Validation of ferroptosis in canine cancer cells to enable comparative oncology and translational medicine

Ferroptosis is a cell death mechanism that has attracted significant attention as a potential basis for the development of new cancer therapies. Validation of ferroptosis biology in species commonly used in translation and pre-clinical development is a necessary foundation for enabling the advancement of such ferroptosis modulating drugs. Here, we demonstrate that canine cancer cells exhibit sensitivity to a wide range of ferroptosis-inducing perturbations in a manner indistinguishable from human cancer cells, and recapitulate characteristic patterns of ferroptotic response across tumor types seen in the human setting. The foundation provided herein establishes the dog as a relevant efficacy and toxicology model for ferroptosis and creates new opportunities to leverage the canine comparative oncology paradigm to accelerate the development of ferroptosis-inducing drugs for human cancer patients.

The validation of new CHD1L inhibitors as a therapeutic strategy for cancer

Chromodomain helicase DNA-binding protein 1 like (CHD1L) is an oncogene that promotes tumor progression, metastasis, and multidrug resistance. CHD1L expression is indicative of poor outcomes and low survival in cancer patients with various cancer types. Herein, we report a set of CHD1L inhibitors (CHD1Li) discovered from high-throughput screening and evaluated using enzyme inhibition, 3D tumor organoid cytotoxicity and mechanistic assays. The structurally distinct compounds 8-11 emerged as hits with promising bioactivity by targeting CHD1L. CHD1Li were further examined for their stability in human and mouse liver microsomes, which showed compounds 9 and 11 to be the most metabolically stable. Additionally, molecular modeling studies of CHD1Li with the target protein shed light on key pharmacophore features driving CHD1L binding. Taken together, these results expand the chemical space of CHD1Li as a potential targeted therapy for colorectal cancer and other cancers.

HTS discovery of PARP1-HPF1 complex inhibitors in cancer

PARP1/2 inhibitors (PARPi) are effective clinically used drugs for the treatment of cancers with BRCA deficiencies. PARPi have had limited success and applicability beyond BRCA deficient cancers, and their effect is diminished by resistance mechanisms. The recent discovery of Histone PARylation Factor (HPF1) and the role it plays in the PARylation reaction by forming a shared active site with PARP1 raises the possibility that novel inhibitors that target the PARP1-HPF1 complex can be identified. Herein we describe a simple and cost-effective high-throughput screening (HTS) method aimed at discovering inhibitors of the PARP1-HPF1 complex. Upon HTS validation, we first applied this method to screen a small PARP-focused library of compounds and then scale up our approach using robotic automation to conduct a pilot screen of 10,000 compounds and validating >100 hits. This work demonstrates for the first time the capacity to discover potent inhibitors of the PARP1-HPF1 complex, which may have utility as probes to better understand the DNA damage response and as therapeutics for cancer.

AST-487 Inhibits RET Kinase Driven TERT Expression in Bladder Cancer

Mutations in the promoter of the human Telomerase Reverse Transcriptase (hTERT) gene are common and associated with its elevated expression in bladder cancer, melanoma, and glioblastoma. Though these mutations and TERT overexpression are associated with aggressive disease and poor outcome, an incomplete understanding of mutant TERT regulation limits treatment options directed at this gene. Herein, we unravel a signaling pathway that leads to upregulated hTERT expression resulting from the −124 bp promoter mutation, the most frequent variant across human cancer. We employed engineered bladder cancer cells that harbor a GFP insertion at the TSS region on −124 hTERT promoter for high-content screening drug discovery using a focused library of ~800 kinase inhibitors. Studies using in vitro and in vivo models prioritized AST-487, an inhibitor of the wild-type, and mutant RET (rearranged during transfection) proto-oncogene as a novel drug inhibitor of both wild-type and mutant promoter-driven hTERT expression. We also identified the RET kinase pathway, targeted by AST-487, as a novel regulator of mutant hTERT promoter-driven transcription in bladder cancer cells. Collectively, our work provides new potential precision medicine approaches for cancer patients with upregulated hTERT expression, perhaps, especially those harboring mutations in both the RET gene and the hTERT promoter, such as in thyroid cancer.

Oxidative stress as a candidate mechanism for accelerated neuroectodermal differentiation due to trisomy 21

The ubiquity of cognitive deficits and early onset Alzheimer's disease in Down syndrome (DS) has focused much DS iPSC-based research on neuron degeneration and regeneration. Despite reports of elevated oxidative stress in DS brains, few studies assess the impact of this oxidative burden on iPSC differentiation. Here, we evaluate cellular specific redox differences in DS and euploid iPSCs and neural progenitor cells (NPCs) during critical intermediate stages of differentiation. Despite successful generation of NPCs, our results indicate accelerated neuroectodermal differentiation of DS iPSCs compared to isogenic, euploid controls. Specifically, DS embryoid bodies (EBs) and neural rosettes prematurely develop with distinct morphological differences from controls. Additionally, we observed developmental stage-specific alterations in mitochondrial superoxide production and SOD1/2 abundance, coupled with modulations in thioredoxin, thioredoxin reductase, and peroxiredoxin isoforms. Disruption of intracellular redox state and its associated signaling has the potential to disrupt cellular differentiation and development in DS lending to DS-specific phenotypes.

