Resistance-modifying Agent Research Articles

Flufenamic Acid, a Promising Agent for the Sensitization of Colistin-Resistant Gram-Negative Bacteria to Colistin.

The continuous development of multidrug-resistant (MDR) Gram-negative bacteria poses a serious risk to public health on a worldwide scale. Colistin is used as the last-line antibiotic for the treatment of MDR pathogens, and colistin-resistant (COL-R) bacterial emergence thus has the potential to have a severe adverse impact on patient outcomes. In this study, synergistic activity was observed when colistin and flufenamic acid (FFA) were combined and used for the in vitro treatment of clinical COL-R Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii strains, as shown by checkerboard and time-kill assays. Crystal violet staining and scanning electron microscopy revealed the synergistic action of colistin-FFA against biofilms. When used to treat murine RAW264.7 macrophages, this combination did not induce any adverse toxicity. Strikingly, the survival rates of bacterially infected Galleria mellonella larvae were improved by such combination treatment, which was also sufficient to reduce the measured bacterial loads in a murine thigh infection model. Mechanistic propidium iodide (PI) staining analysis further demonstrated the ability of these agents to alter bacterial permeability in a manner that enhanced the efficacy of colistin treatment. Together, these data thus demonstrate that colistin and FFA can be synergistically combined to combat the spread of COL-R Gram-negative bacteria, providing a promising therapeutic tool with the potential to protect against COL-R bacterial infections and improve patient outcomes. IMPORTANCE Colistin is a last-line antibiotic used for the treatment of MDR Gram-negative bacterial infections. However, increasing resistance to it has been observed during clinical treatment. In this work, we assessed the efficacy of the combination of colistin and FFA for the treatment of COL-R bacterial isolates, demonstrating that the combined treatment has effective antibacterial and antibiofilm activities. Due to its low cytotoxicity and good therapeutic effects in vitro, the colistin-FFA combination may be a potential candidate for research into a resistance-modifying agent to combat infections caused by COL-R Gram-negative bacteria.

Serendipitous Discovery of a Highly Active and Selective Resistance-Modifying Agent for Colistin-Resistant Gram-Negative Bacteria.

Antibiotic resistance is a growing global health concern. Colistin is one of the last-resort antibiotics that treats multidrug-resistant (MDR) Gram-negative bacterial infection. However, bacteria resistant to colistin have become increasingly prevalent. Using a bacterial whole-cell screen of a fragment-based library, one compound was discovered to resensitize MDR Escherichia coli AR-0493 to colistin with low mammalian toxicity. Interestingly, postscreening validation studies identified a highly related yet distinct compound as the actual substance responsible for the activity. Further studies showed that this novel resistance-modifying agent is not only very potent but also highly selective to potentiate the activity of polymyxin family antibiotics in a wide range of MDR Gram-negative bacteria. Thus, it may be further developed as a combination therapy to prolong the life span of colistin in the clinic.

Yeast β-glucan Increases Etoposide Sensitivity in Lung Cancer Cell Line A549 by Suppressing Nuclear Factor Erythroid 2-Related Factor 2 via the Noncanonical Nuclear Factor Kappa B Pathway.

