Characterization of an Etoposide-Glutathione Conjugate Derived from Metabolic Activation by Human Cytochrome P450

Formation of potentially toxic metabolites of drugs in reactions catalyzed by human drug-metabolizing enzymes

Data are presented on the formation of potentially toxic metabolites of drugs that are substrates of human drug metabolizing enzymes. The tabular data lists the formation of potentially toxic/reactive products. The data were obtained from in vitro experiments and showed that the oxidative reactions predominate (with 96% of the total potential toxication reactions). Reductive reactions (e.g., reduction of nitro to amino group and reductive dehalogenation) participate to the extent of 4%. Of the enzymes, cytochrome P450 (P450, CYP) enzymes catalyzed 72% of the reactions, myeloperoxidase (MPO) 7%, flavin-containing monooxygenase (FMO) 3%, aldehyde oxidase (AOX) 4%, sulfotransferase (SULT) 5%, and a group of minor participating enzymes to the extent of 9%. Within the P450 Superfamily, P450 Subfamily 3A (P450 3A4 and 3A5) participates to the extent of 27% and the Subfamily 2C (P450 2C9 and P450 2C19) to the extent of 16%, together catalyzing 43% of the reactions, followed by P450 Subfamily 1A (P450 1A1 and P450 1A2) with 15%. The P450 2D6 enzyme participated in an extent of 8%, P450 2E1 in 10%, and P450 2B6 in 6% of the reactions. All other enzymes participate to the extent of 14%. The data show that, of the human enzymes analyzed, P450 enzymes were dominant in catalyzing potential toxication reactions of drugs and their metabolites, with the major role assigned to the P450 Subfamily 3A and significant participation of the P450 Subfamilies 2C and 1A, plus the 2D6, 2E1 and 2B6 enzymes contributing. Selected examples of drugs that are activated or proposed to form toxic species are discussed.

Intake of oligoelements with cytarabine or etoposide alters dopamine levels and oxidative damage in rat brain

Research on the relationships between oligoelements (OE) and the development of cancer or its prevention is a field that is gaining increasing relevance. The aim was to evaluate OE and their interactions with oncology treatments (cytarabine or etoposide) to determine the effects of this combination on biogenic amines and oxidative stress biomarkers in the brain regions of young Wistar rats. Dopamine (DA), 5-Hydroxyindoleacetic acid (5-Hiaa), Glutathione (Gsh), Tiobarbituric acid reactive substances (TBARS) and Ca+2, Mg+2 ATPase enzyme activity were measured in brain regions tissues using spectrophometric and fluorometric methods previously validated. The combination of oligoelements and cytarabine increased dopamine in the striatum but decreased it in cerebellum/medulla-oblongata, whereas the combination of oligoelements and etoposide reduced lipid peroxidation. These results suggest that supplementation with oligoelements modifies the effects of cytarabine and etoposide by redox pathways, and may become promising therapeutic targets in patients with cancer.

Cancer sensitizing effect of deazaflavin analogs is associated with increased intracellular drug accumulation

As part of our efforts geared towards developing mechanism-based cancer sensitizing agents, we have previously synthesized and characterized novel deazaflavin analogs as potent tyrosyl DNA phosphodiesterase 2 (TDP2) inhibitors for combination treatments with topoisomerase II (TOP2) poisons. Interestingly, the sensitizing effect of a few analogs toward TOP2 poison etoposide (ETP) was associated with a significant increase in intracellular drug accumulation, which could be an alternative mechanism to boost the clinical efficacy of ETP in cancer chemotherapies. Hence, we evaluated more deazaflavin TDP2 inhibitors for their impact on drug retention in cancer cells. We found that all but one tested TDP2 inhibitors substantially increased the ETP retention in DT40 cells. Particularly, we identified an exceptionally potent analog, ZW-1226, which at 3 nM increased the intracellular ETP by 13-fold. Significantly, ZW-1226 also stimulated cellular accumulation of two other anticancer drugs, TOP2 poison teniposide and antifolate pemetrexed, and produced an effect more pronounced than those of ABC transporter inhibitors verapamil and elacridar in human leukemic CCRF-CEM cells toward ETP. Lastly, ZW-1226 potentiated the action of ETP in the sensitive human CCRF-CEM cells and a few resistant non-small-cell lung cancer (NSCLC) cells, including H460 and H838 cells. Collectively, the results of this study strongly suggest that deazaflavin analog ZW-1226 could be an effective cancer sensitizing agent which warrants further investigation.

