Cytoplasmic synthesis of endogenous Alu complementary DNA via reverse transcription and implications in age-related macular degeneration.

Alu retroelements propagate via retrotransposition by hijacking long interspersed nuclear element-1 (L1) reverse transcriptase (RT) and endonuclease activities. Reverse transcription of Alu RNA into complementary DNA (cDNA) is presumed to occur exclusively in the nucleus at the genomic integration site. Whether Alu cDNA is synthesized independently of genomic integration is unknown. Alu RNA promotes retinal pigmented epithelium (RPE) death in geographic atrophy, an untreatable type of age-related macular degeneration. We report that Alu RNA-induced RPE degeneration is mediated via cytoplasmic L1-reverse-transcribed Alu cDNA independently of retrotransposition. Alu RNA did not induce cDNA production or RPE degeneration in L1-inhibited animals or human cells. Alu reverse transcription can be initiated in the cytoplasm via self-priming of Alu RNA. In four health insurance databases, use of nucleoside RT inhibitors was associated with reduced risk of developing atrophic macular degeneration (pooled adjusted hazard ratio, 0.616; 95% confidence interval, 0.493-0.770), thus identifying inhibitors of this Alu replication cycle shunt as potential therapies for a major cause of blindness.

A novel indole derivative, 2-{3-[1-(benzylsulfonyl)piperidin-4-yl]-2-methyl-1H-indol-1-yl}-1-(pyrrolidin-1-yl)ethenone, suppresses hedgehog signaling and drug-resistant tumor growth.

The Hedgehog (Hh) signaling pathway plays important roles in various physiological functions. Several malignancies, such as basal cell carcinoma (BCC) and medulloblastoma (MB), have been linked to the aberrant activation of Hh signaling. Although therapeutic drugs have been developed to inhibit Hh pathway-dependent cancer growth, drug resistance remains a major obstacle in cancer treatment. Here, we show that the newly identified, 2-{3-[1-(benzylsulfonyl)-1,2,3,6-tetrahydropyridin-4-yl]-2-methyl-1H-indol-1-yl}-1-(pyrrolidin-1-yl)ethenone analog (LKD1214) exhibits comparable potency to vismodegib in suppressing the Hh pathway activation. LKD1214 represses Smoothened (SMO) activity by blocking its ciliary translocation. Interestingly, we also identified that it has a distinctive binding interface with SMO compared with other SMO-regulating chemicals. Notably, it maintains an inhibitory activity against the SmoD477H mutant, as observed in a patient with vismodegib-resistant BCC. Furthermore, LKD1214 inhibits tumor growth in the mouse model of MB. Collectively, these findings suggest that LKD1214 has the therapeutic potential to overcome drug-resistance in Hh-dependent cancers.

Targeting the interaction of AIMP2-DX2 with HSP70 suppresses cancer development.

A tumorigenic factor, AIMP2 lacking exon 2 (AIMP2-DX2), is often upregulated in many cancers. However, how its cellular level is determined is not understood. Here, we report heat-shock protein HSP70 as a critical determinant for the level of AIMP2-DX2. Interaction of the two factors was identified by interactome analysis and structurally determined by X-ray crystallography and NMR analyses. HSP70 recognizes the amino (N)-terminal flexible region, as well as the glutathione S-transferase domain of AIMP2-DX2, via its substrate-binding domain, thus blocking the Siah1-dependent ubiquitination of AIMP2-DX2. AIMP2-DX2-induced cell transformation and cancer progression in vivo was further augmented by HSP70. A positive correlation between HSP70 and AIMP2-DX2 levels was shown in various lung cancer cell lines and patient tissues. Chemical intervention in the AIMP2-DX2-HSP70 interaction suppressed cancer cell growth in vitro and in vivo. Thus, this work demonstrates the importance of the interaction between AIMP2-DX2 and HSP70 on tumor progression and its therapeutic potential against cancer.

Hypoxia-inducible factor-1 (HIF-1) inhibitors from the last decade (2007 to 2016): A "structure-activity relationship" perspective.

