Design, synthesis and antiproliferative activity of raloxifene/histone deacetylase inhibitor hybrids in breast cancer.

Antiestrogen/histone deacetylase inhibitor (HDACi) hybrids were designed by merging structures of raloxifene with suberoylanilide hydroxamic acid, incorporating the HDACi unit into the phenolic ring of the antiestrogen. These hybrids were synthesized with a range of HDACi chain lengths and assessed for bifunctionality. Four hybrids, 21 (YW471), 22 (YW490), 27(YW486), and 28 (YW487) showed good potency both as antiestrogens in a BRET assay and in a fluorometric HDACi assay. The antiproliferative activity of the hybrids was demonstrated in both ER+ MCF7 and ER- MDA-MB-231 breast cancer cell lines.

Bifunctionality and Antitumor Efficacy of ZG-126, a Vitamin D Receptor Agonist/Histone Deacetylase Inhibitor Hybrid Molecule.

Analogues of hormonal vitamin D, 1,25-dihydroxyvitamin D (1,25D), signal through the nuclear vitamin D receptor (VDR). They have potential in combination therapies with other anticancer agents such as histone deacetylase inhibitors (HDACi's). Here, we characterize the ZG series of hybrid compounds that combine HDACi within the backbone of a VDR agonist. All display improved solubility, with ZG-126 being the most robustly bifunctional molecule in multiple cell lines. ZG-126 is well tolerated and strongly induces VDR target gene expression in vivo at therapeutic doses. Its antitumor efficacy is superior to 1,25D and the HDACi SAHA, separately or together, in mouse models of melanoma and triple-negative breast cancer (TNBC). Notably, ZG-126 treatment reduces metastases almost 4-fold in an aggressive TNBC model. ZG-126 also reduces total macrophage infiltration and the proportion of immunosuppressive M2-polarized macrophages in TNBC tumors by 2-fold. ZG-126 thus represents a bifunctional and efficacious anticancer agent with improved physicochemical properties.

Molecular mechanisms of bifunctional vitamin D receptor agonist-histone deacetylase inhibitor hybrid molecules in triple-negative breast cancer.

The active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D), and its analogues signal through the nuclear vitamin D receptor (VDR), a ligand-regulated transcription factor, and have been extensively investigated as anticancer agents. 1,25D and its analogs have potential in combination therapies because they exhibit synergistic activities with other anticancer agents such as histone deacetylase inhibitors (HDACi). We have developed a series of hybrid molecules that combine HDACi within the backbone of a VDR agonist and thus represent fully integrated bifunctional molecules. They exhibit anti-tumor efficacy in reducing tumor growth and metastases in an aggressive model of triple-negative breast cancer. However, their solubility is limited by their hydrophobic diarylpentane cores. Our goals here were two-fold: (1) to improve the solubility of hybrids by introducing nitrogen into diarylpentane cores, and (2) to investigate the molecular mechanisms underlying their anti-tumor efficacy by performing comparative gene expression profiling studies with 1,25D and the potent HDACi suberoylanilide hydroxamic acid (SAHA). We found that substituting aryl with pyrydyl rings did not sacrifice bifunctionality and modestly improved solubility. Notably, one compound, AM-193, displayed enhanced potency as a VDR agonist and in cellular assays of cytotoxicity. RNAseq studies in triple negative breast cancer cells revealed that gene expression profiles of hybrids were very similar to that of 1,25D, as was that observed with 1,25D and SAHA combined. The effects of SAHA alone on gene expression were limited and distinct from those 1,25D or hybrids. The combined results suggest that efficacy of hybrids arises from targeting HDACs that do not have a direct role in gene regulation. Moreover, pathways analysis revealed that hybrids regulate numerous genes controlling immune cell infiltration into tumors and suppress the expression of several secreted molecules that promote breast cancer growth and metastasis.

Dual-function antiandrogen/HDACi hybrids based on enzalutamide and entinostat.

The combination of androgen receptor antagonists with histone deacetylase inhibitors (HDACi) has been shown to be more effective than antiandrogens alone in halting growth of prostate cancer cell lines. Here we have designed, synthesized and assessed a series of antiandrogen/HDACi hybrids by combining structural features of enzalutamide with either SAHA or entinostat. The hybrids are demonstrated to maintain bifunctionality using a fluorometric HDAC assay and a bioluminescence resonance energy transfer (BRET) antiandrogen assay. Antiproliferative assays showed that hybrids bearing o-aminoanilide-based HDACi motifs outperformed hydroxamic acid based HDACi's. The hybrids demonstrated selectivity for epithelial cell lines vs. stromal cell lines, suggesting a potentially useful therapeutic window.

Incorporation of histone deacetylase inhibitory activity into the core of tamoxifen - A new hybrid design paradigm.

