Inhibition of microtubule assembly and cytotoxic effect of graphene oxide on human colorectal carcinoma cell HCT116

Nanomaterials, such as graphene oxide (GO), are increasingly being investigated for their suitability in biomedical applications. Tubulin is the key molecule for the formation of microtubules crucial for cellular function and proliferation, and as such an appealing target for developing anticancer drug. Here we employ biophysical techniques to study the effect of GO on tubulin structure and how the changes affect the tubulin/microtubule assembly. GO disrupts the structural integrity of the protein, with consequent retardation of tubulin polymerization. Investigating the anticancer potential of GO, we found that it is more toxic to human colon cancer cells (HCT116), as compared to human embryonic kidney epithelial cells (HEK293). Immunocytochemistry indicated the disruption of microtubule assembly in HCT116 cells. GO arrested cells in the S phase with increased accumulation in Sub-G1 population of cell cycle, inducing apoptosis by generating reactive oxygen species (ROS) in a dose- and time-dependent manner. GO inhibited microtubule formation by intervening into the polymerization of tubulin heterodimers both in vitro and ex vivo, resulting in growth arrest at the S phase and ROS induced apoptosis of HCT116 colorectal carcinoma cells. There was no significant harm to the HEK293 kidney epithelial cells used as control. Our report of pristine GO causing ROS-induced apoptosis of cancer cells and inhibition of tubulin-microtubule assembly can be of interest in cancer therapeutics and nanomedicine.

In vitro prebiotic potential, digestibility and biocompatibility properties of laminari-oligosaccharides produced from curdlan by β-1,3-endoglucanase from Clostridium thermocellum

Curdlan or laminarin, a β-1,3-glucan was hydrolysed by β-1,3-endoglucanase (CtLam81A) from Clostridium thermocellum to produce laminari-oligosaccharides. TLC analysis of hydrolysed curdlan showed the presence of laminari-oligosaccharides of the degree of polymerization, DP2-DP7. This mixture of laminari-oligosaccharides displayed prebiotic properties. Laminari-oligosaccharides showed an increase in the growth of probiotic bacteria such as Lactobacillus plantarum DM5 and Lactobacillus acidophilus, while they did not promote the growth of non-probiotic bacteria (Escherichia coli and Enterobacter aerogenes). Laminari-oligosaccharides showed higher prebiotic activity score of 0.92 ± 0.01 and 0.64 ± 0.08 for L. plantarum DM5 and L. acidophilus NRRL B-4496, respectively, similar to those shown by inulin. Laminari-oligosaccharides showed higher resistance or low digestibility against α-amylase, artificial gastric juice and intestinal fluid than inulin indicating their bioavailability to the probiotic bacteria present in the gastrointestinal tract of human. The probiotic bacteria consumed laminaribiose and laminariotriose more readily than higher laminari-oligosaccharides as carbon source for their growth. The in vitro cytotoxicity assay of laminari-oligosaccharides (1 mg/ml) on human embryonic kidney (HEK 293) cells showed that the cell viability was not affected even after 72 h indicating their biocompatible nature. All the results amply indicated that laminari-oligosaccharides can serve as potential prebiotic additives for functional food products.

Endoplasmic reticulum stress induces 5-fluorouracil resistance in human colon cancer cells

Colon cancer can be treated with 5-fluorouracil (5-FU), but 5-FU resistance frequently occurs. We determined whether 5-FU resistance arises as a result of endoplasmic reticulum (ER) stress. 5-FU-resistant SNUC5 colon cancer cells (SNUC5/FUR cells) expressed higher levels of ER stress-related proteins than drug-sensitive SNUC5 cells. SNUC5/FUR cells also exhibited more intense ER staining and higher level of mitochondrial Ca(2+) overload. SNUC5/FUR cells transfected with siRNA against GRP78, ATF6, ERK, or AKT were more sensitive to 5-FU than siControl RNA-transfected cells. These results suggested that 5-FU resistance was associated with ER stress in colon cancer.

Identification of an anticancer compound against HT-29 cells from Phellinus linteus grown on germinated brown rice

OBJECTIVE

To isolate and identify the anticancer compound against proliferation of human colon cancer cells from ethyl acetate (EtOAc) extract of Phellinus linteus grown on germinated brown rice (PB).

METHODS

EtOAc extract of PB was partitioned with n-hexane, EtOAc, and water-saturated n-butanol. Anticancer compound of n-hexane layer was isolated and identified by HPLC and NMR, respectively. Cytotoxicity against HT-29 cells was tested by SRB assay.

RESULTS

The n-hexane layer obtained after solvent fractionation of PB EtOAc extracts showed a potent anticancer activity against the HT-29 cell line. Atractylenolide I, a eudesmane-type sesquiterpene lactone, a major anticancer substance of PB, was isolated from the n-hexane layer by silica gel column chromatography and preparative-HPLC. This structure was elucidated by one- and two-dimensional NMR spectroscopic data. Atractylenolide I has not been reported in mushrooms or rice as of yet. The isolated compound dose-dependently inhibited the growth of HT-29 human colon cancer cells.

CONCLUSIONS

Atractylenolide I might contribute to the anticancer effect of PB.

Expression of T-STAR gene is associated with regulation of telomerase activity in human colon cancer cell line HCT-116

AIM: To investigate the effects on telomerase activity of transfection of human T-STAR gene full-length sense cDNA or partial antisense cDNA into human colon cancer cell line HCT-116.

METHODS: mRNA and protein expression levels of T-STAR gene were determined by RT-PCR and western blot, and telomerase activity was measured by PCR-ELISA, after transfection of T-STAR sense or antisense gene into HCT-116 cells with lipofectamine.

RESULTS: T-STAR gene expression was enhanced or knocked down both at mRNA and protein levels, and telomerase activity was significantly increased or decreased.

CONCLUSION: The T-STAR gene may participate in regulation of telomerase activity in human colon cancer HCT-116 cells in a parallel fashion.

Effects of T-STAR gene on activity of telomerase in colon cancer cell line HCT-116

AIM: To investigate the effects of testis-signal transduction and activator of RNA (T-STAR) on telomerase activity in human colon cancer cell line HCT-116.

METHODS: The T-STAR sense or antisense gene was transfected into HCT-116 cells with lipofectamine. The mRNA and protein expression of T-STAR were determined by reverse transcription polymerase chain reaction (RT-PCR) and western blot, and the activity of telomerase was measured by PCR-ELISA.

RESULTS: The expression of T-STAR mRNA and protein were significantly increased in T-STAR transfected cells (296% and 180% respectively, P<0.01), while markedly decreased in antisense T-STAR transfected ones (59% and 83.8% respectively, P<0.01). The activity of telomerase was significantly increased in T-STAR transfected cells, but decreased in antisense T-STAR transfected ones. The expression of T-STAR and the activity of telomerase manifested no significant difference between HCT-116 cells transfected with empty vector and non-transfected ones.

CONCLUSION: T-STAR gene may play an important role in the positive regulation of telomerase activtity in human colon cancer HCT-116 cells.