Targeting the PI3K/Akt pathway in murine MDS/MPN driven by hyperactive Ras

Aurora Kinase A inhibition enhances DNA damage and tumor cell death with 131I-MIBG therapy in high-risk neuroblastoma

BACKGROUND

Neuroblastoma is the most common extra-cranial pediatric solid tumor. 131I-metaiodobenzylguanidine (MIBG) is a targeted radiopharmaceutical highly specific for neuroblastoma tumors, providing potent radiotherapy to widely metastatic disease. Aurora kinase A (AURKA) plays a role in mitosis and stabilization of the MYCN protein in neuroblastoma. We aimed to study the impact of AURKA inhibitors on DNA damage and tumor cell death in combination with 131I-MIBG therapy in a pre-clinical model of high-risk neuroblastoma.

RESULTS

Using an in vivo model of high-risk neuroblastoma, we demonstrated a marked combinatorial effect of 131I-MIBG and alisertib on tumor growth. In MYCN amplified cell lines, the combination of radiation and an AURKA A inhibitor increased DNA damage and apoptosis and decreased MYCN protein levels.

CONCLUSION

The combination of AURKA inhibition with 131I-MIBG treatment is active in resistant neuroblastoma models.

Aurora Kinase A inhibition enhances DNA damage and tumor cell death with 131I-MIBG therapy in high-risk neuroblastoma

Background

Neuroblastoma is the most common extra-cranial pediatric solid tumor. 131I-metaiodobenzylguanidine (MIBG) is a targeted radiopharmaceutical highly specific for neuroblastoma tumors, providing potent radiotherapy to widely metastatic disease. Aurora kinase A (AURKA) plays a role in mitosis and stabilization of the MYCN protein in neuroblastoma. Here we explore whether AURKA inhibition potentiates a response to MIBG therapy.

Results

Using an in vivo model of high-risk neuroblastoma, we demonstrated a marked combinatorial effect of 131I-MIBG and alisertib on tumor growth. In MYCN amplified cell lines, the combination of radiation and an AURKA A inhibitor increased DNA damage and apoptosis and decreased MYCN protein levels.

Conclusion

The combination of AURKA inhibition with 131I-MIBG treatment is active in resistant neuroblastoma models and is a promising clinical approach in high-risk neuroblastoma.

Quercetin-targeted AKT1 regulates the Raf/MEK/ERK signaling pathway to protect against doxorubicin-induced nephropathy in mice

BACKGROUND

Doxorubicin is an anthracycline antitumor agent commonly used in clinical practice, which has some nephrotoxicity and is often used to establish mouse models of kidney injury for basic medical research. This study will investigate the protective effect of quercetin on renal function in doxorubicin-induced nephropathy mice.

METHODS

C57BL/6 mice were divided into control, model, and quercetin low-, and high-dose groups. Serum and urine were collected to analyze markers of kidney function. H&E staining was used to detect pathological changes in renal tissues. Transmission electron microscopy was performed to observe the ultrastructural changes in renal tissues. Immunohistochemistry was performed to detect the changes of Ang II. RT-qPCR was performed to detect the changes of cytokines. ELISA was used to detect changes in serum inflammatory factors. Molecular docking was performed to verify the targeting relationship between quercetin and AKT1. Western blot was performed to detect Bax, Bcl-2, Cyt-c, AKT1, Raf, MEK, and ERK proteins.

RESULTS

Quercetin could induce the recovery of kidney function in kidney-injured mice; H&E results showed that kidney tissue damage and tissue fibrosis were reduced in kidney-injured mice under quercetin. The mitochondrial swollen structure was destroyed by doxorubicin, while the mitochondrial structure was restored under quercetin. The levels of abnormal apoptotic proteins Bax and Bcl-2 were regulated to normal by quercetin. The high expression of Ang II caused by doxorubicin was down-regulated by quercetin. Abnormal inflammatory factors caused by doxorubicin were reversed by quercetin. Western blot experiments showed that quercetin regulated the protein levels of AKT1 and Raf/MEK/ERK and inhibited the detrimental effects of doxorubicin.

CONCLUSION

Quercetin may mitigate doxorubicin-induced kidney injury in mice by regulating renal cell inflammatory factors and Raf/MEK/ERK signaling pathway through AKT1 to promote recovery of renal function.

