Hypoxia-Selective Kinase Inhibitors for Leukemia Therapy

描述(由申请人提供)：癌症和白血病中细胞增殖的解除调控通常发生在称为酪氨酸激酶(TK)的信号分子突变和/或放大之后。Flt3是一种酪氨酸激酶受体，是急性髓系白血病(AML)中最常见的突变基因，其内部串联重复(Flt3-ITD)在20-25%的患者中发生。Flt3-ITD突变与侵袭性疾病特征有关，抑制Flt3激酶可以改善这些白血病患者本来就很差的预后。尽管到目前为止已经报道了20多种对Flt3具有抑制活性的小分子抑制剂，但Flt3抑制剂的临床成功在很大程度上受到药代动力学和药效学困难的限制，无法在没有显著非靶向毒性的情况下实现对Flt3的持续抑制。这表明有必要拓宽治疗窗口。 飞翔TKI的。在这项提议中，我们将利用新的低氧激活的‘前药’技术 由奥克兰大学的杰夫·斯迈尔博士和亚当·帕特森博士开创。它利用了我们最近发现的病理性缺氧，这是白血病而不是正常骨髓的普遍环境。中心假设是，低氧诱导白血病BM利基中TKI的激活将导致更高的局部药物浓度，从而增加对白血病母细胞的疗效，同时限制毒性。 转化为正常细胞。在目标1中，将利用低氧激活的前药策略来增加对Flt3抑制剂的肿瘤选择性，从而拓宽它们的治疗指数。作为该技术的原型，开发了缺氧激活的不可逆泛HER抑制剂PR610，并计划于2012年年中开始第一阶段临床试验。我们将合成已知的Flt3抑制剂AC220、MLN-518、舒尼替尼和crenolanib的硝甲基芳基季铵盐(NMQ)前药。这类前体药物带有永久的正电荷，因此被排除在细胞外，防止正常细胞中的激酶抑制物与其细胞内激酶靶标结合。反过来，前体药物可以进行单电子还原，并在低氧条件下选择性地碎裂，以释放细胞通透性激酶抑制物。这限制了正常组织的暴露，并允许显著增加剂量(通常血浆AUC增加50-100倍)。我们预计，Flt3前体药物将成为白血病低氧激活TKI的第一个原型。我们将表征Flt3支架在Flt3突变的AML中的活性、选择性和效力。MTD/PK/PD检测和Flt3突变的人AML异种移植模型的体内疗效研究将在AIM 2中进行。如果成功，这种方法将为消除缺氧性BM内的白血病细胞提供基于机制的理论基础，并提高AML的治愈率。

DESCRIPTION (provided by applicant): Deregulation of cell proliferation in cancer and leukemia generally occurs following mutation and/or amplification of signalling molecules termed tyrosine kinases (TK). FLT3, a tyrosine kinase receptor, is the most commonly mutated gene in acute myeloid leukemia (AML) with internal tandem duplications (FLT3-ITD) occurring in 20-25% of patients. FLT3-ITD mutations are associated with aggressive disease characteristics, and FLT3 kinase inhibition can improve the otherwise poor prognosis of these leukemia patients. Although more than 20 small molecule inhibitors with inhibitory activity against FLT3 have been reported to date, clinical success of FLT3 inhibitors is largely limited by pharmacokinetic and pharmacodynamic difficulties in achieving sustained FLT3 inhibition without significant off-target toxicity. This indicates the need to broaden the therapeutic window of the FLT3 TKIs. In this proposal, we will utilize novel hypoxia-activated 'prodrug' technologies pioneered by Drs. Jeff Smaill and Adam Patterson at the University of Auckland. It takes advantage of the pathological hypoxia which was recently discovered by us as a prevalent environment of the leukemic but not normal bone marrow. The central hypothesis is that hypoxia-induced activation of TKIs in the leukemic BM niche would result in higher local concentrations of the drug with increased efficacy against leukemic blasts, while limiting toxicity to normal cells. In Aim 1, a hypoxia-activated prodrug strategy will be utilized to introduce increased tumour-selectivity to FLT3 inhibitors and thereby broaden their therapeutic index. As a prototype of this technology, hypoxia-activated irreversible pan-HER inhibitor PR610 was developed, and is scheduled to begin Phase I clinical testing in mid-2012. We will synthesise nitromethylaryl quaternary ammonium salt (NMQ) prodrugs of the known FLT3 inhibitors AC220, MLN-518, sunitinib and crenolanib. This class of prodrugs carry a permanent positive charge and are therefore excluded from cells, preventing binding of the kinase inhibitor with its intracellular kinase target in normal cells. In turn, the prodrug can undergo one-electron reduction and will fragment selectively under hypoxic conditions to release the cell permeable kinase inhibitor. This restricts normal tissue exposures and permits significantly greater doses to be administered (typically 50-100 fold increase in plasma AUC). We anticipate that the FLT3 pro-drugs would be the first prototype of hypoxia-activated TKI in leukemia. We will characterize the activity, selectivity and potency of FLT3 scaffolds in FLT3 mutated AML. MTD/PK/PD testing and in vivo efficacy studies in the FLT3-mutated xenograft model of human AML will be carried out in Aim 2. If successful, this approach will provide mechanism-based rationale for eliminating leukemic cells within the hypoxic BM niches and improve cure rates in AML.