KINETICS OF TRANSPORT OF DIALKYLOXACARBOCYANINES IN MILTIDRUG-RESISTANT CELL-LINES OVEREXPRESSING P-GLYCOPROTEIN - INTERRELATIONSHIP OF DYE ALKYL CHAIN-LENGTH, CELLULAR FLUX, AND DRUG-RESISTANCE

The membrane transport properties of a series of dialkyloxacarbocyanine [DiOC(n)(3)] dyes in multidrug-resistant KB cell lines were investigated to determine the influence of alkyl chain length on the ability of p-glycoprotein (i) to protect cells from the toxicity of the dyes and (ii) to affect the plasma membrane flux of the dyes. Cytotoxicity assays revealed that increased levels of p-glycoprotein led to increased resistance to the toxicity of the DiOC(n)(3) relative to the sensitive KB-3-1 parent line. This resistance could be fully or partially reversed by 10 mu M verapamil. Monitoring of DiOC(n)(3) fluorescence changes allowed the measurement of accumulation and efflux rates for the dyes in the parent and two resistant cell lines at 1.5-s resolution. The flux of DiOC(n)(3) into and out of the KB85 and KBV1 cell lines was shown to be dramatically different from the parental KB-3-1 line when n < 5, while the transport properties of n = 7 were identical in the three cell lines examined. The membrane transport properties were shown not to be correlated with the 7-day toxicity of DiOC(n)(3). Verapamil affected the kinetic processes of DiOC(2-5)(3) involving redistribution of the dyes within the cells once they had initially passed the plasma membrane. Fluorescence microscopy was used to show no alteration in the subcellular distribution of the DiOC(n)(3), in response to neither chain length nor cell line. Our results indicate that an alkyl chain length of 5 carbons is the critical length necessary for p-glycoprotein to affect membrane transport of DiOC(n)(3) but not to protect the cells from the cytotoxicity of the dyes.