A novel prodrug approach for tertiary amines. 2. Physicochemical and in vitro enzymatic evaluation of selected N-phosphonooxymethyl prodrugs

Fosfatriclaben, a prodrug of triclabendazole: Preparation, stability, and fasciolicidal activity of three new intramuscular formulations

In this study, we present the preparation, stability, and in vivo fasciolicidal activity of three new intramuscular formulations in sheep of a prodrug based on triclabendazole, named fosfatriclaben. The new formulations were ready-to-use aqueous solutions with volumes recommended for intramuscular administration in sheep. The use of poloxamers (P-407 and P-188) and polysorbates (PS-20 and PS-80) in the new formulations improved the aqueous solubility of fosfatriclaben by 8-fold at pH 7.4. High-performance liquid chromatography with UV detection was used to evaluate the stability of fosfatriclaben in the three formulations. High recovery (> 90%) of fosfatriclaben was found for all formulations after exposure at 57 ± 2 °C for 50 h. The three intramuscular formulations showed high fasciolicidal activity at a dose of 6 mg/kg, which was equivalent to the triclabendazole content. The fasciolicidal activity of fosfatriclaben was similar to commercial oral (Fasimec®) and intramuscular (Endovet®) triclabendazole formulations at a dose of 12 mg/kg. In the in vivo experiments, all formulations administered intramuscularly reduced egg excretion by 100%, and formulations F1, F2, and F3 presented fasciolicidal activities of 100%, 100%, and 99.6%, respectively.

Fosnetupitant for the Prevention of Chemotherapy-Induced Nausea and Vomiting: A Short Review and Clinical Perspective

Chemotherapy-induced nausea and vomiting (CINV) is often ranked by patients as one of the most distressing and feared consequences of chemotherapy. The novel neurokinin-1 (NK1) receptor antagonist fosnetupitant, a phosphorylated prodrug formulation of netupitant, was approved in Japan in 2022. Fosnetupitant is one of the standard treatments for the prevention of CINV in patients who are receiving highly (any treatment where CINV occurs in more than 90% of patients) or moderately (where CINV occurs in 30-90% of patients) emetogenic chemotherapies. The aim of this commentary is to describe the mechanism of action, tolerability, and antiemetic efficacy of single-agent fosnetupitant in the prevention of CINV, and to discuss its clinical application, in order to aid optimal use.

Carboxylic Acid Counterions in FDA-Approved Pharmaceutical Salts

Salification is one of the powerful and widely employed approaches to improve the biopharmaceutical properties of drugs. The FDA's eighty-year trajectory of new drug approvals depicts around one-third of the drugs clinically used as their pharmaceutical salts. Among various cationic and anionic counterions used in FDA-approved pharmaceutical salts, the carboxylic acids have significantly contributed. A total of 94 pharmaceutical salts discovered during 1943-2020 comprises carboxylic acids as counterions with a major contribution of acetate, maleate, tartrate, fumarate, and succinate. Hydrocodone tartrate is the first FDA-approved carboxylate salt approved in 1943. Overall, the analysis shows that fifteen carboxylic acid counterions are present in FDA-approved pharmaceutical salts with a major share of acetate (18 drugs). This review provides an account of FDA-approved carboxylate salts from 1939 to 2020. The decade-wise analysis indicates that 1991-2000 contributed a maximum number of carboxylate salts (24) and least (3) in 1939-1950. The technical advantage of carboxylate salts over free-base or other counterions is also discussed. Graphical Abstract.

Pathways and progress in improving drug delivery through the intestinal mucosa and blood-brain barriers

One of the major hurdles in developing therapeutic agents is the difficulty in delivering drugs through the intestinal mucosa and blood-brain barriers (BBB). The goal here is to describe the general structures of the biological barriers and the strategies to enhance drug delivery across these barriers. Prodrug methods used to improve drug penetration via the transcellular pathway have been successfully developed, and some prodrugs have been used to treat patients. The use of transporters to improve absorption of some drugs (e.g., antiviral agents) has also been successful in treating patients. Other methods, including blocking the efflux pumps to improve transcellular delivery, and modulation of cell-cell adhesion in the intercellular junctions to improve paracellular delivery across biological barriers, are still in the investigational stage.

