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This work was focused on the enzymatic esterification of glycerol and ibuprofen at high concentrations in two triphasic systems composed of toluene+ibuprofene (apolar) and glycerol or glycerol–water (polar) liquid phases, and a solid phase with the industrial immobilized lipase B from Candida antarctica named Novozym®435 (N435) acting as the biocatalyst. Based on a preliminary study, the concentration of the enzyme was set at 30 g·L−1 and the stirring speed at 720 r.p.m to reduce external mass transfer limitations. To obtain more information on the reaction system, it was conducted at a wide range of temperatures (50 to 80 °C) and initial concentrations of ibuprofen (20–100 g·L−1, that is, 97 to 483 mM). Under these experimental conditions, the external mass transfer, according to the Mears criterion (Me = 1.47–3.33·10−4 << 0.15), was fast, presenting no limitation to the system productivity, regardless of the presence of water and from 50 to 80 °C. Considering that the enzyme is immobilized in a porous ion-exchange resin, limitations due to internal mass transfer can exist, depending on the values of the effectiveness factor (η). It varied from 0.14 to 0.23 at 50 to 80 °C and 0.32–1 mm particle diameter range in the absence of water, and in the same ranges, from 0.40 to 0.66 in the presence of 7.4% w/w water in the glycerol phase. Thus, it is evident that some limitation occurs due to mass transfer inside the pores, while the presence of water in the polar phase increases the productivity 3–4 fold. During the kinetic study, several kinetic models were proposed for both triphasic reacting systems, with and without first-order biocatalyst deactivation, and their fit to all relevant experimental data led to the observation that the best kinetic model was a reversible hyperbolic model with first-order deactivation in the anhydrous reaction system and a similar model, but without deactivation, for the system with added water at zero time. This fact is in sharp contrast to the use of N435 in a water-glycerol monophasic system, where progressive dissolution of ibuprofen in the reacting media, together with a notable enzyme deactivation, is observed. [ABSTRACT FROM AUTHOR]

Tenofovir (TFV) ester prodrugs, a class of nucleotide analogs (NAs), are the first-line clinical anti-hepatitis B virus (HBV) drugs with potent antiviral efficacy, low resistance rate and high safety. In this work, three marketed TFV ester drugs, tenofovir disoproxil fumarate (TDF), tenofovir alafenamide fumarate (TAF) and tenofovir amibufenamide fumarate (TMF), were used as probes to investigate the relationships among prodrug structures, pharmacokinetic characteristics, metabolic activations, pharmacological responses and to reveal the key factors of TFV ester prodrug design. The results indicated that TMF and TAF exhibited significantly stronger inhibition of HBVDNA replication than did TDF in HBV-positive HepG2.2.15 cells. The anti-HBV activity of TMF was slightly stronger than TAF after 9 days of treatment (EC50 7.29 ± 0.71 nM vs. 12.17 ± 0.56 nM). Similar results were observed in the HBV decline period post drug administration to the HBV transgenic mouse model, although these three TFV prodrugs finally achieved the same anti- HBV effect after 42 days treatments. Furthermore, TFV ester prodrugs showed a correcting effect on disordered host hepatic biochemical metabolism, including TCA cycle, glycolysis, pentose phosphate pathway, purine/pyrimidine metabolism, amino acid metabolism, ketone body metabolism and phospholipid metabolism. The callback effects of the three TFV ester prodrugs were ranked as TMF > TAF > TDF. These advantages of TMF were believed to be attributed to its greater bioavailability in preclinical animals (SD rats, C57BL/6 mice and beagle dogs) and better target loading, especially in terms of the higher hepatic level of the pharmacologically active metabolite TFV-DP, which was tightly related to anti-HBV efficacy. Further analysis indicated that stability in intestinal fluid determined the actual amount of TFV prodrug at the absorption site, and hepatic/intestinal stability determined the maintenance amount of prodrug in circulation, both of which influenced the oral bioavailability of TFV prodrugs. In conclusion, our research revealed that improved pharmacokinetics of TFV ester prodrugs (especially intestinal stability) strengthened the inhibition of HBV replication and the rebalance of hepatocellular metabolism, which provides new insights and a basis for the design, modification and evaluation of new TFV prodrugs in the future. [ABSTRACT FROM AUTHOR]

