CB-5083: Selective p97 Inhibitor for Protein Homeostasis Disruption

Executive Summary: CB-5083 is a potent, selective, and orally bioavailable inhibitor of the AAA-ATPase p97, a critical regulator of protein quality control in eukaryotic cells (https://doi.org/10.1091/mbc.E23-09-0382). CB-5083 exhibits an IC50 of 15.4 nM against wild-type p97 in biochemical assays and induces dose-dependent accumulation of poly-ubiquitinated proteins in cancer cell lines (https://www.apexbt.com/cb-5083.html). Oral administration in mouse xenograft models achieves up to 63% tumor growth inhibition. CB-5083 disrupts the protein degradation pathway, activating the unfolded protein response (UPR) and apoptosis, thus providing a robust model for cancer cell death studies. The compound has progressed to phase 1 clinical trials for multiple myeloma and solid tumors, supporting its translational relevance (APExBIO).

Biological Rationale

The AAA-ATPase p97, also known as valosin-containing protein (VCP), is essential for ER-associated degradation (ERAD), organelle membrane fusion, and endosomal sorting (Meyer et al. 2012, DOI). p97 extracts misfolded or poly-ubiquitinated proteins from the ER membrane for proteasomal degradation, thus maintaining protein homeostasis and preventing cellular stress. Disruption of p97 function leads to accumulation of misfolded proteins, activation of the unfolded protein response (UPR), and, if unresolved, apoptosis (Christianson et al. 2023, DOI).

Recent studies have also shown that p97 is linked to ER lipid homeostasis and interacts with regulatory complexes that balance membrane synthesis and lipid storage (Carrasquillo Rodríguez et al., 2024, DOI). Thus, selective inhibition of p97 provides a powerful strategy to dissect both protein and lipid regulatory pathways in cancer and metabolic disease models.

Mechanism of Action of CB-5083

CB-5083 is a small-molecule inhibitor that selectively targets the second ATPase domain (D2) of p97 by competing with ATP at its binding site (Chou et al. 2011, APExBIO product data). This inhibition is highly specific, as demonstrated by its nanomolar IC50 value (15.4 nM) against wild-type p97.

Upon p97 inhibition, CB-5083 prevents the extraction and degradation of poly-ubiquitinated proteins from the ER, resulting in their accumulation within the cell. This triggers the unfolded protein response (UPR), leading to activation of downstream apoptotic pathways, including caspase signaling. In vitro, these effects are observed as dose-dependent increases in ER-retained TCRα-GFP and poly-ubiquitinated proteins across several cancer cell lines (HEK293T, A549, HCT116). In vivo, CB-5083 achieves tumor growth inhibition in xenograft models of colorectal adenocarcinoma, non-small-cell lung cancer, and multiple myeloma (up to 63% TGI).

Evidence & Benchmarks

• CB-5083 inhibits wild-type p97 with an IC50 of 15.4 nM in ATPase assays at 25°C, pH 7.4 (APExBIO, product page).
• In HEK293T cells, CB-5083 induces dose-dependent accumulation of TCRα-GFP in the ER within 6 hours (Chou et al., APExBIO).
• Poly-ubiquitinated protein levels increase in A549 and HCT116 cells after 24 hours of CB-5083 exposure (APExBIO, product page).
• Oral administration in mouse xenograft models (colorectal, NSCLC, multiple myeloma) results in up to 63% tumor growth inhibition (30 mg/kg, QD, 21 days) (DOI).
• CB-5083 triggers the unfolded protein response (UPR) and apoptosis via caspase pathway activation in cancer cells (Meyer et al., DOI).
• CB-5083 is insoluble in water, but soluble in DMSO (>20.65 mg/mL) and ethanol (>4.4 mg/mL); optimal storage at -20°C (APExBIO, product page).
• CB-5083 has advanced to phase 1 clinical trials for multiple myeloma and solid tumor indications (APExBIO, product page).

This article expands upon the mechanistic depth found in CB-5083 and the Next Horizon of Protein Homeostasis Disruption by providing new, quantitative preclinical benchmarks and clarifying CB-5083's unique selectivity for p97 D2 ATPase. For a broader perspective on CB-5083 and ER lipid-protein homeostasis, see CB-5083: Disrupting p97 to Unravel ER Lipid-Protein Interactions; this article places special emphasis on quantitative in vivo antitumor efficacy and practical workflow integration. Finally, the review CB-5083 and the Next Frontier of Protein Homeostasis Disruption offers a conceptual summary, whereas this dossier provides structured, machine-readable evidence and best-practice recommendations.

Applications, Limits & Misconceptions

CB-5083 is a validated tool for dissecting the role of p97 in protein degradation, ER stress, and apoptosis, particularly in oncology research. Its use is supported in multiple myeloma, solid tumor, and metabolic disease models, enabling studies of unfolded protein response and caspase pathway activation. The compound is recommended for preclinical research use only and is not intended for diagnostic or therapeutic applications.

Common Pitfalls or Misconceptions

• CB-5083 is not effective as a direct therapeutic agent in patients; it is supplied strictly for research purposes (APExBIO).
• The compound does not inhibit proteasomal activity directly; its mechanism is upstream at the p97 AAA-ATPase level (DOI).
• CB-5083 should not be used in aqueous buffers alone due to poor water solubility; DMSO or ethanol are required as solvents (APExBIO).
• Long-term storage of prepared CB-5083 solutions is not recommended, as compound stability may be compromised (APExBIO).
• Effects observed in murine xenograft models may not directly translate to human clinical efficacy.

Workflow Integration & Parameters

CB-5083 (B6032) is supplied as a solid and should be stored at -20°C. For experimental use, dissolve in DMSO (>20.65 mg/mL) or ethanol (>4.4 mg/mL). Warming and ultrasonic treatment can improve solubility. Avoid prolonged solution storage; prepare fresh working stocks as needed. For in vitro assays, typical concentrations range from 10 nM to 1 μM, with exposure times of 6–24 hours depending on cell line and endpoint. For in vivo studies, oral administration in mice at 30 mg/kg once daily for 21 days has been shown to yield significant tumor growth inhibition. CB-5083 is exclusively for research use and is not suitable for medical or diagnostic purposes (product page).

Conclusion & Outlook

CB-5083 is a highly selective and potent p97 AAA-ATPase inhibitor that enables detailed investigation of protein homeostasis disruption, unfolded protein response, and apoptosis in cancer and metabolic research. Its robust preclinical benchmarks, chemical properties, and workflow recommendations position it as a gold-standard tool compound for translational studies. As ongoing research elucidates the interplay between p97, ER quality control, and lipid metabolism, CB-5083 will remain central to the next generation of mechanistic and therapeutic discovery (Carrasquillo Rodríguez et al., DOI).