Discovery of CRBN-dependent WEE1 Molecular Glue Degraders from a Multicomponent Combinatorial Library

Small molecules promoting protein-protein interactions produce a range of therapeutic outcomes. Molecular glue degraders exemplify this concept due to their compact drug-like structures and ability to engage targets without reliance on existing cognate ligands. While Cereblon molecular glue degraders containing glutarimide scaffolds have been approved for treatment of multiple myeloma and acute myeloid leukemia, the design of new therapeutically relevant monovalent degraders remains challenging. We report here an approach to glutarimide-containing molecular glue synthesis using multicomponent reactions as a central modular core-forming step. Screening the resulting library identified HRZ-01 derivatives that target casein kinase 1 alpha (CK1α) and Wee-like protein kinase (WEE1). Further medicinal chemistry efforts led to identification of selective monovalent WEE1 degraders that provide a potential starting point for the eventual development of a selective chemical degrader probe. The structure of the hit WEE1 degrader complex with CRBN-DDB1 and WEE1 provides a model of the protein-protein interface and a rationale for the observed kinase selectivity. Our findings suggest that modular synthetic routes combined with in-depth structural characterization give access to selective molecular glue degraders and expansion of the CRBN-degradable proteome.

Proteomics-Based Discovery of First-in-Class Chemical Probes for Programmed Cell Death Protein 2 (PDCD2)

Chemical probes are essential tools for understanding biological systems and for credentialing potential biomedical targets. Programmed cell death 2 (PDCD2) is a member of the B-cell lymphoma 2 (Bcl-2) family of proteins, which are critical regulators of apoptosis. Here we report the discovery and characterization of 10 e, a first-in-class small molecule degrader of PDCD2. We discovered this PDCD2 degrader by serendipity using a chemical proteomics approach, in contrast to the conventional approach for making bivalent degraders starting from a known binding ligand targeting the protein of interest. Using 10 e as a pharmacological probe, we demonstrate that PDCD2 functions as a critical regulator of cell growth by modulating the progression of the cell cycle in T lymphoblasts. Our work provides a useful pharmacological probe for investigating PDCD2 function and highlights the use of chemical proteomics to discover selective small molecule degraders of unanticipated targets.

Chemical Specification of E3 Ubiquitin Ligase Engagement by Cysteine-Reactive Chemistry

Targeted protein degradation relies on small molecules that induce new protein-protein interactions between targets and the cellular protein degradation machinery. Most of these small molecules feature specific ligands for ubiquitin ligases. Recently, the attachment of cysteine-reactive chemical groups to pre-existing small molecule inhibitors has been shown to drive specific target degradation. We demonstrate here that different cysteine-reactive groups can specify target degradation via distinct ubiquitin ligases. By focusing on the bromodomain ligand JQ1, we identify cysteine-reactive functional groups that drive BRD4 degradation by either DCAF16 or DCAF11. Unlike proteolysis-targeting chimeric molecules (PROTACs), the new compounds use a single small molecule ligand with a well-positioned cysteine-reactive group to induce protein degradation. The finding that nearly identical compounds can engage multiple ubiquitination pathways suggests that targeting cellular pathways that search for and eliminate chemically reactive proteins is a feasible avenue for converting existing small molecule drugs into protein degrader molecules.

Exploration of the Tunability of BRD4 Degradation by DCAF16 Trans-labelling Covalent Glues

Small molecules that can induce protein degradation by inducing proximity between a desired target and an E3 ligase have the potential to greatly expand the number of proteins that can be manipulated pharmacologically. Current strategies for targeted protein degradation are mostly limited in their target scope to proteins with preexisting ligands. Alternate modalities such as molecular glues, as exemplified by the glutarimide class of ligands for the CUL4CRBN ligase, have been mostly discovered serendipitously. We recently reported a trans-labelling covalent glue mechanism which we named 'Template-assisted covalent modification', where an electrophile decorated small molecule binder of BRD4 was effectively delivered to a cysteine residue on an E3 ligase DCAF16 as a consequence of a BRD4-DCAF16 protein-protein interaction. Herein, we report our medicinal chemistry efforts to evaluate how various electrophilic modifications to the BRD4 binder, JQ1, affect DCAF16 trans-labeling and subsequent BRD4 degradation efficiency. We discovered a decent correlation between the ability of the electrophilic small molecule to induce ternary complex formation between BRD4 and DCAF16 with its ability to induce BRD4 degradation. Moreover, we show that a more solvent-exposed warhead presentation is optimal for DCAF16 recruitment and subsequent BRD4 degradation. Unlike the sensitivity of CUL4CRBN glue degraders to chemical modifications, the diversity of covalent attachments in this class of BRD4 glue degraders suggests a high tolerance and tunability for the BRD4-DCAF16 interaction. This offers a potential new avenue for a rational design of covalent glue degraders by introducing covalent warheads to known binders.

