Flavin monooxygenases, FMO1 and FMO3, not cytochrome P450 isoenzymes, contribute to metabolism of anti-tumour triazoloacridinone, C-1305, in liver microsomes and HepG2 cells

Integrating machine learning and multi-omics analysis to develop an asparagine metabolism immunity index for improving clinical outcome and drug sensitivity in lung adenocarcinoma

Lung adenocarcinoma (LUAD) is a malignancy affecting the respiratory system. Most patients are diagnosed with advanced or metastatic lung cancer due to the fact that most of their clinical symptoms are insidious, resulting in a bleak prognosis. Given that abnormal reprogramming of asparagine metabolism (AM) has emerged as an emerging therapeutic target for anti-tumor therapy. However, the clinical significance of abnormal reprogramming of AM in LUAD patients is unclear. In this study, we collected 864 asparagine metabolism-related genes (AMGs) and used a machine-learning computational framework to develop an asparagine metabolism immunity index (AMII) for LUAD patients. Through the utilization of median AMII scores, LUAD patients were segregated into either a low-AMII group or a high-AMII group. We observed outstanding performance of AMII in predicting survival prognosis in LUAD patients in the TCGA-LUAD cohort and in three externally independently validated GEO cohorts (GSE72094, GSE37745, and GSE30219), and poorer prognosis for LUAD patients in the high-AMII group. The results of univariate and multivariate analyses showed that AMII can be used as an independent risk factor for LUAD patients. In addition, the results of C-index analysis and decision analysis showed that AMII-based nomograms had a robust performance in terms of accuracy of prognostic prediction and net clinical benefit in patients with LUAD. Excitingly, LUAD patients in the low-AMII group were more sensitive to commonly used chemotherapeutic drugs. Consequently, AMII is expected to be a novel diagnostic tool for clinical classification, providing valuable insights for clinical decision-making and personalized management of LUAD patients.

Dietary phenolics and their microbial metabolites are poor inhibitors of trimethylamine oxidation to trimethylamine N-oxide by hepatic flavin monooxygenase 3

High circulating levels of trimethylamine N-oxide (TMAO) have been associated with cardiovascular disease risk. TMAO is formed through a microbiome-host pathway utilizing primarily dietary choline as a substrate. Specific gut microbiota transform choline into trimethylamine (TMA), and, when absorbed, host hepatic flavin-containing monooxygenase 3 (FMO3) oxidizes TMA into TMAO. Chlorogenic acid and its metabolites reduce microbial TMA production in vitro. However, little is known regarding the potential for chlorogenic acid and its bioavailable metabolites to inhibit the last step: hepatic conversion of TMA to TMAO. We developed a screening methodology to study FMO3-catalyzed production of TMAO from TMA. HepG2 cells were unable to oxidize TMA into TMAO due to their lack of FMO3 expression. Although Hepa-1 cells did express FMO3 when pretreated with TMA and NADPH, they lacked enzymatic activity to produce TMAO. Rat hepatic microsomes contained active FMO3. Optimal reaction conditions were: 50 µM TMA, 0.2 mM NADPH, and 33 µL microsomes/mL reaction. Methimazole (a known FMO3 competitive substrate) at 200 µM effectively reduced FMO3-catalyzed conversion of TMA to TMAO. However, bioavailable chlorogenic acid metabolites did not generally inhibit FMO3 at physiological (1 µM) nor supra-physiological (50 µM) doses. Thus, the effects of chlorogenic acid in regulating TMAO levels in vivo are unlikely to occur through direct FMO3 enzyme inhibition. Potential effects on FMO3 expression remain unknown. Intestinal inhibition of TMA production and/or absorption are thus likely their primary mechanisms of action.

