Targeting G1-S-checkpoint-compromised cancers with cyclin A/B RxL inhibitors

  • Nature. 2025 Aug 20. doi: 10.1038/s41586-025-09433-w.
Shilpa Singh  1 ,  Catherine E Gleason  2 ,  Min Fang  3 ,  Yasmin N Laimon  4 ,  Vishal Khivansara  3 ,  Shanhai Xie  3 ,  Yavuz T Durmaz  1 ,  Aniruddha Sarkar  5 ,  Kenneth Ngo  1  6 ,  Varunika Savla  4 ,  Yixiang Li  1 ,  Muhannad Abu-Remaileh  1 ,  Xinyue Li  1 ,  Marie-Anais Locquet  1 ,  Bishma Tuladhar  6 ,  Ranya Odeh  2 ,  Frances Hamkins-Indik  2 ,  Daphne He  2 ,  Miles W Membreno  2 ,  Meisam Nosrati  2 ,  Nathan N Gushwa  2 ,  Siegfried S F Leung  2 ,  Breena Fraga-Walton  2 ,  Luis Hernandez  2 ,  Miguel P Baldomero  2 ,  Bryan M Lent  2 ,  David Spellmeyer  2 ,  Joshua F Luna  2 ,  Dalena Hoang  2 ,  Yuliana Gritsenko  2 ,  Manesh Chand  2 ,  Megan K DeMart  2 ,  Sammy Metobo  2 ,  Chinmay Bhatt  2 ,  Justin A Shapiro  2 ,  Kai Yang  2 ,  Nathan J Dupper  2 ,  Andrew T Bockus  2 ,  Jinshu Fang  2 ,  Ramesh Bambal  2 ,  Peadar Cremin  2 ,  John G Doench  7 ,  James B Aggen  2 ,  Li-Fen Liu  2 ,  Bernard Levin  2 ,  Evelyn W Wang  2 ,  Iolanda Vendrell  8 ,  Roman Fischer  8 ,  Benedikt Kessler  8 ,  Prafulla C Gokhale  1  6 ,  Sabina Signoretti  4  9 ,  Alexander Spektor  5 ,  Constantine Kreatsoulas  2 ,  Marie Evangelista  2 ,  Rajinder Singh  2 ,  David J Earp  2 ,  Deepak Nijhawan  3 ,  Pablo D Garcia  2 ,  Matthew G Oser  10  11
Affiliations
  • 1. Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA.
  • 2. Circle Pharma, San Francisco, CA, USA.
  • 3. Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
  • 4. Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
  • 5. Department of Radiation Oncology, Dana-Farber Cancer Institute, Brigham & Women's Hospital, Harvard Medical School, Boston, MA, USA.
  • 6. Belfer Center for Applied Cancer Science, Experimental Therapeutics Core, Dana-Farber Cancer Institute, Boston, MA, USA.
  • 7. Broad Institute of MIT and Harvard, Cambridge, MA, USA.
  • 8. Target Discovery Institute, Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
  • 9. Department of Oncologic Pathology, Dana-Farber Cancer Institute, Boston, MA, USA.
  • 10. Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA. [email protected].
  • 11. Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA. [email protected].
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.

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