The present invention relates to compositions a polymeric embolic material and a therapeutic agent incorporated into the polymer matrix. The composition is of use for embolising tumours and delivering cytotoxic agents thereto.
Embolotherapy is a growing area of interventional medicine but normally relies upon the transarterial approach of the catheter to a desired location whereupon an agent is released in order to occlude a particular vessel. This treatment has been used in order to block the blood supply to certain hypervascularised tumours such as hepatocellular carcinoma and more recently is becoming a popular choice of treatment for uterine fibroids.
There is a range of embolic materials in clinical use, that require transcatheter delivery to the site of embolisation, whereupon they are released into the blood stream to block it. This is achieved either by a physical blocking of the vessel using small particles or spheres, or in the case of liquid embolic agents, require some sort of phase change or reaction to set the flowable material and form a cast within the vessel.
The most popular particulate-based embolic agent is poly(vinyl alcohol) (PVA) foam particles (e.g. Ivalon) which has been used for several decades. Recently, this material has been available in particulate, rather than sheet form, and does not require granulation by the surgeon prior to delivery.
In WO-A-0168720, PVA based compositions for embolotherapy are described. The PVA is, initially, derivatised to form a macromonomer, having pendant acrylic groups. Subsequently, these acrylic groups are polymerised, optionally in the presence of comonomer, to form a water-insoluble water-swellable polymer matrix The polymerisation reaction may be carried out in situ, whereby the PVA is rendered water-insoluble after delivery into the vessel, at the embolisation site Alternatively, the polymerisation is conducted prior to delivery, generally to form microspheres, which are delivered in suspension in an aqueous vehicle.
In WO-A0168720, it is suggested that biologically active agents may be included in the embolic compositions, whereby active agent may be delivered from the formed hydrogel. One class of active agents is chemo therapeutic agents Examples of chemo therapeutic agents are cisplatin, doxorubicin and mitomycin. Some general guidance is given as to methods of incorporating the active agents into the embolic compositions. Where the composition is a liquid which is cured in situ, the active may be simply mixed with the liquid. Where the articles are preformed, it is suggested that the active may be incorporated by “encapsulation”, or by coating onto the surface. There are no worked examples in which a therapeutic agent is incorporated into any type of composition.
Microspheres of hydrogel material formed from poly(hydroxyethyl methacrylate), hydrolysed poly(methyl methacrylate) and PVA crosslinked using aldehyde crosslinking agents such as glutaraldehyde, have also been used as embolic agents. Hydroxyethyl methacrylate may be copolymerised with comonomers, for instance having acidic groups. For instance, a crosslinked copolymer of hydroxyethyl methacrylate with about 1-2 mole % acrylic acid cross-linked by 0.3-1.0 mole % ethylene glycol dimethacrylate, has an equilibrium water content in the range 55-60% by weight, and has been used as a contact lens formulation for many years.
One embolic product on the market is marketed by Biosphere, which comprises microspheres of trisacrylgelatin having a coating of collagen. Collagen has an overall cationic charge as physiological pH's. In Ball, D. S. et al, J. Vasc. Interv. Radiol. (2003), 14, 83-88, Biosphere show that the microspheres' mechanical characteristics are not adversely affected when admixed with a range of drugs commonly administered along with the embolic compositions. Doxorubicin, cisplatin and mitoxantrone are specifically tested.