Roles of selected non-P450 human oxidoreductase enzymes in protective and toxic effects of chemicals: review and compilation of reactions

This is an overview of the metabolic reactions of drugs, natural products, physiological compounds, and other (general) chemicals catalyzed by flavin monooxygenase (FMO), monoamine oxidase (MAO), NAD(P)H quinone oxidoreductase (NQO), and molybdenum hydroxylase enzymes (aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR)), including roles as substrates, inducers, and inhibitors of the enzymes. The metabolism and bioactivation of selected examples of each group (i.e., drugs, "general chemicals," natural products, and physiological compounds) are discussed. We identified a higher fraction of bioactivation reactions for FMO enzymes compared to other enzymes, predominately involving drugs and general chemicals. With MAO enzymes, physiological compounds predominate as substrates, and some products lead to unwanted side effects or illness. AOX and XOR enzymes are molybdenum hydroxylases that catalyze the oxidation of various heteroaromatic rings and aldehydes and the reduction of a number of different functional groups. While neither of these two enzymes contributes substantially to the metabolism of currently marketed drugs, AOX has become a frequently encountered route of metabolism among drug discovery programs in the past 10-15 years. XOR has even less of a role in the metabolism of clinical drugs and preclinical drug candidates than AOX, likely due to narrower substrate specificity.

Combined anticancer therapy with imidazoacridinone C-1305 and paclitaxel in human lung and colon cancer xenografts-Modulation of tumour angiogenesis

The acridanone derivative 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) has been described as a potent inhibitor of cancer cell growth. Its mechanism of action in in vitro conditions was attributed, among others, to its ability to bind and stabilize the microtubule network and subsequently exhibit its tumour-suppressive effects in synergy with paclitaxel (PTX). Therefore, the objective of the present study was to analyse the effects of the combined treatment of C-1305 and PTX in vivo. In addition, considering the results of previous genomic analyses, particular attention was given to the effects of this treatment on tumour angiogenesis. Treatment with C-1305 revealed antitumor effect in A549 lung cancer cells, and combined treatment with PTX showed tendency to anticancer activity in HCT116 colon cancer xenografts. It also improved tumour blood perfusion in both tumour models. The plasma level of CCL2 was increased and that of PDGF was decreased after combined treatment with C-1305 and PTX. The experimental results showed that the levels of FGF1, TGF-β and Ang-4 decreased, whereas the levels of ERK1/2 and Akt phosphorylation increased in HCT116 tumour tissue following combined treatment with both drugs. The results of in vitro capillary-like structure formation assay demonstrated the inhibiting effect of C-1305 on this process. Although previous in vitro and in vivo studies suggested a positive effect of C-1305 on cancer cells, combined treatment of HCT116 human colon and A549 lung cancer cells with both PTX and C-1305 in vivo showed that the antitumor activity was restricted and associated with the modulation of tumour angiogenesis.

A comprehensive review on acridone based derivatives as future anti-cancer agents and their structure activity relationships

The development of drug resistance and severe side-effects has reduced the clinical efficacy of the existing anti-cancer drugs available in the market. Thus, there is always a constant need to develop newer anti-cancer drugs with minimal adverse effects. Researchers all over the world have been focusing on various alternative strategies to discover novel, potent, and target specific molecules for cancer therapy. In this direction, several heterocyclic compounds are being explored but amongst them one promising heterocycle is acridone which has attracted the attention of medicinal chemists and gained huge biological importance as acridones are found to act on different therapeutically proven molecular targets, overcome ABC transporters mediated drug resistance and DNA intercalation in cancer cells. Some of these acridone derivatives have reached clinical studies as these heterocycles have shown huge potential in cancer therapeutics and imaging. Here, the authors have attempted to compile and make some recommendations of acridone based derivatives concerning their cancer biological targets and in vitro-cytotoxicity based on drug design and novelty to increase their therapeutic potential. This review also provides some important insights on the design, receptor targeting and future directions for the development of acridones as possible clinically effective anti-cancer agents.

Predicted Contributions of Flavin-containing Monooxygenases to the N-oxygenation of Drug Candidates Based on their Estimated Base Dissociation Constants

AIMS

Base dissociation constants of 30 model chemicals were investigated to constitute potential determinant factors predicting the contributions of flavin-containing monooxygenases (FMOs).

BACKGROUND

The contributions of FMOs to the metabolic elimination of new drug candidates could be underestimated under certain experimental conditions during drug development.

OBJECTIVE

A method for predicting metabolic sites and the contributions of FMOs to N-oxygenations is proposed using a molecular descriptor, the base dissociation constant (pKa base), which can be estimated in silico using commonly available chemoinformatic prediction systems.

METHODS

Model drugs and their oxidative pathways were surveyed in the literature to investigate the roles of FMOs in their N-oxygenations. The acid and base dissociation constants of the nitrogen moieties of 30 model substrates were estimated using well-established chemoinformatic software.

