Biomedical subjects

T Tsuruo

Publications and source records attributed to T Tsuruo.

At least 181 records · Page 10Linked to original sources

PubMed1997

[ICE family proteins].

Interleukin-1 beta-converting enzyme (ICE) was originally identified as a novel type of cysteine protease responsible for the conversion of percursor interleukin-1 beta to mature form. ICE is also a mammalian homologue of the Caenorhabitis elegans cell death protein Ced-3. Several ICE/ced-3 family proteases have been isolated and were recently renamed "Caspase." The overexpression of those proteases induces apoptosis. Moreover, it has been reported that several types of stimuli-induced apoptosis are equally inhibited by caspase-specific inhibitors, indicating that caspase proteases are common mediators of apoptosis. During induction of apoptosis, caspase proteases are thought to be sequentially activated and cleave several cellular proteins essential for cell growth.

Animals↗

PubMed1997

[DT-diaphorase].

Anti-tumor quinone, including mitomycin C (MMC), needs to be activated by bioreduction to exert its cytotoxic activities. The enzymes underlying this bioreductive activation have been the subject of extensive research on Mitomycin C. Cytochrome P450 reductase, cytochrome b5 reductase, xanthine oxidase, xanthine dehydrogenase and DT-diaphorase (DTD) have been shown to be involved in the reduction of MMC. The relationship between bioreductive enzymes and the cytotoxicity of quinone, however, has not been analyzed yet. In this study, we investigated the relationship between the bioreductive enzymes and the cytotoxicity of MMC. We carried out the following experiments and the following results were obtained. I) We isolated an MMC-resistant variant. This cell showed five-fold resistance to MMC as compared with the parental cell line. DTD was deficient in this resistant cell. II) We have examined the bioreductive enzyme activities of DTD and cytochrome P450 reductase and IC50's of MMC in 13 colon and gastric carcinoma cell lines. A positive correlation was not found between the enzyme activities and MMC sensitivities, but the cells with little or no DTD activity showed higher IC50 values compared to the other cell lines. III) To elucidate directly the role of DTD in MMC sensitivity, we introduced NQO1 gene into St-4 cells. NQO1 gene encodes DTD and St-4 cells have no DTD activity. All of the transfectants showed five- to ten-fold higher sensitivity to MMC as compared to the parental St-4 cells. The above data indicate that DTD is a critical determinant of sensitivity to MMC in aerobic conditions.

Antibiotics, Antineoplastic↗

PubMed1997

Kinetic analysis of the disposition of MRK16, an anti-P-glycoprotein monoclonal antibody, in tumors: comparison between in vitro and in vivo disposition.

The kinetics of the disposition of MRK16, an anti-P-glycoprotein monoclonal antibody, was studied in two human colorectal tumor cell lines, HCT-15 and COLO205, whose P-glycoprotein expression is extensive and poor, respectively. In a series of in vitro binding studies, the amount of MRK16 associated with HCT-15 cells at steady state was approximately 40 times greater than that associated with COLO205 cells. In in vivo studies, the disposition of MRK16 was determined in tumor-bearing mice after intravenous administration. The difference in the tumor-to-plasma concentration ratio between the two cell lines was only 2.3-fold at 72 hr after injection. To explain the large difference observed between the in vitro and in vivo results, a series of kinetic simulation studies were performed. By considering the physiological parameters specific for MRK16 (such as permeability-surface area product and the kinetic parameters determined in vitro), the time profiles for the tumor concentration were predicted. The predicted difference in the tumor-to-plasma concentration ratio at 72 hr was calculated to be 2.6-fold, although the permeability-surface area product across the tumor capillary and other physiological parameters were comparable between the two tumor cell lines. The discrepancy between the in vitro and in vivo results was accounted for by the fact that the tumor extracellular fluid concentration at this time point was 13-fold lower in HCT-15 tumors than in COLO205 tumors because of the restricted penetration of MRK16 through the tumor capillaries. This finding suggests that this factor accounts for the in vitro and in vivo difference in the tumor disposition of MRK16.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1997

Retroviral coexpression of two different types of drug resistance genes to protect normal cells from combination chemotherapy.

