Elizabeth Cohen-Jonathan

Combined postoperative radiotherapy and weekly cisplatin infusion for locally advanced head and neck carcinoma: final report of a randomized trial.

PURPOSE To report the final results of a prospective randomized trial that aimed to evaluate efficacy and toxicity of concomitant postoperative radiotherapy and Cisplatin infusion in patients with Stage III or IV squamous cell carcinoma of the head and neck and histological evidence of extracapsular spread of tumor in lymph node metastase(s). METHODS AND MATERIALS Radiotherapy was delivered using a daily dose of 1.7 Gy for the first 54 Gy and 1.8 to 2 Gy until the completion of the treatment. Cisplatin 50 mg i.v. with forced hydratation was given or not every week (i.e., seven to nine cycles) concurrently with radiotherapy. A total of 44 patients were treated by irradiation only (RT group) and 39 by irradiation with chemotherapy (CM group). RESULTS The RT group displayed a higher rate of loco-regional failures as compared to CM group (41 vs. 23%; p = 0.08). The overall survival, the survival corrected for deaths by intercurrent disease, and the disease-free survival were better in CM group as compared to RT group with statistically significant differences. Survival without loco-regional treatment failure was better in the CM group, the difference being close to the level of significance (p = 0.05). Survival without distant metastases were comparable in the two therapeutic groups. Ten severe late complications were observed, four in the RT group (17%) and six in the CM group (22%). Cox univariate analysis confirmed the importance of the therapeutic modality in predicting the overall survival, the survival corrected for deaths by intercurrent disease, and the disease-free survival. CONCLUSIONS The present final report of this phase III study confirms preliminary results. The concomitant use of 50 mg weekly Cisplatin infusion and postoperative radiation improved loco-regional control and survival. No significant increase of late radiation complications was observed in the CM group.

Farnesyltransferase inhibitor, R115777, reverses the resistance of human glioma cell lines to ionizing radiation

We investigated for the first time the ability of farnesyltransferase inhibitors (FTI) to radiosensitize human glioma. For this, human glioma cell lines were treated with the specific FTI, R115777, 48 hr prior to a 2Gy irradiation. The treatment with R115777 decreased by 45% the SF2 value of the more radioresistant glioma cell lines (SF763 and U87) without any significant effect on the radioresistance of the radiosensitive ones (SF767 and U251‐MG). This radiosensitizer effect was due to the induction of post‐mitotic necrotic cell death. We then tested the hypothesis that wild‐type Ras or RhoB, which has been proposed as potential FTI target, could control the glioma radioresistance. For this, we expressed inducible dominant negative forms of Ras (RasN17) and RhoB (RhoBN19) in radioresistant U87 glioma cell line and analyzed the survival after irradiation of the obtained clones. While blocking Ras pathways by expression of RasN17 did not affect the SF2 value of the U87 glioma cell line, the expression of RhoBN19 dramatically reduced the cell survival after irradiation of these cells. Taken together, these data demonstrated that RhoB, but not Ras, is implicated in glioma radioresistance. Furthermore, the R115777 differential radiosensitizer effect underlines the potential therapeutic interest of using this drug as a radiosensitizer of human glioma.

RhoB controls the 24 kDa FGF-2-induced radioresistance in HeLa cells by preventing post-mitotic cell death.

Farnesylated Ras oncoprotein induces a cellular resistance to ionizing radiation that can be reversed by farnesyltransferase inhibitors (FTI). We previously demonstrated that, expression of the 24 kDa FGF2 isoform in wild type ras bearing HeLa cells, induced radioresistance which was also reversed by FTI. We tested the hypothesis that wild type Ras or RhoB, which has been proposed as a potential FTI target, could control the FGF-2-induced radioresistance mechanisms. For this, we expressed inducible dominant negative forms of Ras (RasN17) and Rho (RhoBN19) in 24 kDa FGF2 transfected HeLa cells and analysed their survival after irradiation. While no cell survival modification was observed after RasN17 induction, the expression of RhoBN19 induced a radiosensitization of FGF2 radioresistant HeLa cells in the same range as the one observed after a 48 h treatment with the specific FTI, R115777. Moreover, we showed that activated RhoB but not RhoA induced radioresistance in NIH3T3 cells. The radiosensitizer effect of RhoBN19 expression was due to the induction of the radiation induced post-mitotic cell death. Taken together, these data demonstrate that 24 kDa FGF-2-induced radioresistance is controlled by Rho pathways and suggest that RhoB should be a major determinant in cellular resistance to ionizing radiation.

The radioprotective effect of the 24 kDa FGF-2 isoform in HeLa cells is related to an increased expression and activity of the DNA dependent protein kinase (DNA-PK) catalytic subunit.

We previously reported that overexpression of the 24 kDa basic fibroblast factor (or FGF-2) isoform provides protection from the cytotoxic effect of ionizing radiation (IR). DNA double-strand breaks (DSB), the IR-induced lethal lesions, are mainly repaired in human cells by non-homologous end joining system (NHEJ). NHEJ reaction is dependent on the DNA-PK holoenzyme (composed of a regulatory sub-unit, Ku, and a catalytic sub-unit, DNA-PKcs) that assembles at sites of DNA damage. We demonstrated here that the activity of DNA-PK was increased by twofold in two independent radioresistant cell lines, HeLa 3A and CAPAN A3, overexpressing the 24 kDa FGF-2. This increase was associated with an overexpression of the DNA-PKcs without modification of Ku expression or activity. This overexpression was due to an up-regulation of the DNA-PKcs gene transcription by the 24 kDa FGF-2 isoform. Finally, HeLa 3A cells exhibited the hallmarks of phenotypic changes associated with the overexpression of an active DNA-PKcs. Indeed, a faster repair rate of DSB and sensitization to IR by wortmannin was observed in these cells. Our results represent the characterization of a new mechanism of control of DNA repair and radioresistance in human tumor cells dependent on the overproduction of the 24 kDa FGF-2 isoform.

Preferential cytoplasmic localization of p34cdc2 in recurrent human squamous cell carcinoma after radiotherapy.

Duration of the G2-phase delay and arrest after exposure to ionizing radiation is thought to influence radiosensitivity. The kinase activity of the p34cdc2-cyclin B complex and the p34cdc2-cyclin A complex is implicated in G2- to M-phase transition and in G2-phase arrest after exposure to ionizing radiation. We analyzed the expression level and the subcellular location of p34cdc2, cyclin A and cyclin B in head and neck squamous cell carcinoma (SCC) tumors; samples were obtained from patients with locally nonrecurrent and recurrent tumors that had been treated by surgery and radiotherapy. No significant difference was noticed in cyclin A, cyclin B and p34cdc2 expression. However, we noted a significant preferential cytoplasmic location of p34cdc2 in recurring tumors compared to the nonrecurring ones (P < 0.001). This abnormal location of p34cdc2 occurs even in primary tumors in patients with recurring tumors, suggesting that a default in the activation of p34cdc2 kinase could be implicated in clinical radioresistance.

Inhibiting Signal Transduction as an Approach to Radiosensitizing Tumor Cells

Tumors and normal tissues vary widely in their sensitivity to radiation. A combination of the cellular signals that originate within a cell and those in response to environmental factors outside the cell interact to determine the relative resistance or sensitivity of cells to radiation. Either of these determinants of radiation sensitivity provides potential targets for enhancing radiation-induced tumor cell killing. Of particular interest are signaling pathways that differ in normal and tumor cells as a result of oncogenic activation. Such pathways present potentially useful targets for differential inactivation as an approach to radiosensitization.