Johnson M R, Hageboutros A, Wang K, High L, Smith J B, Diasio R B
Department of Pharmacology and Toxicology and Comprehensive Cancer Center, University of Alabama at Birmingham, 35294, USA.
Clin Cancer Res. 1999 Aug;5(8):2006-11.
In humans, 80-90% of an administered dose of 5-fluorouracil (5-FU) is degraded by dihydropyrimidine dehydrogenase (DPD; EC 1.3.1.2), the initial rate-limiting enzyme in pyrimidine catabolism. Cancer patients with decreased DPD activity are at increased risk for severe toxicity including diarrhea, stomatitis, mucositis, myelosuppression, neurotoxicity, and, in some cases, death. We now report the first known cancer patient who developed life-threatening complications after treatment with topical 5-FU and was shown subsequently to have profound DPD deficiency. RT-PCR and genomic PCR methodologies were used to identify a G to A mutation in the GT 5' splicing recognition sequence of intron 14, resulting in a 165-bp deletion (corresponding to exon 14) in this patient's DPD mRNA. Immunoprecipitation and Western blot analysis were then used to demonstrate that the aberrant DPD mRNA is translated into a nonfunctional DPD protein that is ubiquitinated. We conclude that the presence of this metabolic defect combined with topical 5-FU (a drug demonstrating a narrow therapeutic index) results in the unusual presentation of life-threatening toxicity after treatment with a topical drug. These data further suggest that degradation by the ubiquitin-proteosome-mediated system plays a role in the elimination of the DPD protein.
在人类中，给予的5-氟尿嘧啶（5-FU）剂量的80-90%会被二氢嘧啶脱氢酶（DPD；EC 1.3.1.2）降解，DPD是嘧啶分解代谢中的初始限速酶。DPD活性降低的癌症患者发生严重毒性反应的风险增加，包括腹泻、口腔炎、粘膜炎、骨髓抑制、神经毒性，在某些情况下甚至会死亡。我们现在报告首例已知的癌症患者，该患者在局部使用5-FU治疗后出现危及生命的并发症，随后被证明存在严重的DPD缺乏。采用逆转录聚合酶链反应（RT-PCR）和基因组聚合酶链反应（genomic PCR）方法，在第14内含子的GT 5'剪接识别序列中鉴定出一个从G到A的突变，导致该患者DPD mRNA出现165 bp的缺失（对应于第14外显子）。然后通过免疫沉淀和蛋白质印迹分析证明，异常的DPD mRNA被翻译成一种无功能的、被泛素化的DPD蛋白。我们得出结论，这种代谢缺陷与局部使用5-FU（一种治疗指数较窄的药物）相结合，导致局部用药后出现危及生命的毒性这一不寻常表现。这些数据进一步表明，泛素-蛋白酶体介导的系统降解在DPD蛋白的清除中发挥作用。
