Multidrug resistance-1 gene expression does not increase during tumor progression in the MGH-OGS murine osteosarcoma tumor model

In addition to its possible role in drug resistance, expression of the mult idrug resistance-1 gene may also be associated with a more malignant phenot ype and tumor progression. This study evaluated its expression during tumor progression in the MGH-OGS transplantable murine osteosarcoma tumor model. Three variables of tumor progression were analyzed: tumor size, local recu rrence, and metastasis. With a highly sensitive reverse transcription-polym erase chain reaction method, mRNA levels of multidrug resistance-1 were com pared in primary tumors of different sizes. In addition, the levels were co mpared in primary, locally recurrent, and metastatic tumors isolated from i ndividual mice. No significant difference was found in the levels of expres sion with increasing primary tumor size. In addition, the levels in primary , locally recurrent, and metastatic tumors were not significantly different . Our results indicate that-at least in the MGH-OGS tumor model, which is a nalogous to the majority of spontaneously occurring human osteosarcomas in that it has low levels of multidrug resistance-1/P-glycoprotein and is sens itive to doxorubicin-there is no evidence of upregulation of multidrug resi stance-1 expression during tumor progression.