Heterogeneity of in vitro radiosensitivity in human bladder cancer cells

Palliative radiotherapy in locally advanced head and neck cancer after failure of induction chemotherapy: comparison of two fractionation schemes

Context:

Among patients with locally advanced head and neck squamous cell cancers (LAHNSCC), the prognosis after nonresponse or progression despite induction chemotherapy (IC) is dismal, and further treatment is often palliative in intent. Given that nonresponse to chemotherapy could indicate subsequent radioresistance, we intended to assess the outcomes with two different fractionation schemes.

Aims:

To compare the outcomes of two fractionation schemes- ’standard’ (consisting 3GyX5 daily fractions for 2 consecutive weeks) versus ‘hybrid’ (6GyX3 fractions on alternate days during the 1^st week, followed by 2GyX5 daily fractions in the 2^nd week).

Settings and Design:

Prospective randomized controlled two-arm unblinded trial.

Materials and Methods:

Patients with locally advanced oropharyngeal, laryngeal, and hypopharyngeal cancers treated with a minimum of two cycles of taxane, platinum, and fluorouracil-based IC were eligible if residual disease volume amounted <30 cm³. Kaplan-Meier survival curves were compared by the log-rank test. Response rates were compared using the unpaired t-test. Quality of life (QOL) was measured via patient reported questionnaires.

Results:

Of the initially enrolled 51 patients, 45 patients (24 from standard arm, and 21 from the hybrid arm) were eligible for analysis. Despite being underpowered to attain statistical significance, there still seemed to be a trend towards improvement in progression-free (Hazard ratio (HR) for progression: 0.5966; 95% CI 0.3216-1.1066) and overall survival (HR for death: 0.6062; 95% CI 0.2676-1.3734) with the hybrid arm when compared to the standard arm. Benefits were also observed with regards to response rates and QOL. Rate of complications were similar in both arms.

Conclusions:

In comparison to the routinely used palliative fractionation scheme of 30 Gray (Gy) in 10 fractions (Fr), the use of hybrid fractionation which integrates hypofractionation in the 1^st week, followed by conventional fractionation in the 2^nd week, could possibly offer better response rates, QOL increments, and potential survival benefits among LAHNSCC patients even after failing to respond to IC.

Real-time cell-impedance sensing assay as an alternative to clonogenic assay in evaluating cancer radiotherapy

Intrinsic radiosensitivity of normal and tumour tissues has been shown to be an independent prognostic factor for patients' response to radiotherapy. This study compares the real-time cell-impedance sensing (RT-CES) assay with the conventional clonogenic assay in terms of in-vitro radiosensitivity. One objective in this study was to predict in-vivo response to gold nanoparticle (GNP) treatment on the basis of in-vitro RT-CES testing results. Four adenocarcinoma cancer cell lines were tested using both the RT-CES and the clonogenic assays. Cell-survival curves were plotted, and the mean SF2 values obtained by these two different assay methods were compared using ANOVA. Radiation sensitivities obtained in-vitro were then compared with the in-vivo results. On the basis of the measurement of cell colonies, the RT-CES assay has similar radiosensitivity to the clonogenic assay, but significantly shortens the testing time from 14-21 days to only 72 h. Intrinsic GNP enhanced radiation sensitivity using tumour volume (mm(3)) in vivo is comparable with that using RT-CES cell survival assay in vitro. Furthermore, the RT-CES system provides real-time information regarding the state of cell radiosensitivity that may give useful information towards personalizing radiotherapy. The RT-CES assay enables more reliable and time-efficient results in the evaluation of radiosensitivity.

Paclitaxel enhanced radiation sensitization for the suppression of human prostate cancer tumor growth via a p53 independent pathway

BACKGROUND

This study investigated the influence of p53 status on treatment using combined paclitaxel and irradiation for human prostate cancer (PC) in vitro and in vivo.

