Morgan Adams Foundation Pediatric Brain Tumor Research Program, University of Colorado Denver, Anschutz Medical Campus, Aurora, Colorado.
Cardiovascular Pulmonary Research Laboratories and Pediatric Critical Care Medicine, Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado.
Clin Cancer Res. 2022 Jun 1;28(11):2409-2424. doi: 10.1158/1078-0432.CCR-21-4002.
Tumor relapse after radiotherapy is a major hurdle in treating pediatric H3K27M-mutant diffuse midline gliomas (DMG). Radiotherapy-induced stress increases association of BCL2 family of proteins with BH3 pro-apoptotic activators preventing apoptosis. We hypothesized that inhibition of radiotherapy-induced BCL2 with a clinically relevant inhibitor, venetoclax, will block BCL2 activity leading to increased apoptosis. BCL2 has never been implicated in DMG as a radiotherapy-induced resistant mechanism.
We performed an integrated genomic analysis to determine genes responsible for radioresistance and a targeted drug screen to identify drugs that synergize with radiation in DMG. Effect of venetoclax on radiation-naïve and 6 Gy radiation on cells was evaluated by studying cell death, changes in BCL2 phosphorylation, reactive oxygen species (ROS), and apoptosis, as well as BCL2 association with BH3 apoptosis initiators. The efficacy of combining venetoclax with radiation was evaluated in vivo using orthotopic xenograft models.
BCL2 was identified as a key regulator of tumor growth after radiation in DMGs. Radiation sensitizes DMGs to venetoclax treatment independent of p53 status. Venetoclax as a monotherapy was not cytotoxic to DMG cells. Postradiation venetoclax treatment significantly increased cell death, reduced BCL2-BIM association, and augmented mitochondrial ROS leading to increased apoptosis. Combining venetoclax with radiotherapy significantly enhanced the survival of mice with DMG tumors.
This study shows that venetoclax impedes the antiapoptotic function of radiation-induced BCL2 in DMG, leading to increased apoptosis. Results from these preclinical studies demonstrate the potential use of the BCL2 inhibitor venetoclax combined with radiotherapy for pediatric DMG.
放疗后肿瘤复发是治疗小儿 H3K27M 突变弥漫性中线神经胶质瘤（DMG）的主要障碍。放疗引起的应激会增加 BCL2 家族蛋白与 BH3 促凋亡激活剂的结合，从而阻止细胞凋亡。我们假设，用一种临床相关的抑制剂 venetoclax 抑制放疗诱导的 BCL2，将阻断 BCL2 活性，导致细胞凋亡增加。BCL2 从未被认为是 DMG 中放疗诱导的耐药机制。
我们进行了综合基因组分析，以确定导致放疗抵抗的基因，并进行了靶向药物筛选，以确定与 DMG 中放疗协同作用的药物。通过研究细胞死亡、BCL2 磷酸化、活性氧（ROS）和凋亡的变化，以及 BCL2 与 BH3 凋亡起始因子的结合情况，来评估 venetoclax 对未经辐射的细胞和 6Gy 辐射的影响。使用原位异种移植模型评估 venetoclax 与放疗联合的疗效。
BCL2 被鉴定为 DMG 中放疗后肿瘤生长的关键调节因子。辐射使 DMG 对 venetoclax 治疗敏感，与 p53 状态无关。venetoclax 作为单一疗法对 DMG 细胞没有细胞毒性。放疗后 venetoclax 治疗显著增加细胞死亡，减少 BCL2-BIM 结合，并增加线粒体 ROS，导致凋亡增加。venetoclax 与放疗联合显著提高了携带 DMG 肿瘤小鼠的存活率。
这项研究表明，venetoclax 抑制了 DMG 中放疗诱导的 BCL2 的抗凋亡功能，导致细胞凋亡增加。这些临床前研究的结果表明，BCL2 抑制剂 venetoclax 联合放疗可能用于治疗小儿 DMG。
