Potent Non-Benzoquinone Ansamycin Heat Shock Protein 90 Inhibitors from Genetic Engineering of Streptomyces hygroscopicus (original) (raw)
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Molecular Pharmacology, 2006
We have previously evaluated the role of NAD(P)H:quinone oxidoreductase 1 (NQO1) in the bioreductive metabolism of 17-(allylamino)-demethoxygeldanamycin (17AAG) to the corresponding hydroquinone, a more potent 90-kDa heat shock protein (Hsp90) inhibitor. Here, we report an extensive study with a series of benzoquinone ansamycins, which includes gel-danamycin, 17-(amino)-17-demethoxygeldanamycin, and 17-demethoxy-17-[[2-(dimethylamino)ethyl]amino]-geldanamycin. The reduction of these benzoquinone ansamycins by recombinant human NQO1 to the corresponding hydroquinone ansamycins was monitored by high-performance liquid chromatography (HPLC) and confirmed by liquid chromatography/ mass spectrometry. Inhibition of purified yeast Hsp90 ATPase activity was augmented in the presence of NQO1 and abrogated by 5-methoxy-1,2-dimethyl-3-[(4-nitrophenoxy)methyl-]indole-4,7-dione (ES936), a mechanism-based inhibitor of NQO1, showing that the hydroquinone ansamycins were more potent Hsp90 inhibitors than their parent quinones. An isogenic pair of human breast cancer cell lines, MDA468 and MDA468/ NQ16, differing in expression of NQO1, was used, and HPLC analysis showed that hydroquinone ansamycins were formed by the MDA468/NQ16 cells, which could be prevented by ES936 pretreatment. The MDA468/NQ16 cells were more sensitive to growth inhibition after treatment with the benzoquinone ansamycins compared with the MDA468 cells; this increased sensitivity could be reduced by ES936 pretreatment. The increased duration of benzoquinone ansamycin exposure showed increased potency and -fold inhibition in MDA468/NQ16 cells relative to the parental MDA468 cells. Computational-based molecular modeling studies displayed additional contacts between yeast Hsp90 and the hydroquinone ansamycins, which translated to greater interaction energies compared with the corresponding benzoquinone ansamycins. In conclusion, these studies show that the reduction of this series of benzoquinone ansamycins by NQO1 generates the corresponding hydroquinone ansamycins, which exhibit enhanced Hsp90 inhibition.
BioMed Target Journal, 2023
Heat shock protein (HSP90) is a molecular chaperone involved in numerous physiological processes. The primary role of this is to assist in the process of protein folding and to restore misfolded proteins to their correct shape. Chaperones additionally inhibit protein breakdown and aggregation. HSP90 inhibitors possess a notable characteristic of obstructing many cancer-causing pathways by facilitating the breakdown of numerous oncogenic client proteins. Targeting HSP90 therapeutics has been recognized as a viable approach for treating cancer and inflammatory-associated disorders in clinical studies involving different forms of cancer. Inhibition of HSP90 using natural, synthetic, and semisynthetic chemicals has shown encouraging outcomes. HSP90 inhibitors have been extracted from several fungi, bacteria, and plant species. These naturally occurring chemicals play a crucial function in regulating HSP90 activity and can be utilized to develop innovative semi-synthetic or synthetic inhibitors. Over 120 clinical trials have been carried out to evaluate the effectiveness of HSP90 inhibitors as a supplementary therapy for different types of tumor cells. Presently, ongoing research is being carried out to acquire an understanding of innovative and more efficacious methods for treating cancer. Continuing in this research approach, we aim to investigate the discovery, biosynthesis, mechanism of action, and biological features of geldanamycin and its analogs.
Mechanistic Studies on Hsp90 Inhibition by Ansamycin Derivatives
Journal of Molecular Biology, 2007
Heat shock protein 90 (Hsp90) is a molecular chaperone that is required for the maturation and activation of a number of client proteins, many of which are involved in cancer development. The ansamycin family of natural products and their derivatives, such as geldanamycin (GA), are well-known inhibitors of the essential ATPase activity of Hsp90. Despite structural studies on the complexes of ansamycin derivatives with the ATPase domain of Hsp90, certain aspects of their inhibitory mechanism remain unresolved. For example, it is known that GA in solution exists in an extended conformation with a trans amide bond; however, it binds to Hsp90 in a significantly more compact conformation with a cis amide bond. GA and its derivatives have been shown to bind to Hsp90 with low micromolar affinity in vitro, in contrast to the low nanomolar anti-proliferative activity that these drugs exhibit in vivo. In addition, they show selectivity towards tumour cells. We have studied both the equilibrium binding, and the association and dissociation kinetics of GA derivative, 17-DMAG, and the fluorescently labelled analogue BDGA to both wild-type and mutant Hsp90. The mutants were made in order to test the hypothesis that conserved residues near the ATP-binding site may catalyse the trans-cis isomerisation of GA. Our results show that Hsp90 does not catalyse the trans-cis isomerisation of GA, and suggests that there is no isomerisation step before binding to Hsp90. Experiments with BDGA measured over a wide range of conditions, in the absence and in the presence of reducing agents, confirm recent studies that have suggested that the reduced dihydroquinone form of the drug binds to Hsp90 considerably more tightly than the non-reduced quinone species.
