The Pursuit of Unshocking Hsp90 Inhibitors: Development of Gedunin and Cruentaren A as Chemical Leads

Abstract: The 90 kDa heat shock protein (Hsp90) is a molecular chaperone that is critical cellular survival and growth under both typical and stressful conditions. Hsp90 is responsible for the maturation and stability of more than 200 client proteins involved in a diverse assortment of cellular processes. Disruption of Hsp90's chaperoning activity causes client protein degradation and ultimately leads to cytostasis and/or apoptosis. While this phenomenon is observed in normal cells, the effects of Hsp90 inhibition are more pronounced in oncogenic cell lines as a result of higher expression levels and increased cellular dependence on Hsp90 activity. As such, targeting Hsp90 inhibition with small molecules has emerged as a powerful strategy for the development of anticancer chemotherapeutics. Several small molecule Hsp90 inhibitors are currently under evaluation in FDA sanctioned clinical trials for the treatment of various cancers, however, some undesired side effects have been observed. All of the Hsp90 targeting small molecules involved in these trials are ATP competitive inhibitors that bind at the N-terminal ATP binding domain. Inhibitors of this class elicit non-specific client protein degradation and cause the induction of the heat shock response that results in an upregulation of Hsp90 and other Hsp expression levels following incubation within cells. As a result, untoward toxicological effects are observed and the determination of appropriate dosing schedules to mitigate the heat shock response is highly complicated. A new strategy for Hsp90 inhibition capable of targeting specific client proteins for therapeutic efficacy that avoids heat shock response induction is desired. Presented herein are preliminary studies that investigate potential strategies to target the selective degradation of Hsp90 client proteins while avoiding the heat shock response. Specifically, small molecule natural products that elicit Hsp90 co-chaperone disruption are considered and the chemical and biological results are discussed. These studies provide the first steps toward developing a second generation of Hsp90 inhibitors that circumvent the detrimental effects observed for clinically evaluated inhibitors

Synthesis of Cruentaren A

Cruentaren A, an antifungal benzolactone produced by the myxobacterium Byssovorax cruenta, is highly cytotoxic against various human cancer cell lines and a highly selective inhibitor of mitochondrial F-ATPase. A convergent and efficient synthesis of cruentaren A is reported, based upon a diastereoselective alkylation, a series of stereoselective aldol reactions utilizing Myers’ pseudoephedrine propionamide, an acyl bromide–mediated esterification and a ring-closing metathesis (RCM) as the key steps. The RCM reaction was applied for the first time towards the total synthesis of cruentaren A, which led to a convergent and efficient synthesis of the natural product

A Systematic Protocol for the Characterization of Hsp90 Modulators

This is the author's accepted manuscript. Made available by the permission of the publisher.Several Hsp90 modulators have been identified including the N-terminal ligand geldanamycin (GDA), the C-terminal ligand novobiocin (NB), and the co-chaperone disruptor celastrol. Other Hsp90 modulators elicit a mechanism of action that remains unknown. For example, the natural product gedunin and the synthetic anti-spermatogenic agent H2-gamendazole, recently identified Hsp90 modulators, manifest biological activity through undefined mechanisms. Herein, we report a series of biochemical techniques used to classify such modulators into identifiable categories. Such studies provided evidence that gedunin and H2-gamendazole both modulate Hsp90 via a mechanism similar to celastrol, and unlike NB or GDA

Engineering an Antibiotic to Fight Cancer: Optimization of the Novobiocin Scaffold to Produce Anti-Proliferative Agents

Development of the DNA gyrase inhibitor, novobiocin, into a selective Hsp90 inhibitor was accomplished through structural modifications to the amide side chain, coumarin ring, and sugar moiety. These species exhibit ~700-fold improved anti-proliferative activity versus the natural product as evaluated by cellular efficacies against breast, colon, prostate, lung, and other cancer cell lines. Utilization of structure–activity relationships established for three novobiocin synthons produced optimized scaffolds, which manifest mid-nanomolar activity against a panel of cancer cell lines and serve as lead compounds that manifest their activities through Hsp90 inhibition