For ester prodrugs that are used to improve the gastrointestinal absorption of highly hydrophilic, pharmacologically active substances, it is challenging to predict the human pharmacokinetics (PK) of the prodrugs and their parent compounds using only preclinical data. This research was aimed at constructing a PBPK model for predicting the human PK of the ester prodrug MGS0274 and its parent compound MGS0008 after a single oral administration of MGS0274 besylate. First, we identified carboxylesterase 1 (CES1) as the major enzyme involved in the hydrolysis of MGS0274. Second, we constructed a new compartment model to estimate the passive diffusion clearance (CLpd) of MGS0008, a critical parameter for predicting the PK of highly hydrophilic compounds, based on in vivo monkey PK data. Finally, we constructed a permeability-limited liver PBPK model incorporating the CLpd assumed to be the same in humans. We confirmed that our method reliably predicted the human PK and that the estimated CLpd was comparable to that calculated retrospectively using the PBPK model, suggesting that the methodology for estimating the CLpd was valid. Our proposed methodology is expected to be helpful for human PK prediction of ester prodrugs hydrolysed by CES1 and their hydrophilic parent compounds even during the preclinical phase. [ABSTRACT FROM AUTHOR]

Human carboxylesterase 1 (hCES1) is an enzyme that plays an important role in hydrolysis of pharmaceuticals in the human liver. In this study, elucidation of the chiral recognition ability of hCES1 was attempted using indomethacin esters in which various chiral alcohols were introduced. Indomethacin was condensed with various chiral alcohols to synthesize indomethacin esters. The synthesized esters were hydrolyzed with a human liver microsome (HLM) solution and a human intestine microsome (HIM) solution. High hydrolytic rate and high stereoselectivity were confirmed in the hydrolysis reaction in the HLM solution but not in the HIM solution, and these indomethacin esters were thought to be hydrolyzed by hCES1. Next, these indomethacin esters were hydrolyzed in recombinant hCES1 solution and the hydrolysis rates of the esters were calculated. The stereoselectivity confirmed in HLM solution was also confirmed in the hCES1 solution. In the hydrolysis reaction of esters in which a phenyl group is bonded next to the ester, the Vmax value of the (R) form was 10 times larger than that of the (S) form. [ABSTRACT FROM AUTHOR]

Oral delivery of apomorphine via prodrug principle may be a potential treatment for Parkinson’s disease. The purpose of this study was to investigate the transport and stability of apomorphine and its esters across Caco-2 cell monolayer and their affinity towards chylomicrons. Apomorphine, monolauroyl apomorphine (MLA) and dilauroyl apomorphine (DLA) were subjected to apical to basolateral (A-B) and basolateral to apical (B-A) transport across Caco-2 cell monolayer. The stability of these compounds was also assessed by incubation at intestinal pH and physiological pH with and without Caco-2 cells. Molecular dynamics (MD) simulations were performed to understand the stability of the esters on a molecular level. The affinity of the compounds towards plasma derived chylomicrons was assessed. The A-B transport of intact DLA was about 150 times lower than the transport of apomorphine. In contrast, MLA was highly unstable in the aqueous media leading to apomorphine appearance basolaterally. MD simulations possibly explained the differences in hydrolysis susceptibilities of DLA and MLA. The affinity of apomorphine diesters towards plasma derived chylomicrons provided an understanding of their potential lymphatic transport. The intact DLA transport is not favorable; therefore, the conversion of DLA to MLA is an important step for intestinal apomorphine absorption. [ABSTRACT FROM AUTHOR]

