Multidrug resistance evaluation by confocal microscopy in primary urothelial cancer explant colonies

A fluorescence-based assay for monitoring clinical drug resistance

Background and aims

Multidrug resistance (MDR) limits effectiveness in treating malignancy by modifying internalisation and/or externalisation of drugs through cancer cell membranes. In this study we describe an assay to monitor patients’ responses to chemotherapy.

Methods

The assay is based on the fluorescent properties of doxorubicin alone as well as in combination with methotrexate, vinblastine, doxorubicin and cisplatin (MVAC). The slide-based cell imaging technique was first optimised using a panel of breast and urothelial cancer cell lines and then extended to fine needle breast aspiration biopsy and urine cytology.

Results

The drug fluorescence behaviour observed on smears of clinical specimens is identical to that obtained using fixed cultured cells. The fluorescence of sensitive cells to chemotherapy is mainly localised in the nucleus, whereas resistant cells show a weak fluorescence signal localised in the cytoplasm. The difference in terms of fluorescence intensity is also highlighted through fluorescence spectra.

Conclusions

The results suggest that the assay provides clinically valuable information in predicting responses to doxorubicin and/or MVAC therapy. Originally set up on a confocal microscope, the assay was also effective using a standard epifluorescence microscope; as such it is technically simple, reliable and inexpensive.

The direct effect of nuclear pores on nuclear chemotherapeutic concentration in multidrug resistant bladder cancer: the nuclear sparing phenomenon

PURPOSE

Multidrug resistance commonly limits effectiveness in treating malignancy with chemotherapy. Multidrug resistance has classically been described as a cell membrane phenomenon. Multidrug resistant cells are known to specifically exclude chemotherapy from the nucleus, resulting in lower nuclear concentrations than in the cytoplasm. This phenomenon is known as nuclear sparing and little is known of its etiology. We hypothesized that a component of the nuclear membrane, the nuclear pore, is responsible for this phenomenon.

MATERIALS AND METHODS

In this in vitro study we used the drug sensitive urothelial cancer cell line Massachusetts General Hospital urothelial 1 sensitive and its multidrug resistant subline Massachusetts General Hospital urothelial 1 resistant. After quantitative assessment of nuclear pores resistant and sensitive cells were fused using polyethylene glycol and laser scanning confocal microscopy was used to identify if drug resistant and sensitive nuclei can coexist within the same cell. The effect of inhibiting nuclear pore function using the specific pore inhibitor, wheat germ agglutinin, was assessed in whole cells using confocal microscopy and cytotoxicity assay as well as in isolated nuclei.

RESULTS

Nuclear pores appeared more numerous in multidrug resistance cells. Cell fusion experiments showed that multidrug resistance and sensitive nuclei could coexist with the same cell milieu. Wheat germ agglutinin reversed multidrug resistance in whole cells and isolated nuclei.

CONCLUSIONS

Multidrug resistance is a complex phenomenon occurring at many cellular levels, of which all may be potential therapeutic targets. The nuclear pore is involved in this process, which is to our knowledge a previously undescribed phenomenon. These experiments suggest that it may act to export drug from the nucleus, which is a process inhibited by wheat germ agglutinin.

Furosemide reverses multidrug resistance status in bladder cancer cells in vitro

BACKGROUND

Multidrug resistance (MDR) has a potentially serious influence on cancer treatment and should be taken into consideration in the design and application of therapeutic regimens. It is mediated through the activity of cellular pumps.

AIM

To investigate whether furosemide, itself a pump-blocker, reverses MDR in an in vitro model.

MATERIALS AND METHODS

An MDR bladder cancer cell line (MGH-u 1R) and its parental (drug sensitive) clone were exposed to epirubicin and furosemide, with the concentration of one drug fixed and that of the other serially diluted in a 96-well plate format. Both drugs formed the variable component in separate experiments. After a 1-h exposure, the cells were washed and replenished with fresh medium. To examine the toxicity of epirubicin and furosemide separately and in combination, monotetrazolium-based assays were carried out. Intracellular epirubicin distribution was assessed by confocal microscopy as a second index of resistance status after in vitro exposure.

RESULTS

MGH-u 1R cells incubated with furosemide showed distribution of drug similar to that in the parental cells (MGH-u 1 sensitive). Controls (without furosemide) continued to show a resistant pattern of fluorescence. In cytotoxicity assays furosemide appeared substantially non-toxic. Resistant cells in the toxicity titration experiments showed increased resistance to levels of furosemide over 500 mug/ml. Parental cells were made only marginally more sensitive against increased background toxicity.

