MULTIENZYME-MEDIATED STABLE AND TRANSIENT MULTIDRUG-RESISTANCE AND COLLATERAL SENSITIVITY INDUCED BY XENOBIOTICS

Background: Determinants of cellular sensitivity to anticancer drugs i nclude enzymes that catalyze their biotransformation. Coordinated indu ction of some of these enzymes is known to be caused by a number of di etary constituents, environmental contaminants, pharmacological agents and other xenobiotics, e.g. 3-methylcholanthrene and catechol. Despit e the potential for inducing simultaneous changes in tumor cell sensit ivity to a wide range of drugs, scant attention has been paid to the i mpact that dietary constituents and other xenobiotics might have on th e therapeutic outcome of cancer chemotherapy. Purpose: The aim of this investigation was to demonstrate the potential of xenobiotic-induced multienzyme-mediated stable and transient multidrug resistance/collate ral sensitivity in a model system. Methods: Human breast adenocarcinom a MCF-7/0 cells and a stably oxazaphosphorine-resistant subline thereo f, MCF-7/OAP, were grown in the presence of 3-methylcholanthrene (3 mu M), catechol (30 mu M), or vehicle for 5 days. Spectrophotometric and spectrofluorometric assays were used to quantify catalytic activities and thus cellular levels of cytosolic class 3 aldehyde dehydrogenase, glutathione S-transferase, DT-diaphorase, UDP-glucuronosyl transferas e and cytochrome P450 1A1. A colony-forming assay was used to quantify cellular sensitivities to several anticancer drugs. Results: Relative to their untreated counterparts, MCF-7/0 and MCF-7/OAP cells treated with 3-methylcholanthrene or catechol transiently expressed elevated l evels of cytosolic class 3 aldehyde dehydrogenase, glutathione S-trans ferase. DT-diaphorase and UDP-glucuronosyl transferase, and were trans iently, more resistant to mafosfamide, melphalan, and mitoxantrone, an d more sensitive to EO9. Further, MCF-7/0 and MCF-7/OAP cells treated with 3-methylcholanthrene, but not those treated with catechol, transi ently expressed elevated levels of cytochrome P450 1A1 and were transi ently more sensitive to ellipticine. Relative to MCF-7/0 cells, MCF-7/ OAP cells stably overexpressed all but cytochrome P450 1A1 and were st ably, more resistant to mafosfamide, melphalan and mitoxantrone, and m ore sensitive to EO9. Inclusion of relatively specific inhibitors of, or alternative substrates for, the enzymes of interest during drug exp osure negated the influence of enzyme overexpression on cellular sensi tivities to these agents. Untreated, and 3-methylcholanthrene- or cate chol-treated, MCF-7/0 and MCF-7/OAP cells were equisensitive to vincri stine and nearly so to doxorubicin. Conclusions: Collectively, these e xperiments illustrate the potential for both stable and transient xeno biotic-induced multienzyme-mediated multidrug resistance/collateral se nsitivity that, although also the result of a single event, is mechani stically different from, and pertains to a largely different group of anticancer agents than does, the multidrug resistance caused by cell s urface multidrug transporters.