Potential ApoE Isoform-Specific Detrimental Effects of RXR Agonists in Alzheimer'

描述（由申请人提供）：阿尔茨海默病（AD）的主要遗传危险因素是载脂蛋白E （apoE）的APOE4基因的遗传，APOE4+/+增加了大约15倍的风险，而APOE2的遗传降低了风险。APOE4携带者占AD患者的一半以上，并且对某些治疗干预表现出差异反应，这可能导致临床试验的失败。APOE4引起的阿尔茨海默病的高风险以及与淀粉样蛋白- β肽（Abeta）协同作用的明确证据表明，迫切需要开发将APOE基因型和A β病理结合起来的治疗方法。最近，有报道称，RXR激动剂bexarotene （BEX）在表达家族性AD突变的转基因小鼠中可以增加小鼠apoe水平，在数小时内降低可溶性Abeta，三天后不溶性Abeta，并恢复认知能力。然而，将小鼠数据外推到AD患者身上是有问题的，因为这些研究没有纳入人类载脂蛋白e亚型。遗传数据表明，降低人类载脂蛋白e水平实际上减少了β病理；此外，通过体外和体内突触活力标记物评估，APOE4代表了功能的毒性增益。我们的假设是RXR激动剂诱导的Abeta病理衰减受APOE基因型的差异调节。由于BEX目前正在进入1期临床试验，该研究的结果将是及时和关键的；并将为未来RXR激动剂临床试验的设计提供信息，包括剂量和APOE4受试者的纳入。BEX将与LG268和GRT63同时进行研究，因为BEX具有更高的RXR选择性（优于RAR）。虽然这三种RXR激动剂都具有较高的口服脑生物利用度，但LG268和GRT63具有改善的物理化学特性。Aim 1将建立BEX、LG268和GRT63的预测性PK/PD和DMPK特性，以指导在EFAD-Tg小鼠中测试治疗模式的体内策略（Aim 2），这是一种表达人类APOE和过表达Abeta 42的创新模型。目的1将确定体外和体内RXR激动剂的PK/PD，通过在多个细胞系中建立靶点参与（lxre -荧光素酶构建），RXR生物标志物验证（ABCA1/ABCG1, apoE，细胞因子IL-1 β和tnf - α的诱导），并确定每种激动剂的有效口服剂量。测定体内肝微粒体代谢稳定性、PK和体重。Aim 2将使用Aim 1中确定的有效剂量确定RXR激动剂对EFAD小鼠的治疗效果，比较E4FAD和E3FAD小鼠。rxr介导的APOE3升高被认为是有益的，其特征是减少A β病理和炎症细胞因子，逆转突触蛋白丢失和行为缺陷。然而，RXR诱导ABCA1/ABCG1可能在APOE4携带者中提供更大的净有益效应，因为与apoE3相比，APOE4可能较少脂化，导致部分功能丧失。这些研究将确定在APOE3和APOE4存在的情况下，RXR激动剂在高度创新的AD动物模型中的疗效。

DESCRIPTION (provided by applicant): The primary genetic risk factor for Alzheimer's disease (AD) is inheritance of the APOE4 gene for apolipoprotein E (apoE), increasing the risk approximately 15-fold with APOE4+/+, whereas inheritance of APOE2 reduces risk. APOE4 carriers account for more than half of AD patients, and exhibit a differential response to certain therapeutic interventions, which can contribute to the failure of clinical trials. The strikingly hgh-risk for AD caused by APOE4 and clear evidence for synergistic actions with amyloid-beta peptide (Abeta), point to the urgent need to develop therapeutic approaches that incorporate the APOE genotype and A beta pathology. Recently, the RXR agonist, bexarotene (BEX), was reported to increase mouse-apoE levels, decrease soluble Abeta within hours, insoluble Abeta after three days, and restore cognition in transgenic mice expressing familial AD mutations. However, extrapolation of the mouse data to AD patients is problematic since the studies did not incorporate human-apoE isoforms. Genetic data demonstrates that lowering human-apoE levels actually decreases Abeta pathology in; furthermore, APOE4 represents a toxic gain of function as assessed by markers of synapse viability in vitro and in vivo. Our hypothesis is that RXR agonist-induced attenuation of Abeta pathology is differentially modulated by APOE genotype. Results from this proposed study will be both timely and critical, as BEX is currently entering phase 1 clinical trials; and will inform the design of future clinical trials on RXR agonists, including dosage and the inclusion of APOE4 subjects. BEX will be studied in parallel with LG268 as it has greater RXR selectivity (over RAR), and GRT63, a novel homologue. While all three RXR agonists have high oral brain bioavailability, LG268 and GRT63 have improved physicochemical characteristics. Aim 1 will establish predictive PK/PD and DMPK properties for BEX, LG268 and GRT63 to direct the in vivo strategy to test treatment paradigms in EFAD-Tg mice (Aim 2), an innovative model which expresses human APOE and overexpress Abeta 42. Aim 1 will determine the PK/PD for RXR agonists in vitro and in vivo, by establishing target engagement (LXRE-luciferase construct), RXR biomarker validation (ABCA1/ABCG1, apoE, induction of cytokines IL-1 beta and TNF-alpha) in multiple cell lines, and identifying an effectiv oral dose for each agonist. Metabolic stability in liver microsomes and PK and body weight in vivo will be measured. Aim 2 will determine the therapeutic efficacy of RXR agonists in EFAD mice using efficacious doses identified in Aim 1, comparing E4FAD and E3FAD mice. The RXR-mediated elevation of APOE3 is proposed to be beneficial, characterized by reduced A beta pathology and inflammatory cytokines, and reversal of synaptic protein loss and behavioral deficits. However, RXR induction of ABCA1/ABCG1 may provide a greater net beneficial effect in APOE4 carriers, as apoE4 may be less lipidated, resulting in a partial loss of function compared with apoE3. These studies will determine the efficacy of RXR agonists in the presence of APOE3 and APOE4 in a highly innovative animal model of AD.