Search

Hsp90 is a promising drug target for cancer therapy. However, toxicity and moderate effect are limitations of current inhibitors owing to broad protein degradation. The fungal mycotoxin penisuloxazin A (PNSA) belongs to a new epipolythiodiketopiperazines (ETPs) possessing a rare 3H-spiro[benzofuran-2,2'-piperazine] ring system. PNSA bound to cysteine residues C572/C598 of CT-Hsp90 with disulfide bonds and inhibits Hsp90 activity, resulting in apoptosis and growth inhibition of HCT116 cells in vitro and in vivo. We identified that analogues PEN-A and HDN-1 bound to C572/C597 and C572 of CT-Hsp90α respectively, with binding pattern very similar to PNSA. These ETPs exhibited different effects on ATPase activity, dimerization formation and selectivity on client protein of Hsp90, indicating client recognition of Hsp90 can be exactly regulated by different sites of Hsp90. Our findings not only offer new chemotypes for anticancer drug development, but also help to better understand biological function of Hsp90 for exploring inhibitor with some client protein bias.

Expression of CDC28 protein kinase regulatory subunit 1 (Cks1), an adaptor for cyclin-dependent kinases, is tightly regulated at transcriptional and posttranslational levels. Increased expression of Cks1 has been documented to be attributable to cancer progression, chemoresistance, and chemosensitivity. Here we report that ectopic overexpression of Cks1b in human lung cancer cells (Cks1b-OE) induces chemoresistance of the cells to cisplatin (CDDP) and doxorubicin (DOX) through mechanisms independent of its canonical Skp2-p27 pathway. Further dissection with application of shRNA and selective inhibitors reveals that Hsp90 and MEK1/2 are the critical components of the non-canonical pathways responsible for the Cks1b-induced chemoresistance. Interestingly, inhibition of either Hsp90 or MEK1/2 rendered a similar magnitude of antitumor activity by resensitization of the chemoresistant Cks1b-OE cells to CDDP and DOX, suggesting that both Hsp90 and MEK1/2 are essential to Cks1b for induction of chemoresistance. Moreover, 3-O-(Z)-coumaroyloleanolic acid (3-COA), an active ingredient of oleanolic acid in the leaves of E. oldhamii Maxim, that has been shown to have antitumor activity against A549 lung cancer cells, mimicked PU-H71, a Hsp90-specific inhibitor, in antitumor activity when used alone or in combination with CDDP or DOX in Cks1b-OE cells and recurrent primary human lung cancer cells both in vitro and in vivo, suggesting that 3-COA is a novel Hsp90 inhibitor. Our data report for the first time that Cks1b employs Hsp90 and MEK1/2 pathways in lung cancer cells to develop chemoresistance and identify 3-COA as a potential antitumor drug for clinical treatment of chemoresistant lung cancer.

Inflammatory events are tightly associated with the death caused by Herpes simplex virus 1 (HSV-1) infection of the brain. Heat shock protein 90 (Hsp90) is a molecular chaperone that is stimulated in response to many stressful conditions (e.g., inflammation and hypoxia) and Hsp90 inhibitors are suggested to be potent inhibitors of the inflammatory response. The aim of this study was to investigate the effect of Hsp90 inhibitor AT-533 on HSV-1-induced inflammation. AT-533 at a non-antiviral concentration was found to show a prominent inhibitory effect on the production of cytokines induced by HSV-1 infection, such as tumor necrosis factor α (TNF-α), interleukin 6 (IL-6) and interleukin 1β (IL-1β). Mechanically, HSV-1 early infection induced inflammation through NF-κB signaling and NLRP3 inflammasome activation, as illustrated by the nuclear translocation of NF-κB and the enhanced cleavage of caspase-1. Besides, HSV-1 enhanced the interaction between NLRP3 and Hsp90. Moreover, AT-533 reduced the nuclear translocation of NF-κB and inflammasome activation via inhibiting the chaperone function of Hsp90. Furthermore, AT-533 inhibited the cleavage of pro-IL-1β to mature IL-1β in a NLRP3-independent manner. In summary, AT-533 may be a promising therapeutic strategy in HSV-1-infected inflammation management.

