Bruno Chauffert

EGFR activation is a potential determinant of primary resistance of hepatocellular carcinoma cells to sorafenib

Sorafenib is currently the medical treatment of reference for hepatocellular carcinoma (HCC), but it is not known whether sorafenib is equally active in all HCC. Here, our aim was to explore intrinsic differences in the response of HCC cells to sorafenib, to identify potential mechanisms leading to primary resistance to this treatment. We analyzed a panel of six human HCC cell lines and compared the activity of the main oncogenic kinase cascades, their clonogenic potential, proliferation and apoptosis upon exposure to sorafenib. We report that HCC cells present important differences in their response to sorafenib, and that some cell lines are more resistant to the actions of sorafenib than others. We identify the activated epidermal growth factor receptor (EGFR) as a parameter that promotes the resistance of HCC cells to sorafenib. In resistant cells, the efficacy of sorafenib was increased when EGFR was inhibited, as was demonstrated using two chemical inhibitors (erlotinib or gefitinib), a monoclonal antibody directed against EGFR (cetuximab), and RNA interference directed against EGFR. A combination of EGFR inhibitors and sorafenib affords a better control over HCC proliferation, most likely through an improved blockade of the RAF kinases. Our findings therefore confirm the importance of RAF kinases as therapeutic targets in HCC, and identify EGFR as a determinant of the sensitivity of HCC cells to sorafenib. Our findings bear possible implications for the improvement of the efficacy of sorafenib in HCC, and might be useful for the identification of predictive biomarkers in this context.

Iron-dependent cell death of hepatocellular carcinoma cells exposed to sorafenib

The multikinase inhibitor sorafenib is currently the treatment of reference for advanced hepatocellular carcinoma (HCC). In our report, we examined the cytotoxic effects of sorafenib on HCC cells. We report that the depletion of the intracellular iron stores achieved by using the iron chelator deferoxamine (DFX) strikingly protects HCC cells from the cytotoxic effects of sorafenib. The protective effect of the depletion of intracellular iron stores could not be explained by an interference with conventional forms of programmed cell death, such as apoptosis or autophagic cell death. We also found that DFX did not prevent sorafenib from reaching its intracellular target kinases. Instead, the depletion of intracellular iron stores prevented sorafenib from inducing oxidative stress in HCC cells. We examined the possibility that sorafenib might exert a cytotoxic effect that resembles ferroptosis, a form of cell death in which iron‐dependent oxidative mechanisms play a pivotal role. In agreement with this possibility, we found that pharmacological inhibitors (ferrostatin‐1) and genetic procedures (RNA interference against IREB‐2) previously reported to modulate ferroptosis, readily block the cytotoxic effects of sorafenib in HCC cells. Collectively, our findings identify ferroptosis as an effective mechanism for the induction of cell death in HCC. Ferroptosis could potentially become a goal for the medical treatment of HCC, thus opening new avenues for the optimization of the use of sorafenib in these tumors.

The retinoblastoma (Rb) protein regulates ferroptosis induced by sorafenib in human hepatocellular carcinoma cells

Sorafenib is the treatment of reference for advanced hepatocellular carcinoma (HCC), the most frequent form of primary liver tumour. The loss of function of the retinoblastoma (Rb) protein is an important event during liver carcinogenesis, but it is unclear whether the Rb status modulates the response of HCC cells to sorafenib. Here, we examined this question in HCC cells with reduced levels of Rb achieved through stable RNA interference. We show that HCC cells with reduced levels of Rb exhibit a two- to threefold increase in cell death induction upon exposure to sorafenib compared with controls. Sorafenib treatment of Balb/c nude mice that received tumour xenografts derived from HCC cells with reduced Rb levels resulted in complete tumour regression in 50% of the animals treated, compared with tumour stabilization in mice that received control cells. We show that, upon exposure to sorafenib, the Rb-negative status of HCC cells promotes the occurrence of ferroptosis, a form of oxidative necrosis. The findings highlight the role of Rb in the response of HCC cells to sorafenib and the regulation of ferroptosis.

New biological perspectives for the improvement of the efficacy of sorafenib in hepatocellular carcinoma.

Sorafenib, an orally-available kinase inhibitor, is the only medical treatment with a proven efficacy against Hepatocellular Carcinoma (HCC). Although the overall clinical efficacy of sorafenib is modest, recent experimental results have uncovered new potential strategies that may increase its clinical benefits. The potential implication of Receptor Tyrosine Kinases (RTKs), such as the Epidermal Growth Factor Receptor (EGFR), in the development of resistance to sorafenib highlights the importance of the RAF kinase pathway. Various strategies aiming to optimize the control exerted over this pathway by combining sorafenib with other targeted molecules (such as anti-EGFR, anti-MEK) are under investigation. Increasing the cytotoxicity of sorafenib in HCC, either through apoptosis or through new forms of non-apoptotic cell death, such as ferroptosis, may also promote more sustained tumour regression. Finally, the heterogeneity of individual responses to sorafenib is increasingly recognised, even though clinically-applicable biomarkers remain to be identified. Here, we discuss how molecular genetics and complementary approaches such as short term culture of tumour samples could help to personalize the use of sorafenib.

