Clonal growth of human tumor xenografts. First experiences in drug testing.

Human tumors growing as nude mice xenografts were investigated for growth in a clonogenic assay. Colony formation of more than 30 colonies per plate was obtained in 47 of 63 tumors examined (74.6%). The growth rate was enhanced by raising the concentration of fetal calf serum in the culture medium. Plating efficiency ranged from 0.0003% to 5.5%. To study the applicability of this model for screening new anticancer drugs, preliminary studies in drug sensitivity were conducted with continuous incubation of different anticancer drugs in a dose range of 1/10 to 10 times the maximum achievable plasma level. The highest concentration almost always led to a complete suppression of colony growth. In our opinion the procedure described may be a useful combination of two methods in predictive drug testing, provided drug concentration and mode of drug incubation are adequately considered.