Hybrid antiestrogen/histone deacetylase (HDAC) inhibitors were designed by appending zinc binding groups to the 4-hydroxystilbene core of 4-hydroxytamoxifen. The resulting hybrids were fully bifunctional, and displayed high nanomolar to low micromolar IC50 values against both the estrogen receptor α (ERα) and HDACs in vitro and in cell-based assays. The hybrids were antiproliferative against ER+ MCF-7 breast cancer cells, with hybrid 28b possessing an improved activity profile compared to either 4-hydroxytamoxifen or SAHA. Hybrid 28b displayed gene expression patterns that reflected both ERα and HDAC inhibition.

Homozygous Calcium-Sensing Receptor Polymorphism R544Q Presents as Hypocalcemic Hypoparathyroidism.

Context: Autosomal dominant hypocalcemia type 1 (ADH1) is caused by heterozygous activating mutations in the calcium-sensing receptor gene (CASR). Whether polymorphisms that are benign in the heterozygous state pathologically alter receptor function in the homozygous state is unknown. Objective: To identify the genetic defect in an adolescent female with a history of surgery for bilateral cataracts and seizures. The patient has hypocalcemia, hyperphosphatemia, and low serum PTH level. The parents of the proband are healthy. Methods: Mutation testing of PTH, GNA11, GCM2, and CASR was done on leukocyte DNA of the proband. Functional analysis in transfected cells was conducted on the gene variant identified. Public single nucleotide polymorphism (SNP) databases were searched for the presence of the variant allele. Results: No mutations were identified in PTH, GNA11, and GCM2 in the proband. However, a germline homozygous variant (c.1631G>A; p.R544Q) in exon 6 of the CASR was identified. Both parents are heterozygous for the variant. The variant allele frequency was near 0.1% in SNP databases. By in vitro functional analysis, the variant was significantly more potent in stimulating both the Ca2+i and MAPK signaling pathways than wild type when transfected alone (P < 0.05) but not when transfected together with wild type. The overactivity of the mutant CaSR is due to loss of a critical structural cation-π interaction. Conclusions: The patient's hypoparathyroidism is due to homozygosity of a variant in the CASR that normally has weak or no phenotypic expression in heterozygosity. Although rare, this has important implications for genetic counseling and clinical management.

Efficacy of hybrid vitamin D receptor agonist/histone deacetylase inhibitors in vitamin D-resistant triple-negative 4T1 breast cancer.

Hormonal 1,25-dihydroxyvitamin D (1,25D) and its analogues have shown efficacy in some preclinical models of cancer. However, many models are resistant to the antiproliferative effects of 1,25D or its analogues in vitro or in vivo, and such compounds have failed in the clinic as monotherapies because of tumor resistance. Given the observed synergism between 1,25D analogues and histone deacetylase inhibitors (HDACi) in 1,25D-resistant cells, we previously developed a series of hybrid secosteroidal and easily assembled non-secosteroidal analogues that combined agonism for the vitamin D receptor and HDACi in a single backbone. These compounds displayed enhanced efficacy against 1,25D-resistant malignant cells in vitro. Structure/function studies led to synthesis of several non-secosteroidal variants in which HDACi potency was optimized without substantially sacrificing VDR agonism. Here, we present the first studies of efficacy in vivo of two of these compounds, DK-366 and DK-406, in the aggressive mouse 4T1 model of triple-negative breast cancer, a form of the disease for which treatment options are limited. 4T1 cells are resistant in vitro to the cytostatic and cytotoxic effects of 1,25D and the potent HDACi SAHA individually up to concentrations of 1µM and 50µM, respectively, whereas combinations of the two are efficacious. In vitro, DK-366 or -406 induced dose-dependent arrest of cell proliferation and cytotoxicity at 10-20µM. In vivo, the maximum tolerated dose (MTD) of DK-366 and DK-406 were 2.5 and 5.0mg/kg, respectively. Although the compounds induced hypercalcemia at elevated doses, consistent with VDR agonism in vivo, they both reduced tumor burden at doses below their MTD's. Moreover, in a separate experiment, DK-406 at 5mg/kg reduced 4T1 lung metastases by at least 50%. Under the same conditions, 1,25D (0.25µg/kg) and SAHA (25mg/kg) combined had no effect on tumor burden or on lung metastases. These experiments show that hybrid compounds are bioavailable and efficacious against a particularly aggressive model of metastatic breast cancer, providing strong support for the therapeutic potential of the hybrid concept.

Design, synthesis and evaluation of antiestrogen and histone deacetylase inhibitor molecular hybrids.

