DETAILED DESCRIPTION OF THE INVENTION

[0039] I. Definitions

[0040] Terms used herein are based upon their recognized meanings and should be clearly understood by those skilled in the art.

[0041] The term “alkyl” refers to a straight or branched saturated monovalent hydrocarbon radical having the number of carbon atoms as indicated.

[0042] The term “alkenyl” refers to a straight or branched unsaturated monovalent hydrocarbon radical having the number of carbon atoms as indicated and the distinguishing feature of a carbon-carbon double bond.

[0043] The term “alkynyl” refers to a straight or branched unsaturated monovalent hydrocarbon radical having the number of carbon atoms as indicated and the distinguishing feature of a carbon-carbon triple bond.

[0044] The term “cycloalkyl” refers to a cyclic saturated monovalent hydrocarbon radical having the number of carbon atoms as indicated.

[0045] The terms “cycloalkenyl” and “cycloalkynyl” refer to cyclic unsaturated monovalent hydrocarbon radicals. A “cycloalkenyl” is characterized by a carbon-carbon double bond and a “cycloalkynyl” is characterized by a carbon-carbon triple bond.

[0046] The term “aryl” refers to a monovalent unsaturated aromatic carbocyclic radical having one or two rings, such as phenyl, naphthyl, indanyl or biphenyl, or to a monovalent unsaturated aromatic heterocyclic radical such as quinolyl, dihydroisoxazolyl, furanyl, imidazolyl, pyridyl, phthalimido, thienyl and the like.

[0047] The term “alkaryl” refers to an aryl group substituted with one or more alkyl groups.

[0048] The term “aralkyl” refers to an alkyl group substituted with one or more aryl groups.

[0049] The term “alkanediyl” refers to a straight or branched saturated divalent hydrocarbon radical having the number of carbon atoms indicated.

[0050] The terms “alkenediyl” and “alkynediyl” refer to straight or branched unsaturated divalent hydrocarbon radicals. An “alkenediyl” is characterized by a carbon-carbon double bond and an “alkynediyl” is characterized by a carbon-carbon triple bond.

[0051] The term “cycloalkanediyl” refers to a cyclic saturated divalent hydrocarbon radical having the number of carbon atoms indicated.

[0052] The terms “cycloalkenediyl” and “cycloalkynediyl” refer to cyclic unsaturated divalent hydrocarbon radicals. A “cycloalkenediyl” is characterized by a carbon-carbon double bond and a “cycloalkynediyl” is characterized by a carbon-carbon triple bond.

[0053] The term “arylenediyl” refers to a divalent unsaturated aromatic carbocyclic radical having one or two rings. The term “alkarylenediyl” refers to an arylenediyl substituted with one or more alkyl groups and the term “aralkylenediyl” refers to an alkylenediyl” substituted with one or more aryl groups.

[0054] The term “peptide bond” is used in its common accepted meaning.

[0055] The term “hydrolytically-labile bond” refers to a bond that is capable of undergoing hydrolysis, such as an ester, amide, acetal, or hydrazone bond. Preferably, the hydrolytically-labile bond is labile under acid conditions.

[0056] The term “halo” refers to chloro, bromo, iodo and fluoro atoms.

[0057] The term “saccharide” is used in its common accepted meaning. The terms “polysaccharide” and “oligosaccharide” refer to carbohydrate molecules containing more than one saccharide unit.

[0058] The term “activating/protecting group” refers to a group in a multifinctional compound which may temporarily activate or temporarily block a reactive site wherein a chemical reaction is to be carried out selectively at a reactive site. The reactive site may be other than the site occupied by the “activating/protecting group.” The activating/protecting groups referred to, in the context of the present invention, are those commonly known activating/protecting groups including, but not limited to, activating groups such as N-succinimidyl, pentachlorophenyl, pentafluorophenyl, para-nitrophenyl, dinitrophenyl, N-phthalimido, N-norbomyl, cyanomethyl, pyridyl, trichlorotriazine, 5-chloroquinilino, and protecting groups such as N-(9-fluorenyl-methoxycarbonyl) (Fmoc), carbobenzyloxy (Cbz), 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-ethyl (Dde) and imidazolyl.

[0059] The term “prepolymer” refers to a reactant used to make a polymer, that is, to monomers and other subunits from which polymers may be formed.

[0060] The term “therapeutically effective amount” refers to the amount which, when administered to a patient for treating a disease, is sufficient to effect such treatment for the disease.

[0061] The term “treating” or “treatment” is intended to include inhibiting the disease (i.e., arresting its development) and relieving the disease (i.e., causing regression of the disease).

[0062] II. The Degradable Polymers

[0063] The novel degradable polymers are represented by Formula (I) 2

[0064] wherein R and R ¹ are selected from the group consisting of hydrogen, C _1-18 alkyl, C _2-18 alkenyl, C _2-18 alkynyl, C _6-18 aryl, C _7-18 alkaryl and C _7-18 aralkyl groups;

[0065] X is a group capable of being covalently conjugated to a bioactive agent via a peptidic or a hydrolytically-labile bond;

[0066] Y is a group selected from the group consisting of C _1-200 alkanediyl, C _2-200 alkenediyl, C _2-200 alkynediyl, C _6-200 cycloalkanediyl, C _6-200 cycloalkenediyl, C _6-200 cycloalkynediyl, C _6-200 arylenediyl, C _6-200 alkarylenediyl, C _6-200 aralkylenediyl groups, or any of the above groups wherein the carbon backbone is substituted with one or more oxygen atoms within the carbon backbone; and

[0067] n is an integer of 2-10,000.