Proceedings of the National Academy of Sciences, 1994
The molecular mechanisms by which oncogenic tyrosine kinases induce cellular transformation are unclear. Herbimycin A, geldanamycin, and certain other benzoquinone ansamycins display an unusual capacity to revert tyrosine kinase-induced oncogenic transformation. As an approach to the study of v-src-mediated transformation, we examined ansamycin action in transformed cells and found that drug-induced reversion could be achieved without direct inhibition of src phosphorylating activity. To identify mechanisms other than kinase inhibition for drug-mediated reversion, we prepared a solid phase-immobilized geldanamycin derivative and affinity precipitated the molecular targets with which the drug interacted. In a range of cell lines, immobilized geldanamycin bound elements of a major class of heat shock protein (HSP90) in a stable and pharmacologically specific manner. Consistent with these binding data, we found that soluble geldanamycin and herbimycin A inhibited specifically the formation of a previously described src-HSP90 heteroprotein complex. A related benzoquinone ansamycin that failed to revert transformed cells did not inhibit the formation of this complex. These results demonstrate that HSP participation in multimolecular complex formation is required for src-mediated transformation and can provide a target for drug modulation. to yield a 10-fold molar excess and allowed to react for 2 hr Abbreviations: GA, geldanamycin; HA, herbimycin A; HSP, heat shock protein; DMSO, dimethyl sulfoxide.
Bioorganic & Medicinal Chemistry, 2008
The molecular chaperone Hsp90 plays important roles in maintaining the malignant phenotypes. Recent studies suggest that Hsp90 exerts high affinity interactions with multiple oncoproteins, which are essential for the growth of tumor cells. As a result, research has been focused on finding Hsp90 probes as potential and selective anticancer agents. In a high-throughput screening exercise, we identified quinoline 7 as a moderate inhibitor of Hsp90. Further hit identification, SAR studies and biological investigation revealed several synthetic analogs in this series with micromolar activities in both fluorescent polarization (FP) assay and a cell-based western-blot (WB) assay. These compounds represent a new class of Hsp90 inhibitors with simple chemical structures.
Journal of Medicinal Chemistry, 2007
Heat shock protein 90 (Hsp90) is a molecular chaperone protein implicated in stabilizing the conformation and maintaining the function of many cell-signaling proteins. Many oncogenic proteins are more dependent on Hsp90 in maintaining their conformation, stability, and maturation than their normal counterparts. Furthermore, recent data show that Hsp90 exists in an activated form in malignant cells but in a latent inactive form in normal tissues, suggesting that inhibitors selective for the activated form could provide a high therapeutic index. Hence, Hsp90 is emerging as an exciting new target for the treatment of cancer. We now report on a novel series of 2-amino-6-halopurine Hsp90 inhibitors exemplified by 2-amino-6-chloro-9-(4-iodo-3,5-dimethylpyridin-2-ylmethyl)purine (30). These highly potent inhibitors (IC 50 of 30) 0.009 µM in a HER-2 degradation assay) also display excellent antiproliferative activity against various tumor cell lines (IC 50 of 30) 0.03 µM in MCF7 cells). Moreover, this class of inhibitors shows higher affinity for the activated form of Hsp90 compared to our earlier 8-sulfanylpurine Hsp90 inhibitor series. When administered orally to mice, these compounds exhibited potent tumor growth inhibition (>80%) in an N87 xenograft model, similar to that observed with 17-allylamino-17-desmethoxygeldanamycin (17-AAG), which is a compound currently in phase I/II clinical trials.
The Journal of Organic Chemistry, 2010
A full account of an asymmetric synthesis of reblastatin (1), the first total synthesis of autolytimycin (2) and related structural compounds is described. The syntheses expand the utility of a highly regio-and diastereoselective hydrometalation aldehyde addition sequence to assemble the fully functionalized ansa chain of the natural products. Also documented is an intramolecular copper-mediated amidation reaction to close the 19-membered macrolactams. The amidation reaction was also employed for the generation of structural derivatives (6-9) of phenolic ansamycins. Ansamycin natural products and selected structural analogs were evaluated in a competitive binding assay to breast cancer cell lysate and a cytotoxicity assay. Both reblastatin (1) and autolytimycin (2) were shown to bind the Hsp90 protein with enhanced binding activity (~25 nM) than 17-allylamino-17-demethoxygeldanamycin (17-AAG, 4), a geldanamycin (3) derivative currently under evaluation for treatment of cancer (~100 nM).