The inhibition of angiogenesis is suggested to be an attractive strategy for cancer therapeutics. Heat shock protein 90 (Hsp90) is closely related to tumorigenesis as it regulates the stabilization and activated states of many client proteins that are essential for cell survival and tumor growth. Here, we investigated the mechanism whereby AT-533, a novel Hsp90 inhibitor, inhibits breast cancer growth and tumor angiogenesis. Based on our results, AT-533 suppressed the tube formation, cell migration, and invasion of human umbilical vein endothelial cells (HUVECs), and was more effective than the Hsp90 inhibitor, 17-AAG. Furthermore, AT-533 inhibited angiogenesis in the aortic ring, Matrigel plug, and chorioallantoic membrane (CAM) models. Mechanically, AT-533 inhibited the activation of VEGFR-2 and the downstream pathways, including Akt/mTOR/p70S6K, Erk1/2 and FAK, in HUVECs, and the viability of breast cancer cells and the HIF-1α/VEGF signaling pathway under hypoxia. In vivo, AT-533 also inhibited tumor growth and angiogenesis by inducing apoptosis and the HIF-1α/VEGF signaling pathway in breast cancer cells. Taken together, our findings indicate that the Hsp90 inhibitor, AT-533, suppresses breast cancer growth and angiogenesis by blocking the HIF-1α/VEGF/VEGFR-2 signaling pathway. AT-533 may thus be a potentially useful drug candidate for breast cancer therapy.

Dose-limiting toxicity is a main road blocker for successful cancer chemotherapy. By phenotype screening, a novel chemical agent 2-(2-Chlorophenylimino)-5-(4-dimethylamino-benzylidene) thiazolidin-4-one (CDBT) was found to strongly inhibit the proliferation of non-small cell lung cancer (NSCLC) cells H460 and H322 while displaying no obvious toxicity to normal fast-dividing fibroblast cells NHFB and WI-38 at a concentration 100-fold higher than its EC50 to NSCLC cells. CDBT targets microtubule and heat shock protein 90 (HSP90) simultaneously with moderate affinities compared to microtubule targeting Colchicine and HSP90 inhibitor 17-dimethylaminoethylamino-17-demethoxygaldanamcyin (17-DMAG). CDBT blocks microtubule formation, decreases cancer-essential proteins CRAF-1, ERBB2 and phosphorylated AKT, and causes G2/M arrest and apoptosis. The moderate inhibitory effects of CDBT on targets require a higher cellular concentration of targets, a situation only exist in cancer cells. This accounts for its good cancer selectivity. Furthermore, CDBT effectively inhibits tumor growth by 62.4% relative to the vehicle control after i.p. administration at 30 mg/kg for 11 days while showing no toxicity to normal tissues in NSCLC H460 xenograft mouse model.

Heat shock protein 90 (Hsp90) is a molecular chaperone engaging in multiple cellular signaling by stabilizing oncoproteins (e.g. Akt and c-Raf) in tumor cells. Whereas Hsp90 inhibitors such as 17-AAG exert promising antitumor effects in clinical trials, current efforts focus on developing agents targeting Hsp90 with improved efficacy and lower toxicity. Using a fluorescence polarization assay, we screened over a hundred of synthetic small molecules and identified a resorcinol derivative LD053 that bound the Hsp90 ATP-binding pocket. The binding of LD053 to Hsp90 dissociated the co-chaperone protein cdc37 from Hsp90, resulting in destabilization of Akt and c-Raf and subsequent inhibition of PI3K/Akt and c-Raf/Mek/Erk signaling in BGC823 gastric cancer cells. As a consequence, LD053 decreased cancer cell viability and induced apoptosis evidenced by increased subG0/G1 cell population and increased cleavage of caspase 3 and PARP. Interestingly, normal human cells appeared insensitive to LD053 treatments. Consistent with its in vitro anticancer activities, LD053 significantly inhibited growth of BGC823 xenografts in nude mice without apparent body weight loss. These results thus demonstrate that LD053 is a novel Hsp90 inhibitor and has potential to be used to treat gastric cancer.

