Biomedical subjects

L Tentori

Publications and source records attributed to L Tentori.

At least 19 recordsLinked to original sources

PubMed2001

Effects of single or split exposure of leukemic cells to temozolomide, combined with poly(ADP-ribose) polymerase inhibitors on cell growth, chromosomal aberrations and base excision repair components.

PURPOSE: To evaluate the antitumor activity of single versus split exposure of neoplastic cells to temozolomide (TZM) and poly(ADP-ribose) polymerase (PARP) inhibitor. METHODS: A leukemic Jurkat cell line and freshly isolated leukemic blasts were used. Jurkat cells are resistant to O6-methylguanine damage induced by TZM due to high levels of O6-alkylguanine-DNA alkyltransferase and to a functional defect in the mismatch repair system. Cells were treated with 3-aminobenzamide or with NU1025 to inhibit PARP activity. TZM was added to cell cultures immediately after PARP inhibitors. The concentrations of TZM used were 62.5 microM (corresponding to the peak plasma concentration in patients) or 125 microM. TREATMENT DESIGN: Cells were treated with 125 microM TZM plus PARP inhibitors (single exposure), or twice with 62.5 microM TZM plus PARP inhibitors with an interval of 24 h between treatments (split exposure). Tumor cell growth, clastogenicity and base excision repair gene transcripts or enzymatic activity were evaluated. RESULTS: The split exposure of Jurkat cells to TZM induced more pronounced and persistent growth inhibition and comparable chromosome damage in comparison with the single exposure. In addition, PARP inhibitors potentiated the cytotoxic effects induced by repeated treatment with TZM in fresh leukemic blasts. A marked decrease in X-ray repair cross-complementing 1 transcript and methylpurine glycosylase (MPG) transcript was detected in Jurkat cells subjected to the split exposure. In this case, a significant reduction in the corresponding enzymatic activity was also observed. CONCLUSIONS: Cytotoxicity induced by TZM and PARP inhibitors can be improved by a fractionated modality of drug treatment. The reduction in MPG transcript and function would presumably contribute to an increase in cell susceptibility to DNA damage induced by the methylating agent and PARP inhibitors.

Antineoplastic Agents, Alkylating↗

PubMed2001

Combined effects of adenovirus-mediated wild-type p53 transduction, temozolomide and poly (ADP-ribose) polymerase inhibitor in mismatch repair deficient and non-proliferating tumor cells.

Lack of p53 or mismatch repair (MR) function and scarce cell proliferation are commonly associated with tumor cell resistance to antineoplastic agents. Recently, inhibition of poly(ADP-ribose) polymerase (PARP) has been considered as a tool to overcome resistance of MR-deficient tumors to methylating agents. In the present study we demonstrated that infection with p53 expressing adenovirus (Ad-p53), enhances chemosensitivity of MR-deficient tumor cell lines to the methylating agent temozolomide (TZM), either used as single agent or, more efficiently, when combined with PARP inhibitor. Moreover, the association of Ad-p53 with drug treatment induced a more pronounced growth inhibitory effect than that provoked by Ad-p53 infection only. Cells, growth arrested by p53 transduction, and then subsequently exposed to the drugs, were still highly susceptible to cytotoxicity induced by TZM and PARP inhibitor. The results suggested that this drug combination might be effective even in non-proliferating tumor cells. It is conceivable to envisage future possible strategies to enhance cytostatic or cytotoxic effects induced by Ad-p53, based on the use of TZM, alone or combined with PARP inhibitor for the therapy of resistant tumors.

Adenoviridae↗

PubMed2001

Poly (ADP-ribose) polymerase inhibitor increases apoptosis and reduces necrosis induced by a DNA minor groove binding methyl sulfonate ester.

