Pyropheophorbides and their use in photodynamic therapy

Abstract

Pyropheophorbide compounds are injected into a host and accumulate in tumor tissue to a higher degree than surrounding normal tissues. When the pyropheophorbide compounds are exposed to a particular wavelength of light the compounds become cytotoxic and destroy the tumor or diseased tissue without causing irreversible normal tissue damage. The pyropheophorbide compounds have shown improved results as compared to drugs currently used in photodynamic therapy. Further, they absorb light further in the red, optimizing tissue penetration mad are retained in the skin for short time periods relative to other drugs used in photodynamic therapy.

Description

CROSS-REFERENCE

This application is CH₂OR₂ —CH₂OR₂ where R₂ is a primary or secondary ary alkyl containing 1 to 20 (preferably 5-20) carbons; and R₃ is —COR₄ —CH₂CH₂CO₂R₄ where R₄ is H or an alkyl containing 1 to 20 carbons. Preferred compounds are when R₁ is —CO₂—O—hexyl —CH₂—O—hexyl and R₃ is —CO₂CH₃ —CH₂CH₂CO₂CH₃ or —CO₂H —CH₂CH₂CO₂H. Other compounds of the invention are encompassed by formula II as follows: ##STR00004##
wherein R₅ is —OR₆ where R₅ is a primary or secondary alkyl containing 1 to 20 (preferably 5-20) carbons and R₇ is —CO₂R₈ —CH₂CH₂CO₈ where R₈ is H or an alkyl containing 1 to 20 carbons. Particularly preferred compounds are where R₅ is —O—hexyl and R₇ is —CO₂H —CH₂CH₂CO₂H or —CO₂CH₃ —CH₂CH₂CO₂CH₃.

The pyropheophorbide compounds of structural formulae I and II can be formulated into pharmaceutical compositions and administered to patients in therapeutically effective amounts in order to treat cancer.

Although the invention encompasses all of the compounds of structural formulae I and II it has been found that the compound of structural formula IIa is particularly effective in the treatment of cancer when used in connection with photodynamic therapy. Structural formula IIa is put forth below: ##STR00005##

A generalized reaction scheme for the synthesis of the compound of structural formula IIa is put forth below: ##STR00006##

STARTING MATERIALS

The starting material for preparation of the red light-absorbing compounds is methyl pheophorbide-a, which is isolated from Spirulina destridratada by the method of Smith and Golf (D. Goff, Ph.D. Thesis, Univ. of Calif., Davis, CA 95616. 1994 incorporated herein by reference). Briefly, 500 gm dried Spirulina was slurried in a large volume of acetone and then liquid nitrogen was added to form a frozen slush. The slush was transferred to a 3-necked, 5-liter round bottom flask and heated to reflux under nitrogen with stirring for 2 hours. The mixture was filtered through Whatman paper on a Buchner funnel with extensive acetone washing. The extraction and filtration process was repeated 2 more times; all green color could not be removed from the solid.

The green filtrate was evaporated and purified by flash chromatography on Grade V neutral Alumina, eluting first with n-hexane to remove a fast running yellow band and then with dichloromethane to obtain the major blue/gray peak containing pheophytin-a. Treatment of pheophytin-a with 500 ml sulfuric acid in methanol for 12 hours at room temperature in the dark under nitrogen was followed by dilution with dichloromethane. The reaction mixture was rinsed with water and then 10% aqueous sodium bicarbonate and the organic layer was dried, evaporated, and the residue recrystallized from dichloromethane/methanol to obtain 1.8 gm methyl pheophorbide-a. Methyl pheophorbide-a appears to be inactive in the in vivo tumorcidal activity assay when injected at a done of 5 mg/kg.

CONJUGATES AND LABELED PYROPHEOPHORBIDES

In addition to using compositions which consist essentially of the above-defined compounds or preparations an active ingredient, it is possible to sue derivatized forms in order to provide a specific targeting mechanism. Commonly used target-specific components include monoclonal antibodies and ligands which bind to a cellular receptor. The compositions can also be conveniently labeled.

The target-specific component can then be, for example, an immunoglobulin or portion thereof or a ligand specific for a particular receptor. The immunoglobulin component can be made of a variety of materials. It may be derived from polyclonal or monoclonal antibody preparations and may contain whole antibodies or immunologically reactive fragments of then antibodies such as F(ab′)2, FAB, or FAB′ fragments. Use of such immunologically reactive fragments as substitutes for whole antibodies is well known in the art. See, for example, Spiegelberg, H. L., in “Immunoassays in the Clinical Laboratory” (1978) 3:1-23 incorporated herein by reference.

