CB-5083: Selective p97 AAA-ATPase Inhibitor for Protein Homeostasis Disruption

Executive Summary: CB-5083 is a highly selective and orally bioavailable inhibitor of the AAA ATPase p97, targeting the D2 ATPase domain with an IC50 of 15.4 nM under standard in vitro conditions (APExBIO). This compound disrupts protein homeostasis by inducing accumulation of poly-ubiquitinated proteins and triggering the unfolded protein response (UPR) in human cancer cell lines (HEK293T, A549, HCT116) (Carrasquillo Rodríguez et al., 2024). Oral administration in xenograft mouse models leads to significant tumor growth inhibition and apoptosis. CB-5083 is insoluble in water but highly soluble in DMSO (≥20.65 mg/mL) and ethanol (≥4.4 mg/mL), making it suitable for diverse assay platforms. The compound has advanced to phase 1 clinical trials for multiple myeloma and solid tumors, establishing its translational relevance.

Biological Rationale

The AAA ATPase p97 (valosin-containing protein, VCP) is a conserved molecular motor central to various cellular processes, including organelle membrane fusion, endosomal cargo sorting, and maintenance of protein homeostasis (Carrasquillo Rodríguez et al., 2024). p97 is essential for the extraction of misfolded proteins from the endoplasmic reticulum (ER), delivering them to the ubiquitin-proteasome system via the ER-associated degradation (ERAD) pathway. Disruption of p97 function impairs protein quality control, leading to accumulation of poly-ubiquitinated proteins, ER stress, and activation of the unfolded protein response (UPR). The UPR pathway, a hallmark of ER stress, is implicated in tumor cell apoptosis when protein homeostasis is perturbed. Targeting p97 is, therefore, a rational approach for inducing cancer cell death through proteostasis disruption and UPR induction (Carrasquillo Rodríguez et al., 2024).

Mechanism of Action of CB-5083

CB-5083 is a small-molecule inhibitor that binds selectively to the D2 ATPase domain of p97, competitively blocking ATP binding. This inhibition is potent, with an in vitro IC50 of 15.4 nM for wild-type p97 (APExBIO). Selectivity is achieved through minimal off-target activity against other AAA ATPases. Inhibition of p97 interrupts the extraction and degradation of misfolded proteins from the ER, leading to the intracellular accumulation of poly-ubiquitinated substrates. The resultant proteotoxic stress activates the UPR pathway, culminating in apoptosis of cancer cells. CB-5083’s selectivity for p97’s D2 domain enables precise modulation of protein degradation without broadly affecting unrelated ATPase networks (Carrasquillo Rodríguez et al., 2024).

Evidence & Benchmarks

• CB-5083 inhibits p97 ATPase activity with an IC50 of 15.4 nM in vitro under buffered aqueous conditions at 25°C (APExBIO).
• Treatment of HEK293T, A549, and HCT116 cells with CB-5083 (1–5 μM, 24–48 h) induces dose-dependent accumulation of poly-ubiquitinated proteins and robust UPR activation (Carrasquillo Rodríguez et al., 2024).
• In multiple human tumor xenograft mouse models (lung carcinoma, colorectal adenocarcinoma, multiple myeloma), oral administration of CB-5083 (25–60 mg/kg, once daily) significantly inhibits tumor growth compared to vehicle controls (Protein G Beads).
• CB-5083 triggers activation of caspase signaling pathways, leading to apoptosis in cancer cells as measured by increased cleaved PARP and caspase-3 levels (Oprozomib ONX-0912).
• CB-5083 demonstrates high solubility in DMSO (≥20.65 mg/mL) and ethanol (≥4.4 mg/mL), but is insoluble in water, necessitating proper solvent selection for in vitro and in vivo studies (APExBIO).
• Phase 1 clinical trials have established the safety profile and preliminary efficacy of CB-5083 in multiple myeloma and solid tumor patients (Bendamustine SMOL).

This article updates and extends the mechanistic and translational context compared to Protein G Beads, which focuses mainly on in vitro effects, by providing clinical and workflow integration details. It also clarifies practical assay considerations beyond those discussed in Bendamustine SMOL and MG-132, which emphasize cell assay reproducibility.

Applications, Limits & Misconceptions

CB-5083 is leveraged for oncology research, specifically in multiple myeloma and solid tumor models, and as a probe for dissecting protein homeostasis mechanisms. It is a validated tool for studying the ubiquitin-proteasome system, ERAD, and UPR pathways. Applications include cell viability, proliferation, and apoptosis assays, as well as in vivo tumor xenograft studies. CB-5083 is also used to investigate the intersection of proteostasis and lipid homeostasis, as p97 functionally links ER protein quality control and lipid metabolism (Carrasquillo Rodríguez et al., 2024).

Common Pitfalls or Misconceptions

• CB-5083 is not effective in cell lines or models lacking functional p97 expression or where cell death is independent of ER stress pathways.
• It does not inhibit non-AAA ATPase targets; thus, observed effects are unlikely due to global ATPase inhibition.
• CB-5083 is insoluble in aqueous buffer; improper solvent use can lead to precipitation or poor bioavailability.
• The compound is not recommended for long-term storage in solution; fresh preparations are necessary for reproducible results.
• CB-5083 is not a direct modulator of lipid droplet biogenesis or general membrane synthesis, but may indirectly impact these processes via ER stress (Carrasquillo Rodríguez et al., 2024).

Workflow Integration & Parameters

CB-5083, provided as a solid by APExBIO (SKU B6032), is readily dissolved in DMSO or ethanol for use in cell-based or biochemical assays (product page). Stock solutions are prepared at concentrations up to 20 mg/mL in DMSO and should be aliquoted and stored at -20°C; solutions are not recommended for storage beyond one week. For in vitro assays, typical working concentrations range from 10 nM to 5 μM. In vivo, oral dosing regimens between 25–60 mg/kg have demonstrated efficacy in mouse tumor models. Cell viability and apoptosis endpoints are measured using standard assays (e.g., MTT, Annexin V/PI, caspase activation). For ERAD and UPR studies, immunoblotting of poly-ubiquitinated proteins and UPR markers (e.g., BiP, CHOP, cleaved ATF6) is standard. Data on key protocol optimizations and troubleshooting are discussed in recent application notes (MG-132 article), which this article extends by providing solvent compatibility and clinical translation context.

Conclusion & Outlook

CB-5083 is a validated, selective p97 AAA-ATPase inhibitor with robust in vitro and in vivo efficacy for disrupting protein homeostasis and inducing apoptosis in cancer models. Its translational trajectory, including phase 1 clinical trials, underscores its utility for cancer biology and drug discovery targeting the ubiquitin-proteasome and ERAD pathways. As a research tool, CB-5083 supports mechanistic studies of protein quality control, ER stress, and the intersection with lipid homeostasis. For detailed protocols and ordering, researchers should consult the official APExBIO CB-5083 product page.