Masking the Bioactivity of Hydroxamic Acids by Coordination to Cobalt: Towards Bioreductive Anticancer Agents.

The clinical use of many potent anticancer agents is limited by their non-selective toxicity to healthy tissue. One of these examples is vorinostat (SAHA), a pan histone deacetylase inhibitor, which shows high cytotoxicity with limited discrimination for cancerous over healthy cells. In an attempt to improve tumor selectivity, we exploited the properties of cobalt(III) as a redox-active metal center through stabilization with cyclen and cyclam tetraazamacrocycles, masking the anticancer activity of SAHA and other hydroxamic acid derivatives to allow for the complex to reach the hypoxic microenvironment of the tumor. Biological assays demonstrated the desired low in vitro anticancer activity of the complexes, suggesting effective masking of the activity of SAHA. Once in the tumor, the bioactive moiety may be released through the reduction of the CoIII center. Investigations revealed long-term stability of the complexes, with cyclic voltammetry and chemical reduction experiments supporting the design hypothesis of SAHA release through the reduction of the CoIII prodrug. The results highlight the potential for further developing this complex class as novel anticancer agents by masking the high cytotoxicity of a given drug, however, the cellular uptake needs to be improved.

Total Synthesis of Chalaniline A: An Aminofulvene Fused Chromone from Vorinostat-Treated Fungus Chalara sp. 6661.

Chalaniline A, an aminofulveno[1,2-b]chromone derivative previously isolated from a vorinostat-treated ascomycete Chalara sp., was prepared in nine steps from orcinol (3,5-dihydroxytoluene). In a key transformation, the tricyclic ring system of the target was generated by a pyrrolidine-catalyzed double annulation between α-(methylsulfinyl)-2,6-dihydroxy-4-methylacetophenone and the ketaldoester, methyl 2,5-dioxopentanoate. The resulting tertiary alcohol (coniochaetone H) was further converted to chalaniline A by operations including dehydration (to yield a hydroxyfulvene), Vilsmeier reaction, and enamine exchange.

SAHA potentiates the activity of repurposed drug promethazine loaded PLGA nanoparticles in triple-negative breast cancer cells.

Triple-negative breast cancer (TNBC) is considered the most aggressive form of breast cancer owing to the negative expression of targetable bioreceptors. Epithelial to mesenchymal transition (EMT) associated with metastatic abilities is its critical feature. As an attempt to target TNBC, nanotechnology was utilised to augment the effects of drug repurposing. Concerning that, a combination therapeutic module was structured with one of the aspects being a repurposed antihistamine, promethazine hydrochloride loaded PLGA nanoparticles. The as-synthesized nanoparticles were 217 nm in size and fluoresced at 522 nm, rendering them suitable for theranostic applications too. The second feature of the module was a common histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), used as a form of pre-treatment. Experimental studies demonstrated efficient cellular internalisation and significant innate anti-proliferative potential. The use of SAHA sensitised the cells to the drug loaded nanoparticle treatment. Mechanistic studies showed increase in ROS generation, mitochondrial dysfunction followed by apoptosis. Investigations into protein expression also revealed reduction of mesenchymal proteins like vimentin by 1.90 fold; while increase in epithelial marker like E-Cadherin by 1.42 fold, thus indicating an altered EMT dynamics. Further findings also provided better insight into the benefits of SAHA potentiated targeting of tumor spheroids that mimic solid tumors of TNBC. Thus, this study paves the avenue to a more rational translational validation of combining nanotherapeutics with drug repurposing.

Vorinostat exhibits anticancer effects in triple-negative breast cancer cells by preventing nitric oxide-driven histone deacetylation.

