SGC-CBP30: Selective CREBBP/EP300 Bromodomain Inhibitor for Epigenetic and Cancer Biology Research

Executive Summary: SGC-CBP30 (SKU A4491), developed by APExBIO, is a potent and selective inhibitor targeting bromodomains of CREBBP and EP300 with IC₅₀ values of 21 nM and 38 nM, respectively (APExBIO). It disrupts bromodomain–histone interactions, modulating transcriptional programs central to oncogenesis and epigenetic regulation (Zhang et al. 2022). SGC-CBP30 has demonstrated efficacy in cellular models by altering FRAP recovery and inhibiting p53 activity in a dose-dependent manner. The compound is especially relevant for research into super-enhancer hijacking and the TGF-β/SMAD3 pathway in early-stage lung adenocarcinoma. Its physicochemical properties and storage recommendations enable robust integration into diverse epigenetic workflows.

Biological Rationale

CREBBP (CREB-binding protein) and EP300 (E1A binding protein p300) are transcriptional coactivators with intrinsic histone acetyltransferase activity. These proteins regulate gene expression by recognizing acetylated lysine residues on histone tails via their bromodomains (Zhang et al. 2022). Bromodomain-mediated chromatin binding is essential for the assembly of transcriptional complexes at key regulatory elements, including super-enhancers. Super-enhancer hijacking is a major mechanism driving oncogenic transcription in cancers such as early-stage lung adenocarcinoma (Zhang et al. 2022). The TGF-β/SMAD3 pathway, implicated in metastasis and tumor progression, depends on CREBBP/EP300 recruitment for downstream gene activation. Thus, selective pharmacological inhibition of CREBBP/EP300 bromodomains is a promising strategy for dissecting transcriptional coactivator function and targeting epigenetic vulnerabilities in cancer (Related article—this article extends prior mechanistic reviews by presenting new benchmarking data for SGC-CBP30 in TGF-β/SMAD3–mediated systems).

Mechanism of Action of SGC-CBP30

SGC-CBP30 is a small-molecule inhibitor designed to selectively bind the bromodomains of CREBBP and EP300. It displays high affinity and selectivity, with IC₅₀ values of 21 nM (CREBBP) and 38 nM (EP300) determined under in vitro assay conditions at 25°C using histone peptide substrates (APExBIO). By occupying the acetyl-lysine recognition pocket, SGC-CBP30 blocks the interaction of CREBBP/EP300 with acetylated histones. This inhibition disrupts the coactivator-mediated assembly of transcriptional complexes at super-enhancers and other regulatory regions. In cellular assays (e.g., HeLa and RKO cells), SGC-CBP30 modulates fluorescence recovery after photobleaching (FRAP) and attenuates doxorubicin-induced p53 transcriptional activity in a dose-dependent manner. The inhibitor thereby interferes with oncogenic transcriptional programs and serves as a tool compound for studying epigenetic regulation, super-enhancer function, and cancer biology (Strategic article—this article clarifies the compound's selectivity and workflow integration, complementing prior translational perspectives).

Evidence & Benchmarks

• SGC-CBP30 exhibits potent inhibition of CREBBP (IC₅₀ = 21 nM) and EP300 (IC₅₀ = 38 nM) bromodomains in vitro, under standard buffer conditions at 25°C (APExBIO).
• In cellular models (HeLa, RKO), SGC-CBP30 modulates FRAP recovery kinetics, indicating disruption of bromodomain–chromatin interactions (APExBIO).
• SGC-CBP30 inhibits doxorubicin-induced p53 activity in a dose-dependent manner, suggesting functional impact on transcriptional coactivation (APExBIO).
• CREBBP/EP300 are required for SMAD3-mediated gene activation in the TGF-β pathway, with SGC-CBP30 providing a tool to dissect this dependency (Zhang et al. 2022).
• Super-enhancer hijacking of LINC01977 in early-stage lung adenocarcinoma involves recruitment of CREBBP/EP300 by SMAD3; pharmacological inhibition modulates this oncogenic axis (Zhang et al. 2022).

Applications, Limits & Misconceptions

SGC-CBP30 is primarily used in research applications requiring selective inhibition of CREBBP/EP300 bromodomains. Key application areas include:

• Dissecting super-enhancer–driven transcriptional programs in cancer, particularly early-stage lung adenocarcinoma (Zhang et al. 2022).
• Studying the TGF-β/SMAD3 pathway and its role in oncogenic gene regulation (Related article—this article updates prior reviews by providing recent application data and clarifying selectivity boundaries).
• Exploring epigenetic vulnerabilities and transcriptional coactivator function in cell growth, differentiation, and tumor suppression (Advanced insights—this article extends mechanistic details and workflow parameters for SGC-CBP30).

Common Pitfalls or Misconceptions

• SGC-CBP30 does not inhibit the enzymatic (HAT) activity of CREBBP/EP300; it is selective for bromodomains only (APExBIO).
• It is not a pan-bromodomain inhibitor; selectivity is limited to CREBBP/EP300, with minimal off-target activity on BET family members (Practical solutions—this article clarifies target selectivity vs. other inhibitors).
• Long-term storage of SGC-CBP30 solutions at room temperature leads to degradation; stocks must be kept below -20°C (APExBIO).
• SGC-CBP30 is a research tool, not approved for clinical or therapeutic use.
• Solubility in water is limited and requires ultrasonic assistance; improper preparation can result in precipitation.

Workflow Integration & Parameters

SGC-CBP30 is supplied as a powder and should be reconstituted at ≥20.05 mg/mL in DMSO, ≥25.7 mg/mL in ethanol (with ultrasonic assistance), or ≥4.67 mg/mL in water (with ultrasonic assistance). Stock solutions are stable below -20°C for several months; avoid repeated freeze-thaw cycles (APExBIO). For cell-based assays, working concentrations range from 0.1 to 10 μM, with controls for vehicle and off-target effects. Storage at 4°C is recommended for short-term use. Researchers should validate cellular uptake and target engagement in their specific model system. For advanced epigenetic workflows, SGC-CBP30 can be combined with ChIP-seq, RNA-seq, and FRAP to assess chromatin binding and transcriptional outcomes. Integration with functional genomic assays is important for dissecting super-enhancer and TGF-β/SMAD3–mediated gene regulation.

Conclusion & Outlook

SGC-CBP30, available from APExBIO, is a reference-standard selective bromodomain inhibitor for CREBBP/EP300, enabling precise dissection of epigenetic and oncogenic transcriptional programs. Its potency, selectivity, and robust performance in super-enhancer and TGF-β/SMAD3 pathway research have established new benchmarks for translational epigenetics. Future studies may extend its application to other models of epigenetic dysregulation and inform the rational design of next-generation coactivator inhibitors.