Pharmacokinetic studies of naproxen amides of some amino acid esters with promising colorectal cancer chemopreventive activity

Naproxen (nap) is belonging to Non-steriodal anti-inflammatory drugs (NSAIDs) group of drugs that characterized by their free carboxylic group. The therapeutic activity of nap is usually accompanied by GI untoward side effects. Recently synthesized naproxen amides of some amino acid esters prodrugs to mask the free carboxylic group were reported. Those prodrugs showed a promising colorectal cancer chemopreventive activity. The current study aims to investigate the fate and hydrolysis of the prodrugs kinetically in different pH conditions, simulated gastric and intestinal fluids with pHs of 1.2, 5.5 and 7.4 in vitro at 37 °C. The effect of enzymes on the hydrolysis of prodrugs was also studied through incubation of these prodrugs at 37 °C in human plasma and rat liver homogenates. The pharmacokinetic parameters of selected prodrugs and the liberated nap were studied after oral and intraperitoneal administration in male wistar rats. The results showed the hydrolysis of naproxen amides of amino acid esters to nap through two steps first by degradation of the ester moiety to form the amide of nap with amino acid and the second was through the degradation of the amide link to liberate nap. The two reactions were followed and studied kinetically where K₁ and K₂ (rate constants of degradation) is reported. The hydrolysis of prodrugs was faster in liver homogenates than in plasma. The relative bioavailability of the liberated nap in vivo was higher in case of prodrug containing ethyl glycinate moiety than that occupied l-valine ethyl ester moiety. Each of nap. prodrugs containing ethyl glycinate and l-valine ethyl ester moieties appears promising in liberating nap, decreasing direct GI side effect and consequently their colorectal cancer chemopreventive activity.     

N,N'-Dialkylaminoalkylcarbonyl (DAAC) prodrugs and aminoalkylcarbonyl (AAC) prodrugs of 4-hydroxyacetanilide and naltrexone with improved skin permeation properties

N,N′-Dialkylaminoalkylcarbonyl (DAAC) and aminoalkylcarbonyl (AAC) prodrugs of phenolic drugs acetaminophen (APAP) and naltrexone (NTX) are reported. The effects of incorporation of a basic amine group into the promoiety of an acyl prodrug of a phenolic drug on its skin permeation properties are also presented. DAAC-APAP prodrugs were synthesized via a three-step procedure starting with haloalkylcarbonyl esters which were reacted with five different amines: dimethylamine, diethylamine, dipropylamine, morpholine, and piperidine. The spacing between the amino group and the carbonyl group of the acyl group was 1-3 CH₂. After the hydrolysis of the ester, the carboxylic acid product was subsequently coupled with the parent drug via a dicyclohexyl carbodiimide (DCC) mediated coupling to yield the DAAC-APAP-HCl prodrugs in excellent yields. The AAC prodrugs were synthesized using commercially available Boc-protected amino acids using DCC or EDCI as coupling agents. The yields of the prodrugs synthesized using these two different methods have been compared. Half-lives (t_1/2) of a few members of the DAAC and AAC series were measured in buffer (pH 6.0, 20 mM). The members evaluated in hydrolysis experiments exhibit a t_1/2 range of 15-113 min. Among AAC-APAP prodrugs, the isopropyl group in valinate-APAP-HCl exerted a steric effect that increased the t_1/2 value for this prodrug compared to alaninate-APAP-HCl or prolinate-APAP-HCl. The 2-morpholinylacetate-APAP prodrug was able to achieve twice the flux of APAP in in vitro diffusion cell experiments through hairless mouse skin.     

Design, synthesis and antimycobacterial activities of 1-methyl-2-alkenyl-4(1H)-quinolones

A series of 23 new 1-methyl-2-alkenyl-4(1H)quinolones have been synthesized and evaluated in vitro for their antimycobacterial activities against fast growing species of mycobacteria, such as Mycobacterium fortuitum, M. smegmatis and M. phlei. The compounds displayed good to excellent inhibition of the growth of the mycobacterial test strains with improved antimycobacterial activity compared to the hit compound, evocarpine. The most active compounds, which possessed chain length of 11-13 carbons at position-2 displayed potent inhibitory effects with an MIC value of 1.0 mg/L. In a human diploid embryonic lung cell line, MRC-5 cytotoxicity assay, the alkaloids showed weak to moderate cytotoxic activity. Biological evaluation of these evocarpine analogues on the less pathogenic fast growing strains of mycobacteria showed an interesting antimycobacterial profile and provided significant insight into the structure-activity relationships.     

