Lenalidomide promotes p53 degradation by inhibiting MDM2 auto-ubiquitination in myelodysplastic syndrome with chromosome 5q deletion

Design and synthetic approaches to thalidomide based small molecule degraders

Thalidomide has been used as a repurposed drug for treating multiple myeloma since 1997. Several novel anticancer drugs containing thalidomide active moiety has been discovered since then. Many thalidomide drug candidates with tuned linker size have been instrumental in inhibiting histone deacetylase, kinase, transcription factors etc. and facilitate selective degradation of E3 ligase and other enzymes. Here we are focused on small molecule degraders that are being tailored with tweaking synthetic architectures around thalidomide chemical motif towards the development of promising drug candidates. Interesting biomedical applications of thalidomide-based degraders with recent developments including pharmacokinetic profiles, protein stability, activity studies, degradation assays, and antitumor response are elucidated.

PP2A adapter protein IER5 induces dephosphorylation and degradation of MDM2, thereby stabilizing p53

The tumor suppressor p53 activates transcription of the IER5 gene, which encodes an adapter protein of protein phosphatase PP2A. IER5 binds to both the B55 regulatory subunit of PP2A and PP2A's target proteins, facilitating PP2A/B55-catalyzed dephosphorylation of these proteins. Here, we show that IER5 functions as a positive regulator of p53 by inhibiting its ubiquitination, thereby increasing cellular p53 levels. Mechanistically, this effect of IER5 requires its nuclear localization and binding to both PP2A/B55 and the p53 ubiquitin E3 ligase MDM2. Importantly, IER5 fails to inhibit p53 ubiquitination in cells treated with the MDM2 inhibitor Nutlin-3. The IER5-PP2A/B55 complex dephosphorylates MDM2 at Ser166, leading to MDM2 ubiquitination and a reduction in nuclear MDM2. Altogether, our data provide evidence that IER5-PP2A/B55 regulates the nuclear balance between MDM2 and p53 via MDM2 dephosphorylation.

Abnormalities in Chromosomes 5 and 7 in Myelodysplastic Syndrome and Acute Myeloid Leukemia

Chromosomes 5 and 7 are large chromosomes that contain close to 1,000 genes each. Deletions of the long arms or loss of the entire chromosome (monosomy) are common defects in myeloid disorders, particularly MDS and AML. Loss of material from either chromosome 5 or 7 results in haploinsufficiency of multiple genes, with some implicated in leukemogenesis. Abnormalities of one or both occur in up to 15% of MDS and AML cases and co-segregate in half of these. Generally, these chromosomal abnormalities are harbingers of adverse risk in both myeloid disorders. A notable exception is del(5q) in 5q- syndrome, a subtype of MDS. In this review, we describe the pathogenesis and genetic consequences of deletions in chromosomes 5 and 7. Furthermore, we provide an overview of current testing methodologies used in the assessment of these chromosomal defects in hematological malignancies and describe the disease associations and prognostic implications of aberrations in chromosomes 5 and 7 in both MDS and AML.

Rituximab and lenalidomide for the treatment of relapsed or refractory indolent non-Hodgkin lymphoma: real-life experience

The combination of rituximab and lenalidomide (R-len) stands as an established treatment for relapsed/refractory (R/R) indolent non-Hodgkin lymphoma (iNHL). However, the reproducibility of clinical trial results in routine clinical practice is unknown. To address this gap in knowledge, we reviewed our experience with patients diagnosed with R/R follicular lymphoma (FL) or marginal zone lymphoma (MZL) treated with this combination. Eighty-four patients underwent treatment with R-len, 69 (82%) affected by FL and 15 (18%) by MZL. The median age at the time of treatment initiation was 65 years (range, 39-94), 38 patients (45%) had a pretreatment FLIPI score of 3-5, 19 (23%) had a bulky disease, 29 (37%) had a lymphoma refractory to the last treatment line, while in 20 (24%) cases the disease was refractory to rituximab. The best overall response rate was 82%, and 52% achieved a complete response (CR). The best CR rates for FL and MZL patients were 55% and 40%, respectively. With a median follow-up of 22 months, the median progression- free survival was 22 months (95% confidence interval [CI]: 19-36) and the 2-year overall survival was 83% (95% CI: 74-93). The median duration of CR was 46 months (95% CI: 22-not reached). Factors associated with shorter progression-free survival in multivariate analysis were bulky disease and rituximab refractoriness. The most common adverse events included hematologic toxicity, fatigue and gastrointestinal disorders, such as diarrhea and constipation. Neutropenia and thrombocytopenia were the most common severe toxicities (grade ≥3 in 25% and 4%, respectively). No new safety signals were reported. Real-life results of R-len in patients with R/R iNHL appear consistent with those reported in prospective studies, and further support its use as comparator arm in controlled clinical trials.

A line in shifting sand: Can we define and target TP53 mutated MDS?

Mutations in the tumor suppressor protein, TP53, lead to dismal outcomes in myeloid malignancies, including myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Recent pathological reclassifications have integrated TP53 mutated MDS and AML under a unified category of TP53 mutated myeloid neoplasms, which allows for more flexibility in treatment approaches. Therapeutic strategies have predominantly mirrored those for AML, with allogeneic stem cell transplantation emerging as critical for long-term disease control. The question remains whether there are physiological distinctions within TP53 mutated myeloid neoplasms that will significantly impact prognosis and therapeutic considerations. This review explores the unique aspects of classically defined "TP53 mutated MDS", focusing on its distinct biological characteristics and outcomes. Our current understanding is that TP53 mutated MDS and AML are globally quite similar, but as a group have unique features compared to TP53 wildtype (WT) disease. Optimizing immunotherapy and targeting vulnerabilities due to co-mutations and/or chromosome abnormalities should be the focus of future research.

Targeted protein degradation: from mechanisms to clinic

Targeted protein degradation refers to the use of small molecules to induce the selective degradation of proteins. In its most common form, this degradation is achieved through ligand-mediated neo-interactions between ubiquitin E3 ligases - the principal waste disposal machines of a cell - and the protein targets of interest, resulting in ubiquitylation and subsequent proteasomal degradation. Notable advances have been made in biological and mechanistic understanding of serendipitously discovered degraders. This improved understanding and novel chemistry has not only provided clinical proof of concept for targeted protein degradation but has also led to rapid growth of the field, with dozens of investigational drugs in active clinical trials. Two distinct classes of protein degradation therapeutics are being widely explored: bifunctional PROTACs and molecular glue degraders, both of which have their unique advantages and challenges. Here, we review the current landscape of targeted protein degradation approaches and how they have parallels in biological processes. We also outline the ongoing clinical exploration of novel degraders and provide some perspectives on the directions the field might take.

Low dose lenalidomide versus placebo in non-transfusion dependent patients with low risk, del(5q) myelodysplastic syndromes (SintraREV): a randomised, double-blind, phase 3 trial

BACKGROUND

Lenalidomide is the standard of care for patients who are transfusion dependent with chromosome 5q deletion (del[5q]) myelodysplastic syndromes. In the SintraREV trial, we aimed to investigate whether an early intervention of low lenalidomide doses for 2 years could delay transfusion dependency in patients with anaemia who were not transfusion dependent.

