Cyclization-activated prodrugs

Exploring acetaminophen prodrugs and hybrids: a review

This critical review highlights the advances in developing new molecules for treating pain syndrome, an important issue for human health. Acetaminophen (APAP, known as paracetamol) and nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used in clinical practice despite their adverse effects. Research is being conducted to develop innovative drugs with improved pharmaceutical properties to mitigate these effects. A more practical way to achieve that is to study well-known and time-tested drugs in their molecular combinations. Accordingly, the present work explores APAP and their combined chemical entities, i.e., prodrugs (soft drugs), codrugs (mutual prodrugs), and hybrids. Due to their molecular structure, APAP prodrugs or codrugs could be considered merged or conjugated hybrids; all these names are very fluid terms. This article proposed a structural classification of these entities to better analyze their advances. So, the following: carrier-linked O-modified APAP, -linked N-modified APAP derivatives (prodrugs), and direct- and spacer-N,O-linked APAP hybrids (codrugs) are the central parts of this review and are examined, especially ester and amide NSAID-APAP molecules. The C-linked APAP and nitric oxide (NO)-releasing APAP hybrids were also briefly discussed. Prime examples of APAP-based drugs such as propacetamol, benorylate, acetaminosalol, nitroparacetamol, and agent JNJ-10450232 weave well into this classification. The proposed classification is the first and original, giving a better understanding of the SAR studies for new pain relievers research and the design development for the analgesic APAP-(or NSAID)-based compounds.

Protein and polypeptide mediated delivery to the eye

Hybrid or recombinant protein-polymers, peptide-based biomaterials, and antibody-targeted therapeutics are widely explored for various ocular conditions and vision correction. They have been noted for their potential biocompatibility, potency, adaptability, and opportunities for sustained drug delivery. Unique to peptide and protein therapeutics, their production by cellular translation allows their precise modification through genetic engineering. To a greater extent than drug delivery to other systems, delivery to the eye can benefit from the combination of locally-targeted administration and protein-based specificity. Consequently, a range of delivery platforms and administration methods have been exploited to address the ocular delivery of peptide and protein biomaterials. This review discusses a sample of preclinical and clinical opportunities for peptide-based drug delivery to the eye.

Convenient and Flexible Syntheses of gem-Dimethyl Carboxylic Triggers via Mono-Selective β-C(sp3)-H Arylation of Pivalic Acid with ortho-Substituted Aryl Iodides

This work presents a palladium(II)-catalyzed mono-selective C(sp3)-H arylation of pivalic acid for rapid construction of an important library of 3-aryl-2,2-dimethylpropanoic acids, especially those ortho-substituted-aryl compounds. The strategy greatly streamlines the...

Esterase-Mediated Sustained Release of Peptide-Based Therapeutics from a Self-Assembled Injectable Hydrogel

A synthetic strategy for conjugating small molecules and peptide-based therapeutics, via a cleavable ester bond, to a lipidated β³-tripeptide is presented. The drug-loaded β³-peptide was successfully co-assembled with a functionally inert lipidated β³-tripeptide to form a hydrogel. Quantitative release of lactose from the hydrogel, by the action of serum esterases, is demonstrated over 28 days. The esterase-mediated sustained release of the bioactive brain-derived neurotrophic factor (BDNF) peptide mimics from the hydrogel resulted in increased neuronal survival and normal neuronal function of peripheral neurons. These studies define a versatile strategy for the facile synthesis and co-assembly of self-assembling β³-peptide-based hydrogels with the ability to control drug release using endogenous esterases with potential in vivo applications for sustained localized drug delivery.

Aminoalkoxycarbonyloxymethyl Ether Prodrugs with a pH-Triggered Release Mechanism: A Case Study Improving the Solubility, Bioavailability, and Efficacy of Antimalarial 4(1H)-Quinolones with Single Dose Cures

Preclinical and clinical development of numerous small molecules is prevented by their poor aqueous solubility, limited absorption, and oral bioavailability. Herein, we disclose a general prodrug approach that converts promising lead compounds into aminoalkoxycarbonyloxymethyl (amino AOCOM) ether-substituted analogues that display significantly improved aqueous solubility and enhanced oral bioavailability, restoring key requirements typical for drug candidate profiles. The prodrug is completely independent of biotransformations and animal-independent because it becomes an active compound via a pH-triggered intramolecular cyclization-elimination reaction. As a proof-of-concept, the utility of this novel amino AOCOM ether prodrug approach was demonstrated on an antimalarial compound series representing a variety of antimalarial 4(1H)-quinolones, which entered and failed preclinical development over the last decade. With the amino AOCOM ether prodrug moiety, the 3-aryl-4(1H)-quinolone preclinical candidate was shown to provide single-dose cures in a rodent malaria model at an oral dose of 3 mg/kg, without the use of an advanced formulation technique.