Tenofovir-disoproxil-fumarate (TDF) is a double ester prodrug which enables intestinal uptake of tenofovir (TFV) after oral administration in humans. In this study, prodrug stability was monitored in situ in the human intestine and in vitro using biorelevant media. In fasted state human intestinal fluids, the prodrug was completely degraded within 90 min, resulting in the formation of the mono-ester intermediate and TFV; in fed state intestinal fluids, the degradation rate of TDF was slightly reduced and no TFV was formed. Intestinal fluid samples aspirated after administration of TDF confirmed extensive intraluminal degradation of TDF in fasted state conditions; a relatively fast absorption of TDF partly compensated for the degradation. Although food intake reduced intestinal degradation, the systemic exposure was not proportionally increased. The lower degradation in fed state conditions may be attributed to competing esterase substrates present in food, lower chemical degradation in the slightly more acidic environment and micellar entrapment, delaying exposure to the “degrading” intestinal environment. The results of this study demonstrate premature intestinal degradation of TDF and suggest that TFV may benefit from a more stable prodrug approach; however, fast absorption may compensate for fast degradation, indicating that prodrug selection should not be limited to stability assays. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the intestinal disposition of abiraterone acetate, an ester prodrug of the anticancer agent abiraterone. Stability of the prodrug and solubility and dissolution characteristics of both abiraterone and abiraterone acetate were monitored in vitro. Moreover, the in vivo intraluminal concentrations of abiraterone and abiraterone acetate upon intake of one tablet of 250 mg abiraterone acetate were assessed in healthy volunteers. The intestinal absorption resulting from the intraluminal behavior of the ester prodrug was determined using the rat in situ intestinal perfusion technique with mesenteric blood sampling. Simulated and aspirated human intestinal fluids of the fasted state were used as solvent systems. Upon incubation of abiraterone acetate in human intestinal fluids in vitro , rapid hydrolysis of the prodrug was observed, generating abiraterone concentrations largely exceeding the apparent solubility of abiraterone, suggesting the existence of intestinal supersaturation. These findings were confirmed in vivo , by intraluminal sampling of duodenal fluids upon oral intake of an abiraterone acetate tablet by healthy volunteers. Rat in situ intestinal perfusion experiments performed with suspensions of abiraterone and abiraterone acetate in human intestinal fluids of the fasted state revealed significantly higher flux values upon perfusion with the prodrug than with abiraterone. Moreover, rat in situ intestinal perfusion with abiraterone acetate suspensions in simulated fluids of the fasted state in presence or absence of esterases demonstrated that increased hydrolytic activity of the perfusion medium was beneficial to the intestinal absorption of abiraterone. In conclusion, the rapid hydrolysis of abiraterone acetate in the intraluminal environment appears to result in fast and extensive generation of abiraterone supersaturation, creating a strong driving force for abiraterone absorption. [ABSTRACT FROM AUTHOR]

Chronic hepatitis B virus (HBV) infection may lead to liver cirrhosis and hepatocellular carcinoma, but few drugs are available for its treatment. Acyclic nucleoside phosphonates (ANPs) have remarkable antivirus activities but are not easily absorbed from the gastrointestinal tract and accumulate in the kidneys, resulting in nephrotoxicity. Therefore, there is a need to find effective liver site-specific prodrugs. The dipivaloyloxymethyl ester of 9-(2-phosphonylmethoxyethyl)adenine (PMEA)-adefovir dipivoxil (ADV)-is a first-line therapy drug for chronic hepatitis B with a low therapeutic index because of renal toxicity and low hepatic uptake. In this study, a series of PMEA derivatives were synthesized to enhance plasma stability and liver release. The metabolic stability of ADV (Chemical I) and its two analogues (Chemicals II and III) was evaluated in rat plasma and liver homogenate in vitro. An ion-pair reverse-phase HPLC-UV method and a hybrid ion trap and high-resolution time-of-flight mass spectrometry (LC-IT-TOF-MS) were used to evaluate the degradation rate of the analogues and to identify their intermediate metabolites, respectively. Chemicals I and II were hydrolyzed by cleavage of the C-O bond to give monoesters. Sufficient enzymatic activation in the liver homogenate through a relatively simple metabolic pathway, in addition to a favorable stability profile in rat plasma, made Chemical II an optimal candidate. Next, six analogues based on the structure of Chemical II were synthesized and evaluated in plasma and liver homogenate. Compared to Chemical II, these compounds generated less active PMEA levels in rat liver homogenate. Therefore, chemical modification of Chemical II may lead to new promising PMEA derivatives with enhanced plasma stability and liver activation. [ABSTRACT FROM AUTHOR]

Different types of ketorolac ester prodrugs incorporating tert-butyl ( KT), benzyl ( KB), heptyl ( KH), and diketorolac heptyl ( DKH) promoieties were synthesized for the comparison of percutaneous penetration. The prodrugs were characterized according to their melting point, capacity factor, lipophilicity, solubility in 30% ethanol/buffer, enzymatic hydrolysis, in vitro skin permeation, hair follicle accumulation, and in vivo skin tolerance. Interactions between the prodrugs and esterases were predicted by molecular docking. Both equimolar suspensions and saturated solutions in 30% ethanol/pH 7.4 buffer were employed as the applied dose. All of the prodrugs exhibited a lower melting point than ketorolac. The lipophilicity increased in the following order: ketorolac < KT < KB < KH < DKH. The prodrugs were rapidly hydrolyzed to the parent drug in esterase medium, skin homogenate, and plasma, with KT and KB exhibiting higher degradation rates. KT exhibited the highest skin permeation, followed by KB. The flux of KT and KB exceeded that of ketorolac by 2.5-fold and twofold, respectively. KH and DKH did not improve ketorolac permeation but exhibited a sustained release behavior. KT and KH revealed selective absorption into follicles and a threefold greater follicular uptake compared with ketorolac. KB, KH, and DKH slightly but significantly increased transepidermal water loss ( TEWL) after consecutive administration for 7 days, whereas ketorolac and KT exhibited no influence on TEWL. According to the experimental results, it can be concluded that an optimal balance between lipophilicity and aqueous solubility is important in the design of a successful prodrug. The acceptable skin tolerance for safe application is also an important consideration. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:974-986, 2014 [ABSTRACT FROM AUTHOR]