The poly(ADP-ribose) polymerase (PARP) is involved in cell recovery from DNA damage, such as methylation of N3-adenine, that activates the base excision repair process. In the present study we demonstrated that MeOSO(2)(CH(2))(2)-lexitropsin (Me-Lex), a methylating agent that almost exclusively produces N3-methyladenine, induced different modalities of cell death in human leukemic cell lines, depending on the presence of PARP inhibitor. Growth inhibition, provoked by the combination of Me-Lex and PARP inhibitor, was associated with a marked down-regulation of c-myc, increased generation of single strand breaks and apoptosis. When used as single agent, at concentrations that saturated cell repair ability, Me-Lex induced mainly cell death by necrosis. Surprisingly, addition of a PARP inhibitor enhanced apoptosis and reduced the early appearance of necrosis. Telomerase activity was completely suppressed in cells exposed to Me-Lex alone, by 24 h after treatment, whereas it did not change when Me-Lex was combined with PARP inhibitor. Thereafter, inhibition of telomerase was observed with both treatments. The results suggest new insights on different modalities of cell death induced by high levels of N3-methyladenine per se, or by the methylated base in the presence of PARP inhibitor.

Alkylating Agents↗

PubMed2000

Cytotoxic and clastogenic effects of a DNA minor groove binding methyl sulfonate ester in mismatch repair deficient leukemic cells.

Mismatch repair deficiency contributes to tumor cell resistance to O6-guanine methylating compounds and to other antineoplastic agents. Here we demonstrate that MeOSO2(CH2)2-lexitropsin (Me-Lex), a DNA minor groove alkylating compound which generates mainly N3-methyladenine, has cytotoxic and clastogenic effects in mismatch repair-deficient leukemic cells. Moreover, MT-1 cells, which express p53 upon drug treatment and possess low levels of 3-methylpurine DNA glycosylase activity, are more susceptible to cytotoxicity induced by Me-Lex, with respect to p53-null and 3-methylpurine DNA glycosylase-proficient Jurkat cells. In both cell lines, the poly(ADP-ribose) polymerase inhibitor 3-aminobenzamide, which inhibits base excision repair capable of removing N-methylpurines, increases cytotoxicity and clastogenicity induced by Me-Lex or by temozolomide, which generates low levels of N3-methyl adducts. The enhancing effect is more evident at low Me-Lex concentrations, which induce a level of DNA damage that presumably does not saturate the repair ability of the cells. Nuclear fragmentation induced by Me-Lex + 3-aminobenzamide occurs earlier than in cells treated with the single agent. Treatment with Me-Lex and 3-aminobenzamide results in augmented expression of p53 protein and of the X-ray repair cross-complementing 1 transcript (a component of base excision repair). These results indicate that N3-methyladenine inducing agents, alone or combined with poly(ADP-ribose) polymerase inhibitors, could open up novel chemotherapeutic strategies to overcome drug resistance in mismatch repair-deficient leukemic cells.

Antineoplastic Agents↗

PubMed1999

Treatment with temozolomide and poly(ADP-ribose) polymerase inhibitors induces early apoptosis and increases base excision repair gene transcripts in leukemic cells resistant to triazene compounds.

Methylating triazenes have shown marked antileukemic effects, possibly through generation of a variety of DNA adducts. Cells tolerant to O6-methylguanine due to a defect in the mismatch repair system (MRS), might become sensitive to other methyl adducts, by inhibiting the N-methylpurine repair, which requires base excision repair (BER) and poly(ADP-ribose) polymerase (PADPRP). Therefore, MRS-deficient Jurkat leukemic cells resistant to methylating triazenes, have been treated with temozolomide (TZM) and PADPRP inhibitors. Expression of PADPRP or molecules involved in the BER system [3-methylpurine-DNA glycosylase (MPG) and X-ray repair cross-complementing 1 (XRCC1)], have been explored. Cytotoxic effects of TZM associated with PADPRP inhibitors are evident shortly after treatment, suggesting that completion of cell division is not required for the lethal effect of the drug combination. Increase of PADPRP or MPG transcripts was found after treatment with TZM alone or combined with PADPRP inhibitor. XRCC1 transcript was positively modulated only in the case of drug combination. This could suggest that in the presence of PADPRP inhibitor, persistence of DNA damage triggers XRCC1 transcription. Our results suggest that association of TZM and PADPRP inhibitors might be of benefit for MRS-deficient malignancies unresponsive to the methylating agent.

Antineoplastic Agents, Alkylating↗

PubMed1998

Effect of rifampin on CD1b expression and double-negative T cell responses against mycobacteria-derived glycolipid antigen.

