Transcriptional inhibition of the estrogen response element by antiestrogenic piperidinediones correlates with intercalation into DNA measured by energy calculations

Bioactive Platinum(IV) Complexes Incorporating Halogenated Phenylacetates

A new series of cytotoxic platinum(IV) complexes (1-8) incorporating halogenated phenylacetic acid derivatives (4-chlorophenylacetic acid, 4-fluorophenylacetic acid, 4-bromophenylacetic acid and 4-iodophenylacetic acid) were synthesised and characterised using spectroscopic and spectrometric techniques. Complexes 1-8 were assessed on a panel of cell lines including HT29 colon, U87 glioblastoma, MCF-7 breast, A2780 ovarian, H460 lung, A431 skin, Du145 prostate, BE2-C neuroblastoma, SJ-G2 glioblastoma, MIA pancreas, the ADDP-resistant ovarian variant, and the non-tumour-derived MCF10A breast line. The in vitro cytotoxicity results confirmed the superior biological activity of the studied complexes, especially those containing 4-fluorophenylacetic acid and 4-bromophenylacetic acid ligands, namely 4 and 6, eliciting an average GI₅₀ value of 20 nM over the range of cell lines tested. In the Du145 prostate cell line, 4 exhibited the highest degree of potency amongst the derivatives, displaying a GI₅₀ value of 0.7 nM, which makes it 1700-fold more potent than cisplatin (1200 nM) and nearly 7-fold more potent than our lead complex, 56MESS (4.6 nM) in this cell line. Notably, in the ADDP-resistant ovarian variant cell line, 4 (6 nM) was found to be almost 4700-fold more potent than cisplatin. Reduction reaction experiments were also undertaken, along with studies aimed at determining the complexes' solubility, stability, lipophilicity, and reactive oxygen species production.

Thioamide synthesis via copper-catalyzed C–H activation of 1,2,3-thiadiazoles enabled by slow release and capture of thioketenes

A copper-catalyzed coupling of 1,2,3-thiadiazoles with various amines under base-free conditions was developed as a robust protocol for the synthesis of thioamide derivatives via C–H activation/Cu coordination strategy.

Evidence for the contribution of non-covalent steroid interactions between DNA and topoisomerase in the genotoxicity of steroids

Fifty two steroids and 9 Vitamin D analogs were docked into ten crystallographically-defined DNA dinucleotide sites and two human topoisomerase II ATP binding sites using two computational programs, Autodock and Surflex. It is shown that both steroids and Vitamin D analogs exhibit a propensity for non-covalent intercalative binding to DNA. A higher predicted binding affinity was found, however, for steroids and the ATP binding site of topoisomerase; in fact these drugs exhibited among the highest topo II binding observed in over 1370 docked drugs. These findings along with genotoxicity data from 26 additional steroids not subjected to docking analysis, support a mechanism wherein the long known, but poorly understood, clastogenicity of steroids may be attributable to inhibition of topoisomerase. A "proof of principle" experiment with dexamethasone demonstrated this to be the likely mechanism of clastogenicity of, at least, this steroid. The generality of this proposed mechanism of genotoxicity across the steroids and vitamin-D analogs is discussed.

Phenylketonuria with acute myeloblastic leukemia in a 9-year-old boy: reporting a rare case

Phenylketonuria is a genetic metabolic disorder resulting in phenylalanine accumulation in blood. Phenylacetate, which is an abnormal phenylalanine metabolities, was hypothesized to have anticancer activity. Two-years-old boy was diagnosed with classical phenylketonuria because of mental motor retardation. When the patient was 9-year-old, he developed acute myeloblastic leukemia. Here, we present the case with phenylketonuria and acute myeloblastic leukemia because of its extreme rarity.