Drug resistance genes can protect normal hematopoietic cells from the toxicity of anticancer agents. Because chemotherapeutic agents are often used in combination in current clinical protocols, coexpression of two different drug resistance genes should be useful in protecting normal bone marrow cells from the hematotoxicities caused by combination chemotherapy. In this study, we have combined the human multidrug resistance gene (MDR1) and human O6-methylguanine DNA methyltransferase (MGMT) gene as drug resistance genes. For the coexpression of two drug resistance genes, we have constructed two bicistronic retrovirus vectors. One vector is Ha-MDR-IRES-MGMT, in which translation of the MDR1 cDNA is cap-dependent and MGMT translation is dependent on an internal ribosome entry site (IRES). The other is Ha-MGMT-IRES-MDR, which has cap-dependent MGMT translation and IRES-dependent MDR1 translation. MGMT-negative HeLa derivative (MR) cells transduced with these retroviruses showed resistance to vincristine (from MDR1) and 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosou rea (ACN; from MGMT). Cells transduced with Ha-MDR-IRES-MGMT showed higher resistance to vincristine and lower resistance to ACNU than those transduced with Ha-MGMT-IRES-MDR. In any case, the resistance levels of cells transduced with either vector were high enough to select transduced cells with vincristine or ACNU. The expression levels of P-glycoprotein or MGMT in the transduced cells determined by FACS and Western blot analysis correlated well with the extent of resistance to vincristine and ACNU, respectively. All of the MGMT-transduced cells expressed higher amounts of MGMT than the MGMT-expressing parental cell line HeLa S3. Murine bone marrow cells transduced with Ha-MDR-IRES-MGMT and selected with vincristine also showed simultaneous resistance to vincristine and ACNU. These results suggest that bicistronic retroviral vectors allow the functional coexpression of two different types of drug resistance genes. This strategy could be applicable to any combination of drug resistance genes.

3T3 Cells↗

PubMed1996

Glucose-regulated stresses cause decreased expression of cyclin D1 and hypophosphorylation of retinoblastoma protein in human cancer cells.

Glucose-regulated stress response of cancer cells occurs during the growth of solid tumors and is induced in culture by treatments with various agents, including 2-deoxyglucose, glucosamine, and calcium ionophore A23187. We previously reported that the three stressors commonly induced cell-cycle arrest in the G1 phase and resistance to antitumor drugs in human cancer A2780 and HT-29 cells. In this study, we investigated the mechanisms of stress-induced G1 arrest by determining the expression of cell-cycle-regulating proteins. Among G1 cyclins and cyclin-dependent kinases (cdk) examined, the expression levels of cyclin D1 preferentially decreased in the stressed cells. A time-course study showed that the decrease in cyclin D1 coincided with the appearance of hypophosphorylated retinoblastoma protein (pRb), which is the growth suppressive form. These findings suggest that the stress-induced G1 arrest is mediated through the down-regulation of cyclin D1-associated kinases (cdk4/6), pRb kinases during G1 phase. This was also supported by decreased cdk4 expression in stressed HT-29 cells. In addition, p21WAF1, a cdk inhibitor, was induced in the stressed cells, particularly A23187-treated cells. A23187, compared with the other stressors, caused extreme pRb hypophosphorylation, suggesting that p21WAf1 is involved in the regulation of pRb phosphorylation in the stressed cells. Our present findings could explain a molecular-based mechanism of a growth-arrested quiescent state and also resistance to chemotherapy of solid tumor cells.

Calcimycin↗

PubMed1996

Interleukin-7 inhibits apoptosis of mouse malignant T-lymphoma cells by both suppressing the CPP32-like protease activation and inducing the Bcl-2 expression.

Mouse malignant T-lymphoma CS-21 cells grow in vitro in the presence of CA-12 lymph node stromal cells, but they undergo apoptotic cell death when separated from CA-12 stromal cells. In the course of examining the nursing effects of CA-12 stromal cells, we found that these cells provided some soluble factors that suppressed CS-21 cell apoptosis. We recently found that cysteine was an antiapoptotic soluble factor. In this report, we identify interleukin-7 (IL-7) as another antiapoptotic soluble factor secreted by CA-12 stromal cells. Although the activity of CPP32-like protease was increased in induction of CS-21 cell apoptosis, the addition of IL-7 suppressed the activity. The expression of Bcl-2 protein was down-regulated when CS-21 cells were cultured alone, but the addition of IL-7 recovered the expression of Bcl-2. These results indicate that CA-12 stromal cells inhibit CS-21 cell apoptosis by producing IL-7, which leads to the suppression of CPP32-like protease activation and the expression of Bcl-2 protein.

Animals↗

PubMed1996

Activation of actin-cleavable interleukin 1beta-converting enzyme (ICE) family protease CPP-32 during chemotherapeutic agent-induced apoptosis in ovarian carcinoma cells.

