Mechanism Underlying the Reversal of Drug Resistance in P-Glycoprotein-Expressing Leukemia Cells by Pinoresinol and the Study of a Derivative

Rosmarinic Acid Present in Lepechinia floribunda and Lepechinia meyenii as a Potent Inhibitor of the Adenylyl Cyclase gNC1 from Giardia lamblia

Giardiasis is a parasitosis caused by Giardia lamblia with significant epidemiological and clinical importance due to its high prevalence and pathogenicity. The lack of optimal therapies for treating this parasite makes the development of new effective chemical entities an urgent need. In the search for new inhibitors of the adenylyl cyclase gNC1 obtained from G. lamblia, 14 extracts from Argentinian native plants were screened. Lepechinia floribunda and L. meyenii extracts exhibited the highest gNC1 inhibitory activity, with IC50 values of 9 and 31 µg/mL, respectively. In silico studies showed rosmarinic acid, a hydroxycinnamic acid present in both mentioned species, to be a promising anti-gNC1 compound. This result was confirmed experimentally, with rosmarinic acid showing an IC50 value of 10.1 µM. Theoretical and experimental findings elucidate the molecular-level mechanism of rosmarinic acid, pinpointing the key interactions stabilizing the compound-enzyme complex and the binding site. These results strongly support that rosmarinic acid is a promising scaffold for developing novel compounds with inhibitory activity against gNC1, which could serve as potential therapeutic agents to treat giardiasis.

Novel betulin derivatives as multidrug reversal agents targeting P-glycoprotein

Chemotherapy is a powerful means of cancer treatment but its efficacy is compromised by the emergence of multidrug resistance (MDR), mainly linked to the efflux transporter ABCB1/P-glycoprotein (P-gp). Based on the chemical structure of betulin, identified in our previous work as an effective modulator of the P-gp function, a series of analogs were designed, synthesized and evaluated as a source of novel inhibitors. Compounds 6g and 6i inhibited rhodamine 123 efflux in the P-gp overexpressed leukemia cells, K562/Dox, at concentrations of 0.19 µM and 0.39 µM, respectively, and increased the intracellular accumulation of doxorubicin at the submicromolar concentration of 0.098 µM. Compounds 6g and 6i were able to restore the sensitivity of K562/Dox to Dox at 0.024 µM and 0.19 µM, respectively. Structure-activity relationship analysis and molecular modeling revealed important information about the structural features conferring activity. All the active compounds fitted in a specific region involving mainly transmembrane helices (TMH) 4-6 from one homologous half and TMH 7 and 12 from the other, also showing close contacts with TMH 6 and 12. Compounds that bound preferentially to another region were inactive, regardless of their free energy of binding. It should be noted that compounds 6g and 6i were devoid of toxic effects against peripheral blood mononuclear normal cells and erythrocytes. The data obtained indicates that both compounds might be proposed as scaffolds for obtaining promising P-gp inhibitors for overcoming MDR.

A Novel 3-meta-Pyridine-1,2,4-oxadiazole Derivative of Glycyrrhetinic Acid as a Safe and Promising Candidate for Overcoming P-Glycoprotein-Mediated Multidrug Resistance in Tumor Cells

Given the pharmacophore properties of the nitrogen-containing moiety in the molecular structure of P-glycoprotein (P-gp) inhibitors, we report the evaluation of the P-gp inhibitory and MDR reversal activities of 2g, a 3-meta-pyridin-1,2,4-oxadiazole derivative of 18βH-glycyrrhetinic acid. Through molecular docking, we have shown that 2g has the potential to directly interact with the transmembrane domain of P-gp with a low free binding energy (-10.2 kcal/mol). Using KB-8-5 human cervical carcinoma cells and RLS40 murine lymphosarcoma cells, both of which exhibit a multidrug-resistant (MDR) phenotype mediated by P-gp activation, we have shown that 2g, at nontoxic concentrations, effectively increased the intracellular accumulation of fluorescent P-gp substrates (rhodamine 123 or doxorubicin (DOX)), leading to a marked sensitization of the model cells to the cytotoxic effect of DOX. Considering the comparable activity of 2g with verapamil, a known P-gp inhibitor, 2g can be considered as a promising candidate for the development of agents capable of overcoming P-gp-mediated MDR in tumor cells.

