Effect of 12-deoxyphorbol 13-phenylacetate on daunorubicin resistance and calcium-independent protein-kinase-C isozymes in drug-sensitive murine leukemia p388 cells

Because of a suggested role of protein kinase C (PKC) in multidrug resistance (MDR) and recent. demonstration of molecular and biochemical heterogeneity of PKC, we examined the effect of 12-deoxyphorbol 13-phenylacetate (dPP) on intracellular accumulation and drug sensitivity of daunorubicin (DNR) in drug sensitive P388 murine leukemia cell line. In addition, effect of dPP on Ca++-independent PKC (delta, epsilon and zeta) isozymes was examined with Western blot, using laser densitometry. dPP induced significant resistance to DNR in P388 cells, however had no significant effect on DNR accumulation. In addition, dPP increased the levels of plasma membrane associated PKCdelta and epsilon isozymes in P388 cells and but had no effect on plasma membrane-associated PKCzeta isozyme. This study demonstrates a role of Ca++-independent PKCdelta and epsilon isozymes in drug resistance.

Induction of resistance to daunorubicin in drug-sensitive leukemia p388 cells - a role of pkc-Beta-I isozyme

A role of protein kinase C (PKC) has been suggested in multidrug resistance (MDR). Because of the molecular and biochemical heterogeneity of PKC, we examined a role of PKC beta isozyme in drug sensitive murine leukemia P388 cell line. Drug sensitive P388 and MDR P388/ADR cells were treated with various concentrations of 12-deoxyphorbol-13-O-phenylacetate 20 acetate (DPPA, an agonist of PKC beta I isozyme) and examined for its effect on daunorubicin (DNR) accumulation and sensitivity to DNR. dPPA increased DNR resistance and decreased DNR accumulation in P388 cells but had no effect in P388/ADR cells. The reduced dPPA-induced DNR accumulation was due to decreased uptake without any effect on DNR efflux. Furthermore, treatment of P388 cells with dPPA was associated with translocation of PKC beta isozyme from cytosol to plasma membrane. These data suggest that PKC beta I isozyme plays a role in acquired drug resistance.

Synergistic apoptotic effect of arabinoxylan rice bran (MGN-3/Biobran) and curcumin (turmeric) on human multiple myeloma cell line U266 in vitro

The present study was carried out to investigate the synergistic apoptotic potential of arabinoxylan rice bran (MGN-3/Biobran) and curcumin (turmeric) on human multiple myeloma (MM) cell line U266 , in vitro. U266 cells were cultured with MGN-3 (50 or 100μg/ml) and curcumin (2.5-10μM) for 3 days. The effects of MGN-3 and curcumin on the growth and survival of the U266 cells were determined by trypan blue, MTT assay, flow cytometry analysis of cancer cell cycle, and apoptosis. Expression of proapoptotic Bax, and antiapoptotic Bcl2 was determined by Western blot analysis. Treatment with MGN-3 alone or curcumin alone caused a dose-dependent inhibition in the proliferation of U266 cells. However, a synergistic effect was noticed post-treatment with both agents that maximized at 100μg/ml MGN-3 plus 10μM curcumin. This synergy was characterized by an 87% decrease in cell number and a 2.6 fold increase in the percentage of apoptotic U266 cells. Cell cycle analysis showed a 53% decrease in the percentage of cells in the G0-G1 phase treated with MGN-3 and curcumin (from 36% to 17%). Analysis of the expression of the pro and antiapoptotic molecules Bax and Bcl-2 revealed synergistic effects of these agents, as the expression of Bcl-2 was decreased and Bax was increased. This resulted in a cellular microenvironment favorable for apoptosis. We conclude that MGN-3 and curcumin synergize in the induction of U266 cell apoptosis. This data may establish the foundation for in vivo studies that could have therapeutic implications.

Leukocyte toll-like receptor expression in end-stage kidney disease

BACKGROUND

End-stage renal disease (ESRD) is simultaneously associated with inflammation, impaired immunity and increased susceptibility to microbial infections. Innate immune cells, monocytes and polymorphonuclear leukocytes (PMN) recognize pathogens via toll-like receptors (TLR) triggering phagocytosis, cellular activation and secretion of inflammatory cytokines. Data on expression and function of TLRs in ESRD are limited.

METHODS

Blood samples from 21 stable ESRD patients and 21 normal controls were processed for TLR2, TLR4, TLR7 and TLR 9 expression on monocytes and PMN by flow cytometry. TLR activity was examined by determining the response to TLR4 and TLR2 ligands.

RESULTS

The ESRD group exhibited significant upregulation of TLR2 and TLR4 (but not TLR7 or TLR 9) expressions on monocytes and of TLR4 on PMN. This was coupled with heightened cytokine production in response to TLR4 activation with lipopolysaccharide. However, the response to TLR2 stimulation with peptidoglycan was unchanged in the ESRD group.

CONCLUSIONS

Monocyte TLR2 and TLR4 and neutrophil TLR4 expressions and TLR4 activity are increased hemodialysis patients, representing another dimension of ESRD-associated inflammation.

Differential sensitivity of naïve and subsets of memory CD4+ and CD8+ T cells to hydrogen peroxide-induced apoptosis

CD4+ and CD8+ memory T cells are identified into central and effector memory subsets, which are characterized by distinct homing patterns and functions. In this investigation, we show that naïve and central memory CD4+ and CD8+ T cells are sensitive to hydrogen peroxide (H2O2)-induced apoptosis, whereas effector memory CD4+ and CD8+ T cells are relatively resistant to H2O2-induced apoptosis. Apoptosis in naïve and central memory CD4+ and CD8+ is associated with the release of cytochrome c and activation of caspase-9 and caspase-3, upregulation of Bax and voltage-dependent anion channel (VDAC) expression, and decreased intracellular glutathione (GSH). In vitro GSH and a superoxide dismutase mimetic Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin inhibited H2O2-induced apoptosis in both naïve and central memory CD4+ and CD8+ T cells. Furthermore, VDAC inhibitor 4,4'-diisothiocynostilbene-2,2'-disulfonic acid blocked H2O2-induced apoptosis. These data demonstrate that H2O2 induces apoptosis preferentially in human naïve and central memory CD4+ and CD8+ T cells via the mitochondrial pathway by regulating intracellular GSH and the expression of Bax and VDAC.

