Hydrolytically degradable polymers and hydrogels made therefrom

Details Hydrolytically degradable polymers and hydrogels made therefrom Hydrolytically degradable polymers and hydrogels made therefrom

1999-12-10

2002-02-19

Boykin, Terressa M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From phenol, phenol ether, or inorganic phenolate

C528S198000

Reexamination Certificate

active

06348558

ABSTRACT:

FIELD OF THE INVENTION
This invention generally relates to water soluble, hydrolytically degradable, and nonpeptidic polymers, and particularly to polymers and gels therefrom that are suitable for medical devices, drug enhancement and in vivo delivery of biologically active agents.
BACKGROUND OF THE INVENTION
Conjugation of agents having a known or potential therapeutic benefit to water soluble, non-immunogenic polymers can impart to the agent desirable characteristics including, among others, improved solubility, greater stability, and reduced immunogenicity. It has become increasingly important in the pharmaceutical industry to develop conjugates having these characteristics so as to increase the number of options for therapeutic benefit.
An example of a polymer that can be used to develop conjugates with therapeutic agents is poly(ethylene glycol) (“PEG”). Therapeutic agents conjugated to PEG are sometimes said to be “PEGylated.” Several PEGylated therapeutics have been developed that exhibit enhanced water solubility, longer circulation lifetimes, and lower immunogenicity as compared to the unconjugated therapeutic agent. Because of the rapid motion and heavy hydration of the polymer, PEGs usually are of much higher apparent molecular weight than the therapeutics to which they are attached. Thus, they tend to mask the therapeutic agent from the immune system and to preclude excretion through kidneys.
The term PEG is commonly used to describe any of a series of polymers having the general formula HO—(CH
2
CH
2
—O)
n
—H, where “n” represents the number of ethylene oxide monomers in the polymer. However, the parent polymer is generally unsuitable for attachment to a therapeutic agent. Hydroxyl groups are relatively unreactive toward groups commonly present on therapeutic agents and thus PEG normally has to be “activated” by converting at least one end hydroxyl group into a more reactive form. It is also usually important to activate the PEG polymer with a terminal group that is selective in its reactions. For example, several PEG derivatives have been developed that are more likely to react with amine groups. Others have been developed that preferentially react with thiol groups.
Successful PEG derivatives may have to meet a number of requirements, depending on the specific application. For conjugation to proteins, the PEG derivative should usually have a desirable and suitably selective reactivity at physiologic conditions of temperature, pressure, and pH to preserve the activity of the unconjugated protein. In some circumstances, it is desirable to cleave the PEG polymer from the therapeutic agent at some point after the agent is delivered in vivo.
Some PEG derivatives have been used in combination with other polymers to prepare insoluble gels in which drugs can be entrapped or chemically bound. For example, Sawhney et al.,
Macromolecules,
26:581 (1993) describes the preparation of block copolymers of PEG with polyglycolide or polylactide blocks at both ends of the PEG chain. The copolymers are then activated by terminal substitution with acrylate groups, as shown below.
CH
2
═CH—CO—(O—CH
2
—CO)
n
—O—PEG—O—(CO—CH
2
—O)
n
—CO—CH═CH
2
In the above formula, the glycolide blocks are the —O—CH
2
—CO— units. The addition of a methyl group to the methylene gives a lactide block; n can be multiples of 2. Vinyl polymerization of the acrylate groups produces an insoluble, crosslinked gel with a polyethylene backbone.
The polylactide or polyglycolide segments of the polymer backbone shown above, which are ester groups, are susceptible to slow hydrolytic breakdown, with the result that the crosslinked gel undergoes slow degradation and dissolution. The hydrogel degrades in vivo and can result in non-PEG components being released into the blood stream, which can be undesirable.