METHODS

This randomised, double-blind, phase 3 trial, was conducted at 22 sites (University Hospitals) in Spain, France, and Germany. Eligible patients were aged 18 years or older diagnosed with low-risk or intermediate-1-risk del(5q) myelodysplastic syndromes with non-transfusion-dependent anaemia (according to the IPSS), were erythropoietin-stimulating agents naive, and had an ECOG performance status of 2 or less. Patients were randomly assigned (2:1) by means of a telephone system to receive lenalidomide 5 mg daily in 28-day cycles versus placebo for 2 years. The primary endpoint was time to transfusion dependency based on blinded independent central review. Analysis were by intent-to-treat (ITT) and evaluable population. Safety analyses included all participants who received at least one dose of treatment. This trial is registered with ClinicalTrials.gov (NCT01243476) and EudraCT (2009-013619-36) and is complete.

FINDINGS

Between Feb 15, 2010, and Feb 21, 2018, 61 patients were randomly assigned to receive lenalidomide (n=40; two did not receive treatment) or placebo (n=21). The median age was 72·2 (IQR 65·4-81·9) years, 50 (82%) patients were female, and 11 (18%) were male. The median follow-up time was 60·6 (IQR 32·1-73·9) months. Regarding primary endpoint, median time to transfusion dependency was not reached (95% CI not applicable) in the lenalidomide group versus 11·6 months (95% CI 0·00-30·11) in the placebo group (p=0·0027). Lenalidomide significantly reduced the risk of transfusion dependency by 69·8% (hazard ratio 0·302, 95% CI 0·132-0·692; p=0·0046). The most frequent treatment-related adverse event was neutropenia, occurring in 24 (63%) of 38 patients in the lenalidomide group (grade 3 and 4 in 17 [45%] patients and one [3%], respectively) and in four (19%) of 21 patients in the placebo group (grade 3 in one [5%] patient). Thrombocytopenia was detected in seven (18%) of 38 patients receiving lenalidomide (grade 3 in two [5%] patients). Regarding the non-haematological toxicity, skin disorders (rash nine [23%] of 38 patients) were the most frequently described toxicities among patients receiving lenalidomide, being grade 3 in one (3%) of 38 patients. 19 serious adverse events were reported in 13 patients, 18 in the lenalidomide group and one in the placebo group, five of which were potentially related to the study drug. No treatment-related deaths were identified.

INTERPRETATION

An early approach with low doses of lenalidomide across two years delays the time to transfusion dependency and improves the rate and quality of the responses, with a manageable safety profile in patients who are non-transfusion dependent with del(5q) low-risk myelodysplastic syndromes.

FUNDING

Bristol Myers Squibb.

Myelodysplastic syndromes del(5q): Pathogenesis and its therapeutic implications

Myelodysplastic syndromes (MDS) encompass a heterogeneous set of acquired bone marrow neoplastic disorders characterized by ineffective hematopoiesis within one or more bone marrow lineages. Nearly half of MDS patients carry cytogenetic alterations, with del(5q) being the most prevalent. Since its first description, del(5q) was consistently correlated with a typical clinical phenotype marked by anemia, thrombocytosis, and a low risk of evolving into acute leukemia. Presently, the World Health Organization (WHO) classification of myeloid neoplasms recognizes a specific subtype of MDS known as "myelodysplastic neoplasm with low blast and isolated del(5q)" identified by the sole presence of 5q deletion or in combination with one other abnormality excluding -7/del(7q). Several studies have sought to unravel the biological processes triggered by del(5q) in the development of MDS, revealing the involvement of various genes localized in specific regions of chromosome 5 referred to as common deleted regions (CDR). This intricate biological landscape makes the MDS cells with del(5q) exceptionally sensitive to lenalidomide. Several studies have confirmed the efficacy of lenalidomide in this context. Regrettably, the response to lenalidomide is not conclusive, prompting ongoing research into biological mechanisms that drive patients toward leukemia and strategies to circumvent lenalidomide resistance and disease progression.

Targeting cereblon in hematologic malignancies

The protein cereblon (CRBN) is a substrate receptor of the cullin 4-really interesting new gene (RING) E3 ubiquitin ligase complex CRL4^CRBN. Targeting CRBN mediates selective protein ubiquitination and subsequent degradation via the proteasome. This review describes novel thalidomide analogs, immunomodulatory drugs, also known as CRBN E3 ubiquitin ligase modulators or molecular glues (avadomide, iberdomide, CC-885, CC-90009, BTX-1188, CC-92480, CC-99282, CFT7455, and CC-91633), and CRBN-based proteolysis targeting chimeras (PROTACs) with increased efficacy and potent activity for application in hematologic malignancies. Both types of CRBN-binding drugs, molecular glues, and PROTACs stimulate the interaction between CRBN and its neosubstrates, recruiting target disease-promoting proteins and the E3 ubiquitin ligase CRL4^CRBN. Proteins that are traditionally difficult to target (transcription factors and oncoproteins) can be polyubiquitinated and degraded in this way. The competition of CRBN neosubstrates with endogenous CRBN-interacting proteins and the pharmacology and rational combination therapies of and mechanisms of resistance to CRL4^CRBN modulators or CRBN-based PROTACs are described.

Epigenetic Silencing of PTEN and Epi-Transcriptional Silencing of MDM2 Underlied Progression to Secondary Acute Myeloid Leukemia in Myelodysplastic Syndrome Treated with Hypomethylating Agents

In myelodysplastic syndrome (MDS), resistance to hypomethylating agents (HMA) portends a poor prognosis, underscoring the importance of understanding the molecular mechanisms leading to HMA-resistance. In this study, P39 and Kasumi-1 cells and their azacitidine-resistant and decitabine-resistant sublines were evaluated comparatively with transcriptomic and methylomic analyses. Expression profiling and genome-wide methylation microarray showed downregulation of PTEN associated with DNA hypermethylation in P39 cell lines resistant to azacitidine and decitabine. This pattern of PTEN dysregulation was also confirmed in a cohort of patients failing treatment with HMA. DNA hypomethylation of MDM2 was detected with downregulation of MDM2 in HMA resistant cell lines. Long-read sequencing revealed significant RNA hypomethylation of MDM2 resulting in alternative splicing and production of a truncated MDM2 transcript in azacitidine-resistant P39 cells. The expression of this MDM2 truncated transcript was also significantly increased in HMA-resistant patients compared with HMA-responsive patients. In conclusion, epigenetic and epi-transcriptomic dysregulation of PTEN and MDM2 were associated with resistance to hypomethylating agents.

