Title: The functional effects and therapeutic potential of a novel thalidomide analogue that degrades GSPT1
Funder: Cancer Research UK

Abstract: Background Thalidomide analogues bind the CRL4CRBN ubiquitin ligase and induce recruitment of protein substrates for degradation. This allows therapeutic targeting of proteins key to cancer cell survival that were previously undruggable. CC-885 is a first in class thalidomide analogue that degrades GSPT1, a multifunctional protein recently identified as a dependency in acute myeloid leukaemia (AML). However, the exact mechanism(s) through which GSPT1 loss leads to cytotoxicity, the effects on normal stem cells, the genetic subtypes of leukaemia most sensitive, and potential resistance mechanisms are unknown. These are critical questions to answer for the clinical translation of drugs that degrade GSPT1. Aims I aim to establish how GSPT1 degradation leads to cytotoxicity with a focus on defective translation termination, its functional consequences for a cell, and the relationship to drug sensitivity. I will investigate genetic features of AML associated with vulnerability to GSPT1 degradation and the effects on normal haematopoiesis. I will also examine mechanisms through which cells may acquire drug resistance and use this to design and test combination therapies. Finally, I will identify and interrogate non-GSPT1 targets of CC-885 that might represent new cancer vulnerabilities. Methods I use targeted and genome wide screening approaches. These include sensitivity and resistance CRISPR screens, and fluorescent reporter screens combined with next generation sequencing. A key tool in my research is a novel mouse model with humanized cereblon sensitive to drug induced GSPT1 degradation. This will be used to derive cell lines to investigate sensitivity/resistance and develop important pre-clinical in vivo models to test the results of my genetic screens and response to therapies. How the results of this research will be used The results of this research will define the mechanism of cytotoxicity caused by GSPT1 degradation and which patients with AML are most likely to benefit from treatment with drugs degrading GSPT1. This work will also define anticipated mechanisms of resistance to treatment and inform the rational design of combination therapies. This will be important for the clinical translation of drugs targeting GSPT1. Finally, the study of GSPT1 and other new non-GSPT1 targets of CC-885 will inform the design of new thalidomide analogues and be instructive as to how other cancer types might be similarly targeted.

Lay abstract: Background Thalidomide analogues bind the CRL4CRBN ubiquitin ligase and induce recruitment of protein substrates for degradation. This allows therapeutic targeting of proteins key to cancer cell survival that were previously undruggable. CC-885 is a first in class thalidomide analogue that degrades GSPT1, a multifunctional protein recently identified as a dependency in acute myeloid leukaemia (AML). However, the exact mechanism(s) through which GSPT1 loss leads to cytotoxicity, the effects on normal stem cells, the genetic subtypes of leukaemia most sensitive, and potential resistance mechanisms are unknown. These are critical questions to answer for the clinical translation of drugs that degrade GSPT1. Aims I aim to establish how GSPT1 degradation leads to cytotoxicity with a focus on defective translation termination, its functional consequences for a cell, and the relationship to drug sensitivity. I will investigate genetic features of AML associated with vulnerability to GSPT1 degradation and the effects on normal haematopoiesis. I will also examine mechanisms through which cells may acquire drug resistance and use this to design and test combination therapies. Finally, I will identify and interrogate non-GSPT1 targets of CC-885 that might represent new cancer vulnerabilities. Methods I use targeted and genome wide screening approaches. These include sensitivity and resistance CRISPR screens, and fluorescent reporter screens combined with next generation sequencing. A key tool in my research is a novel mouse model with humanized cereblon sensitive to drug induced GSPT1 degradation. This will be used to derive cell lines to investigate sensitivity/resistance and develop important pre-clinical in vivo models to test the results of my genetic screens and response to therapies. How the results of this research will be used The results of this research will define the mechanism of cytotoxicity caused by GSPT1 degradation and which patients with AML are most likely to benefit from treatment with drugs degrading GSPT1. This work will also define anticipated mechanisms of resistance to treatment and inform the rational design of combination therapies. This will be important for the clinical translation of drugs targeting GSPT1. Finally, the study of GSPT1 and other new non-GSPT1 targets of CC-885 will inform the design of new thalidomide analogues and be instructive as to how other cancer types might be similarly targeted.

Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS;5.1 PHARMACEUTICALS
Health categories: CANCER AND NEOPLASMS