Related Experiment Video
Updated: Sep 10, 2025
Through the Looking Glass: Time-lapse Microscopy and Longitudinal Tracking of Single Cells to Study Anti-cancer Therapeutics
Published on: May 14, 2016
Targeting G1-S-checkpoint-compromised cancers with cyclin A/B RxL inhibitors
Shilpa Singh1, Catherine E Gleason2, Min Fang3
1Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA.
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.
Insights
New macrocyclic peptides selectively kill small-cell lung cancer (SCLC) cells by inhibiting cyclin interactions. These orally available drugs target E2F-driven cancers by inducing apoptosis through spindle assembly checkpoint activation.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- Small-cell lung cancer (SCLC) is characterized by mutations in RB1 and TP53, leading to dysregulated E2F activity.
- Hyperactivation of E2F, while essential for cell cycle progression, can promote apoptosis, presenting a therapeutic vulnerability.
- Targeting the cyclin-substrate interaction interface, specifically RxL motifs, has been challenging.
Purpose of the Study:
- To develop novel cell-permeable, orally bioavailable macrocyclic peptides targeting cyclin RxL motifs.
- To investigate the efficacy of these inhibitors in cancer cells with high E2F activity, including SCLC.
- To elucidate the molecular mechanisms underlying the anti-cancer effects of these novel inhibitors.
Main Methods:
- Development of dual inhibitors targeting cyclin A and cyclin B RxL motifs (cyclin A/Bi).
- Assessment of selective killing of SCLC and other cancer cells with high E2F activity.
- Utilizing genetic screens to identify mechanisms of apoptosis induction.
- Investigating the role of cyclin B, CDK2, and spindle assembly checkpoint activation.
- Evaluating anti-tumor activity in chemotherapy-resistant SCLC patient-derived xenografts.
Main Results:
- Cyclin A/Bi selectively kills SCLC and other cancer cells with high E2F activity.
- Apoptosis is induced via cyclin B- and CDK2-dependent spindle assembly checkpoint activation.
- Cyclin A/Bi blocks cyclin A-E2F and cyclin B-MYT1 RxL interactions, leading to E2F and cyclin B hyperactivation.
- Neomorphic cyclin B-CDK2 complexes are formed, driving mitotic cell death.
- Orally administered cyclin A/Bi demonstrated significant anti-tumor activity in SCLC xenografts.
Conclusions:
- Developed orally bioavailable macrocyclic peptides (cyclin A/Bi) that inhibit cyclin RxL interactions.
- Cyclin A/Bi effectively targets E2F-driven cancers, including SCLC, by inducing apoptosis.
- These findings support the therapeutic potential of cyclin A/Bi for treating chemotherapy-resistant SCLC and other cancers.
More Related Videos
10:33Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors
Published on: October 26, 2015
12:02Studying Cell Cycle-regulated Gene Expression by Two Complementary Cell Synchronization Protocols
Published on: June 6, 2017
Related Concept Videos
02:57Targeted Cancer Therapies
There are several types of targeted therapies against...
02:34Inhibition of Cdk Activity
01:28The Cell Cycle Control System
Cyclins and cyclin-dependent kinases (Cdks) are the primary cell cycle regulators and...
02:15M-Cdk Drives Transition Into Mitosis
Cyclin-dependent kinases, or Cdks, work in concert with cyclins to control cell cycle transitions. M-Cdk, a complex of Cdk1 bound to M cyclin, is a well-known example of this coordinated control that drives the transition from the G2 to the M phase.
M cyclin...
01:23Negative Regulator Molecules
02:39Positive Regulator Molecules