In vitro metabolism of beta-lapachone (ARQ 501) in mammalian hepatocytes and cultured human cells

The possibility of low isomerization of β-lapachone in the human body

β-Lapachone has been reported to have anticancer and various other therapeutic effects, but is limited in clinical applications by its low bioavailability. pH-Dependent isomerization can be suggested as one plausible factor influencing its low bioavailability. Since it is known that β-lapachone is converted to its isomer, α-lapachone in hydrochloric acid (HCl) solution, isomerization in the human body may be driven by HCl in the gastric fluid. The purpose of this study was to evaluate the possibility of isomerization of β-lapachone in the human body. Chemical reactions were conducted using simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 7.5) at 37°C. β-Lapachone was observed in SGF at 37°C for 1 hour and SIF for 3 hours. In addition, biofluid analysis was performed on plasma samples 1 hour and 4 hours, and on urine sample 12 hours after oral administration of 100 mg MB12066, a synthetic β-lapachone, in healthy adult male. All samples were analyzed using liquid chromatography-tandem mass spectrometry. Only β-lapachone peaks existed in the spectra obtained from SGF and SIF. No isomerization of β-lapachone was observed in the analysis of any of the human samples. In the current study, the possibility of pH-dependent isomerization of β-lapachone in the human body was not confirmed.

Synthesis and biological evaluation of β-lapachone and nor-β-lapachone complexes with 2-hydroxypropyl-β-cyclodextrin as trypanocidal agents

We study βLAP and its derivative nor-β-Lapachone (NβL) complexes with 2-hydroxypropyl-β-cyclodextrin to increase the solubility and bioavailability. The formation of true inclusion complexes between βLAP or NβL in 2-HP-β-CD in solid solution was characterization by FT-IR, DSC, powder X-ray was and was confirmed by one- and two-dimensional ¹H NMR experiments. Additionally, the biological activities of βLAP, NβL, ICβLAP, and ICNβL were investigated through trypanocidal assays with T. cruzi and cytotoxicity studies with mouse peritoneal macrophages. Originally, we tested these complexes against T. cruzi viability and observed higher biological activities and lower cytotoxicity when compared to βLAP and NβL. Thus, the complexation of βLAP and NβL with 2-HP-β-CD increases the drug solubility, in addition vectorization was observed, increasing the biological activity against epimastigotes and trypomastigotes T. cruzi forms. Reduced the toxicity of the compounds against mammalian cells. In addition, the selectivity indices higher of the inclusion complexes comparing to substance free and those of benznidazole.

Phenotypic screening reveals topoisomerase I as a breast cancer stem cell therapeutic target

Cancer stem cells (CSCs) are a subpopulation generally thought to be responsible for cancer initiation and progression. Because CSCs are often rare in the total tumor cell population and differentiate rapidly when grown in culture, it has been challenging to uncover compounds that selectively target CSCs. We previously described CSC-emulating cells derived from breast cancer cell lines that maintained a stable undifferentiated state. We optimized a phenotypic assay with these cells and screened 1,280-bioactive compounds, identifying five that preferentially inhibited CSC-like cell proliferation. Using a compound-guided target identification approach, we found high topoisomerase I (Topo I) expression levels in breast CSC-like cells and primary breast CSCs. Structurally unrelated small molecules targeting Topo I preferentially inhibited CSC-like cells. These results illustrate the substantial power of this CSC phenotypic screening platform and promote Topo I as a potential molecular therapeutic target for therapies aimed at expunging CSCs.

Comparative metabolism study of β-lapachone in mouse, rat, dog, monkey, and human liver microsomes using liquid chromatography-tandem mass spectrometry

β-Lapachone (3,4-dihydro-2,2-dimethyl-2H-naphthol[1,2-b]pyran-5,6-dione) is a natural compound extracted from the bark of the lapacho tree (Tabebuia avellanedae) and is undergoing phase II clinical trials as an antitumor drug candidate. The present study characterized in vitro metabolites of β-lapachone in mouse, rat, dog, monkey and human liver microsomes. β-Lapachone (10 μM) was incubated with mouse, rat, dog, monkey, and human liver microsomes in the presence of NADPH. The reaction mixtures were analyzed by LC/MS and the metabolites were identified based on their elemental composition and product ion spectra. A total of 6 metabolites (M1-M6) were detected in liver microsomes with a slight difference between species. M1 and M6 were identified as a decarbonated metabolite and a carboxylated metabolite, respectively; M2, M3, and M4 were identified as monohydroxylated metabolites; and M5 was identified as an O-methylated metabolite. M5, an O-methylated metabolite was found in rat and human liver microsomes, which is thought to be formed from a catechol intermediate by MB-COMT-mediated methylation and reported here for the first time.