Structure-Activity Relationship of Truncated 2,8-Disubstituted-Adenosine Derivatives as Dual A2A/A3 Adenosine Receptor Antagonists and Their Cancer Immunotherapeutic Activity

Based on hA2AAR structures, a hydrophobic C8-heteroaromatic ring in 5'-truncated adenosine analogues occupies the subpocket tightly, converting hA2AAR agonists into antagonists while maintaining affinity toward hA3AR. The final compounds of 2,8-disubstituted-N6-substituted 4'-thionucleosides, or 4'-oxo, were synthesized from d-mannose and d-erythrono-1,4-lactone, respectively, using a Pd-catalyst-controlled regioselective cross-coupling reaction. All tested compounds completely antagonized hA2AAR, including 5d with the highest affinity (Ki,A2A = 7.7 ± 0.5 nM). The hA2AAR-5d X-ray structure revealed that C8-heteroaromatic rings prevented receptor activation-associated conformational changes. However, the C8-substituted compounds still antagonized hA3AR. Structural SAR features and docking studies supported different binding modes at A2AAR and A3AR, elucidating pharmacophores for receptor activation and selectivity. Favorable pharmacokinetics were demonstrated, in which 5d displayed high oral absorption, moderate half-life, and bioavailability. Also, 5d significantly improved the antitumor effect of anti-PD-L1 in vivo. Overall, this study suggests that the novel dual A2AAR/A3AR nucleoside antagonists would be promising drug candidates for immune-oncology.

Targeted and Logical Discovery of Piperazic Acid-Bearing Natural Products Based on Genomic and Spectroscopic Signatures

A targeted and logical discovery method was devised for natural products containing piperazic acid (Piz), which is biosynthesized from ornithine by l-ornithine N-hydroxylase (KtzI) and N-N bond formation enzyme (KtzT). Genomic signature-based screening of a bacterial DNA library (2020 strains) using polymerase chain reaction (PCR) primers targeting ktzT identified 62 strains (3.1%). The PCR amplicons of KtzT-encoding genes were phylogenetically analyzed to classify the 23 clades into two monophyletic groups, I and II. Cultivating hit strains in media supplemented with 15NH4Cl and applying 1H-15N heteronuclear multiple bond correlation (HMBC) along with 1H-15N heteronuclear single quantum coherence (HSQC) and 1H-15N HSQC-total correlation spectroscopy (HSQC-TOCSY) NMR experiments detected the spectroscopic signatures of Piz and modified Piz. Chemical investigation of the hit strains prioritized by genomic and spectroscopic signatures led to the identification of a new azinothricin congener, polyoxyperuin B seco acid (1), previously reported chloptosin (2) in group I, depsidomycin D (3) incorporating two dehydropiperazic acids (Dpz), and lenziamides A and B (4 and 5), structurally novel 31-membered cyclic decapeptides in group II. By consolidating the phylogenetic and chemical analyses, clade-structure relationships were elucidated for 19 of the 23 clades. Lenziamide A (4) inhibited STAT3 activation and induced G2/M cell cycle arrest, apoptotic cell death, and tumor growth suppression in human colorectal cancer cells. Moreover, lenziamide A (4) resensitized 5-fluorouracil (5-FU) activity in both in vitro cell cultures and the in vivo 5-FU-resistant tumor xenograft mouse model. This work demonstrates that the genomic and spectroscopic signature-based searches provide an efficient and general strategy for new bioactive natural products containing specific structural motifs.

Synthesis and biological evaluation of atropisomeric tetrahydroisoquinolines overcoming docetaxel resistance in triple-negative human breast cancer cells

Herein, atropisomeric 8-aryltetrahydroisoquinolines have been synthesized and biologically evaluated. Based on our structure-activity relationship study, a highly bioactive racemic compound has been produced, and it exhibited high antiproliferative activities against various cancer cell lines, including docetaxel-resistant breast cancer cell lines. Each enantiomer can be synthesized in an enantioselective manner by employing the chiral phosphoric acid-catalyzed atroposelective Pictet-Spengler cyclization. An axially (R)-configured enantiomer showed a higher biological activity compared with the axially (S)-configured enantiomer. Further biological studies suggested that the (R)-enantiomer overcomes docetaxel resistance via the downregulation of signal transducer and activator of transcription 3 activation and consequently induces cellular apoptosis in docetaxel-resistant triple-negative breast cancer cell lines.

Design, Synthesis, and Biological Activity of Marinacarboline Analogues as STAT3 Pathway Inhibitors for Docetaxel-Resistant Triple-Negative Breast Cancer

Metastatic triple-negative breast cancer (mTNBC) is a fatal type of breast cancer (BC), and signal transducer and activator of transcription 3 (STAT3) has emerged as an effective target for mTNBC. In the present study, compound MC0704 was found to be a novel synthetic STAT3 pathway inhibitor, and its potential antitumor activity was demonstrated using in vitro and in vivo models in docetaxel-resistant TNBC cells. Based on marinacarboline (MC), a series β-carboline derivatives were synthesized and investigated for their antitumor activities against docetaxel-resistant MDA-MB-231 (MDA-MB-231-DTR) cells. Combining antiproliferation and STAT3 inhibitory activities, MC0704 was selected as the most promising β-carboline compound. MC0704 effectively impeded the metastatic potential of MDA-MB-231-DTR cells in vitro, and the combination of MC0704 and docetaxel exhibited potent antitumor activities in a xenograft mouse model. These findings suggested that MC0704 can be a lead candidate as a target therapeutic agent for TNBC patients with docetaxel resistance.

Antitumor Activity of Piceamycin by Upregulation of N-Myc Downstream-Regulated Gene 1 in Human Colorectal Cancer Cells

Piceamycin (1), a macrocyclic lactam isolated from the silkworm's gut (Streptomyces sp. SD53 strain), reportedly possesses antibacterial activity. However, the potential anticancer activity and molecular processes underlying 1 have yet to be reported. Colorectal cancer (CRC) is high-risk cancer and accounts for 10% of all cancer cases worldwide. The high prevalence of resistance to radiation or chemotherapy means that patients with advanced CRC have a poor prognosis, with high recurrence and metastasis potential. Therefore, the present study investigated the antitumor effect and underlying mechanisms of 1 in CRC cells. The growth-inhibiting effect of 1 in CRC cells was correlated with the upregulation of a tumor suppressor, N-myc downstream-regulated gene 1 (NDRG1). Additionally, 1 induced G₀/G₁ cell cycle arrest and apoptosis and inhibited the migration of CRC cells. Notably, 1 disrupted the interaction between NDRG1 and c-Myc in CRC cells. In a mouse model with HCT116-implanted xenografts, the antitumor activity of 1 was confirmed by NDRG1 modulation. Overall, these findings show that 1 is a potential candidate for CRC treatment through regulation of NDGR1-mediated functionality.

