Resistant Human Colon Cancer Cell Research Articles

Enhancement of Apo2L/TRAIL signaling pathway receptors by theactivation of Klotho genewithCRISPR/Cas9 in Caco-2 colon cancer cells.

Human Klotho gene has many known functions such as anti-aging and anti-tumor, and decreased expression of this gene causes malignant formations in most types of cancer, including colon cancer. Interacting with TRAIL death receptors (DR4 and DR5) induces an apoptotic effect in cancer treatments by reducing the proliferation of cancer cells. The present study aimed to investigate downstream effect of overexpression of Klotho gene, which is known to have an antitumor effect on resistant human colon cancer cells, by examining its action on TRAIL death and decoy (DcR1 and DcR2) receptors for the first time. For this purpose, upregulation of human Klotho gene was achieved with CRISPR/Cas9-mediated system in resistant human colon cancer Caco-2 cells. To determine the effect of upregulation of Klotho gene on cancer cells evaluations with flow cytometry, WST-8, qRT-PCR, ELISA, and immunohistochemical analysis were performed. Then, Klotho gene was knocked out and its apoptotic effect was tested to find out whether it is due to overexpression of Klotho gene or not. Our results indicate that overexpression of Klotho gene in Caco-2 cells via CRISPR/Cas9-sensitized TRAIL death receptor DR4 suppresses the proliferation of cells by leading to apoptosis. Thus, this study conducted on apoptosis-resistant colon cancer cells may bring new insights about the role of Klotho gene in colon cancer.

Jiedu Sangen decoction inhibits chemoresistance to 5-fluorouracil of colorectal cancer cells by suppressing glycolysis via PI3K/AKT/HIF-1α signaling pathway.

Drug resistance is a major obstacle in the development of effective colorectal cancer (CRC) therapy. Our study aimed to explore the reversal abilities of Jiedu Sangen decoction (JSD) on the 5-fluorouracil (5-FU) resistance and its underlying molecular mechanisms. Expression changes in HIF-1 of CRC tissues were firstly revealed by bioinformatics analysis. Afterwards, cell viabilities of JSD and 5-FU treatments on 5-FU resistant human colon cancer cells (HCT-8/5-FU) were determined. Expressions of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT)/p-AKT, hypoxia-inducible factor 1 (HIF-1α), as well as glycolysis related proteins such as L-lactate dehydrogenase A (LDHA), Glucose transporter type 1 (Glut1), Hexokinase 2 (HKII), and cysteinyl aspartate specific proteinase (Caspase) family members in HCT-8/5-FU cells, HIF-1α silenced HCT-8/5-FU cells and tumor tissues were detected by western blotting. HIF-1α was found over expressed in CRC tissues according to public available datasets in Oncomine. Growth inhibition rates of HCT-8/5-FU cells were increased along with the increase of JSD concentrations. JSD caused down-regulated HIF-1α, PI3K, AKT/p-AKT, HKII and Glut1, as well as up-regulated Caspase3 and Caspase9 in HCT-8/5-FU cells and tumor tissues. In HIF-1α silenced HCT-8/5-FU cells, synergistic group showed significantly reduced expression levels of PI3K, AKT, p-AKT. Additionally, up-regulated expressions of Caspase6 and Caspase7 were observed. JSD combined with 5-FU also exhibited obvious inhibitory efficiency on tumor growth in vivo. JSD may reverse 5-FU resistance by suppressing glycolysis via PI3K/AKT/HIF-1α signaling pathway, thereby inhibiting glycolysis and induce apoptosis to enhance anti-tumor activity.

Noscapine Induces Apoptosis in Human Colon Cancer Cells by Regulating Mitochondrial Damage and Warburg Effect via PTEN/PI3K/mTOR Signaling Pathway.

