Targeting Iron in Colon Cancer via Glycoconjugation of

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Targeting Iron in Colon Cancer via Glycoconjugation of Thiosemicarbazone Prochelators Eman A. Akam and Elisa Tomat* Department of Chemistry and Biochemistry, The University of Arizona, 1306 East University Boulevard, Tucson, Arizona 85721-0041, United States S Supporting Information *

ABSTRACT: The implication of iron in the pathophysiology of colorectal cancer is documented at both the biochemical and epidemiological levels. Iron chelators are therefore useful molecular tools for the study and potential treatment of this type of cancer characterized by high incidence and mortality rates. We report a novel prochelation strategy that utilizes a disulfide redox switch to connect a thiosemicarbazone ironbinding unit with carbohydrate moieties targeting the increased expression of glucose transporters in colorectal cancer cells. We synthesized three glycoconjugates (GA2TC4, G6TC4, and M6TC4) with different connectivity and/or carbohydrate moieties, as well as an aglycone analog (ATC4). The sugar conjugates present increased solubility in neutral aqueous solutions, and the ester-linked conjugates M6TC4 and G6TC4 compete as effectively as D-glucose for transporter-mediated cellular uptake. The glycoconjugates show improved selectivity compared to the aglycone analog and are 6−11 times more toxic in Caco-2 colorectal adenocarcinoma cells than in normal CCD18-co colon fibroblasts.

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make disulfides attractive activation switches.13,14 Specifically, we chose a thiosemicarbazone scaffold common to several potent chelators,15 and introduced a disulfide group within the S,N,S donor set of the metal-binding unit.11 Reduction in the intracellular milieu results in the generation of a thiolate and formation of a low-spin Fe(III) complex.12 Herein, we describe a new prochelator design (Scheme 1) in which the disulfide switch is employed also as a linker to a carbohydrate moiety with the aim to (i) enhance the aqueous solubility of the

INTRODUCTION Colorectal cancer is one of the most commonly diagnosed cancers worldwide (third in men and second in women) and it consistently lies within the five most fatal types of cancer each year.1 Its incidence varies geographically, connected to iron-rich diets high in red and processed meats that are prevalent in the Americas, Europe, and Australia.2 Indeed the link between high dietary iron and increased risk of colorectal cancer has been reported widely.3−5 At a molecular level, altered iron regulation in colorectal cancer cells is characterized by increased expression of iron import proteins and downregulation of iron efflux mechanisms leading to an overall increase of iron content in human colorectal tumors.5,6 Both epidemiological and biochemical observations therefore support the strong association between iron and colorectal cancer. The higher demand for iron in cancer cells is a general characteristic of malignancy and a promising target for cancer therapy.7 Several families of iron scavengers (chelators) are currently under investigation for cancer chemotherapy.8,9 In this context, prodrug approaches and targeted delivery methods10 are expected to enhance selectivity and curb systemic toxicity problems and side effects that have hampered the advancement of antiproliferative iron chelators through clinical trials. We recently developed a prochelation approach featuring a disulfide switch for intracellular reduction/ activation.11,12 The higher concentrations of reduced glutathione (GSH) in cancer cells, particularly in hypoxic tumors, © XXXX American Chemical Society

Scheme 1. Design of a Redox-Directed Glycoconjugate Prochelator Strategy

Received: June 23, 2016 Revised: July 24, 2016

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DOI: 10.1021/acs.bioconjchem.6b00332 Bioconjugate Chem. XXXX, XXX, XXX−XXX