The combination of antiestrogens and histone deacetylase inhibitors (HDACi) has been found to be antiproliferative in breast cancer models. We designed and synthesized hybrid structures which combined structural features of the pure antiestrogen ICI-164,384 and HDACi's SAHA and entinostat in a single bifunctional molecule. The hybrids retained antiestrogenic and HDACi activity and, in the case of benzamide hybrids, were selective for Class I HDAC3 over Class II HDAC6. The hybrids possessed low micromolar to high nanomolar activity against both ER+ MCF-7 and ER- MDA-MB-231 breast cancer cell models.

Optimization of histone deacetylase inhibitor activity in non-secosteroidal vitamin D-receptor agonist hybrids.

The combination of (1α,25)-dihydroxyvitamin D3 (1,25D) and histone deacetylase inhibitor (HDACi) trichostatin A is highly antiproliferative in numerous cancer cell lines. We have previously prepared novel non-secosteroidal hybrid molecules which simultaneously act as both vitamin D receptor (VDR) agonists and HDACi. These molecules function as cytostatic and cytotoxic agents in 1,25D-resistant SCC4 squamous carcinoma cells. Here we have extended the scope of the hybrids by making several modifications to the diarylpentane core and to the aliphatic spacer unit to develop molecules with increased potency towards HDACs while maintaining VDR agonist activity. Notably, hybrid DK-366 (33a), a direct analog of first-generation hybrids but lacking a methyl group on one aryl ring possesses low micromolar potency for HDAC3 and HDAC6 and is a highly effective antiproliferative agent in SCC4 cells. Chain extended hybrids such as DK-367 (33c) possess even greater HDAC potency and are also highly antiproliferative. These results show that we can optimize HDACi potency in hybrid molecules without sacrificing VDR agonism.

Docking ligands into flexible and solvated macromolecules. 6. Development and application to the docking of HDACs and other zinc metalloenzymes inhibitors.

Metalloenzymes are ubiquitous proteins which feature one or more metal ions either directly involved in the enzymatic activity and/or structural properties (i.e., zinc fingers). Several members of this class take advantage of the Lewis acidic properties of zinc ions to carry out their various catalytic transformations including isomerization or amide cleavage. These enzymes have been validated as drug targets for a number of diseases including cancer; however, despite their pharmaceutical relevance and the availability of crystal structures, structure-based drug design methods have been poorly and indirectly parametrized for these classes of enzymes. More specifically, the metal coordination component and proton transfers of the process of drugs binding to metalloenzymes have been inadequately modeled by current docking programs, if at all. In addition, several known issues, such as coordination geometry, atomic charge variability, and a potential proton transfer from small molecules to a neighboring basic residue, have often been ignored. We report herein the development of specific functions and parameters to account for zinc-drug coordination focusing on the above-listed phenomena and their impact on docking to zinc metalloenzymes. These atom-type-dependent but atomic charge-independent functions implemented into Fitted 3.1 enable the simulation of drug binding to metalloenzymes, considering an acid-base reaction with a neighboring residue when necessary with good accuracy.

Synthetically accessible non-secosteroidal hybrid molecules combining vitamin D receptor agonism and histone deacetylase inhibition.

1,25-Dihydroxyvitamin D(3) (1,25D), the hormonal form of vitamin D, and several analogs have failed as monotherapies for cancer because of poor efficacy or acquired resistance. However, 1,25D analogs are amenable to bifunctionalization. Preclinical studies have revealed combinatorial effects of 1,25D analogs and histone deacetylase inhibitors (HDACi). Secosteroidal hybrid molecules combining vitamin D receptor (VDR) agonism with HDACi displayed enhanced efficacy but are laborious to synthesize. Here, we have developed easily assembled, fully integrated, non-secosteroidal VDR agonist/HDACi hybrids. The most promising are full VDR agonists with ~10-fold lower potency than 1,25D. Structure/function studies revealed that antiproliferative activity against 1,25D-resistant squamous carcinoma cells required VDR agonism and HDACi. Remarkably, modeling and X-ray crystallography reveal non-secosteroidal hybrids bind in the VDR ligand binding domain in the opposite orientation of their secosteroidal counterparts.

Role of SUMOylation in full antiestrogenicity.

The selective estrogen receptor downregulator (SERD) fulvestrant can be used as second-line treatment for patients relapsing after treatment with tamoxifen, a selective estrogen receptor modulator (SERM). Unlike tamoxifen, SERDs are devoid of partial agonist activity. While the full antiestrogenicity of SERDs may result in part from their capacity to downregulate levels of estrogen receptor alpha (ERα) through proteasome-mediated degradation, SERDs are also fully antiestrogenic in the absence of increased receptor turnover in HepG2 cells. Here we report that SERDs induce the rapid and strong SUMOylation of ERα in ERα-positive and -negative cell lines, including HepG2 cells. Four sites of SUMOylation were identified by mass spectrometry analysis. In derivatives of the SERD ICI164,384, SUMOylation was dependent on the length of the side chain and correlated with full antiestrogenicity. Preventing SUMOylation by the overexpression of a SUMO-specific protease (SENP) deSUMOylase partially derepressed transcription in the presence of full antiestrogens in HepG2 cells without a corresponding increase in activity in the presence of agonists or of the SERM tamoxifen. Mutations increasing transcriptional activity in the presence of full antiestrogens reduced SUMOylation levels and suppressed stimulation by SENP1. Our results indicate that ERα SUMOylation contributes to full antiestrogenicity in the absence of accelerated receptor turnover.

