AU2001287915A1 - Photosensitisers - Google Patents

Description

PHOTOSENSITISE S

Field of the Invention

This invention relates to chemical compounds which act as photosensitisers and may be used in a type of medical treatment known as photodynamic therapy (PDT), as well as for the diagnosis and detection of medical conditions and related uses in photochemical internalisation, in the production of cancer vaccines and in the treatment of bacterial infections including photodisinfections.

Background to the Invention

Photodynamic therapy is used in the treatment of cancer and other diseases. In this treatment a light absorbing compound (the photosensitiser) is applied to a tumour or other lesion. Subsequently laser light is used to activate the photosensitiser and the tumour tissue is destroyed in a process known as the photodynamic effect.

When the photosensitiser absorbs light it can produce a short-lived but highly active species known as singlet oxygen. Also produced by the activated photosensitiser is superoxide ion, O₂ ^~. Singlet oxygen is thought to be the main agent effective against the tumour although the superoxide ion may also participate.

It is believed that the photosensitiser destroys the blood supply to the malignant cells of the tumour, thereby ultimately starving the tumour of oxygen and nutrients. Alternatively, the photosensitiser may cause direct breakdown of tumour cells.

One photosensitiser currently used in PDT is a complex mixture of porphyrins (cyclic tetrapyrroles) known as haematoporphyrin derivative (HpD). A commercial version of HpD is available as Photofiin®. Although approved in various countries for treating various types of tumour, Photofiin has various limitations including the accumulation of the material in the skin for a prolonged period, thereby inducing undesirable photosensitivity under normal daylight.

Various other photosensitisers have been proposed for use in PDT. These include specific porphyrins, phmalocyanines, naphthalocyanines and chlorins. Sulphonated phthalocyanines have been reported to be particularly effective (Rosenthal. L, Photochem. Photobiol, 1991, 53, 859-70.

Photosensitisers may also be used in the diagnosis and detection of medical conditions. For these applications, the photosensitiser is administered to the patient either internally or topically. Abnormal cells take up the photosensitiser to a greater extent than normal cells and, accordingly, when light is applied to the region under investigation an area containing abnormal cells will exhibit greater fluorescence than an area containing only normal cells.

Tetrasulphonyla inoglycine zinc (II) phthalocyanine (TGly) has been described in J.

Photochem. Photobiol B: Biology., 45 (1998) 28-35 as a potential agent for PDT.

The performance of TGly as a photosensitiser in non-biological situations compared favourably with two clinically used photosensitisers and two others under test. However TGly was relatively poor in its ability to effect haemolysis of red blood cells and would therefore not be considered as a potential agent for use in PDT, diagnosis or detection applied to the human or animal body.

In general, there are various requirements, both chemical and biological, for a useful and clinically effective photosensitiser. The chemical properties include .purity, a high quantum yield of singlet oxygen upon activation, the ability to be activated by wavelengths of light in the red to infra-red region (since such radiation penetrates deeply into tissue) and solubility in water. However, sensitisers which satisfy these chemical criteria do not necessarily possess advantageous biological properties for use in clinical PDT. These properties, which include localisation in target tissues (e.g. tumours), lack of skin photosensitivity, rapid clearance from the body and appropriate sub-cellular location are not predictable from chemical structure with current knowledge.

Statements of the Invention

According to the present invention there is provided a compound for use as a photosensitiser in PDT, in photochemical internalisation in the production of a cancer vaccine or in the diagnosis or detection of medical conditions, the compound having the formula I

[Phot] [-SO₂ - N - X - CO₂ H]_n i

where Phot is a photosensitising chromophoric system, that is to say, a radical representing a photosensitising chromophoric system, such that the molecular species [PhofJHn is capable of photosensitising Type I and Type II photoxidations, X is linear or branched alkyl having from 0 to 5 carbon atoms which optionally may be substituted by one or more hydrophilic groups such as hydroxy methoxy, ethoxy or carboxy, Y is hydrogen or linear or branched alkyl having from 1 to 5 carbon atoms, which optionally may be substituted by one or more hydroxy groups, and n is an integer of from 1 to 4, or a salt, preferably on a pharmaceutically acceptable salt, thereof.