Design, Synthesis, and Biological Evaluation of the First Inhibitors of Oncogenic CHD1L

Chromodomain helicase DNA-binding protein 1 like (CHD1L) is an oncogene implicated in tumor progression, multidrug resistance, and metastasis in many types of cancer. In this article, we described the optimization of the first lead CHD1L inhibitors (CHD1Li) through drug design and medicinal chemistry. More than 30 CHD1Li were synthesized and evaluated using a variety of colorectal cancer (CRC) tumor organoid models and functional assays. The results led to the prioritization of six lead CHD1Li analogues with improved potency, antitumor activity, and drug-like properties including metabolic stability and in vivo pharmacokinetics. Furthermore, lead CHD1Li 6.11 proved to be an orally bioavailable antitumor agent, significantly reducing the tumor volume of CRC xenografts generated from isolated quasi mesenchymal cells (M-phenotype), which possess enhanced tumorigenic properties. In conclusion, we reported the optimization of first-in-class inhibitors of oncogenic CHD1L as a novel therapeutic strategy with potential for the treatment of cancer.

High Throughput Screen Identifies the DNMT1 (DNA Methyltransferase-1) Inhibitor, 5-Azacytidine, as a Potent Inducer of PTEN (Phosphatase and Tensin Homolog): Central Role for PTEN in 5-Azacytidine Protection Against Pathological Vascular Remodeling

OBJECTIVE

Our recent work demonstrates that PTEN (phosphatase and tensin homolog) is an important regulator of smooth muscle cell (SMC) phenotype. SMC-specific PTEN deletion promotes spontaneous vascular remodeling and PTEN loss correlates with increased atherosclerotic lesion severity in human coronary arteries. In mice, PTEN overexpression reduces plaque area and preserves SMC contractile protein expression in atherosclerosis and blunts Ang II (angiotensin II)-induced pathological vascular remodeling, suggesting that pharmacological PTEN upregulation could be a novel therapeutic approach to treat vascular disease. Approach and Results: To identify novel PTEN activators, we conducted a high-throughput screen using a fluorescence based PTEN promoter-reporter assay. After screening ≈3400 compounds, 11 hit compounds were chosen based on level of activity and mechanism of action. Following in vitro confirmation, we focused on 5-azacytidine, a DNMT1 (DNA methyltransferase-1) inhibitor, for further analysis. In addition to PTEN upregulation, 5-azacytidine treatment increased expression of genes associated with a differentiated SMC phenotype. 5-Azacytidine treatment also maintained contractile gene expression and reduced inflammatory cytokine expression after PDGF (platelet-derived growth factor) stimulation, suggesting 5-azacytidine blocks PDGF-induced SMC de-differentiation. However, these protective effects were lost in PTEN-deficient SMCs. These findings were confirmed in vivo using carotid ligation in SMC-specific PTEN knockout mice treated with 5-azacytidine. In wild type controls, 5-azacytidine reduced neointimal formation and inflammation while maintaining contractile protein expression. In contrast, 5-azacytidine was ineffective in PTEN knockout mice, indicating that the protective effects of 5-azacytidine are mediated through SMC PTEN upregulation.

CONCLUSIONS

Our data indicates 5-azacytidine upregulates PTEN expression in SMCs, promoting maintenance of SMC differentiation and reducing pathological vascular remodeling in a PTEN-dependent manner.

First-in-Class Inhibitors of Oncogenic CHD1L with Preclinical Activity against Colorectal Cancer

Since the discovery of CHD1L in 2008, it has emerged as an oncogene implicated in the pathology and poor prognosis of a variety of cancers, including gastrointestinal cancers. However, a mechanistic understanding of CHD1L as a driver of colorectal cancer has been limited. Until now, there have been no reported inhibitors of CHD1L, also limiting its development as a molecular target. We sought to characterize the clinicopathologic link between CHD1L and colorectal cancer, determine the mechanism(s) by which CHD1L drives malignant colorectal cancer, and discover the first inhibitors with potential for novel treatments for colorectal cancer. The clinicopathologic characteristics associated with CHD1L expression were evaluated using microarray data from 585 patients with colorectal cancer. Further analysis of microarray data indicated that CHD1L may function through the Wnt/TCF pathway. Thus, we conducted knockdown and overexpression studies with CHD1L to determine its role in Wnt/TCF-driven epithelial-to-mesenchymal transition (EMT). We performed high-throughput screening (HTS) to identify the first CHD1L inhibitors. The mechanism of action, antitumor efficacy, and drug-like properties of lead CHD1L inhibitors were determined using biochemical assays, cell models, tumor organoids, patient-derived tumor organoids, and in vivo pharmacokinetics and pharmacodynamics. Lead CHD1L inhibitors display potent in vitro antitumor activity by reversing TCF-driven EMT. The best lead CHD1L inhibitor possesses drug-like properties in pharmacokinetic/pharmacodynamic mouse models. This work validates CHD1L as a druggable target and establishes a novel therapeutic strategy for the treatment of colorectal cancer.

