ABCG2-mediated suppression of chlorin e6 accumulation and photodynamic therapy efficiency in glioblastoma cell lines can be reversed by KO143.

BACKGROUND: Photodynamic therapy (PDT) of malignant brain tumors is a promising adjunct to standard treatment, especially if tumor stem cells thought to be responsible for tumor progression and therapy resistance were also susceptible to this kind of treatment. However, some photosensitizers have been reported to be substrates of ABCG2, one of the membrane transporters mediating resistance to chemotherapy. Here we investigate, whether inhibition of ABCG2 can restore sensitivity to photosensitizer chlorin e6-mediated PDT. METHODS: Accumulation of chlorin e6 in wild type U87 and doxycycline-inducible U251 glioblastoma cells with or without induction of ABCG2 expression or ABCG2 inhibition by KO143 was analyzed using flow cytometry. In U251 cells, ABCG2 was inducible by doxycycline after stable transfection with a tet-on expression plasmid. Tumor sphere cultivation under low attachment conditions was used to enrich for cells with stem cell-like properties. PDT was done on monolayer cell cultures by irradiation with laser light at 665nm. RESULTS: Elevated levels of ABCG2 in U87 cells grown as tumor spheres or in U251 cells after ABCG2 induction led to a 6-fold lower accumulation of chlorin e6 and the light dose needed to reduce cell viability by 50% (LD50) was 2.5 to 4-fold higher. Both accumulation and PDT response can be restored by KO143, an efficient non-toxic inhibitor of ABCG2. CONCLUSION: Glioblastoma stem cells might escape phototoxic destruction by ABCG2-mediated reduction of photosensitizer accumulation. Inhibition of ABCG2 during photosensitizer accumulation and irradiation promises to restore full susceptibility of this crucial tumor cell population to photodynamic treatment.

Biosensor-expressing spheroid cultures for imaging of drug-induced effects in three dimensions.

In the past, the majority of antitumor compound-screening approaches had been performed in two-dimensional (2D) cell cultures. Although easy to standardize, this method provides results of limited significance because cells are surrounded by an artificial microenvironment, are not exposed to hypoxia gradients, and lack cell-cell contacts. These nonphysiological conditions directly affect relevant parameters such as the resistance to anticancer drugs. Multicellular tumor spheroids more closely resemble the in vivo situation in avascularized tumors. To monitor cellular reactions within this three-dimensional model system, we stably transfected a spheroid-forming glioblastoma cell line with Grx1-roGFP2, a green fluorescent protein (GFP)-based glutathione-specific redox sensor that detects alterations in the glutathione redox potential. Functionality and temporal dynamics of the sensor were verified with redox-active substances in 2D cell culture. Based on structured illumination microscopy using nonphototoxic light doses, ratio imaging was then applied to monitor the response of the glutathione system to exogenous hydrogen peroxide in optical sections of a tumor spheroid. Our approach provides a proof of concept for biosensor-based imaging in 3D cell cultures.

Growth of human gastric cancer cells in nude mice is delayed by a ketogenic diet supplemented with omega-3 fatty acids and medium-chain triglycerides.

BACKGROUND: Among the most prominent metabolic alterations in cancer cells are the increase in glucose consumption and the conversion of glucose to lactic acid via the reduction of pyruvate even in the presence of oxygen. This phenomenon, known as aerobic glycolysis or the Warburg effect, may provide a rationale for therapeutic strategies that inhibit tumour growth by administration of a ketogenic diet with average protein but low in carbohydrates and high in fat enriched with omega-3 fatty acids and medium-chain triglycerides (MCT). METHODS: Twenty-four female NMRI nude mice were injected subcutaneously with tumour cells of the gastric adenocarcinoma cell line 23132/87. The animals were then randomly split into two feeding groups and fed either a ketogenic diet (KD group; n = 12) or a standard diet (SD group; n = 12) ad libitum. Experiments were ended upon attainment of the target tumor volume of 600 mm3 to 700 mm3. The two diets were compared based on tumour growth and survival time (interval between tumour cell injection and attainment of target tumour volume). RESULTS: The ketogenic diet was well accepted by the KD mice. The tumour growth in the KD group was significantly delayed compared to that in the SD group. Tumours in the KD group reached the target tumour volume at 34.2 +/- 8.5 days versus only 23.3 +/- 3.9 days in the SD group. After day 20, tumours in the KD group grew faster although the differences in mean tumour growth continued significantly. Importantly, they revealed significantly larger necrotic areas than tumours of the SD group and the areas with vital tumour cells appear to have had fewer vessels than tumours of the SD group. Viable tumour cells in the border zone surrounding the necrotic areas of tumours of both groups exhibited a glycolytic phenotype with expression of glucose transporter-1 and transketolase-like 1 enzyme. CONCLUSION: Application of an unrestricted ketogenic diet enriched with omega-3 fatty acids and MCT delayed tumour growth in a mouse xenograft model. Further studies are needed to address the impact of this diet on other tumour-relevant functions such as invasive growth and metastasis.