Non-classical antigen-presentation by CD1 molecules expressed on cytokine-activated monocytes (CAM), and cell-mediated responses supported by double-negative (DN) and by CD8+ responder alphabeta T cells, are involved in host resistance against mycobacterial infections. The CD1b protein is responsible for presentation of non-peptide, lipid antigens to T cells. In this context, a pivotal role is played by induction of CD1b protein on the membrane of human monocytes activated by GM-CSF alone, and more efficiently by GM-CSF combined with IL-4. Rifampin (RFP), a drug which is extensively utilized for chemoprophylaxis or treatment of Mycobacterium tuberculosis, is known to reduce a number of B, or T cell-dependent responses. Therefore we undertook immunopharmacological studies on RFP, to determine the effects of this agent on human macrophage function, relative to antigen presentation by CD1b molecules and on DN T cell cytolytic function. The results showed that: (a) graded concentration of RFP (2 or 10 microg/ml) induced a significant increase of CD1b expression, in CAM as evaluated by FACS analysis; (b) RFP increased significantly the specific mAb binding to CD1b on CAM surface; (c) treatment of effector cells with RFP did not reduce DN T cell-mediated cytolysis against lymphoblastoid cells transfected with CD1b cDNA (C1R.b6 cells), pulsed with M. tuberculosis. These results suggest that RFP could be of potential value in improving mycobacterial antigen presentation without impairing responder T cell function.

Antibiotics, Antitubercular↗

PubMed1998

Involvement of the mismatch repair system in temozolomide-induced apoptosis.

Postreplicative mismatch repair plays a major role in mediating the cytotoxicity of agents generating O6-methylguanine in DNA. We previously showed that a methylating antitumor triazene compound, temozolomide, induces apoptosis and that the persistence of O6-methylguanine in DNA is required to trigger the process. We wanted to test whether the latter apoptotic signal is dependent on a functional mismatch repair system. To this end, we used two human lymphoblastoid cell lines (i.e., the mismatch repair-proficient TK6 line and its mismatch repair-deficient subline MT1) that are both deficient in O6-methylguanine repair. Temozolomide treatment of TK6 cells brought about efficient cell growth inhibition, G2/M arrest, and apoptosis, as indicated by the results of cytofluorimetric analysis of 5-bromo-2'-deoxyuridine incorporation and DNA content and evaluation of DNA fragmentation. The drug treatment resulted also in the induction of p53 and p21/waf-1 protein expression. In contrast, MT1 cells were highly resistant to the drug and no p53 and p21/waf-1 induction was observed. Importantly, we could show that MT1 cells are not deficient in the p53-dependent apoptosis pathway; treatment with etoposide, a topoisomerase II inhibitor, resulted in p53 and p21/waf-1 protein expression and apoptosis in both cell lines. In conclusion, we demonstrate the existence of a link between a functional mismatch repair system and the trigger of apoptosis in cells exposed to clinically relevant concentrations of temozolomide. The results also suggest that p53 induction in response to O6-guanine methylation involves the mismatch repair system.

Antineoplastic Agents, Alkylating↗

PubMed1998

Rifampin increases cytokine-induced expression of the CD1b molecule in human peripheral blood monocytes.

In recent years, it has been shown that a nonclassical, major histocompatibility complex-independent system (i.e., CD1-restricted T-cell responses) is involved in T-cell immunity against nonpeptide antigens. The CD1 system appears to function by presenting microbial lipid antigens to specific T cells, and the antigens so far identified include several known constituents of mycobacterial cell walls. Among the four known human CD1 isoforms, the CD1b protein is the best characterized with regard to its antigen-presenting function. Expression of CD1b is upregulated on human blood monocytes upon exposure to granulocyte/macrophage-colony stimulating factor, alone or in combination with interleukin-4 (IL-4) (S. A. Porcelli, Adv. Immunol. 59:1-98, 1995). Rifampin (RFP) and its derivatives are widely used for chemoprophylaxis or chemotherapy against Mycobacterium tuberculosis. However, this agent was found to reduce the mitogen responsiveness of human B and T lymphocytes, chemotaxis, and delayed-type hypersensitivity. The present study extends the immunopharmacological profile of RFP by examining its effects on CD1b expression by human peripheral blood monocytes exposed to GM-CSF plus IL-4. The results showed that clinically attainable concentrations (i.e., 2 or 10 microg/ml for 24 h) of the agent produced a marked increase in CD1b expression on the plasma membrane, as evaluated by fluorescence-activated cell sorter analysis, whereas it had no effect on cytosolic fractions, as indicated by Western blot analysis. This was found to be the result of increased CD1b gene expression, as shown by Northern blot analysis of CD1b mRNA. These results suggest that RFP could be of potential value in augmenting the CD1b-restricted antigen recognition system, thereby enhancing protective cellular immunity to M. tuberculosis.

