A disadvantage of the non-covalent approach is that in order to prevent uncontrolled, burst-type release of the drug, encapsulation of the drug has to be highly efficient by creating a sterically highly crowded environment.
Restraining the diffusion of an unbound, water soluble drug molecule requires strong van der Waals contacts, frequently mediated through hydrophobic moieties. In addition, such amino-containing drugs readily undergo side reactions with carrier degradation products see, for example, D.
Lee et al. Furthermore, dependence of the release mechanism of the drug upon biodegradation may cause interpatient variability. Alternatively, the drugs may be conjugated to a carrier through permanent covalent bonds.
This approach is applied to various classes of molecules, from so-called small molecules, through natural products up to larger proteins. Liraglutide is an example of a peptide drug that achieves an extended half-life by permanent covalent modification with a palmitoyl moiety. The fatty acid alkyl chain serves to provide albumin binding in vivo and the palmitoylated peptide forms an albumin complex that acts as a drug reservoir in the blood stream.
Albuferon is an example of a protein drug that achieves an extended half-life by permanent covalent modification with another protein that in itself has a long half-life.
The corresponding fusion protein of albumin and interferon alpha, Albuferon, exhibits a significantly extended half-life as compared to interferon alpha. Many small molecule medicinal agents, like alkaloids and anti-tumor agents, show low solubility in aqueous fluids. One way to solubilize these small molecule compounds is to conjugate the small molecule compounds to hydrophilic water-soluble polymers. A variety of water-soluble polymers, such as human serum albumin, dextran, lectins, poly ethylene glycol PEG , poly styrene-co-maleic anhydride , poly N-hydroxypropylmethacrylamide , poly divinyl ether-co-maleic anhydride , hyaluronic acid have been described for this purpose R.
Duncan, Nature Rev. Drug Disc. Covalent modification of biological molecules with poly ethylene glycol has been extensively studied since the late s. So-called PEGylated proteins have shown improved therapeutic efficacy by increasing solubility, reducing immunogenicity, and increasing circulation half-live in vivo due to reduced renal clearance and proteolysis by enzymes see, for example, Caliceti P.
Drug Deliv. However, many biological molecules such as IFNalfa2, saquinavir or somatostatin are inactive or show decreased biological activity when a carrier is covalently conjugated to the drug T. Peleg-Shulman et al. In order to avoid shortcomings imposed by either the non-covalent polymer mixtures or the permanent covalent attachment, it may be preferable to employ a prodrug approach for chemical conjugation of the drug to the polymer carrier.
In such polymeric prodrugs, the biologically active moieties drugs, therapeutic, biological molecule, etc. Prodrugs are therapeutic agents that are almost inactive per se but are predictably transformed into active molecular entities see B.
Testa, J. The carrier prodrug approach may be applied in such a fashion that the drug is released in vivo from the polymer in order to regain its biological activity. The reduced biological activity of the prodrug as compared to the released drug is of advantage if a slow or controlled release of the drug is desired. In this case, a relatively large amount of prodrug may be administered without concomitant side effects and the risk of overdosing.
Release of the drug occurs over time, thereby reducing the necessity of repeated and frequent administration of the drug. Prodrug activation may occur by enzymatic or non-enzymatic cleavage of the temporary bond between the carrier and the drug molecule, or a sequential combination of both, i. In an enzyme-free in-vitro environment such as an aqueous buffer solution, a temporary bond such as an ester or amide may undergo hydrolysis, but the corresponding rate of hydrolysis may be much too slow and thus outside the therapeutically useful range.
In an in vivo environment, esterases or amidases are typically present and the esterases and amidases may cause significant catalytic acceleration of the kinetics of hydrolysis from twofold up to several orders of magnitude see, for example, R. Greenwald et al. Prodrugs fall in two classes, bioprecursors and carrier-linked prodrugs. Bioprecursors do not contain a carrier group and are activated by the metabolic creation of a functional group.
In carrier-linked prodrugs the active substance is linked to a carrier moiety by a temporary linkage. The carrier may be biologically inert, such as, for instance, PEG or may have targeting properties, conferred by antibodies, for example. This invention is concerned with polymeric carrier-linked or macromolecular prodrugs, where the carrier itself is a macromolecule such as a carrier protein or polysaccharide or poly ethylene glycol.
Cleavage of a carrier prodrug generates a molecular entity drug of increased bioactivity and at least one side product, the carrier. After cleavage, the bioactive entity will reveal at least one previously conjugated and thereby protected functional group, and the presence of this group typically contributes to the drug's bioactivity. In order to implement a prodrug strategy, at least one selected functional group in the drug molecule is employed for attachment of the carrier polymer.
Preferred functional groups are hydroxyl or amino groups. Consequently, both the attachment chemistry and hydrolysis conditions depend on the type of functional group employed. Numerous macromolecular prodrugs are described in the literature where the temporary linkage is a labile ester bond.
In these cases, the functional group provided by the bioactive entity is either a hydroxyl group or a carboxylic acid e. Greenwald, A. Pendri, C. Conover, H. Zhao, Y. Biosynthesis of the morphine alkaloids. Kirby GW. Graphical Abstract Open in a separate window 1.