[0068] III. Presently Preferred Embodiments

[0069] In a preferred embodiment, R and R ¹ in Formula (I) are the same and are selected from hydrogen, C _1-12 alkyl, C _2-12 alkenyl, C _2-12 alkynyl, C _6-12 aryl, C _7-12 alkaryl and C _7-12 aralkyl groups; more preferably hydrogen, C _1-4 alkyl, C _2-4 alkenyl, C _2-4 alkynyl, C _6-10 aryl, C _7-10 alkaryl and C _7-10 aralkyl groups; most preferably hydrogen, C _1-4 alkyl, and C _2-4 alkenyl.

[0070] In a preferred embodiment X is a C _1-24 alkanediyl group, where the alkanediyl group is optionally substituted within the carbon backbone with one or more groups selected from C(O), C(O)NR ¹ , C(O)O, >NR ^2′ , wherein N is bound to two carbon atoms within the carbon backbone and R ^2′ is hydrogen, or is a group capable of displacement so that N is capable of linking to a bioactive agent, or is a group capable of linking to a bioactive agent, —O— and —S—, and the alkanediyl group may comprise a pendant group or groups selected from haloaryl, haloalkyl, aryl, alkaryl, aralkyl, alkoxyaryl, alkoxyalkyl, aminoalkyl, mono-, di- and tri-alkylaminoalkyl, arylaminoalkyl, aminoacyl, N-aryl-N-alkylaminoalkyl aminoaryl, alkoxy, alkenyloxy, alkynyloxy, cycloalkoxy, cycloalkenyloxy, cycloalkynyloxy, haloalkoxy, aralkoxy, alkoxyaryloxy, alkoxyalkoxy, aminoalkoxy, mono-, di- and trialkylaminoalkoxy, arylaminoalkoxy, N-aryl-N-alkylamino-alkoxy, acyloxy, acyloxyalkyl, acylaminoalkyl, N-diacyl-iminoalkyl groups, acylamino, alkylamino and hydroxy groups.

[0071] In an embodiment of the invention, the alkanediyl group or the pendant group or groups comprises a primary, secondary, or tertiary amine group.

[0072] Most preferably, X does not comprise a saccharide, oligosaccharide or polysaccharide.

[0073] In the definition of X, any alkyl group or moiety is preferably C _1-18 alkyl, any alkenyl group or moiety is preferably C _2-18 alkenyl, any alkynyl group or moiety is preferably C _2-12 alkynyl, any aryl group or moiety is preferably C _6-24 aryl, any alkaryl group or moiety is preferably C _7-24 alkaryl and any aralkyl group or moiety is preferably C _7-24 aralkyl, any cycloalkyl group or moiety is preferably C _4-24 cycloalkyl, any cycloalkenyl group or moiety is preferably C _5-24 cycloalkenyl, and any cycloalkynyl group or moiety is preferably C _5-24 cycloalkynyl.

[0074] Most preferably X is selected from the groups (IV)-(VIII) below: 3

[0075] wherein R ² and R ³ are independently selected from covalent bonds or C _1-18 alkanediyl groups terminating in OH or vinyl ether;

[0076] each R ¹² is independently selected from synthetic or natural amino acid side chains;

[0077] each R ⁴ is independently selected from the group consisting of hydrogen, activating/protecting groups and the groups (IX), (X), (XI) and (XII) 4

[0078] R ⁵ and R ⁶ are selected from the group consisting of —NH _2′ —NHR ¹³ , —OR ¹³ , wherein each R ¹³ is independently selected from hydrogen, C _1-4 alkyl, and activating/protecting groups; and

[0079] m is an integer of 0-20.

[0080] Y preferably is represented by the formula —(C _n H _2n O) _q C _n H _2n —, wherein n is an integer of 2-10, preferably 2 or 3 and q is an integer of 1 to 200.

[0081] The molecular weight of the polymer of Formula (I) is preferably in the range of 10,000-100,000.

[0082] IV. Preparation of the Polymer of Formula (1)

[0083] The polymer of Formula I 5

[0084] wherein R and R ¹ are selected from the group consisting of hydrogen, C _1-18 alkyl, C _2-18 alkenyl, C _2-18 alkynyl, C _6-18 aryl, C _7-18 alkaryl and C _7-18 aralkyl groups;

[0085] X is a group capable of being covalently conjugated to a bioactive agent via a peptidic or a hydrolytically-labile bond;

[0086] Y is a group selected from the group consisting of C _1-200 alkanediyl, C _2-200 alkenediyl, C _2-200 alkynediyl, C _6-200 cycloalkanediyl, C _6-200 cycloalkenediyl, C _6-200 cycloalkynediyl, C _6-200 arylenediyl, C _6-200 alkarylenediyl, C _6-200 aralkylenediyl groups, or any of the above groups wherein the carbon backbone is substituted with one or more oxygen atoms within the carbon backbone; and

[0087] n is an integer of 2-10,000

[0088] may be prepared by the reaction of a diol of Formula (II) 6

[0089] with a divinyl ether of Formula (III) 7

[0090] wherein R, R ¹ , X and Y are as defined above.

[0091] The diol of Formula (II) preferably is a polyethylene glycol or polypropylene glycol compound having a molecular weight in the range 100-20,000, more preferably polyethylene glycol having a molecular weight in the range 200-10,000, most preferably polyethylene glycol having a molecular weight in the range 200-5,000, in particular a molecular weight of approximately 200-4,000. Such materials are widely available from such commercial sources as Sigma-Aldrich Corporation (St. Louis, Mo.) and Shearwater Polymers. Inc. (Huntsville, Ala.). It will be understood by one of ordinary skill in the art that the reactant of Formula (II) may also comprise any diol of Formula (II), such as other glycols and diols suitable for use in biomaterials.

