The cytostatic deoxycytidine analog cytarabine (ara-C) is the most active agent available against acute myelogenous leukemia (AML). Together with anthracyclines, ara-C forms the backbone of AML treatment for children and adults. In AML, both the cytotoxicity of ara-C in vitro and the clinical response to ara-C therapy are correlated with the ability of AML blasts to accumulate the active metabolite ara-C triphosphate (ara-CTP), which causes DNA damage through perturbation of DNA synthesis. Differences in expression levels of known transporters or metabolic enzymes relevant to ara-C only partially account for patient-specific differential ara-CTP accumulation in AML blasts and response to ara-C treatment. Here we demonstrate that the deoxynucleoside triphosphate (dNTP) triphosphohydrolase SAM domain and HD domain 1 (SAMHD1) promotes the detoxification of intracellular ara-CTP pools. Recombinant SAMHD1 exhibited ara-CTPase activity in vitro, and cells in which SAMHD1 expression was transiently reduced by treatment with the simian immunodeficiency virus (SIV) protein Vpx were dramatically more sensitive to ara-C-induced cytotoxicity. CRISPR-Cas9-mediated disruption of the gene encoding SAMHD1 sensitized cells to ara-C, and this sensitivity could be abrogated by ectopic expression of wild-type (WT), but not dNTPase-deficient, SAMHD1. Mouse models of AML lacking SAMHD1 were hypersensitive to ara-C, and treatment ex vivo with Vpx sensitized primary patient-derived AML blasts to ara-C. Finally, we identified SAMHD1 as a risk factor in cohorts of both pediatric and adult patients with de novo AML who received ara-C treatment. Thus, SAMHD1 expression levels dictate patient sensitivity to ara-C, providing proof-of-concept that the targeting of SAMHD1 by Vpx could be an attractive therapeutic strategy for potentiating ara-C efficacy in hematological malignancies.

Purpose: Heat shock protein 90 (HSP90) is a chaperone for several client proteins involved in transcriptional regulation, signal transduction, and cell cycle control. HSP90 is abundantly expressed by a variety of tumor types and has been recently targeted for cancer therapy. The objective of this study was to determine the role of HSP90 in promoting growth and survival of Hodgkin's lymphoma and to determine the molecular consequences of inhibiting HSP90 function by the small-molecule 17-allylamino-17-demethoxy-geldanamycin (17-AAG) in Hodgkin's lymphoma. Experimental Design: HSP90 expression in Hodgkin's lymphoma cell lines was determined by Western blot and in primary lymph node sections from patients with Hodgkin's lymphoma by immunohistochemistry. Cell viability was determined by the 3-(4,5-dimethyl-thiazol-2yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Apoptosis and cell cycle fractions were determined by flow cytometry. Expression of intracellular proteins was determined by Western blot. Results: HSP90 is overexpressed in primary and cultured Hodgkin's lymphoma cells. Inhibition of HSP90 function by 17-AAG showed a time-and dose-dependent growth inhibition of Hodgkin's lymphoma cell lines.17-AAG induced cell cycle arrest and apoptosis, which were associated with a decrease in cyclin-dependent kinase (CDK) 4, CDK 6, and polo-like kinase1 (PLK1), and induced apoptosis by caspase-dependent and caspase-independent mechanisms. Furthermore, 17-AAG depleted cellular contents of Akt, decreased extracellular signal^regulated kinase (ERK) phosphorylation, and reduced cellular FLICE-like inhibitory protein levels (FLIP), and thus enhanced the cytotoxic effect of doxorubicin and agonistic anti^tumor necrosis factor^related apoptosisinducing ligand (TRAIL) death receptor antibodies. Conclusion: Inhibition of HSP90 function induces cell death and enhances the activity of chemotherapy and anti^tumor necrosis factor^related apoptosis-inducing ligand death receptor antibodies, suggesting that targeting HSP90 function might be of therapeutic value in Hodgkin's lymphoma.

