Bcl-2 expression correlates with apoptosis induction but not tumor growth delay in transplantable murine lymphomas treated with different chemotherapy drugs

Murine models of B-cell lymphomas: promising tools for designing cancer therapies

Human B-cell lymphomas, the fourth most common hematologic malignancy, are currently the subject of extensive research. The limited accessibility of biopsies, the heterogeneity among patients, and the subtypes of lymphomas have necessitated the development of animal models to decipher immune escape mechanisms and design new therapies. Here, we summarize the cell lines and murine models used to study lymphomagenesis, the lymphoma microenvironment, and the efficacy of new therapies. These data allow us to understand the role of the immune system in the fight against tumors. Exploring the advantages and limitations of immunocompetent versus immunodeficient models improves our understanding of the molecular and cellular mechanisms of tumor genesis and development as well as the fundamental processes governing the interaction of tumors and their host tissues. We posit that these basic preclinical investigations will open up new and promising approaches to designing better therapies.

Reduction of cyclophosphamide-induced DNA damage and apoptosis effects of ginsenoside Rb(1) on mouse bone marrow cells and peripheral blood leukocytes

The present study investigated the protective effects of ginsenoside Rb(1) (GRb(1)) against genotoxicity induced by cyclophosphamide (CP). Single cell gel electrophoresis, flow cytometry assay with annexin V-FITC/propidine iodide (PI) and acridine orange (AO)/ethidium bromide (EB) staining assay were employed to measure DNA damage and cell apoptosis, respectively. The activities of total superoxide dismutase (T-SOD) and glutathione peroxidase (GPx) and the malondialdehyde (MDA) content were also investigated by a number of colormetric methods. The results showed that the CP produced significant DNA damage and cell apoptosis in mouse bone marrow cells or peripheral blood leukocytes, markedly inhibited the activities of T-SOD and GPx, and markedly increased the MDA content. GRb(1) significantly inhibited DNA damages and cell apoptosis in mouse bone marrow cells or peripheral blood leukocytes induced by CP and antagonized the reduction of CP-induced T-SOD and GPx activities, and inhibited the increase in MDA content induced by CP. The anti-tumor study of GRb(1) showed that GRb(1) did not affect the anti-tumor activities of CP. In conclusion, GRb(1) had significant protective effects against DNA damage and apoptosis induced by CP.

Protective effects of total saponins from stem and leaf of Panax ginseng against cyclophosphamide-induced genotoxicity and apoptosis in mouse bone marrow cells and peripheral lymphocyte cells

BACKGROUND

Cyclophosphamide (CP), commonly used anti-cancer, induces oxidative stress and is cytotoxic to normal cells. It is very important to choice the protective agent combined CP to reduce the side effects in cancer treatment. Ginsenosides are biological active constituents of Panax ginseng C.A. Meyer that acts as the tonic agent for the cancer patients to reduce the side effects in the clinic application. Because CP is a pro-oxidant agent and induces oxidative stress by the generation of free radicals to decrease the activities of anti-oxidant enzymes, the protective effects of the total saponins from stem and leaf of P. ginseng C.A. Meyer (TSPG) act as an anti-oxidant agent against the decreased anti-oxidant enzymes, the genotoxicity and apoptosis induced by CP was carried out.

METHODS

The alkaline single cell gel electrophoresis was employed to detect DNA damage; flow cytometry assay and AO/EB staining assay were employed to measure cell apoptosis; the enzymatic anti-oxidants (T-SOD, CAT and GPx) and non-enzymatic anti-oxidant (GSH) were measured by the various colorimetric methods.

RESULTS

CP induced the significant DNA damage in mouse peripheral lymphocytes in time- and dose-dependent manners, inhibited the activities of T-SOD, GPx and CAT, and decreased the contents of GSH in mouse blood, triggered bone marrow cell apoptosis at 6 and 12h. TSPG significantly reduced CP-induced DNA damages in bone marrow cells and peripheral lymphocyte cells, antagonized CP-induced reduction of T-SOD, GPx, CAT activities and the GSH contents, decreased the bone marrow cell apoptosis induced by CP.

CONCLUSIONS

TSPG, significantly reduced the genotoxicity of CP in bone marrow cells and peripheral lymphocyte cells, and decreased the apoptotic cell number induced by CP in bone marrow cells. The effects of TSPG on T-SOD, GPx, CAT activities and GSH contents might partially contribute to its protective effects on CP-induced cell toxicities.

