1-Aminomethyl SAR in a novel series of flavagline-inspired eIF4A inhibitors: Effects of amine substitution on cell potency and in vitro PK properties.

Flavaglines such as silvestrol (1) and rocaglamide (2) constitute an interesting class of natural products with promising anticancer activities. Their mode of action is based on inhibition of eukaryotic initiation factor 4A (eIF4A) dependent translation through formation of a stable ternary complex with eIF4A and mRNA, thus blocking ribosome scanning. Herein we describe initial SAR studies in a novel series of 1-aminomethyl substituted flavagline-inspired eIF4A inhibitors. We discovered that a variety of N-substitutions at the 1-aminomethyl group are tolerated, making this position pertinent for property and ADME profile tuning. The findings presented herein are relevant to future drug design efforts towards novel eIF4A inhibitors with drug-like properties.

Targeting Oncogene mRNA Translation in B-Cell Malignancies with eFT226, a Potent and Selective Inhibitor of eIF4A.

The PI3K/AKT/mTOR pathway is often activated in lymphoma through alterations in PI3K, PTEN, and B-cell receptor signaling, leading to dysregulation of eIF4A (through its regulators, eIF4B, eIF4G, and PDCD4) and the eIF4F complex. Activation of eIF4F has a direct role in tumorigenesis due to increased synthesis of oncogenes that are dependent on enhanced eIF4A RNA helicase activity for translation. eFT226, which inhibits translation of specific mRNAs by promoting eIF4A1 binding to 5'-untranslated regions (UTR) containing polypurine and/or G-quadruplex recognition motifs, shows potent antiproliferative activity and significant in vivo efficacy against a panel of diffuse large B-cell lymphoma (DLBCL), and Burkitt lymphoma models with ≤1 mg/kg/week intravenous administration. Evaluation of predictive markers of sensitivity or resistance has shown that activation of eIF4A, mediated by mTOR signaling, correlated with eFT226 sensitivity in in vivo xenograft models. Mutation of PTEN is associated with reduced apoptosis in vitro and diminished efficacy in vivo in response to eFT226. In models evaluated with PTEN loss, AKT was stimulated without a corresponding increase in mTOR activation. AKT activation leads to the degradation of PDCD4, which can alter eIF4F complex formation. The association of eFT226 activity with PTEN/PI3K/mTOR pathway regulation of mRNA translation provides a means to identify patient subsets during clinical development.

Strategic Diastereoselective C1 Functionalization in the Aza-Rocaglamide Scaffold toward Natural Product-Inspired eIF4A Inhibitors.

Rocaglates, rocaglamides, and related flavagline natural products exert their remarkable anticancer activity through inhibition of eukaryotic initiation factor 4A (eIF4A) but generally display suboptimal drug-like properties. In our efforts to identify potent drug-like eIF4A inhibitors, we developed synthetic strategies for diastereoselectively functionalizing the C1 position of aza-rocaglamide scaffolds (cf. 14 and 18), which proceed via retention or inversion of configuration at C1 depending on the C2 substituent (cf. 15 and 21) and ultimately enabled the discovery of novel and potent eIF4A inhibitors such as 25.

Design of Development Candidate eFT226, a First in Class Inhibitor of Eukaryotic Initiation Factor 4A RNA Helicase.

Dysregulation of protein translation is a key driver for the pathogenesis of many cancers. Eukaryotic initiation factor 4A (eIF4A), an ATP-dependent DEAD-box RNA helicase, is a critical component of the eIF4F complex, which regulates cap-dependent protein synthesis. The flavagline class of natural products (i.e., rocaglamide A) has been shown to inhibit protein synthesis by stabilizing a translation-incompetent complex for select messenger RNAs (mRNAs) with eIF4A. Despite showing promising anticancer phenotypes, the development of flavagline derivatives as therapeutic agents has been hampered because of poor drug-like properties as well as synthetic complexity. A focused effort was undertaken utilizing a ligand-based design strategy to identify a chemotype with optimized physicochemical properties. Also, detailed mechanistic studies were undertaken to further elucidate mRNA sequence selectivity, key regulated target genes, and the associated antitumor phenotype. This work led to the design of eFT226 (Zotatifin), a compound with excellent physicochemical properties and significant antitumor activity that supports clinical development.

