BRD4 PROTAC Degrader ARV-825 Inhibits T-Cell Acute Lymphoblastic Leukemia by Targeting 'Undruggable' Myc-pathway Genes

Abstract

BackgroundT-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease with a high risk of induction failure and poor outcomes, with relapse due to drug resistance. Targeting bromodomains and extra-terminal (BET) protein inhibitors are promising anti-cancer agents, and ARV-825, comprising a BET inhibitor conjugated with cereblon, was recently shown to attenuate the growth of multiple tumors in vitro and in vivo. However, the functional and molecular mechanisms of ARV-825 in T-ALL remain unclear. This study aimed to investigate the therapeutic efficacy and potential mechanism of ARV825 in T-ALL.MethodsExpression levels of the BET protein BRD4 were determined in pediatric T-ALL samples and differential gene expression after ARV-825 treatment was explored by RNA-seq and quantitative reverse transcription-polymerase chain reaction. T-ALL cell viability was measured by CCK8 assay after ARV-825 administration. Cell cycle was analyzed by propidium iodide (PI) staining and apoptosis was assessed by Annexin V/PI staining. The functional and molecular pathways involved in ARV-825 treatment of T-ALL were verified by western blot and chromatin immunoprecipitation (ChIP).ResultsBRD4 expression was higher in pediatric T-ALL samples compared with T-cells from healthy donors. High BRD4 expression indicated a poor outcome. ARV-825 suppressed cell proliferation in vitro by arresting the cell cycle and inducing apoptosis, with elevated poly-ADP ribose polymerase and cleaved caspase 3. BRD4, BRD3, and BRD2 were degraded in line with reduced cereblon expression in T-ALL cells. ARV-825 had a lower IC50 in T-ALL cells compared with the BET inhibitors JQ1 and dBET1. ARV-825 perturbed the H3K27Ac-Myc pathway and reduced c-Myc protein levels in T-ALL cells according to RNA-seq and ChIP. Moreover, ARV-825 inhibited cell proliferation by depleting BET and c-Myc proteins in T cell lines and in pediatric T-ALL patients. ConclusionsBRD4 indicates a poor prognosis in T-ALL. The BRD4 degrader ARV-825 can effectively suppress the proliferation and promote apoptosis of T-ALL cells via BET protein depletion and c-Myc inhibition, thus providing a new strategy for the treatment of T-ALL.

Development of an N-Terminal BRD4 Bromodomain-Targeted Degrader

“…20 Similar results have been observed in other cancers [21][22][23] supporting BRD4 as the most relevant BET protein to target for degradation. 24 We envisioned an approach using a ligand with high BRD4 specificity and affinity to degrade BRD4 in a cell line with high BRD4 sensitivity (e.g., multiple myeloma, MM.1S), but only a few molecules with high selectivity for inhibiting BRD4 exist. 25,26 By leveraging selectivity properties and structural information of our BD1-selective inhibitors, 27,28 we hypothesized we could degrade BRD4 through an individual bromodomain.…”