Abstract
Click chemistry–based modification of BET inhibitors allows use as molecular probes in vitro and in vivo.
Major finding: Click chemistry–based modification of BET inhibitors allows use as molecular probes in vitro and in vivo.
Concept: These probes may be used to evaluate the toxicity and efficacy of BET inhibitors or other drugs.
Impact: Click chemistry provides a framework to characterize the mechanisms of action of targeted therapies.
Targeted cancer therapeutics have shown great promise in preclinical research, but relatively few have had clinical success, in part due to a poor understanding of the molecular and cellular effects of the targeted agents. Tyler, Vappiani, and colleagues used a click-chemistry approach to chemically modify BET bromodomain inhibitors, which are under investigation in multiple malignancies, for use as molecular probes to allow assessment of the cellular localization, protein and genomic targets, and effects of the drug in animal models without impairing cellular drug uptake or drug-target interactions. This approach aimed to preserve the functional integrity of BET inhibitors and allowed fluorochromes or affinity tags to be reacted with the BET inhibitors within cells. Clickable derivatives of the BET inhibitors JQ1 and IBET-762 were synthesized [JQ1-Propargyl Amide, JQ1-trans-cyclooctene (JQ1-TCO), and IBET-762-TCO]. The clickable BET inhibitors phenocopied the parental compounds, resulting in displacement of BET proteins from chromatin, reduced proliferation, and nearly identical gene expression signatures. Using click sequencing to discover drug–chromatin target interactions within cells revealed that genes downregulated by BET inhibition exhibited higher chromatin occupancy of the drug, indicating that this approach can identify drug-responsive genes. Further, the JQ1 and IBET derivatives associated with the same protein complexes, demonstrating that these compounds have an overlapping molecular activity. In vivo in a mouse model of acute myeloid leukemia (AML), the activity of JQ1-TCO was higher in AML cells in the spleen compared with the bone marrow, providing a possible explanation for the development of refractory leukemic stem cells in the bone marrow, and suggesting that BET inhibitor efficacy may be improved by increased bone marrow penetration. Moreover, intracellular drug levels were higher in AML cells compared with normal hematopoietic cells. This click-chemistry approach provides insight into the mechanism of action of BET inhibitors and may allow for preclinical characterization of a wide range of targeted cancer therapies.
Note: Research Watch is written by Cancer Discovery editorial staff. Readers are encouraged to consult the original articles for full details. For more Research Watch, visit Cancer Discovery online at http://cancerdiscovery.aacrjournals.org/content/early/by/section.
RSS Feeds