Naïve and central memory T-cell lymphopenia in end-stage renal disease

End-stage renal disease (ESRD) is associated with increased propensity to infections, diminished response to vaccination, impaired cell-mediated immunity, and reduced CD4+/CD8+ T-lymphocyte ratio. Four subsets of CD4+ and CD8+ T cells have been recently identified: naïve cells (as yet uncommitted), central memory (CM) cells (previously programmed), and CD45RA-positive and CD45RA-negative effector memory (EM) cells (programmed to perform specific effector functions). The effect of ESRD on subpopulations of T lymphocytes is unclear and was studied here. Twenty-one hemodialysis patients and 21 age-matched controls were studied. Pre- and post-dialysis blood samples were obtained and analyzed by three-color flow cytometry. CD4+/CD8+ ratio and the numbers of the naïve and CM CD4+ and CD8+ T cells were significantly reduced, whereas the numbers of EM CD4+ and CD8+ T cells were unchanged in the ESRD group. The reduction of the naïve and CM T-cell counts in the ESRD group was associated with increased apoptosis of these cells. Negative correlations were found between severity of azotemia, oxidative stress, and hyperphosphatemia with the number of naïve T cells. Comparison of diabetic with non-diabetic ESRD patients revealed higher numbers of total CD8+ cells and EM CD8+ T cells in the diabetic group. Dialysis did not significantly change the naïve and CM CD4+ or CD8+ cell counts, but significantly lowered CD8+ EM cell count. Thus, ESRD results in increased apoptosis and diminished populations of naïve and CM T lymphocytes. This phenomenon may, in part, contribute to the impaired immune response in this population.

Role of NF-κB signaling pathway in increased tumor necrosis factor-α-induced apoptosis of lymphocytes in aged humans

In human aging, lymphocytes display increased sensitivity to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. TNF-alpha induces both survival and apoptotic signals. The survival signal is mediated by the activation of NF-kappaB. Although a role of certain proapoptotic molecules in aging has been reported, a role of altered NF-kappaB signaling pathway has not been explored in detail. In this study, we have compared TNF-alpha-induced activation of NF-kappaB, phosphorylation of IkappaBalpha, and the expression of IKKbeta between lymphocytes from young and aged humans. Furthermore, we have explored a role of IKKbeta in increased susceptibility of lymphocytes from aged humans to TNF-alpha-induced apoptosis. Lymphocytes from aged humans displayed decreased activation of NF-kappaB, reduced phosphorylation of IkappaBalpha, and decreased expression of IKKbeta. In addition, overexpression of IKKbeta in lymphocytes from aged humans normalized TNF-alpha-induced apoptosis to the level of young subjects. These data suggest a deficiency of NF-kappaB signaling pathway and a role of IKKbeta, at least in part, for increased sensitivity of lymphocytes from aged humans to TNF-alpha-induced apoptosis.

Efficacy of telithromycin in the treatment of experimental Bacteroides fragilis intraabdominal abscess in the senescent mice

The efficacy of telithromycin (HMR 3647), a new ketolide, in the treatment of experimental Bacteroides fragilis intraabdominal abscess in young and senescent mice was evaluated. Two different age groups of mice, young (2-3 months) and senescent (18-24 months) were used in this study. Telithromycin (50mg/kg/bid) was compared with clindamycin and metronidazole, both administered in 100 mg/kg/bid doses. Telithromycin cured the infection in 74% of the young and 67% of the old mice but this difference was not significant. Telithromycin efficacy was comparable to that of clindamycin which cured 82% of the young and 75% of the old, but was superior to the efficacy of metronidazole, which cured 61% of the young and 50% of the senescent mice. Young animals that were not cured by any of the three antibiotics showed decrease in the viable bacterial cell counts by two logs while the senescent mice had a one log difference. Serum, pus and tissue concentrations of telithromycin were five-fold higher in the old mice than in the young. Age by itself had no adverse effect on therapeutic outcome of any of the three antibiotics used.

Increased spontaneous, tumor necrosis factor receptor- and CD95 (Fas)-mediated apoptosis in cord blood T-cell subsets from Turner's syndrome

Increased spontaneous as well as TNF-alpha-induced and CD95-mediated apoptosis were observed in CD4+ and CD8+ T cells from the cord blood of a patient with Turner's syndrome as compared to normal cord blood. Increased apoptosis was associated with an increased expression of TNFR-1, TNFR-2, and CD95L and decreased expression of cIAP1 and FLIP(L). No significant difference was observed in the expression of Bcl-2 family members (Bcl-2, Bax) between Turner's syndrome cord blood and normal cord blood lymphocytes. This study demonstrates that increased apoptosis of T-cell subsets in Turner's syndrome occurs via the death receptor pathway and may play a role in the pathogenesis of immunological defects associated with Turner's syndrome.

Biochemical and molecular basis of thimerosal-induced apoptosis in T cells: a major role of mitochondrial pathway

The major source of thimerosal (ethyl mercury thiosalicylate) exposure is childhood vaccines. It is believed that the children are exposed to significant accumulative dosage of thimerosal during the first 2 years of life via immunization. Because of health-related concerns for exposure to mercury, we examined the effects of thimerosal on the biochemical and molecular steps of mitochondrial pathway of apoptosis in Jurkat T cells. Thimerosal and not thiosalcylic acid (non-mercury component of thimerosal), in a concentration-dependent manner, induced apoptosis in T cells as determined by TUNEL and propidium iodide assays, suggesting a role of mercury in T cell apoptosis. Apoptosis was associated with depolarization of mitochondrial membrane, release of cytochrome c and apoptosis inducing factor (AIF) from the mitochondria, and activation of caspase-9 and caspase-3, but not of caspase-8. In addition, thimerosal in a concentration-dependent manner inhibited the expression of XIAP, cIAP-1 but did not influence cIAP-2 expression. Furthermore, thimerosal enhanced intracellular reactive oxygen species and reduced intracellular glutathione (GSH). Finally, exogenous glutathione protected T cells from thimerosal-induced apoptosis by upregulation of XIAP and cIAP1 and by inhibiting activation of both caspase-9 and caspase-3. These data suggest that thimerosal induces apoptosis in T cells via mitochondrial pathway by inducing oxidative stress and depletion of GSH.