Many of the natural products and their semisynthetic derivatives have served as front line therapeutics to treat a wide variety of diseases, ranging from microbial infections, cancer, cardiovascular conditions, and as immunosuppressants.
Based on biosynthetic origin and fundamental building blocks, the major families of natural products include polyketides PKs , nonribosomal peptides NRPs , ribosomally synthesized and post-translationally modified peptides RiPPs , isoprenoids, alkaloids including phenylpropanoids and indole alkaloids, aminoglycosides, nucleosides, etc.
The first phase involves the polymerization of building blocks, such as acetate for PKs, amino acids for NRPs and RiPPs, and isoprene units for terpenes. The polymerization process builds the carbon backbone of the molecules, and in most cases, cyclizes the molecule in a regioselective fashion to yield a basic scaffold of the final natural product. This scaffold, which can be called the aglycone in some cases, is then subjected to a barrage of post-assembly modifications that serve a variety of purposes, such as rigidifying the molecule and fixing the three-dimensional conformation; introducing polar groups to increase the water solubility; reveal structural motifs and reactive sites as warheads for target inhibition; and appending oligosaccharides that bind to specific DNA sequences.
It is during the post-assembly steps that the natural products can undergo significant structural morphing to result in the final bioactive compounds. The types of enzyme modifications that will be reviewed here are cyclization reactions through redox alteration of acyclic substrates.
The term "hyperbranched moiety" refers to a moiety comprising at least one branching point. Such branching point comprises, for example, an at least 3-fold substituted carbocycle, an at least 3-fold substituted heterocycle, a tertiary carbon atom, a quaternary carbon atom or a tertiary nitrogen atom. The term "functional group" refers to specific groups of atoms within molecules that can undergo characteristic chemical reactions. For example, the reaction of an amine functional group with a carboxyl functional group results in an amide linkage.
A "therapeutically effective amount" of carrier-linked prodrug as used herein means an amount sufficient to cure, alleviate or partially arrest the clinical manifestations of a given disease and its complications. An amount adequate to accomplish this is defined as "therapeutically effective amount". Effective amounts for each purpose will depend on the severity of the disease or injury as well as the weight and general state of the subject.
It will be understood that determining an appropriate dosage may be achieved using routine experimentation, by constructing a matrix of values and testing different points in the matrix, which is all within the ordinary skills of a trained physician.
The remainder can be made up of other polymers. The term "poly oxazoline -based polymer" is defined accordingly. A "peptide" is a single linear polymer chain of up to about amino acids, preferably up to about 50 amino acids, more preferably up to about 25 amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
Preferably, a peptide is a single linear polymer chain of at least about 4 amino acids, more preferably of at least about 6 amino acids. A "protein" or "polypeptide" is a single linear polymer chain of more than about amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
Proteins or polypeptides may comprise modifications, for example by C-terminal amidation. The term "polymer cassette" relates to peptides of defined, individual amino acid stretches. Polymer cassettes may be used to form a polypeptide moiety POL. Thus, a polypeptide moiety POL comprises, preferably consists of one or more, in particular of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 polymer cassette s , which may be of the same or of different sequence.
As used herein, the term "random coil" relates to any conformation of a polymeric molecule, including proteins, in which the individual monomeric elements that form said polymeric structure are essentially randomly oriented towards the adjacent monomeric elements while still being chemically bound to said adjacent monomeric elements.
In particular, a polypeptide or protein having random coil conformation substantially lacks a defined secondary and tertiary structure. The nature of polypeptide random coils and their methods of experimental identification are known to the person skilled in the art. In particular, the lack of secondary and tertiary structure of a protein may be determined by circular dichroism CD measurements.
CD spectroscopy represents a light absorption spectroscopy method in which the difference in absorbance of right- and left-circularly polarized light by a substance is measured. The secondary structure of a protein can be determined by CD spectroscopy using far-ultraviolet spectra with a wavelength between approximately and nm. At these wavelengths the different secondary structures commonly found in conformations each give rise to a characteristic shape and magnitude of the CD spectrum.
Accordingly, by using CD spectrometry the skilled artisan is readily capable of determining whether an amino acid polymer adopts random coil conformation at physiological conditions. When determining whether a peptide or protein adopts random coil conformation under experimental conditions using the methods as described herein, the biophysical parameters such as temperature, pH, osmolarity and protein content may be different to the physiological conditions normally found in vivo.
Examples of such buffers are, e. Generally, the pH of a buffer representing physiological conditions should lie in a range from 6. Accordingly, the pharmaceutical compositions of the present invention encompass any composition obtainable by admixing a water-soluble carrier-linked prodrug of the present invention and optionally one or morepharmaceutically acceptable excipient.
The term "excipient" refers to a diluent, adjuvant, or vehicle with which a water-soluble carrier-linked prodrug is administered. Such pharmaceutical excipient can be sterile liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, including but not limited to peanut oil, soybean oil, mineral oil, sesame oil and the like.
