MET increases the sensitivity of gefitinib-resistant cells to SN-38, an active metabolite of irinotecan, by up-regulating the topoisomerase I activity.
BACKGROUND
Most non-small-cell lung cancer tumors with epidermal growth factor receptor mutations are responsive to EGFR tyrosine kinase inhibitors, such as gefitinib and erlotinib, but almost all such tumors ultimately acquire resistance. We previously found that a gefitinib-resistant cell line, PC-9/Met in which MET (MNNG-HOS transforming gene) is amplified, was more sensitive than its parent cell line (PC-9) to 7-ethyl-10-hydroxy-camptothecin (SN-38), an active metabolite of irinotecan. The purpose of this study was to investigate the mechanisms responsible for the increased sensitivity of the gefitinib-resistant cell line to SN-38.


METHODS
The sensitivity of PC-9 and PC-9/Met to SN-38 was assessed by performing water soluble tetrazolium salt (WST-1) assays. Topoisomerase I (topo I) activities were determined for the cell lines cultured in the presence of hepatocyte growth factor and for those of which MET expression was knocked down by introducing a MET-specific small interfering RNA.


RESULTS
PC-9/Met exhibited higher topo I activities, and higher topo I gene and protein expression levels than PC-9 did. Suppression of MET expression by a MET-specific small interfering RNA led to a decrease in the topo I protein expression in the PC-9/Met cells. The stimulation of PC-9 with hepatocyte growth factor caused an increase in the topo I protein level via the activation of MET.


CONCLUSIONS
The increased sensitivity of PC-9/Met cells to SN-38 compared with that of PC-9 cells was partially because of topo I activities resulting from increased topo I mRNA and protein expression caused by MET signaling.
Respiratory Medicine, Cellular Transplantation Biology, Division of Cancer Medicine, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan.
Asao
A
Sakai
Kazuo
K
Kasahara
Tohru
T
Ohmori
Hideharu
H
Kimura
Takashi
T
Sone
Masaki
M
Fujimura
Shinji
S
Nakao
D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D049109:Cell Proliferation; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D000077156:Gefitinib; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D000077146:Irinotecan; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D019859:Proto-Oncogene Proteins c-met / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011799:Quinazolines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D011799:Quinazolines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; C491743:MET protein, human; D019859:Proto-Oncogene Proteins c-met; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D000077156:Gefitinib; D002166:Camptothecin