Influence of IGF-I and cell density on MDR1 expression in the T-lymphoblastoid cell line CCRF-CEM

The debate about a direct or indirect effect of GH and IGF-I on the recurre nce of malignancy, especially in the case of rhGH therapy in patients with leukemia, is still going on. Recent studies suggested that IGF-I plays a ro le in drug resistance during anticancer therapy. This resistance to diverse cytotoxic drugs, named multidrug-resistance (MDR), is mainly due to high l evels of P-glycoprotein (P-gp). The gene encoding this membrane-associated transporter protein was named MDR?, and increased levels of P-gp are linked to enhanced MDR1 mRNA expression. Our aim was to investigate a possible ef fect of rhIGF-1 on MDR1 gene expression in vitro. We cultured the T-lymphob lastoid cell line CCRF-CEM with different rhIGF-I concentrations (0, 5, 20 and 50 ng/ml) in serum-free medium for 3 days. CCRF-CEM cells are drug-sens itive and express MDR1 at low levels. MDR1 mRNA expression was measured by semiquantitative RT-PCR using a competitive assay with a heterologous DNA c onstruct. In addition, GAPDH mRNA was amplified as an internal control for RNA integrity. P-gp activity was determined by a flow cytometric assay meas uring rhodamine 123 accumulation. Furthermore, cell proliferation was monit ored in all experiments. Our data do not support an effect of rhIGF-I on MD R1 mRNA expression, P-gp activity or cell proliferation in the CCRF-CEM cel l line. MDR1 mRNA levels were inversely correlated to cell density with hig h significance (p < 0.0001). In conclusion, multidrug resistance linked to P-gp is not induced by IGF-I in CCRF-CEM cells. Ar high density, CCRF-CEM c ells downregulate MDR1 gene expression. Our experimental model provides a v ery useful tool for monitoring the influence of growth factors on multidrug resistance in vitro. Copyright (C) 2000 S. Karger AG, Basel.