Advanced High-Content-Screening Applications of Clonogenicity in Cancer

Since its first report in 1956 by Puck and Marcus, the clonogenic assay has not been completely adapted into high-content-screening (HCS) workflows despite the numerous automated systems available. Initially, clonogenic assays were used to observe the effects of radiation on cell survival, particularly with cancer cells. The clonogenic assay has since been well characterized as a measure of cancer stem cell (CSC) stemness, demonstrating that a single CSC can generate clonogenic colonies. CSCs are highly tumorigenic with an unlimited proliferation potential and capacity to generate malignant tumors. Furthermore, CSCs are also known to resist conventional chemotherapy as well as more contemporary targeted therapies alike. Therefore, given the complexity of CSCs and their clinical relevance, new methods must follow to more effectively study and characterize CSC mechanisms that allow them to proliferate and persist, and to develop drugs and other therapies that can more effectively target these populations. Herein, we present a HCS method to quantify the number and size of colonies in 2D and 3D culture models and to distinguish colonies based on fluorescent markers using an Opera Phenix high-content-screening system. In addition, we present a method to scan at low magnification and rescan at a higher magnification to capture in greater detail colonies or even single cells of interest. These methods can be adapted to numerous applications or other imaging systems to study CSC biology using high-content analysis and for high-throughput drug discovery.

Drug Design Targeting T-Cell Factor-Driven Epithelial-Mesenchymal Transition as a Therapeutic Strategy for Colorectal Cancer

Metastasis is the cause of 90% of mortality in cancer patients. For metastatic colorectal cancer (mCRC), the standard-of-care drug therapies only palliate the symptoms but are ineffective, evidenced by a low survival rate of ∼11%. T-cell factor (TCF) transcription is a major driving force in CRC, and we have characterized it to be a master regulator of epithelial-mesenchymal transition (EMT). EMT transforms relatively benign epithelial tumor cells into quasi-mesenchymal or mesenchymal cells that possess cancer stem cell properties, promoting multidrug resistance and metastasis. We have identified topoisomerase IIα (TOP2A) as a DNA-binding factor required for TCF-transcription. Herein, we describe the design, synthesis, biological evaluation, and in vitro and in vivo pharmacokinetic analysis of TOP2A ATP-competitive inhibitors that prevent TCF-transcription and modulate or reverse EMT in mCRC. Unlike TOP2A poisons, ATP-competitive inhibitors do not damage DNA, potentially limiting adverse effects. This work demonstrates a new therapeutic strategy targeting TOP2A for the treatment of mCRC and potentially other types of cancers.

Establishment and Characterization of Four Novel Thyroid Cancer Cell Lines and PDX Models Expressing the RET/PTC1 Rearrangement, BRAFV600E, or RASQ61R as Drivers

Cancer cell lines are critical models to study tumor progression and response to therapy. In 2008, we showed that approximately 50% of thyroid cancer cell lines were redundant or not of thyroid cancer origin. We therefore generated new authenticated thyroid cancer cell lines and patient-derived xenograft (PDX) models using in vitro and feeder cell approaches, and characterized these models in vitro and in vivo. We developed four thyroid cancer cell lines, two derived from 2 different patients with papillary thyroid cancer (PTC) pleural effusions, CUTC5, and CUTC48; one derived from a patient with anaplastic thyroid cancer (ATC), CUTC60; and one derived from a patient with follicular thyroid cancer (FTC), CUTC61. One PDX model (CUTC60-PDX) was also developed. Short tandem repeat (STR) genotyping showed that each cell line and PDX is unique and match the original patient tissue. The CUTC5 and CUTC60 cells harbor the BRAF (V600E) mutation, the CUTC48 cell line expresses the RET/PTC1 rearrangement, and the CUTC61 cells have the HRAS (Q61R) mutation. Moderate to high levels of PAX8 and variable levels of NKX2-1 were detected in each cell line and PDX. The CUTC5 and CUTC60 cell lines form tumors in orthotopic and flank xenograft mouse models. IMPLICATIONS: We have developed the second RET/PTC1-expressing PTC-derived cell line in existence, which is a major advance in studying RET signaling. We have further linked all cell lines to the originating patients, providing a set of novel, authenticated thyroid cancer cell lines and PDX models to study advanced thyroid cancer.

Targeting HIV-1 Protease Autoprocessing for High-throughput Drug Discovery and Drug Resistance Assessment

HIV-1 protease autoprocessing liberates the free mature protease from its Gag-Pol polyprotein precursor through a series of highly regulated autoproteolysis reactions. Herein, we report the development and validation (Z' ≥ 0.50) of a cell-based functional assay for high-throughput screening (HTS) of autoprocessing inhibitors using fusion precursors in combination with AlphaLISA (amplified luminescent proximity homogeneous assay ELISA). Through pilot screening of a collection of 130 known protease inhibitors, the AlphaLISA assay confirmed all 11 HIV protease inhibitors in the library capable of suppressing precursor autoprocessing at low micromolar concentrations. Meanwhile, other protease inhibitors had no impact on precursor autoprocessing. We next conducted HTS of ~23,000 compounds but found no positive hits. Such high selectivity is advantageous for large-scale HTS campaigns and as anticipated based on assay design because a positive hit needs simultaneously to be nontoxic, cell permeable, and inhibiting precursor autoprocessing. Furthermore, AlphaLISA quantification of fusion precursors carrying mutations known to cause resistance to HIV protease inhibitors faithfully recapitulated the reported resistance, suggesting that precursor autoprocessing is a critical step contributing to drug resistance. Taken together, this reported AlphaLISA platform will provide a useful tool for drug discovery targeting HIV-1 protease autoprocessing and for quantification of PI resistance.