BACKGROUND.CXC chemokine receptor 4 (CXCR4) expression in acute myeloid leukemia (AML) is reported to correlate with FLT3 gene mutation and poorer prognosis. The prognostic significance of CXCR4 expression in patients with AML that have a normal karyotype and no evidence of FLT3 gene mutations was examined.METHODS.The prognostic significance of CXCR4 expression in 122 AML patients with normal karyotype and no evidence of FLT3 gene mutation treated at our institution between 1997 and 2003 was analyzed. All patients received intensive chemotherapy according to institutional protocols; 84% received cytarabine‐containing regimens. Bone marrow biopsy or clot specimens obtained before treatment were immunostained for CXCR4.RESULTS.There were 70 men and 52 women with a median age of 62 years (range, 22–82 years). Median follow‐up was 18 months (range, <1–97 months). Seventy‐six patients achieved complete remission (CR); 39 had recurrence. Sixty‐six patients died, including 9 with no evidence of disease. CXCR4 was positive in 70 and negative in 52 patients, with CR rates of 58% and 71%, respectively (P = .09). Multivariate analysis demonstrated that CXCR4 expression, presence of multilineage dysplasia, and high creatinine level predicted poorer overall (OS) and event‐free (EFS) survival.CONCLUSIONS.The results suggest that CXCR4 expression is associated with poor prognosis in AML patients with an unmutated FLT3 gene. Cancer 2007. © 2007 American Cancer Society.

Summary Activation of the phosphatidylinositol 3‐kinase (PI3K) pathway has been linked with tumour cell growth, survival and resistance to therapy in several cancer types. The active, phosphorylated form of Akt (pAkt) was found to be aberrantly expressed in Hodgkin lymphoma (HL)‐derived cell lines and in Hodgkin–Reed–Sternberg (HRS) cells in 27 of 42 (64·3%) of primary lymph node sections of HL, indicative of PI3K activity. Akt phosphorylation was not associated with loss of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) expression, but with its phosphorylation in HL‐cell lines, suggesting that its biological function is impaired. Akt phosphorylation was further induced by CD30 ligand (CD30L), CD40L and receptor activator of nuclear factor kappa B (RANK) ligand. The PI3K inhibitor LY294002 demonstrated antiproliferative effects in a dose‐ and time‐dependent manner, which was associated with Akt dephosphorylation on Thr308 and Ser473 sites and dephosphorylation of the downstream ribosomal protein S6. LY209002 induced cell cycle arrest in the G0/G1 phase and apoptosis, which were associated with upregulation of MDM2, downregulation of cyclin D1, activation of caspase 9 and poly‐ADP‐ribose polymerase cleavage. The Akt inhibitor QLT394 also demonstrated antiproliferative effects in a dose‐ and time‐dependent manner, dephosphorylated ribosomal S6 and cleaved caspase 9. Collectively, these data suggest that the aberrant activation of the PI3K/Akt survival pathway in HRS cells is not because of loss of PTEN expression. Our data suggest that PTEN phosphorylation and activation of CD30, CD40 and RANK may play a role in activating Akt in HRS cells.

Clusterin expression has been reported to be characteristic of systemic anaplastic large cell lymphoma and usually negative in cutaneous anaplastic large cell lymphoma as well as other lymphoma types. We surveyed clusterin expression using immunohistochemical methods in 266 cases of nonHodgkin's lymphoma and Hodgkin's disease to further assess the diagnostic utility of this marker. Clusterin immunostaining was observed in 40 of 49 (82%) systemic anaplastic large cell lymphomas and 12 of 29 (41%) cutaneous anaplastic large cell lymphomas. Clusterin also was expressed in 5 of 43 (12%) diffuse large B-cell lymphomas (4 of 5 CD30؉), 1 of 14 (7%) peripheral T-cell lymphomas, 1 of 32 (3%) cases of nodular sclerosis Hodgkin's disease, and 1 case of mycosis fungoides in large cell transformation. Clusterin was negative in all other neoplasms assessed including follicular lymphoma of all grades (n ‫؍‬ 24), mantle cell lymphoma (n ‫؍‬ 13), marginal zone B-cell lymphoma (n ‫؍‬ 12), precursor T-cell or B-cell lymphoblastic leukemia/lymphoma (n ‫؍‬ 10), mixed cellularity Hodgkin's disease (n ‫؍‬ 8), chronic lymphocytic leukemia/small lymphocytic lymphoma (n ‫؍‬ 7), Burkitt lymphoma (n ‫؍‬ 7), mycosis fungoides (n ‫؍‬ 4), nodular lymphocyte predominant Hodgkin's disease (n ‫؍‬ 3), lymphoplasmacytic lymphoma/Waldenstrom macroglobulinemia (n ‫؍‬ 2), and plasmacytoma (n ‫؍‬ 2). We conclude that clusterin is a marker of anaplastic large cell lymphoma and that addition of clusterin to antibody panels designed to distinguish systemic anaplastic large cell lymphoma from classical Hodgkin's disease is useful. However, clusterin is also positive in a substantial subset of cutaneous anaplastic large cell lymphomas, a smaller subset of diffuse large B-cell lymphomas, and rarely in cases of peripheral T-cell lymphoma and nodular sclerosis Hodgkin's disease.