Tumor hypoxia is a common feature in most solid tumors and is associated with overexpression of the hypoxia response pathway. Overexpression of the hypoxia-inducible factor (HIF-1) protein leads to angiogenesis, metastasis, apoptosis resistance, and many other pro-tumorigenic responses in cancer development. HIF-1 is a promising target in cancer drug development to increase the patient's response to chemotherapy and radiotherapy as well as the survival rate of cancer patients. Since up to 1% of genes are hypoxia-sensitive, a target-specific HIF-1 inhibitor may be a better clinical candidate in cancer drug discovery. Though no HIF-1 inhibitor is clinically available to date, a lot of effort has been applied during the last decade in search of potent HIF-1 inhibitors. In this review, we will summarize the structure-activity relationship of ten different chemotypes reported to be HIF-1 inhibitors in the last decade (2007-2016), their mechanisms of action for HIF-1 inhibition, progress in the way of target-specific inhibitors, and problems associated with current inhibitors. It is anticipated that the results of these research on the medicinal chemistry of HIF-1 inhibitors will provide decent information in the design and development of future inhibitors.

HIF-1α suppressing small molecule, LW6, inhibits cancer cell growth by binding to calcineurin b homologous protein 1.

Hypoxia inducible factor-1 alpha (HIF-1α) plays an important role in angiogenesis and metastasis and is a promising therapeutic target for the development of anti-cancer drugs. We recently developed a new synthetic small molecule inhibitor of HIF-1α, LW6, which results in inhibition of angiogenesis. To investigate its underlying mechanism, target protein identification was conducted by reverse chemical proteomics using phage display. We identified calcineurin b homologous protein 1 (CHP1) as a target protein of LW6, which specifically binds to CHP1 in a Ca(2+) dependent manner. Covalent labeling of LW6 using photoaffinity and click chemistry demonstrated its co-localization with CHP1 in live cells. HIF-1α was decreased by CHP1 knockdown in HepG2 cells, and angiogenesis was not induced in HUVEC cells by treatment with conditioned media from CHP1 knockdown cells compared to the control. These data demonstrated that LW6 inhibited HIF-1α stability via direct binding with CHP1 resulting in suppression of angiogenesis, providing a new insight into the role of CHP1 in HIF-1α regulation. LW6 could serve as a new chemical probe to explore CHP1 function.

Synthesis and biological evaluation of isoxazoline derivatives as potent M1 muscarinic acetylcholine receptor agonists.

A series of azacyclic compounds substituted with isoxazole and 5-substituted isoxazolines were synthesized as acyclic modifications of the oxime class M1 mACh receptor agonist. Among them, 3-(tetrahydropyrin-3-yl)-5-(2-pyrrolodin-1-yl)isoxazoline compound 4f displayed potent and selective M1 mACh receptor agonist activity in the functional calcium mobilization assay (EC50=31 nM). Introduction of 2-pyrrolidinone and 3-tetrahydropyridine groups are pivotal to the high potency. Moreover, 4f was found to facilitate non-amyloidogenic amyloid precursor protein (APP) processing by significantly increasing ERK1/2 phosphorylation and sAPPα secretion, known disease-modifying effects related to M1 mAChR agonists in Alzheimer's disease (AD).

Synthesis and in vitro evaluation of the antitubercular and antibacterial activity of novel oxazolidinones bearing octahydrocyclopenta[c]pyrrol-2-yl moieties.

A novel series of oxazolidinone-class antimicrobial agents with 5-substituted octahydrocyclopenta[c]pyrrole moieties at the C-ring of linezolid and an acetamide or 1,2,3-triazole ring as the C-5 side chain of the oxazolidinone ring were prepared. The resulting series of compounds were evaluated for in vitro antimicrobial activity against Mycobacterium tuberculosis and a panel of clinically important resistant Gram-positive and -negative bacteria. Among them, endo-alcohol 2a and exo-alcohol 2b showed potent inhibitory activity against M. tuberculosis H37Rv, which was superior to that of linezolid. Several analogues in this series showed potent in vitro antibacterial activity against the clinically important vancomycin-resistant bacteria and showed similar or better potency against linezolid-resistant methicillin-resistant Staphylococcus aureus (MRSA) strains. The hydroxyl group in the azabicyclic C-ring interacted with the same hydrophobic pocket as linezolid based on a docking study. Selected compounds with high antimicrobial activity showed good human microsomal stability and low CYP isozyme and monoamine oxidase (MAO) inhibition.

Brain-Permeable Immunoproteasome-Targeting Macrocyclic Peptide Epoxyketones for Alzheimer's Disease.