Acanthamoeba polyphaga-enhanced growth of Mycobacterium smegmatis

Background

Mycobacterium smegmatis is a rapidly-growing mycobacterium causing rare opportunistic infections in human patients. It is present in soil and water environments where free-living amoeba also reside, but data regarding M. smegmatis-amoeba relationships have been contradictory from mycobacteria destruction to mycobacteria survival.

Methodology/Principal Findings

Using optic and electron microscopy and culture-based microbial enumeration we investigated the ability of M. smegmatis mc² 155, M. smegmatis ATCC 19420^T and M. smegmatis ATCC 27204 organisms to survive into Acanthamoeba polyphaga trophozoites and cysts. We observed that M. smegmatis mycobacteria penetrated and survived in A. polyphaga trophozoites over five-day co-culture resulting in amoeba lysis and the release of viable M. smegmatis mycobacteria without amoebal cyst formation. We further observed that amoeba-co-culture, and lysed amoeba and supernatant and pellet, significantly increased five-day growth of the three tested M. smegmatis strains, including a four-fold increase in intra-amoebal growth.

Conclusions/Significance

Amoebal co-culture increases the growth of M. smegmatis resulting in amoeba killing by replicating M. smegmatis mycobacteria. This amoeba-M. smegmatis co-culture system illustrates an unusual paradigm in the mycobacteria-amoeba interactions as mycobacteria have been mainly regarded as amoeba-resistant organisms. Using these model organisms, this co-culture system could be used as a simple and rapid model to probe mycobacterial factors implicated in the intracellular growth of mycobacteria.     

MmpL11 Protein Transports Mycolic Acid-containing Lipids to the Mycobacterial Cell Wall and Contributes to Biofilm Formation in Mycobacterium smegmatis

A growing body of evidence indicates that MmpL (mycobacterial membrane protein large) transporters are dedicated to cell wall biosynthesis and transport mycobacterial lipids. How MmpL transporters function and the identities of their substrates have not been fully elucidated. We report the characterization of Mycobacterium smegmatis MmpL11. We showed previously that M. smegmatis lacking MmpL11 has reduced membrane permeability that results in resistance to host antimicrobial peptides. We report herein the further characterization of the M. smegmatis mmpL11 mutant and identification of the MmpL11 substrates. We found that biofilm formation by the M. smegmatis mmpL11 mutant was distinct from that by wild-type M. smegmatis. Analysis of cell wall lipids revealed that the mmpL11 mutant failed to export the mycolic acid-containing lipids monomeromycolyl diacylglycerol and mycolate ester wax to the bacterial surface. In addition, analysis of total lipids indicated that the mycolic acid-containing precursor molecule mycolyl phospholipid accumulated in the mmpL11 mutant compared with wild-type mycobacteria. MmpL11 is encoded at a chromosomal locus that is conserved across pathogenic and nonpathogenic mycobacteria. Phenotypes of the M. smegmatis mmpL11 mutant are complemented by the expression of M. smegmatis or M. tuberculosis MmpL11, suggesting that MmpL11 plays a conserved role in mycobacterial cell wall biogenesis.     