Design of a PEGylated Antimicrobial Prodrug with Species-Specific Activation

The rise of multidrug-resistant (MDR) "superbugs" has created an urgent need to develop new classes of antimicrobial agents to target these organisms. Oligothioetheramides (oligoTEAs) are a unique class of antimicrobial peptide (AMP) mimetics with one promising compound, BDT-4G, displaying potent activity against MDR Pseudomonas aeruginosa clinical isolates. Despite widely demonstrated potency, BDT-4G and other AMP mimetics have yet to enjoy broad preclinical success against systemic infections, primarily due to their cytotoxicity. In this work, we explore a prodrug strategy to render BDT-4G inactive until it is exposed to an enzyme secreted by the targeted bacteria. The prodrug consists of polyethylene glycol (PEG) conjugated to BDT-4G by a peptide substrate. PEG serves to inactivate and reduce the toxicity of BDT-4G by masking its cationic charge and antimicrobial activity is recovered following site-specific cleavage of the short peptide linker by LasA, a virulence factor secreted by P. aeruginosa. This approach concurrently reduces cytotoxicity by greater than 1 order of magnitude in vitro and provides species specificity through the identity of the cleavable linker.

Fluorogenic Enzyme-Triggered Domino Reactions Producing Quinoxalin-2(1H)-one-based Heterocycles

A simple and effective biocompatible domino reaction triggered by a model protease and leading to the formation of strongly fluorescent quinoxalin-2(1H)-one N-heterocycles is described. Some positive attributes including versatility and the ability to provide outstanding fluorescence "OFF-ON" responses were revealed by this work. They open the way for practical applications of this novel type of "covalent-assembly"-based fluorescent probe in the fields of sensing and bioimaging.

A curcumin-diglutaric acid conjugated prodrug with improved water solubility and antinociceptive properties compared to curcumin

In this work, a curcumin-diglutaric acid (CurDG) prodrug was synthesized by conjugation of curcumin with glutaric acid via an ester linkage. The water solubility, partition coefficient, release characteristics, and antinociceptive activity of CurDG were compared to those of curcumin. The aqueous solubility of CurDG (7.48 μg/mL) is significantly greater than that of curcumin (0.068 μg/mL). A study in human plasma showed that the CurDG completely releases curcumin within 2 h, suggesting the ability of CurDG to serve as a prodrug of curcumin. A hot plate test in mice showed the highest antinociceptive effect dose of curcumin at 200 mg/kg p.o., whereas CurDG showed the same effect at an effective dose of 100 mg/kg p.o., indicating that CurDG significantly enhanced the antinociceptive effect compared to curcumin. The enhanced antinociceptive effect of CurDG may be due to improved water solubility and increased oral bioavailability compared to curcumin.

Self-assembling prodrugs

Covalent modification of therapeutic compounds is a clinically proven strategy to devise prodrugs with enhanced treatment efficacies. This prodrug strategy relies on the modified drugs that possess advantageous pharmacokinetic properties and administration routes over their parent drug. Self-assembling prodrugs represent an emerging class of therapeutic agents capable of spontaneously associating into well-defined supramolecular nanostructures in aqueous solutions. The self-assembly of prodrugs expands the functional space of conventional prodrug design, affording a possible pathway to more effective therapies as the assembled nanostructure possesses distinct physicochemical properties and interaction potentials that can be tailored to specific administration routes and disease treatment. In this review, we will discuss the various types of self-assembling prodrugs in development, providing an overview of the methods used to control their structure and function and, ultimately, our perspective on their current and future potential.