Previously, we demonstrated that linear peptide epoxyketones targeting the immunoproteasome (iP) could ameliorate cognitive deficits in mouse models of Alzheimer's disease (AD) independently of amyloid deposition. We also reported the first iP-targeting macrocyclic peptide epoxyketones, which exhibit improved metabolic stability compared with their linear counterparts. Here, we prepared additional macrocyclic peptide epoxyketones and compared them with existing macrocyclic iP inhibitors by assessing Caco2 cell-based permeability and microsomal stability, providing the four best macrocyclic iP inhibitors. We then evaluated the four compounds using the Ames test and the potency assays in BV2 cells, selecting compound 5 as our AD drug lead. When 5 was administered intravenously (40 mg/kg) or orally (150 mg/kg) into healthy BALB/c mice, we observed considerable iP inhibition in the mouse brain, indicating good blood-brain barrier permeability and target engagement. Combined results suggest that 5 is a promising AD drug lead that may need further investigation.

Macrocyclic Immunoproteasome Inhibitors as a Potential Therapy for Alzheimer's Disease.

Previously, we reported that immunoproteasome (iP)-targeting linear peptide epoxyketones improve cognitive function in mouse models of Alzheimer's disease (AD) in a manner independent of amyloid ß. However, these compounds' clinical prospect for AD is limited due to potential issues, such as poor brain penetration and metabolic instability. Here, we report the development of iP-selective macrocyclic peptide epoxyketones prepared by a ring-closing metathesis reaction between two terminal alkenes attached at the P2 and P3/P4 positions of linear counterparts. We show that a lead macrocyclic compound DB-60 (20) effectively inhibits the catalytic activity of iP in ABCB1-overexpressing cells (IC50: 105 nM) and has metabolic stability superior to its linear counterpart. DB-60 (20) also lowered the serum levels of IL-1α and ameliorated cognitive deficits in Tg2576 mice. The results collectively suggest that macrocyclic peptide epoxyketones have improved CNS drug properties than their linear counterparts and offer promising potential as an AD drug candidate.

Alu complementary DNA is enriched in atrophic macular degeneration and triggers retinal pigmented epithelium toxicity via cytosolic innate immunity.

Long interspersed nuclear element-1 (L1)­mediated reverse transcription (RT) of Alu RNA into cytoplasmic Alu complementary DNA (cDNA) has been implicated in retinal pigmented epithelium (RPE) degeneration. The mechanism of Alu cDNA­induced cytotoxicity and its relevance to human disease are unknown. Here we report that Alu cDNA is highly enriched in the RPE of human eyes with geographic atrophy, an untreatable form of age-related macular degeneration. We demonstrate that the DNA sensor cGAS engages Alu cDNA to induce cytosolic mitochondrial DNA escape, which amplifies cGAS activation, triggering RPE degeneration via the inflammasome. The L1-extinct rice rat was resistant to Alu RNA­induced Alu cDNA synthesis and RPE degeneration, which were enabled upon L1-RT overexpression. Nucleoside RT inhibitors (NRTIs), which inhibit both L1-RT and inflammasome activity, and NRTI derivatives (Kamuvudines) that inhibit inflammasome, but not RT, both block Alu cDNA toxicity, identifying inflammasome activation as the terminal effector of RPE degeneration.

LMP2 Inhibitors as a Potential Treatment for Alzheimer's Disease.

The immunoproteasome (iP), an inducible proteasome variant harboring three immunosubunits, low molecular mass polypeptide-2 (LMP2), multicatalytic endopeptidase complex subunit-1, and low molecular mass polypeptide-7 (LMP7), is involved in multiple facets of inflammatory responses. We recently reported that YU102, a dual inhibitor of the iP subunit LMP2 and the constitutive proteasome catalytic subunit ß1, ameliorates cognitive impairments in mouse models of Alzheimer's disease (AD) independently of amyloid deposits. To investigate whether inhibition of LMP2 is sufficient to improve the cognitive functions of AD mice, here we prepared 37 YU102 analogues and identified a potent LMP2 inhibitor DB-310 (28) (IC50: 80.6 nM) with improved selectivity and permeability in cells overexpressing ABCB1 transporters. We show that DB-310 induces suppression of IL-1α production in microglia cells and improves cognitive functions in the Tg2576 transgenic mouse model of AD. This study supports that inhibition of LMP2 is a promising therapeutic strategy for treatment of AD.

Synthesis and Structure-Activity Relationships of Arylsulfonamides as AIMP2-DX2 Inhibitors for the Development of a Novel Anticancer Therapy.

