The existing proteasome inhibitors, such as bortezomib and ixazomib, are effective in multiple myeloma, but have little activity against solid tumors. These are covalent boronic acid-based compounds and are associated with undesired side effects, mainly hematologic toxicity and peripheral neuropathy. A variety of improved covalent proteasome inhibitors have been developed, but lack of oral availability and low distribution in tumors make them ineffective in solid tumors. In addition, they still have a narrow therapeutic window due to unexpected adverse effects such as cardiac and pulmonary toxicity. We report a non-covalent and rapidly reversible proteasome inhibitor as a potential anti-cancer agent against solid tumors as well as multiple myeloma. These novel inhibitors, called QL compounds, are non-covalent chymotrypsin-like selective proteasome inhibitors that can be taken orally. They effectively inhibited tumor growth in multiple myeloma xenograft model without hematologic toxicity through improved PK properties, especially partition of compound between plasma and RBC. Moreover, this improved PK properties of the QL compounds allowed for sufficient distribution outside the blood compartment and induced tumor growth inhibition in some types of solid cancer xenograft models that were sensitive to proteasome inhibition. These results indicate that non-covalent and rapidly reversible proteasome inhibitors are an ideal strategy for multiple myeloma and potential agents for solid tumors.

Citation Format: Won-Gyun Ahn, Yeejin Jeon, Yeong-In Yang, Jaeseung Kim, Seung-Joo Lee, Uwe Koch, Gunther Zischinsky, Axel Choidas, Ayesha Pasha, Bert Klebl, Robert Huber, Michael Hamacher, Kiyean Nam. A novel non-covalent and rapidly reversible proteasome inhibitor for multiple myeloma and various solid cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 416.