Poly(ethylene glycol) derivatives with proximal reactive groups

Details Poly(ethylene glycol) derivatives with proximal reactive groups Poly(ethylene glycol) derivatives with proximal reactive groups

2001-11-05

2002-08-20

Nutter, Nathan M. (Department: 1711)

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

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Processes of preparing a desired or intentional composition...

C525S056000, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56, 56

Reexamination Certificate

active

06437025

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to derivatives of polyethylene glycol and related hydrophilic polymers suitable for chemical coupling to another molecule, including, for example, proteins, enzymes, small drugs, and the like.
BACKGROUND OF THE INVENTION
Chemical attachment of the hydrophilic polymer poly(ethylene glycol) (“PEG”) to molecules and surfaces is of great utility in biotechnology. In its most common form PEG is a linear polymer terminated at each end with hydroxyl groups:
HO—CH
2
CH
2
O—(CH
2
CH
2
O)
n
—CH
2
CH
2
—OH
This polymer can be represented in brief form as HO—PEG—OH where it is understood that the -PEG-symbol represents the following structural unit:
—CH
2
CH
2
O—(CH
2
CH
2
O)
n
—CH
2
CH
2
—
In typical form n ranges from about 10 to about 2000.
PEG is commonly used as methoxy PEG—OH, or mPEG in brief, in which one terminus is the relatively inert methoxy group, while the other terminus is a hydroxyl group that is subject to ready chemical modification.
CH
3
O—(CH
2
CH
2
O)
n
—CH
2
CH
2
—OH mPEG
PEG is also commonly used in branched forms that can be prepared by addition of ethylene oxide to various polyols, such as glycerol, pentaerythritol and sorbitol. For example, the four-arm, branched PEG prepared from pentaerythritol is shown below:
C(CH
2
—OH)
4
+n C
2
H
4
O→C[CH
2
—O—(CH
2
CH
2
O)
n
—CH
2
CH
2
—OH]
4
The branched PEGs can be represented in general form as R(—PEG—OH)
n
in which R represents the central “core” molecule, such as glycerol or pentaerythritol, and n represents the number of arms.
Branched PEGs can also be prepared in which two PEG “arms” are attached to a central linking moiety having a single functional group capable of joining to other molecules; e.g., Matsushima et al., (Chem. Lett., 773, 1980) have coupled two PEGs to a central cyanuric chloride moiety.
PEG is a well known polymer having the properties of solubility in water and in many organic solvents, lack of toxicity, and lack of immunogenicity. One use of PEG is to covalently attach the polymer to insoluble molecules to make the resulting PEG-molecule “conjugate” soluble. For example, it has been shown that the water-insoluble drug paclitaxel, when coupled to PEG, becomes water-soluble. Greenwald, et al.,
J. Org. Chem.,
60:331-336 (1995).
In related work, U.S. Pat. No. 4,179,337 to Davis et al. discloses that proteins coupled to PEG have enhanced blood circulation lifetime because of reduced rate of kidney clearance and reduced immunogenicity. These and other applications are also described in
Biomedical and Biotechnical Applications of Polyethylene Glycol Chemistry
, J. M. Harris, Ed., Plenum, New York (1992), and
Poly
(
ethylene glycol
)
Chemistry and Biological Applications
, J. M. Harris and S. Zalipsky, Eds., ACS, Washington D.C. (1997).
To couple PEG to a molecule such as a protein, it is often necessary to “activate” the PEG to prepare a derivative of the PEG having a functional group at the terminus. The functional group can react with certain moieties on the protein such as an amino group, thus forming a PEG-protein conjugate. Many activated derivatives of PEG have been described. An example of such an activated derivative is the succinimidyl succinate “active ester”:
CH
3
O—PEG—O
2
C—CH
2
CH
2
—CO
2
—NS
where NS═
Hereinafter, the succinimidyl active ester moiety will be represented as —CO
2
—NS in chemical drawings.
The succinimidyl active ester is a useful compound because it reacts rapidly with amino groups on proteins and other molecules to form an amide linkage (—CO—NH—). For example, U.S. Pat. No. 4,179,337 to Davis et al. describes coupling of this derivative to proteins (represented as PRO—NH
2
):
mPEG—O
2
CCH
2
CH
2
CO
2
NS+PRO—NH
2
→mPEG—O
2
C—CH
2
CH
2
