Aster-dependent nonvesicular transport facilitates dietary cholesterol uptake

Intestinal absorption is an important contributor to systemic cholesterol homeostasis. Niemann-Pick C1 Like 1 (NPC1L1) assists in the initial step of dietary cholesterol uptake, but how cholesterol moves downstream of NPC1L1 is unknown. We show that Aster-B and Aster-C are critical for nonvesicular cholesterol movement in enterocytes. Loss of NPC1L1 diminishes accessible plasma membrane (PM) cholesterol and abolishes Aster recruitment to the intestinal brush border. Enterocytes lacking Asters accumulate PM cholesterol and show endoplasmic reticulum cholesterol depletion. Aster-deficient mice have impaired cholesterol absorption and are protected against diet-induced hypercholesterolemia. Finally, the Aster pathway can be targeted with a small-molecule inhibitor to manipulate cholesterol uptake. These findings identify the Aster pathway as a physiologically important and pharmacologically tractable node in dietary lipid absorption.

Development of a novel histone deacetylase inhibitor unveils the role of HDAC11 in alleviating depression by inhibition of microglial activation

Histone deacetylases (HDACs) are key epigenetic regulators and classified into four subtypes. Despite the various roles of each HDAC isoform, the lack of selective HDAC inhibitors has limited the elucidation of their roles in biological systems. HDAC11, the sole class-IV HDAC, is highly expressed in the brain, however, the role of HDAC11 in microglia is not fully understood. Based on the modification of MC1568, we developed a novel HDAC inhibitor, 5. Interestingly, 5 suppresses lipopolysaccharide-induced microglial activation by the initiation of autophagy and subsequent inhibition of nitric oxide production. Furthermore, we demonstrated that 5 significantly alleviates depression-like behavior by inhibiting microglial activation in mouse brain. Our discovery reveals that specific pharmacological regulation of HDAC11 induces autophagy and reactive nitrogen species balance in microglia for the first time, which makes HDAC11 a new therapeutic target for depressive disorder.

Aster-dependent non-vesicular transport facilitates dietary cholesterol uptake

Intestinal cholesterol absorption is an important contributor to systemic cholesterol homeostasis. Niemann-Pick C1 Like 1 (NPC1L1), the target of the drug ezetimibe (EZ), assists in the initial step of dietary cholesterol uptake. However, how cholesterol moves downstream of NPC1L1 is unknown. Here we show that Aster-B and Aster-C are critical for non-vesicular cholesterol movement in enterocytes, bridging NPC1L1 at the plasma membrane (PM) and ACAT2 in the endoplasmic reticulum (ER). Loss of NPC1L1 diminishes accessible PM cholesterol in enterocytes and abolishes Aster recruitment to the intestinal brush border. Enterocytes lacking Asters accumulate cholesterol at the PM and display evidence of ER cholesterol depletion, including decreased cholesterol ester stores and activation of the SREBP-2 transcriptional pathway. Aster-deficient mice have impaired cholesterol absorption and are protected against diet-induced hypercholesterolemia. Finally, we show that the Aster pathway can be targeted with a small molecule inhibitor to manipulate dietary cholesterol uptake. These findings identify the Aster pathway as a physiologically important and pharmacologically tractable node in dietary lipid absorption.

One-Sentence Summary

Identification of a targetable pathway for regulation of dietary cholesterol absorption.

Abstract 510: Targeting metabolic vulnerabilities to reduce triple negative breast cancer health disparities

Triple negative breast cancer (TNBC) occurs in 10-15% of all breast cancer (BC) patients, yet it accounts for almost half of all BC deaths. Women of African ancestry (WAA) are twice as likely as women of European Ancestry (WEA) to be diagnosed with advanced TNBC with worse prognosis. Emerging data shows that insulin resistance and high circulating levels of insulin are more prevalent in WAA with invasive BCs than in WEA, and activation of the AKT/mTOR pathway by insulin may occur in aggressive TNBC. Reports show diabetic patients treated with metformin, a biguanide drug used to treat diabetes type 2, have reduced incidence of BC and improved survival. However, anticancer actions of metformin require use of high drug doses with limiting side effects in vivo. To address this challenge, we used a structure-activity strategy to develop biguanide analogues with more potent anticancer action and safety at lower doses in vivo. Using TNBC cell proliferation in vitro to screen analogues, promising candidates were identified that exerted dose-dependent inhibition of cell proliferation at significantly lower doses than that of parental metformin (P<0.01). As antitumor effects of metformin are attributed in part to activation of LKB1-AMPK pathways, we find that biguanide analogues also strongly induce AMPK phosphorylation on Western immunoblots and significantly reduce phosphorylation of downstream mTOR signaling pathway components including p70S6K, S6 ribosomal protein and 4E-BP1. Further, analogues induce TNBC cell apoptosis in vitro at lower doses than metformin. In vivo, analogues were more effective than metformin in stopping human TNBC xenograft progression in nude mouse models (P<0.001). Notably, analogues were also more effective than metformin at blocking lung metastases in syngeneic murine 4T1 TNBC models (P<0.05). Transcriptome analyses comparing mammary tumors and lung metastases revealed that analogue JD006 down-regulated genes related to oxidative phosphorylation in lung metastases treated with JD006 and increased expression of genes related to T-cell activation. Further, gene expression in tumors treated with JD006 showed significant down-regulation of long non-coding RNAs that associate with the up-regulation of malignant transformation and activation of M1 macrophages. Importantly, our data indicate that analogue JD006 modulates the activity/trafficking of myeloid-derived suppressor cells (MDSC) and tumor infiltrating lymphocytes (TIL) that may significantly impact TNBC responses to immune checkpoint inhibitors. Further understating of potential biologic differences between TNBC of WAA and WEA is needed to design more effective therapeutic strategies to reduce TNBC health disparities. New targeted treatments could be beneficial for patients afflicted with this deadly disease. (Funding: CBCRP B27IB3869, 4IB-0058; NCI U54 CA143930; JCCC BC Award, Team Research Grant; UCLA TDG).

Citation Format: Diana C. Márquez-Garban, Gang Deng, Lorena P. Burton, Gaoyuan Ma, Vishaka Muhunthan, Begonya Comin-Anduix, Gabriela Llarena, Neda Moatamed, Jennifer Murphy, Nalo Hamilton, Daivd Shackelford, Michael E. Jung, Richard J. Pietras. Targeting metabolic vulnerabilities to reduce triple negative breast cancer health disparities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 510.

Intramolecular N-H⋅⋅⋅F Hydrogen Bonding Interaction in a Series of 4-Anilino-5-Fluoroquinazolines: Experimental and Theoretical Characterization of Electronic and Conformational Effects

The 4-anilino-6,7-ethylenedioxy-5-fluoroquinazoline scaffold is presented as a novel model system for the characterization of the weak NH⋅⋅⋅F hydrogen bonding (HB) interaction. In this scaffold, the aniline NH proton is forced into close proximity with the nearby fluorine (d_H,F ∼2.0 Å, ∠∼138°), and a through-space interaction is observed by NMR spectroscopy with couplings (^1h J_NH,F ) of 19±1 Hz. A combination of experimental (NMR spectroscopy and X-ray crystallography) and theoretical methods (DFT calculations) were used for the characterization of this weak interaction. In particular, the effects of conformational rigidity and steric compression on coupling were investigated. This scaffold was used for the direct comparison of fluoride with methoxy as HB acceptors, and the susceptibility of the NH⋅⋅⋅F interaction to changes in electron distribution and resonance was probed by preparing a series of molecules with different electron-donating or -withdrawing groups in the positions para to the NH and F. The results support the idea that fluorine can act as a weak HB acceptor, and the HB strength can be modulated through additive and linear electronic substituent effects.

