Comparison of daunorubicin and Fluo-3 for detection of multidrug resistance in human tumor cells.

The detection of multidrug resistance (MDR) in clinical samples is still a topic for discussion. One method, proven extremely useful for detection of membrane proteins in patients with hematological malignancies is the flow cytometrical analysis of individual tumor cells. Recently an assay was described based on the labeling of the P-glycoprotein (P-gp) with the monoclonal antibody MRK16, combined with detection of active daunorubicin (DNR) extrusion. In order to improve the specificity of the assay, on line with the results obtained by Wall et al., we exploited staining with Fluo-3. Both assays prove to be able to discriminate between drug-resistant and drug-sensitive cells. A major drawback of labeling with Fluo-3 in combination with the monoclonal antibody MRK16 is the important overlap of emission spectra of both fluorochromes. Moreover, using Fluo-3 for the detection of MDR might be complicated by the fact that differences in fluorescence intensities are not solely dependent on the presence of P-gp, but also on the activity of cytosolic esterases and the intracellular calcium concentration. Combination of the detection of structural and functional aspects of the MDR-associated protein may lead to a more precise detection of the MDR-positive patient.

[In vitro effects of piracetam on the radiosensitivity of hypoxic cells (adaptation of MTT assay to hypoxic conditions)]. / Effets in vitro du piracetam sur la radiosensibilité des cellules hypoxiques (adaptation du test au MTT aux conditions d'hypoxie).

This paper describes the adaptation of the MTT assay to hypoxic conditions in order to test the in vitro effect of piracetam on hypoxic cells and particularly on the radiosensitivity of hypoxic cells since this drug has shown clinical effect on acute and chronic hypoxia. The V79 cell line was selected by reference to preliminary hypoxic experiments using clonogenic assay and euoxic experiments using clonogenic and MTT assays. Cell growth and survival in our hypoxic conditions were assessed using MTT assay with an enclosure and special 48-well plates both made of glass. Growth curves on glass versus reference polystyrene plates were comparable and confirm the validity of using special glass plates. Growth curves on glass plates after 1-hour exposure to nitrogen versus air were comparable, so there is no bias effect due to gas composition. Survival curves using MTT versus reference clonogenic assay were comparable after radiation exposure in eu- and hypoxic conditions, and confirm the validity of our original technique for creating hypoxia. The Oxygen Enhancement Ratio was of about 3 for 1-hour hypoxic exposure. Piracetam gave no cytotoxic effect up to 10 mM of piracetam. Growth curves after continuous drug exposure and 1-hour euoxic versus hypoxic exposure gave no cytotoxic effect up to 10 mM of piracetam. Survival curves after continuous drug exposure to 10 mM of piracetam gave no significant effect on the radiosensitivity of hypoxic V79 cells using MTT or clonogenic assay. However, this does not preclude a potential in vivo effect of piracetam on the radiosensitivity owing to its action on microcirculation and its rheologic properties. The adaptation of the MTT assay to hypoxic irradiation conditions yields the easy screening of radiosensitizing drugs: shorter incubation, semi-automatic method and simultaneous analysis with different serial concentrations thanks to the special 48-well glass plates.

Cytotoxic activity of 7-N-(2-((2-(-gamma-L-glutamylamino)- ethyl)dithio)ethyl)-mitomycin C and metabolites in cell lines with different resistance patterns.

In this study the activity of KW-2149 and two of its metabolites, M-16 and M-18, was measured against cell lines with different types of resistance. The influence of these metabolites and of the exposure time on the cytotoxic efficacy of KW-2149 was investigated. Against the human ovarian carcinoma cell lines, AOvC and A2780, KW-2149 was more active than mitomycin C (MMC), with an IC50 of, respectively, 3.4 nM and 9.82 microM for KW-2149 and 18.2 nM and 67.71 microM for MMC. Activity of M-18 was significant against both cell lines and was comparable with that of KW-2149. Against an MMC-resistant cell line, AOvCMMC, the resistance factor (RF) for KW-2149 was 3.1 versus 8.0 for MMC. Tested against a cisplatin-resistant cell line, AOvCCDDP, KW-2149 had a RF of 7.7 versus 2.4 for MMC. Increasing the exposure time from 1 to 8 h decreased the RF for KW-2149 from 7.7 to 3.0. In an MDR mediated resistant cell line, A2780mdr+, prolongation of exposure time increased RF for KW-2149 and MMC but decreased RF for M-18 from 7.0 at 1 h to 5.3 at 8 h. Tested against a rat colon carcinoma cell line CC531, KW-2149 and M-18 again demonstrated superior or equal activity compared with MMC, IC50 being, respectively, 0.6, 2.1 and 2.6. Here again M-18 showed an aberrant sensitivity pattern, as its activity decreased with mdr-1 expression in contrast to the other mitomycins. Our data confirm the activity of KW-2149 as an agent with equal or superior activity as compared with MMC. It is concluded that the metabolite M-18 can contribute to the activity of KW-2149. Efficacy of both KW-2149 and its metabolites increases with increasing exposure times. The increments of exposure time appeared even as a means to overcome resistance in some instances.