Application Value of Antimicrobial Peptides in Gastrointestinal Tumors

Gastrointestinal cancer is a common clinical malignant tumor disease that seriously endangers human health and lacks effective treatment methods. As part of the innate immune defense of many organisms, antimicrobial peptides not only have broad-spectrum antibacterial activity but also can specifically kill tumor cells. The positive charge of antimicrobial peptides under neutral conditions determines their high selectivity to tumor cells. In addition, antimicrobial peptides also have unique anticancer mechanisms, such as inducing apoptosis, autophagy, cell cycle arrest, membrane destruction, and inhibition of metastasis, which highlights the low drug resistance and high specificity of antimicrobial peptides. In this review, we summarize the related studies on antimicrobial peptides in the treatment of digestive tract tumors, mainly oral cancer, esophageal cancer, gastric cancer, liver cancer, pancreatic cancer, and colorectal cancer. This paper describes the therapeutic advantages of antimicrobial peptides due to their unique anticancer mechanisms. The length, net charge, and secondary structure of antimicrobial peptides can be modified by design or modification to further enhance their anticancer effects. In summary, as an emerging cancer treatment drug, antimicrobial peptides need to be further studied to realize their application in gastrointestinal cancer diseases.

An integrative computational approach for the identification of dual inhibitors of isocitrate dehydrogenase 1 and 2 from phytocompounds of Phyllantus amarus

Genetic alterations of the genes encoding the isocitrate dehydrogenase (IDH) enzymes have been identified in about 20% of acute myeloid leukemia (AML) cases as well as many other forms of cancers. Notable among these alterations are the neomorphic IDH1_R132H and IDH2_R140Q mutations which lead to the production of an oncometabolite. Hence, their inhibition is widely considered a therapeutic strategy in the treatment of many cancers. While many inhibitors of the mutant enzymes have been developed, an inhibitor that is capable of co-inhibiting both enzymes are currently lacking while drug resistance has also limited the clinical usage of previously identified mono inhibitors. Consequently, this study employed molecular modeling approaches, such as molecular docking, molecular mechanics generalized Born Surface area (MM/GBSA), molecular dynamics (MD) simulation, and density functional theory (DFT) analysis to identify potential dual inhibitors of the previously mentioned mutant IDH1/2 from the phytocompounds of Phyllantus amarus. Of the 31 phytocompounds identified, 20 showed good binding affinities for both IDH1 _R132H and IDH2 _R140Q (ranging from -5.2 Kca/mol to -9.6 Kcal/mol) and had desirable pharmacokinetic properties. However, ellagic acid and pinoresinol possessed better pharmacokinetic properties, rendering suitable hits. Investigation of the behavior of the IDH1_R132H and IDH2_R140Q complexes with ellagic acid and pinoresinol via the RMSD, RMSF, and contact map analyses showed that all the complexes-maintained stability throughout the simulation time. Ultimately, ellagic acid and pinoresinol were identified as promising hits for the development of IDH1_R132H and IDH2_R140Q dual inhibitors. However, further experimental studies are needed to confirm their potential as therapies.Communicated by Ramaswamy H. Sarma.

Microphysiological Conditions Do Not Affect MDR1-Mediated Transport of Rhodamine 123 above an Artificial Proximal Tubule

Despite disadvantages, such as high cost and their poor predictive value, animal experiments are still the state of the art for pharmaceutical substance testing. One reason for this problem is the inability of standard cell culture methods to emulate the physiological environment necessary to recapitulate in vivo processes. Microphysiological systems offer the opportunity to close this gap. In this study, we utilize a previously employed microphysiological system to examine the impact of pressure and flow on the transportation of substances mediated by multidrug resistance protein 1 (MDR1) across an artificial cell-based tubular barrier. By using a miniaturized fluorescence measurement device, we could continuously track the MDR1-mediated transport of rhodamine 123 above the artificial barrier over 48 h. We proved that applying pressure and flow affects both active and passive transport of rhodamine 123. Using experimental results and curve fittings, the kinetics of MDR1-mediated transport as well as passive transport were investigated; thus, a kinetic model that explains this transport above an artificial tubular barrier was identified. This kinetic model demonstrates that the simple Michaelis-Menten model is not an appropriate model to explain the MDR1-mediated transport; instead, Hill kinetics, with Hill slope of n = 2, is a better fit. The kinetic values, K_m, V_max, and apparent permeability (P_app), obtained in this study are comparable with other in vivo and in vitro studies. Finally, the presented proximal tubule-on-a-chip can be used for pharmaceutical substance testing and to investigate pharmacokinetics of the renal transporter MDR1.

