The development of resistance to chemotherapeutic agents is observed in the clinic, and has been studied extensively in tissue culture cells. One unusual phenotype is that of multidrug resistance, in which cells that are challenged with any one of a variety of cytotoxic drugs develop resistance not only to the selective agent but also cross-resistance to other, seemingly unrelated, compounds. This multidrug-resistant (mdr) phenotype is associated in many cases with the overproduction of a small family of membrane glycoproteins called p-glycoproteins (pgp's), which are thought to act as ATP-activated efflux pumps. Of the three family members in hamster, it is the homolog of human mdr1 (known to be overexpressed in human tumors), pgp1, that is most frequently involved with the establishment and maintenance of multidrug-resistance in tissue culture cell lines, and is the primary subject of this application. Little is known concerning the efflux mechanism supported by pgp1, the manner in which cross-resistance patterns are established, or how reversal of mdr by agents such as Verapamil and Cyclosporin A is achieved. Nor is it understood what function if any is played by the small pgp1 related RNA transcripts present in all mammalian cells. While each of these issues is of importance to pgp1 mediated mdr, it is clear that non-pgp related forms of mdr, supported by multidrug-resistance associated protein (MRP), and topoisomerase, also exist and must be accounted for if we are to extend our understanding of tumor cell drug resistance. Using a variety of recombinant DNA techniques, gene transfection assays, site directed mutagenesis, and short-term drug selection protocols we propose to 1) continue the molecular genetic study of transmembrane domain 6 in pgp1, a region that is known to mediate cross-resistance patterns and to be closely, if not directly, involved with the mechanism of Cyclosproin A reversal, 2) analyze additional naturally occurring mutants of pgp1 to further delineate its drug binding site(s) 3) determine the order of emergence of mdr mechanisms during short term selections using different antineoplastic drugs and 4) attempt to clarify the function of the 2.3kb poly (A)+ RNA transcript thought to be a splicing product of pgp1.

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National Cancer Institute (NCI)
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Experimental Therapeutics Subcommittee 1 (ET)
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University of Maryland Baltimore
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Song, J; Melera, P W (2001) Further characterization of the sixth transmembrane domain of Pgp1 by site-directed mutagenesis. Cancer Chemother Pharmacol 48:339-46
Song, J; Melera, P W (2001) Transmembrane domain (TM) 9 represents a novel site in P-glycoprotein that affects drug resistance and cooperates with TM6 to mediate [125I]iodoarylazidoprazosin labeling. Mol Pharmacol 60:254-61
Ma, J F; Grant, G; Staelens, B et al. (1999) In vitro translation of a 2.3-kb splicing variant of the hamster pgp1 gene whose presence in transfectants is associated with decreased drug resistance. Cancer Chemother Pharmacol 43:19-28
Ma, J F; Grant, G; Melera, P W (1997) Mutations in the sixth transmembrane domain of P-glycoprotein that alter the pattern of cross-resistance also alter sensitivity to cyclosporin A reversal. Mol Pharmacol 51:922-30
Devine, S E; Melera, P W (1994) Functional studies with a full-length P-glycoprotein cDNA encoded by the hamster pgp1 gene. Cancer Chemother Pharmacol 33:465-71
Devine, S E; Melera, P W (1994) Diversity of multidrug resistance in mammalian cells. J Biol Chem 269:6133-9
Hussain, A; Lewis, D; Yu, M et al. (1992) Construction of a dominant selectable marker using a novel dihydrofolate reductase. Gene 112:179-88
Hussain, A; Lewis, D; Sumbilla, C et al. (1992) Coupled expression of Ca2+ transport ATPase and a dihydrofolate reductase selectable marker in a mammalian cell system. Arch Biochem Biophys 296:539-46
Devine, S E; Hussain, A; Davide, J P et al. (1991) Full length and alternatively spliced pgp1 transcripts in multidrug-resistant Chinese hamster lung cells. J Biol Chem 266:4545-55