METHODS

Enhancement of the radiation response by paclitaxel was determined by MTT and clonogenic assays in four sublines of the human PC cell line, LNCaP, stably transfected to express different p53 mutations found in PC patients. Suppression of xenograft growth by combined paclitaxel and radiation was assessed in NOD.SCID mice in vivo. Expression of p53 and downstream functional proteins, p21 and Bax, was assessed by Western blotting.

RESULTS

Paclitaxel (8-10 nM) suppressed cell proliferation by 50% by inducing G2M mitotic arrest in LNCaP cell lines transfected to overexpress wild-type or mutant p53. Exposure to 20 nM paclitaxel before radiation therapy enhanced cytotoxicity in clonogenic assays. The dose and duration of paclitaxel exposure were important in inducing both G2M arrest and cell growth suppression and were critical factors in paclitaxel/irradiation combination therapy. Western blotting indicated that combination therapy increased p21 protein expression to varying degrees in all cell lines. In vivo studies indicated that paclitaxel pre-treatment followed by irradiation significantly suppressed tumor growth compared with either treatment alone.

CONCLUSIONS

Pre-treatment with paclitaxel enhances radiation efficacy on cell killing and suppression of growth of human PC cell lines in vitro and in vivo via p53 independent pathways. Paclitaxel has potential for use as a radiosensitizer in the treatment of patients with PC with either wild-type or mutant p53 genetic status.

Hyperradiosensibilité aux très faibles doses: impact en radiothérapie des micrométastases

Radiobiologists have pointed out a novel radiobiological phenomenon observed in many tumor and normal cell lines: hyper-radiosensitivity to very low-dose (HRS) followed by induced radioresistance (IRR) after a threshold dose of 0.1-0.3 Gy that depends on the cell line. Radioresistance at high dose (i.e. higher than 0.5 Gy) and metastatic potential of tumor cells are likely major factors of failure in radiotherapy. A careful review of literature suggests that: 1) radiotherapy does not increase the metastatic potential of tumor cells; 2) radioresistance at high dose and metastatic potential are not related. However, inside a given tumor cell line, highly metastatic clones may elicit more cells showing HRS or are more radiosensitive at high dose than poorly metastatic ones. Recent data obtained from molecular techniques (comet and immunofluorescence assays) applied to single cells irradiated at very low radiation doses (1-100 mGy) suggest that DNA single-strand breaks (SSB) and double-strand breaks (DSB) may be the key-lesions responsible for the HRS phenomenon. These data suggest that the HRS phenomenon may find application in radiotherapy for micrometastasis. These early disseminated and probably unvascularised cells may escape the influence of high-dose chemotherapy after excision of the primary tumor. Considering the link between metastatic potential and HRS, we have previously proposed to apply very low-dose total body irradiation (TBI) at M(0) stage that may prevent the development of micrometastases. Literature data suggest that the smallest radiation dose that can produce HRS without increasing the risk of cancer may be in the milliGrays range.

Carbonic anhydrase IX expression and outcome after radiotherapy for muscle-invasive bladder cancer

AIMS

Carbonic anhydrase IX (CA IX) expression has been described as an endogenous marker of hypoxia in solid neoplasms. Furthermore, CA IX expression has been associated with an aggressive phenotype and resistance to radiotherapy. We assessed the prognostic significance of CA IX expression in patients with muscle-invasive bladder cancer treated with radiotherapy.

MATERIALS AND METHODS

A standard immunohistochemistry technique was used to show CA IX expression in 110 muscle-invasive bladder tumours treated with radiotherapy. Clinicopathological data were obtained from medical case notes.

RESULTS

CA IX immunostaining was detected in 89 ( approximately 81%) patients. Staining was predominantly membranous, with areas of concurrent cytoplasmic and nuclear staining and was abundant in luminal and perinecrotic areas. No significant correlation was shown between the overall CA IX status and the initial response to radiotherapy, 5-year bladder cancer-specific survival or the time to local recurrence.