Identification of small RNAs in Mycobacterium smegmatis using heterologous Hfq

Gene regulation by small RNAs (sRNAs) has been extensively studied in various bacteria. However, the presence and roles of sRNAs in mycobacteria remain largely unclear. Immunoprecipitation of RNA chaperone Hfq to enrich for sRNAs is one of the effective methods to isolate sRNAs. However, the lack of an identified mycobacterial hfq restricts the feasibility of this approach. We developed a novel method that takes advantage of the conserved inherent sRNAs-binding capability of heterologous Hfq from Escherichia coli to enrich sRNAs from Mycobacterium smegmatis, a model organism for studying Mycobacterium tuberculosis. We validated 12 trans-encoded and 12 cis-encoded novel sRNAs in M. smegmatis. Many of these sRNAs are differentially expressed at exponential phase compared with stationary phase, suggesting that sRNAs are involved in the growth of mycobacteria. Intriguingly, five of the cis-encoded novel sRNAs target known transposases. Phylogenetic conservation analysis shows that these sRNAs are pathogenicity dependent. We believe that our findings will serve as an important reference for future analysis of sRNAs regulation in mycobacteria and will contribute significantly to the development of sRNAs prediction programs. Moreover, this novel method of using heterologous Hfq for sRNAs enrichment can be of general use for the discovery of bacterial sRNAs in which no endogenous Hfq is identified.     

A Novel marRAB Operon Contributes to the Rifampicin Resistance in Mycobacterium smegmatis

The multiple-antibiotic resistance regulator (MarR) plays an important role in modulating bacterial antibiotic resistance. However, the regulatory model of the marRAB operon in mycobacteria remains to be characterized. Here we report that a MarR, encoded by Ms6508, and its marRAB operon specifically contribute to rifampicin (RIF) resistance in Mycobacterium smegmatis. We show that the MarR recognizes a conserved 21-bp palindromic motif and negatively regulates the expression of two ABC transporters in the operon, encoded by Ms6509–6510. Unlike other known drug efflux pumps, overexpression of these two ABC transporters unexpectedly increased RIF sensitivity and deletion of these two genes increased mycobacterial resistance to the antibiotic. No change can be detected for the sensitivity of recombinant mycobacterial strains to three other anti-TB drugs. Furthermore, HPLC experiments suggested that Ms6509–Ms6510 could pump RIF into the mycobacterial cells. These findings indicated that the mycobacterial MarR functions as a repressor and constitutively inhibits the expression of the marRAB operon, which specifically contributes to RIF resistance in M. smegmatis. Therefore, our data suggest a new regulatory mechanism of RIF resistance and also provide the new insight into the regulatory model of a marRAB operon in mycobacteria.     

Real-time PCR detection of environmental mycobacteria in house dust

Analysing the number and species of microbes in indoor dust is needed for assessment of human exposure to microbes in dwellings. Environmental mycobacteria are common heterotrophic bacteria in both natural and man-made environments and potential inducers of human immune system. Culture of mycobacteria from samples rich with other microbes is difficult due to the slow growth rate of mycobacteria and this has hampered the studies on their role in indoor human exposure. A quantitative, real-time 5'-nuclease (TaqMan) PCR assay was developed to detect environmental mycobacteria in indoor dust samples. The specificity of the primers and the probe targeting the 16S rDNA of mycobacteria, tested with 26 mycobacterial and 10 non-mycobacterial but related species, proved to be high. When tested on 20 indoor dust samples collected from five homes, the assay gave counts varying between 4.8 × 10⁴ and 7.2 × 10⁶ cell/g, being on average 1.1 × 10³ times higher than culture. Seasonal variation in the dust counts of mycobacteria was observed by both culture and qPCR. Total of 140 isolates considered as mycobacteria by Ziehl-Neelsen staining and GLC-analyses were subjected to PCR analysis with the mycobacterial primers, and 39 isolates to partial 16S rDNA sequencing. All proved to be mycobacteria and revealed high diversity of mycobacterial species in the dust samples. Majority of the sequences were related to M. terrae and M. avium complexes.     

Synthesis and pharmacological evaluation of nucleoside prodrugs designed to target siderophore biosynthesis in Mycobacterium tuberculosis