—CONH—PRO
Bifunctional PEGs with active groups at both ends of the linear polymer chain are also useful compounds when formation of a crosslinked insoluble network is desired. Many such bifunctional PEGs are known in the art. For example, U.S. Pat. No. 5,162,430 to Rhee, et al. discloses using such bifunctional PEGs to crosslink collagen.
Reactive PEGs have also been synthesized in which several active functional groups are placed along the backbone of the polymer. For example, lysine-PEG conjugates have been prepared in the art in which a number of activated groups are placed along the backbone of the polymer. Zalipsky et al.
Bioconjugate Chemistry,
4:54-62 (1993).
U.S. Pat. No. 5,283,339 to Arnold et al. discloses PEG compounds capable of chelating metals. The PEG compounds have a terminal metal chelating group which has two free carboxylic acid or amino groups, typically linked to a nitrogen atom. The PEG compounds are used to extract and precipitate proteins from solutions with the carboxylic acid or amino groups together with the nitrogen atom capable of forming ionic complexes with metal ions. However, the metal chelating groups disclosed in the patent generally are not useful in covalently coupling the PEG compounds to proteins, peptides, or small drugs bearing functional groups such as amines. The patent does not teach forming an activated PEG derivative for covalently coupling to another molecule to form a conjugate.
SUMMARY OF THE INVENTION
The invention described herein provides a water soluble polymer such as poly(ethylene glycol) or related polymers that have a branched moiety at one end of the polymer chain and two free reactive groups linked to the branched moiety for covalent attachment to another molecule. Each reactive moiety can have a tethering group, such as an alkyl chain, linking a reactive group to the branched moiety. Thus, the branched terminus allows the activated water soluble polymer of this invention to react with two molecules to form conjugates.
Because a tethering group having a desirable length can be selected in preparing an activated polymer, the two reactive groups can be held at a predetermined distance apart from each other. The two molecules conjugated to the activated polymer through the two reactive groups can also be held at a predetermined distance apart. Accordingly, an activated PEG is provided in accordance with the invention having two free reactive moieties branching out from one PEG chain at a branched moiety. The two free reactive moieties are capable of reacting with biologically active agents such as proteins, thereby linking the activated polymer to the biologically active agents.
In accordance with one embodiment of this invention, an activated water soluble polymer is provided having the formula:
wherein POLY is a water soluble, substantially non-immunogenic polymer backbone, Y is a hydrolytically stable linkage, X and X′ are reactive groups capable of reacting with a moiety in another molecule such as a protein. Typically, the polymer backbone is selected from the group consisting of linear and branched poly(ethylene glycol), linear and branched poly(alkylene oxide), linear and branched poly(vinyl pyrrolidone), linear and branched poly(vinyl alcohol), linear and branched polyoxazoline, linear and branched poly(acryloylmorpholine), and derivatives thereof. Preferably, the polymer backbone is poly(ethylene glycol) or a derivative thereof. The polymer backbone POLY can have a capping group selected from the group consisting of —OH, alkyls, and —Y—CHXX′ wherein Y, X and X′ are as described above and can be the same or different on each terminus of the PEG.
In a preferred embodiment, X and X′ are represented by —W—Z and—W′—Z′ respectively, in which Z and Z′ represent reactive moieties for conjugating the polymer to another molecule. W and W′ represent tethering groups comprising a substantially linear chain of atoms, e.g., alkyl chains, ether chains, ester chains, amide chains, and combinations thereof. Examples of the reactive moieties include, but are not limited to, active esters, active carbonates, aldehydes, isocyanates, isothiocyanates, epoxides, alcohols, maleimides, vinylsulfones, hydrazides, dithiopyridines, and iodoacetamides.
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