Evolution of severe (transfusion-dependent) anaemia in myelodysplastic syndromes with 5q deletion is characterized by a macrophage-associated failure of the eythropoietic niche

Evolution of erythrocyte transfusion-dependent (RBC-TD) anaemia associated with haploinsufficiency of the ribosomal protein subunit S14 gene (RPS14) is a characteristic complication of myelodysplastic syndromes (MDS) with del(5q) [MDS.del(5q)]. Evaluating 39 patients with MDS.del(5q), <5% of anaemia progression was attributable to RPS14-dependent alterations of normoblasts, pro-erythroblasts, or CD34⁺ CD71⁺ precursors. Ninety-three percent of anaemia progression and 70% of the absolute decline in peripheral blood Hb value were attributable to disappearance of erythroblastic islands (Ery-Is). Ery-Is loss occurred independently of blast excess, TP53 mutation, additional chromosome aberrations and RPS14-dependent alterations of normoblasts and pro-erythroblasts. It was associated with RPS14-dependent intrinsic (S100A8⁺ ) and extrinsic [tumour necrosis factor α (TNF-α)-overproduction] alterations of (CD169⁺ ) marrow macrophages (p < 0.00005). In a mouse model of RPS14 haploinsufficiency, Ery-Is disappeared to a similar degree: approximately 70% of Ery-Is loss was related to RPS14-dependent S100A8 overexpression of marrow macrophages, less than 20% to that of CD71^high Ter119^- immature precursors, and less than 5% to S100A8/p53 overexpression of normoblasts or pro-erythroblasts. Marked Ery-Is loss predicted reduced efficacy (erythrocyte transfusion independence) of lenalidomide therapy (p = 0.0006). Thus, erythroid hypoplasia, a characteristic complication of MDS.del(5q), seems to result primarily from a macrophage-associated failure of the erythropoietic niche markedly reducing the productive capacity of erythropoiesis as the leading factor in anaemia progression and evolution of RBC-TD in MDS.del(5q).

Novel Molecular Mechanism of Lenalidomide in Myeloid Malignancies Independent of Deletion of Chromosome 5q

Lenalidomide as well as other immunomodulatory drugs (IMiDs) have achieved clinical efficacies in certain sub-types of hematologic malignancies, such as multiple myeloma, lower-risk myelodysplastic syndromes (MDS) with a single deletion of chromosome 5q (del(5q)) and others. Despite superior clinical response to lenalidomide in hematologic malignancies, relapse and resistance remains a problem in IMiD-based therapy. The last ten years have witnessed the discovery of novel molecular mechanism of IMiD-based anti-tumor therapy. IMiDs bind human cereblon (CRBN), the substrate receptor of the CRL4 E3 ubiquitin ligase complex. Binding of CRBN with IMiDs leads to degradation of the Ikaros family zinc finger proteins 1 and 3 (IKZF1 and IKZF3) and casein kinase 1 alpha. We have found that lenalidomide-mediated degradation of IKZF1 leads to activation of the G protein-coupled receptor 68 (GPR68)/calcium/calpain pro-apoptotic pathway and inhibition of the regulator of calcineurin 1 (RCAN1)/calcineurin pro-survival pathway in MDS and acute myeloid leukemia (AML). Calcineurin inhibitor Cyclosporin-A potentiates the anti-leukemia activity of lenalidomide in MDS/AML with or without del(5q). These findings broaden the therapeutic potential of IMiDs. This review summarizes novel molecular mechanism of lenalidomide in myeloid malignancies, especially without del(5q), in the hope to highlight novel therapeutic targets.

TIFAB Regulates USP15-Mediated p53 Signaling during Stressed and Malignant Hematopoiesis

TRAF-interacting protein with a forkhead-associated domain B (TIFAB) is implicated in myeloid malignancies with deletion of chromosome 5q. Employing a combination of proteomic and genetic approaches, we find that TIFAB regulates ubiquitin-specific peptidase 15 (USP15) ubiquitin hydrolase activity. Expression of TIFAB in hematopoietic stem/progenitor cells (HSPCs) permits USP15 signaling to substrates, including MDM2 and KEAP1, and mitigates p53 expression. Consequently, TIFAB-deficient HSPCs exhibit compromised USP15 signaling and are sensitized to hematopoietic stress by derepression of p53. In MLL-AF9 leukemia, deletion of TIFAB increases p53 signaling and correspondingly decreases leukemic cell function and development of leukemia. Restoring USP15 expression partially rescues the function of TIFAB-deficient MLL-AF9 cells. Conversely, elevated TIFAB represses p53, increases leukemic progenitor function, and correlates with MLL gene expression programs in leukemia patients. Our studies uncover a function of TIFAB as an effector of USP15 activity and rheostat of p53 signaling in stressed and malignant HSPCs.

Niederkorn et al. identify TIFAB as a critical node in hematopoietic cells under stressed and oncogenic cell states. Their studies indicate that deregulation of the TIFAB-USP15 complex, as observed in del(5q) myelodysplasia or MLL-rearranged leukemia, modulates p53 activity and has critical functional consequences for stressed and malignant hematopoietic cells.

Mechanisms of lenalidomide sensitivity and resistance

The discovery that the immunomodulatory imide drugs (IMiDs) possess antitumor properties revolutionized the treatment of specific types of hematological cancers. Since then, much progress has been made in understanding why the IMiDs are so efficient in targeting the malignant clones in difficult-to-treat diseases. Despite their efficacy, IMiD resistance arises eventually. Herein we summarize the mechanisms of sensitivity and resistance to lenalidomide in del(5q) myelodysplastic syndrome and multiple myeloma, two diseases in which these drugs are at the therapeutic frontline. Understanding the molecular and cellular mechanisms underlying IMiD efficacy and resistance may allow development of specific strategies to eliminate the malignant clone in otherwise incurable diseases.

Ribosomopathies: New Therapeutic Perspectives

Ribosomopathies are a group of rare diseases in which genetic mutations cause defects in either ribosome biogenesis or function, given specific phenotypes. Ribosomal proteins, and multiple other factors that are necessary for ribosome biogenesis (rRNA processing, assembly of subunits, export to cytoplasm), can be affected in ribosomopathies. Despite the need for ribosomes in all cell types, these diseases result mainly in tissue-specific impairments. Depending on the type of ribosomopathy and its pathogenicity, there are many potential therapeutic targets. The present manuscript will review our knowledge of ribosomopathies, discuss current treatments, and introduce the new therapeutic perspectives based on recent research. Diamond–Blackfan anemia, currently treated with blood transfusion prior to steroids, could be managed with a range of new compounds, acting mainly on anemia, such as L-leucine. Treacher Collins syndrome could be managed by various treatments, but it has recently been shown that proteasomal inhibition by MG132 or Bortezomib may improve cranial skeleton malformations. Developmental defects resulting from ribosomopathies could be also treated pharmacologically after birth. It might thus be possible to treat certain ribosomopathies without using multiple treatments such as surgery and transplants. Ribosomopathies remain an open field in the search for new therapeutic approaches based on our recent understanding of the role of ribosomes and progress in gene therapy for curing genetic disorders.