The nucleoside antibiotic, 5′-O-[N-(salicyl)sulfamoyl]adenosine (1), possesses potent whole-cell activity against Mycobacterium tuberculosis (Mtb), the etiological agent of tuberculosis (TB). This compound is also active in vivo, but suffers from poor drug disposition properties that result in poor bioavailability and rapid clearance. The synthesis and evaluation of a systematic series of lipophilic ester prodrugs containing linear and α-branched alkanoyl groups from two to twelve carbons at the 3′-position of a 2′-fluorinated analog of 1 is reported with the goal to improve oral bioavailability. The prodrugs were stable in simulated gastric fluid (pH 1.2) and under physiological conditions (pH 7.4). The prodrugs were also remarkably stable in mouse, rat, and human serum (relative serum stability: human ∼ rat ≫ mouse) displaying a parabolic trend in the SAR with hydrolysis rates increasing with chain length up to eight carbons (t_1/2 = 1.6 h for octanoyl prodrug 7 in mouse serum) and then decreasing again with higher chain lengths. The permeability of the prodrugs was also assessed in a Caco-2 cell transwell model. All of the prodrugs were found to have reduced permeation in the apical-to-basolateral direction and enhanced permeation in the basolateral-to-apical direction relative to the parent compound 2, resulting in efflux ratios 5–28 times greater than 2. Additionally, Caco-2 cells were found to hydrolyze the prodrugs with SAR mirroring the serum stability results and a preference for hydrolysis on the apical side. Taken together, these results suggest that the described prodrug strategy will lead to lower than expected oral bioavailability of 2 and highlight the contribution of intestinal esterases for prodrug hydrolysis.     

A diazen-1-ium-1,2-diolated nitric oxide donor ester prodrug of 3-(4-hydroxymethylphenyl)-4-(4-methanesulfonylphenyl)-5H-furan-2-one: synthesis, biological evaluation and nitric oxide release studies

A novel hybrid nitric oxide-releasing anti-inflammatory (AI) ester prodrug (NONO-coxib 14) wherein an O²-acetoxymethyl 1-(2-carboxypyrrolidin-1-yl)diazen-1-ium-1,2-diolate (O²-acetoxymethyl PROLI/NO) NO-donor moiety was covalently coupled to the CH₂OH group of 3-(4-hydroxymethylphenyl)-4-(4-methylsulfonylphenyl)-5H-furan-2-one (12), was synthesized. The prodrug 14 released a low amount of NO (4.2%) upon incubation with phosphate buffer (PBS) at pH 7.4 which was significantly higher (34.8% of the theoretical maximal release of two molecules of NO/molecule of the parent hybrid ester prodrug) upon incubation in the presence of rat serum. These incubation studies suggest that both NO and the parent compound 12 would be released from the prodrug 14 upon in vivo cleavage by non-specific serum esterases. The prodrug ester 14 is a selective COX-2 inhibitor that exhibited AI activity (ED₅₀ = 72.2 mmol/kg po) between that of the reference drugs celecoxib (ED₅₀ = 30.9 μmol/kg po) and ibuprofen (ED₅₀ = 327 μmol/kg po). The NO donor compound 14 exhibited enhanced inhibition of phenylephrine-induced vasoconstriction of isolated mesenteric arteries compared with that observed under control conditions. These studies indicate hybrid ester AI/NO donor prodrugs (NONO-coxibs) constitutes a plausible drug design concept targeted toward the development of selective COX-2 inhibitory AI drugs that are devoid of adverse cardiovascular effects.     

Gut bacterium of Dendrobaena veneta (Annelida: Oligochaeta) possesses antimycobacterial activity

The new bacterial strain with antimycobacterial activity has been isolated from the midgut of Dendrobaena veneta (Annelida). Biochemical and molecular characterization of isolates from 18 individuals identified all as Raoultella ornithinolytica genus with 99% similarity. The bacterium is a possible symbiont of the earthworm D. veneta. The isolated microorganism has shown the activity against four strains of fast-growing mycobacteria: Mycobacterium butiricum, Mycobacterium jucho, Mycobacterium smegmatis and Mycobacterium phlei. The multiplication of the gut bacterium on plates with Sauton medium containing mycobacteria has caused a lytic effect. After the incubation of the cell free extract prepared from the gut bacterium with four strains of mycobacteria in liquid Sauton medium, the cells of all tested strains were deformed and divided to small oval forms and sometimes created long filaments. The effect was observed by the use of light, transmission and scanning microscopy. Viability of all examined species of mycobacteria was significantly decreased. The antimycobacterial effect was probably the result of the antibiotic action produced by the gut bacterium of the earthworm. The application of ultrafiltration procedure allowed to demonstrate that antimicrobial substance with strong antimycobacterial activity from bacterial culture supernatant, is a protein with the molecular mass above 100 kDa.     