Elimination of the differential chemoresistance between the murine B-cell lymphoma LY-ar and LY-as cell lines after arsenic (As2O3) exposure via the overexpression of gsto1 (p28)

PURPOSE

Arsenic, in the form of As(2)O(3), has gained therapeutic importance because it has been shown to be very effective clinically in the treatment of acute promyelocytic leukemia (APL). Via numerous pathways arsenic induces cellular alterations such as induction of apoptosis, inhibition of cellular proliferation, stimulation of differentiation, and inhibition of angiogenesis. Responses vary depending on cell type, dose and the form of arsenic. GSTO1, a member of the glutathione S-transferase superfamily omega, has recently been shown to be identical to the rate-limiting enzyme, monomethyl arsenous (MMA(V)) reductase which catalyzes methylarsonate (MMA(V)) to methylarsenous acid (MMA(III)) during arsenic biotransformation. In this study, we investigated whether arsenic trioxide (As(2)O(3)) induces apoptosis in both chemosensitive and chemoresistant cell lines that varied in their expression of p28 (gsto1), the mouse homolog of GSTO1.

METHODS

The cytotoxicity of arsenic in the gsto1- and bcl-2-expressing chemoresistant and radioresistant LY-ar mouse lymphoma cell line, was compared with that of the LY-ar's parental cell line, LY-as. LY-as cells are radiosensitive, apoptotically permissive, and do not express gsto1 or bcl-2. Cell survival, glutathione (GSH) levels, mitochondrial membrane potential, and stress-activated kinase status after arsenic treatment were examined in these cell lines.

RESULTS

As(2)O(3) induced an equivalent dose- and time-dependent increase in apoptosis in these cell lines. Cellular survival, as measured after a 24-h exposure, was also the same in each cell line. Reduced GSH was modulated in a similar time- and dose-dependent manner. Apoptosis was preceded by loss of mitochondrial membrane potential that triggered caspase-mediated pathways associated with apoptosis. With a prolonged exposure of As(2)O(3), both cell lines showed decreased activation of ERK family members, ERK1, ERK2 and ERK5. As(2)O(3) enhanced the death signals in LY-ar cells through a decrease in GSH, loss of mitochondrial membrane potential, and abatement of survival signals. This effect is similar to that seen when LY-ar cells are treated with thiol-depleting agents or by the removal of methionine and cysteine (GSH precursor) from the growth medium. This response is also completely contrary to that seen for radiation, actinomycin D, VP-16 and other agents, where LY-ar cells do not succumb to apoptosis.

CONCLUSIONS

The overexpression of gsto1 in normally chemoresistant and radioresistant LY-ar cells renders them vulnerable to the cytotoxic effects of As(2)O(3), despite the 30-fold overexpression of the survival factor bcl-2. Gsto1 and its human homolog, GSTO1, may serve as a marker for arsenic sensitivity, particularly in cells that are resistant to other chemotherapeutic agents.

Cytotoxicity, DNA strand breakage and DNA–protein crosslinking by a novel transplatinum compound in human A2780 ovarian and MCF-7 breast carcinoma cells

Cisplatin, cis-[PtCl2(NH3)2], is commonly utilized in various combination chemotherapy protocols for the treatment of both ovarian and breast cancer while the corresponding trans isomer is therapeutically inactive. This work describes efforts to elucidate the cellular mechanism of action of a novel trans-platinum compound, trans-(dichloroamminethiazole)platinum(II) (ATZ), which demonstrates antiproliferative and cytotoxic effects against both MCF-7 human breast and A2780 human ovarian carcinoma cells in culture. A2780 cells were approximately twofold more sensitive to ATZ than MCF-7 cells in both cell growth and clonogenic survival assays. Dye exclusion studies revealed a 50-70% loss in cell viability within the first 12 h of drug treatment in both cell lines. This initial wave of cell death was succeeded by a prolonged interval of growth arrest during which a small fraction of apoptotic cells was detected. Binding of ATZ to DNA, as estimated by atomic absorption spectroscopy, was similar for the two cell lines and was almost completely reversed 24 h after drug removal. ATZ also induced DNA strand breakage as well as DNA-protein crosslinking during the initial 12 h period when the bulk of cell death was evident. However, neither the extent of DNA strand breakage nor that of DNA protein crosslinking was sufficient to explain the different drug sensitivity in the two cell lines. At 24 and 48 h after exposure of MCF-7 cells to high concentrations of ATZ, the formation of DNA-topoisomerase I complexes is detected, coincident with a high degree of apoptosis. These studies suggest that ATZ has the capacity to interfere with topoisomerase I in the tumor cell, a function not evident in cis-platinum-based drugs.

