Lewis Acid-Promoted, Stereocontrolled, Gram Scale, Diels-Alder Cycloadditions of Electronically Matched 2-Pyrones and Vinyl Ethers: The Critical Importance of Molecular Sieves and the Temperature of Titanium Coordination with the Pyrone

(R)-(+)-Binol-titanium coordinates with commercial methyl 2-pyrone-3-carboxylate and promotes mild, highly enantiocontrolled Diels-Alder cycloadditions with electron-rich vinyl ether CH(2)=CHOCH(2)-1-naphthyl and vinyl silyl ether CH(2)=CHOSiMe(2)Bu-t leading to valuable 1alpha,25-dihydroxyvitamin D(3) (calcitriol) intermediate (-)-2. Unexpectedly, two subtle variables were found to be critical for obtaining reproducibly over 90% enantioselectivities in gram scale cycloadditions: (1) the moisture content (15-17% is best) of the molecular sieves used to prepare the binol-titanium complex according to the Mikami protocol and (2) the temperature (50 degrees C is best) at which the pyrone ester is mixed with the binol-titanium complex. Unsubstituted 2-pyrone undergoes ytterbium-promoted, high-pressure, regioselective, and stereoselective Diels-Alder cycloaddition with benzyl vinyl ether to form versatile bicyclic lactone (+/-)-4 on gram scale.

Tumor-targeted bioconjugate based delivery of camptothecin: design, synthesis and in vitro evaluation

Camptothecin (CPT) presents numerous challenges associated with optimal transport and delivery including variability in clinically observed effects, low target tissue concentrations and severe and unpredictable toxicity. The objective of the present study was to optimize the delivery of CPT by targeting it to cancer cells using an endogenous receptor system. A novel CPT bioconjugate was synthesized using carbodiimide chemistry with a linear poly(ethylene glycol) (PEG) and amino acid glycine as the spacer and linker respectively. Folic acid was used as the targeting ligand to take advantage of folate receptor mediated endocytosis. The bioconjugate was extensively characterized using MALDI, proton NMR, FT-IR and amino acid analysis. Furthermore, the bioconjugate was evaluated in vitro for specific targeting to folate receptor-expressing KB cells, a human nasopharyngeal carcinoma. Finally, the delivery system was evaluated for cytotoxicity using a MTT based assay. The results indicate significantly higher efficacy of the bioconjugate in comparison to CPT. A control conjugate without PEG demonstrated no improvement in efficacy over untargeted CPT emphasizing the importance of spacer between the anticancer compounds and targeting moiety. This bioconjugate represents the 'first-in-series' of targeted bioconjugates and serves as prototype for improving tumor cell concentration and efficacy.

Antitumor Activity of New Substituted 3-(5-Imidazo[2,1-b]thiazolylmethylene)-2-indolinones and Study of Their Effect on the Cell Cycle

This paper reports the synthesis of a new series of 3-(5-imidazo[2,1-b]thiazolylmethylene)-2-indolinones which were tested as potential antitumor agents at the National Cancer Institute. Two derivatives are now under review by BEC (Biological Evaluation Committee of NCI). To investigate the mechanism of action, the effect on cell cycle progression was studied by monitoring them in colon adenocarcinoma HT-29: both were able to block HT-29 in mitosis. 3-[(2,6-Dimethylimidazo[2,1-b]thiazol-5-yl)methylene]-5-chloro-2-indolinone was the most active compound.

Structure-activity relations of nanolipoblockers with the atherogenic domain of human macrophage scavenger receptor A

Oxidized low density lipoprotein (oxLDL) uptake by macrophages is mediated by scavenger receptors and leads to unregulated cholesterol accumulation. Micellar nanolipoblockers (NLBs) consist of alkyl chains and polyethylene glycol on mucic acid. NLBs functionalized with anionic groups inhibit oxLDL uptake via the scavenger receptor A (SR-A). Molecular modeling and docking approaches were used to understand the structure-activity relationship (SAR) between NLBs and SR-A. Six NLB models were docked to the SR-A homology model to investigate charge placement and clustering. NLB models with the most favorable binding energy were also the most effective oxLDL inhibitors in THP-1 macrophages. Mutant SR-A models were generated by replacing charged residues with alanine. All charged residues in the region were necessary, with Lys60, Lys63, and Lys66 having the greatest effect on binding. We hypothesize that structural studies aided by theoretical modeling and docking can be used to design promising NLB candidates with optimal binding properties.