Insight into the molecular basis of substrate recognition by the wall teichoic acid glycosyltransferase TagA

Wall teichoic acid (WTA) polymers are covalently affixed to the Gram-positive bacterial cell wall and have important functions in cell elongation, cell morphology, biofilm formation, and β-lactam antibiotic resistance. The first committed step in WTA biosynthesis is catalyzed by the TagA glycosyltransferase (also called TarA), a peripheral membrane protein that produces the conserved linkage unit, which joins WTA to the cell wall peptidoglycan. TagA contains a conserved GT26 core domain followed by a C-terminal polypeptide tail that is important for catalysis and membrane binding. Here, we report the crystal structure of the Thermoanaerobacter italicus TagA enzyme bound to UDP-N-acetyl-d-mannosamine, revealing the molecular basis of substrate binding. Native MS experiments support the model that only monomeric TagA is enzymatically active and that it is stabilized by membrane binding. Molecular dynamics simulations and enzyme activity measurements indicate that the C-terminal polypeptide tail facilitates catalysis by encapsulating the UDP-N-acetyl-d-mannosamine substrate, presenting three highly conserved arginine residues to the active site that are important for catalysis (R214, R221, and R224). From these data, we present a mechanistic model of catalysis that ascribes functions for these residues. This work could facilitate the development of new antimicrobial compounds that disrupt WTA biosynthesis in pathogenic bacteria.

Classes of Drugs that Mitigate Radiation Syndromes

We previously reported several vignettes on types and classes of drugs able to mitigate acute and, in at least one case, late radiation syndromes in mice. Most of these had emerged from high throughput screening (HTS) of bioactive and chemical drug libraries using ionizing radiation-induced lymphocytic apoptosis as a readout. Here we report the full analysis of the HTS screen of libraries with 85,000 small molecule chemicals that identified 220 "hits." Most of these hits could be allocated by maximal common substructure analysis to one of 11 clusters each containing at least three active compounds. Further screening validated 23 compounds as being most active; 15 of these were cherry-picked based on drug availability and tested for their ability to mitigate acute hematopoietic radiation syndrome (H-ARS) in mice. Of these, five bore a 4-nitrophenylsulfonamide motif while 4 had a quinoline scaffold. All but two of the 15 significantly (p < 0.05) mitigated H-ARS in mice. We had previously reported that the lead 4-(nitrophenylsulfonyl)-4-phenylpiperazine compound (NPSP512), was active in mitigating multiple acute and late radiation syndromes in mice of more than one sex and strain. Unfortunately, the formulation of this drug had to be changed for regulatory reasons and we report here on the synthesis and testing of active analogs of NPSP512 (QS1 and 52A1) that have increased solubility in water and in vivo bioavailability while retaining mitigator activity against H-ARS (p < 0.0001) and other radiation syndromes. The lead quinoline 057 was also active in multiple murine models of radiation damage. Taken together, HTS of a total of 150,000 bioactive or chemical substances, combined with maximal common substructure analysis has resulted in the discovery of diverse groups of compounds that can mitigate H-ARS and at least some of which can mitigate multiple radiation syndromes when given starting 24 h after exposure. We discuss what is known about how these agents might work, and the importance of formulation and bioavailability.

Novel Metformin Analogues for Treatment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDCA) is a leading cause of cancer death in the US. Patients diagnosed with PDCA generally present with advanced disease with poor prognosis and limited treatment options. African American patients have higher incidence and mortality of PDCA than Caucasian American or any other ethnic group. Different factors have been attributed to contribute to this health disparity, among them higher incidence of Diabetes Mellitus type 2. To address the need for new therapeutic approaches, we note epidemiologic reports that patients with diabetes mellitus-type 2 treated with the biguanide drug metformin, but not other antidiabetic drugs, have a reduced risk of PDCA and an increased survival rate among those with PDCA. The main physiologic effect of metformin is to lower blood glucose and reduce hyperinsulinemia associated with insulin resistance. In the cell, metformin stimulates AMP-activated protein kinase (AMPK) that in turn inhibits mTORC1 which integrates signals from an array of intracellular pathways to regulate cell growth. Recent clinical trials describe modest antiproliferative effects from use of neoadjuvant metformin, but no significant clinical benefit occurred when metformin was dosed at glycemic control levels in patients with advanced cancers. These findings suggest that development of more potent anticancer analogues of metformin may help to boost clinical benefit and patient survival. Hence, we have designed new biguanide analogues of metformin, and screening of these compounds in preclinical PDCA models show that selected analogues are more efficacious in blocking tumor progression than parental metformin at lower doses. Using proliferation assays in vitro, PDCA cells (Panc 1, MIA Paca-2) were treated 72-hrs with metformin or analogues, and greater dose-dependent inhibition of PDCA cell proliferation was found with analogues as compared to metformin (P<0.001). Further, apoptosis was also markedly induced by metformin analogues as compared to parental metformin (P<0.01). Antitumor effects of metformin are attributed in part to activation LKB1-AMPK pathways and downstream blockade of mTOR signaling, which is often increased in PDCA cells. Using PDCA cells treated in vitro with analogues for 24-hrs, we find that analogues induce AMPK phosphorylation and suppression of mTOR signaling, thus blocking protein synthesis and tumor proliferation. With an in vivo PANC 1 xenograft model in nude mice, lead metformin analogues given by oral gavage daily significantly inhibited tumor progression over 28-days as compared to appropriate controls (P<0.0001). Our findings show that selected metformin analogues have potent anticancer activity in preclinical PDCA models and may have promise as new targeted therapeutics for patients afflicted with this deadly disease. [Funded by NIH/NCI R21CA176337 and NIH/NCI U54 CA143930]

Development of Novel Mitochondrial Pyruvate Carrier Inhibitors to Treat Hair Loss

Herein, we report the synthesis and evaluation of novel analogues of UK-5099 both in vitro and in vivo for the development of mitochondrial pyruvate carrier (MPC) inhibitors to treat hair loss. A comprehensive understanding of the structure-activity relationship was obtained by varying four positions of the hit compound, namely, the alkyl group on the N1 position, substituents on the indole core, various aromatic and heteroaromatic core structures, and various Michael acceptors. The major discovery was that the inhibitors with a 3,5-bis(trifluoromethyl)benzyl group at the N1 position were shown to have much better activity than JXL001 (UK-5099) to increase cellular lactate production. Additionally, analogue JXL069, possessing a 7-azaindole heterocycle, was also shown to have significant MPC inhibition activity, which further increases the chemical space for drug design. Finally, more than 10 analogues were tested on shaved mice by topical treatment and promoted obvious hair growth on mice.

Development of a Potent Brain-Penetrant EGFR Tyrosine Kinase Inhibitor against Malignant Brain Tumors

The epidermal growth factor receptor (EGFR) is genetically altered in nearly 60% of glioblastoma tumors; however, tyrosine kinase inhibitors (TKIs) against EGFR have failed to show efficacy for patients with these lethal brain tumors. This failure is attributed to the inability of clinically tested EGFR TKIs to cross the blood-brain barrier (BBB) and achieve adequate pharmacological levels to inhibit various oncogenic forms of EGFR that drive glioblastoma. Through SAR analysis, we developed compound 5 (JCN037) from an anilinoquinazoline scaffold by ring fusion of the 6,7-dialkoxy groups to reduce the number of rotatable bonds and polar surface area and by introduction of an ortho-fluorine and meta-bromine on the aniline ring for improved potency and BBB penetration. Relative to the conventional EGFR TKIs erlotinib and lapatinib, JCN037 displayed potent activity against EGFR amplified/mutant patient-derived cell cultures, significant BBB penetration (2:1 brain-to-plasma ratio), and superior efficacy in an EGFR-driven orthotopic glioblastoma xenograft model.