Targeted Discovery of an Enediyne-Derived Cycloaromatized Compound, Jejucarboside A, from a Marine Actinomycete

A genomic and spectroscopic signature-based search revealed a cycloaromatized enediyne, jejucarboside A (1), from a marine actinomycete strain. The structure of 1 was determined as a new cyclopenta[a]indene glycoside bearing carbonate functionality by nuclear magnetic resonance, high-resolution mass spectrometry (MS), MS/MS, infrared spectroscopy, and a modified Mosher's method. An iterative enediyne synthase pathway has been proposed for the putative biosynthesis of 1 by genomic analysis. Jejucarboside A exhibited cytotoxicity against the HCT116 colon carcinoma cells.

Antitumor Activity of Rutaecarpine in Human Colorectal Cancer Cells by Suppression of Wnt/β-Catenin Signaling

Alkaloids derived from natural products have been traditionally used to treat various diseases, including cancers. Rutaecarpine (1), a β-carboline-type alkaloid obtained from Evodia rutaecarpa, has been previously reported as an anti-inflammatory agent. Nonetheless, its anticancer activity and the underlying molecular mechanisms remain to be explored. In the procurement of Wnt/β-catenin inhibitors from natural alkaloids, 1 was found to exhibit activity against the Wnt/β-catenin-response reporter gene. Since the abnormal activation of Wnt/β-catenin signaling is highly involved in colon carcinogenesis, the antitumor activity and molecular mechanisms of 1 were investigated in colorectal cancer (CRC) cells. The antiproliferative activity of 1 was associated with the suppression of the Wnt/β-catenin-mediated signaling pathway and its target gene expression in human CRC cells. 1 also induced G₀/G₁ cell cycle arrest and apoptotic cell death, and the antimigration and anti-invasion potential of 1 was confirmed through epithelial-mesenchymal transition biomarker inhibition by the regulation of Wnt signaling. The antitumor activity of 1 was supported in an Ls174T-implanted xenograft mouse model via Wnt target gene regulation. Overall, these findings suggest that targeting the Wnt/β-catenin signaling pathway by 1 is a promising therapeutic option for the treatment of human CRC harboring β-catenin mutation.

Antitumor Activity of Pulvomycin via Targeting Activated-STAT3 Signaling in Docetaxel-Resistant Triple-Negative Breast Cancer Cells

Although docetaxel-based regimens are common and effective for early-stage triple-negative breast cancer (TNBC) treatment, acquired drug resistance frequently occurs. Therefore, a novel therapeutic strategy for docetaxel-resistant TNBC is urgently required. Signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in the tumorigenesis and metastasis of numerous cancers, and STAT3 signaling is aberrantly activated in TNBC cells. In this study, a docetaxel-resistant TNBC cell line (MDA-MB-231-DTR) was established, and mechanisms for the antitumor activity of pulvomycin, a novel STAT3 inhibitor isolated from marine-derived actinomycete, were investigated. Levels of activated STAT3 (p-STAT3 (Y705)) increased in docetaxel-resistant cells, and knockdown of STAT3 recovered the sensitivity to docetaxel in MDA-MB-231-DTR cells. Pulvomycin effectively inhibited the proliferation of both cell lines. In addition, pulvomycin suppressed the activation of STAT3 and subsequently induced G0/G1 cell cycle arrest and apoptosis. Pulvomycin also significantly inhibited the invasion and migration of MDA-MB-231-DTR cells through the modulation of epithelial-mesenchymal transition markers. In an MDA-MB-231-DTR-bearing xenograft mouse model, the combination of pulvomycin and docetaxel effectively inhibited tumor growth through STAT3 regulation. Thus, our findings demonstrate that the combination of docetaxel and STAT3 inhibitors is an effective strategy for overcoming docetaxel resistance in TNBC.

Antitumor Activity of Asperphenin B by Induction of Apoptosis and Regulation of Glyceraldehyde-3-phosphate Dehydrogenase in Human Colorectal Cancer Cells

Colorectal cancer (CRC) is a common and intractable malignancy with a high mortality risk. Conventional chemotherapeutics are effective for patients with early stage CRC, but the majority of deaths of CRC patients are linked to acquired drug resistance or metastasis occurrence. Asperphenin B (1), a lipopeptidyl benzophenone isolated from a marine-derived Aspergillus sp. fungus, reportedly possesses antiproliferative activity against cancer cells. However, its antitumor activity and the underlying molecular mechanisms remain unexplored. In this study, 1 induced G2/M phase cell cycle arrest and subsequent apoptotic cell death and inhibited tumor growth in a xenograft model. The 1-induced G2/M phase arrest was associated with the regulation of checkpoint proteins, including Chk1/2 and Cdc25c. The 1-induced apoptosis was correlated with an upregulation of p53 and cleaved caspases and a downregulation of survivin. Further experiments revealed that 1-mediated suppression of migration and invasion of metastatic HCT116 cells was partially associated with the downregulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression. The antimetastatic potential of 1 was also confirmed by E-cadherin upregulation and N-cadherin and Snail downregulation, which were in turn associated with the GAPDH regulation. These findings highlight the potential use of 1 as a novel candidate for treating metastatic CRC with the modulation of GAPDH function.