A highly water soluble benzimidazole derivative useful for the treatment of fasciolosis

This study describes the synthesis of compound (7), a highly hydrosoluble phosphonooxymethyl prodrug of compound alpha (4). Compound (7) improved the aqueous solubility of its precursor compound (4) by 50,000 times and it is stable at neutral pH. The prodrug showed faciolicidal activity when evaluated in vitro against excysted Fasciola hepatica metacercariae. The in vivo evaluation of (7) was carried out via oral, intramuscular and subcutaneous administration in sheep artificially infected with F. hepatica metacercariae. At an intramuscular dose of 4 mg/kg, the activity of (7) was similar to that of compound alpha (4) at an oral dose of 15 mg/kg.

In vitro and in vivo evaluation of a primaquine prodrug without red blood cell membrane destabilization property

Primaquine is an important therapeutic resource for malaria treatment and it has wide activity against several pathogens. The haematotoxicity of primaquine is the major problem for its therapeutic application. This effect is aggravated by repeated use at high doses and by the wide fluctuation of plasma levels after administration. The primaquine prodrug (Phe-Ala-PQ) was planned in order to modify the pharmacokinetics and toxicity of primaquine. The in vitro conversion of Phe-Ala-PQ to primaquine, and the primaquine pharmacokinetics were evaluated in four groups of rats: two groups that received a single dose of Phe-Ala-PQ, one by intravenous and the other by gavage route, and two other groups that received primaquine diphosphate, by intravenous and gavage routes. In addition, the erythrocyte osmotic fragility was compared in two groups of rats that received multiple doses of primaquine diphosphate or Phe-Ala-PQ, as a parameter of haematotoxicity. The in vitro conversion of Phe-Ala-PQ to primaquine by plasma enzyme action was observed. The pharmacokinetic profile of primaquine from Phe-Ala-PQ was more favourable due to the lower fluctuation of plasma concentrations. Haematotoxicity was not evidenced in the prodrug administration. The results reinforce the need for further studies with this prodrug, promising an alternative in the therapeutic use of primaquine.

A novel prodrug strategy for beta-dicarbonyl carbon acids: syntheses and evaluation of the physicochemical characteristics of C-phosphoryloxymethyl (POM) and phosphoryloxymethyloxymethyl (POMOM) prodrug derivatives

The C-phosphoryloxymethyl (POM) and phosphoryloxymethyloxymethyl (POMOM) prodrugs resulting from derivatization at the reactive alpha-carbon of beta-dicarbonyl carbon acid drugs represent a unique approach for improving their chemical stability and aqueous solubility. This work evaluates the physicochemical and in vitro enzymatic bioconversion lability of selected prodrugs of phenylbutazone and phenindione. The POM and POMOM prodrug derivatives of phenylbutazone are highly water soluble (>or=250 mg/mL), chemically stable with projected shelf-lives of 4.5 years (pH 3.5, 25 degrees C) and 1.1 years (pH 6.0, 25 degrees C), respectively. Interestingly, both prodrug derivatives do not display a pH-dependency typical of many phosphate monoesters, although the similarities of their apparent thermodynamic activation parameters indicate a hydrolysis mechanism similar to other phosphates. These prodrugs undergo alkaline phosphatases catalyzed bioconversion to their respective carbon acids with an expected faster rate exhibited by the POMOM derivatives. Additionally, in marked contrast to the oxidative instability of phenindione, its POM prodrug is stable. The results from these studies reaffirm the rationale of transiently "masking" the reactive alpha-carbon/proton bond by covalently incorporating a POM or POMOM promoiety. This prodrug strategy presents a twofold advantage, enhancement of aqueous solubility and prevention of oxidative instability, two intrinsic formulation limitations found for beta-dicarbonyl carbon acid drugs.

Prodrugs for amines

The purpose of this work is to review the published strategies for the production of prodrugs of amines. The review is divided in two main groups of approaches: those that rely on enzymatic activation and those that take advantage of physiological chemical conditions for release of the drugs. A compilation of the most important approaches is presented in the form of a table, where the main advantages and disadvantages of each strategy are also referred.