Abstract 692: Discovery of novel metformin derivatives with potent antitumor activity in combination with immunotherapy for treatment of triple-negative breast cancer

Triple negative breast cancer (TNBC) occurs in about 15% of breast cancer (BC) patients, yet it accounts for almost 50% of all BC deaths. TNBC is characterized by lack of expression of estrogen, progesterone and HER2 receptors, and it cannot be treated with current targeted therapies. TNBCs are heterogeneous and occur often in younger and African American women. Although initially responsive to some chemotherapies, TNBCs tend to relapse early and metastasize, leading to poor survival. Development of new therapeutic approaches for clinical translation is a high priority. Emerging evidence from epidemiologic and preclinical work suggests that metformin, the most widely used drug to treat type 2 diabetes mellitus, exerts anticancer activity in BC. Diabetic patients treated with metformin have a reduced incidence and better survival from BC. Moreover, TNBC cells are reported to be uniquely sensitive to metformin in vitro, but strong antitumor effects require relatively high metformin doses in vivo. To address this challenge, we used a structure-activity strategy to develop metformin analogues with more potent anticancer action and safety at lower doses in vivo. Using TNBC cell proliferation in vitro to screen drug candidates, selected new metformin analogues were identified that exerted dose-dependent inhibition of cell proliferation at significantly lower concentrations than that of parental metformin (P&lt;0.01). As antitumor effects of metformin are attributed in part to activation of the LKB1-AMPK pathway, we find that metformin analogues also strongly induced phosphorylation of AMPK by Western blot assays and significantly reduced phosphorylation of mTOR downstream signaling pathway components (p70S6K, S6 ribosomal protein, 4E-BP1). Analogues also induced TNBC cell apoptosis at lower doses than metformin. In vivo, metformin analogues were more effective at lower doses given by oral gavage than metformin in suppressing TNBC human tumor xenograft progression in nude mouse models (P&lt;0.001). It is notable that data from clinical trials with immune checkpoint inhibitors (ICI) indicate that TNBCs are susceptible to immunotherapy, but only a minority of patients to date have had clinical benefit. Importantly, our studies indicate that metformin analogues modulate the activity and trafficking of myeloid-derived suppressor cells (MDSC) and tumor infiltrating lymphocytes (TIL) that may significantly impact TNBC responses to ICIs. Thus, combination therapy with metformin analogues and anti-PD-L1 antibodies was more effective at blocking tumor growth in vivo than either treatment given alone using murine 4T1 TNBC implants in syngeneic, immune-competent BALB/C mouse models. In the TNBC microenvironment, analogue treatment with ICIs elicited significant infiltration of predominantly effector T-cells, increased populations of tissue-resident memory T-cells, and a reduction of exhausted T-cells as compared to controls (P&lt;0.01). Moreover, MDSC were significantly decreased after combination therapy as compared to appropriate controls (P&lt;0.05). Since there are currently no specific treatments for TNBC, identification of a new targeted therapeutic approach could ultimately be beneficial for managing patients afflicted with this deadly disease. Funding by California BC RP, NCI U54 CA143930.

Citation Format: Diana C. Márquez-Garban, Gang Deng, Begonya Comin-Anduix, Vishaka Muhunthan, Gaoyuan Ma, Jennifer Murphy, Alejandro J. Garcia, Cristian D. Yanes, Lorena R. Burton, Nalo Hamilton, David Shackelford, Michael E. Jung, Richard J. Pietras. Discovery of novel metformin derivatives with potent antitumor activity in combination with immunotherapy for treatment of triple-negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 692.

A Cell-based Screen in Actinomyces oris to Identify Sortase Inhibitors

Sortase enzymes are attractive antivirulence drug targets that attach virulence factors to the surface of Staphylococcus aureus and other medically significant bacterial pathogens. Prior efforts to discover a useful sortase inhibitor have relied upon an in vitro activity assay in which the enzyme is removed from its native site on the bacterial surface and truncated to improve solubility. To discover inhibitors that are effective in inactivating sortases in vivo, we developed and implemented a novel cell-based screen using Actinomyces oris, a key colonizer in the development of oral biofilms. A. oris is unique because it exhibits sortase-dependent growth in cell culture, providing a robust phenotype for high throughput screening (HTS). Three molecules representing two unique scaffolds were discovered by HTS and disrupt surface protein display in intact cells and inhibit enzyme activity in vitro. This represents the first HTS for sortase inhibitors that relies on the simple metric of cellular growth and suggests that A. oris may be a useful platform for discovery efforts targeting sortase.

Cardiorespiratory fitness and accelerometer-determined physical activity following one year of free-living high-intensity interval training and moderate-intensity continuous training: a randomized trial

Background

Free-living adherence to high-intensity interval training (HIIT) has not been adequately tested. This randomized trial examined changes in cardiorespiratory fitness (CRF) and accelerometer-measured purposeful physical activity over 12 months of free-living HIIT versus moderate-intensity continuous training (MICT).

Methods

Ninety-nine previously low-active participants with overweight/obesity were randomly assigned to HIIT (n = 47) or MICT (n = 52). Both interventions were combined with evidence-based behaviour change counselling consisting of 7 sessions over 2 weeks. Individuals in HIIT were prescribed 10 X 1-min interval-based exercise 3 times per week (totalling 75 min) whereas individuals in MICT were prescribed 150 min of steady-state exercise per week (50 mins 3 times per week). Using a maximal cycling test to exhaustion with expired gas analyses, CRF was assessed at baseline and after 6 and 12 months of free-living exercise. Moderate-to-vigorous physical activity of 10+ minutes (MVPA10+) was assessed by 7-day accelerometry at baseline, 3, 6, 9, and 12 months. Intention to treat analyses were conducted using linear mixed models.

Results

CRF was improved over the 12 months relative to baseline in both HIIT (+ 0.15 l/min, 95% CI 0.08 to 0.23) and MICT (+ 0.11 l/min, 95% CI 0.05 to 0.18). Both groups improved 12-month MVPA10+ above baseline (HIIT: + 36 min/week, 95% CI 17 to 54; MICT: + 69 min/week, 95% CI 49 to 89) with the increase being greater (by 33 min, 95% CI 6 to 60) in MICT (between group difference, P = 0.018).

Conclusion

Despite being prescribed twice as many minutes of exercise and accumulating significantly more purposeful exercise, CRF improvements were similar across 12 months of free-living HIIT and MICT in previously low-active individuals with overweight/obesity.

Isoquinoline thiosemicarbazone displays potent anticancer activity with in vivo efficacy against aggressive leukemias

A potent class of isoquinoline-based α-N-heterocyclic carboxaldehyde thiosemicarbazone (HCT) compounds has been rediscovered; based upon this scaffold, three series of antiproliferative agents were synthesized through iterative rounds of methylation and fluorination modifications, with anticancer activities being potentiated by physiologically relevant levels of copper. The lead compound, HCT-13, was highly potent against a panel of pancreatic, small cell lung carcinoma, prostate cancer, and leukemia models, with IC₅₀ values in the low-to-mid nanomolar range. Density functional theory (DFT) calculations showed that fluorination at the 6-position of HCT-13 was beneficial for ligand-copper complex formation, stability, and ease of metal-center reduction. Through a chemical genomics screen, we identify DNA damage response/replication stress response (DDR/RSR) pathways, specifically those mediated by ataxia-telangiectasia and Rad3-related protein kinase (ATR), as potential compensatory mechanism(s) of action following HCT-13 treatment. We further show that the cytotoxicity of HCT-13 is copper-dependent, that it promotes mitochondrial electron transport chain (mtETC) dysfunction, induces production of reactive oxygen species (ROS), and selectively depletes guanosine nucleotide pools. Lastly, we identify metabolic hallmarks for therapeutic target stratification and demonstrate the in vivo efficacy of HCT-13 against aggressive models of acute leukemias in mice.