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Bioconjugate Chemistry

positions 2 and 6 of glucose or mannose moieties were then selected because they are tolerated well by glucose transporters.17 For instance, a 2-amino-2-deoxyglucose conjugate of adriamycin enters cells via a GLUT-mediated mechanism27 and several conjugates to the C6 position of glucose also undergo GLUT1-mediated uptake.24,28 Our series of TC4-glycoconjugate prototypes therefore allows an initial evaluation of the impact of connectivity (C2 vs C6) and carbohydrate moiety (glucose vs mannose) on cellular uptake and biological activity. For the synthesis of the glucosamine conjugate GA2TC4 (Scheme 2), the key compound 2 was prepared by amide linkage of 2-amino-2-deoxy-D-glucose (D-glucosamine) to crosslinker 1 using dicyclohexyl carboiimide (DCC) as a coupling reagent as adapted from literature procedures.29 Compound 2 is then used in excess in the presence of thiol TC4-SH for the disulfide exchange reaction resulting in GA2TC4. The synthesis of the conjugates featuring an ester linkage to the C6 alcohol on the hexose scaffold (Scheme 3) required

compounds, and (ii) increase tumor selectivity by taking advantage of the Warburg effect, namely, the increased uptake of glucose and the higher rates of aerobic glycolysis in cancer cells compared to nonmalignant tissue.16 Supported by the widespread clinical use of radiolabeled glucose analogs for tumor visualization and staging by positron emission tomography (PET), glycoconjugation is undergoing intense scrutiny as a methodology to increase cancer specificity of antiproliferative agents.17 These approaches exploit the overexpression of glucose transporters in a large percentage of cancer phenotypes18 and they are particularly relevant to the study and treatment of colorectal cancer. Higher expression of the glucose transporter GLUT1 in colorectal carcinogenesis is correlated with poorer prognosis.19,20 Recently, a gene expression analysis of several effectors of aerobic glycolysis (including hexokinase-1, GLUT1, and lactate dehydrogenaseA) confirmed that a high glycolytic profile correlates with poor prognosis for colorectal cancer patients.21 Glycoconjugation of metal complexes has been employed extensively for radiolabeling methods22 and more recently for the selective delivery of platinum-based anticancer drugs.23,24 Additionally, carbohydrate conjugates of metal prochelators have been investigated for applications related to neurodegeneration25 and Wilson’s disease.26 Herein, we report the synthesis and biological evaluation of sugar conjugates designed to deliver a thiosemicarbazone iron chelator (TC4-SH, Scheme 1) to cancer cells. This approach concurrently targets the strong association between iron and colorectal cancer and the opportunity for selectivity offered by the Warburg effect in this type of cancer.

Scheme 3. Synthesis of Mannose and Glucose Ester-Linked Prochelators

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RESULTS AND DISCUSSION Synthesis and Chemical Characterization of Prochelators. The planned prochelation strategy (Scheme 1) required development of synthetic methods to connect carbohydrate moieties to thiosemicarbazone TC4-SH, an analog of previously reported chelator TC1-SH (featuring a phenyl group in place of a 4-methoxyphenyl group)11 and one of the antiproliferative thiosemicarbazones under investigation in our laboratory. The disulfide switch of reduction/activation in this family of compounds was selected for glycoconjugation through a heterodisulfide linkage. In particular, we employed the established chemistry of 2-pyridyl disulfide cross-linker 3-(2pyridyldithio)propionic acid 1 (Scheme 2). Substitutions at

trimethylsilyl (TMS) protection of the other hydroxyl groups of the sugar.30,31 Ester coupling with 1 in the presence of DCC and disulfide exchange with TC4-SH resulted in the TMSprotected glucose and mannose conjugates. Deprotection following chromatographic purification afforded the glucose ester-linked conjugate G6TC4 and the mannose analog M6TC4 (Scheme 3). An aglycone that retains the general structure of the glycoconjugates but lacks the carbohydrate targeting moiety was prepared as a control compound (Scheme 4). Specifically,

Scheme 2. Synthesis of Glucosamine-Based Prochelator

Scheme 4. Synthesis of Aglycone Prochelator

the sugar motif was replaced with a methyl group, thus protecting the carboxylate and maintaining a scaffold that would be neutral at biological pH. Fisher esterification of 1 and a disulfide exchange reaction similar to those conducted for the other conjugates resulted in the desired compound ATC4 (Scheme 4). B


