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Summary: Background. Myeloproliferative neoplasms (MPN) are disorders characterized by an alteration at the hematopoietic stem cell (HSC) level, where the JAK2 mutation is the most common genetic alteration found in classic MPN (polycythemia vera, essential thrombocythemia, and primary myelofibrosis). We and others previously demonstrated that metformin reduced splenomegaly and platelets counts in peripheral blood in JAK2V617F pre-clinical MPN models, which highlighted the antineoplastic potential of biguanides for MPN treatment. Phenformin is a biguanide that has been used to treat diabetes, but was withdrawn due to its potential to cause lactic acidosis in patients. Aims. We herein aimed to investigate the effects of phenformin in MPN disease burden and stem cell function in Jak2V617F-knockin MPN mice. Results. In vitro phenformin treatment reduced cell viability and increased apoptosis in SET2 JAK2V67F cells. Long-term treatment with 40 mg/kg phenformin in Jak2V617F knockin mice increased the frequency of LSK, myeloid progenitors (MP), and multipotent progenitors (MPP) in the bone marrow. Phenformin treatment did not affect peripheral blood counts, spleen weight, megakaryocyte count, erythroid precursors frequency, or ex vivo clonogenic capacity. Ex vivo treatment of bone marrow cells from Jak2V617F knockin mice with phenformin did not affect hematologic parameters or engraftment in recipient mice. Conclusions. Phenformin increased the percentages of LSK, MP, and MPP populations, but did not reduce disease burden in Jak2V617F-knockin mice. Additional studies are necessary to further understand the effects of phenformin on early hematopoietic progenitors. [ABSTRACT FROM AUTHOR]

Summary: Stathmin 1 (STMN1) is a microtubule-destabilizing protein highly expressed in hematological malignancies and involved in proliferation and differentiation. Although a previous study found that the PML–RARα fusion protein, which contributes to the pathophysiology of acute promyelocytic leukemia (APL), positively regulates STMN1 at the transcription and protein activity levels, little is known about the role of STMN1 in APL. In this study, we aimed to investigate the STMN1 expression levels and their associations with laboratory, clinical, and genomic data in APL patients. We also assessed the dynamics of STMN1 expression during myeloid cell differentiation and cell cycle progression, and the cellular effects of STMN1 silencing and pharmacological effects of microtubule-stabilizing drugs on APL cells. We found that STMN1 transcripts were significantly increased in samples from APL patients compared with those of healthy donors (all p < 0.05). However, this had no effect on clinical outcomes. STMN1 expression was associated with proliferation- and metabolism-related gene signatures in APL. Our data confirmed that STMN1 was highly expressed in early hematopoietic progenitors and reduced during cell differentiation, including the ATRA-induced granulocytic differentiation model. STMN1 phosphorylation was predominant in a pool of mitosis-enriched APL cells. In NB4 and NB4-R2 cells, STMN1 knockdown decreased autonomous cell growth (all p < 0.05) but did not impact ATRA-induced apoptosis and differentiation. Finally, treatment with paclitaxel (as a single agent or combined with ATRA) induced microtubule stabilization, resulting in mitotic catastrophe with repercussions for cell viability, even in ATRA-resistant APL cells. This study provides new insights into the STMN1 functions and microtubule dynamics in APL. [ABSTRACT FROM AUTHOR]

Summary: Chronic myeloid leukemia (CML) is successfully treated with BCR-ABL1 tyrosine kinase inhibitors, but a significant percentage of patients develop resistance. Insulin receptor substrate 1 (IRS1) has been shown to constitutively associate with BCR-ABL1, and IRS1-specific silencing leads to antineoplastic effects in CML cell lines. Here, we characterized the efficacy of NT157, a pharmacological inhibitor of IGF1R-IRS1/2, in CML cells and observed significantly reduced cell viability and proliferation, accompanied by induction of apoptosis. In human K562 cells and in murine Ba/F3 cells, engineered to express either wild-type BCR-ABL1 or the imatinib-resistant BCR-ABL1T315I mutant, NT157 inhibited BCR-ABL1, IGF1R, IRS1/2, PI3K/AKT/mTOR, and STAT3/5 signaling, increased CDKN1A, FOS and JUN tumor suppressor gene expression, and reduced MYC and BCL2 oncogenes. NT157 significantly reduced colony formation of human primary CML cells with minimal effect on normal hematopoietic cells. Exposure of primary CML cells harboring BCR-ABL1T315I to NT157 resulted in increased apoptosis, reduced cell proliferation and decreased phospho-CRKL levels. In conclusion, NT157 has antineoplastic effects on BCR-ABL1 leukemogenesis, independent of T315I mutational status. [ABSTRACT FROM AUTHOR]

Non-T cell activation linker (NTAL) is a lipid raft-membrane protein expressed by normal and leukemic cells and involved in cell signaling. In acute promyelocytic leukemia (APL), NTAL depletion from lipid rafts decreases cell viability through regulation of the Akt/PI3K pathway. The role of NTAL in APL cell processes, and its association with clinical outcome, has not, however, been established. Here, we show that reduced levels of NTAL were associated with increased all-trans retinoic acid (ATRA)-induced differentiation, generation of reactive oxygen species, and mitochondrial dysfunction. Additionally, NTAL-knockdown (NTAL-KD) in APL cell lines led to activation of Ras, inhibition of Akt/mTOR pathways, and increased expression of autophagy markers, leading to an increased apoptosis rate following arsenic trioxide treatment. Furthermore, NTAL-KD in NB4 cells decreased the tumor burden in (NOD scid gamma) NSG mice, suggesting its implication in tumor growth. A retrospective analysis of NTAL expression in a cohort of patients treated with ATRA and anthracyclines, revealed that NTAL overexpression was associated with a high leukocyte count (P = 0.007) and was independently associated with shorter overall survival (Hazard Ratio: 3.6; 95% Confidence Interval: 1.17–11.28; P = 0.026). Taken together, our data highlights the importance of NTAL in APL cell survival and response to treatment. [ABSTRACT FROM AUTHOR]

Summary: JAK2V617F can mimic growth factor signaling, leading to PI3K/AKT/mTOR activation and inhibition of autophagy. We hypothesized that selective inhibition of JAK1/2 by ruxolitinib could induce autophagy and limit drug efficacy in myeloproliferative neoplasms (MPN). Therefore, we investigated the effects of ruxolitinib treatment on autophagy-related genes and cellular processes, to determine the potential benefit of autophagy inhibitors plus ruxolitinib in JAK2V617F cells, and to verify the frequency and clinical impact of autophagy-related gene mutations in patients with MPNs. In SET2 JAK2V617F cells, ruxolitinib treatment induced autophagy and modulated 26 out of 79 autophagy-related genes. Ruxolitinib treatment reduced the expressions of important autophagy regulators, including mTOR/p70S6K/4EBP1 and the STAT/BCL2 axis, in a dose- and time-dependent manner. Pharmacological inhibition of autophagy was able to significantly suppress ruxolitinib-induced autophagy and increased ruxolitinib-induced apoptosis. Mutations in autophagy-related genes were found in 15.5% of MPN patients and were associated with increased age and a trend towards worse survival. In conclusion, ruxolitinib induces autophagy in JAK2V617F cells, potentially by modulation of mTOR-, STAT- and BCL2-mediated signaling. This may lead to inhibition of apoptosis. Our results suggest that the combination of ruxolitinib with pharmacological inhibitors of autophagy, such as chloroquine, may be a promising strategy to treat patients with JAK2V617F-mutated MPNs. [ABSTRACT FROM AUTHOR]