Incapacitated Capicua in Sorafenib-Resistant HCC.

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related mortality. A majority of patients with HCC present at advanced stages, and are ineligible for potentially curative treatments such as liver transplantation or resection. Sorafenib is a multikinase inhibitor that has long been used as a first-line treatment for advanced unresectable HCC. Although it moderately improves median survival, primary or acquired sorafenib resistance occurs and HCC ultimately progresses. A better understanding of resistance mechanisms may lead to improved treatment approaches such as combination drug therapies or molecular-guided therapy.

High-throughput sequencing technologies have helped to identify primary resistance mechanisms such as alterations in mitogen-activated protein kinase 14 and vascular endothelial growth factor A,, but acquired resistance from the clonal selection of cells with mutations has not been examined in patients. In this issue of Cellular and Molecular Gastroenterology and Hepatology, Hashiba et al provide a proof-of-concept study of discovery of acquired sorafenib resistance resulting from a mutation in capicua transcriptional repressor (CIC), by examining tissues from a patient who developed recurrent HCC while on sorafenib.

This patient was part of the Sorafenib as Adjuvant Treatment in the Prevention Of Recurrence of Hepatocellular Carcinoma (STORM) trial, which evaluated the benefit of sorafenib as an adjuvant treatment in patients at the highest risk of developing HCC. Although this was a negative study, secondary analysis has identified a molecular signature that can predict response to sorafenib. The patient described by Hashiba et al had an early stage HCC, underwent a resection, and developed a recurrent HCC despite 2 years of sorafenib treatment. Hashiba et al conducted exome sequencing of presorafenib and postsorafenib HCC sample tumor tissues and identified 38 and 46 somatic mutations, respectively. There were 29 mutations in common between the 2 HCC samples, indicating a common origin. They developed a cell line which they termed HCC-sorafenib resistant (HCC-SR) from the postsorafenib HCC samples. Paradoxically, a low concentration of sorafenib increased the proliferation rate of HCC-SR, rather than decreasing it. Whole-exome sequencing showed only 1 mutation was present in both the postsorafenib HCC sample, and in HCC-SR: a single substitution in CIC.

Capicua is a transcriptional repressor that is mutated in multiple cancers. It is regulated by the receptor tyrosine kinase pathway through phosphorylation-mediated degradation or cytoplasmic localization. It acts as a tumor suppressor in multiple cancers including lung cancer, gastric cancer, and HCC. This new study implicates Capicua as having a role in sorafenib resistance, rendering it an interesting target for further validation.

Assuming that the mutation in CIC (S1595P) leads to a loss of function, Hashiba et al studied the role of CIC in HCC cell lines. CIC expression levels were decreased significantly in sorafenib-resistant cell lines. Knockdown of CIC led to sorafenib resistance in Huh7 cells. Introduction of wild-type CIC into HCC-SR re-established sensitivity to sorafenib. Hashiba et al obtained 2 sorafenib-resistant clones (Huh1-SR and Huh7-SR) through long-term culture in sorafenib. CIC expression levels were decreased significantly, accompanied by an increase in the mitogen-activated protein kinase pathway activity. These data indicate that CIC levels are correlated inversely with sorafenib resistance in HCC cell lines.

To evaluate the prognostic value of CIC in sorafenib-treated patients with HCC, tumor samples from 30 sorafenib-treated patients were classified as CIC-high or CIC-low based on immunohistochemistry results before sorafenib treatment. Survival analysis showed better overall survival in CIC-high patients. There were 3 patients with high CIC protein levels before sorafenib treatment who developed disease progression after sorafenib treatment. In all of these patients, CIC expression was diminished in tissues after sorafenib treatment. Hashiba et al defined a CIC gene signature that is composed of potential CIC target genes, which had a good predictive value for benefit from adjuvant therapy with sorafenib using outcome data from the STORM trial.

In summary, this study identified a novel mutation in CIC from paired samples in a patient with a sorafenib-resistant HCC recurrence. It was a proof-of-concept study that showed that mutations responsible for acquired drug resistance can be identified from clinical samples. Inactivation of CIC led to resistance to sorafenib. Interestingly, resistance did not develop with the structurally similar drug regorafenib. Their data also suggest a prognostic value of CIC levels, although it used relatively few patient samples. A limitation of the study was that it was based on samples from only 1 patient and only 1 mutation was identified specifically in the postsorafenib sample.

In the future, this approach should be applied to more patients to validate the role of CIC and to discover new genomic alterations linked to acquired sorafenib resistance. In addition, the mechanism of down-regulation of CIC leading to sorafenib resistance, but not regorafenib, should be explored further. Finally, prospective clinical trials are needed that incorporate molecular profiles of tumors to guide therapies.