Fructose as a carbon source induces an aggressive phenotype in MDA-MB-468 breast tumor cells

Aberrant glycosylation is a universal feature of cancer cells, and certain glycan structures are well-known markers for tumor progression. Availability and composition of sugars in the microenvironment may affect cell glycosylation. Recent studies of human breast tumor cell lines indicate their ability to take up and utilize fructose. Here we tested the hypothesis that adding fructose to culture as a carbon source induces phenotypic changes in cultured human breast tumor cells that are associated with metastatic disease. MDA-MB-468 cells were adapted to culture media in which fructose was substituted for glucose. Changes in cell surface glycan structures, expression of genes related to glycan assembly, cytoskeleton F-actin, migration, adhesion and invasion were determined. Cells cultured in fructose expressed distinct cell-surface glycans. The addition of fructose affected sialylation and fucosylation patterns. Fructose feeding also increased binding of leukoagglutinating Phaseolus vulgaris isolectin, suggesting a possible rise in expression of branching beta-1, 6 GlcNAc structures. Rhodamine-phalloidin staining revealed an altered F-actin cytoskeletal system. Fructose accelerated cellular migration and increased invasion. These data suggest that changing the carbon source of the less aggressive MDA-MB-468 cell line induced characteristics associated with more aggressive phenotypes. These data could be of fundamental importance due to the markedly increased consumption of sweeteners containing free fructose in recent years, as they suggest that the presence of fructose in nutritional microenvironment of tumor cells may negatively affect the outcome for some breast cancer patients.

(1)H nuclear magnetic resonance metabolomic analysis of mammary tumors from lean and obese Zucker rats exposed to 7,12-dimethylbenz[a]anthracene

Obesity increases mammary tumor development in Zucker rats following a single administration of the procarcinogen 7,12-dimenthylbenz(a)anthracene (DMBA). Fifty-day-old obese and lean female Zucker rats were orally gavaged with 65 mg/kg DMBA and sacrificed 139 days post DMBA treatment. At the end of the experiment, mammary tumors were detected in 68% of the obese rats compared to 32% of the lean group (P<0.001). 1H nuclear magnetic resonance (1H-NMR) spectra obtained for hydrophilic and lipophilic extracts from excised tumors illustrated fundamental differences in metabolic profiles between the two groups. Differences were observed for key choline compounds, namely phosphocholine and glycerophosphocholine, both markers of malignancy and apoptosis. In addition, levels of lactate, creatine, myo-inositol, alpha-glucose, alanine, leucine, glutamate, glutamine, tyrosine, phenylalanine, and NADH varied between the lean and obese groups. Principal component analysis indicated class separation between tumors from lean and obese rats based on their metabolic profiles, illustrating the potential for using 1H-NMR metabolomic methods for identifying altered metabolic pathways. Our results suggest that obesity enhances the risk for DMBA-induced mammary tumor development in rats. However, the mechanism for this increase in risk is currently unknown and will require further studies for elucidation.

Obesity increases the incidence of 7,12-dimethylbenz(a)anthracene-induced mammary tumors in an ovariectomized Zucker rat model

Obesity is associated with increased risk for postmenopausal, but not premenopausal breast cancer. Recently, we reported that intact obese Zucker rats had increased susceptibility to DMBA-induced mammary tumors compared to lean Zucker rats. In the present study, we investigated whether excessive adipose tissue would promote mammary tumor induction in the absence of ovarian estrogen. Lean and obese rats were sham-operated or ovariectomized at 40 days old and were gavaged at 50 days old with 65 mg/kg DMBA. Rats were weighed and palpated twice weekly for detection of mammary tumors and sacrificed 135 days post-DMBA treatment. Obese sham-operated (O/S) rats had a shorter latency period (102 days) compared to lean sham-operated (L/S) (134 days) and obese ovariectomized (O/O) rats (123 days). At the end of the experiment, 36% of the O/O rats developed mammary tumors while lean ovariectomized (L/O) rats developed no mammary tumors (P<0.001), and 59% of the O/S rats developed mammary tumors compared to 30% of the L/S rats (P<0.05). In summary, obesity increases the susceptibility of ovariectomized Zucker rats to DMBA-induced mammary tumors, suggesting that adipose tissue-derived estrogen in obese animals may be sufficient to promote DMBA-induced tumors in this model. These results suggest that obesity in postmenopausal women may increase breast cancer risk due to increased breast tissue exposure to adipose tissue-derived estrogen. In conclusion, we have developed an animal model to further investigate the role of obesity in breast cancer development in postmenopausal women.