MEK/ERK and PI3K/AKT pathway inhibitors affect the transformation of myelodysplastic syndrome into acute myeloid leukemia via H3K27me3 methylases and de‑methylases

The transformation of myelodysplastic syndrome (MDS) into acute myeloid leukemia (AML) poses a significant clinical challenge. The trimethylation of H3 on lysine 27 (H3K27me3) methylase and de‑methylase pathway is involved in the regulation of MDS progression. The present study investigated the functional mechanisms of the MEK/ERK and PI3K/AKT pathways in the MDS‑to‑AML transformation. MDS‑AML mouse and SKM‑1 cell models were first established and this was followed by treatment with the MEK/ERK pathway inhibitor, U0126, the PI3K/AKT pathway inhibitor, Ly294002, or their combination. H3K27me3 methylase, enhancer of zeste homolog (EZH)1, EZH2, demethylase Jumonji domain‑containing protein‑3 (JMJD3) and ubiquitously transcribed tetratricopeptide repeat on chromosome X (UTX) and H3K27me3 protein levels were determined using western blot analysis. Cell viability, cycle distribution and proliferation were assessed using CCK‑8, flow cytometry, EdU and colony formation assays. The ERK and AKT phosphorylation levels in clinical samples and established models were determined, and SKM‑1 cell behaviors were assessed. The levels of H3K27me3 methylases and de‑methylases and distal‑less homeobox 5 (DLX5) were measured. The results revealed that the ERK and AKT phosphorylation levels were elevated in patients with MDS and MDS‑AML, and in mouse models. Treatment with U0126, a MEK/ERK pathway inhibitor, and Ly294002, a PI3K/AKT pathway inhibitor, effectively suppressed ERK and AKT phosphorylation in mice with MDS‑AML. It was observed that mice with MDS treated with U0126/Ly294002 exhibited reduced transformation to AML, delayed disease transformation and increased survival rates. Treatment of the SKM‑1 cells with U0126/Ly294002 led to a decrease in cell viability and proliferation, and to an increase in cell cycle arrest by suppressing ERK/PI3K phosphorylation. Moreover, treatment with U0126/Ly294002 downregulated EZH2/EZH1 expression, and upregulated JMJD3/UTX expression. The effects of U0126/Ly294002 were nullified when EZH2/EZH1 was overexpressed or when JMJD3/UTX was inhibited in the SKM‑1 cells. Treatment with U0126/Ly294002 also resulted in a decreased H3K27me3 protein level and H3K27me3 level in the DLX5 promoter region, leading to an increased DLX5 expression. Overall, the findings of the present study suggest that U0126/Ly294002 participates in MDS‑AML transformation by modulating the levels of H3K27me3 methylases and de‑methylases, and regulating DLX5 transcription and expression.

XBP1 promotes NRASG12D pre-B acute lymphoblastic leukaemia through IL-7 receptor signalling and provides a therapeutic vulnerability for oncogenic RAS

Activating point mutations of the RAS gene act as driver mutations for a subset of precursor-B cell acute lymphoblastic leukaemias (pre-B ALL) and represent an ambitious target for therapeutic approaches. The X box-binding protein 1 (XBP1), a key regulator of the unfolded protein response (UPR), is critical for pre-B ALL cell survival, and high expression of XBP1 confers poor prognosis in ALL patients. However, the mechanism of XBP1 activation has not yet been elucidated in RAS mutated pre-B ALL. Here, we demonstrate that XBP1 acts as a downstream linchpin of the IL-7 receptor signalling pathway and that pharmacological inhibition or genetic ablation of XBP1 selectively abrogates IL-7 receptor signalling via inhibition of its downstream effectors, JAK1 and STAT5. We show that XBP1 supports malignant cell growth of pre-B NRASG12D ALL cells and that genetic loss of XBP1 consequently leads to cell cycle arrest and apoptosis. Our findings reveal that active XBP1 prevents the cytotoxic effects of a dual PI3K/mTOR pathway inhibitor (BEZ235) in pre-B NRASG12D ALL cells. This implies targeting XBP1 in combination with BEZ235 as a promising new targeted strategy against the oncogenic RAS in NRASG12D -mutated pre-B ALL.

Oncogenic RAS promotes leukemic transformation of CUX1-deficient cells

-7/del(7q) is prevalent across subtypes of myeloid neoplasms. CUX1, located on 7q22, encodes a homeodomain-containing transcription factor, and, like -7/del(7q), CUX1 inactivating mutations independently carry a poor prognosis. As with loss of 7q, CUX1 mutations often occur early in disease pathogenesis. We reported that CUX1 deficiency causes myelodysplastic syndrome in mice but was insufficient to drive acute myeloid leukemia (AML). Given the known association between -7/del(7q) and RAS pathway mutations, we mined cancer genome databases and explicitly linked CUX1 mutations with oncogenic RAS mutations. To determine if activated RAS and CUX1 deficiency promote leukemogenesis, we generated mice bearing NrasG12D and CUX1-knockdown which developed AML, not seen in mice with either mutation alone. Oncogenic RAS imparts increased self-renewal on CUX1-deficient hematopoietic stem/progenitor cells (HSPCs). Reciprocally, CUX1 knockdown amplifies RAS signaling through reduction of negative regulators of RAS/PI3K signaling. Double mutant HSPCs were responsive to PIK3 or MEK inhibition. Similarly, low expression of CUX1 in primary AML samples correlates with sensitivity to the same inhibitors, suggesting a potential therapy for malignancies with CUX1 inactivation. This work demonstrates an unexpected convergence of an oncogene and tumor suppressor gene on the same pathway.

