Fluoroquinolone Derivatives in the Treatment of Mycobacterium tuberculosis Infection.

Tuberculosis (TB) is currently one of the leading causes of death due to infective agents, and the growing rate of multidrug-resistant tuberculosis (MDR TB) cases poses an emergent public health threat. Fluoroquinolones are commonly used in the treatment of both MDR TB and drug-sensitive tuberculosis patients who are intolerant to first-line antitubercular agents. Unfortunately, these drugs have mild side effects, relevant to the prolonged treatment regimens and diminished bioavailability due to binding of metal ions. Moreover, the resistance to fluoroquinolones is also on the rise, a characteristic of extensively drug-resistant TB (XDR TB). Here, we developed esters as prodrugs of the fluoroquinolones levofloxacin and ciprofloxacin, with long-chain fatty alcohols. Both the alcohols and the quinolone have previously shown antimycobacterial activity and the aim was to develop esters with improved lipophilicity and capable of delivering the free acid inside mycobacterial cells. The carboxylic acid group of fluoroquinolones is essential to the mode of action but is also responsible for many of its side effects and metal-chelating properties. The synthesis, stability in biological media, and antibacterial activity were evaluated, the latter not only against Mycobacterium tuberculosis but also against other clinically relevant bacterial species, since the parent compounds display a broad spectrum of activity. The biological results show a reduction in the antitubercular activity of the synthesized derivatives, probably due to deficient activation of the ester prodrug. Despite this, it was found that the derivatives exhibit bioactivity against other fluoroquinolone-resistant bacteria, indicating a different mode of action and suggesting that it may be worthwhile to research further modifications to the carboxylic acid group. This might lead to new compounds that are efficient against resistant strains. This idea that the compounds may act by a different mechanism of action was further supported by a brief computer investigation that demonstrated the potential lack of selectivity of the esters to the fluoroquinolone target.

Plant Terpenoids as Hit Compounds against Trypanosomiasis.

Human African trypanosomiasis (sleeping sickness) and American trypanosomiasis (Chagas disease) are vector-borne neglected tropical diseases, caused by the protozoan parasites Trypanosoma brucei and Trypanosoma cruzi, respectively. These diseases were circumscribed to South American and African countries in the past. However, human migration, military interventions, and climate changes have had an important effect on their worldwide propagation, particularly Chagas disease. Currently, the treatment of trypanosomiasis is not ideal, becoming a challenge in poor populations with limited resources. Exploring natural products from higher plants remains a valuable approach to find new hits and enlarge the pipeline of new drugs against protozoal human infections. This review covers the recent studies (2016-2021) on plant terpenoids, and their semi-synthetic derivatives, which have shown promising in vitro and in vivo activities against Trypanosoma parasites.

Bioactive compounds from the African medicinal plant Cleistochlamys kirkii as resistance modifiers in bacteria.

Cleistochlamys kirkii (Benth) Oliv. (Annonaceae) is a medicinal plant traditionally used in Mozambique to treat infectious diseases. The aim of this study was to find resistance modifiers in C. kirkii for Gram-positive and Gram-negative model bacterial strains. One of the most important resistance mechanisms in bacteria is the efflux pump-related multidrug resistance. Therefore, polycarpol (1), three C-benzylated flavanones (2-4), and acetylmelodorinol (5) were evaluated for their multidrug resistance-reverting activity on methicillin-susceptible and methicillin-resistant Staphylococcus aureus and Escherichia coli AG100 and AG100 A strains overexpressing and lacking the AcrAB-TolC efflux pump system. The combined effects of antibiotics and compounds (2 and 4) were also assessed by using the checkerboard microdilution method in both S. aureus strains. The relative gene expression of the efflux pump genes was determined by real-time reverse transcriptase quantitative polymerase chain reaction. The inhibition of quorum sensing was also investigated. The combined effect of the antibiotics and compound 2 or 4 on the methicillin-sensitive S. aureus resulted in synergism. The most active compounds 2 and 4 increased the expression of the efflux pump genes. These results suggested that C. kirkii constituents could be effective adjuvants in the antibiotic treatment of infections.