Genetic Analysis of 779 Advanced Differentiated and Anaplastic Thyroid Cancers

Purpose: To define the genetic landscape of advanced differentiated and anaplastic thyroid cancer (ATC) and identify genetic alterations of potential diagnostic, prognostic, and therapeutic significance.Experimental Design: The genetic profiles of 583 advanced differentiated and 196 ATCs generated with targeted next-generation sequencing cancer-associated gene panels MSK-IMPACT and FoundationOne were analyzed.Results: ATC had more genetic alterations per tumor, and pediatric papillary thyroid cancer had fewer genetic alterations per tumor when compared with other thyroid cancer types. DNA mismatch repair deficit and activity of APOBEC cytidine deaminases were identified as mechanisms associated with high mutational burden in a subset of differentiated thyroid cancers and ATCs. Copy number losses and mutations of CDKN2A and CDKN2B, amplification of CCNE1, amplification of receptor tyrosine kinase genes KDR, KIT, and PDGFRA, amplification of immune evasion genes CD274, PDCD1LG2, and JAK2, and activating point mutations in small GTPase RAC1 were associated with ATC. An association of KDR, KIT, and PDGFRA amplification with the sensitivity of thyroid cancer cells to lenvatinib was shown in vitro Three genetically distinct types of ATCs are proposed.Conclusions: This large-scale analysis describes genetic alterations in a cohort of thyroid cancers enriched in advanced cases. Many novel genetic events previously not seen in thyroid cancer were found. Genetic alterations associated with anaplastic transformation were identified. An updated schematic of thyroid cancer genetic evolution is proposed. Clin Cancer Res; 24(13); 3059-68. ©2018 AACR.

Identification of small molecule inhibitors of the Chikungunya virus nsP1 RNA capping enzyme

Chikungunya virus (CHIKV) is an arthropod-borne alphavirus. Alphaviruses are positive strand RNA viruses that require a 5' cap structure to direct translation of the viral polyprotein and prevent degradation of the viral RNA genome by host cell nucleases. Formation of the 5' RNA cap is orchestrated by the viral protein nsP1, which binds GTP and provides the N-7 methyltransferase and guanylyltransferase activities that are necessary for cap formation. Viruses with aberrant nsP1 activity are unable to replicate effectively suggesting that nsP1 is a promising target for antiviral drug discovery. Given the absence of commercially available antiviral therapies for CHIKV, it is imperative to identify compounds that could be developed as potential therapeutics. This study details a high-throughput screen of 3051 compounds from libraries containing FDA-approved drugs, natural products, and known bioactives against CHIKV nsP1 using a fluorescence polarization-based GTP competition assay. Several small molecule hits from this screen were able to compete with GTP for the CHIKV nsP1 GTP binding site at low molar concentrations. Compounds were also evaluated with an orthogonal assay that measured the ability of nsP1 to perform the guanylation step of the capping reaction in the presence of inhibitor. In addition, live virus assays with CHIKV and closely related alphavirus, Sindbis virus, were used in conjunction with cell toxicity assays to determine the antiviral activity of compounds in cell culture. The naturally derived compound lobaric acid was found to inhibit CHIKV nsP1 GTP binding and guanylation as well as attenuate viral growth in vitro at both 24 hpi and 48 hpi in hamster BHK21 and human Huh 7 cell lines. These data indicate that development of lobaric acid and further exploration of CHIKV nsP1 as a drug target may aid in the progress of anti-alphaviral drug development strategies.

Inhibition of α-glucosidase, α-amylase, and aldose reductase by potato polyphenolic compounds

Diabetes mellitus is a chronic disease that is becoming a serious global health problem. Diabetes has been considered to be one of the major risks of cataract and retinopathy. Synthetic and natural product inhibitors of carbohydrate degrading enzymes are able to reduce type 2 diabetes and its complications. For a long time, potatoes have been portrayed as unhealthy for diabetic patients by some nutritionist due to their high starch content. However, purple and red potato cultivars have received considerable attention from consumers because they have high levels of polyphenolic compounds that have potent antioxidant activities. In this study, we screened the total phenolics (TP) and total anthocyanins (TA) and analyzed the phenolic and anthocyanin compounds in selected potato cultivars and advanced selections with distinct flesh colors (purple, red, yellow and white). Purple and red potato cultivars had higher levels of TP and TA than tubers with other flesh colors. Chlorogenic acid is the predominant phenolic acid, and major anthocyanin is composed of the derivatives of petunidin, peonidin, malvidin and pelargonidin. We tested the potential inhibitory effect of potato extracts on the activities of α-amylase and α-glucosidase, which were targeted to develop antidiabetic therapeutic agents. We also measured inhibitory effect of potato extracts on aldose reductase (AR) which is a key enzyme that has been a major drug target for the development of therapies to treat diabetic complications. Purple flesh tubers extract showed the most effective inhibition of α-amylase, α-glucosidase, and aldose reductase with IC₅₀ values 25, 42, and 32 μg/ml, respectively. Kinetic studies showed that anthocyanins are noncompetitive inhibitors of these enzymes, whereas phenolic acids behaved as mixed inhibitors for α-amylase and α-glucosidase and noncompetitive inhibitors for AR. This study supports the development of a positive and healthful image of potatoes, which is an important issue for consumers.

