3.3.1. Potential of the “Metagenome” 3016 3.3.2. Cryptic Clusters in Bacteria and Fungi 3016 3.3.3. Cyanophytes 3017 3.3.4. Marine Microbes (Non-Cyanophytes) 3018 3.3.5. Extremophiles 3018 3.3.6. Microbial Symbionts 3019 3.3.7. Plant Endophytes 3020 3.3.8. Combinatorial Biosynthesis 3020 4. Development of Drugs from Natural Products 3020 4.1. Synthesis Based on Natural Products 3021 4.1.1. Derivatization and Semisynthesis 3021 4.1.2. Total Synthesis 3021 4.1.3. Diverted Total Synthesis 3021 4.2. Natural Product-Inspired Combinatorial Synthesis 3022

Impact of natural products on developing new anti-cancer agents

A primary pathologic component of Alzheimer's disease (AD) is the formation of neurofibrillary tangles composed of hyperphosphorylated tau (p-tau). Expediting the removal of these p-tau species may be a relevant therapeutic strategy. Here we report that inhibition of Hsp90 led to decreases in p-tau levels independent of heat shock factor 1 (HSF1) activation. A critical mediator of this mechanism was carboxy terminus of Hsp70-interacting protein (CHIP), a tau ubiquitin ligase. Cochaperones were also involved in Hsp90-mediated removal of p-tau, while those of the mature Hsp90 refolding complex prevented this effect. This is the first demonstration to our knowledge that blockade of the refolding pathway promotes p-tau turnover through degradation. We also show that peripheral administration of a novel Hsp90 inhibitor promoted selective decreases in p-tau species in a mouse model of tauopathy, further suggesting a central role for the Hsp90 complex in the pathogenesis of tauopathies. When taken in the context of known high-affinity Hsp90 complexes in affected regions of the AD brain, these data implicate a central role for Hsp90 in the development of AD and other tauopathies and may provide a rationale for the development of novel Hsp90-based therapeutic strategies.

https://dm5migu4zj3pb.cloudfront.net/manuscripts/29000/29715/JCI0729715.v1.pdf

The high-affinity HSP90-CHIP complex recognizes and selectively degrades phosphorylated tau client proteins

The molecular chaperone HSP90 has emerged as an exciting target for cancer treatment. We review the potential advantages of HSP90 inhibitors, particularly the simultaneous combinatorial depletion of multiple oncogenic "client" proteins, leading to blockade of many cancer-causing pathways and the antagonism of all of the hallmark pathological traits of malignancy. Cancer selectivity is achieved by exploiting cancer "dependencies," including oncogene addiction and the stressed state of malignant cells. The multiple downstream effects of HSP90 inhibitors should make the development of resistance more difficult than with agents having more restricted effects. We review the various classes of HSP90 inhibitor that have been developed, including the natural products geldanamycin and radicicol and also the purine scaffold and pyrazole/isoxazole class of synthetic small molecule inhibitors. A first-in-class HSP90 drug, the geldanamycin analog 17-AAG, has provided proof of concept for HSP90 inhibition in patients at well tolerated doses and therapeutic activity has been seen. Other inhibitors show promise in preclinical and clinical development. Opportunities and challenges for HSP90 inhibitors are discussed, including use in combination with other agents. Most of the current HSP90 inhibitors act by blocking the essential nucleotide binding and ATPase activity required for chaperone function. Potential new approaches are discussed, for example, interference with cochaperone binding and function in the superchaperone complex. Biomarkers for use with HSP90 inhibitors are described.

Drugging the cancer chaperone HSP90: combinatorial therapeutic exploitation of oncogene addiction and tumor stress.

We describe the biological properties of NVP-AUY922, a novel resorcinylic isoxazole amide heat shock protein 90 (HSP90) inhibitor. NVP-AUY922 potently inhibits HSP90 (K(d) = 1.7 nmol/L) and proliferation of human tumor cells with GI(50) values of approximately 2 to 40 nmol/L, inducing G(1)-G(2) arrest and apoptosis. Activity is independent of NQO1/DT-diaphorase, maintained in drug-resistant cells and under hypoxic conditions. The molecular signature of HSP90 inhibition, comprising induced HSP72 and depleted client proteins, was readily demonstrable. NVP-AUY922 was glucuronidated less than previously described isoxazoles, yielding higher drug levels in human cancer cells and xenografts. Daily dosing of NVP-AUY922 (50 mg/kg i.p. or i.v.) to athymic mice generated peak tumor levels at least 100-fold above cellular GI(50). This produced statistically significant growth inhibition and/or regressions in human tumor xenografts with diverse oncogenic profiles: BT474 breast tumor treated/control, 21%; A2780 ovarian, 11%; U87MG glioblastoma, 7%; PC3 prostate, 37%; and WM266.4 melanoma, 31%. Therapeutic effects were concordant with changes in pharmacodynamic markers, including induction of HSP72 and depletion of ERBB2, CRAF, cyclin-dependent kinase 4, phospho-AKT/total AKT, and hypoxia-inducible factor-1alpha, determined by Western blot, electrochemiluminescent immunoassay, or immunohistochemistry. NVP-AUY922 also significantly inhibited tumor cell chemotaxis/invasion in vitro, WM266.4 melanoma lung metastases, and lymphatic metastases from orthotopically implanted PC3LN3 prostate carcinoma. NVP-AUY922 inhibited proliferation, chemomigration, and tubular differentiation of human endothelial cells and antiangiogenic activity was reflected in reduced microvessel density in tumor xenografts. Collectively, the data show that NVP-AUY922 is a potent, novel inhibitor of HSP90, acting via several processes (cytostasis, apoptosis, invasion, and angiogenesis) to inhibit tumor growth and metastasis. NVP-AUY922 has entered phase I clinical trials

https://cancerres.aacrjournals.org/content/canres/68/8/2850.full.pdf

NVP-AUY922: A Novel Heat Shock Protein 90 Inhibitor Active against Xenograft Tumor Growth, Angiogenesis, and Metastasis