RESULTS

The base dissociation constants of 30 model chemicals were classified into two groups based on the reported optimal in vitro pH of 8.4 for FMO enzymes as a key determinant factor. Among 18 substrates (e.g., trimethylamine, benzydamine, and itopride) with pKa (base) values in the range of 8.4-9.8, all N-oxygenated metabolites were reported to be predominantly catalyzed by FMOs. Except for three cases (xanomeline; L-775,606; and tozasertib), the nine substrates with pKa (base) values in the range 2.7-7.9 were only moderately or minorly N-oxygenated by FMOs in addition to their major metabolic pathway of oxidation mediated by cytochrome P450s. N-Oxygenation of T-1032 (with a pKa of 4.8) is mediated predominantly by P450 3A5, but not by FMO1/3.

CONCLUSION

The predicted contributions of FMOs to the N-oxygenation of drug candidates can be simply estimated using classic base dissociation constants.

Use of dietary phytochemicals for inhibition of trimethylamine N-oxide formation

Trimethylamine-N-oxide (TMAO) has been reported as a risk factor for atherosclerosis development, as well as for other cardiovascular disease (CVD) pathologies. The objective of this review is to provide a useful summary on the use of phytochemicals as TMAO-reducing agents. This review discusses the main mechanisms by which TMAO promotes CVD, including the modulation of lipid and bile acid metabolism, and the promotion of endothelial dysfunction and oxidative stress. Current knowledge on the available strategies to reduce TMAO formation are discussed, highlighting the effect and potential of phytochemicals. Overall, phytochemicals (i.e., phenolic compounds or glucosinolates) reduce TMAO formation by modulating gut microbiota composition and/or function, inhibiting host's capacity to metabolize TMA to TMAO, or a combination of both. Perspectives for design of future studies involving phytochemicals as TMAO-reducing agents are discussed. Overall, the information provided by this review outlines the current state of the art of the role of phytochemicals as TMAO reducing agents, providing valuable insight to further advance in this field of study.

A strong preference for the TA/TA dinucleotide step discovered for an acridine-based, potent antitumor dsDNA intercalator, C-1305: NMR-driven structural and sequence-specificity studies

Triazoloacridinone C-1305, a potent antitumor agent recommended for Phase I clinical trials, exhibits high activity towards a wide range of experimental colon carcinomas, in many cases associated with complete tumor regression. C-1305 is a well-established dsDNA intercalator, yet no information on its mode of binding into DNA is available to date. Herein, we present the NMR-driven and MD-refined reconstruction of the 3D structures of the d(CGATATCG)₂:C-1305 and d(CCCTAGGG)₂:C-1305 non-covalent adducts. In both cases, the ligand intercalates at the TA/TA site, forming well-defined dsDNA:drug 1:1 mol/mol complexes. Orientation of the ligand within the binding site was unambiguously established by the DNA/ligand proton-proton NOE contacts. A subsequent, NMR-driven study of the sequence-specificity of C-1305 using a series of DNA duplexes, allowed us to confirm a strong preference towards TA/TA dinucleotide steps, followed by the TG/CA steps. Interestingly, no interaction at all was observed with duplexes containing exclusively the AT/AT, GG/CC and GA/TC steps.

Enhanced Activity of P4503A4 and UGT1A10 Induced by Acridinone Derivatives C-1305 and C-1311 in MCF-7 and HCT116 Cancer Cells: Consequences for the Drugs' Cytotoxicity, Metabolism and Cellular Response

Activity modulation of drug metabolism enzymes can change the biotransformation of chemotherapeutics and cellular responses induced by them. As a result, drug-drug interactions can be modified. Acridinone derivatives, represented here by C-1305 and C-1311, are potent anticancer drugs. Previous studies in non-cellular systems showed that they are mechanism-based inhibitors of cytochrome P4503A4 and undergo glucuronidation via UDP-glucuronosyltranspherase 1A10 isoenzyme (UGT1A10). Therefore, we investigated the potency of these compounds to modulate P4503A4 and UGT1A10 activity in breast MCF-7 and colon HCT116 cancer cells and their influence on cytotoxicity and cellular response in cells with different expression levels of studied isoenzymes. We show that C-1305 and C-1311 are inducers of not only P4503A4 but also UGT1A10 activity. MCF-7 and HCT116 cells with high P4503A4 activity are more sensitive to acridinone derivatives and undergo apoptosis/necrosis to a greater extent. UGT1A10 was demonstrated to be responsible for C-1305 and C-1311 glucuronidation in cancer cells and glucuronide products were excreted outside the cell very fast. Finally, we show that glucuronidation of C-1305 antitumor agent enhances its pro-apoptotic properties in HCT116 cells, while the cytotoxicity and cellular response induced by C-1311 did not change after drug glucuronidation in both cell lines.

