The thymidine dideoxynucleoside analog, alovudine, inhibits the mitochondrial DNA polymerase γ, impairs oxidative phosphorylation and promotes monocytic differentiation in acute myeloid leukemia.

Mitochondrial DNA encodes 13 proteins that comprise components of the respiratory chain that maintain oxidative phosphorylation. The replication of mitochondrial DNA is performed by the sole mitochondrial DNA polymerase γ. As acute myeloid leukemia (AML) cells and stem cells have an increased reliance on oxidative phosphorylation, we sought to evaluate polymerase γ inhibitors in AML. The thymidine dideoxynucleoside analog, alovudine, is an inhibitor of polymerase γ. In AML cells, alovudine depleted mitochondrial DNA, reduced mitochondrial encoded proteins, decreased basal oxygen consumption, and decreased cell proliferation and viability. To evaluate the effects of polymerase γ inhibition with alovudine in vivo, mice were xenografted with OCI-AML2 cells and then treated with alovudine. Systemic administration of alovudine reduced leukemic growth without evidence of toxicity and decreased levels of mitochondrial DNA in the leukemic cells. We also showed that alovudine increased the monocytic differentiation of AML cells. Genetic knockdown and other chemical inhibitors of polymerase γ also promoted AML differentiation, but the effects on AML differentiation were independent of reductions in oxidative phosphorylation or respiratory chain proteins. Thus, we have identified a novel mechanism by which mitochondria regulate AML fate and differentiation independent of oxidative phosphorylation. Moreover, we highlight polymerase γ inhibitors, such as alovudine, as novel therapeutic agents for AML.

Emerging therapies for acute myeloid leukemia: translating biology into the clinic.

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with a poor outcome; overall survival is approximately 35% at two years and some subgroups have a less than 5% two-year survival. Recently, significant improvements have been made in our understanding of AML biology and genetics. These fundamental discoveries are now being translated into new therapies for this disease. This review will discuss recent advances in AML biology and the emerging treatments that are arising from biological studies. Specifically, we will consider new therapies that target molecular mutations in AML and dysregulated pathways such as apoptosis and mitochondrial metabolism. We will also discuss recent advances in immune and cellular therapy for AML.

Leveraging increased cytoplasmic nucleoside kinase activity to target mtDNA and oxidative phosphorylation in AML.

Mitochondrial DNA (mtDNA) biosynthesis requires replication factors and adequate nucleotide pools from the mitochondria and cytoplasm. We performed gene expression profiling analysis of 542 human acute myeloid leukemia (AML) samples and identified 55% with upregulated mtDNA biosynthesis pathway expression compared with normal hematopoietic cells. Genes that support mitochondrial nucleotide pools, including mitochondrial nucleotide transporters and a subset of cytoplasmic nucleoside kinases, were also increased in AML compared with normal hematopoietic samples. Knockdown of cytoplasmic nucleoside kinases reduced mtDNA levels in AML cells, demonstrating their contribution in maintaining mtDNA. To assess cytoplasmic nucleoside kinase pathway activity, we used a nucleoside analog 2'3'-dideoxycytidine (ddC), which is phosphorylated to the activated antimetabolite, 2'3'-dideoxycytidine triphosphate by cytoplasmic nucleoside kinases. ddC is a selective inhibitor of the mitochondrial DNA polymerase γ. ddC was preferentially activated in AML cells compared with normal hematopoietic progenitor cells. ddC treatment inhibited mtDNA replication, oxidative phosphorylation, and induced cytotoxicity in a panel of AML cell lines. Furthermore, ddC preferentially inhibited mtDNA replication in a subset of primary human leukemia cells and selectively targeted leukemia cells while sparing normal progenitor cells. In animal models of human AML, treatment with ddC decreased mtDNA, electron transport chain proteins, and induced tumor regression without toxicity. ddC also targeted leukemic stem cells in secondary AML xenotransplantation assays. Thus, AML cells have increased cytidine nucleoside kinase activity that regulates mtDNA biogenesis and can be leveraged to selectively target oxidative phosphorylation in AML.

Autoimmunity and novel therapies in immune-mediated thrombocytopenia.

Immune-mediated thrombocytopenic purpura (ITP) is recognized as a cell-specific autoimmune disorder, yet, multifactorial in origin. The development of thrombocytopenia is well proven to be mediated by both humoral (anti-platelet antibodies) and cellular (T-cell) mediated mechanisms. In some cases other autoantibodies are also induced, eg, antinuclear antibody (ANA), anti-dsDNA, and anti-cardiolipin, in addition to anti-platelet antibodies. The persistance of these autoantibodies during the course of ITP could herald future development of another autoimmune disease, eg, systemic lupus erythematosus (SLE) or anti-phospholipid syndrome (APS). Due to the better understanding of the pathophysiology of ITP, new novel therapies were introduced aiming to achieve long-lasting remissions. In this review we will focus on the autoimmune nature of the disease and on some of the mechanisms of action of these new therapies.

[IgM enriched immunoglobulins as a therapy for sepsis and autoimmune diseases].

The importance of natural autoreactive antibodies of the immunogtobulin M (IgM) isotype, raised the issue of the innate immune response being immunoregulatory. These antibodies have low affinity and a wide range of specificity, thus acting as protective autoantibodies. Bearing this in mind, many have proposed the therapeutics potential of IgM enriched intravenous immunoglobulin (IVIg) in sepsis and in autoimmune diseases. We will summarize the emerging knowledge of these natural autoreactive IgM antibodies, their role and mechanisms of action in the above mentioned diseases.

Coronary Artery Disease in an Asymptomatic Population Undergoing a Multidetector Computed Tomography (MDCT) Coronary Angiography.

AIM: To assess the prevalence of coronary artery disease (CAD) in asymptomatic subjects using multidetector computed tomography (MDCT) and its relationships to demographic and clinical risk factors. MATERIAL AND METHOD: We enrolled consecutive asymptomatic volunteers with no evidence of ischemic heart disease that underwent MDCT for the early detection of CAD. All MDCT findings were correlated with demographic and risk factors. A total of 2820 coronary segments were analyzed in 188 asymptomatic subjects (150 males and 38 females), aged 54.4 +/- 7.4 years. RESULTS: A total of 128 (68%) demonstrated MDCT findings compatible with CAD; of these 111 (86.7%) had non-significant (diameter stenosis /= 50%). Compared with older subjects (mean age 56+/-8 years), younger subjects had a lower prevalence of MDCT findings of CAD 55.5% vs. 12.5%, respectively (P<0.001), regardless of risk factors. Males had more CAD (mostly non-significant) compared with females (109 [72.7%] vs. 19 [50.3%], respectively; P= 0.007). Subjects with >/= 2 risk factors had a higher prevalence of CAD in general and significant CAD in particular (P<0.001). CONCLUSION: CAD in asymptomatic population seems to be not uncommon. Using MDCT a high prevalence of non-significant and low prevalence of significant CAD was discovered in middle age asymptomatic population.