Doxorubicin and other anthracyclines have been incorporated into a variety of polymeric matrices based delivery systems, such as microspheres of polylactides or polyglycolides and cross-linked fibrinogen and albumin microspheres Juni, K. et al in Chem. Pharm. Bull. (1985), 33(1), 313-318 describe the incorporation of doxorubicin into poly(lactic acid) microspheres and the delivery of the composition intra arterially to dog liver. The composition embolised peripheral hepatic arteries. These types of microspheres are hard and are not easy to store and deliver Doxorubicin has been covalently linked to the surface of cross-linked poly(vinyl alcohol) and tested for its cytotoxic properties (Wingard, L B et al. Cancer Research (1985) 45(8) 3529-3536) Since the drug is covalently bonded to the polymer it must be cleaved before being released from the surface and hence may not be released under physiological conditions
Jones, C. et al in Brit. J. Cancer (1989) 59(5) describe incorporation of doxorubicin into ion-exchange microspheres and the use of the compositions in the chemoembolotherapy of tumours in a rat model
A new composition according to the invention suitable for embolisation, comprises particles having a matrix of water-swellable water-insoluble polymer and, absorbed in the matrix, a water-soluble therapeutic agent, and is characterised in that the polymer has an overall anionic charge at a pH in the range 6 to 8, in that the particles, when swollen to equilibrium in water have particle sizes in the range 40-1500 μm and in that the therapeutic agent is an anthracycline compound having at least one amine group
The polymer in the invention must be water-swellable, but water-insoluble. In the presence of aqueous liquid, therefore, the polymer will form a hydrogel. Generally the polymer is covalently crosslinked, although it may be appropriate for the polymer to be ionically crosslinked, at least in part. The polymer may be formed by polymerising ethylenically unsaturated monomers in the presence of di- or higher-functional crosslinking monomers, the ethylenically unsaturated monomers including an anionic monomer. Copolymers of hydroxyethyl methacrylate, acrylic acid and cross-linking monomer, such as ethylene glycol dimethacrylate or methylene bisacrylamide, as used for etafilcon A based contact lenses may be used
Another type of polymer which may be used to form the water-swellable water-insoluble matrix is polyvinyl alcohol crosslinked using aldehyde type crosslinking agents such as glutaraldehyde. For such products, the polyvinyl alcohol must be rendered anionic, for instance by providing pendant anionic groups by reacting a functional acidic group containing monomer with the hydroxyl groups. Examples of suitable reagents are di-acids, for instance dicarboxylic acids
The invention is of particular value where the polymer matrix is formed of a polyvinyl alcohol macromer, having more than one ethylenically unsaturated pendant group per molecule by copolymensation with ethylenically unsaturated monomers including an acidic monomer. The PVA macromer may be formed, for instance, by providing PVA polymer, of a suitable molecular weight such as in the range 1000 to 500,000 D, preferably 10,000 to 100,000 D, with pendant vinylic or acrylic groups. Pendant acrylic groups may be provided, for instance, by reacting acrylic or methacrylic acid with PVA to form ester linkages through some of the hydroxyl groups. Methods for attaching vinylic groups capable of polymerisation onto polyvinyl alcohol are described in, for instance, U.S. Pat. No. 4,978,713 and, preferably, U.S. Pat. Nos. 5,508,317 and 5,583,163 Thus the preferred macromer comprises a backbone of polyvinyl alcohol to which is linked, via a cyclic acetal linkage, to an (alk)acrylaminoalkyl moiety. Example 1 describes the synthesis of such a macromer. Preferably the PVA macromers have about 2 to 20 pendant ethylenic groups per molecule, for instance 5 to 10
Where PVA macromers are copolymerised with ethylenically unsaturated monomers inclulding an acidic monomer, the acidic monomer preferably has the general formula I
in which Y1
is selected from
OOCCR═CRC(O)—O—, RCH═CHC(O)O—, RCH═C(COOR2
R is hydrogen or a C1-C4 alkyl group;
R1 is hydrogen or a C1-C4 alkyl group;
R2 is hydrogen or a C1-4 alkyl group or BQ where B and Q are as defined below:
A is —O— or —NR1—
K1 is a group —(CH2)rOC(O)—, —(CH2)rC(O)O—, —(CH2)rOC(O)O—, —(CH2)rNR3—, —(CH2)rNR3C(O)—, —(CH2)rC(O)NR3—, —(CH2)rNR3C(O)O—, —(CH2), OC(O)NR3—, —(CH2)rNR3C(O)NR3—(in which the groups R3 are the same or different), —(CH2)rO—, —(CH2)rSO3—, or, optionally in combination with B1, a valence bond and r is from 1 to 12 and R3 is hydrogen or a C1-C4 alkyl group;
B is a straight or branched alkanediyl oxaalkylene, alkanediyloxaalkanediyl or alkanediyloligo(oxaalkanediyl) chain optionally containing one or more fluorine atoms up to and including perfluorinated chains or, if Q or Y1 contains a terminal carbon atom bonded to B a valence bond; and
Q is an anionic group.
The anionic group may be, for instance, a carboxylate, carbonate, sulpnonate, sulphate, nitrate, phosphonate or phosphate group, preferably a sulphonate group. The monomer may be polymerised as the free acid or in salt form. Preferably the pK8 of the conjugate acid is less than 5.
