Suppression of the doxorubicin response by hypoxia-inducible factor-1α is strictly dependent on oxygen concentrations under hypoxic conditions.

Hypoxia-inducible factor-1α (HIF-1α) and p53 are involved in anticancer drug resistance under hypoxic conditions. Here, we found that the cytotoxicity of anticancer drugs (doxorubicin, gemcitabine, and cisplatin) was lower at 1% O2 than at 5% O2. We examined the effects of these drugs on HIF-1α and p53 expression under different hypoxic oxygen concentrations. At 5% O2, the drugs decreased HIF-1α expression and increased p53 levels. At 1% O2, the drugs increased HIF-1α expression but did not alter p53 levels. When the HIF-1α protein was stabilized by DMOG under normoxic conditions, doxorubicin did not increase the level of p53 expression. These results show that the maintenance of HIF-1α expression blocked doxorubicin-dependent increases in p53 expression. We hypothesized the mechanism of HIF-1α protein translation might be different between at 5% and at 1% O2, because many reports indicate that the same mechanism of HIF-1α protein stabilization occurs under hypoxic conditions, such as 5% and 1% O2. The level of phosphorylated-4E-BP1, which causes translation of HIF-1α, was higher at 1% O2 than at 5% O2. Our results suggest that the sensitivity of tumor cells to anticancer drugs is dependent oxygen concentrations under hypoxic conditions, and involves 4E-BP1-dependent stabilization of the HIF-1α protein.

Synergistic antitumor effect of combined 5-fluorouracil (5-FU) with 5-chloro-2,4-dihydroxypyridine on 5-FU-resistant gastric cancer cells: possible role of a dihydropyrimidine dehydrogenase-independent mechanism.

BACKGROUND: S-1 is an oral fluorouracil antitumor drug that combines three pharmacological agents: tegafur, a prodrug of 5-fluorouracil (5-FU); 5-chloro-2,4-dihydroxypyridine (CDHP), an inhibitor of dihydropyrimidine dehydrogenase (DPD); and potassium oxonate, an agent included to reduce gastrointestinal toxicity. S-1 has a potent antitumor effect on gastric cancer, even in 5-FU-refractory cases. However, there is a lack of basic information to account for this clinical outcome. This study was performed to determine the differences in antitumor effects of combined administration of 5-FU and CDHP between NUGC-3 cells and NUGC-3/5FU/L cells, which are resistant to 5-FU (established by repeated cultures of NUGC-3 with escalating concentrations of 5-FU), and to determine the mechanisms involved. METHODS: Both cell lines were incubated with various concentrations of 5-FU and/or CDHP. The antitumor effect was assessed using an MTS assay and cell counts. DPD levels were assayed by using enzyme-linked immunosorbent assay. Expression of DPD and thymidylate synthase (TS) mRNA was quantified using real-time quantitative polymerase chain reaction analysis. RESULTS: The combination of 5-FU (IC15) with CDHP exerted a synergistic antitumor effect on NUGC-3/5FU/L, but not on NUGC-3, while CDHP by itself did not affect cell growth in either cell line. Expression of DPD was not detected in NUGC-3/5FU/L. In NUGC-3/5FU/L, 5-FU-enhanced expression of TS mRNA was inhibited by the addition of CDHP. In contrast, in NUGC-3, administration of 5-FU with or without CDHP did not alter TS mRNA expression. CONCLUSIONS: The inhibitory mechanism of CDHP, which is independent of DPD, may in part contribute to the antitumor effect of S-1 even in 5-FU-resistant gastric cancer cases.

Growth inhibition of colon cancer cells by transfection of dominant-negative apoptosis signal-regulating kinase-1.

Apoptosis signal-regulating kinase-1 (ASK-1) is an important molecule for the pro-apoptotic signaling. ASK-1 also contributes to the cellular survival for many types of cells. Thus, ASK-1 has a broad range of biological activities depending on the cell type. The present study assessed the role(s) of ASK-1 in colorectal cancer cells (HT-29) by using adenovirus vectors expressing wild-type (WT)-ASK-1 or dominant-negative (DN) mutant of ASK-1 and recombinant adenovirus containing the bacterial beta-galactosidase gene (Ad-LacZ), a negative control for Ad-DN-ASK-1. Selective phosphorylation of ASK-1 at Thr 845, a kinase domain site, but not Ser 83 nor 967 sites was induced by serum stimulation in a time-dependent manner. Transfection with Ad-DN-ASK-1 inhibited the serum-induced phosphorylation of p38 mitogen-activated protein kinase, a downstream molecule of ASK-1. Transfection with Ad-DN-ASK-1 diminished the serum-induced cell proliferation in a dose-dependent manner, whereas WT-ASK-1 increased it. Apoptosis assessed by Hoechst staining was induced in the Ad-DN-ASK-1 treated cells. In vivo transfection of Ad-DN-ASK-1 into tumor xenografts of HT-29 cells in nude mice significantly decreased the tumor volume on day 29. Cleaved caspase-3 was found in the tumors of DN-ASK-1 treated mice. We obtained the first evidence that DN-ASK-1 transfection exerted significant antitumor effects on colon cancer mediated by apoptosis.

Depressed-type (0-IIc) colorectal neoplasm in patients with family history of first-degree relatives with colorectal cancer: A cross-sectional study.

AIM: To investigate the correlation of depressed-type (0-IIc) colorectal neoplasm and family history of first-degree relatives (FDR) with colorectal cancer (CRC). METHODS: This cross-sectional study was conducted from June 2000 to October 2002 at National Cancer Center Hospital East. Eligible patients undergoing initial total colonoscopy were surveyed regarding family history of CRC among FDR by a questionnaire prior to colonoscopic examinations. All endoscopic findings during colonoscopy were recorded and the macroscopic classification of the early stage neoplasm/cancer was classified into two types (0-IIc vs non 0-IIc). Odds ratios (OR) and 95% confidence intervals (CI) were calculated by univariate and multivariate logistic regression to estimate the association between macroscopic features and clinicopathological data including gender, age, and family history of FDR with CRC. RESULTS: The OR of an association between family history of FDR with CRC and overall early stage neoplasm adjusted by gender and age was 1.85 (95% CI: 1.31-2.61, P = 0.0004), that for non 0-IIc neoplasm was 1.71 (95% CI: 1.22-2.41, P = 0.0017) and for 0-IIc colorectal neoplasm was 2.78 (95% CI: 1.49-5.16, P = 0.0031). CONCLUSION: Our study shows a significant association between a family history of FDR with CRC and 0-IIc colorectal neoplasm. When patients with a family history of FDR with CRC undergo colonoscopy, colonoscopists should check carefully for not only polypoid, but also depressed-type (0-IIc) lesions.