Inhibition of P-glycoprotein, multidrug resistance-associated protein 2 and cytochrome P450 3A4 improves the oral absorption of octreotide in rats with portal hypertension

The aim of the present study was to increase the intestinal transport of octreotide (OCT) by targeting the first-pass impact to identify a potential method for decreasing portal vein pressure (PVP) using oral OCT. Thus, the bioavailability of intestinally absorbed OCT was evaluated in normal rats and rats with portal hypertension (PH) that had been administered P-glycoprotein/multidrug resistance-associated protein 2/cytochrome P450 3A4 (P-gp/MRP2/CYP3A4) inhibitors. The mRNA and protein expression levels of P-gp, MRP2 and CYP3A4 were evaluated in normal and PH rats with or without OCT and the inhibitors using RT-PCR, western blot and immunohistochemical analyses. The potential effects of the inhibitor administration on PVP were also examined. The results suggest that P-gp, MRP2 and CYP3A4 play important roles in prohibiting the enteral absorption of OCT, particularly under a PH environment. Moreover, inhibitors of P-gp, MRP2 and CYP3A4 decrease the first-pass effects of OCT and effectively reduce PVP under PH conditions. Therefore, the present results suggest P-gp, MRP2 and CYP3A4 are key factors in the intestinal absorption of OCT. The inhibition of P-gp, MRP2 and CYP3A4 can markedly decrease the first-pass effects of OCT, and their use may facilitate the use of orally administered OCT.

A novel N-terminal degradation reaction of peptides via N-amidination

The cleavage of amide bonds requires considerable energy. It is difficult to cleave the amide bonds in peptides at room temperature, whereas ester bonds are cleaved easily. If peptide bonds can be selectively cleaved at room temperature, it will become a powerful tool for life science research, peptide prodrug, and tissue-targeting drug delivery systems. To cleave a specific amide bond at room temperature, the decomposition reaction of arginine methyl ester was investigated. Arginine methyl ester forms a dimer; the dimer releases a heterocyclic compound and ornithine methyl ester at room temperature. We designed and synthesized N-amidinopeptides based on the decomposition reaction of arginine methyl ester. Alanyl-alanine anilide was used as the model peptide and could be converted into N-degraded peptide, alanine anilide, via an N-amidination reaction at close to room temperature. Although the cleavage rate in pH 7.4 phosphate buffered saline (PBS) at 37°C was slow (t1/2=35.7h), a rapid cleavage rate was observed in 2% NaOH aq (t1/2=1.5min). To evaluate the versatility of this reaction, a series of peptides with Lys, Glu, Ser, Cys, Tyr, Val, and Pro residue at the N-terminal were synthesized; they showed rapid cleavage rates of t1/2 values from 1min to 10min.

Irreversible sortase A-mediated ligation driven by diketopiperazine formation

Sortase A (SrtA)-mediated ligation has emerged as an attractive tool in bioorganic chemistry attributing to the remarkable specificity of the ligation reaction and the physiological reaction conditions. However, the reversible nature of this reaction limits the efficiency of the ligation reaction and has become a significant constraint to its more widespread use. We report herein a novel set of SrtA substrates (LPETGG-isoacyl-Ser and LPETGG-isoacyl-Hse) that can be irreversibly ligated to N-terminal Gly-containing moieties via the deactivation of the SrtA-excised peptide fragment through diketopiperazine (DKP) formation. The convenience of the synthetic procedure and the stability of the substrates in the ligation buffer suggest that both LPETGG-isoacyl-Ser and LPETGG-isoacyl-Hse are valuable alternatives to existing irreversible SrtA substrate sequences.

Glycine homopeptides: the effect of the chain length on the crystal structure and solid state reactivity

A series of linear oligoglycines has been studied to reveal the trends in their crystal structure, molecular conformation and thermally induced reactions.

Two-step activation prodrugs: transplatin mediated binding of chemotherapeutic agents to vitamin B12

Clinically approved organic chemotherapeutic drugs such as cytarabine, dacarbazine and anastrozole were attached to B12via a {CN-trans-Pt(NH3)2}-bridge to yield [{Co}-CN-{trans-Pt(NH3)2}-{drug}](2+). The active organic drugs are protected by the platinum complex and by B12, which represents at the same time the targeting vector. We refer to these bioconjugates as two-step activation prodrugs since two reactions are finally required to liberate the actual organic drugs. All three prodrugs are soluble and stable in water. The physiological stability and the therapeutic efficiency of [{Co}-CN-{trans-Pt(NH3)2}-{cytarabine}](2+) (2) were studied. Under physiological conditions, 2 is stable for 3 days. Its affinity to the cobalamin transport proteins (haptocorrin, intrinsic factor and transcobalamin) is not substantially affected despite the introduction of a bulky group in the β-axial position. The cleavage of the [trans-CN-Pt(NH3)2-{cytarabine}](+) complex was observed upon chemical reduction of Co(III)→ Co(II) with Zn(0). Cytarabine was subsequently released from the cleaved complex to exhibit its cytotoxicity. 2 displayed a reduced cytotoxicity (IC50 = 230 ± 62 nM) as compared to cytarabine (IC50 = 30 ± 5 nM). However, cytarabine released from 2 showed comparable cytotoxicity (IC50 = 30 ± 11 nM).