Targeted therapy in juvenile myelomonocytic leukemia: Where are we now?

Juvenile myelomonocytic leukemia (JMML) is a rare and aggressive clonal neoplasm of early childhood, classified as an overlap myeloproliferative/myelodysplastic neoplasm by the World Health Organization. In 90% of the patients with JMML, typical initiating mutations in the canonical Ras pathway genes NF1, PTPN11, NRAS, KRAS, and CBL can be identified. Hematopoietic stem cell transplantation (HSCT) currently is the established standard of care in most patients, although long-term survival is still only 50-60%. Given the limited therapeutic options and the important morbidity and mortality associated with HSCT, new therapeutic approaches are urgently needed. Hyperactivation of the Ras pathway as disease mechanism in JMML lends itself to the use of targeted therapy. Targeted therapy could play an important role in the future treatment of patients with JMML. This review presents a comprehensive overview of targeted therapies already developed and evaluated in vitro and in vivo in patients with JMML.

The genetics of myelodysplastic syndromes and the opportunities for tailored treatments

Genomic instability, microenvironmental aberrations, and somatic mutations contribute to the phenotype of myelodysplastic syndrome and the risk for transformation to AML. Genes involved in RNA splicing, DNA methylation, histone modification, the cohesin complex, transcription, DNA damage response pathway, signal transduction and other pathways constitute recurrent mutational targets in MDS. RNA-splicing and DNA methylation mutations seem to occur early and are reported as driver mutations in over 50% of MDS patients. The improved understanding of the molecular landscape of MDS has led to better disease and risk classification, leading to novel therapeutic opportunities. Based on these findings, novel agents are currently under preclinical and clinical development and expected to improve the clinical outcome of patients with MDS in the upcoming years. This review provides a comprehensive update of the normal gene function as well as the impact of mutations in the pathogenesis, deregulation, diagnosis, and prognosis of MDS, focuses on the most recent advances of the genetic basis of myelodysplastic syndromes and their clinical relevance, and the latest targeted therapeutic approaches including investigational and approved agents for MDS.

Targeting Akt/PKB in pediatric tumors: A review from preclinical to clinical trials

The serine/threonine kinase Akt is a major player in the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway, and its modulation impacts multiple cellular processes such as growth, proliferation, and survival. Several abnormalities in this pathway have been documented over the years, and these alterations were shown to have great implications in tumorigenesis and resistance to chemotherapy. Thus, multiple Akt inhibitors have been developed and tested in adult tumors, and some of them are currently undergoing phase I, II, and III clinical trials for distinct cancers that arise during adulthood. Despite that, the impact of these inhibitors is still not fully understood in pediatric tumors, and Akt-specific targeting seems to be a promising approach to treat children affected by cancers. This review summarizes recent available evidence of Akt inhibitors in pediatric cancers, from both preclinical and clinical studies. In short, we demonstrate the impact that Akt inhibition provides in tumorigenesis, and we suggest targeting the PI3K/Akt/mTOR signaling pathway, alone or in combination with other inhibitors, is a feasible tool to achieve better outcomes in pediatric tumors.

Molecular Pathogenesis of Chronic Myelomonocytic Leukemia and Potential Molecular Targets for Treatment Approaches

Numerous examples in oncology have shown that better understanding the pathophysiology of a malignancy may be followed by the development of targeted treatment concepts with higher efficacy and lower toxicity as compared to unspecific treatment. The pathophysiology of chronic myelomonocytic leukemia (CMML) is heterogenous and complex but applying different research technologies have yielded a better and more comprehensive understanding of this disease. At the moment treatment for CMML is largely restricted to the unspecific use of cytotoxic drugs and hypomethylating agents (HMA). Numerous potential molecular targets have been recently detected by preclinical research which may ultimately lead to treatment concepts that will provide meaningful benefits for certain subgroups of patients.