Etoposide is regarded as one of the main standard cytotoxic drugs for lung cancer. However, mutations in Kelch-like ECH-associated protein 1 (Keap1), the main regulator of nuclear factor erythroid 2-related factor 2 (Nrf2), are often detected in lung cancer and lead to chemoresistance. Since the aberrant activation of Nrf2 enhances drug resistance, the suppression of the Nrf2 pathway is a promising therapeutic strategy for lung cancer. We herein used the human lung adenocarcinoma cell line A549 because it harbors a Keap1 loss-of-function mutation. A treatment with β-glucan, a major component of the fungal cell wall, reduced Nrf2 protein levels; downregulated the expression of cytochrome P450 3A5, UDP glucuronosyltransferase 1A1, and multidrug resistance protein 1; and increased etoposide sensitivity in A549 cells. Furthermore, the ephrin type-A receptor 2 (EphA2) receptor was important for the recognition and biologic activity of β-glucan in A549 cells. EphA2 signaling includes nuclear factor kappa B (NF-κB), signal transducer and activator of transcription 3 (STAT3), and p38 mitogen-activated protein kinase (MAPK). However, treatment of cells with stattic (STAT3 inhibitor) or SB203580 (p38 MAPK inhibitor) did not diminish the effects of β-glucan. In contrast, knockdown of v-rel reticuloendotheliosis viral oncogene homolog B (RelB) abolished the effects of β-glucan, suggesting the involvement of the noncanonical NF-κB pathway. The β-glucan effects were also attenuated by the knockdown of WD40 Repeat protein 23 (WDR23). The β-glucan treatment and RelB overexpression induced the expression of Cullin-4A (CUL4A), which increased WDR23 ligase activity and promoted the subsequent depletion of Nrf2. These results revealed a novel property of β-glucan as a resistance-modifying agent in addition to its widely reported immunomodulatory effects for lung cancer therapy via the EphA2-RelB-CUL4A-Nrf2 axis. SIGNIFICANCE STATEMENT: Chemotherapeutic resistance remains a major obstacle in cancer therapy despite extensive efforts to elucidate the underlying molecular mechanisms and overcome multidrug resistance. The present study revealed a novel resistance-modifying property of β-glucan, thereby expanding our knowledge on the beneficial roles of β-glucan and providing an alternative strategy to prevent drug resistance by cancer. The present results provide evidence for the involvement of a novel mode of NF-κB and Nrf2 crosstalk in the drug resistance phenotype.

In silico screening and in vitro validation of phytocompounds as multidrug efflux pump inhibitor against E. coli

Multiple drug resistance (MDR) in bacteria has increased globally in recent times. This has reduced the efficacy of antibiotics and increasing the rate of therapeutic failure. Targeting efflux pump by natural and synthetic compounds is one of the strategies to develop an ideal broad-spectrum resistance-modifying agent. Very few inhibitors of AcrB from natural sources have been reported till date. In the current study, 19 phytocompounds were screened for efflux pump inhibitory activity against AcrB protein of E. coli TG1 using molecular docking studies. The molecular dynamics simulation provided stability the protein (AcrB) and its complex with chlorogenic acid under physiological conditions. Moreover, the detailed molecular insights of the binding were also explored. The Lipinski rule of 5 and the drug-likeness prediction was determined using Swiss ADME server, while toxicity prediction was done using admetSAR and PROTOX-II webservers. Chlorogenic acid showed the highest binding affinity (−9.1 kcal mol−1) with AcrB protein among all screened phytocompounds. Consequently, all the phytocompounds that accede to Lipinski’s rule, demonstrated a high LD50 value indicating that they are non-toxic except the phytocompound reserpine. Chlorogenic acid and capsaicin are filtered out based on the synergy with tetracycline having FIC index of 0.25 and 0.28. The percentage increase of EtBr fluorescence by chlorogenic acid was 36.6% followed by piperine (24.2%). Chlorogenic acid may be a promising efflux pump inhibitor that might be employed in combination therapy with tetracycline against E. coli, based on the above relationship between in silico screening and in vitro positive efflux inhibitory activity. Communicated by Ramaswamy H. Sarma.

Bacillus subtilis revives conventional antibiotics against Staphylococcus aureus osteomyelitis

As treatment of Staphylococcus aureus (S. aureus) osteomyelitis is often hindered by the development of antibiotic tolerance, novel antibacterial therapeutics are required. Here we found that the cell-free supernatant of Bacillus subtilis (B. subtilis CFS) killed planktonic and biofilm S. aureus, and increased S. aureus susceptibility to penicillin and gentamicin as well. Further study showed that B. subtilis CFS suppressed the expression of the genes involved in adhesive molecules (Cna and ClfA), virulence factor Hla, quorum sensing (argA, argB and RNAIII) and biofilm formation (Ica and sarA) in S. aureus. Additionally, our data showed that B. subtilis CFS changed the membrane components and increased membrane permeabilization of S. aureus. Finally, we demonstrated that B. subtilis CFS increased considerably the susceptibility of S. aureus to penicillin and effectively reduced S. aureus burdens in a mouse model of implant-associated osteomyelitis. These findings support that B. subtilis CFS may be a potential resistance-modifying agent for β-lactam antibiotics against S. aureus.

