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

The membrane transport properties of a series of dialkyloxacarbocyanin e [DiOC(n)(3)] dyes in multidrug-resistant KB cell lines were investig ated to determine the influence of alkyl chain length on the ability o f p-glycoprotein (i) to protect cells from the toxicity of the dyes an d (ii) to affect the plasma membrane flux of the dyes. Cytotoxicity as says revealed that increased levels of p-glycoprotein led to increased resistance to the toxicity of the DiOC(n)(3) relative to the sensitiv e KB-3-1 parent line. This resistance could be fully or partially reve rsed by 10 mu M verapamil. Monitoring of DiOC(n)(3) fluorescence chang es allowed the measurement of accumulation and efflux rates for the dy es 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 s hown 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 th ree 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 redistributio n of the dyes within the cells once they had initially passed the plas ma membrane. Fluorescence microscopy was used to show no alteration in the subcellular distribution of the DiOC(n)(3), in response to neithe r chain length nor cell line. Our results indicate that an alkyl chain length of 5 carbons is the critical length necessary for p-glycoprote in to affect membrane transport of DiOC(n)(3) but not to protect the c ells from the cytotoxicity of the dyes.