Loss of 5q in myeloid malignancies - A gain in understanding of biological and clinical consequences

Hemizygous interstitial or terminal deletion of the long arm of chromosome 5 [del(5q)] is a recurrent cytogenetic abnormality in myeloid malignancies, including myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). These deletions cause loss of a large contiguous chromosomal region encompassing more than 30 genes, which results in disease through haploinsufficiency of one or more genes including RPS14. In MDS, del(5q) in isolation is a lower-risk cytogenetic anomaly and is sometimes associated with a unique clinicopathological phenotype, but in AML it represents a higher-risk lesion, often denoting secondary AML arising from prior MDS. Lenalidomide effectively targets the del(5q)-bearing clone in MDS, resulting in sustained erythroid transfusion independence in most patients and cytogenetic remission in a subset of treated patients. Since the initial regulatory approval of lenalidomide for del(5q) MDS in 2005, translational research endeavors in del(5q)-associated myeloid malignancies have improved our understanding of how allelic haploinsufficiency underlies both the hematological phenotype and selective sensitivity to lenalidomide therapy. This review will focus on the molecular pathogenesis of del(5q) in myeloid malignancies, clinical development of lenalidomide and emerging data on lenalidomide-refractory del (5q) MDS, and possible novel targeted therapeutic strategies.

Regulating tumor suppressor genes: post-translational modifications

Tumor suppressor genes cooperate with each other in tumors. Three important tumor suppressor proteins, retinoblastoma (Rb), p53, phosphatase, and tensin homolog deleted on chromosome ten (PTEN) are functionally associated and they regulated by post-translational modification (PTMs) as well. PTMs include phosphorylation, SUMOylation, acetylation, and other novel modifications becoming growing appreciated. Because most of PTMs are reversible, normal cells use them as a switch to control the state of cells being the resting or proliferating, and PTMs also involve in cell survival and cell cycle, which may lead to abnormal proliferation and tumorigenesis. Although a lot of studies focus on the importance of each kind of PTM, further discoveries shows that tumor suppressor genes (TSGs) form a complex "network" by the interaction of modification. Recently, there are several promising strategies for TSGs for they change more frequently than carcinogenic genes in cancers. We here review the necessity, characteristics, and mechanisms of each kind of post-translational modification on Rb, p53, PTEN, and its influence on the precise and selective function. We also discuss the current antitumoral therapies of Rb, p53 and PTEN as predictive, prognostic, and therapeutic target in cancer.

TP53 in Myelodysplastic Syndromes: Recent Biological and Clinical Findings

TP53 dysregulation plays a pivotal role in the molecular pathogenesis of myelodysplastic syndromes (MDS), identifying a subgroup of patients with peculiar features. In this review we report the recent biological and clinical findings of TP53-mutated MDS, focusing on the molecular pathways activation and on its impact on the cellular physiology. In MDS, TP53 mutational status is deeply associated with del(5q) syndrome and its dysregulation impacts on cell cycle, DNA repair and apoptosis inducing chromosomal instability and the clonal evolution of disease. TP53 defects influence adversely the MDS clinical outcome and the treatment response rate, thus new therapeutic approaches are being developed for these patients. TP53 allelic state characterization and the mutational burden evaluation can therefore predict prognosis and identify the subgroup of patients eligible for targeted therapy. For these reasons, in the era of precision medicine, the MDS diagnostic workup cannot do without the complete assessment of TP53 mutational profile.

Higher-risk myelodysplastic syndromes with del(5q): does the del(5q) matter?

Introduction: Myelodysplastic Syndrome (MDS) represents a group of cancers characterized by abnormal blood cell formation and maturation, leading to various degrees of cytopenias and potential transformation to acute myeloid leukemia. Deletion of the long arm of chromosome 5 (del(5q)) is the most common clonal chromosomal anomaly in MDS, yet the population in this disease subtype is quite heterogeneous. This manuscript analyzes literature on high-risk MDS with del(5q) abnormalities.Areas covered: The paper will review outcomes with lenalidomide among high-risk MDS patients with del(5q). It will discuss the implications of harboring TP53 gene mutations, and share the data for allogeneic hematopoietic stem cell transplantations in this setting. Finally, the report evaluates the risk of disease progression in these patients.Expert commentary: Improved characterization of MDS has enhanced our understanding of patients with anomalies involving del(5q). Emerging literature is exploring combination therapy beyond lenalidomide, and next-generation sequencing may identify secondary mutations that could be an additional avenue for treatment.

Cyclosporine Broadens the Therapeutic Potential of Lenalidomide in Myeloid Malignancies

The immunomodulatory drug lenalidomide is used for the treatment of certain hematologic malignancies, including myelodysplastic syndromes (MDS). Lenalidomide interacts with cereblon (CRBN), a component of the CRL4CRBN E3 ubiquitin ligase complex, leading to ubiquitination and subsequent degradation of substrates, such as transcription factor Ikaros (Ikaros family zinc finger 1, IKZF1). With a genome loss of function screen, we recently identified two novel pathways mediated by lenalidomide in MDS. In this review, we summarized the major findings of these two pathways and their clinical implications. Depletion of G protein-coupled receptor 68 (GPR68) or an endogenous calcineurin (CaN) inhibitor, regulator of calcineurin 1 (RCAN1), reversed the inhibitory effect of lenalidomide on MDSL cells, an MDS cell line. Intriguingly, both GPR68 and RCAN1 expression levels were upregulated in MDSL cells after treatment with lenalidomide that was dependent on diminishment of IKZF1, indicating that IKZF1 functioned as a transcription repressor for GPR68 and RCAN1. Mechanistic studies revealed that upregulation or activation of GPR68 induced a Ca2+/calpain pro-apoptotic pathway, while upregulation of RCAN1 inhibited the CaN pro-survival pathway in MDSL cells. Notably, the pharmacological CaN inhibitor, cyclosporine, enhanced the sensitivity to lenalidomide in MDS as well as acute myeloid leukemia (AML). Surprisingly, pretreatment with lenalidomide reversed the immunosuppressive effects of cyclosporine on T lymphocytes. Our studies suggest that lenalidomide mediates degradation of IKZF1, leading to derepression of GPR68 and RCAN1 that activates the Ca2+/calpain pro- apoptotic pathway and inhibits the CaN pro-survival pathway, respectively. Our studies implicate that cyclosporine extends the therapeutic potential of lenalidomide to myeloid malignancies without compromising immune function.

