CB-6644 Is a Selective Inhibitor of the RUVBL1/2 Complex with Anticancer Activity.

RUVBL1 and RUVBL2 are ATPases associated with diverse cellular activities (AAAs) that form a complex involved in a variety of cellular processes, including chromatin remodeling and regulation of gene expression. RUVBLs have a strong link to oncogenesis, where overexpression is correlated with tumor growth and poor prognosis in several cancer types. CB-6644, an allosteric small-molecule inhibitor of the ATPase activity of the RUVBL1/2 complex, interacts specifically with RUVBL1/2 in cancer cells, leading to cell death. Importantly, drug-acquired-resistant cell clones have amino acid mutations in either RUVBL1 or RUVBL2, suggesting that cell killing is an on-target consequence of RUVBL1/2 engagement. In xenograft models of acute myeloid leukemia and multiple myeloma, CB-6644 significantly reduced tumor growth without obvious toxicity. This work demonstrates the therapeutic potential of targeting RUVBLs in the treatment of cancer and establishes a chemical entity for probing the many facets of RUVBL biology.

Design, Synthesis, Molecular Modeling, and Biological Evaluation of Novel Amine-based Histone Deacetylase Inhibitors.

Histone deacetylases (HDACs) are promising drug targets for a variety of therapeutic applications. Herein we describe the design, synthesis, biological evaluation in cellular models of cancer, and preliminary drug metabolism and pharmacokinetic studies (DMPK) of a series of secondary and tertiary N-substituted 7-aminoheptanohydroxamic acid-based HDAC inhibitors. Introduction of an amino group with one or two surface binding groups (SBGs) yielded a successful strategy to develop novel and potent HDAC inhibitors. The secondary amines were found to be generally more potent than the corresponding tertiary amines. Docking studies suggested that the SBGs of tertiary amines cannot be favorably accommodated at the gorge region of the binding site. The secondary amines with naphthalen-2-ylmethyl, 5-phenylthiophen-2-ylmethyl, and 1H-indol-2-ylmethyl (2 j) substituents exhibited the highest potency against class I HDACs: HDAC1 IC50 39-61 nm, HDAC2 IC50 260-690 nm, HDAC3 IC50 25-68 nm, and HDAC8 IC50 320-620 nm. The cytotoxicity of a representative set of secondary and tertiary N-substituted 7-aminoheptanoic acid hydroxyamide-based inhibitors against HT-29, SH-SY5Y, and MCF-7 cancer cells correlated with their inhibition of HDAC1, 2, and 3 and was found to be similar to or better than that of suberoylanilide hydroxamic acid (SAHA). Compounds in this series increased the acetylation of histones H3 and H4 in a time-dependent manner. DMPK studies indicated that secondary amine 2 j is metabolically stable and has plasma and brain concentrations >23- and >1.6-fold higher than the IC50 value for class I HDACs, respectively. Overall, the secondary and tertiary N-substituted 7-aminoheptanoic acid hydroxyamide-based inhibitors exhibit excellent lead- and drug-like properties and therapeutic capacity for cancer applications.

Discovery of a First-in-Class, Potent, Selective, and Orally Bioavailable Inhibitor of the p97 AAA ATPase (CB-5083).

The AAA-ATPase p97 plays vital roles in mechanisms of protein homeostasis, including ubiquitin-proteasome system (UPS) mediated protein degradation, endoplasmic reticulum-associated degradation (ERAD), and autophagy. Herein we describe our lead optimization efforts focused on in vitro potency, ADME, and pharmaceutical properties that led to the discovery of a potent, ATP-competitive, D2-selective, and orally bioavailable p97 inhibitor 71, CB-5083. Treatment of tumor cells with 71 leads to significant accumulation of markers associated with inhibition of UPS and ERAD functions, which induces irresolvable proteotoxic stress and cell death. In tumor bearing mice, oral administration of 71 causes rapid accumulation of markers of the unfolded protein response (UPR) and subsequently induces apoptosis leading to sustained antitumor activity in in vivo xenograft models of both solid and hematological tumors. 71 has been taken into phase 1 clinical trials in patients with multiple myeloma and solid tumors.

Targeting the AAA ATPase p97 as an Approach to Treat Cancer through Disruption of Protein Homeostasis.

p97 is a AAA-ATPase with multiple cellular functions, one of which is critical regulation of protein homeostasis pathways. We describe the characterization of CB-5083, a potent, selective, and orally bioavailable inhibitor of p97. Treatment of tumor cells with CB-5083 leads to accumulation of poly-ubiquitinated proteins, retention of endoplasmic reticulum-associated degradation (ERAD) substrates, and generation of irresolvable proteotoxic stress, leading to activation of the apoptotic arm of the unfolded protein response. In xenograft models, CB-5083 causes modulation of key p97-related pathways, induces apoptosis, and has antitumor activity in a broad range of both hematological and solid tumor models. Molecular determinants of CB-5083 activity include expression of genes in the ERAD pathway, providing a potential strategy for patient selection.

