Activation of the antitumor agent aminoflavone (NSC 686288) is mediated by induction of tumor cell cytochrome P450 1A1/1A2

Genic-intergenic polymorphisms of CYP1A genes and their clinical impact

The humancytochrome P450 1A (CYP1A) subfamily genes, CYP1A1 and CYP1A2, encoding monooxygenases are critically involved in biotransformation of key endogenous substrates (estradiol, arachidonic acid, cholesterol) and exogenous compounds (smoke constituents, carcinogens, caffeine, therapeutic drugs). This suggests their significant involvement in multiple biological pathways with a primary role of maintaining endogenous homeostasis and xenobiotic detoxification. Large interindividual variability exist in CYP1A gene expression and/or catalytic activity of the enzyme, which is primarily due to the existence of polymorphic alleles which encode them. These polymorphisms (mainly single nucleotide polymorphisms, SNPs) have been extensively studied as susceptibility factors in a spectrum of clinical phenotypes. An in-depth understanding of the effects of polymorphic CYP1A genes on the differential metabolic activity and the resulting biological pathways is needed to explain the clinical implications of CYP1A polymorphisms. The present review is intended to provide an integrated understanding of CYP1A metabolic activity with unique substrate specificity and their involvement in physiological and pathophysiological roles. The article further emphasizes on the impact of widely studied CYP1A1 and CYP1A2 SNPs and their complex interaction with non-genetic factors like smoking and caffeine intake on multiple clinical phenotypes. Finally, we attempted to discuss the alterations in metabolism/physiology concerning the polymorphic CYP1A genes, which may underlie the reported clinical associations. This knowledge may provide insights into the disease pathogenesis, risk stratification, response to therapy and potential drug targets for individuals with certain CYP1A genotypes.

The Role of the Aryl Hydrocarbon Receptor (AhR) and Its Ligands in Breast Cancer

Breast cancer is a complex disease which is defined by numerous cellular and molecular markers that can be used to develop more targeted and successful therapies. The aryl hydrocarbon receptor (AhR) is overexpressed in many breast tumor sub-types, including estrogen receptor -positive (ER+) tumors; however, the prognostic value of the AhR for breast cancer patient survival is not consistent between studies. Moreover, the functional role of the AhR in various breast cancer cell lines is also variable and exhibits both tumor promoter- and tumor suppressor- like activity and the AhR is expressed in both ER-positive and ER-negative cells/tumors. There is strong evidence demonstrating inhibitory AhR-Rα crosstalk where various AhR ligands induce ER degradation. It has also been reported that different structural classes of AhR ligands, including halogenated aromatics, polynuclear aromatics, synthetic drugs and other pharmaceuticals, health promoting phytochemical-derived natural products and endogenous AhR-active compounds inhibit one or more of breast cancer cell proliferation, survival, migration/invasion, and metastasis. AhR-dependent mechanisms for the inhibition of breast cancer by AhR agonists are variable and include the downregulation of multiple genes/gene products such as CXCR4, MMPs, CXCL12, SOX4 and the modulation of microRNA levels. Some AhR ligands, such as aminoflavone, have been investigated in clinical trials for their anticancer activity against breast cancer. In contrast, several publications have reported that AhR agonists and antagonists enhance and inhibit mammary carcinogenesis, respectively, and differences between the anticancer activities of AhR agonists in breast cancer may be due in part to cell context and ligand structure. However, there are reports showing that the same AhR ligand in the same breast cancer cell line gives opposite results. These differences need to be resolved in order to further develop and take advantage of promising agents that inhibit mammary carcinogenesis by targeting the AhR.

Potential of cytochrome P450, a family of xenobiotic metabolizing enzymes, in cancer therapy

SIGNIFICANCE

Targeted cancer therapy with minimal off-target consequences has shown promise for some cancer types. Although cytochrome P450 (CYP) consists of 18 families, CYP1-4 families play key role in metabolizing xenobiotics and cancer drugs. This eventually affects the process of carcinogenesis, treatment outcome, and cancer drug resistance. Differential overexpression of CYPs in transformed cells, together with phenotypic alterations in tumors, presents a potential for therapeutic intervention.

RECENT ADVANCES

Recent advances in molecular tools and information technology have helped utilize CYPs as cancer targets. The precise expression in various tumors, X-ray crystal structures, improved understanding of the structure-activity relationship, and new approaches in the development of prodrugs have supported the ongoing efforts to develop CYPs-based drugs with a better therapeutic index.

CRITICAL ISSUES

Narrow therapeutic index, off-target effects, drug resistance, and tumor heterogeneity limit the benefits of CYP-based conventional cancer therapies. In this review, we address the CYP1-4 families as druggable targets in cancer. An emphasis is given to the CYP expression, function, and the possible mechanisms that drive expression and activity in normal and transformed tissues. The strategies that inhibit or activate CYPs for therapeutic benefits are also discussed.

FUTURE DIRECTIONS

Efforts are needed to develop more selective tools that will help comprehend molecular and metabolic alterations in tumor tissues with biological end-points in relation to CYPs. This will eventually translate to developing more specific CYP inhibitors/inducers.

Diversity-Oriented Synthesis: Amino Acetophenones as Building Blocks for the Synthesis of Natural Product Analogs

Diversity-Oriented Synthesis (DOS) represents a strategy to obtain molecule libraries with diverse structural features starting from one common compound in limited steps of synthesis. During the last two decades, DOS has become an unmissable strategy in organic synthesis and is fully integrated in various drug discovery processes. On the other hand, natural products with multiple relevant pharmacological properties have been extensively investigated as scaffolds for ligand-based drug design. In this article, we report the amino dimethoxyacetophenones that can be easily synthesized and scaled up from the commercially available 3,5-dimethoxyaniline as valuable starting blocks for the DOS of natural product analogs. More focus is placed on the synthesis of analogs of flavones, coumarins, azocanes, chalcones, and aurones, which are frequently studied as lead compounds in drug discovery.

An Overview of the Recent Development of Anticancer Agents Targeting the HIF-1 Transcription Factor

Hypoxia, a characteristic feature of solid tumors, is associated with the malignant phenotype and therapy resistance of cancers. Hypoxia-inducible factor 1 (HIF-1), which is responsible for the metazoan adaptive response to hypoxia, has been recognized as a rational target for cancer therapy due to its critical functions in hypoxic regions. In order to efficiently inhibit its activity, extensive efforts have been made to elucidate the molecular mechanism underlying the activation of HIF-1. Here, we provide an overview of relevant research, particularly on a series of HIF-1 activators identified so far and the development of anticancer drugs targeting them.

Molecular modeling approaches to address drug-metabolizing enzymes (DMEs) mediated chemoresistance: a review

Resistance against clinically approved anticancer drugs is the main roadblock in cancer treatment. Drug metabolizing enzymes (DMEs) that are capable of metabolizing a variety of xenobiotic get overexpressed in malignant cells, therefore, catalyzing drug inactivation. As evident from the literature reports, the levels of DMEs increase in cancer cells that ultimately lead to drug inactivation followed by drug resistance. To puzzle out this issue, several strategies inclusive of analog designing, prodrug designing, and inhibitor designing have been forged. On that front, the implementation of computational tools can be considered a fascinating approach to address the problem of chemoresistance. Various research groups have adopted different molecular modeling tools for the investigation of DMEs mediated toxicity problems. However, the utilization of these in-silico tools in maneuvering the DME mediated chemoresistance is least considered and yet to be explored. These tools can be employed in the designing of such chemotherapeutic agents that are devoid of the resistance problem. The current review canvasses various molecular modeling approaches that can be implemented to address this issue. Special focus was laid on the development of specific inhibitors of DMEs. Additionally, the strategies to bypass the DMEs mediated drug metabolism were also contemplated in this report that includes analogs and pro-drugs designing. Different strategies discussed in the review will be beneficial in designing novel chemotherapeutic agents that depreciate the resistance problem.

