A MODIFIED COMPUTER-ASSISTED COLORIMETRIC MICROTITRE ASSAY (MTT) TO ASSESS IN-VITRO RADIOSENSITIVITY OF V79, CASKI, HELA AND WIDR CELLS

The non-clonogenic MTT assay, based on the reduction of a tetrazolium salt to a purple formazan precipitate by living cells, was modified an d a new procedure of analysis is proposed. The colorimetric assay coul d be performed semiautomatically using microtitre plate reader connect ed to a personal computer. Data are processed and plotted with a custo mized program. To ensure that both control and irradiated microtitre p lates contain exponentially growing cells at the time of analysis, the calculation of relative survival is based on a series of well-defined cell numbers initially seeded. To make the two endpoints of non-clono genic and clonogenic assays comparable, i.e. counting of living cells versus counting of colonies, radiation-induced progression delay was i ncorporated into the calculation. Radiation-induced cell killing and p rogression delay could be determined in a single analysis, but in an i ndependent way. X-ray survival curves were generated for V79, CaSki, W iDr and HeLa cells using the non-clonogenic and a standard clonogenic assay. Using the linear-quadratic formula, the resulting parameters al pha,beta and the mean inactivation dose were not significantly differe nt. The described assay is a feasible and reproducible technique for d etermination of cellular survival, which may be able to incorporate pr ogression delay. The equivalence to a clonogenic survival assay could be proven.