Brusatol inhibits HIF-1 signaling pathway and suppresses glucose uptake under hypoxic conditions in HCT116 cells

Abstract

Hypoxia-inducible factor-1 (HIF-1) is an important transcription factor that induces adaptive responses upon low oxygen conditions in human cancers and triggers off a poor prognostic outcome of conventional treatments. In this study, we discovered for the first time that brusatol (BRU), a quassinoid extracted from Brucea Esters, has the capability to inhibit HIF-1 signaling pathway. We found that BRU concentration-dependently down-regulated HIF-1α protein levels under hypoxia or CoCl2-induced mimic hypoxia in HCT116 cells without causing significant cytotoxicity. Besides, the transactivation activity of HIF-1 was suppressed by BRU under hypoxic conditions, as well as the expression of HIF-1 target genes, including VEGF, GLUT1, HK2 and LDHA. In addition, BRU can also decrease glucose consumption under hypoxia through inhibition of HIF-1 signaling pathway. Further studies revealed that the inhibitory effect of BRU on HIF-1 signaling pathway might be attributed to promoting degradation of HIF-1α. Interestingly, intracellular reactive oxygen species (ROS) levels and mitochondrial ROS level were both decreased by BRU treatment, indicating the involvment of mitochondrial ROS regulation in the action of BRU. Taken together, these results provided clear evidence for BRU-mediated HIF-1α regulation and suggested its therapeutic potential in colon tumors.

Brusatol Protects HepG2 Cells against Oxygen-Glucose Deprivation-Induced Injury via Inhibiting Mitochondrial Reactive Oxygen Species-Induced Oxidative Stress

“…Recently, we found for the first time that BRU has the ability to inhibit HIF-1 pathway under hypoxia in colon cancer cells at nmol/L concentration, which subsequently been confirmed by other group [10,15]. We also found that BRU significantly reduced hypoxia-induced mitochondrial ROS generation in cancer cells, which may be responsible .…”

“…The most possible reason is the dose of BRU used in this study may be too low, although it has been identified that when the cells were treated with high concentrations of BRU (> 100 nmol/L), significant cell viability loss was found. In fact, BRU at these high concentrations only induced the inhibition of cell proliferation instead of cell death [10]. And we have found that normal cells are better tolerant to BRU than tumor cells (data not shown).…”

“…Furthermore, BRU has the ability to inhibit the proliferation of cancer cells and increases the sensitivity of cancer cells to chemotherapeutic drugs by enhancing the ubiquitination of Nrf2 [9]. Our recent finding indicated that BRU inhibited the HIF-1 signaling pathway under hypoxia by reducing mitochondrial ROS level without inducing apoptosis [10]. Therefore, we hypothesized that BRU has the potential to reduce I/R-induced damage by inhibiting mitochondrial ROS production.…”

Brusatol-Mediated Inhibition of c-Myc Increases HIF-1α Degradation and Causes Cell Death in Colorectal Cancer under Hypoxia

“…For example, brusatol has been shown to inhibit c‑Myc expression in leukemic cells, thereby increasing cytotoxicity of the cells 2 , and increase the efficacy of chemotherapy by inhibiting NRF2 (nuclear factor-erythroid 2-related factor-2) expression in cancer cells 5 . Additionally, it has been reported that brusatol regulates HIF-1α (hypoxia-inducible factor-1) protein, but not mRNA expression 6 . However, the mechanism by which brusatol downregulates HIF‑1α protein expression and induces cancer cell death under hypoxic conditions is unclear.…”

“…As mentioned, HIF-1 is a major regulator protein in the tumor survival and progression, as well as chemoreisistance and radioresistance 13 . Therefore, HIF-1 has been regarded as an attractive target for cancer therapy over the past several years 6 , 13 . Recently, specific inhibitors targeting HIF-1 by inhibiting its mRNA expression, protein synthesis, protein stability and transactivation have been identified 6 .…”