Increased malignant behavior in neuroblastoma cells with acquired multi-drug resistance does not depend on P-gp expression

Acquisition of P-gp-mediated multidrug-resistance does not always correlate with observed malignant behavior of NB. To characterize alterations accompanying development of multidrug-resistance in NB we established two neuroblastoma cell sublines resistant to vincristine (UKF-NB-3 r VCR 10 ) and doxorubicin (UKF-NB-3 r DOX 20 ). UKF-NB-3 r VCR 10 and UKF-NB-3 r DOX 20 overexpressed functional P-gp and developed an increased malignant phenotype: presented constitutive phosphorylation of AKT, resistance to γ-irradiation, and had increased survival in serum-free medium. Inhibition of P-gp restored chemosensitivity but did not affect increased survival in serum-free medium and sensitivity to γ-irradiation. Inhibition of AKT had no influence on chemoresistance but restored sensitivity to serum starvation. Both resistant cell lines acquired additional chromosomal changes. UKF-NB-3 r VCR 10 cells acquired a missense P53 mutation in exon 5, an increased MYCN amplification, an enhanced adhesion to endothelium, a decreased NCAM expression, a distinctly higher clonogenicity, and an increased in vivo tumorigenicity. We conclude that acquisition of increased malignant behavior in neuroblastoma occurs concomitantly with multidrug-resistance and is P-gp-independent.