DESCRIPTION: The overall aim of the project is to complete the final stage of development of a paradigm for assessing the nature and intensity of empirical drug combined-action called the universal response surface approach (URSA). The following subprojects will be completed: (i) the validity and utility of a set of theoretical/empirical mathematical/statistical models, which were derived to describe concentration-effect (dose-response) phenomena and agent interaction, will be investigated in laboratory studies of anticancer agents and combinations of agents with three assays: a total growth assay (TGA), a colony count assay (CCA), and an individual colony formation assay (iCFA). The laboratory emphasis will be on the two clonogenic assays. Much of the work completed during the previous funding period with the TGA will be replicated in a more limited manner with the clonogenic assays. With the TGA, the applicant will emphasize the conduct of combined-action experiments with three or more agents. (ii) Based upon the results of subproject #1, older models will be modified when appropriate, and newer models will be created and tested when needed. Improvements will also be made to design and model-fitting techniques. (iii) The mechanistic basis of the super synergy found between dihydrofolate reductase inhibitors and polyglutamylatable antifolates will be explored with several intracellular assays, including assays of folate and antifolate polyglutamate distributions. (iv) The software package, SYNFIT, developed under RR10742, will be revised and distributed. Comments will be solicited from users, and appropriate additional improvements and enhancements made. A special effort will be made to enhance user aids, such as the tutorial, manual, and HELP functions. This will facilitate the proper use of the statistical approach.