MMP9 inhibition increases erythropoiesis in RPS14-deficient del(5q) MDS models through suppression of TGF-β pathways

The del(5q) myelodysplastic syndrome (MDS) is a distinct subtype of MDS, associated with deletion of the ribosomal protein S14 (RPS14) gene that results in macrocytic anemia. This study sought to identify novel targets for the treatment of patients with del(5q) MDS by performing an in vivo drug screen using an rps14-deficient zebrafish model. From this, we identified the secreted gelatinase matrix metalloproteinase 9 (MMP9). MMP9 inhibitors significantly improved the erythroid defect in rps14-deficient zebrafish. Similarly, treatment with MMP9 inhibitors increased the number of colony forming unit-erythroid colonies and the CD71+ erythroid population from RPS14 knockdown human BMCD34+ cells. Importantly, we found that MMP9 expression is upregulated in RPS14-deficient cells by monocyte chemoattractant protein 1. Double knockdown of MMP9 and RPS14 increased the CD71+ population compared with RPS14 single knockdown, suggesting that increased expression of MMP9 contributes to the erythroid defect observed in RPS14-deficient cells. In addition, transforming growth factor β (TGF-β) signaling is activated in RPS14 knockdown cells, and treatment with SB431542, a TGF-β inhibitor, improved the defective erythroid development of RPS14-deficient models. We found that recombinant MMP9 treatment decreases the CD71+ population through increased SMAD2/3 phosphorylation, suggesting that MMP9 directly activates TGF-β signaling in RPS14-deficient cells. Finally, we confirmed that MMP9 inhibitors reduce SMAD2/3 phosphorylation in RPS14-deficient cells to rescue the erythroid defect. In summary, these study results support a novel role for MMP9 in the pathogenesis of del(5q) MDS and the potential for the clinical use of MMP9 inhibitors in the treatment of patients with del(5q) MDS.

Getting personal with myelodysplastic syndromes: is now the right time?

INTRODUCTION

Commonly used scoring systems rely on blood counts, histological and cytological examination of bone marrow and peripheral blood as well as cytogenetic assessments to estimate prognosis of patients with myelodysplastic syndromes (MDS) and guide therapy decisions. Next-generation sequencing (NGS) has identified recurrent genetic abnormalities in up to 90% of patients with MDS and may provide important information regarding the pathogenesis of the disease, diagnostic and prognostic evaluation, and therapy selection. Areas covered: Herein, the authors review the role of NGS in diagnosis, treatment, and prognosis of MDS at various disease stages, and discuss advantages and caveats of incorporating molecular genetics in routine management of MDS. While a vast majority of patients harbor recurrent mutations implicated in MDS pathogenesis, similar mutations can be detected in otherwise healthy individuals with other hematologic malignancies. Besides establishing a diagnosis, NGS may be used to monitor minimal residual disease following treatment. Expert opinion: As more targeted therapies become available, assessment of genetic mutations will become central to individualized therapy selection and may improve diagnostic accuracy and further guide management for each patient. However, multiple challenges remain before NGS can be incorporated into routine clinical practice.

Molecular pathogenesis of myelodysplastic syndromes with deletion 5q

The molecular pathogenesis of deletion 5q (del(5q)) myelodysplastic syndrome (MDS) has recently been realized as a result of major advances in our understanding of the mechanisms responsible for clinical phenotype. Identification of commonly deleted genes such as RPS14, miRNA-145, HSPA9, CD78, and CSNK1a1 have elucidated the precise biological changes responsible for the anemia, leukopenia, and thrombocytosis that characterizes del(5q) MDS and highlighted the importance of allelic haploinsufficiency in the hematological phenotype. Recent elegant investigations have also identified a critical role of innate immune signaling in del(5q) pathogenesis. TP53 and Wnt/β-catenin pathways have also been found to be involved in clonal expansion and progression of the disease as well as resistance and poor outcomes to available therapy. Understanding the molecular pathogenesis of the disease has provided a critical foundation in identifying the biological targets of lenalidomide in del(5q) MDS, which has led to the development of novel therapeutic agents in hematologic malignancies as well as potential alternative targets to exploit in patients who have failed lenalidomide treatment.

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.

PTEN deletion in luminal cells of mature prostate induces replication stress and senescence in vivo

Genetic ablation of the tumor suppressor PTEN in prostatic epithelial cells (PECs) induces cell senescence. However, unlike oncogene-induced senescence, no hyperproliferation phase and no signs of DNA damage response (DDR) were observed in PTEN-deficient PECs; PTEN loss-induced senescence (PICS) was reported to be a novel type of cellular senescence. Our study reveals that PTEN ablation in prostatic luminal epithelial cells of adult mice stimulates PEC proliferation, followed by a progressive growth arrest with characteristics of cell senescence. Importantly, we also show that proliferating PTEN-deficient PECs undergo replication stress and mount a DDR leading to p53 stabilization, which is however delayed by Mdm2-mediated p53 down-regulation. Thus, even though PTEN-deficiency induces cellular senescence that restrains tumor progression, as it involves replication stress, strategies promoting PTEN loss-induced senescence are at risk for cancer prevention and therapy.

Immunomodulatory Drugs Exert Anti-Leukemia Effects in Acute Myeloid Leukemia by Direct and Immunostimulatory Activities

Immunomodulatory drugs (IMiDs) are anticancer drugs with immunomodulatory, anti-angiogenesis, anti-proliferative, and pro-apoptotic properties. IMiDs are currently used for the treatment of multiple myeloma, myelodysplastic syndrome, and B-cell lymphoma; however, little is known about efficacy in acute myeloid leukemia (AML). We proposed in this study to investigate the relevance of IMiDs therapy for AML treatment. We evaluated the effect of IMiDs on primary AML blasts (n = 24), and the impact in natural killer (NK) cell-mediated immunosurveillance of AML. Using primary AML cells and an immunodeficient mouse leukemia xenograft model, we showed that IMiDs induce AML cell death in vitro and impair leukemia progression in vivo. In addition, treatment of AML blasts with IMiDs resulted in enhanced allogeneic NK cell anti-leukemia reactivity. Treatment by pomalidomide of AML blasts enhanced lysis, degranulation, and cytokine production by primary allogeneic NK cells. Furthermore, the treatment with lenalidomide of patients with myeloid malignancies resulted in NK cell phenotypic changes similar to those observed in vitro. IMiDs increased CD56 and decreased NKp30, NKp46, and KIR2D expression on NK cells. Finally, AML blasts treatment with IMiDs induced phenotypic alterations including downregulation of HLA-class I. The effect of pomalidomide was not correlated with cereblon expression and A/G polymorphism in AML cells. Our data revealed, a yet unobserved, dual effects on AML affecting both AML survival and their sensitivity to NK immunotherapy using IMiDs. Our study encourages continuing investigation for the use of IMiDs in AML, especially in combination with conventional therapy or immunotherapy strategies.

FGFR2 mutations in bent bone dysplasia syndrome activate nucleolar stress and perturb cell fate determination

Fibroblast Growth Factor (FGF) signaling promotes self-renewal in progenitor cells by encouraging proliferation and inhibiting cellular senescence. Yet, these beneficial effects can be hijacked by disease-causing mutations in FGF receptor (FGFR) during embryogenesis. By studying dominant FGFR2 mutations that are germline in bent bone dysplasia syndrome (BBDS), we reveal a mechanistic connection between FGFR2, ribosome biogenesis, and cellular stress that links cell fate determination to disease pathology. We previously showed that FGFR2 mutations in BBDS, which amplify nucleolar targeting of FGFR2, activate ribosomal DNA (rDNA) transcription and delay differentiation in osteoprogenitor cells and patient-derived bone. Here we find that the BBDS mutations augment the ability of FGFR2 to recruit histone-remodeling factors that epigenetically activate transcriptionally silent rDNA. Nucleolar morphology is controlled by chromatin structure, and the high levels of euchromatic rDNA induced by the BBDS mutations direct nucleolar disorganization, alter ribosome biogenesis, and activate the Rpl11-Mdm2-p53 nucleolar stress response pathway. Inhibition of p53 in cells expressing the FGFR2 mutations in BBDS rescues delayed osteoblast differentiation, suggesting that p53 activation is an essential pathogenic factor in, and potential therapeutic target for, BBDS. This work establishes rDNA as developmentally regulated loci that receive direct input from FGF signaling to balance self-renewal and cell fate determination.

