Authors: Yongxin Ren, Qiaoling Sun, Jingwen Long, Shiming Fan, Renxiang Tang, Wei Zhang, Xuelei Ge, Jianxing Tang, Linfang Wang, Dongxia Shi, Hongbo Chen, Min Cheng, Weiguo Qing and Weiguo Su
The development of therapies targeting tumor angiogenesis, tumor driver gene alterations and tumor immune evasion has made tremendous advancement in improving overall survival (“OS”). However, efficacy may be limited and resistance often develops rapidly when targeting a single axis of tumorigenesis. Therefore, it is worthwhile to explore rational combination of therapies based on tumor-specific features. Fruquintinib is a potent and selective oral VEGFR inhibitor currently in Phase III clinical trials for non-small-cell lung cancer (“NSCLC”) and colorectal cancer (“CRC”). We report here the evaluation of anti-tumor effect of fruquintinib in preclinical animal tumor models in combination with therapies targeting tumor driver gene alterations such as epidermal growth factor receptor (“EGFR”) and mesenchymal growth factor receptor (“c-MET”) or with immune checkpoints.
In NSCLC xenograft models with EGFR activation such as activating mutations, gene amplification or protein overexpression, fruquintinib plus an EGFR tyrosine kinase inhibitor such as gefitinib or theliatinib (HMPL-309) was found to be more efficacious than either monotherapy. For instance, in PC-9 subcutaneous tumor model carrying EGFR exon 19 deletion, single agent treatment with fruquintinib at 2 mg/kg and gefitinib at 5 mg/kg produced the tumor growth inhibition (“TGI”) of 58% and 63%, respectively, while the combination treatment resulted in a TGI of 100% and tumor regression was observed in 11 of 16 mice treated with combinational therapy. In multiple xenograft models derived from lung cancer or renal cell cancer with c-MET activation (amplification or over-expression), addition of fruquintinib to a c-MET inhibitor savolitinib (AZD6094, HMPL-504) also improved the tumor growth inhibition substantially. At the end of the efficacy studies, CD31 and phosphorylation of EGFR, c-MET, protein kinase B (AKT) and extracellular signal–regulated kinase (ERK) were analyzed with immunohistochemistry and western blotting method in tumor tissues. The results suggested that the enhanced anti-tumor effect in combination therapy could be attributed to the simultaneous blockade of cell signaling in tumor cells (EGFR or c-MET) and VEGFR suppression in the tumor microenvironment.
Up-regulation of the immune inhibitory checkpoints induced by VEGF is one of the important mechanisms for tumor cells to escape immune surveillance. In a syngeneic murine tumor model, co-administration of fruquintinib and anti-Programmed death-ligand 1 (“PD-L1”) antibody was found to provide improved anti-tumor effect compared to fruquintinib or anti-PD-L1 single agent alone. Studies to understand the mechanism responsible for the combination effect are underway.
All combinations with fruquintinib described above were well tolerated. The efficacy observed in these models suggested that simultaneous blockade of tumor angiogenesis and tumor cell signaling or immune evasion may be a promising approach in improving treatment outcomes.