In the monomer of general formula I preferably Y1 is a group CH2═CRCOA—in which R is H or methyl, preferably methyl, and in which A is preferably NH. B is preferably an alkanediyl group of 1 to 12, preferably 2 to 6 carbon atoms.
One particularly preferred type of monomer is an (alk)acrylamido alkane-sulphonic acid, such as 2-acrylamido-2-methyl-1-propane-sulphonic acid (AMPS).
There may be included in the ethylenically unsaturated monomer diluent monomer, for instance non-ionic monomer. Such monomer may be useful to control the pK8 of the acid groups, to control the hydrophilicity or hydrophobicity of the product, to provide hydrophobic regions in the polymer, or merely to act as inert diluent. Examples of non-ionic diluent monomer are, for instance, alkyl (alk) acrylates and (alk) acrylamides, especially such compounds having alkyl groups with 1 to 12 carbon atoms, hydroxy, and di-hydroxy-substituted alkyl(alk) acrylates and-(alk) acrylamides, vinyl lactams, styrene and other aromatic monomers.
The ethylenically unsaturated monomer may also include zwitterionic monomer, for instance to increase the hydrophilicity, lubricity, biocompatibility and/or haemocompatibility of the particles. Suitable zwitterionic monomers are described in our earlier publications WO-A-9207885, WO-A-9416748, WO-A-9416749 and WO-A-9520407. Preferably a zwitterionic monomer is 2-methacryloyloxy-2′-trimethylammonium ethyl phosphate inner salt (MPC).
In the polymer matrix, the level of anion is preferably in the range 0.1 to 10 meq g−1, preferably at least 1 0 meq g−1.
Where PVA macromer is copolymerised with other ethylenically unsaturated monomers, the weight ratio of PVA macromer to other monomer is preferably in the range of 50:1 to 1 5, more preferably in the range 20:1 to 1 2 In the ethylenically unsaturated monomer the anionic monomer is preferably present in an amount in the range 10 to 100 mole %, preferably at least 25 mole %
Preferably the water-insoluble water-swellable polymer has an equilibrium water content measured by gravimetric analysis of 40 to 99 weight %, preferably 75 to 95%.
The polymer may be formed into particles in several ways. For instance, the crosslinked polymer may be made as a bulk material, for instance in the form of a sheet or a block, and subsequently be comminuted to the desired size Alternatively, the crosslinked polymer may be formed as such in particulate form, for instance by polymerising in droplets of monomer in a dispersed phase in a continuous immiscible carrier. Examples of suitable water-in-oil polymerisations to produce particles having the desired size, when swollen, are known. For instance U.S. Pat. No. 4,224,427 describes processes for forming uniform spherical beads of up to 5 mm in diameter, by dispersing water-soluble monomers into a continuous solvent phase, in a presence of suspending agents. Stabilisers and surfactants may be present to provide control over the size of the dispersed phase particles. After polymerisation, the crosslinked microspheres are recovered by known means, and washed and optionally sterilised. Preferably the particles eg microspheres, are swollen in an aqueous liquid, and classified according to their size.
The therapeutic active used in the present invention is an anthracycline compound, which comprises an anthraquinone group to which is attached an amine sugar. The amino group on the sugar is believed to associate with the anionic groups in the polymer matrix, to allow high levels of loading and controlled delivery after administration.
Examples of suitable anthracyclines have the general formula II
We have found that doxorubicin, which has been thoroughly tested for efficacy on various tumours, has particularly interesting loading and release characteristics. The drug appears to have a particular affinity for poly(vinyl alcohol-graft-acrylamido propane sulphonic acid), so that high levels of doxorubicin are capable of incorporation into the polymer, and release over many days.
In the invention it is important that the drug is not covalently attached to the polymer matrix.