Biological roles of cytochrome P450 1A1, 1A2, and 1B1 enzymes

Human cytochrome P450 enzymes (CYPs) play a critical role in various biological processes and human diseases. CYP1 family members, including CYP1A1, CYP1A2, and CYP1B1, are induced by aryl hydrocarbon receptors (AhRs). The binding of ligands such as polycyclic aromatic hydrocarbons activates the AhRs, which are involved in the metabolism (including oxidation) of various endogenous or exogenous substrates. The ligands that induce CYP1 expression are reported to be carcinogenic xenobiotics. Hence, CYP1 enzymes are correlated with the pathogenesis of cancers. Various endogenous substrates are involved in the metabolism of steroid hormones, eicosanoids, and other biological molecules that mediate the pathogenesis of several human diseases. Additionally, CYP1s metabolize and activate/inactivate therapeutic drugs, especially, anti-cancer agents. As the metabolism of drugs determines their therapeutic efficacy, CYP1s can determine the susceptibility of patients to some drugs. Thus, understanding the role of CYP1s in diseases and establishing novel and efficient therapeutic strategies based on CYP1s have piqued the interest of the scientific community.

Human Family 1-4 cytochrome P450 enzymes involved in the metabolic activation of xenobiotic and physiological chemicals: an update

This is an overview of the metabolic activation of drugs, natural products, physiological compounds, and general chemicals by the catalytic activity of cytochrome P450 enzymes belonging to Families 1-4. The data were collected from > 5152 references. The total number of data entries of reactions catalyzed by P450s Families 1-4 was 7696 of which 1121 (~ 15%) were defined as bioactivation reactions of different degrees. The data were divided into groups of General Chemicals, Drugs, Natural Products, and Physiological Compounds, presented in tabular form. The metabolism and bioactivation of selected examples of each group are discussed. In most of the cases, the metabolites are directly toxic chemicals reacting with cell macromolecules, but in some cases the metabolites formed are not direct toxicants but participate as substrates in succeeding metabolic reactions (e.g., conjugation reactions), the products of which are final toxicants. We identified a high level of activation for three groups of compounds (General Chemicals, Drugs, and Natural Products) yielding activated metabolites and the generally low participation of Physiological Compounds in bioactivation reactions. In the group of General Chemicals, P450 enzymes 1A1, 1A2, and 1B1 dominate in the formation of activated metabolites. Drugs are mostly activated by the enzyme P450 3A4, and Natural Products by P450s 1A2, 2E1, and 3A4. Physiological Compounds showed no clearly dominant enzyme, but the highest numbers of activations are attributed to P450 1A, 1B1, and 3A enzymes. The results thus show, perhaps not surprisingly, that Physiological Compounds are infrequent substrates in bioactivation reactions catalyzed by P450 enzyme Families 1-4, with the exception of estrogens and arachidonic acid. The results thus provide information on the enzymes that activate specific groups of chemicals to toxic metabolites.

Identification and targeting of selective vulnerability rendered by tamoxifen resistance

BACKGROUND

The estrogen receptor (ER)-positive breast cancer represents over 80% of all breast cancer cases. Even though adjuvant hormone therapy with tamoxifen (TMX) is saving lives of patients with ER-positive breast cancer, the acquired resistance to TMX anti-estrogen therapy is the main hurdle for successful TMX therapy. Here we address the mechanism for TMX resistance and explore the ways to eradicate TMX-resistant breast cancer in both in vitro and ex vivo experiments.

EXPERIMENTAL DESIGN

To identify compounds able to overcome TMX resistance, we used short-term and long-term viability assays in cancer cells in vitro and in patient samples in 3D ex vivo, analysis of gene expression profiles and cell line pharmacology database, shRNA screen, CRISPR-Cas9 genome editing, real-time PCR, immunofluorescent analysis, western blot, measurement of oxidative stress using flow cytometry, and thioredoxin reductase 1 enzymatic activity.

RESULTS

Here, for the first time, we provide an ample evidence that a high level of the detoxifying enzyme SULT1A1 confers resistance to TMX therapy in both in vitro and ex vivo models and correlates with TMX resistance in metastatic samples in relapsed patients. Based on the data from different approaches, we identified three anticancer compounds, RITA (Reactivation of p53 and Induction of Tumor cell Apoptosis), aminoflavone (AF), and oncrasin-1 (ONC-1), whose tumor cell inhibition activity is dependent on SULT1A1. We discovered thioredoxin reductase 1 (TrxR1, encoded by TXNRD1) as a target of bio-activated RITA, AF, and ONC-1. SULT1A1 depletion prevented the inhibition of TrxR1, induction of oxidative stress, DNA damage signaling, and apoptosis triggered by the compounds. Notably, RITA efficiently suppressed TMX-unresponsive patient-derived breast cancer cells ex vivo.

CONCLUSION

We have identified a mechanism of resistance to TMX via hyperactivated SULT1A1, which renders selective vulnerability to anticancer compounds RITA, AF, and ONC-1, and provide a rationale for a new combination therapy to overcome TMX resistance in breast cancer patients. Our novel findings may provide a strategy to circumvent TMX resistance and suggest that this approach could be developed further for the benefit of relapsed breast cancer patients.

Evaluation of the time-dependent antiproliferative activity and liver microsome stability of 3 phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates as promising CYP1A1-dependent antimicrotubule prodrugs

OBJECTIVES

In this study, the antiproliferative activity of 3 phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates (PAIB-SOs) was assessed in a time-dependent manner together with their hepatic stability and metabolism using human, mouse and rat liver microsomes.

METHODS

CEU-818, -820 and -913 were selected as promising hit compounds. Their antiproliferative activity on human breast carcinoma MCF-7 cells was evaluated using escalating concentrations of drugs at 24, 36 and 48 h and the sulforhodamine B assay. Their hepatic stability was evaluated by HPLC-UV of extracts obtained from human, mouse and rat liver microsomes.

KEY FINDINGS

The antiproliferative activity of PAIB-SOs is concentration and time-dependent and requires between 24 and 36 h of contact with MCF-7 cells to detect a significant antiproliferative activity. PAIB-SOs stability in microsomes usually decreases following this order: human ≈ (rat > mouse). The CEU-913 exhibits the longest half-life in rat and human liver microsomes while the CEU-820 exhibits the longest half-life in mouse liver microsomes.

CONCLUSIONS

Our in vitro results suggest that PAIB-SOs should have a minimum contact time of 24 h with the tumour to trigger significant antitumoural activity. The activity of mouse liver microsomes towards PAIB-SOs is higher than rat microsomes and tends to be higher than human liver microsomes.

The aryl hydrocarbon receptor (AhR) as a breast cancer drug target

Breast cancer is the most common cancer in women, with more than 1.7 million diagnoses worldwide per annum. Metastatic breast cancer remains incurable, and the presence of triple-negative phenotypes makes targeted treatment impossible. The aryl hydrocarbon receptor (AhR), most commonly associated with the metabolism of xenobiotic ligands, has emerged as a promising biological target for the treatment of this deadly disease. Ligands for the AhR can be classed as exogenous or endogenous and may have agonistic or antagonistic activity. It has been well reported that agonistic ligands may have potent and selective growth inhibition activity in a number of oncogenic cell lines, and one (aminoflavone) has progressed to phase I clinical trials for breast cancer sufferers. In this study, we examine the current state of the literature in this area and elucidate the promising advances that are being made in hijacking the cytosolic-to-nuclear pathway of the AhR for the possible future treatment of breast cancer.

