Antitumor screening procedures of the National Cancer Institute

From the time of its inception in 1955, the Drug Development Program of the National Cancer Institute has relied primarily on transplanted rodent tumor systems in vivo for the evaluation and selection of potential antitumor agents. Although greater emphasis has been placed in recent years on rationally designed drugs, the major effort throughout the history of the program has involved the empirical screening of a wide variety of chemical structures and natural products of varying sources. The initial screening spectrum consisted of three mouse tumors, Sarcoma 180, Carcinoma 755 and Leukemia 1210, based on the retrospective analysis presented in the GELLHORN-HIRSCHBERG Report. As a result of further expermental studies and analyses, the screens changed successively to (1) L1210 plus a spectrum of mouse, rat and hamster tumors, (2) L1210 plus the rat tumor, WALKER 256, (3) L1210, plus P388 for natural products and B16 melanoma and LEWIS lung carcinoma for special studies, and finally (4) P388 as a pre-screen followed by a panel of transplanted tumors and xenografts representing the major tumor sites. The rationale underlying each of the successive changes, and results obtained with each approach, will be discussed.