Genetic susceptibility to thalidomide embryopathy in humans: Study of candidate development genes

Thalidomide is a drug used worldwide for several indications, but the molecular mechanisms of its teratogenic property are not fully understood. Studies in animal models suggest the oxidative stress, the inhibition of angiogenesis, and the binding to E3-ubiquitin ligase complex as mechanisms by which thalidomide can change the expression of genes important to embryonic development. In this study, seven polymorphisms in genes related to development (FGF8, FGF10, BMP4, SHH, TP53, TP63, and TP73) were analyzed in people with thalidomide embryopathy (TE) and compared to people without malformations. The sample consisted of 36 people with TE and 135 unrelated and nonsyndromic people who had their DNA genotyped by PCR real-time. Although no allelic or genotypic differences were observed between the groups, we hypothesized that other regions in these genes and related genes may play an important role in thalidomide teratogenesis, which is known to have a genetic contribution. Identifying such molecular mechanisms is essential for the development of a molecule that will be analogue to thalidomide but safe enough to avoid the emergence of new cases of TE.

Dyserythropoiesis of myelodysplastic syndromes

PURPOSE OF REVIEW

Myelodysplastic syndromes (MDS) are heterogeneous diseases of the hematopoietic stem cell in the elderly. Anemia is the main symptom that mostly correlates with dysplastic erythropoiesis in the bone marrow. We will review the recent advances in understanding the diverse mechanisms of dyserythropoiesis.

RECENT FINDINGS

Dyserythropoiesis defined as 10% dysplastic erythroid cells in the bone marrow is found in more than 80% of early MDS. Immature erythroblasts accumulate at the expense of mature erythroblasts due to differentiation arrest and apoptosis. In early MDS with dyserythropoiesis, caspase-dependent cleavage of the erythroid transcription factor GATA-1 occurring in basophilic erythroblasts accounts for impairment of final maturation. Depending on initiating genetic alteration, specific mechanisms contribute to erythroid defect. In MDS with 5q deletion, the haploinsufficiency of ribosomal protein gene, RPS14, opposes the transition of immature to mature erythroblasts by inducing a p53-dependent ribosome stress, cell cycle arrest and apoptosis. Recent work identifies the activation of a p53-S100A8/9 innate immune pathway that both intrinsically and extrinsically contributes to defective erythropoiesis. In MDS with ring sideroblasts, a paradigm of dyserythropoiesis, a unique mutation in SF3B1 splicing factor gene induces a multiplicity of alterations at RNA level that deeply modifies the patterns of gene expression.

SUMMARY

Insights in the pathophysiology of MDS with dyserythropoiesis may guide the choice of the appropriate therapy, for instance lenalidomide in MDS with del(5q). A better understanding of the mechanisms of dyserthropoiesis is required to treat anemia in non-del(5q) MDS, especially in case of resistance to first-line therapy by erythropoiesis-stimulating agents.

Lenalidomide: Myelodysplastic syndromes with del(5q) and beyond

Myelodysplastic syndrome (MDS) with deletion 5q (del(5q)) is a distinct clinical and pathological disease subset that is exquisitely sensitive to lenalidomide for the treatment of red blood cell transfusion-dependent anemia. Although lenalidomide has erythropoeitic promoting activity in MDS without del(5q) (non-del(5q) MDS), the frequency of response to treatment is lower and relates to biologically separate drug effects. In del(5q) MDS, lenalidomide suppresses the malignant clone to restore effective erythropoiesis by virtue of synthetic lethality, arising from cereblon-dependent degradation of haplodeficient proteins encoded within the commonly deleted region of the chromosome 5q deletion. In contrast, in non-del(5q) MDS, lenalidomide restores effective erythropoiesis via enhancement of erythropoietin (EPO) receptor-initiated transcriptional response arising from the assembly of signaling-competent receptor complexes within membrane lipid raft domains. Recently, large phase III clinical studies have explored the role of lenalidomide, alone and in combination with, erythropoiesis-stimulating agents showing additive improvement in erythroid responses. Herein, we will describe the mechanisms of lenalidomide action in MDS and pivotal clinical studies testing the benefit of lenalidomide in both del(5q) and non-del(5q) MDS. Furthermore, we discuss evidence-based strategies to incorporate lenalidomide into the treatment algorithm for patients with MDS.

p53-related protein kinase confers poor prognosis and represents a novel therapeutic target in multiple myeloma

p53-related protein kinase (TP53RK, also known as PRPK) is an upstream kinase that phosphorylates (serine residue Ser15) and mediates p53 activity. Here we show that TP53RK confers poor prognosis in multiple myeloma (MM) patients, and, conversely, that TP53RK knockdown inhibits p53 phosphorylation and triggers MM cell apoptosis, associated with downregulation of c-Myc and E2F-1-mediated upregulation of pro-apoptotic Bim. We further demonstrate that TP53RK downregulation also triggers growth inhibition in p53-deficient and p53-mutant MM cell lines and identify novel downstream targets of TP53RK including ribonucleotide reductase-1, telomerase reverse transcriptase, and cyclin-dependent kinase inhibitor 2C. Our previous studies showed that immunomodulatory drugs (IMiDs) downregulate p21 and trigger apoptosis in wild-type-p53 MM.1S cells, Importantly, we demonstrate by pull-down, nuclear magnetic resonance spectroscopy, differential scanning fluorimetry, and isothermal titration calorimetry that IMiDs bind and inhibit TP53RK, with biologic sequelae similar to TP53RK knockdown. Our studies therefore demonstrate that either genetic or pharmacological inhibition of TP53RK triggers MM cell apoptosis via both p53-Myc axis-dependent and axis-independent pathways, validating TP53RK as a novel therapeutic target in patients with poor-prognosis MM.

The role of p53 in myelodysplastic syndromes and acute myeloid leukemia: molecular aspects and clinical implications

TP53 gene mutations occurring in patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) are associated with high-risk karyotypes including 17p abnormalities, monosomal and complex cytogenetics. TP53 mutations in these disorders portend rapid disease progression and resistance to conventional therapeutics. Notably, the size of the TP53 mutant clone as measured by mutation allele burden is directly linked to overall survival (OS) confirming the importance of p53 as a negative prognostic variable. In nucleolar stress-induced ribosomopathies, such as del(5q) MDS, disassociation of MDM2 and p53 results in p53 accumulation in erythroid precursors manifested as erythroid hypoplasia. P53 antagonism by lenalidomide or other therapeutics such as antisense oligonucleotides, repopulates erythroid precursors and enhances effective erythropoiesis. These findings demonstrate that p53 is an intriguing therapeutic target that is currently under investigation in MDS and AML. This study reviews molecular advances in understanding the role of p53 in MDS and AML, and explores potential therapeutic strategies in this era of personalized medicine.