Electronic structure and gas-phase chemistry of protonated α- and β-quinonoid compounds: a mass spectrometry and computational study

RATIONALE

The use of quinonoid compounds against tropical diseases and as antitumor agents has prompted the search for new naturally occurring and synthetic derivatives. Among these quinonoid compounds, lapachol and its isomers (α- and β-lapachone) serve as models for the synthesis of new compounds with biological activity, and the use of electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis as a tool to elucidate and characterize these products has furnished important information about these compounds.

METHODS

ESI-MS/MS analysis under collision-induced dissociation conditions was used to describe the fragmentation mechanisms for protonated 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone, and β-lapachone. The B3LYP/6-31+G(d,p) model was used to obtain proton affinities, gas-phase basicities, and molecular electrostatic potential maps, thus indicating the probable protonation sites. Fragmentation pathways were suggested on the basis of the relative enthalpies of the product ions.

RESULTS

The ESI-MS signals of the cationized molecules of ortho quinonoid compounds were more intense than those of the protonated molecule. Formation of the major product ions with m/z 187 from protonated α- and β-lapachone has been attributed to a retro-Diels-Alder (RDA) reaction.

CONCLUSIONS

MS/MS studies on lapachol isomers (α- and β-lapachone) will facilitate the interpretation of the liquid chromatography (LC)-MS/MS analysis of new metabolites. MS/MS data on the 1,4-naphthoquinone, 1,2-naphthoquinone, α-lapachone and β-lapachone core will help characterize new derivatives from in vitro/in vivo metabolism studies in complex matrices. The product ions revealed the major fragmentation mechanisms and these ions will serve as diagnostic ions to identify each studied compound.

Administration of the optimized β-Lapachone-poloxamer-cyclodextrin ternary system induces apoptosis, DNA damage and reduces tumor growth in a human breast adenocarcinoma xenograft mouse model

β-Lapachone (β-Lap) is a 1,2-orthonaphthoquinone that selectively induces cell death in human cancer cells through NAD(P)H:quinone oxidoreductase-1 (NQO1). NQO1 is overexpressed in a variety of tumors, as compared to normal adjacent tissue. However, the low solubility and non-specific distribution of β-Lap limit its suitability for clinical assays. We formulated β-Lap in an optimal random methylated-β-cyclodextrin/poloxamer 407 mixture (i.e., β-Lap ternary system) and, using human breast adenocarcinoma MCF-7 cells and immunodeficient mice, performed in vitro and in vivo evaluation of its anti-tumor effects on proliferation, cell cycle, apoptosis, DNA damage, and tumor growth. This ternary system is fluid at room temperature, gels over 29 °C, and provides a significant amount of drug, thus facilitating intratumoral delivery, in situ gelation, and the formation of a depot for time-release. Administration of β-Lap ternary system to MCF-7 cells induces an increase in apoptosis and DNA damage, while producing no changes in cell cycle. Moreover, in a mouse xenograft tumor model, intratumoral injection of the system significantly reduces tumor volume, while increasing apoptosis and DNA damage without visible toxicity to liver or kidney. These anti-tumoral effects and lack of visible toxicity make this system a promising new therapeutic agent for breast cancer treatment.

Metabolic profile, enzyme kinetics, and reaction phenotyping of β-lapachone metabolism in human liver and intestine in vitro

β-Lapachone (β-Lap) is an

NAD(P)H

quinone oxidoreductase 1 (NQO1) target antitumor drug candidate in phase II clinical trials. The present study aimed to uncover the metabolic profile, enzyme kinetics, and enzyme isoforms for the metabolism of β-Lap in human liver and intestine in vitro. NQO1-mediated quinone reduction and subsequent glucuronidation is the predominant metabolic pathway for β-Lap in humans; a pair of regioisomers (M1 and M2) of reduced β-Lap glucuronides were the major metabolites found from human S9 incubations. The overall glucuronidation clearance of β-Lap in human liver S9 was 4754.90 μL/min/mg of protein and was 8.1-fold of that in human intestinal S9. Recombinant UDP-glucuronosyltransferase (UGT) screening, correlation analysis, enzyme kinetics, and chemical inhibition study were performed to determine the UGT isoforms involved in β-Lap metabolism. UGT1A7, UGT1A8, and UGT1A9 are the predominant isoforms responsible for the formation of M2 while UGT2B7 is the main isoform for M1, suggesting a regioselective glucuronidation of reduced quinone by UGTs. It was of interest to find that β-Lap underwent nonenzymatic two-electron reduction, providing a novel explanation for the toxicities of β-Lap to NQO1-negative cells at high concentration and with long-time incubation. In conclusion, this study contributes to a better understanding of not only β-Lap metabolism but its antitumor property as well.