Carcinogenic effects in a phenylketonuria mouse model

Phenylketonuria (PKU) is a metabolic disorder caused by impaired phenylalanine hydroxylase (PAH). This condition results in hyperphenylalaninemia and elevated levels of abnormal phenylalanine metabolites, among which is phenylacetic acid/phenylacetate (PA). In recent years, PA and its analogs were found to have anticancer activity against a variety of malignancies suggesting the possibility that PKU may offer protection against cancer through chronically elevated levels of PA. We tested this hypothesis in a genetic mouse model of PKU (PAH(enu2)) which has a biochemical profile that closely resembles that of human PKU. Plasma levels of phenylalanine in homozygous (HMZ) PAH(enu2) mice were >12-fold those of heterozygous (HTZ) littermates while tyrosine levels were reduced. Phenylketones, including PA, were also markedly elevated to the range seen in the human disease. Mice were subjected to 7,12 dimethylbenz[a]anthracene (DMBA) carcinogenesis, a model which is sensitive to the anticancer effects of the PA derivative 4-chlorophenylacetate (4-CPA). Tumor induction by DMBA was not significantly different between the HTZ and HMZ mice, either in total tumor development or in the type of cancers that arose. HMZ mice were then treated with 4-CPA as positive controls for the anticancer effects of PA and to evaluate its possible effects on phenylalanine metabolism in PKU mice. 4-CPA had no effect on the plasma concentrations of phenylalanine, phenylketones, or tyrosine. Surprisingly, the HMZ mice treated with 4-CPA developed an unexplained neuromuscular syndrome which precluded its use in these animals as an anticancer agent. Together, these studies support the use of PAH(enu2) mice as a model for studying human PKU. Chronically elevated levels of PA in the PAH(enu2) mice were not protective against cancer.

Small molecule intercalation with double stranded DNA: implications for normal gene regulation and for predicting the biological efficacy and genotoxicity of drugs and other chemicals

The binding of small molecules to double stranded DNA including intercalation between base pairs has been a topic of research for over 40 years. For the most part, however, intercalation has been of marginal interest given the prevailing notion that binding of small molecules to protein receptors is largely responsible for governing biological function. This picture is now changing with the discovery of nuclear enzymes, e.g. topoisomerases that modulate intercalation of various compounds including certain antitumor drugs and genotoxins. While intercalators are classically flat, aromatic structures that can easily insert between base pairs, our laboratories reported in 1977 that a number of biologically active compounds with greater molecular thickness, e.g. steroid hormones, could fit stereospecifically between base pairs. The hypothesis was advanced that intercalation was a salient feature of the action of gene regulatory molecules. Two parallel lines of research were pursued: (1) development of technology to employ intercalation in the design of safe and effective chemicals, e.g. pharmaceuticals, nutraceuticals, agricultural chemicals; (2) exploration of intercalation in the mode of action of nuclear receptor proteins. Computer modeling demonstrated that degree of fit of certain small molecules into DNA intercalation sites correlated with degree of biological activity but not with strength of receptor binding. These findings led to computational tools including pharmacophores and search engines to design new drug candidates by predicting desirable and undesirable activities. The specific sequences in DNA into which ligands best intercalated were later found in the consensus sequences of genes activated by nuclear receptors implying intercalation was central to their mode of action. Recently, the orientation of ligands bound to nuclear receptors was found to match closely the spatial locations of ligands derived from intercalation into unwound gene sequences suggesting that nuclear receptors may be guiding ligands to DNA with remarkable precision. Based upon multiple lines of experimental evidence, we suggest that intercalation in double stranded DNA is a ubiquitous, natural process and a salient feature of the regulation of genes. If double stranded DNA is proven to be the ultimate target of genomic drug action, intercalation will emerge as a cornerstone of the future discovery of safe and effective pharmaceuticals.

Modulation by phenylacetate of early estrogen-mediated events in MCF-7 breast cancer cells

PURPOSE

Phenylacetate (PA) and its derivatives constitute a group of small aromatic fatty acids that have been of considerable interest due to their anticancer properties in a number of experimental systems. We previously showed that PA can inhibit the growth of estrogen receptor (ER)+ breast cancer cells and that this activity is, at least in part, mediated by the ability of the compound to inhibit transcriptional activation driven by estrogen response elements (EREs). We now shed additional light on the antiestrogenic action of PA by determining its effects on early events in the estrogen-signaling pathway.

