The Efficacy and Mechanism of Proteasome Inhibitors in Solid Tumor Treatment

BACKGROUND: The ubiquitin-proteasome system (UPS) is critical in cellular protein degradation and widely involved in the regulations of cancer hallmarks. Targeting the UPS pathway has emerged as a promising novel treatment in hematological malignancies and solid tumors. OBJECTIVE: This review mainly focuses on the preclinical results of proteasome inhibitors in solid tumors. METHODS: We analyzed the published articles associated with the anticancer results of proteasome inhibitors alone or combination chemotherapy in solid tumors. Important data presented in abstract form were also discussed in this review. RESULTS/CONCLUSION: Proteasome inhibitors, such as bortezomib and carfilzomib, are highly effective in treating solid tumors. The anticancer efficacy is not limited to affect the proteasomal inhibition- associated signaling pathways but also widely involves the signaling pathways related to cell cycle, apoptosis, and epithelial-mesenchymal transition (EMT). In addition, proteasome inhibitors overcome the conventional chemo-resistance of standard chemotherapeutics by inhibiting signaling pathways, such as NF-κB or PI3K/Akt. Combination chemotherapy of proteasome inhibitors and standard chemotherapeutics are widely investigated in multiple relapsed or chemo-resistant solid tumor types, such as breast cancer and pancreatic cancer. The proteasome inhibitors re-sensitize the standard chemotherapeutic regimens and induce synergistic anticancer effects. The development of novel proteasome inhibitors and delivery systems also improves the proteasome inhibitors' anticancer efficacy in solid tumors. This review summarizes the current preclinical results of proteasome inhibitors in solid tumors and reveals the potential anticancer mechanisms.