Indole and Indoline Scaffolds in Antimicrobials: Overview, Synthesis and Recent Advances in Antimicrobial Research.

At present, a pandemic of antibiotic-resistant infectious diseases is an evergrowing threat. The need for new antibiotics and ways to combat antibiotic resistance is glaring. This review will focus on two different privileged scaffolds, the indole and the indoline, as useful nuclei for novel antibacterial compounds. The indole, a moiety found in numerous approved drugs for many disease states, has recently been studied for its usefulness as a scaffold for compounds that have activity against antibiotic-resistant bacteria, especially against methicillin-resistant Staphylococcus aureus (MRSA). The indoline is a scaffold with significantly less historical studies and FDA-approved drugs and it has attracted new interest in drug design and development. In recent years, indoline-containing compounds have been shown to have antibacterial activity as well as activity as a resistance- modifying agent (RMA), which act to improve the effectiveness of current antibiotic therapies that have known resistance.

PEITC by regulating Aurora Kinase A reverses chemoresistance in breast cancer cells

Development of acquired chemoresistance renders a challenge in breast cancer therapy. Aurora kinases, a family of serine/threonine mitotic kinases play pivotal roles in the acquirement of chemoresistance. Aurora A is intricately associated with mitotic events and is overexpressed in different cancers including breast cancer. Amplification or overexpression Aurora A confers chemoresistance and are considered as a promising therapeutic target in cancers. Therefore, targeting Aurora A by natural means particularly by using Phenethyl isothiocyanate (PEITC), a natural isothiocyanate might be an effective strategy for reversing resistance towards chemotherapeutics. The present study investigated the modulatory role of PEITC on Aurora A and their downstream target proteins in breast adenocarcinoma cell line (MCF-7) and its paclitaxel-resistant counterpart; designated as MCF-7Pacli/R. Paclitaxel resistance was warranted by P-gp1, MRP1, Ki-67 overexpression, rhodamine 123 accumulations and upregulation of Aurora-A along with phospho-IκBα. Multidrug resistance was confirmed by MTT assay. Western blotting, RT-PCR analysis revealed overexpression of Aurora-A in MCF-7Pacli/R cells; which was eventually diminished by PEITC. PEITC by targeting Aurora A and their downstream proteins (phospho-p53, phospho-IκBα) acted as a resistance-modifying agent and ultimately led to paclitaxel- induced apoptosis. These findings demonstrated that PEITC reverses chemoresistance by regulating Aurora A and restores chemosensitivity towards paclitaxel.

Jatrorrhizine suppresses the antimicrobial resistance of methicillin-resistant Staphylococcus aureus.

Bacterial resistance to antimicrobial agents, including multidrug resistance, is an increasing problem in the treatment of infectious diseases. The development of resistance-modifying agents represents a potential strategy to alleviate the spread of bacterial resistance to antibiotics. A checkerboard microdilution assay was used to determine the synergy of jatrorrhizine and the antibiotic, norfloxacin (NFX). A bacterial ethidium bromide efflux assay, reverse transcription semi-quantitative polymerase chain reaction analysis and molecular docking study were performed. The three-dimensional structure of NorA multidrug efflux pump (NorA) was generated using a multiple threading approach. A murine thigh infection model was used to evaluate the in vivo synergistic effect. As a natural product, jatrorrhizine exhibited little antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) SA1199B with a minimum inhibitory concentration (MIC) of 64 mg/l. According to the investigations of the mechanism, jatrorrhizine significantly inhibited bacterial drug efflux and the expression of NorA in the mRNA level as it can bind to NorA by hydrogen-bonds, hydrophobic and electrostatic interactions. The in vivo synergistical bactericidal activity of jatrorrhizine and NFX against MRSA was confirmed in a murine thigh infection model. As a novel resistance-modifying agent, jatrorrhizine exhibited in vitro and in vivo synergistic activities against MRSA, and inhibited bacterial drug efflux. The effects were mediated by the suppression of NorA mRNA expression and/or interactions with NorA efflux pump. These data support the hypothesis that jatrorrhizine is a potential agent for therapeutic use in infections caused by MRSA.