Nf1 and Sh2b3 mutations cooperate in vivo in a mouse model of juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is initiated in early childhood by somatic mutations that activate Ras signaling. Although some patients have only a single identifiable oncogenic mutation, others have 1 or more additional alterations. Such secondary mutations, as a group, are associated with an increased risk of relapse after hematopoietic stem cell transplantation or transformation to acute myeloid leukemia. These clinical observations suggest a cooperative effect between initiating and secondary mutations. However, the roles of specific genes in the prognosis or clinical presentation of JMML have not been described. In this study, we investigate the impact of secondary SH2B3 mutations in JMML. We find that patients with SH2B3 mutations have adverse outcomes, as well as higher white blood cell counts and hemoglobin F levels in the peripheral blood. We further demonstrate this interaction in genetically engineered mice. Deletion of Sh2b3 cooperates with conditional Nf1 deletion in a dose-dependent fashion. These studies illustrate that haploinsufficiency for Sh2b3 contributes to the severity of myeloproliferative disease and provide an experimental system for testing treatments for a high-risk cohort of JMML patients.

Mutations in chronic myelomonocytic leukemia and their prognostic relevance

Chronic myelomonocytic leukemia (CMML) is a hematologic malignancy that overlaps with myeloproliferative neoplasms (MPN) and myelodysplastic syndromes (MDS) and tends to transform into acute myeloid leukemia (AML). Among cases of CMML, > 90% have gene mutations, primarily involving TET2 (~ 60%), ASXL1 (~ 40%), SRSF2 (~ 50%), and the RAS pathways (~ 30%). These gene mutations are associated with both the clinical phenotypes and the prognosis of CMML, special CMML variants and pre-phases of CMML. Cytogenetic abnormalities and the size of genome are also associated with prognosis. Meanwhile, cases with ASXL1, DNMT3A, NRAS, SETBP1, CBL and RUNX1 mutations may have inferior prognoses, but only ASXL1 mutations were confirmed to be independent predictors of the patient outcome and were included in three prognostic models. Novel treatment targets related to the various gene mutations are emerging. Therefore, this review provides new insights to explore the correlations among gene mutations, clinical phenotypes, prognosis, and novel drugs in CMML.

Traipsing Through Muddy Waters: A Critical Review of the Myelodysplastic Syndrome/Myeloproliferative Neoplasm (MDS/MPN) Overlap Syndromes

Myelodysplastic syndrome/Myeloproliferative neoplasms (MDS/MPNs) are molecularly complex, clinically heterogeneous diseases that exhibit proliferative and dysplastic features. Diagnostic criteria use clinical, pathologic, and genomic features to distinguish between disease entities, though considerable clinical and genetic overlap persists. MDS/MPNs are associated with a poor prognosis, save for MDS/MPN with ring sideroblasts and thrombocytosis, which can behave more indolently. The current treatment approach is risk-adapted and symptom-directed and largely extrapolated from experience in MDS or MPN. Gene sequencing has demonstrated frequent mutations involving signaling, epigenetic, and splicing pathways, which present numerous therapeutic opportunities for clinical investigation.

Pediatric Neoplasms Presenting with Monocytosis

PURPOSE OF REVIEW

Juvenile myelomonocytic leukemia (JMML) is a rare but severe pediatric neoplasm with hematopoietic stem cell transplant as its only established curative option. The development of targeted therapeutics for JMML is being guided by an understanding of the pathobiology of this condition. Here, we review JMML with an emphasis on genetics in order to (i) demonstrate the relationship between JMML genotype and clinical phenotype and (ii) explore potential genetic targets of novel JMML therapies.

RECENT FINDINGS

DNA hypermethylation studies have demonstrated consistently that methylation is related to disease severity. Increasing understanding of methylation in JMML may open the door to novel therapies, such as DNA methyltransferase inhibitors. The PI3K/AKT/MTOR, JAK/STAT, and RAF/MEK/ERK pathways are being investigated as therapeutic targets for JMML. Future therapy for JMML will be driven by an increased understanding of pathobiology. Targeted therapeutic approaches hold potential for improving outcomes in patients with JMML.

After 95 years, it's time to eRASe JMML

Juvenile myelomonocytic leukaemia (JMML) is a rare clonal disorder of early childhood. Constitutive activation of the RAS pathway is the initial event in JMML. Around 90% of patients diagnosed with JMML carry a mutation in the PTPN11, NRAS, KRAS, NF1 or CBL genes. It has been demonstrated that after this first genetic event, an additional somatic mutation or epigenetic modification is involved in disease progression. The available genetic and clinical data have enabled researchers to establish relationships between JMML and several clinical conditions, including Noonan syndrome, Ras-associated lymphoproliferative disease, and Moyamoya disease. Despite scientific progress and the development of more effective treatments, JMML is still a deadly disease: the 5-year survival rate is ~50%. Here, we report on recent research having led to a better understanding of the genetic and molecular mechanisms involved in JMML.