P-glycoprotein, FK-binding Protein-12, and the Intracellular Tacrolimus Concentration in T-lymphocytes and Monocytes of Kidney Transplant Recipients

BACKGROUND

. Transplant recipients may develop rejection despite having adequate tacrolimus whole blood predose concentrations (C 0 ). The intra-immune cellular concentration is potentially a better target than C 0 . However, little is known regarding intracellular tacrolimus concentration in T-lymphocytes and monocytes. We investigated the tacrolimus concentrations in both cell types and their relation with the expression and activity of FK-binding protein (FKBP)-12 and P-glycoprotein (P-gp).

METHODS

. T-lymphocytes and monocytes were isolated from kidney transplant recipients followed by intracellular tacrolimus concentration measurement. FKBP-12 and P-gp were quantified with Western blot, flow cytometry, and the Rhodamine-123 assay. Interleukin-2 and interferon-γ in T-lymphocytes were measured to quantify the effect of tacrolimus.

RESULTS

. Tacrolimus concentration in T-lymphocytes was lower than in monocytes (15.3 [8.5-33.4] versus 131.0 [73.5-225.1] pg/million cells; P < 0.001). The activity of P-gp (measured by Rhodamine-123 assay) was higher in T-lymphocytes than in monocytes. Flow cytometry demonstrated a higher expression of P-gp (normalized mean fluorescence intensity 1.5 [1.2-1.7] versus 1.2 [1.1-1.4]; P = 0.012) and a lower expression of FKBP-12 (normalized mean fluorescence intensity 1.3 [1.2-1.7] versus 1.5 [1.4-2.0]; P = 0.011) in T-lymphocytes than monocytes. Western blot confirmed these observations. The addition of verapamil, a P-gp inhibitor, resulted in a 2-fold higher intra-T-cell tacrolimus concentration. This was accompanied by a significantly fewer cytokine-producing cells.

CONCLUSIONS

. T-lymphocytes have a higher activity of P-gp and lower concentration of the FKBP-12 compared with monocytes. This explains the relatively lower tacrolimus concentration in T-lymphocytes. The addition of verapamil prevents loss of intracellular tacrolimus during the cell isolation process and is required to ensure adequate intracellular concentration measurement.

Extracts from Argentinian native plants reverse fluconazole resistance in Candida species by inhibiting the efflux transporters Mdr1 and Cdr1

BACKGROUND

The development of multidrug resistance (MDR) associated with the overexpression of the efflux transporters Mdr1 and Cdr1 in Candida species impedes antifungal therapies. The urgent need for novel agents able to inhibit the function of both pumps, led us to evaluate this property in 137 extracts obtained from Argentinian plants.

METHODS

The ability of the extracts to reverse efflux pump-mediated MDR was determined with an agar chemosensitization assay using fluconazole (FCZ) resistant Mdr1- and Cdr1-overexpressing clinical isolates of Candida albicans and Candida glabrata as well as Saccharomyces cerevisiae strains selectively expressing Mdr1 (AD/CaMDR1) or Cdr1 (AD/CaCDR1). The resistance-reversing activity of the most potent extracts was further confirmed using a Nile Red accumulation assay.

RESULTS

Fifteen plant extracts overcame the FCZ resistance of Candida albicans 1114, which overexpresses CaMdr1 and CaCdr1, and AD/CaMDR1, with those from Acalypha communis and Solanum atriplicifolium being the most effective showing 4- to 16-fold reversal of resistance at concentrations ≥ 25 µg/mL. Both extracts, and to a lesser extent that from Pterocaulon alopecuroides, also restored FCZ sensitivity in CgCdr1-overexpressing C. glabrata 109 and in AD/CaCDR1 with fold reversal values ranging from 4 to 32 and therefore demonstrating a dual effect against Mdr1 and Cdr1. Both, A. communis and S. atriplicifolium extracts at concentrations ≥ 12.5 and ≥ 25 µg/mL, respectively, increased the intracellular Nile Red accumulation in all yeast strains overexpressing efflux pumps.