Radiometallic Complexes of DO3A-Benzothiazole Aniline for Nuclear Medicine Theranostics

To develop a radioactive metal complex platform for tumor theranostics, we introduced three radiopharmaceutical derivatives of 1,4,7,10-tetraazacyclododecane-1,4,7-trisacetic acid-benzothiazole aniline (DO3A-BTA, L1) labeled with medical radioisotopes for diagnosis (⁶⁸Ga/⁶⁴Cu) and therapy (¹⁷⁷Lu). The tumor-targeting ability of these complexes was demonstrated in a cellular uptake experiment, in which ¹⁷⁷Lu-L1 exhibited markedly higher uptake in HeLa cells than the ¹⁷⁷Lu-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid complex. According to in vivo positron emission tomography imaging, high accumulation of ⁶⁸Ga-L1 and ⁶⁴Cu-L1 was clearly visualized in the tumor site, while ¹⁷⁷Lu-L1 showed therapeutic efficacy in therapy experiments. Consequently, this molecular platform represents a useful approach in nuclear medicine toward tumor-theranostic radiopharmaceuticals when ⁶⁸Ga-L1 or ⁶⁴Cu-L1 is used for diagnosis, ¹⁷⁷Lu-L1 is used for therapy, or two of the compounds are used in conjunction with each other.

Modulation of CYP1A1 metabolism: From adverse health effects to chemoprevention and therapeutic options

The human cytochrome P450 (CYP) 1A1 gene encodes a monooxygenase that metabolizes multiple exogenous and endogenous substrates. CYP1A1 has become infamous for its oxidative metabolism of benzo[a]pyrene and related polycyclic aromatic hydrocarbons, converting these chemicals into very potent human carcinogens. CYP1A1 expression is mainly controlled by the aryl hydrocarbon receptor (AHR), a transcription factor whose activation is induced by binding of persistent organic pollutants, including polycyclic aromatic hydrocarbons and dioxins. Accordingly, induction of CYP1A1 expression and activity serves as a biomarker of AHR activation and associated xenobiotic metabolism as well as toxicity in diverse animal species and humans. Determination of CYP1A1 activity is integrated into modern toxicological concepts and testing guidelines, emphasizing the tremendous importance of this enzyme for risk assessment and regulation of chemicals. Further, CYP1A1 serves as a molecular target for chemoprevention of chemical carcinogenesis, although present literature is controversial on whether its inhibition or induction exerts beneficial effects. Regarding therapeutic applications, first anti-cancer prodrugs are available, which require a metabolic activation by CYP1A1, and thus enable a specific elimination of CYP1A1-positive tumors. However, the application range of these drugs may be limited due to the frequently observed downregulation of CYP1A1 in various human cancers, probably leading to a reduced metabolism of endogenous AHR ligands and a sustained activation of AHR and associated tumor-promoting responses. We here summarize the current knowledge on CYP1A1 as a key player in the metabolism of exogenous and endogenous substrates and as a promising target molecule for prevention and treatment of human malignancies.

Activation of Phenyl 4-(2-Oxo-3-alkylimidazolidin-1-yl)benzenesulfonates Prodrugs by CYP1A1 as New Antimitotics Targeting Breast Cancer Cells

Prodrug-mediated utilization of the cytochrome P450 (CYP) 1A1 to obtain the selective release of potent anticancer products within cancer tissues is a promising approach in chemotherapy. We herein report the rationale, preparation, biological evaluation, and mechanism of action of phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates (PAIB-SOs) that are antimicrotubule prodrugs activated by CYP1A1. Although PAIB-SOs are inert in most cells tested, they are highly cytocidal toward several human breast cancer cells, including hormone-independent and chemoresistant types. PAIB-SOs are N-dealkylated into cytotoxic phenyl 4-(2-oxo-3-imidazolidin-1-yl)benzenesulfonates (PIB-SOs) in CYP1A1-positive cancer cells, both in vitro and in vivo. In conclusion, PAIB-SOs are novel chemotherapeutic prodrugs with no equivalent among current antineoplastics and whose selective action toward breast cancer is tailored to the characteristic pattern of CYP1A1 expression observed in a large percentage of human breast tumors.

Comparative Metabolism of Batracylin (NSC 320846) and N-acetylbatracylin (NSC 611001) Using Human, Dog, and Rat Preparations In Vitro

BACKGROUND

Batracylin is a heterocyclic arylamine topoisomerase inhibitor with preclinical anticancer activity. Marked species differences in sensitivity to the toxicity of batracylin were observed and attributed to differential formation of N-acetylbatracylin by N-acetyltransferase. A Phase I trial of batracylin in cancer patients with slow acetylator genotypes identified a dose-limiting toxicity of hemorrhagic cystitis. To further explore the metabolism of batracylin and N-acetylbatracylin across species, detailed studies using human, rat, and dog liver microsomal and hepatocyte preparations were conducted.

METHODS

Batracylin or N-acetylbatracylin was incubated with microsomes and hepatocytes from human, rat, and dog liver and with CYP-expressing human and rat microsomes. Substrates and metabolites were analyzed by HPLC with diode array, fluorescence, radiochemical, or mass spectrometric detection. Covalent binding of radiolabeled batracylin and N-acetylbatracylin to protein and DNA was measured in 3-methylcholanthrene-induced rat, human, and dog liver microsomes, and with recombinant human cytochromes P450.

RESULTS

In microsomal preparations, loss of batracylin was accompanied by formation of one hydroxylated metabolite in human liver microsomes and five hydroxylated metabolites in rat liver microsomes. Six mono- or di-hydroxy-N-acetylbatracylin metabolites were found in incubations of this compound with 3MC rat liver microsomes. Hydroxylation sites were identified for some of the metabolites using deuterated substrates. Incubation with recombinant cytochromes P450 identified rCYP1A1, rCYP1A2, hCYP1A1 and hCYP1B1 as the major CYP isoforms that metabolize batracylin and N-acetylbatracylin. Glucuronide conjugates of batracylin were also identified in hepatocyte incubations. NADPH-dependent covalent binding to protein and DNA was detected in all batracylin and most N-acetylbatracylin preparations evaluated.

CONCLUSIONS

Microsomal metabolism of batracylin and N-acetylbatracylin results in multiple hydroxylated products (including possible hydroxylamines) and glutathione conjugates. Incubation of batracylin with hepatocytes resulted in production primarily of glucuronides and other conjugates. There was no clear distinction in the metabolism of batracylin and N-acetylbatracylin across species that would explain the differential toxicity.

AhR ligand Aminoflavone inhibits α6-integrin expression and breast cancer sphere-initiating capacity

Traditional chemotherapies debulk tumors but fail to produce long-term clinical remissions due to their inability to eradicate tumor-initiating cells (TICs). This necessitates therapy with activity against the TIC niche. Αlpha6-integrin (α6-integrin) promotes TIC growth. In contrast, aryl hydrocarbon receptor (AhR) signaling activation impedes the formation of mammospheres (clusters of cells enriched for TICs). We investigated the ability of AhR agonist Aminoflavone (AF) and AF pro-drug (AFP464) to disrupt mammospheres derived from breast cancer cells and a M05 mammary mouse model of breast cancer respectively. We further examined the capacity of AF and AFP464 to exhibit anticancer activity and modulate the expression of 'stemness' genes including α6-integrin using immunofluorescence, flow cytometry and qRT-PCR analysis. AF disrupted mammospheres and prevented secondary mammosphere formation. In contrast, AF did not disrupt mammospheres derived from AhR ligand-unresponsive MCF-7 cells. AFP464 treatment suppressed M05 tumor growth and disrupted corresponding mammospheres. AF and AFP464 reduced the expression and percentage of cells that stained for 'stemness' markers including α6-integrin in vitro and in vivo respectively. These data suggest AFP464 thwarts bulk breast tumor and TIC growth via AhR agonist-mediated α6-integrin inhibition.