BackgroundNoscapine is an opium alkaloid that has recently been shown to potentiate anti-cancer therapeutic effects by inducing apoptosis in various malignant cells without any detectable toxicity. However, the mechanism by which noscapine induces apoptosis in colon cancer cells remains unclear.Materials and MethodsIn this study, we explored the anti-cancer activity of noscapine in 5-fluorouracil (5-FU)-resistant human colon cancer cell lines HT29/5-FU and LoVo/5-FU and investigated the possible underlying mechanism. The apoptosis and mitochondrial morphology of cells were detected by TUNEL assay and transmission electron microscopy (TEM). The mitochondrial membrane potential (MMP) was determined using JC-1. The mitochondrial permeability transition pore (mPTP) opening was detected by the calcein-AM/cobalt assay. The levels of glucose, lactic, and ATP in cells were evaluated by ELISA kits. Relative protein expression levels were detected by Western blot.ResultsWe verified that PTEN was involved in noscapine-induced apoptosis in HT29/5-FU and LoVo/5-FU cells. Noscapine greatly increased mitochondrial damage by altering mitochondrial morphology, inducing mitochondrial membrane potential depolarization, and enabling mitochondrial permeability transition pore opening in HT29/5-FU and LoVo/5-FU cells. In addition, noscapine inhibited the Warburg effect by decreasing the levels of glucose, lactic acid, and ATP and inhibiting the protein expression of glucose transporter 1, lactate dehydrogenase-B, hexokinase 2, and pyruvate kinase M2 in HT29/5-FU and LoVo/5-FU cells. However, PTEN interference counteracted the effect of noscapine on mitochondrial damage and the Warburg effect in HT29/5-FU and LoVo/5-FU cells by decreasing the activation of PI3K/mTOR signaling.ConclusionThese results indicated that noscapine induced the apoptosis of HT29/5-FU and LoVo/5-FU human colon cancer cells by regulating mitochondria damage and the Warburg effect via PTEN, and the process is closely related to the PI3K/mTOR signaling pathway.

Organosilicon Compounds, SILA-409 and SILA-421, as Doxorubicin Resistance-Reversing Agents in Human Colon Cancer Cells.

Multidrug resistance (MDR) that occurs in cancer cells constitutes one of the major reasons for chemotherapy failure. The main molecular mechanism of MDR is overexpression of protein transporters from the ATP-binding cassette (ABC) superfamily, such as ABCB1 (multidrug resistance protein 1 (MDR1), P-glycoprotein). At the expense of ATP hydrolysis, ABCB1 pumps a diverse range of substrates (including anticancer drugs) out of the cell, thereby reducing their intracellular concentration. In the present study, the ability of two patented disiloxanes (SILA-409 and SILA-421) to reverse drug resistance in human colon adenocarcinoma cell lines LoVo and LoVo/Dx was investigated. It was demonstrated that both compounds in concentrations of 0.5–1 µM strongly increased the sensitivity of LoVo/Dx cells to doxorubicin. By means of an accumulation test in which rhodamine 123 was used as an ABCB1 substrate analogue, both organosilicon compounds were also shown to inhibit ABCB1 transport activity. The intracellular accumulation of doxorubicin was also increased, and more drug entered the cellular nuclei of resistant cells in the presence of the studied compounds. In conclusion, both SILA-409 and SILA-421 were demonstrated to be effective MDR reversal agents in resistant human colon cancer cells.

Reversal of Multidrug Resistance in Human Colon Cancer and Human Leukemia Cells by Three Plant Extracts and Their Major Secondary Metabolites.

Background: We studied the effect of three plant extracts (Glycyrrhiza glabra, Paeonia lactiflora, Eriobotrya japonica) and six of their major secondary metabolites (glycyrrhizic acid, 18β glycyrrhetinic acid, liquiritigenin, isoliquiritigenin, paeoniflorin, ursolic acid) on the multidrug resistant human colon cancer cell line Caco-2 and human leukemia cell line CEM/ADR 5000 as compared to the corresponding sensitive cell line CCRF-CEM, and human colon cancer cells HCT-116, which do not over-express ATP-binding cassette (ABC) transporters. Methods: The cytotoxicity of single substances in sensitive and resistant cells was investigated by MTT assay. We also applied combinations of extracts or single compounds with the chemotherapeutic agent doxorubicin or doxorubicin plus the saponin digitonin. The intracellular retention of the ABC transporter substrates rhodamine 123 and calcein was examined by flow cytometry to explore the effect of the substances on the activity of ABC transporters P-glycoprotein and MRP1. Real-time PCR was applied to analyse the gene expression changes of ABCB1, ABCC1, caspase 3, caspase 8, AhR, CYP1A1, and GSTP1 in resistant cells under the treatment of the substances. Results: All the substances moderately inhibited cell growth in sensitive and resistant cells to some degree. Whereas ursolic acid showed IC50 of 14 and 22 µM in CEM/ADR 5000 and Caco-2 cells, respectively, glycyrrhizic acid and paeoniflorin were inactive with IC50 values above 400 μM. Except for liquiritigenin and isoliquiritigenin, all the other substances reversed MDR in CEM/ADR 5000 and Caco-2 cells to doxorubicin. Ue, ga, 18ga, and urs were powerful reversal agents. In CEM/ADR 5000 cells, high concentrations of all the substances, except Paeonia lactiflora extract, increased calcein or rhodamine 123 retention in a dose-dependent manner. In Caco-2 cells, all the substances, except liquiritigenin, retained rhodamine 123 in a dose-dependent manner. We also examined the effect of the plant secondary metabolite (PSM) panel on the expression of ABCB1, ABCC1, caspase 3, caspase 8, AhR, CYP1A1, and GSTP1 genes in MDR cells. Conclusions: The extracts and individual PSM could reverse MDR in CEM/ADR 5000 and Caco-2 cells, which overexpress ABC transporters, in two- and three-drug combinations. Most of the PSM also inhibited the activity of ABC transporters to some degree, albeit at high concentrations. Ue, ga, 18ga, and urs were identified as potential multidrug resistance (MDR) modulator candidates, which need to be characterized and validated in further studies.

