Multidrug resistance in a small cell lung cancer line: rapid selection with etoposide and differential chemosensitization with cyclosporin A.
We developed a multidrug resistant small cell lung cancer line, VPR-2, by exposing H69 parent cells to etoposide (20 microM) for 1 h daily for 3 days every 21-28 days, a schedule similar to that used in the clinic. Resistance (20-fold) to the cytostatic and DNA cleavage activities of etoposide emerged after the third treatment, and this phenotype was stable in the absence of drug exposure for 2.5 years. VPR-2 cells exhibited cross resistance to intercalating agents and vinca alkaloids, but remained sensitive to X-radiation, cisplatin and 5-fluorouracil. The human mdr1 gene was overexpressed in the resistant line, but steady-state concentrations of etoposide were reduced only 1.5-fold. Topoisomerase II catalytic and etoposide stimulated DNA cleavage activity in nuclear extracts from both lines were identical despite retention of a 3-fold level of resistance to etoposide-induced strand breaks in isolated nuclei from VPR-2 cells. Cyclosporin A and verapamil, both of which bind to P-glycoprotein, enhanced accumulation of etoposide in VPR-2 cells, and H69 cells to a lesser extent. Yet only cyclosporin A was effective in differentially enhancing etoposide cytostasis in VPR-2 relative to H69. In VPR-2 whole cells, cyclosporin A enhanced etoposide-induced DNA single-strand break frequency 9-fold but had no effect in isolated nuclei. Rapid selection of this line with a clinically relevant drug exposure schema and stability of the resistant phenotype suggest these cells may have been a steady subpopulation of the parent line through years of serial passage in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)
Glisson
B S
BS
Department of Medical Oncology, University of Texas MD Anderson Cancer Center, Houston 77030.
Alpeter
M D
MD
D000468:Alkalies; D001692:Biological Transport / Q000502:physiology; D018288:Carcinoma, Small Cell / Q000188:drug therapy*; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects; D016572:Cyclosporine / Q000493:pharmacokinetics / Q000494:pharmacology*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004351:Drug Resistance / Q000235:genetics; D005047:Etoposide / Q000493:pharmacokinetics / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000188:drug therapy*; D015388:Organelles / Q000187:drug effects; D010641:Phenotype; D012260:Ribonucleases; D014407:Tumor Cells, Cultured
D000468:Alkalies; D005047:Etoposide; D016572:Cyclosporine; D012260:Ribonucleases; D004250:DNA Topoisomerases, Type II