Kamenecka Theodore M., Busby Scott A., Kumar Naresh, Choi Jang Hyun, Banks Alexander S., Vidovic Dušica, Cameron Michael D., Schurer Stephan C., Mercer Becky A., Hodder Peter, Spiegelman Bruce M., Griffin Patrick R.
Department of Chemistry, Scripps Florida, 130 Scripps Way, Jupiter, FL 33458
Department of Molecular Therapeutics, Scripps Florida, 130 Scripps Way, Jupiter, FL 33458
The incidence of diabetes is increasing rapidly as the percentage of the population ages and becomes more obese. According to the National Center for Health Statistics diabetes is now the sixth leading cause of death in the US. The biguanide metformin is typically the first-line medication used for treatment of type 2 diabetes mellitus (T2DM) as safety concerns over the use of the thiazolidinedione class [(TZD); rosiglitazone (Avandia) and pioglitazone (Actos) [1]] of insulin sensitizers has grown. This is unfortunate as TZDs have consistently shown robust efficacy for treatment of T2DM. TZDs target the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) and are classified as full agonists. While weight gain is associated with use of TZDs, the major safety concerns include edema, plasma volume expansion (PVE or hemodilution) which is likely linked to cardiomegaly and increased risk of congestive heart failure, and an increased risk of bone fractures. The latter risk is most troublesome as detection is typically only made when a patient suffers a fracture. Studies in animal models and in clinical trials have shown that indicators of weight gain and PVE, while not eliminated, can be minimized without loss of insulin sensitization by the use of modulators that are weak or partial agonists of PPARγ (e.g., minimal agonism of the receptor as compared to TZDs). Partial agonists have been referred to as selective PPARγ modulators or SPPARγMs and this class of ligand has been shown to have a different binding mode in the PPARγ ligand binding pocket (LBP) as compared to the full agonists [2]. Selective recruitment of transcriptional coactivators by partial agonists has also been demonstrated. A combination of different ligand binding mode and distinct coactivator recruitment profile may explain the change in gene expression patterns compared to that of full agonists [3]. While it is unclear if the bone fracture risk has been minimized with use of such agents, these studies clearly demonstrate that the anti-diabetic efficacy of partial agonists is uncoupled from their transcriptional activity but does correlate well with binding potency. Recently we have shown that many PPARγ-based drugs have a separate biochemical activity, blocking the obesity-linked phosphorylation of PPARγ by Cdk5. Due to their improved adverse event profile of partial agonists and the observation of separate biochemical activities of PPARγ ligands, we sought to develop compounds with high affinity binding to PPARγ but that lacked classical agonism and block the Cdk5-mediated phosphorylation in cultured adipocytes and in insulin-resistant mice. Here we describe one such compound, ML244, which has a unique mode of binding to PPARγ, has potent anti-diabetic activity while not causing the fluid retention and weight gain that are serious side effects of many of the PPARγ drugs. Unlike TZDs, ML244 does not interfere with bone formation in culture. These data illustrate that new classes of anti-diabetes drugs can be developed by specifically targeting the Cdk5-mediated phosphorylation of PPARγ.
随着人口老龄化和肥胖率的上升，糖尿病的发病率正在迅速增加。根据美国国家卫生统计中心的数据，糖尿病目前是美国第六大死因。由于对噻唑烷二酮类胰岛素增敏剂（如罗格列酮（文迪雅）和吡格列酮（艾可拓））使用的安全性担忧增加，双胍类药物二甲双胍通常是用于治疗2型糖尿病（T2DM）的一线药物。这很不幸，因为噻唑烷二酮类药物一直显示出对T2DM治疗的强大疗效。噻唑烷二酮类药物作用于核受体过氧化物酶体增殖物激活受体γ（PPARγ），并被归类为完全激动剂。虽然体重增加与噻唑烷二酮类药物的使用有关，但主要的安全问题包括水肿、血浆容量扩张（PVE或血液稀释），这可能与心脏肥大和充血性心力衰竭风险增加有关，以及骨折风险增加。后一种风险最为麻烦，因为通常只有在患者发生骨折时才会被发现。动物模型和临床试验研究表明，通过使用PPARγ的弱激动剂或部分激动剂（例如，与噻唑烷二酮类药物相比，受体的激动作用最小），体重增加和PVE的指标虽然没有消除，但可以最小化，同时不丧失胰岛素敏感性。部分激动剂被称为选择性PPARγ调节剂或SPPARγM，与完全激动剂相比，这类配体在PPARγ配体结合口袋（LBP）中具有不同的结合模式[2]。部分激动剂对转录共激活因子的选择性募集也得到了证实。与完全激动剂相比，不同的配体结合模式和独特的共激活因子募集谱的组合可能解释了基因表达模式的变化[3]。虽然尚不清楚使用此类药物是否已将骨折风险降至最低，但这些研究清楚地表明，部分激动剂的抗糖尿病疗效与其转录活性无关，但与结合效力密切相关。最近我们发现，许多基于PPARγ的药物具有单独的生化活性，可阻断Cdk5对PPARγ的肥胖相关磷酸化。由于部分激动剂的不良事件谱有所改善，以及观察到PPARγ配体的单独生化活性，我们试图开发与PPARγ具有高亲和力结合但缺乏经典激动作用并能在培养的脂肪细胞和胰岛素抵抗小鼠中阻断Cdk5介导的磷酸化的化合物。在此我们描述一种这样的化合物ML244，它与PPARγ具有独特的结合模式，具有强大的抗糖尿病活性，同时不会引起许多PPARγ药物严重副作用的液体潴留和体重增加。与噻唑烷二酮类药物不同，ML244在培养中不干扰骨形成。这些数据表明，通过特异性靶向Cdk5介导的PPARγ磷酸化，可以开发新型抗糖尿病药物。