Oxidative stress induced by Etoposide anti-cancer chemotherapy drives the emergence of tumor-associated bacteria resistance to fluoroquinolones

INTRODUCTION

Antibiotic-resistant bacterial infections, such as Pseudomonas aeruginosa and Staphylococcus aureus, are prevalent in lung cancer patients, resulting in poor clinical outcomes and high mortality. Etoposide (ETO) is an FDA-approved chemotherapy drug that kills cancer cells by damaging DNA through oxidative stress. However, it is unclear if ETO can cause unintentional side effects on tumor-associated microbial pathogens, such as inducing antibiotic resistance.

OBJECTIVES

We aimed to show that prolonged ETO treatment could unintendedly confer fluoroquinolone antibiotic resistance to P. aeruginosa, and evaluate the effect of tumor-associated P. aeruginosa on tumor progression.

METHODS

We employed experimental evolution assay to treat P. aeruginosa with prolonged ETO exposure, evaluated the ciprofloxacin resistance, and elucidated the gene mutations by DNA sequencing. We also established a lung tumor-P. aeruginosa bacterial model to study the role of ETO-evolved intra-tumoral bacteria in tumor progression using immunostaining and confocal microscopy.

RESULTS

ETO could generate oxidative stress and lead to gene mutations in P. aeruginosa, especially the gyrase (gyrA) gene, resulting in acquired fluoroquinolone resistance. We further demonstrated using a microfluidic-based lung tumor-P. aeruginosa coculture model that bacteria can evolve ciprofloxacin (CIP) resistance in a tumor microenvironment. Moreover, ETO-induced CIP-resistant (EICR) mutants could form multicellular biofilms which protected tumor cells from ETO killing and enabled tumor progression.

CONCLUSION

Overall, our preclinical proof-of-concept provides insights into how anti-cancer chemotherapy could inadvertently allow tumor-associated bacteria to acquire antibiotic resistance mutations and shed new light on the development of novel anti-cancer treatments based on anti-bacterial strategies.

Studies on 1,4-Quinone Derivatives Exhibiting Anti-Leukemic Activity along with Anti-Colorectal and Anti-Breast Cancer Effects

Colorectal cancer (CRC), breast cancer, and chronic myeloid leukemia (CML) are life-threatening malignancies worldwide. Although potent therapeutic and screening strategies have been developed so far, these cancer types are still major public health problems. Therefore, the exploration of more potent and selective new agents is urgently required for the treatment of these cancers. Quinones represent one of the most important structures in anticancer drug discovery. We have previously identified a series of quinone-based compounds (ABQ-1-17) as anti-CML agents. In the current work, ABQ-3 was taken to the National Cancer Institute (NCI) for screening to determine its in vitro antiproliferative effects against a large panel of human tumor cell lines at five doses. ABQ-3 revealed significant growth inhibition against HCT-116 CRC and MCF-7 breast cancer cells with 2.00 µM and 2.35 µM GI₅₀ values, respectively. The MTT test also showed that ABQ-3 possessed anticancer effects towards HCT-116 and MCF-7 cells with IC₅₀ values of 5.22 ± 2.41 μM and 7.46 ± 2.76 μM, respectively. Further experiments indicated that ABQ-3 induced apoptosis in both cell lines, and molecular docking studies explicitly suggested that ABQ-3 exhibited DNA binding in a similar fashion to previously reported compounds. Based on in silico pharmacokinetic prediction, ABQ-3 might display drug-like features enabling this compound to become a lead molecule for future studies.

Use of antioxidant could ameliorate the negative impact of etoposide on human sperm DNA during chemotherapy

RESEARCH QUESTION

A previous study showed that N-acetylcysteine (NAC), used after in-vitro exposure to the gonadotoxic chemotherapeutic drug etoposide, has the ability to decrease DNA damage in human spermatozoa; however, it showed no benefit when used before exposure. This study aimed to evaluate the impact of the NAC on the preservation of sperm quality during in-vitro exposure to etoposide.

