细胞周期蛋白 E 是 CDK2 的调节亚基，介导 S 期进入和进展。全长细胞周期蛋白 E (FL-cycE) 裂解为低分子量异构体 (LMW-E) 会显着改变底物特异性，促进 G1/S 细胞周期转变并加速有丝分裂退出。大约 70% 的三阴性乳腺癌 (TNBC) 表达 LMW-E，这与不良预后相关。 PKMYT1 还通过抑制 CDK1 阻止有丝分裂过早进入，在有丝分裂中发挥重要作用，这表明它可能是表达 LMW-E 的 TNBC 的治疗靶点。在这里，对 TNBC 患者肿瘤样本的分析表明，LMW-E 和 PKMYT1 催化的 CDK1 磷酸化的共表达预示着对新辅助化疗的不良反应。与 FL-cycE 相比，LMW-E 特异性上调 PKMYT1 表达和蛋白质稳定性，从而提高 CDK1 磷酸化。用选择性抑制剂 RP-6306 (lunresertib) 抑制 PKMYT1 会引发 LMW-E 依赖性抗肿瘤作用，加速有丝分裂过早进入，抑制复制叉重新启动，并增强 DNA 损伤、染色体断裂、细胞凋亡和复制应激。重要的是，表达 LMW-E 的 TNBC 细胞系异种移植物比具有空载体或 FL-cycE 的肿瘤对 RP-6306 表现出更高的敏感性。此外，RP-6306 在 LMW-E 转基因小鼠乳腺肿瘤和 LMW-E 高 TNBC 患者来源的异种移植物中发挥肿瘤抑制作用，但在平行检查的 LMW-E 无效模型中没有发挥肿瘤抑制作用。最后，转录组学和免疫分析表明，RP-6306 治疗可诱导 LMW-E 高肿瘤微环境中的干扰素反应和 T 细胞浸润，从而增强抗肿瘤免疫反应。这些发现强调了 LMW-E/PKMYT1/CDK1 调节轴作为 TNBC 的一个有前途的治疗靶点，为进一步临床开发 PKMYT1 抑制剂在这种侵袭性乳腺癌亚型中的应用提供了理论依据。

Cyclin E is a regulatory subunit of CDK2 that mediates S phase entry and progression. Cleavage of full-length cyclin E (FL-cycE) to low molecular weight isoforms (LMW-E) dramatically alters the substrate specificity, promoting G1/S cell cycle transition and accelerating mitotic exit. Approximately 70% of triple-negative breast cancers (TNBC) express LMW-E, which correlates with poor prognosis. PKMYT1 also plays an important role in mitosis by inhibiting CDK1 to block premature mitotic entry, suggesting it could be a therapeutic target in TNBC expressing LMW-E. Here, analysis of TNBC patient tumor samples revealed that co-expression of LMW-E and PKMYT1-catalyzed CDK1 phosphorylation predicted poor response to neoadjuvant chemotherapy. Compared to FL-cycE, LMW-E specifically upregulated PKMYT1 expression and protein stability, elevating CDK1 phosphorylation. Inhibiting PKMYT1 with the selective inhibitor RP-6306 (lunresertib) elicited LMW-E dependent antitumor effects, accelerating premature mitotic entry, inhibiting replication fork restart, and enhancing DNA damage, chromosomal breaks, apoptosis, and replication stress. Importantly, TNBC cell line xenografts expressing LMW-E showed greater sensitivity to RP-6306 than tumors with empty vector or FL-cycE. Furthermore, RP-6306 exerted tumor suppressive effects in LMW-E transgenic murine mammary tumors and LMW-E-high TNBC patient-derived xenografts but not in the LMW-E null models examined in parallel. Lastly, transcriptomic and immune profiling demonstrated that RP-6306 treatment induced interferon responses and T-cell infiltration in the LMW-E-high tumor microenvironment, enhancing the antitumor immune response. These findings highlight the LMW-E/PKMYT1/CDK1 regulatory axis as a promising therapeutic target in TNBC, providing the rationale for further clinical development of PKMYT1 inhibitors in this aggressive breast cancer subtype.