Drug resistance in rat colon cancer cell lines is associated with minor changes in susceptibility to cytotoxic cells.

The development of resistance to anticancer drugs urges the search for different treatment modalities. Several investigators have reported the concomitant development of drug resistance and resistance to natural killer (NK), lymphokine-activated killer (LAK) or monocyte/macrophage cell lysis, while others described unchanged or even increased susceptibility. We investigated this subject in the rat colon carcinoma cell line, CC531-PAR, which is intrinsically multidrug-resistant (MDR), and in three sublines derived from this parental cell line: a cell line with an increased MDR phenotype (CC531-COL), a revertant line from CC531-COL (CC531-REV), which demonstrates enhanced sensitivity to anticancer drugs of the MDR phenotype, and an independently developed cisplatin-resistant line (CC531-CIS). In a 4-h 51Cr-release assay we found no difference in susceptibility to NK cell lysis. No significant differences in lysability by adherent LAK (aLAK) cells were observed in a 4-h assay. In a prolonged 20-h 51Cr-release assay an enhanced sensitivity to aLAK-cell-mediated lysis was observed in the revertant, P-glycoprotein-negative cell line and in the cisplatin-resistant cell line (CC531-CIS). None of the cell lines was completely resistant to lysis by aLAK cells. Therefore, a role for immunotherapy in the treatment of drug-resistant tumors remains a realistic option.

In vitro and in vivo chemosensitizing effect of cyclosporin A on an intrinsic multidrug-resistant rat colon tumour.

Colon tumours are intrinsically resistant to chemotherapy and most of them express the multidrug transporter P glycoprotein (Pgp). Whether this Pgp expression determines their resistance to anticancer agents in patients is not known. We report here on the reversibility of intrinsic multidrug resistance in a syngeneic, solid tumour model. CC531 is a rat colon carcinoma that expresses Pgp, as was shown with the monoclonal antibody C-219. In vitro the sensitivity to doxorubicin, daunorubicin and colchicine was enhanced by the addition of the chemosensitizers verapamil and cyclosporin A (CsA), while the sensitivity to cisplatin was not enhanced. In a daunorubicin accumulation assay verapamil and CsA enhanced the daunorubicin content of CC531 cells. In vivo CsA was injected intramuscularly for 3 consecutive days at a dose of 20 mg kg-1 day-1. This resulted in whole-blood CsA levels above 2 mumol/l, while intratumoral CsA levels amounted to 3.6 mumol/kg. In a subrenal capsule assay the maximal tolerable dose of doxorubicin (4 mg/kg) significantly reduced tumour growth. Doxorubicin at 3 mg/kg was not effective, but in combination with CsA this dose was as effective as 4 mg/kg doxorubicin. These experiments show that adequate doses of the chemosensitizing drug CsA can be obtained in vivo, resulting in increased antitumoral activity of doxorubicin in vivo. The in vitro and in vivo data together suggest that the chemosensitization by CsA is mediated by Pgp. This finding may have implications for the application of CsA and CsA-like chemosensitizers in the clinical setting.

Fluorouracil catabolism in the combination treatment of cyclophosphamide, methotrexate and fluorouracil.