Functional decline in aging and disease: a role for apoptosis

The process of aging and senescence is associated with a decline in several organ functions and ultimately takes away independence and reduces quality of life. The precariously marginal functional reserves of the immune, pulmonary, and cardiovascular systems are among the most important causes of increased hospitalization in the older population. When complicated by chronic diseases, as is often the case, the problem is magnified. Apoptosis, or programmed cell death, is a process that goes on continuously throughout life. It is involved in embryogenesis for proper organ and tissue development. After birth and through adulthood, it helps eliminate unneeded and damaged cells. There is evidence that advanced age is associated with dysregulation of apoptosis. Several studies have shown age-related changes in the levels of proteins and factors that regulate apoptosis. This could explain the age-associated increased prevalence of cancers, certain autoimmune diseases, and neurodegenerative disorders in older people. More studies are needed to further elucidate the process of apoptosis. With this knowledge, the use of gene therapy and apoptosis modulators may someday have therapeutic value in preventing the functional decline we see in the older population.

TNF-alpha-induced apoptosis in neonatal lymphocytes: TNFRp55 expression and downstream pathways of apoptosis

Previously we have shown decreased Fas-mediated apoptosis in cord blood lymphocyte subsets. In this study, we compared tumor necrosis factor (TNF)-alpha-induced apoptosis in T lymphocytes and their subsets between cord blood and peripheral blood from healthy young controls. The expression of TNF receptor I (TNFR-I) was assessed by flow cytometry and quantitative RT-PCR. The expression of adapter molecules TNF receptor-associated death domain (TRADD), Fas-associated death domain (FADD) and TNF-associated factor-2 (TRAF-2) and caspase 3 was analyzed by Western blotting. The activity of caspase 3 and caspase 8 was measured by colorimetric assay. The susceptibility of CD4+ and CD8+ T cells to TNF-alpha-induced apoptosis was measured by terminal deoxytidyl transferase-mediated dUTP nick end labelling (TUNEL) assay. Both CD4+ and CD8+ T cell subsets from cord blood demonstrated decreased susceptibility to TNF-alpha-induced apoptosis that was associated with decreased activation of both caspase 8 and caspase 3 as compared to T cell subsets in peripheral blood. Furthermore, expression of TNFR-I, TRADD and caspase 3 was decreased in cord blood lymphocytes as compared to peripheral blood lymphocytes. The significance of these observations is discussed.

P-glycoprotein (encoded by multidrug resistance genes) is not required for interleukin-2 secretion in mice and humans

P-glycoprotein (encoded by multidrug resistance genes), a member of the ATP-binding cassette transporter protein superfamily, has been shown to play a role in the secretion of cytokines. This conclusion was based upon the inhibition of cytokine secretion by anti-P-gp monoclonal antibodies. In this study, we show that anti-CD3-stimulated lymphocytes from wild-type, mdr1a knock out and mdr1ab double knock out mice produce similar amounts of IL-2, IFN-gamma, IL-4, and IL-10. In addition, Jurkat T cells that lack P-gp and MDR1-transfected Jurkat T cells (JurkatP-gp) as well as purified human peripheral blood CD4+ P-gp+ and CD4+ P-gp- and CD8+ P-gp+ and CD8+ P-gp- T cell subsets produced comparable amounts of IL-2. These data show that P-gp is not required for secretion of IL-2, IFN-gamma, IL-4, and IL-10 secretion in mice and IL-2 secretion in humans.

Modulation of endothelin-1 expression in pulmonary epithelial cell line (A549) after exposure to RSV

Respiratory syncytial virus (RSV) is one of the most important respiratory tract pathogens in infants and young children. The airway epithelial cells are the primary target cells for RSV infection. The airway epithelial layer is not only a physical barrier, but also plays a role in a synthesis of a variety of major inflammatory cytokines (IL-6, IL-8, GM-CSF etc.) as previously reported. Endothelin-1 (ET-1) is a potent bronchoconstrictor and vasoconstrictor factor, and involved in pathogenesis of various diseases of the respiratory tract. We hypothesized that RSV may induce the release of ET-1 from the bronchial epithelial cell line. No previous data is available regarding association between RSV infection and ET-1 release. We evaluated the effect of RSV with different concentrations of RSV (MOI 0.1, 1 and 3 pfu/cell) on bronchial epithelial cell line (A549) and measured the production of ET-1 at both protein and mRNA level. A549 cells were treated with different conditions by using LPS, heat-inactivated RSV, RSV or medium alone as control. We observed time-dependent ET-1 release by RSV-infected A549 cells at 4 h, 24 h and maximum at 72 h. ET-1 was expressed in unstimulated A549 cells and was further increased by RSV. RSV with concentration MOI 0.1 (pfu/cell) and LPS appeared to have strongest stimulation on production of ET-1. In addition, ET-1 mRNA was increased significantly by 16 h and decreased to relatively low-level at 24 h. These experiments suggested that airway epithelial cells might play a role in the local airway smooth muscle tone through the production of endothelin-1 during RSV infection.

Salmonella typhimurium-induced reactivation of latent HIV-1 in promonocytic U1 cells is inhibited by trovafloxacin

We have previously reported that virulent Salmonella typhimurium induces replication of latent HIV-1 in U1 cells, via activation of tumor necrosis factor-alpha (TNF-alpha) production. In the present study, we show that Trovafloxacin, a new quinolone antibiotic, inhibits S. typhimurium-induced TNF-alpha production and HIV-1 replication. In addition, Trovafloxacin inhibits TNF-alpha-induced reactivation of latent HIV-1 in U1 cells. The concentrations of Trovafloxacin that inhibited HIV-1 replication are comparable to the plasma and tissue levels achieved by therapeutic dosage used in the treatment of bacterial infections. Therefore, Trovafloxacin is a potential candidate for adjunct therapy in HIV-1 infection.