Proteomic Analysis of an Induced Pluripotent Stem Cell Model Reveals Strategies to Treat Juvenile Myelomonocytic Leukemia

Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm of early childhood with a poor survival rate, thus there is a requirement for improved treatment strategies. Induced pluripotent stem cells offer the ability to model disease and develop new treatment strategies. JMML is frequently associated with mutations in PTPN11. Children with Noonan syndrome, a development disorder, have an increased incidence of JMML associated with specific germline mutations in PTPN11. We undertook a proteomic assessment of myeloid cells derived from induced pluripotent stem cells obtained from Noonan syndrome patients with PTPN11 mutations, either associated or not associated with an increased incidence of JMML. We report that the proteomic perturbations induced by the leukemia-associated PTPN11 mutations are associated with TP53 and NF-Kκb signaling. We have previously shown that MYC is involved in the differential gene expression observed in Noonan syndrome patients associated with an increased incidence of JMML. Thus, we employed drugs to target these pathways and demonstrate differential effects on clonogenic hematopoietic cells derived from Noonan syndrome patients, who develop JMML and those who do not. Further, we demonstrated these small molecular inhibitors, JQ1 and CBL0137, preferentially extinguish primitive hematopoietic cells from sporadic JMML patients as opposed to cells from healthy individuals.

Tissue-Specific Oncogenic Activity of KRASA146T

KRAS is the most frequently mutated oncogene. The incidence of specific KRAS alleles varies between cancers from different sites, but it is unclear whether allelic selection results from biological selection for specific mutant KRAS proteins. We used a cross-disciplinary approach to compare KRASG12D, a common mutant form, and KRASA146T, a mutant that occurs only in selected cancers. Biochemical and structural studies demonstrated that KRASA146T exhibits a marked extension of switch 1 away from the protein body and nucleotide binding site, which activates KRAS by promoting a high rate of intrinsic and guanine nucleotide exchange factor-induced nucleotide exchange. Using mice genetically engineered to express either allele, we found that KRASG12D and KRASA146T exhibit distinct tissue-specific effects on homeostasis that mirror mutational frequencies in human cancers. These tissue-specific phenotypes result from allele-specific signaling properties, demonstrating that context-dependent variations in signaling downstream of different KRAS mutants drive the KRAS mutational pattern seen in cancer. SIGNIFICANCE: Although epidemiologic and clinical studies have suggested allele-specific behaviors for KRAS, experimental evidence for allele-specific biological properties is limited. We combined structural biology, mass spectrometry, and mouse modeling to demonstrate that the selection for specific KRAS mutants in human cancers from different tissues is due to their distinct signaling properties.See related commentary by Hobbs and Der, p. 696.This article is highlighted in the In This Issue feature, p. 681.

Rigosertib ameliorates the effects of oncogenic KRAS signaling in a murine model of myeloproliferative neoplasia

Aberrant signaling triggered by oncogenic or hyperactive RAS proteins contributes to the malignant phenotypes in a significant percentage of myeloid malignancies. Of these, juvenile myelomonocytic leukemia (JMML), an aggressive childhood cancer, is largely driven by mutations in RAS genes and those that encode regulators of these proteins. The Mx1-cre kras^+/G12D mouse model mirrors several key features of this disease and has been used extensively to determine the utility and mechanism of small molecule therapeutics in the context of RAS-driven myeloproliferative disorders. Treatment of disease-bearing KRAS^G12D mice with rigosertib (RGS), a small molecule RAS mimetic that is in phase II and III clinical trials for MDS and AML, decreased the severity of leukocytosis and splenomegaly and extended their survival. RGS also increased the frequency of HSCs and rebalanced the ratios of myeloid progenitors. Further analysis of KRAS^G12D HSPCs in vitro revealed that RGS suppressed hyperproliferation in response to GM-CSF and inhibited the phosphorylation of key RAS effectors. Together, these data suggest that RGS might be of clinical benefit in RAS-driven myeloid disorders.