Genetics and Epigenetics of Myelodysplastic Syndromes and Response to Drug Therapy: New Insights

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematologic neoplasms ocurring mostly in the elderly. The clinical outcome of MDS patients is still poor despite progress in treatment approaches. About 90% of patients harbor at least one somatic mutation. This review aimed to assess the potential of molecular abnormalities in understanding pathogenesis, prognosis, diagnosis and in guiding choice of proper therapy in MDS patients. Papers related to this topic from 2000 to 2016 in PubMed and Scopus databases were searched and studied. The most common molecular abnormalities were TET2, ASXL1 as well as molecules involved in spliceosome machinery (U2AF1, SRSF2 and SF3B1). Patients with defects in TET2 molecule show better response to treatment with azacitidine. IDH and DNMT3A mutations are associated with a good response to decitabine therapy. In addition, patients with del5q subtype harboring TP53 mutation do not show a good response to lenalidomide therapy. In general, the results of this study show that molecular abnormalities can be associated with the occurrence of a specific morphological phenotype in patients. Therefore, considering the morphology of patients, different gene profiling methods can be selected to choice the most appropriate therapeutic measure in these patients in addition to faster and more cost-effective diagnosis of molecular abnormalities.

TP53 and MDM2 single nucleotide polymorphisms influence survival in non-del(5q) myelodysplastic syndromes

P53 is a key regulator of many cellular processes and is negatively regulated by the human homolog of murine double minute-2 (MDM2) E3 ubiquitin ligase. Single nucleotide polymorphisms (SNPs) of either gene alone, and in combination, are linked to cancer susceptibility, disease progression, and therapy response. We analyzed the interaction of TP53 R72P and MDM2 SNP309 SNPs in relationship to outcome in patients with myelodysplastic syndromes (MDS). Sanger sequencing was performed on DNA isolated from 208 MDS cases. Utilizing a novel functional SNP scoring system ranging from +2 to −2 based on predicted p53 activity, we found statistically significant differences in overall survival (OS) (p = 0.02) and progression-free survival (PFS) (p = 0.02) in non-del(5q) MDS patients with low functional scores. In univariate analysis, only IPSS and the functional SNP score predicted OS and PFS in non-del(5q) patients. In multivariate analysis, the functional SNP score was independent of IPSS for OS and PFS. These data underscore the importance of TP53 R72P and MDM2 SNP309 SNPs in MDS, and provide a novel scoring system independent of IPSS that is predictive for disease outcome.

A calcium- and calpain-dependent pathway determines the response to lenalidomide in myelodysplastic syndromes

Despite the high response rates of individuals with myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)) to treatment with lenalidomide (LEN) and the recent identification of cereblon (CRBN) as the molecular target of LEN, the cellular mechanism by which LEN eliminates MDS clones remains elusive. Here we performed an RNA interference screen to delineate gene regulatory networks that mediate LEN responsiveness in an MDS cell line, MDSL. We identified GPR68, which encodes a G-protein-coupled receptor that has been implicated in calcium metabolism, as the top candidate gene for modulating sensitivity to LEN. LEN induced GPR68 expression via IKAROS family zinc finger 1 (IKZF1), resulting in increased cytosolic calcium levels and activation of a calcium-dependent calpain, CAPN1, which were requisite steps for induction of apoptosis in MDS cells and in acute myeloid leukemia (AML) cells. In contrast, deletion of GPR68 or inhibition of calcium and calpain activation suppressed LEN-induced cytotoxicity. Moreover, expression of calpastatin (CAST), an endogenous CAPN1 inhibitor that is encoded by a gene (CAST) deleted in del(5q) MDS, correlated with LEN responsiveness in patients with del(5q) MDS. Depletion of CAST restored responsiveness of LEN-resistant non-del(5q) MDS cells and AML cells, providing an explanation for the superior responses of patients with del(5q) MDS to LEN treatment. Our study describes a cellular mechanism by which LEN, acting through CRBN and IKZF1, has cytotoxic effects in MDS and AML that depend on a calcium- and calpain-dependent pathway.

Delayed globin synthesis leads to excess heme and the macrocytic anemia of Diamond Blackfan anemia and del(5q) myelodysplastic syndrome

Diamond Blackfan anemia (DBA) and myelodysplastic syndrome (MDS) with isolated del(5q) are severe macrocytic anemias; although both are associated with impaired ribosome assembly, why the anemia occurs is not known. We cultured marrow cells from DBA (n = 3) and del(5q) MDS (n = 6) patients and determined how heme (a toxic chemical) and globin (a protein) are coordinated. We show that globin translation initiates slowly, whereas heme synthesis proceeds normally. This results in insufficient globin protein, excess heme and excess reactive oxygen species in early erythroid precursors, and CFU-E (colony-forming unit-erythroid)/proerythroblast cell death. The cells that can more rapidly and effectively export heme or can slow heme synthesis preferentially survive and appropriately mature. Consistent with these observations, treatment with 10 μM succinylacetone, a specific inhibitor of heme synthesis, improved the erythroid cell output of DBA and del(5q) MDS marrow cultures by 68 to 95% (P = 0.03 to 0.05), whereas the erythroid cell output of concurrent control marrow cultures decreased by 4 to 13%. Our studies demonstrate that erythropoiesis fails when heme exceeds globin. Our data further suggest that therapies that decrease heme synthesis (or facilitate heme export) could improve the red blood cell production of persons with DBA, del(5q) MDS, and perhaps other macrocytic anemias.

Lenalidomide Stabilizes the Erythropoietin Receptor by Inhibiting the E3 Ubiquitin Ligase RNF41

In a subset of patients with non-del(5q) myelodysplastic syndrome (MDS), lenalidomide promotes erythroid lineage competence and effective erythropoiesis. To determine the mechanism by which lenalidomide promotes erythropoiesis, we investigated its action on erythropoietin receptor (EpoR) cellular dynamics. Lenalidomide upregulated expression and stability of JAK2-associated EpoR in UT7 erythroid cells and primary CD71+ erythroid progenitors. The effects of lenalidomide on receptor turnover were Type I cytokine receptor specific, as evidenced by coregulation of the IL3-Rα receptor but not c-Kit. To elucidate this mechanism, we investigated the effects of lenalidomide on the E3 ubiquitin ligase RNF41. Lenalidomide promoted EpoR/RNF41 association and inhibited RNF41 auto-ubiquitination, accompanied by a reduction in EpoR ubiquitination. To confirm that RNF41 is the principal target responsible for EpoR stabilization, HEK293T cells were transfected with EpoR and/or RNF41 gene expression vectors. Steady-state EpoR expression was reduced in EpoR/RNF41 cells, whereas EpoR upregulation by lenalidomide was abrogated, indicating that cellular RNF41 is a critical determinant of drug-induced receptor modulation. Notably, shRNA suppression of CRBN gene expression failed to alter EpoR upregulation, indicating that drug-induced receptor modulation is independent of cereblon. Immunohistochemical staining showed that RNF41 expression decreased in primary erythroid cells of lenalidomide-responding patients, suggesting that cellular RNF41 expression merits investigation as a biomarker for lenalidomide response. Our findings indicate that lenalidomide has E3 ubiquitin ligase inhibitory effects that extend to RNF41 and that inhibition of RNF41 auto-ubiquitination promotes membrane accumulation of signaling competent JAK2/EpoR complexes that augment Epo responsiveness. Cancer Res; 76(12); 3531-40. ©2016 AACR.

