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Discovery and characterization of bromodomain 2-specific inhibitors of BRDT
Zhifeng Yu1, Angela F Ku1, Justin L Anglin1
1Center for Drug Discovery, Department of Pathology & Immunology, Baylor College of Medicine, Houston, TX 77030.
Abstract:
Bromodomain testis (BRDT), a member of the bromodomain and extraterminal (BET) subfamily that includes the cancer targets BRD2, BRD3, and BRD4, is a validated contraceptive target. All BET subfamily members have two tandem bromodomains (BD1 and BD2). Knockout mice lacking BRDT-BD1 or both bromodomains are infertile. Treatment of mice with JQ1, a BET BD1/BD2 nonselective inhibitor with the highest affinity for BRD4, disrupts spermatogenesis and reduces sperm number and motility. To assess the contribution of each BRDT bromodomain, we screened our collection of DNA-encoded chemical libraries for BRDT-BD1 and BRDT-BD2 binders. High-enrichment hits were identified and resynthesized off-DNA and examined for their ability to compete with JQ1 in BRDT and BRD4 bromodomain AlphaScreen assays. These studies identified CDD-1102 as a selective BRDT-BD2 inhibitor with low nanomolar potency and >1,000-fold selectivity over BRDT-BD1. Structure-activity relationship studies of CDD-1102 produced a series of additional BRDT-BD2/BRD4-BD2 selective inhibitors, including CDD-1302, a truncated analog of CDD-1102 with similar activity, and CDD-1349, an analog with sixfold selectivity for BRDT-BD2 versus BRD4-BD2. BROMOscan bromodomain profiling confirmed the great affinity and selectivity of CDD-1102 and CDD-1302 on all BET BD2 versus BD1 with the highest affinity for BRDT-BD2. Cocrystals of BRDT-BD2 with CDD-1102 and CDD-1302 were determined at 2.27 and 1.90 Å resolution, respectively, and revealed BRDT-BD2 specific contacts that explain the high affinity and selectivity of these compounds. These BD2-specific compounds and their binding to BRDT-BD2 are unique compared with recent reports and enable further evaluation of their nonhormonal contraceptive potential in vitro and in vivo.
Insights
Researchers developed selective inhibitors targeting the BRDT-BD2 bromodomain, a key factor in male fertility. These compounds show promise for developing novel nonhormonal contraceptives by specifically inhibiting spermatogenesis.
Area of Science:
- Reproductive Biology
- Medicinal Chemistry
- Structural Biology
Background:
- Bromodomain testis (BRDT) is a validated target for male contraception.
- BRDT, like other bromodomain and extraterminal (BET) subfamily members (BRD2, BRD3, BRD4), possesses two tandem bromodomains (BD1 and BD2).
- Selective inhibition of BRDT bromodomains is crucial for developing targeted contraceptives.
Purpose of the Study:
- To identify selective inhibitors for BRDT bromodomains (BRDT-BD1 and BRDT-BD2).
- To assess the contribution of individual BRDT bromodomains in spermatogenesis.
- To develop novel nonhormonal contraceptives targeting BRDT.
Main Methods:
- Screening of DNA-encoded chemical libraries for BRDT-BD1 and BRDT-BD2 binders.
- Resynthesis and in vitro evaluation of high-enrichment hits using AlphaScreen assays.
- Structure-activity relationship studies and X-ray crystallography of BRDT-BD2-inhibitor complexes.
Main Results:
- Identification of CDD-1102, a potent and selective BRDT-BD2 inhibitor (>1,000-fold selectivity over BRDT-BD1).
- Development of additional selective inhibitors, including CDD-1302 and CDD-1349, with varying selectivity profiles.
- X-ray crystallography revealed unique BRDT-BD2 specific contacts explaining compound selectivity and affinity.
Conclusions:
- Selective inhibition of BRDT-BD2 is achievable with novel chemical compounds.
- These BRDT-BD2 specific inhibitors offer a unique approach for nonhormonal male contraception.
- Further in vitro and in vivo evaluation of these compounds is warranted for contraceptive development.
