17-Demethoxy-reblastatin, an Hsp90 inhibitor, induces mitochondria-mediated apoptosis through downregulation of Mcl-1 in human hepatocellular carcinoma cells

Decoding the roles of heat shock proteins in liver cancer

Hepatocellular carcinoma (HCC) is one of the most common gastrointestinal malignancies, characterized by insidious onset and high propensity for metastasis and recurrence. Apart from surgical resection, there are no effective curative methods for HCC in recent years, due to resistance to radiotherapy and chemotherapy. Heat shock proteins (HSP) play a crucial role in maintaining cellular homeostasis and normal organism development as molecular chaperones for intracellular proteins. Both basic research and clinical data have shown that HSPs are crucial participants in the HCC microenvironment, as well as the occurrence, development, metastasis, and resistance to radiotherapy and chemotherapy in various malignancies, particularly liver cancer. This review aims to discuss the molecular mechanisms and potential clinical value of HSPs in HCC, which may provide new insights for HSP-based therapeutic interventions for HCC.

The Disassociation of the A20/HSP90 Complex via Downregulation of HSP90 Restores the Effect of A20 Enhancing the Sensitivity of Hepatocellular Carcinoma Cells to Molecular Targeted Agents

NF-κB (nuclear factor κB) is a regulator of hepatocellular cancer (HCC)-related inflammation and enhances HCC cells' resistance to antitumor therapies by promoting cell survival and anti-apoptosis processes. In the present work, we demonstrate that A20, a dominant-negative regulator of NF-κB, forms a complex with HSP90 (heat-shock protein 90) and causes the disassociation of the A20/HSP90 complex via downregulation of HSP90. This process restores the antitumor activation of A20. In clinical specimens, the expression level of A20 did not relate with the outcome in patients receiving sorafenib; however, high levels of HSP90 were associated with poor outcomes in these patients. A20 interacted with and formed complexes with HSP90. Knockdown of HSP90 and treatment with an HSP90 inhibitor disassociated the A20/HSP90 complex. Overexpression of A20 alone did not affect HCC cells. Downregulation of HSP90 combined with A20 overexpression restored the effect of A20. Overexpression of A20 repressed the expression of pro-survival and anti-apoptosis-related factors and enhanced HCC cells' sensitivity to sorafenib. These results suggest that interactions with HSP90 could be potential mechanisms of A20 inactivation and disassociation of the A20/HSP90 complex and could serve as a novel strategy for HCC treatment.

The role of HSP90 molecular chaperones in hepatocellular carcinoma

Misfolded proteins have enhanced formation of toxic oligomers and nonfunctional protein copies lead to recruiting wild-type protein types. Heat shock protein 90 (HSP90) is a molecular chaperone generated by cells that are involved in many cellular functions through regulation of folding and/or localization of large multi-protein complexes as well as client proteins. HSP90 can regulate a number of different cellular processes including cell proliferation, motility, angiogenesis, signal transduction, and adaptation to stress. HSP90 makes the mutated oncoproteins able to avoid misfolding and degradation and permits the malignant transformation. As a result, HSP90 is an important factor in several signaling pathways associated with tumorigenicity, therapy resistance, and inhibiting apoptosis. Clinically, the upregulation of HSP90 expression in hepatocellular carcinoma (HCC) is linked with advanced stages and inappropriate survival in cases suffering from this kind of cancer. The present review comprehensively assesses HSP90 functions and its possible usefulness as a potential diagnostic biomarker and therapeutic option for HCC.

HSP90 interacts with HMGCR and promotes the progression of hepatocellular carcinoma

Heat shock protein 90 (HSP90) has been reported to promote the growth and inhibit apoptosis of hepatocellular carcinoma (HCC) cells. However, the underlying mechanisms are not fully understood. Immunostaining of the tissue array demonstrated that HSP90 was upregulated in HCC clinical samples and was associated with clinical features. HSP90 interacted with 3‑hydroxy‑3‑methylglutaryl‑CoA reductase (HMGCR), the rate‑limiting enzyme of mevalonate pathway, in the immunoprecipitation assay and regulated its protein expression level by inhibiting protein degradation. In addition, lovastatin, an inhibitor of HMGCR, impaired the oncogenic functions of HSP90 in the cell growth, migration and colony formation assays. Taken together, this study demonstrated that HSP90 promoted the progression of HCC by positively regulating the mevalonate pathway and indicated that HSP90 may be a promising therapeutic target.

Heat shock protein-guided dual-mode CT/MR imaging of orthotopic hepatocellular carcinoma tumor

Au@PEI-Gd-AAG NP nanoprobes hold enormous promise for highly efficient tumor diagnosis and dual-mode CT/T₁ positive MR imaging.

Mitochondrial pathway-mediated apoptosis is associated with erlotinib-induced cytotoxicity in hepatic cells

For advanced non-small-cell lung cancer (NSCLC) with mutations to the epidermal growth factor receptor (EGFR), EGFR tyrosine kinase inhibitors, including erlotinib are indicated for the first-line treatment. Liver injury is one of the multiple adverse effects of erlotinib and may affect its safety. The present study investigated the mechanism of erlotinib-induced hepatotoxicity in vitro and provided experimental evidence for the screening of potential hepatoprotectors. Erlotinib induced dose-dependent cytotoxicity in human L-02 hepatic cells 72 h after treatment. In other experiments, L-02 cells were treated with erlotinib for 48 h and thereafter exhibited typical features of apoptosis. Erlotinib caused alterations to nuclear morphology, including chromatin condensation and karyopyknosis; it also increased the fraction of late apoptotic cells and regulated apoptotic protein levels, activating caspase-3 and cleaving of poly-ADP-ribose polymerase. Furthermore, 48 h exposure to erlotinib disturbed mitochondrial function by decreasing the ratio of B-cell lymphoma 2 (Bcl-2) to Bcl-associated X proteins and reducing mitochondrial membrane potential. The results of this in vitro study indicate that erlotinib-induced hepatotoxicity may occur through mitochondrial-pathway-mediated apoptosis.

