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Background: Torin2 is a second-generation ATP-competitive inhibitor of the mammalian target of rapamycin (mTOR). Dysregulation of mTOR signaling pathway, consisting of mTOR complexes mTORC1 and mTORC2, is a promising therapeutic target in some human malignancies. We examined antitumor effects of Torin2 in adult T-cell leukemia/lymphoma (ATL)-related cell lines compared to those of rapamycin, a classical mTOR inhibitor., Materials and Methods: Cell growth was monitored by detecting viable cells with Cell Counting Kit-8 or trypan blue. Cell cycle was studied by flow cytometric analysis. The phosphorylation status of proteins in the mTOR signaling pathway was examined by western blot analysis., Results: Torin2 exhibited greater efficacy in cell growth inhibition than rapamycin, associated with a strong reduction of phosphorylated v-akt murine thymoma viral oncogene homolog (AKT) (Ser 473), that is downstream of mTORC2., Conclusion: Since mTORC2 activates AKT, Torin2 might inhibit both mTORC1 and mTORC2, resulting in stronger growth inhibition of ATL cells., (Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.)

Background: Asparaginase (ASNase) is an essential component of most treatment protocols for childhood acute lymphoblastic leukemia (ALL). Although increased asparagine synthetase (ASNS) expression may contribute to ASNase resistance, there is conflicting data from patient samples with regard to correlation between ASNS mRNA content and ASNase sensitivity., Procedure: Both T-cell and B-cell derived ALL cell lines were treated with ASNase and then monitored for cell proliferation, cell death, and ASNS mRNA and protein expression., Results: Despite elevated ASNS mRNA following ASNase treatment, different ALL cell lines varied widely in translation to ASNS protein. Although ASNS mRNA levels did not consistently reflect ASNase sensitivity, there was an inverse correlation between ASNS protein and ASNase-induced cell death. Expression of ASNS in an ASNase-sensitive cell line resulted in enhanced ASNase resistance, and conversely, siRNA-mediated inhibition of ASNS expression promoted increased drug sensitivity., Conclusions: These observations provide an explanation for the ASNase sensitivity of ALL cells and demonstrate the importance of measuring ASNS protein rather than mRNA in predicting ASNase responsiveness., ((c) 2007 Wiley-Liss, Inc.)

Background: Acute lymphoblastic leukemia (ALL) is the most common hematological malignancy affecting children. Despite significant progress and success in the treatment of ALL, a significant number of children continue to relapse and for them, outcome remains poor. Therefore, the search for novel therapeutic approaches is warranted. The aim of this study was to investigate the AMP activated protein kinase (AMPK) as a potential target in childhood acute lymphoblastic leukemia (ALL) subtypes characterized by non-random translocation signature profiles. We evaluated the effects of the AMPK activator AICAR on cell growth, cell cycle regulators and apoptosis of various childhood ALL cells., Results: We found that treatment with AICAR inhibited cell proliferation, induced cell cycle arrest in G1-phase, and apoptosis in CCRF-CEM (T-ALL), NALM6 (Bp-ALL), REH (Bp-ALL, TEL/AML1) and SupB15 (Bp-ALL, BCR/ABL) cells. These effects were abolished by treatment with the adenosine kinase inhibitor 5'-iodotubericidin prior to addition of AICAR indicating that AICAR's cytotoxicity is mediated through AMPK activation. Moreover, we determined that growth inhibition exerted by AICAR was associated with activation of p38-MAPK and increased expression of the cell cycle regulators p27 and p53. We also demonstrated that AICAR mediated apoptosis through the mitochondrial pathway as revealed by the release of cytochrome C and cleavage of caspase 9. Additionally, AICAR treatment resulted in phosphorylation of Akt suggesting that activation of the PI3K/Akt pathway may represent a compensatory survival mechanism in response to apoptosis and/or cell cycle arrest. Combined treatment with AICAR and the mTOR inhibitor rapamycin resulted in additive anti-proliferative activity ALL cells., Conclusion: AICAR-mediated AMPK activation was found to be a proficient cytotoxic agent in ALL cells and the mechanism of its anti-proliferative and apoptotic effect appear to be mediated via activation of p38-MAPK pathway, increased expression of cell cycle inhibitory proteins p27 and p53, and downstream effects on the mTOR pathway, hence exhibiting therapeutic potential as a molecular target for the treatment of childhood ALL. Therefore, activation of AMPK by AICAR represents a novel approach to targeted therapy, and suggests a role for AICAR in combination therapy with inhibitors of the PI3K/Akt/mTOR pathways for the treatment of childhood in ALL.