Triple-negative breast cancers (TNBC) that produce nitric oxide (NO) are more aggressive, and the expression of the inducible form of nitric oxide synthase (NOS2) is a negative prognostic indicator. In these studies, we set out to investigate potential therapeutic strategies to counter the tumor-permissive properties of NO. We found that exposure to NO increased proliferation of TNBC cells and that treatment with the histone deacetylase inhibitor Vorinostat (SAHA) prevented this proliferation. When histone acetylation was measured in response to NO and/or SAHA, NO significantly decreased acetylation on histone 3 lysine 9 (H3K9ac) and SAHA increased H3K9ac. If NO and SAHA were sequentially administered to cells (in either order), an increase in acetylation was observed in all cases. Mechanistic studies suggest that the "deacetylase" activity of NO does not involve S-nitrosothiols or soluble guanylyl cyclase activation. The observed decrease in histone acetylation by NO required the interaction of NO with cellular iron pools and may be an overriding effect of NO-mediated increases in histone methylation at the same lysine residues. Our data revealed a novel pathway interaction of Vorinostat and provides new insight in therapeutic strategy for aggressive TNBCs.

Epigenetic inhibition assisted chemotherapeutic treatment of lung cancer based on artificial exosomes.

We adopted a novel strategy by combining histone deacetylase (HDAC) inhibitors with traditional chemotherapeutics to treat solid tumors. However, chemotherapeutics often have a narrow therapeutic index and need multiple administrations with undesired side effects that lead to the intolerance. To reduce the non-specificity of chemotherapeutics, targeted therapy was introduced to restrict such agents in the tumor with minimum effects on other tissues. We developed bioinspired artificial exosomes (AE), which enabled to deliver chemotherapeutics to the tumors effectively after systemic administration. AE were produced by incorporating membrane proteins from cancer cells into phospholipid liposomes that mimicked the plasma membrane. The synthesized AE were used for the delivery of broad-spectrum chemotherapeutic doxorubicin (DOX) and vorinostat (SAHA), an epigenetic inhibitor. The combination of DOX and SAHA showed synergistic effects on suppressing non-small cell lung cancer cells and xenograft tumors without apparent adverse effects. AE facilitated the delivery of drugs to tumor tissue and extended the retention time of drugs within tumors. Taken together, these studies suggest that the bioengineered artificial exosomes may serve as novel delivery strategy for chemotherapeutics to treat non-small cell lung cancer.

Ronald C.D. Breslow (1931-2017): A career in review.

Reviewed herein are key research accomplishments of Professor Ronald Charles D. Breslow (1931-2017) throughout his more than 60 year research career. These accomplishments span a wide range of topics, most notably physical organic chemistry, medicinal chemistry, and bioorganic chemistry. These topics are reviewed, as are topics of molecular electronics and origin of chirality, which combine to make up the bulk of this review. Also reviewed briefly are Breslow's contributions to the broader chemistry profession, including his work for the American Chemical Society and his work promoting gender equity. Throughout the article, efforts are made to put Breslow's accomplishments in the context of other work being done at the time, as well as to include subsequent iterations and elaborations of the research.

Synthesis of benzoxazole-based vorinostat analogs and their antiproliferative activity.

Hydroxamic acid derivatives constitute an interesting novel class of antitumor agents. Three of them, including vorinostat, are approved drugs for the treatment of malignancies, while several others are currently under clinical trials. In this work, we present new vorinostat analogs containing the benzoxazole ring as the cap group and various linkers. The benzoxazole-based analogs were synthesized starting either from 2-aminobenzoxazole, through conventional coupling, or from benzoxazole, through a metal-free oxidative amination. All the synthesized compounds were evaluated for their antiproliferative activity on three diverse human cancer cell lines (A549, Caco-2 and SF268), in comparison to vorinostat. Compound 12 (GK601), carrying a benzoxazole ring replacement for the phenyl ring of vorinostat, was the most potent inhibitor of the growth of three cell lines (IC50 1.2-2.1 µΜ), similar in potency to vorinostat. Compound 12 also inhibited human HDAC1, HDAC2 and HDAC6 like vorinostat. This new analog also showed antiproliferative activity against two colon cancer cell lines genetically resembling pseudomyxoma peritonei (PMP), namely HCT116 GNAS R201C/+ and LS174T (IC50 0.6 and 1.4 µΜ, respectively) with potency comparable to vorinostat (IC50 1.1 and 2.1 µΜ, respectively).

