Discovery of a Series of Acridinones as Mechanism-Based Tubulin Assembly Inhibitors with Anticancer Activity

Microtubules play critical roles in vital cell processes, including cell growth, division, and migration. Microtubule-targeting small molecules are chemotherapeutic agents that are widely used in the treatment of cancer. Many of these compounds are structurally complex natural products (e.g., paclitaxel, vinblastine, and vincristine) with multiple stereogenic centers. Because of the scarcity of their natural sources and the difficulty of their partial or total synthesis, as well as problems related to their bioavailability, toxicity, and resistance, there is an urgent need for novel microtubule binding agents that are effective for treating cancer but do not have these disadvantages. In the present work, our lead discovery effort toward less structurally complex synthetic compounds led to the discovery of a series of acridinones inspired by the structure of podophyllotoxin, a natural product with important microtubule assembly inhibitory activity, as novel mechanism-based tubulin assembly inhibitors with potent anticancer properties and low toxicity. The compounds were evaluated in vitro by wound healing assays employing the metastatic and triple negative breast cancer cell line MDA-MB-231. Four compounds with IC50 values between 0.294 and 1.7 μM were identified. These compounds showed selective cytotoxicity against MDA-MB-231 and DU-145 cancer cell lines and promoted cell cycle arrest in G2/M phase and apoptosis. Consistent with molecular modeling results, the acridinones inhibited tubulin assembly in in vitro polymerization assays with IC50 values between 0.9 and 13 μM. Their binding to the colchicine-binding site of tubulin was confirmed through competitive assays.

微管（Microtubules）在细胞生长、分裂、迁移等关键生命活动中发挥核心作用。靶向微管的小分子化合物是一类广泛应用于癌症治疗的化疗药物。此类化合物中多数为结构复杂的天然产物（如紫杉醇（paclitaxel）、长春碱（vinblastine）、长春新碱（vincristine）），且含有多个手性中心。由于天然来源稀缺、部分或全合成难度大，且存在生物利用度、毒性及耐药性等问题，亟需开发既能有效治疗癌症又无上述缺陷的新型微管结合剂。本研究在针对结构更简易的合成化合物开展的先导化合物发现工作中，以具有重要微管组装抑制活性的天然产物鬼臼毒素（podophyllotoxin）的结构为灵感，发现了一系列吖啶酮类化合物；这类化合物作为新型基于作用机制的微管蛋白组装抑制剂，兼具强效抗癌活性与低毒性。本研究采用转移性三阴性乳腺癌细胞系MDA-MB-231进行伤口愈合实验，对上述化合物开展体外评价，最终筛选得到4个半最大效应浓度（IC50）介于0.294至1.7 μM之间的活性化合物。此类化合物对MDA-MB-231与DU-145癌细胞系展现出选择性细胞毒性，并可诱导细胞周期阻滞于G2/M期及细胞凋亡。与分子模拟结果一致，吖啶酮类化合物在体外聚合实验中可抑制微管蛋白组装，其半最大效应浓度介于0.9至13 μM之间。竞争性结合实验证实，此类化合物可结合微管蛋白的秋水仙碱结合位点。