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Bioconjugate Chemistry Glycoconjugation is an established method to impart increased aqueous solubility to hydrophobic scaffolds including several drugs such as aspirin,32 warfarin,33 and oxaliplatin.23 The effect of the sugar motif on the aqueous solubility of the synthesized prochelators was investigated by UV−visible absorption spectroscopy. Determination of molar extinction coefficients of each compound in aqueous buffered solutions (5.0 mM TRIS, pH 7.40) allowed measurement of their concentration at saturation. The sugar conjugates display moderate solubility in neutral aqueous solutions (Table 1), Table 1. Aqueous Solubility of Disulfide Prochelators concentration at saturationa compound GA2TC4 G6TC4 M6TC4 ATC4

μM 53 36 25 11

± ± ± ±

Figure 1. Assessment of uptake of glycoconjugates via glucose transporters using fluorescent probe 2-NBDG as competitor in Caco-2 cells. Transporter-mediated uptake of the tested compounds (50 μM, 40 min) results in decreased intracellular fluorescence compared to that of cells treated with 2-NBDG (100 μM) alone. Cotreatment with glucose (10 mM) or GLUT1 inhibitor phloretin (100 μM, 30 min) is employed for positive controls. Experiments were conducted in triplicate and values shown are averages ± standard deviation. Statistical analysis: ** p < 0.01, *** p < 0.001 as compared to the control.

mg/L 2 5 1 1

31 21 14 4.7

± ± ± ±

1 3 1 0.5

a

Concentration in a buffered solution (5.0 mM TRIS, pH 7.40) saturated with the indicated compound was measured by UV−vis absorption spectroscopy. Values are averages of triplicate sets ± standard deviation.

The aglycone ATC4, which has no glucose targeting unit, does not compete for GLUT1-mediated uptake and hence displays a fluorescence value that is, within error, identical to that of the control. Interestingly, GA2TC4, the glucosamine conjugate of TC4-SH, also displays no significant competition with 2-NBDG in this assay. In contrast, the ester conjugates G6TC4 and M6TC4 display aggressive competitiveness with 2NBDG for uptake by its receptor(s). Notably, both glucose and mannose are substrates for glycotransporters, although the latter presents a lower affinity for GLUT1.38 The differences observed among the tested glycoconjugates in these experiments indicate that the position of substitution and type of linkage to the carbohydrate may affect transporter-mediated uptake and that the C6 ester linkages are more effective in these experimental conditions. Investigations of antiproliferative activity were conducted in Caco-2 cells and also in the normal colon cell line CCD18-co (ATCC CRL-1459) in order to evaluate the therapeutic indexes of the compounds. Because differences in expression levels of glucose transporters are key to the selectivity of glycoconjugates, we examined the amount of cell surface GLUT1 in these two cell lines by immunostaining methods (Figure 2). We found that cell surface GLUT1 levels in Caco-2 cells were 1.7 (±0.1) times higher than those in CCD18-co cells in our cell culture conditions. This observation is in line with values obtained for overall GLUT1 expression quantified by RT-PCR and showing levels that are two to four times higher in cancer cells from various origins when compared to normal cells.39 We assessed the cytotoxicity of the prochelators using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) assays after 72 h incubations (Table 2). In all cases, the prochelator conjugates are more toxic (lower IC50 values) in the malignant Caco-2 cells than in the normal CCD18-co cells. Although studies on the impact of iron deprivation on Caco-2 cells remains rare,40 our data indicate that disulfidebased prochelators are effective antiproliferative agents in this colorectal cancer model.