An o-aminoanilide analogue of 1α,25-dihydroxyvitamin D(3) functions as a strong vitamin D receptor antagonist.

Vitamin D receptor (VDR) antagonists have therapeutic potential in treatment of allergic conditions and hypercalcemia driven by granulomatous diseases. We have identified an o-aminoanilide analogue of the hormonal form of vitamin D with a dienyl side chain that functions as a strong VDR antagonist. Modeling studies indicate that antagonism arises from side chain rigidity, when compared to a more flexible saturated analogue, which interferes with H12 folding/alignment.

Vitamin D receptor agonist/histone deacetylase inhibitor molecular hybrids.

Incorporation of zinc-binding groups into the side-chain of 1alpha,25-dihydroxyvitamin D(3) (1,25D) fully bifunctional hybrid molecules which act both as vitamin D receptor agonists and histone deacetylase inhibitors. These bifunctional hybrids display in vitro antiproliferative activity against the AT84 squamous carcinoma cell line while lacking the in vivo hypercalcemic effects of 1,25D.

Increased NOD2-mediated recognition of N-glycolyl muramyl dipeptide.

Peptidoglycan-derived muramyl dipeptide (MDP) activates innate immunity via the host sensor NOD2. Although MDP is N-acetylated in most bacteria, mycobacteria and related Actinomycetes convert their MDP to an N-glycolylated form through the action of N-acetyl muramic acid hydroxylase (NamH). We used a combination of bacterial genetics and synthetic chemistry to investigate whether N-glycolylation of MDP alters NOD2-mediated immunity. Upon infecting macrophages with 12 bacteria, tumor necrosis factor (TNF) alpha secretion was NOD2 dependent only with mycobacteria and other Actinomycetes (Nocardia and Rhodococcus). Disruption of namH in Mycobacterium smegmatis obrogated NOD2-mediated TNF secretion, which could be restored upon gene complementation. In mouse macrophages, N-glycolyl MDP was more potent than N-acetyl MDP at activating RIP2, nuclear factor kappaB, c-Jun N-terminal kinase, and proinflammatory cytokine secretion. In mice challenged intraperitoneally with live or killed mycobacteria, NOD2-dependent immune responses depended on the presence of bacterial namH. Finally, N-glycolyl MDP was more efficacious than N-acetyl MDP at inducing ovalbumin-specific T cell immunity in a model of adjuvancy. Our findings indicate that N-glycolyl MDP has a greater NOD2-stimulating activity than N-acetyl MDP, consistent with the historical observation attributing exceptional immunogenic activity to the mycobacterial cell wall.

Incorporation of histone deacetylase inhibition into the structure of a nuclear receptor agonist.

1,25-dihydroxyvitamin D(3) (1,25D) regulates gene expression by signaling through the nuclear vitamin D receptor (VDR) transcription factor and exhibits calcium homeostatic, anticancer, and immunomodulatory properties. Histone deacetylase inhibitors (HDACis) alter nuclear and cytoplasmic protein acetylation, modify gene expression, and have potential for treatment of cancer and other indications. The function of nuclear receptor ligands, including 1,25D, can be enhanced in combination with HDACi. We designed triciferol, a hybrid molecule in which the 1,25D side chain was replaced with the dienyl hydroxamic acid of HDACi trichostatin A. Triciferol binds directly to the VDR, and functions as an agonist with 1,25D-like potency on several 1,25D target genes. Moreover, unlike 1,25D, triciferol induces marked tubulin hyperacetylation, and augments histone acetylation at concentrations that largely overlap those where VDR agonism is observed. Triciferol also exhibits more efficacious antiproliferative and cytotoxic activities than 1,25D in four cancer cell models in vitro. The bifunctionality of triciferol is notable because (i) the HDACi activity is generated by modifying the 1,25D side chain without resorting to linker technology and (ii) 1,25D and HDACi have sympathetic, but very distinct biochemical targets; the hydrophobic VDR ligand binding domain and the active sites of HDACs, which are zinc metalloenzymes. These studies demonstrate the feasibility of combining HDAC inhibition with nuclear receptor agonism to enhance their therapeutic potential.