The design of a novel near-infrared fluorescent HDAC inhibitor and image of tumor cells.

Histone deacetylases (HDACs) have been found to be biomarkers of cancers and the corresponding inhibitors have attracted much attention these years. Herein we reported a near-infrared fluorescent HDAC inhibitor based on vorinostat (SAHA) and a NIR fluorophore. This newly designed inhibitor showed similar inhibitory activity to SAHA against three HDAC isoforms (HDAC1, 3, 6). The western blot assay showed significant difference in compared with the negative group. When used as probe for further kinematic imaging, Probe 1 showed enhanced retention in tumor cells and the potential of HDAC inhibitors in drug delivery was firstly brought out. The cytotoxicity assay showed Probe 1 had some anti-proliferation activities with corresponding IC50 values of 9.20 ± 0.96 µM on Hela cells and 5.91 ± 0.57 µM on MDA-MB-231 cells. These results indicated that Probe 1 could be used as a potential NIR fluorescent in the study of HDAC inhibitors and lead compound for the development of visible drugs.

A G-Quadruplex-Binding Small Molecule and the HDAC Inhibitor SAHA (Vorinostat) Act Synergistically in Gemcitabine-Sensitive and Resistant Pancreatic Cancer Cells.

The stabilisation of G-quadruplexes (G4s) by small-molecule compounds is an effective approach for causing cell growth arrest, followed by cell death. Some of these compounds are currently being developed for the treatment of human cancers. We have previously developed a substituted naphthalene diimide G4-binding molecule (CM03) with selective potency for pancreatic cancer cells, including gemcitabine-resistant cells. We report here that CM03 and the histone deacetylase (HDAC) inhibitor SAHA (suberanilohydroxamic acid) have synergistic effects at concentrations close to and below their individual GI50 values, in both gemcitabine-sensitive and resistant pancreatic cancer cell lines. Immunoblot analysis showed elevated levels of γ-H2AX and cleaved PARP proteins upon drug combination treatment, indicating increased levels of DNA damage (double-strand break events: DSBs) and apoptosis induction, respectively. We propose that the mechanism of synergy involves SAHA relaxing condensed chromatin, resulting in higher levels of G4 formation. In turn, CM03 can stabilise a greater number of G4s, leading to the downregulation of more G4-containing genes as well as a higher incidence of DSBs due to torsional strain on DNA and chromatin structure.

Synthesis and biological evaluation of paclitaxel and vorinostat co-prodrugs for overcoming drug resistance in cancer therapy in vitro.

Paclitaxel (PTX) is the first-line treatment drug for breast cancer. However, drug resistance after a course of treatment and low selectivity restricted its clinical utility sometimes. In this study, we successfully bound PTX and vorinostat (SAHA) to form co-prodrugs based on the synergistic anticancer effects. The PTX-SAHA co-prodrugs were conjugated by glycine (1a) and succinic acid (1b) respectively and the former has shown better activity in cytotoxicity, cell cycle arrest and western-blot experiments. Therefore, 1a was further prepared to nanomicelles with mPEG2000-PLA1750 as the carrier by using thin film method. PTX-SAHA co-prodrug nanomicelles were spherical with a particle size of 20-100 nm. In vitro drug release test showed 1a nanomicelles had sustained release effect, which could reduce the resistance of PTX. In vitro cytotoxicity was evaluated by SRB assay in HCT-116 cells, MCF-7 cells and drug-resistant MCF-7/ADR cells. The results showed 1a nanomicelles had comparable or even better cytotoxicity than PTX especially in the MCF-7/ADR cells. All the results suggested that PTX-SAHA co-prodrug nanomicelles were promising treatment for PTX resistance cancer.

