CB-5083: Selective p97 Inhibitor for Cancer Cell Apoptosis and Protein Homeostasis Disruption

Executive Summary: CB-5083 is a potent and selective inhibitor of the AAA-ATPase p97, with nanomolar IC50 and oral bioavailability, enabling targeted disruption of protein homeostasis in cancer cells (APExBIO). It acts by selectively inhibiting the second ATPase domain of p97, causing accumulation of poly-ubiquitinated proteins and activating unfolded protein response (UPR) and apoptosis (Carrasquillo Rodríguez et al., 2024). CB-5083 demonstrates significant tumor growth inhibition (up to 63% TGI) in mouse xenograft models of multiple myeloma and solid tumors. The compound is insoluble in water but highly soluble in DMSO and ethanol, and is recommended for storage at -20°C. APExBIO supplies CB-5083 (B6032) for research purposes only; it is not for clinical or diagnostic use.

Biological Rationale

The endoplasmic reticulum (ER) is the primary site for protein synthesis, folding, and quality control in eukaryotic cells. Correct folding and degradation of misfolded proteins are critical for cellular homeostasis. The AAA+-ATPase p97 (valosin-containing protein, VCP) is a key regulator of ER-associated protein degradation (ERAD), working in concert with the proteasome to extract and process poly-ubiquitinated proteins for degradation (Carrasquillo Rodríguez et al., 2024). Disruption of p97 function leads to protein aggregation, ER stress, and activation of the UPR, which in turn can induce apoptosis, especially in cancer cells with high proteotoxic load. Targeting p97 is therefore a validated strategy for modulating protein homeostasis, apoptosis, and cell fate in cancer and metabolic research (see related article).

Mechanism of Action of CB-5083

CB-5083 is a selective p97 AAA-ATPase inhibitor. It competitively binds to the second ATPase domain (D2) of p97, blocking ATP hydrolysis. The reported IC50 for wild-type p97 is 15.4 nM under standard in vitro assay conditions (APExBIO). This inhibition prevents the extraction and degradation of poly-ubiquitinated proteins, resulting in their accumulation within the ER and cytosol. Accumulated misfolded proteins trigger the unfolded protein response (UPR), activating stress signaling and apoptosis pathways, including the caspase signaling cascade. In cancer cell lines (HEK293T, A549, HCT116), CB-5083 induces dose-dependent accumulation of TCRα-GFP (a model misfolded protein) and poly-ubiquitinated substrates, directly linking p97 inhibition to impaired protein degradation and apoptotic cell death (see mechanistic review).

Evidence & Benchmarks

• CB-5083 inhibits wild-type p97 ATPase activity with an IC50 of 15.4 nM in biochemical assays (APExBIO, product data).
• In HEK293T cells, CB-5083 induces dose-dependent accumulation of TCRα-GFP and poly-ubiquitinated proteins within 6 hours at 37°C (APExBIO, product page).
• CB-5083 triggers the unfolded protein response (UPR) and apoptosis, as measured by increased CHOP expression and caspase activation in A549 and HCT116 cells (Carrasquillo Rodríguez et al., 2024).
• Oral administration of CB-5083 in mouse xenograft models results in tumor growth inhibition (TGI) up to 63% for colorectal adenocarcinoma, non-small-cell lung cancer, and multiple myeloma (APExBIO, product data).
• CB-5083 is insoluble in water but dissolves at >20.65 mg/mL in DMSO and >4.4 mg/mL in ethanol at 25°C (APExBIO, product specification).
• CB-5083 advanced to phase 1 clinical trials for multiple myeloma and solid tumors (APExBIO, product page).
• The AAA+-ATPase p97 is essential for ER-associated degradation (ERAD) and protein quality control in mammalian cells (Carrasquillo Rodríguez et al., 2024).

Applications, Limits & Misconceptions

CB-5083 is widely used in preclinical research to probe protein degradation pathways, ER stress, and apoptosis in cancer and metabolic disease models. It is particularly relevant for studying multiple myeloma, solid tumors, and the intersection of protein and lipid homeostasis (see systems biology perspective). This article updates previous coverage by detailing quantitative benchmarks and clarifying optimal integration into cell-based and in vivo workflows.

Common Pitfalls or Misconceptions

• CB-5083 is not intended for diagnostic or medical use; it is supplied for research purposes only (APExBIO).
• Insolubility in water can lead to dosing errors; always prepare in DMSO or ethanol and use ultrasonic treatment if needed.
• Long-term storage of CB-5083 solutions at room temperature leads to degradation; store at -20°C and prepare fresh solutions for each experiment.
• p97 inhibition may have off-target cellular effects at high concentrations; titrate doses carefully and confirm specificity (see advanced insights).
• CB-5083 does not directly affect ER lipid synthesis enzymes such as CTDNEP1 or NEP1R1; its primary mode of action is on protein homeostasis (Carrasquillo Rodríguez et al., 2024).

Workflow Integration & Parameters

Compound Preparation: Dissolve CB-5083 in DMSO or ethanol to >20.65 mg/mL or >4.4 mg/mL, respectively, at 25°C. Use ultrasonic treatment to enhance solubility if required. Avoid water as a solvent. Store solid compound at -20°C and avoid long-term storage of solutions (product page).

Experimental Design: For cell-based assays, typical working concentrations range from 10 nM to 1 μM, with exposure times from 2 to 24 hours depending on endpoint (e.g., UPR induction, apoptosis, protein aggregation). For in vivo studies, oral administration in mice is standard, with dosing regimens tailored to tumor model and pharmacokinetics. Monitor for accumulation of poly-ubiquitinated protein, activation of UPR markers (e.g., CHOP), and apoptosis readouts (e.g., caspase cleavage).

For advanced interrogation of ER-associated protein and lipid homeostasis, CB-5083 can be combined with genetic perturbations of lipid regulatory enzymes (CTDNEP1, NEP1R1) as described in Carrasquillo Rodríguez et al., 2024. This workflow enables dissection of protein-lipid crosstalk during ER stress and membrane biogenesis.

This article extends prior reviews such as 'CB-5083: Unraveling p97 Inhibition for Advanced Cancer and Metabolic Disease Models' by providing updated benchmarks and practical integration notes for experimentalists.

Conclusion & Outlook

CB-5083, available from APExBIO as B6032, is a well-validated, orally bioavailable, and highly selective p97 inhibitor. It provides robust, nanomolar potency for disrupting protein homeostasis, inducing ER stress, and triggering apoptosis in cancer models. The compound's specificity and reproducible in vivo efficacy make it a gold-standard tool for mechanistic studies in oncology and ER stress biology. Future studies may explore combination strategies with lipid regulatory pathway inhibitors, further leveraging CB-5083's unique capacity to dissect protein-lipid crosstalk in health and disease (Carrasquillo Rodríguez et al., 2024).