Received for publication October 26, 2006.
Revised February 8, 2007.
Accepted for publication February 9, 2007.

Differential subcellular distribution of mitoxantrone in relation to chemosensitization in two human breast cancer cell lines

Abstract

The present work investigates the relation between cancer cell chemosensitivity and subcellular distribution, molecular interaction and metabolism of an anticancer drug. To get insights into this relation, we took advantage of the differential sensitivity of two breast cancer cell lines, MDA-MB-231 and MCF-7 to anthracyclins, along with the property of docosahexaenoic acid (DHA, 22:6n-3), to differentially enhance their cytotoxic activity. The fluorescent drug mitoxantrone (MTX) was utilized because of the possibility to study its subcellular accumulation by confocal spectral imaging (CSI). CSI allowed us to obtain semi-quantitative maps of four intracellular species: nuclear MTX bound to DNA, MTX oxidative metabolite in endoplasmic reticulum, cytosolic MTX and finally, MTX in a low polarity environment characteristic of membranes. MDA-MB-231 were found to be more sensitive to MTX (IC₅₀ = 18 nM) than MCF-7 (IC₅₀ =196 nM). According to fluorescence levels, the nuclear and cytosolic MTX content was higher in MCF-7 than in MDA-MB-231, indicating that mechanisms other than nuclear MTX accumulation account for chemosensitivity. In the cytosol, the relative proportion of oxidized MTX was higher in MDA-MB-231 (60%) than in MCF-7 (7%). DHA sensitized MDA-MB-231 (about 4 fold) but not MCF-7 cells to MTX and increased MTX accumulation by 1.5 fold in MDA-MB-231 only. The DHA-stimulated accumulation of MTX was mainly attributed to the oxidative metabolite. Antioxydant N-acetyl-cystein inhibited the DHA effect on both metabolite accumulation and cell sensitization to MTX. We conclude that drug metabolism and compartimentalization are associated with cell chemosensitization and the related cytotoxicity mechanisms may involve oxidative stress.

Key words: analytical chemistry, anticancer agents, drug efficacy, drug interactions, fatty acid metabolism, metabolite identification, oxidative stress