| Abstract: |
High-dose methotrexate is a major component of current protocols for the treatment of osteosarcoma, but some tumors seem to be resistant. Potential mechanisms of resistance include decreased transport through the reduced folate carrier (RFC) and increased expression of dihydrofolate reductase (DHFR). To investigate methotrexate resistance, tumors were obtained from 42 patients with high-grade osteosarcoma. RFC and DHFR mRNA expression were studied by semiquantitative reverse transcription-PCR. The RFC and DHFR genes were studied for deletions and amplification by Southern blot. Thirteen of 20 (65%) osteosarcoma samples were found to have decreased RFC expression at the time of initial biopsy. At definitive surgery and relapse, 10 of 22 (45%) were found to have decreased RFC expression. Seventeen of 26 (65%) samples with a poor response to chemotherapy had decreased RFC expression, whereas 5 of 14 (36%) samples with a good response had a decrease (P = 0.03). None of the samples had an RFC gene deletion. Two of 20 samples (10%) showed increased DHFR expression at initial biopsy. The frequency of increased DHFR expression was significantly higher in metastatic or recurrent tumors (62%, P = 0.014). None of the samples showed evidence of DHFR gene amplification. The high frequency of decreased RFC expression in the biopsy material suggests that impaired transport of methotrexate is a common mechanism of intrinsic resistance in osteosarcoma. Increased DHFR expression in the pulmonary metastases may be a mechanism of acquired methotrexate resistance or a difference between primary and metastatic lesions. |
| Keywords: |
osteosarcoma; adolescent; adult; child; clinical article; human tissue; protein expression; aged; middle aged; excision; gene deletion; methotrexate; reverse transcription polymerase chain reaction; gene amplification; antimetabolites, antineoplastic; membrane proteins; drug resistance, neoplasm; gene expression regulation, neoplastic; bone marrow biopsy; rna, messenger; folinic acid; carrier proteins; folic acid; dihydrofolate reductase; tetrahydrofolate dehydrogenase; biological transport; southern blotting; trimetrexate; membrane transport proteins; blotting, southern; humans; human; male; female; priority journal; article
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