MFTZ-1 reduces constitutive and inducible HIF-1α accumulation and VEGF secretion independent of its topoisomerase II inhibition

Heat shock response regulates stimulus-specificity and sensitivity of the pro-inflammatory NF-κB signalling

BACKGROUND

Ability to adapt to temperature changes trough the Heat Shock Response (HSR) pathways is one of the most fundamental and clinically relevant cellular response systems. Heat Shock (HS) affects the signalling and gene expression responses of the Nuclear Factor κB (NF-κB) transcription factor, a critical regulator of proliferation and inflammation, however, our quantitative understanding of how cells sense and adapt to temperature changes is limited.

METHODS

We used live-cell time-lapse microscopy and mathematical modelling to understand the signalling of the NF-κB system in the human MCF7 breast adenocarcinoma cells in response to pro-inflammatory Interleukin 1β (IL1β) and Tumour Necrosis Factor α (TNFα) cytokines, following exposure to a 37-43 °C range of physiological and clinical temperatures.

RESULTS

We show that exposure to 43 °C 1 h HS inhibits the immediate NF-κB signalling response to TNFα and IL1β stimulation although uptake of cytokines is not impaired. Within 4 h after HS treatment IL1β-induced NF-κB responses return to normal levels, but the recovery of the TNFα-induced responses is still affected. Using siRNA knock-down of Heat Shock Factor 1 (HSF1) we show that this stimulus-specificity is conferred via the Inhibitory κB kinase (IKK) signalosome where HSF1-dependent feedback regulates TNFα, but not IL1β-mediated IKK recovery post HS. Furthermore, we demonstrate that through the temperature-dependent denaturation and recovery of IKK, TNFα and IL1β-mediated signalling exhibit different temperature sensitivity and adaptation to repeated HS when exposed to a 37-43 °C temperature range. Specifically, IL1β-mediated NF-κB responses are more robust to temperature changes in comparison to those induced by TNFα treatment.

CONCLUSIONS

We demonstrate that the kinetics of the NF-κB system following temperature stress is cytokine specific and exhibit differential adaptation to temperature changes. We propose that this differential temperature sensitivity is mediated via the IKK signalosome, which acts as a bona fide temperature sensor trough the HSR cross-talk. This novel quantitative understanding of NF-κB and HSR interactions is fundamentally important for the potential optimization of therapeutic hyperthermia protocols. Video Abstract.

Tanshinone I inhibits tumor angiogenesis by reducing Stat3 phosphorylation at Tyr705 and hypoxia-induced HIF-1α accumulation in both endothelial and tumor cells

Tanshinone I (Tanshinone-1), a major active principle of Salvia miltiorrhiza (Danshen), has been shown to overcome tumor drug resistance and metastasis. Here we report that tanshinone-1 inhibits angiogenesis. Tanshinone-1 inhibited proliferation, migration and tube formation of vascular endothelial cells, rat aortic ring sprouting and the neovascularization of the chick chorioallantoic membrane in a concentration-dependent manner. In endothelial cells, tanshinone-1 almost completely inhibited phosphorylation of Stat3 at Tyr705 regardless of hypoxia or normoxia but only slightly decreased the hypoxia-induced HIF-1α accumulation. In tumor cells, contrastively, tanshinone-1 could not only make phosphorylation of Stat3 at Tyr705 disappear but also reduce the hypoxia-induced accumulation of HIF-1α to its baseline levels at normoxia. Consequently, VEGF secretion from tumor cells was reduced, which could potentiate the direct inhibition of tanshinone-1 on endothelial cells. Together with its overcoming tumor drug resistance and metastasis, our results reveal unique characteristics of tanshinone-1 and its improved derivatives as promising angiogenesis inhibitors.