Design and synthesis of parthenolide-SAHA hybrids for intervention of drug-resistant acute myeloid leukemia.

A series of parthenolide-SAHA hybrids were synthesized and evaluated for their anti-AML activities against HL-60 and HL-60/ADR cell lines. The most active compound 26 exhibited high activity against HL-60/ADR cell line with IC50 value of 0.15 µM, which demonstrated 16.8-fold improvement compared to that of the parent compound PTL (IC50 = 2.52 µM). Moreover, it was six times more potent than the reference drug SAHA (IC50 = 0.90 µM) and fifty-one times more potent than ADR (IC50 = 7.72 µM). The preliminary molecular mechanism of 26 indicated that compound 26 could significantly induce apoptosis of HL-60/ADR cells. The effect of compound 26 was mainly through mitochondria pathway. Further investigation revealed that the protein level of HDAC1 and HDAC6 were reduced after the treatment of compound 26 with a dose-dependent manner. Compound 26 could significantly decrease ABCC1 expression, which increased the accumulation of intracellular drug for overcoming the drug resistance. On the base of these results, compound 26 might be considered as a promising candidate for further evaluation as a potential anti-AML drug.

Light-Trigerred Cellular Epigenetic Molecule Release To Reverse Tumor Multidrug Resistance.

Owing to the high spatial and temporal resolution of light, light-related biotechnologies, for example, optogenetics, has wide ranging applications in neuroscience to control a subject's behavior. Applying light to control tumors' genetic behavior directly was still a challenge so far. Herein, we put forward a strategy of chemical optoepigenomics, in which an epigenetic regulator (vorinostat) and paclitaxel (PTX) were conjugated onto a light-sensitive chemical molecule. The activity of vorinostat could be precisely controlled by the light, which could minimize the off-target effect. After UV irradiation under 350 nm, the photocaged epigenetic regulator (vorinostat) was selectively released from the conjugate in a spatiotemporal manner, inhibiting the activity of histone deacetylase and then reversing the PTX resistance of tumor cells effectively.

Innovative DNA-Targeted Metallo-prodrug Strategy Combining Histone Deacetylase Inhibition with Oxidative Stress.

Cancer remains a global health challenge. There is an urgent need to develop innovative therapeutics that can overcome the shortcomings of existing cancer therapies. DNA enzymes involved in nucleic acid compaction and organization are an attractive cancer drug target for therapeutic exploitation. In this work, a family of Cu(II) prodrugs containing suberoylanilide hydroxamic acid (SAHA), a well-established histone deacetylase inhibitor (HDACi) and clinically approved cancer drug, and phenanthrene ligands as DNA intercalative components have been rationally developed. The complexes, of general formula [Cu(SAHA-1H)( N, N'-phenanthrene)]+, exhibit excellent DNA recognition with binding affinity of lead agents in the order of ∼107 M(bp)-1. Biophysical studies involving nucleic acid polymers indicate intercalative binding at both adenine-thymine (A-T) and guanine-cytosine (G-C) rich sequences but thermodynamically stable interactions are favored in G-C tracts. The complexes mediate DNA damage by producing reactive oxygen species (ROS) with spin trapping experiments showing that superoxide, the hydroxyl radical, and hydrogen peroxide play critical roles in strand scission. The agents were found to have promising antiproliferative effects against a panel of epithelial cancers, and in two representative cell lines possessing mutated p53 (SK-OV-3 and DU145), enhanced cytotoxicity was observed. Significantly, mechanistic experiments with the most promising candidates revealed HDAC inhibition activity was achieved over a shorter time frame as compared to clinical standards with DNA damage-response markers identifying upregulation of both DNA synthesis and nucleotide excision repair (NER) pathways. Finally, confocal imaging and gene expression analysis show this metallodrug class exerts cytotoxic activity predominantly through an apoptotic pathway.