higher than that of the aglycone compound in all cases. Because symmetric disulfide systems of this family typically present low solubilities in aqueous solutions, these data highlight an advantageous aspect of the glycoconjugation approach for these prochelators. As previously noted for other disulfide-based thiosemicarbazone prochelators,11 the four constructs showed no indication of Fe(II) binding (up to 3 equiv) in neutral aqueous solutions at micromolar concentrations (Figure S5, SI). All four compounds therefore behave as prochelators thereby presenting low iron affinity prior to intracellular reduction/activation of the disulfide linkage.12 Biological Assays. The biological activity of the new glycoconjugate prochelators was evaluated on the colorectal adenocarcinoma cell line Caco-2 (ATCC HTB-37). This in vitro model of human colon adenocarcinoma34 is especially relevant to the study of glycoconjugates because Caco-2 cells express high levels of GLUT1 protein and RNA (Human Protein Atlas, SLC2A1 gene).35 We investigated the cellular uptake of the prochelators through a competition experiment with 2-(N-(7-nitrobenz-2oxa-1,3-diazol-4-yl)amino)-2-deoxy-glucose (2-NBDG), a fluorescent substrate of GLUT1.36 In these experiments, the introduction in the cell growth media of a compound that competes with 2-NBDG for GLUT1-mediated transport results in decreased uptake of the fluorescent substrate, which is detected as lower intracellular fluorescence emission by flow cytometry. The data (Figure 1) are expressed as percent emission difference compared to control cells treated with 2NBDG alone; therefore, a more negative difference indicated more aggressive competition for GLUT1 by the tested glycoconjugate. Phloretin was used as a positive control because this inhibitor of GLUT1 blocks uptake of substrates.37 In addition, α-D-glucose, i.e., the primary substrate for GLUT1, was included as a noninhibitory positive control. Both phloretin and glucose suppress the uptake of 2-NBDG very effectively, with more than 20% difference in fluorescence compared to the control. C



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CONCLUSIONS Thiosemicarbazones are among the most potent antiproliferative iron chelators reported to date. Several lead compounds of this class (e.g., Triapine, Dp44mT) have been studied extensively in vitro and in vivo,15,41,42 and the secondgeneration compound DpC is slated to enter a Phase 1 clinical trial in 2016.43 The polypharmacological activity profile of certain compounds of this class is particularly effective as they impact not only tumor growth but also metastasis and drug resistance.43 Herein, we described the molecular design of thiosemicarbazone constructs in which a disulfide-based prochelation approach is combined with a tumor targeting strategy. The reported methods for the synthesis of 2-pyridyl disulfide derivatives of the selected carbohydrate units allowed preparation of glycoconjugates featuring an amidic linkage at the C2 position (GA2TC4) or an ester linkage at the C6 position (G6TC4 and M6TC4). The modular assembly of the prochelator components (from the linker to the carbohydrate to the metal-binding unit) will be amenable to the preparation of multiple series of compounds of this general design. The prepared glycoconjugates offer a considerable advantage as they are significantly more soluble than the aglycone analog and the homodisulfide prochelators in neutral aqueous solutions. To the best of our knowledge, this is the first study on the impact of glycoconjugation on the toxicity and selectivity of an antiproliferative iron chelator. We sought to examine the biological activity of our prochelators in colorectal cancer cells because of the established implication of iron in the pathophysiology of this type of cancer.3−5 Furthermore, overexpression of glucose transporters (e.g., GLUT1) is a negative prognostic biomarker in colorectal cancer patients; therefore, glycoconjugation could provide targeted access to malignant cells.16 In our cell culture conditions, colon carcinoma Caco-2 cells were found to express GLUT1 at almost twice the level of normal colon fibroblasts CCD18-co. Consistently, the glycoconjugates are 6−11 times more toxic in Caco-2 cells than in CCD18-co cells. In contrast, the aglycone is only 3 times more toxic in the cancer cell line. Notably, ester-linked C6-glucosyl prochelator G6TC4 competes aggressively with fluorescent glycoconjugate 2-NBDG for transporter-mediated cellular uptake and displays the highest therapeutic index among the tested glycoconjugates within this comparison in colorectal cell lines. As previously noted for other glycoconjugates of antiproliferative agents,23,24,27,39 glycoconjugation did not dramatically impact the cytotoxicity of the constructs. With IC50 values in the low micromolar range, the toxicity of the glycoconjugates is similar to those of the aglycone and of previously reported disulfide-based prochelators of this class (albeit determined in different cancer cell lines).11 Nevertheless, the glycoconjugate prochelators present improved therapeutic indexes in the tested colorectal cell lines. This study shows that disulfide-based glycoconjugate prochelation strategies offer viable options to target intracellular metal ions upon preferential uptake by cells presenting overexpression of glucose transporters. In addition to colorectal cancer, potential applications of this approach are relevant to several other human cancer phenotypes (e.g., breast, pancreatic, and lung carcinomas)44 characterized by metabolic alterations of iron and glucose handling.

