PhD thesis defense in biomedical and pharmaceutical sciences by Eléonore HARDY

Targeting the Pin1-regulated c-Myc pathway to enhance radiotherapy: overcoming breast cancer stem cell resistance

Candidate

Eléonore HARDY

Promoters

Prof. Anne-Catherine HEUSKIN, UNamur, Department of physics, Physics of Matter and Radiation (PMR), Laboratory of Analysis by Nuclear Reaction (LARN) - promoter

Prof. Edmond STERPIN, UCLouvain, IREC / KU Leuven - co-promoter

Jury

• Patsy Renard, UNamur (president)
• Anne-Catherine Heuskin, UNamur
• Edmon Sterpin, UCLouvain / KU Leuven
• Pierre Sonveaux, UCLouvain
• Jean-François Daisne, Iridium Cancer Network, Antwerp
• Bernard Gallez, UCLouvain

Summary

Despite major advances in scientific knowledge, cancer remains one of the leading causes of mortality worldwide. Global projections indicate that the annual number of new cancer cases will continue to rise substantially, with estimates suggesting an increase from approximately 20 million cases in 2022 to more than 30 million by 2050. This underscores the growing need to unravel the mechanisms driving this disease and to develop novel, more effective therapeutic strategies. This thesis focuses on radiotherapy, one of the cornerstone treatments for cancer. Although it is theoretically capable of eradicating all malignant cells, its effectiveness is constrained by the collateral damage it can inflict on surrounding healthy tissues. Furthermore, in some cases despite successful initial eradication of the tumor, recurrence may still occur, sometimes several years after the end of the treatment. Following irradiation, cells can undergo adaptive changes that lead to the development of radioresistance. Multiple factors influence this process: radioresistance may arise from intrinsic properties already present before irradiation or from adaptive traits acquired in response to irradiation.

The first aim of this thesis is the investigation of the metabolic characteristics that enable cancer cells to respond to treatment. In this context, cancer stem cells are of particular interest, as they are known for their remarkable metabolic plasticity. To address this, we developed cell models that evolved across three key dimensions: radioresistance, metabolism, and stemness.

Through this approach, in the second part of this project, we identified a potential target that may contribute to the mechanisms linking these processes. Our findings highlight the c-Myc oncoprotein as a central feature in this interplay. Although c-Myc is a well-established oncogenic driver, it remains a significant therapeutic challenge due to the difficulty of directly targeting its structural properties and transcriptional activity. Furthermore, the combination of c-Myc inhibition with radiation therapy has been only minimally investigated and has never been explored in the context of breast cancer.

The final part of the work focuses on reversing acquired radioresistance through the inhibition of the target c-Myc. The feasibility of this strategy depends on achieving systemic blockade while maintaining a tolerable response in normal cells. In this context, we identified the co-upregulation of the peptidyl-prolyl isomerase Pin1, a more attractive therapeutic target due to its high specificity, well-defined active site and low expression in normal tissues. Pin1 is a key regulator of the activity and crosstalk of multiple oncogenic proteins, including c-Myc. In vitro, pretreatment with the Pin1 inhibitor KPT-6566 prior to X-ray irradiation reduced the survival of radioresistant cells. In vivo, the combined therapy decreased tumor growth derived from radioresistant cells. The selective inhibition of Pin1, together with the enhanced reactive oxygen species production induced by KPT-6566 in cancer cells, represents the main advantage over other c-Myc-targeting agents in combinatorial treatment strategies. For potential clinical translation, we propose that the co-upregulation of c-Myc and Pin1 may serve as a decisional biomarker to guide the use of a novel therapeutic approach.

Altogether, this project highlights a strategy based on the application of KPT-6566 as a radiosensitizer in combination with radiotherapy in breast cancer.