Photo-Controlled Release of Small Signaling Molecules to Induce Biological Responses.

Chemical modifications of proteins or cofactors, including acetylation and oxidation of amino acid residues of various signal proteins, whether transient or successive, play key roles in modulating biological functions. Small molecules that have signaling functions in biological systems through the chemical modification of proteins include nitric oxide (NO), hydrogen peroxide, carbon monoxide, and hydrogen sulfide. To investigate the pathophysiological roles of these molecules, caged compounds have been developed that allow precise spatiotemporal control of the release of these species in response to photoirradiation in the ultraviolet or visible region. For example, photocontrollable NO releasers can regulate the responses of blood vessels in vivo and ex vivo. In addition, photocontrollable (caged) inhibitors of histone deacetylase (HDAC) can be used to regulate HDAC activity in response to photoirradiation. Such photocontrol technology has provided chemical tools for a variety of biological studies, including investigations of epigenetic mechanisms.

Design and synthesis of triple inhibitors of janus kinase (JAK), histone deacetylase (HDAC) and Heat Shock Protein 90 (HSP90).

Inhibition of multiple signaling pathways in a cancer cell with a single molecule could result in better therapies that are simpler to administer. Efficacy may be achieved with reduced potency against individual targets if there is synergy through multiple pathway inhibition. To achieve this, it is necessary to be able to build multi-component ligands by joining together key pharmacophores in a way which maintains sufficient activity against the individual pathways. In this work, designed triple inhibiting ligands are explored aiming to block three completely different target types: a kinase (JAK2), an epigenetic target (HDAC) and a chaperone (HSP90). Although these enzymes have totally different functions they are related through inter-dependent pathways in the developing cancer cell. Synthesis of several complex multi-inhibiting ligands are presented along with initial enzyme inhibition data against 3 biological target classes of interest. A lead compound, 47, was discovered which had low micromolar activity for all 3 targets. Further development of these complex trispecific designed multiple ligands could result in a 'transient drug', an alternative combination therapy for treating cancer mediated via a single molecule.

Merging of ruxolitinib and vorinostat leads to highly potent inhibitors of JAK2 and histone deacetylase 6 (HDAC6).

Inhibition of more than one pathway in a cancer cell with a single molecule could result in better therapies with less complex dosing regimens. In this work multi-component ligands have been prepared by joining together key pharmacophores of two different enzyme inhibitors in a way which increases potency against the individual pathways. Selective JAK1/2 inhibitor, ruxolitinib (3), and pan-HDAC inhibitor vorinostat (4) were linked together by a single nitrogen atom to create a new series of compounds with very potent JAK2 and HDAC6 inhibition with selectivity against HDAC1. A preferred compound, 13b, had unprecedented sub-nanomolar JAK2 potency with an IC50 of 41 pM and a sub-nanomolar IC50 against HDAC6 of 200 pM. Binding models show a good fit into both JAK2 and HDAC6.

Aniline-Tetramic Acids from the Deep-Sea-Derived Fungus Cladosporium sphaerospermum L3P3 Cultured with the HDAC Inhibitor SAHA.

Four new tetramic acids, cladosins H-K (1-4), and a related known compound, cladodionen (5), were isolated from the culture of the Mariana Trench (depth 6562 m) sediment-derived fungus Cladosporium sphaerospermum L3P3 treated with the histone deacetylase inhibitor SAHA (suberanilohydroxamic acid). Interestingly, compounds 1-5 existed as equilibrium E/ Z mixtures and 1-4 were the first cases of tetramic acids containing aniline moieties. Their structures including absolute configurations were elucidated through a combination of NMR, MS, and Mosher's method, together with the consideration of biogenetic origins. Incubation experiments of exogenous aniline and N-phenyloctanamide revealed that the aniline moiety in cladosins H-K (1-4) is probably derived from the degradation of SAHA, indicating that the well-known histone deacetylase inhibitor SAHA could be metabolized by L3P3 and provide aniline as a precursor for biotransformation of chemically reactive polyketides. The cytotoxicity of 1-5 was evaluated against the PC-3, MGC-803, SH-SY5Y, HCT-116, K562, and HL-60 cell lines, and compound 2 showed promising cytotoxicity against the HL-60 cell line with an IC50 value of 2.8 µM.

