Meyer W H, Loftin S K, Houghton J A, Houghton P J
Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, TN 38105.
Cancer Commun. 1990;2(6):219-29. doi: 10.3727/095535490820874407.
High doses of methotrexate with leucovorin rescue are routinely used in the treatment of patients with osteosarcoma; the rationale for this application is controversial. Using human osteosarcoma xenografts growing in mice as a clinically relevant model, we compared the accumulation, intracellular metabolism, and tumor response of methotrexate administered as either high-dose (2400 mg/kg) or low-dose (150 mg/kg) infusions. The high-dose regimen, which included i.v. hydration and leucovorin rescue, resulted in plasma methotrexate levels that approximated those in patients receiving the drug at 12 g/m2. The low-dose infusion produced essentially the same toxicity as the higher dose level, without use of leucovorin. The HxOs33 tumor line was moderately sensitive to the high-dose infusion (55-day delay in tumor volume doubling time), whereas the second line, HxOs2, did not respond. Neither xenograft had a measurable response to low-dose methotrexate. Methotrexate was present in both tumors for up to 72 hr post-infusion, regardless of the dosage regimen. Only shorter-chain polyglutamates (MTXglu2 and MTXglu3) were detected over this period in the high-dose trial, and levels of these derivatives were uniformly higher in the resistant HxOs2 xenograft. Low-dose infusions were associated with formation of longer-chain polyglutamate species, with more abundant production in the HxOs2 line. Methotrexate polyglutamates exceeded baseline [3H]MTX binding of dihydrofolate reductase, as measured in tumor homogenates, at all testing intervals through 72 hr in both tumor lines. Nonetheless, high-dose methotrexate-induced suppression of [14C]formate incorporation into DNA was greater in the drug-sensitive HxOs33 tumor than in HxOs2. These results suggest a therapeutic advantage for high-dose methotrexate regimens in the treatment of human osteosarcoma but show that formation of tumor MTX polyglutamates is not the sole determinant of response to this agent.
大剂量甲氨蝶呤联合亚叶酸钙解救疗法常用于骨肉瘤患者的治疗；这种应用的基本原理存在争议。我们以在小鼠体内生长的人骨肉瘤异种移植物作为临床相关模型，比较了高剂量（2400毫克/千克）或低剂量（150毫克/千克）输注甲氨蝶呤后的蓄积、细胞内代谢及肿瘤反应。高剂量方案包括静脉补液和亚叶酸钙解救，其导致的血浆甲氨蝶呤水平与接受12克/平方米该药物治疗的患者相近。低剂量输注产生的毒性与高剂量水平基本相同，且无需使用亚叶酸钙。HxOs33肿瘤细胞系对高剂量输注中度敏感（肿瘤体积倍增时间延迟55天），而第二个细胞系HxOs2则无反应。两种异种移植物对低剂量甲氨蝶呤均无明显反应。无论给药方案如何，输注后两种肿瘤中甲氨蝶呤均可存在长达72小时。在高剂量试验中，此期间仅检测到较短链的聚谷氨酸盐（MTXglu2和MTXglu3），且在耐药的HxOs2异种移植物中这些衍生物的水平始终较高。低剂量输注与较长链聚谷氨酸盐种类的形成有关，在HxOs2细胞系中产生更为丰富。在两个肿瘤细胞系中，直至72小时的所有检测时间点，通过肿瘤匀浆检测发现甲氨蝶呤聚谷氨酸盐均超过二氢叶酸还原酶的基线[3H]MTX结合水平。尽管如此，高剂量甲氨蝶呤诱导的[14C]甲酸掺入DNA的抑制作用在药物敏感的HxOs33肿瘤中比在HxOs2中更大。这些结果表明高剂量甲氨蝶呤方案在治疗人骨肉瘤方面具有治疗优势，但表明肿瘤甲氨蝶呤聚谷氨酸盐的形成并非对该药物反应的唯一决定因素。
