Do glutathione and related enzymes play a role in drug resistance in small cell lung cancer cell lines?

Bg Campling,K Baer,Sp Cole,Hm Baker,Y-M Lam

doi:10.1038/bjc.1993.336

Abstract

Small cell lung cancer (SCLC) is treated primarily with combination chemotherapy. Despite high initial response rates, most patients eventually die with drug resistant disease. In some tumours, resistance to multiple chemotherapeutic agents is attributed to overexpression of P-glycoprotein (P-gp). However, this does not appear to be a frequent occurrence in drug resistant SCLC. Increased levels of glutathione (GSH) and related enzymes may play a role in resistance to alkylating agents as well as natural product drugs. We measured levels of GSH, glutathione S-transferase (GST), glutathione reductase (GSH Red), glutathione peroxidase (GSH Px), and gamma-glutamyl transpeptidase (gamma-GT) in a panel of 20 SCLC cell lines. Most of these lines were established from patients treated at this centre. Each cell line had a characteristic and reproducible profile of GSH and related enzyme levels. Immunoblot analysis indicated that the predominant GST in the cell lines was the anionic pi isoenzyme. The relative sensitivity of each of these cell lines to 16 different chemotherapeutic agents was measured using a modified MTT assay. Spearman rank correlation analysis was used to determine the relationships between the relative chemosensitivity of these cell lines and the levels of GSH and related enzymes. The number of positive correlations was no greater than expected by chance alone. Furthermore, there was no correlation with the treatment history of the patients from whom the cell lines were derived. These data suggest that alterations in glutathione metabolism do not play a major role in resistance to chemotherapeutic agents in these human SCLC cell lines.

Highlights

Despite impressive initial responses to chemotherapy, the majority of patients eventually succumb to their disease, and the major reason for treatment failure is the acquisition of resistance to multiple chemotherapeutic agents
NADPH, oxidised and reduced GSH, GSH glutathione reductase (Red), DTNB, CDNB, rat liver and human placental glutathione S-transferase (GST), cumene hydroperoxide, bovine serum albumin (BSA), goat anti-rabbit IgG alkaline phosphatase conjugate, hydrocortisone, insulin, transferrin, estradiol, sodium selenite, and '-GT kit were purchased from Sigma
The results are expressed as area under the dose response curve, calculated using the trapezoidal method as described (Lam et al, 1990)

Summary

Introduction

Despite impressive initial responses to chemotherapy, the majority of patients eventually succumb to their disease, and the major reason for treatment failure is the acquisition of resistance to multiple chemotherapeutic agents (multidrug resistance). The most frequently described alteration in multidrug resistant cells of various tumour types is the overexpression of a plasma membrane protein, termed P-glycoprotein (P-gp), which serves to actively export drugs from cells (Bradley et al, 1988). P-glycoprotein overexpression has been detected in some multidrug resistant SCLC lines (Reeve et al, 1989; Minato et al, 1990), other multidrug resistant SCLC cell lines do not overexpress this drug efflux pump (Mirski et al, 1987; Cole et al, 1991; de Jong et al, 1990; Nygren et al, 1991). Studies of large numbers of SCLC cell lines and clinical samples indicate that P-gp overexpression does not occur frequently in this disease (Lai et al, 1989; Noonan et al, 1990; Milroy et al, 1992). There has been interest in other potential mechanisms of multidrug resistance in SCLC

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