Cytotoxicity and Adjuvant Activity of Cationic Photosensitizers in a Multidrug Resistant Cell Line

Abstract

The toxicities and phototoxicities of methylene blue (MB), toluidine blue O (TBO) and Victoria blue BO (VBBO) in a murine mammary tumour cell line (EMT6-S) and a multidrug resistant (MDR) sub-line (EMT6-R) were measured and their efficacy against the resistant sub-line was compared to that of doxorubicin and cis-platinum. The MDR cell line was considerably more susceptible to VBBO than to the conventional agent doxorubicin. VBBO was also pho-totoxic whereas illumination did not alter the activity of doxorubicin or of cis-platin. Both TBO and MB showed limited light activation (2-fold) in both the sensitive and resistant cell lines.Pre-treatment with VBBO prior to exposure to doxorubicin caused a twofold increase in doxorubicin toxicity in both cell lines. MB and TBO, however, increased doxorubicin toxicity in EMT6-R cells ×2 and ×3 respectively, but had less effect on the sensitive cell line (increase ×l.4 and ×2 respectively). Thus MB and TBO may act on the MDR cell line via a different mechanism to that of VBBO.