Prodrug strategies to overcome poor water solubility

Drug design in recent years has attempted to explore new chemical spaces resulting in more complex, larger molecular weight molecules, often with limited water solubility. To deliver molecules with these properties, pharmaceutical scientists have explored many different techniques. An older but time-tested strategy is the design of bioreversible, more water-soluble derivatives of the problematic molecule, or prodrugs. This review explores the use of prodrugs to effect improved oral and parenteral delivery of poorly water-soluble problematic drugs, using both marketed as well as investigational prodrugs as examples. Prodrug interventions should be considered early in the drug discovery paradigm rather than as a technique of last resort. Their importance is supported by the increasing percentage of approved new drug entities that are, in fact, prodrugs.

Bioreversible quaternary N-acyloxymethyl derivatives of the poorly soluble tertiary amine Lu 28-179—Synthesis, pharmaceutical chemical characterization and bioavailability studies in dogs

Quaternary prodrug types of poorly water-soluble tertiary amines have been shown to possess significantly enhanced solubilities as compared to the parent amine. In the present study, the N-acyloxymethylation approach to improve the aqueous solubility of Lu 28-179 a tertiary amine exhibiting an intrinsic solubility in the nanomolar range, have been investigated. The acetyl-, propanoyl-, butanoyl-, isobutanoyl- and pivaloyloxymethyl derivatives were isolated as chloride salts and the aqueous solubilities (S) far exceeded that of the parent tertiary amine (S(0)). S/S(0) ratios in the range 2-4 x 10(6) were found for the most soluble prodrugs. The prodrugs were reasonable stable to hydrolysis in aqueous buffer solutions (pH 0.1-7.4), but susceptible to undergo enzyme-mediated regeneration of Lu 28-179 after incubation in human plasma, simulated intestinal fluid and duodenum juice from pigs and dogs. Despite promising in vitro properties the prodrugs were unable to improve the oral bioavailability of Lu 28-179 as compared to that obtained after administration of a reference formulation of the parent drug in the dog.

Betamethasone pharmacokinetics after two prodrug formulations in sheep: implications for antenatal corticosteroid use

Maternal administration of betamethasone to enhance fetal lung maturation for women who threaten preterm labor is common clinical practice. However, recommendations regarding the choice of betamethasone formulations for perinatal use are vague. The disposition of betamethasone from two commonly used antenatal formulations is poorly understood. We therefore designed a study to capture the true pharmacokinetic profiles of betamethasone from these fast acting and dual-release formulations. Betamethasone in sheep plasma was measured by a newly designed, highly sensitive liquid chromatography/tandem mass spectrometry assay after intramuscular injection (n = 4) of 0.25 mg/kg betamethasone phosphate and 0.5 mg/kg betamethasone phosphate/acetate formulations. Compartmental modeling was performed using the ADAPT II program. Betamethasone pharmacokinetics could be captured for 24 h for the phosphate and for 5 days for the phosphate/acetate formulations. The phosphate formulation profile had the appearance of a traditional Bateman function with a terminal half-life of 4 h, whereas the phosphate/acetate formulation produced a biexponential decline with a terminal half-life of 14 h. The latter is much longer than is commonly reported and has been missed in the literature due to assay limitations. Extrapolations to humans indicate that although both formulations might have similar therapeutic indices, the dual formulation might be associated with a lower safety profile. In light of this newly identified long terminal half-life for the betamethasone dual formulation, dosing practices for betamethasone in pregnancy need to be reassessed.

Bioreversible quaternary N-acyloxymethyl derivatives of the tertiary amines bupivacaine and lidocaine—synthesis, aqueous solubility and stability in buffer, human plasma and simulated intestinal fluid