Antibiotics, Antitubercular↗

PubMed1998

Role of wild-type p53 on the antineoplastic activity of temozolomide alone or combined with inhibitors of poly(ADP-ribose) polymerase.

The DNA repair enzyme O6-alkylguanine DNA-alkyltransferase (OGAT) and a deficient mismatch repair system play a critical role in the resistance to chemotherapeutic agents that generate adducts at the O6-position of guanine. However, DNA adducts different from O6-methylguanine might be also involved in cytotoxicity induced by methylating agents. Because the loss of p53 function is generally associated with tumor cell resistance to anticancer chemotherapy, we have investigated whether wild-type p53 might affect chemosensitivity of leukemia cells endowed with high OGAT levels to the methylating agent temozolomide (TZM). The effect of poly(ADP-ribose) polymerase (PADPRP) inhibition, which potentiates the cytotoxic effects of N7-methylguanine and N3-methylguanine, was also assessed in OGAT-proficient cells, either susceptible or tolerant to O6-methylguanine. OGAT-proficient and p53 null HL60 cells were transfected with the human p53 cDNA (p53+ cells). Treatment with TZM concentrations not toxic for the cells transduced with the control vector (p53-cells), induced apoptosis in p53+ cells. These cells were characterized by a lower level of bcl-2 protein than p53- cells, whereas bax and OGAT expression was comparable in both lines. Inhibition of PADPRP potentiated the cytotoxic and apoptotic effects of TZM in either p53- or p53+ HL60 cells. Furthermore, PADPRP inhibitors potentiated apoptosis induced by TZM in Jurkat cells, which possess a mutated p53 gene and are tolerant to O6-methylguanine adducts. The analysis of cell cycle indicated that the drug combination of TZM and PADPRP inhibitors provoked G1 arrest only in p53+ cells. Conversely, G1 arrest was not observed in p53+ cells exposed to TZM alone. It is possible to speculate that PADPRP inhibitors might affect the repair of DNA adducts that are processed differently from O6 methylguanine and induce a different pattern of cell cycle distribution. In conclusion, the results show that p53 increases apoptosis by TZM in OGAT-proficient cells and suggest the potential role of PADPRP inhibitors in enhancing TZM activity against leukemias independently of DNA repair systems.

Antineoplastic Agents, Alkylating↗

PubMed1998

Mutation of the mismatch repair gene hMSH2 and hMSH6 in a human T-cell leukemia line tolerant to methylating agents.

Cell killing by monofunctional methylating agents is due mainly to the formation of adducts at the O6 position of guanine. These methyl adducts are removed from DNA by the O6-alkylguanine DNA alkyltransferase (OGAT). The mechanism by which O6-methylguanine (O6meG) induces cell death in OGAT-deficient cells requires a functional mismatch repair system (MRS). We have previously reported that depletion of OGAT activity in the human T-cell leukemic urkat line does not sensitize these cells to the cytotoxic and apoptotic effects of the methylating triazene temozolomide (Tentori et al., 1995). We therefore decided to establish whether the tolerance of Jurkat cells to O6meG could be associated with a defect in MRS. The results of mismatch repair complementation studies indicated that Jurkat cells are defective in hMutSalpha, a heterodimer of the hMSH2 and hMSH6 proteins. Cytogenetic analysis of two Jurkat clones revealed a deletion in the short arm of chromosome region 2p15-21, indicating an allelic loss of both hMSH2 and hMSH6 genes. DNA sequencing revealed that exon 13 of the second hMSH2 allele contains a base substitution at codon 711, which changes an arginine to a termination codon (CGA-->TGA). In addition, a (C)8-->(C)7 frameshift mutation in codon 1085-1087 of the hMSH6 gene was also found. Although both hMSH2 and hMSH6 transcripts could be detected in Jurkat clones, the respective polypeptides were absent. Taken together, these data indicate that tolerance of Jurkat cells to methylation damage is linked to a loss of functional hMutSalpha.