Cross talk between progesterone receptors and retinoic acid receptors in regulation of cytokeratin 5-positive breast cancer cells

Half of estrogen receptor-positive breast cancers contain a subpopulation of cytokeratin 5 (CK5)-expressing cells that are therapy resistant and exhibit increased cancer stem cell (CSC) properties. We and others have demonstrated that progesterone (P4) increases CK5+ breast cancer cells. We previously discovered that retinoids block P4 induction of CK5+ cells. Here we investigated the mechanisms by which progesterone receptors (PR) and retinoic acid receptors (RAR) regulate CK5 expression and breast CSC activity. After P4 treatment, sorted CK5+ compared to CK5- cells were more tumorigenic in vivo. In vitro, P4-treated breast cancer cells formed larger mammospheres and silencing of CK5 using small hairpin RNA abolished this P4-dependent increase in mammosphere size. Retinoic acid (RA) treatment blocked the P4 increase in CK5+ cells and prevented the P4 increase in mammosphere size. Dual small interfering RNA (siRNA) silencing of RARα and RARγ reversed RA blockade of P4-induced CK5. Using promoter deletion analysis, we identified a region 1.1 kb upstream of the CK5 transcriptional start site that is necessary for P4 activation and contains a putative progesterone response element (PRE). We confirmed by chromatin immunoprecipitation that P4 recruits PR to the CK5 promoter near the -1.1 kb essential PRE, and also to a proximal region near -130 bp that contains PRE half-sites and a RA response element (RARE). RA induced loss of PR binding only at the proximal site. Interestingly, RARα was recruited to the -1.1 kb PRE and the -130 bp PRE/RARE regions with P4, but not RA alone or RA plus P4. Treatment of breast cancer xenografts in vivo with the retinoid fenretinide reduced the accumulation of CK5+ cells during estrogen depletion. This reduction, together with the inhibition of CK5+ cell expansion through RAR/PR cross talk, may explain the efficacy of retinoids in prevention of some breast cancer recurrences.

Larrea tridentata: A novel source for anti-parasitic agents active against Entamoeba histolytica, Giardia lamblia and Naegleria fowleri

Protozoan parasites infect and kill millions of people worldwide every year, particularly in developing countries where access to clean fresh water is limited. Among the most common are intestinal parasites, including Giardia lamblia and Entamoeba histolytica. These parasites wreak havoc on the epithelium lining the small intestines (G. lamblia) and colon (E. histolytica) causing giardiasis and amebiasis, respectively. In addition, there are less common but far more deadly pathogens such as Naegleria fowleri that thrive in warm waters and infect the central nervous systems of their victims via the nasal passages. Despite their prevalence and associated high mortality rates, there remains an unmet need to identify more effective therapeutics for people infected with these opportunistic parasites. To address this unmet need, we have surveyed plants and traditional herbal medicines known throughout the world to identify novel antiparasitic agents with activity against G. lamblia, E. histolytica, and N. fowleri. Herein, we report Larrea tridentata, known as creosote bush, as a novel source for secondary metabolites that display antiparasitic activity against all three pathogens. This report also characterizes the lignan compound classes, nordihydroguairetic acid and demethoxyisoguaiacin, as novel antiparasitic lead agents to further develop more effective drug therapy options for millions of people worldwide.

Entamoeba histolytica, Giardia lamblia, and Naegleria fowleri pathogens are widespread throughout the world infecting and killing hundreds of thousands of people every year. They are also listed as category B bioterrorism agents by the NIH and the CDC. However, there is a serious unmet need to develop more effective therapies to treat these deadly pathogens. Herein we describe that lignans isolated from the creosote bush, common to the southwestern U.S.A. and throughout Mexico, display relatively potent antiparasitic activity against E. histolytica, G. lamblia, and N. fowleri.

Characterization of Emodin as a Therapeutic Agent for Diabetic Cataract

Aldose reductase (AR) in the lens plays an important role in the pathogenesis of diabetic cataract (DC) by contributing to osmotic and oxidative stress associated with accelerated glucose metabolism through the polyol pathway. Therefore, inhibition of AR in the lens may hold the key to prevent DC formation. Emodin, a bioactive compound isolated from plants, has been implicated as a therapy for diabetes. However, its inhibitory activity against AR remains unclear. Our results showed that emodin has good selectively inhibitory activity against AR (IC50 = 2.69 ± 0.90 μM) but not other aldo-keto reductases and is stable at 37 °C for at least 7 days. Enzyme kinetic studies demonstrated an uncompetitive inhibition against AR with a corresponding inhibition constant of 2.113 ± 0.095 μM. In in vivo studies, oral administration of emodin reduced the incidence and severity of morphological markers of cataract in lenses of AR transgenic mice. Computational modeling of the AR-NADP(+)-emodin ternary complex indicated that the 3-hydroxy group of emodin plays an essential role by interacting with Ser302 through hydrogen bonding in the specificity pocket of AR. All the findings above provide encouraging evidence for emodin as a potential therapeutic agent to prevent cataract in diabetic patients.

