A novel HIF-1α/VMP1-autophagic pathway induces resistance to photodynamic therapy in colon cancer cells.

Colon cancer is the third most frequent cancer and the fourth most common cause of cancer-related mortality worldwide and the standard therapy is surgical resection plus adjuvant chemotherapy. Photodynamic therapy (PDT) has been proposed as an adjuvant therapy because it can prevent the tumor recurrence after surgical excision in colon cancer patients. Hypoxia is a common feature in solid tumors and leads to chemo/radioresistance. Recently, it has been shown that in response to hypoxia, cells can induce HIF-1α-mediated autophagy to survive in this hostile microenvironment. Moreover, hypoxia and autophagy have been implicated in the resistance to antitumor PDT. However, the molecular signals by which HIF-1α induces autophagy in the PDT context have not been studied yet. Here we evaluate the interplay between HIF-1α and autophagy as well as the underlying mechanism in the PDT resistance of colon cancer cells. Our study demonstrates that HIF-1α stabilization significantly increases VMP1-related autophagy through binding to hypoxia responsive elements in the VMP1 promoter. We show that HIF-1α-induced autophagy increases colon cancer cell survival as well as decreases cell death after PDT. Moreover, here we demonstrate that HIF-1α-induced autophagy is mediated by VMP1 expression, since the downregulation of VMP1 by the RNA interference strategy reduces HIF-1α-induced autophagy and cell survival after PDT. In conclusion, PDT induces autophagy as a survival mechanism and the induction of the novel HIF-1α/VMP1-autophagic pathway may explain, at least in part, the resistance of colon cancer cells to PDT. The knowledge of the molecular mechanisms involved in PDT resistance may lead to more accurate therapeutic strategies.

Photodynamic activity of anthraquinones isolated from Heterophyllaea pustulata Hook f. (Rubiaceae) on MCF-7c3 breast cancer cells.

Searching for agents that could be effective in the treatment of cancer, special highlight has focused on the study of numerous plant-derived compounds. We previously demonstrated that anthraquinones (AQs) isolated from a vegetal species: Heterophyllaea pustulata Hook f. (Rubiaceae), such as rubiadin, rubiadin-1-methyl ether, soranjidiol, soranjidiol-1-methyl ether exhibit photosensitizing properties without antecedents as photodynamic agents in malignant cells. In the present study, we investigated the potential role of these AQs as a phototoxic agent against human breast carcinoma using MCF-7c3 cells. All AQs exhibited significant photocytotoxicity on cancer cells at the concentration of 100 µM with 1 J/cm(2) light dose, resulting soranjidiol-1-methyl ether in complete cell destruction. The observed cellular killing by photoactivated AQs exhibited close relation with singlet oxygen production, except for soranjidiol-1-methyl ether, where cell viability decrease is in relation to uptake by tumor cells.

Effects of 2,4-dichlorophenoxyacetic acid on polyamine synthesis in Chinese hamster ovary cells.

It was found that 1 mM 2,4-dichlorophenoxyacetate (2,4-D) inhibited DNA and protein synthesis in Chinese hamster ovary (CHO) cells. When the possible relationship of this phenomenon to the presence of polyamines in the culture medium was investigated, it was found that: (a) the pesticide inhibited ornithine decarboxylase activity; (b) when the concentration of polyamines present in cells treated with the pesticide was determined, the putrescine concentration did not change, and the spermine and spermidine concentration decreased; (c) the addition of spermidine and spermine to CHO cells grown in the presence of 2,4-D normalized DNA and protein synthesis. Putrescine did not have any effect.

Changes in 2-aminoisobutyric acid and cycloleucine uptake produced by 2,4-dichlorophenoxyacetic acid in Chinese hamster ovary cells.

The effect of dichlorophenoxyacetic acid on the transport of two non-metabolizable amino acids, 2-aminoisobutyric acid (AIB) and cycloleucine (CL) was studied in chinese hamster ovary (CHO) cells. The herbicide did not exert any direct effect on the AIB transport. However, when the pesticide was in contact with the cells for 24 h an inhibition of the uptake was observed. Removal of the pesticide from the culture medium restored the influx of the amino acids which reached maximum values 1 h before cell division. The transport kinetics showed changes in Vmax but no variations in Km. These results may indicate that 2,4-dichlorophenoxyacetic acid produces a decrease in the carrier number but without modification of the affinity.

DNA and protein synthesis inhibition in Chinese hamster ovary cells by dichlorophenoxyacetic acid.

The effects of the herbicide dichlorophenoxyacetic acid (2,4-D) on DNA and protein synthesis were investigated in chinese hamster ovary cells (CHO) employing two different methods. The results showed that the herbicide affects DNA and protein synthesis depending on the stage of growth and method of treatment. 2,4-D action appears to concentrate the cells mainly in the G1/S boundary of the cell cycle. The effect is expressed as an inhibition of DNA and protein synthesis. This effect was revealed not only by the chemical determination of DNA and protein synthesis but also by experiments using autoradiography, using the labelling index to detect the incorporation of [3H]thymidine into the cells. Labelling of the cell nucleus was reduced markedly when cells treated with 2,4-D were in confluency for 4 days after reaching plateau growth.