Design of water-soluble prodrugs may constitute a means to improve the oral bioavailability of drugs suffering from dissolution rate-limited absorption. The model drug bupivacaine containing a tertiary amine function has been converted into bioreversible quaternary N-acyloxymethyl derivatives. The pH-independent solubility of the N-butanoyloxymethyl derivate exceeded 1000 mg ml-1 corresponding approximately to a 10,000-fold increase in water solubility compared to that of bupivacaine base. The kinetics of hydrolysis of the prodrugs was studied in the pH range 0.1-9.8 (37 degrees C). Decomposition was found to follow first-order kinetics and U-shaped pH-rate profiles were constructed. The observed differences between the hydrolytic lability of the derivatives might most likely be ascribed to steric effects. In most cases, the prodrugs were quantitatively converted into bupivacaine. However, for the hydrolysis of the N-butanoyloxymethyl derivative at neutral to slightly alkaline pH parallel formation of bupivacaine (approximately 80%) and an unknown compound X (approximately 20%) was observed. LC-MS analysis of the latter compound suggests that an aromatic imide structure has been formed from an intramolecular acyl transfer reaction involving a nucleophilic attack of the amide nitrogen atom on the ester carbonyl carbon atom. Whereas the derivatives were poor substrates for plasma enzymes; they were hydrolyzed rapidly to parent bupivacaine in the presence of pancreatic enzymes (simulated intestinal fluid) at 37 degrees C. The data indicate that such prodrugs possess sufficient stability in the acidic environment of the stomach to reach the small intestine in intact form where they can be cleaved efficiently by action of pancreatic enzymes prior to drug absorption. Thus, the N-acyloxymethyl approach might be of potential utility to enhance oral bioavailability of tertiary amines exhibiting pKa values below approximately 6 and intrinsic solubilities in the low microM range.

Assessment of the combined approach of N-alkylation and salt formation to enhance aqueous solubility of tertiary amines using bupivacaine as a model drug

Quaternary prodrug types of poorly water-soluble tertiary amines have been shown to exhibit significantly enhanced solubilities as compared to the parent amine. In the present study the combined effect of N-alkylation and salt formation to enhance aqueous solubility of tertiary amines have been investigated using bupivacaine as a model compound. X-ray structure analyses of selected salts were included to investigate the potential existence of correlations between salt solubility and crystal packing modes. Alkyl groups were methyl, ethyl, propyl, and butyl and the derivatives were isolated as their iodide salts. Chloride, mesylate, formate, acetate, glycolate, and tosylate salts were obtained by anion exchange of the N-methyl-bupivacaine derivative. N-Alkylation and salt formation afforded quaternary ammonium salts possessing pH-independent aqueous solubilities far exceeding that of the parent tertiary amine (up to a factor of 3200 at pH 8). A moderate reduction in solubility with increasing length of the alkyl chain was observed for the iodide salts of the N-alkylated bupivacaine derivatives. In case of the N-methyl-bupivacaine derivative variation of the counterion had a significant impact on the solubility with the iodide salt being 200 times less soluble than the chloride salt. X-ray analysis revealed that both the alkyl substituent and the anionic counterion influenced salt packing modes, however, in an unpredictable manner making establishment of quantitative correlations between crystal packing and solubility difficult even for a series of closely related derivatives.

A mechanistic and kinetic study of the E-ring hydrolysis and lactonization of a novel phosphoryloxymethyl prodrug of camptothecin

PURPOSE

This study was done to determine the E-ring hydrolysis and lactonization mechanism of a water-soluble 20-phosphoryloxymethyl (POM) prodrug of camptothecin (P-CPT). Specifically, the role of the phosphate group in facilitating E-ring hydrolysis was examined.

METHODS

Resolution between the lactone and carboxylate forms of P-CPT and camptothecin (CPT) was achieved with a RPHPLC assay using UV-visible detection. E-ring P-CPT hydrolysis and lactonization kinetics were followed using 20 mM acetate or phosphate buffer (micro = 0.15 NaCl) over the pH range of 4 to 8 at 25.0 degrees C. A kinetic solvent isotope effect (KSIE) study was used to further probe the mechanism of E-ring hydrolysis.

RESULTS

The hydrolysis and lactonization reactions followed pseudo-first-order kinetics in the approach to equilibrium. The equilibrium ratio of the open and closed forms of P-CPT was dependent on pH, with the closed form dominant at low pH and the open form dominant at high pH. Buffer concentration changes had little to no effect on the rate of P-CPT E-ring hydrolysis. The KSIE study provided an overall isotope effect of 2.47 and a proton inventory KSIE consistent with an intramolecular general base catalysis.

CONCLUSIONS

P-CPT has a pH-dependent equilibrium between the lactone and carboxylate forms similar but not identical to that of CPT. The results suggest a hydrolysis reaction mechanism that involves a single site hydrogen exchange facilitated intramolecularly by the dianionic phosphate moiety of P-CPT via either general base catalysis of the lactone ring attack by water or breakdown of the tetrahedral intermediate.

