Hypoxia induces universal but differential drug resistance and impairs anticancer mechanisms of 5-fluorouracil in hepatoma cells

Abstract

Hepatocellular carcinoma (HCC) is one of the most refractory cancers. The mechanisms by which hypoxia further aggravates therapeutic responses of advanced HCC to anticancer drugs remain to be clarified. Here, we report that hypoxia (1% O) caused 2.55-489.7-fold resistance to 6 anticancer drugs (sorafenib, 5-fluorouracil [5-FU], gemcitabine, cisplatin, adriamycin and 6-thioguanine) in 3 HCC cell lines (BEL-7402, HepG2 and SMMC-7721). Among the 6 drugs, sorafenib, the sole one approved for HCC therapy, inhibited proliferation with little influence from hypoxia and displayed the smallest variation among the 3 HCC cell lines tested. By contrast, the inhibition of proliferation by 5-FU, which has been extensively tested in clinical trials but has not been approved for HCC therapy, was severely affected by hypoxia and showed a large variation among these cell lines. In 5-FU-treated HCC cells, hypoxia reduced the levels of basal thymidylate synthase (TS) and functional TS, leading to decreased dTMP synthesis and DNA replication. Hypoxia also affected the accumulation of FdUTP and its misincorporation into DNA. Consequently, both single-strand breaks and double-strand breaks in DNA were reduced, although hypoxia also inhibited DNA repair. In 5-FU-treated HCC cells, hypoxia further abated S-phase arrest, alleviated the loss of mitochondrial membrane potential, diminished the activation of caspases, and finally resulted in reduced induction of apoptosis. Thus, hypoxia induces universal but differential drug resistance. The extensive impacts of hypoxia on the anticancer mechanisms of 5-FU contributes to its hypoxia-induced resistance in HCC cells. We propose that hypoxia-induced drug resistance and interference of hypoxia with anticancer mechanisms could be used as candidate biomarkers in selecting and/or developing anticancer drugs for improving HCC therapy.

Sorafenib resistance in hepatocarcinoma: role of hypoxia-inducible factors

“…It was reported that hypoxia confers sorafenib resistance in myeloid leukemia, renal, or gastric cancer cells 35 – 38 and is responsible for the acquired resistance to different anticancer drugs in HCC cells, including doxorubicin, etoposide, cisplatin, SN38, and 5-fluorouracil 39 – 43 . In fact, Liang et al 32 reported that the continued administration of sorafenib in HCC subcutaneous mouse tumor models increases the protein levels and transcriptional activity of HIF-1α.…”

Mechanisms of Anticancer Drug Resistance in Hepatoblastoma

“…Regarding MOC-6, several studies have demonstrated tumor progression associated with high oxygen consumption and lower blood supply in tumor microenvironment, and that hypoxia enhances resistance to antitumor drugs. Thus, under hypoxia, HepG2 cells were more resistant to cisplatin than under normal conditions [42], which could be due, at least in part, to the up-regulation of the ABC pumps induced by hypoxia that would reduce intracellular cisplatin concentration [43]. ADAM17 is a transmembrane metalloproteinase found overexpressed in a variety of human tumors.…”

Stabilization of Hypoxia-Inducible Factors and BNIP3 Promoter Methylation Contribute to Acquired Sorafenib Resistance in Human Hepatocarcinoma Cells

“…Unlike what happened with HepG2 cells, no differences were detected in the growth of the HepG2S1 and HepG2S3 lines between normoxia and hypoxia, which suggest that resistant cells display adaptive mechanisms related to hypoxic conditions. Hypoxia contribution to chemoresistance development in HCC has been described after the administration of drugs, such as 5-fluorouracil (5-FU) [25], doxorubicin, and cisplatin [26]. Involvement of hypoxic environment in the acquired resistance to sorafenib has also been reported in renal cancer [27,28], gastric cancer [29], and acute myeloid leukaemia [30].…”