Structure-activity relationships of polybiguanides with activity against human immunodeficiency virus type 1

Previous investigations showing that polydisperse biguanide (PDBG) molecules have activity against human immunodeficiency virus type 1 (HIV-1) also suggested a relationship between PDBG biologic activity and the lengths of hydrocarbon linkers surrounding the positively charged biguanide unit. To better define structure-activity relationships, PDBG molecules with select linker lengths were evaluated for cytotoxicity, anti-HIV-1 activity, and in vivo toxicity. Results of the in vitro experiments demonstrated that increases in linker length (and, therefore, increases in compound lipophilicity) were generally associated with increases in cytotoxicity and antiviral activity against HIV-1. However, a relationship between linker length asymmetry and in vitro therapeutic index (TI) suggested structural specificity in the mechanism of action against HIV-1. Polyethylene hexamethylene biguanide (PEHMB; biguanide units spaced between alternating ethylene and hexamethylene linkers) was found to have the highest in vitro TI (CC₅₀/IC₅₀) among the compounds examined. Recent improvements in PEHMB synthesis and purification have yielded preparations of PEHMB with in vitro TI values of 266 and 7000 against HIV-1 strains BaL and IIIB, respectively. The minimal toxicity of PEHMB relative to polyhexamethylene biguanide (PHMB; biguanide units alternating with hexamethylene linkers) in a murine model of cervicovaginal microbicide toxicity was consistent with considerable differences in cytotoxicity between PEHMB and PHMB observed during in vitro experiments. These structure-activity investigations increase our understanding of PDBG molecules as agents with activity against HIV-1 and provide the foundation for further preclinical studies of PEHMB and other biguanide-based compounds as antiviral and microbicidal agents.

Molecular characterization of thyroid toxicity: anchoring gene expression profiles to biochemical and pathologic end points

Organic iodides have been shown to induce thyroid hypertrophy and increase alterations in colloid in rats, although the mechanism involved in this toxicity is unclear. To evaluate the effect that free iodide has on thyroid toxicity, we exposed rats for 2 weeks by daily gavage to sodium iodide (NaI). To compare the effects of compounds with alternative mechanisms (increased thyroid hormone metabolism and decreased thyroid hormone synthesis, respectively), we also examined phenobarbital (PB) and propylthiouracil (PTU) as model thyroid toxicants. Follicular cell hypertrophy and pale-staining colloid were present in thyroid glands from PB-treated rats, and more severe hypertrophy/colloid changes along with diffuse hyperplasia were present in thyroid glands from PTU-treated rats. In PB- and PTU-treated rats, thyroid-stimulating hormone (TSH) levels were significantly elevated, and both thyroxine and triiodothyronine hormone levels were significantly decreased. PB induced hepatic uridine diphosphate-glucuronyltransferase (UDPGT) activity almost 2-fold, whereas PTU reduced hepatic 5 -deiodinase I (5 -DI) activity to < 10% of control in support of previous reports regarding the mechanism of action of each chemical. NaI also significantly altered liver weights and UDPGT activity but did not affect thyroid hormone levels or thyroid pathology. Thyroid gene expression analyses using Affymetrix U34A GeneChips, a regularized t-test, and Gene Map Annotator and Pathway Profiler demonstrated significant changes in rhodopsin-like G-protein-coupled receptor transcripts from all chemicals tested. NaI demonstrated dose-dependent changes in multiple oxidative stress-related genes, as also determined by principal component and linear regression analyses. Differential transcript profiles, possibly relevant to rodent follicular cell tumor outcomes, were observed in rats exposed to PB and PTU, including genes involved in Wnt signaling and ribosomal protein expression.

