Mechanisms of resistance to chemosensitizers in a multidrug resistant human multiple myeloma cell line.

Persistent Link:
http://hdl.handle.net/10150/187140
Title:
Mechanisms of resistance to chemosensitizers in a multidrug resistant human multiple myeloma cell line.
Author:
Abbaszadegan, Mohammad Reza.
Issue Date:
1995
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Tumor cells in cancer patients acquire drug resistance as a result of chemotherapy. One type of acquired drug resistance is multidrug resistance (MDR) caused by the overexpression of P-glycoprotein, a transmembrane efflux protein. Inhibitors of P-glycoprotein or chemosensitizers such as verapamil are used to reverse MDR in cancer patients. Clinical studies have shown that some patients with P-glycoprotein positive cancer cells respond to the chemosensitizing effect of verapamil. However, this response is short lived and tumor cells become resistant to chemosensitizers. In order to study the mechanism of resistance to chemosensitizers, a human myeloma cell line, 8226/MDR₁₀V, was selected from a P-glycoprotein positive cell line, 8226/Dox₄₀, in the continuous presence of doxorubicin and verapamil. MDR₁₀V cells are consistently more resistant to MDR drugs than the parent cells, Dox₄₀. Chemosensitizers were less effective in reversing resistance in the MDR₁₀V compared to D0X₄₀ cells. Despite higher resistance to cytotoxic agents, MDR₁₀V expresses less P-glycoprotein in the plasma membrane compared to Dox₄₀. However, total cellular P-glycoprotein was the same in both cell lines suggesting a relocation of P-glycoprotein from plasma membrane into cytoplasm. Confocal immunofluorescence microscopy showed 2.5X more P-glycoprotein in the cytoplasm of MDR₁₀V cells as compared to D0X₄₀ cells. The relocation of P-glycoprotein was associated with a redistribution of doxorubicin. In D0X40 cells, doxorubicin was concentrated in the nucleus, whereas in MDR₁₀V cells, 90% of doxorubicin was found in the cytoplasm. We hypothesized that P-glycoprotein trafficking from the endoplasmic reticulum to the plasma membrane may be interrupted resulting in a higher concentration in the cytoplasm. To test this hypothesis, endoglycosidase H sensitivity of newly sensitized P-glycoprotein was examined. Medial Golgi processing of P-glycoprotein was identical between the two cell lines and the N-glycosylation of P-glycoprotein was complete by 3 hours. No mutations were found in MDR1 cDNA from MDR₁₀V cells compared to Dox₄₀ cells. These results suggest that increased resistance to cytotoxic drugs and chemosensitizers is associated with an altered intracellular location of P-glycoprotein which in turn causes a redistribution of doxorubicin.
Type:
text; Dissertation-Reproduction (electronic)
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Pharmacology and Toxicology; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Dalton, William

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleMechanisms of resistance to chemosensitizers in a multidrug resistant human multiple myeloma cell line.en_US
dc.creatorAbbaszadegan, Mohammad Reza.en_US
dc.contributor.authorAbbaszadegan, Mohammad Reza.en_US
dc.date.issued1995en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractTumor cells in cancer patients acquire drug resistance as a result of chemotherapy. One type of acquired drug resistance is multidrug resistance (MDR) caused by the overexpression of P-glycoprotein, a transmembrane efflux protein. Inhibitors of P-glycoprotein or chemosensitizers such as verapamil are used to reverse MDR in cancer patients. Clinical studies have shown that some patients with P-glycoprotein positive cancer cells respond to the chemosensitizing effect of verapamil. However, this response is short lived and tumor cells become resistant to chemosensitizers. In order to study the mechanism of resistance to chemosensitizers, a human myeloma cell line, 8226/MDR₁₀V, was selected from a P-glycoprotein positive cell line, 8226/Dox₄₀, in the continuous presence of doxorubicin and verapamil. MDR₁₀V cells are consistently more resistant to MDR drugs than the parent cells, Dox₄₀. Chemosensitizers were less effective in reversing resistance in the MDR₁₀V compared to D0X₄₀ cells. Despite higher resistance to cytotoxic agents, MDR₁₀V expresses less P-glycoprotein in the plasma membrane compared to Dox₄₀. However, total cellular P-glycoprotein was the same in both cell lines suggesting a relocation of P-glycoprotein from plasma membrane into cytoplasm. Confocal immunofluorescence microscopy showed 2.5X more P-glycoprotein in the cytoplasm of MDR₁₀V cells as compared to D0X₄₀ cells. The relocation of P-glycoprotein was associated with a redistribution of doxorubicin. In D0X40 cells, doxorubicin was concentrated in the nucleus, whereas in MDR₁₀V cells, 90% of doxorubicin was found in the cytoplasm. We hypothesized that P-glycoprotein trafficking from the endoplasmic reticulum to the plasma membrane may be interrupted resulting in a higher concentration in the cytoplasm. To test this hypothesis, endoglycosidase H sensitivity of newly sensitized P-glycoprotein was examined. Medial Golgi processing of P-glycoprotein was identical between the two cell lines and the N-glycosylation of P-glycoprotein was complete by 3 hours. No mutations were found in MDR1 cDNA from MDR₁₀V cells compared to Dox₄₀ cells. These results suggest that increased resistance to cytotoxic drugs and chemosensitizers is associated with an altered intracellular location of P-glycoprotein which in turn causes a redistribution of doxorubicin.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePharmacology and Toxicologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairDalton, Williamen_US
dc.contributor.committeememberDorr, Robert T.en_US
dc.contributor.committeememberBernstein, Harrisen_US
dc.contributor.committeememberSipes, I. Glennen_US
dc.contributor.committeememberHalonen, Marilyn J.en_US
dc.identifier.proquest9531160en_US
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