Tetrahydrolipstatin Inhibition,Functional Analyses,and Three-dimensional Structure of a Lipase Essential for Mycobacterial Viability

The highly complex and unique mycobacterial cell wall is critical to the survival of Mycobacteria in host cells. However, the biosynthetic pathways responsible for its synthesis are, in general, incompletely characterized. Rv3802c from Mycobacterium tuberculosis is a partially characterized phospholipase/thioesterase encoded within a genetic cluster dedicated to the synthesis of core structures of the mycobacterial cell wall, including mycolic acids and arabinogalactan. Enzymatic assays performed with purified recombinant proteins Rv3802c and its close homologs from Mycobacterium smegmatis (MSMEG_6394) and Corynebacterium glutamicum (NCgl2775) show that they all have significant lipase activities that are inhibited by tetrahydrolipstatin, an anti-obesity drug that coincidently inhibits mycobacterial cell wall biosynthesis. The crystal structure of MSMEG_6394, solved to 2.9 Å resolution, revealed an α/β hydrolase fold and a catalytic triad typically present in esterases and lipases. Furthermore, we demonstrate direct evidence of gene essentiality in M. smegmatis and show the structural consequences of loss of MSMEG_6394 function on the cellular integrity of the organism. These findings, combined with the predicted essentiality of Rv3802c in M. tuberculosis, indicate that the Rv3802c family performs a fundamental and indispensable lipase-associated function in mycobacteria.     

Synthesis and biological evaluation of aryl phosphoramidate prodrugs of fosfoxacin and its derivatives

Aryl phosphoramidate prodrugs of fosfoxacin derivatives 15a-b and 8a-b were synthesized and investigated for their ability to target bacteria. No growth inhibition was observed neither for Mycobacterium smegmatis nor for Escherichia coli on solid medium, demonstrating the absence of release of the active compounds in the bacterial cells. Investigation of the stability of the prodrugs and their multienzymatic cleavage in abiotic and biotic conditions showed that the use of aryl phosphoramidate prodrug approach to deliver non-nucleotides compounds is not obvious and might not be appropriate for an antimicrobial drug.     

Cell wall proteome analysis of <Emphasis Type="Italic">Mycobacterium smegmatis</Emphasis> strain MC2 155

Background  

The usually non-pathogenic soil bacterium Mycobacterium smegmatis is commonly used as a model mycobacterial organism because it is fast growing and shares many features with pathogenic mycobacteria. Proteomic studies of M. smegmatis can shed light on mechanisms of mycobacterial growth, complex lipid metabolism, interactions with the bacterial environment and provide a tractable system for antimycobacterial drug development. The cell wall proteins are particularly interesting in this respect. The aim of this study was to construct a reference protein map for these proteins in M. smegmatis.     

Recycling of the Posttermination Complexes of Mycobacterium smegmatis and Escherichia coli Ribosomes Using Heterologous Factors

In eubacteria, ribosome recycling factor (RRF) and elongation factor G (EFG) function together to dissociate posttermination ribosomal complexes. Earlier studies, using heterologous factors from Mycobacterium tuberculosis in Escherichia coli revealed that specific interactions between RRF and EFG are crucial for their function in ribosome recycling. Here, we used translation factors from E. coli, Mycobacterium smegmatis and M. tuberculosis, and polysomes from E. coli and M. smegmatis, and employed in vivo and in vitro experiments to further understand the role of EFG in ribosome recycling. We show that E. coli EFG (EcoEFG) recycles E. coli ribosomes with E. coli RRF (EcoRRF), but not with mycobacterial RRFs. Also, EcoEFG fails to recycle M. smegmatis ribosomes with either EcoRRF or mycobacterial RRFs. On the other hand, mycobacterial EFGs recycle both E. coli and M. smegmatis ribosomes with either of the RRFs. These observations suggest that EFG establishes distinct interactions with RRF and the ribosome to carry out ribosome recycling. Furthermore, the EFG chimeras generated by swapping domains between mycobacterial EFGs and EcoEFG suggest that while the residues needed to specify the EFG interaction with RRF are located in domains IV and V, those required to specify its interaction with the ribosome are located throughout the molecule.     

