New therapeutics for myelodysplastic syndromes

Srsf2P95H initiates myeloid bias and myelodysplastic/myeloproliferative syndrome from hemopoietic stem cells

Mutations in SRSF2 occur in myelodysplastic syndromes (MDS) and MDS/myeloproliferative neoplasms (MPN). SRSF2 mutations cluster at proline 95, with the most frequent mutation being a histidine (P95H) substitution. They undergo positive selection, arise early in the course of disease, and have been identified in age-related clonal hemopoiesis. It is not clear how mutation of SRSF2 modifies hemopoiesis or contributes to the development of myeloid bias or MDS/MPN. Two prior mouse models of Srsf2^P95H mutation have been reported; however, these models do not recapitulate many of the clinical features of SRSF2-mutant disease and relied on bone marrow (BM) transplantation stress to elicit the reported phenotypes. We describe a new conditional murine Srsf2^P95H mutation model, where the P95H mutation is expressed physiologically and heterozygously from its endogenous locus after Cre activation. Using multiple Cre lines, we demonstrate that during native hemopoiesis (ie, no BM transplantation), the Srsf2^P95H mutation needs to occur within the hemopoietic stem-cell-containing populations to promote myelomonocytic bias and expansion with corresponding transcriptional and RNA splicing changes. With age, nontransplanted Srsf2^P95H animals developed a progressive, transplantable disease characterized by myeloid bias, morphological dysplasia, and monocytosis, hallmarks of MDS/MPN in humans. Analysis of cooccurring mutations within the BM demonstrated the acquisition of additional mutations that are recurrent in humans with SRSF2 mutations. The tractable Srsf2^P95H/+ knock-in model we have generated is highly relevant to human disease and will serve to elucidate the effect of SRSF2 mutations on initiation and maintenance of MDS/MPN.

Determination of Degradation Kinetics and Effect of Anion Exchange Resin on Dissolution of Novel Anticancer Drug Rigosertib in Acidic Conditions

Rigosertib is a novel anticancer drug in clinical development by Onconova therapeutics, Inc. Currently, it is in pivotal phase III clinical trials for myelodysplastic syndrome (MDS) patients. Chemically, it is a sodium salt of weak acid with low solubility in lower pH solutions. In the preliminary studies, it was found that rigosertib is unstable in acidic conditions and forms multiple degradation products. In this research, drug degradation kinetics of rigosertib were studied in acidic conditions. Rigosertib follows pseudo-first-order general acid catalysis reaction. Cholestyramine, which is a strong anion exchange resin, was used to form complex with drug to improve stability and dissolution in acidic conditions. Drug complex with cholestyramine showed better dissolution profile compared to drug alone. Effect of polyethylene glycol was investigated on the release of drug from the drug resin complex. Polyethylene glycol further improved dissolution profile by improving drug solubility in acidic medium.

[Management of myelodysplastic syndromes]

Myelodysplastic syndromes are heterogeneous diseases whose molecular characteristics have only been identified in recent years. Better identification of prognostic factors, larger access to allogeneic stem cell transplantation and the advent of new drugs notably hypomethylating agents (azacitidine, decitabine) and lenalidomide have improved patient outcome.

Rigosertib induces cell death of a myelodysplastic syndrome-derived cell line by DNA damage-induced G2/M arrest

A multi-kinase inhibitor, rigosertib (ON 01910.Na) has recently been highlighted as a novel type of anti-cancer agent for the treatment of the myelodysplastic syndromes (MDS), but its action mechanisms remain to be clarified. We investigated the in vitro effects of rigosertib on an MDS-derived cell line MDS-L and a myeloid leukemia cell line HL-60. Rigosertib suppressed the proliferation of both HL-60 and MDS-L cells and induced apoptosis by inhibition of the PI3 kinase/Akt pathway. As the effects on cell cycle, rigosertib treatment promoted the phosphorylation of histone H2AX and led to the DNA damage-induced G2/M arrest. In addition, an immunofluorescence staining study demonstrated the abnormal localization of aurora A kinase, suggesting that rigosertib causes perturbation of spindle assembly and deregulated mitotic patterns towards cell cycle arrest and apoptosis. We also found that rigosertib exerted growth inhibitory effects on two lymphoid cell lines, Jurkat and Ramos. We further examined the molecular pathways influenced by rigosertib from the gene expression profiling data of MDS-L cells and found a possible involvement of rigosertib treatment in the upregulation of the genes related to microtubule kinetics and the downregulation of the mRNA degradation system. The gene set enrichment analysis showed the suppression of "nonsense-mediated mRNA decay (NMD)" as the most significantly affected gene set. These data provide a new aspect and a potential utility of rigosertib for the treatment of refractory hematopoietic malignancies.