DUOX2-mediated production of reactive oxygen species induces epithelial mesenchymal transition in 5-fluorouracil resistant human colon cancer cells

The therapeutic benefits offered by 5-fluorouracil (5-FU) are limited because of the acquisition of drug resistance, the main cause of treatment failure and metastasis. The ability of the cancer cells to undergo epithelial-mesenchymal transition (EMT) contributes significantly to cancer metastatic potential and chemo-resistance. However, the underlying molecular mechanisms of 5-FU-resistance have remained elusive. Here, we show that reactive oxygen species (ROS), produced by dual oxidase 2 (DUOX2), promote 5-FU-induced EMT. First, we showed that 5-FU–resistant SNUC5 colon cancer cells (SNUC5/FUR cells) undergo EMT by analyzing the expression of EMT markers such as N-cadherin, vimentin and E-cadherin. In addition, we found that the resistant cells expressed higher levels of Snail, Slug, Twist and Zeb1, which are all critical EMT regulators and had enhanced migratory and invasive capabilities. Furthermore, SNUC5/FUR cells had increased level of DUOX2, resulting in increased ROS level. This effect was due to the enhanced binding of the ten eleven translocation 1 (TET1) demethylase to the DUOX2 promoter in the SNUC5/FUR cells. Importantly, silencing of TET1 reversed the effects of 5-FU on the cells. Finally, the antioxidant N-acetylcysteine attenuated the effects of 5-FU on EMT and metastasis. Our study demonstrates the existence of a TET1/DUOX2/ROS/EMT axis that could play a role in colon cancer chemo-resistance and the aggressiveness of this cancer.

Curcumin Co-Treatment Sensitizes Multi-Drug Resistant Ht29 Colon Cancer Cell Line

Colorectal cancer has been confirmed to be the third most dreadful cancer across the world. The latest reports show that the colorectal cancer is increasing in India at a high rate due to food habits, particularly consuming the foods with high fat content. Chemotherapy has been considered as a potential treatment in the control of a wide range of cancers recently, such as gastrointestinal cancers and so on. The scientists are looking to come up with new drugs to treat cancer by regulating the carcinogenesis with minimal toxicity. Curcumin is a phytochemical extracted from turmeric. It is highly effective product of the rhizomes of Curcuma longa L. (Zingiberaceae). It is also considered as a valuable drug for chemotherapeutic treatments in cancer. In case of animal studies, it has been clearly mentioned that curcumin controls carcinogenesis in various other organs as well as colon. Curcumin exhibits the capability to act as anti-mutagenic, anti-inflammatory drug as well. It has also been confirmed that the P-gp expression regulation is carried out by curcumin by inhibiting the COX-2 expression. Also, it has been clearly stated that curcumin down-regulates NF-kB pathway in various cell lines like Colo 205 colon cancer cell line etc. Multi Drug Resistance (MDR) plays a key role in case of the cancer cells to exhibit the resistance against the cytotoxicity of various chemotherapeutic drugs. This type of characteristics in cancer cells is developed due to low levels of the chemotherapeutic drug accumulated inside the cells during repeated exposure to the drug, showing the over-expression of P-glycoprotein (MDR-1). P-glycoprotein, a transporter protein, allows the cells to expel the wide range of chemotherapeutic drugs. The latest reports show that COX-2 expression and P-gp expression possess strong correlation with each other. In this research study, we generated the Multi-Drug Resistant HT29 Human colon cancer cells by treating the cells with increasing concentrations of a chemotherapeutic drug namely Doxorubicin Hydrochloride (DOX) and further we estimated the intracellular drug concentration in treated live as well as dead cells with the help of Doxorubicin Accumulation Assay. Also, the cell morphology change was studied in HT29 cells after every 24 hours of the DOX treatment separately as well as curcumin co-treatment (DOX+Curcumin). The curcumin co-treatment was carried out to observe the effect of curcumin on multi-drug resistant HT29 colon cancer cells and further study can be extended to investigate the various inflammatory genes controlled by NFkB at mRNA and protein level as well as the levels of cytokines which may get down-regulated by treatment. This study will help to completely understand the mechanism of reducing the effect of Multidrug Resistance (a unique property of cancer) by curcumin in case of colon cancer.

