Activation of apoptosis pathways in peripheral blood lymphocytes by in vivo chemotherapy

Abstract

In addition to myelosuppression, anticancer drugs cause rapid and persistent depletion of lymphocytes, possibly by direct apoptosis induction in mature T and B cells. Induction of apoptosis regulators was analyzed in peripheral blood lymphocytes from pediatric patients undergoing first-cycle chemotherapy for solid tumors. In vivo chemotherapy induced a significant increase in lymphocyte apoptosis ex vivo. The activation of initiator caspase-8 and effector caspase-3 and the cleavage of caspase substrates was detected 12 to 48 hours after the onset of therapy. Caspase inhibition by Z-VAD-fmk did not reduce ex vivo lymphocyte apoptosis in all patients, indicating the additional involvement of caspaseindependent cell death. No evidence for the involvement of activation-induced cell death was found in the acute phase of lymphocyte depletion as analyzed by activation marker expression and sensitivity for CD95 signaling. Lymphocyte apoptosis in vivo appeared to be predominantly mediated by the mitochondrial pathway because a marked decrease of mitochondrial membrane potential (⌬⌿ M ) was detected after 24 to 72 hours of treatment, preceded by the increased expression of Bax. Interestingly, despite the use of DNAdamaging agents, p53 remained completely undetectable throughout treatment. In contrast, in vitro treatment with cytarabine and etoposide induced p53 protein, CD95 receptor expression, CD95 sensitivity, and CD95 receptor-ligand interaction in stimulated cycling lymphocytes, but no such induction was seen in resting cells. These data suggest that chemotherapy-induced lymphocyte depletion involves distinct mechanisms of apoptosis induction, such as direct mitochondrial and caspase-dependent pathways in resting cells and p53-dependent pathways in cycling lymphocytes. IntroductionAnticancer drugs used in chemotherapy for tumors and leukemias inhibit proliferation and induce cell death in malignant cells. In addition to the therapeutic effect on malignant cells, chemotherapy causes severe toxicity in normal tissue, leading to side effects such as mucositis, hair loss, and myelosuppression. In addition, chemotherapy induces acute lymphopenia and chronic depletion of CD4 T cells, leading to increased susceptibility to opportunistic infection. 1,2 The molecular mechanisms by which cytotoxic drugs induce depletion of lymphocytes have not been defined and may involve proliferative arrest in lymphocyte precursor compartments or, alternatively, direct induction of apoptosis in mature cells.Regulation of apoptosis or programmed cell death involves different molecular compartments, such as death receptors, 3 Bcl-2 family member proteins, 4 mitochondria, 5 p53, and caspases. 6 In tissue culture cell lines, cytotoxic drugs induce the molecular regulators of physiologic apoptosis 7,8 Cytotoxic drug-induced apoptosis in leukemia 9 and carcinoma 28 cell lines critically depends on the activation of caspases. Caspases are activated by death receptor signaling or are a consequence of mitochondrial alterations including the release ...

Central Role of Fas-associated Death Domain Protein in Apoptosis Induction by the Mitogen-activated Protein Kinase Kinase Inhibitor CI-1040 (PD184352) in Acute Lymphocytic Leukemia Cells in Vitro

“…This inhibitor caused a transient delay in etoposide-induced apoptosis in Jurkat cells (Fig. 6C, right panel), confirming previous reports that a Fas-dependent process might accelerate etoposide-induced apoptosis under certain conditions but is not essential for this process (31,57). In contrast, IETD(OMe)-fmk completely abrogated CI-1040-induced apoptosis (Fig.…”

Pharmacokinetic, pharmacodynamic and intracellular effects of PEG-asparaginase in newly diagnosed childhood acute lymphoblastic leukemia: results from a single agent window study

“…We, like others 36 were not able to demonstrate a change in the percentage of in vivo apoptotic cells after administration of PEG-asparaginase. If however, ALL cells were in vitro exposed to L-asparaginase, a significant increase in time of the apoptotic markers was found, confirming previous findings.…”

Alterations in the apoptotic machinery and their potential role in anticancer drug resistance

“…After institution of therapy for acute leukemia, apoptosis can also be detected in circulating blasts (Li et al, 1994;Seiter et al, 1997;Stahnke et al, 2001), providing evidence that apoptotic pathways are also activated in these disorders in vivo. In the solid tumor setting it is more difficult to demonstrate an increase in apoptosis because (i) the poor response of many solid tumors to existing agents limits the amount of apoptosis that might be expected and (ii) efficient phagocytosis of apoptotic cells makes it possible for extensive tumor regressions to occur with only modest increases in the number of apoptotic cells present at any point in time (Kyprianou et al, 1990).…”