Phenylalanine Monitoring via Aptamer-Field-Effect Transistor Sensors

Determination of the amino acid phenylalanine is important for lifelong disease management in patients with phenylketonuria, a genetic disorder in which phenylalanine accumulates and persists at levels that alter brain development and cause permanent neurological damage and cognitive dysfunction. Recent approaches for treating phenylketonuria focus on injectable medications that efficiently break down phenylalanine but sometimes result in detrimentally low phenylalanine levels. We have identified new DNA aptamers for phenylalanine in two formats, initially as fluorescent sensors and then, incorporated with field-effect transistors (FETs). Aptamer-FET sensors detected phenylalanine over a wide range of concentrations (fM to mM). para-Chlorophenylalanine, which inhibits the enzyme that converts phenylalanine to tyrosine, was used to induce hyperphenylalaninemia during brain development in mice. Aptamer-FET sensors were specific for phenylalanine versus para-chlorophenylalanine and differentiated changes in mouse serum phenylalanine at levels expected in patients. Aptamer-FETs can be used to investigate models of hyperphenylalanemia in the presence of structurally related enzyme inhibitors, as well as naturally occurring amino acids. Nucleic acid-based receptors that discriminate phenylalanine analogs, some that differ by a single substituent, indicate a refined ability to identify aptamers with binding pockets tailored for high affinity and specificity. Aptamers of this type integrated into FETs enable rapid, electronic, label-free phenylalanine sensing.

Development and preclinical pharmacology of a novel dCK inhibitor, DI-87

BACKGROUND

Deoxycytidine kinase (dCK) is an essential enzyme for production of nucleotides via the salvage pathway; DI-87 is a novel dCK inhibitor in preclinical development for use in anticancer therapy. The current study utilizes PET imaging to evaluate PK-PD relationships and to determine optimal dosing of the drug.

METHODS

NSG mice bearing CEM tumors had plasma and tumor PK assessed using mass spectrometry following oral administration of DI-87. dCK inhibition was assessed after a single dose of oral DI-87 followed by a [¹⁸F]CFA PET probe and PET imaging. Tumor growth inhibition was assessed by orally administering DI-87 with concurrent intraperitoneal thymidine.

RESULTS

DI-87 had an in vitro EC₅₀ of 10.2 nM with low protein binding. Peak DI-87 concentrations were observed between 1-3 h and 3-9 h in plasma and tumor, respectively, with tumor concentrations less than one third of plasma. Full dCK inhibition, as evaluated by PET imaging, was observed as early as 3 h following 25 mg/kg dosing and was maintained for 12 h, with full recovery of enzyme activity after 36 h. When DI-87 was administered as repeated doses in combination with thymidine, full dCK inhibition was maintained at 12 h (25 mg/kg twice daily dose) and led to maximal tumor growth inhibition.

CONCLUSIONS

DI-87 is a promising new compound for use in combination therapy against tumors expressing dCK. Utilizing a [¹⁸F]CFA PET probe targeting the pathway of interest allowed for efficient and accurate identification of the optimal dose for growth inhibition.

Metabolic Modifier Screen Reveals Secondary Targets of Protein Kinase Inhibitors within Nucleotide Metabolism

Biosynthesis of the pyrimidine nucleotide uridine monophosphate (UMP) is essential for cell proliferation and is achieved by the activity of convergent de novo and salvage metabolic pathways. Here we report the development and application of a cell-based metabolic modifier screening platform that leverages the redundancy in pyrimidine metabolism for the discovery of selective UMP biosynthesis modulators. In evaluating a library of protein kinase inhibitors, we identified multiple compounds that possess nucleotide metabolism modifying activity. The JNK inhibitor JNK-IN-8 was found to potently inhibit nucleoside transport and engage ENT1. The PDK1 inhibitor OSU-03012 (also known as AR-12) and the RAF inhibitor TAK-632 were shown to inhibit the therapeutically relevant de novo pathway enzyme DHODH and their affinities were unambiguously confirmed through in vitro assays and co-crystallization with human DHODH.

Antiestrogens in combination with immune checkpoint inhibitors in breast cancer immunotherapy

Breast cancers (BCs) with expression of estrogen receptor-alpha (ERα) occur in more than 70% of newly-diagnosed patients in the U.S. Endocrine therapy with antiestrogens or aromatase inhibitors is an important intervention for BCs that express ERα, and it remains one of the most effective targeted treatment strategies. However, a substantial proportion of patients with localized disease, and essentially all patients with metastatic BC, become resistant to current endocrine therapies. ERα is present in most resistant BCs, and in many of these its activity continues to regulate BC growth. Fulvestrant represents one class of ERα antagonists termed selective ER downregulators (SERDs). Treatment with fulvestrant causes ERα down-regulation, an event that helps overcome several resistance mechanisms. Unfortunately, full antitumor efficacy of fulvestrant is limited by its poor bioavailability in clinic. We have designed and tested a new generation of steroid-like SERDs. Using ERα-positive BC cells in vitro, we find that these compounds suppress ERα protein levels with efficacy similar to fulvestrant. Moreover, these new SERDs markedly inhibit ERα-positive BC cell transcription and proliferation in vitro even in the presence of estradiol-17β. In vivo, the SERD termed JD128 significantly inhibited tumor growth in MCF-7 xenograft models in a dose-dependent manner (P < 0.001). Further, our findings indicate that these SERDs also interact with ER-positive immune cells in the tumor microenvironment such as myeloid-derived suppressor cells (MDSC), tumor infiltrating lymphocytes and other selected immune cell subpopulations. SERD-induced inhibition of MDSCs and concurrent actions on CD8+ and CD4 + T-cells promotes interaction of immune checkpoint inhibitors with BC cells in preclinical models, thereby leading to enhanced tumor killing even among highly aggressive BCs such as triple-negative BC that lack ERα expression. Since monotherapy with immune checkpoint inhibitors has not been effective for most BCs, combination therapies with SERDs that enhance immune recognition may increase immunotherapy responses in BC and improve patient survival. Hence, ERα antagonists that also promote ER downregulation may potentially benefit patients who are unresponsive to current endocrine therapies.

PTPσ inhibitors promote hematopoietic stem cell regeneration

Receptor type protein tyrosine phosphatase-sigma (PTPσ) is primarily expressed by adult neurons and regulates neural regeneration. We recently discovered that PTPσ is also expressed by hematopoietic stem cells (HSCs). Here, we describe small molecule inhibitors of PTPσ that promote HSC regeneration in vivo. Systemic administration of the PTPσ inhibitor, DJ001, or its analog, to irradiated mice promotes HSC regeneration, accelerates hematologic recovery, and improves survival. Similarly, DJ001 administration accelerates hematologic recovery in mice treated with 5-fluorouracil chemotherapy. DJ001 displays high specificity for PTPσ and antagonizes PTPσ via unique non-competitive, allosteric binding. Mechanistically, DJ001 suppresses radiation-induced HSC apoptosis via activation of the RhoGTPase, RAC1, and induction of BCL-XL. Furthermore, treatment of irradiated human HSCs with DJ001 promotes the regeneration of human HSCs capable of multilineage in vivo repopulation. These studies demonstrate the therapeutic potential of selective, small-molecule PTPσ inhibitors for human hematopoietic regeneration.