The therapeutic active may be incorporated into the polymer matrix by a variety of techniques. In one method, the therapeutic active may be mixed with a precursor of the polymer, for instance a monomer or macromer mixture or a cross-linkable polymer and cross-linker mixture, prior to polymerising or crosslinking. Alternatively, the active may be loaded into the polymer after it has been crosslinked. For instance, particulate dried polymer may be swollen in a solution of therapeutic active, preferably in water, optionally with subsequent removal of non-absorbed agent and/or evaporation of solvent. A solution of the active, in an organic solvent such as an alcohol, or, more preferably, in water, may be sprayed onto a moving bed of particles, whereby drug is absorbed into the body of the particles with simultaneous solvent removal Most conveniently, we have found that it is possible merely to contact swollen particles suspended in a continuous liquid vehicle, such as water, with a solution of drug, over an extended period, whereby drug becomes absorbed into the body of the particles. This is believed to be analogous to a cation exchange type process. The swelling vehicle may subsequently be removed or, conveniently, may be retained with the particles as part of the product for subsequent use as an embolic agent
Alternatively, the suspension of particles can be filtered to remove any remaining drug loading solution and the particles dried by any of the classical techniques employed to dry pharmaceutical-based products This could include, but is not limited to, air drying at room or elevated temperatures or under reduced pressure or vacuum; classical freeze-drying, atmospheric pressure-freeze drying; solution enhanced dispersion of supercritical fluids (SEDS). Alternatively the drug-loaded microspheres may be dehydrated using an organic solvent to replace water in a series of steps, followed by evaporation of the more volatile organic solvent A solvent should be selected which is a non solvent for the drug.
In brief, a typical classical freeze drying process might proceed as follows: the sample is aliquoted into partially stoppered glass vials, which are placed on a cooled, temperature controlled shelf within the freeze dryer. The shelf temperature is reduced and the sample is frozen to a uniform, defined temperature. After complete freezing, the pressure in the dryer is lowered to a defined pressure to initiate primary drying During the primary drying, water vapour is progressively removed from the frozen mass by sublimation whilst the shelf temperature is controlled at a constant, low temperature. Secondary drying is initiated by increasing the shelf temperature and reducing the chamber pressure further so that water absorbed to the semi-dried mass can be removed until the residual water content decreases to the desired level The vials can be sealed, in situ, under a protective atmosphere if required.
Atmospheric pressure freeze drying is accomplished by rapidly circulating very dry air over a frozen product. In comparison with the classical freeze-drying process, freeze-drying without a vacuum has a number of advantages. The circulating dry gas provides improved heat and mass transfer from the frozen sample, in the same way as washing dries quicker on a windy day. Most work in this area is concerned with food production, and it has been observed that there is an increased retention of volatile aromatic compounds, the potential benefits of this to the drying of biologicals is yet to be determined Of particular interest is the fact that by using atmospheric spray drying processes instead of a cake, a fine, free-flowing powder is obtained Particles can be obtained which have submicron diameters, this is tenfold smaller than can be generally obtained by milling The particulate nature, with its high surface area results in an easily rehydratable product, currently the fine control over particle size required for inhalable and transdermal applications is not possible, however there is potential in this area.
The composition which is administered to a patient in need of embolotherapy having a solid tumour, for instance a hepatocellular carcinoma, is an aqueous suspension of swollen particles containing absorbed drug. It is often desirable for the suspension to be mixed prior to delivery with an imaging agent such as a conventional radiopaque agent, as is used for gel type embolic compositions. Alternatively or additionally the particles may be pre-loaded with radiopaque material, in addition to the anthracycline. The composition which is administered may also be admixed with other therapeutic agents, or may be administered in separately but in combination with other therapeutic agents. Usually the composition is administered from a reservoir in a syringe using the conventional delivery devices, such as an intra-arterial catheter.
There is provided as a second aspect of the invention the use of an anthracycline compound in the manufacture of a composition for use in the treatment of a solid tumour by embolotherapy, in which treatment the anthracycline is delivered from a polymer matrix formed by the copolymerisation of a poly(vinyl alcohol) macromer having at least 2 pendant ethylenically unsaturated groups per molecule and an ethylenically unsaturated anionic monomer.
In this aspect of the invention the polymer matrix may be formed in situ. Thus a liquid composition comprising the macromer and the anionic monomer and anthracycline may be delivered into the circulation of a patient and subjected to conditions to initiate polymerisation at the target site whereby an embolising gel is formed. Alternatively the polymer matrix may be preformed before administration, as described in the first aspect of the invention.
The PVA macromer and anionic monomer are preferably as described above in connection with the first aspect. Other monomers may also be copolymerised, as described in connection with the first aspect of the invention