Water is a preferred excipient when the pharmaceutical composition is administered orally. Saline and aqueous dextrose are preferred excipients when the pharmaceutical composition is administered intravenously. Saline solutions and aqueous dextrose and glycerol solutions are preferably employed as liquid excipients for injectable solutions. Suitable pharmaceutical excipients include starch, glucose, lactose, sucrose, mannitol, trehalose, gelatin, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, dried skim milk, glycerol, propylene, glycol, water, ethanol and the like.
The composition, if desired, can also contain minor amounts of wetting or emulsifying agents, pH buffering agents, like, for example, acetate, succinate, tris, carbonate, phosphate, HEPES 4- 2-hydroxyethyl piperazineethanesulfonic acid , MES 2- N-morpholino ethanesulfonic acid , or can contain detergents, like Tween, poloxamers, poloxamines, CHAPS, Igepal, or amino acids like, for example, glycine, lysine, or histidine. These compositions can take the form of solutions, suspensions, emulsions, tablets, pills, capsules, powders, sustained-release formulations and the like.
The composition can be formulated as a suppository, with traditional binders and excipients such as triglycerides. Oral formulation can include standard excipients such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc. Examples of suitable pharmaceutical excipients are described in "Remington's Pharmaceutical Sciences" by E. The formulation should suit the mode of administration. Suitable methods for drying are spray-drying and lyophilization freeze-drying.
The preferred method of drying is lyophilization. This terminology does not exclude additional drying steps which may occur in the manufacturing process prior to filling the composition into the final container. Typically, the sublimed water is collected by desublimation. Optionally, one or more hydrogen atom s of an alkyl carbon may be replaced by a substituent as indicated herein.
The term C alkynyl is defined accordingly.
Delivery of chondroitinase ABC and glial cell line-derived neurotrophic factor from silk fibroin conduits enhances peripheral nerve regeneration. Those of ordinary skill in the art will recognize that other elements are desirable for implementing the present invention. In particular, the lack of secondary and tertiary structure of a protein may be determined by circular dichroism CD measurements. EP 10 Synthesis of two subunits of the macrolide domain of the immunosuppressive agent sanglifehrin a and assembly of a macrolactone precursor. Synthesis of the [14C]-labeled antiobesity agent Ro
Furthermore, as isocyanate formation is not observed for secondary carbamate hydrolysis, such groups offer more predictable release rates and predictable hydrolysis products with a greatly improved safety profile compared to primary carbamates. Such shape may be of any geometry and it is understood that such an individual hydrogel object is to be considered as a single molecule consisting of components wherein each component is connected to each other component through chemical bonds. Typically, the sublimed water is collected by desublimation. Total synthesis of - epicylindrospermopsin, a toxic metabolite of the freshwater cyanobacterium aphanizomenonovalisporum, and assignment of its absolute configuration. Journal of the American Chemical Society. Strategies for the synthesis of the cyclopropyl-substituted lactone family of oxylipins Synlett.
A "peptide" is a single linear polymer chain of up to about amino acids, preferably up to about 50 amino acids, more preferably up to about 25 amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. A new cobalt-salen catalyst for asymmetric cyclopropanation. Many of the natural products and their semisynthetic derivatives have served as front line therapeutics to treat a wide variety of diseases, ranging from microbial infections, cancer, cardiovascular conditions, and as immunosuppressants. The term 9 to 11 membered heterobicycle also includes spiro structures of two rings like 1,4-dioxaazaspiro[4. Oral formulation can include standard excipients such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc. A "traceless prodrug linker" refers to a linker from which a drug is released in its free form, meaning that upon release from the promoiety the drug does not contain any traces of the promoiety.
This approach is applied to various classes of molecules, from so-called small molecules, through natural products up to larger peptides and proteins. Synthesis of the C9-C32 segment of phorboxazole A.
The transformations from acyclic precursors to cyclized products can afford morphed scaffolds, structural rigidity and biological activities. Covalent modification of biological molecules with poly ethylene glycol has been extensively studied since the late s. In addition, the subterm "aromatic amine-containing" means that the respective biologically active moiety D and analogously the corresponding drug D-H contains at least one aromatic fragment which is substituted with at least one amino group. If the linker structure is designed such that the first amine may intramolecularly catalyze the hydrolysis of the carbamate bond to the drug moiety, the hydrolysis of the carbamate bond may be facilitated to the extent that hydrolysis under physiological conditions in a time range useful for drug delivery is possible. Synthesis and antiproliferative evaluation of new zampanolide mimics.
This scaffold, which can be called the aglycone in some cases, is then subjected to a barrage of post-assembly modifications that serve a variety of purposes, such as rigidifying the molecule and fixing the three-dimensional conformation; introducing polar groups to increase the water solubility; reveal structural motifs and reactive sites as warheads for target inhibition; and appending oligosaccharides that bind to specific DNA sequences. After cleavage, the bioactive entity will reveal at least one previously conjugated and thereby protected functional group, and the presence of this group typically contributes to the drug's bioactivity. Buffering capacity may be adjusted to match the conditions most sensitive to pH stability.