The biopharmaceutical and physicochemical properties of two new cyclic prodrugs (CA-[cychexalanine (Cha4), d-Leu5]-Enkephalin (Enk) and coumarinic acid (CA)-[Cha4, d-Ala5]-Enk) of opioid peptides that were designed to be stable to oxidative metabolism by cytrochrome P-450 enzymes in the intestinal mucosa are described in this paper. Two-dimensional nuclear magnetic resonance studies and molecular dynamics simulations showed that these cyclic prodrugs exhibit unique solution conformations (i.e., type I β-turns), which are favorable for transcellular permeation. The calculated molecular surface areas and cLog P values confirmed that these new cyclic prodrugs are more lipophilic than linear opioid peptides and, thus, they should exhibit better transcellular permeation characteristics. However, Caco-2 cell permeation studies showed that the cyclic prodrugs were substrates for apically polarized efflux transporters (e.g., P-glycoprotein, which significantly limited their transcellular permeation). Permeability studies using an in situ rat intestinal perfusion model confirmed the poor intestinal permeation characteristics of CA-[Cha4, d-Leu5]-Enk and CA-[Cha4, d-Ala5]-Enk as well as the stability of these two new cyclic prodrugs of opioid peptides to oxidative metabolism. In conclusion, these data clearly show that oral absorption of cyclic prodrugs of opioid peptides can only be achieved by designing molecules devoid of substrate activity for both cytrochrome P-450 enzymes and efflux transporters in the intestinal mucosa. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:3500-3510, 2012 [ABSTRACT FROM AUTHOR]

The phenomenon known as multiple-drug resistance, whereby anti-cancer agents are expelled from cancer cells, makes it necessary to develop methods that will reliably increase the accumulation of anti-cancer agents within cancer cells. To accomplish this goal, a new model compound, Val-SN-38, was synthesized by introducing valine to SN-38, an active ingredient of irinotecan. Val-SN-38 improved intracellular accumulation approximately 5-fold in MCF7 cells, compared with SN-38, and rather than changes in membrane permeability, the amino acid transporter ATB0,+ played a role, whereas the dipeptide transporter PEPT1 did not. Other sodium-dependent amino acid transporters, namely ATA1, ATA2, and ASCT2, were unexpectedly involved in the uptake of Val-SN-38 as well. The efflux of Val-SN-38 by major efflux transporters was variably changed, but not significantly. In summary, the enhanced accumulation of Val-SN-38 in cancer cells was due to augmented uptake via various amino acid transporters. The results of the present study make a compelling argument in favour of a prodrug concept that can improve intracellular accumulation and take advantage of amino acid transporters without significantly inducing multiple-drug resistance. [ABSTRACT FROM AUTHOR]

Abstract: A novel hybrid nitric oxide-releasing anti-inflammatory (AI) ester prodrug (NONO-coxib 14) wherein an O 2-acetoxymethyl 1-(2-carboxypyrrolidin-1-yl)diazen-1-ium-1,2-diolate (O 2-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 =72.2mmol/kg po) between that of the reference drugs celecoxib (ED50 =30.9μmol/kg po) and ibuprofen (ED50 =327μmol/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. [Copyright &y& Elsevier]

The aim of this study was to develop and characterize lipid nanoparticle systems for the transdermal delivery of buprenorphine and its prodrugs. A panel of three buprenorphine prodrugs with ester chains of various lengths was synthesized and characterized by solubility, capacity factor (log K′), partitioning between lipids and water and the ability to penetrate nude mouse skin. Colloidal systems made of squalene (lipid emulsion, LE), squalene + Precirol (nanostructured lipid carriers, NLC) and Precirol (solid lipid nanoparticles, SLN) as the lipid core material were prepared. Differential scanning calorimetry showed that the SLN had a more-ordered crystalline lattice in the inner matrix compared to the NLC. The particle size ranged from 220–300 nm, with NLC showing the smallest size. All prodrugs were highly lipophilic and chemically stable, but enzymatically unstable in skin homogenate and plasma. The in vitro permeation results exhibited a lower skin delivery of drug/prodrug with an increase in the alkyl chain length. SLN produced the highest drug/prodrug permeation, followed by the NLC and LE. A small inter-subject variation was also observed with SLN carriers. SLN with soybean phosphatidylcholine (SLN-PC) as the lipophilic emulsifier showed a higher drug/prodrug delivery across the skin compared to SLN with Myverol, a palmitinic acid monoglyceride. The in vitro permeation of the prodrugs occurred in a sustained manner for SLN-PC. The skin permeation of buprenorphine could be adjusted within a wide range by combining a prodrug strategy and lipid nanoparticles. [ABSTRACT FROM AUTHOR]

