D. Schoenherr

Determining if low dose hyper-radiosensitivity (HRS) can be exploited to provide a therapeutic advantage: A cell line study in four glioblastoma multiforme (GBM) cell lines

Abstract Purpose: To determine if ultra-fractionation using repeated pulses of radiation (10 × 0.2 Gray [Gy]) would be more cytotoxic than continuously-delivered radiation to the same total dose (2 Gy) in four glioma cell lines. Materials and methods: Human T98G, U373, U87MG and U138MG cells were conventionally X-irradiated with 0.1–8 Gy and clonogenic survival assessed. Next, cells were treated with either a single dose of 2 Gy or 10 pulses of 0.2 Gy using a 3-min inter-pulse interval and DNA (Deoxyribonucleic acid) repair (pHistone H2A.X), G2-phase cell cycle checkpoint arrest (pHistone H3) and apoptosis (caspase-3) compared between the two regimens. A dose of 0.2 Gy was selected as this reflects the hyper- radiosensitivity (HRS)/increased radioresistance (IRR) transition point of the low-dose cell survival curve. Results: T98G, U87MG and U138MG exhibited distinct HRS responses and survival curves were well-described by the Induced Repair model. Despite the prolonged delivery time, ultra-fractionation (10 × 0.2 Gy) was equally effective as a single continuously-delivered 2 Gy dose. However, ultra-fractionation was more effective when given for five consecutive days to a total dose of 10 Gy. The increased effectiveness of ultra-fractionation could not be attributed directly to differences in DNA damage, repair processes or radiation-induced apoptosis. Conclusions: Ultra-fractionation (10 × 0.2 Gy) is an effective modality for killing glioma cell lines compared with standard 2 Gy dosing when multiple days of treatment are given.

PROSTATE-SPECIFIC NATURAL HEALTH PRODUCTS (DIETARY SUPPLEMENTS) RADIOSENSITIZE NORMAL PROSTATE CELLS

PURPOSE Prostate-specific health products (dietary supplements) are taken by cancer patients to alleviate the symptoms linked with poor prostate health. However, the effect of these agents on evidence-based radiotherapy practice is poorly understood. The present study aimed to determine whether dietary supplements radiosensitized normal prostate or prostate cancer cell lines. METHODS AND MATERIALS Three well-known prostate-specific dietary supplements were purchased from commercial sources available to patients (Trinovin, Provelex, and Prostate Rx). The cells used in the study included normal prostate lines (RWPE-1 and PWR-1E), prostate tumor lines (PC3, DU145, and LNCaP), and a normal nonprostate line (HaCaT). Supplement toxicity was assessed using cell proliferation assays [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] and cellular radiosensitivity using conventional clonogenic assays (0.5-4Gy). Cell cycle kinetics were assessed using the bromodeoxyuridine/propidium iodide pulse-labeling technique, apoptosis by scoring caspase-3 activation, and DNA repair by assessing gammaH2AX. RESULTS The cell growth and radiosensitivity of the malignant PC3, DU145, and LNcaP cells were not affected by any of the dietary prostate supplements (Provelex [2 microg/mL], Trinovin [10 microg/mL], and Prostate Rx [50 microg/mL]). However, both Trinovin (10 microg/mL) and Prostate Rx (6 microg/mL) inhibited the growth rate of the normal prostate cell lines. Prostate Rx increased cellular radiosensitivity of RWPE-1 cells through the inhibition of DNA repair. CONCLUSION The use of prostate-specific dietary supplements should be discouraged during radiotherapy owing to the preferential radiosensitization of normal prostate cells.

Radiosensitivity in Prostate Cancer Cell Lines following Combination Treatment with Prostate-specific Dietary Supplements and 5-alpha-reductase Inhibitors

Purpose/Objective(s): Benign prostatic hyperplasia (BPH) is often treated with 5-alpha-reductase inhibitors (5ARIs) such as finasteride and dutasteride. Studies in our laboratory have demonstrated that the use of dietary supplements may lead to radiosensitization of normal prostate cells. This study examines if the addition of these supplements can alter the survival and radiosensitivity of prostate cell lines in combination with 5-ARI treatment. Materials/Methods: Prostate tumor cell lines with differing androgen receptor (AR) status (PC3, DU145, LNCaP and VCaP) and normal prostate cell lines (RWPE-1 and PWR-1E) were studied. Two prostate-specific dietary supplements were used: Trinovin (10 ug/mL) and Prostate Rx (50 ug/mL or 6 ug/mL for normal cells). Treatments of finasteride and dutasteride were given at 1 uM. Dietary supplement and 5-ARI toxicity was assessed using MTT proliferation and survival assays. Radiosensitivity was measured using conventional clonogenic assays (0.5-4 Gy, dose rate = 0.69 Gy min -1 ). Results: No significant changes were evident in the proliferative responses of paired cell lines (by tumorgenicity/AR status) following treatment with 5-ARIs plus dietary supplements so one of each pair was evaluated for survival. In the LNCaP and RWPE-1 cells, treatment with Prostate Rx alone reduced survival to 55% and 25% respectively. In LNCaP cells the combination of finasteride with Prostate Rx decreased survival to 25% and in combination with Trinovin, survival decreased to 40%. Treatment with dutasteride did not change survival. In normal RWPE-1 cells, 5-ARIs in combination with Prostate Rx did not decrease survival while a 30% reduction in survival was seen in cells treated with Trinovin plus dutasteride. Radiosensitivity was increased in LNCaP cells treated with Prostate Rx alone (SF1Gy decreased from 0.9 to 0.25) and in combination with 5-ARIs (SF1Gy 0.6 to 0.2 for finasteride and 0.7 to 0.05 for dutasteride). There was also a pronounced decrease in survival of the normal prostate RWPE-1 cells in combination with finasteride (SF1Gy decreased from 0.9 to 0.01) and dutasteride (SF1Gy decreased from 0.9 to 0.15) in the presence of Prostate Rx. Trinovin treatment was found to have little effect on radiosensitivity. No change in survival was seen in the DU-145 cell line following any combination of treatments. Conclusions: Prostate-specific dietary supplements changed the biological effect of finasteride and dutasteride. This was further exacerbated following radiation treatment, particularly in the normal cell line. These data suggest that the use of prostate specific dietary supplements should also be discouraged when either radiation and/or 5-alphareductase inhibitors are prescribed.