A novel small molecule RAD51 inactivator overcomes imatinib‐resistance in chronic myeloid leukaemia

Jiewen Zhu,Xiao‐Long Qiu,Wen‐Hwa Lee,Heiko Konig,Longen Zhou,Guideng Li,Chi‐Fen Chen,Xiaoqin Lin,Chun‐Mei Hu,Erin Goldblatt,Ravi Bhatia,A Richard Chamberlin,Phang‐Lang Chen,Guikai Wu

doi:10.1002/emmm.201201760

Abstract

RAD51 recombinase activity plays a critical role for cancer cell proliferation and survival, and often contributes to drug-resistance. Abnormally elevated RAD51 function and hyperactive homologous recombination (HR) rates have been found in a panel of cancers, including breast cancer and chronic myeloid leukaemia (CML). Directly targeting RAD51 and attenuating the deregulated RAD51 activity has therefore been proposed as an alternative and supplementary strategy for cancer treatment. Here we show that a newly identified small molecule, IBR2, disrupts RAD51 multimerization, accelerates proteasome-mediated RAD51 protein degradation, reduces ionizing radiation-induced RAD51 foci formation, impairs HR, inhibits cancer cell growth and induces apoptosis. In a murine imatinib-resistant CML model bearing the T315I Bcr-abl mutation, IBR2, but not imatinib, significantly prolonged animal survival. Moreover, IBR2 effectively inhibits the proliferation of CD34+ progenitor cells from CML patients resistant to known BCR-ABL inhibitors. Therefore, small molecule inhibitors of RAD51 may suggest a novel class of broad-spectrum therapeutics for difficult-to-treat cancers.

Highlights

Homologous recombination (HR) is a critical cellular process, allowing cells to cope with genotoxic stresses by repairing DNA double-stranded breaks (DSBs), interstrand crosslinks, and abnormal replication forks with high fidelity
Identification of a small molecule (IBR2) that binds to RAD51 Using a forward chemical-genetics approach, we employed an inducible reverse yeast two-hybrid system, which allows yeast growth when the candidate compound abolishes the interaction between the BRC and RAD51-derived probes (TetRBRC and a GAL1-inducible AD-RAD51 fusion, Fig 1A)
Given the unstable genomic background of cancer cells, tyrosine kinases are prone to secondary mutations, leading to drug-resistance issues (Deininger et al, 2005; Gorre et al, 2001; Nardi et al, 2004)

Summary

Introduction

Homologous recombination (HR) is a critical cellular process, allowing cells to cope with genotoxic stresses by repairing DNA double-stranded breaks (DSBs), interstrand crosslinks, and abnormal replication forks with high fidelity. RAD51 can multimerize and form nucleofilaments on ssDNA, a step critical for the pairing of homologous DNA sequences and the subsequent strand exchange (Baumann et al, 1996; Conway et al, 2004; Haaf et al, 1995; Sung & Robberson, 1995). These RAD51-dependent processes are facilitated by many accessory factors including the breast cancer susceptibility gene product BRCA2. Even though cells deficient in the accessory factors may be viable, those without RAD51 are not, primarily because of the indispensable role of RAD51 in the HR pathway

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