CONCLUSION

Furosemide is effective in reversing MDR status in bladder cancer cell lines in vitro. It may also have an increment of intrinsic cytotoxicity, but only at higher concentrations. We propose a potential for further investigation of furosemide as an adjunct to chemotherapy for superficial bladder cancer.

The nuclear membrane in multidrug resistance: microinjection of epirubicin into bladder cancer cell lines

OBJECTIVE

To assess whether microinjecting epirubicin into cells showing multidrug resistance (MDR, common to many cancers, including bladder cancer, with resistance to, e.g. anthracyclines and mitomycin C) spares the nucleus, as when these drugs accumulate, distribution in MDR cells characteristically spares the nucleus, suggesting that the nuclear membrane is responsible for excluding cytotoxic drugs from MDR nuclei.

MATERIALS AND METHODS

Nuclear exclusion of drugs is an important feature of resistance in MDR cells, as many MDR-susceptible drugs have cytotoxic actions within the nucleus. Drug accumulation in 'classical' P-glycoprotein-mediated MDR cells is greatly reduced by efflux. Microinjection of epirubicin into the cytoplasm of MDR cells bypasses the P-glycoprotein efflux pump on the plasma membrane. Nuclear sparing would directly implicate the nuclear membrane in this phenomenon. Because of their fluorescence properties, which allow study by confocal microscopy and flow cytometry, anthracyclines have also been used extensively to investigate MDR. Thus sensitive (MGH-U1 and RT112) and MDR (MGH-U1R and MGH-U1-MMC) bladder cancer cell lines were used. Adherent cells from each cell line were individually microinjected with epirubicin (0.5 mg/mL) and a 77 kDa fluorescein isothiocyanate (FITC)-dextran (0.5 mg/mL). The pattern of nuclear epirubicin uptake in injected cells was then evaluated by confocal microscopy. The 77 kDa FITC-dextran allowed easier identification of injected cells and was also excluded from their nuclei.

RESULTS

Sensitive bladder cancer cell lines all showed a nuclear accumulation pattern of epirubicin, consistent with their normal uptake after exposure to epirubicin. The MDR cell lines showed the characteristic nuclear-sparing pattern of epirubicin uptake, similar to the normal uptake pattern after epirubicin exposure. The 77 kDa FITC-dextran showed clearly which cells had been microinjected, and was excluded from the nuclei of all injected cells. Cell viability was confirmed by acridine-orange staining after initial visualization of injected cells.

CONCLUSION

The nuclear membrane is responsible for the nuclear exclusion of epirubicin in MDR cells. Further work is necessary to determine the mechanisms involved.

Intravesical pH: a potentially important variable affecting efficacy and the further development of anthracycline chemotherapy for superficial bladder cancer

OBJECTIVE

To assess, using epirubicin-sensitive and multidrug resistant (MDR) derivatives of human bladder cancer cell lines in vitro, the probable effect of intravesical pH changes, with and without the MDR antagonist verapamil, on the uptake, intracellular distribution and cytotoxicity of epirubicin during intravesical chemotherapy.

MATERIALS AND METHODS

Incubations for cytotoxicity testing were carried out in buffered medium containing epirubicin, at pH values of 6.0-8.5, with verapamil where appropriate. The cytotoxicity of epirubicin, with and without verapamil, was determined using the tetrazolium cytotoxicity assay. Intracellular epirubicin fluorescence was assessed using flow cytometry and confocal microscopy. Flow cytometric total intracellular epirubicin fluorescence was measured at pH 6.0, 6.4, 6.8, 7.2, and 7.6, and confocal microscopy was carried out at pH 6.0 and 8.0. The MDR-reversing agent verapamil was added at 100 micro g/mL to some incubations.

RESULTS

Epirubicin cytotoxicity in resistant cell lines appears considerably enhanced by adding verapamil and further improved, especially in MDR cells, by alkalinization of the drug solution to pH 8.0. Flow cytometry results showed striking and consistent differences in epirubicin handling with pH. Sensitive cells can be induced to absorb considerably more drug at alkaline pH, whilst resistant cells show no such behaviour. Nuclear drug fluorescence was greater in sensitive cells at alkaline pH, but cytoplasmic drug fluorescence in the resistant cells was little changed by pH. Adding verapamil to resistant cells restored the sensitive phenotype of drug handling.