Hypoxia-Targeted Drug Q6 Induces G2-M Arrest and Apoptosis via Poisoning Topoisomerase II under Hypoxia

In spite of the tremendous efforts dedicated to developing hypoxia-activated prodrugs, no agents yet have been approved for clinical therapy. In the present study, the hypoxic selective anti-cancer activity as well as the cellular target of a novel tirapazamine (TPZ) analogue, 7-methyl-3-(3-chlorophenyl)-quinoxaline-2-carbonitrile 1,4-dioxide (Q6) were investigated. Q6 implemented anti-cancer effects via poisoning topoisomerase II (topo II) under hypoxia. Modified trapped in agarose DNA immunostaining (TARDIS) assay showed more topo II-DNA cleavage complexes trapped by Q6 than TPZ at even lower concentration. In addition, by introducing ataxia-telangiectasia-mutated (ATM) kinase inhibitors caffeine and KU-60019, we displayed that Q6-triggered apoptosis was attributed, at least partially, to DNA double-strand breaks generated by the topo II-targeting effect. Collectively, Q6 stood out for its better hypoxia-selectivity and topo II-poisoning than the parental compound TPZ. All these data shed light on the research of Q6 as a promising hypoxia-activated prodrug candidate for human hepatocellular carcinoma therapy.

Hypoxia-Targeted Drug Q6 Induces G2-M Arrest and Apoptosis via Poisoning Topoisomerase II under Hypoxia

In spite of the tremendous efforts dedicated to developing hypoxia-activated prodrugs, no agents yet have been approved for clinical therapy. In the present study, the hypoxic selective anti-cancer activity as well as the cellular target of a novel tirapazamine (TPZ) analogue, 7-methyl-3-(3-chlorophenyl)-quinoxaline-2-carbonitrile 1,4-dioxide (Q6) were investigated. Q6 implemented anti-cancer effects via poisoning topoisomerase II (topo II) under hypoxia. Modified trapped in agarose DNA immunostaining (TARDIS) assay showed more topo II–DNA cleavage complexes trapped by Q6 than TPZ at even lower concentration. In addition, by introducing ataxia-telangiectasia-mutated (ATM) kinase inhibitors caffeine and KU-60019, we displayed that Q6-triggered apoptosis was attributed, at least partially, to DNA double-strand breaks generated by the topo II-targeting effect. Collectively, Q6 stood out for its better hypoxia-selectivity and topo II-poisoning than the parental compound TPZ. All these data shed light on the research of Q6 as a promising hypoxia-activated prodrug candidate for human hepatocellular carcinoma therapy.

Cross talk between cytokine and hyperthermia-induced pathways: identification of different subsets of NF-κB-dependent genes regulated by TNFα and heat shock

Heat shock inhibits NF-κB signaling, yet the knowledge about its influence on the regulation of NF-κB-dependent genes is limited. Using genomic approaches, i.e., expression microarrays and ChIP-Seq, we aimed to establish a global picture for heat shock-mediated impact on the expression of genes regulated by TNFα cytokine. We found that 193 genes changed expression in human U-2 osteosarcoma cells stimulated with cytokine (including 77 genes with the κB motif in the proximal promoters). A large overlap between sets of genes modulated by cytokine or by heat shock was revealed (86 genes were similarly affected by both stimuli). Binding sites for heat shock-induced HSF1 were detected in regulatory regions of 1/3 of these genes. Furthermore, pre-treatment with heat shock affected the expression of 2/3 of cytokine-modulated genes. In the largest subset of co-affected genes, heat shock suppressed the cytokine-mediated activation (antagonistic effect, 83 genes), which genes were associated with the canonical functions of NF-κB signaling. However, subsets of co-activated and co-repressed genes were also revealed. Importantly, pre-treatment with heat shock resulted in the suppression of NF-κB binding in the promoters of the cytokine-upregulated genes, either antagonized or co-activated by both stimuli. In conclusion, we confirmed that heat shock inhibited activation of genes involved in the classical cytokine-mediated functions of NF-κB. On the other hand, genes involved in transcription regulation were over-represented in the subset of genes upregulated by both stimuli. This suggests the replacement of NF-κB-mediated regulation by heat shock-mediated regulation in the latter subset of genes, which may contribute to the robust response of cells to both stress conditions.