It is desirable to develop improved polymers providing additional choices for use in drug delivery and other applications.
SUMMARY OF THE INVENTION
This invention provides a water soluble, nonpeptidic polymer having two or more oligomers linked together by hydrolytically degradable carbonate linkages. The polymer can be hydrolytically degraded into small oligomers in an aqueous environment, including in vivo conditions. The polymer is easy to prepare and the molecular weight of the oligomers resulting from polymer degradation can be easily controlled, which can be desirable for some applications. The polymer can be conjugated to a biologically active agent such as a protein or peptide. The polymer can impart desirable characteristics to the conjugates of improved water solubility and reduced immunogenicity. The polymer is useful for preparing insoluble cross linked structures, including hydrogels, that are hydrolytically degradable into soluble polymers of predetermined molecular weight.
The oligomers are alkylene oxide oligomers. Typically, the oligomers are ethylene oxide oligomers, and the polymer is a poly(ether carbonate) having the formula of:
HO—[(—CH
2
CH
2
—O)
n
—CO
2
]
m
—(—CH
2
CH
2
—O)
n
H
where n is from about 1 to 2,000, normally from 2 to 2,000, and m is from about 2 to 200. Since carbonate linkages are hydrolytically degradable under mild conditions, the polymer will hydrolyze to produce oligomer fragments of much lower molecular weight than the starting polymer:
HO—[(—CH
2
CH
2
—O)
n
—CO
2
]
m
—(—CH
2
CH
2
—O)
n
H+(m+1)H
2
O→(m+1)HO—(—CH
2
CH
2
—O—)
n
—H+mCO
2
In addition to providing many of the desirable features of other polymers, including poly (ethylene glycol) as described above, this new polymer can degrade in the body and thus facilitates removal of the polymer from the body. The degradation products are themselves normally nontoxic small PEGs that typically are rapidly cleared from the body.
The polymer can be prepared in a number of ways. In one embodiment of this invention, the poly(ether carbonate) is prepared by polymerizing an activated oligomer having the formula of:
HO—(—CH
2
CH
2
—O—)
n
—CO
2
—Z
where n can be from about 2 to 2000 and Z is a reactive leaving group such as N-succinimidyl, 1-benzotriazolyl, or p-nitrophenyl.
The polymer can be prepared by polymerizing ethylene oxide oligomers of the formula:
HO—(—CH
2
CH
2
—O—)
n
—H
where n can be from about 2 to 2000 with an activating molecule of Z—O—CO
2
—Z, where Z is as described.
Alternatively, the ethylene oxide oligomer
HO—(—CH
2
CH
2
—O—)
n
—H
can be polymerized with a bifunctional ethylene oxide oligomer:
Z—OCO
2
—(—CH
2
CH
2
—O—)
n
—CO
2
—Z
where n and Z are as described above, to form the poly(ether carbonate).
The polymerization reactions may be conducted either in an organic solvent or in a melt, in the presence of an organic base. Examples of suitable solvents include acetonitrile, THF, dimethylformamide, dimethylsulfoxide, benzene, toluene, the xylenes, chloroform, and methylene chloride. Examples of suitable organic bases include triethylamine, pyridine, quinoline, 4,4-dimethylaminopyridine and triethylamine. The polymerization reactions can be conducted at a temperature of from about 37° C. to 100° C., typically from about 45° C. to 100° C., and advantageously from about 70° C. to 90° C.
The polymer of this invention can be modified at one termius with alkyl or aryl groups to make one end of the polymer inert. The polymer can be activated at one or more of its termini to form a terminal reactive moiety. Thus, a modified or activated poly(ether carbonate) of this invention can be represented as:
X—O—[(CH
2
CH
2
—O)
n
—CO
2
]
m
—(CH
2
CH
2
—O)
n
—Y
where m and n are as defined above, and where X and Y can independently be H, alkyl, alkenyl, aryl, and reactive terminal moieties, including N-succinimidyloxycarbonyl, 1-benzotriazolyloxycarbonyl, p-nitrophenyloxycarbonyl, or others. Alternatively, X and Y can include linker groups terminating in active groups such as aldehyde N-maleimidyl or —S—S-ortho-pyridyl. A wide variety of activating groups and linkers can be used.
The activated polymer of this invention can be reacted with an active group on a bi

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