CONCLUSIONS

The non-toxic and highly active extracts from A. communis and S. atripicifolium, provide promising sources of compounds for potentiating the antifungal effect of FCZ by blocking the efflux function of Mdr1 and Cdr1 transporters.

Extra Virgin Olive Oil Secoiridoids Modulate the Metabolic Activity of Dacarbazine Pre-Treated and Treatment-Naive Melanoma Cells

Nowadays, many individuals, whether healthy or diagnosed with disease, tend to expose themselves to various easily accessible natural products in hopes of benefiting their health and well-being. Mediterranean populations have traditionally used olive oil not only in nutrition but also in cosmetics, including skincare. In this study, the phenolic profile—composed of twelve compounds altogether, including the secoiridoids oleocanthal (OCAL) and oleacein (OCEIN)—of extra virgin olive oil (EVOO) from autochthonous cultivars from Croatia was determined using ¹H qNMR spectroscopy and HPLC-DAD analysis, and its biological activity was investigated in melanoma cell lines. The EVOO with the highest OCEIN content had the strongest anti-cancer activity in A375 melanoma cells and the least toxic effect on the non-cancerous keratocyte cell line (HaCaT). On the other hand, pure OCAL was shown to be more effective and safer than pure OCEIN. Post-treatment with any of the EVOO phenolic extracts (EVOO-PEs) enhanced the anti-cancer effect of the anti-cancerous drug dacarbazine (DTIC) applied in pre-treatment, while they did not compromise the viability of non-cancerous cells. The metastatic melanoma A375M cell line was almost unresponsive to the EVOO-PEs themselves, as well as to pure OCEIN and OCAL. Our results demonstrate that olive oils and/or their compounds may have a potentially beneficial effect on melanoma treatment. However, their usage can be detrimental or futile, especially in healthy cells, due to inadequately applied concentrations/combinations or the presence of resistant cells.

Structure activity relationships and the binding mode of quinolinone-pyrimidine hybrids as reversal agents of multidrug resistance mediated by P-gp

P-gp-associated multidrug resistance is a major impediment to the success of chemotherapy. With the aim of finding non-toxic and effective P-gp inhibitors, we investigated a panel of quinolin-2-one-pyrimidine hybrids. Among the active compounds, two of them significantly increased intracellular doxorubicin and rhodamine 123 accumulation by inhibiting the efflux mediated by P-gp and restored doxorubicin toxicity at nanomolar range. Structure-activity relationships showed that the number of methoxy groups, an optimal length of the molecule in its extended conformation, and at least one flexible methylene group bridging the quinolinone to the moiety bearing the pyrimidine favored the inhibitory potency of P-gp. The best compounds showed a similar binding pattern and interactions to those of doxorubicin and tariquidar, as revealed by MD and hybrid QM/MM simulations performed with the recent experimental structure of P-gp co-crystallized with paclitaxel. Analysis of the molecular interactions stabilizing the different molecular complexes determined by MD and QTAIM showed that binding to key residues from TMH 4-7 and 12 is required for inhibition.

Increasing the accumulation of aptamer AS1411 and verapamil conjugated silver nanoparticles in tumor cells to enhance the radiosensitivity of glioma