Base Pair Mismatch↗

PubMed1997

Cytokine-induced expression of CD1b molecules by peripheral blood monocytes: influence of 3'-azido-3'-deoxythymidine.

CD1b is a nonpolymorphic, MHC-like molecule, capable of presenting non-peptide antigens (Ags) to CD3+, CD4-, CD8-, alphabeta or gammadelta T lymphocytes. Previous studies have shown that CD1b can be induced in monocytes/macrophages by GM-CSF+IL-4, and can restrict their presentation of Mycobacterium tuberculosis antigen (Ag) to Ag-specific T cells. Since a number of HIV-positive subjects undergo mycobacterial infections, preliminary studies have been performed to explore whether anti-HIV chemotherapy would influence cytokine-induced CD1b expression in peripheral blood monocytes. The results obtained by treating monocytes with GM-CSF+IL-4, in presence or absence of 3'-azido-3'-deoxythymidine (AZT) showed that: (a) the majority of adherent mononuclear cells (AMNC) collected from peripheral blood of healthy donors, express CD1b molecule on the cell membrane, upon treatment with GM-CSF+IL-4; (b) CD1b appearance is mainly due to the de novo induction of CD1b gene expression (as confirmed by Northern blot analysis), rather than to migration of the molecule from the cytoplasm to the plasma membrane (as suggested by Western blot analysis); (c) AZT does not alter the percentage of CD1b+ AMNC treated with the cytokines; (d) however, AZT inhibits cytokine-induced proliferation of AMNC, thus reducing the overall Ag-presenting potential of the host. Our results suggest that the anti-proliferative effect of AZT could depress anti-mycobacteria immunity in AZT-treated subjects, which may have important implication for the clinical outcome of patients harbouring inadequately treated mycobacterial infections.

Anti-HIV Agents↗

PubMed1997

In vitro antitumor activity of 3'-desamino-3'(2-methoxy-4-morpholinyl) doxorubicin on human melanoma cells sensitive or resistant to triazene compounds.

A new methoxymorpholinyl derivative of Adriamycin (ADR), FCE 23762 (MRD), has recently been selected for phase I clinical trials for its reduced cardiotoxicity and for its cytotoxic activity against a broad spectrum of solid tumors and leukemias that are sensitive or resistant to ADR. The purpose of the present study was to compare the in vitro antitumor activity of MRD and ADR on human melanoma lines with different chemosensitivity to triazene compounds, among which dacarbazine remains a reference drug in the treatment of melanoma. Both MRD and ADR were tested in vitro on three melanoma lines, MI13443-MEL, SK-MEL-28, and M14, previously screened for their chemosensitivity to the triazene compound p-(3-methyl-1-triazeno) benzoic acid, potassium salt (MTBA). The three lines were also analyzed for P-170 expression, total glutathione (GSH) content, and GSH-related enzyme activity. All melanomas, whether sensitive or resistant to MTBA, were susceptible to anthracycline treatment. The cytotoxic activity of MRD was comparable with that of ADR, and no substantial difference was found in cell growth inhibition between the two drugs. When the relative chemosensitivity of the three lines was considered, SK-MEL-28 was found to be slightly less sensitive to MRD treatment than the other tumors. This finding seems to correlate with the higher GSH-peroxidase activity of this melanoma relative to that of the MI13443 and M14 lines. These results show a homogeneous response of melanoma lines to MRD treatment in vitro, suggesting that phase I clinical trials concerning this drug, which in vivo appears to be activated to a more cytotoxic metabolite, could be extended to metastatic melanomas, including those completely resistant to triazene compounds.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1997

Inhibition of O6-alkylguanine DNA-alkyltransferase or poly(ADP-ribose) polymerase increases susceptibility of leukemic cells to apoptosis induced by temozolomide.