Electrochemical and in silico approaches for liver metabolic oxidation of antitumor-active triazoloacridinone C-1305

5-Dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) is a promising antitumor compound developed in our laboratory. A better understanding of its metabolic transformations is still needed to explain the multidirectional mechanism of pharmacological action of triazoloacridinone derivatives at all. Thus, the aim of the current work was to predict oxidative pathways of C-1305 that would reflect its phase I metabolism. The multi-tool analysis of C-1305 metabolism included electrochemical conversion and in silico sites of metabolism predictions in relation to liver microsomal model. In the framework of the first approach, an electrochemical cell was coupled on-line to an electrospray ionization mass spectrometer. The effluent of the electrochemical cell was also injected onto a liquid chromatography column for the separation of different products formed prior to mass spectrometry analysis. In silico studies were performed using MetaSite software. Standard microsomal incubation was employed as a reference procedure. We found that C-1305 underwent electrochemical oxidation primarily on the dialkylaminoalkylamino moiety. An unknown N-dealkylated and hydroxylated C-1305 products have been identified. The electrochemical system was also able to simulate oxygenation reactions. Similar pattern of C-1305 metabolism has been predicted using in silico approach. Both proposed strategies showed high agreement in relation to the generated metabolic products of C-1305. Thus, we conclude that they can be considered as simple alternatives to enzymatic assays, affording time and cost efficiency.

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Three different strategies for the investigation of C-1305 oxidative metabolism were presented.

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Phase I products of the antitumor agent were easily generated within a matrix-free environment.

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Products of C-1305 electrochemical oxidation were typical for P450-catalyzed reactions.

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We observed a good accordance between electrochemical, in silico, and enzymatic results.

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Electrochemical and in silico methods are fast alternatives for enzymatic assays.

Hepatocellular Toxicity of Imidazole and Triazole Antimycotic Agents

Hepatotoxicity has been described for all antimycotic azoles currently marketed. A possible mechanism involving mitochondrial dysfunction has been postulated for ketoconazole, but not for the other azoles. The aim of the current investigations was to study the toxicity of different azoles in human cell models and to find out mechanisms of their toxicity. In HepG2 cells, posaconazole and ketoconazole were cytotoxic starting at 20 and 50 µM and decreased the cellular ATP content starting at 5 and 10 µM, respectively. In HepaRG cells, cytotoxicity started at 20 and 100 µM for posaconazole and ketoconazole, respectively, and was slightly accentuated by cytochrome P450 3A4 induction with rifampicin and 1A2 with 3-methylcholantrene. Voriconazole and fluconazole were not cytotoxic. In isolated mouse liver mitochondria, ketoconazole impaired membrane potential and complex I activity, whereas the other azoles were not toxic. In HepG2 cells exposed for 24 h, both posaconazole and ketoconazole (but not fluconazole or voriconazole) decreased the mitochondrial membrane potential, impaired the function of enzyme complexes of the electron transport chain, were associated with mitochondrial superoxide accumulation, decreased mitochondrial DNA and induced apoptosis. In HepG2 cells with mitochondrial dysfunction induced by the vitamin B12 antagonist hydroxy-cobalamin[c-lactam], cytotoxicity and/or ATP depletion was more accentuated than in untreated cells. We conclude that ketoconazole and posaconazole are mitochondrial toxicants starting at concentrations, which can be reached in vivo. Cytotoxicity and ATP depletion are more accentuated in cells with mitochondrial damage, suggesting that preexisting mitochondrial dysfunction is a susceptibility factor for hepatotoxicity associated with these drugs.