Characterization of agronomic traits and markers of recombinant inbred lines from intra- and interracial populations of Phaseolus vulgaris L

The value of intra- and interracial populations in common bean (Phaseolus vulgaris L.) needs to be determined in order to create useful genetic variation for maximizing gains from selection, broadening the genetic base of commercial cultivars, and making efficient use of available resources. Five large-seeded parents of race Nueva Granada (N), two small-seeded race Mesoamerica (M), and one medium-seeded race Durango (D) were hybridized to produce one intraracial (N x N) and three interracial (two N x M and one N x D) populations. Seventy-nine F2-derived F6 lines randomly taken from each population along with their parents were evaluated for agronomic traits and markers at Palmira and Popayán, Colombia, in 1990 and 1991. Variation for agronomic traits and for morphological, protein, and isozyme markers was larger in interracial populations than in the intraracial population. Mean seed yield of all lines as well as yield of the highest yielding line from two interracial populations were significantly higher than that of the intraracial population. The highest (≥ 0.80±0.15) heritability was recorded for 100-seed weight. Values for seed yield varied from 0.19±0.17 to 0.50±0.16. Gains from selection (at 20% selection pressure) for seed yield ranged from 3.9% to 11.4%. Seed yield was positively associated with biomass yield, pods/m(2), and days to maturity, but harvest index showed negative correlations with these traits and a positive value with 100-seed weight. Polymorphism was recorded for phaseolin, lectins, protein Group-1 and protein Group-2 fractions, and six isozyme loci. Lines with indeterminate growth habit had significantly (P < 0.01) higher seed yield than lines with determinate growth habit in a Redkloud x MAM 4 population. Also, 23 other associations of markers with agronomic traits other than seed yield were recorded. Of these associations, lines with T phaseolin, the Diap1 (2) allele, and lilac flower color tended to possess greater seed weight.

Experimental Design of Formulations Utilizing High Dimensional Model Representation

Many applications involve formulations or mixtures where large numbers of components are possible to choose from, but a final composition with only a few components is sought. Finding suitable binary or ternary mixtures from all the permissible components often relies on simplex-lattice sampling in traditional design of experiments (DoE), which requires performing a large number of experiments even for just tens of permissible components. The effect rises very rapidly with increasing numbers of components and can readily become impractical. This paper proposes constructing a single model for a mixture containing all permissible components from just a modest number of experiments. Yet the model is capable of satisfactorily predicting the performance for full as well as all possible binary and ternary component mixtures. To achieve this goal, we utilize biased random sampling combined with high dimensional model representation (HDMR) to replace DoE simplex-lattice design. Compared with DoE, the required number of experiments is significantly reduced, especially when the number of permissible components is large. This study is illustrated with a solubility model for solvent mixture screening.

Oncogene expression profiles in K6/ODC mouse skin and papillomas following a chronic exposure to monomethylarsonous acid

We have previously observed that a chronic drinking water exposure to monomethylarsonous acid [MMA(III)], a cellular metabolite of inorganic arsenic, increases tumor frequency in the skin of keratin VI/ornithine decarboxylase (K6/ODC) transgenic mice. To characterize gene expression profiles predictive of MMA(III) exposure and mode of action of carcinogenesis, skin and papilloma RNA was isolated from K6/ODC mice administered 0, 10, 50, and 100 ppm MMA(III) in their drinking water for 26 weeks. Following RNA processing, the resulting cRNA samples were hybridized to Affymetrix Mouse Genome 430A 2.0 GeneChips(R). Micoarray data were normalized using MAS 5.0 software, and statistically significant genes were determined using a regularized t-test. Significant changes in bZIP transcription factors, MAP kinase signaling, chromatin remodeling, and lipid metabolism gene transcripts were observed following MMA(III) exposure as determined using the Database for Annotation, Visualization and Integrated Discovery 2.1 (DAVID) (Dennis et al., Genome Biol 2003;4(5):P3). MMA(III) also caused dose-dependent changes in multiple Rho guanine nucleotide triphosphatase (GTPase) and cell cycle related genes as determined by linear regression analyses. Observed increases in transcript abundance of Fosl1, Myc, and Rac1 oncogenes in mouse skin support previous reports on the inducibility of these oncogenes in response to arsenic and support the relevance of these genomic changes in skin tumor induction in the K6/ODC mouse model.

