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

Executive Summary: CB-5083 is a highly selective and orally bioavailable p97 AAA-ATPase inhibitor (IC₅₀ 15.4 nM, wild-type p97), disrupting protein homeostasis and inducing apoptosis in diverse cancer cell lines (APExBIO). In mouse xenograft models, CB-5083 significantly suppresses tumor growth and activates the unfolded protein response (UPR) and caspase signaling pathways. The compound is insoluble in water but dissolves readily in DMSO (≥20.65 mg/mL) and ethanol (≥4.4 mg/mL), with recommended storage at -20°C. CB-5083 has advanced to phase 1 clinical trials for multiple myeloma and solid tumors, highlighting its translational relevance (Carrasquillo Rodríguez et al., 2024).

Biological Rationale

Protein homeostasis is essential for cell survival and function. The AAA ATPase p97 (also known as valosin-containing protein, VCP) plays a central role in protein quality control by extracting misfolded or unwanted proteins from membranes for proteasomal degradation (Carrasquillo Rodríguez et al., 2024). Disruption of p97 function leads to accumulation of misfolded proteins, triggering the unfolded protein response (UPR) and potentially apoptosis. Cancer cells often rely on robust protein quality control to cope with high protein synthesis and mutation-induced misfolding. Pharmacologic inhibition of p97, such as with CB-5083, disrupts these pathways, selectively inducing stress and cell death in tumor cells with elevated proteostatic demand (site article; clarifies upstream ERAD dependency compared to earlier overviews).

Mechanism of Action of CB-5083

CB-5083 is a small molecule inhibitor that binds competitively to the second ATPase domain (D2) of p97, blocking ATP hydrolysis and substrate processing. By preventing conformational cycling of p97, CB-5083 stalls ER-associated degradation (ERAD) and related protein turnover mechanisms. This leads to accumulation of polyubiquitinated proteins in the cytosol, induction of endoplasmic reticulum stress, and activation of the UPR pathway. Persistent UPR triggers pro-apoptotic signaling, including upregulation of CHOP and activation of caspases, culminating in cell death (site article; extends on the UPR pathway depth described previously). CB-5083 does not significantly affect other AAA ATPases at similar concentrations, demonstrating high selectivity for p97 (APExBIO).

Evidence & Benchmarks

• CB-5083 displays an IC₅₀ of 15.4 nM against wild-type p97 in ATPase assays (DMSO buffer, 25°C, 1 h) (APExBIO).
• In vitro, CB-5083 increases cytosolic protein degradation and induces dose-dependent apoptosis in HEK293T, A549, and HCT116 cancer cell lines (24–72 h, 1–10 μM) (site article).
• Oral administration in mouse xenograft models (lung carcinoma, colorectal adenocarcinoma, multiple myeloma) led to significant tumor growth inhibition (50–100 mg/kg, daily, up to 21 days) (Carrasquillo Rodríguez et al., 2024).
• CB-5083 induces robust UPR activation, including elevation of CHOP and spliced XBP1 in tumor tissues (RT-qPCR, immunoblot) (site article; updates with quantitative markers).
• Phase 1 clinical trial data show tolerability and early efficacy signals in relapsed/refractory multiple myeloma and select solid tumors (clinicaltrials.gov, NCT02243917) (APExBIO).

Applications, Limits & Misconceptions

CB-5083 is primarily applied in preclinical and translational research targeting protein homeostasis pathways in oncology. It is used to dissect ERAD, UPR, and apoptosis signaling in cell and animal models. The compound’s selectivity allows for mechanistic studies of p97-specific effects, distinguishing them from broader proteasome inhibition. Its oral bioavailability supports in vivo dosing regimens. For a comprehensive workflow comparison, see this article; this review adds updated benchmarks and detailed solubility parameters.

Common Pitfalls or Misconceptions

• CB-5083 does not inhibit the proteasome directly; it targets p97-mediated upstream processes.
• It is not soluble in water; use DMSO or ethanol for stock solutions.
• CB-5083's effects in non-cancerous cells at low doses are limited; cytotoxicity is more pronounced in cells with high proteostatic load.
• Long-term storage of CB-5083 solutions is discouraged due to potential degradation; prepare fresh aliquots as needed.
• Clinical efficacy is not yet established; all therapeutic claims remain investigational.

Workflow Integration & Parameters

CB-5083 is supplied as a solid (molecular weight: 413.47 g/mol, SKU: B6032) by APExBIO (product page). For cell-based assays, dissolve in DMSO to ≥20.65 mg/mL or ethanol to ≥4.4 mg/mL. Typical in vitro concentrations range from 0.1 to 10 μM. For in vivo studies, oral gavage at 50–100 mg/kg/day is standard. Store dry powder at -20°C in the dark; avoid repeated freeze-thaw cycles. Solutions should be freshly prepared and used promptly. CB-5083 is compatible with assays monitoring UPR (e.g., XBP1 splicing), caspase activity, and protein aggregation. Comparative studies may include proteasome or ERAD inhibitors to parse mechanistic specificity (site article; this article details precise dosing and storage not found in earlier summaries).

Conclusion & Outlook

CB-5083 has emerged as a next-generation, selective p97 AAA-ATPase inhibitor for dissecting protein homeostasis and apoptosis pathways in oncology research. Its demonstrated efficacy in preclinical models and advancement to early-phase trials underscore its potential. Continued investigation will clarify its clinical utility, optimal dosing regimens, and mechanistic boundaries in cancer and beyond. For further details or to acquire the B6032 kit, see APExBIO's CB-5083 product page.