Belkov V M, Krynetski E Y, Schuetz J D, Yanishevski Y, Masson E, Mathew S, Raimondi S, Pui C H, Relling M V, Evans W E
St Jude Children's Research Hospital, Memphis, TN; and the University of Tennessee, Memphis, TN, USA.
Blood. 1999 Mar 1;93(5):1643-50.
Methotrexate (MTX) is one of the most active and widely used agents for the treatment of acute lymphoblastic leukemia (ALL). To elucidate the mechanism for higher accumulation of MTX polyglutamates (MTX-PG) in hyperdiploid ALL and lower accumulation in T-lineage ALL, expression of the reduced folate carrier (RFC) was assessed by reverse transcription-polymerase chain reaction in ALL blasts isolated from newly diagnosed patients. RFC expression exhibited a 60-fold range among 29 children, with significantly higher expression in hyperdiploid B-lineage ALL (median, 11.3) compared with nonhyperdiploid ALL (median, 2.1; P <.0006), but no significant difference between nonhyperdiploid B-lineage and T-lineage ALL. Furthermore, mRNA levels of RFC (mapped by FISH to chromosome 21) were significantly related to chromosome 21 copy number (P =.0013), with the highest expression in hyperdiploid ALL blasts with 4 copies of chromosome 21. To assess the functional significance of gene copy number, MTX-PG accumulation was compared in ALL blasts isolated from 121 patients treated with either low-dose MTX (LDMTX; n = 60) or high-dose MTX (HDMTX; n = 61). After LDMTX, MTX-PG accumulation was highest in hyperdiploid B-lineage ALL with 4 copies of chromosome 21 (P =.011), but MTX-PG accumulation was not significantly related to chromosome 21 copy number after HDMTX (P =.24). These data show higher RFC expression as a mechanism for greater MTX accumulation in hyperdiploid B-lineage ALL and indicate that lineage differences in MTX-PG accumulation are not due to lower RFC expression in T-lineage ALL.
甲氨蝶呤（MTX）是治疗急性淋巴细胞白血病（ALL）最有效的且应用最广泛的药物之一。为阐明MTX多聚谷氨酸盐（MTX-PG）在超二倍体ALL中蓄积较高而在T系ALL中蓄积较低的机制，采用逆转录-聚合酶链反应对新诊断患者分离出的ALL原始细胞中还原型叶酸载体（RFC）的表达进行了评估。在29名儿童中，RFC表达呈现60倍的差异范围，与非超二倍体ALL（中位数为2.1；P<.0006）相比，超二倍体B系ALL（中位数为11.3）中的表达显著更高，但非超二倍体B系ALL与T系ALL之间无显著差异。此外，RFC的mRNA水平（通过荧光原位杂交定位到21号染色体）与21号染色体拷贝数显著相关（P =.0013），在具有4份21号染色体拷贝的超二倍体ALL原始细胞中表达最高。为评估基因拷贝数的功能意义，比较了121例接受低剂量MTX（LDMTX；n = 60）或高剂量MTX（HDMTX；n = 61）治疗的患者分离出的ALL原始细胞中MTX-PG的蓄积情况。接受LDMTX治疗后，具有4份21号染色体拷贝的超二倍体B系ALL中MTX-PG蓄积最高（P =.011），但接受HDMTX治疗后，MTX-PG蓄积与21号染色体拷贝数无显著相关性（P =.24）。这些数据表明较高的RFC表达是超二倍体B系ALL中MTX蓄积更多的机制，并表明MTX-PG蓄积的谱系差异并非由于T系ALL中RFC表达较低所致。
