Cisplatin is a broad-spectrum anticancer drug that is also widely used in experimental studies on DNA damage-induced apoptosis. Induction of apoptosis within 24-48 hr requires cisplatin concentrations that are at least one order of magnitude higher than the IC 50 . Here, we show that such high, apoptosis-inducing cisplatin concentrations induce cellular superoxide formation and that apoptosis is inhibited by superoxide scavengers. The same concentration limit and the requirement for superoxide are also true for induction of caspase activation in enucleated cells (cytoplasts), showing that cisplatin-induced apoptosis occurs independently of nuclear DNA damage. In contrast, lower cisplatin concentrations, which do not induce acute apoptosis, are sufficient for induction of DNA damage signaling. We propose that the antiproliferative effects of cisplatin at IC 50 doses involve premature senescence and secondary, nonstress-induced apoptosis. The higher doses currently used in in vitro studies lead to acute, stress-induced apoptosis that involves induction of superoxide but is largely DNA damage-independent. ' 2006 Wiley-Liss, Inc.Key words: cisplatin; DNA damage; apoptosis; senescence Cis-diamminedichloroplatinum (II) (cisplatin) is a commonly used anticancer agent, especially effective in the treatment of testicular carcinoma and also used to treat other malignancies such as ovarian, cervix, head-and-neck and small-cell lung cancer. 1 Cisplatin forms covalent bonds to the N7 positions of DNA purines to form intra-or interstrand crosslinks, and DNA is generally acknowledged as the primary target of cisplatin. 2,3 Cisplatin is a commonly used model agent for induction of DNA damage-dependent apoptosis in vitro. Acute apoptosis is induced within 24-36 hr, and major efforts have been performed to elucidate apoptotic signaling pathways induced by cisplatin within this time frame. These various studies have highlighted the roles of c-ABL, stressactivated protein kinases and p53 as downstream mediators of cisplatin-induced DNA damage and as mediators of apoptotic signaling (recently reviewed in 3 ). In addition to induction of apoptosis, cisplatin also induces premature senescence. 4 Premature senescence is currently thought to be related to replicative senescence, which has been demonstrated to be a DNA damage response. 5 During replicative senescence, signaling pathways involving ATM (Ataxia telangiectasia mutated) and p53 are activated by telomere uncapping. 5,6 The same signaling mechanisms are believed to be involved in premature senescence induced by DNA damaging drugs. 6,7 Apoptosis and senescence are obviously mutually exclusive cellular outcomes. The factors that decide whether cisplatin will trigger apoptosis or senescence are not clearly understood. In one scenario, senescence and apoptosis represent graded responses to increasing DNA damage. In more complex scenarios, cisplatin induces senescence and apoptosis by different (or partially different) mechanisms.As inducer of apoptosis, cisplatin is used at very d...

The p53 protein activates cellular death programs through multiple pathways. Because the high frequency of p53 mutations in human tumors is believed to contribute to resistance to commonly used chemotherapeutic agents, it is important to identify drugs that induce p53-independent cell death and to define the mechanisms of action of such drugs. Here we screened a drug library (the National Cancer Institute mechanistic set; 879 compounds with diverse mechanisms of actions) and identified 175 compounds that induced caspase cleavage of cytokeratin-18 in cultured HCT116 colon cancer cells at <5 M. Interestingly, whereas most compounds elicited a stronger apoptotic response in cells with functional p53, significant apoptosis was observed also in p53-null cells. A subset of 15 compounds showing weak or no dependence on p53 for induction of apoptosis was examined in detail. Of these compounds, 11 were capable of activating caspase-3 in enucleated cells. Seven such compounds with nonnuclear targets were found to induce lysosomal membrane permeabilization (LMP). Translocation of the lysosomal proteases cathepsin B and cathepsin D into the cytosol was observed after treatment with these drugs, and apoptosis was inhibited by pepstatin A, an inhibitor of cathepsin D. Apoptosis depended on Bax, suggesting that LMP induced a mitochondrial apoptotic pathway. We conclude that a large number of potential anticancer drugs induce p53-independent apoptosis and that LMP is a mediator of many such responses.anticancer drugs ͉ cathepsin D ͉ M30 antibody

Summary. Introduction: Apixaban is an oral direct factor Xa inhibitor developed for the prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary, but the effects on common coagulation reagents and assays constitute clinically valuable information. Objectives: To investigate the effects of apixaban on commonly used coagulation methods, and to evaluate anti-FXa assays for specific determination of the drug concentration. Materials and Methods: Apixaban was added to plasma from healthy subjects in the concentration range 0-1000 lg L À1 , and analyses were performed with different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, protein C, and protein S. A lupus anticoagulant assay and an APTT assay with varying phospholipid concentrations were used to study the phospholipid dependence. Results: In general, apixaban showed fewer effects in vitro than have been shown for rivaroxaban, another direct FXa inhibitor. The concentration needed to double the APTT varied between 2200 and 4700 lg L À1, and the concentration needed to double the PT varied between 700 and 3900 lg L À1. The effects on antithrombin, protein C and protein S assays were dependent on the type of reagent. Apixaban did not cause false-positive lupus anticoagulant results. Chromogenic anti-FXa assays showed linear dose-response curves with apixaban. Conclusions: Therapeutic concentrations of apixaban variably affect different assay groups, and even different reagents within an assay group. The effects were much smaller than with rivaroxaban. The use of APTT and/or PT assays to screen the anticoagulant activity of apixaban cannot be recommended. A chromogenic anti-FXa assay can be used for reliable measurements of apixaban concentration.