Although immune checkpoint blockade (ICB) represents a major breakthrough in cancer immunotherapy, only a limited number of patients with cancer benefit from ICB-based immunotherapy because most immune checkpoint inhibitors (ICIs) target only T cell activation. Therefore, targeting non-T cell components in the tumor microenvironment (TME) can help subvert resistance and increase the applications of ICB-based therapy. Axl and Mer are involved in the carcinogenesis of multiple types of cancer by modulating immune and biological behaviors within tumors. Colony stimulating factor 1 receptor (CSF1R) mediates tumorigenesis in the TME by enhancing tumor associated macrophage (TAM) and myeloid-derived suppressor cell (MDSC) infiltration, facilitating immune escape. Therefore, the simultaneous inhibition of Axl, Mer, and CSF1R kinases may improve therapeutic efficacy by targeting non-T cell components in the TME. Here, we present Q702, a selective, potent small molecule inhibitor targeting Axl, Mer, and CSF1R, for oral administration. Q702 induced antitumor activity in syngeneic tumor mouse models by: remodeling the TME toward immune stimulation; expanding M1 macrophage and CD8 T cell populations and decreasing M2 macrophage and MDSC populations in the TME; and increasing MHC class I and E-cadherin expression in tumor cells. Thus, Q702 may have great potential to broaden the coverage of populations benefiting from ICB-based immunotherapy.

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.

This study investigates the transcriptional impact of Q901, a highly selective cyclin-dependent kinase 7 (CDK7) inhibitor in clinical development. Q901 primarily disrupted MYC and E2F-dependent transcription programs, down-regulating cell cycle control and DNA damage repair pathways. CDK7 binding at the promoter-proximal regions was markedly stabilized by Q901, leading to reduced occupancy of MYC, E2F, and RNA polymerase II (RNAPII). These findings offered a novel therapeutic strategy to enhance cancer susceptibility to topoisomerase I (TOP1) DNA-protein cross-links (TOP1-DPCs) induced by TOP1 inhibitors. Resistance to TOP1 inhibitors arises through activation of DNA repair pathways when elongating RNAPII encounters TOP1-DPCs. By suppressing RNAPII transition from initiation to elongation and DNA repair pathways, Q901 stabilizes TOP1-DPCs and sensitizes tumors to TOP1 inhibitors. Preclinical studies demonstrated enhanced tumor suppression when combining Q901 with TOP1 inhibitor–based antibody-drug conjugates (TOP1i-ADCs), highlighting its potential as a therapeutic option for cancers resistant to TOP1i-ADC therapy.