Metallothionein-1 as a biomarker of altered redox metabolism in hepatocellular carcinoma cells exposed to sorafenib

BackgroundSorafenib, a kinase inhibitor active against various solid tumours, induces oxidative stress and ferroptosis, a new form of oxidative necrosis, in some cancer cells. Clinically-applicable biomarkers that reflect the impact of sorafenib on the redox metabolism of cancer cells are lacking.MethodsWe used gene expression microarrays, real-time PCR, immunoblot, protein-specific ELISA, and gene reporter constructs encoding the enzyme luciferase to study the response of a panel of cancer cells to sorafenib. Tumour explants prepared from surgical hepatocellular carcinoma (HCC) samples and serum samples obtained from HCC patients receiving sorafenib were also used.ResultsWe observed that genes of the metallothionein-1 (MT1) family are induced in the HCC cell line Huh7 exposed to sorafenib. Sorafenib increased the expression of MT1G mRNA in a panel of human cancer cells, an effect that was not observed with eight other clinically-approved kinase inhibitors. We identified the minimal region of the MT1G promoter that confers inducibility by sorafenib to a 133 base pair region containing an Anti-oxidant Response Element (ARE) and showed the essential role of the transcription factor NRF2 (Nuclear factor erythroid 2-Related Factor 2). We examined the clinical relevance of our findings by analysing the regulation of MT1G in five tumour explants prepared from surgical HCC samples. Finally, we showed that the protein levels of MT1 increase in the serum of some HCC patients receiving sorafenib, and found an association with reduced overall survival.ConclusionThese findings indicate that MT1 constitute a biomarker adapted for exploring the impact of sorafenib on the redox metabolism of cancer cells.

Alpha-fetoprotein is a biomarker of unfolded protein response and altered proteostasis in hepatocellular carcinoma cells exposed to sorafenib

Sorafenib is the treatment of reference for advanced hepatocellular carcinoma (HCC). A decrease in the serum levels of Alpha-fetoprotein (AFP) is reported to be the biological parameter that is best associated with disease control by sorafenib. In order to provide a biological rationale for the variations of AFP, we analyzed the various steps of AFP production in human HCC cell lines exposed to sorafenib. Sorafenib dramatically reduced the levels of AFP produced by HCC cells independently of its effect on cell viability. The mRNA levels of AFP decreased upon sorafenib treatment, while the AFP protein remained localized in the Golgi apparatus. Sorafenib activated the Regulated Inositol-Requiring Enzyme-1α (IRE-1α) and the PKR-like ER Kinase (PERK)-dependent arms of the Unfolded Protein Response (UPR). The inhibition of IRE-1α partially restored the mRNA levels of AFP upon treatment with sorafenib. The inhibition of both pathways partially prevented the drop in the production of AFP induced by sorafenib. The findings provide new insights on the regulation of AFP, and identify it as a biomarker suitable for the exploration of HCC cell proteostasis in the context of therapeutic targeting.

Short-term culture of tumour slices reveals the heterogeneous sensitivity of human head and neck squamous cell carcinoma to targeted therapies

BackgroundDespite recent progress, investigating the impact of targeted therapies on Head and Neck Squamous Cell Carcinoma (HNSCC) remains a challenge. We investigated whether short-term culture of tumour fragments would permit the evaluation of tumour sensitivity to targeted therapies at the individual level.MethodsWe cultivated tumour slices prepared from 18 HNSCC tumour samples obtained during surgical resection. The samples were treated for 48xa0h with a panel of 8 targeted therapies directed against selected oncogenic transduction pathways. We analysed the cell proliferation index (CPI) of tumour cells using Ki67 labelling and the activation status of the RAF-MEK-ERK cascade through ERK phosphorylation analysis.ResultsFourteen tumours were successfully analysed after short-term culture of tumour samples, revealing a striking individual heterogeneity of HNSCC in terms of tumour cell sensitivity to targeted therapies. Using 50xa0% inhibition of CPI as threshold, sorafenib was shown to be active in 5/14 tumours. Cetuximab, the only approved targeted drug against HNSCC, was active in only 2/14 tumours. A more than 50xa0% inhibition was observed with at least one drug out of the eight tested in 10/14 tumours. Cluster analysis was carried out in order to examine the effect of the drugs on cell proliferation and the RAF-MEK-ERK cascade.ConclusionsIn vitro culture of tumour fragments allows for the evaluation of the effects of targeted therapies on freshly resected human tumours, and might be of value as a possible guide for the design of clinical trials and for the personalization of the medical treatment of HNSCC.

Probing Tumour Proteostasis and the UPR with Serum Markers

Tumour proteostasis and the unfolded protein response (UPR) are emerging drivers of tumour progression and important determinants of clinical efficacy of cancer therapy. Recent findings indicate that they also regulate the production of protein tumour markers. Here, we discuss how this new knowledge opens up new perspectives for cancer therapeutics.

Combining genomic analyses with tumour-derived slice cultures for the characterization of an EGFR -activating kinase mutation in a case of glioblastoma

BackgroundEpidermal growth factor receptor (EGFR) gene alterations and amplification are frequently reported in cases of glioblastoma (GBM). However, EGFR-activating mutations that confer proven sensitivity to tyrosine kinase inhibitors (TKIs) in lung cancer have not yet been reported in GBM.Case presentationUsing next-generation sequencing, array comparative genomic hybridization and droplet digital PCR, we identified the p.L861Q EGFR mutation in a case of GBM for the first time. The mutation was associated with gene amplification. L861Q may be a clinically valuable mutation because it is known to sensitize non-small-cell lung cancers to treatment with the second-generation EGFR TKI afatinib in particular. Furthermore, we used slice culture of the patient’s GBM explant to evaluate the tumour’s sensitivity to various EGFR-targeting drugs. Our results suggested that the tumour was not intrinsically sensitive to these drugs.ConclusionsOur results highlight (i) the value of comprehensive genomic analyses for identifying patient-specific, targetable alterations, and (ii) the need to combine genomic analyses with functional assays, such as tumour-derived slice cultures.