Evaluation of trovafloxacin in the treatment of Klebsiella pneumoniae lung infection in tumour-bearing mice

Trovafloxacin, a new trifluoroquinolone, was evaluated for its therapeutic efficacy against Klebsiella pneumoniae lung infection in tumour (P388 murine leukaemia cells)-bearing mice, treated with or without a chemotherapeutic agent, daunorubicin (DNR) and in mice without tumour. Its activity was compared with ciprofloxacin and cephazolin. The effect on therapeutic efficacy of the addition of recombinant granulocyte colony stimulating factor (rGCSF) was also examined. Our study showed that both quinolones successfully cured pneumonia owing to infection with K. pneumoniae in mice without tumours but that all antibiotics failed in tumour-bearing mice if DNR was withheld. Substantial differences were noted in DNR-treated tumour-bearing mice with infection-the cure rate with trovafloxacin was 91% whereas the cure rate with ciprofloxacin or cephazolin was 57%. Addition of rGCSF to ciprofloxacin did not substantially improve its efficacy (when assessed by protection against death owing to infection; the survival rate was 41%). Trovafloxacin cure rates ranged from 80 to 90% whether or not rGCSF was added to the treatment regimen. Our results suggest that prior cancer chemotherapy had no adverse effect on the therapeutic efficacy of trovafloxacin, and that trovafloxacin may be a promising therapeutic agent for treatment of bacterial infections in the presence of leucopenia.

Increased TNF-alpha-induced apoptosis in lymphocytes from aged humans: changes in TNF-alpha receptor expression and activation of caspases

Aging is characterized by increased T cell lymphopenia, T cell dysfunction, and increased serum TNF levels. In this study, we have examined the role of TNF-induced apoptosis in T cell deficiency in lymphocytes from aged humans. The constitutive expression of TNF receptors (TNFRI and TNFRII) and the adapter molecules, including TNFR-associated death domain protein (TRADD), TNFR-associated factor 2 (TRAF-2), and receptor interacting protein (RIP), were analyzed both at the protein level by flow cytometry or Western blotting, and at the mRNA level using quantitative PCR or Northern blotting in lymphocytes from aged and young subjects. The susceptibility of T cells to undergo TNF-induced apoptosis was analyzed using terminal deoxynucleotidyltransferase-mediated UTP-end-labeling (TUNEL) and DNA ladder assays. Caspase (caspase-8 and caspase-3) activation was compared between aged and young subjects using Western blotting and colorimetric assays. In lymphocytes from aged humans, there was an increased susceptibility of CD4+ and CD8+ T cells to undergo TNF-alpha-induced apoptosis, as observed by TUNEL assay and DNA fragmentation ladder assay. Increased TNF-alpha-induced apoptosis was also observed in both CD45RA+ and CD45RO+ T cells from aging subjects. An increased constitutive expression of TNFRI and TRADD and decreased expression of TNFRII and TRAF-2 were observed in lymphocytes from aged as compared with young controls. In addition, there was an early and increased activation of caspases (caspase-8 and caspase-3) involved in TNFR/TNF signaling pathway, as evident by early cleavage of caspase-8, poly(ADP-ribose) polymerase (PARP), and caspase-3 substrate DEVD-p-nitroamilide NA. These data suggest that an increased TNF-alpha-induced apoptosis may play a role in T cell deficiency associated with human aging.

Ciprofloxacin inhibits activation of latent human immunodeficiency virus type 1 in chronically infected promonocytic U1 cells

The effect of ciprofloxacin, a quinolone antibiotic widely used to treat opportunistic bacterial infections in AIDS patients, was examined in the context of reactivation of latent HIV-1 in chronically infected promonocytic U1 cells. Ciprofloxacin inhibited, in a dose-dependent manner, HIV-1 expression in U1 cells activated with phorbol 12-myristate 13-acetate (PMA). The inhibitory effect of ciprofloxacin was associated with a reduction in the production of tumor necrosis factor alpha, inhibition of activation of transcriptional factor NF-kappaB, and HIV LTR-driven gene expression. Furthermore, ciprofloxacin inhibited TNF-alpha-induced HIV expression in U1 cells. The concentrations of ciprofloxacin that inhibited HIV production are readily achievable in vivo.

Altered expression of the genes regulating apoptosis in multidrug resistant human myeloid leukemia cell lines overexpressing MDR1 or MRP gene

Development of multidrug resistance (MDR) in cancer cells is associated with an overexpression of ATP-binding cassette proteins [e.g. P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP)] and with decreased chemotherapeutic agent-induced apoptosis. In this study, we investigated whether MDR in cancer cells was associated with altered expression of genes regulating apoptosis using a drug sensitive human myeloid leukemia cell line (HL60), and its MDR sublines, overexpressing MRP (HL60/AR) or P-gp (HL60/taxol). Expression of apoptotic Genes was examined at the protein level by flow cytometry and at the mRNA level by reverse transcriptase-polymerase chain reaction (RT-PCR). We observed that the MDR cells either did not express or expressed a reduced level of the apoptosis promoters Fas, Bcl-x(s), and Bax, whereas expression of the apoptosis repressor Bcl-x, was increased. Both vincristine and anti-Fas monoclonal antibody induced apoptosis in HL60 cells but failed to do so in both MDR cell lines. These data suggest that acquired MDR in cancer cells, regardless of the type of overexpressed ABC transporter, may be associated with increased expression of antipeptidic genes and decreased expression of pro-apoptotic Genes.

Efficacy of trovafloxacin for treatment of experimental Bacteroides infection in young and senescent mice

We investigated the efficacy of trovafloxacin, a new quinolone, in comparison with that of clindamycin in the treatment of intra-abdominal abscesses caused by Bacteroides fragilis in young and senescent mice. The development of abscess formation, the number of viable organisms, and antibiotic concentrations were measured, and the values for young and old mice were compared. Trovafloxacin was well distributed to the tissues in both young and old animals. Although the pharmacokinetics and concentrations of trovafloxacin in serum were similar between young and old mice, the levels in tissue were higher in senescent mice than in young mice. Trovafloxacin therapy sterilized abscesses in 94% of young mice and in 73% of old mice, but this difference was not significant. This therapeutic response to trovafloxacin was similar to that seen with clindamycin. These results suggest that aging may not have any adverse effect on the therapeutic outcome for intra-abdominal abscesses caused by B. fragilis.