Radioresistance significantly decreases the efficacy of radiotherapy, which can ultimately lead to tumor recurrence and metastasis. As a novel type of nano-radiosensitizer, silver nanoparticles (AgNPs) have shown promising radiosensitizing properties in the radiotherapy of glioma, but their ability to efficiently enter and accumulate in tumor cells needs to be improved. In the current study, AS1411 and verapamil (VRP) conjugated bovine serum albumin (BSA) coated AgNPs (AgNPs@BSA-AS-VRP) were synthesized and characterized. Dark-field imaging and inductively coupled plasma mass spectrometry were applied to investigate the accumulation of AgNPs@BSA-AS and AgNPs@BSA-AS-VRP mixed in different ratios in U251 glioma cells. To assess the influences of 19:1 mixed AgNPs@BSA-AS and AgNPs@BSA-AS-VRP on the P-glycoprotein (P-gp) efflux activity, rhodamine 123 accumulation assay was carried out. Colony formation assay and tumor-bearing nude mice model were employed to examine the radiosensitizing potential of 19:1 mixed AgNPs@BSA-AS and AgNPs@BSA-AS-VRP. Thioredoxin Reductase (TrxR) Assay Kit was used to detect the TrxR activity in cells treated with different functionally modified AgNPs. Characterization results revealed that AgNPs@BSA-AS-VRP were successfully constructed. When AgNPs@BSA-AS and AgNPs@BSA-AS-VRP were mixed in a ratio of 19:1, the amount of intracellular nanoparticles increased greatly through AS1411-mediated active targeting and inhibition of P-gp activity. In vitro and in vivo experiments clearly showed that the radiosensitization efficacy of 19:1 mixed AgNPs@BSA-AS and AgNPs@BSA-AS-VRP was much stronger than that of AgNPs@BSA and AgNPs@BSA-AS. It was also found that 19:1 mixed AgNPs@BSA-AS and AgNPs@BSA-AS-VRP significantly inhibited intracellular TrxR activity. These results indicate that 19:1 mixed AgNPs@BSA-AS and AgNPs@BSA-AS-VRP can effectively accumulate in tumor cells and have great potential as high-efficiency nano-radiosensitizers in the radiotherapy of glioma.

Cytotoxic Activity of Germacrane-Type Sesquiterpene Lactones from Dimerostemma aspilioides

The need for effective candidates as cytotoxic drugs that at the same time challenge cancer multidrug resistance encouraged a search for these in plants of central Argentina. Bioassay-guided fractionation of the cytotoxic extract from Dimerostemma aspilioides led to the isolation of the germacranolide tomenphantin A (1), along with three new analogues (2-4). These efficiently inhibited the proliferation of the leukemia cell lines K562 and CCRF-CEM and their resistant variants, Lucena 1 and CEM/ADR5000, respectively, with IC₅₀ values ranging from 0.40 to 7.7 μM. The structures and relative configurations of compounds 1-4 were elucidated by analysis of the spectroscopic data, in particular NMR spectroscopy. The most active among these was compound 1 (IC₅₀ = 0.40-5.1 μM), and, therefore, this was selected as a model for a mechanistic study, which revealed that its antiproliferative effect was mediated by cell cycle arrest in the G₂/M phase followed by apoptosis. The activity of compound 1 was selective, given the absence of cytotoxicity toward peripheral blood mononuclear cells. The results show the potential of these compounds, and in particular of compound 1, as leads for the development of drug candidates to fight sensitive and resistant leukemia cells.

The art of suicidal molecular seduction for targeting drug resistance

The development of drug resistance is one of the most significant challenges of the current century in the pharmaceutical industry. Superinfections, cancer chemoresistance, and resistance observed in many non-infectious diseases are nullifying the efforts and monetary supplies, put in the advent of new drug molecules. Millions of people die because of this drug resistance developed gradually through extensive use of the drugs. Inherently, some drugs are less prone to become ineffective by drug resistance than others. Covalent inhibitors bind to their targets via a biologically permanent bound with their cognate receptor and therefore display more potent inhibiting characteristics. Suicide inhibitors or mechanism-based inhibitors are one of the covalent inhibitors, which require a pre-activation step by their targeting enzyme. This step accrues their selectivity and specificity with respect to other covalent inhibitors. After that pre-activation step, they produce an analogue of the transition state of the catalytic enzyme, which is practically incapable of dissociating from the enzyme. Suicide inhibitors, due to their high intrinsic affinity toward the related enzyme, are resistant to many mechanisms involved in the development of drug resistance and can be regarded as one of the enemies of this scientific hurdle. These inhibitors compete even with monoclonal antibodies in terms of their cost-effectiveness and efficacy.

Dual-responsive TPGS crosslinked nanocarriers to overcome multidrug resistance

Efficient delivery of chemotherapeutic agents into tumor cells and reversal of chemoresistance are crucially important to enhance cancer therapy.