Vitexin induces apoptosis by suppressing autophagy in multi-drug resistant colorectal cancer cells.

Cancer treatment is limited due to the diverse multidrug resistance acquired by cancer cells and the collateral damage caused to adjacent normal cells by chemotherapy. The flavonoid compound vitexin exhibits anti-oxidative, anti-inflammatory and anti-tumor activity. This study elucidated the antitumor effects of vitexin and its underlying mechanisms in a multi-drug resistant human colon cancer cell line (HCT-116DR), which exhibits higher levels of multidrug-resistant protein 1 (MDR1) expression as compared with its parental cell line (HCT-116). Here, we observed that vitexin suppressed MDR-1 expression and activity in HCT-116DR cells and showed cytotoxic effect in HCT-116DR cells by inhibiting autophagy and inducing apoptosis in a concentration-dependent manner. Additionally, vitexin treatment caused cleavage of caspase-9 and caspase-3, and upregulated the expression of the pro-apoptotic proteins, BID and Bax. Moreover, the expression of autophagy-related proteins, such as ATG5, Beclin-1 and LC3-II, was markedly reduced by vitexin treatment. Furthermore, in vivo experiments showed that vitexin induced apoptosis and suppressed tumor growth in HCT-116DR xenograft model. These results revealed that vitexin induced apoptosis through suppression of autophagy in vitro and in vivo and provide insight into the therapeutic potential of vitexin for the treatment of chemo-resistant colorectal cancer.

Clitocine potentiates TRAIL-mediated apoptosis in human colon cancer cells by promoting Mcl-1 degradation.

Among anti-cancer candidate drugs, TRAIL might be the most specific agent against cancer cells due to its low toxicity to normal cells. Unfortunately, cancer cells usually develop drug resistance to TRAIL, which is a major obstacle for its clinical application. One promising strategy is co-administrating with sensitizer to overcome cancer cells resistance to TRAIL. Clitocine, a natural amino nucleoside purified from wild mushroom, is recently demonstrated that can induce apoptosis in multidrug-resistant human cancer cells by targeting Mcl-1. In the present study,we found that pretreatment with clitocine dramatically enhances TRAIL lethality in its resistant human colon cancer cells by inducing apoptosis. More importantly, combination of clitocine and TRAIL also effectively inhibits xenograft growth and induces tumor cells apoptosis in athymic mice. The disruption of the binding between Mcl-1 and Bak as well as mitochondrial translocation of Bax mediated by clitocine are identified as the key underlying mechanisms, which leading to mitochondrial membrane permeabilization. Enforced exogenous Mcl-1 can effectively attenuate clitocine/TRAIL-induced apoptosis by suppressing the activation of intrinsic apoptotic pathway. Furthermore, clitocine regulates Mcl-1 expression at the posttranslational level as no obvious change is observed on mRNA level and proteasome inhibitor MG132 almost blocks the Mcl-1 suppression by clitocine. In fact, more ubiquitinated Mcl-1 was detected under clitocine treatment. Our findings indicate that clitocine is potentially an effective adjuvant agent in TRAIL-based cancer therapy.

Characterization of DNA topoisomerase I in three SN-38 resistant human colon cancer cell lines reveals a new pair of resistance-associated mutations.