A Novel Therapeutic Induces DEPTOR Degradation in Multiple Myeloma Cells with Resulting Tumor Cytotoxicity

Prior work indicates DEPTOR expression in multiple myeloma cells could be a therapeutic target. DEPTOR binds to mTOR via its PDZ domain and inhibits mTOR kinase activity. We previously identified a drug, which prevented mTOR-DEPTOR binding (NSC126405) and induced multiple myeloma cytotoxicity. We now report on a related therapeutic, drug 3g, which induces proteasomal degradation of DEPTOR. DEPTOR degradation followed drug 3g binding to its PDZ domain and was not due to caspase activation or enhanced mTOR phosphorylation of DEPTOR. Drug 3g enhanced mTOR activity, and engaged the IRS-1/PI3K/AKT feedback loop with reduced phosphorylation of AKT on T308. Activation of TORC1, in part, mediated multiple myeloma cytotoxicity. Drug 3g was more effective than NSC126405 in preventing binding of recombinant DEPTOR to mTOR, preventing binding of DEPTOR to mTOR inside multiple myeloma cells, in activating mTOR and inducing apoptosis in multiple myeloma cells. In vivo, drug 3g injected daily abrogated DEPTOR expression in xenograft tumors and induced an antitumor effect although modest weight loss was seen. Every-other-day treatment, however, was equally effective without weight loss. Drug 3g also reduced DEPTOR expression in normal tissues. Although no potential toxicity was identified in hematopoietic or hepatic function, moderate cardiac enlargement and glomerular mesangial hypertrophy was seen. DEPTOR protected multiple myeloma cells against bortezomib suggesting anti-DEPTOR drugs could synergize with proteasome inhibitors (PI). Indeed, combinations of drug NSC126405 + bortezomib were synergistic. In contrast, drug 3g was not and was even antagonistic. This antagonism was probably due to prevention of proteasomal DEPTOR degradation.

Abstract 1012: Selective estrogen receptor downregulators and immune checkpoint inhibitors in breast cancer immunotherapy

Breast cancers (BC) with expression of estrogen receptor-alpha (ERα) occur in more than 70% of newly-diagnosed patients in the U.S. Endocrine therapy with antiestrogens or aromatase inhibitors is an important intervention for BCs that express ERα, and it remains one of the most effective targeted treatments. However, substantial numbers of patients with localized disease, and almost all patients with metastatic BC, become resistant to current endocrine therapies. ERα is present in most resistant BCs, and in many of these its activity continues to regulate BC growth. Fulvestrant represents a class of ERα antagonists that elicit selective ER downregulation (SERDs), an action that helps overcome several resistance mechanisms. Unfortunately, full antitumor efficacy of fulvestrant is limited by its poor bioavailability in clinic. We have designed and tested a new generation of steroid-like SERDs. Using ERα-positive BC cells in vitro, we find that these compounds suppress ERα protein levels with efficacy similar to fulvestrant. Moreover, these new SERDs markedly inhibit ERα-positive BC cell proliferation in vitro even in the presence of estradiol-17β. In vivo, SERD-128 significantly inhibits tumor growth in MCF-7 xenograft models in a dose-dependent manner (P&lt;0.001). Further, our findings show that new SERDs as well as fulvestrant also interact with immune cells expressing ER such as myeloid-derived suppressor cells (MDSC), dendritic cells and T-lymphocytes. Importantly, MDSCs act to protect tumors from immune recognition and elimination in vivo. Since a fraction of triple-negative breast cancers (TNBC; ERα-/PR-/HER2-) but not other BC subtypes respond to immune checkpoint inihbitors (ICIs), we assessed the antitumor effects of SERDs in murine TNBCs in immune-competent, syngeneic mouse models. Notably, SERD treatment induced a blockade of MDSC populations in tumors and rendered TNBCs in vivo more susceptible to ICIs, thereby leading to enhanced tumor killing. Since monotherapy with checkpoint inhibitors has not been effective for most TNBCs, combination therapies with SERDs that enhance immune recognition may increase immunotherapy responses in TNBC and improve patient survival. In addition, SERDs combined with ICIs may potentially benefit patients with other BC subtypes that are unresponsive to current endocrine treatment strategies. [Funded by Tower Cancer Research Foundation-Jessica M. Berman Fund, NCI U54 CA-14393 and UCLA Innovation Fund].

Citation Format: Diana C. Márquez-Garban, Gang Deng, Begonya Comin-Anduix, Alejandro J. Garcia, Emelyine Diers, Gaoyuan Ma, Nalo Hamilton, Michael E. Jung, Richard J. Pietras. Selective estrogen receptor downregulators and immune checkpoint inhibitors in breast cancer immunotherapy [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 1012.

Synthesis of β-Amino Diaryldienones Using the Mannich Reaction

The Mannich reaction has been used for decades to prepare many pharmaceutically important molecules. Here, using a "double-Mannich-β-elimination" synthetic sequence, we report the synthesis and the characterization details of a novel class of β-amino diaryldienones with prominent antiprostate cancer activity. Through these studies, we correct an erroneous structure in the current literature, present a discussion of the stereochemical outcome of a new reaction, and probe the mechanism(s) of byproduct formation through isotopic studies.

Formation of Aryl [1-Cyano-4-(dialkylamino)butadienyl] Ketones from Pyridines

Treatment of 2-chloropyridine with LDA and the Weinreb amide of benzoic acid afforded three unusual products, namely N-methylbenzamide, 2-chloropyridine-3-methanol, and the ring-opened addition product. This same final product could also be obtained from 2-chloro-3-benzoylpyridine on treatment with LDA. Mechanistic insight for the formation of these products is provided.

Molecules targeting the androgen receptor (AR) signaling axis beyond the AR-Ligand binding domain

Prostate cancer (PCa) is the second most common cause of cancer-related mortality in men in the United States. The androgen receptor (AR) and the physiological pathways it regulates are central to the initiation and progression of PCa. As a member of the nuclear steroid receptor family, it is a transcription factor with three distinct functional domains (ligand-binding domain [LBD], DNA-binding domain [DBD], and transactivation domain [TAD]) in its structure. All clinically approved drugs for PCa ultimately target the AR-LBD. Clinically active drugs that target the DBD and TAD have not yet been developed due to multiple factors. Despite these limitations, the last several years have seen a rise in the discovery of molecules that could successfully target these domains. This review aims to present and comprehensively discuss such molecules that affect AR signaling through direct or indirect interactions with the AR-TAD or the DBD. The compounds discussed here include hairpin polyamides, niclosamide, marine sponge-derived small molecules (eg, EPI compounds), mahanine, VPC compounds, JN compounds, and bromodomain and extraterminal domain inhibitors. We highlight the significant in vitro and in vivo data found for each compound and the apparent limitations and/or potential for further development of these agents as PCa therapies.