Structure-based Design of Pyridone-Aminal eFT508 Targeting Dysregulated Translation by Selective Mitogen-activated Protein Kinase Interacting Kinases 1 and 2 (MNK1/2) Inhibition.

Dysregulated translation of mRNA plays a major role in tumorigenesis. Mitogen-activated protein kinase interacting kinases (MNK)1/2 are key regulators of mRNA translation integrating signals from oncogenic and immune signaling pathways through phosphorylation of eIF4E and other mRNA binding proteins. Modulation of these key effector proteins regulates mRNA, which controls tumor/stromal cell signaling. Compound 23 (eFT508), an exquisitely selective, potent dual MNK1/2 inhibitor, was designed to assess the potential for control of oncogene signaling at the level of mRNA translation. The crystal structure-guided design leverages stereoelectronic interactions unique to MNK culminating in a novel pyridone-aminal structure described for the first time in the kinase literature. Compound 23 has potent in vivo antitumor activity in models of diffuse large cell B-cell lymphoma and solid tumors, suggesting that controlling dysregulated translation has real therapeutic potential. Compound 23 is currently being evaluated in Phase 2 clinical trials in solid tumors and lymphoma. Compound 23 is the first highly selective dual MNK inhibitor targeting dysregulated translation being assessed clinically.

Identification of novel HSP90α/ß isoform selective inhibitors using structure-based drug design. demonstration of potential utility in treating CNS disorders such as Huntington's disease.

A structure-based drug design strategy was used to optimize a novel benzolactam series of HSP90α/ß inhibitors to achieve >1000-fold selectivity versus the HSP90 endoplasmic reticulum and mitochondrial isoforms (GRP94 and TRAP1, respectively). Selective HSP90α/ß inhibitors were found to be equipotent to pan-HSP90 inhibitors in promoting the clearance of mutant huntingtin protein (mHtt) in vitro, however with less cellular toxicity. Improved tolerability profiles may enable the use of HSP90α/ß selective inhibitors in treating chronic neurodegenerative indications such as Huntington's disease (HD). A potent, selective, orally available HSP90α/ß inhibitor was identified (compound 31) that crosses the blood-brain barrier. Compound 31 demonstrated proof of concept by successfully reducing brain Htt levels following oral dosing in rats.

Correlation between chemotype-dependent binding conformations of HSP90α/ß and isoform selectivity-Implications for the structure-based design of HSP90α/ß selective inhibitors for treating neurodegenerative diseases.

HSP90 continues to be a target of interest for neurodegeneration indications. Selective knockdown of the HSP90 cytosolic isoforms α and ß is sufficient to reduce mutant huntingtin protein levels in vitro. Chemotype-dependent binding conformations of HSP90α/ß appear to strongly influence isoform selectivity. The rational design of HSP90α/ß inhibitors selective versus the mitochondrial (TRAP1) and endoplasmic reticulum (GRP94) isoforms offers a potential mitigating strategy for mechanism-based toxicities. Better tolerated HSP90 inhibitors would be attractive for targeting chronic neurodegenerative diseases such as Huntington's disease.

Optimization of alpha-ketoamide based p38 inhibitors through modifications to the region that binds to the allosteric site.

We have optimized a novel series of potent p38 MAP kinase inhibitors based on an alpha-ketoamide scaffold through structure based design that due to their extended molecular architecture bind, in addition to the ATP site, to an allosteric pocket. In vitro ADME, in vivo PK and efficacy studies show these compounds to have drug-like characteristics and have resulted in the nomination of a development candidate which is currently in phase II clinical trials for the oral treatment of inflammatory conditions.

The design and synthesis of novel alpha-ketoamide-based p38 MAP kinase inhibitors.

We have identified a novel series of potent p38 MAP kinase inhibitors through structure-based design which due to their extended molecular architecture bind, in addition to the ATP site, to an allosteric pocket. In vitro ADME and in vivo PK studies show these compounds to have drug-like characteristics which could result in the development of an oral treatment for inflammatory conditions.