RP-MDM2-p53 Pathway: Linking Ribosomal Biogenesis and Tumor Surveillance

Ribosomal biogenesis is tightly associated with cellular activities, such as growth, proliferation, and cell cycle progression. Perturbations in ribosomal biogenesis can initiate so-called nucleolar stress. The process through which ribosomal proteins (RPs) transduce nucleolar stress signals via MDM2 to p53 has been described as a crucial tumor-suppression mechanism. In this review we focus on recent progress pertaining to the function and mechanism of RPs in association with the MDM2-p53 tumor-suppression network, and the potential implications this surveillance network has for cancer development.

Short- and long-term benefits of lenalidomide treatment in patients with lower-risk del(5q) myelodysplastic syndromes

In patients with transfusion-dependent, lower-risk, del(5q) myelodysplastic syndromes, lenalidomide effectively reduces red blood cell transfusion burden and acts as a disease-modifying agent, altering the natural history of the disease by suppressing the del(5q) clone. Hematologic and/or cytogenetic responses correlate with delayed acute myeloid leukemia progression and better overall survival.

The treatment of patients with myelodysplastic syndromes (MDS) begins with assessment of karyotype and risk. Lenalidomide is approved for the treatment of patients who have transfusion-dependent anemia due to lower-risk MDS with chromosome 5q deletion (del(5q)) with or without additional cytogenetic abnormalities, and isolated del(5q) only in the European Union. Mounting evidence suggests that lenalidomide is effective not only in reducing red blood cell (RBC) transfusion burden, but also in modifying the disease natural history by suppressing the malignant clone. Data discussed here from the pivotal phase 2 (MDS-003) and phase 3 (MDS-004) studies of lenalidomide demonstrate that lenalidomide treatment was associated with both short- and long-term benefits. These clinical benefits included high rates of RBC-transfusion independence (TI) with prolonged durations of response, high rates of cytogenetic response (CyR) associated with achievement of durable RBC-TI, no significant difference in rates of progression to acute myeloid leukemia (AML), and improvements in health-related quality of life (HRQOL). Achievement of RBC-TI and CyR with lenalidomide treatment was associated with extended survival and time to AML progression. Achievement of RBC-TI and hemoglobin response was additionally associated with HRQOL benefits. Recent data describing the impact of TP53 mutations and p53 expression on the prognosis of patients with del(5q) and the impact on response to lenalidomide are also discussed. The authors provide practical recommendations for the use of lenalidomide in patients with lower-risk del(5q) MDS.

New therapeutic approaches in myelodysplastic syndromes: Hypomethylating agents and lenalidomide

Recent advances in the treatment of myelodysplastic syndromes have come from the use of the hypomethylating agents decitabine and azacitidine as well as the immunomodulatory drug lenalidomide. Their clinical benefit has been demonstrated by randomized phase III clinical trials, mostly in high-risk and del(5q) myelodysplastic syndromes, respectively. Neither drug, however, appears to eradicate myelodysplastic stem cells, and thus they currently do not represent curative options. Here, we review data from both clinical and translational research on those drugs to identify their molecular and cellular mechanisms of action and to delineate paths for improved treatment allocation and further therapeutic advances in myelodysplastic syndromes.

Recent Advances in the 5q- Syndrome

The 5q- syndrome is the most distinct of the myelodysplastic syndromes (MDS) and patients with this disorder have a deletion of chromosome 5q [del(5q)] as the sole karyotypic abnormality. Several genes mapping to the commonly deleted region of the 5q- syndrome have been implicated in disease pathogenesis in recent years. Haploinsufficiency of the ribosomal gene RPS14 has been shown to cause the erythroid defect in the 5q- syndrome. Loss of the microRNA genes miR-145 and miR-146a has been associated with the thrombocytosis observed in 5q- syndrome patients. Haploinsufficiency of CSNK1A1 leads to hematopoietic stem cell expansion in mice and may play a role in the initial clonal expansion in patients with 5q- syndrome. Moreover, a subset of patients harbor mutation of the remaining CSNK1A1 allele. Mouse models of the 5q- syndrome, which recapitulate the key features of the human disease, indicate that a p53-dependent mechanism underlies the pathophysiology of this disorder. Importantly, activation of p53 has been demonstrated in the human 5q- syndrome. Recurrent TP53 mutations have been associated with an increased risk of disease evolution and with decreased response to the drug lenalidomide in del(5q) MDS patients. Potential new therapeutic agents for del(5q) MDS include the translation enhancer L-leucine.

The relationship of TP53 R72P polymorphism to disease outcome and TP53 mutation in myelodysplastic syndromes

Nonsynonymous TP53 exon 4 single-nucleotide polymorphism (SNP), R72P, is linked to cancer and mutagen susceptibility. R72P associations with specific cancer risk, particularly hematological malignancies, have been conflicting. Myelodysplastic syndrome (MDS) with chromosome 5q deletion is characterized by erythroid hypoplasia arising from lineage-specific p53 accumulation resulting from ribosomal insufficiency. We hypothesized that apoptotically diminished R72P C-allele may influence predisposition to del(5q) MDS. Bone marrow and blood DNA was sequenced from 705 MDS cases (333 del(5q), 372 non-del(5q)) and 157 controls. Genotype distribution did not significantly differ between del(5q) cases (12.6% CC, 38.1% CG, 49.2% GG), non-del(5q) cases (9.7% CC, 44.6% CG, 45.7% GG) and controls (7.6% CC, 37.6% CG, 54.8% GG) (P=0.13). Allele frequency did not differ between non-del(5q) and del(5q) cases (P=0.91) but trended towards increased C-allele frequency comparing non-del(5q) (P=0.08) and del(5q) (P=0.10) cases with controls. Median lenalidomide response duration increased proportionate to C-allele dosage in del(5q) patients (2.2 (CC), 1.3 (CG) and 0.89 years (GG)). Furthermore, C-allele homozygosity in del(5q) was associated with prolonged overall and progression-free survival and non-terminal interstitial deletions that excluded 5q34, whereas G-allele homozygozity was associated with inferior outcome and terminal deletions involving 5q34 (P=0.05). These findings comprise the largest MDS R72P SNP analysis.