The mechanism whereby cells develop resistance to vincristine and other (natural product) chemotherapeutic agents including actinomycin D and adriamycin are not entirely known. Accumulated observations on our wide variety of cultured cell lines with acquired resistance to drugs has, over the years, places under scrutiny several specific areas of this research which are relevant to the study of multidrug resistance development and unique to this laboratory. While research in many laboratories has implicated P- glycoprotein (gp150-180) as a major factor, diverse characteristics of resistant cells suggest that other cell components may play supportive or modulatory roles in defining the phenotype. The areas of concentration of this proposed research are: (1) The 22kD protein sorcin (previously called V19) is overproduced by many but not all multidrug-resistant sublines. Sorcin overproduction has been shown to result from amplification of a sorcin-encoding gene tightly linked to P-glycoprotein genes. Sorcin's function, if any, in multidrug resistance and its role in normal cells will be studied. Elucidation of some of its properties may supply new information about cell function in general and facets of multidrug resistance development in particular. (2) All multidrug-resistant Chinese hamster and mouse cells in this laboratory are reverse transformed or """"""""normalized"""""""". We will ask whether this phenomenon occurs in human cells and whether it is tissue-specific. Markers for determination of state of transformation, and possibly differentiation, will be N-myc, TGF alpha, and fibronectin mRNA level nd growth in calcium-free medium and in soft agar. (3) Calcium channel blockers have been shown to override multidrug resistance and, in the case of verapamil, to displace vinblastine- bindings to gp150-180. Analysis of this phenomenon will be initiated in a study of collateral sensitivity of multidrug- resistant cells to various calcium channel blockers and study of cell which are simultaneously resistant to vincristine or actinomycin D and channel blocker. (4) Initial cytogenetic events and early expression of genes in newly emerging resistant cell populations have not been carefully studied. Such early manifestations may be relevant to clinical resistance development. In situ hybridization and cytogenetic methods with P-glycoprotein, sorcin, and N-myc probes will be used to being this study. Identification of parameters related to resistance development in the drug-treated patient is a long term goal.
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