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

Acridine as an Anti-Tumour Agent: A Critical Review

This review summarized the current breakthroughs in the chemistry of acridines as anti-cancer agents, including new structural and biologically active acridine attributes. Acridine derivatives are a class of compounds that are being extensively researched as potential anti-cancer drugs. Acridines are well-known for their high cytotoxic activity; however, their clinical application is restricted or even excluded as a result of side effects. The photocytotoxicity of propyl acridine acts against leukaemia cell lines, with C1748 being a promising anti-tumour drug against UDP-UGT's. CK0403 is reported in breast cancer treatment and is more potent than CK0402 against estrogen receptor-negative HER2. Acridine platinum (Pt) complexes have shown specificity on the evaluated DNA sequences; 9-anilinoacridine core, which intercalates DNA, and a methyl triazene DNA-methylating moiety were also studied. Acridine thiourea gold and acridinone derivatives act against cell lines such as MDA-MB-231, SK-BR-3, and MCF-7. Benzimidazole acridine compounds demonstrated cytotoxic activity against Dual Topo and PARP-1. Quinacrine, thiazacridine, and azacridine are reported as anti-cancer agents, which have been reported in the previous decade and were addressed in this review article.

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.

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.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Electrochemical simulation of metabolism for antitumor-active imidazoacridinone C-1311 and in silico prediction of drug metabolic reactions

The metabolism of antitumor-active 5-diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) has been investigated widely over the last decade but some aspects of molecular mechanisms of its metabolic transformation are still not explained. In the current work, we have reported a direct and rapid analytical tool for better prediction of C-1311 metabolism which is based on electrochemistry (EC) coupled on-line with electrospray ionization mass spectrometry (ESI-MS). Simulation of the oxidative phase I metabolism of the compound was achieved in a simple electrochemical thin-layer cell consisting of three electrodes (ROXY^™, Antec Leyden, the Netherlands). We demonstrated that the formation of the products of N-dealkylation reactions can be easily simulated using purely instrumental approach. Newly reported products of oxidative transformations like hydroxylated or oxygenated derivatives become accessible. Structures of the electrochemically generated metabolites were elucidated on the basis of accurate mass ion data and tandem mass spectrometry experiments. In silico prediction of main sites of C-1311 metabolism was performed using MetaSite software. The compound was evaluated for cytochrome P450 1A2-, 3A4-, and 2D6-mediated reactions. The results obtained by EC were also compared and correlated with those of reported earlier for conventional in vitro enzymatic studies in the presence of liver microsomes and in the model peroxidase system. The in vitro experimental approach and the in silico metabolism findings showed a quite good agreement with the data from EC/ESI-MS analysis. Thus, we conclude here that the electrochemical technique provides the promising platform for the simple evaluation of drug metabolism and the reaction mechanism studies, giving first clues to the metabolic transformation of pharmaceuticals in the human body.

Chemical Probes for Human UDP-Glucuronosyltransferases: A Comprehensive Review

UGTs play crucial roles in the metabolism and detoxification of both endogenous and xenobiotic compounds. The key roles of UGTs in human health have garnered great interest in the design and development of specific probes for human UGTs. However, in contrast to other human enzymes, the probe substrates for human UGTs are rarely reported, owing to the highly overlapping substrate specificities of UGTs and the lack of the integrated crystal structures of UGTs. Over the past decades, many efforts are made to develop specific probe substrates for UGTs and use them in both basic research and drug discovery. This review focuses on recent progress in the development of probe substrates for UGTs and their biomedical applications. A long list of chemical probes for UGTs, including non-fluorescent and fluorescent probes along with their structural information and kinetic parameters, are prepared and analyzed. Additionally, challenges and future directions in this field are highlighted in the final section. All information and knowledge presented in this review provide practical tools/methods for measuring UGT activities in complex biological samples, which will be very helpful for rapid screening and characterization of UGT modulators, and for exploring the relevance of UGT enzymes to human diseases.

Modulation of UDP-glucuronidation by acridinone antitumor agents C-1305 and C-1311 in HepG2 and HT29 cell lines, despite slight impact in noncellular systems

BACKGROUND

Among the studied antitumor acridinone derivatives developed in our laboratory, 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) and 5-diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) exhibited cytotoxic and antitumor properties against several cancer types and were selected to be evaluated in preclinical and early-phase clinical trials. In the present work, we investigated the impact of C-1305 and C-1311 on UDP-glucuronosyltransferase (UGT) activity.

METHODS

Enzyme activity modulation was studied using HPLC by analyzing standard UGT substrate metabolism in the presence and absence of antitumor drugs. The investigations were performed in two model systems: (i) under noncellular conditions, including human liver microsomes (HLM) and recombinant UGT1A1, 1A9 and 1A10 isoenzymes and (ii) in tumor cells.

RESULTS

There was observed a slight impact of studied drugs on enzyme activity. Only UGT1A1 action was altered by both compounds. The modulatory effects of UGT activity in cellular systems depended on the tumor cell type. In the case of HepG2, C-1305 and C-1311 strongly induced UGT activity, particularly for C-1311, at concentrations significantly lower than the EC₅₀. This effect contradicted irinotecan mediated UGT inhibition. HT29 colon tumor cells were less sensitive than HepG2 to enzyme modulation in the presence of the studied compounds, particularly C-1305, where enzymatic inhibition similar to that of irinotecan was observed.

CONCLUSIONS

The results demonstrated that UGT activity modulation should be expected in the case of antitumor therapy with C-1305 or/and C-1311. Analysis of the results indicated that these modulations would occur via cellular regulatory pathways not by direct drug-enzyme interactions.

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 role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

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.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

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.

CYP3A4 overexpression enhances apoptosis induced by anticancer agent imidazoacridinone C-1311, but does not change the metabolism of C-1311 in CHO cells

AIM

To examine whether CYP3A4 overexpression influences the metabolism of anticancer agent imidazoacridinone C-1311 in CHO cells and the responses of the cells to C-1311.

METHODS

Wild type CHO cells (CHO-WT), CHO cells overexpressing cytochrome P450 reductase (CPR) [CHO-HR] and CHO cells coexpressing CPR and CYP3A4 (CHO-HR-3A4) were used. Metabolic transformation of C-1311 and CYP3A4 activity were measured using RP-HPLC. Flow cytometry analyses were used to examine cell cycle, caspase-3 activity and cell apoptosis. The expression of pH 6.0-dependent β-galactosidase (SA-β-gal) was studied to evaluate accelerated senescence. ROS generation was analyzed with CM-H2 DCFDA staining.

RESULTS

CYP3A4 overexpression did not change the metabolism of C-1311 in CHO cells: the levels of all metabolites of C-1311 increased with the exposure time to a similar extent, and the differences in the peak level of the main metabolite M3 were statistically insignificant among the three CHO cell lines. In CHO-HR-3A4 cells, C-1311 effectively inhibited CYP3A4 activity without affecting CYP3A4 protein level. In the presence of C-1311, CHO-WT cells underwent rather stable G2/M arrest, while the two types of transfected cells only transiently accumulated at this phase. C-1311-induced apoptosis and necrosis in the two types of transfected cells occurred with a significantly faster speed and to a greater extent than in CHO-WT cells. Additionally, C-1311 induced ROS generation in the two types of transfected cells, but not in CHO-WT cells. Moreover, CHO-HR-3A4 cells that did not die underwent accelerated senescence.

CONCLUSION

CYP3A4 overexpression in CHO cells enhances apoptosis induced by C-1311, whereas the metabolism of C-1311 is minimal and does not depend on CYP3A4 expression.

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.