transplant should be considered as this is the only potential curative option for MDS. With the use of molecular genetic testing, a personalized approach to therapy in MDS has ensued. As the treatment landscape in MDS continues to flourish with novel targeted agents, we ambitiously seek to improve survival rates especially among the relapsed/refractory and transplant ineligible.

Luspatercept as a therapy for myelodysplastic syndromes with ring sideroblasts

INTRODUCTION

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell diseases characterized by cell dysplasia, ineffective hematopoiesis and risk of transformation to acute myeloid leukemia (AML). The median age of 75 years at diagnosis is associated with the presence of comorbidities, which preclude intensive therapies like allogeneic hematopoietic stem cell transplantation in most MDS patients. Risk stratification using the (Revised) International Prognostic Scoring System (IPSS/IPSS-R) is necessary to plan individualized treatment.

AREAS COVERED

Luspatercept (ACE-536), a specific activin receptor fusion protein, promotes late-stage erythropoiesis. Two clinical trials, PACE-MDS (phase 2) and MEDALIST (phase 3), yielded positive results in terms of improved hemoglobin levels and loss of transfusion dependence, with hardly any side effects. A phase 3 trial to compare luspatercept to ESAs (COMMANDS study) is ongoing.

EXPERT OPINION

Luspatercept is a promising alternative to ESAs for a subset of transfusion-dependent patients with lower risk MDS, namely those with a sideroblastic phenotype who are either not suitable for or have already failed erythropoietin-based treatment. The favorable safety profile and convenient subcutaneous administration every 3 weeks are more conducive to patients' quality of life than chronic red blood cell transfusion therapy.

Luspatercept in the treatment of lower-risk myelodysplastic syndromes

Transforming growth factor beta (TGF-β) signaling pathway is key to hematopoiesis regulation. Increased activation of this pathway contributes to ineffective terminal erythroid differentiation in myelodysplastic syndromes (MDS). Luspatercept is a novel fusion protein that traps TGF-β ligands preventing them from binding to Type II TGF-β receptors, thereby decreasing phosphorylated SMAD2/3 resulting in the downstream effect of promoting erythropoiesis. Seminal clinical trials using luspatercept, PACE-MD and MEDALIST, demonstrated impressive efficacy in the treatment of transfusion-dependent anemia in intermediate risk or lower MDS had led to the US FDA approval for this indication. This review summarizes luspatercept mechanisms of action, efficacy/safety data supporting its use and ongoing clinical trials in MDS.

Clinical and Molecular Insights in Erythropoiesis Regulation of Signal Transduction Pathways in Myelodysplastic Syndromes and β-Thalassemia

Erythropoiesis regulation is essential in normal physiology and pathology, particularly in myelodysplastic syndromes (MDS) and β-thalassemia. Several signaling transduction processes, including those regulated by inositides, are implicated in erythropoiesis, and the latest MDS or β-thalassemia preclinical and clinical studies are now based on their regulation. Among others, the main pathways involved are those regulated by transforming growth factor (TGF)-β, which negatively regulates erythrocyte differentiation and maturation, and erythropoietin (EPO), which acts on the early-stage erythropoiesis. Also small mother against decapentaplegic (SMAD) signaling molecules play a role in pathology, and activin receptor ligand traps are being investigated for future clinical applications. Even inositide-dependent signaling, which is important in the regulation of cell proliferation and differentiation, is specifically associated with erythropoiesis, with phospholipase C (PLC) and phosphatidylinositol 3-kinase (PI3K) as key players that are becoming increasingly important as new promising therapeutic targets. Additionally, Roxadustat, a new erythropoiesis stimulating agent targeting hypoxia inducible factor (HIF), is under clinical development. Here, we review the role and function of the above-mentioned signaling pathways, and we describe the state of the art and new perspectives of erythropoiesis regulation in MDS and β-thalassemia.

Treatment options for lower-risk myelodysplastic syndromes. Where are we now?

Myelodysplastic syndromes (MDS) are a spectrum of clonal stem-cell disorders characterized clinically by bone-marrow failure. Resultant cytopenias are responsible for significant mortality and decreased quality of life in patients with MDS. In patients with low-risk MDS (LR-MDS), anemia is the most common cytopenia and erythropoiesis-stimulating agents (ESA) are usually used as first-line therapy. Those patients who become refractory to ESA have a poor survival. Available treatment options such as lenalidomide, hypomethylating agents, and immunosuppressive therapy can provide some hematologic response among selected subsets of patients, however durable responses are limited, and these agents can carry significant adverse effects. Chronic transfusions help to alleviate symptoms of anemia but still carry risks associated with transfusion and iron overload. Luspatercept, recently approved for those LR-MDS with ring sideroblasts refractory to ESA, was found to have an improvement in transfusion independence with a well-tolerated safety profile. While anemia is the most common cytopenia, thrombocytopenia and neutropenia management is challenging and the co-occurrence of these cytopenias with anemia may dictate the choice of therapy. In this article, we review LR-MDS and discuss the optimal use of current treatment options and explore new therapeutic options on the horizon.

Population Pharmacokinetics and Exposure-Response of Luspatercept, an Erythroid Maturation Agent, in Anemic Patients With Myelodysplastic Syndromes

Luspatercept is a recombinant fusion protein that enhances late‐stage erythroid maturation. This report describes the population pharmacokinetics and exposure–response relationship of luspatercept in 260 patients with anemia due to myelodysplastic syndromes. Luspatercept displayed linear and time‐invariant pharmacokinetics over a dose range of 0.125–1.75 mg/kg administered subcutaneously once every 3 weeks. Body weight was the only clinically relevant covariate of luspatercept exposure, supporting the weight‐based dosing. The probability of achieving transfusion independence ≥ 8 weeks increased with time‐averaged luspatercept serum exposure, reaching the plateau at doses 1.0–1.75 mg/kg. The probability of achieving multiple efficacy end points increased with slower luspatercept clearance, independent of effects of luspatercept exposure or disease characteristics. The probability of experiencing severe treatment‐emergent adverse events decreased with increasing luspatercept exposure, especially during long‐term treatment. These results provide a positive benefit–risk profile for the titration‐to‐response dose regimen (1.0–1.75 mg/kg) recommended for this population.

Controversies on the Consequences of Iron Overload and Chelation in MDS

Many patients with MDS are prone to develop systemic and tissue iron overload in part as a consequence of disease-immanent ineffective erythropoiesis. However, chronic red blood cell transfusions, which are part of the supportive care regimen to correct anemia, are the major source of iron overload in MDS. Increased systemic iron levels eventually lead to the saturation of the physiological systemic iron carrier transferrin and the occurrence of non-transferrin-bound iron (NTBI) together with its reactive fraction, the labile plasma iron (LPI). NTBI/LPI-mediated toxicity and tissue iron overload may exert multiple detrimental effects that contribute to the pathogenesis, complications and eventually evolution of MDS. Until recently, the evidence supporting the use of iron chelation in MDS was based on anecdotal reports, uncontrolled clinical trials or prospective registries. Despite not fully conclusive, these and more recent studies, including the TELESTO trial, unravel an overall adverse action of iron overload and therapeutic benefit of chelation, ranging from improved hematological outcome, reduced transfusion dependence and superior survival of iron-loaded MDS patients. The still limited and somehow controversial experimental and clinical data available from preclinical studies and randomized trials highlight the need for further investigation to fully elucidate the mechanisms underlying the pathological impact of iron overload-mediated toxicity as well as the effect of classic and novel iron restriction approaches in MDS. This review aims at providing an overview of the current clinical and translational debated landscape about the consequences of iron overload and chelation in the setting of MDS.