Applications of the human tumor stem cell assay to new drug evaluation and screening.

The potential applications of the human tumor stem cell assay to primary drug screening and Phase I-II new drug evaluation are of very broad scope and have not been completely addressed in this exploratory analysis. As in most other areas of science, careful and stepwise testing in many laboratories will be required to confirm or refute the utility of these approaches. Of the two areas discussed, the applications to new drug screening are still most uncertain and subject to change. From my perspective, in vitro growth conditions, for clonogenic human tumor cells, are perhaps at a similar stage of development as culture techniques for bacterial cells were in the 1930s. Availability of those techniques, and a combination of good ideas, serendipidy, and hard work led to the subsequent development of penicillin and other antibiotics which now can be used to cure most forms of infectious disease. The value of a simple and reproducible assay for screening therefore cannot be overemphasized. Applications of the tumor stem cell assay to Phase I-II drug evaluation already show preliminary signs of utility. Given this background and the more limited preclinical data on other agents now under study, broadened testing of this approach to new drug screening appears warranted. If use of an in vitro approach such as this proves successful for both primary and secondary screening, it would not be surprising if significant qualitative and quantitative changes occurred in the areas of new drug development and cancer clinical trials.