The Aftermath of Surviving Acute Radiation Hematopoietic Syndrome and its Mitigation

Intensive research is underway to find new agents that can successfully mitigate the acute effects of radiation exposure. This is primarily in response to potential counterthreats of radiological terrorism and nuclear accidents but there is some hope that they might also be of value for cancer patients treated with radiation therapy. Research into mitigation countermeasures typically employs classic animal models of acute radiation syndromes (ARS) that develop after whole-body irradiation (WBI). While agents are available that successfully mitigate ARS when given after radiation exposure, their success raises questions as to whether they simply delay lethality or unmask potentially lethal radiation pathologies that may appear later in time. Life shortening is a well-known consequence of WBI in humans and experimental animals, but it is not often examined in a mitigation setting and its causes, other than cancer, are not well-defined. This is in large part because delayed effects of acute radiation exposure (DEARE) do not follow the strict time-dose phenomena associated with ARS and present as a diverse range of symptoms and pathologies with low mortality rates that can be evaluated only with the use of large cohorts of subjects, as in this study. Here, we describe chronically increased mortality rates up to 660 days in large numbers of mice given LD_70/30 doses of WBI. Systemic myeloid cell activation after WBI persists in some mice and is associated with late immunophenotypic changes and hematopoietic imbalance. Histopathological changes are largely of a chronic inflammatory nature and variable incidence, as are the clinical symptoms, including late diarrhea that correlates temporally with changes in the content of the microbiome. We also describe the acute and long-term consequences of mitigating hematopoietic ARS (H-ARS) lethality after LD_70/30 doses of WBI in multiple cohorts of mice treated uniformly with radiation mitigators that have a common 4-nitro-phenylsulfonamide (NPS) pharmacophore. Effective NPS mitigators dramatically decrease ARS mortality. There is slightly increased subacute mortality, but the rate of late mortalities is slowed, allowing some mice to live a normal life span, which is not the case for WBI controls. The study has broad relevance to radiation late effects and their potential mitigation and epitomizes the complex interaction between radiation-damaged tissues and immune homeostasis.

Broad-spectrum antiviral JL122 blocks infection and inhibits transmission of aquatic rhabdoviruses

The aquaculture industry is growing rapidly to meet the needs for global protein consumption. Viral diseases in aquaculture are quite challenging due to lack of treatment options as well as limited injection-delivery vaccines, which are costly. Thus, water-immersion antiviral treatments are highly desirable. This study focused on broad-spectrum, light-activated antivirals that target the viral membrane (envelope) of viruses to prevent viral-cell membrane fusion, ultimately blocking viral entry into cells. Of the tested small-molecules, JL122, a new broad-spectrum antiviral previously unexplored against aquatic viruses, blocked infection of three aquatic rhabdoviruses (IHNV, VHSV and SVCV) in cell culture and in two live fish challenge models. Importantly, JL122 inhibited transmission of IHNV from infected to uninfected rainbow trout. Further, the effective antiviral concentrations were not toxic to cells or susceptible fish. These results show promise for JL122 to become an immersion treatment option for outbreaks of aquatic enveloped viral infections.

Synthesis and Structure-Activity Relationship (SAR) Studies of Novel Pyrazolopyridine Derivatives as Inhibitors of Enterovirus Replication

A series of novel pyrazolopyridine compounds have been designed and prepared by a general synthetic route. Their activities against the replication of poliovirus-1, EV-A71, and CV-B3 enteroviruses were evaluated. The comprehensive understanding of the structure-activity relationship was obtained by utilizing the variation of four positions, namely, N1, C6, C4, and linker unit. From the screened analogues, the inhibitors with the highest selectivity indices at 50% inhibition of viral replication (SI₅₀) were those with isopropyl at the N1 position and thiophenyl-2-yl unit at C6 position. Furthermore, the C4 position offered the greatest potential for improvement because many different N-aryl groups had better antiviral activities and compatibilities than the lead compound JX001. For example, JX040 with a 2-pyridyl group was the analogue with the most potent activity against non-polio enteroviruses, and JX025, possessing a 3-sulfamoylphenyl moiety, had the best activity against polioviruses. In addition, analogue JX037, possessing a novel pyrazolopyridine heterocycle, was also shown to have good antienteroviral activity, which further enlarges the compound space for antienteroviral drug design.

Structure-activity relationship study of small molecule inhibitors of the DEPTOR-mTOR interaction

DEPTOR is a 48kDa protein that binds to mTOR and inhibits this kinase within mTORC1 and mTORC2 complexes. Over-expression of DEPTOR specifically occurs in the multiple myeloma (MM) tumor model and DEPTOR knockdown is cytotoxic to MM cells, suggesting it is a potential therapeutic target. Since mTORC1 paralysis protects MM cells against DEPTOR knockdown, it indicates that the protein-protein interaction between DEPTOR and mTOR is key to MM viability vs death. In a previous study, we used a yeast two-hybrid screen of a small inhibitor library to identify a compound that inhibited DEPTOR/mTOR binding in yeast. This therapeutic (compound B) also prevented DEPTOR/mTOR binding in MM cells and was selectively cytotoxic to MM cells. We now present a structure-activity relationship (SAR) study around this compound as a follow-up report of this previous work. This study has led to the discovery of five new leads - namely compounds 3g, 3k, 4d, 4e and 4g - all of which have anti-myeloma cytotoxic properties superior to compound B. Due to their targeting of DEPTOR, these compounds activate mTORC1 and selectively induce MM cell apoptosis and cell cycle arrest.

4-(Nitrophenylsulfonyl)piperazines mitigate radiation damage to multiple tissues

Our ability to use ionizing radiation as an energy source, as a therapeutic agent, and, unfortunately, as a weapon, has evolved tremendously over the past 120 years, yet our tool box to handle the consequences of accidental and unwanted radiation exposure remains very limited. We have identified a novel group of small molecule compounds with a 4-nitrophenylsulfonamide (NPS) backbone in common that dramatically decrease mortality from the hematopoietic acute radiation syndrome (hARS). The group emerged from an in vitro high throughput screen (HTS) for inhibitors of radiation-induced apoptosis. The lead compound also mitigates against death after local abdominal irradiation and after local thoracic irradiation (LTI) in models of subacute radiation pneumonitis and late radiation fibrosis. Mitigation of hARS is through activation of radiation-induced CD11b⁺Ly6G⁺Ly6C⁺ immature myeloid cells. This is consistent with the notion that myeloerythroid-restricted progenitors protect against WBI-induced lethality and extends the possible involvement of the myeloid lineage in radiation effects. The lead compound was active if given to mice before or after WBI and had some anti-tumor action, suggesting that these compounds may find broader applications to cancer radiation therapy.

Specific blockade of Rictor-mTOR association inhibits mTORC2 activity and is cytotoxic in glioblastoma

A small molecule which specifically blocks the interaction of Rictor and mTOR was identified utilizing a high-throughput yeast two-hybrid screen and evaluated as a potential inhibitor of mTORC2 activity in glioblastoma multiforme (GBM). In vitro, CID613034 inhibited mTORC2 kinase activity at submicromolar concentrations and in cellular assays specifically inhibited phosphorylation of mTORC2 substrates, including AKT (Ser-473), NDRG1 (Thr-346) and PKCα (Ser-657), while having no appreciable effects on the phosphorylation status of the mTORC1 substrate S6K (Thr-389) or mTORC1-dependent negative feedback loops. CID613034 demonstrated significant inhibitory effects on cell growth, motility and invasiveness in GBM cell lines and sensitivity correlated with relative Rictor or SIN1 expression. Structure-activity relationship analyses afforded an inhibitor, JR-AB2-011, with improved anti-GBM properties and blocked mTORC2 signaling and Rictor association with mTOR at lower effective concentrations. In GBM xenograft studies, JR-AB2-011 demonstrated significant anti-tumor properties. These data support mTORC2 as a viable therapeutic target in GBM and suggest that targeting protein-protein interactions critical for mTORC2 function is an effective strategy to achieve therapeutic responses.