[0092] The divinyl ether of Formula (III) may be obtained commercially or may be made by any suitable means known in the art. For example, commercially-obtained amino vinyl ether may be combined with methyl esters to provide the divinyl ethers of Formula (III). Similarly, the hydroxy vinyl ether compound is commercially available, and may be used to make polyacetal polymers with ester moieties in the main chain. The methyl esters may comprise, for example, esters such as malonates, imines such as iminodiacetates, and other compounds known in the art. Symmetric, achiral methyl esters are preferred synthetic precursors.

[0093] The polymerization reaction may be carried out in a solventless system, although preferably the reaction takes place in the presence of an organic solvent selected from aliphatic or aromatic hydrocarbons, which may be optionally halogenated, ethers (including cyclic ethers), dialkylsulfoxides and alcohols (preferably sterically hindered alcohols, for example secondary or tertiary alcohols). Preferred solvents include tetrahydrofuran (THF), dichloromethane, and toluene. A particularly preferred solvent is toluene.

[0094] The polymerization is generally carried out in the presence of a suitable catalyst such as a catalyst for acid-catalysis, for example, hydrochloric acid, sulfuiric acid, phosphoric acid, p-toluenesulfonic acid, methanesulfonic acid, acetic acid, n-butyric acid, trifluoroacetic acid or oxalic acid. A preferred catalyst is p-toluene sulfonic acid (p-TSA).

[0095] The polymerization is conducted at a temperature of −10° C.−200° C., preferably 20° C.-120° C., most preferably between about 25° C. and 60° C.

[0096] V. Polyacetal Conjugates of Bioactive Agents and Their Preparation

[0097] The functionalized polymers of the invention comprise polymers with bioactive functionality, and thus comprise polymers that include bioactive agents. The degradable polyacetal polymers of the invention comprising bioactive functionality may be formed from substrates that include bioactive agents, from polymers to which bioactive agents are conjugated, and from substrates that combine to form bioactive agents.

[0098] A bioactive agent may be attached to X in Formula (I). In a particularly preferred embodiment, when X is (IX), (X), (XI), (XII), or >NR ^2′ , wherein N is bound to two carbon atoms within the carbon backbone and R ^2′ is hydrogen, or is a group capable of displacement so that N is capable of linking to a bioactive agent, or is a group capable of linking to a bioactive agent, the N atoms of the groups >NR2′, (IX), (X), (XI) and (XII) are, or are capable of being covalently attached to the bioactive agent.

[0099] The bioactive agent preferably is a pharmaceutically active agent (a “drug”). Suitable drugs include any drugs for which prolonged action and/or a targeted intracellular delivery is desirable, and include anticancer agents, for example doxorubicin, daunomycin, paclitaxel, taxotere, and the like, most preferably, doxorubicin. Other bioactive agents include polypeptides and proteins. The method of attachment may vary somewhat according to the bioactive agent, as is described below; and a person of ordinary skill in the art will be able, having selected a desired bioactive agent, using their knowledge and the disclosure of this application, to attach the bioactive agent to a degradable polyacetal polymer of this invention, thereby forming a conjugated polymer of this invention.

[0100] The attachment of the bioactive agent to the polymer of Formula (I) may be effected by the reaction of the polymer with the bioactive agent or a bioactive agent precursor. Bioactive agents may be attached to the polymer in any suitable manner. Preferably the attachment is effected subsequent to the polymerization reaction to produce the degradable polymer of Formula (I).

[0101] Attachment of bioactive agents may be effected in other ways as well. For example, attachment may be by linkages comprised of groups that covalently couple and cross-link the agents to the polymers. Such linkages may comprise disulfide linkages or ester bonds, or may be acid-labile linkages such as hydrazone linkage as described by Greenfield et al., Cancer Res., 50, 6600-6607 (1990), and references therein. Alternatively, the attachment may be via a “protected” disulfide bond that sterically inhibits attack from thiolate ions, such as are found in the coupling agents S-4-succinimidyloxycarbonyl-α-methyl benzyl thiosulfate (SMBT) and 4-succinimidyloxycarbonyl-α-methyl-α-(2-pyridyldithio) toluene (SMPT), in the manner disclosed in U.S. Pat. No. 6,048,736 to Kosak.

[0102] Where the bioactive agent has an amino group, it may be useful to form a reactive carbonate half ester in the polymer, P, P—O—CO—X, wherein X is a good leaving group, using reagents such as carbonyl diimidazole, p-nitrophenyl chloroformate or bis-N-succinimidyl carbonate. The activated polymer P, P—O—CO—X, may then be reacted with the bioactive agent under conditions which do not destroy its activity, leading predominantly to urethane linkages attached through the amino group. For example, carbonyl diimidazole, can be reacted with terminal hydroxyl groups of the polymer. The reaction mixture may be quenched in aqueous solution at neutral pH and the activated polymer isolated, for example by dialysis or size exclusion chromatography, as disclosed in U.S. Pat. No. 5,468,478 to Saifer et al.

[0103] Attachment (conjugation) of bioactive agents may be effected by reaction with polymers or monomers with electrophilic functionality. For example, prepolymers comprising electrophilic pendant chain functionalized monomers which comprise, for example, diols or bis-vinyl ethers, may be used for this purpose.

[0104] The following reaction scheme illustrates one route to the production of a polymer-doxorubicin drug conjugate: 8

[0105] In this scheme, PEG is the residue of a polyethylene glycol (without the terminal hydroxy groups), the termninal OH groups of the polyethylene glycol being explicitly shown when the entire glycol is meant.

[0106] Bioactive agents that may be attached (conjugated) to the polyacetal polymers of the invention include polypeptides and proteins. Such conjugation may be effected at pendant chains and at termninal groups. For example, conjugated polyacetal polymers of the invention include proteins conjugated with a degradable polyacetal polymer.

