MK-1775 attenuates recovery during fractionated radiation As we have established that a concentration of 100 nmol/L MK-1775 results in both modest attenuation of radiation-inducedG2 arrest and enhanced radiosensitivity , yet had no independent cytotoxicity for up to 72 hours of exposure , we extended our investigations to Vorinostat selleck determine the capacity of MK-1775 to modulate the more clinically relevant approach of fractionated radiation using the clonogenic assay.For these studies, a recovery rate was calculated, which was obtained by dividing the percentage of cell survival following fractionated radiation by the percentage of cell survival following an equivalent dose of radiation delivered as a single fraction.As expected, on the basis of the capacity of repairing sublethal damage, T98G cells showed increased survival following fractionated radiation when compared with single fraction radiation, resulting in recovery rates of 1.22 and 1.64 at 4 and 6 Gy, respectively.Continuous exposure of T98G to MK-1775 during fractionated radiation completely abrogated recovery, resulting in a recover rate of 0.79 and 0.80 at 4 and 6 Gy, respectively.
Clonogenic peptide synthesis selleck chemicals hybrids Although the clonogenic assay is the gold standard in measuring radiation-induced cell death, it can only be applied to cell lines that grow as colonies, limiting its application to several model systems, including normal astrocytes.Therefore, to gain insight into the potential of MK-1775 to enhance radiation response in astrocytes, and thereby mitigating its potential clinical application, a modified clonogenic hybrid assay was developed.
This assay was initially optimized in T98G, which showed clear radiosensitization of MK-1775 using the traditional clonogenic assay.Simulating the treatment protocol used in the clonogenic assay, 12-well tissue culture plates were seeded as single cells, and viable cells were counted 5 days following treatment.Consistent with the initial clonogenic survival data , 24-hour exposure of MK-1775 alone resulted in approximately 60% of viable cells when compared with vehicle control.The combination of MK-1775 with irradiation resulted in 33% of viable cells when compared with cells exposed to radiation alone.A combination index was then calculated to normalize for the independent cytotoxicity of MK-1775 alone, by dividing the percentage of viable cells from the MK-1775/radiation combination by the percentage of viable cells from MK-1775 alone.A CI ? 1 would suggest no interaction between radiation and MK-1775, a CI > 1 would suggest a subadditive interaction and a CI < 1 a supra-additive interaction.