We have previously reported that actin cleavage activity (ACA) by interleukin 1beta-converting enzyme (ICE) family protease was elevated during anticancer drug-induced apoptosis in human leukemia U937 cells. In this study, the involvement of ACA in the drug-induced apoptosis in solid tumor cells was investigated. Human ovarian carcinoma OVCAR-3 cells undergo apoptotic cell death when cells are treated with chemotherapeutic agents such as cisplatin and etoposide. The induction of the actin cleavage activity accompanied the development of apoptosis. ICE/ced-3 family protease inhibitors such as Z-VAD-CH2DCB and Z-EVD-CH2DCB at 100 microg/ml prevented both the emergence of ACA and the morphological change, characteristics of apoptosis, in cisplatin-treated OVCAR-3 cells. The ACA in apoptotic OVCAR-3 cell lysate was greatly adsorbed by antibody against CPP-32, an ICE family protease. Furthermore, the immunoprecipitated CPP-32 from OVCAR-3 lysate could cleave actin to generate a 15-kDa fragment, as did the apoptotic OVCAR-3 cell lysate, indicating that CPP-32 is a major protease responsible for the ACA. The activation of CPP-32 in the drug-treated cell lysate was verified with Western blot analysis. Our present results indicate that CPP-32, an actin cleavage ICE/ced-3 family protease, could be a common mediator involved in the process of chemotherapy-induced apoptosis of cancer cells.

Actins↗

PubMed1996

Glucose-regulated stresses induce resistance to camptothecin in human cancer cells.

The glucose-regulated stress response in mammalian cells is characterized by the increased synthesis of glucose-regulated proteins (GRPs). In this study, we found that GRP-inducing conditions in culture led to induction of resistance to the topoisomerase I-targeted drug camptothecin in human colon cancer HT-29 and ovarian cancer A2780 cells. The induction of camptothecin resistance was accompanied by decreased levels of camptothecin-induced cleavable complexes, as measured by a topoisomerase I band depletion assay. However, topoisomerase I protein levels were the same in both stressed and non-stressed cells. Furthermore, when isolated nuclei from stressed and non-stressed cells were treated with camptothecin, similar levels of cleavable complexes were obtained, suggesting that the activity of topoisomerase I did not change in stressed cells. In contrast, intracellular accumulation of camptothecin decreased in stressed cells. Our results indicate that stress-induced camptothecin resistance could be explained by reduced camptothecin accumulation, leading to decreased numbers of cleavable complexes, without quantitative or qualitative changes in topoisomerase I levels. In addition, cell cycle analysis revealed that the GRP-inducing treatments resulted in an accumulation of G1/G0-phase cells. As camptothecin shows an S-phase-specific cytotoxicity, the G1/G0-phase accumulation is another mechanism for camptothecin resistance. Since a glucose-regulated response is produced by hypoxia and nutrient deprivation that occur naturally in solid tumors, the resistance observed here can occur in some solid tumors and can be an obstacle to chemotherapy.

Antineoplastic Agents, Alkylating↗

PubMed1996

Abnormal expression of a 170-kilodalton P-glycoprotein encoded by MDR1 gene, a metabolically active efflux pump, in CD4+ and CD8+ T cells from patients with human immunodeficiency virus type 1 infection.

Peripheral blood CD4+ and CD8+ T cells from 16 patients with HIV-1 infection, 8 each with CD4+ T cell counts of > 200/mm3 (group I) and with CD4+ T cell counts of < 200/mm3 (group II), and 8 age- and sex-matched controls, were examined for the expression of P-glycoprotein (P-gp), a 170-kDa phosphoglycoprotein encoded by the MDR1 gene, using dual-color flow cytometric analysis. The function of P-glycoprotein was assessed by the accumulation of rhodamine-123 (Rh123) dye in the presence or absence of cyclosporin A (which inhibits Rh123 efflux). A significantly increased proportion of CD4+ T cells from patients with HIV-1 infection expressed P-glycoprotein as compared to controls, resulting in a significantly increased ratio of the proportions of CD4+P-gp+/CD8+P-gp+ cells. The ratio of CD4+P-gp+/CD8+P-gp+ in group II patients was significantly higher (p = 0.02) than in group I patients, suggesting a progressive increase in P-gp expression with the advancement of HIV-1 infection. The proportions of CD4+P-gp+ and CD8+P-gp+ T cells did not differ significantly between those who received AZT and those who were not treated with AZT. Contrary to expectation, both CD4+ and CD8+ T cells from patients accumulated significantly more Rh123 as compared to controls. Furthermore, cyclosporin A failed to increase intracellular accumulation of Rh123 in CD4+ and CD8+ T cells from patients. These data suggest a functionally defective P-gp expression in HIV-1 infection that appears to increase with the progression of HIV-1 infection. A study of a large number of patients with HIV-1 infection is needed to determine the effects of opportunistic infection and antiretroviral therapy on the expression of P-gp and to determine whether the expression of P-gp could serve as another surrogate marker for the progression of HIV-1 infection.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Potentiation of the reversal activity of SDZ PSC833 on multi-drug resistance by an anti-P-glycoprotein monoclonal antibody MRK-16.