[0107] VI. Administration and Pharmaceutical Composition

[0108] Compositions comprising the degradable polyacetal polymers, with or without attached bioactive agents, are water-soluble or colloidal suspension compositions suitable for incorporation into pharmaceutical solutions or pharmaceutical compositions, or for delivery to an animal or patient for treatment. For example, polyacetal polymers of the invention are soluble in water and water solutions, such as saline, phosphate buffered saline (PBS), and other buffered solutions. The polyacetal polymers are soluble in solutions of widely varying pH.

[0109] In general, degradable polyacetal polymer compositions will be administered in therapeutically effective amounts by any of the usual modes known in the art. Degradable polyacetal polymers with attached bioactive agents may be directly delivered to solutions bathing cells, tissues or organs in vitro. Pharmaceutical compositions comprising bioactive agents attached to degradable polyacetal polymers may be administered to an animal, including a human, by one of the following routes: oral, topical, systemic (e.g. transdermal, intranasal, or by suppository), or parenteral (e.g. intramuscular, subcutaneous, or intravenous injection). Compositions may take the form of tablets, pills, capsules, semisolids, powders, sustained release formulations, solutions, suspensions, elixirs, aerosols, or any other appropriate compositions; and comprise a bioactive agent attached to a degradable polyacetal polymer of the invention in combination with at least one pharmaceutically acceptable excipient. Suitable excipients are well known to persons of ordinary skill in the art, and they, and the methods of formulating the compositions, may be found in such standard references as Alfonso AR: Remington's Pharmaceutical Sciences, 17th ed., Mack Publishing Company, Easton Pa., 1985. Suitable liquid carriers, especially for injectable solutions, include water, aqueous saline solution, aqueous dextrose solution, and glycols.

[0110] Pharmaceutical formulations comprising bioactive agents attached to degradable polyacetal polymers of the invention can be prepared according to any method known to the art for the manufacture of pharmaceuticals. Such formulations can contain sweetening agents, flavoring agents, coloring agents and preserving agents. Any such formulation can be admixed with nontoxic pharmaceutically acceptable excipients which are suitable for manufacture.

[0111] Pharmaceutical formulations for oral administration can be formulated using pharmaceutically acceptable carriers well known in the art in dosages suitable for oral administration. Such carriers enable the pharmaceutical formulations to be formulated in unit dosage forms as tablets, pills, powder, dragees, capsules, liquids, lozenges, gels, syrups, slurries, suspensions, etc. suitable for ingestion by the patient.

[0112] Intravenous injectable compositions are comprised of a polymer-drug conjugate of the invention in combination with at least one pharmaceutically acceptable liquid carrier. Acceptable liquid carriers are non-toxic, aid administration, and do not adversely affect the therapeutic benefit of the polymer-drug conjugate. Such suitable carriers include, but are not limited to, water, saline, aqueous dextrose and glycols. Further, excipients and other agents may be included in pharmaceutical compositions along with the degradable polyacetal polymers and attached bioactive agents. In addition, other additives and agents, such as antioxidants, antiseptic or antibiotic agents, buffers, stabilizers, solubilizers and other agents, may be added to degradable polyacetal polymer compositions of the invention. For example, dimethylsulfoxide, benzoic acid, ascorbic acid, or tocopherol may be included in pharmaceutical compositions comprising degradable polyacetal polymer compositions of the invention. Thus, injectable compositions comprising bioactive agents conjugated to degradable polyacetal polymers will preferably comprise water or saline solutions or emulsions, pharmaceutically acceptable carriers, and may further comprise buffering agents, such as phosphate buffer or HEPES buffer, and optionally other agents.

[0113] In general, the polymer-drug conjugates of the invention will be administered in therapeutically effective amounts via intravenous injection. A therapeutically effective amount may vary depending on the severity of the disease, the age and relative health of the subject, the potency of the conjugate used and other factors. A therapeutically effective amount may range from about 0.001 milligram per Kg (mg/Kg) body weight per day to 100 mg/Kg body weight per day. Preferably the amount will be about 0.1 to 10 mg/Kg/day. Therefore, a therapeutically effective amount for a 70 Kg patient may range from about 0.07 to 7000 mg/day, preferably about 7 to 700 mg/day. A person of ordinary skill in the art of treating diseases such as cancer will, without undue experimentation, having regard to that skill and this disclosure, be able to determine a therapeutically effective amount of a particular bioactive agent attached to a degradable polyacetal polymer for practice of this invention.

[0114] The degradable polyacetal polymers of the invention, with or without attached bioactive agents, may be dried or lyophilized and stored in that condition for a considerable length of time without significant degradation or decomposition. Such dried or lyophilized compositions may be reconstituted for use, e.g., for injection, at a convenient time after storage by addition of an appropriate amount of a suitable liquid, preferably a buffered water solution, such as saline. An appropriate amount is that amount sufficient to provide the desired volume so as to result in a solution of the desired final concentration.

[0115] Excipients useful for preparation of lyophilized or freeze-dried compositions include saccharides, amino acids, and salts such as inorganic salts. Saccharides may be, for example, monosaccharides, such as glucose and fructose, disaccharides such as maltose, lactose, and sucrose, polysaccharides such as dextran and starch, and sugar alcohols, such as mannitol sorbitol and glycerol. Amino acids may include, for example, glycine, and salts may include, for example, sodium chloride and potassium chloride. Such excipients may be used alone or in combination, and may be useful for inhibiting aggregation in the reconstituted polymer solution.

[0116] The amount of a polymer-drug conjugate of the invention in the composition may vary. In general, the final composition will comprise from about 0.001% w/w to 30% w/w of the polymer-drug conjugate, preferably about 0.01% w/w to 10% w/w, more preferably about 0.1% w/w to 5% w/w with the remainder being the carrier or carriers.