Preferably Phot is a residue of a metal phthalocyanine, a benzoporphyrin, a purpurin, a chlorin or a bacteriochlorin..

A preferred compound in accordance with the present invention is a phthalocyanine (Pc) derivative having the formula II

where R is -NH-X-CO₂H, preferred examples of X being -CH₂- (referred to above as TGly and hereinbelow as TSZnPc-glycine), -CH₂CH₂- (TSZnPc-β-alanine),- CH(CH₃)- (TSZnPc-α-alanine), -(CH₂)₃- (TSZnPc-aminobutyric acid), -(CH₂)₄- (TSBuPc aminovaleric acid and -(CH₂)₅ (TSZnPc-aminocaproic acid).

Examples of other compounds falling within the scope of the present invention are as follows:

a) mono-, di-and tri-substituted analogues of the above shown tetra-substituted phthalocyanine structures, that is to say, compounds of the first-mentioned general formula π where n is 1 , 2 or 3 ;

b) chloroaluminium and hydroxyaluminium analogues of the mono-, di-, hi- and tetra- substituted zinc phthalocyanines;

c) porphyrins bearing one or more of the sulphonyl amino acid side chains;

d) benzoporphyrins bearing one or more of the sulphonyl amino acid side chains;

e) chlorins bearing one or more of the sulphonyl amino acid side chains, such as a compound represented by the following formula HI where R is -NH-X-CO₂H and X is a linear or branched alkyl chain having from 0-5 carbon atoms;

and /) bacteriochlorins bearing one or more of the sulphonyl amino acid side chains, such as a compound of the formula in in which a double bond in one of the 5- membered rings is absent.

Surprisingly, compounds of the invention not only are highly effective as photosensitising agents when used in vivo but also are rapidly cleared from the body, have little or no skin photosensitivity and unlike some other sensitisers, do not cause unacceptable skin discoloration.

Examples of uses of the compounds of the present invention are as photosensitising drugs for PDT to treat pre-cancerous conditions (e.g. Barrett's oesophagus and cervical intraepithehal neoplasia), cancer (e.g. bladder cancer and colon cancer), ophthalmological disease including macular degeneration, vascular problems such as cardiovascular disease, arteriosclerosis and restenosis and autoimmune diseases such as rheumatoid arthritis, skin diseases such as psoriasis, acne and excema and other benign conditions such as endometriosis and mennorrhagia. The compounds may also be used as anti-microbial treatments for skin and wound infections, other local infections as well as in the treatment of dental bacterial disease. The compounds may also be used in photochemical internalisation and in the production of cancer vaccines through their photosensitising properties and in non-therapeutic uses such as in photodetection and photodiagnosis through their fluorescence properties. Compounds of the present invention may be useful is the treatment, diagnosis and/or detection of conditions in various parts of the body including the skin, lungs, brain, eye, colon, bladder, cervix and oesophagus.

It is found that the combination of the non-ionic polar sulphonamide residue and the weakly acidic carboxylic acid group results in the compound of the present invention having good water solubility allowing easy formulation of appropriate compositions for use in medical treatment.

The present invention also provides a pharmaceutical composition comprising a compound of formula I together with one or more diluents, excipients or adjuvants.

The present invention also provides a compound of formula I excluding the compound tetrasulphonylaminoglycine zinc (I) phthalocyanine. In addition the present invention provides the use of a compound of formula I in the manufacture of a medicament for treatment of a condition by photodynamic therapy or for photochemical internalisation in the production of a cancer vaccine or in the manufacture of an agent for use as a photosensitiser in the diagnosis or detection of a medical condition.

Furthermore, the present invention provides a method of treatment of an animal, including a human being, by photodynamic therapy in which the photosensitiser comprises a compound of formula I or a method of diagnosis or detection using a compound of formula I as a photosensitiser.

Detailed description of the invention The invention will now be illustrated, by way of examples only, by reference to photosensitisers of formula H

(A) Synthesis of sensitisers

(1) TSZnPc-β-alanine

Synthesis of zinc phthalocyanine tetrasulphonyl chloride

Method 1.