AIMP2-DX2, a splicing variant of AIMP2, is up-regulated in lung cancer, possesses oncogenic activity, and results in tumorigenesis. Specifically inhibiting the interaction between AIMP2-DX2 and HSP70 to suppress AIMP2-DX2-dependent cancers with small molecules is considered a promising avenue for cancer therapeutics. Optimization of hit BC-DXI-04 (IC50 = 40.1 µM) provided new potent sulfonamide based AIMP2-DX2 inhibitors. Among these, BC-DXI-843 showed improved inhibition against AIMP2-DX2 (IC50 = 0.92 µM) with more than 100-fold selectivity over AIMP2 in a luciferase assay. Several binding assays indicated that this compound effectively induces cancer cell apoptosis by specifically interrupting the interaction between DX2 and HSP70, which leads to the degradation of DX2 via Siah1-mediated ubiquitination. More importantly, BC-DXI-843 demonstrated in vivo efficacy in a tumor xenograft mouse model (H460 cells) at a dosage of 50 mg/kg, suggesting it as a promising lead for development of novel therapeutics targeting AIMP2-DX2 in lung cancer.

H727 cells are inherently resistant to the proteasome inhibitor carfilzomib, yet require proteasome activity for cell survival and growth.

The second-in-class proteasome inhibitor (PI) carfilzomib (Kyprolis, Cfz) has contributed to a substantial advancement in multiple myeloma treatment by improving patient survival and quality of life. A considerable portion of patients however display intrinsic resistance to Cfz. Our mechanistic understanding of intrinsic Cfz resistance is limited due to a lack of suitable cell-based models. We report that H727 human bronchial carcinoid cells are inherently resistant to Cfz, yet susceptible to other PIs and inhibitors targeting upstream components of the ubiquitin-proteasome system (UPS). These results indicate that H727 cells remain dependent on the UPS for cell survival and growth despite harboring intrinsic resistance to Cfz. Alterations in the composition of proteasome catalytic subunits via interferon-γ treatment or siRNA knockdown results in sensitization of H727 cells to Cfz. We postulate that a potential link may exist between the composition of proteasome catalytic subunits and the cellular response to Cfz. Overall, H727 cells may serve as a useful cell-based model for de novo Cfz resistance and our results suggest previously unexplored mechanisms of de novo PI resistance.

Development of Novel Epoxyketone-Based Proteasome Inhibitors as a Strategy To Overcome Cancer Resistance to Carfilzomib and Bortezomib.

Over the past 15 years, proteasome inhibitors (PIs), namely bortezomib, carfilzomib (Cfz) and ixazomib, have significantly improved the overall survival and quality-of-life for multiple myeloma (MM) patients. However, a significant portion of MM patients do not respond to PI therapies. Drug resistance is present either de novo or acquired after prolonged therapy through mechanisms that remain poorly defined. The lack of a clear understanding of clinical PI resistance has hampered the development of next-generation PI drugs to treat MM patients who no longer respond to currently available therapies. Here, we designed and synthesized novel epoxyketone-based PIs by structural modifications at the P1' site. We show that a Cfz analog, 9, harboring a hydroxyl substituent at its P1' position was highly cytotoxic against cancer cell lines displaying de novo or acquired resistance to Cfz. These results suggest that peptide epoxyketones incorporating P1'-targeting moieties may have the potential to bypass resistance mechanisms associated with Cfz and to provide additional clinical options for patients resistant to Cfz.

A dual inhibitor of the proteasome catalytic subunits LMP2 and Y attenuates disease progression in mouse models of Alzheimer's disease.

The immunoproteasome (iP) is a variant of the constitutive proteasome (cP) that is abundantly expressed in immune cells which can also be induced in somatic cells by cytokines such as TNF-α or IFN-γ. Accumulating evidence support that the iP is closely linked to multiple facets of inflammatory response, eventually leading to the development of several iP inhibitors as potential therapeutic agents for autoimmune diseases. Recent studies also found that the iP is upregulated in reactive glial cells surrounding amyloid ß (Aß) deposits in brains of Alzheimer's disease (AD) patients, but the role it plays in the pathogenesis of AD remains unclear. In this study, we investigated the effects of several proteasome inhibitors on cognitive function in AD mouse models and found that YU102, a dual inhibitor of the iP catalytic subunit LMP2 and the cP catalytic subunit Y, ameliorates cognitive impairments in AD mouse models without affecting Aß deposition. The data obtained from our investigation revealed that YU102 suppresses the secretion of inflammatory cytokines from microglial cells. Overall, this study indicates that there may exist a potential link between LMP2/Y and microglia-mediated neuroinflammation and that inhibition of these subunits may offer a new therapeutic strategy for AD.

Design, synthesis, and biological evaluation of structurally modified isoindolinone and quinazolinone derivatives as hedgehog pathway inhibitors.