Mechanism-based inactivation of human cytochrome P450 1A2 and 3A4 isoenzymes by anti-tumor triazoloacridinone C-1305

1. 5-Dimethylaminopropylamino-8-hydroxytriazoloacridinone, C-1305, is a promising anti-tumor therapeutic agent with high activity against several experimental tumors. 2. It was determined to be a potent and selective inhibitor of liver microsomal and human recombinant cytochrome P450 (CYP) 1A2 and 3A4 isoenzymes. Therefore, C-1305 might modulate the effectiveness of other drugs used in multidrug therapy. 3. The objective of this study was to investigate the mechanism of the observed C-1305-mediated inactivation of CYP1A2 and CYP3A4. 4. Our findings indicated that C-1305 produced a time- and concentration-dependent decrease in 7-ethoxycoumarin O-deethylation (CYP1A2, K_I = 10.8 ± 2.14 μM) and testosterone 6β-hydroxylation (CYP3A4, K_I = 9.1 ± 2.82 μM). The inactivation required the presence of NADPH, was unaffected by a nucleophilic trapping agent (glutathione) and a reactive oxygen species scavenger (catalase), attenuated by a CYP-specific substrate (7-ethoxycoumarin or testosterone), and was not reversed by potassium ferricyanide. The estimated partition ratios of 1086 and 197 were calculated for the inactivation of CYP1A2 and CYP3A4, respectively. 5. In conclusion, C-1305 inhibited human recombinant CYP1A2 and CYP3A4 isoenzymes by mechanism-based inactivation. The obtained knowledge about specific interactions between C-1305 and/or its metabolites, and CYP isoforms would be useful for predicting the possible drug-drug interactions in potent multidrug therapy.

The antitumor compound triazoloacridinone C-1305 inhibits FLT3 kinase activity and potentiates apoptosis in mutant FLT3-ITD leukemia cells

AIM

FMS-like receptor tyrosine kinase (FLT3) is expressed in some normal hematopoietic cell types and plays an important role in the pathogenesis of acute myeloid leukemia (AML). In this study, we examined the effects of triazoloacridinone C-1305, an antitumor compound, on AML cells with different FLT3 status in vitro.

METHODS

A panel of human leukemic cell lines with different FLT3 status was used, including FLT3 internal tandem duplication mutations (FLT3-ITD, MV-4-11), wild-type FLT3 (RS-4-11) and null-FLT3 (U937) cells. Cell proliferation was estimated using MTT assays, and apoptosis was studied with flow cytometry and fluorescence microscopy. FLT3 kinase activity (phosphorylation of FLT3 at Tyr591) was determined with ELISA and Western blotting. FLT3 downstream signaling proteins involving AKT, MAPK and STAT5 were examined by Western blotting. RNA silencing was used to decrease the endogenous FLT3.

RESULTS

The mutant FLT3-ITD cells were more sensitive to C-1305 than the wild-type FLT3 and null-FLT3 cells (the IC50 values measured at 24 h were 1.2±0.17, 2.0±09, 7.6±1.6 μmol/L, respectively). C-1305 (1-10 μmol/L) dose-dependently inhibited the kinase activity of FLT3, which was more pronounced in the mutant FLT3-ITD cells than in the wild-type FLT3 cells. Furthermore, C-1305 dose-dependently decreased the phosphorylation of STAT5 and MAPK and the inhibitory phosphorylation of Bad, and induced time- and dose-dependent apoptosis in the 3 cell lines with the null-FLT3 cells being the least susceptible to C-1305-induced apoptosis. Knockdown of FLT3 with siRNA significantly decreased C-1305-induced cytotoxicity in the mutant FLT3-ITD cells.

CONCLUSION

C-1305 induces apoptosis in FLT3-ITD-expressing human leukemia cells in vitro, suggesting that mutated FLT3 kinase can be a new target for C-1305, and C-1305 may be a drug candidate for the therapeutic intervention in FLT3-associated AML.

