Authors' Affiliations: OHSU Knight Cancer Institute, Oregon Health & Science University, Portland, Oregon; Howard Hughes Medical Institute, Chevy Chase, Maryland; Huntsman Cancer Institute; Division of Hematology and Hematologic Malignancies, The University of Utah, Salt Lake City, Utah; Novartis Institutes for BioMedical Research, Basel, Switzerland; and Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Cancer Res. 2013 Sep 15;73(18):5775-86. doi: 10.1158/0008-5472.CAN-13-1318. Epub 2013 Jul 25.
Imatinib and other BCR-ABL1 inhibitors are effective therapies for chronic myelogenous leukemia (CML), but these inhibitors target additional kinases including KIT, raising the question of whether off-target effects contribute to clinical efficacy. On the basis of its involvement in CML pathogenesis, we hypothesized that KIT may govern responses of CML cells to imatinib. To test this, we assessed the growth of primary CML progenitor cells under conditions of sole BCR-ABL1, sole KIT, and dual BCR-ABL1/KIT inhibition. Sole BCR-ABL1 inhibition suppressed mature CML progenitor cells, but these effects were largely abolished by stem cell factor (SCF) and maximal suppression required dual BCR-ABL1/KIT inhibition. In contrast, KIT inhibition did not add to the effects of BCR-ABL1 inhibition in primitive progenitors, represented by CD34(+)38(-) cells. Long-term culture-initiating cell assays on murine stroma revealed profound depletion of primitive CML cells by sole BCR-ABL1 inhibition despite the presence of SCF, suggesting that primitive CML cells are unable to use SCF as a survival factor upon BCR-ABL1 inhibition. In CD34(+)38(+) cells, SCF strongly induced pAKT(S473) in a phosphoinositide 3-kinase (PI3K)-dependent manner, which was further enhanced by inhibition of BCR-ABL1 and associated with increased colony survival. In contrast, pAKT(S473) levels remained low in CD34(+)38(-) cells cultured under the same conditions. Consistent with reduced response to SCF, KIT surface expression was significantly lower on CD34(+)38(-) compared with CD34(+)38(+) CML cells, suggesting a possible mechanism for the differential effects of SCF on mature and primitive CML progenitor cells.
伊马替尼和其他 BCR-ABL1 抑制剂是治疗慢性髓性白血病 (CML) 的有效疗法，但这些抑制剂除了靶向 BCR-ABL1 外，还靶向包括 KIT 在内的其他激酶，这引发了一个问题，即是否存在脱靶效应会影响临床疗效。基于 KIT 在 CML 发病机制中的作用，我们假设 KIT 可能调控 CML 细胞对伊马替尼的反应。为了验证这一点，我们评估了在单独 BCR-ABL1、单独 KIT 和双重 BCR-ABL1/KIT 抑制条件下，原发性 CML 祖细胞的生长情况。单独 BCR-ABL1 抑制可抑制成熟的 CML 祖细胞，但这些作用在很大程度上被干细胞因子 (SCF) 所消除，而最大的抑制作用则需要双重 BCR-ABL1/KIT 抑制。相比之下，KIT 抑制在原始祖细胞（由 CD34(+)38(-)细胞代表）中并不能增强 BCR-ABL1 抑制的作用。在小鼠基质上进行长期培养起始细胞测定显示，尽管存在 SCF，但单独的 BCR-ABL1 抑制可显著耗竭原始 CML 细胞，这表明原始 CML 细胞在 BCR-ABL1 抑制后无法将 SCF 用作生存因子。在 CD34(+)38(+)细胞中，SCF 以磷脂酰肌醇 3-激酶 (PI3K) 依赖的方式强烈诱导 pAKT(S473)，而 BCR-ABL1 的抑制作用进一步增强了 pAKT(S473)，并与集落存活增加相关。相比之下，在相同条件下培养的 CD34(+)38(-)细胞中 pAKT(S473)水平仍然较低。与对 SCF 的反应降低一致，CD34(+)38(-)细胞上的 KIT 表面表达明显低于 CD34(+)38(+) CML 细胞，这表明了 SCF 对成熟和原始 CML 祖细胞的不同作用的一种可能机制。