Identification of leads for antiproliferative activity on MDA-MB-435 human breast cancer cells through pharmacophore and CYP1A1-mediated metabolism

CYP1A1 is a potential target for anticancer drug development due to its overexpression in certain cancer cells and role in cancer progression. To identify new leads for CYP1A1 mediated anticancer action, we attempted ligand based pharmacophore mapping, virtual screening of databases, molecular docking, MetaSite based filtering, and molecular dynamics simulations. Initial computational and in vitro screening identified 11 compounds from which we identified two lead compounds, ZINC33468944 and ZINC32101539, showed potential antitumor activity on MDA-MB-435 cell lines (GI50 < 0.1 μM) and CYP1A1 inhibition of 0.13 and 0.3 μM, respectively. Furthermore, the lead compounds were evaluated for CYP1A1 mediated metabolism, showing N-hydroxylated metabolites, which have potential of DNA adduct formation and cause cancerous cell death. Analysis of molecular dynamics simulations provided important guidelines for the further modification of the lead compounds. Hence, we claim the lead molecules for further development in anticancer drug discovery.

Characterization of differences in substrate specificity among CYP1A1, CYP1A2 and CYP1B1: an integrated approach employing molecular docking and molecular dynamics simulations

Recent trends in new drug discovery of anticancer drugs have made oncologists more aware of the fact that the new drug discovery must target the developing mechanism of tumorigenesis to improve the therapeutic efficacy of antineoplastic drugs. The drugs designed are expected to have high affinity towards the novel targets selectively. Current research highlights overexpression of CYP450s, particularly cytochrome P450 1A1 (CYP1A1), in tumour cells, representing a novel target for anticancer therapy. However, the CYP1 family is identified as posing significant problems in selectivity of anticancer molecules towards CYP1A1. Three members have been identified in the human CYP1 family: CYP1A1, CYP1A2 and CYP1B1. Although sequences of the three isoform have high sequence identity, they have distinct substrate specificities. The understanding of macromolecular features that govern substrate specificity is required to understand the interplay between the protein function and dynamics, design novel antitumour compounds that could be specifically metabolized by only CYP1A1 to mediate their antitumour activity and elucidate the reasons for differences in substrate specificity profile among the three proteins. In the present study, we employed a combination of computational methodologies: molecular docking and molecular dynamics simulations. We utilized eight substrates for elucidating the difference in substrate specificity of the three isoforms. Lastly, we conclude that the substrate specificity of a particular substrate depends upon the type of the active site residues, the dynamic motions in the protein structure upon ligand binding and the physico-chemical characteristics of a particular ligand. Copyright © 2016 John Wiley & Sons, Ltd.

Comparative proteomics among cytochrome p450 family 1 for differential substrate specificity

Apart from playing key roles in drug metabolism and adverse drug-drug interactions, CYPs are potential drug targets to treat a variety of diseases. The intervention of over expression of P450 1A1 (CYP1A1) in tumor cells is identified as a novel strategy for anticancer therapy. We investigated three isoforms of CYP1 family (CYP1A1, CYP1A2, and CYP1B1) for their substrate specificity. The understanding of macromolecular features that govern substrate specificity is required to understand the interplay between the protein function and dynamics. This can help in design of new antitumor molecule specifically metabolized by CYP1A1 to mediate their antitumor activity. In the present study, we carried out the comparative protein structure analysis of the three isoforms. Sequence alignment, root mean square deviation (RMSD) analysis, B-factor analysis was performed to give a better understanding of the macromolecular features involved in substrate specificity and to understand the interplay between protein dynamics and functions which will have important implications on rational design of anticancer drugs. We identified the differences in amino acid residues among the three isoforms of CYP1 family, which may account for differential substrate specificity. Six putative substrate recognition sequences are characterized along with the regions they form in the protein structure. Further the RMSD and B-factor analysis provides the information about the identified residues having the maximum RMSD and B-factor deviations.

Estrogen receptor α and aryl hydrocarbon receptor independent growth inhibitory effects of aminoflavone in breast cancer cells

Background

Numerous studies have implicated the aryl hydrocarbon receptor (AhR) as a potential therapeutic target for several human diseases, including estrogen receptor alpha (ERα) positive breast cancer. Aminoflavone (AF), an activator of AhR signaling, is currently undergoing clinical evaluation for the treatment of solid tumors. Of particular interest is the potential treatment of triple negative breast cancers (TNBC), which are typically more aggressive and characterized by poorer outcomes. Here, we examined AF’s effects on two TNBC cell lines and the role of AhR signaling in AF sensitivity in these model cell lines.

Methods

AF sensitivity in MDA-MB-468 and Cal51 was examined using cell counting assays to determine growth inhibition (GI₅₀) values. Luciferase assays and qPCR of AhR target genes cytochrome P450 (CYP) 1A1 and 1B1 were used to confirm AF-mediated AhR signaling. The requirement of endogenous levels of AhR and AhR signaling for AF sensitivity was examined in MDA-MB-468 and Cal51 cells stably harboring inducible shRNA for AhR. The mechanism of AF-mediated growth inhibition was explored using flow cytometry for markers of DNA damage and apoptosis, cell cycle analysis, and β-galactosidase staining for senescence. Luciferase data was analyzed using Student’s T test. Three-parameter nonlinear regression was performed for cell counting assays.

Results

Here, we report that ERα-negative TNBC cell lines MDA-MB-468 and Cal51 are sensitive to AF. Further, we presented evidence suggesting that neither endogenous AhR expression levels nor downstream induction of AhR target genes CYP1A1 and CYP1B1 is required for AF-mediated growth inhibition in these cells. Between these two ERα negative cell lines, we showed that the mechanism of AF action differs slightly. Low dose AF mediated DNA damage, S-phase arrest and apoptosis in MDA-MB-468 cells, while it resulted in DNA damage, S-phase arrest and cellular senescence in Cal51 cells.

Conclusions

Overall, this work provides evidence against the simplified view of AF sensitivity, and suggests that AF could mediate growth inhibitory effects in ERα-positive and negative breast cancer cells, as well as cells with impaired AhR expression and signaling. While AF could have therapeutic effects on broader subtypes of breast cancer, the mechanism of cytotoxicity is complex, and likely, cell line- and tumor-specific.

Reactivation of estrogen receptor α by vorinostat sensitizes mesenchymal-like triple-negative breast cancer to aminoflavone, a ligand of the aryl hydrocarbon receptor

OBJECTIVE

Aminoflavone (AF) acts as a ligand of the aryl hydrocarbon receptor (AhR). Expression of estrogen receptor α (ERα) and AhR-mediated transcriptional induction of CYP1A1 can sensitize breast cancer cells to AF. The objective of this study was to investigate the combined antitumor effect of AF and the histone deacetylase inhibitor vorinostat for treating mesenchymal-like triple-negative breast cancer (TNBC) as well as the underlying mechanisms of such treatment.

METHODS

In vitro antiproliferative activity of AFP464 (AF prodrug) in breast cancer cell lines was evaluated by MTS assay. In vitro, the combined effect of AFP464 and vorinostat on cell proliferation was assessed by the Chou-Talalay method. In vivo, antitumor activity of AFP464, given alone and in combination with vorinostat, was studied using TNBC xenograft models. Knockdown of ERα was performed using specific, small-interfering RNA. Western blot, quantitative RT-PCR, immunofluorescence, and immunohistochemical staining were performed to study the mechanisms underlying the combined antitumor effect.

RESULTS

Luminal and basal A subtype breast cancer cell lines were sensitive to AFP464, whereas basal B subtype or mesenchymal-like TNBC cells were resistant. Vorinostat sensitized mesenchymal-like TNBC MDA-MB-231 and Hs578T cells to AFP464. It also potentiated the antitumor activity of AFP464 in a xenograft model using MDA-MB-231 cells. In vitro and in vivo mechanistic studies suggested that vorinostat reactivated ERα expression and restored AhR-mediated transcriptional induction of CYP1A1.

CONCLUSION

The response of breast cancer cells to AF or AFP464 was associated with their gene expression profile. Vorinostat sensitized mesenchymal-like TNBC to AF, at least in part, by reactivating ERα expression and restoring the responsiveness of AhR to AF.