Synthesis and biological activity of selenopsammaplin A and its analogues as antitumor agents with DOT1L inhibitory activity

Disruptor of telomeric silencing-1 like (DOT1L) is a histone H3 methyltransferase which specifically catalyzes the methylation of histone H3 lysine-79 residue. Recent findings demonstrate that DOT1L is abnormally overexpressed and the upregulated DOT1L evokes the proliferation and metastasis in human breast cancer cells. Therefore, the DOT1L inhibitor is considered a promising strategy to treat breast cancers. Non-nucleoside DOT1L inhibitors, selenopsammaplin A and its analogues, were firstly reported in the present study. Selenopsammaplin A was newly designed and synthesized with 25% overall yield in 8 steps from 3-bromo-4-hydroxybenzaldahyde, and thirteen analogues of selenopsammaplin A were prepared for structure-activity relationship studies of their cytotoxicity against cancer cells and inhibitory activity toward DOT1L for antitumor potential. All synthetic selenopsammaplin A analogues exhibited the higher cytotoxicity compared to psammaplin A with up to 6 - 60 times depending on cancer cells, and most analogues showed significant inhibitory activities against DOT1L. Among the prepared analogues, the phenyl analogue (10) possessed the most potent activity with both cytotoxicity and inhibition of DOT1L. Compound 10 also exhibited the antitumor and antimetastatic activity in an orthotopic mouse metastasis model implanted with MDA-MB-231 human breast cancer cells. These biological findings suggest that analogue 10 is a promising candidate for development as a cancer chemotherapeutic agent in breast cancers.

Inhibition of DOT1L by Half-Selenopsammaplin A Analogs Suppresses Tumor Growth and EMT-Mediated Metastasis in Triple-Negative Breast Cancer

Due to a lack of hormone receptors, current treatment strategies for triple-negative breast cancer (TNBC) are limited with frequent disease recurrence and metastasis. Recent findings have suggested that aberrant methylation of histone H3 lysine 79 residue (H3K79me) by the histone methyltransferase disruptor of telomeric silencing 1-like (DOT1L) is a potential therapeutic target for TNBC clinical management. Therefore, we developed DOT1L inhibitors as potential antitumor agents against TNBC cells. We reveal that a synthetic half-selenopsammaplin A analog 9l (subsequently known as 9l) exhibited inhibitory activity against DOT1L-mediated H3K79 methylation, and showed antitumor activity in TNBC cells. The analog 9l also significantly inhibited TNBC invasion and migration via the modulation of epithelial-mesenchymal transition (EMT) markers, including N-cadherin and vimentin downregulation and E-cadherin upregulation. In an MDA-MB-231/Luc-implanted orthotopic mouse metastasis model, treatment with 9l effectively inhibited tumor growth and lung metastasis via DOT1L regulatory activity and EMT processes. Taken together, these findings highlight the potential of 9l as a novel therapeutic candidate for treating metastatic TNBC via DOT1L modulation.

Anti-Proliferative Activity of Nodosin, a Diterpenoid from Isodon serra, via Regulation of Wnt/β-Catenin Signaling Pathways in Human Colon Cancer Cells

Colorectal cancer (CRC) is one of the most malignant type of cancers and its incidence is steadily increasing, due to life style factors that include western diet. Abnormal activation of canonical Wnt/β-catenin signaling pathway plays an important role in colorectal carcinogenesis. Therefore, targeting Wnt/β-catenin signaling has been considered a crucial strategy in the discovery of small molecules for CRC. In the present study, we found that Nodosin, an ent-kaurene diterpenoid isolated from Isodon serra, effectively inhibits the proliferation of human colon cancer HCT116 cells. Mechanistically, Nodosin effectively inhibited the overactivated transcriptional activity of β-catenin/T-cell factor (TCF) determined by Wnt/β-catenin reporter gene assay in HEK293 and HCT116 cells. The expression of Wnt/β-catenin target genes such as Axin2, cyclin D1, and survivin were also suppressed by Nodosin in HCT116 cells. Further study revealed that a longer exposure of Nodosin induced the G₂/M phase cell cycle arrest and subsequently apoptosis in HCT116 cells. These findings suggest that the anti-proliferative activity of Nodosin in colorectal cancer cells might in part be associated with the regulation of Wnt/β-catenin signaling pathway.

Bioactive Bianthraquinones and Meroterpenoids from a Marine-Derived Stemphylium sp. Fungus

Three new bianthraquinones, alterporriol Z1-Z3 (1-3), along with three known compounds of the same structural class, were isolated from the culture broth of a marine-derived Stemphylium sp. fungus. Based upon the results of spectroscopic analyses and ECD measurements, the structures of new compounds were determined to be the 6-6'- (1 and 2) and 1-5'- (3) C-C connected pseudo-dimeric anthraquinones, respectively. Three new meroterpenoids, tricycloalterfurenes E-G (7-9), isolated together with the bianthraquinones from the same fungal culture broth, were structurally elucidated by combined spectroscopic methods. The relative and absolute configurations of these meroterpenoids were determined by modified Mosher's, phenylglycine methyl ester (PGME), and computational methods. The bianthraquinones significantly inhibited nitric oxide (NO) production and suppressed inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression in LPS-stimulated RAW 264.7 cells.

