Caspase 2 and Caspase 3 Protein Levels as Predictors of Survival in Acute Myelogenous Leukemia

Abstract

Because caspase activation is an essential step in programmed cell death (apoptosis) and cytotoxic drug-induced apoptosis is mediated by caspase 2 and caspase 3, we hypothesized that caspase 2 and 3 levels predict clinical outcome in acute myelogenous leukemia (AML). Using quantitative Western blot analysis, we studied the levels of nonactivated (uncleaved) caspase 2 and 3 in peripheral blood low-density cells from 185 patients with newly diagnosed AML. We also measured the level of activated (cleaved) caspase 3 in 41 randomly selected samples from the 185 patients. Finally, we analyzed the effect of caspase 2 and 3 levels and other prognostic variables on patient survival using a multivariate Cox model. We found that median levels of nonactivated caspase 2 and 3 were higher in AML than in normal peripheral blood cells (P < .001 and P <.02, respectively). There was no association between caspase level and either the percentage of peripheral blasts or any specific type of leukemia cell cytogenetic abnormalities. When the effect of each uncleaved caspase was considered individually, a high level of uncleaved caspase 3 (P = .04), but not of caspase 2 (P = .16), was associated with decreased survival. Conversely, a high level of cleaved caspase 3 denoted improved survival and correlated with the inactivation of the DNA-repair enzyme poly(ADP-ribose) polymerase. Thus, cleaved caspase 3 could stimulate the apoptotic cascade further, and lack of its activation likely caused an accumulation of the uncleaved caspase. Although uncleaved caspase 2 level per se had no prognostic significance, the interactive effect of high levels of both uncleaved caspase 2 and 3 denoted very poor survival (P < .001) and had the largest effect of all prognostic variables (P < .001; estimated relative risk, 2.49; 95% confidence interval, 1.59 to 3. 90). Taken together, caspase 2 and caspase 3 protein levels obtained at diagnosis may constitute a reliable prognostic factor in AML.