SDZ PSC833 (PSC833), an analogue of cyclosporines, is one of the most potent modulators of multi-drug resistance (MDR). We previously reported that MRK-16, an anti-P-glycoprotein MAb, enhanced MDR reversal activity of cyclosporin A (CsA) through inhibition of P-glycoprotein-mediated CsA transport. We have examined here whether MRK-16 can enhance MDR reversal activity of PSC833. We found that MRK-16 potentiated the MDR reversal activity of PSC833, and of CsA, in MDR sublines of human myelocytic leukemia K562 and human ovarian cancer A2780 cells. Like MRK-16 combined with CsA, MRK-16 enhanced the effect of a sub-optimum dose of PSC833 on vincristine accumulation in MDR cells. However, MRK-16 could not increase cellular accumulation of PSC833 in MDR tumor cells, yet it could increase cellular accumulation of CsA. P-glycoprotein could not transport PSC833 but could transport CsA. Our results indicate that MRK-16 potentiates the MDR reversal activity of both PSC833 and CsA, yet also suggest that the molecular mechanism of the potentiation differs between the two substances.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Novel metastasis model of human lung cancer in SCID mice depleted of NK cells.

Metastasis is a critical problem in the treatment of human lung cancer. Thus, a suitable animal model of metastasis of human lung cancer is required for in vivo biological and preclinical studies. In this study, we tried to establish a suitable model for this, using SCID mice. Neither human SCLC H69/VP cells (5 x 10(6)) nor squamous-cell carcinoma RERF-LC-AI cells (1 x 10(6)), injected through a tail vein, formed metastases in untreated SCID mice. Pre-treatment of SCID mice with anti-asialo GM1 serum resulted in only a few metastases of H69/VP cells, but pre-treatment with anti-mouse IL-2 receptor beta chain Ab (TM-beta 1) resulted in numerous lymph-node metastases 56 days after tumor inoculation. H69/VP-M cells, an in vivo-selected variant line, formed significant numbers of lymph-node metastases even in SCID mice pre-treated with anti-asialo GM1 serum. SCID mice depleted of NK cells by treatment with TM-beta 1 showed different patterns of metastasis when inoculated intravenously with the 2 different human lung cancer cell lines (H69/VP and RERF-LC-AI cells): H69/VP cells formed metastases mainly in systemic lymph nodes and the liver, whereas RERF-LC-AI cells formed metastases mainly in the liver and kidneys, with only a few in lymph nodes. A histopathological study showed that the metastatic colonies consisted of cancer cells. The numbers of metastatic colonies formed by the 2 cell lines increased with the number of cells inoculated. TM-beta 1 treatment of SCID mice efficiently removed NK cells from peripheral blood for at least 6 weeks, whereas, after treatment of the mice with anti-asialo GM1 serum, NK cells were recovered within 9 days. These findings suggest that NK-cell-depleted SCID mice may be useful as a model in biological and pre-clinical studies on metastasis of human lung cancer.

Animals↗

PubMed1996

Brain capillary endothelial cells express two forms of erythropoietin receptor mRNA.

To study the existence of the erythropoietin receptor (Epo-R) mRNA in brain capillary endothelial cells, the reverse transcription (RT) PCR was performed using total RNAs from rat brain capillary endothelial cells (RBECs) and MBEC4, which is one of the established mouse brain capillary endothelial cell lines. Southern analysis of the RT-PCR products indicated that both RBECs and MBEC4 expressed an authentic form of Epo-R mRNA as a minor form and an intron-5-inserted form of Epo-R mRNA, thus a soluble form of Epo-R mRNA, as a major form. Furthermore, the effect of recombinant human erythropoietin (rHuEpo) on the DNA synthesis in RBECs was analyzed. rHuEpo showed a dose-dependent mitogenic action on RBECs as a competence factor. Radioiodinated rHuEpo was bound specifically to RBECs with time, cell number and dose dependencies. Binding studies with 125I-rHuEpo showed that RBECs had a single class of receptors with low-affinity (Kd = 860 pM) and that the number of sites/cell (10300) was abundant. These results suggest that brain capillary endothelial cells express not only an authentic form of Epo-R but also a soluble form of Epo-R and that erythropoietin acts directly on brain capillary endothelial cells as a competence factor.