In vivo efficacy of trovafloxacin (CP-99,217), a new quinolone, in experimental intra-abdominal abscesses caused by Bacteroides fragilis and Escherichia coli

The efficacy of trovafloxacin in treating Bacteroides fragilis and Escherichia coli infections was investigated and compared to the efficacy of combined clindamycin and gentamicin therapy in an experimental model of intra-abdominal abscesses in rats. Rats were treated with different doses of CP-116,517-27, a parenteral prodrug of trovafloxacin. Response to treatment was evaluated by mortality rate and elimination of infection (cure rate). Mortality in the control group was 85.4%, whereas in rats treated with trovafloxacin, it was close to 0%. The highest cure rate (89.3%) resulted from the administration of 40 mg of CP-116,517-27 per kg of body weight three times a day (TID) for 10 days (equivalent to 18.15 mg of active drug trovafloxacin per rat per day). The therapeutic response with trovafloxacin was comparable to that of a combination therapy of clindamycin (75 mg/kg) plus gentamicin (20 mg/kg) TID (cure rate, 74%; mortality rate, 5%). The measured peak levels of trovafloxacin in serum and abscess pus were 2.6 +/- 0.3 and 5.2 micrograms/ml, respectively. The tumor necrosis factor alpha levels in the untreated animals were high compared to those for rats treated with trovafloxacin or clindamycin plus gentamicin. These results demonstrate that trovafloxacin as a single agent appears to be as successful as clindamycin plus gentamicin in the treatment of experimental intra-abdominal abscesses in rats.

Probenecid reverses multidrug resistance in multidrug resistance-associated protein-overexpressing HL60/AR and H69/AR cells but not in P-glycoprotein-overexpressing HL60/Tax and P388/ADR cells

PURPOSE

To determine whether probenecid, an inhibitor of organic anion transport, is able to reverse multidrug resistance (MDR) through modulation of the drug transport function of MDR-associated protein (MRP) and P-glycoprotein (P-gP).

METHODS

Two MRP-overexpressing cell lines (HL60/AR and H69/AR) and two P-gP-overexpressing cell lines (HL60/Tax and P388/ADR) were cultured with different concentrations of daunorubicin (DNR) or vincristine (VCR) in the presence or absence of various concentrations of probenecid (0.01-10 mM). Drug sensitivity was determined using an MTT assay. DNR accumulation and subcellular distribution were determined by flow cytometry and confocal microscopy respectively. VCR accumulation was determined by scintillation spectrometry.

RESULTS

Probenecid, in a concentration-dependent manner, reversed resistance to DNR and VCR in HL60/AR and H69/AR tumor cell lines. This effect of probenecid on MDR was associated with an increased accumulation of DNR and VCR and correction of the altered subcellular distribution of DNR. The concentrations of probenecid that reversed MDR are clinically achievable in vivo. In contrast, probenecid did not reverse MDR in either HL60/Tax or P388/ADR tumor cell lines that overexpress P-gP.

CONCLUSION

These results suggest that probenecid is an effective chemosensitizer of MRP-associated MDR tumor cells and is a potential candidate for clinical use to reverse MDR.

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.

Dioxin activates human immunodeficiency virus-1 expression in chronically infected promonocytic U1 cells by enhancing NF-kappa B activity and production of tumor necrosis factor-alpha

Dioxin, a prevalent environmental pollutant, is known to enhance replication of viruses in animals, but the mechanism is poorly understood. Here we report that dioxin triggers human immunodeficiency virus-1 (HIV-1) gene expression, resulting in increased production of HIV in chronically infected promonocytic U1 cells. This effect of dioxin is mediated, in part, via activation of nuclear factor kappa-B (NF-kappa B), a key cellular transcription factor that plays an important role in the induction of HIV genes and cytokine genes that regulate HIV-replication. Dioxin stimulated the production of tumor necrosis-alpha in U1 cells, and pentoxifylline, an inhibitor of TNF-alpha synthesis, inhibited dioxin induced HIV production and TNF-alpha. These studies provide a molecular and cellular basis for increased viral replication in cells exposed to dioxin.

Role of protein kinase C-beta isozyme in activation of latent human immunodeficiency virus type 1 in promonocytic U1 cells by phorbol-12-myristate acetate

Protein kinase C (PKC) appears to play a role in replication of human immunodeficiency virus type 1 (HIV-1). PKC is a family of at least 12 isozymes. In this study, we investigated a role of Ca(2+)-dependent PKC isozymes (alpha, beta, and gamma) in activation of latent HIV-1 in U1, a chronically infected promonocytic cell line, using polyclonal rabbit anti-PKC isozyme antibodies as specific inhibitors. Antibodies were introduced intracellularly by electroporation and then cells were stimulated with PMA. HIV-1 production was measured as p24 antigen using ELISA and reverse transcriptase activity. Anti-PKC beta antibody significantly inhibited PMA-induced HIV-1 production, whereas antibodies against PKC alpha and gamma had no significant effect. Furthermore, anti-PKC beta antibody inhibited PMA-induced activation of NF-kappa B and HIV-1 LTR. Preincubation of anti-PKC beta antibody with its antigenic peptide reversed the inhibitory effect of anti-PKC beta antibody. This study suggest that PKC beta plays a role in PMA-induced activation of latent HIV-1.

Sapphire fibers: optical attenuation and splicing techniques

The optical attenuation in sapphire fibers was examined. Attenuation was found to depend heavily on injection conditions. A number of techniques for making sapphire-silica fiber splices were attempted, with an effort toward optimizing injection conditions in the sapphire fiber. The most successful of these techniques, interior capillary-tube splicing, produced robust splices with an attenuation of less than 1 dB.

Difloxacin reverses multidrug-resistance in p388 adr cells via a mechanism independent of p-glycoprotein and without correcting drug transport or subcellular drug distribution

In this study, we have examined in vitro chemosensitizing activity of difloxacin, a quinolone antimicrobial agent, in multidrug resistant murine leukemia P388/ADR cell line that overexpresses P-glycoprotein and exhibits decreased accumulation of anthracyclines and vincristine. Difloxacin, in a concentration-dependent manner, increased the sensitivity of P388/ADR cells to daunorubicin, adriamycin and vincristine without correcting the altered drug accumulation and subcellular distribution of daunorubicin. Furthermore, difloxacin had no significant effect on intracellular accumulation of rhodamine 123 dye, a substrate for P-glycoprotein. In addition, difloxacin increased the sensitivity of drug sensitive parental P388 cells to vincristine. Taken together these data suggest that difloxacin reverses MDR by a mechanism independent of P-glycoprotein. The chemosensitizing effect of difloxacin was observed at clinically achievable plasma concentrations. These data suggest that difloxacin is an effective chemosensitizer of multidrug resistant tumor cells and is a potential candidate for clinical use to reverse MDR.