The sodium salt of zinc phthalocyanine tetrasulphonic acid (5.0 g) was added with stirring to chlorosulphonic acid (58 ml) at ambient temperature, then heated to 55°C for 2 hours. Thionyl chloride (7.5 ml) was then added slowly and stirring continued for a further 4 hours at 50 - 55°C. The mixture was allowed to cool and stirred overnight at room temperature, and ice was then added with vigorous stirring, giving a final volume of 500 ml. The blue solid was filtered off, washed well with ice- water, and dried as much as possible on the vacuum pump. The filter cake was then used immediately for subsequent reactions with amines.

Method 2.

To a stirred mixture of zinc phthalocyanine tetrasulphonic acid (4 g), dimethylacetamide (10 ml), and acetonitrile (40 ml) was added phosphorus oxychloride (15 ml) dropwise over 15 minutes. The mixture was then warmed to 60 °C , held at that temperature for 1 hour, cooled to room temperature, and then ice/ water was added with vigorous stirring. The precipitated tetrasulphonyl chloride was filtered off, washed well with ice/water, dried as much as possible at the filter pump, and the filter cake was used immediately for the preparation of derivatives. Conversion to TsZnPc-β-alanine.

The tetrasulphonyl chloride filter cake made from 5.0 grams of zinc phthalocyanine tetrasulphonic acid was added to a solution of β-alanine (12 g) in a mixture of dimethylformamide (45 ml) and dimethylacetamide (5 ml), simultaneously adding dropwise dilute sodium hydroxide solution to ensure slight alkalinity. The solution was then stirred for 12 hours at ambient temperature, diluted with water (100 ml), and dialysed for 1 week with frequent changes of water. The dialysed solution was then evaporated to dryness and dried in the oven to give TsZnPc-β-alanine (1.4 g). Found:- C, 35.3; H, 3.3; N, 10.8 %.

C₄₄H₃₂Ni2θι₆S₄ZnNa₄.12H₂O requires: C, 35.5; H, 3.8; N, 11.3 % .

Molar absorption coefficient - 124,260 1 mol^"1 cm^"1 in DMF at X___Ά 672 run

(2) TsZnPc-α-alanine The procedure described in Example 1 was followed, using 5 grams of zinc phthalocyanine tetrasulphonyl chloride and 12 grams of α-alanine. The resultant solution was dialysed for 1 week with f equent changes of water, and then evaporated to dryness and the residue dried in an oven to give TsZnPc-α-alanine ( 1.27 g).

Found: C, 36.45; H, 3.55; N, 11.7 %. C₄₄H₃₂Nι₂θ^'ι₆S₄ZnNa4.10H₂O requires C, 36.44; H, 3.59; N, 11.6 %.

Mass spectrum (electrospray): Found M 1180; C H₃₆Nι O₁₆S Zn requires M = 1180.

Molar absorption coefficient = 141,400 1 mol^"1 cm^"1 in DMF at λ_max=672 nm

(3) TsZnPc-aminobutyric acid

Zinc phthalocyanine tetrasulphonyl chloride (4.0 g) was converted into the tetrasulphonyl chloride and the filter cake was added to a solution of 4-aminobutyric acid (6.5 gm) in dimethylformamide (45 ml) and dimethyl acetamide (5 ml), simultaneously adding dropwise dilute sodium hydroxide solution to maintain slight alkalinity. The solution was stirred for 12 hours at ambient temperature, diluted with water (50 ml) and dialysed for 1 week with frequent changes of water. The dialysed solution was then evaporated to dryness and the residue dried in an oven to give

TsZnPc-aminobutyric acid (1.11 g).

Found: C, 39.4; H, 3.5; N, 12.5 %

C₄₈H₄₀N₁₂O₁₆S₄Zn Na4 .6H₂O requires: C, 40.2; H, 3.6; N, 11.7 %.

Molar absorption coefficient = 103,0001 mol^"1 cm^"1 in DMF at λ_ma = 672 nm

(4) TsZnPc-aminovaleric acid

Zinc phthalocyanine tetrasulphonyl chloride (5.0 g) was converted into the tetrasulphonyl chloride and the filter cake was added to a solution of 5-aminovaleric acid (5 g) in dimethylformamide (45 ml) and dimethylacetamide (5 ml), simultaneously adding dropwise dilute sodium hydroxide to maintain slight alkalinity. The solution was stirred for 12 hours at ambient temperature, diluted with water (50 ml) and dialysed for 48 hours with frequent changes of water. The dialysed solution was evaporated to dryness and the blue residue dried in an oven to give TsZnPc-aminovaleric acid (1.40 g).

