Abstract 5460: Preclinical characterization of QLH11906, a novel pan-RAF inhibitor
Authors: Cheng Zhe , Chen Fei , Liu Xile , Gao Cong , Jia Linchao , Lao Yuanzhi 
Published: June 2022

Background: The type 1/2 BRAF inhibitors (e.g., vemurafenib) have been used for patients with BRAFV600E-mutant tumors. But the application of the inhibitors was restricted to a few types of tumors (e.g., melanoma). Common adverse effects such as pruritus and skin papilloma have limited the usage. It could be attributed to the paradoxical activation of the MAPK pathway. The paradoxical activation also leads to tumor promotion in BRAF wild-type melanoma and skin toxicity in 30%-70% patients with KRAS mutations. Therefore, development of type II pan-RAF inhibitors which avoid MAPK paradoxical activation is necessary.

Methods: The selective pan-RAF inhibitor QLH11906 was tested on A/B/C RAF kinases and a representative kinase panel. Both 2D and 3D proliferation studies were conducted for cell lines with BRAF and various KRAS mutations, followed by both immunoprecipitation and ERK phosphorylation assays to elucidate the mode of action. Combination studies with MEK inhibitors were implemented in both KRAS-mutant cell lines and BRAF/KRAS-mutant patient derived organoids (PDO). Single-agent and combination studies were also carried out in vivo on both BRAF/KRAS-mutant cell line-derived xenograft (CDX) and KRAS-mutant patient-derived xenograft (PDX) models.

Results: QLH11906 inhibited wild-type A/B/C RAF and BRAFV600E with the IC50 of 4.9, 1.9, 0.5, and 1.1 nM, respectively, and showed no inhibition at 1 μM in a selectivity panel of 28 kinases except for DDR1 and DDR2. Under 2D culture condition, QLH11906 inhibited proliferation of various BRAF/KRAS-mutant cell lines (IC50 300-1700 nM) and suppressed ERK phosphorylation (IC50 20-600 nM). In 3D cultures, QLH11906 showed higher activity in proliferation suppression in both HCT116 (KRASG13D, IC50 24 nM 3D vs 1186 nM 2D) and Calu-6 (KRASQ61K, IC50 85 nM 3D vs 1411 nM 2D). In immunoprecipitation studies with HCT116 and Calu-6 cells, both BRAF homodimers and BRAF/CRAF heterodimers could be detected under the treatment of QLH11906. QLH11906 showed synergistic effect when combined with MEK inhibitors trametinib or cobimetinib in KRAS-mutant cell lines, including A549 (KRASG12S), Calu-6, HCT116, NCIH2122 (KRASG12C) and Panc1005 (KRASG12D), and 77%-99% tumor suppression was reached at the expected clinical Ctrough concentrations. Synergistic effects with trametinib were observed in PDO models including pancreatic cancers (KRASG12D and KRASG12V), colon cancers (KRASG12D and KRASG13D) and lung cancers (KRASG12V). QLH11906 also promoted tumor shrinkage in vivo as a single agent in Calu-6, HCT116, and Colo-205 (BRAFV600E) CDX models or combined with trametinib in PDX models (KRASG12C lung cancers and KRASG12C colon cancers)

Conclusion: QLH11906 is a highly selective pan-RAF inhibitor with promising antitumor activity both in vitro and in vivo. It is hopeful to be a therapeutic agent for BRAF and KRAS-mutant tumor patients.

Citation Format: Zhe Cheng, Fei Chen, Xile Liu, Cong Gao, Linchao Jia, Yuanzhi Lao. Preclinical characterization of QLH11906, a novel pan-RAF inhibitor [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 5460.