Synthesis and structure-activity relationships of novel abietane diterpenoids with activity against Staphylococcus aureus

Aim: To find alternative compounds against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA), novel derivatives from dehydroabietic acid were synthesized. Methods & results: Compound 12 was the most effective against 15 MRSA and 11 MSSA with minimum inhibitory concentration values ranging from 3.9 to 15.6 μg/ml. Although less active than 12, compound 11, followed by 25 and 13, also exhibited anti-staphylococcal activity. Additional studies showed that compound 12 is devoid of toxic effect on non-target cells. A structure-activity relationship study revealed that an oxime at C-13 together with a hydroxyl at C-12 could play a key role in the activity. Conclusion: These structures, in particular compound 12, could arise as templates for the development of agents against MRSA and MSSA.

Accelerated degradation of cFLIPL and sensitization of the TRAIL DISC-mediated apoptotic cascade by pinoresinol, a lignan isolated from Rubia philippinensis

Plant-derived lignans have numerous biological effects including anti-tumor and anti-inflammatory activities. Screening of purified constituents of Rubia philippinensis from human glioblastoma cells resistant to TNF-related apoptosis-inducing ligand (TRAIL) has suggested that the lignan pinoresinol was a highly active TRAIL sensitizer. Here we show that treatment with nontoxic doses of pinoresinol in combination with TRAIL induced rapid apoptosis and caspase activation in many types of glioblastoma cells, but not in normal astrocytes. Analyses of apoptotic signaling events revealed that pinoresinol enhanced the formation of TRAIL-mediated death-inducing signaling complex (DISC) and complete processing of procaspase-8 within the DISC in glioblastoma cells, in which caspase-8 was inactivated. Mechanistically, pinoresinol downregulated the expression of cellular FLICE-inhibitory protein (cFLIP_L) and survivin through proteasome-mediated degradation, without affecting death receptors or downstream intracellular apoptosis-related proteins. Furthermore, the sensitization of TRAIL-mediated apoptosis by pinoresinol strictly depended on the expression level of cFLIP_L, which was regulated through de novo protein synthesis, rather than by NF-κB or p53 signaling. Taken together, our results indicate that pinoresinol facilitates DISC-mediated caspase-8 activation by targeting cFLIP_L in an early event in apoptotic signaling, which provides a potential therapeutic module for TRAIL-based chemotherapy.

Antibacterial effects of extracts obtained from plants of Argentina: Bioguided isolation of compounds from the anti-infectious medicinal plant Lepechinia meyenii

ETHNOPHARMACOLOGICAL RELEVANCE

The mostly native species from Argentina are used in traditional medicine generally for the treatment of pain and inflammation, respiratory, gastro-intestinal and urinary disorders and as antiseptics.

AIM OF THE STUDY

Since these ailments may be associated with bacterial infections and that it is necessary to discover alternative compounds with antibacterial activity, 69 extracts from these plants were screened for their activity against pathogenic bacteria. The most effective extract was then submitted to bioguided isolation to obtain the compounds responsible for this activity.

MATERIALS AND METHODS

Extracts and fractions were screened using agar dilution, and compounds using microbroth dilution methods. A large panel of pathogenic bacteria was used, especially methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Bioguided fractionation was performed using successive chromatographic techniques, while the chemical structures of the isolated compounds were determined by nuclear magnetic resonance (NMR). Additionally, a series of derivatives of the most active compound were prepared in order to study the chemical features required for achieving the antibacterial effect.

RESULTS

Lepechinia meyenii (Walp.) Epling (Lamiaceae) extract showed itself the most effective, with minimum inhibitory concentration (MIC) against Gram positive and negative bacteria ranging from 62.5 to 500 μg/mL, and showing better activity on MRSA than on MSSA. Activity-guided fractionation yielded the abietanes carnosol (1), rosmanol (2) and carnosic acid (3) as active principles, with MICs ranging from 15.6-31.2, 15.6-62.5 and 7.8-15.6 μg/mL, respectively against 15 MRSA strains, and 15.6-31.2, 31.2-62.5 and 7.8-15.6 μg/mL, respectively against 11 MSSA strains, maintaining higher activity against the resistant bacteria, as does the extract. In addition, Enterococcus faecalis was sensitive to 1-3 with MICs of 15.6-62.5 μg/mL. The structure activity analysis showed that 12-OH is necessary for remarkable activity, but methylation in C-20 significantly increased this, as observed with 20-methyl carnosate (5) displaying the greatest effect, even more so than 3, with MICs of 3.9 μg/mL against all the tested MRSA and 3.9-7.8 μg/mL against the MSSA.

