In 1985, the hypothesis was put forward that a human tumor cell line screen could help investigators discover cell type-specific agents with clinical activity against solid tumors. The emerging reality was that while correlation of in vitro histology to clinical activity is poor, the pattern of cellular sensitivity and resistance of the cell lines to a drug may correlate with molecular target expression.
Since April 1990, DTP has used the human tumor cell line in vitro screen as its primary assay, with follow-up in vivo evaluation in mouse models. The screen is currently composed of 60 human tumor cell lines (NCI-60), representing leukemia, melanoma, and cancers of the lung, colon, brain, ovary, breast, prostate, and kidney. These cell lines were selected partly on pragmatic terms: those selected behaved best under typical assay conditions. The screen was designed so that for each compound tested, both the absolute and the relative sensitivities of individual cell lines were reproducible to the extent that a characteristic profile or fingerprint of cellular response was generated.
Although the particular inhibitory response of a single cell line might be relatively uninformative, the pattern of response of the cell lines as a group can be used to rank a compound according to the likelihood of sharing common mechanisms. The COMPARE algorithm (a computer program) qualifies this pattern and searches an inventory of screened agents to compile a list of the compounds that have the most similar patterns of cellular sensitivity and resistance.
Extramural researchers who wish to access this service should complete the online submission form at http://dtp.nci.nih.gov/compsub/index.html. Pure compounds must be of known molecular structure, and the investigator is required to enter the molecular structure on the online submission form before sending samples of the test compound. Additional information is available on DTP’s Website at http://dtp.nci.nih.gov/docs/misc/common_files/submit_compounds.html.
In September 2005, DTP’s human tumor cell line in vitro screening assay was reviewed by a panel of extramural experts. Because of reproducibility issues, DTP’s standard operating procedures were evaluated and a series of recommendations was made to improve quality control.
DTP has also instituted, as the first step in the screening process, a one-dose NCI-60 screen. This screen has a higher throughput and thus more rapid turn-around time for suppliers. Compounds that pass criteria are screened against the NCI-60 at five doses.