CONCLUSION

Buffering epirubicin to an alkaline pH before intravesical application should increase its intrinsic cytotoxicity. The potential for synergy at certain drug combinations will be enhanced by applying these findings. MDR reversal and fatty acid augmentation of drug uptake are discussed as examples.

A model of superficial bladder cancer using fluorescent tumour cells in an organ-culture system

OBJECTIVE

To develop a reproducible in vitro simulation of superficial bladder cancer for testing cytotoxic agents at clinically relevant concentrations.

MATERIALS AND METHODS

Square explants (5 mm) of rat bladder were cultured in Petri dishes in minimal volumes of Waymouth's MB 752/1 medium supplemented with 10% fetal calf serum, antibiotics and glutamine. Parental and resistant MGH-U1 urothelial cancer cells were transfected with a green fluorescent protein (GFP) vector. Transfectants were purified by flow cytometry. Cells were seeded onto the prepared organ cultures and images obtained using confocal microscopy. The tumour colonies were confirmed using scanning electron microscopy. Conventional intravesical cytotoxic agents including epirubicin, mitomycin-C and estramustine were tested in the system.

RESULTS

Colonies of GFP-MGH-U1 cells became established on the explants and were identified by confocal microscopy; the development of the colonies was then followed over several days. Staining the explant for viability allowed imaging of normal urothelium on the explant surface or surrounding skirt of urothelial cells. The conventional cytotoxic agents epirubicin, mitomycin C and estramustine showed the expected differential responses to parental and resistant cell types. The colonies were able to survive high concentrations of the drug, equivalent to those in clinical use. The colonies were imaged serially over a period of several days.

CONCLUSION

This system provides a more realistic model for testing cytotoxic agents for use in intravesical therapy, by allowing clinically relevant concentrations of drugs to be tested. The differential properties of the parental and resistant cells are maintained. The model also enables the same tumour colony to be imaged over several days in culture. The model may also be adapted for use in testing the effects of drugs on normal urothelium and the study of the effects of growth factors.

Epirubicin: a review of its intravesical use in superficial bladder cancer

The anthracycline epirubicin has been investigated for intravesical use in patients with superficial bladder cancer. In multicentre, randomised trials, prophylaxis with intravesical epirubicin 30 to 80 mg after transurethral resection (TUR) was more effective than no prophylaxis in the prevention of disease recurrence. Intravesical prophylaxis with epirubicin was as effective as that with equivalent dosages of doxorubicin after TUR. Data are conflicting concerning the relative efficacy of intravesical epirubicin and bacillus Calmette-Guerin (BCG) in patients at intermediate risk of recurrence after TUR, but epirubicin was less effective than BCG in those at high risk. The efficacy and tolerability of prophylaxis with epirubicin relative to that with mitomycin is not yet established. The efficacy of epirubicin as prophylaxis after TUR in combination with BCG or interferon-alpha-2b, or as treatment in patients with superficial bladder cancer has been evaluated in small, noncomparative trials, but requires clarification. Adverse events associated with intravesical epirubicin were generally mild and transient. The most common adverse events were localised to the bladder (cystitis, haematuria and urinary tract infection). Systemic adverse events (cardiac, haematological or related to hypersensitivity) were not reported in many trials of intravesical epirubicin, and when reported generally occurred in < or =5% of patients who received the drug. Intravesical epirubicin was generally tolerated as well as intravesical doxorubicin and was associated with a lower incidence of mild chemical cystitis in 1 clinical trial. The incidence of adverse events associated with intravesical epirubicin was markedly lower than that associated with intravesical BCG.

CONCLUSIONS

Intravesical epirubicin has shown efficacy in preventing disease recurrence after TUR of superficial bladder cancer. In comparison with equivalent dosages of doxorubicin, the efficacy of epirubicin for this indication is generally similar, and the tolerability profile may be more favourable. Epirubicin is less effective than BCG as intravesical prophylaxis in patients at high risk of recurrence after TUR; the relative efficacy of epirubicin and BCG after TUR in patients at intermediate risk is not yet clear. Intravesical epirubicin is generally tolerated better than BCG. Intravesical epirubicin may be used as prophylaxis after TUR in patients who are at low or intermediate risk of recurrence of superficial bladder cancer.