Cytochrome P450 1A1-mediated anticancer drug discovery: in silico findings

INTRODUCTION

Target-specific drugs may offer fewer side/adverse effects in comparison with other anticancer agents and thus save normal healthy cells to a greater extent. The selective overexpression of cytochrome P450 1A1 (CYP1A1) in tumor cells induces the metabolism of benzothiazole and aminoflavone compounds to their reactive species, which are responsible for DNA adduct formation and cell death. This review encompasses the novelty of CYP1A1 as an anticancer drug target and explores the possible in silico strategies that would be applicable in the discovery and development of future antitumor compounds.

AREAS COVERED

This review highlights the various ligand-based and target-based in silico methodologies that were efficiently used in exploration of CYP1A1 as a novel antitumor target. These methodologies include electronic structure analysis, CoMFA studies, homology modeling, molecular docking, molecular dynamics analysis, pharmacophore mapping and quantitative structure activity relationship (QSAR) studies. It also focuses on the various approaches used in the development of the lysyl amide prodrug of 5F-203 (NSC710305) and dimethanesulfonate salt of 5-aminoflavone (NSC710464) as clinical candidates from their less potent analogues.

EXPERT OPINION

Selective overexpression of CYP1A1 in cancer cells offers tumor-specific drug design to ameliorate the current adverse effects associated with existing antitumor agents. Medicinal chemistry and in vitro driven approaches, in combination with knowledge-based drug design and by using the currently available tools of in silico methodologies, would certainly make it possible to design and develop novel anticancer compounds targeting CYP1A1.

New emerging drugs targeting the genomic integrity and replication machinery in ovarian cancer

INTRODUCTION

Ovarian cancer is a difficult to treat cancer entity with a high relapse rate. After initial surgery and chemotherapy, only a few options for therapeutic treatment remain in case of cancer recurrence. New treatment options with improved efficacies to circumvent acquired or pre-existing drug resistance are needed.

MATERIALS

This survey focuses on new prospective drugs for ovarian cancer treatment that either cause direct damage to the nuclear DNA or inhibit chromosome segregation by acting as mitotic spindle inhibitors.

RESULTS

Among a plethora of currently tested and proposed new drugs for ovarian cancer treatment, only a few appear to meet the criteria of sufficient and reliable efficacy with tolerable toxicity. These include the naturally occurring DNA-alkylating alkaloid trabectedin, the nitrogen mustard prodrug canfosfamide, and the synthetic kinase inhibitor ON-01910. The latter inhibits mitotic spindle formation without a direct tubulin interaction, avoiding adverse neurotoxic reactions common to the taxanes. Further, epothilones and oxaliplatin, already approved drugs for other cancer entities, show promising activity against ovarian cancer; they are even of interest as a first-line treatment option.

DISCUSSION

Although the current focus and interest of modern cancer drug design tends to be more specific and targeted therapies, including therapeutic antibodies and specific small molecules to inhibit growth-, apoptosis-, and angiogenesis-regulating signalling cascades, the main target for ovarian cancer treatment appears to remain its basic, though uncontrolled working proliferation machinery. This includes the current gold standard for ovarian cancer chemotherapy, carboplatin, and taxanes, as well as the few remaining alternatives, such as topotecan, doxorubicin, and gemcitabine, which all rely on their ability to bind to or to modify the DNA or the chromosome-separating spindle apparatus. Thus, the genomic integrity and replication machinery of ovarian cancer cells prove to represent an established, and obviously still effective target to be tackled for ovarian cancer treatment.

Aminoflavone, a ligand of the aryl hydrocarbon receptor, inhibits HIF-1alpha expression in an AhR-independent fashion

Aminoflavone (AF), the active component of a novel anticancer agent (AFP464) in phase I clinical trials, is a ligand of the aryl hydrocarbon receptor (AhR). AhR dimerizes with HIF-1beta/AhR, which is shared with HIF-1alpha, a transcription factor critical for the response of cells to oxygen deprivation. To address whether pharmacologic activation of the AhR pathway might be a potential mechanism for inhibition of HIF-1, we tested the effects of AF on HIF-1 expression. AF inhibited HIF-1alpha transcriptional activity and protein accumulation in MCF-7 cells. However, inhibition of HIF-1alpha by AF was independent from a functional AhR pathway. Indeed, AF inhibited HIF-1alpha expression in Ah(R100) cells, in which the AhR pathway is functionally impaired, yet did not induce cytotoxicity, providing evidence that these effects are mediated by distinct signaling pathways. Moreover, AF was inactive in MDA-MB-231 cells, yet inhibited HIF-1alpha in MDA-MB-231 cells transfected with the SULT1A1 gene. AF inhibited HIF-1alpha mRNA expression by approximately 50%. Notably, actinomycin-D completely abrogated the ability of AF to downregulate HIF-1alpha mRNA, indicating that active transcription was required for the inhibition of HIF-1alpha expression. Finally, AF inhibited HIF-1alpha protein accumulation and the expression of HIF-1 target genes in MCF-7 xenografts. These results show that AF inhibits HIF-1alpha in an AhR-independent fashion, and they unveil additional activities of AF that may be relevant for its further clinical development.

Xenobiotic metabolism: a view through the metabolometer

The combination of advanced ultraperformance liquid chromatography coupled with mass spectrometry, chemometrics, and genetically modified mice provide an attractive raft of technologies with which to examine the metabolism of xenobiotics. Here, a reexamination of the metabolism of the food mutagen PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine), the suspect carcinogen areca alkaloids (arecoline, arecaidine, and arecoline 1-oxide), the hormone supplement melatonin, and the metabolism of the experimental cancer therapeutic agent aminoflavone is presented. In all cases, the metabolic maps of the xenobiotics were considerably enlarged, providing new insights into their toxicology. The inclusion of transgenic mice permitted unequivocal attribution of individual and often novel metabolic pathways to particular enzymes. Last, a future perspective for xenobiotic metabolomics is discussed and its impact on the metabolome is described. The studies reviewed here are not specific to the mouse and can be adapted to study xenobiotic metabolism in any animal species, including humans. The view through the metabolometer is unique and visualizes a metabolic space that contains both established and unknown metabolites of a xenobiotic, thereby enhancing knowledge of their modes of toxic action.

Association of human cytochrome P450 1A1 (CYP1A1) and sulfotransferase 1A1 (SULT1A1) polymorphisms with differential metabolism and cytotoxicity of aminoflavone

Aminoflavone (AF), a clinically investigational novel anticancer agent, requires sequential metabolic activation by CYP1A1 and SULT1A1 to exert its antitumor activities. The purpose of this study was to determine the functional significance of common polymorphisms of human CYP1A1 and SULT1A1 on the metabolism and cytotoxicity of AF. To this end, Chinese Hamster V79 cells were genetically engineered to stably express human CYP1A1*1 (wild-type), CYP1A1*2C (I462V), or CYP1A1*4 (T461N) and coexpress human CYP1A1*1 with human SULT1A1*1 (wild-type), SULT1A1*2 (R213H), or SULT1A1*3 (M223V). The metabolism and cytotoxicity of AF were evaluated in these cellular models. All common variants of CYP1A1 and SULT1A1 were actively involved in the metabolic activation of AF, but with a varying degree of activity. Whereas CYP1A1 I462V variant exhibited a superior activity (mainly caused by a significantly higher V(max)) for hydroxylations of AF, expression of different CYP1A1 variants did not confer cell differential sensitivity to AF. The cells coexpressing CYP1A1*1 with SULT1A1*1, SULT1A1*2, or SULT1A1*3 displayed SULT1A1 allele-specific sensitivity to AF: SULT1A1*3 exhibited the highest sensitivity (IC(50), 0.01 μmol/L), followed by SULT1A1*1 (IC(50), 0.5 μmol/L), and SULT1A1*2 showed the lowest sensitivity (IC(50), 4.4 μmol/L). These data suggest that the presence of low-activity SULT1A1*2 may predict poor response to AF, whereas the presence of high-activity CYP1A1/SULT1A1 alleles, especially combination of CYP1A1*2C and SULT1A1*3 or SULT1A1*1, may be beneficial to patients receiving AF. The present study provides a foundation for future clinical investigations of potential genetic biomarkers that may enable selection of patients for the greatest potential benefit from AF treatment.

