Cancer Chemother Pharmacol (1994) 34:109 - 118 ancer hemotherapy harmacology 9 Springer-Verlag 1994 and Cellular pharmacology of the partially non-cross-resistant anthracycline annamycin entrapped in liposomes in KB and KB-V1 cells Roman Perez-Soler 1, Yi He Ling 1, Yiyu Zou 1, Waldemar Priebe 2 1Department of Thoracic/Head and Neck Medical Oncology,The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA 2 Department of Clinical Investigation, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA Received: 27 August 1993/Accepted: 22 December 1993 Abstract. The in vitro cytotoxicity, cellular pharmacology, and DNA lesions induced by the lipophilic anthracycline annamycin (Ann) were studied in KB and KB-V1 (mul- tidrug-resistant) cells. Ann was tested in suspension in saline and 10% dimethylsulfoxide (DMSO: final con- centration, 0.05%-0.5%) or entrapped in multilamellar li- posomes (median size, 1.57 ~tm). Doxorubicin (Dox) was about twice as cytotoxic as Ann or liposome-entrapped Ann (L-Ann) against KB cells. Both Ann and L-Ann displayed a partial lack of cross-resistance with Dox (resistance in- dices: >60 for Dox, 4.7 for Ann, 4.0 for L-Ann). Accu- mulation of Ann in KB and KB-V1 cells was consistently about 2-3 and 10-20 times higher, respectively, than that of Dox. Cellular retention of Ann in KB and KB-V1 cells was about 2 and 30 times higher, respectively, than that of Dox as a result of the different efflux patterns of the two drugs: Dox was not effluxed from KB cells but was sig- nificantly effluxed from KB-V1 cells (66% at 1 h, whereas Ann efflux was similar in both cell lines (about 50% at 1 h). Dox retention in KB-V1 cells was increased by a factor of 2 in the presence of verapamil or cyclosporine A, but Ann retention was not. In addition, accumulation of Dox in KB- V1 cells was enhanced by the metabolic inhibitor deoxy- glucose/azide and the membrane carboxylic ionophore monensin, whereas accumulation of Ann was not affected by either agent. All these findings indicate significant dif- ferences in the cellular transmembrane transport systems between Dox and Ann and suggest that Ann efflux is not mediated by P-glycoprotein. Liposome entrapment reduced by a factor of 1.3-2.0 the cellular accumulation of Ann without affecting its cytotoxicity. As compared with Dox, both Ann and L-Ann induced 3 times more DNA double- and single-strand breaks in KB cells. In KB-V1 cells, Dox did not induce DNA damage, whereas the extent of DNA This work was supported in part by NIH grant CA 50270 and a grant from Argus Pharmaceuticals, Inc Correspondence to: Roman Perez-Soler, M. D., Box 80, The Uni- versity of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA breaks induced by both Ann and L-Ann was similar to that induced by Dox in KB cells. Our results indicate (1) that the lack of cross-resistance between Ann and Dox is as- sociated with a markedly enhanced accumulation and re- tention of Ann in KB-V1 cells and (2) that the type of li- posomes used does not significantly affect the cellular ef- fects of Ann. Introduction Tumor drug resistance at maximum tolerated doses remains the most important obstacle to the successful treatment of disseminated human cancer with cytotoxic therapy. Ac- quired multidrug resistance (MDR) to different natural drugs is a phenomenon that is being extensively studied and is mediated in most cases by the overexpression of a membrane energy-dependent efflux pump, P-glycoprotein, which is capable of reducing the intracellular accumulation of different and structurally unrelated antitumor agents [1, 2]. The precise mechanism of drug efflux is not known, but direct drug binding to P-glycoprotein has been suggested. Recent studies suggest that overexpression of P-glycopro- rein may be a clinically relevant mechanism of resistance in several human malignances such as leukemia, lymphoma, and breast carcinoma and an independent adverse prog- nostic factor in diseases such as childhood neuroblastoma or soft-tissue sarcoma [3, 4]. Different ways of overcoming MDR have been explored and have proved to be effective at least in in vitro systems, including the use of modulators that can inhibit drug efflux mediated by P-glycoprotein [5]. The preparation of struc- turally different analogs of MDR drugs with decreased interaction with P-glycoprotein or other drug-efflux me- chanisms constitutes an alternative approach. In the case of anthracyclines, several analogs with a lack of cross-re- sistance properties have been reported during the last few years [6-141.