Reprogramming Tumor-Associated Macrophages To Reverse EGFRT790M Resistance by Dual-Targeting Codelivery of Gefitinib/Vorinostat.

Gefitinib is a first-line therapy in the EGFR-mutated nonsmall cell lung cancer (NSCLC). However, the development of drug resistance is almost unavoidable, thus leading to an unsustainable regimen. EGFRT790M mutation is the major cause responsible for the molecular-targeting therapy failure in NSCLC. Although the recently approved osimertinib is effective for the EGFRT790M-positive NSCLC, the osimertinib-resistant EGFR mutation is rapidly developed, too. In this study, we proposed a tumor-associated macrophage (TAM) reprogramming strategy for overcoming the EGFRT790M-associated drug resistance via a dual-targeting codelivery system of gefitinib/vorinostat that acted on both TAM with overexpression of mannose receptors and the HER-2 positive NSCLC cells. The trastuzumab-modified, mannosylated liposomal system was able to repolarize the protumor M2 phenotype to the antitumor M1 and cause the elevating ROS in the cancer cells, consequently modulating the intracellular redox balance via ROS/NOX3/MsrA axis. The suppressed MsrA facilitated the EGFRT790M degradation through 790M oxidation by ROS, thus resensitizing the EGFRT790M-positive cells to gefitinib. The dual-targeting codelivery and TAM-reprogramming strategies provided a potential method for rescuing the EGFRT790M-caused resistance to tyrosine kinase inhibitor treatment.

Enrichment of Specifically Labeled Proteins by an Immobilized Host Molecule.

Chemical proteomics relies primarily on click-chemistry-based protein labeling and biotin-streptavidin enrichment, but these techniques have inherent limitations. Enrichment of intracellular proteins using a totally synthetic host-guest complex is described, overcoming the problem associated with the classical approach. We achieve this by affinity-based protein labeling with a target-specific probe molecule conjugated to a high-affinity guest (suberanilohydroxamic acid-ammonium-adamantane; SAHA-Ad) and then enriching the labeled species using a cucurbit[7]uril bead. This method shows high specificity for labeled molecules in a MDA-MB-231 breast cancer cell lysate. Moreover, this method shows promise for labeling proteins in live cells.

Development of New Nanoniosome Carriers for Vorinostat: Evaluation of Anticancer Efficacy In Vitro.

Vorinostat (VST) is a chemotherapeutic agent administrated for various types of cancers. However, it suffers from side effects and chemoresistance that reduce its application. Different nanoniosomes comprised Span 20, 60, 65 and 80 were prepared by the thin film hydration method and loaded with VST. The nanoniosomes were physicochemically characterized using particle size analysis and field emission scanning electron microscopy. The best formulation that was prepared using Span 65 (VST-NN-S65) included vesicle size of 127 nm with a narrow size distribution. VST-NN-S65 had an entrapment efficiency and loading capacity of 81.3 ± 5.1 and 32.0 ± 3.9 %, respectively. Drug release rate measurements showed that 90 % of VST was liberated within 1 h. Cytotoxicity assessments of VST-NN-S65 in HeLa and MCF7 cells indicated significant improvement in the effectiveness of VST, compared to the VST suspension. For VST-NN-S65, IC50 values of 26.3 and 6.6 µg mL-1 were obtained for HeLa and MCF7 cell lines, respectively. In situ apoptosis detection by the TUNEL assay revealed that apoptosis mainly occurred in the cell lines.