Reduced drug uptake is an important mechanism of chemoresistance. Down-regulation of SLC22A1 encoding the organic cation transporter-1 (OCT1) may affect the response of hepatocellular carcinoma (HCC) and cholangiocarcinoma (CGC) to sorafenib, a cationic drug. Here we investigated whether SLC22A1 variants may contribute to sorafenib chemoresistance. Complete sequencing and selective variant identification were carried out to detect single nucleotide polymorphisms (SNPs) in SLC22A1 complementary DNA (cDNA). In HCC and CGC biopsies, in addition to previously described variants, two novel alternative spliced variants and three SNPs were identified. To study their functional consequences, these variants were mimicked by directed mutagenesis and expressed in HCC (Alexander and SK-Hep-1) and CGC (TFK1) cells. The two novel described variants, R61S fs*10 and C88A fs*16, encoded truncated proteins unable to reach the plasma membrane. Both variants abolished OCT1-mediated uptake of tetraethylammonium, a typical OCT1 substrate, and were not able to induce sorafenib sensitivity. In cells expressing functional OCT1 variants, OCT1 inhibition with quinine prevented sorafenib-induced toxicity. Expression of OCT1 variants in Xenopus laevis oocytes and determination of quinine-sensitive sorafenib uptake by high-performance liquid chromatography-dual mass spectrometry confirmed that OCT1 is able to transport sorafenib and that R61S fs*10 and C88A fs*16 abolish this ability. Screening of these SNPs in 23 HCC and 15 CGC biopsies revealed that R61S fs*10 was present in both HCC (17%) and CGC (13%), whereas C88A fs*16 was only found in HCC (17%). Considering all SLC22A1 variants, at least one inactivating SNP was found in 48% HCC and 40% CGC. Conclusion: Development of HCC and CGC is accompanied by the appearance of aberrant OCT1 variants that, together with decreased OCT1 expression, may dramatically affect the ability of sorafenib to reach active intracellular concentrations in these tumors. (HEPATOLOGY 2013;58:1065-1073 H epatocellular carcinoma (HCC) and cholangiocarcinoma (CGC) are important causes of cancer-related death worldwide. Although surgery is potentially curative for patients with localized disease, these tumors are often in an advanced stage at the time of diagnosis, when surgery is no longer the

Farnesoid X receptor (FXR) has been recently reported to enhance chemoresistance through bile acid-independent mechanisms. Thus, FXR transfection plus activation with GW4064 resulted in reduced sensitivity to cisplatin-induced toxicity. This is interesting because primary tumors of the liver, an organ where FXR is expressed, exhibit marked refractoriness to pharmacological treatment. Here we have determined whether FXR is upregulated in hepatocellular carcinoma (HCC), cholangiocarcinoma (CGC) and hepatoblastoma (HPB) and whether this is related with the expression of genes involved in mechanisms of chemoresistance. Using RT-QPCR and Taqman low density arrays we have analyzed biopsies from healthy livers or surgically removed tumors from naive patients and cell lines derived from HCC (SK-HEP-1, Alexander and Huh7), CGC (TFK1) and HPB (HepG2), before and after exposure to cisplatin at IC50 for 72 h. In liver tumors FXR expression was not enhanced but significantly decreased (healthy liver > HCC > HPB ≈ CGC). Except for CGC, this was not accompanied by changes in the proportions of FXR isoforms. Changes in 36 genes involved in drug uptake/efflux and metabolism, expression/function of molecular targets, and survival/apoptosis balance were found. Changes affecting SLC22A1, CYP2A1 and BIRC5 were shared by HCC, CGC and HPB. Similarity in gene expression profiles between cell lines and parent tumors was found. Pharmacological challenge with cisplatin induced changes that increased this resemblance. This was not dependent upon FXR expression. Thus, although FXR may play a role in inducing chemoresistance under certain circumstances, its upregulation does not seem to be involved in the multidrug resistance phenotype characteristic of HCC, CGC and HPB.

Although surgical resection is the standard curative therapy for gastric cancer, these tumors are often diagnosed at an advanced stage, when surgery is not recommended. Alternative treatments such as radiotherapy and chemotherapy achieve only very modest results. There is therefore an urgent need to advance in this field of oncologic gastroenterology. The poor response of gastric cancer to chemotherapy is usually due to a combination of mechanisms of chemoresistance (MOC), which may include a reduction in drug uptake (MOC-1a), enhanced drug efflux (MOC-1b), a reduced proportion of active agents in tumor cells due to a reduction in pro-drug activation or an enhancement in drug inactivation (MOC-2), changes in the expression/function of the molecular targets of anticancer drugs (MOC-3), an enhanced ability of cancer cells to repair anticancer drug-induced DNA damage (MOC-4), and decreased expression/function of pro-apoptotic factors or up-regulation of anti-apoptotic genes (MOC-5). Two major goals of modern pharmacology aimed at overcoming this situation are the prediction of a lack of response to chemotherapy and the identification of the underlying mechanisms accounting for primary or acquired refractoriness to anticancer drugs. These are important issues if we are to select the best pharmacological regime for each patient and develop novel strategies to overcome chemoresistance. The present review reports updated information regarding the mechanisms of chemoresistance (from MOC-1 to MOC-5) in gastric cancer, the advances made in the prediction of the failure of chemotherapeutic treatment, and novel strategies based on gene therapy currently being developed to treat these tumors.