Targeting G1–S-checkpoint-compromised cancers with cyclin A/B RxL inhibitors
Shilpa Singh, Catherine E. Gleason, Min Fang, Yasmin Nabil Laimon, Vishal Khivansara, Shanhai Xie, Yavuz T. Durmaz, Aniruddha Sarkar, Kenneth Ngo, Varunika Savla, Yixiang Li, Muhannad Abu‐Remaileh, Xinyue Li, Marie-Anaïs Locquet, Bishma Tuladhar, Ranya Odeh, Frances Hamkins-Indik, Daphne He, Miles W. Membreño, Meisam Nosrati, Nathan N. Gushwa, Siegfried S. F. Leung, Breena Fraga-Walton, Luis Ortiz-Hernández, Miguel P. Baldomero, Bryan M. Lent, David C. Spellmeyer, Joshua F. Luna, Dalena Hoang, Yuliana Gritsenko, Manesh Chand, Megan K. DeMart, Sammy Metobo, Chinmay Bhatt, Justin A. Shapiro, Kai Yang, Nathan J. Dupper, Andrew T. Bockus, Jinshu Fang, Ramesh Bambal, Peadar Cremin, John G. Doench, James B. Aggen, Lifen Liu, Bernard Levin, Evelyn W. Wang, Iolanda Vendrell, Román Fischer, Benedikt M. Kessler, Prafulla C. Gokhale, Sabina Signoretti, Alexander Spektor, Constantine Kreatsoulas, Marie Evangelista, Rajinder Singh, David J. Earp, Deepak Nijhawan, Pablo D. García, Matthew G. Oser
Abstract
Small-cell lung cancers (SCLCs) contain near-universal loss-of-function mutations in RB1 and TP53, compromising the G1–S checkpoint and leading to dysregulated E2F activity1. Other cancers similarly disrupt the G1–S checkpoint through loss of CDKN2A or amplification of cyclin D or cyclin E, also resulting in excessive E2F activity2,3. Although E2F activation is essential for cell cycle progression, hyperactivation promotes apoptosis4–9, presenting a therapeutic vulnerability. Cyclin proteins use a conserved hydrophobic patch to bind to substrates bearing short linear RxL motifs10–13. Cyclin A represses E2F through an RxL-dependent interaction10,14, which, when disrupted, hyperactivates E2F15. However, this substrate interface has remained difficult to target. Here we developed cell-permeable, orally bioavailable macrocyclic peptides that inhibit RxL-mediated interactions of cyclins with their substrates. Dual inhibitors of cyclin A and cyclin B RxL motifs (cyclin A/Bi) selectively kill SCLC cells and other cancer cells with high E2F activity. Genetic screens revealed that cyclin A/Bi induces apoptosis through cyclin B- and CDK2-dependent spindle assembly checkpoint activation. Mechanistically, cyclin A/Bi hyperactivates E2F and cyclin B by blocking cyclin A–E2F and cyclin B–MYT1 RxL interactions. Notably, cyclin A/Bi promoted the formation of neomorphic cyclin B–CDK2 complexes, which drive spindle assembly checkpoint activation and mitotic cell death. Finally, orally administered cyclin A/Bi showed robust anti-tumour activity in chemotherapy-resistant SCLC patient-derived xenografts. These findings reveal gain-of-function mechanisms through which cyclin A/Bi triggers apoptosis and support their development for E2F-driven cancers. Dual cyclin A/B RxL inhibitors selectively kill small cell lung cancer cells and other cancer cells with high E2F activity.