Pharmacologic validation of human tumor clonogenic assays based on pleiotropic drug resistance: implications for individualized chemotherapy and new drug screening programs.
Because of the bias toward successful cloning of human tumor cells from more advanced malignancies, alternative approaches to clinical correlations of drug resistance are needed to determine the validity of the human tumor clonogenic assay (HTCA) as a clinically useful test. Capitalizing on the prevalence of clinical drug resistance among these advanced malignancies, we have taken an independent approach to testing the validity of HTCAs based upon pharmacologic principles rather than tumor response. A database of results from drug sensitivity/resistance testing in 1,777 HTCAs has been examined retrospectively for specimens exhibiting either the MDR1 or Topo-II pleiotropic drug resistance phenotype. Twenty specimens were identified as MDR1 based upon test results showing resistance to adriamycin, vinca alkaloid, and etoposide. Test results with mitomycin-c confirmed the MDR1 phenotype in eight out of nine of these specimens. Seven out of eight of the confirmed MDR1 samples were resistant to either cis-platinum or alkylating agents or to both. There was no significant difference in the 5-fluorouracil resistance of these MDR1 specimens and the database as a whole, demonstrating the specific nature of this drug resistance phenotype in vitro. One specimen, a squamous carcinoma of the lung, was mitomycin-c sensitive, even though it exhibited all the other drug resistances characteristic of the MDR1 phenotype. Six specimens with the Topo-II phenotype were identified based upon resistance to adriamycin and etoposide with sensitivity to vinca alkaloids. Surprisingly, the Topo-II phenotype showed a strong association with increased cis-platinum resistance and a weaker one with decreased 5-fluorouracil resistance. Thus, 26/30 (87%) of analyzable specimens showed some form of clinically characterized multidrug resistance, illustrating how easily one can obtain 90% accuracy in predicting clinical drug resistance with HTCAs that are heavily biased by a disproportionate number of successful cloning assays with advanced malignancies. The data analysis also shows that prediction of adriamycin resistance based on lack of Topoisomerase II expression will not be very accurate, in contrast to a previous claim. Until cell culture technology can facilitate frequent successes in the cloning of early detected, drug-sensitive lesions, this bias will remain in HTCA databases, and studies comparing HTCA results with clinical response will continue to be uninformative. However, the in vitro identification of pleiotropic drug resistance phenotypes exactly analogous to those previously observed in patients provides pharmacologic validation at least for the prediction of drug resistance as measured by current HTCAs using suprapharmacologic drug concentrations.
Parchment
R E
RE
Hipple Cancer Research Center, Dayton, Ohio.
Soleimanpour
K
K
Petrose
S
S
Murphy
M J
MJ
D000970:Antineoplastic Agents / Q000494:pharmacology; D004250:DNA Topoisomerases, Type II; D016206:Databases, Bibliographic; D004351:Drug Resistance; D010641:Phenotype; D012189:Retrospective Studies; D014410:Tumor Stem Cell Assay / Q000379:methods*
D000970:Antineoplastic Agents; D004250:DNA Topoisomerases, Type II