Decrease In Clonogenicity Research Articles

Effect of free radicals induced by ultrasonic cavitation on cell killing.

The present study was undertaken to elucidate the mechanism of in vitro cell killing induced by 1.0 MHz continuous wave ultrasound at an intensity of 5.8 W/cm2. The chemical effects and mechanical effects arising from acoustic cavitation were determined by the amount of liberated iodine and the number of DNA double-strand breaks, respectively. The survival of mouse L cells immediately after irradiation was estimated by counting the number of cells which are not stained by trypan blue and the clonogenicity of surviving cells remaining immediately after irradiation was monitored by colony-forming ability. The effectiveness of the dissolved gases in liberating iodine was in the order O2 greater than Ar greater than N2 greater than N2O approximately 0. However, the effect of dissolved gases on the yield of double-strand breaks of DNA and on the two kinds of end points of cell killing was in the order O2 = Ar = N2 greater than N2O approximately 0. These results suggest that the different amounts of free radicals induced by ultrasound are not directly related to the ultrasonically induced cell killing. The presence of cysteamine (2 mmol dm-3) during sonication completely inhibited a decrease in clonogenicity of surviving cells, but did not inhibit that of cell survival immediately after sonication. These results suggest that the decrease of survival immediately after sonication is due to mechanical shear stress arising from cavitation, while the decrease of clonogenicity of the remaining surviving cells is due to free radicals induced by cavitation. The contribution of free radicals to total cell killing was estimated as about 1 per cent at the level of 95 per cent cell killing immediately after sonication.

Drug and light dose dependence of photodynamic therapy: a study of tumor cell clonogenicity and histologic changes.

Abstract— The dependence of photodynamic therapy (PDT) on changes in drug and light doses was determined in C3H/HeJ mice bearing the RIF tumor. Measurements of tumor clonogenicity were determined 24 h after PDT over a range of drug and light doses. Representative histological samples were prepared at each of these doses. Both the drug and light dose dependence experiments showed an exponential decrease in clonogenicity after an initial shoulder region. Reciprocity of drug and light dose was established from those clonogenicity curves. Histological examination of tumors gave information concerning the localization of gross damage within tumors. Increases of light dose in PDT were shown to extend the depth of necrosis within tumors. Increases of drug dose produced enlargements in the area of necrotic spots produced by PDT

MECHANISM OF CYTOTOXICITY OF 2-CHLORO AND 2-BROMO DEOXYADENOSINE FOR A HUMAN LYMPHOBLASTIC CELL LINE, CCRF-CEM: 15

Cytotoxicity as measured by inhibition of growth and DNA synthesis (IC50) and by decrease in clonogenicity (EC50) has been compared with that of dAdo. IC50 for growth and for DNA synthesis is similar in all 3 cases. IC50 for 2-CldAdo (0.045 μM) is lower than for 2-BrdAdo (0.068 μM) and dAdo (0.9 μM). For 2-CldAdo and 2-BrdAdo, EC50 is somewhat higher than IC50 and much greater in the case of dAdo. About 20% of cells are resistant to concentrations of 2-BrdAdo >>EC50 but viability is decreased to approximately 2% by 18 hr exposure to 2-CldAdo at 20 × EC50 or to dAdo at 3 × EC50. Treatment with 2-CldAdo or dAdo sufficient to cause large losses in viability result in accumulation of cells at the G1/S border. The nucleosides are converted over 24 hr to increasing levels of the triphosphates. The latter inhibit reduction of CDP and of ADP by L1210 ribonucleotide reductase with IC50 in the order: 2-BrdATP < 2-CldATP < dATP << ara-ATP. In intact CCRF-CEM cells dAdo specifically decreases dGTP with other dNTPs increasing, whereas 2-CldAdo and 2-BrdAdo decrease dCTP and dATP with a transitory decrease in dGTP but dGTP and dTTP are elevated above controls by 24 hr. Data indicate that inhibition of ribonucleotide reductase possibly contributes to inhibition of DNA synthesis but is probably not the lesion critical for cell death. Supported by American Lebanese Syrian Associated Charities.