Found C = 40.0; H, 3.8; N, 11.75 %,

C∞HttNuOiβS-tZn Na-t . 10H₂O requires C, 40.0; H, 4.4; N, 10.8 %

Molar absorption coefficient = 72,000 1 mol^"1 cm^"1 in DMF at λ_max 672 nm

(5) TsZnPc-aminocaproic acid

Zinc phthalocyanine tetrasulphonyl chloride (5.0 g) was converted into the tetrasulphonyl chloride and the filter cake was added to a solution of 6-aminocaproic acid (7.0 g) in dimethylformamide (45 ml) and dimethylacetamide (5 ml), simultaneously adding dilute sodium hydroxide solution to maintain slight alkalinity. The solution was stirred for 12 hours at ambient temperature, diluted with water (50 ml), and dialysed for 48 hours with frequent changes of water. The dialysed solution was evaporated to dryness and the residue dried in the oven to give TsZnPc- aminocaproic acid (1.16 g).

Found C = 39.7%, H = 3.8%, N = 11.1%, C₅₆H₅₆Nι₂Oι₆S₄Zn N- . 10H₂O requires C = 41.5%, H = 4.7%, N = 10.4 % Molar absorption coefficient = 106,000 1 mol^"1 cm^"1 in DMF at λ_max 672 nm.

(B) Phototoxicity of various compounds towards cells in culture

The following table (Table 1) shows the photocytotoxic activity of various compounds in accordance with the present invention in killing RTF-1 (murine fibrosarcoma) cells in culture.

Table 1

[Phot] = Zinc Phthalocyanine; n = 4; LD₅₀ is the concentration of drug needed to cause 50% cell death in two hours of illumination

(C) Photoactivity of various compounds towards tumours

Data are shown in two animals models, the rat and the mouse. Comparative data are also shown for PHP (analogous to Photofiin). Growth delay measures the additional time taken for a treated tumour to grow to a given size, compared with an untreated tumour. Zero growth delay signifies no effect and growth delays of 5 days or longer imply substantial PDT activity. In both models, it is clearly seen that certain compounds of the present invention have at least equal and in some cases considerably higher phototactivity than PHP (Photofiin).

(1 ) PDT-induced LSBD_j tumour growth delay in BDD rats

Sub-cutaneous tumours were treated interstitially with light from Cu-vapour laser (400J, lOOmW at 680nm for phthalocyanines and 630nm for PHP).

Tumour growth delay is calculated as the number of days for treated tumour to reach a mean diameter of 15mm minus the number of days for a control tumour to reach a mean diameter of 15mm. Data for various compounds are shown in Table 2, which also indicates the times (drug-light interval) at which effects occurred.

Figure la) and le) show tumour growth delay at different drug-light intervals for the compounds tested. Where error bars are shown data given are the means of at least 3 rats ± s.e. Figure 2 shows the best response obtained for each compound tested. Figure 3 shows light dose response curves for PHP and the β-alanine pc derivative. Data points are the mean of 6 rats ± s.e.

Table 2 Growth delays for various compounds in days

(2) PDT-induced area of necrosis in CaNT tumours (in CBA/Gy mice)

Sub-cutaneous rumours were treated superficially with light from the Paterson xenon are lamp (60J/cm², 50 mW/cm/²). For PHP a 630 ± 15nm filter was used, for the β- alanine derivative 685± 15nm filter was used. At 72h post PDT mice were killed and area of necrosis was determined from a mid-section of tumour

Figure 4 shows a dose-response curve for the β-alanine derivative. Figure 5 compares PHP and the β-alanine derivative at equimolar amounts at different drug- light intervals.

(D) Skin photosensitivity measurements

Skin photosensitivity is a major problem with some currently-used photosensitisers. Patients sometimes have to avoid light after drug administration for several weeks. The following data show skin photosensitivity scores for various compounds of the present invention, compared with PHP (Photofiin) in both rat and mouse models. There are clear advantages of some compounds of the present invention in having very low or zero skin photosensitivity.