BackgroundDNA topoisomerase I (Top1) is a DNA unwinding protein and the specific target of the camptothecin class of chemotherapeutic drugs. One of these, irinotecan, acting through its active metabolite SN-38, is used in the treatment of metastatic colorectal cancer. However, resistance to irinotecan represents a major clinical problem. Since molecular alterations in Top1 may result in resistance to irinotecan, we characterized Top1 in three human colon cancer cell lines with acquired resistance to SN-38.MethodsThree SN-38 resistant (20–67 fold increased resistance) cell lines were generated and compared to wild-type parental cells with regards to: TOP1 gene copy number and gene sequence, Top1 expression (mRNA and protein), Top1 enzymatic activity in the absence and presence of drug, and Top1-DNA cleavage complexes in drug treated cells. TOP1 mutations were validated by PCR using mutant specific primers. Furthermore, cross-resistance to two indenoisoquinoline Top1-targeting drugs (NSC 725776 and NSC 743400) and two Top2-targeting drugs (epirubicin and etoposide) was investigated.ResultsTwo of three SN-38 resistant cell lines carried TOP1 gene copy number aberrations: A TOP1 gene copy gain and a loss of chromosome 20, respectively. One resistant cell line harbored a pair of yet unreported TOP1 mutations (R364K and G717R) in close proximity to the drug binding site. Mutant TOP1 was expressed at a markedly higher level than wild-type TOP1. None or very small reductions were observed in Top1 expression or Top1 activity in the absence of drug. In all three SN-38 resistant cell lines Top1 activity was maintained in the presence of high concentrations of SN-38. None or only partial cross-resistance were observed for etoposide and epirubicin, respectively. SN-38 resistant cells with wild-type TOP1 remained sensitive to NSC 743400, while cells with mutant TOP1 was fully cross-resistant to both indenoisoquinolines. Top1-DNA cleavage complex formation following drug treatment supported the other findings.ConclusionsThis study adds to the growing knowledge about resistance mechanisms for Top1-targeting chemotherapeutic drugs. Importantly, two yet unreported TOP1 mutations were identified, and it was underlined that cross-resistance to the new indenoisoquinoline drugs depends on the specific underlying molecular mechanism of resistance to SN-38.

Hepatic Vitamin A Preloading Reduces Colorectal Cancer Metastatic Multiplicity in a Mouse Xenograft Model

Previous research in our laboratory showed that retinol inhibited all-trans retinoic acid (ATRA)-resistant human colon cancer cell invasion via a retinoic acid receptor-independent mechanism in vitro. The objective of the current study was to determine if dietary vitamin A supplementation inhibited metastasis of ATRA-resistant colon cancer cells in a nude mouse xenograft model. Female nude mice (BALB/cAnNCr-nu/nu, n = 14 per group) consumed a control diet (2,400 IU retinyl palmitate/kg diet) or a vitamin A supplemented diet (200,000 IU retinyl palmitate/kg diet) for 1 mo prior to tumor cell injection to preload the liver with vitamin A. HCT-116, ATRA-resistant, human colon cancer cells were intrasplenically injected. Mice continued to consume their respective diets for 5 wk following surgery. Consumption of supplemental vitamin A decreased hepatic metastatic multiplicity to 17% of control. Hepatic and splenic retinol and retinyl ester concentrations were significantly higher in the mice supplemented with vitamin A when compared to mice consuming the control diet. Supplemental vitamin A did not decrease body weight, feed intake, or cause toxicity. Thus, supplemental dietary vitamin A may decrease the overall number of hepatic metastasis resulting from colon cancer.

A Peptide of SPARC Interferes with the Interaction between Caspase8 and Bcl2 to Resensitize Chemoresistant Tumors and Enhance Their Regression In Vivo