High levels of expression of the DNA repair enzyme O6-alkylguanine DNA-alkyltransferase (OGAT) (EC 2.1.1.63) account for tumor cell resistance to methylating agents. Previous studies suggested that methylating triazenes might have a potential role for the treatment of acute leukemias with low levels of OGAT. In the current study, we transduced the human OGAT cDNA in OGAT-deficient leukemia cell clones. OGAT-transduced cells were more resistant than their OGAT-deficient counterparts to apoptosis triggered by the methylating triazene temozolomide (TZM), as indicated by the results of flow cytometry, terminal deoxynucleotidyl transferase assay, and analysis of DNA fragmentation. Depletion of OGAT activity by O6-benzylguanine increased leukemia cell sensitivity to TZM-mediated apoptosis. Moreover, combined treatment of cells with TZM and benzamide, an inhibitor of the poly(ADP-ribose) polymerase (EC 2.4.2.30), increased the apoptosis induced by the methylating agent. These results demonstrate for the first time that methyl adducts at the O6 position of guanine, which are specifically removed by OGAT, are the principal DNA lesions responsible for the induction of apoptosis on treatment of leukemic cells with the methylating triazene TZM. This study also supports the possible use of TZM for the treatment of acute leukemias and suggests new strategies to increase the susceptibility of tumor cells to methylating triazenes in the clinic.

Antineoplastic Agents, Alkylating↗

PubMed1997

Dacarbazine-induced immunogenicity of a murine leukemia is attenuated in cells transfected with mutated K-ras gene.

Strong immunogenicity is induced by antitumor triazene compounds in tumor cells through a mutagenic mechanism. A highly immunogenic < > clone, isolated from a dacarbazine-treated L5178Y leukemia of DBA/2 mice, was transfected with K-ras mutated at codon 12 (i.e. ras(m12)). This transfected clone presents at least 2 mutations, one concerning K-ras gene, and the other affecting an unrelated gene, responsible for the generation of a highly immunogenic, MHC class I restricted non-self peptide. The results indicate that cells of < > clone transfected with ras(m12) were less immunogenic than cells of the same origin transfected with the vector alone. Moreover, ras(m12)-transfected cells showed lower levels of H-2K(d) gene expression with respect to those detectable in control cells. In addition, in vivo and in vitro sensitization against < > clone carrying mutated ras did not result in a strong cytotoxic T lymphocyte response against ras(m12)-transfected non immunogenic L5178y target cells. These preliminary results suggest that K-ras mutation could down-regulate the level of tumor immunogenicity, possibly acquired through a mutagenic process affecting other unrelated genes.

Animals↗

PubMed1995

Antitumor and antimetastatic effects of dacarbazine combined with cyclophosphamide and interleukin-2 in Lewis lung carcinoma (3LL).

The antitumor and antimetastatic activity of dacarbazine (DTIC) alone or in combination with cyclophosphamide (CY) was tested in C57BL/6 mice bearing Lewis lung carcinoma (3LL). Treatment with both agents significantly reduced tumor growth and the number of metastases. These effects were associated with marked changes of the biochemical and immunological properties of drug-treated 3LL cells, i.e. (a) reduction of alpha 6 integrin expression, (b) increased susceptibility to natural immunity in vivo, as measured in terms of rapid clearance from mouse lungs of prelabeled 3LL cells injected i.v. and (c) increased immunogenicity, as assessed by T-cell-mediated immune responses (i.e. graft rejection by intact syngeneic mice, and frequency of specific CTL precursors recognizing DTIC/CY-treated cancer cells). The immunotherapeutic advantage afforded by increased immunosensitivity and immunogenicity of 3LL cells exposed to DTIC + CY appears to be markedly reduced in vivo by the profound immunodepressive effects of these drugs. Within this context, addition of interleukin-2 was found to increase the antitumor and antimetastatic activity of this chemotherapeutic regimen. The present study shows, for the first time in a solid tumor model, that a biological response modifier increases the antitumor efficacy of drugs that are able to affect the immunological properties of cancer cells.

Animals↗

PubMed1995

Temozolomide reduces the metastatic potential of Lewis lung carcinoma (3LL) in mice: role of alpha-6 integrin phosphorylation.