Tetracyclic indolines as a novel class of β-lactam-selective resistance-modifying agent for MRSA

Antibiotic-resistant bacterial infections have seen a marked increase in recent years, while antibiotic discovery has waned. Resistance-modifying agents (RMA) offer an intriguing alternative strategy to fight against resistant bacteria. Here we report the discovery, antibiotic profiling, and structure-activity relationships of a novel class of RMAs, tetracyclic indolines. These selectively potentiate β-lactam antibiotics in methicillin-resistant Staphylococcus aureus (MRSA) without antibacterial or β-lactamase inhibitory activity on their own. The most potent analogue, 6a, showed strong potentiation of amoxicillin/clavulanic acid in a variety of hospital-acquired and community-acquired MRSA strains with low mammalian toxicity. These compounds may be further developed to extend the clinic life span of β-lactam antibiotics.

<b>Phytochemical analysis and modulation in aminoglycosides antibiotics activity by <i>Lantana camara</i> L.

Several plants have been evaluated not only for alone antimicrobial activity, but as resistance-modifying agent. This work is the first on the modulation of antibiotic activity by Lantana camara L. extracts against multiresistant strains of Escherichia coli and Staphylococcus aureus . The antibacterial activities of leaf and root ethanol extracts alone or in association with aminoglycosides were determined against bacterial strains by a microdilution test. The minimum inhibitory concentration (MIC) of the extracts was compared with of the aminoglycosides. Phytochemical prospection revealed the presence of quinones, steroids, flavonoids, saponins, tannins, triterpenoids and alkaloids. The results showed antibacterial activities of the extracts and synergistic effects combined with aminoglycosides. The most expressive effects were obtained with root extract but gentamicin or but neomycin against E. coli with MICs decreased (312 to 5 µg mL -1 ). The data from this study are indicative of the antibacterial activity of L. camara ’s extracts and its potential in modifying the resistance of aminoglycosides analyzed.

Discovery and initial structure–activity relationships of N-benzyl tricyclic indolines as antibacterials for methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent drug resistant bacteria. In 2012, over 11,000 fatalities in the United States were directly attributable to MRSA. In an effort to develop novel structural and mechanistic classes of antibacterial agents to fight against MRSA, we have optimized a hit compound, Of4, previously discovered in a screening campaign of a bio-inspired polycyclic indoline library previously developed in our lab. We took advantage of our concise and versatile synthetic strategy to conduct initial structure–activity relationship studies of Of4, and we now report the discovery of compound 4k as a more potent antibacterial agent against S. aureus. Compound 4k also displayed equivalent activity in four MRSA and a methicillin-susceptible strains while demonstrating an improved mammalian cytotoxicity profile compared to Of4. Interestingly, 4k shares the same tricyclic indoline core as Of1, a β-lactam-selective resistance-modifying agent, but harbors a distinct modification pattern conferring unique bioactivity. This phenomenon is reminiscent of many bioactive natural products.

Holarrhena antidysenterica as a resistance modifying agent against Acinetobacter baumannii: Its effects on bacterial outer membrane permeability and efflux pumps