Calcineurin is a calcium-activated serine/threonine phosphatase critical to a number of developmental processes in the cardiovascular, nervous and immune systems. In the T-cell lineage, calcineurin activation is important for pre-T-cell receptor (TCR) signaling, TCR-mediated positive selection of thymocytes into mature T cells, and many aspects of the immune response. The critical role of calcineurin in the immune response is underscored by the fact that calcineurin inhibitors, such as cyclosporin A (CsA) and FK506, are powerful immunosuppressants in wide clinical use. We observed sustained calcineurin activation in human B- and T-cell lymphomas and in all mouse models of lymphoid malignancies analyzed. In intracellular NOTCH1 (ICN1)- and TEL-JAK2-induced T-cell lymphoblastic leukemia, two mouse models relevant to human malignancies, in vivo inhibition of calcineurin activity by CsA or FK506 induced apoptosis of leukemic cells and rapid tumor clearance, and substantially prolonged mouse survival. In contrast, ectopic expression of a constitutively activated mutant of calcineurin favored leukemia progression. Moreover, CsA treatment induced apoptosis in human lymphoma and leukemia cell lines. Thus, calcineurin activation is critical for the maintenance of the leukemic phenotype in vivo, identifying this pathway as a relevant therapeutic target in lymphoid malignancies.

Nuclear factor kappaB (NF-kappaB) plays a major role in the pathogenesis of human T-cell lymphotrophic virus I-associated malignancy. Proteasome inhibitors provide a rational approach to control constitutively activated NF-kappaB in human T-cell lymphotrophic virus I-infected T cells. We report that the proteasome inhibitor PS-341 decreased NF-kappaB DNA binding activity by preventing degradation of IkappaB(alpha). In our murine model of adult T-cell leukemia, PS-341 used alone did not yield prolongation of the survival of tumor-bearing mice. However, when combined with the current clinically approved drug humanized anti-Tac, therapy with PS-341 was associated with a complete remission in a proportion of treated animals, whereas only a partial response was observed in animals treated with humanized anti-Tac alone.

The 1,2,4-triazolidine-3,5-diones, 1-(1-(3-methylphenyl)ethylidineamino)-4,4-diethyl-3,5-azetidinediones, and 4,4-disubstituted-3,5-pyrazolidinediones proved to be potent competitive inhibitors of human Tmolt4 leukemia Type II IMP dehydrogenase [IMPDH] activity, an enzyme isoform which is induced in highly proliferating cells. On the other hand, the 3,5-isoxazolidinediones were shown to be uncompetitive inhibitors of Type II IMPDH activity. The correlation between inhibition of Type II IMPDH activity with the agents' ability to suppress DNA and purine syntheses in these Tmolt4 leukemia cell was positive. Type I IMPDH (i.e., the isoform that is present in normal cells) was not inhibited by these compounds suggesting that these agents would be less toxic to normal cells and have selective inhibition towards proliferating cells.

Retinoids, the analogues of vitamin A, have a broad range of effects on different cell types. One biologically active form of vitamin A is all-trans-retinoic acid (ATRA), which binds to retinoic acid receptors, as does its intracellular metabolite, 9-cis-RA. Earlier studies have documented G1 cell cycle arrest and the induction of apoptosis in human adult T-cell leukemia cells after ATRA treatment. Previous work exploring the growth-inhibitory activity of ATRA in human malignancies has implicated several mechanisms that can arrest cells in the G1 phase of the cell cycle, including activation of p21Waf1 and inhibition of cyclin D1 expression. Therefore, we decided to examine the effects of ATRA exposure on G1 cell cycle components in human adult T-cell leukemia cells. Our data demonstrate a correlation between cyclin/cyclin-dependent kinase activity and subunit complex formation with duration of drug exposure. We also observed an increase in p53 protein levels that were not associated with an increase in p21Waf1 levels. Furthermore, we observed a differential effect on cell cycle progression that was temporally related to length of ATRA exposure. These observations, consistent with a bimodal effect of ATRA on cell cycle progression, may have important implications for the clinical application of ATRA.

Since the discovery of several potent anticancer agents which are specific inhibitors of DNA topoisomerases, the key enzymes in the DNA metabolism, efforts to elucidate the mechanism of acquired resistance to these agents and to overcome them have been focused on these enzymes, the cellular targets of the anticancer agents. These trends were briefly reviewed.