Efforts are under way to further evaluate the effects of regorafenib on sorafenib-resistant HCC cells, including the role of suppressing the ERK signaling pathway.
Taro Yamashita, MD, PhD
A supplemental new drug application (sNDA) was recently submitted to the FDA for the use of regorafenib (Stivarga) in patients with unresectable hepatocellular carcinoma (HCC) who progress on standard first-line treatment with sorafenib (Nexavar).
The sNDA is based on the phase III RESORCE trial,1 in which regorafenib reduced the risk of death by 38% versus placebo in patients with HCC who progressed on frontline sorafenib (HR, 0.62; P <.001); however, it remains unclear how regorafenib works to inhibit HCC growth after sorafenib failure.
In a poster presented at the 2016 Annual Liver Meeting of the American Association for the Study of Liver Diseases, researchers summarized their efforts to further evaluate the effects of regorafenib on sorafenib-resistant HCC cells, including the role of suppressing the ERK signaling pathway.2
Drs Tomimo Hashiba and Taro Yamashita from Kanazawa University Hospital in Ishikawa, Japan, and colleagues obtained 2 HCC cell lines (Huh1 and Huh7) and 2 primary HCC cells from a surgically resected specimen. These cells were cultured routinely. Sorafenib (5-10 mM) was supplemented for 3 months to generate sorafenib-resistant clones in Huh1and Huh7.
There were differences in the 2 cell lines. KH cell had an etiology of hepatitis C, results of 10 ng/mL for the biomarker α-fetoprotein (AFP), and the patient’s prior treatment was resection and adjuvant sorafenib for 2 years. KM cells were sorafenib naïve, had an etiology of hepatitis B, results of 39 ng/mL AFP and pretreatment of transcatheter arterial chemoembolization and radiofrequency ablation.
Whole exome sequence was performed to detect mutations. Only the KH cell line was positive for MAPK or P13K-mTOR pathway related genes, and some mutation was found in only KH.
“We evaluated the mutations of all genes by whole exome sequence analysis and tried to pick up genes specifically mutated in sorafenib-resistant cells. KM, Huh1, and Huh7 cells were derived from HCC patients who did not receive sorafenib, so genes specifically mutated in KH might be related to the sorafenib resistance,” said Yamashita.
Protein expression of phospho-AKT (Ser473), -STAT3, and -ERK was evaluated by Western blotting and suggested sorafenib had no effect on suppression of AKT, ERK, and STAT3 signaling pathways. In contrast, regorafenib suppressed the phosporphorylation of STAT3 and ERK signaling in KH cells.
“STAT3 and downstream genes were not mutated in sorafenib-resistant KH cells,” said Yamashita. “Potential target genes such as c-Kit and PDGF were also evaluated, but were found not mutated.” When sensitivity was tested in vitro, KH cells showed chemosensitivities to regorafenib but not to sorafenib.
A subcutaneous xenotransplantation model was used to evaluate the efficacy of orally administered sorafenib (30 mg/kg/day) or regorafenib (20 mg/kg/day) on sorafenib-resistant clones in vivo. Although all sorafenib-resistant clones (KH, sorafenib-resistant Huh1 and Huh7 cells) showed frequent missense/nonsense mutations compared with the naive clones, no common mutations including sorafenib target genes BRAF, KIT, PDGFR, and STAT3 were detected among all sorafenib-resistant clones.
The researchers concluded that regorafenib did inhibit the growth of sorafenib resistant HCC cells potentially through the suppression of the ERK signaling. However, regorafenib and sorafenib showed similar antitumor effects in sorafenib-naïve HCC cells. Just as the phase III RESORCE trial showed promising data on overall survival, the efficacy of regorafenib on the sorafenib-resistant clones suggests potential utility as a second-line treatment in HCC.
Data from this study suggests regorafenib works to inhibit HCC growth after sorafenib failure and Hashiba said, “Tumor growth and suppression with regorafenib may be occurring through the ERK signaling pathway and possibly other pathways. There were cells from only 2 patients in this study, therefore no conclusions could be made at this time.”
Yamashita agreed, “This data suggests…regorafenib may inhibit the tumor in sorafenib-resistant as well as sorafenib-naïve tumors.” Further research plans are to identify biomarkers that potentially select HCC patients who will have a survival benefit through treatment with regorafenib after sorafenib failure.
Regorafenib is currently approved by the FDA for the treatment of patients with metastatic colorectal cancer and advanced gastrointestinal stromal tumors.
Although regorafenib treatment suppressed the subcutaneous tumor growth of sorafenib-resistant Huh7 clones with significantly prolonged overall survival (P = .014), regorafenib and sorafenib showed similar antitumor effects in naïve Huh7 cells.