Animals↗

PubMed1996

Chromosome 22 complements apoptosis in Fas-and TNF-resistant mutant UK110 cells.

Fas and p55 tumor necrosis factor receptor (TNFR) transfer an apoptosis signal when they are crosstinked with their ligands or agonistic antibodies. However, the signal transduction mechanism of apoptosis via Fas and p55 TNFR has not yet been elucidated. We previously described a recessive mutant UK110 from the human monocytic leukemia U937 cell line, that showed resistance against Fas- and p55 TNFR-mediated apoptosis. By cytogenetic analysis and microcell-fusion method, we demonstrate here that introduction of chromosome 22 can specifically restore the sensitivity to Fas- and TNF-mediated apoptosis in UK110 cells. Moreover, introduction of chromosome 22 into UK110 can complement the processing of interleukin-1 beta converting enzyme (ICE)-like proteases, such as CPP32/Yama/Apopain and ICH-1L, after treatment with anti-Fas and anti-p55 TNFR antibodies. These results suggest that the product of a gene located on chromosome 22 participates in the Fas-and p55 TNFR-mediated apoptosis at a point upstream of ICE-like proteases.

Amino Acid Sequence↗

PubMed1996

Antitumor activity of a novel podophyllotoxin derivative (TOP-53) against lung cancer and lung metastatic cancer.

We synthesized a potent new antitumor podophyllotoxin derivative (4beta-aminoalkyl-4'-O-demethyl-4-desoxypodophyllotoxin; TOP-53) in our search for a drug that has strong activity against lung cancer and lung metastatic cancer. TOP-53 exhibited twice the inhibitory activity of etoposide (VP-16) against topoisomerase II and induced DNA strand breaks but showed no inhibitory activity against tubulin polymerization. The in vitro cytotoxic activity of TOP-53 assessed as IC50 was 0.016-0.37 microg/ml and 0.26-8.9 microg/ml against marine tumor and human non-small cell lung cancer (NSCLC) cell lines, respectively. TOP-53 exerted significant efficacy equivalent to that of VP-16 on s.c.-implanted murine solid tumors (Colon 26, B16-BL6, and Lewis lung carcinoma) at doses 3-5 times lower than that of VP-16. In human tumor xenografts using NSCLC, TOP-53 was active for four of five tumors, whereas VP-16 was active for two of five tumors. Potent inhibitory activity of TOP-53 was also found against a lung tumor (Lewis lung carcinoma) and four lung metastatic tumors (NL-22 and NL-17 colon cancer, UV2237M fibrosarcoma, and K1735M2 melanoma). TOP-53 appeared to be more active against four of them than VP-16. Thus, TOP-53 is not only active against s.c.-implanted lung cancers but also strongly active against lung localized tumor and metastatic tumors in the lungs. The high selectivity of TOP-53 was attributed to its high distribution into the lung and its persistence. TOP-53 is expected to be highly effective against lung cancer including NSCLC and various lung metastatic tumors in the clinical field.

Animals↗

PubMed1996

DT-diaphorase as a critical determinant of sensitivity to mitomycin C in human colon and gastric carcinoma cell lines.

Mitomycin C (MMC), a known cytotoxic agent, requires cellular enzyme-mediated activation for effective antitumor activity. To study the bioreductive enzymes responsible for MMC activation in tumor cells, we examined the enzyme activities of DT-diaphorase (DTD) and NADPH:cytochrome P-450 reductase in 13 colon and gastric carcinoma cell lines and then compared these activities to the respective cellular MMC sensitivity. We found that cell lines with nonexistent or marginal DTD activity, such as St-4 and MKN7, showed resistance to MMC, in comparison to cell lines with DTD activity ranging from 210 to 1420 nmol/min/mg protein. No correlation was found between NADPH:cytochrome P-450 reductase activity and MMC sensitivity in these cell lines. To confirm the role of DTD in cellular MMC sensitivity, we constructed an expression vector containing NQO1, a gene that codes for DTD, and transfected the vector into St-4 cells expressing no DTD activity. Several transfectant clones with DTD activity from 144 to 2085 nmol/min/mg protein were obtained. All of the transfectants showed 5-10-fold higher sensitivity to MMC compared to the parental St-4 cells. Consistent with the MMC sensitivity, we also found that MMC-DNA adduct was formed more extensively in the NQO1 transfectants than in the St-4 cells. These results indicate that DTD activity is required for effective cytotoxicity of MMC in colon and gastric carcinoma cells.