Terphenyl-Based Bak BH3 alpha-helical proteomimetics as low-molecular-weight antagonists of Bcl-xL.

We describe a general method for the mimicry of one face of an alpha-helix based on a terphenyl scaffold that spatially projects functionality in a manner similar to that of two turns of an alpha-helix. The synthetic scaffold reduces the flexibility and molecular weight of the mimicked protein secondary structure. We have applied this design to the development of antagonists of the alpha-helix binding protein Bcl-x(L). Using a sequential synthetic strategy, we have prepared a library of terphenyl derivatives to mimic the helical region of the Bak BH3 domain that binds Bcl-x(L). Fluorescence polarization assays were carried out to evaluate the ability of terphenyl derivatives to displace the Bcl-x(L)-bound Bak peptide. Terphenyl 14 exhibited good in vitro affinity with a K(i) value of 0.114 muM. These terphenyl derivatives were more selective at disrupting the Bcl-x(L)/Bak over the HDM2/p53 interaction, which involves binding of the N-terminal alpha-helix of p53 to HDM2. Structural studies using NMR spectroscopy and computer-aided docking simulations suggested that the helix binding area on the surface of Bcl-x(L) is the target for the synthetic ligands. Treatment of human embryonic kidney 293 (HEK293) cells with terphenyl derivatives resulted in the disruption of the binding of Bcl-x(L) to Bax in intact cells.

Protein recognition using synthetic surface-targeted agents.

The design of synthetic agents to disrupt protein-protein interactions has received relatively little attention in recent years. In this review we describe strategies for targeting different types of protein surfaces using mimetics of protein secondary or tertiary structure. In this way strong and selective binding to a protein surface has be achieved and disruption of clinically important protein-protein interactions has been demonstrated in models of human disease.

XTT formazan widely used to detect cell viability inhibits HIV type 1 infection in vitro by targeting gp41.

XTT can be metabolically reduced by mitochondrial dehydrogenase in viable cells to a water-soluble formazan product. Thus XTT has been widely used to evaluate cell viability and to screen anti-HIV agents and the cytotoxicity of these agents. The present studies demonstrated that XTT formazan derived from XTT in cell culture significantly inhibits the fusion of HIV-1-infected cells with uninfected cells. Synthetic XTT formazan effectively inhibited the replication of laboratory-adapted and primary HIV-1 isolates and cell-to-cell fusion with low cytotoxicity. It blocks the six-helix bundle formation between peptides derived from the N- and C-terminal heptad repeat regions of the gp41 ectodomain (designated N- and C-peptides, respectively). Analysis by a computer-aided docking program indicates that XTT formazan may bind to the highly conserved hydrophobic pocket on the surface of the central trimeric coiled coil of gp41. These results suggest that XTT formazan inhibits HIV-1 entry by targeting the alpha-helical coiled-coil domain of gp41. This small molecular nonpeptide antiviral compound can be used as a lead for designing more effective HIV-1 entry inhibitors targeting the fusion stage of HIV-1 infection. But because XTT formazan itself has anti-HIV-1 activity, caution should be exercised when XTT is used to evaluate HIV-1 infectivity.

Development of a potent Bcl-x(L) antagonist based on alpha-helix mimicry.

The rational design of low-molecular weight ligands that disrupt protein-protein interactions is still a challenging goal in medicinal chemistry. Our approach to this problem involves the design of molecular scaffolds that mimic the surface functionality projected along one face of an alpha-helix. Using a terphenyl scaffold, which in a staggered conformation closely reproduces the projection of functionality on the surface of an alpha-helix, we designed mimics of the pro-apoptotic alpha-helical Bak-peptide as inhibitors of the Bak/Bcl-xL interaction. This led to the development of a potent Bcl-xL antagonist (KD = 114 nM), whose binding affinity for Bcl-xL was assessed by a fluorescence polarization assay. To determine the binding site of the developed inhibitor we used docking studies and an HSQC-NMR experiment with 15N-labeled Bcl-xL protein. These studies suggest that the inhibitor is binding in the same hydrophobic cleft as the Bak- and Bad-peptides.