Profiling potential targets of anlotinib in human synovial sarcoma patients and immunocompetent mouse models

Synovial sarcoma (SS) is an aggressive translocation-driven malignancy characterized by its driving SS18::SSX fusion oncogene. This rare but deadly cancer presents limited treatment options despite an emerging understanding of its dependency on receptor tyrosine kinases (RTKs). Anlotinib is a multi-target tyrosine kinase inhibitor (TKI) that was recently approved in China for treatment of soft tissue sarcomas (STSs), and is now on route through the U.S. clinical pipeline, currently designated an orphan drug. To better understand the therapeutic efficacy of anlotinib for SS, we here investigate the molecular impact of SS on RTK targets of anlotinib. Integrating RNAseq data from STS patient tumors with analyses of our genetically engineered mouse SS models, we performed RNAseq, single-cell transcriptomics, epigenetic profiling, and immunohistochemistry to interrogate a predicted set of kinase anlotinib targets. We identified FGFR1-3 and PDGFRA as the most highly expressed RTKs in SS, targeted both directly and indirectly via enhancer looping by the chromatin-bound SS18::SSX2 oncoprotein. This finding underscores the possibility that rewiring of FGFR (and PDGFRA) signaling--both of which are reported targets of anlotinib--is a fundamental feature of SS. Although FGFRs1-3 are reportedly targets of anlotinib, TKIs with greater specificity for FGF pathway targets may provide better defense against SS tumor aggression. Our treated SS mice demonstrated only modest attenuation of tumor growth for approximately six weeks, a response that mirrors anlotinib treatment efficacy seen in human patients. SignificanceAnlotinib is a small molecule inhibitor shown to inhibit proteins critical to several cancer pathways. We interrogated published human transcriptome datasets and performed preclinical anlotinib trials in an immunocompetent mouse model of synovial sarcoma (SS) to establish a molecular understanding of anlotinib therapy in this rare, but deadly cancer.