A similar strong association has been observed between the expression of P-glycoprotein and outcome of treatment in certain malignancies in children, such as neuroblastoma, rhabdomyosarcoma, and acute lymphoblastic leukemia.
The results indicate that the level of MDR1 mRNA expression is associated with previous chemotherapy, including drugs that select the multidrug resistance phenotype in vitro regardless of neuroblastoma tissue origin or N-myc content in the genome.
Because expression of mdr-1 is increased in neuroblastoma cell lines by differentiating agents, the authors hypothesized a similar correlation with differentiation in vivo in neuroblastomas.
Many of the neuroblastoma samples were also evaluated for N-myc amplification but there was no correlation between N-myc copy number and the level of MDR1 mRNA expression.
Decreased expression of the N-myc oncogene in neuroblastoma cell lines SH-SY5Y and BE(2)-C, following treatment with retinoic acid, was paralleled by down-regulation of MRP gene expression, contrasting with increased expression of the MDR1 gene.