Tea polyphenol (-)-epigallocatechin-3-gallate inhibits DNA methyltransferase and reactivates methylation-silenced genes in cancer cell lines

Hypermethylation of CpG islands in the promoter regions is an important mechanism to silence the expression of many important genes in cancer. The hypermethylation status is passed to the daughter cells through the methylation of the newly synthesized DNA strand by 5-cytosine DNA methyltransferase (DNMT). We report herein that (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol from green tea, can inhibit DNMT activity and reactivate methylation-silenced genes in cancer cells. With nuclear extracts as the enzyme source and polydeoxyinosine-deoxycytosine as the substrate, EGCG dose-dependently inhibited DNMT activity, showing competitive inhibition with a K(i) of 6.89 microM. Studies with structural analogues of EGCG suggest the importance of D and B ring structures in the inhibitory activity. Molecular modeling studies also support this conclusion, and suggest that EGCG can form hydrogen bonds with Pro(1223), Glu(1265), Cys(1225), Ser(1229), and Arg(1309) in the catalytic pocket of DNMT. Treatment of human esophageal cancer KYSE 510 cells with 5-50 microM of EGCG for 12-144 h caused a concentration- and time-dependent reversal of hypermethylation of p16(INK4a), retinoic acid receptor beta (RARbeta), O(6)-methylguanine methyltransferase (MGMT), and human mutL homologue 1 (hMLH1) genes as determined by the appearance of the unmethylation-specific bands in PCR. This was accompanied by the expression of mRNA of these genes as determined by reverse transcription-PCR. The re-expression of RARbeta and hMLH1 proteins by EGCG was demonstrated by Western blot. Reactivation of some methylation-silenced genes by EGCG was also demonstrated in human colon cancer HT-29 cells, esophageal cancer KYSE 150 cells, and prostate cancer PC3 cells. The results demonstrate for the first time the inhibition of DNA methylation by a commonly consumed dietary constituent and suggest the potential use of EGCG for the prevention or reversal of related gene-silencing in the prevention of carcinogenesis.

Abstract 5548: Novel small-molecule delta opioid receptor ligands modeled from naltrindole inhibit the proliferation of human U266 multiple myeloma cells

Multiple myeloma is an invasive plasma cell neoplasm that proliferates in the bone marrow, and is responsible for 10% of all hematological malignancies. Naltrindole, synthesized by Portoghese and colleagues (1988) is a synthetic alkaloid derived from naltrexone, and has the pharmacological profile of a selective delta opioid receptor antagonist. Naltrindole also acts as a potent immunosuppressant in the allogeneic mixed lymphocyte reaction and in inhibiting renal graft rejection, and Gaveriaux-Ruff and colleagues (2001) demonstrated that a non-opioid receptor target was involved in the immunosuppressant activity of naltrindole. In a recent report (Mundra et al., J. Pharmacol. Exp. Ther. 342: 273-287, 2012), naltrindole inhibited human multiple myeloma cell proliferation in vitro and in a murine xenograft model in vivo, by interaction with a non-opioid receptor target. In this study, it was discovered that four novel small-molecule delta opioid receptor ligands (DOPs) derived from naltrindole by rational design (see Peng et al., Bioorgan. & Med. Chem. 17: 6442-6450, 2009) competed for specific 3H-naltrindole binding to human U266 multiple myeloma cells. The apparent dissociation constant, KD, of naltrindole binding to intact multiple myeloma cells was 20 μM, and the Bmax was 1.8 nmol/mg protein. Whole cells were incubated with 10 nM 3H-naltrindole in the absence and presence of 500 μM unlabeled naltrindole (to define specific binding), and the ability of the DOP ligands to displace specific naltrindole binding was assayed at room temperature following a 30 min incubation of each DOP compound at 50 μM. DOP 108 inhibited specific naltrindole binding down to 22 ± 6 % of control (78% inhibition of binding); DOP 121 reduced binding to 36 ± 10 % control; DOP 126 inhibited binding to 12 ± 5 % control, and DOP 402 inhibited binding to 16 ± 7 % control. More detailed competition curves will be performed, but it appears that the affinity of the DOP ligands for the naltrindole binding site are similar or higher than naltrindole itself. When U266 multiple myeloma cells were incubated at 37°C for 72 h in the presence of naltrindole or the DOP ligands, each at 50 μM, the number of viable myeloma cells was inhibited to 42 ± 7, 49 ±11, 31 ± 8, 29 ± 8, and 28 ± 9 % of the number of control untreated cells by naltrindole, DOP 108, DOP 121, DOP 126, and DOP 402, respectively, demonstrating that the efficacy of the DOP compounds to inhibit multiple myeloma cell growth was similar or better than naltrindole. This study provides a rationale basis for further evaluation of the DOP compounds as anti-multiple myeloma therapeutic agents.