[0117] VII. Pharmacology and Utility

[0118] Degradable polymers are useful in a wide variety of pharmaceutical and biomedical applications. Uses for degradable polymers include coatings for drug tablets, contact lens coatings, coatings for surgical implants and medical devices, gels, as ingredients in topical and optical pharmaceutical solutions, in pharmaceutical formulations including delayed release pharmaceutical formulations and in targeted drug formulations. Conjugation of bioactive agents, such as anticancer drugs, with degradable polymers helps to enhance the efficacy of the bioactive agent.

[0119] Degradable polyacetal polymers of the invention are suitable for use in pharmaceutical and biomedical applications with superior properties compared to prior materials. The polyacetal polymers of the invention are degradable under physiological conditions on a time-scale suitable for effective delivery of bioactive agents in an animal. In addition, the biodistribution of degradable polyacetal polymers of the invention within the body and bloodstream of the animal receiving the polymer is favorable for the effective delivery of bioactive agents for the treatment of many diseases. The polymers and bioactive agents remain in the bloodstream for hours, not minutes, do not preferentially go to the liver, but remain in circulation so as to provide for the prolonged action of the bioactive agents, and are not toxic.

[0120] The stability of the degradable polyacetals of the invention differs in solutions of different pH. Degradable polyacetals of the invention are quite stable in water solutions near neutral pH, less so in more acidic solutions. As shown in FIG. 1 , polyacetal 3 (at pH 7 and at 37° C.) was quite stable, with little change in the molecular weight at time points ranging from 1 to 505 h (21 days). However, polyacetal 3 was less stable when dissolved at pH 5.5 at 37° C. As shown in FIG. 2 , polyacetal 3 had essentially degraded to the PEG monomeric units by 155 h (6.5 days). The results of three such stability experiments are shown in FIG. 3 , in which the degradation of polyacetal 3 over time is shown as the percent molecular weight loss (Mw) at each pH value vs. time for the pH 5.5, 6.5 and 7.4.

[0121] The polyacetal polymers of the invention are not toxic to cells. This is shown in FIG. 4 , which present the results of a red blood cell (RBC) lysis assay of amino polyacetal 3. No RBC lysis was observed in this assay for polyacetal 3. Dextran was the control which did not display RBC lysis, while poly(ethylene imine) (PEI) was the control which caused RBC lysis. In addition, direct measurements of cell toxicity on cells in culture resulted in no measured cytotoxicity. As shown in FIG. 5 , the cytotoxicity of polyacetal 3 was measured using the B16F10 cell line. Polyacetal 3 did not display cytoxicity in this assay compared to polylysine which was used as a cytotoxic control. Dextran was used as a noncytotoxic control.

[0122] Similar to the results shown with polyacetal polymer 3, polyacetal polymer 22 is also sensitive to pH. This is shown in FIG. 6 , in which are shown superimposed GPC traces of amino polyacetal 22 from a phosphate buffered solution at pH 7.4 and a solution where the pH was adjusted to pH 1-2 by addition of HCl. The polyacetal 22 completely degraded within minutes upon exposure at pH 1-2 to give the trace shown by the arrow labeled pH 1-2. This GPC trace is consistent with the molecular weight of PEG _3,400 . The degradation profile of amino polyacetal 22 at pH 7.5 and pH 5.5 is shown in FIG. 7 , where the loss in molecular weight is shown as a function of time. The degradation study shown in FIG. 7 was conducted at 37° C. and at a concentration of 3 mg/ml of polyacetal 22; three separate samples were analyzed at each pH. Polyacetal 22 degrades more rapidly in the mildly acidic medium at pH 5.5 than in the relatively neutral physiological pH 7.4. Lysosomal pH is in the range of pH 5.0 to pH 5.5. The experimental pH value of 5.5 was selected to match the lysosomal pH, which would be that encountered by a physiologically soluble polymer conjugate upon cellular uptake by endocytosis within the lysosome.

[0123] The in vitro biocompatibility of amino polyacetal 22 is shown in FIGS. 8 a , 8 b , and 9 . FIG. 8 a shows the results of red blood cell lysis experiments at 1 hour, and FIG. 8 b shows the results of red blood cell lysis experiments at 5 hours. FIG. 9 shows the results of cytotoxicity experiments. These experiments show that polyacetal 22 is not lytic or toxic to these cells, and so has a favorable biocompatibility profile.

[0124] Polyacetal polymers of the invention do not cause lysis of red blood cells. The results of a red blood cell (RBC) lysis assay of amino polyacetal 22 and its degradation products is shown over a 1 hour time period in FIG. 8 a . The degradation products were obtained by dissolving polyacetal 22 in phosphate buffered saline (PBS), adjusting the pH to 1-2 by the addition of HCl to allow the polyacetal to degrade, then adding a small amount of NaOH to readjust the pH to 7.4. No RBC lysis was observed in this assay for polyacetal 22. Dextran was used as a control; it did not display RBC lysis. Poly(ethylene imine) (PEI) was also used as a control; it caused RBC lysis. Similarly, in FIG. 8 b , the results of a red blood cell lysis assay of amino polyacetal 22 and its degradation products are shown over a 5 hour time period. No RBC lysis was observed in this assay for polyacetal 22. Dextran and poly(ethylene imine) (PEI) were used as control compounds again: dextran did not display RBC lysis, while PEI did cause RBC lysis. Thus, the results shown in FIGS. 8 a and 8 b demonstrate that the polyacetal polymer of the invention, polyacetal 22, was not lytic for red blood cells for up to five hours.

[0125] In addition, polyacetal polymers of the invention are not cytotoxic. A cytotoxicity assay of amine pendant chain polyacetal 22 using B16F10 cell line is shown in FIG. 9 . As shown in FIG. 9 , polylysine is cytotoxic at concentrations well below 0.1 mg/ml. However, polyacetal 22 did not display cytoxicity in this assay at concentrations of up to several mg/ml, and thus is extremely well tolerated by these cells as compared to the cytotoxic control compound, polylysine. Dextran, used as a noncytotoxic control, was also found not to be cytotoxic even at relatively high concentrations.