Increasing rates of infections caused by multidrug resistant Acinetobacter baumannii (MDRAB) and extensively drug resistant A. baumannii (XDRAB) have caused the need for searching alternative agents. The purposed of this project was to search plant-derived natural products that act as resistant modifying agents (RMAs) against A. baumannii. In this study, we further evaluated the activity of Holarrhena antidysenterica that has been previously proposed as RMA of novobiocin for a model strain, A. baumannii ATCC 19606 on clinically isolated non-MDRAB, MDRAB, and XDRAB. Effects of H. antidysenterica on outer membrane permeability and efflux pumps of the pathogen were conducted to preliminary elucidate mechanisms of this resistant modifier. Novobiocin was selected as a model antibiotic because it is well-established as an effective agent against Gram-positive pathogens. But, it possessed low level of antibacterial activity against Gram-negative pathogens due to an effective permeability barrier of these pathogens. H. antidysenterica ethanol extract possessed weak intrinsic antibacterial activity with minimum inhibitory concentration (MIC) more than 1000μg/mL. The extract, at concentrations of 250, 125, and 62.5μg/mL, remarkably enhanced the inhibitory effects of novobiocin (1/4×MIC; 1–4μg/mL) against XDRAB isolates. Synergistic effects of novobiocin at 1/4×MIC and 1/8×MIC in combination with H. antidysenterica either at 31.2, 15.6, or 7.8μg/mL against clinical isolates non-MDRAB, MDRAB, and XDRAB were evidenced for 80% of the combinations (189 out of 234 combinations). Although, no enhancement of the accumulation of ethidium bromide was observed after treated with H. antidysenterica, this plant extract weakened the outer membrane of the pathogen as indicated by an increase in the N-phenyl-1-naphthylamine uptake. Our results suggested that H. antidysenterica which primarily interrupts membrane permeability should be further investigated as a promising resistant modifier for A. baumannii.

Bio-inspired synthesis yields a tricyclic indoline that selectively resensitizes methicillin-resistant Staphylococcus aureus (MRSA) to β-lactam antibiotics

The continuous emergence of resistant bacteria has become a major worldwide health threat. The current development of new antibacterials has lagged far behind. To discover reagents to fight against resistant bacteria, we initiated a chemical approach by synthesizing and screening a small molecule library, reminiscent of the polycyclic indole alkaloids. Indole alkaloids are a class of structurally diverse natural products, many of which were isolated from plants that have been used as traditional medicine for millennia. Specifically, we adapted an evolutionarily conserved biosynthetic strategy and developed a concise and unified diversity synthesis pathway. Using this pathway, we synthesized 120 polycyclic indolines that contain 26 distinct skeletons and a wide variety of functional groups. A tricyclic indoline, Of1, was discovered to selectively potentiate the activity of β-lactam antibiotics in multidrug-resistant methicillin-resistant Staphylococcus aureus (MRSA), but not in methicillin-sensitive S. aureus. In addition, we found that Of1 itself does not have antiproliferative activity but can resensitize several MRSA strains to the β-lactam antibiotics that are widely used in the clinic, such as an extended-spectrum β-lactam antibiotic amoxicillin/clavulanic acid and a first-generation cephalosporin cefazolin. These data suggest that Of1 is a unique selective resistance-modifying agent for β-lactam antibiotics, and it may be further developed to fight against resistant bacteria in the clinic.

