Targeting therapeutic resistance in glioblastoma

多形性胶质母细胞瘤（GBM）是一种高度侵袭性的脑肿瘤，预后极差 和生存。虽然在美国一般人群中相对罕见，但GBM是第三大常见原因。 美国现役军人中的癌症死亡人数。目前临床反应的相对短暂性 现有的治疗方法强调了开发其他治疗策略的紧迫性。多 研究已经证明在GBM中存在侵袭性癌症干细胞（CSC）亚群， 描述了它们对GBM进展、治疗抗性和复发的贡献;然而， 消除或功能性调节这些治疗难治性亚群迄今为止遇到了有限的 成功ATP结合盒，亚家族B（MDR/TAP），成员5（ABCB 5），一种完整的质膜 由申请人首次克隆和表征的蛋白质（Frank等，J Biol Chem.2003），通过 包括GBM在内的几种恶性肿瘤中的正常组织特异性干细胞和CSC。ABCB 5表达于 原发性GBM肿瘤，其中其表达与CSC标志物CD 133显著相关， 总体生存率差（Lee et al. J Biol Chem. 2020）。在GBM-CSC中，已显示ABCB 5介导 对替莫唑胺（TMZ）的临床相关耐药性。ABCB 5阻断抑制CD 133阳性GBM- CSC自我更新和消除TMZ诱导的G2/M期阻滞。最近，申请人发现了一种新的关键 正常干细胞维持所需的ABCB 5的抗凋亡功能（Ksander等人，Nature 2014）， 作为必然结果，对于CSC驱动的肿瘤生长、侵袭和治疗抗性，部分涉及ABCB 5- RTKAXL信号转导的依赖性调节（Guo等，J Biol Chem.2018）。重要的是 申请人最近的初步研究进一步揭示了ABCB 5作为一种新的受体， 磷脂酰肌醇4，5-二磷酸（PIP 2），与ABCB 5/PIP 2结合显示为PIP 3所需 磷酸化PIP 2衍生的PIP 3作为受体酪氨酸激酶（RTK）信号传导的关键介质， 并因此激活下游PI 3 K/AKT信号级联。值得注意的是，ABCB 5-PIP 2的抑制 通过ABCB 5单克隆抗体阻断或ABCB 5基因敲除（KO）结合抑制PIP 2 磷酸化，阻断PIP 3产生并中断下游PI 3 K/pAKT的pAKT活化 信号通路，损害ABCB 5阳性GBM-CSC上的RTK信号转导。基于这个新的 确定的中央机制，我们假设ABCB 5是关键需要多个RTK依赖 在人类GBM中的功能，包括干细胞内在自我更新、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抗性相关的细胞周期阻滞 (Lee等人J Biol Chem.2020）。所提出的研究将进一步支持ABCB 5作为一种新的药物的开发。 GBM的治疗靶点，并为成功根除ABCB 5阳性GBM干细胞铺平道路 用于改善临床治疗。

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.