Figure 2. Relative amounts of cell-surface GLUT1 in human colon adenocarcinoma Caco-2 cells and normal CCD18-co colon fibroblasts. Average fluorescence values (left) and flow cytometry histograms (right) following immunostaining of cell-surface GLUT1 with rabbit anti-GLUT1 and AlexaFluor488-conjugated antibodies. Experiments were conducted in triplicate and values are plotted as the average of the median values from the flow cytometry histogram ± standard deviation. Values are statistically different (p < 0.01).

Table 2. Antiproliferative Activity of TC4 Prochelators in Caco-2 and CCD18-co Cell Lines IC50a (μM, 72 h) Caco-2 GA2TC4 G6TC4 M6TC4 ATC4

2.6 6.9 10.1 8.1

± ± ± ±

0.3 0.4 0.3 0.2

CCD18-co 22.5 76 62.2 27.5

± ± ± ±

0.8 2 0.1 0.4

therapeutic indexb 9 11 6.2 3.4

± ± ± ±

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1 1 0.4 0.1

a

IC50 values are obtained from MTT assays after 72-h exposure to the tested compounds. Values are averages of triplicate sets ± standard deviation. bTherapeutic index is calculated as the ratio of IC50 values in the normal cell line relative to the malignant cell line.

The aglycone prochelator ATC4 presents the lowest therapeutic index in this data set. This observation is consistent with an increased glucose uptake in cancer cells owing to the Warburg effect, and also with the relative expression levels of glucose transporter GLUT1 determined experimentally for the cell cultures under investigation (Figure 2). Of the three glycoconjugate prototypes, the mannose construct M6TC4 is both the least toxic and least selective. Notably, M6TC4 competed successfully with 2-NBDG for transporter-mediated uptake at the 50 μM concentration level (Figure 1); therefore, the observed toxicity parameters could reflect lower affinity and/or overall uptake for the mannose unit relative to the glucose unit in this type of conjugates. In contrast, the glucosamine conjugate GA2TC4, which did not compete for uptake with 2-NBDG in the assay conditions (Figure 1), showed better toxicity and selectivity relative to the aglycone. Because it is conducted on a much shorter time scale, the competition assay could overlook slower kinetics of uptake. In addition, the observed toxicity parameters could indicate differential uptake by the available collection of transporters compared to 2-NBDG (and different affinities thereof). Notably, the ester-linked glucose conjugate G6TC4, which competes strongly with 2-NBDG for uptake (Figure 1), maintains a toxicity level similar to the aglycone in Caco-2 cells but is significantly less toxic to normal CCD18-co cells. Overall, both glucose conjugates GA2TC4 and G6TC4 displayed a significantly improved therapeutic index (3-fold or higher) in this comparative study of colorectal cell lines. D