CONCLUSIONS

The results of this study contribute to validate the traditional antibacterial use of species native to Argentina, particularly of L. meyenii. The chemical structures of the compounds obtained may aid the design of antibacterial agents, especially those effective against MRSA.

Usnea Acid as Multidrug Resistance (MDR) Reversing Agent against Human Chronic Myelogenous Leukemia K562/ADR Cells via an ROS Dependent Apoptosis

PURPOSE

Multidrug resistance (MDR) is a major obstacle in chemotherapy of leukemia treatments. In this paper, we investigated Usnea Acid (UA) as MDR reversal agent on hematologic K562/ADR cells via ROS dependent apoptosis.

METHODS

CCK8 assay was used to measure cell viability rate of K562/ADR. Intracellular reactive oxygen species (ROS) generation, cell cycle distribution, cell apoptosis were measured with flow cytometry, respectively. Proteins related to apoptosis were measured by Western blot. Intracellular Adriamycin accumulation was observed by confocal microscopy and measured by flow cytometry.

RESULTS

In vitro study showed intracellular Adriamycin accumulation was remarkably increased by UA. Cell viability treated with Adr (4 μM) was decreased from 89.8%  ± 4.7 to 32%  ± 8.9 by combined with UA (4 μM). Adr-induced apoptosis and G1/G0 phase cell cycle arrest were remarkably increased by UA, as well as, intracellular ROS level. However, MDR reversing activity of UA was inhibited by N-acetyl cysteine (NAC), a ROS scavenger.

CONCLUSION

These data provide compelling evidence that UA is a promising agent against MDR in leukemia cell line and suggest a promising therapeutic approach for leukemia.

Inhibitory effects of compounds isolated from Lepechinia meyenii on tyrosinase

To contribute enzymatic browning inhibitors to the food industry and also extend knowledge about the phytochemical profile of the anti-tyrosinase plant Lepechinia meyenii, its ethanol extract was subjected to bioguided fractionation. Three hydroxycinnamic acids, p-coumaric acid (1), caffeic acid (2) and rosmarinic acid (3), were isolated as mainly responsible for its activity. Compounds 1, 2 and 3 showed themselves highly effective for inhibiting tyrosinase with IC₅₀ values of 0.30, 1.50 and 4.14 μM, respectively, for monophenolase activity and 0.62, 2.30 and 8.59 μM, respectively for diphenolase activity. This is the first report describing the isolation of the compounds causing the tyrosinase inhibitory activity of L. meyenii extract. The inhibitory kinetics of 1-3 using both L-tyrosine and L-DOPA as substrates was investigated and the results obtained were discussed at molecular level by docking analysis. The resulting compounds 1-3 and a phenolic-enriched fraction of the extract, 2.9-fold more active than the starting material, may be suitable as non-toxic and inexpensive alternatives for the control of deleterious enzymatic darkening.

Analogues of the Lignan Pinoresinol as Novel Lead Compounds for P-glycoprotein (P-gp) Inhibitors

To find novel P-gp-inhibitors, a library of pregnane X receptor (PXR) ligands and the ZINC DrugsNow library were superimposed on the P-gp inhibitor (+)-pinoresinol (1) used as a query for a three-dimensional similarity search. After determining the TanimotoCombo index of similarity with 1, eight compounds from the PXR library and two ZINC compounds were selected for biological evaluation. The P-gp inhibition study showed that compounds 7, 8, and 9 successfully increased intracellular doxorubicin (DOX) accumulation in the P-gp overexpressed Lucena 1 cells from 25, 12.5, and 6.25 μM, respectively. Among a series of analogues of 9, compounds 26-30 were shown to be active, with 26 and 27 causing a significant increase in DOX accumulation from 1.56 μM and rendering Lucena 1 sensitive to DOX from 1.56 and 0.78 μM, respectively. Molecular modeling studies showed that both compounds bind to the P-gp at transmembrane helices (TMH) 4, 5, and 6, with 27 also showing contacts with TMH 3.