SPARC, a matricellular protein with tumor suppressor properties in certain human cancers, was initially identified in a genome-wide analysis of differentially expressed genes in chemotherapy resistance. Its exciting new role as a potential chemosensitizer arises from its ability to augment the apoptotic cascade, although the exact mechanisms are unclear. This study further examines the mechanism by which SPARC may be promoting apoptosis and identifies a smaller peptide analogue with greater chemosensitizing and tumor-regressing properties than the native protein. We examined the possibility that the apoptosis-enhancing activity of SPARC could reside within one of its three biological domains (N-terminus (NT), the follistatin-like (FS), or extracellular (EC) domains), and identified the N-terminus as the region with its chemosensitizing properties. These results were not only confirmed by studies utilizing stable cell lines overexpressing the different domains of SPARC, but as well, with a synthetic 51-aa peptide spanning the NT-domain. It revealed that the NT-domain induced a significantly greater reduction in cell viability than SPARC, and that it enhanced the apoptotic cascade via its activation of caspase 8. Moreover, in chemotherapy resistant human colon, breast and pancreatic cancer cells, its chemosensitizing properties also depended on its ability to dissociate Bcl2 from caspase 8. These observations translated to clinically significant findings in that, in-vivo, mouse tumor xenografts overexpressing the NT-domain of SPARC had significantly greater sensitivity to chemotherapy and tumor regression, even when compared to the highly-sensitive SPARC-overexpressing tumors. Our results identified an interplay between the NT-domain, Bcl2 and caspase 8 that helps augment apoptosis and as a consequence, a tumor's response to therapy. This NT-domain of SPARC and its 51-aa peptide are highly efficacious in modulating and enhancing apoptosis, thereby conferring greater chemosensitivity to resistant tumors. Our findings provide additional insight into mechanisms involved in chemotherapy resistance and a potential novel therapeutic that specifically targets this devastating phenomenon.

Hypoxic Single-Pass Isolated Hepatic Perfusion of Hypotonic Cisplatin: Safety Study in the Pig

Isolated hepatic perfusion (IHP) of chemotherapy has been proposed to deliver high doses of drug while avoiding systemic toxicity. Hypotonic cisplatin has a high in vitro activity on human colon cancer cells. We studied the safety of a 30-min hypoxic single-pass IHP with hypotonic cisplatin. A preliminary in vitro assay was performed to compare the cytotoxicity of cisplatin and oxaliplatin, in either a normotonic or hypotonic medium. Cisplatin in hypotonic medium was then chosen for the in vivo IHP. Eleven pigs underwent 30 min of IHP with 0, 50, 75, or 100 mg/L of cisplatin in a hypotonic solution under total vascular exclusion of the liver. Clinical and biological parameters were recorded for 30 days, and liver histology was performed at necropsy. The cytotoxic activity of the effluent against resistant human colon cancer cells was tested in vitro. No hepatic failure was recorded after IHP with cisplatin, but limited foci of necrosis were found at necropsy in animals receiving 75 or 100 mg/L of cisplatin. No clinical, biological, macroscopic, or microscopic toxicity was observed after IHP with 50 mg/L of hypotonic cisplatin. The liver effluent showed high in vitro cytotoxic activity against colon cancer cells. A hypoxic single-pass isolated liver perfusion with hypotonic cisplatin is feasible and safe. Effluent from the liver is highly cytotoxic on cancer cells. A clinical study with 50 mg/L of hypotonic cisplatin is warranted in patients with unresectable liver metastases from colon cancer.

Dietary Vitamin A Supplementation Decreases Colorectal Cancer Liver Metastases in Mice

Previously, we showed that retinol inhibited all‐trans‐retinoic acid (ATRA)‐resistant human colon cancer cell invasion via a retinoic acid receptor‐independent mechanism in vitro. The objective of the current study was to determine if dietary retinol inhibited the metastasis of ATRA‐resistant colon cancer cells in a nude mouse xenograft model. Ninety female nude mice (BALB/cAnNCr‐nu/nu) aged 6 to 8 weeks old were intrasplenically injected with 2 x 106 wild type HCT‐116 ATRA‐resistant human colon cancer cells. Purified AIN‐76 rodent diet was consumed pre‐injection. Immediately following injection the mice were randomly assigned to diets containing 2,400 (control), 12,000, 25,000, 50,000, 100,000 or 200,000 IU vitamin A/kg diet as retinyl palmitate. These diets provided 1, 5, 10, 20, 40 and 80X the daily vitamin A requirement of mice. The mice consumed these diets for five weeks prior to sacrifice. Livers and spleens were excised at the time of sacrifice and examined for the presence of primary tumors (spleen) or metastases (liver). Consumption of diets containing 50,000, 100,000, or 200,000 IU vitamin A/kg diet resulted in a decrease in tumor incidence to 72.6%, 72.6%, and 45.2%, respectively, of control. Thus, supplemental dietary vitamin A may be an effective chemotherapeutic agent to decrease the hepatic metastasis of colon cancer.Grant Funding SourceNIH grant # 5 R21 CA120414‐02 to M.L.

Galectin-3 stabilizes heterogeneous nuclear ribonucleoprotein Q to maintain proliferation of human colon cancer cells.