Targeting cancer cell mitochondria as a therapeutic approach: recent updates

Mitochondria play a key role in ATP generation, redox homeostasis and regulation of apoptosis. Due to the essential role of mitochondria in metabolism and cell survival, targeting mitochondria in cancer cells is considered as an attractive therapeutic strategy. However, metabolic flexibility in cancer cells may enable the upregulation of compensatory pathways, such as glycolysis to support cancer cell survival when mitochondrial metabolism is inhibited. Thus, compounds capable of both targeting mitochondria and inhibiting glycolysis may be particularly useful to overcome such drug-resistant mechanism. This review provides an update on recent development in the field of targeting mitochondria and novel compounds that impact mitochondria, glycolysis or both. Key challenges in this research area and potential solutions are also discussed.

Non-benzoquinone geldanamycin analogs trigger various forms of death in human breast cancer cells

Background

Hsp90 proteins are important therapeutic targets for many anti-cancer drugs in clinical trials. Geldanamycin (GA) was identified as the first natural inhibitor of Hsp90, increasing evidence suggests that GA was not a good choice for clinical trials. In this study, we investigated two new non-benzoquinone geldanamycin analogs of Hsp90 inhibitors, DHQ3 and 17-demethoxy-reblastatin (17-DR), to explore the molecular mechanisms of their anti-cancer activity in vivo and vitro.

Methods

MTT and colony formation assays were used to measure cell viability. Flow cytometry, DAPI staining, ATP assay, electron microscopy, western blots, siRNAs transfection and immunofluorescence were used to determine the molecular mechanism of DHQ3- or 17-DR-induced different forms of death in human breast cancer MDA-MB-231 cells. Malachite green reagent was used to measure ATPase activity of the analogs.

Results

DHQ3 and 17-DR presented efficiently inhibitory effect in MDA-MB-231 cell lines, and DHQ3 induced necroptosis by activation of the RIP1-RIP3-MLKL necroptosis cascade. And DHQ3-induced cell death was inhibited by a necroptosis inhibitor, necrostatin-1 (Nec-1), but not by a caspase inhibitor z-VAD-fmk. On the other hand, 17-DR induced apoptosis in MDA-MB-231 cells, indicating a caspase-dependent killing mechanism. We further demonstrated that down-regulation of RIP1 and RIP3 by siRNA protected against DHQ3 but not 17-DR induced cell death. These results were confirmed by electron microscopy. DHQ3 and 17-DR induced the degradation of Hsp90 client proteins, and they showed strong antitumor effects in MDA-MB-231 cell-xenografted nude mice.

Conclusions

These findings supported that DHQ3 and 17-DR induce different forms of death in some cancer cell line via activation of different pathways. All of the results provided evidence for its anti-tumorigentic action with low hepatotoxicity in vivo, making them promising anti-breast cancer agents.

HSP90 inhibits apoptosis and promotes growth by regulating HIF-1α abundance in hepatocellular carcinoma

Heat shock protein (HSP)90 functions as a general oncogene by targeting several well-known oncoproteins for ubiquination and proteasomal degradation. However, the clinical significance of HSP90, as well as the mechanisms responsible for the tumor-promoting effects of HSP90 in hepatocellular carcinoma (HCC) remain unclear. In this study, HSP90 and hypoxia-inducible factor (HIF)-1α expression in 60 samples of HCC tissues and matched normal tumor-adjacent tissue were assessed using immunohistochemistry (IHC) or western blot analysis. Flow cytometry, BrdU cell proliferation assay, caspase-3/7 activity assay and MTT assay were used to detect the apoptosis and proliferation of the HCC cells. The regulatory effect of HSP90 on HIF-1α in the HCC cells was confirmed by immunofluorescence staining, western blot analysis and RT-qPCR. The interaction between HIF-1α and HSP90 was analyzed by co-immunoprecipitation. A subcutaneous tumor xenograft model in nude mice was established and TUNEL assay was performed to evaluate cancer cell apoptosis and growth in vivo. We found that HSP90 expression was higher in the HCC tissues than in the normal tissues and that a high HSP90 expression correlated with poor clinicopathological characteristics, including venous infiltration, an advanced TNM stage and high pathological grading. Furthermore, we confirmed that patients with a negative expression of HSP90 had an improved 3-year survival, and that HSP90 was an independent factor for predicting the prognosis of patients with HCC. We demonstrated that HSP90 promoted HCC by inhibiting apoptosis and promoting cancer cell growth. Pearson's correlation coefficient analysis indicated that HSP90 expression positively correlated with HIF-1α protein expression in the HCC tissues. Furthermore, we found that HSP90 regulated HIF-1α protein abundance by inhibiting the ubiquitination and proteasomal degradation of HIF-1α in HCC cells. Additionally, the upregulation of HIF-1α expression partially abrogated HSP90 siRNA-induced HCC cell growth arrest and apoptosis in vitro and in vivo. These results indicate that HSP90 may be used as a prognostic marker and that HIF-1α may be one of the potential therapeutic targets of HSP90 in HCC.