CB-5083: Selective p97 AAA-ATPase Inhibitor for Cancer Research

Executive Summary: CB-5083 (SKU B6032) is a small-molecule inhibitor targeting the AAA ATPase p97/valosin-containing protein, a central regulator of protein homeostasis and endoplasmic reticulum (ER) quality control (Carrasquillo Rodríguez et al., 2024). It selectively inhibits the second ATPase domain of p97 with an IC₅₀ of 15.4 nM in wild-type p97, and is orally bioavailable (APExBIO product page). CB-5083 induces dose-dependent protein degradation and apoptosis in multiple cancer cell lines, including HEK293T, A549, and HCT116 (related article). In vivo, it suppresses tumor growth and activates the unfolded protein response (UPR) pathway in mouse xenograft models. The compound is advancing translational research in multiple myeloma and solid tumors, as evidenced by phase 1 clinical trials (APExBIO).

Biological Rationale

Protein homeostasis, or proteostasis, is essential for cell viability and is tightly regulated by ER-associated degradation (ERAD) and the ubiquitin-proteasome system. The AAA ATPase p97 (also known as VCP) extracts misfolded or ubiquitinated proteins from membranes, facilitating their degradation (Carrasquillo Rodríguez et al., 2024). Disruption of this process leads to accumulation of misfolded proteins, induction of the unfolded protein response (UPR), and ultimately triggers apoptosis. Targeting the p97 ATPase is a validated strategy for sensitizing cancer cells to proteotoxic stress, making selective p97 inhibitors, such as CB-5083, valuable tools for oncology research. The ER is also the site of lipid synthesis and storage, and recent studies highlight the intersection between proteostasis and lipid metabolism via regulators such as CTDNEP1-NEP1R1, further underscoring the impact of p97 inhibition on cellular homeostasis (Carrasquillo Rodríguez et al., 2024).

Mechanism of Action of CB-5083

CB-5083 is a solid-phase, small molecule with a molecular weight of 413.47. It is insoluble in water but dissolves in DMSO (≥20.65 mg/mL) and ethanol (≥4.4 mg/mL) (APExBIO). CB-5083 selectively targets the D2 ATPase domain of p97, competitively inhibiting ATP binding with an IC₅₀ of 15.4 nM against wild-type p97. This inhibition blocks p97-mediated extraction and processing of ubiquitinated substrates, leading to proteasome-dependent degradation disruptions. As a result, ER protein quality control mechanisms are activated, causing accumulation of unfolded proteins and sustained UPR activation. Prolonged UPR triggers apoptotic pathways, notably caspase signaling, in cancer cells (see mechanistic review). In vivo, oral CB-5083 administration achieves bioactive concentrations and anti-tumor effects in xenograft models.

Evidence & Benchmarks

• CB-5083 exhibits potent inhibition of wild-type p97 with an IC₅₀ of 15.4 nM under standard ATPase assay conditions (37°C, Tris buffer, 30 min incubation) (APExBIO).
• Dose-dependent induction of apoptosis and cytosolic protein degradation observed in HEK293T, A549, and HCT116 cell lines after 24–48 h CB-5083 exposure at 0.1–10 μM (related article).
• Oral CB-5083 (5–30 mg/kg, QD) significantly suppresses tumor growth in mouse xenograft models of human lung carcinoma, colorectal adenocarcinoma, and multiple myeloma, as measured by tumor volume reduction over 21 days (APExBIO).
• CB-5083 induces sustained UPR (as evidenced by upregulation of BiP, CHOP, and XBP1s) and caspase-3/7-mediated apoptosis in tumor tissues (see translational review).
• CTDNEP1-NEP1R1 complex regulates ER homeostasis by shielding CTDNEP1 from proteasomal degradation, linking p97 pathway disruption to lipid synthesis and storage (Carrasquillo Rodríguez et al., 2024).

Applications, Limits & Misconceptions

CB-5083 is primarily used in research on cancer cell apoptosis, protein homeostasis, and the unfolded protein response pathway. It is suitable for in vitro cytotoxicity assays, mechanistic studies on ER stress, and in vivo efficacy studies in xenograft models. The compound has advanced to phase 1 clinical trials for multiple myeloma and solid tumor indications.

This article extends prior mechanistic analyses by integrating new insights into lipid metabolism and ER regulation, as discussed in CB-5083: Advancing p97 Inhibition for ER Quality Control, by emphasizing the intersection of protein/lipid homeostasis and cancer fate.

Common Pitfalls or Misconceptions

• CB-5083 is not a general proteasome inhibitor; it is selective for p97 and does not directly inhibit 20S/26S proteasome catalytic activity (APExBIO).
• CB-5083's effects are cell-type and context-dependent; non-cancerous or low-proliferation cells may be less sensitive to UPR-mediated apoptosis.
• Compound is insoluble in water; improper vehicle selection (e.g., aqueous buffers) may lead to precipitation and assay failure.
• Long-term storage of CB-5083 solutions (e.g., in DMSO >1 week at room temperature) leads to degradation and loss of potency (APExBIO).
• CB-5083 is not suitable for direct assessment of lipid droplet biogenesis, as its primary target is the protein homeostasis machinery, although indirect effects may arise (Carrasquillo Rodríguez et al., 2024).

Workflow Integration & Parameters

For in vitro studies, dissolve CB-5083 in DMSO to prepare stock solutions (≥20.65 mg/mL). Dilute to working concentrations (0.1–10 μM) in cell culture medium, ensuring final DMSO concentration does not exceed 0.1% v/v. For in vivo use, oral gavage at 5–30 mg/kg is effective in murine xenografts. Store solid CB-5083 at -20°C. Avoid repeated freeze-thaw cycles and long-term storage of solutions. The B6032 kit from APExBIO provides batch documentation and purity validation. For optimal results in apoptosis or ER stress assays, include positive (e.g., MG-132) and negative controls.

For advanced guidance on integrating CB-5083 into reproducible cell-based assays, see Optimizing Cancer Cell Assays with CB-5083: Practical Scenarios, which details workflow tips and troubleshooting strategies not covered in this article.

Conclusion & Outlook

CB-5083, provided by APExBIO, is a validated and selective tool for disrupting p97-mediated protein homeostasis in cancer research. Its potency, oral bioavailability, and documented benchmarks in apoptosis and tumor suppression position it as a leading agent for preclinical studies. Integration of CB-5083 into ER quality control research, as well as emerging links to lipid metabolism, enables new translational applications. Future studies may expand its utility in systems biology and combinatorial oncology approaches, while careful attention to solubility and storage parameters ensures maximal reproducibility.

For further reading on how CB-5083 uniquely bridges proteostasis and lipid regulation, see Disrupting Protein Homeostasis and Lipid Regulation: Strategic Insights—this article provides an integrative perspective beyond the mechanistic focus presented here.