Comparative analysis of proteomes using 5-fluorouracil (5-FU)-resistant human colon cancer cell line revealed that decreased galectin-3 expression was significantly associated with retarded proliferation. However, in the presence of 5-FU proliferation rate of cells with suppressed galectin-3 expression did not differ from that of cells with normal galectin-3 expression, even galectin-3 suppression augmented apoptosis. Mechanism by which galectin-3 regulates cancer cell proliferation has been identified in immunoprecipitates of the anti-galectin-3 antibody. Heterogeneous nuclear ribonucleoprotein Q (hnRNP Q) was identified as a protein interacting with galectin-3. Interestingly, while galectin-3 protein was not affected by the hnRNP Q level, its suppression was accompanied by a decrease in hnRNP Q expression. The present study demonstrates that galectin-3 stabilizes hnRNP Q via complex formation, and reduction in the hnRNP Q level leads to slow proliferation and less susceptibility to 5-FU.

Vascular Endothelial Growth Factor Receptor-1 Contributes to Resistance to Anti–Epidermal Growth Factor Receptor Drugs in Human Cancer Cells

The resistance to selective EGFR inhibitors involves the activation of alternative signaling pathways, and Akt activation and VEGF induction have been described in EGFR inhibitor-resistant tumors. Combined inhibition of EGFR and other signaling proteins has become a successful therapeutic approach, stimulating the search for further determinants of resistance as basis for novel therapeutic strategies. We established human cancer cell lines with various degrees of EGFR expression and sensitivity to EGFR inhibitors and analyzed signal transducers under the control of EGFR-dependent and EGFR-independent pathways. Multitargeted inhibitor vandetanib (ZD6474) inhibited the growth and the phosphorylation of Akt and its effector p70S6 kinase in both wild-type and EGFR inhibitor-resistant human colon, prostate, and breast cancer cells. We found that the resistant cell lines exhibit, as common feature, VEGFR-1/Flt-1 overexpression, increased secretion of VEGF and placental growth factor, and augmented migration capabilities and that vandetanib is able to antagonize them. Accordingly, a new kinase assay revealed that in addition to VEGF receptor (VEGFR)-2, RET, and EGFR, vandetanib efficiently inhibits also VEGFR-1. The contribution of VEGFR-1 to the resistant phenotype was further supported by the demonstration that VEGFR-1 silencing in resistant cells restored sensitivity to anti-EGFR drugs and impaired migration capabilities, whereas exogenous VEGFR-1 overexpression in wild-type cells conferred resistance to these agents. This study shows that VEGFR-1 contributes to anti-EGFR drug resistance in different human cancer cells. Moreover, vandetanib inhibits VEGFR-1 activation, cell proliferation, and migration, suggesting its potential utility in patients resistant to EGFR inhibitors.

Retinol Increases β-Catenin-RXRα Binding Leading to the Increased Proteasomal Degradation of β-Catenin and RXRα

Retinol utilizes a retinoid X receptor (RXR)-mediated degradation pathway to decrease β-catenin protein in all-trans retinoic acid (ATRA)-resistant human colon cancer cells. In this study, we examined interactions between RXRα and β-catenin in ATRA-resistant human colon cancer cells treated with retinol. Retinol treatment triggers relocation of β-catenin and RXRα proteins. Cells treated with retinol for 8 and 24 h displayed increased cytosolic but decreased nuclear β-catenin and RXRα. Retinol treatment increased β-catenin and RXRα protein interaction. Previously, we showed that 24 h of retinol treatment increased RXRα protein. Here we show this increase in RXRα levels is due to increased RXRα messenger RNA. Treatment with 48 h with retinol decreased RXRα protein levels. Last, by transfecting HCT-116 cells with a RXRα construct lacking the activation function-1 and DNA binding domains, we show RXRα and β-catenin binding is required for proteosomal degradation of β-catenin. These results suggest retinol induces RXRα and β-catenin binding and transport to the cytosol where they are proteasomally degraded.