Topoisomerase IIα mediates TCF-dependent epithelial-mesenchymal transition in colon cancer

Aberrant T-cell factor (TCF) transcription is implicated in the majority of colorectal cancers (CRCs). TCF transcription induces epithelial–mesenchymal transition (EMT), promoting a tumor-initiating cell (TIC) phenotype characterized by increased proliferation, multidrug resistance (MDR), invasion and metastasis. The data presented herein characterize topoisomerase IIα (TopoIIα) as a required component of TCF transcription promoting EMT. Using chromatin immunoprecipitation (ChIP) and protein co-immunoprecipitation (co-IP) studies, we show that TopoIIα forms protein–protein interactions with β-catentin and TCF4 and interacts with Wnt response elements (WREs) and promoters of direct target genes of TCF transcription, including: MYC, vimentin, AXIN2 and LEF1. Moreover, both TopoIIα and TCF4 ChIP with the N-cadherin promoter, which is a new discovery indicating that TCF transcription may directly regulate N-cadherin expression. TopoIIα N-terminal ATP-competitive inhibitors, exemplified by the marine alkaloid neoamphimedine (neo), block TCF activity in vitro and in vivo. Neo effectively inhibits TopoIIα and TCF4 from binding WREs/promoter sites, whereas protein–protein interactions remain intact. Neo inhibition of TopoIIα-dependent TCF transcription also correlates with significant antitumor effects in vitro and in vivo, including the reversion of EMT, the loss of TIC-mediated clonogenic colony formation, and the loss of cell motility and invasion. Interestingly, non-ATP-competitive inhibitors of TopoIIα, etoposide and merbarone, were ineffective at preventing TopoIIα-dependent TCF transcription. Thus, we propose that TopoIIα participation in TCF transcription may convey a mechanism of MDR to conventional TopoIIα inhibitors. However, our results indicate that TopoIIα N-terminal ATP-binding sites remain conserved and available for drug targeting. This article defines a new strategy for targeted inhibition of TCF transcription that may lead to effective therapies for the treatment of CRC and potentially other Wnt-dependent cancers.

High-throughput imaging: Focusing in on drug discovery in 3D

3D organotypic culture models such as organoids and multicellular tumor spheroids (MCTS) are becoming more widely used for drug discovery and toxicology screening. As a result, 3D culture technologies adapted for high-throughput screening formats are prevalent. While a multitude of assays have been reported and validated for high-throughput imaging (HTI) and high-content screening (HCS) for novel drug discovery and toxicology, limited HTI/HCS with large compound libraries have been reported. Nonetheless, 3D HTI instrumentation technology is advancing and this technology is now on the verge of allowing for 3D HCS of thousands of samples. This review focuses on the state-of-the-art high-throughput imaging systems, including hardware and software, and recent literature examples of 3D organotypic culture models employing this technology for drug discovery and toxicology screening.

Novel Microtubule-Targeting 7-Deazahypoxanthines Derived from Marine Alkaloid Rigidins with Potent in Vitro and in Vivo Anticancer Activities

Docking studies of tubulin-targeting C2-substituted 7-deazahypoxanthine analogues of marine alkaloid rigidins led to the design and synthesis of compounds containing linear C2-substituents. The C2-alkynyl analogue was found to have double- to single-digit nanomolar antiproliferative IC50 values and showed statistically significant tumor size reduction in a colon cancer mouse model at nontoxic concentrations. These results provide impetus and further guidance for the development of these rigidin analogues as anticancer agents.

Aldose reductase inhibition alleviates hyperglycemic effects on human retinal pigment epithelial cells

Chronic hyperglycemia is an important risk factor involved in the onset and progression of diabetic retinopathy (DR). Among other effectors, aldose reductase (AR) has been linked to the pathogenesis of this degenerative disease. The purpose of this study was to investigate whether the novel AR inhibitor, beta-glucogallin (BGG), can offer protection against various hyperglycemia-induced abnormalities in human adult retinal pigment epithelial (ARPE-19) cells. AR is an enzyme that contributes to cellular stress by production of reactive oxygen species (ROS) under high glucose conditions. A marked decrease in cell viability (from 100% to 78%) following long-term exposure (4 days) of RPE cells to high glucose (HG) was largely prevented by siRNA-mediated knockdown of AR gene expression (from 79% to 97%) or inhibition using sorbinil (from 66% to 86%). In HG, BGG decreased sorbitol accumulation (44%), ROS production (27%) as well as ER stress (22%). Additionally, we demonstrated that BGG prevented loss of mitochondrial membrane potential (MMP) under HG exposure. We also showed that AR inhibitor pretreatment reduced retinal microglia-induced apoptosis in APRE-19 cells. These results suggest that BGG may be useful as a therapeutic agent against retinal degeneration in the diabetic eye by preventing RPE cell death.