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(12) Akam, E. A., Chang, T. M., Astashkin, A. V., and Tomat, E. (2014) Intracellular reduction/activation of a disulfide switch in thiosemicarbazone iron chelators. Metallomics 6, 1905−1912. (13) Lee, M. H., Yang, Z., Lim, C. W., Lee, Y. H., Dongbang, S., Kang, C., and Kim, J. S. (2013) Disulfide-Cleavage-Triggered Chemosensors and Their Biological Applications. Chem. Rev. 113, 5071−5109. (14) Lee, M. H., Sessler, J. L., and Kim, J. S. (2015) Disulfide-Based Multifunctional Conjugates for Targeted Theranostic Drug Delivery. Acc. Chem. Res. 48, 2935−2946. (15) Yu, Y., Kalinowski, D. S., Kovacevic, Z., Siafakas, A. R., Jansson, P. J., Stefani, C., Lovejoy, D. B., Sharpe, P. C., Bernhardt, P. V., and Richardson, D. R. (2009) Thiosemicarbazones from the old to new: iron chelators that are more than just ribonucleotide reductase inhibitors. J. Med. Chem. 52, 5271−5294. (16) Vander Heiden, M. G. (2011) Targeting cancer metabolism: a therapeutic window opens. Nat. Rev. Drug Discovery 10, 671−684. (17) Calvaresi, E. C., and Hergenrother, P. J. (2013) Glucose conjugation for the specific targeting and treatment of cancer. Chem. Sci. 4, 2319−2333. (18) Younes, M., Lechago, L. V., and Lechago, J. (1996) Overexpression of the human erythrocyte glucose transporter occurs as a late event in human colorectal carcinogenesis and is associated with an increased incidence of lymph node metastases. Clin. Cancer Res. 2, 1151−1154. (19) Haber, R. S., Rathan, A., Weiser, K. R., Pritsker, A., Itzkowitz, S. H., Bodian, C., Slater, G., Weiss, A., and Burstein, D. E. (1998) GLUT1 glucose transporter expression in colorectal carcinoma - A marker for poor prognosis. Cancer 83, 34−40. (20) Shen, Y. M., Arbman, G., Olsson, B., and Sun, X. F. (2011) Overexpression of GLUT1 in colorectal cancer is independently associated with poor prognosis. Int. J. Biol. Markers 26, 166−172. (21) Graziano, F., Ruzzo, A., Giacomini, E., Ricciardi, T., Aprile, G., Loupakis, F., Lorenzini, P., Ongaro, E., Zoratto, F., Catalano, V., et al. (2016) Glycolysis gene expression analysis and selective metabolic advantage in the clinical progression of colorectal cancer. Pharmacogenomics J., DOI: 10.1038/tpj.2016.13. (22) Mikata, Y., and Gottschaldt, M. (2014) Metal Complexes of Carbohydrate-targeted Ligands in Medicinal Inorganic Chemistry. In Ligand Design in Medicinal Inorganic Chemistry (Storr, T., Ed.) pp 145−173, Chapter 6, John Wiley & Sons, Ltd, Chichester, UK. (23) Liu, P. X., Lu, Y. H., Gao, X. Q., Liu, R., Zhang-Negrerie, D., Shi, Y., Wang, Y. Q., Wang, S. Q., and Gao, Q. Z. (2013) Highly watersoluble platinum(II) complexes as GLUT substrates for targeted therapy: improved anticancer efficacy and transporter-mediated cytotoxic properties. Chem. Commun. 49, 2421−2423. (24) Patra, M., Johnstone, T. C., Suntharalingam, K., and Lippard, S. J. (2016) A Potent Glucose-Platinum Conjugate Exploits Glucose Transporters and Preferentially Accumulates in Cancer Cells. Angew. Chem., Int. Ed. 55, 2550−2554. (25) Storr, T., Scott, L. E., Bowen, M. L., Green, D. E., Thompson, K. H., Schugar, H. J., and Orvig, C. (2009) Glycosylated tetrahydrosalens as multifunctional molecules for Alzheimer’s therapy. Dalton Trans., 3034−3043. (26) Pujol, A. M., Cuillel, M., Jullien, A. S., Lebrun, C., Cassio, D., Mintz, E., Gateau, C., and Delangle, P. (2012) A Sulfur Tripod Glycoconjugate that Releases a High-Affinity Copper Chelator in Hepatocytes. Angew. Chem., Int. Ed. 51, 7445−7448. (27) Cao, J., Cui, S. S., Li, S. W., Du, C. L., Tian, J. M., Wan, S. N., Qian, Z. Y., Gu, Y. Q., Chen, W. R., and Wang, G. J. (2013) Targeted Cancer Therapy with a 2-Deoxyglucose-Based Adriamycin Complex. Cancer Res. 73, 1362−1373. (28) Halmos, T., Santarromana, M., Antonakis, K., and Scherman, D. (1996) Synthesis of glucose-chlorambucil derivatives and their recognition by the human GLUT1 glucose transporter. Eur. J. Pharmacol. 318, 477−484. (29) Guenin, R., and Schneider, C. H. (1983) Synthesis and Anaphylactogenicity of Monohaptenic Carbohydrate Conjugates. Helv. Chim. Acta 66, 1101−1109.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.bioconjchem.6b00332. Synthetic procedures and chemical characterization data for all new compounds, experimental details of cell cultures and cell-based assays (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the University of Arizona Office for Research and Discovery. The UACC/ARL Cytometry Core Facility at the University of Arizona is funded by Cancer Center Support Grant CA 023074. We gratefully acknowledge Aline Kraus and Tsuhen (Michelle) Chang for assistance with synthetic procedures. We thank Paula Campbell and John Fitch for helpful discussions and assistance at the Cytometry Core Facility.