Anti-CD3-induced changes in protein kinase C isozymes expression in human CD4+ and CD8+ T lymphocytes

In order to determine whether there is a differential expression and activation of PKC isozymes between CD4+ and CD8+ T cells, peripheral blood mononuclear cells were stimulated with anti-CD3 monoclonal antibody (moAb) for various time intervals and the expression of calcium-dependent PKC isozymes (alpha, beta, gamma) and calcium-independent PKC isozymes (delta, epsilon, zeta) was analyzed with dual color flow cytometry, using anti-PKC isozyme antibodies and anti-CD4 or anti-CD8 antibodies. The basal fluorescence intensity of all PKC isozymes was comparable between CD4+ T cells and CD8+ T cells. Following activation with anti-CD3 moAb a marked increase in the fluorescence intensity of all PKC isozymes in both CD4+ and CD8+ T cells, albeit to a different extent and with different kinetics was observed. Among all PKC isozymes studied, the least striking changes were observed in PKC zeta isozyme and the most striking changes were observed in PKC-epsilon isozyme. Laser-based confocal microscopic studies confirmed that the increase in fluorescence intensity of PKC isozymes following anti-CD3 moAb stimulation, as measured by flow cytometry was accompanied by the translocation of PKC isozymes from cytosol to the plasma membrane. This study demonstrates a differential effect of anti-CD3 moAb on the expression of PKC isozymes between CD4+ and CD8+ T cells and suggests that flow cytometry can be used to study the translocation of PKC isozymes from cytosol to the plasma membrane.

beta-Endorphin enhances the replication of neurotropic human immunodeficiency virus in fetal perivascular microglia

The effect of an endogenous opiate, beta-endorphin, on the replication of HIV was investigated in brain perivascular microglia. Beta-endorphin enhanced the synthesis of p-24 antigen and transactivation of HIV promoter. Dialysed culture supernatants of endorphin-treated microglia re-activated latent HIV infection. These culture supernatants showed elevated levels of interleukin-1 beta, IL-6 and tumor necrosis factor alpha. Sub-optimal concentration of beta-endorphin potentiated GP-120-induced synthesis of these cytokines. Nalaxone reversed beta-endorphin-induced, but not GP-120-induced, cytokine production and enhanced HIV replication. These results suggest that endogenous opiates may contribute to the progression of AIDS dementia complex.

Isolation of a previously unidentified polysaccharide (MAR-10) from Hyssop officinalis that exhibits strong activity against human immunodeficiency virus type 1

A polysaccharide (MAR-10) was isolated from the aqueous extract of the plant Hyssop officinalis and examined for its activity against HIV-1 (SF strain) in HUT78 T cell line and primary cultures of peripheral blood mononuclear cells. MAR-10, in a concentration-dependent manner, inhibited HIV-1 replication as demonstrated by the inhibition of HIV-1 p24 antigen and syncytia formation. Furthermore, MAR-10 had no significant direct toxicity or effect on lymphocyte functions or CD4+ and CD8+ T cell counts. In addition, MAR-10 has broad spectrum anti-glycosidase activity. Our study demonstrates that MAR-10 contains strong anti-HIV-1 activity that may be useful in the treatment of patients with HIV-1 infection.

Role of protein kinase beta isozyme in multidrug resistance in murine leukemia P388/ADR cells

To define a role of protein kinase C (PKC) in multidrug resistance (MDR), we examined the influence of PKC isozyme specific antibodies delivered intracellularly, on drug sensitivity and drug accumulation in P388/ADR cells. Drug sensitive (P388) and drug resistant (P388/ADR) cells were permeabilized at 4 degrees C with L-lysolecithin and were incubated with rabbit anti-PKC, alpha, beta antibodies, or normal rabbit serum for 10 minutes at 37 degrees C. Daunorubicin (DNR) accumulation and drug sensitivity were studied by flow cytometry and MTT assay, respectively. Anti-PKC beta antibody partially corrected drug accumulation defect and completely reversed resistance to DNR. Anti-PKC alpha antibody had no effect on either parameter of MDR. These results suggest that PKC beta plays an important role in MDR in P388/ADR cells. Furthermore, the technique of intracellular delivery of antibodies provides a new approach to discern the role of PKC isoforms in multidrug resistance in various tumor cells.

12-Deoxyphorbol-13-O-phenylacetate 20 acetate [an agonist of protein kinase C beta 1 (PKC beta 1)] induces DNA synthesis, interleukin-2 (IL-2) production, IL-2 receptor alpha-chain (CD25) and beta-chain (CD122) expression, and translocation of PKC beta isozyme in human peripheral blood lymphocytes: evidence for a role of PKC beta 1 in human T cell activation

To determine a role of protein kinase C (PKC) isozymes in lymphocyte activation, human peripheral blood mononuclear cells were activated with 12-deoxyphorbol-13-O-phenylacetate (dPP; an agonist of both calcium-dependent and calcium-independent PKC isozymes), thymeleatoxin (TX; an activator of calcium-dependent PKC alpha, beta, and gamma), and 12-deoxyphorbol-13-O-phenylacetate 20 acetate (dPPA; an activator of PKC beta 1 isozyme) and examined for DNA synthesis, lymphocyte proliferation, interleukin-2 (IL-2) production, expression of IL-2 receptor alpha and beta chains on CD3+, CD4+, and CD8+ T lymphocytes and CD20+ B lymphocytes, and translocation of PKC beta isozyme from cytosol to membrane fraction. The results show that dPPA activates lymphocytes by inducing the above changes in a manner analogous to that of dPP, TX, and phorbol myristate acetate. These data suggest that PKC beta 1 is involved in the activation of human peripheral blood T and B lymphocytes.