Anticancer efficacy and subcellular site of action investigated by real-time monitoring of cellular responses to localized drug delivery in single cells

Subcellular-targeted drug delivery has much potential to defeat infectious diseases and cancers. Medical and/or biochemical effects of drugs/bioactive molecules delivered to subcellular compartments and their subcellular sites of action need to be investigated but have not been explored. Here the subcellular location-dependent biochemical responses of a potent anticancer drug, β-lapachone (β-lap), is investigated by a reduced graphene oxide (rGO)-functionalized optical nanoprobe, which can deliver and simultaneously monitor the drug effects at nanoscales. For the first time, distinct oxidative responses and calcium alterations in three selected subcellular domains are observed and clearly pinpoint that the perinuclear region is the optimal subcellular site for β-lap to have the best anticancer efficacy. The results presented here provide not only scientific insights of subcellular drug-cell interaction that is not obtainable from conventional methods, but they also provide valuable knowledge for rational design of subcellular-targeted delivery or spatially resolved signal intervention.

Phase-II conjugation ability for PAH metabolism in amphibians: characteristics and inter-species differences

The present study examines amphibian metabolic activity - particularly conjugation - by analysis of pyrene (a four ring, polycyclic aromatic hydrocarbon) metabolites using high-performance liquid chromatography (HPLC) with fluorescence detector (FD), a mass spectrometry detector (MS) system and kinetic analysis of conjugation enzymes. Six amphibian species were exposed to pyrene (dissolved in water): African claw frog (Xenopus laevis); Tago's brown frog (Rana tagoi); Montane brown frog (Rana ornativentris); Wrinkled frog (Rana rugosa); Japanese newt (Cynops pyrrhogaster); and Clouded salamander (Hynobius nebulosus); plus one fish species, medaka (Oryzias latipes); and a fresh water snail (Clithon retropictus), and the resultant metabolites were collected. Identification of pyrene metabolites by HPLC and ion-trap MS system indicated that medaka mainly excreted pyrene-1-glucuronide (PYOG), while pyrene-1-sulfate (PYOS) was the main metabolite in all amphibian species. Pyrene metabolites in amphibians were different from those in invertebrate fresh water snails. Inter-species differences were also observed in pyrene metabolism among amphibians. Metabolite analysis showed that frogs relied more strongly on sulfate conjugation than did Japanese newts and clouded salamanders. Furthermore, urodelan amphibians, newts and salamanders, excreted glucose conjugates of pyrene that were not detected in the anuran amphibians. Kinetic analysis of conjugation by hepatic microsomes and cytosols indicated that differences in excreted metabolites reflected differences in enzymatic activities. Furthermore, pyrenediol (PYDOH) glucoside sulfate was detected in the Japanese newt sample. This novel metabolite has not been reported previously to this report, in which we have identified unique characteristics of amphibians in phase II pyrene metabolism.

Oxidative stress and therapeutic opportunities: focus on the Ewing's sarcoma family of tumors

Reactive oxygen species (ROS) are highly reactive by-products of energy production that can have detrimental as well as beneficial effects. Unchecked, high levels of ROS result in an imbalance of cellular redox state and oxidative stress. High levels of ROS have been detected in most cancers, where they promote tumor development and progression. Many anticancer agents work by further increasing cellular levels of ROS, to overcome the antioxidant detoxification capacity of the cancer cell and induce cell death. However, adaptation of the level of cellular antioxidants can lead to drug resistance. The challenge for the design of effective cancer therapeutics exploiting oxidative stress is to tip the cellular redox balance to induce ROS-dependent cell death but without increasing the antioxidant activity of the cancer cell or inducing toxicity in normal cells.

Light effect on the stability of β-lapachone in solution: pathways and kinetics of degradation

OBJECTIVES

The purpose of this work was to study the chemical stability of the new antitumoral β-lapachone (βLAP) to determine the degradation pathway/s of the molecule and the degradation kinetics in addition to identifying several degradation products.

METHOD

Samples of βLAP in solution were stored under conditions of darkness and illumination at 40°C at which the pseudo-first order rate constants for the βLAP degradation were determined. Furthermore, drug degraded solutions were concentrated and purified using Sephadex LH-20 and preparative thin-layer chromatography and degradation products were identified by nuclear magnetic resonance spectroscopy.

KEY FINDINGS

The results revealed that βLAP shows two different degradation routes: hydrolysis in the dark and photolysis under the light. The βLAP exposure to light accelerated the drug degradation about 140 fold, compared with the samples stored in the absence of light. The hydrolysis produced hydroxylapachol as the main degradation product. The photolysis yielded phthalic acid, 6-hydroxy-3methylene-3H-isobenzofuran-1-one and a benzomacrolactone together with a complex mixture of other phthalate-derivatives such as 2-(2-carboxy-acetyl)-benzoic acid.

CONCLUSIONS

This study provides useful information for the development of βLAP dosage forms, their storage, manipulation and quality control.