An improved high yield total synthesis and cytotoxicity study of the marine alkaloid neoamphimedine: an ATP-competitive inhibitor of topoisomerase IIα and potent anticancer agent

Recently, we characterized neoamphimedine (neo) as an ATP-competitive inhibitor of the ATPase domain of human Topoisomerase IIα. Thus far, neo is the only pyridoacridine with this mechanism of action. One limiting factor in the development of neo as a therapeutic agent has been access to sufficient amounts of material for biological testing. Although there are two reported syntheses of neo, both require 12 steps with low overall yields (≤6%). In this article, we report an improved total synthesis of neo achieved in 10 steps with a 25% overall yield. In addition, we report an expanded cytotoxicity study using a panel of human cancer cell lines, including: breast, colorectal, lung, and leukemia. Neo displays potent cytotoxicity (nM IC50 values) in all, with significant potency against colorectal cancer (lowest IC50 = 6 nM). We show that neo is cytotoxic not cytostatic, and that neo exerts cytotoxicity by inducing G2-M cell cycle arrest and apoptosis.

Design of an amide N-glycoside derivative of β-glucogallin: a stable, potent, and specific inhibitor of aldose reductase

β-Glucogallin (BGG), a major component of the Emblica officinalis medicinal plant, is a potent and selective inhibitor of aldose reductase (AKR1B1). New linkages (ether/triazole/amide) were introduced via high yielding, efficient syntheses to replace the labile ester, and an original two-step (90%) preparation of BGG was developed. Inhibition of AKR1B1was assessed in vitro and using transgenic lens organ cultures, which identified the amide linked glucoside (BGA) as a stable, potent, and selective therapeutic lead toward the treatment of diabetic eye disease.

A high-content assay to identify small-molecule modulators of a cancer stem cell population in luminal breast cancer

Breast cancers expressing hormone receptors for estrogen (ER) and progesterone (PR) represent ~70% of all cases and are treated with both ER-targeted and chemotherapies, with near 40% becoming resistant. We have previously described that in some ER(+) tumors, the resistant cells express cytokeratin 5 (CK5), a putative marker of breast stem and progenitor cells. CK5(+) cells have lost expression of ER and PR, express the tumor-initiating cell surface marker CD44, and are relatively quiescent. In addition, progestins, which increase breast cancer incidence, expand the CK5(+) subpopulation in ER(+)PR(+) breast cancer cell lines. We have developed models to induce and quantitate CK5(+)ER(-)PR(-) cells, using CK5 promoter-driven luciferase (Fluc) or green fluorescent protein (GFP) reporters stably transduced into T47D breast cancer cells (CK5Pro-GFP or CK5Pro-Luc). We validated the CK5Pro-GFP-T47D model for high-content screening in 96-well microplates and performed a pilot screen using a focused library of 280 compounds from the National Institutes of Health clinical collection. Four hits were obtained that significantly abrogated the progestin-induced CK5(+) cell population, three of which were members of the retinoid family. Hence, this approach will be useful in discovering small molecules that could potentially be developed as combination therapies, preventing the acquisition of a drug-resistant subpopulation.

The isolation and characterization of β-glucogallin as a novel aldose reductase inhibitor from Emblica officinalis

Diabetes mellitus is recognized as a leading cause of new cases of blindness. The prevalence of diabetic eye disease is expected to continue to increase worldwide as a result of the dramatic increase in the number of people with diabetes. At present, there is no medical treatment to delay or prevent the onset and progression of cataract or retinopathy, the most common causes of vision loss in diabetics. The plant Emblica officinalis (gooseberry) has been used for thousands of years as a traditional Indian Ayurvedic preparation for the treatment of diabetes in humans. Extracts from this plant have been shown to be efficacious against the progression of cataract in a diabetic rat model. Aldose reductase (ALR2) is implicated in the development of secondary complications of diabetes including cataract and, therefore, has been a major drug target for the development of therapies to treat diabetic disease. Herein, we present the bioassay-guided isolation and structure elucidation of 1-O-galloyl-β-D-glucose (β-glucogallin), a major component from the fruit of the gooseberry that displays selective as well as relatively potent inhibition (IC₅₀ = 17 µM) of AKR1B1 in vitro. Molecular modeling demonstrates that this inhibitor is able to favorably bind in the active site. Further, we show that β-glucogallin effectively inhibits sorbitol accumulation by 73% at 30 µM under hyperglycemic conditions in an ex-vivo organ culture model of lenses excised from transgenic mice overexpressing human ALR2 in the lens. This study supports the continued development of natural products such as β-glucogallin as therapeutic leads in the development of novel therapies to treat diabetic complications such as cataract.

Neoamphimedine circumvents metnase-enhanced DNA topoisomerase IIα activity through ATP-competitive inhibition

Type IIα DNA topoisomerase (TopoIIα) is among the most important clinical drug targets for the treatment of cancer. Recently, the DNA repair protein Metnase was shown to enhance TopoIIα activity and increase resistance to TopoIIα poisons. Using in vitro DNA decatenation assays we show that neoamphimedine potently inhibits TopoIIα-dependent DNA decatenation in the presence of Metnase. Cell proliferation assays demonstrate that neoamphimedine can inhibit Metnase-enhanced cell growth with an IC₅₀ of 0.5 μM. Additionally, we find that the apparent K_m of TopoIIα for ATP increases linearly with higher concentrations of neoamphimedine, indicating ATP-competitive inhibition, which is substantiated by molecular modeling. These findings support the continued development of neoamphimedine as an anticancer agent, particularly in solid tumors that over-express Metnase.

