Targeting therapeutic resistance in glioblastoma

摘要多形性胶质母细胞瘤是一种高度侵袭性的脑肿瘤，预后极差。 和生存。虽然在美国普通人群中相对罕见，但GBM是第三种最常见的疾病 美国现役军人死于癌症。目前临床反应的相对暂时性 现有的治疗方法突显了开发更多治疗策略的紧迫性。多重 研究表明，在GBM和BM中存在侵袭性肿瘤干细胞(CSC)亚群。 描述了他们对GBM进展、治疗耐药和复发的贡献；然而，努力 消除或从功能上调整这些治疗--到目前为止，难治性亚群遇到的困难有限 成功。ATP结合盒，B亚家族(MDR/TAP)，成员5(ABCB5)，完整的质膜 申请人首先克隆并鉴定了蛋白质(Frank等人)。J生物化学。2003)，被高度表达为 包括基底膜在内的几种恶性肿瘤中的正常组织特异性干细胞和干细胞。ABCB5表示为 原发基底膜肿瘤中其表达与CSC标记物CD133和 总体存活率较低(Lee等人J生物化学。2020)。在GBM-CSCs中，ABCB5已被证明在 临床上对替莫唑胺(TMZ)的耐药性。ABCB5阻断抑制CD133阳性的GBM- CSC自我更新并取消TMZ诱导的G2/M期停滞。最近，申请者确定了一部新的批评者 正常干细胞维持所需的ABCB5的抗凋亡功能(Ksander等人)。自然2014年)和， 作为推论，对于CSC驱动的肿瘤生长、侵袭和治疗耐药，部分涉及ABCB5- RTK Axl信号转导的依赖调节(Guo等，J Biol Chem.2018年)。重要的是， 申请人最新的初步研究进一步表明，ABCB5是一种新的受体 磷脂酰肌醇4，5-二磷酸(PIP2)，显示PIP3需要ABCB5/PIP2结合 磷酸化。PIP2衍生的PIP3是受体酪氨酸激酶(RTK)信号的关键介体， 从而激活下游的PI3K/AKT信号级联。值得注意的是，ABCB5-PIP2的抑制 通过ABCB5单抗阻断或ABCB5基因敲除(KO)结合抑制PIP2 磷酸化，阻断PIP3的产生并中断PI3K/PAKT下游的PACT激活 信号通路，损害ABCB5阳性的GBM-CSC的RTK信号转导。基于这一新的 确定了中枢机制，我们假设ABCB5对于多种RTK依赖是至关重要的 人类基底膜的功能，包括干细胞内在的自我更新、抗凋亡、促血管生成和侵袭性 能力、干细胞驱动的表观遗传进化和治疗耐药相关的细胞周期停滞 (Lee等人)J生物化学。2020)。拟议的研究将进一步支持ABCB5作为一种小说的发展 GBM的治疗靶点，应为成功根除ABCB5阳性的GBM干细胞铺平道路 用于改进临床治疗的人类患者的细胞。

Glioblastoma multiforme (GBM) is a highly aggressive brain tumor associated with extremely poor prognosis and survival. Although relatively rare in the US general population, GBM is the third most common cause of cancer death in the US active-duty military. The relatively transient nature of clinical responses to currently available therapies underlines the urgency for the development of additional therapeutic strategies. Multiple studies have demonstrated the existence of aggressive cancer stem cell (CSC) subpopulations in GBM and characterized their contribution to GBM progression, therapeutic resistance and recurrence; however, efforts to eliminate or functionally modulate these therapy-refractory subpopulations have thus far met with limited success. ATP-binding cassette, sub-family B (MDR/TAP), member 5 (ABCB5), an integral plasma membrane protein first cloned and characterized by the applicant (Frank et al. J Biol Chem. 2003), is highly expressed by normal tissue-specific stem cells and CSCs in several malignancies, including GBM. ABCB5 is expressed in primary GBM tumors, in which its expression is significantly correlated with the CSC marker CD133 and with overall poor survival (Lee et al. J Biol Chem. 2020). In GBM-CSCs, ABCB5 has been shown to mediate clinically relevant drug resistance to temozolomide (TMZ). ABCB5 blockade inhibited CD133-positive GBM- CSC self-renewal and abrogated TMZ-induced G2/M arrest. Recently, the applicant identified a novel critical anti-apoptotic function of ABCB5 required for normal stem cell maintenance (Ksander et al. Nature 2014) and, as a corollary, for CSC-driven tumor growth, invasion and therapeutic resistance, involving, in part, ABCB5- dependent regulation of signal transduction of the RTK AXL (Guo et al., J Biol Chem. 2018). Importantly, the applicant’s most recent preliminary studies further revealed that ABCB5 serves as a novel receptor for Phosphatidylinositol 4,5-bisphosphate (PIP2), with ABCB5/PIP2 binding shown to be required for PIP3 phosphorylation. PIP2-derived PIP3 serves as a critical mediator of receptor tyrosine kinase (RTK) signaling, and hence activation of the downstream PI3K/AKT signaling cascade. Remarkably, inhibition of ABCB5-PIP2 binding through ABCB5 monoclonal antibody blockade or ABCB5 gene knockout (KO) inhibits PIP2 phosphorylation, blocks PIP3 production and interrupts down-stream pAKT activation of the PI3K/pAKT signaling pathway, impairing RTK signal transduction on ABCB5-positive GBM-CSC. Based on this newly identified central mechanism, we hypothesize that ABCB5 is critically required for multiple RTK-dependent functions in human GBM, including stem cell-intrinsic self-renewal, anti-apoptotic, pro-angiogenic and invasive capacities, and stem cell-driven epigenetic evolution and therapeutic resistance associated cell cycle arrest (Lee et al. J Biol Chem. 2020). The proposed studies will further support the development of ABCB5 as a novel therapeutic target in GBM and should pave the way to successful eradication of ABCB5_positive GBM stem cells in human patients for improved clinical therapy.