Herbs and Drug Resistance: Part 1—Herbs and Microbial Resistance to Antibiotics

Alternative and Complementary TherapiesVol. 8, No. 4 ArticlesHerbs and Drug Resistance: Part 1—Herbs and Microbial Resistance to AntibioticsKathy Abascal and Eric YarnellKathy AbascalSearch for more papers by this author and Eric YarnellSearch for more papers by this authorPublished Online:5 Jul 2004https://doi.org/10.1089/107628002320351370AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetailsCited byInvestigation of Antibacterial Effect of Bupleurum lancifolium Hornem.10 October 2022 | Kahramanmaraş Sütçü İmam Üniversitesi Tarım ve Doğa DergisiJatrorrhizine suppresses the antimicrobial resistance of methicillin‑resistant Staphylococcus aureus23 September 2019 | Experimental and Therapeutic MedicineIsovalerylshikonin, a new resistance-modifying agent from Arnebia euchroma, supresses antimicrobial resistance of drug-resistant Staphylococcus aureusInternational Journal of Antimicrobial Agents, Vol. 53, No. 1Plants for Addressing Multidrug Resistance: An Update Kathy Abascal and Eric Yarnell18 June 2013 | Alternative and Complementary Therapies, Vol. 19, No. 3Plants as sources of new antimicrobials and resistance-modifying agentsNatural Product Reports, Vol. 29, No. 9Clinical Botanical Medicine Eric Yarnell, Kathy Abascal, and Robert Rountree23 May 2009Natural Approach to Chronic Prostatitis and Chronic Pelvic Pain Syndromes23 May 2009Natural Approaches to Treating Chronic Prostatitis and Chronic Pelvic Pain Syndromes Eric Yarnell and Kathy Abascal11 October 2005 | Alternative and Complementary Therapies, Vol. 11, No. 5Botanical Treatment and Prevention of Malaria: Part 2—Selected Botanicals Eric Yarnell and Kathy Abascal29 November 2004 | Alternative and Complementary Therapies, Vol. 10, No. 5Antimicrobial ResistanceClinical Nurse Specialist, Vol. 17, No. 5 Volume 8Issue 4Aug 2002 To cite this article:Kathy Abascal and Eric Yarnell.Herbs and Drug Resistance: Part 1—Herbs and Microbial Resistance to Antibiotics.Alternative and Complementary Therapies.Aug 2002.237-241.http://doi.org/10.1089/107628002320351370Published in Volume: 8 Issue 4: July 5, 2004PDF download

Alteration in Epirubicin Pharmacokinetics and Metabolism by Dexverapamil: Results from a Phase II Study in Patients with Metastatic Breast Cancer

Background: To study the effect of the resistance-modifying agent (RMA) dexverapamil on the pharmacokinetics and metabolism of epirubicin. Methods: Nine women with metastatic breast cancer who received epirubicin (120 mg/m 2 ) as a 0.25-hour infusion without dexverapamil during the first treatment cycle and with dexverapamil (12 × 300 mg p. o. every 6 h) during the third treatment cycle were monitored with frequent plasma samples up to 48 h postinfusion. Epirubicin and its metabolites and dexverapamil and its main metabolite nordexverapamil were measured using a reverse-phase high-pressure liquid chromatography assay. Results: The concomitant administration of dexverapamil resulted in an increase in mean (±SD) epirubicin clearance from 1,408 (610) ml/min/m 2 to 2,004 (1,696) ml/min/m 2 , a decrease in epirubicin exposure (area under the curve (AUC)) from 2,968 (1,219) mg × h/ml to 1,901 (494) mg × h/ml, and an increase of the volume of distribution at steady state from 1,436 (1,231) l/m 2 to 2,425 (1,340) l/m 2 . The mean residence time and the elimination half-life were not different. There was a significant increase of epiglucuronide and the 7-deoxy-aglycones. At the time of epirubicin administration mean dexverapamil and nordexverapamil plasma levels were 790±409 and 755 ± 274 ng/ml, respectively. Conclusion: Dexverapamil had a significant effect on the pharmacokinetics and metabolism of epirubicin. However, other than observed in previous studies of RMAs and cytotoxic drugs, dexverapamil did not increase but reduce the AUC of epirubicin and had no effect on its toxicity. These data suggest that the type of pharmacologic interaction between RMAs and cytotoxic drugs can differ depending on the particular compounds used in combination.

Reversal of P-glycoprotein-mediated multidrug resistance by XR9051, a novel diketopiperazine derivative.

