Anti-leukemic activity and tolerability of anti-human CD47 monoclonal antibodies.

CD47, a broadly expressed cell surface protein, inhibits cell phagocytosis via interaction with phagocyte-expressed SIRPα. A variety of hematological malignancies demonstrate elevated CD47 expression, suggesting that CD47 may mediate immune escape. We discovered three unique CD47-SIRPα blocking anti-CD47 monoclonal antibodies (mAbs) with low nano-molar affinity to human and cynomolgus monkey CD47, and no hemagglutination and platelet aggregation activity. To characterize the anti-cancer activity elicited by blocking CD47, the mAbs were cloned into effector function silent and competent Fc backbones. Effector function competent mAbs demonstrated potent activity in vitro and in vivo, while effector function silent mAbs demonstrated minimal activity, indicating that blocking CD47 only leads to a therapeutic effect in the presence of Fc effector function. A non-human primate study revealed that the effector function competent mAb IgG1 C47B222-(CHO) decreased red blood cells (RBC), hematocrit and hemoglobin by >40% at 1 mg/kg, whereas the effector function silent mAb IgG2σ C47B222-(CHO) had minimal impact on RBC indices at 1 and 10 mg/kg. Taken together, our findings suggest that targeting CD47 is an attractive therapeutic anti-cancer approach. However, the anti-cancer activity observed with anti-CD47 mAbs is Fc effector dependent as are the side effects observed on RBC indices.

The p53 family and programmed cell death.

The p53 tumor suppressor continues to hold distinction as the most frequently mutated gene in human cancer. The ability of p53 to induce programmed cell death, or apoptosis, of cells exposed to environmental or oncogenic stress constitutes a major pathway whereby p53 exerts its tumor suppressor function. In the past decade, we have discovered that p53 is not alone in its mission to destroy damaged or aberrantly proliferating cells: it has two homologs, p63 and p73, that in various cellular contexts and stresses contribute to this process. In this review, the mechanisms whereby p53, and in some cases p63 and p73, induce apoptosis are discussed. Other reviews have focused more extensively on the contribution of individual p53-regulated genes to apoptosis induction by this protein, whereas in this review, we focus more on those factors that mediate the decision between growth arrest and apoptosis by p53, p63 and p73, and on the post-translational modifications and protein-protein interactions that influence this decision.

Polymorphisms in the p53 pathway.

The p53 tumor suppressor gene continues to be distinguished as the most frequently mutated gene in human cancer; this gene can be found mutated in up to 50% of human tumors of diverse histological type. It is generally accepted that the ability of p53 to induce either growth arrest or programmed cell death in response to diverse stimuli underlies the powerful selection against this protein in the development of cancer. It is somewhat surprising, then, to find p53 and several target genes in this pathway containing polymorphisms that impair their function. The nature of these polymorphic variants, and the mechanism whereby they impair the function of the p53 pathway, are reviewed here-in. The impact of these polymorphisms on cancer risk and the efficacy of therapy are only now becoming unraveled. Of particular relevance in these efforts will be the generation of mouse models of polymorphic variants in p53 and its target genes. Equally important will be better-controlled human studies, where-in haplotypes for p53 (that is, combinations of different polymorphisms in the p53 gene) and for p53-target genes are taken into account, instead of analyses of single gene variants, which have largely predominated to date. Studies in both regards should shed light on an emerging area in cancer biology, the significance of inter-individual differences in genotype on cancer risk, prognosis, and the efficacy of cancer therapy.

Ethanol stimulates the production of reactive oxygen species at mitochondrial complexes I and III.

The aim of this study was to investigate the hepatocellular site of reactive oxygen species generation during acute ethanol metabolism. Reactive oxygen species production was detected using the 2',7'-dichlorofluorescein fluorescence assay and cell injury was determined by lactate dehydrogenase release. Incubation with 1 and 10 mM ethanol increased the production of reactive oxygen species by 72% and 151%, respectively, which was associated with mild decreases in cell viability. Antimycin, a mitochondrial complex III inhibitor, elicited a 17-fold increase in the levels of reactive oxygen species and markedly decreased hepatocyte viability and ATP levels. Ethanol increased reactive oxygen species production and the cytosolic NADH/NAD+ ratio in antimycin-treated cells. Rotenone, a mitochondrial complex I inhibitor that allows electron flow through the flavin mononucleotide (FMN), but prevents electron flow to complex III, significantly increased reactive oxygen species production in untreated cells, but decreased reactive oxygen species production in antimycin plus ethanol-treated cells. Diphenyliodonium, a mitochondrial complex I inhibitor that inhibits electron flow through FMN, attenuated reactive oxygen species generation in all groups. Fructose prevented cytotoxicity in all treatment groups. Though they do not eliminate the participation of other intracellular compartments, these results indicate that the NADH dehydrogenase complex, as well as complex III of mitochondria, are involved in ethanol-related production of reactive oxygen species.