HIF-1alpha modulation by topoisomerase inhibitors in non-small cell lung cancer cell lines.
OBJECTIVE
This study was to investigate whether the topoisomerase (Top) I inhibitor topotecan and the Top II inhibitor etoposide could modulate the hypoxia-induced HIF-1alpha expression in non-small cell lung cancer (NSCLC) cell lines.


METHODS
Hypoxic conditions were maintained in a humidified airtight anaerobic incubator flushed with a mixture of gas consisting of 1% O(2), 5% CO(2) and 94% N(2). The expressions of HIF-1alpha and Akt phosphorylation were measured by Western blotting or quantitative reverse transcription-polymerase chain reaction. Small interfering RNA treatment was done to inhibit the expressions of Top I and IIalpha. Constitutively active akt was expressed by transient transfection using pUSEamp(+)/myr Akt.


RESULTS
The HIF-1alpha was increased and this peaked at 9 h in hypoxic conditions. Both topotecan and etoposide in a dose- and time-dependent manner inhibited the accumulation of hypoxia-induced HIF-1alpha protein. Interestingly, the daily addition of these drugs at a lower concentration could inhibit the HIF-1alpha expression more effectively than a single treatment, which shows that their effects are schedule-dependent. This down-regulation of HIF-1alpha was associated with proteosomal degradation and decreased Akt phosphorylation. Top I and Top IIalpha were required for the inhibitory effect of topotecan and etoposide, respectively.


CONCLUSIONS
Both Top I and II inhibitors could suppress the HIF-1alpha expression in a schedule-dependent manner, and this suggests that these drugs might be useful to overcome the therapeutic resistance induced by tumor hypoxia in NSCLC.
Choi
Yun Jung
YJ
Department of Internal Medicine, Korea Cancer Center Hospital, Korea Institute of Radiological and Medical Science, 215-4, Gongneung-dong, Nowon-gu, Seoul 139-706, Korea.
Rho
Jin Kyung
JK
Lee
Sun Joo
SJ
Jang
Won Seok
WS
Lee
Seung Sook
SS
Kim
Cheol Hyeon
CH
Lee
Jae Cheol
JC
D000970:Antineoplastic Agents / Q000494:pharmacology*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology* / Q000378:metabolism; D045744:Cell Line, Tumor; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D019772:Topotecan / Q000494:pharmacology*
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D019772:Topotecan; D051057:Proto-Oncogene Proteins c-akt; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II