Retinoid X receptors (RXRs) are nuclear transcription factors that partner with other nuclear receptors to regulate numerous physiological processes. Although RXR represents a valid therapeutic target, only a few RXR-specific ligands (rexinoids) have been identified, in part due to the lack of clarity on how rexinoids selectively modulate RXR response. Previously, we showed that rexinoid UAB30 potentiates all-trans-retinoic acid (ATRA) signaling in human keratinocytes, in part by stimulating ATRA biosynthesis. Here, we examined the mechanism of action of next-generation rexinoids UAB110 and UAB111 that are more potent in vitro than UAB30 and the FDA-approved Targretin. Both UAB110 and UAB111 enhanced ATRA signaling in human organotypic epithelium at a 50-fold lower concentration than UAB30. This was consistent with the 2- to 5- fold greater increase in ATRA in organotypic epidermis treated with UAB110/111 versus UAB30. Furthermore, at 0.2 μM, UAB110/111 increased the expression of ATRA genes up to 16-fold stronger than Targretin. The less toxic and more potent UAB110 also induced more changes in differential gene expression than Targretin. Additionally, our hydrogen deuterium exchange mass spectrometry analysis showed that both ligands reduced the dynamics of the ligand-binding pocket but also induced unique dynamic responses that were indicative of higher affinity binding relative to UAB30, especially for Helix 3. UAB110 binding also showed increased dynamics towards the dimer interface through the Helix 8 and Helix 9 regions. These data suggest that UAB110 and UAB111 are potent activators of RXR–RAR signaling pathways but accomplish activation through different molecular responses to ligand binding.

类视黄醇 X 受体 (RXR) 是核转录因子，与其他核受体配合调节多种生理过程。尽管 RXR 代表了有效的治疗靶点，但仅鉴定了少数 RXR 特异性配体（rexinoids），部分原因是 rexinoids 如何选择性调节 RXR 反应尚不清楚。此前，我们发现rexinoid UAB30可增强人角质形成细胞中的全反式视黄酸（ATRA）信号传导，部分是通过刺激ATRA生物合成来实现的。在这里，我们研究了下一代 rexinoids UAB110 和 UAB111 的作用机制，它们在体外比 UAB30 和 FDA 批准的 Targretin 更有效。UAB110 和 UAB111 均能增强人器官上皮中的 ATRA 信号传导，其浓度比 UAB30 低 50 倍。这与用 UAB110/111 处理的器官型表皮中 ATRA比用UAB30处理的增加 2 至 5 倍一致。此外，在 0.2 μM 浓度下，UAB110/111 使 ATRA 基因的表达量比 Targretin 强 16 倍。与 Targretin 相比，毒性更小、更有效的 UAB110 也能诱导更多的差异基因表达变化。此外，我们的氢氘交换质谱分析表明，两种配体都降低了配体结合袋的动力学，但也诱导了独特的动态响应，这表明相对于 UAB30 具有更高的亲和力结合，特别是对于 Helix 3。UAB110 结合也显示出增强的动力学通过螺旋 8 和螺旋 9 区域朝向二聚体界面。这些数据表明 UAB110 和 UAB111 是 RXR-RAR 信号通路的有效激活剂，但通过对配体结合的不同分子反应来完成激活。