NMR structure-based optimization of Staphylococcus aureus sortase A pyridazinone inhibitors

Staphylococcus aureus is a leading cause of hospital-acquired infections in the USA and is a major health concern as methicillin-resistant S. aureus and other antibiotic-resistant strains are common. Compounds that inhibit the S. aureus sortase (SrtA) cysteine transpeptidase may function as potent anti-infective agents as this enzyme attaches virulence factors to the bacterial cell wall. While a variety of SrtA inhibitors have been discovered, the vast majority of these small molecules have not been optimized using structure-based approaches. Here we have used NMR spectroscopy to determine the molecular basis through which pyridazinone-based small molecules inhibit SrtA. These inhibitors covalently modify the active cysteine thiol and partially mimic the natural substrate of SrtA by inducing the closure of an active site loop. Computational and synthetic chemistry methods led to second-generation analogues that are ~70-fold more potent than the lead molecule. These optimized molecules exhibit broad-spectrum activity against other types of class A sortases, have reduced cytotoxicity, and impair SrtA-mediated protein display on S. aureus cell surface. Our work shows that pyridazinone analogues are attractive candidates for further development into anti-infective agents, and highlights the utility of employing NMR spectroscopy and solubility-optimized small molecules in structure-based drug discovery.

Fluorinated Nucleotide Modifications Modulate Allele Selectivity of SNP-Targeting Antisense Oligonucleotides

Antisense oligonucleotides (ASOs) have the potential to discriminate between subtle RNA mismatches such as SNPs. Certain mismatches, however, allow ASOs to bind at physiological conditions and result in RNA cleavage mediated by RNase H. We showed that replacing DNA nucleotides in the gap region of an ASO with other chemical modification can improve allele selectivity. Herein, we systematically substitute every position in the gap region of an ASO targeting huntingtin gene (HTT) with fluorinated nucleotides. Potency is determined in cell culture against mutant HTT (mtHTT) and wild-type HTT (wtHTT) mRNA and RNase H cleavage intensities, and patterns are investigated. This study profiled five different fluorinated nucleotides and showed them to have predictable, site-specific effects on RNase H cleavage, and the cleavage patterns were rationalized from a published X-ray structure of human RNase H1. The results herein can be used as a guide for future projects where ASO discrimination of SNPs is important.

Partial Amelioration of Peripheral and Central Symptoms of Huntington's Disease via Modulation of Lipid Metabolism

BACKGROUND

Huntington's disease (HD) is a fatal, inherited neurodegenerative disorder characterized by uncontrollable dance-like movements, as well as cognitive deficits and mood changes. A feature of HD is a metabolic disturbance that precedes neurological symptoms. In addition, brain cholesterol synthesis is significantly reduced, which could hamper synaptic transmission.

OBJECTIVE

Alterations in lipid metabolism as a potential target for therapeutic intervention in the R6/2 mouse model of HD were examined.

METHODS

Electrophysiological recordings in vitro examined the acute effects of cholesterol-modifying drugs. In addition, behavioral testing, effects on synaptic activity, and measurements of circulating and brain tissue concentrations of cholesterol and the ketone β-hydroxybutyrate (BHB), were examined in symptomatic R6/2 mice and littermate controls raised on normal chow or a ketogenic diet (KD).

RESULTS

Whole-cell voltage clamp recordings of striatal medium-sized spiny neurons (MSNs) from symptomatic R6/2 mice showed increased frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) compared with littermate controls. Incubation of slices in cholesterol reduced the frequency of large-amplitude sIPSCs. Addition of BHB or the Liver X Receptor (LXR) agonist T0901317 reduced the frequency and amplitude of sIPSCs. Surprisingly, incubation in simvastatin to reduce cholesterol levels also decreased the frequency of sIPSCs. HD mice fed the KD lost weight more gradually, performed better in an open field, had fewer stereotypies and lower brain levels of cholesterol than mice fed a regular diet.

CONCLUSIONS

Lipid metabolism represents a potential target for therapeutic intervention in HD. Modifying cholesterol or ketone levels acutely in the brain can partially rescue synaptic alterations, and the KD can prevent weight loss and improve some behavioral abnormalities.

Synthesis of 2-Ethenylcyclopropyl Aryl Ketones via Intramolecular SN2-like Displacement of an Ester

The efficient synthesis of trans-2-ethenylcyclopropyl aryl ketones via an intramolecular S_N2-like displacement of an allylic ester is reported. A novel 1,5-acyl shift process is also observed that contributes to the product mixture. Theoretical calculations provide a rationale for the observed product ratio.

Cytotoxic Properties of a DEPTOR-mTOR Inhibitor in Multiple Myeloma Cells

DEPTOR is a 48 kDa protein that binds to mTOR and inhibits this kinase in TORC1 and TORC2 complexes. Overexpression of DEPTOR specifically occurs in a model of multiple myeloma. Its silencing in multiple myeloma cells is sufficient to induce cytotoxicity, suggesting that DEPTOR is a potential therapeutic target. mTORC1 paralysis protects multiple myeloma cells against DEPTOR silencing, implicating mTORC1 in the critical role of DEPTOR in multiple myeloma cell viability. Building on this foundation, we interrogated a small-molecule library for compounds that prevent DEPTOR binding to mTOR in a yeast-two-hybrid assay. One compound was identified that also prevented DEPTOR-mTOR binding in human myeloma cells, with subsequent activation of mTORC1 and mTORC2. In a surface plasmon resonance (SPR) assay, the compound bound to recombinant DEPTOR but not to mTOR. The drug also prevented binding of recombinant DEPTOR to mTOR in the SPR assay. Remarkably, although activating TORC1 and TORC2, the compound induced apoptosis and cell-cycle arrest in multiple myeloma cell lines and prevented outgrowth of human multiple myeloma cells in immunodeficient mice. In vitro cytotoxicity against multiple myeloma cell lines was directly correlated with DEPTOR protein expression and was mediated, in part, by the activation of TORC1 and induction of p21 expression. Additional cytotoxicity was seen against primary multiple myeloma cells, whereas normal hematopoietic colony formation was unaffected. These results further support DEPTOR as a viable therapeutic target in multiple myeloma and suggest an effective strategy of preventing binding of DEPTOR to mTOR. Cancer Res; 76(19); 5822-31. ©2016 AACR.

Mechanistic Target of Rapamycin (mTOR) Inhibition Synergizes with Reduced Internal Ribosome Entry Site (IRES)-mediated Translation of Cyclin D1 and c-MYC mRNAs to Treat Glioblastoma

Our previous work has demonstrated an intrinsic mRNA-specific protein synthesis salvage pathway operative in glioblastoma (GBM) tumor cells that is resistant to mechanistic target of rapamycin (mTOR) inhibitors. The activation of this internal ribosome entry site (IRES)-dependent mRNA translation initiation pathway results in continued translation of critical transcripts involved in cell cycle progression in the face of global eIF-4E-mediated translation inhibition. Recently we identified compound 11 (C11), a small molecule capable of inhibiting c-MYC IRES translation as a consequence of blocking the interaction of a requisite c-MYC IRES trans-acting factor, heterogeneous nuclear ribonucleoprotein A1, with its IRES. Here we demonstrate that C11 also blocks cyclin D1 IRES-dependent initiation and demonstrates synergistic anti-GBM properties when combined with the mechanistic target of rapamycin kinase inhibitor PP242. The structure-activity relationship of C11 was investigated and resulted in the identification of IRES-J007, which displayed improved IRES-dependent initiation blockade and synergistic anti-GBM effects with PP242. Mechanistic studies with C11 and IRES-J007 revealed binding of the inhibitors within the UP1 fragment of heterogeneous nuclear ribonucleoprotein A1, and docking analysis suggested a small pocket within close proximity to RRM2 as the potential binding site. We further demonstrate that co-therapy with IRES-J007 and PP242 significantly reduces tumor growth of GBM xenografts in mice and that combined inhibitor treatments markedly reduce the mRNA translational state of cyclin D1 and c-MYC transcripts in these tumors. These data support the combined use of IRES-J007 and PP242 to achieve synergistic antitumor responses in GBM.

