Related Experiment Videos
Selective photodynamic inactivation of a multidrug transporter by a cationic photosensitising agent
1Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201.
Abstract:
We have characterised sites of photodamage catalysed by the cationic photosensitiser tetrabromorhodamine 123, using P388 murine leukaemia cells and a subline (P388/ADR) which has a multidrug resistance phenotype and hyperexpresses mdr1 mRNA for P-glycoprotein. Fluorescence emission spectra were consistent with sensitiser localisation in hydrophobic regions of the P388 cell, and in more aqueous loci in P388/ADR. Subsequent irradiation resulted in photodamage to the P388 cells, resulting in loss of viability. In contrast, P388/ADR cells were unaffected except for an irreversible inhibition of P-glycoprotein, leading to enhanced accumulation of daunorubicin and rhodamine 123 and a corresponding increase in daunorubicin cytotoxicity. These results are consistent with the premise that substrates for P-glycoprotein are confined to membrane loci associated with the transporter, and indicate a very limited migration of cytotoxic photo-products in a cellular environment.
Insights
Photodamage using tetrabromorhodamine 123 affected P388 cells but only inhibited P-glycoprotein in resistant cells. This suggests limited photo-product migration and P-glycoprotein substrate confinement.
Area of Science:
- Cell biology
- Photochemistry
- Pharmacology
Background:
- Multidrug resistance (MDR) in cancer is a significant clinical challenge.
- P-glycoprotein (P-gp) is a key efflux pump contributing to MDR.
- Rhodamine dyes are fluorescent probes and photosensitizers.
Purpose of the Study:
- To investigate the cellular sites of photodamage induced by tetrabromorhodamine 123.
- To determine the effect of this photosensitizer on P-glycoprotein function in drug-resistant cells.
- To explore the localization and migration of photo-induced cytotoxic products.
Main Methods:
- Utilized P388 murine leukemia cells and a multidrug-resistant subline (P388/ADR) overexpressing P-glycoprotein.
- Employed fluorescence emission spectroscopy to determine photosensitizer localization.
- Assessed cell viability and drug accumulation following photosensitization and irradiation.
Main Results:
- Tetrabromorhodamine 123 localized in hydrophobic regions of sensitive cells and aqueous loci in resistant cells.
- Irradiation caused photodamage and loss of viability in sensitive P388 cells.
- P388/ADR cells showed irreversible P-glycoprotein inhibition, increased daunorubicin accumulation, and enhanced cytotoxicity.
Conclusions:
- Photodamage is dependent on photosensitizer localization within the cell.
- P-glycoprotein substrates are confined to membrane sites associated with the transporter.
- Cytotoxic photo-products exhibit limited migration within the cellular environment.