Retinol decreases phosphatidylinositol 3‐kinase activity in colon cancer cells

Previously, we showed that retinol inhibited all-trans-retinoic acid (ATRA)-resistant human colon cancer cell invasion via a retinoic acid receptor-independent mechanism. Because phosphatidylinositol 3-kinase (PI3K) regulates cell invasion, the objective of the current study was to determine if retinol affected PI3K activity. Following 24 h of serum starvation, the ATRA resistant human colon cancer cell lines HCT-116 and SW620 were treated with 0, 1, or 10 microM retinol. Thirty minutes of retinol treatment resulted in a significant decrease in PI3K activity in both cell lines. To determine the mechanism by which retinol reduces PI3K activity, the levels and heterodimerization of the regulatory subunit, p85, and the catalytic subunit, p110, of PI3K were examined. Retinol treatment did not alter p85 or p110 protein levels or the heterodimerization of these subunits at any time point examined. To determine if retinol affected the ability of PI3K to phosphorylate the substrate, phosphatidylinositol (PI), PI3K was immunoprecipitated from control cells and incubated with 10 microg PI and increasing concentrations of retinol or 10 microg retinol and increasing concentrations of PI. Retinol decreased PI3K activity in a dose-responsive manner and increased PI suppressed the inhibitory effect of retinol on PI3K activity. Finally, the PI3K inhibitor, LY294002, mimicked the ability of retinol to decrease cell invasion. Computational modeling revealed that retinol may inhibit PI3K activity in a manner similar to that of wortmannin. Thus, a decrease in PI3K activity due to retinol treatment may confer the ability of retinol to inhibit ATRA-resistant colon cancer cell invasion.

Transcriptional regulation of aldo-keto reductase 1C1 in HT29 human colon cancer cells resistant to methotrexate: Role in the cell cycle and apoptosis

While studying differentially expressed genes between sensitive and 10 −5 M Methotrexate (MTX) resistant HT29 human colon cancer cells, we identified some members of the aldo-keto reductase (AKR) superfamily. The study was followed with the member AKR1C1 (EC 1.1.1.213), validating its increase in mRNA and protein levels in MTX resistant cells. The genomic content for AKR1C1 remained unchanged between sensitive and resistant cells, thereby excluding a mechanism of AKR1C1 gene amplification. Thus, we cloned the AKR1C1 human promoter and performed luciferase experiments that revealed a transcriptional regulation of the gene in the resistant cells. Computational studies showed a putative binding site for the transcription factor Sp1. The co-transfection of Sp1 or Sp3 with different constructs of AKR1C1 promoter deletions, including and excluding the proximal GC-box, demonstrated a key role for these factors in regulating AKR1C1 transcriptional activity. Gel-shift assays revealed an increase in Sp1 and Sp3 binding in resistant compared to sensitive cells, without differences in Sp1 protein levels. Dephosphorylation of the extracts coincided with a decrease in Sp1 binding, which is consistent with a process of regulation of Sp1 by phosphorylation. We also investigated the possible relationship between AKR1C1 expression and MTX action. Overexpression of AKR1C1 counteracted the S-phase accumulation of cells and apoptosis caused by MTX treatment. This suggests a role of AKR1C1 in cell proliferation. Finally, overexpression of AKR1C1 in MTX sensitive HT29 cells conferred resistance to the chemotherapeutic agent and silencing of AKR1C1 by means of iRNA technology sensitized the cells to MTX.

Retinol Inhibits the Invasion of Retinoic Acid–Resistant Colon Cancer Cells In Vitro and Decreases Matrix Metalloproteinase mRNA, Protein, and Activity Levels

Retinol inhibits the growth of all-trans-retinoic acid (ATRA)-resistant human colon cancer cell lines through a retinoic acid receptor (RAR)-independent mechanism. The objectives of the current study were to determine if retinol inhibited the invasion of ATRA-resistant colon cancer cells independent of RAR and the effects of retinol on matrix metalloproteinases (MMPs). Retinol inhibited the migration and invasion of two ATRA-resistant colon cancer cell lines, HCT-116 and SW620, in a dose-dependent manner. To determine if transcription, particularly RAR-mediated transcription, or translation of new genes was required for retinol to inhibit cell invasion, cells were treated with retinol and cycloheximide, actinomycin D, or an RAR pan-antagonist. Treatment of cells with retinol and cycloheximide, actinomycin D, or an RAR pan-antagonist did not block the ability of retinol to inhibit cell invasion. In addition, retinol decreased MMP-1 mRNA levels in both cell lines, MMP-2 mRNA levels in the SW620 cell line, and MMP-7 and -9 mRNA levels in the HCT-116 cell line. Retinol also decreased the activity of MMP-2 and -9 and MMP-9 protein levels while increasing tissue inhibitor of MMP-1 media levels. In conclusion, retinol reduces the metastatic potential of ATRA-resistant colon cancer cells via a novel RAR-independent mechanism that may involve decreased MMP mRNA levels and activity.