Cleistochlamys kirkii chemical constituents: Antibacterial activity and synergistic effects against resistant Staphylococcus aureus strains.

ETHNOPHARMACOLOGICAL RELEVANCE: Cleistochlamys kirkii (Benth) Oliv., (Annonaceae) is a medicinal plant traditionally used in Mozambique to treat infectious diseases. AIMS OF THE STUDY: To find antibacterial lead compounds from C. kirkii and provide scientific validation for its use in traditional medicine. MATERIALS AND METHODS: Through bioassay-guided fractionation, nine compounds (1-9), with different scaffolds, were isolated from the methanol extract of C. kirkii whose structures were identified by spectroscopic methods. Compounds 1-9 were evaluated for their in vitro antibacterial activity against a panel of eight Gram-positive, including five drug-resistant strains of Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and two Gram-negative bacteria strains. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined. A chemosensitization assay, using the checkerboard method, was also performed in order to evaluate the type of interaction of compounds with antibiotics/compounds against two S. aureus resistant strains (ATCC 9144 and CIP 106760) and a susceptible strain (ATCC 6538). RESULTS: Dichamanetin (3), a rare C-benzylated flavanone, was very active against all the Gram-positive strains tested, displaying MIC values in the range of 1-7.5 µg/mL. The C-benzylated flavanones chamanetin (1), isochamanetin (2), and the α,ß-unsaturated lactone (-)-cleistenolide (6) also showed relevant antibacterial activity against some of the Gram-positive strains assayed. Compounds 4, 5, and 7-9 have shown no significant activity at the concentration ranges tested. In the combination with antibiotics, polycarpol (8) (MIC 125 µg/mL) showed a strong synergistic effect against the methicillin-resistant S. aureus ATCC 9144. When combined with oxacillin (MIC 125 µg/mL), compound 8 reduced the MIC to 1.5 µg/mL (FICI=0.11). Similarly, it reduced the MIC of amoxicillin (MIC 250 µg/mL) to 7.5 µg/mL (FICI=0.18). Synergy was also obtained when this compound was combined with both ß-lactam antibiotics (FICI=0.30) and with vancomycin (FICI=0.24) against vancomycin-intermediate S. aureus (VISA) CIP 106760. Remarkable, compound 8 was also able to reduce synergistically the MIC value of dichamanetin (3) (FICI=0.18) against this strain. CONCLUSIONS: These results suggested that C. kirkii constituents may be valuable as a leads for restoring antibiotic activity against resistant S. aureus strains.

Antioxidant and antimycotic activities of two native lavandula species from portugal.

The antioxidant and antimycotic activities of the essential oils and extracts of two native Portuguese Lavandula species, L. stoechas subsp. luisieri and L. pedunculata, were evaluated by in vitro assays. The total phenolics and flavonoids content were also determined. The antioxidant potential was assessed through DPPH radical scavenging, inhibition of lipid peroxidation (ILP), and DNA protection assays. All samples displayed a high DPPH scavenging activity, some of them showing concentration dependence. The majority of the samples were also able to inhibit lipid peroxidation. A strong correlation was observed between the results of DPPH and ILP assays and the flavonoids content of the samples. In the DNA protection assay, all the extracts were able to preserve DNA integrity. The antimycotic activity was performed against twelve fungi belonging to Basidiomycota and Ascomycota Divisions. L. stoechas subsp. luisieri exhibited the broadest activity spectra. L. pedunculata extracts were active against five fungi. Cryptococcus neoformans was the most sensitive, being inhibited by all the extracts. Our results led to the conclusion that L. stoechas subsp. luisieri and L. pedunculata can be useful as new sources of natural antioxidants and antimycotic agents, providing a possible valorization of the existing biodiversity and resources of Portuguese flora.

Improving the MDR reversal activity of 6,17-epoxylathyrane diterpenes.