CYP3A4-dependent cellular response does not relate to CYP3A4-catalysed metabolites of C-1748 and C-1305 acridine antitumor agents in HepG2 cells

High CYP3A4 expression sensitizes tumor cells to certain antitumor agents while for others it can lower their therapeutic efficacy. We have elucidated the influence of CYP3A4 overexpression on the cellular response induced by antitumor acridine derivatives, C-1305 and C-1748, in two hepatocellular carcinoma (HepG2) cell lines, Hep3A4 stably transfected with CYP3A4 isoenzyme, and HepC34 expressing empty vector. The compounds were selected considering their different chemical structures and different metabolic pathways seen earlier in human and rat liver microsomes C-1748 was transformed to several metabolites at a higher rate in Hep3A4 than in HepC34 cells. In contrast, C-1305 metabolism in Hep3A4 cells was unchanged compared to HepC34 cells, with each cell line producing a single metabolite of comparable concentration. C-1748 resulted in a progressive appearance of sub-G1 population to its high level in both cell lines. In turn, the sub-G1 fraction was dominated in CYP3A4-overexpressing cells following C-1305 exposure. Both compounds induced necrosis and to a lesser extent apoptosis, which were more pronounced in Hep3A4 than in wild-type cells. In conclusion, CYP3A4-overexpressing cells produce higher levels of C-1748 metabolites, but they do not affect the cellular responses to the drug. Conversely, cellular response was modulated following C-1305 treatment in CYP3A4-overexpressing cells, although metabolism of this drug was unaltered.

Pregnane X receptor dependent up-regulation of CYP2C9 and CYP3A4 in tumor cells by antitumor acridine agents, C-1748 and C-1305, selectively diminished under hypoxia

Induction of proteins involved in drug metabolism and in drug delivery has a significant impact on drug-drug interactions and on the final therapeutic effects. Two antitumor acridine derivatives selected for present studies, C-1748 (9-(2'-hydroxyethylamino)-4-methyl-1-nitroacridine) and C-1305 (5-dimethylaminopropylamino-8-hydroxy-triazoloacridinone), expressed high and low susceptibility to metabolic transformations with liver microsomes, respectively. In the current study, we examined the influence of these compounds on cytochrome P450 3A4 (CYP3A4) and 2C9 (CYP2C9) enzymatic activity and gene expression in HepG2 tumor cells. Luminescence and HPLC examination, real-time RT-PCR and western blot analyses along with transfection of pregnane X receptor (PXR) siRNA and CYP3A4 reporter gene assays were applied. We found that both compounds strongly induced CYP3A4 and CYP2C9 activity and expression as well as expression of UGT1A1 and MDR1 in a concentration- and time-dependent manner. C-1748-mediated CYP3A4 and CYP2C9 mRNA induction equal to rifampicin occurred at extremely low concentrations (0.001 and 0.01μM), whereas 10μM C-1305 induced three-times higher CYP3A4 and CYP2C9 mRNA levels than rifampicin did. CYP3A4 and CYP2C9 expressions were shown to be PXR-dependent; however, neither compound influenced PXR expression. Thus, the observed drug-mediated induction of isoenzymes occurs on a PXR-mediated regulatory level. Furthermore, C-1748 and C-1305 were demonstrated to be selective PXR agonists. These effects are hypoxia-inhibited only in the case of C-1748, which is sensitive to P450 metabolism. In summary, PXR was found to be a new target of the studied compounds. Thus, possible combinations of these compounds with other therapeutics might lead to the PXR-dependent enzyme-mediated drug-drug interactions.

CYP3A4 overexpression enhances the cytotoxicity of the antitumor triazoloacridinone derivative C-1305 in CHO cells

AIM

To examine how the higher expression level of CYP3A4 isoenzyme influenced the cytotoxicity of the antitumor triazoloacridinone derivative C-1305 in Chinese hamster ovary (CHO) cells.

METHODS

Three CHO cell lines were examined: wild-type CHO cells; CHO-HR cells with overexpression of human cytochrome P450 reductase (CPR); and CHO-HR-3A4 cells with coexpression of human CYP3A4 and CPR. Cellular responses caused by C-1305 were monitored using DAPI staining, cell cycle analysis, phosphatydilserine externalization analysis and SA-β-galactosidase expression analysis. Cell viability was assessed with simultaneous FDA and PI staining.

