Translational Studies to facilitate Rational Therapeutic Combinations of Letrozole for the Treatment of Glioblastoma

胶质母细胞瘤（GBM）是最致命的脑肿瘤之一，其患者的预后仍然令人沮丧。我们 最近的发现提供了强有力的证据表明，来曲唑（LTZ），一种用于 乳腺癌的治疗，具有成为治疗GBM的突破性治疗的潜力。我们 数据包括：1）患者来源的GBM细胞的LTZ处理显著降低细胞活力和球状体生长; 2)LTZ增强替莫唑胺（TMZ）的活性，TMZ是用于GBM化疗的主要药物。 耐药细胞; 3）免疫活性大鼠的药代动力学/药效学（PK/PD）研究 原位植入C6大鼠胶质瘤显示LTZ容易穿过血脑屏障（BBB）， 显著减小肿瘤体积并延长存活期（对照组与LTZ组相比，10天与> 60天）;以及4） 组织的免疫组织化学分析（N > 90例患者）表明芳香化酶表达是 在GBM中相对于低级别胶质瘤显著更高（> 5倍）。此外，在正在进行的0/1期临床试验中， 复发性GBM患者在手术切除前接受LTZ（2.5 - 12.5 mg，N = 14例受试者），分析 的切除的肿瘤显示，LTZ容易穿越人的血脑屏障。RNAseq分析显示， 显著下调驱动细胞增殖标记物的癌基因和上调肿瘤抑制 标记物（DNA损伤修复能力降低）。我们的长期目标是 将LTZ改造为抗GBM药物鉴于GBM的表型/基因型复杂性， 将是临床必需品。为了支持这一目标，我们的目标是进行全面的PK/PD研究 患者源性原位异种移植（PDOX）免疫缺陷（无胸腺裸）中LTZ和联合药物的 大鼠通常，利用无胸腺/SCID小鼠进行此类研究。然而， 小鼠中的LTZ较短（约2.5小时），而大鼠中的LTZ PK更接近于需要使用 无胸腺裸鼠。因此，我们建议进行一项基于里程碑的定量研究， 复发性患者源性GBM。我们将严格测试LTZ的组合药物，强烈建议 通过我们的RNAseq和其他数据，合理地推进2-3个组合用于II期临床试验。 具体目的：1：基于针对GBM系的协同效应的LTZ的等级顺序组合伴侣， 体外2：测定组合药剂± LTZ的体内BBB渗透性。3：建立PDOX无胸腺裸鼠 体内PK/PD研究的模型，4：采用PDOX模型评价LTZ ±联合药物的PK/PD。 R61阶段里程碑包括细胞活力（组合指数，CI< 1）和BBB的协同抑制 渗透性（血浆至脑分配）（目的1和2）。同时，建立无胸腺裸鼠模型， 在目标3中建立/验证。在R33阶段（目标4）使用这些模型，剂量-反应关系将 将2-3种LTZ联合用药推进到II期临床试验。多学科合作者团队 将参与这一重要的下一步，重新利用LTZ治疗GBM，这是一个迫切的未满足的医疗需求。

The prognosis for patients with glioblastoma (GBM), one of the most lethal brain tumors, remains dismal. Our recent discoveries provide robust evidence suggesting that letrozole (LTZ), an aromatase inhibitor used in the treatment of breast cancer, has the potential to be a breakthrough therapeutic for the treatment of GBM. Our data include: 1) LTZ treatment of patient-derived GBM cells markedly reduced cell viability and spheroid growth; 2) LTZ potentiated the activity of temozolomide (TMZ), the primary agent used in chemotherapy of GBM in TMZ- resistant cells; 3) Pharmacokinetics/Pharmacodynamics (PK/PD) studies in immunocompetent rats orthotopically implanted with C6 rat glioma revealed that LTZ readily crosses the blood-brain barrier (BBB), markedly reduces tumor volume and extends survival (10 vs. > 60 days in control vs. LTZ); and 4) immunohistochemical analysis of tissues (N > 90 patients) demonstrated that the aromatase expression is strikingly higher (> 5X) in GBM relative to low-grade gliomas. Moreover, in an ongoing phase 0/1 clinical trial in which recurrent GBM patients received LTZ (2.5 -12.5 mg, N = 14 subjects) prior to surgical resection, analyses of the excised tumor revealed that LTZ readily traverses the BBB in humans. RNAseq analysis showed significant downregulation of oncogenes driving cell proliferation markers and upregulation of tumor suppression markers (reduced DNA damage repair capacity) in a LTZ dose-dependent manner. Our long-term goal is to repurpose LTZ as an anti-GBM drug. Given the phenotypic/genotypic complexity of GBM, combination therapy will be a clinical necessity. To support this goal, our objective here is to conduct comprehensive PK/PD studies of LTZ and combination agents in patient-derived orthotopic xenograft (PDOX) immunodeficient (athymic nude) rats. Typically, such studies are performed utilizing athymic/SCID mice. However, the elimination half-life of LTZ in mice is short (~ 2.5 hours), whereas LTZ PK in rats are closer to that in humans requiring the use of athymic nude rats. Thus, we propose to conduct a quantitative milestone-based study employing primary and recurrent patient-derived GBM. We will rigorously test combination agents for LTZ, strongly suggested collectively by our RNAseq and other data and rationally advance 2-3 combinations for phase II clinical trials. Specific Aims: 1: Rank-order combination partners for LTZ based on synergistic effects against GBM lines in vitro 2: Determine in vivo BBB permeability of combination agents ± LTZ. 3: Establish PDOX athymic nude rat models for in vivo PK/PD studies, 4: Evaluate PK/PD of LTZ ± combination agent employing the PDOX models. The R61 phase milestones include synergistic inhibition of cell viability (Combination Index, CI< 1) and BBB permeability (plasma to brain partitioning) (Aims 1 and 2). Concurrently, an athymic nude rat models will be established/validated in Aim 3. Using these models in the R33 phase (Aim 4), dose-response relationship will be derived to advance 2-3 LTZ combinations to phase II clinical trials. A multidisciplinary team of collaborators will participate in this important next step to repurpose LTZ for GBM treatment, an urgent unmet medical need.