To improve oral absorption of sanfetrinem, a broad-spectrum, beta-lactamase-stable antibiotic, two different ester prodrugs have been selected. Both prodrugs proved to be readily hydrolyzed after absorption before reaching the systemic circulation. The objective of this study was to evaluate the role of intestinal and liver metabolism in the conversion of the two prodrugs into the active compound. In vitro experiments were performed in different rat tissues involved in the absorption process. Moreover data obtained with in vitro experiments have been integrated with data obtained in vivo using a surgically prepared rat model which allows for the measurement of the amount of intact prodrug that overcomes the intestinal mucosa and its presence in the portal vein. Both prodrugs proved to be readily cleaved by jejunum and liver microsomes. The rates of ester hydrolysis with these two tissues were 10- to 30-fold higher than those calculated in intestinal juice at pH 7.4 and about 100-fold higher than in buffer at pH 5.5. These data suggest that both the intestinal wall and liver could play an important role in the conversion of the two prodrugs in active parent compound. In the in vivo experiment, relative to sanfetrinem levels, very low concentrations of intact esters were measured in the portal vein blood, indicating that the two prodrugs are nearly completely hydrolyzed to the active drug by the intestinal wall. In conclusion this study demonstrated that the intestinal epithelium plays a major role in the conversion of the two prodrugs into sanfetrinem. The liver, despite its high esterase activity seems to be only marginally involved. [Copyright &y& Elsevier]

Purpose. To explore the usefulness of fruit extracts as enhancers of the oral absorption of esterase-sensitive prodrugs. Methods. Inhibition of esterase-mediated degradation by nature-identical fruit extracts was evaluated using 1) p-nitrophenylacetate (model substrate for esterase-activity) in rat intestinal homogenates and 2) bis(isopropyloxycarbonyloxymethyl)-( R)-9-[(2-phosphonomethoxy) propyl]adenine [bis(POC)-PMPA] (esterase-sensitive prodrug of the antiviral agent PMPA) in Caco-2 cell homogenates and in intestinal homogenates from rat, pig and man. Subsequently, transport of the ester prodrug was studied across Caco-2 monolayers in the presence or absence of fruit extracts. Results. In homogenates from rat ileum, the esterase activity could be reduced significantly by the inclusion of fruit extracts (1%): the initial enzymatic degradation of p-nitrophenylacetate was inhibited by 77% (strawberry), 16% (passion fruit) and 57% (banana). A similar inhibition of bis(POC)-PMPA metabolism by fruit extracts was observed in intestinal homogenates from several species and in homogenates from Caco-2 cells. Transport of total PMPA across Caco-2 monolayers was enhanced 3-fold by co-incubation with strawberry extract (1%). The fraction of intact prodrug appearing in the acceptor compartment increased from virtually zero to 67%. Conclusions. The results suggest that co-incubation with nature-identical fruit extracts might be useful as a strategy to enhance the transepithelial transport of esterase-sensitive prodrugs through inhibition of intracellular metabolism of the prodrug. [ABSTRACT FROM AUTHOR]

The chemical and enzymatic reactivity of 5-fluoro-2′-deoxyuridine prodrugs esterified at the 3′ and 5′ positions with several acyl groups has been investigated. The enzymatic reactivity was affected by the acyl structure, the site of esterification, and the number of esters in the prodrug molecule. [ABSTRACT FROM AUTHOR]

Abstract: A series of ester prodrugs of 7-O-methyl derivative of Zanamivir (compound 3) was synthesized and their efficacy was evaluated in an influenza infected mice model by intranasal administration. Compound 7c (CS-8958), octanoyl ester prodrug of the C-9 alcohol of compound 3, was found to be much longer-acting than Zanamivir. Furthermore, the in vivo efficacies of compounds 12a, 12b, and 12c, the linear alkyl ester prodrug of the carboxylic acid, were comparable to that exerted by compound 7c. [Copyright &y& Elsevier]