First trimester elevation in circulating endothelin-1 and arterial stiffness are predictive of late pregnancy preeclampsia

Preeclampsia (PE) is characterized by late pregnancy hypertension and proteinuria. PE causes significant morbidity for the maternal-fetal unit. Circulating endothelin-1 (ET-1), a potent vasoconstrictor, is elevated at the time of diagnosis of human PE. In addition, women with PE demonstrate arterial stiffness as early as the end of the first trimester. However, it is unknown if arterial stiffness is associated with a first trimester elevation in ET-1 and post-delivery placental ET-1. We hypothesized that 1) first trimester plasma ET-1 is elevated and is associated with arterial stiffness in women who develop PE; 2) first trimester ET-1 is predictive of PE; and 3) placental ET-1 is increased in PE. To address these questions, we performed a nested case-control study in women at risk for P

High-Redshift SDSS Quasars with Weak Emission Lines

We identify a sample of 74 high-redshift quasars (z>3) with weak emission lines from the Fifth Data Release of the Sloan Digital Sky Survey and present infrared, optical, and radio observations of a subsample of four objects at z>4. These weak emission-line quasars (WLQs) constitute a prominent tail of the Lya+NV equivalent width distribution, and we compare them to quasars with more typical emission-line properties and to low-redshift active galactic nuclei with weak/absent emission lines, namely BL Lac objects. We find that WLQs exhibit hot (T~1000 K) thermal dust emission and have rest-frame 0.1-5 micron spectral energy distributions that are quite similar to those of normal quasars. The variability, polarization, and radio properties of WLQs are also different from those of BL Lacs, making continuum boosting by a relativistic jet an unlikely physical interpretation. The most probable scenario for WLQs involves broad-line region properties that are physically distinct from those of normal quasars.Comment: Updated to match version published in ApJ. 20 pages, 12 figure

Measurement of the Branching Fraction for B- --> D0 K*-

We present a measurement of the branching fraction for the decay B- --> D0 K*- using a sample of approximately 86 million BBbar pairs collected by the BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the K*- through its decay to K0S pi-. We measure the branching fraction to be B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid Communications

Study of e+e- --> pi+ pi- pi0 process using initial state radiation with BABAR

The process e+e- --> pi+ pi- pi0 gamma has been studied at a center-of-mass energy near the Y(4S) resonance using a 89.3 fb-1 data sample collected with the BaBar detector at the PEP-II collider. From the measured 3pi mass spectrum we have obtained the products of branching fractions for the omega and phi mesons, B(omega --> e+e-)B(omega --> 3pi)=(6.70 +/- 0.06 +/- 0.27)10-5 and B(phi --> e+e-)B(phi --> 3pi)=(4.30 +/- 0.08 +/- 0.21)10-5, and evaluated the e+e- --> pi+ pi- pi0 cross section for the e+e- center-of-mass energy range 1.05 to 3.00 GeV. About 900 e+e- --> J/psi gamma --> pi+ pi- pi0 gamma events have been selected and the branching fraction B(J/psi --> pi+ pi- pi0)=(2.18 +/- 0.19)% has been measured.Comment: 21 pages, 37 postscript figues, submitted to Phys. Rev.

Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions

The weak nucleon axial-vector form factor for quasi-elastic interactions is determined using neutrino interaction data from the K2K Scintillating Fiber detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of which half are charged-current quasi-elastic interactions nu-mu n to mu- p occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for oxygen and assume the form factor is approximately a dipole with one parameter, the axial vector mass M_A, and fit to the shape of the distribution of the square of the momentum transfer from the nucleon to the nucleus. Our best fit result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated vector form factors from recent electron scattering experiments and a discussion of the effects of the nucleon momentum on the shape of the fitted distributions.Comment: 14 pages, 10 figures, 6 table