A novel small molecule STAT3 inhibitor SLSI-1216 suppresses proliferation and tumor growth of triple-negative breast cancer cells through apoptotic induction

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer, characterized by the lack of expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Owing to the absence of molecular targets, there are limited treatment options, and TNBC patients exhibit high mortality rates. Signal transducer and activator of transcription 3 (STAT3) is overexpressed and aberrantly activated in TNBC cells. Therefore, inhibition of STAT3-mediated signaling provides a potential strategy for the treatment of TNBC. In this study, A series of synthetic derivatives of SLSI-1 (a STAT3 inhibitor) were designed and evaluated for antitumor activity in TNBC cells. A novel derivative (SLSI-1216) exhibited the most potent anti-proliferative activity. SLSI-1216 effectively inhibited STAT3 activity and activation of STAT3, leading to the downregulation of AXL, a downstream target of STAT3 and epithelial-mesenchymal transition (EMT) progression. The inhibition of EMT by SLSI-1216 was associated with modulation of E-cadherin and N-cadherin. Furthermore, SLSI-1216 induced apoptosis by targeting STAT3 and effectively inhibited tumor growth in vivo. These findings suggest that SLSI-1216, as a potential inhibitor of STAT3, may be a promising therapeutic agent for TNBC.

Antiproliferative and Antimigration Activities of Fluoro-Neplanocin A via Inhibition of Histone H3 Methylation in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is among the most aggressive and potentially metastatic malignancies. Most affected patients have poor clinical outcomes due to the lack of specific molecular targets on tumor cells. The upregulated expression of disruptor of telomeric silencing 1-like (DOT1L), a histone methyltransferase specific for the histone H3 lysine 79 residue (H3K79), is strongly correlated with TNBC cell aggressiveness. Therefore, DOT1L is considered a potential molecular target in TNBC. Fluoro-neplanocin A (F-NepA), an inhibitor of S-adenosylhomocysteine hydrolase, exhibited potent antiproliferative activity against various types of cancer cells, including breast cancers. However, the molecular mechanism underlying the anticancer activity of F-NepA in TNBC cells remains to be elucidated. We determined that F-NepA exhibited a higher growth-inhibitory activity against TNBC cells relative to non-TNBC breast cancer and normal breast epithelial cells. Moreover, F-NepA effectively downregulated the level of H3K79me2 in MDA-MB-231 TNBC cells by inhibiting DOT1L activity. F-NepA also significantly inhibited TNBC cell migration and invasion. These activities of F-NepA might be associated with the upregulation of E-cadherin and downregulation of N-cadherin and Vimentin in TNBC cells. Taken together, these data highlight F-NepA as a strong potential candidate for the targeted treatment of high-DOT1L-expressing TNBC.

Absolute Configuration and Antibiotic Activity of Piceamycin

The cultivation of a Streptomyces sp. SD53 strain isolated from the gut of the silkworm Bombyx mori produced two macrolactam natural products, piceamycin (1) and bombyxamycin C (2). The planar structures of 1 and 2 were identified by a combination of NMR, MS, and UV spectroscopic analyses. The absolute configurations were assigned based on chemical and chromatographic methods as well as ECD calculations. A new chromatography-based experimental method for determining the configurations of stereogenic centers β to nitrogen atoms in macrolactams was established and successfully applied in this report. These compounds exhibited significant bioactivities against the silkworm entomopathogen Bacillus thuringiensis and various human pathogens as well as human cancer cell lines. In particular, piceamycin potently inhibited Salmonella enterica and Proteus hauseri with MIC values of 0.083 μg/mL and 0.025 μg/mL, respectively. The biosynthetic pathway involved in the formation of the cyclopentenone moiety in piceamycin is discussed.

Antitumor Activity of Ohmyungsamycin A through the Regulation of the Skp2-p27 Axis and MCM4 in Human Colorectal Cancer Cells

Ohmyungsamycin A (1), a novel cyclic peptide discovered from a marine Streptomyces sp., was previously reported with antibacterial and anticancer activities. However, the antitumor activities and the underlying molecular mechanisms of 1 remain to be elucidated. Compound 1 inhibited the proliferation and tumor growth of HCT116 human colorectal cancer cells based on both in vitro cell cultures and an in vivo animal model. A cDNA microarray analysis revealed that 1 downregulated genes involved in cell cycle checkpoint control. Compound 1 also induced G₀/G₁ cell cycle arrest that was mediated by the regulation of S-phase kinase-associated protein 2 (Skp2)-p27 axis and minichromosome maintenance protein 4 (MCM4). Furthermore, a longer exposure of 1 exhibited an accumulation of a sub-G₁ phase cell population, which is characteristic of apoptotic cells. The induction of apoptosis by 1 was also associated with the modulation of caspase family proteins. Compound 1 effectively suppressed tumor growth in a xenograft mouse model subcutaneously implanted with HCT116 cells. In addition, analysis of tumors revealed that 1 upregulated the expression of the CDK inhibitor p27 but downregulated the expression of Skp2 and MCM4. These findings demonstrate the involvement of 1 in cell cycle regulation and the induction of apoptosis in human colorectal cancer cells.