The "Lid" in the Streptococcus pneumoniae SrtC1 Sortase Adopts a Rigid Structure that Regulates Substrate Access to the Active Site

Many species of Gram-positive bacteria use sortase enzymes to assemble long, proteinaceous pili structures that project from the cell surface to mediate microbial adhesion. Sortases construct highly stable structures by catalyzing a transpeptidation reaction that covalently links pilin subunits together via isopeptide bonds. Most Gram-positive pili are assembled by class C sortases that contain a "lid", a structurally unique N-terminal extension that occludes the active site. It has been hypothesized that the "lid" in many sortases is mobile and thus capable of readily being displaced from the enzyme to facilitate substrate binding. Here, we show using NMR dynamics measurements, in vitro assays, and molecular dynamics simulations that the lid in the class C sortase from Streptococcus pneumoniae (SrtC1) adopts a rigid conformation in solution that is devoid of large magnitude conformational excursions that occur on mechanistically relevant time scales. Additionally, we show that point mutations in the lid induce dynamic behavior that correlates with increased hydrolytic activity and sorting signal substrate access to the active site cysteine residue. These results suggest that the lid of the S. pneumoniae SrtC1 enzyme has a negative regulatory function and imply that a significant energetic barrier must be surmounted by currently unidentified factors to dislodge it from the active site to initiate pilus biogenesis.

2-Hydroxyglutarate Inhibits ATP Synthase and mTOR Signaling

We discovered recently that the central metabolite α-ketoglutarate (α-KG) extends the lifespan of C. elegans through inhibition of ATP synthase and TOR signaling. Here we find, unexpectedly, that (R)-2-hydroxyglutarate ((R)-2HG), an oncometabolite that interferes with various α-KG-mediated processes, similarly extends worm lifespan. (R)-2HG accumulates in human cancers carrying neomorphic mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes. We show that, like α-KG, both (R)-2HG and (S)-2HG bind and inhibit ATP synthase and inhibit mTOR signaling. These effects are mirrored in IDH1 mutant cells, suggesting a growth-suppressive function of (R)-2HG. Consistently, inhibition of ATP synthase by 2-HG or α-KG in glioblastoma cells is sufficient for growth arrest and tumor cell killing under conditions of glucose limitation, e.g., when ketone bodies (instead of glucose) are supplied for energy. These findings inform therapeutic strategies and open avenues for investigating the roles of 2-HG and metabolites in biology and disease.

Structure of the Bacillus anthracis Sortase A Enzyme Bound to Its Sorting Signal: A FLEXIBLE AMINO-TERMINAL APPENDAGE MODULATES SUBSTRATE ACCESS

The endospore forming bacterium Bacillus anthracis causes lethal anthrax disease in humans and animals. The ability of this pathogen to replicate within macrophages is dependent upon the display of bacterial surface proteins attached to the cell wall by the B. anthracis Sortase A ((Ba)SrtA) enzyme. Previously, we discovered that the class A (Ba)SrtA sortase contains a unique N-terminal appendage that wraps around the body of the protein to contact the active site of the enzyme. To gain insight into its function, we determined the NMR structure of (Ba)SrtA bound to a LPXTG sorting signal analog. The structure, combined with dynamics, kinetics, and whole cell protein display data suggest that the N terminus modulates substrate access to the enzyme. We propose that it may increase the efficiency of protein display by reducing the unproductive hydrolytic cleavage of enzyme-protein covalent intermediates that form during the cell wall anchoring reaction. Notably, a key active site loop (β7/β8 loop) undergoes a disordered to ordered transition upon binding the sorting signal, potentially facilitating recognition of lipid II.

Development of 2-Deoxy-2-[(18)F]fluororibose for Positron Emission Tomography Imaging Liver Function in Vivo

Life-threatening acute liver failure can be triggered by a variety of factors, including common drugs such as acetaminophen. Positron emission tomography (PET) is rarely used to monitor liver function, in part because of a lack of specific imaging agents for liver function. Here we report a new PET probe, 2-deoxy-2-[(18)F]fluororibose ([(18)F]-2-DFR), for use in imaging liver function. [(18)F]-2-DFR was synthesized and validated as a competitive substrate for the ribose salvage pathway. [(18)F]-2-DFR was prepared through an efficient late stage radiofluorination. The desired selectivity of fluorination was achieved using an unorthodox protecting group on the precursor, which could withstand harsh SN2 reaction conditions with no side reactions. [(18)F]-2-DFR accumulated preferentially in the liver and was metabolized by the same enzymes as ribose. [(18)F]-2-DFR could distinguish between healthy liver and liver damaged by acetaminophen. [(18)F]-2-DFR is expected to be a useful PET probe for imaging and quantifying liver functions in vivo, with likely significant clinical utility.

CSF1 receptor targeting in prostate cancer reverses macrophage-mediated resistance to androgen blockade therapy

Growing evidence suggests that tumor-associated macrophages (TAM) promote cancer progression and therapeutic resistance by enhancing angiogenesis, matrix-remodeling, and immunosuppression. In this study, prostate cancer under androgen blockade therapy (ABT) was investigated, demonstrating that TAMs contribute to prostate cancer disease recurrence through paracrine signaling processes. ABT induced the tumor cells to express macrophage colony-stimulating factor 1 (M-CSF1 or CSF1) and other cytokines that recruit and modulate macrophages, causing a significant increase in TAM infiltration. Inhibitors of CSF1 signaling through its receptor, CSF1R, were tested in combination with ABT, demonstrating that blockade of TAM influx in this setting disrupts tumor promotion and sustains a more durable therapeutic response compared with ABT alone.

Multivalent N-acetylgalactosamine-conjugated siRNA localizes in hepatocytes and elicits robust RNAi-mediated gene silencing

Conjugation of small interfering RNA (siRNA) to an asialoglycoprotein receptor ligand derived from N-acetylgalactosamine (GalNAc) facilitates targeted delivery of the siRNA to hepatocytes in vitro and in vivo. The ligands derived from GalNAc are compatible with solid-phase oligonucleotide synthesis and deprotection conditions, with synthesis yields comparable to those of standard oligonucleotides. Subcutaneous (SC) administration of siRNA-GalNAc conjugates resulted in robust RNAi-mediated gene silencing in liver. Refinement of the siRNA chemistry achieved a 5-fold improvement in efficacy over the parent design in vivo with a median effective dose (ED50) of 1 mg/kg following a single dose. This enabled the SC administration of siRNA-GalNAc conjugates at therapeutically relevant doses and, importantly, at dose volumes of ≤1 mL. Chronic weekly dosing resulted in sustained dose-dependent gene silencing for over 9 months with no adverse effects in rodents. The optimally chemically modified siRNA-GalNAc conjugates are hepatotropic and long-acting and have the potential to treat a wide range of diseases involving liver-expressed genes.

Structure-guided development of deoxycytidine kinase inhibitors with nanomolar affinity and improved metabolic stability

Recently, we have shown that small molecule dCK inhibitors in combination with pharmacological perturbations of de novo dNTP biosynthetic pathways could eliminate acute lymphoblastic leukemia cells in animal models. However, our previous lead compound had a short half-life in vivo. Therefore, we set out to develop dCK inhibitors with favorable pharmacokinetic properties. We delineated the sites of the inhibitor for modification, guided by crystal structures of dCK in complex with the lead compound and with derivatives. Crystal structure of the complex between dCK and the racemic mixture of our new lead compound indicated that the R-isomer is responsible for kinase inhibition. This was corroborated by kinetic analysis of the purified enantiomers, which showed that the R-isomer has >60-fold higher affinity than the S-isomer for dCK. This new lead compound has significantly improved metabolic stability, making it a prime candidate for dCK-inhibitor based therapies against hematological malignancies and, potentially, other cancers.