Newly discovered angiogenesis inhibitors and their mechanisms of action

In the past decade, the success of angiogenesis inhibitors in clinical contexts has established the antiangiogenic strategy as an important part of cancer therapy. During that time period, we have discovered and reported 17 compounds that exert potent inhibition on angiogenesis. These compounds exhibit tremendous diversity in their sources, structures, targets and mechanisms. These studies have generated new models for further modification and optimization of inhibitory compounds, new information for mechanistic studies and a new drug candidate for clinical development. In particular, through studies on the antiangiogenic mechanism of pseudolaric acid B, we discovered a novel mechanism by which the stability of hypoxia-inducible factor 1α is regulated by the transcription factor c-Jun. We also completed a preclinical study of AL3810, a compound with the potential to circumvent tumor drug resistance to a certain extent. All of these findings will be briefly reviewed in this article.

Towards single cell heat shock response by accurate control on thermal confinement with an on-chip microwire electrode

Metal electrodes with micron scale width enable the heating of less than a dozen cells in a confluent layer at predictable temperatures up to 85 °C with an accuracy of ±2 °C. Those performances were obtained by a preliminary robust temperature calibration based on biotin-rhodamine fluorescence and by controlling the temperature map on the substrate through thermal modeling. The temperature accuracy was proved by inducing the expression of heat shock proteins (HSP) in a few NIH-3T3 cells through a confined and precise temperature rise. Our device is therefore effective to locally induce a heat shock response with almost single-cell resolution. Furthermore, we show that cells heated at a higher temperature than the one of heat shock remain alive without producing HSP. Electrode deposition being one of the most common engineering processes, the fabrication of electrode arrays with a simple control circuit is clearly within reach for parallel testing. This should enable the study of several key mechanisms such as cell heat shock, death or signaling. In nanomedicine, controlled drug release by external stimuli such as for example temperature has attracted much attention. Our device could allow fast and efficient testing of thermoactivable drug delivery systems.

Suppression of hypoxia-inducible factor 1α (HIF-1α) by tirapazamine is dependent on eIF2α phosphorylation rather than the mTORC1/4E-BP1 pathway

Hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor that mediates the adaptation of tumor cells and tissues to the hypoxic microenvironment, has attracted considerable interest as a potential therapeutic target. Tirapazamine (TPZ), a well-characterized bioreductive anticancer agent, is currently in Phase II and III clinical trials. A major aspect of the anticancer activity of TPZ is its identity as a tumor-specific topoisomerase IIα inhibitor. In the study, for the first time, we found that TPZ acts in a novel manner to inhibit HIF-1α accumulation driven by hypoxia or growth factors in human cancer cells and in HepG2 cell-derived tumors in athymic nude mice. We investigated the mechanism of TPZ on HIF-1α in HeLa human cervical cancer cells by western blot analysis, reverse transcription-PCR assay, luciferase reporter assay and small interfering RNA (siRNA) assay. Mechanistic studies demonstrated that neither HIF-1α mRNA levels nor HIF-1α protein degradation are affected by TPZ. However, TPZ was found to be involved in HIF-1α translational regulation. Further studies revealed that the inhibitory effect of TPZ on HIF-1α protein synthesis is dependent on the phosphorylation of translation initiation factor 2α (eIF2α) rather than the mTOR complex 1/eukaryotic initiation factor 4E-binding protein-1 (mTORC1/4E-BP1) pathway. Immunofluorescence analysis of tumor sections provide the in vivo evidences to support our hypothesis. Additionally, siRNA specifically targeting topoisomerase IIα did not reverse the ability of TPZ to inhibit HIF-1α expression, suggesting that the HIF-1α inhibitory activity of TPZ is independent of its topoisomerase IIα inhibition. In conclusion, our findings suggest that TPZ is a potent regulator of HIF-1α and provide new insight into the potential molecular mechanism whereby TPZ serves to reduce HIF-1α expression.

Increased accumulation of hypoxia-inducible factor-1α with reduced transcriptional activity mediates the antitumor effect of triptolide

Background

Hypoxia-inducible factor-1α (HIF-1α), a critical transcription factor to reduced O₂ availability, has been demonstrated to be extensively involved in tumor survival, aggressive progression, drug resistance and angiogenesis. Thus it has been considered as a potential anticancer target. Triptolide is the main principle responsible for the biological activities of the Traditional Chinese Medicine tripterygium wilfordii Hook F. Triptolide possesses great chemotherapy potential for cancer with its broad-spectrum anticancer, antiangiogenesis, and drug-resistance circumvention activities. Numerous biological molecules inhibited by triptolide have been viewed as its possible targets. However, the anticancer action mechanisms of triptolide remains to be further investigated. Here we used human ovarian SKOV-3 cancer cells as a model to probe the effect of triptolide on HIF-1α.

