Fig. 6

Silencing circRNA-SORE substantially improves sorafenib efficacy in vivo. a BALB/c nude mice (4- to 6-week-old males) were orthotopically implanted with SKhep1-SR-luc-NC or SKhep1-SR-luc-shcircRNA-SORE cells. On week 4, the mice were treated with sorafenib (30 mg/kg/day) for 4 weeks. In vivo luminescent imaging was performed weekly starting on week 4. Animals were sacrificed on week 8. Luminescence intensity ranges from low (blue) to high (red). b BALB/c nude mice (4- to 6-week-old males) were subcutaneously injected with LM3-SR cells. On week 4, the mice were treated with sorafenib (30 mg/kg/day) for 4 weeks and then injected at the implantation site with in vivo-grade si-circRNA-SORE or si-NC twice a week for 2 weeks. Animals were sacrificed on week 8. c NOD/SCID mice (4- to 6-week-old males) were subcutaneously implanted with HCC patient-derived xenograft (PDX) and treated with sorafenib (30 mg/kg/day) by oral gavage starting on week 4. Eight weeks later, the sorafenib-resistant xenograft was removed for a second round of orthotopic implantation. On week 4, the second PDX generation mice were treated with sorafenib (30 mg/kg/day) for 4 weeks and were injected at the implantation site with in vivo-grade si-circRNA-SORE or si-NC twice a week for 2 weeks. Animals were sacrificed and the second-generation PDX was isolated on week 8. d Immunohistochemistry for YBX1 in si-circRNA-SORE and si-NC LM3-SR xenografts. Scale bar, 50 µm. e Immunohistochemistry for YBX1 in si-circRNA-SORE and control PDX. Scale bar, 50 µm. f Model for circRNA-SORE-mediated sorafenib resistance in HCC. CircRNA-SORE is necessary for the development and maintenance of sorafenib resistance in HCC, and silencing circRNA-SORE substantially increases sorafenib-induced apoptosis. CircRNA-SORE specifically binds to the master oncogenic protein YBX1 and thus sequesters YBX1 in the cytoplasm, which prevents YBX1 ubiquitination and degradation by PRP19 in the nucleus. CircRNA-SORE is transmitted by exosomes, allowing for the spread of sorafenib resistance among HCC cells. Data are expressed as mean ± SEM (error bars). Statistical analyses used Student’s t test. ***p < 0.001