The Hedgehog (Hh) signaling pathway is associated with diverse aspects of cellular events, such as cell migration, proliferation, and differentiation throughout embryonic development and tissue patterning. An abnormal Hh signaling pathway is linked to numerous human cancers, including basal cell carcinoma (BCC), medulloblastoma (MB), lung cancer, prostate cancer, and ovarian cancer, and it is therefore a promising target in cancer therapy. Using a structure-hopping approach, we designed new Hh signaling pathway inhibitors with isoindolinone or quinazolinone moieties, which were synthesized and biologically evaluated using an 8xGli-luciferase (Gli-Luc) reporter assay in NIH3T3 cells. Compounds 9-11 and 14 with isoindolinone scaffolds demonstrated moderate Hh inhibitory activity; whereas quinazolinone derivatives 24, 29, 32, 34, and 35 exhibited good potency with submicromolar IC50 values and the analog 28 showed nanomolar IC50 value. Although sonidegib shows a decrease in inhibitory effect on vismodegib resistance-conferring Smo mutants, the structurally modified new compounds not only possess the pharmacophoric properties of Hh pathway inhibition but also preserve the suppressive potency in drug-resistant Smo mutants. Mechanistically, quinazolinone derivatives 28 and 34 suppress Hh signaling by blocking Smo and Gli translocation into the cilia, similar to vismodegib and sonidegib. Additionally, the human microsomal stability of the representative analogs 28 and 34 were determined to be comparable to that of the reference compound sonidegib. Thus, these new scaffolds can serve as a platform for the development of novel cancer therapeutics targeting the Hh pathway.

An Insight into Drug Repositioning for the Development of Novel Anti-Cancer Drugs.

Increased investments and development of new technologies in drug discovery have barely improved the outcome of medicinal entities in the drug discovery market from a long time. Minimal success rates of drug approvals, poor safety profiles, and long development processes are some of many hurdles encountered in the drug discovery field. Therefore, drug repurposing can provide an alternative approach to meet the demands of the new, potent and safe anti-cancer agents in terms of both economic cost and time efficiency. The common molecular pathways of different diseases and secondary indications of most of the approved drugs, and advances in genomics, informatics and biology, as well as the availability of approved or safe drug libraries can certainly provide an improved and efficient way of screening safer drugs for new indications. Promising results of drug repurposing in different therapeutic areas have encouraged the scientific community to discover new drugs for different diseases using this methodology. Herein, we provide a general overview of structurally and functionally diverse approved drugs that have been repurposed as anti-cancer drugs.

Phytosphingosine promotes megakaryocytic differentiation of myeloid leukemia cells.

We report that phytosphingosine, a sphingolipid found in many organisms and implicated in cellular signaling, promotes megakaryocytic differentiation of myeloid leukemia cells. Specifically, phytosphingosine induced several hallmark changes associated with megakaryopoiesis from K562 and HEL cells including cell cycle arrest, cell size increase and polyploidization. We also confirmed that cell type specific markers of megakaryocytes, CD41a and CD42b are induced by phytosphingosine. Phospholipids with highly similar structures were unable to induce similar changes, indicating that the activity of phytosphingosine is highly specific. Although phytosphingosine is known to activate p38 MAPK-mediated apoptosis, the signaling mechanisms involved in megakaryopoiesis appear to be distinct. In sum, we present another model for dissecting molecular details of megakaryocytic differentiation which in large part remains obscure.

2-(trimethylammonium) ethyl (R)-3-methoxy-3-oxo-2-stearamidopropyl phosphate suppresses osteoclast maturation and bone resorption by targeting macrophage-colony stimulating factor signaling.

2-(Trimethylammonium) ethyl (R)-3-methoxy-3-oxo-2-stearamidopropyl phosphate [(R)-TEMOSPho], a derivative of an organic chemical identified from a natural product library, promotes highly efficient megakaryopoiesis. Here, we show that (R)-TEMOSPho blocks osteoclast maturation from progenitor cells of hematopoietic origin, as well as blocking the resorptive function of mature osteoclasts. The inhibitory effect of (R)-TEMOSPho on osteoclasts was due to a disruption of the actin cytoskeleton, resulting from impaired downstream signaling of c-Fms, a receptor for macrophage-colony stimulating factor linked to c-Cbl, phosphoinositol-3-kinase (PI3K), Vav3, and Rac1. In addition, (R)-TEMOSPho blocked inflammation-induced bone destruction by reducing the numbers of osteoclasts produced in mice. Thus, (R)-TEMOSPho may represent a promising new class of antiresorptive drugs for the treatment of bone loss associated with increased osteoclast maturation and activity.