Molecular basis of the ability of new antitumour agents - benzoperimidines and anthrapyridones - to overcome multidrug resistance.

Jolanta Tarasiuka, Barbara Stefanskaa, Katarzyna Tkaczyk-Gobisa, Arlette Garnier-Suillerotbc, Edward Borowskia

aDepartment of Pharmaceutical Technology and Biochemistry, Technical University of Gdansk, Poland; b Laboratoire de Physicochimie Biomoleculaire et Cellulaire ESA Centre National de la Recherche Scientifique 7033, Universite Paris Nord, Paris, France. c Department of Biochemistry, University of Szczecin, Poland

The ability of neoplastic cells to develop multi-drug resistance (MDR) to chemotherapeutic agents (e.g. anthracyclines, vinca alkaloids, podophylotoxins, colchicine), structurally dissimilar and having different intracellular targets, constitutes the major problem in cancer therapy. MDR is a wellcharacterized phenomenon, associated with the presence of membrane proteins belonging to the ATP-binding cassette protein family (P-glycoprotein, MRP1, c MOAT proteins). These transporters are responsible for the active ATP-dependent efflux of drugs out of resistant cells resulting in the decreased intracellular accumulation insufficient to inhibit resistant cell proliferation. The search of new compounds able to overcome multidrug resistance is of prime importance. Our approach to search for non-cross resistant antitumour agents is based on the fact that the intracellular drug concentration attainable in resistant cells depends on the difference between the kinetics of passive cellular uptake and kinetics of active ABC transporter-mediated efflux. It might be possible to design derivatives which, for the reason of their physicochemical properties, diffuse very rapidly into the cell and in such cases the protein transporter responsible for the effective drug export out of the cell essentially operates in a futile cycle. Based on this approach we have synthesized recently two families of antitumour agents: benzoperimidines and anthrapyridones, having additional six membered heterocyclic ring fused to the anthracenedione system. The interaction of these derivatives with erythroleukemia K562 sensitive and K562/DOX resistant (overexpressing P-glycoprotein) cell lines as well as with small cell lung cancer cell line GLC4 sensitive and resistant GLC4/ADR (overexpressing MRP1/LRP) has been examined. The study was performed using a spectrofluorometric method which allows to continuously follow the uptake and efflux of fluorescent molecules by living cells. It was demonstrated that benzoperimidines and anthrapyridones having hydrophobic substituents on the side chain had the very fast cellular uptake exceeding the rate of P-gp as well as MRP1 dependent efflux out of the cell. For these derivatives, very high accumulation (the same for sensitive and resistant cells) was observed and the in vitro biological data confirmed that these compounds exhibited comparable cytotoxic activity towards sensitive and P-gp and MRP1/LRP resistant cell lines. In contrast, anthrapyridones modified with hydrophylic substituents, designed in our study as a negative control, exhibited relatively low kinetics of cellular uptake. For these derivatives decreased accumulation in resistant cells was observed and the in vitro biological data demonstrated that they were much less active against P-gp resistant cells in comparison to sensitive cells. We postulate that the presence of additional heterocyclic ring (five or six membered), fused to the anthracenedione or acridine ring system, is the structural factor which extremely favours the passive diffusion of obtained derivatives across the plasma membrane. In addition, the data obtained for a series of anthrapyridones, having respectively hydrophobic or hydrophylic substituents demonstrate that the modulation of the kinetics of passive cellular uptake of anthrapyridones is much easier to perform by suitable structure modifications. The kinetics of P-gp- and MRP1 dependent - active efflux is the parameter much less susceptible to modulate by chemical modifications of antitumour agents, pointing to the similarity of the substrate spectrum of all tested compounds for ATP-dependent drug efflux pumps.

For more information, contact

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Multidrug Resistance - MDR.