(1) Skin photosensitivity-visual assessment in rodent skin patch

The skin of wistar rats was depilated and rats were injected with sensitiser (i.v.) at 0.5, 2, 5 or 10 mg/kg. At 24h the skin patch was exposed to broad band white light from a xenon arc lamp (91.8 J cm-²). Light exposure was repeated on untreated skin at 2 weeks post-drug injection. Skin reactions were scored according to Table 3. Data are shown in Table 4 and in Figure 6. Table 3

Table 4

(2) Skin photosensitivity murine ear swelling response

CBA/Gy mice were injected with sensitiser at 16.7 μmol/kg. At 24h post drug injection ears were exposed to broad band white light from a xenon arc lamp (25J/cm², 30mW/cm²). Change in ear thickness was measured as: ear thickness at 24h post illumination minus ear thickness pre-illumination. Light exposure and ear measurements were repeated at 2 weeks post drug injection on the previously untreated ear. Results are shown in Figure 7. Increased ear thickness measures increased skin photosensitivity. (E) Skin coloration

Certain photosensitiser drugs can cause a transient skin coloration immediately after drug administration. Whilst this may not present a physical health problem, it may cause psychological difficulties and make treatment cosmetically unacceptable. Compounds in the present invention have therefore been assessed for skin coloration against an acceptable limit. Data in both rat and mouse models are shown below.

(1) Skin coloration - Wistar rats

The skin of Wistar rats ears was depilated and rats were injected with sensitiser at 0.5, 2, 5 or 10 mg/kg. Skin coloration was measured daily using a sphere spectrophotometer and compared to the skin of a control rat (no drug). Results are shown in Figure 8 for 10 mg/kg.

(2) Skin coloration - CBA Gy mice

The skin of CBA/Gy mice was depilated and skin coloration was measured using a sphere spectrophotometer. Mice were injected with sensitiser at 16.7 16.7 μmol/kg. Skin colour was remeasured at 10 mins, 3h, 24h then daily for 14 days or until witrrih control levels. Results are shown in Figure 9.

Claims (9)

1. A compound for use as a photosensitiser in PDT, in photochemical internalisation, in the production of cancer vaccines or in the diagnosis or detection of medical conditions, the compound having the formula I

[Phot] [-SO₂ - N - X - CO₂ H]_n j

I

Y where Phot is a photosensitising chromophoric system, X is linear or branched alkyl having from 0 to 5 carbon atoms, which optionally may be substituted by one or more hydrophilic groups, Y is hydrogen or linear or branched alkyl having from 1 to 5 carbon atoms, which optionally may be substituted by one or more hydroxy groups and n is an integer of from 1 to 4, or a salt thereof

2. A compound according to Claim 1 wherein Phot is a residue of a metal phthalocyanine, a benzoporphyrin, a purpurin, a chlorin or a bacteriochlorin.

3. A compound according to Claim 1 and having the formula II

where R is - NH - X - CO₂H, X being as defined in Claim 1.

4. A compound according to Claim 1 wherein X is -CH₂-, -CH₂CH₂ -, -CH(CH₃) -(CH₂)₃ - or - (CH₂) ₄ -.

5. A pharmaceutical composition comprising a compound of any of the preceding claims together with one or more diluents, excipients or adjuvants.

6. A compound of the formula I, as defined in Claim 1, or a pharaceutically acceptable sale thereof excluding the compound tetrasulphonyl-iminoglycine zinc (IT) phthalocyanine.

7. The use of a compound of the formula I, as defined in Claim 1, in the manufacture of a medicament for the treatment of a condition by photodynamic therapy or for photochemical internalisation in the production of a cancer vaccine or in the manufacture of an agent for use as a photosensitiser in the diagnosis or detection of a medical condition.

8. A method of treatment of an animal, including a human being, by PDT in which the photosensitiser comprises a compound of formula I, as defined in Claim 1.

9. A method of diagnosis or detection of a medical condition in an animal, including a human being, comprising applying a compound of formula I, as defined in Claim 1, to the animal and irradiating the animal to elicit a fluorescent response from the compound.