Hsp90 is a chaperone protein that interacts with client proteins that are known to be in the cell cycle, signaling and chromatin-remodeling pathways. Hsp90 inhibitors act additively or synergistically with many other drugs in the treatment of both solid tumors and leukemias in murine tumor models and humans. Hsp90 inhibitors potentiate the actions of anti-cancer drugs that target Hsp90 client proteins, including trastuzumab (Herceptin™) which targets Her2/Erb2B, as Hsp90 inhibition elicits the drug effects in cancer cell lines that are otherwise resistant to the drug. A phase II study of the Hsp90 inhibitor 17-AAG and trastuzumab showed that this combination therapy has anticancer activity in patients with HER2-positive metastatic breast cancer progressing on trastuzumab. In this review, we discuss the results of Hsp90 inhibitors in combination with trastuzumab and other cancer drugs. We also discuss recent results from yeast focused on the genetics of drug resistance when Hsp90 is inhibited and the implications that this might have in understanding the effects of genetic variation in treating cancer in humans.

Heat shock protein 90 (Hsp90), a highly conserved molecular chaperone, is one of the most promising targets for cancer drug development. Whether any resistance to these Hsp90 inhibitor drugs could arise by Hsp90 mutation is still unknown. Yeast is readily engineered so that its essential Hsp90 function is provided by either isoform of the human cytosolic Hsp90, Hsp90alpha or Hsp90beta. However, its high intrinsic resistance to most drugs poses a major obstacle to the use of such Hsp90alpha- or Hsp90beta-expressing yeast cells as a model system to analyse whether drug resistance might arise by Hsp90 mutation. In order to overcome this problem, we have generated a strain that is both hypersensitive to Hsp90 inhibitors as it lacks multiple drug resistance genes, and in which different heterologous and mutant Hsp90s can be expressed by plasmid exchange. It is not rendered appreciably stress sensitive when made to express Hsp90alpha or Hsp90beta as its sole form of Hsp90. Should there be any development of resistance to the Hsp90 drugs now in cancer clinic trials, this system can provide a rapid initial test of whether any single nucleotide polymorphism appearing within the coding regions of Hsp90alpha or Hsp90beta could be a contributory factor in this resistance. We have used this strain to demonstrate that significant levels of resistance to the Hsp90 inhibitors radicicol and 17-allylamino-demethoxygeldanamycin (17-AAG) are generated as a result of the same single point mutation within the native Hsp90 of yeast (A107N), the human Hsp90alpha (A121N) and the human Hsp90beta (A116N).

Hsp90 and topoisomerase I are both targets for chemotherapeutic agents. Topoisomerase I poisons are standard clinical treatments, whilst Hsp90 inhibitors are progressing through clinical trials. We have demonstrated that when an Hsp90 inhibitor and topoisomerase I poison are combined they produce a synergistic increase in apoptosis in both p53⁺/⁺ and p53⁻/⁻ HCT116 human colon cancer cells. Lack of p53 is associated with an increase in sensitivity to the combination treatment; p53⁺/⁺ cells treated with the topoisomerase I poison topotecan (TPT) arrest at G2, whereas in p53⁻/⁻ cells the additional presence of the Hsp90 inhibitor geldanamycin (GA) selectively abrogates the G2M checkpoint. More importantly we report that there is a common underlying p53-independent mechanism behind the observed synergistic combined drug effect. We show that concurrent treatment with GA and TPT is able to reverse TPT induced up-regulation of the anti-apoptotic protein Bcl2 in both p53⁺/⁺ and p53⁻/⁻ HCT116 cells. The data suggests that inhibition of Hsp90 mediates down-regulation of Bcl2 following the combination treatment and cause a synergistic increase in apoptosis in both p53⁺/⁺ and p53⁻/⁻ HCT116 cells; p53⁻/⁻ HCT116 cells are more sensitive to the treatment because they also fail to arrest at G2 in the cell cycle.