XR9051 (N-(4-(2-(6,7-Dimethoxy-1,2,3,4-tetrahydro-2-isoquinolyl)ethyl)phe nyl)-3-((3Z,6Z)-6-benzylidene-1-methyl-2,5-dioxo-3-pipera zinylidene) methylbenzamide) was identified as a potent modulator of P-glycoprotein-mediated multidrug resistance (MDR) following a synthetic chemistry programme based on a natural product lead compound. The activity of XR9051 was determined using a panel of human and murine drug-resistant cell lines (H69/LX4, 2780AD, EMT6/AR 1.0, MC26 and P388/DX Johnson). XR9051 was able to reverse resistance to a variety of cytotoxic drugs, including doxorubicin, etoposide and vincristine, which are associated with classical MDR. At a concentration of 0.3-0.5 microM, XR9051 was able to fully sensitize resistant cells to cytotoxics, whereas little or no effect was observed on the corresponding parental cell lines. No effect of XR9051 was observed on the response of cells to non-MDR cytotoxics such as methotrexate and 5-fluorouracil. XR9051 was consistently more potent than cyclosporin A (CsA) and verapamil (Vpm) in all assays used. XR9051 inhibited the efflux of [3H]daunorubicin from preloaded cells and, unlike CsA and Vpm, remained active for several hours after removal of resistance-modifying agent. In photoaffinity labelling experiments employing [3H]azidopine, XR9051 was able to displace binding to P-glycoprotein. In binding studies using [3H]vinblastine, XR9051 was shown to be a potent inhibitor of the binding of the cytotoxic to P-glycoprotein (EC50 = 1.4 +/- 0.5 nM). Taken together, the results indicate that XR9051 reverses the MDR phenotype through direct interaction with P-glycoprotein.

Effects of verapamil on the pharmacokinetics and metabolism of epirubicin.

Experimental data suggest that multidrug resistance in cancer may be overcome by using an increased dose of anticancer agent(s) in combination with a resistance-modifying agent (RMA). We studied the pharmacokinetics and metabolism of both epirubicin (EPI) and verapamil (VPL) to explore the possible pharmacokinetic interactions between these two drugs. Ten patients with advanced breast cancer were given EPI (40 mg/m2 in a daily i.v. bolus for 3 consecutive days), and five of them also received VPL (4 x 120 mg/daily p.o. for 4 consecutive days). The data indicated a significant interaction between these two drugs that affected their metabolism. The areas under the concentration-time curves (AUC) obtained for epirubicin glucuronide, epirubicinol glucuronide, and both of the 7-deoxy-aglycones were higher in the EPI + VPL group as compared with the EPI group. The AUC, terminal half-life, mean residence time, volume of distribution at steady state, and plasma clearance of EPI alone as compared with EPI + VPL did not differ significantly. These results suggest either an induction of enzymes necessary for drug metabolism or an increase in the liver blood flow, resulting in an enhanced generation of metabolites with time or in an inhibition of excretion processes. Comparisons of the AUC values obtained for EPI and its metabolites after the first, second, and third injections of EPI revealed a cumulative effect for the metabolites that was more pronounced in the EPI + VPL group, being significant (P < 0.05) for epirubicin glucuronide in both treatment groups and for epirubicinol glucuronide in the EPI + VPL group. Maximal concentrations of VPL and nor-VPL reached 705 +/- 473 and 308 +/- 122 ng/ml, respectively, with the steady-state concentrations being 265 +/- 42 ng/ml for VPL and 180 +/- 12 ng/ml for nor-VPL.

Antiproliferative Effects of Mitoxantrone in Adr-Sensitive and Adr-Resistant P388 Leukemia Cells Enhanced by Vitamin K3

Vitamin K3 was employed as a resistance-modifying agent to investigate its activity in enhancing mitoxantrone (MITO)-induced cytotoxicity in parental (P388/S) and multidrug resistant (P388/ADR) P388 leukemia cells. Vitamin K3 potentiated the antitumor effects of MITO in P388/S and P388/ADR tumor cells as monitored by inhibition of tumor cell survival (MTT assay). MITO and vitamin K3 in combination effected an enhanced inhibition of [3H]thymidine (DNA synthesis) and [3H]uridine (RNA synthesis) and also increased the life span of the sensitive and resistant tumor-bearing animals. The effect of vitamin K3 on the induction of DNA strand breaks by MITO was also examined. Increased fragmentation of DNA was illustrated in the sensitive and resistant P388 leukemia cells exposed to the combination. Observations indicate the restoration of sensitivity in P388/ADR cells to MITO by vitamin K3 that may be due to its ability to increase the MITO-induced DNA strand breaks.