Inhibition of CXCR7 extends survival following irradiation of brain tumours in mice and rats.

BACKGROUND: In experimental models of glioblastoma multiforme (GBM), irradiation (IR) induces local expression of the chemokine CXCL12/SDF-1, which promotes tumour recurrence. The role of CXCR7, the high-affinity receptor for CXCL12, in the tumour's response to IR has not been addressed. METHODS: We tested CXCR7 inhibitors for their effects on tumour growth and/or animal survival post IR in three rodent GBM models. We used immunohistochemistry to determine where CXCR7 protein is expressed in the tumours and in human GBM samples. We used neurosphere formation assays with human GBM xenografts to determine whether CXCR7 is required for cancer stem cell (CSC) activity in vitro. RESULTS: CXCR7 was detected on tumour cells and/or tumour-associated vasculature in the rodent models and in human GBM. In human GBM, CXCR7 expression increased with glioma grade and was spatially associated with CXCL12 and CXCL11/I-TAC. In the rodent GBM models, pharmacological inhibition of CXCR7 post IR caused tumour regression, blocked tumour recurrence, and/or substantially prolonged survival. CXCR7 expression levels on human GBM xenograft cells correlated with neurosphere-forming activity, and a CXCR7 inhibitor blocked sphere formation by sorted CSCs. CONCLUSIONS: These results indicate that CXCR7 inhibitors could block GBM tumour recurrence after IR, perhaps by interfering with CSCs.

Cell cycle-dependent effects of wortmannin on radiation survival and mutation.

Wortmannin, a known radiation sensitizer, has been used in experiments with synchronized cells to compare its effect on radiation survival and mutation induction within the cell cycle. PL61 cells (CHO cells with an inactivated HPRT gene containing a single active copy of a bacterial gpt gene) were synchronized by mitotic selection. Wortmannin administered before gamma irradiation caused a greater sensitization in G(1)-phase cells relative to late S/G(2)-phase cells. Preferential radiosensitization of G(1)-phase cells by wortmannin sets a limit to the proposed use of wortmannin in radiation therapy, since, in contrast to normal tissues, tumors usually have high proportions of S-phase cells. Wortmannin increased mutation frequencies in both G(1)- and S/G(2)-phase cells. Interestingly, relative increases in radiation-induced mutations in G(1) and S/G(2) phases were comparable. The results are discussed in terms of the contributions of different repair modes in the production of mutations.

Wortmannin sensitizes mammalian cells to radiation by inhibiting the DNA-dependent protein kinase-mediated rejoining of double-strand breaks.

Wortmannin has been shown to be an efficient radiosensitizer. Since wortmannin is able to inhibit DNA-dependent protein kinase (DNA-PK) and double-strand break (DSB) rejoining, it is believed that its mechanism of radiation sensitization is through the inhibition of DNA-PK-mediated repair of DSBs. However, since wortmannin is not a specific inhibitor, the possibility that other kinases are inhibited and thereby may contribute to radiosensitization cannot be ruled out. Here we present data confirming the radiosensitizing effect of wortmannin on cells of different cell lines. In the same range of wortmannin concentrations, survival after exposure to ionizing radiation correlated well with DSB rejoining and the induction of micronuclei, suggesting that the inhibition of the processing of DSBs is involved in the sensitizing effect. Pretreatment with wortmannin enhanced the radiosensitivity of ataxia telangiectasia (AT) cells, thereby precluding the participation of ATM protein in the radiation sensitization by wortmannin. At the same time, irradiated DNA-PK-deficient cells were not significantly affected by pretreatment with wortmannin. These observations support a likely mechanism; that is, wortmannin sensitizes cells to radiation through inhibition of the DNA-PK-mediated rejoining of DSBs.

[A comparison of the patterns of delayed cell death after exposure to genotoxic agents]. / Sravnenie zakonomernostei otdalennoi gibeli kletok posle vozdeistviia genotoksicheskikh agentov.

A lot of data have been provided on different types of cells showing that ionizing radiation induces a hereditable genome instability, which may lead to mutations chromosome aberrations and cell death. In this paper we studied delayed death, proliferative activity, sensitivity to genotoxic agents to progeny of HeLa and LL cells following treatment with ionizing radiation, cis-platinum, methylhydroxurea which induce different types of lesions with different rate of repair. The rate of death of the progeny, dynamics of the clonogen ability recovery, growth rate recovery after the treatment with genotoxic agents are different. We have supposed that the delayed cell death may be associated with different types of hereditable lesions.

[Effect of low-dose ionizing radiation on radiosensitivity to the next irradiation]. / Vliianie malykh doz ioniziruiushchei radiatsii na chuvstvitelnost k posleduiushchemu oblucheniiu.

The action of low dose irradiation on the radiosensitivity of HeLa cells was studied. It was shown that preliminary irradiation of sells by dose of 3 cGy induces the adaptive response: decreasing of number of cells with micronuclei after posterior irradiation by doses of 2.0 and 3.0 Gy. The maximum level of the adaptive response is reached in 4 h and is observed in 3 cell cycles. When the dose of preliminary irradiation increases to 40 cGy the adaptive response is not observed, however the radiosensitivity of cells increases.

[The action of low doses of nitrosomethylurea on a stationary cell population. An experiment and modelling]. / Deistvie malykh doz nitrozometilmocheviny na statsionarnuiu kletochnuiu populiatsiiu. Eksperiment i modelirovanie.

The change of stationary cell population (murine spleen) following an exposure to low doses of methylnitrosourea (10(-11)-10(-5) g/kg of mouse weight) was investigated and modelled mathematically. The suggested model is based on the idea that the effect of cytotoxic agent in low doses has nondestructive "signal" character, changing dynamic balance between cells in proliferating and quiescent compartments.