Solubilization of therapeutic agents in micellar nanomedicines.

We use atomistic molecular dynamics simulations to reveal the binding mechanisms of therapeutic agents in PEG-ylated micellar nanocarriers (SSM). In our experiments, SSM in buffer solutions can solubilize either ≈11 small bexarotene molecules or ≈6 (2 in low ionic strength buffer) human vasoactive intestinal peptide (VIP) molecules. Free energy calculations reveal that molecules of the poorly water-soluble drug bexarotene can reside at the micellar ionic interface of the PEG corona, with their polar ends pointing out. Alternatively, they can reside in the alkane core center, where several bexarotene molecules can self-stabilize by forming a cluster held together by a network of hydrogen bonds. We also show that highly charged molecules, such as VIP, can be stabilized at the SSM ionic interface by Coulombic coupling between their positively charged residues and the negatively charged phosphate headgroups of the lipids. The obtained results illustrate that atomistic simulations can reveal drug solubilization character in nanocarriers and be used in efficient optimization of novel nanomedicines.

Photoreactive "nanorulers" detect a novel conformation of full length HDAC3-SMRT complex in solution.

Histone deacetylase 3 (HDAC3) is a promising epigenetic drug target for multiple therapeutic applications. Direct interaction between the Deacetylase Activating Domain of the silencing mediator for retinoid or thyroid-hormone receptors (SMRT-DAD) is required for activation of enzymatic activity of HDAC3. The structure of this complex and the nature of interactions with HDAC inhibitors in solution are unknown. Using novel photoreactive HDAC probes, "nanorulers", we determined the distance between the catalytic site of the full-length HDAC3 and SMRT-DAD in solution at physiologically relevant conditions and found it to be substantially different from that predicted by the X-ray model with a Δ379-428 aa truncated HDAC3. Further experiments indicated that in solution this distance might change in response to chemical stimuli, while the enzymatic activity remained unaffected. These observations were further validated by Saturation Transfer Difference (STD) NMR experiments. We propose that the observed changes in the distance are an important part of the histone code that remains to be explored. Mapping direct interactions and distances between macromolecules with such "nanorulers" as a function of cellular events facilitates better understanding of basic biology and ways for its manipulation in a cell- and tissue-specific manner.

Novel histone deacetylase 8 ligands without a zinc chelating group: exploring an 'upside-down' binding pose.

A novel series of HDAC8 inhibitors without a zinc-chelating hydroxamic acid moiety is reported. Photoaffinity labeling and molecular modeling studies suggest that these ligands are likely to bind in an 'upside-down' fashion in a secondary binding site proximal to the main catalytic site. The most potent ligand in the series exhibits an IC(50) of 28 µM for HDAC8 and is found to inhibit the deacetylation of H4 but not α-tubulin in SH-SY5Y cell line.

Design, synthesis, modeling, biological evaluation and photoaffinity labeling studies of novel series of photoreactive benzamide probes for histone deacetylase 2.

The design, modeling, synthesis, biological evaluation of a novel series of photoreactive benzamide probes for class I HDAC isoforms is reported. The probes are potent and selective for HDAC1 and 2 and are efficient in crosslinking to HDAC2 as demonstrated by photolabeling experiments. The probes exhibit a time-dependent inhibition of class I HDACs. The inhibitory activities of the probes were influenced by the positioning of the aryl and alkyl azido groups necessary for photocrosslinking and attachment of the biotin tag. The probes inhibited the deacetylation of H4 in MDA-MB-231 cell line, indicating that they are cell permeable and target the nuclear HDACs.

Structure and dynamics of highly PEG-ylated sterically stabilized micelles in aqueous media.

Molecular assemblies of highly PEG-ylated phospholipids are important in many biomedical applications. We have studied sterically stabilized micelles (SSMs) of self-assembled DSPE­PEG2000 in pure water and isotonic HEPES-buffered saline solution. The observed SSM sizes of 2­15 nm largely depend on the solvent and the lipid concentration used. The critical micelle concentration of DSPE­PEG2000 is 10 times higher in water than in buffer, and the viscosity of the dispersion dramatically increases with the lipid concentration. To explain the experimentally observed results, we performed atomistic molecular dynamics simulations of solvated SSMs. Our modeling revealed that the observed assemblies have very different aggregation numbers (N(agg) ≈ 90 in saline solution and N(agg) < 8 in water) because of very different screening of their charged PO4(­) groups. We also demonstrate that the micelle cores can inflate and their coronas can fluctuate strongly, thus allowing storage and delivery of molecules with different chemistries.