Magnetogenesis under physiological conditions with probes that report on (bio-)chemical stimuli

Switched on: A molecular concept allows the generation of magnetism in an aqueous sample under the influence of a freshly added (bio-)chemical analyte. The analyte (a chemical reagent or enzyme) triggers the conversion of the probe, a diamagnetic chelate compound, into a paramagnetic compound (see scheme). The two probes prepared are easily accessible iron(II) chelates, and are operative at physiological conditions and/or in serum.

Synthesis and characterization of novel quick-release propofol prodrug via lactonization

The water-soluble derivatives of propofol have gained attention as a method to increase solubility of propofol. According to the principle of lactonization, the lead compound HX0969 was synthesized first and then the pharmacological features of HX0969 were evaluated in a comparison with those of propofol in the SD rats. Then, HX0969 disodium phosphate monoester (HX0969W) and glycine ester trifluoroacetic acid salt (HX101230) were synthesized, and their pharmacological features were compared with those of Lusedra®, which has been recognized and marketed as a water-soluble prodrug of propofol since 2008. The results showed that HX0969 could produce an anesthetic effect within a few seconds (3.6±3.0s) and its therapeutic index was 4.66 in the SD rat. The pharmacodynamic characteristics of HX0969W were similar to those of the Lusedra®. HX101230 could still produce an anesthetic effect within 60s in the rats though its therapeutic index was not so high (TI=2.96). Therefore, our study has indicated that HX0969 is a potentially useful lead compound of propofol derivative. Its rapid anesthetic effect is probably associated with lactonization.

Flexible or fixed: a comparative review of linear and cyclic cancer-targeting peptides

Peptides can serve as versatile cancer-targeting ligands and have been used for clinically relevant applications such as cancer imaging and therapy. A current and long-standing focus within peptide research is the creation of structurally constrained peptides generated through cyclization. Cyclization is envisioned to enhance the selective binding, uptake, potency and stability of linear precursors. This review compares closely related linear and cyclic peptides in these respects. Peptide cyclization generally improves the selective binding and stability of linear precursors; however, not all cyclization strategies and constrained geometries enhance these properties to the same extent. In some instances, linear analogues actually have better cancer-targeting properties compared with their cyclic counterparts. Although cyclization does not necessarily improve the cancer-targeting properties of linear analogues, cyclic peptides may obtain properties that allow them to be used for additional applications. This review aims to convey the advantages and limitations of cyclic cancer-targeting peptides.

Design, synthesis, and evaluation of potential prodrugs of DFMO for reductive activation

A series of potential DFMO prodrugs was designed through the incorporation of 4-nitrobenzyl ester or carbamate groups for potential activation by trypanosomal nitroreductase. It was found that only modification of N(ε)-amino group of DFMO by 4-nitro-2-fluorobenzyloxycarbonyl resulted in significant trypanocidal activity and could serve as a lead for further investigation.

Dipeptidyl peptidase IV-activated prodrugs of anti-varicella zoster virus bicyclic nucleoside analogues containing different self-cleavage spacer systems

A new type of double prodrug of the antiviral family of bicyclic nucleoside analogues (BCNA) bearing cyclization self-cleavage spacers between the Val-Pro dipeptide sequence as well as the parent compound were synthesized and evaluated with regard to activation by the DPPIV/CD26 enzyme and for their stability in human and bovine serum. In buffer solution, carbamate and ester prodrugs were found to be chemically stable. Most prodrugs containing a dipeptidyl linker efficiently converted into the BCNA parent drug. In contrast, the Val-Pro alkyldiamino prodrugs converted predominantly into their alkyldiamino prodrug intermediates in the presence of CD26 and human serum. A marked increase in water solubility was observed for all prodrugs. In contrast to the parent compound, a tetrapeptide prodrug containing the Val-Val dipeptide as a self-cleavage spacer released substantial amounts of the BCNA parent drug at the basolateral side of Caco-2 cell cultures and exhibited 15- to 20-fold increased bioavailability in mice relative to the poorly bioavailable parent compound.