Synergistic interactions between aminoflavone, paclitaxel and camptothecin in human breast cancer cells

PURPOSE

Aminoflavone is a unique DNA damaging agent currently undergoing phase I evaluation in a prodrug form (AFP464). In anticipation of combination regimens, interactions between aminoflavone and several anticancer drugs were investigated in MCF-7 breast cancer cells to determine whether synergistic cancer cell killing effects were observed.

METHODS

Colony formation assays were performed to assess the effect of combining aminoflavone with a variety of anticancer drugs. Changes in initial uptake, retention or efflux of aminoflavone and the second agent were compared to the behavior of drugs alone. Key features required for aminoflavone activity in cell culture models were also explored, focusing on the obligatory induction of CYP1A1/1A2 and binding of reactive aminoflavone metabolites to tumor cell total macromolecules and DNA.

RESULTS

Aminoflavone was synergistic when co-incubated with paclitaxel, camptothecin or SN38. Uptake of neither aminoflavone nor any of the other three compounds was altered in combination incubations. Paclitaxel did not inhibit DNA binding of aminoflavone metabolites, while camptothecin did. Aminoflavone-induced CYP1A1 induction was observed in the presence of camptothecin or paclitaxel.

CONCLUSIONS

Aminoflavone is a promising therapeutic agent for breast cancer due to its unique mechanism of action compared to commonly used drugs. Combined treatments utilizing aminoflavone in conjunction with paclitaxel or camptothecin may provide an even greater cytotoxic effect than achieved with aminoflavone alone.

Validation and implementation of a liquid chromatography/tandem mass spectrometry assay to quantitate aminoflavone (NSC 686288) in human plasma

A reverse-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method was developed and validated for determination of aminoflavone (AF) in human plasma. Sample preparation involved a liquid-liquid extraction by the addition of 0.25 mL of plasma with 1.0 mL ethyl acetate containing 50 ng/mL of the internal standard zileuton. The analytes were separated on a Waters X-Terra MS C(18) column using a mobile phase consisting of methanol/water containing 0.45% formic acid (70:30, v/v) and isocratic flow at 0.2 mL/min for 6 min. The analytes were monitored by tandem mass spectrometry with electrospray positive ionization. Linear calibration curves were generated over the AF concentration range of 5-2000 ng/mL in human plasma. The lower limit of quantitation (LLOQ) was 5 ng/mL for AF in human plasma. The accuracy and within- and between-day precisions were within the generally accepted criteria for bioanalytical method (<15%). This method was successfully applied to characterize AF plasma concentration-time profile in the cancer patients in a phase I trial.

Comparative analysis of family 1 cytochrome p-450 mRNA expression in human intestinal adenocarcinoma and intact portion of the intestine

The expression of mRNA of proteins involved in the transformations of cytostatics (cytochrome P-450 1A1 and 1B1 isoforms) and genes encoding proteins participating in their regulation (Ah receptor, AHRR and ARNT) in intestinal tumors and intact portions of the intestine were studied. The expression of cytochrome P-450 1A1 increased in poorly differentiated tumors in comparison with its expression in intact portions of the intestine (tumor/intact tissue=1.65). The expression of cytochrome P-450 1B1 was higher in well-differentiated tumors (tumor/intact tissue=1.62). The possibility of practical use of high expression of cytochrome P-450 isoforms in tumors in comparison with intact intestinal tissue is discussed.

Aminoflavone induces oxidative DNA damage and reactive oxidative species-mediated apoptosis in breast cancer cells

Aminoflavone (5-amino-2-(4-amino-3-fluorophenyl)-6,8-difluoro-7-methylchromen-4-one; AF; NSC 686288), a novel anticancer candidate agent, is undergoing clinical evaluation. AF induces DNA-protein cross-links (DPCs), Gamma-H2AX phosphorylation, aryl hydrocarbon receptor (AhR) signaling, apoptosis and its own metabolism via cytochrome P4501A1 and 1A2 (CYP1A1/1A2) activation in sensitive estrogen receptor positive (ER+) MCF7 breast cancer cells. Estrogen receptor negative (ER-) breast cancer is typically more aggressive with a poorer prognosis. In this investigation, we evaluated the ability of AF to induce reactive oxygen species (ROS) formation, oxidative DNA damage and apoptosis in ER- MDA-MB-468 breast cancer cells. The antioxidant, N-acetyl-L-cysteine (NAC), attenuated the cytotoxic effects of AF in MDA-MB-468 cells; an effect is also observed in ER+ T47D breast cancer cells. Nonmalignant MCF10A breast epithelial cells were resistant to the cytotoxic effects of AF. AF increased intracellular ROS, an effect blocked by NAC and the CYP1A1/1A2 inhibitor, alpha-Naphthoflavone (alpha-NF). AF induced oxidative DNA damage as evidenced by increased 8-oxo-7,8-dihydroguanine (8-oxodG) levels and DPC formation in these cells. AF caused S-phase arrest corresponding to an increase in p21((waf1/cip1)) protein expression. AF induced caspase 3, 8 and 9 activation, caspase-dependent apoptotic body formation and poly [ADP-ribose] polymerase (PARP) cleavage. Pretreatment with the pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-DL-Asp(OMe)-fluoromethylketone inhibited apoptosis and partially inhibited ROS formation and oxidative DNA damage. Pretreatment with NAC attenuated AF-induced apoptotic body formation and caspase 3 activation. These studies suggest AF inhibits the growth of breast cancer cells in part, by inducing ROS production, oxidative DNA damage and apoptosis and has the potential to treat hormone-independent breast cancer.

Activation of aminoflavone (NSC 686288) by a sulfotransferase is required for the antiproliferative effect of the drug and for induction of histone gamma-H2AX

Aminoflavone (AF) is entering clinical trials. We recently reported that AF induces DNA-protein cross-links (DPC) and gamma-H2AX in MCF-7 human breast cancer cells. To elucidate the mechanism of action of AF and provide biomarkers indicative of AF activity, we correlated AF activity profile (GI(50)) with gene expression patterns in the NCI-60 cell lines. Sulfotransferases (SULT) showed the highest positive correlation coefficients among approximately 14,000 probe sets analyzed (r = 0.537, P < 0.001). Stable transfection of SULT1A1 into AF-resistant MDA-MB-231 cells sensitized these cells to AF. AF produced DPCs, gamma-H2AX foci, and S-phase arrest in the SULT1A1-transfected but not in the parent MDA-MB-231 cells. Conversely, cells in which SULT1A1 was knocked down by small interfering RNA failed to induce gamma-H2AX. Inhibition of SULTs and cytochrome P450 (CYP) enzymes by natural flavonoids blocked the antiproliferative activity of AF and the formation of AF-DNA adducts. AF also induces SULT1A1 and CYP expression in MCF-7 cells, suggesting the existence of an aryl hydrocarbon receptor-mediated positive feedback for AF activation by CYP and SULT1A1. Metabolism studies showed that AF can be oxidized by CYP at two amino groups to form N-hydroxyl metabolites that are substrates for bioactivation by SULTs. We propose that both N-sulfoxy-groups can be further converted to nitrenium ions that form adducts with DNA and proteins. The results reported here show the importance of SULT1A1 and CYP for AF activation and anticancer activity. They also suggest using SULT1A1 and gamma-H2AX as biomarkers for prediction of AF activity during patient selection and monitoring of clinical trials.

