In vitro induction of apoptosis in U937 cells by perillyl alcohol with sensitization by pentoxifylline: increased BCL-2 and BAX protein expression

BACKGROUND

Chemotherapy is effective against a wide variety of tumor cells, although its use is limited by side effects. In vitro experiments and phase I and II trials have shown that phytochemicals such as perillyl alcohol (P-OH) have antitumor effects. Pentoxifylline (PTX), a synthetic methylxanthine used mainly to treat pathologies associated with hematological diseases, sensitizes tumor cells to chemotherapy. The aim of this study was to determine whether PTX amplifies the antitumor effects of P-OH in U937 human myelomonocytic leukemia cells.

METHODS

Apoptosis was measured by the loss of mitochondrial membrane potential determined by flow cytometry using dihexyloxacarbocyanine iodide (DiOC6) and propidium iodide. Bcl-2 and Bax protein expression was also assessed by Western blot analysis.

RESULTS

P-OH and PTX induced loss of the mitochondrial membrane potential in U937 cells in vitro. Culturing the cells in the presence of both compounds caused a significant increase (p < 0.001) in apoptosis and expression of anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins. However, despite their coexistence, Bax expression prevailed in our experiments. These data suggest that the effects of PTX might be attributable to changes in the mitochondrial membrane potential.

CONCLUSION

PTX sensitizes tumor cells to the anti-neoplastic action of P-OH. These observations may have clinical relevance in the treatment of cancer patients.

In vivo and in vitro sensitization of leukemic cells to adriamycin-induced apoptosis by pentoxifyllineInvolvement of caspase cascades and IκBα phosphorylation

The aim of this work was to investigate whether in vivo and in vitro pentoxifylline (PTX) sensitizes hematological tumor cells to adriamycin (ADM)-induced apoptosis, and to investigate the involvement of caspase cascades and phosphorylated forms of IkappaBalpha. Balb/c mice inoculated intraperitoneally with L5178-Y murine lymphoma cells were used for in vivo experiments and for survival studies. The U937 human monocytic cell line was used for in vitro experiments. Both cell lines were treated under similar experimental conditions with PTX and/or ADM to assess their effects on apoptosis. Apoptosis was evaluated by fluorescence microscopy with ethidium bromide and acridine orange staining and confirmed by electrophoretic DNA analysis. Caspase inhibitors Z-VAD-fmk, Z-DEVD-fmk, and Z-LEHD-fmk were used to investigate the involvement of caspase cascades. C-terminally and Ser32 phosphorylated forms of IkappaBalpha were evaluated in cytoplasmic extracts in the absence or presence of TNFalpha.

RESULTS

In vivo, PTX (50 mg/kg) with ADM (5 mg/kg) increased the apoptotic index relative to PTX or ADM administered alone, time- and dose-dependently. DNA laddering appeared in lymphoma cells treated with PTX+ADM at 24 h, whereas neither untreated control, PTX-, nor ADM-treated cells showed DNA fragmentation. All (100%) tumor-bearing mice treated with PTX (25 mg/kg)+ADM (2.5 mg/kg) survived for 1 year, whereas the mortality rates of mice treated with either PTX or ADM alone at the same doses were similar to that of untreated tumor-bearing mice (28+/-3 days). Caspase inhibitors inhibited apoptosis more efficiently in PTX- or ADM-treated cultures than in PTX+ADM-treated cultures. Pretreatment with TNFalpha (10 ng/mL) increased apoptosis in PTX- or ADM-treated U937 cells. However, the apoptotic index of PTX+ADM-treated cultures was significantly reduced and the expression of C-terminally and Ser32 phosphorylated IkappaBalpha was reduced. PTX sensitizes hematological malignancies to ADR-induced apoptosis. An independent caspase pathway is involved in PTX+ADM-induced apoptosis. The phosphorylation status of IkappaBalpha is closely related via TNFalpha to the possible mechanisms of drug resistance.

In vivo modification of adriamycin-induced apoptosis in L-5178Y lymphoma cell-bearing mice by (+)-alpha-tocopherol and superoxide dismutase

Apoptosis was followed in L5178Y lymphoma cell-bearing mice at different times after intraperitoneal injections of adriamycin (ADM). Apoptosis was determined morphologically and confirmed by DNA laddering on electrophoresis. Apoptosis was observed 36h after injection of 5mg/kg ADM (apoptotic cell index 64.2+/-5.6 vs. 1.5+/-2.1 from the untreated group) and confirmed by DNA electrophoresis. However, when the animals were pretreated with (+)-alpha-tocopherol acid succinate or superoxide dismutase before ADM administration apoptotic index significantly diminished (P<0.05) and the DNA electrophoresis did not show fragmentations. We conclude that in ADM-treated mice, tumour cell death occurs in two ways: first by necrosis, then later by apoptosis. These observations are likely to be associated with or caused by the generation of reactive oxygen species.

Gamma-irradiation induced apoptosis in peritoneal macrophages by oxidative stress. Implications of antioxidants in caspase mitochondrial pathway

The in vivo and in vitro development of apoptosis induced by gamma-irradiation was studied in mouse peritoneal macrophages. The apoptosis index was measured by fluorescence microscopy and DNA electrophoresis. In vivo apoptosis was greatest eight days after 8 Gy total body gamma-irradiation. A DNA ladder electrophoretic pattern was only observed in the gamma-irradiated group. The participation of reactive oxygen species in apoptosis induction was investigated by pretreating mice with the antioxidants superoxide dismutase, catalase, vitamin E or lipopolysaccharide before gamma-irradiation. Measurement of serum lipoperoxides showed oxidative stress in the gamma-irradiated mice and the protection given by the antioxidants. These results were confirmed using in vitro cultures of peritoneal macrophages: gamma-irradiated groups and antioxidant-pretreated gamma-irradiation groups showed results similar to those observed with in vivo irradiation. A loss of mitochondrial membrane potential (delta psi(m)) was also observed by microscopy in the gamma-irradiated cell cultures. Experiments with caspase inhibitors confirmed the participation of caspase 3 and caspase 9.

In vivo adriamycin-induced apoptosis in peritoneal murine macrophages: partial participation of a caspase cascade

BACKGROUND

Adriamycin (ADM) is a potent antitumor drug that induces apoptosis (AP) in tumor cells. AP is modulated by caspases and by mitogen-activated protein kinases (MAPK) as well as by the mitochondrial membrane potential (deltapsim). We studied the participation of these systems in peritoneal macrophages from ADM-treated mice.

MATERIALS AND METHODS

Balb/c mice were either treated with ADM (5 mg/kg, i.p.) or with 0.85% NaCl solution (controls). One hour later, peritoneal cells were harvested and cultured for 28 h. AP was evaluated by ethidium bromide and acridine orange staining; deltapsim was monitored using a MitoCapture stain Kit; DNA integrity was assessed by electrophoretic analysis. Animals were treated (i.p.) 1 h before ADM administration with Z-LEHD-FMK, Z-DEVD-FMK, or Z-VAD-FMK (caspase-9, caspases-3, 7,10 and general caspase inhibitors, respectively) or with PD169316 (a MAPKp38 inhibitor).

RESULTS

ADM induced a higher rate of AP and the characteristic electrophoretic DNA ladder pattern. Mice treated with caspases inhibitors plus ADM showed significant reductions in AP and DNA laddering; in contrast, no differences were observed in mice treated with PD169316 plus ADM in comparison with ADM alone. ADM also induced early loss of the deltapsim.

CONCLUSION

In these experimental conditions, ADM induced AP in a mainly caspase-9-dependent manner and this was related to a reduction in the deltapsim.