CONCLUSIONS

The distribution of CA IX expression in paraffin-embedded tissue sections seen in this series is consistent with previous studies in bladder cancer, but does not provide significant prognostic information with respect to the response to radiotherapy at 3 months and disease-specific survival after radical radiotherapy.

A fast, simple method for screening radiation susceptibility genes by RNA interference

Radiotherapy can cause unacceptable levels of damage to normal tissues in some cancer patients. To understand the molecular mechanisms underlying radiation-induced physiological responses, and to be able to predict the radiation susceptibility of normal tissues in individual patients, it is important to identify a comprehensive set of genes responsible for radiation susceptibility. We have developed a simple and rapid 96-well screening protocol using cell proliferation assays and RNA interference to identify genes associated with radiation susceptibility. We evaluated the performance of alamarBlue-, BrdU-, and sulforhodamine B-based cell proliferation assays using the 96-well format. Each proliferation assay detected the known radiation susceptibility gene, PRKDC. In a trial screen using 28 shRNA vectors, another known gene, CDKN1A, and one new radiation susceptibility gene, ATP5G3, were identified. Our results indicate that this method may be useful for large-scale screens designed to identify novel radiation susceptibility genes.

Retinoblastoma protein expression is an independent predictor of both radiation response and survival in muscle-invasive bladder cancer

The objective of the study was to investigate the predictive value of various clinical, biochemical, and histopathological parameters, with special emphasis on the expression of the retinoblastoma protein (pRB), on the radiation response in bladder cancer. In order to obtain a truly objective response measure, patients receiving preoperative radiotherapy followed by cystectomy were studied. Pretreatment tumour samples and clinical data from 108 consecutive patients were collected. End points were complete response (CR) to radiotherapy, relapse-free survival time and overall survival time. Expression of pRB was assessed by immunohistochemical staining as present or absent. Complete response to radiotherapy was obtained in 42 of 106 evaluable patients (40%). Predictive for CR to radiotherapy, in univariate analysis, was transurethral resection (as opposed to biopsy), B-haemoglobin, no upper urinary retention, and loss of pRB staining. Loss of pRB staining was the strongest independent predictor of radiation response in multivariate logistic regression analysis and absence of upper urinary retention was the only other significant factor. Loss of pRB was the only parameter showing statistically significant, independent association with relapse-free survival, whereas B-haemoglobin was also independently associated with overall survival. Loss of pRB expression seems to indicate a phenotype displaying enhanced radiosensivity and may be of benefit by denoting patients who would selectively benefit from a treatment schedule containing radiotherapy.

Comparison of the sulforhodamine B assay and the clonogenic assay for in vitro chemoradiation studies

PURPOSE

Since there is a growing interest in preclinical research on interactions between radiation and cytotoxic agents, this study focused on the development of an alternative to the very laborious clonogenic assay (CA).

METHODS

The colorimetric sulforhodamine B (SRB) assay was compared to the clonogenic assay for radiosensitivity testing in two lung cancer cell lines (A549, H292), one colon cancer cell line (HT-29) and one breast cancer cell line (MCF-7). In addition, the combination of the radiosensitizing agent gemcitabine and radiation was investigated with both assays.

RESULTS

The dose-response curves obtained with the SRB assay and the CA were very similar up to 6 Gy. The radiosensitivity parameters (SF(2), alpha, beta, MID and ID(50)) obtained from the SRB assay and the CA were not significantly different between H292, A549 and MCF-7 cells. The radiation dose-response curves for A549 and H292 cells pretreated with 4 n M gemcitabine for 24 h clearly showed a radiosensitizing effect with both assays. The dose-enhancement factors obtained with the SRB assay and the CA were 1.80 and 1.76, respectively, for A549 cells, and 1.52 and 1.41 for H292 cells.

CONCLUSIONS

The SRB assay was shown to be as useful as the more traditional CA for research on chemotherapy/radiotherapy interactions in cell lines with moderate radiosensitivity. This assay will be used for more extensive in vitro research on radiosensitizing compounds in these cell lines.