Targeting cytochrome P450 enzymes: a new approach in anti-cancer drug development

Cytochrome P450s (CYPs) represent a large class of heme-containing enzymes that catalyze the metabolism of multitudes of substrates both endogenous and exogenous. Until recently, however, CYPs have been largely overlooked in cancer drug development, acknowledged only for their role in phase I metabolism of chemotherapeutics. The first successful strategy targeting CYP enzymes in cancer therapy was the development of potent inhibitors of CYP19 (aromatase) for the treatment of breast cancer. Aromatase inhibitors ushered in a new era in hormone ablation therapy for estrogen dependent cancers, and have paved the way for similar strategies (i.e., inhibition of CYP17) that combat androgen dependent prostate cancer. Identification of CYPs involved in the inactivation of anti-cancer metabolites of vitamin D(3) and vitamin A has triggered development of agents that target these enzymes as well. The discovery of the over-expression of exogenous metabolizing CYPs, such as CYP1B1, in cancer cells has roused interest in the development of inhibitors for chemoprevention and of prodrugs designed to be activated by CYPs only in cancer cells. Finally, the expression of CYPs within tumors has been utilized in the development of bioreductive molecules that are activated by CYPs only under hypoxic conditions. This review offers the first comprehensive analysis of strategies in drug development that either inhibit or exploit CYP enzymes for the treatment of cancer.

Urinary metabolite profiling reveals CYP1A2-mediated metabolism of NSC686288 (aminoflavone)

NSC686288 [aminoflavone (AF)], a candidate chemotherapeutic agent, possesses a unique antiproliferative profile against tumor cells. Metabolic bioactivation of AF by drug-metabolizing enzymes, especially CYP1A monooxygenases, has been implicated as an underlying mechanism for its selective cytotoxicity in several cell culture-based studies. However, in vivo metabolism of AF has not been investigated in detail. In this study, the structural identities of 13 AF metabolites (12 of which are novel) in mouse urine or from microsomal incubations, including three monohydroxy-AFs, two dihydroxy-AFs and their sulfate and glucuronide conjugates, as well as one N-glucuronide, were determined by accurate mass measurements and liquid chromatography-tandem mass spectrometry fragmentation patterns, and a comprehensive map of the AF metabolic pathways was constructed. Significant differences between wild-type and Cyp1a2-null mice, within the relative composition of urinary metabolites of AF, demonstrated that CYP1A2-mediated regioselective oxidation was a major contributor to the metabolism of AF. Comparisons between wild-type and CYP1A2-humanized mice further revealed interspecies differences in CYP1A2-mediated catalytic activity. Incubation of AF with liver microsomes from all three mouse lines and with pooled human liver microsomes confirmed the observations from urinary metabolite profiling. Results from enzyme kinetic analysis further indicated that in addition to CYP1A P450s, CYP2C P450s may also play some role in the metabolism of AF.

Antitumor polycyclic acridines. 17. Synthesis and pharmaceutical profiles of pentacyclic acridinium salts designed to destabilize telomeric integrity

Palladium(0)-mediated Suzuki-Miyaura and Heck transformations have been exploited to provide examples of 8-methylquino[4,3,2-kl]acridines and 8,13-dimethylquino[4,3,2-kl]acridinium iodides bearing bulky saturated (3-acetoxy)propyl or (E)-3-(morpholin-4-yl)-3-oxopropenyl substituents variously in the 3-, 6-, or 10-positions of the pentacyclic nucleus. The pharmacological/pharmaceutical properties of four compounds (4, RHPS4), (5, IH383), (6, RHPS16), and (17, RHPS19) were measured to assess their clinical potential as DNA G-quadruplex-stabilizing/telomerase inhibitory agents. The following properties were measured: stability in tissue culture media in the presence of A549 lung and MCF-7 breast tumor cells, metabolic stability when incubated with rat liver microsomes, and rate of uptake and subcellular location in A549 and MCF-7 cells. Compound 17 was unstable in tissue culture media, failed to achieve nuclear access, and was excluded from further consideration. Of the other agents, 4 exhibited the most favorable pharmaceutical profile: the agent has appropriate stability in the presence of tumor cells and rat liver microsomes and achieves rapid ingress into cell nuclei where the putative molecular target is located.

Differential gene expression as a potential classifier of 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole-sensitive and -insensitive cell lines

2-(4-Amino-3-methylphenyl)-5-fluorobenzothiazole (5F-203) is a candidate antitumor agent empirically discovered with the aid of the National Cancer Institute (NCI) Anticancer Drug Screen. In an effort to determine whether basal expression of genes could be used to classify cell sensitivity to this agent, serial analysis of gene expression (SAGE) libraries were generated for three sensitive and two insensitive human tumor cell lines. When the SAGE tags expressed within these cell line libraries were compared and evaluated for differences, several genes seemed more highly expressed in 5F-203-sensitive cell lines than in the insensitive cell lines. Constitutive expressions of 15 genes identified by the analysis were then measured by quantitative reverse-transcription polymerase chain reaction in the 60 cell lines of the NCI Anticancer Drug Screen. This generated a pattern of relative basal gene expression across the cell lines and also confirmed the differential expression of SAGE-discovered genes within the initial set of five cell lines. Further analyses of these expression data in 60 cell lines suggested that a smaller subset of genes could be used to classify tumor cell sensitivity to 5F-203. In contrast, the same set of genes did not predict with equivalent precision sensitivity to unrelated active drugs, and another set of genes could not better classify the cell lines in terms of 5F-203 sensitivity. These results suggest that constitutive gene expression profiles, in which the genes are not necessarily known to be related to the mechanism of action of a given drug, may be viewed as a general tool to extend and improve the concept of a single predictive gene to groups of predictive genes.

Anti-tumor drug candidate 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole induces single-strand breaks and DNA-protein cross-links in sensitive MCF-7 breast cancer cells

PURPOSE

The fluorinated benzothiazole analogue 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) exhibits selective and potent anticancer activity, and its lysylamide prodrug (Phortress, NSC 710305) recently entered Phase I clinical trials in the United Kingdom. Only cancer cells sensitive to the anti-proliferative effects of 5F 203 deplete this drug candidate from nutrient media. 5F 203 induces cell cycle arrest, cytochrome P450 1A1 (CYP 1A1) mRNA and protein expression, and is metabolized into reactive electrophilic species that can covalently bind to DNA and form adducts in sensitive (i.e., MCF-7) but not in resistant (i.e., MDA-MB-435) breast cancer cells.

METHODS

In this present study, we investigated additional anticancer effects of 5F 203 in MCF-7 cells. In addition, we sought to determine if cells deficient in the xeroderma pigmentosum D gene, a gene critical in DNA repair, would show greater sensitivity to the cytotoxic effects of 5F 203 than those complemented with XPD.

RESULTS

Alkaline Elution revealed that 5F 203 induced single-strand breaks and DNA-protein cross-links in sensitive MCF-7 cells. In contrast, we detected no double-strand breaks or protein-associated strand breaks typically associated with topoisomerase I (top1) or topoisomerase II (top2) inhibition. In addition, 5F 203 was unable to trap top1- or top2-DNA cleavage complexes in MCF-7 cells. 5F 203 induced cell cycle arrest in MCF-7 cells following DNA damage after brief exposures. Cells deficient in the nucleotide excision repair xeroderma pigmentosum group D (XPD) gene displayed sensitivity to 5F 203 while cells complemented with XPD displayed resistance to 5F 203.

CONCLUSION

These data suggest that the anti-cancer activity of 5F 203 depends upon targets other than top1 or top2 and on the ability of this benzothiazole to form single-strand breaks and DNA-protein cross-links in cancer cells.

CYP1A1 activation of aminoflavone leads to DNA damage in human tumor cell lines

PURPOSE

Aminoflavone (5-amino-2,3-fluorophenyl)-6,8-difluoro-7-methyl-4H-1-benzopyran-4-one; AF; NSC 686288) is a novel anticancer agent with a unique pattern of growth inhibitory activity in the National Cancer Institute (NCI) 60 tumor cell line screen. Phase I clinical trials with AF will begin soon. We previously demonstrated extensive metabolism of AF by cytochrome P450 (CYP) 1A1 and CYP1A2, metabolic activation, formation of irreversible protein and DNA adducts and p53 stabilization in sensitive, but not resistant, human tumor cell lines treated with AF [9]. The present studies focus on the effects of AF on cellular DNA and cellular responses to DNA damage.

