Implications for the role of the multidrug transporter P-glycoprotein in targets and effectors of interleukin-2-activated killer cells.

摘要

The objective of this thesis was the investigation of the relationship between multidrug resistance (MDR) and immune effector cell susceptibility. MDR is one of the major obstacles to successful cancer chemotherapy. MDR is a complex and multifactorial phenomenon. One important and common mechanism used by cancer cells as a defense against cytotoxic drugs is a 170-kDa plasma membrane glycoprotein, P-glycoprotein (P-gp) which confers resistance by actively pumping cytotoxic drugs out of cancer cells. The sensitivity of tumour cells to lysis by natural killer (NK) and lymphokine-activated killer (LAK) cells was studied in multidrug resistant (NMR) small cell lung carcinoma (SCLC), breast cancer, fibrosarcoma, multiple myeloma and B lymphoblastoid cells in addition to our previous work with ovarian carcinoma by 51 Chromium release and conjugate formation assays. The following observations were made: P-glycoprotein positive (P-gp+) MDR variants were lysed by human LAK cells to a greater extent than were their drug sensitive counterparts. In contrast, P-gp-, but multidrug resistance protein positive (MRP+), glutathione S-transferase-pi positive (GST+ ), or lung resistance protein positive (LRP+) variants did not exhibit an increased susceptibility to LAK cells. Differential LAK susceptibility is not due to a generalized increase in target fragility to cellular immunity, because NK sensitivity was not increased in P-gp + variants. Moreover, the P-gp+ MDR cells showed a greater frequency of effector-target binding to LAK cells than did the drug-sensitive parental line. In order to investigate the underlying mechanism of increased LAK susceptibility of P-gp+ MDR cells functional P-gp activity was assessed by flow cytometry using a natural substrate for the P-gp transporter, and P-gp function inhibitors. Both NK and LAK cells were shown to have significant P-gp efflux pump function. This activity was especially prominent in activated lymphocytes. Moreover, the P-gp content of NK, LAK and T cells, demonstrated using monoclonal antibodies (mAbs), was enhanced after incubation with interleukin-2 (IL-2). The structural and functional existence of P-glycoprotein in LAK and NK cells has possible implications in killer cell self-protection and killer cell activity against targets.; This thesis also reports the first P-gp+ chemotherapy and radiotherapy resistant malignant melanoma patient with brain metastasis in the literature, demonstrating a remarkable response to a IL-2, interferon-α (IFN), 5 fluorouracil (5FU) regimen.; These finding have implications for immunotherapy/chemotherapy/P-gp antagonist combination therapies, and for myelosuppression/immunosuppression after chemotherapy.