[0126] Polyacetals of the invention remain in circulation in the blood with relatively little loss from the blood circulation to the organs. ¹²⁵ I labeled polyacetal polymers of the invention may be formed using Bolton-Hunter methods, as shown in FIGS. 10 and 11 and described in Example 7. In the body distribution study shown in FIG. 12 , polyacetal 23 was predominantly in the blood, at both at 5 min and at 1 hour after administration. The continued presence of polyacetal 23 in the blood in significant amounts at one hour is a surprising and favorable property of the polyacetal of the invention. This study shows that polyacetal 23 remains in the blood without accumulating in the organs shown. In particular, and in contrast to many previously-known polymers, the polyacetal of the invention is not significantly taken up by the liver but remains substantially in circulation in the blood for an hour. Thus, the polyacetal of the invention possesses the favorable properties of long-duration presence in the blood, of very little removal from circulation by the organs, and, since very little of the polyacetal is lost to the liver, relatively little degradation by the liver.

[0127] Functionalized polymers of the invention, such as may be formed by synthesis from functionalized precursors or by attachment of bioactive agents, such as anticancer drugs, to degradable polyacetal polymers of the invention may be effective to enhance the efficacy of the bioactive agent. As shown in FIG. 12 , polyacetal polymers remain in circulation with relatively little removal or loss from the blood on a timescale of hours, a property which enhances the effectiveness of anticancer drugs attached to degradable polyacetal polymers of the invention. Higher dosages of the anticancer drugs, which are more effective in treating the cancerous tissue than lower dosages, are tolerated by animals when anticancer drugs are attached to degradable polyacetal polymers of the invention.

[0128] VIH. Prepolymers of Formula (XIII)

[0129] The prepolymers are novel divinylethers represented by Formula (XIII) 9

[0130] wherein R ⁷ and R ⁸ are selected from the same groups as R and R1, Z is a C _1-24 alkanediyl group, optionally substituted within the carbon backbone with one or more or a mixture of the groups selected from carbonyl, peptide, ester, >NR ^2′ , wherein N is bound to two carbon atoms within the carbon backbone and R ^2′ is hydrogen, or is a group capable of displacement so that N is capable of linking to a bioactive agent, or is a group capable of linking to a bioactive agent, —O— and —S—, and the alkanediyl group comprises a pendant group R ⁹ , wherein R ⁹ , is selected from haloaryl, haloalkyl, aryl, alkaryl, aralkyl, alkoxyaryl, alkoxyalkyl, aminoalkyl, mono-, di- and tri-alkylaminoalkyl, arylaminoalkyl, aminoacyl, N-aryl-N-alkylaminoalkyl aminoaryl, alkoxy, alkenyloxy, alkynyloxy, cycloalkoxy, cycloalkenyloxy, cycloalkynyloxy, haloalkoxy, aralkoxy, alkoxyaryloxy, alkoxyalkoxy, aminoalkoxy, mono-, di- and trialkylamninoalkoxy, arylaminoalkoxy, N-aryl-N-alkylamino-alkoxy, acyloxy, acyloxyalkyl, acylaminoalkyl, N-diacyl-iminoalkyl groups, acylamino, alkylamino and hydroxy groups.

[0131] In a preferred embodiment, R ⁹ contains at least one activating/protecting group.

[0132] In the definition of Z, any alkyl group or moiety is preferably C _1-18 alkyl, any alkenyl group or moiety is preferably C _2-18 alkenyl, any alkynyl group or moiety is preferably C _2-12 alkynyl, any aryl group or moiety is preferably C _6-24 aryl, any alkaryl group or moiety is preferably C _7-24 alkaryl and any aralkyl group or moiety is preferably C _7-24 aralkyl, any cycloalkyl group or moiety is preferably C _4-24 cycloalkyl, any cycloalkenyl group or moiety is preferably C _5-24 cycloalkenyl, and any cycloalkynyl group or moiety is preferably C _5-24 cycloalkynyl. Symmetric achiral methyl esters are preferred synthetic precursors.

[0133] Preferably Z has a structure (XIV), (XV), (XVI), (XVII) and (XVIII), below: 10

[0134] wherein R ¹⁰ and R ¹¹ are selected from covalent bonds, and C _1-6 alkanediyl groups;

[0135] R ⁹ is as defined above,

[0136] R ¹² are selected from synthetic or natural amino acid side chains; and

[0137] p is an integer of 0-20.

[0138] Prepolymers as disclosed herein may be formed by any suitable method, including such methods as are disclosed in the Examples, such as Examples 3, 4 and following.

[0139] A process for the preparation of a prepolymer of Formula (XIII) may comprise the following steps. To prepare a prepolymer of Formula (XIII): 11

[0140] wherein

[0141] R ⁷ and R ⁸ are selected from the group consisting of hydrogen, C _1-18 alkyl, C _2-18 alkenyl, C _2-18 alkynyl, C _6-18 a aryl, C _7-18 alkaryl and C _7-18 aralkyl groups;

[0142] Z is a C _1-24 alkanediyl group, where the alkanediyl group is optionally substituted within the carbon backbone with one or more groups selected from C(O), C(O)NR ¹ , C(O)O, >NR ^2′ , wherein N is bound to two carbon atoms within the carbon backbone and R ^2′ is hydrogen, or is a group capable of displacement so that N is capable of linking to a bioactive agent, or is a group capable of linking to a bioactive agent, —O— and —S—, and the alkanediyl group comprises a pendant group R ⁹ selected from haloaryl, haloalkyl, aryl, alkaryl, aralkyl, alkoxyaryl, alkoxyalkyl, aminoalkyl, mono-, di- and tri-alkylaminoalkyl, arylaminoalkyl, aminoacyl, N-aryl-N-alkylaminoalkyl aminoaryl, alkoxy, alkenyloxy, alkynyloxy, cycloalkoxy, cycloalkenyloxy, cycloalkynyloxy, haloalkoxy, aralkoxy, alkoxyaryloxy, alkoxyalkoxy, aminoalkoxy, mono-, di- and trialkylaminoalkoxy, arylaminoalkoxy, N-aryl-N-alkylamino-alkoxy, acyloxy, acyloxyalkyl; acylaminoalkyl, N-diacyl-iminoalkyl groups, acylamino, alkylamino and hydroxy groups;