The CMF-regimen is amongst the most effective chemotherapeutic approaches in the treatment of breast cancer. It is generally accepted that the efficacy of the combination of the three agents used in the regimen, i.e., cyclophosphamide (CY), methotrexate (MTX) and fluorouracil (FUra), is based on interactions between the drugs at the intratumoral level. In WAG/Rij rats we previously demonstrated that change of FUra clearance at the first day of the CMF-regimen occurs owing to concomitant CY + MTX. In the present study clearance of FUra and the first product of FUra catabolism, FUraH2, were monitored at day 1 and day 8 of the regimen upon treatment with single agent FUra (F), MTX + FUra (MF), CY + FUra (CF), and CY + MTX + FUra (CMF). At the first day of treatment, FUra and FUraH2 systemic exposure was demonstrated to be increased in CMF-treated rats owing to concomitant CY+MTX. At the eighth day of treatment it was found that repeated CY administration during the previous seven days in CF-treated rats resulted in increased FUra and FUraH2 systemic exposure and therefore increased the dose of FUra artificially. It is concluded that altered FUra clearance owing to extratumoral interactions by concomitant CY and MTX contributes to the efficacy of the CMF-regimen.

Resistance patterns between cis-diamminedichloroplatinum(II) and ionizing radiation.

Cross-resistance between cis-diamminedichloroplatinum(II) (CDDP) and radiation resistance has been suggested from clinical and experimental data (C. T. Coughlin and R. C. Richmond, Semin. Oncol., 16: 31-43, 1989). To determine whether cross-resistance patterns between both cytotoxic approaches exist, resistance against CDDP and ionizing radiation was induced separately in human ovarian cancer cells in a cross-over design. Subsequently sensitivity changes were determined for both treatment modalities. CDDP resistance was induced previously (P. J. Kuppen et al., Cancer Res., 48: 3355-3359, 1988), and resistant cells were grown at three different levels of CDDP:0 ng/ml; 250 ng/ml; and 500 ng/ml. Resistance with resistance factor (RF) 3.4 to 5.1 proved to be stable, since withdrawal of CDDP pressure for at least 6 mo did not alter resistance patterns. CDDP-resistant cells also demonstrated stable resistance against ionizing radiation, with RF ranging from 1.7 to 2.0. The resistance patterns could not be explained by differences in growth kinetics and DNA content. Resistance to ionizing radiation was induced in the same human ovarian cancer cells as used for CDDP resistance studies. Exposure with 1.5 Gy of intermittent irradiation during 6 mo, at time intervals of 48 h, resulted in cells which were able to grow under chronic ionizing radiation pressure. RF was 2.0; the resistance was lost after 6 mo of culturing without ionizing radiation pressure. With intermittent radiation doses of 0.5 and 1.0 Gy, no significant resistance could be induced. Cells intermittently exposed to 0.5, 1.0, and 1.5 Gy during 6 mo demonstrated increased sensitivity to CDDP, with 0.22 less than RF less than 0.43. Increased sensitivity was associated with proportionally increased formation of the platinum-DNA adducts. Differences in sensitivity for both ionizing radiation and CDDP were lost after 6 mo of culturing without radiation pressure; therefore, resistance toward ionizing radiation and, likewise, the increased sensitivity to CDDP, were judged to be unstable. In conclusion, data of the present study demonstrated that development of stable resistance to CDDP is associated with development of stable resistance to ionizing radiation in human ovarian cancer. Contrastingly, increased sensitivity to CDDP was found when resistance against irradiation was induced in the same cells.

Flow cytometric double labeling technique for screening of multidrug resistance.

We investigated the capabilities of flow cytometry in the analysis of a multidrug resistant (MDR) human ovarian cancer cell line 2780AD and its drug sensitive parental A2780. A functional assay using daunorubicin (DNR) as a fluorescent probe was combined with an immunofluorescence assay of P-glycoprotein (P-gp) using the monoclonal antibody MRK-16. Functionally MDR could be demonstrated by the lower DNR-content of MDR cells compared to DNR-content of drug sensitive cells. When incubation was performed with DNR in the presence of verapamil, DNR-content increased in the MDR cells. However the content of the A2780 cells was never attained. Differences in DNR-content were not related to differences in DNA-content. In experimental cell lines immunofluorescence data were inversely related with those of DNR-content: MDR cells had high levels of P-gp expression and low levels of DNR-content (and vice versa in drug sensitive cells). Both assays can be easily combined in a multiparametric flow cytometric procedure to evaluate both parameters simultaneously in the same cells. Analysis of clinical samples demonstrates the existence of aberrant subpopulations which would not be detected by using a single parameter assay.