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REFERENCES

(1) Ferlay, J., Soerjomataram, I., Dikshit, R., Eser, S., Mathers, C., Rebelo, M., Parkin, D. M., Forman, D., and Bray, F. (2015) Cancer incidence and mortality worldwide: sources, methods and major patterns in GLOBOCAN 2012. Int. J. Cancer 136, E359−386. (2) Bingham, S., and Riboli, E. (2004) Diet and cancer–the European Prospective Investigation into Cancer and Nutrition. Nat. Rev. Cancer 4, 206−215. (3) Nelson, R. L. (2001) Iron and colorectal cancer risk: Human studies. Nutr. Rev. 59, 140−148. (4) Chua, A. C., Klopcic, B., Lawrance, I. C., Olynyk, J. K., and Trinder, D. (2010) Iron: an emerging factor in colorectal carcinogenesis. World J. Gastroenterol. 16, 663−672. (5) Padmanabhan, H., Brookes, M. J., and Iqbal, T. (2015) Iron and colorectal cancer: evidence from in vitro and animal studies. Nutr. Rev. 73, 308−317. (6) Brookes, M. J., Hughes, S., Turner, F. E., Reynolds, G., Sharma, N., Ismail, T., Berx, G., McKie, A. T., Hotchin, N., Anderson, G. J., et al. (2006) Modulation of iron transport proteins in human colorectal carcinogenesis. Gut 55, 1449−1460. (7) Torti, S. V., and Torti, F. M. (2013) Iron and cancer: more ore to be mined. Nat. Rev. Cancer 13, 342−355. (8) Merlot, A. M., Kalinowski, D. S., and Richardson, D. R. (2013) Novel Chelators for Cancer Treatment: Where Are We Now? Antioxid. Redox Signaling 18, 973−1006. (9) Kalinowski, D. S., and Richardson, D. R. (2005) The evolution of iron chelators for the treatment of iron overload disease and cancer. Pharmacol. Rev. 57, 547−583. (10) Perez, L. R., and Franz, K. J. (2010) Minding metals: tailoring multifunctional chelating agents for neurodegenerative disease. Dalton Trans. 39, 2177−2187. (11) Chang, T. M., and Tomat, E. (2013) Disulfide/thiol switches in thiosemicarbazone ligands for redox-directed iron chelation. Dalton Trans. 42, 7846−7849. E