Entinostat reverses P-glycoprotein activation in snail-overexpressing adenocarcinoma HCC827 cells

Epithelial-to-mesenchymal transition (EMT) in cancer cells facilitates tumor progression by promoting invasion and metastasis. Snail is a transcriptional factor that induces EMT, while P-glycoprotein (P-gp) is an efflux transporter involved in anticancer drug resistance, and P-gp efflux activity is stimulated in Snail-overexpressing lung cancer cells with EMT characteristics. Since the histone deacetylase (HDAC) inhibitor entinostat (Ent) reverses EMT features, our aim in this study was to determine whether Ent also suppresses P-gp activation in Snail-induced cells. First, we confirmed that Ent treatment reduced migration activity, downregulated E-cadherin and upregulated vimentin at the mRNA level in Snail-overexpressing cells, thus inhibiting EMT. Efflux and uptake assays using rhodamine123 (Rho123), a fluorescent P-gp substrate, showed that Ent also inhibited Snail-induced activation of P-gp. Moreover, P-gp activity was more strongly inhibited by Ent in Snail-overexpressing cells than in Mock cells. When we evaluated the uptakes of Rho123 by LLC-PK1 cells and P-gp-overexpressing LLC-GA5COL150 cells, Rho123 accumulation in LLC-GA5COL150 cells was significantly decreased compared with that in LLC-PK1 cells. Coincubation with Ent had no effect on Rho123 accumulation in either of the cell lines. Thus, Ent appears to be an inhibitor, but not a substrate, of P-gp at low concentration. Our results suggest that Ent treatment might suppress not only Snail-induced cancer malignant alteration, but also P-gp-mediated multidrug resistance.

Cytotoxic Activity of Extracts from Plants of Central Argentina on Sensitive and Multidrug-Resistant Leukemia Cells: Isolation of an Active Principle from Gaillardia megapotamica

Plants are a significant reservoir of cytotoxic agents, including compounds with the ability to interfere with multidrug-resistant (MDR) cells. With the aim of finding promising candidates for chemotherapy, 91 native and naturalized plants collected from the central region of Argentina were screened for their cytotoxic effect toward sensitive and MDR P-glycoprotein (P-gp) overexpressing human leukemia cells by means of MTT assays. The ethanol extracts obtained from Aldama tucumanensis, Ambrosia elatior, Baccharis artemisioides, Baccharis coridifolia, Dimerostemma aspilioides, Gaillardia megapotamica, and Vernonanthura nudiflora presented outstanding antiproliferative activity at 50 μg/mL, with inhibitory values from 93 to 100%, when tested on the acute lymphoblastic leukemia (ALL) cell line CCRF-CEM and the resistant derivative CEM-ADR5000, while 70-90% inhibition was observed against the chronic myelogenous leukemia (CML) cell K562 and its corresponding resistant subline, Lucena 1. Subsequent investigation showed these extracts to possess marked cytotoxicity with IC50 values ranging from 0.37 to 29.44 μg/mL, with most of them being below 7 μg/mL and with ALL cells, including the drug-resistant phenotype, being the most affected. G. megapotamica extract found to be one of the most effective and bioguided fractionation yielded helenalin (1). The sesquiterpene lactone displayed IC50 values of 0.63, 0.19, 0.74, and 0.16 μg/mL against K562, CCRF-CEM, Lucena 1, and CEM/ADR5000, respectively. These results support the potential of these extracts as a source of compounds for treating sensitive and multidrug-resistant leukemia cells and support compound 1 as a lead for developing effective anticancer agents.

Novel Quinoxaline-2-Carbonitrile-1,4-Dioxide Derivatives Suppress HIF1α Activity and Circumvent MDR in Cancer Cells

A series of 3-aryl/hetarylquinoxaline-2-carbonitrile-1,4-dioxides was synthesized and evaluated against breast cancer cell lines in normoxia and hypoxia. Selected compounds in this series demonstrated better cytotoxicity and comparable hypoxia selectivity than tirapazamine. In contrast to Dox, quinoxaline-1,4-dioxides showed potent cytotoxicity against different MDR cells. Compound 2g inhibits of cancer cell growth through p53-independent mechanisms. Our results showed that compound 2g sensitized MCF-7 cells to metformin in hypoxia. Treatment with 2g results in the increase of ROS accumulation in cancer cells. Compound 2g can be considered as the lead compound for further anticancer drug design, evaluation, and development of new potent antitumor agents.