Salmonella typhimurium activates human immunodeficiency virus type 1 in chronically infected promonocytic cells by inducing tumor necrosis factor-alpha production

The effect of phagocytosis of Salmonella typhimurium on human immunodeficiency virus type 1 (HIV-1) production was investigated using a chronically infected promonocytic cell line (U1) that contains HIV-1 provirus but produces little or no HIV-1. The phagocytosis of virulent S. typhimurium by U1 cells resulted in an increased HIV-1 expression as evidenced by significant increase in HIV-1 p24 antigen in culture supernatants. In contrast, heat-killed S. typhimurium failed to induce HIV-1 expression. In addition, phagocytosis of virulent S. typhimurium and not of heat-killed S. typhimurium resulted in a significant induction of tumor necrosis factor-alpha (TNF-alpha) mRNA expression and secretion of TNF-alpha by U1 cells. Furthermore, anti-TNF-alpha monoclonal antibody inhibited S. typhimurium-induced HIV-1 p24 antigen production. These data suggest that S. typhimurium induces HIV-1 expression in U1 cells via production of TNF-alpha.

Salmonella typhimurium induces expression of P glycoprotein (multidrug resistance 1 gene product) in a promonocytic cell line chronically infected with human immunodeficiency virus type 1

This investigation showed that phagocytosis of virulent Salmonella typhimurium by promonocytic leukemia cell line U1, which contains human immunodeficiency virus type 1 (HIV-1) provirus but produces minimal or no virus, and not by uninfected U937 cell line resulted in expression of a functional P glycoprotein. Anti-tumor necrosis factor-alpha (TNF alpha) monoclonal antibody failed to inhibit S. typhimurium-induced P glycoprotein expression. Furthermore, recombinant TNF alpha had no effect on the induction of P glycoprotein expression in U1 cells. These data demonstrate that phagocytosis of virulent S. typhimurium results in an induction of P glycoprotein in association with HIV-1 infection; however, TNF alpha does not appear to play a significant role. Thus, secondary microbial infection in HIV-1-positive persons may play a role in multidrug resistance against antiviral and other antimicrobial agents by an induction of P glycoprotein.

Mycobacterium tuberculosis induces expression of P-glycoprotein in promonocytic U1 cells chronically infected with HIV type 1

A productive infection with HIV-1 is associated with an increased expression of a 170 kd plasma membrane P-glycoprotein (P-gp), that functions as a metabolically active drug efflux pump, in human T and macrophage cell lines. In this investigation we show that phagocytosis of M. tuberculosis by U1 cells, that are chronically infected with HIV-1 but produce minimal or no virus, resulted in an expression of P-gp that was associated with increased production of HIV-1 p24 antigen. In addition, U1 cells that had phagocytosed M. tuberculosis accumulated significantly less intracellular isoniazid (INH) as compared to U1 cells. Furthermore, verapamil, that binds to P-gp, increased the intracellular accumulation of INH and the sensitivity of M. tuberculosis to INH. These data suggest induction of P-gp expression may be one of the host mechanisms for the development of multidrug resistant M. tuberculosis in HIV 1 infection.

Human immunodeficiency virus-1 recombinant gp120 induces changes in protein kinase C isozymes--a preliminary report

Human immunodeficiency virus 1 (HIV-1) and its purified proteins activate target cell functions. Because protein kinase C (PKC) plays a crucial role in signal transduction and there is a molecular heterogeneity of PKC, we compared the effect of recombinant HIV-1 gp120 and phorbol ester (PMA) on PKC isozymes in monocytic U937 cells, with isozyme-specific antibodies using flow cytometry. All PKC isozymes except PKC-gamma were present in U937 cells. Both PMA and HIV-1 gp120 increased levels of calcium-dependent and -independent PKC isozymes. The most striking change was observed in PKC-zeta isozymes levels. This study for the first time demonstrates that HIV-1 gp120 affects calcium-independent PKC isozymes in U937 cells.

Role of protein kinase C isozymes in activation of human immunodeficiency virus type 1 in chronically infected promonocytic cells: evidence against a role of PKC beta 1

Protein kinase C (PKC) plays an important role in activation of human immunodeficiency virus type 1 (HIV-1). Because of a molecular and biochemical heterogeneity of PKC, we have studied the effects of PKC isozymes in HIV-1 activation in a latently infected promonocytic cell line, U1, using various PKC isozyme agonists. 12-Deoxyphorbol 13-phenylacetate (dPP), an agonist of both Ca(++)-dependent and Ca(++)-independent isozymes, and thymeleatoxin (TT), an agonist of Ca(++)-dependent PKC isozymes, induced HIV-1 production at 10 nM with increase in a concentration dependent manner, whereas 12-deoxyphorbol 13-phenylacetate 20-acetate (dPPA), an PKC beta I isozyme agonist, did not induce viral production at 100 nM. We verified that dPPA induced translocation of PKC beta isozyme with the isozyme-specific monoclonal antibody using flow cytometry. This study demonstrates that activation of PKC isozymes leads to an induction of latent HIV-1 in U1 cells whereas PKC beta I isozyme may not be important.

Expression of protein-kinase-C isozymes in multidrug-resistant murine leukemia p388/adr cells

Because of a suggested role of protein kinase C (PKC) in multidrug resistance (MDR) and recent molecular cloning of PKC isozymes, we compared the expression of Ca++-dependent PKCalpha. beta and gamma, and Ca++-independent PKCdelta, epsilon, and zeta isozymes between drug sensitive murine leukemia P388 and its MDR subline P388/ADR, using qualitative and quantitative polymerase chain reaction (PCR) and Western blot techniques. The expression of PKCalpha and PKCbeta mRNA and their proteins was higher in P388/ADR as compared to P388 cells. In contrast, PKCdelta, epsilon, zeta mRNA were decreased in P388/ADR cells as compared to P388 cells. However, at the protein level the expression of PKCdelta, epsilon, and zeta was also increased in P388/ADR cells as compared to P388 cells, suggesting an increased rate of translation of PKCdelta, epsilon, and zeta isozymes in P388/ADR cells. No PKCgamma isozyme was detected by PCR and Western blot analyses. Confocal microscopic examination revealed a distinct pattern of subcellular distribution of PKCbeta isozymes in P388/ADR when compared with P388 cells. This study demonstrates the presence of altered levels of PKC isozymes in P388/ADR cells that may suggest a role of certain PKC isozymes in MDR.