Beyond hypomethylating agents failure in patients with myelodysplastic syndromes

PURPOSE OF REVIEW

Although hypomethylating agents (HMAs) significantly improve outcomes in myelodysplastic syndromes (MDS), only half the patients achieve objective responses, and most responders lose response within 1-2 years. Azacitidine prolongs survival by a median of only 9.5 months. Failure of HMA therapy is associated with a very dismal prognosis. Therefore, novel therapeutic approaches are clearly needed.

RECENT FINDINGS

The sequential use of the alternative HMA after failure of first line HMA is associated with modest efficacy. The improved understanding of the biologic underpinnings of the disease have opened the door to study investigational agents that target disrupted molecular pathways critical to the pathogenesis of MDS. Combination treatment strategies using an azacitidine backbone are demonstrating promising early results. Expanding the applicability of allogeneic stem cell transplantation (alloSCT), the only curative modality, by reducing toxicity and relapse rates is another area of active research.

SUMMARY

Sequential switching to the alternative HMA, clinical trials of novel targeted therapies, azacitidine-based combination therapeutic strategies, and improvements in the alloSCT platform are the main directions in improving outcomes of MDS post HMA failure.

Nuclear PI-PLCβ1: an appraisal on targets and pathology

Lipid signalling molecules are essential components of the processes that allow one extracellular signal to be transferred inside the nucleus, where specific lipid second messengers elicit reactions capable of regulating gene transcription, DNA replication or repair and DNA cleavage, eventually resulting in cell growth, differentiation, apoptosis or many other cell functions. Nuclear inositides are independently regulated, suggesting that the nucleus constitutes a functionally distinct compartment of inositol lipids metabolism. Indeed, nuclear inositol lipids themselves can modulate nuclear processes, such as transcription and pre-mRNA splicing, growth, proliferation, cell cycle regulation and differentiation. Nuclear PI-PLCβ1 is a key molecule for nuclear inositide signalling, where it plays a role in cell cycle progression, proliferation and differentiation. Here we review the targets and possible involvement of nuclear PI-PLCβ1 in human physiology and pathology.

TP53 suppression promotes erythropoiesis in del(5q) MDS, suggesting a targeted therapeutic strategy in lenalidomide-resistant patients

Stabilization of p53 in erythroid precursors in response to nucleosomal stress underlies the hypoplastic anemia in myelodysplastic syndromes (MDS) with chromosome 5q deletion [del(5q)]. We investigated whether cenersen, a clinically active 20-mer antisense oligonucleotide complementary to TP53 exon10, could suppress p53 expression and restore erythropoiesis in del(5q) MDS. Cenersen treatment of ribosomal protein S-14-deficient erythroblasts significantly reduced cellular p53 and p53-up-regulated modulator of apoptosis expression compared with controls, accompanied by a significant reduction in apoptosis and increased cell proliferation. In a two-stage erythroid differentiation assay, cenersen significantly suppressed nuclear p53 in bone marrow CD34+ cells isolated from patients with del(5q) MDS, whereas erythroid burst recovery increased proportionally to the magnitude of p53 suppression without evidence of del(5q) clonal suppression (r = -0.6; P = 0.005). To explore the effect of p53 suppression on erythropoiesis in vivo, dexamethasone, a glucocorticoid receptor-dependent p53 antagonist, was added to lenalidomide treatment in eight lower-risk, transfusion-dependent, del(5q) MDS patients with acquired drug resistance. Transfusion independence was restored in five patients accompanied by expansion of erythroid precursors and decreased cellular p53 expression. We conclude that targeted suppression of p53 could support effective erythropoiesis in lenalidomide-resistant del(5q) MDS.

Current therapy of myelodysplastic syndromes

After being a neglected and poorly-understood disorder for many years, there has been a recent explosion of data regarding the complex pathogenesis of myelodysplastic syndromes (MDS). On the therapeutic front, the approval of azacitidine, decitabine, and lenalidomide in the last decade was a major breakthrough. Nonetheless, the responses to these agents are limited and most patients progress within 2 years. Allogeneic stem cell transplantation remains the only potentially curative therapy, but it is associated with significant toxicity and limited efficacy. Lack or loss of response after standard therapies is associated with dismal outcomes. Many unanswered questions remain regarding the optimal use of current therapies including patient selection, response prediction, therapy sequencing and combinations, and management of resistance. It is hoped that the improved understanding of the underpinnings of the complex mechanisms of pathogenesis will be translated into novel therapeutic approaches and better prognostic/predictive tools that would facilitate accurate risk-adaptive therapy.