Inhibitors of the Hsp90 molecular chaperone are showing considerable promise as potential chemotherapeutic agents for cancer. Here, we describe the structure-based design, synthesis, structure-activity relationships and pharmacokinetics of potent small-molecule inhibitors of Hsp90 based on the 4,5-diarylisoxazole scaffold. Analogues from this series have high affinity for Hsp90, as measured in a fluorescence polarization (FP) competitive binding assay, and are active in cancer cell lines where they inhibit proliferation and exhibit a characteristic profile of depletion of oncogenic proteins and concomitant elevation of Hsp72. Compound 40f (VER-52296/NVP-AUY922) is potent in the Hsp90 FP binding assay (IC50 = 21 nM) and inhibits proliferation of various human cancer cell lines in vitro, with GI(50) averaging 9 nM. Compound 40f is retained in tumors in vivo when administered i.p., as evaluated by cassette dosing in tumor-bearing mice. In a human colon cancer xenograft model, 40f inhibits tumor growth by similar to 50%.

4,5-Diarylisoxazole Hsp90 Chaperone Inhibitors: Potential Therapeutic Agents for the Treatment of Cancer

We report on the discovery of benzo- and pyridino- thiazolothiopurines as potent heat shock protein 90 inhibitors. The benzothiazole moiety is exceptionally sensitive to substitutions on the aromatic ring with a 7'-substituent essential for activity. Some of these compounds exhibit low nanomolar inhibition activity in a Her-2 degradation assay (28-150 nM), good aqueous solubility, and oral bioavailability profiles in mice. In vivo efficacy experiments demonstrate that compounds of this class inhibit tumor growth in an N87 human colon cancer xenograft model via oral administration as shown with compound 37 (8-(7-chlorobenzothiazol-2-ylsulfanyl)-9-(2-cyclopropylamino-ethyl)-9H- purin-6-ylamine).

7'-substituted benzothiazolothio- and pyridinothiazolothio-purines as potent heat shock protein 90 inhibitors.

Novel purine compounds and tautomers and pharmaceutically acceptable salts thereof are described, as are pharmaceutical compositions comprising the same, complexes comprising the same, e.g., HSP90 complexes, and methods of using the same. Methods of using the novel purine compounds of the invention,and tautomers and pharmaceutically acceptable salts thereof, include their use in inhibiting heat shock protein 90's (HSP90*s) to thereby treat or prevent HSP90-dependent diseases, e.g., proliferative disorders such as breast cancer.

Orally active purine-based inhibitors of heat shock protein 90

Novel purine compounds and tautomers and pharmaceutically acceptable salts thereof are described, as are pharmaceutical compositions comprising the same, complexes comprising the same, e.g., HSP90 complexes, and methods of using the same.

Purine analogs having HSP90-inhibiting activity

The selective heat shock protein 90 (HSP90) inhibitor 17-allyamino-17-demethoxygeldanamycin (17-AAG) is currently in phase I/II clinical studies at numerous institutions. Heretofore, the biomarkers to detect 17-AAG bioactivity (Hsp70, Raf-1, and cyclin-dependent kinase 4) had to be analyzed by Western blot of cellular samples, either from tumor biopsies or peripheral blood leukocytes, a method that is both laborious and invasive. We have identified two new biomarkers [insulin-like growth factor binding protein-2 (IGFBP2) and HER-2 extracellular domain] that can be readily detected in patient sera by ELISA. Both secreted proteins are derived from or regulated by Hsp90 client proteins, raising hopes that they might be sensitive serum markers of HSP90 inhibitor activity. Several structurally unrelated HSP90 inhibitors dose-dependently decreased secretion of both IGFBP-2 and HER-2 extracellular domain into culture medium, and both proteins were more sensitive to HSP90 inhibitors than previously identified biomarkers. In sera from BT474 tumor-bearing mice, both IGFBP-2 and HER-2 extracellular domain were down-regulated by 17-AAG in a time-dependent and dose-dependent manner, coincident with the degradation of HER-2 and attenuation of AKT activity in the tumors. Furthermore, IGFBP-2 levels at the end of treatment correlated with residual tumor load, suggesting that IGFBP-2 might serve as an early indicator of therapeutic response. In addition, we also found that both IGFBP-2 and HER-2 extracellular domain levels are elevated in patient sera from several cancer types, suggesting that these novel secreted biomarkers could be valuable pharmacodynamic tools in clinical trials of HSP90 inhibitors. [Mol Cancer Ther 2006;5(5):1256–64]

https://mct.aacrjournals.org/content/molcanther/5/5/1256.full.pdf

Identification of new biomarkers for clinical trials of Hsp90 inhibitors

Ansamycins and methods of preparing and using the same are described. At least some of these ansamycins exhibit one or more of improved aqueous formulation ability, chemical stability, and bioavailability. Some of the derivatives described are dimers. These and others described can include one or more solubilizing groups that have expected merit in rendering the overall compounds useful as drugs and prodrugs.

Ansamycins having improved pharmacological and biological properties

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