METHODS

Phosphorylation of H2AX in MCF7 cells treated with AF was determined with immunofluorescence. MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4- sulfophenyl)-2H-tetrazolium) assays were used to determine the effect of cotreatment with caffeine or wortmannin, inhibitors of ataxia-telangiectasia-mutated protein (ATM) and ATR (ATM- and rad3-related protein), on the AF IC(50) values for MCF7 cells. DNA damage in MCF7 cells treated with AF was determined by alkaline elution. DNA-topoisomerase complex stabilization was ascertained by the ICE (in vitro complex of enzyme) assay.

RESULTS

Treatment of sensitive cells with AF resulted in phosphorylation of H2AX, a histone 2A variant that is phosphorylated in response to DNA damage. AF IC(50) values for MCF7 cells were lowered by cotreatment with caffeine or wortmannin, further implicating DNA damage in AF cytotoxicity. There was no evidence of DNA-DNA cross-linking in sensitive cells, but protein-associated single-strand breaks were observed after AF treatment. Although this pattern of DNA damage is commonly associated with topoisomerase poisons, there was no evidence for AF-induced stabilization of either topoisomerase I- or II-DNA complexes.

CONCLUSIONS

These studies further implicate DNA damage in the cytotoxicity of AF and identify biochemical features of that damage including formation of protein-associated single-strand breaks not involving topoisomerase I or II.

DNA-protein cross-links and replication-dependent histone H2AX phosphorylation induced by aminoflavone (NSC 686288), a novel anticancer agent active against human breast cancer cells

Aminoflavone (5-amino-2,3-fluorophenyl)-6,8-difluoro-7-methyl-4H-1-benzopyran-4-one) (NSC 686288) is a candidate for possible advancement to phase I clinical trial. Aminoflavone has a unique activity profile in the NCI 60 cell lines (COMPARE analysis; http://www.dtp.nci.nih.gov/docs/dtp_search.html), and exhibits potent cellular and animal antitumor activity. To elucidate the mechanism of action of aminoflavone, we studied DNA damage in MCF-7 cells. Aminoflavone induced DNA-protein cross-links (DPC) and DNA single-strand breaks (SSB). Aminoflavone induced high levels of DPC and much lower level of SSB than camptothecin, which induces equal levels of DPC and SSB due to the trapping topoisomerase I-DNA complexes. Accordingly, neither topoisomerase I nor topoisomerase II were detectable in the aminoflavone-induced DPC. Aminoflavone also induced dose- and time-dependent histone H2AX phosphorylation (gamma-H2AX). Gamma-H2AX foci occurred with DPC formation, and like DPC, persisted after aminoflavone removal. Aphidicolin prevented gamma-H2AX formation, suggesting that gamma-H2AX foci correspond to replication-associated DNA double-strand breaks. Accordingly, no gamma-H2AX foci were found in proliferating cell nuclear antigen-negative or in mitotic cells. Bromodeoxyuridine incorporation and fluorescence-activated cell sorting analyses showed DNA synthesis inhibition uniformly throughout the S phase after exposure to aminoflavone. Aminoflavone also induced RPA2 and p53 phosphorylation, and induced p21(Waf1/Cip1) and MDM2, demonstrating S-phase checkpoint activation. These studies suggest that aminoflavone produces replication-dependent DNA lesions and S-phase checkpoint activation following DPC formation. Gamma-H2AX may be a useful clinical marker for monitoring the efficacy of aminoflavone in tumor therapies.

Fluorinated 2-(4-amino-3-methylphenyl)benzothiazoles induce CYP1A1 expression, become metabolized, and bind to macromolecules in sensitive human cancer cells

Fluorinated 2-(4-amino-3-methylphenyl)benzothiazoles possess potent antiproliferative activity against certain cancer cells, similar to the unfluorinated 2-(4-amino-3-methylphenyl)benzothiazole (DF 203, NSC 674495). In "sensitive" cancer cells, DF 203 is metabolized by, can induce expression of, and binds covalently to CYP1A1. Metabolism appears to be essential for its antiproliferative activity through DNA adduct formation. However, a biphasic dose-response relationship compromises its straightforward development as a chemotherapeutic agent. We investigated whether fluorinated benzothiazoles inhibit cancer cell growth without the biphasic dose-response, and whether the fluorinated benzothiazoles are also metabolized into reactive species, with binding to macromolecules in sensitive cancer cells. One fluorinated benzothiazole, 2-(4-amino-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) did exhibit potent, antiproliferative activity without a biphasic dose-response. The fluorinated benzothiazoles were also metabolized only in cells, which subsequently showed evidence of cell death. We used microsomes from genetically engineered human B-lymphoblastoid cells expressing cytochromes P450 (CYP1A1, CYP1A2, or CYP1B1) to clarify the basis for fluorinated benzothiazole metabolism. 5F 203 induced CYP1A1 and CYP1B1 mRNA expression in sensitive breast and renal cancer cells, whereas 5F 203 induced CYP1A1 mRNA but not CYP1B1 mRNA expression in sensitive ovarian cancer cells. 5F 203 did not induce CYP1A1 or CYP1B1 mRNA expression in any "resistant" cancer cells. The fluorinated benzothiazoles induced CYP1A1 protein expression exclusively in sensitive cells. [14C]5F 203 bound substantially to subcellular fractions in sensitive cells but only minimally in resistant cells. These data are concordant with the antiproliferative activity of fluorinated benzothiazoles deriving from their ability to become metabolized and bind to macromolecules within sensitive cells.

Aryl hydrocarbon receptor activation of an antitumor aminoflavone: Basis of selective toxicity for MCF-7 breast tumor cells

Aminoflavone (4H-1-benzopyran-4-one, 5-amino-2-(4-amino-3-fluorophenyl)-6,8-difluoro-7-methyl; NSC 686288) demonstrates differential antiproliferative activity in the National Cancer Institute's anticancer drug screen. We demonstrate here that MCF-7 human breast cancer cells are sensitive to aminoflavone both in vitro and when grown in vivo as xenografts in athymic mice. As previous work has indicated that aminoflavone requires metabolic activation by cytochrome P450 1A1 (CYP1A1), we investigated the effect of aminoflavone on CYP1A1 expression and on the aryl hydrocarbon receptor (AhR), a transcriptional regulator of CYP1A1. In aminoflavone-sensitive but not aminoflavone-resistant cells, the drug caused a 100-fold induction of CYP1A1 mRNA and a corresponding increase in ethoxyresorufin-O-deethylase activity. An AhR-deficient variant of the MCF-7 breast carcinoma, AHR100, with diminished CYP1A1 inducibility, exhibits cellular resistance to aminoflavone and is refractory to CYP1A1 mRNA induction by the drug. The increase in CYP1A1 mRNA in the aminoflavone-sensitive MCF-7 breast tumor cell results from transcriptional activation of xenobiotic-responsive element (XRE)–controlled transcription. Aminoflavone treatment causes a translocation of the AhR from the cytoplasm to the nucleus with subsequent formation of AhR-XRE protein DNA complexes. In contrast to the aminoflavone-sensitive MCF-7 cells, the resistant cell lines (MDA-MB-435, PC-3, and AHR100) demonstrated constitutive nuclear localization of AhR. Additionally, aminoflavone failed to induce ethoxyresorufin-O-deethylase activity, CYP1A1 transcription, AhR-XRE complex formation, and apoptosis in aminoflavone-resistant cells. These results suggest that the cytotoxicity of aminoflavone in a sensitive breast tumor cell line is the result of the engagement of AhR-mediated signal transduction.