RESULTS

Treatment with C-1305 for 72 h exhibited different levels of cytotoxicity in the 3 cell lines, and the values of IC80 in CHO, CHO-HR and CHO-HR-3A4 cells were 0.087±0.005, 0.032±0.0001, and 0.064±0.0095 μmol/L, respectively. The cell cycle analysis revealed that both CHO and CHO-HR cells underwent transient G(2)/M arrest, whereas CHO-HR-3A4 cells did not accumulate in this phase. Prolonged exposure up to 120 h caused time-dependent increase in the sub-G(1) fraction in all the 3 cell lines. Treatment with C-1305 caused cell death through apoptosis and necrosis. However, these processes were more pronounced in the transfected CHO cells than in the wild-type cells. The cells surviving after C-1305 exposure underwent senescence.

CONCLUSION

CYP3A4 overexpression potently enhances the cellular responses (apoptosis, necrosis and senescence) caused by C-1305 in CHO cells.

Metabolic transformation of antitumor acridinone C-1305 but not C-1311 via selective cellular expression of UGT1A10 increases cytotoxic response: implications for clinical use

The acridinone derivates 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) and 5-diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) are promising antitumor agents with high activity against several experimental cellular and tumor models and are under evaluation in preclinical and early phase clinical trials. Recent evidence from our laboratories has indicated that both compounds were conjugated by several uridine diphosphate-glucuronyltransferase (UGT) isoforms, the most active being extrahepatic UGT1A10. The present studies were designed to test the ability and selectivity of UGT1A10 in the glucuronidation of acridinone antitumor agents in a cellular context. We show that in KB-3 cells, a HeLa subline lacking expression of any UGT isoforms, both C-1305 and C-1311 undergo metabolic transformation to the glucuronidated forms on overexpression of UGT1A10. Furthermore, UGT1A10 overexpression significantly increased the cytotoxicity of C-1305, but not C-1311, suggesting that the glucuronide was more potent than the C-1305 parent compound. These responses were selective for UGT1A10 because documented overexpression of UGT2B4 failed to produce glucuronide products and failed to alter the cytotoxicity for both compounds. These findings contribute to our understanding of the mechanisms of action of these agents and are of particular significance because data for C-1305 contradict the dogma that glucuronidation typically plays a role in detoxification or deactivation. In summary, these studies suggest that extrahepatic UGT1A10 plays an important role in the metabolism and the bioactivation of C-1305 and constitutes the basis for further mechanistic studies on the mode of action of this drug, as well as translational studies on the role of this enzyme in regulation of C-1305 toxicity in cancer.

Role of human UDP-glucuronosyltransferases in the biotransformation of the triazoloacridinone and imidazoacridinone antitumor agents C-1305 and C-1311: highly selective substrates for UGT1A10

5-Diethylaminoethylamino-8-hydroxyimidazoacridinone, C-1311 (NSC-645809), is an antitumor agent shown to be effective against breast cancer in phase II clinical trials. A similar compound, 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone, C-1305, shows high activity against experimental tumors and is expected to have even more beneficial pharmacological properties than C-1311. Previously published studies showed that these compounds are not substrates for cytochrome P450s; however, they do contain functional groups that are common targets for glucuronidation. Therefore, the aim of this work was to identify the human UDP-glucuronosyltransferases (UGTs) able to glucuronidate these two compounds. High-performance liquid chromatography analysis was used to examine the activities of human recombinant UGT1A and UGT2B isoforms and microsomes from human liver [human liver microsomes (HLM)], whole human intestinal mucosa [human intestinal microsomes (HIM)], and seven isolated segments of human gastrointestinal tract. Recombinant extrahepatic UGT1A10 glucuronidated 8-hydroxyl groups with the highest catalytic efficiency compared with other recombinant UGTs, V(max)/K(m) = 27.2 and 8.8 μl · min⁻¹ · mg protein⁻¹, for C-1305 and C-1311, respectively. In human hepatic and intestinal microsomes (HLM and HIM, respectively), high variability in UGT activities was observed among donors and for different regions of intestinal tract. However, both compounds underwent UGT-mediated metabolism to 8-O-glucuronides by microsomes from both sources with comparable efficiency; V(max)/K(m) values were from 4.0 to 5.5 μl · min⁻¹ · mg protein⁻¹. In summary, these studies suggest that imid azoacridinone and triazoloacridinone drugs are glucuronidated in human liver and intestine in vivo and may form the basis for future translational studies of the potential role of UGTs in resistance to these drugs.