Effect of Calphostin C (PKC inhibitor) on daunorubicin resistance in P388/ADR and HL60/AR cells: reversal of drug resistance possibly via P-glycoprotein

Calphostin C is a potent and specific inhibitor of protein kinase C (PKC). In this investigation we examined the effect of Calphostin C (without prior exposure to light) on daunorubicin (DNR) accumulation and sensitivity to DNR in multidrug-resistant (MDR) murine leukemia P388/ADR and human myeloid leukemia HL60/AR cells. P388/ADR cells overexpress P-glycoprotein, whereas HL60/AR cells lack any expression of P-glycoprotein (both at mRNA and protein levels). Calphostin C, in a concentration-dependent manner, increased the accumulation of DNR in P388/ADR cells and partially reversed (threefold) the DNR resistance in P388/ADR cells but had no effect on either of the parameters in HL60/AR cells. Calphostin C-induced increased accumulation of DNR in P388/ADR cells was due to increased uptake and decreased efflux of DNR. Furthermore, Calphostin C increased the uptake and decreased the efflux of rhodamine 123 (a substrate for P-gp) in P388/ADR cells but had no such effect in P388 cells. In addition, Calphostin C without exposure to light did not inhibit PKC activity in any of the cell lines studied. Taken together, these data suggest that Calphostin C may reverse drug resistance via P-glycoprotein independently of its effect on PKC activity. Therefore, any data regarding the effect of Calphostin C on the reversal of MDR should be interpreted in the light of these findings.

P-glycoprotein (MDR 1 gene product) in cells of the immune system: its possible physiologic role and alteration in aging and human immunodeficiency virus-1 (HIV-1) infection

P-glycoprotein, a 170-kd glycoprotein encoded by the MDR 1 gene, is a member of a highly conserved superfamily of ATP-binding cassette (ABC) transport proteins. It shares extensive homology with numerous bacterial and eukaryotic ABC transport proteins. P-glycoprotein acts as an energy-dependent efflux pump that appears to transport structurally diverse agents ranging from ions to peptides. P-glycoprotein (P-gP) has been implicated as playing a role in multidrug (MDR) resistance in cancer, chloroquine-resistant Plasmodium falciparum infection, and possibly human immunodeficiency virus-1 (HIV-1) resistance to nucleoside compounds. A number of normal tissues in humans and rodents have been shown to express high levels of P-gp. The expression and function of P-gp in cells of the immune system have been explored in the past 2 years. This review presents a state of the art regarding the expression, regulation, and function of Pgp in cells of the immune system. In addition, its alteration in aging and HIV-1 infection is reviewed. A possible physiologic role of P-gp in cytokine secretion, antigen processing/presentation, and effector functions is also discussed.

Preferential expression and activity of multidrug resistance gene 1 product (P-glycoprotein), a functionally active efflux pump, in human CD8 + T cells: A role in cytotoxic effector function

The multidrug resistance gene 1 (mdr 1) product, the P-glycoprotein (Pgp), is a 170-kD transmembrane transport protein, whose overexpression is associated with multidrug resistance in cancer cells and in chloroquine-resistant Plasmodium falciparum infection. In this study we show that normal freshly isolated human lymphocytes express low levels of mdr 1 mRNA and membrane Pgp. Although Pgp is expressed in both CD4+ and CD8+ T cells, it is preferentially expressed in CD8+ T cells. Activation of T lymphocytes with phytohemagglutinin leads to an amplification of both mdr 1 mRNA and membrane Pgp in T cells. P-glycoprotein in T cells is a functionally active efflux pump as demonstrated by decreased retention of rhodamine-123 and its increased accumulation by cyclosporin A, an inhibitor of Pgp function. In addition, MRK-16 antibody increased accumulation of Rh123 in CD8+ T cells. Furthermore, MRK16 anti-P-glycoprotein monoclonal antibody, in a concentration-dependent manner, inhibited T lymphocyte-mediated cytotoxicity. These data suggest a physiologic role of P-glycoprotein in cytotoxic T-lymphocyte effector function.

Lack of reversal of daunorubicin resistance in HL60/AR cells by cyclosporin A

Cyclosporin A and verapamil are substrates for P-glycoprotein. Both agents are known to reverse multidrug resistance in cells overexpressing P-glycoprotein. In this investigation, we have examined the effects of cyclosporin A and verapamil on multidrug resistance in HL60/AR cells that lack P-glycoprotein. In addition, a correlation was sought between an alteration in plasma membrane potential as measured with cationic dye DIOC5 and overexpression of P-glycoprotein. HL60/AR cells accumulated 3 fold less daunorubicin than HL60 cells. The drug accumulation defect and drug resistance in HL60/AR cells were partially corrected by verapamil and buthionine sulfoximine. However, cyclosporin A had no detectable effect on daunorubicin accumulation or drug resistance in HL60/AR cells. The multidrug resistant P338/ADR cell line overexpressed P-glycoprotein and exhibited depolarization of plasma membrane when compared to its corresponding drug sensitive parental cell line. In contrast, HL60/AR cells lacked P-glycoprotein and plasma membrane potentials were similar to those of drug sensitive HL60 cells. These results suggest that [1] verapamil modulates daunorubicin transport by a mechanism independent of P-glycoprotein, [2] the mechanisms of reversal of multidrug resistance by verapamil and cyclosporin A are distinct, and [3] the plasma membrane depolarization in multidrug resistant cell lines that overexpress P-glycoprotein, as determined by DIOC5, may be due to an increased efflux of cationic dye by P-glycoprotein, rather than a true measurement of plasma membrane potential in multidrug resistant cells.

Abnormal chloride conductance in multidrug resistant HL60/AR cells

Chloride channel currents were measured in drug sensitive parental HL60 and multidrug resistant (MDR) subline HL60/AR cells, using a whole cell patch-clamp technique. In addition, the in vitro effects of 4,4' diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), a Cl- channel blocker, on intracellular accumulation and sensitivity to daunorubicin and intracellular pH (pH(i)) in HL60 cells were examined. Baseline DIDS blockable Cl- currents were consistently lower in HL60/AR cells (0.9 pA/pF) as compared to HL60 cells (7.0 pA/pF). Similarly cAMP-activated Cl- currents were minimal in HL60/AR cells (0.2 pA/pF) as compared to HL60 cells (8 pA/pF). In vitro treatment of drug sensitive HL60 cells with DIDS resulted in concentration-dependent decreased accumulation and increased resistance to daunorubicin and decreased pH(i). These data show that altered Cl- permeability is associated with MDR and suggest that Cl- channels may play a role in MDR.