METHODS

MCF-7 breast cancer cells were used in this study. ER-ERE binding activity, and subsequent effects on ER and progesterone receptors (PR), c-myc, and the cyclin-dependent kinase inhibitor p21ASF1/CP1/MDA-6 (p21) were evaluated using electrophoretic mobility shift assays, real-time RT-PCR, and western blotting methodologies. Effects of PA on p21 promoter activity were assessed in transient transfection experiments utilizing p21 promoter-reporter gene constructs.

RESULTS

We demonstrate that PA treatment can block ER-ERE binding activity and that this effect is accompanied by downregulation of PR and c-myc, two genes which are transcriptionally regulated by estrogen through novel-ER-binding sites. Suppression of c-myc by PA is followed by increased mRNA levels of p21, an effect that is mediated by PA activation of the p21 promoter. Forced overexpression of c-myc through co-transfection of MCF-7 cells with a c-myc expression plasmid prevented PA upregulation of p21 promoter activity.

CONCLUSIONS

These findings confirm the potent antiestrogenic properties of PA, indicate that its effects are mediated by inhibiting ER-ERE interactions, and suggest that downregulation of c-myc is an early event leading to increased p21 expression and cell growth inhibition.

XR5944: A potent inhibitor of estrogen receptors

The anticancer drug XR5944 was originally developed as a topoisomerase inhibitor and was subsequently shown to be a transcription inhibitor. It has shown exceptional anticancer activity both in vitro and in vivo and was significantly more potent than traditional topoisomerase inhibitors. The solution structure of the XR5944/DNA complex recently obtained in our laboratory indicates that XR5944 bis-intercalates at the 5'-(TpG):(CpA) site of duplex DNA, which is found in the consensus DNA-binding site of estrogen receptor (ER). Thus, we tested the ability of XR5944 to inhibit ER activity both in vitro and in cultured cells. In electrophoretic mobility shift assays, it is seen that the DNA binding of recombinant ERalpha protein, as well as ER from nuclear extracts, is inhibited by XR5944 in a dose-dependent manner. In luciferase reporter assays, XR5944 inhibited the reporter gene expression from an estrogen response element-containing promoter but not from a basal promoter sequence that lacks any cis-acting elements. In contrast, the RNA polymerase inhibitor actinomycin D inhibits the transcription from both the above-mentioned promoters. The specificity of XR5944 activity is displayed by a separate reporter assay in which the transactivation of reporter gene expression by Sp1 proteins was not inhibited by XR5944. Collectively, these data suggest that XR5944 is capable of specifically inhibiting the binding of ER to its consensus DNA sequence and its subsequent activity. This represents a novel mechanism of ER inhibition, which may allow the development of agents capable of overcoming resistance to current antiestrogens.

Inhibition of estrogen-induced mammary tumor formation in MMTV-aromatase transgenic mice by 4-chlorophenylacetate

Treatment of estrogen-sensitive breast cancer with selective estrogen selective modulators (SERMs) and, more recently, aromatase inhibitors has met with wide success. However, antagonism of estrogen receptor (ER) activity in breast carcinomas by SERMs such as tamoxifen has been associated with increased risk of cancer in other tissue such as the endometrium. Furthermore, current therapies using aromatase inhibitors have side effects on bone resulting in development of osteoporosis in some patients. We present in this paper the results of a study using 4-chlorophenylacetate (4-CPA), a compound which belongs to a family of small aromatic fatty acids that has been shown to possess anticancer properties, to treat DMBA exposed MMTV-aromatase mice. These animals exhibit elevated levels of estrogen in their mammary glands and develop estrogen-responsive tumors. Consistent with our earlier findings showing that 4-CPA inhibited the growth of ER positive breast cancer cells in vitro, we now demonstrate that this compound inhibits tumor formation in MMTV-aromatase mice. This effect was not associated with reduction of ER expression in their mammary tissue, or to alteration of aromatase levels or activity. The data suggest that 4-CPA is a novel therapeutic agent that could be used in the prevention or treatment of estrogen-sensitive breast cancer.