CHANGES IN DOXORUBICIN DISTRIBUTION AND TOXICITY IN MICE PRETREATED WITH THE CYCLOSPORINE ANALOG SDZ-PSC-833

SDZ PSC 833 (PSC 833) is a cyclosporin A analogue that is under clinical investigation in combination with doxorubicin (Dr) or other anticancer agents as a type-1 multidrug resistance (MDR-1)-reversing agent. The present study was focused on the effects of PSC 833 on the distribution and toxicity of Dr in non-tumor-bearing CDF1 male mice. Mice were given PSC 833 i.p. at 30 min before i.v. Dr treatment. Dr levels were determined by a high-performance liquid chromatography (HPLC) assay at different times during a 72-h period following Dr treatment in the serum, heart, intestine, liver, kidney, and adrenals of mice. In all tissues, Dr area under the concentration-time curve (AUG) values were much greater in mice receiving 10 mg/kg Dr in combination with 12.5 or 25 mg/kg PSC 833 than in mice receiving Dr alone. The highest increase in Dr concentrations was found in the intestine, liver, kidney, and adrenals. Lower, albeit significant, differences were found in the heart. PSC 833 did not appear to influence either urinary or fecal Dr elimination or Dr metabolism to a great extent. Doses of PSC 833 devoid of any toxicity potentiated the acute and delayed toxicity of Dr dramatically. The mechanism responsible for this enhanced toxicity has not yet been elucidated but is likely to be related to an increased tissue retention of Dr due to inhibition of the P-glycoprotein (Pgp) pump by PSC 833, as has recently been proposed for cyclosporin A.