Chondroitin sulfate glycosaminoglycans as major P-selectin ligands on metastatic breast cancer cell lines

The metastatic breast cancer cell line, 4T1, abundantly expresses the oligosaccharide sialylated Lewis x (sLe(x)). SLe(x) oligosaccharide on tumor cells can be recognized by E- and P-selectin, contributing to tumor metastatic process. We observed that both selectins reacted with this cell line. However, contrary to the E-selectin reactivity, which was sLe(x) dependent, P-selectin reactivity with this cell line was sLe(x)-independent. The sLe(x)-Neg variant of the 4T1 cell line with markedly diminished expression of sLe(x) and lack of sLe(a), provided a unique opportunity to characterize P-selectin ligands and their contribution to metastasis in the absence of overlapping selectin ligands and E-selectin binding. We observed that P-selectin binding was Ca(2+)-independent and sulfation-dependent. We found that P-selectin reacted primarily with cell surface chondroitin sulfate (CS) proteoglycans, which were abundantly and stably expressed on the surface of the 4T1 cell line. P-selectin binding to the 4T1 cells was inhibited by heparin and CS glycosaminoglycans (GAGs). Moreover, Heparin administration significantly inhibited experimental lung metastasis. In addition, the data suggest that surface CS GAG chains were involved in P-selectin mediated adhesion of the 4T1 cells to murine platelets and human umbilical vein endothelial cells. The data suggest that CS GAGs are also the major P-selectin-reactive ligands on the surface of human MDA-MET cells. The results warrant conducting clinical studies on the involvement of cell surface CS chains in breast cancer metastasis and evaluation of various CS types and their biosynthetic pathways as target for development of treatment strategies for antimetastatic therapy of this disease.

Characterization of the glycosylation profile of the human breast cancer cell line, MDA-231, and a bone colonizing variant

The mechanisms that guide organ-specific metastases are not fully established. The aberrant expression of carbohydrates may play a fundamental role in defining the molecular mechanisms for metastases to distant organs and facilitate positive interactions within the target organ. The purpose of the present study was to determine the glycomic profile of a variant of the MDA-MB-231 breast cancer cell line that colonizes the bone and to ascribe mechanistic functions mediated by carbohydrates that might correlate with clinical bone metastases. The carbohydrate expression profiles of osteolytic MDA-MET breast cancer cells and non-osteolytic parental MDA-MB-231 cells were determined. MDA-MET cells were derived from MDA-MB-231 cells by in vivo selection of metastatic bone lesions following intracardiac inoculation. The two related breast cancer cell lines expressed distinct carbohydrate profiles; MDA-MET cells displayed an increased expression of alpha (2,6) linked sialic acid, N-beta1-6 GlcNAc, and sialylated Lewis-A antigen, and decreased expression of Galbeta1,3GalNAc as detected using a combination of lectins and anti-carbohydrate antibodies. Microarray analysis demonstrated an increased expression of glycosyltransferase genes, correlative for the distinct glycomic phenotype. The altered glycomic phenotypes of MDA-MET cells include effects on the differential binding to bone marrow endothelial cells, enhanced ECM binding and an increase in invasive potential. These data suggest that the glycomic phenotype of MDA-MET cells is associated with a select set of accumulated functions that collectively impact on the bone metastases and bone colonization capacity of breast cancer cells.

Reduction of spontaneous metastases through induction of carbohydrate cross-reactive apoptotic antibodies

The selective targeting of tumor-associated carbohydrate Ags by the induction of serum Abs that trigger apoptosis of tumor cells as a means to reduce circulating tumor cells and micrometastases would be an advantage in cancer vaccine development. Some plant lectins like Griffonia simplicifolia lectin I and wheat germ agglutinin mediate the apoptosis of tumor cells. We investigated the possibility of using these lectins as templates to select peptide mimotopes of tumor-associated carbohydrate Ags as immunogens to generate cross-reactive Abs capable of mediating apoptosis of tumor cells. In this study, we show that immunization with a mimotope selected based on its reactivity with Griffonia simplicifolia lectin I and wheat germ agglutinin induced serum IgM Abs in mice that mediated the apoptosis of murine 4T1 and human MCF7 cell lines in vitro, paralleling the apoptotic activity of the lectins. Vaccine-induced anti-carbohydrate Abs reduced the outgrowth of micrometastases in the 4T1 spontaneous tumor model, significantly increasing survival time of tumor-bearing animals. This finding parallels suggestions that carbohydrate-reactive IgM with apoptotic activity may have merit in the adjuvant setting if the right carbohydrate-associated targets are identified.

Deficiency in surface expression of E-selectin ligand promotes lung colonization in a mouse model of breast cancer

Expression of sialyl Lewis(x) (sLe(x)) and sLe(a) on tumor cells is thought to facilitate metastasis by promoting cell adhesion to selectins on vascular endothelial cells. Experiments supporting this concept usually bypass the early steps of the metastatic process by employing tumor cells that are injected directly into the blood. We investigated the relative role of sLe(x) oligosaccharide in the dissemination of breast carcinoma, employing a spontaneous murine metastasis model. An sLe(x) deficient subpopulation of the 4T1 mammary carcinoma cell line was produced by negative selection using the sLe(x)-reactive KM93 MAb. This subpopulation was negative for E-selectin binding but retained P-selectin binding. Both sLe(x)-negative and -positive cells grew at the same rate; however, sLe(x)-negative cells spread more efficiently on plates and had greater motility in wound-scratch assays. Mice inoculated in the mammary fat pad with sLe(x)-negative and -positive variants produced lung metastases. However, the number of lung metastases was significantly increased in the group inoculated with the sLe(x)-negative variant (p = 0.0031), indicating that negative selection for the sLe(x) epitope resulted in enrichment for a subpopulation of cells with a high metastatic phenotype. Cell variants demonstrated significant differences in cellular morphology and pattern of tumor growth in primary and secondary tumor sites. These results strongly suggest that loss of sLe(x) may facilitate the metastatic process by contributing to escape from the primary tumor mass.