Aiming to optimize macrocyclic lathyrane-type diterpenes as effective Pgp modulators, the phytochemical study of the methanolic extract of Euphorbia boetica aerial parts was carried out. Two new macrocyclic 6,17-epoxylathyrane-type diterpenes, named epoxyboetiranes A (1) and B (2), along with three known analogues (3-5) were isolated. Epoxyboetirane A (1), a triacetate isolated in large amounts, was hydrolyzed to give epoxylathyrol (6). In order to study the effect of the substitution pattern of the macrocyclic scaffold on MDR reversal, 6 was acylated with aroyl, phenylacetyl, cinnamoyl and alkanoyl chlorides/anhydrides, yielding eight new esters, epoxyboetiranes C-J (7-14). The ability of compounds 1-14 as P-glycoprotein (Pgp, ABCB1) modulators was evaluated through combination of transport and chemosensitivity assays, using L5178Y mouse T lymphoma cell line transfected with the human MDR1 gene. In the transport assay, excepting 1, 3 and 6, the compounds, at non-cytotoxic concentrations, displayed strong MDR reversing activity in a dose-dependent mode, exhibiting all the new acyl derivatives (7-14) a many fold increase in the activity when compared with 1. Apart from 11 and 12, all compounds exhibited remarkable synergistic effects in combination with doxorubicin. An ATPase assay, using membrane vesicles from mammalian cells overexpressing Pgp, was also performed with two representatives of the modulators (4 and 5). The results suggest that both compounds compete with substrates for the Pgp drug-binding sites.

The effects of jatrophane derivatives on the reversion of MDR1- and MRP-mediated multidrug resistance in the MDA-MB-231 (HTB-26) cell line.

Multidrug resistance (MDR) of cancer cells can be the result of a variety of mechanisms that are not completely understood. One of the most significant among them concerns altered membrane transport in tumor cells, often referred to as typical or classic MDR. This mechanism is related to the overexpression of a variety of proteins, that belong to the super family of ABC transporters. The aim or this study was to look for new effective modulators of MDR1 and multidrug resistance-associated protein (MRP) transporters. Ten diterpenes based on the jatrophane skeleton, including rearranged polycyclic derivatives, were studied on the MDA-MB-231 (HTB-26) human breast cancer cell line. The majority of those compounds were able to strongly enhance the rhodamine 123 accumulation of the human MDR1 gene transfected mouse lymphoma cell line, as previously described. In the present study, the MDR reversal of the same jatrophanes on MDR1- and MRP- mediated resistance of human breast cancer cells is reported. These cells simultaneously express MDR1 and MRP proteins when identified by monoclonal antibodies. However, in a functional assay, where rhodamine 123 accumulation was measured and verapamil was the traditional positive control, only MRP was active, while MDR1 was inactive. Carboxyfluorescein served as a substrate for MRP-mediated drug efflux, and indomethacine was the positive control used as an inhibitor of MRP in the flow cytometric experiments. The effectivity of various jatrophanes was different on the carboxyfluorescein efflux inhibition of the human breast cancer cells. These results may have importance in the planning of a new type of combination chemotherapy.

Effect of cycloartanes on reversal of multidrug resistance and apoptosis induction on mouse lymphoma cells.

The ability of fifteen cycloartanes, isolated from Euphorbia species, to reverse multidrug resistance (MDR) and apoptosis induction in L5178Y mouse lymphoma cells, including its multidrug-resistant subline, was studied by flow cytometry. Reversion of MDR was investigated using a standard functional assay with rhodamine 123 as a fluorescent substrate analogue. For the evaluation of apoptosis, the cells were stained with FITC-labeled annexin V and propidium iodide. The majority of the compounds were able to reverse MDR of the tested human MDR1 gene-transfected mouse lymphoma cells. Some of the compounds were able to induce moderate apoptosis in the PAR cell line, but this effect was less effective on multidrug-resistant cells. The results indicate that cycloartanes can be substrates of ABC transporters, which might compete with certain anticancer chemotherapeutics.