[0143] the steps of the process comprise:

[0144] reacting a methyl ester of Formula (XIX) 12

[0145] with a vinylether of Formula (XX) 13

[0146] or Formula (XXI) 14

[0147] wherein X comprises a group capable of being covalently conjugated to a bioactive agent via a peptidic or a hydrolytically-labile bond, and Y is a group selected from the group consisting of linear and branched C _1-200 alkanediyl, C _2-200 alkenediyl, C _2-200 alkynediyl, C _6-200 cycloalkanediyl, C _6-200 cycloalkenediyl, C _6-200 cycloalkynediyl, C _6-200 arylenediyl, C _7-200 alkarylenediyl, C _7-200 . aralkylenediyl groups, or any of the above groups wherein the carbon backbone is substituted with one or more oxygen atoms within the carbon backbone.

[0148] In a preferred embodiment of the method of preparing a prepolymer of Formula (XIII), R ⁹ contains at least one activating/protecting group.

[0149] These prepolymers are particularly useful for the preparation of the polymers of Formula (1) by methods known in the art and as illustrated in the Examples. Functionalized prepolymers, such as prepolymers functionalized with bioactive agents or precursors to bioactive agents, are useful for the preparation of polymers of formula comprising bioactive agents. The following structures represent some particularly preferred prepolymers of the present invention. 15

EXAMPLES

[0150] General

[0151] The degradable polymers of the present invention may be prepared by the reaction of poly(ethylene glycol) (PEG) as the source of diol (PEG's with molecular weights of 3,400 g/mol were used) and commercially available triethylene glycol di-vinyl ether. PEG is selected as the diol because it is generally recognized as safe (GRAS) by drug regulatory authorities and is widely used in pharmaceutical formulation. However, it will be appreciated by those of ordinary skill in the art that other diols, including PEGs of lower or higher molecular weight, are also suitable for the practice of the invention. The use of the unfunctionalized divinyl ether, triethylene glycol di-vinyl ether, in the preliminary experiments was conducted to confirm a suitable degradation profile (needed for lysosomal degradation) and to confirm in vitro biocompatibility. It will be understood by one of ordinary skill in the art that degradable polyacetal polymers of the invention may also be prepared from functionalized starting materials. For example, functionalized vinyl ethers, particularly functionalized divinyl ethers, may be used as starting materials in the preparation of the degradable polyacetal polymers of the invention. Each following experimental example is preceded by a scheme summarizing the reaction involved. In each case m is an integer representing a PEG molecule of the identified molecular weight Mn.

Example 1

Synthesis of Polyacetal 3 by Polymerization in Toluene

[0152] 16

[0153] Poly(ethylene glycol) (Mn=3,400 g/mol, 17.0 g, 5.0 mmol, 1.0 eq), para-toluenesulfonic acid monohydrate (0.03 g, 0.15 mmol, 0.03 eq) and toluene (60 ml) were added to a 100 ml round bottom flask which was equipped with a stirring bar and fitted with a thermometer, Dean Stark trap and condenser. An azeotropic distillation of the stirred toluene solution (oil bath, T=150° C.) under nitrogen proceeded for two hours. The solution was then allowed to cool to ˜50° C. and tri(ethylene glycol) divinyl ether (1.073 g, 1.083 ml, 5.2 mmol, 1.04 eq) was added by syringe. Within one minute the reaction mixture became visibly more viscous and after 15 minutes the viscosity appeared to be very high. Toluene (30.0 ml) was added to decrease the viscosity and the clear colorless reaction mixture was stirred a further 2 hours at ambient temperature. Aqueous NaHCO ₃ (8.0%, 2.0 ml) was added to the reaction mixture which was then rapidly stirred for 15 minutes. The aqueous phase was allowed to settle and the toluene phase was carefully decanted into stirred hexane (200 ml) to precipitate the polyacetal. After stirring in the hexane for an additional 10 minutes the polyacetal was collected and placed into a fresh solution of hexane and stirred for a further 10 minutes. The polyacetal was again collected and then dried in vacuum at 50° C. for 4 hours to give a white fluffy solid. The molecular weight was determined to be Mw=42,806 g/mol, Mn=26760 g/mol; polydispersity-1.60 by GPC. The GPC was calibrated with PEG standards; 56,000, 23,500 and 5598 g/mol.

Example 2

Synthesis of Polyacetal 3 by Polymerization in THF

[0154] A suspension of PEG ₃₄₀₀ (1.041 g, 0.306 mmol) and para-toluenesulfonic acid (25 mg) in toluene (50 ml) was heated to reflux; the flask was fitted with a Dean and Stark trap and a balloon of argon was fitted to the condenser. After 150 min most of the toluene was distilled off. To the residue was added the divinyl ether (0.306 mmol, 1.0 eq) in freshly distilled THF (10 ml). The mixture was stirred at room temperature under argon for 16 h. Triethylamine (0.2 ml) was added and the mixture was stirred for 5 minutes. The mixture was poured into hexane (300 ml) with rapid stirring, after 5 min the hexane was decanted off and the residue was washed with further hexane (200 ml) for 30 minutes. The polymer was filtered off.

[0155] This same procedure was used for polymerizations conducted in dichloromethane.

