Dawson M I, Elstner E, Kizaki M, Chen D L, Pakkala S, Kerner B, Koeffler H P
Bio-Organic Chemistry Laboratory, SRI International, Menlo Park, CA.
Blood. 1994 Jul 15;84(2):446-52.
Retinoids, such as all-trans-retinoic acid and 9-cis-retinoic acid, are naturally occurring ligands of the nuclear retinoic acid receptors (RARs). In concert with binding of ligand, these receptors from heterodimers with the retinoic X receptor (RXR) and transactivate RAR/RXR-responsive genes. Retinoids can differentiate leukemic cell lines in vitro and induce clinically complete remissions in patients with acute promyelocytic leukemia. Synthetic ligands to the RAR and RXR receptors have been developed that selectively bind and activate RAR/RXR (TTAB) and RXR/RXR dimers (SR11217). We investigated the affect of these ligands, either alone or in combination, on in vitro growth and differentiation of cells from the HL-60, KG-1, THP-1, and WEHI-3 myeloid cell lines as well as on clonal growth of fresh myeloid leukemic blasts from patients. Clonal inhibition of proliferation of these cells was studied in soft agar cultures. Cells were plated in the presence of either one or a combination of retinoids at concentrations of 10(-5) to 10(-10) mol/L. TTAB inhibited 50% clonal growth at an effective dose (ED50) that was about 1,000-fold lower than the concentration of SR11217 required to achieve an ED50 for the same leukemic cells. Combination of both ligands at a variety of concentrations showed no synergistic effects. Superoxide production (nitroblue tetrazolium reduction) and CD11b expression as parameters of differentiation of HL-60 cells were also examined. Results paralleled those of clonal growth, with SR11217 being markedly less potent than TTAB. These results show that the ligand selective for RXR-homodimers has little effect on either inducing differentiation or inhibiting clonal growth of leukemic cells. The differentiating and antiproliferative effects of retinoids are mainly induced through RAR/RXR heterodimers, and development of therapeutic analogs should focus on this category of retinoids.
维甲酸，如全反式维甲酸和9-顺式维甲酸，是核维甲酸受体（RARs）的天然配体。与配体结合协同作用，这些受体与维甲酸X受体（RXR）形成异二聚体并反式激活RAR/RXR反应基因。维甲酸可在体外使白血病细胞系分化，并诱导急性早幼粒细胞白血病患者临床完全缓解。已开发出RAR和RXR受体的合成配体，它们能选择性结合并激活RAR/RXR（TTAB）和RXR/RXR二聚体（SR11217）。我们研究了这些配体单独或联合使用对HL-60、KG-1、THP-1和WEHI-3髓系细胞系细胞体外生长和分化的影响，以及对患者新鲜髓系白血病原始细胞克隆生长的影响。在软琼脂培养中研究了这些细胞增殖的克隆抑制情况。细胞在浓度为10^(-5)至10^(-10) mol/L的一种或多种维甲酸存在下接种。TTAB以有效剂量（ED50）抑制50%的克隆生长，该有效剂量比相同白血病细胞达到ED50所需的SR11217浓度低约1000倍。两种配体在各种浓度下联合使用均未显示出协同作用。还检测了超氧化物产生（硝基蓝四唑还原）和CD11b表达作为HL-60细胞分化的参数。结果与克隆生长结果相似，SR11217的效力明显低于TTAB。这些结果表明，对RXR同二聚体具有选择性的配体对诱导白血病细胞分化或抑制其克隆生长几乎没有作用。维甲酸的分化和抗增殖作用主要通过RAR/RXR异二聚体诱导，治疗类似物的开发应聚焦于此类维甲酸。
