SUBMISSION OF SEQUENCE LISTING ON ASCII TEXT FILE

The content of the following submission on ASCII text file is incorporated herein by reference in its entirety: a computer readable form (CRF) of the Sequence Listing (file name: 670572000611SeqList.txt, date recorded: Aug. 29, 2019, size: 1,072 bytes).

BACKGROUND ART

A hydrogel is a 3-dimensional network of natural or synthetic hydrophilic polymer chains in which water (up to 99%) is the dispersion medium. Fragile macromolecules often require a well-hydrated environment for activity and structural integrity, and the high degree of hydration of a hydrogel may preserve the folding of a protein needed for its bioactivity. The high water content of the hydrogels render the material biocompatible and minimize inflammatory reactions of tissues in contact with the gel, and provide a flexibility comparable to that of living tissue. Hydrogels are thus of interest in biomedical engineering, as absorbent materials for wound dressings and disposable diapers, and as carriers for extended drug release. Hydrogels have been prepared by physical or chemical crosslinking of hydrophilic natural or synthetic polymers.

Examples of hydrogels formed from crosslinking of natural polymers include those formed from hyaluronans, chitosans, collagen, dextran, pectin, polylysine, gelatin or agarose (see: Hennink, W. E., et al.,Adv. Drug Del. Rev. (2002) 54:13-36; Hoffman, A. S.,Adv. Drug Del. Rev. (2002) 43:3-12). These hydrogels consist of high-molecular weight polysaccharide or polypeptide chains. Some examples of their use include the encapsulation of recombinant human interleukin-2 in chemically crosslinked dextran-based hydrogels (Cadee, J. A., et al.,J Control. Release(2002) 78:1-13) and insulin in an ionically crosslinked chitosan/hyaluronan complex (Surini, S., et al.,J. Control. Release(2003) 90:291-301).

Examples of hydrogels formed by chemical or physical crosslinking of synthetic polymers include poly(lactic-co-glycolic)acid (PLGA) polymers, (meth)acrylate-oligolactide-PEO-oligolactide-(meth)acrylate, poly(ethylene glycol) (PEO), poly(propylene glycol) (PPO), PEO-PPO-PEO copolymers (Pluronic®), poly(phosphazene), poly(methacrylates), poly(N-vinylpyrrolidone), PL(G)A-PEO-PL(G)A copolymers, poly(ethylene imine), and others (see, for example, Hoffman, A. S.,Adv. Drug Del. Rev(2002) 43:3-12). Examples of protein-polymer encapsulation using such hydrogels include the encapsulation of insulin in physically crosslinked PEG-g-PLGA and PLGA-g-PEG copolymers (Jeong, B., et al.,Biomacromolecules(2002) 3:865-868) and bovine serum albumin in chemically crosslinked acrylate-PGA-PEO-PGA-acrylate macromonomers (Sawhney A. S., et al.,Macromolecules(1993) 26:581-587).

Depending on the pore size, degradation of a hydrogel is typically required for release of the encapsulated compounds. Degradation increases the size of the pores to the extent that the drug may diffuse out of the interior of the hydrogel into surrounding body fluids. Degradation is further desirable in order to remove the hydrogel from the body once drug delivery is complete, as surgical removal of the spent hydrogel carrier is often painful. While many of the known hydrogels are theoretically biodegradable, in practice the degradation is uncontrolled and thus unpredictable. Thus, a need exists for new hydrogel materials that biodegrade at a predetermined rate.

In order to effect degradation of the hydrogel, it is helpful to have crosslinking agents that are cleavable under physiological conditions. In one approach, enzymatic cleavage of the crosslinker as a substrate can effect this result. However, dependence on enzymatic degradation results in inter-patient variability as well as differences between in vivo and in vitro results.

The present invention takes advantage of a cleavage mechanism described in a different context—namely drug release from macromolecular carriers which is disclosed, for example in U.S. application US2006/0171920 and in WO2009/158668, WO2011/140393, WO2011/140392 and WO2011/140376. The elimination reaction relies on a modulating group to control the acidity of a proton; ionization of this proton results in release of the drug.

To applicants' knowledge, this mechanism has not been used to establish a cleavable crosslinker for hydrogels which results in the degradation of the gel.

DISCLOSURE OF THE INVENTION

This invention provides hydrogels that degrade to smaller, soluble components in a non-enzymatic process upon exposure to physiological conditions and to methods to prepare them. The hydrogels are prepared from crosslinking agents that undergo elimination reactions under physiological conditions, thus cleaving the crosslinking agent from the backbone of the hydrogel. The invention also relates to the crosslinking agents themselves and intermediates in forming the hydrogels of the invention. The biodegradable hydrogels prepared according to the methods of the invention may be of use in diverse fields, including biomedical engineering, absorbent materials, and as carriers for drug delivery.

Thus, in one aspect, the invention is directed to a hydrogel that is biodegradable under physiological conditions which hydrogel comprises one or more polymers crosslinked by a linker that decomposes by an elimination reaction. More specifically, the hydrogels contain linkers that when disposed in the polymer residues of formula (1):



wherein at least one of R1, R2or R5along with X is coupled to said one or more polymers.Alternatively, the linker is a residue of formula (2):



wherein at least two of said R1, R2or R5are coupled to one or more polymers.

The definitions of R1, R2, R5, m, X, W, s, n, t, and Q are set forth in detail herein-below. In the case of formula (2), the coupling may be through two R1's that exist in the same molecule of formula (2) or through one R1and one R5, for example, in formula (2). That is the requirement that at least two of these substituents as coupled to one or more polymers simply means that in the crosslinker of formula (2) itself, there must be at least two points of attachment. In some embodiments the R1, R2and R5substituents are uniform in each of the t “arms”.

The hydrogel may further contain one or more drugs. The drug(s) may be simply contained in the pores of the hydrogel, or may be coupled to a crosslinking agent which is in turn coupled to the polymeric backbone of the hydrogel.

The invention also provides methods for preparing biodegradable hydrogels comprising either simultaneously or sequentially contacting at least one reactive polymer and a cleavable crosslinker compound wherein said cleavable crosslinker compound comprises a functional group that reacts with the reactive polymer and a moiety that cleaves by elimination under physiological conditions also comprising a functional group that reacts with one or more polymers. The invention also provides methods for the preparation of drug-releasing biodegradable hydrogels wherein the rates of drug release and of hydrogel biodegradation are controlled.

Thus, the drugs or other agent may simply be entrapped in the hydrogel or may be included in the hydrogel by virtue of coupling through a linker that releases the drug through an elimination reaction as well, without necessity for the degradation of the gel itself.

In another aspect, the invention provides crosslinking reagents comprising a moiety capable of being cleaved by elimination under physiological conditions and further comprising reactive groups capable of forming covalent bonds with reactive polymers.

In still another aspect, the invention provides intermediates formed by reaction of the crosslinking reagents of the invention, with at least one reactive polymer.

