The Role of Intercellular Communication in Cytotoxic Drug Resistance

Bradley, Christopher (1992) The Role of Intercellular Communication in Cytotoxic Drug Resistance. MD thesis, University of Glasgow.

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The gap junction is an array of channels spanning the two membranes of adjacent cells and linking their cytoplasms. The aim of this thesis was to examine the role which intercellular communication through gap junctions might play in the development of cytotoxic drug resistance. Increased junctional communication has been associated with resistance to radiation and to cytotoxic lymphokines. The explanation for this phenomenon is not clear, although it is possible that sharing of metabolic pools between coupled cells may allow them to withstand damage more effectively than isolated cells. To investigate whether this relationship between communication and resistance is a generalised one, applicable to conventional cytotoxic drugs, the strength of coupling of a panel of seven human NSCLC cell lines was measured and compared with the chemosensitivity of these lines to adriamycin. Communication was assessed by autoradiographic detection of transfer of 3H uridine nucleotides between cells. The strength of coupling varied widely between the cell lines and they could be separated into three groups: those which exhibit strong coupling, L-DAN and A549; those which exhibit weak coupling, SK-MES-1, Calu-3 and NCI- H125; and an intermediate group, WIL and NCI-H23. Adriamycin chemosensitivity of each cell line was assessed in monolayer by both clonogenic and MTT assays. The range of IC50 values as measured by either assay was extremely narrow with no important differences between the cell lines. Thus, despite the wide spectrum of junctional communication observed in these lines, this did not correlate with their adriamycin resistance. Chemosensitivity of three dimensional spheroids of L-DAN and SK-MES-1 was also assessed by clonogenic assay but again this was not related to their communication. Interaction between drug sensitive and resistant cell lines has been demonstrated in mixed culture. Nitrosourea resistance is transferred between cells in spheroids and ouabain resistance is transferred in monolayer culture by the rapid diffusion of K+ and Na+ ions through gap junctions. The membrane pumps in the ouabain resistant cells maintain physiological ion concentrations in the cytoplasms of both cell types. It seems possible, therefore, that other forms of drug resistance which are dependent on the cytoplasmic concentration of small ions or molecules should be transferred between cells joined by gap junctions. The MDR phenotype has been related to the presence of a membrane pump, P-glycoprotein, which reduces intracellular drug concentration. The behaviour of normal (CHO-Kl), resistant (Adrr) and hypersensitive (ADR-6) Chinese hamster cell lines which have been shown to exhibit junctional communication was examined in mixed culture. The CHO-Kl cells were genetically marked by transfection with a bacterial ?-galactosidase gene. Its enzyme produces a blue product with appropiate substrate and allows identification of the individual response of two cell types in mixed culture. Clonogenic assays were performed after exposure of mixed monolayer or spheroid culture to either adriamycin, mitozantrone or vincristine. In individual assays Adrr is xl00 more resistant to adriamycin and x20 more resistant to mitozantrone than CHO-Kl, whereas ADR-6 is x2 more sensitive to vincristine. However, in mixed culture, the chemosensitivities of the cell lines were unchanged with no evidence of resistance transfer in this system.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Additional Information: Adviser: John Pitts
Keywords: Medicine, Oncology, Pharmacology
Date of Award: 1992
Depositing User: Enlighten Team
Unique ID: glathesis:1992-74724
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 16:58
Last Modified: 27 Sep 2019 16:58

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