Guo W, Healey J H, Meyers P A, Ladanyi M, Huvos A G, Bertino J R, Gorlick R
Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Clin Cancer Res. 1999 Mar;5(3):621-7.
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.
大剂量甲氨蝶呤是目前骨肉瘤治疗方案的主要组成部分，但有些肿瘤似乎具有耐药性。潜在的耐药机制包括通过还原型叶酸载体（RFC）的转运减少以及二氢叶酸还原酶（DHFR）表达增加。为了研究甲氨蝶呤耐药性，从42例高级别骨肉瘤患者获取肿瘤组织。通过半定量逆转录 - PCR研究RFC和DHFR mRNA表达。通过Southern印迹研究RFC和DHFR基因的缺失和扩增情况。在20例骨肉瘤样本中，有13例（65%）在初次活检时发现RFC表达降低。在根治性手术和复发时，22例中有10例（45%）发现RFC表达降低。对化疗反应不佳的26例样本中有17例（65%）RFC表达降低，而反应良好的14例样本中有5例（36%）表达降低（P = 0.03）。所有样本均未出现RFC基因缺失。20例样本中有2例（10%）在初次活检时显示DHFR表达增加。在转移性或复发性肿瘤中，DHFR表达增加的频率显著更高（62%，P = 0.014）。所有样本均未显示DHFR基因扩增的证据。活检材料中RFC表达降低的高频率表明，甲氨蝶呤转运受损是骨肉瘤固有耐药的常见机制。肺转移灶中DHFR表达增加可能是获得性甲氨蝶呤耐药的机制或原发性和转移性病变之间的差异。