DESIGN

Twenty semen samples were submitted to four experimental conditions: control, NAC-only incubation, etoposide-only incubation, and concomitant etoposide and NAC incubation. After in-vitro incubation, semen parameters, sperm chromatin condensation, sperm DNA fragmentation, sperm oxidative stress and sperm metabolism were used to evaluate the role of NAC in protecting human spermatozoa from etoposide.

RESULTS

Etoposide did not affect semen parameters, nor did it cause sperm oxidative damage or alterations in glycolytic profile. However, it induced chromatin decondensation and DNA fragmentation, which were fully prevented by NAC.

CONCLUSIONS

NAC was able to protect sperm DNA integrity during etoposide treatment in vitro, suggesting that NAC may be useful as an adjuvant agent in preserving male fertility during chemotherapy treatments.

Mass spectrometry in the pharmacokinetic studies of anticancer natural products

In the history of medicine, nature has represented the main source of medical products. Indeed, the therapeutic use of plants certainly goes back to the Sumerian and Hippocrates and nowadays nature still represents the major source for new drugs discovery. Moreover, in the cancer treatment, drugs are either natural compounds or have been developed from naturally occurring parent compounds firstly isolated from plants and microbes from terrestrial and marine environment. A critical element of an anticancer drug is represented by its severe toxicities and, after administration, the drug concentrations have to remain in an appropriate range to be effective. Anyway, the drug dosage defined during the clinical studies could be inappropriate for an individual patient due to differences in drug absorption, metabolism and excretion. For this reason, personalized medicine, based on therapeutic drug monitoring (TDM), represents one of most important challenges in cancer therapy. Mass spectrometry sensitivity, specificity and fastness lead to elect this technique as the Golden Standard for pharmacokinetics and drug metabolism studies therefore for TDM. This review focuses on the mass spectrometry-based methods developed for pharmacokinetic quantification in human plasma of anticancer drugs derived from natural sources and already used in clinical practice. Particular emphasis was placed both on the pre-analytical and analytical steps, such as: sample preparation procedures, sample size required by the analysis and the limit of quantification of drugs and metabolites to give some insights on the clinical practice applicability. © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 36:213-251, 2017.

Formation and Biological Targets of Quinones: Cytotoxic versus Cytoprotective Effects

Quinones represent a class of toxicological intermediates, which can create a variety of hazardous effects in vivo including, acute cytotoxicity, immunotoxicity, and carcinogenesis. In contrast, quinones can induce cytoprotection through the induction of detoxification enzymes, anti-inflammatory activities, and modification of redox status. The mechanisms by which quinones cause these effects can be quite complex. The various biological targets of quinones depend on their rate and site of formation and their reactivity. Quinones are formed through a variety of mechanisms from simple oxidation of catechols/hydroquinones catalyzed by a variety of oxidative enzymes and metal ions to more complex mechanisms involving initial P450-catalyzed hydroxylation reactions followed by two-electron oxidation. Quinones are Michael acceptors, and modification of cellular processes could occur through alkylation of crucial cellular proteins and/or DNA. Alternatively, quinones are highly redox active molecules which can redox cycle with their semiquinone radical anions leading to the formation of reactive oxygen species (ROS) including superoxide, hydrogen peroxide, and ultimately the hydroxyl radical. Production of ROS can alter redox balance within cells through the formation of oxidized cellular macromolecules including lipids, proteins, and DNA. This perspective explores the varied biological targets of quinones including GSH, NADPH, protein sulfhydryls [heat shock proteins, P450s, cyclooxygenase-2 (COX-2), glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1, (NQO1), kelch-like ECH-associated protein 1 (Keap1), IκB kinase (IKK), and arylhydrocarbon receptor (AhR)], and DNA. The evidence strongly suggests that the numerous mechanisms of quinone modulations (i.e., alkylation versus oxidative stress) can be correlated with the known pathology/cytoprotection of the parent compound(s) that is best described by an inverse U-shaped dose-response curve.