Results

Triptolide was observed to inhibit the proliferation of SKOV-3 cells, and meanwhile, to enhance the accumulation of HIF-1α protein in SKOV-3, A549 and DU145 cells under different conditions. Triptolide did not change the kinetics or nuclear localization of HIF-1α protein or the 26 S proteasome activity in SKOV-3 cells. However, triptolide was found to increase the levels of HIF-1α mRNA. Unexpectedly, the HIF-1α protein induced by triptolide appeared to lose its transcriptional activity, as evidenced by the decreased mRNA levels of its target genes including VEGF, BNIP3 and CAIX. The results were further strengthened by the lowered secretion of VEGF protein, the reduced sprout outgrowth from the rat aorta rings and the inhibitory expression of the hypoxia responsive element-driven luciferase reporter gene. Moreover, the silencing of HIF-1α partially prevented the cytotoxicity and apoptosis triggered by triptolide.

Conclusions

The potent induction of HIF-1α protein involved in its cytotoxicity, together with the suppression of HIF-1 transcriptional activity, indicates the great therapeutic potential of triptolide as an anticancer drug. Meanwhile, our data further stress the possibility that HIF-1α functions in an unresolved nature or condition.

Q39, a quinoxaline 1,4-Di-N-oxide derivative, inhibits hypoxia-inducible factor-1α expression and the Akt/mTOR/4E-BP1 signaling pathway in human hepatoma cells

Cumulative evidence has established that hypoxia-inducible factor-1α (HIF-1α) and its downstream target, vascular endothelial growth factor (VEGF), play a critical role in hepatocellular carcinoma angiogenesis, invasiveness and metastasis. 3-(4-bromophenyl)-2-(ethylsulfonyl)-6-methylquinoxaline 1,4-dioxide (Q39) has recently shown great antiproliferative activity in extensive cell lines in normoxia and hypoxia. In this study, Q39 exhibited high antiproliferative activity against hepatoma both in vitro and in vivo, mainly by inducing apoptosis. In addition, suppression of HIF-1α by Q39 resulted in a drastic decrease in VEGF expression. These results indicate that Q39 is an effective inhibitor of HIF-1α and provide new perspectives into the mechanism of its anticancer activity. Interestingly, neither the HIF-1α degradation rate nor the HIF-1α steady-state mRNA level was affected by Q39. Instead, suppression of HIF-1α accumulation by Q39 correlated with prominent dephosphorylation of mTOR and 4E-BP1, a pathway known to regulate protein expression at the translational level.

Q39, a quinoxaline 1,4-Di-N-oxide derivative, inhibits hypoxia-inducible factor-1α expression and the Akt/mTOR/4E-BP1 signaling pathway in human hepatoma cells

Cumulative evidence has established that hypoxia-inducible factor-1α (HIF-1α) and its downstream target, vascular endothelial growth factor (VEGF), play a critical role in hepatocellular carcinoma angiogenesis, invasiveness and metastasis. 3-(4-bromophenyl)-2-(ethylsulfonyl)-6-methylquinoxaline 1,4-dioxide (Q39) has recently shown great antiproliferative activity in extensive cell lines in normoxia and hypoxia. In this study, Q39 exhibited high antiproliferative activity against hepatoma both in vitro and in vivo, mainly by inducing apoptosis. In addition, suppression of HIF-1α by Q39 resulted in a drastic decrease in VEGF expression. These results indicate that Q39 is an effective inhibitor of HIF-1α and provide new perspectives into the mechanism of its anticancer activity. Interestingly, neither the HIF-1α degradation rate nor the HIF-1α steady-state mRNA level was affected by Q39. Instead, suppression of HIF-1α accumulation by Q39 correlated with prominent dephosphorylation of mTOR and 4E-BP1, a pathway known to regulate protein expression at the translational level.