Citation Format: Richard D. Howells, Jyoti Joshi Mundra, Alessandro Howells, Giovanni Howells, Youyi Peng, William Welsh. Novel small-molecule delta opioid receptor ligands modeled from naltrindole inhibit the proliferation of human U266 multiple myeloma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5548. doi:10.1158/1538-7445.AM2013-5548

Abstract A13: Discovery of selective inhibitors of the kinase and metastatic activities of the activated Cdc42-associated kinase (ACK1)

Activated Cdc42-associated kinase (ACK1) is a non-receptor tyrosine kinase and an effector protein of Cdc42. Previous reports have demonstrated that ACK1 is a critical factor in the cellular transformation of a number of cancer cell lines. ACK1 also contributes to cellular motility, and overexpression in certain cell lines results in enhanced motility. The significance of tyrosine kinase proteins such as ACK1 in cancer-related signaling pathways, and the implications of metastasis in the prognosis of cancer patients, point to the importance of the discovery of a potent yet selective inhibitor for this protein. As a result, we are engaged in a study focused on applying computational approaches to identify novel inhibitor molecules of ACK that will also hamper its ability to promote motility of cancer cells.

We employed customized in-house computational tools to retrieve approximately 50 small-molecule hits from our chemical databases that may bind with high affinity to the ACK1 ATP binding pocket. These hits were further screened for drug-like properties (Lipinski's Rule of 5) and rescored using GOLD docking to the ACK1 crystal structure (PDB3EQR). After rescoring, the top 25 hits were then tested for in vitro cytotoxicity in a variety of cancer cell lines. Compounds were specifically examined for their impact on the kinase activity of purified ACK1 and for their ability to modulate its metastatic properties in wound healing and transwell migration assays.

Our screening has revealed that several compounds have the ability to inhibit the in vitro kinase activity of ACK1 and also inhibit the in vitro growth of cancer cells. Ongoing immunofluorescence, cellular transformation, and cellular motility studies suggest that the selected compounds may modulate the effect of ACK1 on the motility of cancer cells. We are actively proceeding with specific structural modifications of our initial inhibitor compounds in order to find molecules which possess increased cytotoxicity to cancer cells and improved specificity for the inhibition of ACK.

Citation Information: Clin Cancer Res 2010;16(14 Suppl):A13.

Abstract 348: Small molecule Axl Ig1-Gas6 inhibitors block Gas6-inducible Axl signaling and suppress tumorigenicity

TAM receptors (Tyro-3, Axl, and Mer) are a family of three homologous receptor tyrosine kinases (RTKs) expressed predominantly on myeloid-derived hematopoietic cells and epithelial cells which function as inhibitory receptors that dampen inflammatory responses and maintain tissue tolerance. Additionally, all three TAMs have been implicated in various human malignancies, where level of expression is often associated with more aggressive staging of the cancers, poorer predicted patient survival, as well as drug-resistant cancers. Over the past several years, considerable effort has been made to generate small molecule tyrosine kinase inhibitors and biological therapeutics (such as monoclonal antibodies and soluble extracellular receptor traps) targeting TAM receptors in human cancers. Early preclinical studies show promising anti-tumor activities using either kinase inhibitors or monoclonal antibodies against Axl and Mer, although cross-reactivity with other tyrosine kinase inhibitors is associated with off-target specificities. Here, we report the development and characterization of a series of small molecule inhibitors that target the interface between the Ig1 domain of Axl and Gas6, and inhibit native receptors and Axl reporter lines with sub-micro-molar affinities. Additionally, these compounds inhibit Gas6 inducible motility and invasion in Axl-expressing cell lines, and suppress tumor growth in xenograft models of non small cell lung cancer. Together, these observations demonstrate that Axl can be targeted by small molecules that bind to the Ig1 domain/Gas6 interaction, and validate Ig1 inhibitors as novel agents for treatment of cancer.

Citation Format: Nitu Bansal, Stanley Kimani, Kamlendra Singh, Thomas Comollo, Sushil Kumar, Vladyslav Kholodovych, Youyi Peng, William Welsh, Bertino Joseph, Raymond B. Birge. Small molecule Axl Ig1-Gas6 inhibitors block Gas6-inducible Axl signaling and suppress tumorigenicity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 348.