Targeting Histone Methyltransferase DOT1L by a Novel Psammaplin A Analog Inhibits Growth and Metastasis of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most intractable cancer in women with a high risk of metastasis. While hyper-methylation of histone H3 catalyzed by disruptor of telomeric silencing 1-like (DOT1L), a specific methyltransferase for histone H3 at lysine residue 79 (H3K79), is reported as a potential target for TNBCs, early developed nucleoside-type DOT1L inhibitors are not sufficient for effective inhibition of growth and metastasis of TNBC cells. We found that TNBC cells had a high expression level of DOT1L and a low expression level of E-cadherin compared to normal breast epithelial cells and non-TNBC cells. Here, a novel psammaplin A analog (PsA-3091) exhibited a potent inhibitory effect of DOT1L-mediated H3K79 methylation. Consistently, PsA-3091 also significantly inhibited the proliferation, migration, and invasion of TNBC cells along with the augmented expression of E-cadherin and the suppression of N-cadherin, ZEB1, and vimentin expression. In an orthotopic mouse model, PsA-3091 effectively inhibited lung metastasis and tumor growth by the regulation of DOT1L activity and EMT biomarkers. Together, we report here a new template of DOT1L inhibitor and suggest that targeting DOT1L-mediated H3K79 methylation by a novel PsA analog may be a promising strategy for the treatment of metastatic breast cancer patients.

Abstract 75: Anti-tumor activity of a novel selenonucleoside via targeting Skp2 degradation in paclitaxel-resistant prostate cancer

Prostate cancer (PC) is the most common disease in men over age 50, and its prevalence rate has been gradually increasing since 1980. Taxane-derived anticancer agents are the primary agents used to treat metastatic prostate cancer patients; however, the side effects and acquired drug resistance limit the success of these therapies. Because there is no specific treatment for paclitaxel-resistant prostate cancer, it is necessary to develop new targets and therapeutic strategies to overcome the acquired resistance. In this study, the antitumor activity of a novel selenonucleoside (4′-selenofuranosyl-2,6-dichloropurine, LJ-2618), a third-generation nucleoside, and its plausible mechanisms of action in paclitaxel-resistant prostate cancer (PC-3-Pa) cells were investigated. The established PC-3-Pa cells exhibited over 100-fold resistance against paclitaxel compared to the paclitaxel-sensitive PC-3 cells. LJ-2618, however, effectively inhibited the proliferation of both cell lines with similar IC50values in vitro. In PC-3-Pa cells, the activated PI3K/Akt signaling pathway was suppressed by LJ-2618 treatment. In addition, Skp2 was found to be over-expressed in paclitaxel-resistant cells, and the transfection of Skp2 siRNA recovered the sensitivity of paclitaxel in PC-3-Pa cells. Furthermore, LJ-2618 significantly down-regulated Skp2 expression in PC-3-Pa cells by promoting degradation and inducing destabilization of Skp2, which triggers G2/M cell cycle arrest. In a xenograft mouse model implanted with PC-3-Pa cells, LJ-2618 (3 or 10 mg/kg) effectively inhibited tumor growth with the enhancement of Skp2 degradation and induction of p27 expression in tumor tissues. These findings suggest that LJ-2618 may have a potential for overcoming paclitaxel resistance via promoting Skp2 degradation and stabilizing p27 expression in PC-3-Pa cells. Therefore, the novel selenonucleoside LJ-2618 may lead to the development of a new treatment strategy for patients with paclitaxel-resistant, castration-resistant prostate cancer. This study was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean Government (NRF-2016M3A9B6903499).

Citation Format: Woong Sub Byun, Minkyung Jin, Jinha Yu, Won Kyung Kim, Lak Shin Jeong, Sang Kook Lee. Anti-tumor activity of a novel selenonucleoside via targeting Skp2 degradation in paclitaxel-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 75.

Camporidines A and B: Antimetastatic and Anti-inflammatory Polyketide Alkaloids from a Gut Bacterium of Camponotus kiusiuensis

Chemical studies of gut bacteria of the carpenter ant Camponotus kiusiuensis led to the discovery of two new alkaloids, camporidines A and B (1 and 2), from Streptomyces sp. STA1. The structures of 1 and 2 were established as new polyketide alkaloids bearing a piperidine-cyclopentene-epoxide 6/5/3 tricyclic system based on NMR spectroscopic and mass spectrometric analysis. The relative configurations of the camporidines were determined by their ¹H-¹H NOESY/ROESY and 1D NOE NMR correlations. The experimental ECD spectra of 1 and 2 were compared with their calculated ECD spectra to assign their absolute configurations. Camporidine A (1) displayed antimetastatic activity by suppression of cell invasion against the metastatic breast cancer cell line MDA-MB-231 and showed an anti-inflammatory effect by suppressing nitric oxide production induced by lipopolysaccharide. In addition, the putative biosynthetic gene cluster of the camporidines was identified, and the biosynthetic pathway of the camporidines was proposed based on bioinformatic analysis of the full genome of Streptomyces sp. STA1. Camporidines A and B (1 and 2) could be biosynthesized by a modular type I PKS containing an acyl transferase domain that accepts an unusual extender unit, which becomes the (C1'-C6') hexyl side chain. The post-PKS modification enzymes were predicted to perform an amination and an oxidation along with spontaneous Schiff base formation and generate the unique piperidine-cyclopentene-epoxide 6/5/3 tricyclic framework.