Example 3

Synthesis of Bis-Vinyl Ethers Useful for Preparing Polyacetals

[0156] The vinyl ethers were made from methyl esters using the commercially available amino vinyl ether. This avoided the use of heavy metals to make the vinyl ether moiety. 17

[0157] A solution of 3-amino-1-propanol vinyl ether 5 (0.27 mmol, 2.2 eq) and dimethyl malonate 4 (0.12 mmol, 1 eq) in dichloromethane (5.0 ml) was stirred at ambient temperature for 3 days. The reaction mixture was diluted with dichloromethane (50 ml) and washed with water (2×35 ml), conc. NaCl solution (35 ml) and dried over MgSO ₄ . The solvent was evaporated to give a semi-solid residue which was triturated with ether-hexane (1:1) to give the bis vinyl ether 6.

Example 4

Synthesis of Bis-Vinyl Ethers Useful for Preparing Polyacetals with Functionality to Conjugate Bioactive Compounds

[0158] 18

[0159] A saturated aqueous Na ₂ CO ₃ solution (20 ml) of dimethyl iminodiacetate 7 (10 mmol, 1.0 eq) and 3-amino-1-propanol vinyl ether 5 (40 mmol, 4.0 eq) was stirred for 1 h at 90° C. The solution was cooled and extracted three times with ethyl acetate (80 ml each time). The organic layer was washed with brine, dried over MgSO ₄ , and rotoevaporated to give the bis-vinyl ether 8 as a white crystalline solid.

[0160] The bis-vinyl ether 8 was then allowed to react with various acylating agents (e.g. Fmoc protected glycine N-hydroxysuccinimde ester and benzyl chloroformate) to protect (block) the amino functionality in 8 prior to polymerization. The protecting (blocking) group is important because it allows polymerization to proceed without competitive side reactions with the conjugating functionality. After polymerization it must be removed without causing degradation of the polyacetal. This strategy is illustrated in Example 5 for the preparation and polymerization of glutamic acid derived bis-vinyl ether 11 and the subsequent deprotection of the polyacetal.

Example 5

Synthesis of Bis-Vinyl Ethers Useful for Preparing Polyacetals with a Protected Primary Amine Functionality (9→11). Preparation of a Amino Pendant Chain Functionalized Polyacetal using a Pendant Chain Functionalized Bis-Vinyl Ether Monomer (11→13)

[0161] Synthesis of Fmoc-glutamnyl chloride 10 (9→10) 19

[0162] To a suspension of Fmoc-glutamic acid 9 (3.13 g, 8.5 mmol) in anhydrous CH ₂ Cl ₂ (50 ml) was added oxalyl chloride (5.0 g, 39 mmol). The mixture was cooled to 0° C. and DMF (2 drops) was added. The mixture was stirred at 0° C. for 1 h then at ambient temperature for 1 h under argon atmosphere. Freshly distilled TEF (6.0 ml) was added and the mixture was stirred at room temperature for 1 h under argon. Hexane (400 ml) was added and the mixture stirred at ambient temperature for 30 minutes. The hexane was decanted off and the residue recrystallized from CH ₂ Cl ₂ /hexane to give 10 as white crystals (1.41 g).

[0163] Synthesis of Fmoc Glutamic Acid Divinyl Ether 11 (10→11)

[0164] To the bis-acid chloride 10 (1.41 g, 3.47 mmol) in anhydrous CH ₂ Cl ₂ (25 ml) was added a solution of 3-aminopropyl vinyl ether 5 (701 mg, 6.94 mmol) and NaHCO ₃ in water (10 ml) dropwise over 5 min with vigorous stirring at 0° C. The mixture was stirred at 0° C. for 10 min then at ambient temperature for 1 hour. The mixture was diluted with CH ₂ Cl ₂ (200 ml) then washed with 2% aqueous NaHCO ₃ (150 ml), brine (150 ml) and then dried with MgSO ₄ . Evaporation gave a pale brown solid which was recrystallized from isopropanol/hexane to yield the divinyl ether 11 as an off white solid (910 mg).

[0165] Synthesis of amino-functionalized bis-vinyl ether monomer 13 (11→3) 20

[0166] A suspension of PEG ₃₄₀₀ 1 (1.041 g, 0.306 mmol) and p-toluene sulfonic acid (25 mg) in toluene (50 ml) was heated to reflux in a round bottom flask fitted with a Dean and Stark trap to collect the water. After no further increase in water collection was observed, most of the toluene was distilled from the round bottom flask. To the residue was added the divinyl ether 11 (164 mg, 0.306 mmol) in freshly distilled (sodium-benzophenone) THF (10 ml). The mixture was stirred at room temperature under argon for 16 h. Triethylamine (0.2 ml) was added and the mixture was stirred for 5 minutes. The mixture was poured into hexane (300 ml) with rapid stirring to precipitate the polyacetal 12. After 5 min the hexane was decanted off and the polyacetal 12 was stirred with fresh hexane (200 ml) for 30 min. The polyacetal 12 was filtered, collected and dried in vacuum. The weight average molecular weight as determined by GPC (eluent: water, 1 ml/min; PEG standards) was 14300 g/mol. The Fmoc group was removed by dissolving the polymer into an dichloromethane (7% weight percent) followed by the addition of morpholine and the reaction stirred for 15 min at ambient temperature. The amino functionalized polyacetal 13 was precipitated into a stirred solution of hexane (200 ml).

Example 6

Synthesis of a Symmetric, Achiral Bis-Vinyl Ether 16 with a Protected Primary Amine Useful for Preparing Polyacetals with Functionality to Conjugate Bioactive Compounds

[0167] 21

[0168] A solution of Cbz-gly-NHS (0.75 g, 2.5 mmol), dimethyl aminomalonate hydrochloride 14 (0.45 g, 2.5 mmol) and triethylamine (0.375 ml) in