Cyclophosphamide induces caspase 9-dependent apoptosis in 9L tumor cells

Cyclophosphamide (CPA), a widely used oxazaphosphorine anti-cancer prodrug, is inactive until it is metabolized by cytochrome P450 to yield phosphoramide mustard and acrolein, which alkylate DNA and proteins, respectively. Tumor cells transduced with the human cytochrome P450 gene CYP2B6 are greatly sensitized to CPA, however, the pathway of CPA-induced cell death is unknown. The present study investigates the cytotoxic events induced by CPA in 9L gliosarcoma cells retrovirally transduced with CYP2B6, or induced in wild-type 9L cells treated with mafosfamide (MFA) or 4-hydroperoxyifosfamide (4OOH-IFA), chemically activated forms of CPA and its isomer ifosfamide. CPA and MFA were both shown to effect tumor cell death by stimulating apoptosis, as evidenced by the induction of plasma membrane blebbing, DNA fragmentation, and cleavage of the caspase 3 and caspase 7 substrate poly(ADP-ribose) polymerase (PARP) in drug-treated cells. Caspase 9 was identified as the regulatory upstream caspase activated in 9L cells treated with CPA, MFA, or 4OOH-IFA, implicating the mitochondrial apoptotic pathway in oxazaphosphorine-induced tumor cell death. Correspondingly, expression of the mitochondrial proapoptotic factor Bax enhanced caspase 9 activation, plasma membrane blebbing, and drug-induced cytotoxicity. Conversely, overexpression of the mitochondrial antiapoptotic factor Bcl-2 blocked caspase 9 activation, leading to an inhibition of drug-induced plasma membrane permeability and blebbing, terminal deoxynucleotidyl transferase dUTP nick-end labeling positivity, PARP cleavage, Annexin V positivity, and drug-induced cell death. Although Bcl-2 thus blocked the cytotoxic effects of activated CPA, it did not inhibit the drug's cytostatic effects. CPA induced S-phase cell cycle arrest followed by conversion to an apoptotic pre-G1 state in wild-type 9L cells; by contrast, Bcl-2-expressing 9L cells accumulated in G2/M in response to CPA treatment. Intratumoral expression of Bcl-2 and related family members, including both apoptotic and antiapoptotic factors, is thus an important determinant of the responsiveness of tumor cells to CPA and ifosfamide, both in the context of conventional chemotherapy and in patients sensitized to these oxazaphosphorine drugs by the use of cytochrome P450-based gene therapy.

Bcl-2 expression in higher-grade human glioma: a clinical and experimental study

Bcl-2 protein plays an important role in inhibiting apoptosis and protecting normal and neoplastic cells from toxicity. Bcl-2 overexpression in malignant tumors, on the other hand, may cause resistance against adjuvant treatment. Since there are subpopulations of patients with glioma that differ considerably in their treatment benefit, it is important to identify prognostic factors for outcome and to tailor adjuvant protocols in accordance with specific biological features of the respective tumor. The present study aimed at investigating the role of bcl-2 expression in higher-grade glioma (WHO grade III and IV). Bcl-2 expression was correlated with clinical and paraclinical parameters, and evaluated in univariate and multivariate statistical models. In addition, bcl-2-overexpressing human glioma cells in culture were used for modeling the in vivo findings and for investigating the importance of bcl-2 for tumor resistance against cytotoxic treatment. A group of 86 patients with higher-grade glioma were investigated. Anaplastic astrocytoma (AA; WHO G III, n = 29) showed bcl-2 expression in 48% of the cases, and immunohistochemical positivity was associated with a significantly shorter survival time (p = 0.0068). In glioblastoma patients (GBM; WHO G IV, n = 57), 51% of tumors were bcl-2 positive, but bcl-2 expression did not correlate significantly with survival (p = 0.39). In a Cox proportional hazards regression model, bcl-2 positivity was confirmed as a negative prognostic parameter in AA, but not in GBM. Bcl-2 overexpressing and control human glioma cell clones (T98MG line) were treated in culture with the cytotoxic drugs carmustine (BCNU), paclitaxel, vincristine, and doxorubicin. In addition, bcl-2-overexpressing and control cells were infected with a retrovirus carrying the herpes-simplex-virus thymidine kinase gene (HSV-tk), and then treated with ganciclovir (GCV). Bcl-2 overexpression significantly increased tumor cell resistance against all of the above cytotoxic drugs, and also against HSV-TK/GCV mediated gene therapy.