Coculture of Marine Streptomyces sp. With Bacillus sp. Produces a New Piperazic Acid-Bearing Cyclic Peptide

Microbial culture conditions in the laboratory, which conventionally involve the cultivation of one strain in one culture vessel, are vastly different from natural microbial environments. Even though perfectly mimicking natural microbial interactions is virtually impossible, the cocultivation of multiple microbial strains is a reasonable strategy to induce the production of secondary metabolites, which enables the discovery of new bioactive natural products. Our coculture of marine Streptomyces and Bacillus strains isolated together from an intertidal mudflat led to discover a new metabolite, dentigerumycin E (1). Dentigerumycin E was determined to be a new cyclic hexapeptide incorporating three piperazic acids, N-OH-Thr, N-OH-Gly, β-OH-Leu, and a pyran-bearing polyketide acyl chain mainly by analysis of its NMR and MS spectroscopic data. The putative PKS-NRPS biosynthetic gene cluster for dentigerumycin E was found in the Streptomyces strain, providing clear evidence that this cyclic peptide is produced by the Streptomyces strain. The absolute configuration of dentigerumycin E was established based on the advanced Marfey's method, ROESY NMR correlations, and analysis of the amino acid sequence of the ketoreductase domain in the biosynthetic gene cluster. In biological evaluation of dentigerumycin E (1) and its chemical derivatives [2-N,16-N-deoxydenteigerumycin E (2) and dentigerumycin methyl ester (3)], only dentigerumycin E exhibited antiproliferative and antimetastatic activities against human cancer cells, indicating that N-OH and carboxylic acid functional groups are essential for the biological activity.

A novel selenonucleoside suppresses tumor growth by targeting Skp2 degradation in paclitaxel-resistant prostate cancer

Prostate cancer (PC) is the most common disease in men over age 50, and its prevalence rate has been gradually increasing since 1980. Taxane-derived anticancer agents are the primary agents used to treat metastatic prostate cancer patients; however, the side effects and acquired drug resistance limit the success of these therapies. Because there is no specific treatment for paclitaxel-resistant prostate cancer, it is necessary to develop new targets and therapeutic strategies to overcome the acquired resistance. In this study, the antitumor activity of a novel selenonucleoside (4'-selenofuranosyl-2,6-dichloropurine, LJ-2618), a third-generation nucleoside, and its plausible mechanisms of action in paclitaxel-resistant prostate cancer (PC-3-Pa) cells were investigated. The established PC-3-Pa cells exhibited over 100-fold resistance against paclitaxel compared to the paclitaxel-sensitive PC-3 cells. LJ-2618, however, effectively inhibited the proliferation of both cell lines with similar IC₅₀ values in vitro. In PC-3-Pa cells, the activated PI3K/Akt signaling pathway was suppressed by LJ-2618 treatment. In addition, Skp2 was found to be over-expressed in paclitaxel-resistant cells, and the transfection of Skp2 siRNA recovered the sensitivity of paclitaxel in PC-3-Pa cells. Furthermore, LJ-2618 significantly down-regulated Skp2 expression in PC-3-Pa cells by promoting degradation and inducing destabilization of Skp2, which triggers G₂/M cell cycle arrest. In a xenograft mouse model implanted with PC-3-Pa cells, LJ-2618 (3 or 10 mg/kg) effectively inhibited tumor growth with the enhancement of Skp2 degradation and induction of p27 expression in tumor tissues. These findings suggest that LJ-2618 may have potential for overcoming paclitaxel resistance via promoting Skp2 degradation and stabilizing p27 expression in PC-3-Pa cells. Therefore, the novel selenonucleoside LJ-2618 may lead to the development of a new treatment strategy for patients with paclitaxel-resistant, castration-resistant prostate cancer.

Cyclopeptides from the Sponge Stylissa flabelliformis

Three new cyclopeptides, phakellistatins 20-22 (1-3), as well as 10 known cyclopeptides of the same structural class were isolated from the tropical sponge Stylissa flabelliformis. By a combination of chemical and spectroscopic methods, the structures of the new compounds were determined to be an epimeric mixture of cycloheptapeptides (1) and two epimeric cyclodecapeptides (2 and 3) related to the phakellistatins. The cyclopeptides were evaluated for in vitro cytotoxicity against a variety of cancer cell lines, and compounds 2 and 3 exhibited significant activity.

Design, synthesis and anticancer activity of fluorocyclopentenyl-purines and - pyrimidines

Based on the potent anticancer activity of 6'-fluorocyclopentenyl-cytosine 2b in phase IIa clinical trials for the treatment of gemcitabine-resistant pancreatic cancer, we carried out a systematic structure-activity relationship study of 6'-fluorocyclopentenyl-pyrimidines 3a-i and -purines 3j-o to discover novel anticancer agents. We also synthesized the phosphoramidate prodrug 3p of adenine derivative 1b to determine if the anticancer activity depended on the inhibition of DNA and/or RNA polymerase in cancer cells and/or on the inhibition of S-adenosylhomocysteine (SAH) hydrolase. All of the synthesized pyrimidine nucleosides exhibited much less potent anticancer activity in vitro than the cytosine derivative 2b, acting as RNA and/or DNA polymerase inhibitor, indicating that they could not be efficiently converted to their triphosphates for anticancer activity. Among all the synthesized purine nucleosides, adenine derivative 1b and N⁶-methyladenine derivative 3k showed potent anticancer activity, showing equipotent inhibitory activity as the positive control, neplanocin A (1a) or Ara-C. However, the phosphoramidate prodrug 3p showed less anticancer activity than 1b, indicating that it did not act as a RNA and/or DNA polymerase inhibitor like 2b. This result also demonstrates that the anticancer activity of 1b largely depends on the inhibition of histone methyltransferase, resulting from strong inhibition of SAH hydrolase. The deamination of the N⁶-amino group, the addition of the bulky alkyl group at the N⁶-amino group, or the introduction of the amino group at the C2 position almost abolished the anticancer activity.

