Original article: The clonogenic assay with human tumor xenografts: Evaluation, predictive value and application for drug screening

Abstract

The feasibility, evaluation and predictive value of the colony-forming assay with human tumor xenografts for screening anticancer drugs have been studied. Using human tumors grown in serial passage in nude mice, adequate colony formation was observed in 215 of 251 (86%) different solid human tumors of various histologies. Based on in vitro growth characteristics, a quality-controlled assay protocol was developed. With the proposed criteria for standardized evaluation of individual experiments a substantial increase in assay reliability was achieved. The five clinically established agents, cisplatin, doxorubicin, etoposide, mitomycin-C and vindesine, were studied for anticancer activity in the clonogenic assay. Drugs were applied over a wide dose range by continuous exposure, yielding clear dose-response effects with coefficients of correlation between r = 0.946 and 0.995. Relevant dose levels predicting correctly for the clinical efficacy of the agents were determined by comparison of in vitro anticancer activity to in vitro toxicity on human bone marrow as follows: cisplatin 0.1 μ/l, doxorubicin 0.01 μ/ml, etoposide 0.1 μg/ml, mitomycin-C 0.005 μ/ml, vindesine 0.01 μ/ml. At these concentrations, clinically sensitive tumor types showed inhibition of colony formation in 99 of 240 cases (41%, whereas 11% (19/176) of clinically resistant tumors were responsive. The relevant dose levels used equal between 0.3% and 4.0% of the achievable peak plasma concentrations in man. The predictive value of the clonogenic assay was determined by treatment of the same tumors in vitro and in vivo in tumor-bearing nude mice. In 174/220 comparisons (79%), in vitro data predicted correctly for the in vivo sensitivity of the xenografted malignancies. The overall positive and negative predictive accuracy of the assay were determined as 56% and 91%, respectively. A quality controlled colony-forming assay with well characterized human tumor xenografts seems to be a useful tool for anticancer drug screening and development. The use of xenotransplanted tumors provides a possibility to check in vitro data in the same tumor lines in vivo in athymic nude mice. A combined approach (nude mouse/clonogenic assay) should find increased application as a screen for new anticancer drugs. © 1990 Kluwer Academic Publishers.