Contributions of human enzymes in carcinogen metabolism

Considerable support exists for the roles of metabolism in modulating the carcinogenic properties of chemicals. In particular, many of these compounds are pro-carcinogens that require activation to electrophilic forms to exert genotoxic effects. We systematically analyzed the existing literature on the metabolism of carcinogens by human enzymes, which has been developed largely in the past 25 years. The metabolism and especially bioactivation of carcinogens are dominated by cytochrome P450 enzymes (66% of bioactivations). Within this group, six P450s--1A1, 1A2, 1B1, 2A6, 2E1, and 3A4--accounted for 77% of the P450 activation reactions. The roles of these P450s can be compared with those estimated for drug metabolism and should be considered in issues involving enzyme induction, chemoprevention, molecular epidemiology, interindividual variations, and risk assessment.

A phase I trial of the HIV protease inhibitor nelfinavir with concurrent chemoradiotherapy for unresectable stage IIIA/IIIB non-small cell lung cancer: a report of toxicities and clinical response

BACKGROUND

The objective of this phase I trial was to determine dose-limiting toxicities (DLT) and the maximally tolerated dose of the radiosensitizer Nelfinavir in combination with concurrent chemoradiotherapy in locally advanced non-small cell lung cancer (NSCLC).

METHODS

Nelfinavir (dose level 1: 625 mg orally [PO] twice a day; dose level 2: 1250 mg PO twice a day) was administered for 7 to 14 days before and concurrently with concurrent chemoradiotherapy to patients with biopsy confirmed IIIA or IIIB unresectable NSCLC. Five patients were treated at dose level 1; eight patients were treated at dose level 2. Patients were treated with concurrent chemoradiotherapy to a dose of 66.6 Gy. DLTs were defined as any treatment-related grade 4 hematologic toxicity requiring a break in therapy or nonhematologic grade 3 or higher toxicity except esophagitis and pneumonitis.

RESULTS

Sixteen patients were enrolled and 13 patients received at least one dose of nelfinavir. Twelve patients were treated with nelfinavir and concurrent chemoradiotherapy. No DLTs have been observed at either dose level. The maximum tolerated dose of nelfinavir was therefore 1250 mg PO twice a day. Six patients experienced grade 4 leukopenia. One patient experienced grade 4 thromobcytopenia. Median follow-up for all 12 response-evaluable patients was 31.6 months and for survivors is 23.5 months. Nine of the 12 patients had evaluable posttreatment positron emission tomography/computed tomography with metabolic response as follows: overall response: 9/9 (100%); complete response: 5/9 (56%); and partial response: 4/9 (44%).

CONCLUSION

Nelfinavir administered with concurrent chemoradiotherapy is associated with acceptable toxicity in stage IIIA/IIIB NSCLC. The metabolic response and tumor response data suggest that nelfinavir has promising activity in this disease.

Myeloperoxidase-dependent oxidation of etoposide in human myeloid progenitor CD34+ cells

Etoposide is a widely used anticancer drug successfully used for the treatment of many types of cancer in children and adults. Its use, however, is associated with an increased risk of development of secondary acute myelogenous leukemia involving the mixed-lineage leukemia (MLL) gene (11q23) translocations. Previous studies demonstrated that the phenoxyl radical of etoposide can be produced by action of myeloperoxidase (MPO), an enzyme found in developing myeloid progenitor cells, the likely origin for myeloid leukemias. We hypothesized, therefore, that one-electron oxidation of etoposide by MPO to its phenoxyl radical is important for converting this anticancer drug to genotoxic and carcinogenic species in human CD34(+) myeloid progenitor cells. In the present study, using electron paramagnetic resonance spectroscopy, we provide conclusive evidence for MPO-dependent formation of etoposide phenoxyl radicals in growth factor-mobilized CD34(+) cells isolated from human umbilical cord blood and demonstrate that MPO-induced oxidation of etoposide is amplified in the presence of phenol. Formation of etoposide radicals resulted in the oxidation of endogenous thiols, thus providing evidence for etoposide-mediated MPO-catalyzed redox cycling that may play a role in enhanced etoposide genotoxicity. In separate studies, etoposide-induced DNA damage and MLL gene rearrangements were demonstrated to be dependent in part on MPO activity in CD34(+) cells. Together, our results are consistent with the idea that MPO-dependent oxidation of etoposide in human hematopoietic CD34(+) cells makes these cells especially prone to the induction of etoposide-related acute myeloid leukemia.