Germline and Somatic NF1 Alterations Are Linked to Increased HER2 Expression in Breast Cancer

NF1 germline mutation predisposes to breast cancer. NF1 mutations have also been proposed as oncogenic drivers in sporadic breast cancers. To understand the genomic and histologic characteristics of these breast cancers, we analyzed the tumors with NF1 germline mutations and also examined the genomic and proteomic profiles of unselected tumors. Among 14 breast cancer specimens from 13 women affected with neurofibromatosis type 1 (NF1), 9 samples (NF + BrCa) underwent genomic copy number (CN) and targeted sequencing analysis. Mutations of NF1 were identified in two samples and TP53 were in three. No mutation was detected in ATM, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, NBN, PALB2, PTEN, RAD50, and STK11 HER2 (ErbB2) overexpression was detected by IHC in 69.2% (9/13) of the tumors. CN gain/amplification of ERBB2 was detected in 4 of 9 with DNA analysis. By evaluating HER2 expression and NF1 alterations in unselected invasive breast cancers in TCGA datasets, we discovered that among samples with ERBB2 CN gain/amplification, the HER2 mRNA and protein expression were much more pronounced in NF1-mutated/deleted samples in comparison with NF1-unaltered samples. This finding suggests a synergistic interplay between these two genes, potentially driving the development of breast cancer harboring NF1 mutation and ERBB2 CN gain/amplification. NF1 gene loss of heterozygosity was observed in 4 of 9 NF + BrCa samples. CDK4 appeared to have more CN gain in NF + BrCa and exhibited increased mRNA expression in TCGA NF1--altered samples. Cancer Prev Res; 11(10); 655-64. ©2018 AACR.

The genetic and molecular pathogenesis of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) comprise a diverse group of clonal and malignant myeloid disorders characterized by ineffective hematopoiesis, resultant peripheral cytopenias, and a meaningful increased risk of progression to acute myeloid leukemia. A wide array of recurring genetic mutations involved in RNA splicing, histone manipulation, DNA methylation, transcription factors, kinase signaling, DNA repair, cohesin proteins, and other signal transduction elements has been identified as important substrates for the development of MDS. Cytogenetic abnormalities, namely those characterized by loss of genetic material (including 5q- and 7q-), have also been strongly implicated and may influence the clonal architecture which predicts such mutations and may provoke an inflammatory bone marrow microenvironment as the substrate for clonal expansion. Other aspects of the molecular pathogenesis of MDS continue to be further elucidated, predicated upon advances in gene expression profiling and the development of new, and improved high-throughput techniques. More accurate understanding of the genetic and molecular basis for the development of MDS directly provides additional opportunity for treatment, which to date remains limited. In this comprehensive review, we examine the current understanding of the molecular pathogenesis and pathophysiology of MDS, as well as review future prospects which may enhance this understanding, treatment strategies, and hopefully outcomes.

Mutation-specific signaling profiles and kinase inhibitor sensitivities of juvenile myelomonocytic leukemia revealed by induced pluripotent stem cells

Juvenile myelomonocytic leukemia (JMML) is an uncommon myeloproliferative neoplasm driven by Ras pathway mutations and hyperactive Ras/MAPK signaling. Outcomes for many children with JMML remain dismal with current standard-of-care cytoreductive chemotherapy and hematopoietic stem cell transplantation. We used patient-derived induced pluripotent stem cells (iPSCs) to characterize the signaling profiles and potential therapeutic vulnerabilities of PTPN11-mutant and CBL-mutant JMML. We assessed whether MEK, JAK, and PI3K/mTOR kinase inhibitors (i) could inhibit myeloproliferation and aberrant signaling in iPSC-derived hematopoietic progenitors with PTPN11 E76K or CBL Y371H mutations. We detected constitutive Ras/MAPK and PI3K/mTOR signaling in PTPN11 and CBL iPSC-derived myeloid cells. Activated signaling and growth of PTPN11 iPSCs were preferentially inhibited in vitro by the MEKi PD0325901 and trametinib. Conversely, JAK/STAT signaling was selectively activated in CBL iPSCs and abrogated by the JAKi momelotinib and ruxolitinib. The PI3Kδi idelalisib and mTORi rapamycin inhibited signaling and myeloproliferation in both PTPN11 and CBL iPSCs. These findings demonstrate differential sensitivity of PTPN11 iPSCs to MEKi and of CBL iPSCs to JAKi, but similar sensitivity to PI3Ki and mTORi. Clinical investigation of mutation-specific kinase inhibitor therapies in children with JMML may be warranted.