Chemical stability of esters of nicotinic acid intended for pulmonary administration by liquid ventilation

PURPOSE

It has been suggested that fluorocarbon liquid may be a unique vehicle for the delivery of drugs directly to the acutely injured lung. A prodrug approach was used as a means of enhancing the solubility of a model drug (nicotinic acid) in the fluorocarbon. The solubility, the chemical stability of the putative prodrugs, and the sensitivity to enzymatic hydrolysis was investigated.

METHODS

The solubility of each nicotinic acid ester was determined in buffer as a function of pH and in perflubron. The octanol/buffer partition coefficient was determined at pH 7.4. The chemical stability of the putative prodrugs was determined as a function of pH, temperature, buffer content, and ionic strength. In addition, sensitivity of the esters to enzymatic degradation was evaluated.

RESULTS

Compared with nicotinic acid, the solubility in perflubron of the esters was significantly enhanced. In aqueous buffers, the esters exhibited pseudo-first order degradation kinetics, with both acid and base catalyzed loss. Studies of the fluorobutyl ester indicate quantitative loss of the putative prodrug and release of the parent nicotinic acid. Porcine esterase accelerated the loss of fluorobutyl ester by a factor of over 200 compared with chemical hydrolysis at pH 7.4.

CONCLUSIONS

The properties of the fluorinated esters suggest that they may be suitable candidates for further testing as possible prodrugs of nicotinic acid based upon higher solubility in perflubron, rapid release of the parent drug after simple hydrolysis, and sensitivity to the presence of a model esterase enzyme.

Optically active antifungal azoles. XII. Synthesis and antifungal activity of the water-soluble prodrugs of 1-[(1R,2R)-2-(2,4-difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-1-tetrazolyl)phenyl]-2-imidazolidinone

1-[(1R,2R)-2-(2,4-Difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-1-tetrazolyl)phenyl]-2-imidazolidinone (1: TAK-456) was selected as a candidate for clinical trials, but since its water-solubility was insufficient for an injectable formulation, the quaternary triazolium salts 2 were designed as water-soluble prodrugs. Among the prodrugs prepared, 4-acetoxymethyl-1-[(2R,3R)-2-(2,4-difluorophenyl)-2-hydroxy-3-[2-oxo-3-[4-(1H-1-terazolyl)phenyl]-1-imidazolidinyl]butyl]-1H-1,2,4-triazolium chloride (2a: TAK-457) was selected as an injectable candidate for clinical trials based on the results of evaluations on solubility, stability, hemolytic effect and in vivo antifungal activities.

A novel prodrug approach for tertiary amines. 3. In vivo evaluation of two N-phosphonooxymethyl prodrugs in rats and dogs

N-phosphonooxymethyl derivatives of tertiary amine containing drugs have been identified as a novel prodrug approach for improving aqueous solubility. The in vivo reversion of two prodrugs to the corresponding parent compounds following iv and im administration to rats and dogs was investigated. Equimolar doses of parent drugs (loxapine or cinnarizine) and the corresponding prodrugs were each administered via a rapid iv infusion to rats and dogs. Equimolar doses of loxapine and its prodrug were each administered im to rats only. Blood samples were collected over 12 h, and plasma was assayed for both parent drug and intact prodrug by HPLC. Comparison of the plasma AUC for the parent drugs following administration of the parent drugs and prodrugs allowed estimation of the apparent bioavailability of parent drug from prodrug dosing. Plasma levels of the prodrugs fell below the limit of detection 5 min after iv infusion with an approximate half-life of 1 min. The mean AUCs following iv and im dosing of parent drugs were not statistically different from the parent drug AUCs obtained after prodrug dosing. The results are consistent with rapid and quantitative prodrug to parent drug reversion following administration of the phosphonooxymethyl prodrugs to the rats and dogs. This information, together with previous studies on the synthesis and physicochemical evaluation of the prodrugs, suggests that this novel prodrug strategy is a very promising approach for overcoming solubility limitations seen with many tertiary amine containing drugs at physiological pH values.