Antibiotics, Antineoplastic↗

PubMed1996

A novel anti-Thy-1 (CD90) monoclonal antibody induces apoptosis in mouse malignant T-lymphoma cells in spite of inducing bcl-2 expression.

Mouse malignant T-lymphoma CS-21 cells can survive and proliferate in vitro when co-cultured with CA-12 stromal cells isolated from lymph nodes, but CS-21 cells undergo apoptotic cell death with DNA fragmentation when cultured alone. We immunized rats with CS-21 cells and raised monoclonal antibodies (MAbs) that recognized Thy-1 (CD90) or CD45 protein. The majority of these MAbs were able to inhibit the adhesion and apoptosis of CS-21 cells. When anti-Thy-1 MAbs were examined for their recognition site on Thy-1 glycoprotein, one of them, MCS-34, was found to recognize both Thy-1.1 and Thy-1.2. In addition, MCS-34, just like the anti-Thy-1 MAb G7, recognized the Thy-1A epitope. G7 was known to induce apoptosis in some T-cell hybridomas and in thymocytes. In CS-21 cells, however, G7 could not induce apoptosis, but MCS-34 could. Interestingly, MCS-34 enhanced the expression of bcl-2 protein, in spite of its ability to induce apoptosis. Upon examining the apoptosis-inducing mechanisms of MCS-34, we found that it promoted a sustained increase in cytoplasmic-free calcium in CS-21 cells. Calcium ionophore A23187 was also found to induce apoptosis in a dose-dependent manner. These results indicate that a sustained increase in cytoplasmic-free calcium by MCS-34 induces apoptosis in CS-21 cells in spite of bcl-2 protein expression.

Animals↗

PubMed1996

Measurement of P-glycoprotein expression in multidrug-resistant human neuroblastoma cell lines using self-competitive binding assay.

To date, all reported measurements of multidrug resistance have been semiquantitative. The purpose of the present study is to establish and validate the self-competitive binding assay technique utilizing monoclonal antibody for quantitative estimation of multidrug resistance in tumor cells. This technique is used for P-glycoprotein concentration measurement in BE(2)-C human neuroblastoma cell line and its sublines with primary resistance to colchicine and actinomycin D. Monoclonal antibody MRK-16 was used in this study. It was labeled with iodine-125 (125I) to trace the concentration of antibody-antigen complexes. The binding data were obtained by varying the concentration of the unlabeled antibody. The results were fitted to a model equation to estimate the number of binding sites and antibody-antigen dissociation constant. The P-glycoprotein concentration was significantly higher in the resistant sublines than in the sensitive line. The highest levels were achieved in actinomycin D-resistant cells: 2.1 x 10(6) binding sites/cell versus 5.4 x 10(4) binding sites/cell in the sensitive cells. The consistency of the results was verified by repeating the study three times for each cell line. The binding assay results were confirmed by Western blot experiments performed on the same cell lines.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Sensitivity of multidrug-resistant tumor cell lines to immunologic effector cells.

The ability of malignant cells to survive exposure to cytotoxic agents is a major obstacle to cure in patients with cancer. Multidrug resistance and the expression of P-glycoprotein are emerging as a cause of chemotherapy failure. Immunologic effector cells such as lymphokine-activated killer (LAK) cells or cytokine-induced killer (CIK) cells are capable of killing a broad range of tumor cell lines or freshly isolated tumor cells. As demonstrated here, LAK, and CIK cells possess a high level of cytotoxic activity against tumor cell lines both resistant and sensitive to chemotherapeutic agents such as doxorubicin or vinblastine. CIK cells possessed a higher level of cytotoxic activity than LAK cells as determined by 51Cr release and a tumor colony assay. Monoclonal antibodies against P-glycoprotein did not block the lysis of tumor cells resistant to chemotherapy by CIK cells. In contrast, antibodies to LFA-1 and ICAM-1 blocked CIK cell-mediated tumor cell lysis. These data demonstrate that immunological approaches to cancer therapy may be useful in overcoming disease caused by drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