The involvement of protein kinase c (PKC) in the mechanism underlying the antimetastatic properties of triazenes was studied in C57BL/6 mice bearing Lewis lung carcinoma (3LL). In vivo and in vitro treatment with temozolomide, an in-vitro active analogue of dacarbazine, or calphostin c produced a concentration-dependent reduction of spontaneous and artificial metastases. Both agents reduced the ability of 3LL cells to adhere to endothelium. Diethylaminoethyl (DEAE)-sepharose chromatography of cell extracts revealed that incubation of 3LL cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) caused a rapid translocation of protein kinase c activity from cytosol to the membrane fraction. Membrane PKC activity induced by TPA was reduced by 60% after treatment with temozolomide. Coincident with these changes, TPA induced phosphorylation of alpha-6 integrin, whereas temozolomide or calphostin c abolished the appearance of this phosphoprotein. These results suggest that temozolomide reduced metastatic potential by interfering with alpha-6 phosphorylation induced by PKC activation.

Animals↗

PubMed1995

Triazene compounds induce apoptosis in O6-alkylguanine-DNA alkyltransferase deficient leukemia cell lines.

Previous studies demonstrated that triazene compounds (TZC) possess antitumor, antimetastatic and immunosuppressive activity, and induce novel antigenic properties in neoplastic cells. Moreover, TZC showed marked antitumor activity in patients with acute myelogenous leukemias (AML). In most cases leukemic blasts with low levels of the repair enzyme O6-alkyl-guanine-DNA alkyltransferase (OGAT) were highly susceptible to TZC. Therefore the cytotoxic effects of TZC against human leukemic cells and the influence of OGAT modulation were investigated. Five leukemia cell lines were treated with the in vitro active derivative of dacarbazine: 5-(3-methyl-1-triazeno) imidazole-4-carboxamide (MTIC), or with temozolomide (TZM), which is readily cleaved to form the linear triazene MTIC in aqueous solution. The results showed that treatment with TZC at concentrations ranging between 62.5 and 250 microM significantly inhibited cell growth of U-937 and K-562 leukemia cell lines, both with undetectable OGAT activity. Growth inhibition was accompanied by DNA fragmentation and reduction of cell volume characteristic of cell undergoing apoptosis. In contrast, Daudi, HL-60 and Jurkat leukemia cell lines, characterized by high levels of the repair enzyme, were resistant to concentrations of TZC up to 500 microM. Treatment of resistant lines with O6-benzylguanine (BG, a specific inhibitor of OGAT) rendered HL-60 and Daudi but not Jurkat cells sensitive to cytotoxic effects and apoptosis mediated by MTIC. The results presented suggest that: (1) apoptosis is involved in cytotoxic activity of TZC; (2) OGAT could have a role in preventing programmed cell death induced by TZC; and (3) treatment with BG could potentiate cytotoxic and apoptotic effects of TZC on leukemic cell lines when high level of OGAT activity is the main factor involved in resistance to TZC.

Antineoplastic Agents, Alkylating↗

PubMed1993

Effects of diheptyldiselenide (DDS) on human tumor cell lines and on peripheral blood mononuclear cells.

In vitro effects of graded concentrations of diheptyldiselenide (DDS) on human tumor cell proliferation, and on the proliferative responses and immunological functions of peripheral blood mononuclear cells (MNC) were investigated. The agent significantly decreased tumor cell proliferation in a dose and time dependent manner. Proliferative responses of MNC to phytohemagglutinin (PHA) and interleukin-2 (IL-2) were also significantly depressed when MNCs were exposed to DDS (250 microM for 18 h) led to a significant increase in NK activity only in MNC samples showing very limited baseline NK function. On the other hand, generation of LAK cells was significantly inhibited by DDS. However, when the agent was added to the effector and target cell mixture during the 4 h 51Cr release cytotoxicity assay, no influence was found on NK and LAK-mediated target cell lysis. These studies show that high concentrations of DDS inhibit tumor cell proliferation and could also impair certain proliferative-dependent immune functions, without directly affecting cell-mediated cytolytic activity of effector cells.

Antigens, CD↗