CB-5083: Selective p97 Inhibitor for Protein Homeostasis Disruption

Executive Summary: CB-5083 is an orally bioavailable, highly potent, and selective inhibitor of the p97 AAA-ATPase (valosin-containing protein), central to protein homeostasis and degradation (ApexBio). It competitively inhibits the second ATPase domain of p97 with an IC₅₀ of 15.4 nM (standard ATPase assay, 37°C), blocking degradation of polyubiquitinated proteins and triggering the unfolded protein response (UPR) and apoptosis in cancer cells (Carrasquillo Rodríguez et al., 2024). In vitro, CB-5083 causes dose-dependent accumulation of TCRα-GFP and polyubiquitinated proteins in HEK293T, A549, and HCT116 cells, while in vivo, it achieves up to 63% tumor growth inhibition (TGI) in mouse xenograft models (Ami-1.com). The compound is insoluble in water but highly soluble in DMSO (>20.65 mg/mL) and ethanol (>4.4 mg/mL), and should be stored at -20°C for stability (ApexBio). CB-5083 is for research use only and is not suitable for diagnostic or clinical applications.

Biological Rationale

The AAA+ ATPase p97 (valosin-containing protein) is essential for multiple cellular processes, including organelle membrane fusion, endosomal cargo sorting, and regulation of the protein degradation pathway via the ubiquitin-proteasome system (Carrasquillo Rodríguez et al., 2024). p97 extracts misfolded or unwanted proteins from the endoplasmic reticulum (ER) membrane, targeting them for proteasomal degradation and maintaining cellular protein quality control. Disruption of this pathway leads to the accumulation of polyubiquitinated proteins, activation of ER stress, and induction of the unfolded protein response (UPR). Cancer cells, due to high rates of protein synthesis and turnover, are particularly dependent on efficient protein homeostasis mechanisms. Inhibiting p97 impairs protein clearance, causing proteotoxic stress and selectively inducing apoptosis in cancerous cells (Chelerythrinechloride.com). This article extends previous discussions by providing granular mechanistic and benchmarking insights, including recent findings on p97's role in ER lipid-protein quality control.

Mechanism of Action of CB-5083

CB-5083 is a small-molecule inhibitor that selectively targets the second ATPase domain (D2) of p97. It acts as an ATP-competitive antagonist, preventing ATP hydrolysis required for p97's unfolding and extraction activities. By inhibiting p97, CB-5083 disrupts the ER-associated degradation (ERAD) pathway, resulting in the accumulation of misfolded and polyubiquitinated proteins in the cytoplasm. This accumulation activates the UPR, leading to increased expression of chaperones and, if unresolved, triggers apoptosis via the caspase signaling pathway. The selectivity of CB-5083 for p97 D2 ensures minimal off-target effects compared to broader proteasome inhibitors (Carrasquillo Rodríguez et al., 2024). In vitro, CB-5083 induces dose-dependent accumulation of TCRα-GFP fusion protein in the ER, confirming blockade of protein degradation. In multiple cancer cell lines, CB-5083 triggers apoptotic markers such as caspase-3 activation and PARP cleavage, confirming mechanism-based cytotoxicity (Ubiquitin-specific-protease-3-fragment.com), updating previous summaries by integrating recent apoptosis pathway data.

Evidence & Benchmarks

• CB-5083 inhibits p97 ATPase activity with an IC₅₀ of 15.4 nM in purified recombinant wild-type p97 at 37°C (ApexBio, product page).
• CB-5083 causes dose-dependent accumulation of TCRα-GFP in the ER and polyubiquitinated proteins in HEK293T, A549, and HCT116 cell lines (Carrasquillo Rodríguez et al., 2024, DOI).
• Oral administration in mouse xenograft models (colorectal adenocarcinoma, non-small-cell lung cancer, multiple myeloma) results in up to 63% tumor growth inhibition after 21 days at 60 mg/kg/day (Ami-1.com).
• CB-5083 induces apoptosis in cancer cells, evidenced by caspase-3 cleavage and PARP cleavage within 24 hours of treatment at 1–10 μM in vitro (Ubiquitin-specific-protease-3-fragment.com).
• The compound is insoluble in water but soluble in DMSO (>20.65 mg/mL) and ethanol (>4.4 mg/mL); recommended storage at -20°C (product page).

Applications, Limits & Misconceptions

Research Applications: CB-5083 is used for dissecting the role of p97 in protein homeostasis, ER stress, and UPR signaling. It enables modeling of cancer cell vulnerability to proteotoxic stress and evaluating the interplay between protein degradation and ER lipid synthesis (GSK1363089.com). This article clarifies and updates previous reports by directly linking CB-5083 data to emerging lipid-protein quality control pathways described in the 2024 Carrasquillo Rodríguez et al. study.

Common Pitfalls or Misconceptions

• CB-5083 is not a pan-proteasome inhibitor; its activity is limited to p97 and does not broadly inhibit the 26S proteasome complex.
• CB-5083 is not approved for clinical use, diagnosis, or therapy; it is for research purposes only.
• CB-5083 is insoluble in water; improper solvents will reduce experimental efficacy.
• Long-term storage of prepared solutions (>24 hours at room temperature) leads to compound degradation and loss of potency.
• CB-5083 effects are context-dependent and may vary across cell lines with different proteostasis or UPR baselines.

Workflow Integration & Parameters

CB-5083 (SKU: B6032) is supplied as a solid (molecular weight 413.47, chemical formula C₂₄H₂₃N₅O₂). Dissolve in DMSO (>20.65 mg/mL) or ethanol (>4.4 mg/mL) using warming and ultrasonic treatment for optimal solubility. Recommended storage is at -20°C, avoiding repeated freeze-thaw cycles. For in vitro use, typical working concentrations range from 0.1–10 μM; in vivo, oral dosing up to 60 mg/kg/day has demonstrated efficacy in mouse models. CB-5083 enables synchronized induction of protein degradation blockade, UPR, and apoptosis. For detailed protocol integration and troubleshooting, refer to the product page. For a deeper mechanistic perspective on the interface with ER lipid homeostasis, see our coverage at cy7-azide.com, which this article extends by including quantitative in vivo efficacy data.

Conclusion & Outlook

CB-5083 is a validated, selective inhibitor of the p97 AAA-ATPase, crucial for investigating protein homeostasis, ER stress, and cellular apoptosis in cancer and metabolic disease research. Its robust in vitro and in vivo benchmarks, oral bioavailability, and defined selectivity profile make it a premier research tool for dissecting the mechanistic underpinnings of proteostasis and ER signaling. Ongoing studies are refining its applications in integrating protein and lipid homeostasis, with potential broader implications for metabolic disease models and next-generation targeted therapies (Carrasquillo Rodríguez et al., 2024).