motexafin-gadolinium and Lymphoma--Follicular

Loss of p53 renders cells more susceptible to acute oxidant stress induced by oxidant-generating agents such as motexafin gadolinium (MGd). We hypothesized that reactive oxygen species (ROS)-generating MGd results in low-level p53 expression, making cells more susceptible to oxidant stress.. Lymphoma cells were incubated with different concentrations of MGd with or without zinc (Zn) and ascorbate, and ROS, apoptosis, proteins, and oxidant genes were measured.. MGd, with ascorbate and Zn, induced apoptosis in lymphoma cells. This was accompanied by reduction of p53 protein but not message, and by reduction of p53 downstream targets p21, glutathione peroxidase 1 (GPx1), and p53 up-regulated modulator of apoptosis (PUMA). p53 protein reduction was reversed by MG132, and nutlin-3.. Our data are consistent with a pathway of cell death that is independent of p53-mediated induction of PUMA; the cellular response to reduce p53 represents a cell survival adjustment to ROS-mediated stress.

Topics: Apoptosis; Ascorbic Acid; Burkitt Lymphoma; Cell Line, Tumor; Gene Expression; Humans; Imidazoles; Leupeptins; Lymphoma, Follicular; Metalloporphyrins; Piperazines; Proto-Oncogene Proteins c-mdm2; Reactive Oxygen Species; Tumor Suppressor Protein p53; Zinc

Motexafin gadolinium (MGd, Xcytrin) is a tumor-localizing redox mediator that catalyzes the oxidation of intracellular reducing molecules including NADPH, ascorbate, protein and non-protein thiols, generating reactive oxygen species (ROS). MGd localizes to tumors and cooperates with radiation and chemotherapy to kill tumor cells in tissue culture and animal models. In this report, we demonstrate that MGd triggers the mitochondrial apoptotic pathway in the HF-1 lymphoma cell line as determined by loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, activation of caspase-9 prior to caspase-8, cleavage of PARP and annexin V binding. There was minimal effect on MGd-induced apoptosis by the caspase inhibitor z-VAD-fmk, even though caspase-3 activity (as measured by DEVD-cleavage) was completely inhibited. However, MGd-induced apoptosis was reduced to baseline levels by the more potent caspase inhibitor Q-VD-OPh, demonstrating that MGd-induced apoptosis is indeed caspase-dependent. Apoptosis induced by dexamethasone, doxorubicin and etoposide (mediated through the mitochondrial pathway) was also more sensitive to inhibition by Q-VD-OPh than z-VAD-fmk. Our results demonstrating differential sensitivity of drug-induced apoptosis to caspase inhibitors suggest that the term "caspase-independent apoptosis" cannot be solely defined as apoptosis that is not inhibited by z-VAD-fmk as has been utilized in some published studies.

Topics: Amino Acid Chloromethyl Ketones; Annexin A5; Antineoplastic Agents; Apoptosis; Caspase Inhibitors; Caspases; Cell Line, Tumor; Drug Resistance, Neoplasm; Humans; Lymphoma, Follicular; Lymphoma, Large B-Cell, Diffuse; Metalloporphyrins; Mitochondria; Poly(ADP-ribose) Polymerases; Quinolines