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Cellular daunomycin fluorescence in multidrug resistant 2780AD cells and its relation to cellular drug localisation
J Lankelma1, H S Mülder, F van Mourik
1Department of Oncology, Free University Hospital, Amsterdam, The Netherlands.
Abstract:
Multidrug resistant (MDR) 2780AD human ovarian carcinoma cells were loaded with the fluorescent anticancer agent daunomycin (DN). Fluorescence anisotropy was lower than for corresponding A2780 wild-type cells, indicating that DN was less rigidly bound than in the wild-type cells. Average fluorescence quenching of DN was lower for 2780AD cells. Data were fitted into a model with a highly quenched fraction (fraction A), corresponding to DN intercalated in DNA, and an unquenched fraction (fraction B). The ratio A/B was one order of magnitude lower for the MDR cells than for the wild-type cells. Two other MDR cell lines were investigated and low A/B ratios were found in both cases. Thus, evidence has been provided that in MDR cells the DNA-bound fraction is relatively low and that more free DN is present, for example in acidic vesicles.
Insights
Multidrug resistant ovarian cancer cells show less daunomycin (DN) bound to DNA. This suggests more free drug is available in resistant cells, potentially impacting treatment strategies.
Area of Science:
- Pharmacology
- Cell Biology
- Biophysics
Background:
- Multidrug resistance (MDR) in cancer limits therapeutic efficacy.
- Daunomycin (DN) is a fluorescent anticancer agent that intercalates into DNA.
Purpose of the Study:
- To investigate the binding characteristics of daunomycin in multidrug resistant (MDR) human ovarian carcinoma cells compared to wild-type cells.
- To quantify the fraction of daunomycin bound to DNA versus free drug in MDR cells.
Main Methods:
- Loading MDR (2780AD) and wild-type (A2780) ovarian carcinoma cells with fluorescent daunomycin.
- Measuring fluorescence anisotropy and quenching to assess drug binding.
- Fitting data to a model distinguishing DNA-bound (fraction A) and unquenched (fraction B) daunomycin.
Main Results:
- Lower fluorescence anisotropy in MDR cells indicated less rigid binding of daunomycin.
- Average fluorescence quenching of daunomycin was reduced in MDR cells.
- The ratio of DNA-bound to free daunomycin (A/B) was significantly lower (by one order of magnitude) in MDR cells compared to wild-type cells.
- Similar low A/B ratios were observed in two additional MDR cell lines.
Conclusions:
- Multidrug resistant ovarian cancer cells exhibit a reduced fraction of daunomycin bound to DNA.
- A higher proportion of free daunomycin is present in MDR cells, possibly sequestered in cellular compartments like acidic vesicles.
- These findings provide evidence for altered drug distribution in MDR cells, which may have implications for drug efficacy and resistance mechanisms.