Communication

Bioconjugate Chemistry (30) Fan, W., Wu, Y., Li, X. K., Yao, N., Li, X., Yu, Y. G., and Hai, L. (2011) Design, synthesis and biological evaluation of brain-specific glucosyl thiamine disulfide prodrugs of naproxen. Eur. J. Med. Chem. 46, 3651−3661. (31) Cui, Y. L., Cheng, Z. D., Mao, J. W., and Yu, Y. P. (2013) Regioselective 6-detrimethylsilylation of per-O-TMS-protected carbohydrates in the presence of ammonium acetate. Tetrahedron Lett. 54, 3831−3833. (32) Jacob, J. N., and Tazawa, M. J. (2012) Glucose-aspirin: Synthesis and in vitro anti-cancer activity studies. Bioorg. Med. Chem. Lett. 22, 3168−3171. (33) Peltier-Pain, P., Timmons, S. C., Grandemange, A., Benoit, E., and Thorson, J. S. (2011) Warfarin Glycosylation Invokes a Switch from Anticoagulant to Anticancer Activity. ChemMedChem 6, 1347− 1350. (34) Saaf, A. M., Halbleib, J. M., Chen, X., Yuen, S. T., Leung, S. Y., Nelson, W. J., and Brown, P. O. (2007) Parallels between global transcriptional programs of polarizing Caco-2 intestinal epithelial cells in vitro and gene expression programs in normal colon and colon cancer. Mol. Biol. Cell 18, 4245−4260. (35) Harris, D. S., Slot, J. W., Geuze, H. J., and James, D. E. (1992) Polarized Distribution of Glucose Transporter Isoforms in Caco-2 Cells. Proc. Natl. Acad. Sci. U. S. A. 89, 7556−7560. (36) O’Neil, R. G., Wu, L., and Mullani, N. (2005) Uptake of a fluorescent deoxyglucose analog (2-NBDG) in tumor cells. Mol. Imaging Biol. 7, 388−392. (37) Xintaropoulou, C., Ward, C., Wise, A., Marston, H., Turnbull, A., and Langdon, S. P. (2015) A comparative analysis of inhibitors of the glycolysis pathway in breast and ovarian cancer cell line models. Oncotarget 6, 25677−25695. (38) Barnett, J. E. G., Holman, G. D., and Munday, K. A. (1973) Structural Requirements for Binding to Sugar-Transport System of Human Erythrocyte. Biochem. J. 131, 211−221. (39) Lin, Y. S., Tungpradit, R., Sinchaikul, S., An, F. M., Liu, D. Z., Phutrakul, S., and Chen, S. T. (2008) Targeting the Delivery of Glycan-Based Paclitaxel Prodrugs to Cancer Cells via Glucose Transporters. J. Med. Chem. 51, 7428−7441. (40) Sun, X. S., Ge, R. G., Cai, Z. W., Sun, H. Z., and He, Q. Y. (2009) Iron depletion decreases proliferation and induces apoptosis in a human colonic adenocarcinoma cell line, Caco2. J. Inorg. Biochem. 103, 1074−1081. (41) Lane, D. J. R., Mills, T. M., Shafie, N. H., Merlot, A. M., Moussa, R. S., Kalinowski, D. S., Kovacevic, Z., and Richardson, D. R. (2014) Expanding horizons in iron chelation and the treatment of cancer: Role of iron in the regulation of ER stress and the epithelialmesenchymal transition. Biochim. Biophys. Acta, Rev. Cancer 1845, 166−181. (42) Whitnall, M., Howard, J., Ponka, P., and Richardson, D. R. (2006) A class of iron chelators with a wide spectrum of potent antitumor activity that overcomes resistance to chemotherapeutics. Proc. Natl. Acad. Sci. U. S. A. 103, 14901−14906. (43) Jansson, P. J., Kalinowski, D. S., Lane, D. J. R., Kovacevic, Z., Seebacher, N. A., Fouani, L., Sahni, S., Merlot, A. M., and Richardson, D. R. (2015) The renaissance of polypharmacology in the development of anti-cancer therapeutics: Inhibition of the ″Triad of Death″ in cancer by Di-2-pyridylketone thiosemicarbazones. Pharmacol. Res. 100, 255−260. (44) Medina, R. A., and Owen, G. I. (2002) Glucose transporters: expression, regulation and cancer. Biol. Res. 35, 9−26.

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Targeting Iron in Colon Cancer via Glycoconjugation of

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