Depsidomycins B and C: New Cyclic Peptides from a Ginseng Farm Soil-Derived Actinomycete

LC/MS-based chemical profiling of a ginseng farm soil-derived actinomycete strain, Streptomyces sp. BYK1371, enabled the discovery of two new cyclic heptapeptides, depsidomycins B and C (1 and 2), each containing two piperazic acid units and a formyl group at their N-terminus. The structures of 1 and 2 were elucidated by a combination of spectroscopic and chemical analyses. These new compounds were determined to possess d-leucine, d-threonine, d-valine, and S-piperazic acid based on the advanced Marfey's method and a GITC (2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl isothiocyanate) derivatization of their hydrolysates, followed by LC/MS analysis. Depsidomycins B and C displayed significant antimetastatic activities against metastatic breast cancer cells (MDA-MB-231).

Esculetin suppresses tumor growth and metastasis by targeting Axin2/E-cadherin axis in colorectal cancer

Colorectal cancer (CRC) is the most common malignant disease worldwide due to its metastasis via the epithelial-mesenchymal transition (EMT) process. E-cadherin and Wnt signaling are emerging as potential targets for suppressing the EMT. In this context, Axin2 has been recognized as a negative regulator that inhibits glycogen synthase kinase 3β (GSK3β)-mediated degradation of Snail1, a transcriptional repressor of E-cadherin. However, Axin2 can also impede Wnt signaling via β-catenin degradation. Therefore, Axin2 may serve as either a promoter or suppressor of tumors, and the effects of its inhibition on the cell proliferation and metastasis of CRC require further elucidation. Here, esculetin (ES), a coumarin, was found to have the most potential effects on both β-catenin-responsive transcriptional and E-cadherin promoter activities. ES also showed anti-proliferative and anti-invasive activities in CRC cells. Mechanistically, Axin2 suppression by ES contributed to E-cadherin-mediated Wnt signaling inhibition. Moreover, the ability of ES to inhibit tumor growth and metastasis via Axin2 suppression was further supported in an HCT116-implanted orthotopic mouse model. Collectively, these findings suggest that targeting the Axin2/E-cadherin axis by ES may be an attractive therapeutic strategy for the treatment of metastatic CRC.

Abstract 3169: SerpinB2 enhances invadopodia-like structure protrusions and is down-regulated in acquired gefitinib-resistant non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) is a major type of lung cancer which accounts for approximately 80-85% of all lung cancers. The targeted therapies have significantly improved the survival of advanced NSCLC patients, but the failure of targeted therapy due to the resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib, is now considered a major problem. SerpinB2 is a component of the urokinase plasminogen activator (uPA) system and has been recognized as a biomarker for the progression and metastasis of lung cancer. We found that SerpinB2 is down-regulated in gefitinib-resistant (H292-Gef) cells compared to gefitinib-sensitive (H292) cells. The low SerpinB2 levels in H292-Gef cells were also associated with an enhancement in invasiveness and increase in the length of invadopodia-like structures in the cells. The effect on invasiveness and gefitinib sensitivity was confirmed by knockdown and overexpression of SerpinB2. In addition, an antitumor agent yuanhuadine (YD) was used to test the possibility to overcome the resistance through the up-regulation of SerpinB2. YD effectively elevated SerpinB2 levels and suppressed invasive properties in H292-Gef cells. Collectively, these findings demonstrate the prospective role of SerpinB2 as a novel biomarker for acquired gefitinib resistance and a potential target for NSCLC treatment.

Acknowledgement

This study was funded by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2015R1D1A1A02062012).

Citation Format: Song Yi Bae, Donghwa Kim, Hyen Joo Park, Woong Sub Byun, Ji-Young Hong, Hye-Jung Lee, Sang Kook Lee. SerpinB2 enhances invadopodia-like structure protrusions and is down-regulated in acquired gefitinib-resistant non-small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3169. doi:10.1158/1538-7445.AM2017-3169

Abstract 4070: Salternamide A, a marine natural product, suppresses hypoxia-induced accumulation of HIF-1α and induces apoptosis in human colorectal cancer cells

Hypoxia inducible factor-1α (HIF-1α) is an essential regulator of the cellular response to low oxygen concentrations, activating a broad range of genes that provide adaptive responses to oxygen deprivation. HIF-1α is overexpressed in various cancers and therefore represents a considerable chemotherapeutic target. Salternamide A (SA), a novel small molecule that is isolated from a halophilic Streptomyces sp., is a potent cytotoxic agent against a variety of human cancer cell lines. However, the mechanisms by which SA inhibits tumor growth remain to be elucidated. In the present study, we demonstrate that SA efficiently inhibits the hypoxia-induced accumulation of HIF-1α in a time- and concentration-dependent manner in various human cancer cells. In addition, SA suppresses the upstream signaling of HIF-1α, such as PI3K/Akt/mTOR, p42/p44 MAPK, and STAT3 signaling under hypoxic conditions. Furthermore, we found that SA induces cell death by stimulating G2/M cell cycle arrest and apoptosis in human colorectal cancer cells. Taken together, SA was identified as a novel small molecule HIF-1α inhibitor from marine natural products and is potentially a leading candidate in the development of anticancer agents.

Acknowledgment

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean Government (MEST) (MRC No. 2009-0083533)

Citation Format: Duc-Hiep Bach, Woong Sub Byun, Seong-Hwan Kim, Ji-Young Hong, Hyen Joo Park, Dong-Chan Oh, Sang Kook Lee. Salternamide A, a marine natural product, suppresses hypoxia-induced accumulation of HIF-1α and induces apoptosis in human colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4070. doi:10.1158/1538-7445.AM2017-4070