Advances in simultaneous DSC-FTIR microspectroscopy for rapid solid-state chemical stability studies: some dipeptide drugs as examples

The solid-state chemistry of drugs has seen growing importance in the pharmaceutical industry for the development of useful API (active pharmaceutical ingredients) of drugs and stable dosage forms. The stability of drugs in various solid dosage forms is an important issue because solid dosage forms are the most common pharmaceutical formulation in clinical use. In solid-state stability studies of drugs, an ideal accelerated method must not only be selected by different complicated methods, but must also detect the formation of degraded product. In this review article, an analytical technique combining differential scanning calorimetry and Fourier-transform infrared (DSC-FTIR) microspectroscopy simulates the accelerated stability test, and simultaneously detects the decomposed products in real time. The pharmaceutical dipeptides aspartame hemihydrate, lisinopril dihydrate, and enalapril maleate either with or without Eudragit E were used as testing examples. This one-step simultaneous DSC-FTIR technique for real-time detection of diketopiperazine (DKP) directly evidenced the dehydration process and DKP formation as an impurity common in pharmaceutical dipeptides. DKP formation in various dipeptides determined by different analytical methods had been collected and compiled. Although many analytical methods have been applied, the combined DSC-FTIR technique is an easy and fast analytical method which not only can simulate the accelerated drug stability testing but also at the same time enable to explore phase transformation as well as degradation due to thermal-related reactions. This technique offers quick and proper interpretations.

Investigation into drug release from colon-specific azoreductase-activated steroid prodrugs using in-vitro models

OBJECTIVES

The aim of this study was to investigate drug release from a double steroid prodrug, OPN501, which incorporates a phenylpropionate linker, and its phenylacetate analogue. The prodrugs, which were designed to deliver prednisolone to the colon for the treatment of inflammatory bowel disease, are based on a novel design that requires sequential azoreductase activity and cyclization of an amino ester to trigger drug release. We sought to explain the divergent effects of the two compounds in anti-inflammatory models and to justify the selection of OPN-501 for clinical development.

METHODS

The compounds were incubated in mouse colonic contents (10%) fermented in brain heart infusion under anaerobic conditions. The disappearance of the prodrugs and release of prednisolone was monitored by HPLC. We then developed a method for assessment of prodrug activation using suspensions of Clostridium perfringens, an anaerobe from the human colon. The cyclization of the compounds was studied in various media, assessing the influence of pH and bulk solvent polarity on cyclization rate using HPLC and NMR.

KEY FINDINGS

The prodrugs were activated via multiple pathways releasing prednisolone in mouse colonic ferment. The compounds released prednisolone by reduction-cyclization in C perfringens suspension. The active OPN-501 generated a stoichiometric amount of prednisolone following azoreductase activation, whereas its analogue did not. The pH rate profile for the cyclization of the amino intermediates of the two compounds revealed significant differences in rate at pH values relevant to the inflamed colon, which explain in part the different amounts of drug produced.

CONCLUSIONS

The steroid prodrug OPN-501 has optimal drug release characteristics for colon targeting because of a kinetic advantage of a six-membered ring formation in the aminolysis reactions of anilides. The results are relevant to the development of OPN-501 but also to cyclization strategies in prodrug design especially for colon targeting.

N-(2,2-Dimethyl-2-(2-nitrophenyl)acetyl)-4-aminocyclophosphamide as a potential bioreductively activated prodrug of phosphoramide mustard

N-(2,2-Dimethyl-2-(2-nitrophenyl)acetyl)-4-aminocyclophosphamide isomers (DMNA-NH-CPA, 4) were synthesized stereospecifically from Boc-L-Hse(OBn)-OH and the degradation of the corresponding reduced amine 5a was investigated by UV/vis spectroscopy and LC/MS. The rate of cyclization of 5a was found to increase with decreasing pH, with half-lives ranging from 3.2 to 54 min at pH 4-7.4, suggesting that the cyclization is catalyzed by the hydronium ions. LC/MS analysis of the degradation products of 5a indicates that 4-aminocyclophosphamide is rapidly released from 4 upon reductive activation under acidic conditions and further decomposes into the cytotoxic phosphoramide mustard. These results validated 4-aminocyclophosphamide as a prodrug form of phosphoramide mustard and suggest that compound 4 can potentially be used as a prodrug of phosphoramide mustard for bioreductive activation.