3D models of epithelial-mesenchymal transition in breast cancer metastasis: high-throughput screening assay development, validation, and pilot screen

Despite advancements in therapies developed for the treatment of cancer, patient prognosis and mortality rates have improved minimally, and metastasis remains the primary cause of cancer mortality worldwide. An underlying mechanism promoting metastasis in many types of cancer is epithelial-mesenchymal transition (EMT). Here the authors report a novel 3D model of EMT and metastatic breast cancer suitable for high-throughput screening (HTS) drug discovery. The primary assay incorporates the expression of the prognostic biomarker vimentin, as a luciferase reporter of EMT, in basil-like/triple-negative MDA-MB-231 breast carcinoma spheroids. Using this model, the authors developed a number of known antitumor agents as control modulators of EMT. U0126, PKC412, PF2341066, dasatinib, and axitinib downregulated vimentin expression by 70% to 90% as compared to untreated spheroids. Counterassays were developed to measure spheroid viability and the invasive potential of MDA-MB-231 spheroids after small-molecule treatment and used to confirm hits from primary screening. Finally, the authors conducted a pilot screen to validate this model for HTS using a purified library of marine secondary metabolites. From 230 compounds screened, they obtained a Z' score of 0.64, indicative of an excellent assay, and confirmed 4 hits, including isonaamidine B, papuamine, mycalolide E, and jaspamide. This HTS model demonstrates the potential to identify small-molecule modulators of EMT that could be used to discover novel antimetastatic agents for the treatment of cancer.

The total synthesis of neoamphimedine

Neoamphimedine, a pyridoacridine alkaloid from Xestospongia sp., is a potent antitumor agent both in vitro and in vivo. Neoamphimedine can efficiently induce topoisomerase II mediated catenation of plasmid DNA in vitro and is the only member of more than one hundred pyridoacridines thus far to have this mechanism of action. Herein we report the first total synthesis of neoamphimedine.

Synthesis and Biological Evaluation of Imidazoquinoxalinones, Imidazole Analogues of Pyrroloiminoquinone Marine Natural Products

This report describes the synthesis and biological activity of imidazoquinoxalines, benzimidazole-based analogues of indole-based pyrroloiminoquinone marine natural products. Our analogues consist of series 1, which possesses the ethylene tether and extended amidine feature found in the pyrroloiminoquinone natural products, and series 2, which also has the ethylene tether but with an electrostatically stabilized iminoquinone rather than a resonance stabilized iminoquinone (i.e., extended amidine). The biological properties of series 1 analogues, bearing electron-rich side chain rings (indole and phenol), display cytostatic and cytotoxic properties similar to that of the pyrroloiminoquinone natural products. In contrast, COMPARE analysis suggests that analogues bearing benzyl and phenethyl side chains possess a different cytotoxicity mechanism. Hollow fiber assays of analogs of 1 indicate promising antitumor activity and acceptable levels of toxicity. One analogue of 2 is active only against breast cancer cell lines, but the cellular target is as yet unknown.

Halogenated cyclic peptides isolated from the sponge Corticium sp

Fractionation of two Fijian specimens of the sponge Corticium sp. led to the isolation of the known active alkaloid steroid plakinamine A and two new halogenated cyclic peptides, corticiamide A (1) and cyclocinamide B (2). Structural elucidation of 1 and 2 was achieved by an extensive combination of high-field NMR and HRFT MS/MS experiments, and the absolute stereochemistry of 2 was determined by acid hydrolysis and Marfey's analysis. Corticiamide A (1) and cyclocinamide B (2) represent the first peptides to be described from the genus Corticium.

New destruxins from the marine-derived fungus Beauveria felina

Chemical investigation of the cytotoxic and anti-tuberculosis active butanone extract obtained from the growth media of the marine-derived fungus Beauveria felina led to the isolation of two new destruxins, [beta-Me-Pro] destruxin E chlorohydrin (1) and pseudodestruxin C (3), along with five known cyclic depsipeptides. The structures of the new destruxin derivatives were established by analysis of spectroscopic data, while the absolute configuration of the common amino acid residues was established by Marfey's analysis. The absolute configuration of the 2(R),4(S)-5-chloro-2,4-dihydroxypentanoic acid residue in 1 could be established by application of a J-based configuration method followed by derivatization with R-MPA-Cl and NMR analysis.

Solution Kinetics of CC-1065 A-Ring Opening: Substituent Effects and General Acid/Base Catalysis

pH-rate studies were carried out on 2-substituted derivatives of the CC 1065 A-ring over the range of pH 5 to 0. The goals were to document the presence of general-acid-catalyzed cyclopropyl ring opening near neutrality and to assess the role of the 2-substituent on the rate of nucleophile trapping by the cyclopropyl ring. Our studies show that the cyclopropyl group undergoes reversible general-acid/base-catalyzed trapping of chloride nucleophiles above pH 4. This finding implies that the general-acid-catalyzed alkylation of DNA minor groove by the A-ring is feasible. pH-rate studies also showed that the 2-substituent does not influence the pKa of the protonated carbonyl of the A-ring (pKa approximately 1) and has relatively little effect on the rate of nucleophile trapping. This finding is consistent with calculations that show the fused pyrrolo ring as the source of carbonyl oxygen electron density. The 2-nitrogen, on the other hand, only releases electrons to the carbonyl of the 2-substituent and does not greatly influence trapping of nucleophiles by the A-ring cyclopropyl group.