Wild-type Kras expands and exhausts hematopoietic stem cells

Oncogenic Kras expression specifically in hematopoietic stem cells (HSCs) induces a rapidly fatal myeloproliferative neoplasm in mice, suggesting that Kras signaling plays a dominant role in normal hematopoiesis. However, such a conclusion is based on expression of an oncogenic version of Kras. Hence, we sought to determine the effect of simply increasing the amount of endogenous wild-type Kras on HSC fate. To this end, we utilized a codon-optimized version of the murine Kras gene (Krasex3op) that we developed, in which silent mutations in exon 3 render the encoded mRNA more efficiently translated, leading to increased protein expression without disruption to the normal gene architecture. We found that Kras protein levels were significantly increased in bone marrow (BM) HSCs in Krasex3op/ex3op mice, demonstrating that the translation of Kras in HSCs is normally constrained by rare codons. Krasex3op/ex3op mice displayed expansion of BM HSCs, progenitor cells, and B lymphocytes, but no evidence of myeloproliferative disease or leukemia in mice followed for 12 months. BM HSCs from Krasex3op/ex3op mice demonstrated increased multilineage repopulating capacity in primary competitive transplantation assays, but secondary competitive transplants revealed exhaustion of long-term HSCs. Following total body irradiation, Krasex3op/ex3op mice displayed accelerated hematologic recovery and increased survival. Mechanistically, HSCs from Krasex3op/ex3op mice demonstrated increased proliferation at baseline, with a corresponding increase in Erk1/2 phosphorylation and cyclin-dependent kinase 4 and 6 (Cdk4/6) activation. Furthermore, both the enhanced colony-forming capacity and in vivo repopulating capacity of HSCs from Krasex3op/ex3op mice were dependent on Cdk4/6 activation. Finally, BM transplantation studies revealed that augmented Kras expression produced expansion of HSCs, progenitor cells, and B cells in a hematopoietic cell-autonomous manner, independent from effects on the BM microenvironment. This study provides fundamental demonstration of codon usage in a mammal having a biological consequence, which may speak to the importance of codon usage in mammalian biology.

Mechanistic and Preclinical Insights from Mouse Models of Hematologic Cancer Characterized by Hyperactive Ras

RAS genes are mutated in 5%-40% of a spectrum of myeloid and lymphoid cancers with NRAS affected 2-3 times more often than KRAS Genomic analysis indicates that RAS mutations generally occur as secondary events in leukemogenesis, but are integral to the disease phenotype. The tractable nature of the hematopoietic system has facilitated generating accurate mouse models of hematologic malignancies characterized by hyperactive Ras signaling. These strains provide robust platforms for addressing how oncogenic Ras expression perturbs proliferation, differentiation, and self-renewal programs in stem and progenitor cell populations, for testing potential therapies, and for investigating mechanisms of drug response and resistance. This review summarizes recent insights from key studies in mouse models of hematologic cancer that are broadly relevant for understanding Ras biology and for ongoing efforts to implement rational therapeutic strategies for cancers with oncogenic RAS mutations.

Targeting few to help hundreds: JAK, MAPK and ROCK pathways as druggable targets in atypical chronic myeloid leukemia

Atypical Chronic Myeloid Leukemia (aCML) is a myeloproliferative neoplasm characterized by neutrophilic leukocytosis and dysgranulopoiesis. From a genetic point of view, aCML shows a heterogeneous mutational landscape with mutations affecting signal transduction proteins but also broad genetic modifiers and chromatin remodelers, making difficult to understand the molecular mechanisms causing the onset of the disease. The JAK-STAT, MAPK and ROCK pathways are known to be responsible for myeloproliferation in physiological conditions and to be aberrantly activated in myeloproliferative diseases. Furthermore, experimental evidences suggest the efficacy of inhibitors targeting these pathways in repressing myeloproliferation, opening the way to deep clinical investigations. However, the activation status of these pathways is rarely analyzed when genetic mutations do not occur in a component of the signaling cascade. Given that mutations in functionally unrelated genes give rise to the same pathology, it is tempting to speculate that alteration in the few signaling pathways mentioned above might be a common feature of pathological myeloproliferation. If so, targeted therapy would be an option to be considered for aCML patients.

Survival of pancreatic cancer cells lacking KRAS function

Activating mutations in the proto-oncogene KRAS are a hallmark of pancreatic ductal adenocarcinoma (PDAC), an aggressive malignancy with few effective therapeutic options. Despite efforts to develop KRAS-targeted drugs, the absolute dependence of PDAC cells on KRAS remains incompletely understood. Here we model complete KRAS inhibition using CRISPR/Cas-mediated genome editing and demonstrate that KRAS is dispensable in a subset of human and mouse PDAC cells. Remarkably, nearly all KRAS deficient cells exhibit phosphoinositide 3-kinase (PI3K)-dependent mitogen-activated protein kinase (MAPK) signaling and induced sensitivity to PI3K inhibitors. Furthermore, comparison of gene expression profiles of PDAC cells retaining or lacking KRAS reveal a role of KRAS in the suppression of metastasis-related genes. Collectively, these data underscore the potential for PDAC resistance to even the very best KRAS inhibitors and provide insights into mechanisms of response and resistance to KRAS inhibition.