A novel screening method based on menadione mediated rapid reduction of tetrazolium salt for testing of anti-mycobacterial agents

A microplate-based rapid, inexpensive and robust technique is developed by using tetrazolium salt 2, 3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) and menadione to determine the viability of Mycobacterium tuberculosis, Mycobacterium bovis BCG and Mycobacterium smegmatis bacilli in microplate format. In general, XTT reduction is an extremely slow process which takes almost 24 h to produce a detectable signal. Menadione could drastically induce this reduction to an almost equal extent within a few minutes in a dose dependent manner. The reduction of XTT is directly proportional to the cell concentration in the presence of menadione. The standardized protocol used 200 μM of XTT and 60 μM of menadione in 250 μl of cell suspension grown either in aerobic or anaerobic conditions. The cell suspension of M. bovis BCG and M. tuberculosis were incubated for 40 min before reading the optical density at 470 nm whereas M. smegmatis was incubated for 20 min. Calculated Signal/Noise (S/N) ratios obtained by applying this protocol were 5.4, 6.4 and 9.4 using M. bovis BCG, M. tuberculosis and M. smegmatis respectively. The calculated Z′ factors were > 0.8 for all mycobacterium bacilli indicating the robustness of the XTT Reduction Menadione Assay (XRMA) for rapid screening of inhibitors. The assay protocol was validated by applying 10 standard anti-tubercular agents on M. tuberculosis, M. bovis BCG and M. smegmatis. The Minimum Inhibitory Concentration (MIC) values were found to be similar to reported values from Colony Forming Unit (CFU) and REMA (resazurin microplate assay) assays. Altogether, XRMA is providing a novel anti-tubercular screening protocol which could be useful in high throughput screening programs against different physiological stages of the bacilli.     

Properties of beta-lactamases produced by three species of mycobacteria

1. Mycobacterium smegmatis (N.C.T.C. 8158), M. fortuitum and M. phlei (MPI) produce a constitutive β-lactamase that has penicillinase and cephalosporinase activity. 2. The β-lactamases of these three species of acid-fast bacteria were mainly cell-bound, only small amounts of activity being liberated into the extracellular fluid. The total β-lactamase activity of these mycobacteria was much lower than that of certain Gram-positive organisms, but comparable with that reported for species of Gram-negative bacteria. 3. The β-lactamases of intact cells of the mycobacteria were not freely accessible to any of the substrates tested, but the apparent crypticity factor to benzylpenicillin was greater than that to cephaloridine and cephalosporin C. 4. Attempts to induce β-lactamase activity in M. smegmatis and M. phlei failed even with high concentrations of inducer. 5. The β-lactamases obtained from the three species of mycobacteria showed different substrate specificities, including different relative activities as cephalosporinases and penicillinases respectively. 6. Certain derivatives of 6-aminopenicillanic acid and 7-aminocephalosporanic acid were found to be resistant to hydrolysis by β-lactamases of M. smegmatis and M. fortuitum. 7. The β-lactamase of M. smegmatis was competitively inhibited by a number of β-lactamase-resistant derivatives of 6-aminopenicillanic acid, but not by similar derivatives of 7-aminocephalosporanic acid.     

Expression of heat shock protein 70a mRNA in Bombyx mori diapause eggs

In an effort to understand whether heat shock protein 70 (Hsp70) participates in the environmental 5 °C signal reception/transduction toward breaking embryonic diapause of the silkworm Bombyx mori, we isolated a cDNA for Hsp70a and examined the expression of Hsp70a mRNA in B. mori diapause and nondiapause eggs by quantitative real-time PCR. Hsp70a mRNA gradually increased in diapause eggs continuously kept at 25 °C after oviposition to maintain diapause. When diapause eggs were exposed to the diapause-terminating condition of 5 °C beginning at 2 days post-oviposition, Hsp70a mRNA increased beginning at 5 days post-cold treatment. Even in nondiapause eggs, Hsp70a mRNA increased slightly with exposure to 5 °C. These results suggest that Hsp70a is involved in reception/transduction of the diapause-terminating (5 °C) signal via gene activation. The expression patterns of Hsp70a mRNA are discussed in relation to those of the cold-response gene Samui.