Pancreatic cancer cells may develop resistance to KRAS inhibitors due to activation of compensatory pathways. In this study, the authors demonstrate that KRAS is dispensable in a subset of pancreatic cancer and that PI3K signalling may have an important role in mediating tumor growth following KRAS inhibition.

Pharmacologic inhibition of PI3K p110δ in mutant Shp2E76K-expressing mice

Juvenile myelomonocytic leukemia is a childhood malignancy that lacks effective chemotherapies and thus has poor patient outcomes. PI3K p110δ has been found to promote hyperproliferation of cells expressing mutant Shp2. In this study, we tested the efficacy of a PI3Kδ inhibitor in mice expressing the Shp2 gain-of-function mutation, E76K. We found that in vivo treatment of mice led to significantly decreased splenomegaly, reduced frequency of bone marrow progenitor cells, and increased terminally differentiated peripheral blood myeloid cells. The survival of drug-treated mice was significantly prolonged compared to vehicle-treated controls, although mice from both groups ultimately succumbed to a similar myeloid cell expansion. PI3Kδ inhibitors are currently used to treat patients with relapsed lymphoid malignancies, such as chronic lymphocytic leukemia. The current findings provide evidence for using PI3Kδ inhibitors as a treatment strategy for JMML and potentially other myeloid diseases.

Turning the tide in myelodysplastic/myeloproliferative neoplasms

Myelodysplastic syndromes/myeloproliferative neoplasms (MDS/MPN) are aggressive myeloid malignancies recognized as a distinct category owing to their unique combination of dysplastic and proliferative features. Although current classification schemes still emphasize morphology and exclusionary criteria, disease-defining somatic mutations and/or germline predisposition alleles are increasingly incorporated into diagnostic algorithms. The developing picture suggests that phenotypes are driven mostly by epigenetic mechanisms that reflect a complex interplay between genotype, physiological processes such as ageing and interactions between malignant haematopoietic cells and the stromal microenvironment of the bone marrow. Despite the rapid accumulation of genetic knowledge, therapies have remained nonspecific and largely inefficient. In this Review, we discuss the pathogenesis of MDS/MPN, focusing on the relationship between genotype and phenotype and the molecular underpinnings of epigenetic dysregulation. Starting with the limitations of current therapies, we also explore how the available mechanistic data may be harnessed to inform strategies to develop rational and more effective treatments, and which gaps in our knowledge need to be filled to translate biological understanding into clinical progress.

How I treat chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic malignancy that may deserve specific management. Defined by a persistent peripheral blood monocytosis ≥1 × 10⁹/L and monocytes accounting for ≥10% of the white blood cells, this aging-associated disease combines cell proliferation as a consequence of myeloid progenitor hypersensitivity to granulocyte-macrophage colony-stimulating factor with myeloid cell dysplasia and ineffective hematopoiesis. The only curative option for CMML remains allogeneic stem cell transplantation. When transplantation is excluded, CMML is stratified into myelodysplastic (white blood cell count <13 × 10⁹/L) and proliferative (white blood cell count ≥13 × 10⁹/L) CMML. In the absence of poor prognostic factors, the management of myelodysplastic CMML is largely inspired from myelodysplastic syndromes, relying on erythropoiesis-stimulating agents to cope with anemia, and careful monitoring and supportive care, whereas the management of proliferative CMML usually relies on cytoreductive agents such as hydroxyurea, although ongoing studies will help delineate the role of hypomethylating agents in this patient population. In the presence of excessive blasts and other poor prognostic factors, hypomethylating agents are the preferred option, even though their impact on leukemic transformation and survival has not been proved. The therapeutic choice is illustrated by 4 clinical situations among the most commonly seen. Although current therapeutic options can improve patient's quality of life, they barely modify disease evolution. Improved understanding of CMML pathophysiology will hopefully lead to the exploration of novel targets that potentially would be curative.

Germ line mutations associated with leukemias

Several genetic syndromes have long been associated with a predisposition to the development of leukemia, including bone marrow failure syndromes, Down syndrome, and Li Fraumeni syndrome. Recent work has better defined the leukemia risk and outcomes in these syndromes. Also, in the last several years, a number of other germ line mutations have been discovered to define new leukemia predisposition syndromes, including ANKRD26, GATA2, PAX5, ETV6, and DDX41 In addition, data suggest that a substantial proportion of patients with therapy related leukemias harbor germ line mutations in DNA damage response genes such as BRCA1/2 and TP53 Recognition of clinical associations, acquisition of a thorough family history, and high index-of-suspicion are critical in the diagnosis of these leukemia predisposition syndromes. Accurate identification of patients with germ line mutations associated with leukemia can have important clinical implications as it relates to management of the leukemia, as well as genetic counseling of family members.