Polyclonal anti-sera are prepared in conventional ways by injecting a suitable mammal with antigen to which antibody is desired, assaying the antibody level in serum against the antigen, and preparing anti-sera when the titers are high. Monoclonal antibody preparations may also be prepared conventionally such as by the method of Koehler and Milstein using peripheral blood lymphocytes or spleen cells from immunized animals and immortalizing these cells either by viral infection, by fusion with myelomas, or by other conventional procedures, and screening for production of the desired antibodies by isolated colonies. Formation of the fragments from either monoclonal a polyclonal preparations is effected by conventional means as described by Spiegelberg, H. L., supra.

Particularly useful antibodies include the monoclonal antibody preparation CAMALI which can be prepared as described by Malcolm, A., et al, Ex Hematol (1984) 12:539-547; polyclonal or monoclonal preparations of anti-MI antibody as described by New, D. et al, J Immunol (1983) 130:1473-1477 (supra) and B16G antibody which is prepared as described by Maier, T., et al, J Immunol (1913) 131:1843; Steel, J. K., et al, Cell Immunol (1984) 90:303 all of which publications are incorporated by reference.

The foregoing list is exemplary and certainly not limiting; once the target tissue is known, antibody specific for this tissue may be prepared by conventional means. Therefore the invention is applicable to effecting toxicity against any desired target.

The ligand specific for receptor refers to a moiety which binds a receptor at cell surfaces, and thus contains contacts and charge patterns which are complementary to those of the receptor. It is well understood that a wide variety of cell types have specific receptors designed to bind hormones, growth factors, or neurotransmitters. However, while these embodiments of ligands specific for receptor are known and understood, the phrase “ligand specific for receptor,” as used herein, refers to any substance, natural of synthetic, which binds specifically to a receptor.

Examples of each ligands include the steroid hormones, such as progesterone, estrogen, androgens, and the adrenal cortical hormones; growth factors, such as epidermal growth factor, nerve growth factor, fibroblast growth factor, and so forth; other protein hormones, such as human growth hormone, parathyroid hormone, and so forth; and neurotransmitters, such as acetylcholine, serotonin, and dopamine. Any analog of these substances which succeeds in binding to the receptor is also included.

The conjugation of the target-cell-specific component to the compounds of the invention can be effected by any convenient means. For proteins, such Ig and certain receptor ligand, a direct covalent bond between these moieties may be effected, for example, using a dehydrating agent such as a carbodiimide. A particularly preferred method of covalently binding the compounds of the invention to the immunoglobulin moiety is treatment with 1-ethyl-3-(3-dimethylamino propyl) carbodiimide (EDCI) in the presence of a reaction medium consisting essentially of dimethyl sulfoxide (DMSO).

Of course, other dehydrating agents such as dicyclohexylcarbodiimide or diethylcarbodilmide could also be used as well as conventional aqueous and partially aqueous media.

Nonprotein receptor ligands can be conjugated to be dimers and trimers according to their relevant functional groups by means known in the art.

The active moieties of the conjugate may also be conjugated through linker compounds which are bifunctional, and are capable of covalently binding each of the two active components. A large variety of these linkers is commercially available, and a typical list would include those found, for example, in the catalog of the Pierce Chemical Co. These linkers are either homoor heterobifunctional moieties and include functionalities capable of forming disulfides, amides, hydrazones, and a wide variety of other linkages.

Other linkers include polymers such a polyamines, polyethers, polyamine alcohols, derivatized to the components by moms of ketones, acids, aldehydes, isocyanates, or a variety of usher groups.

The techniques employed in conjugating the active moieties of the conjugate to the target-specific component include any standard mean and the method for conjugation does as form part of the invention. Therefore, any effective technique knows in the art to produce such conjugates falls within the scope of the invention, and the linker moiety is accordingly broadly defined only as being either a covalent bond or any linker moiety available is the art or derivable therefrom using standard techniques.

The compounds of the invention per se or the conjugates may be further derivatized to a compound or ion which labels the drug. A wide variety, of labeling moieties can be used, including radioisotopes and fluorescent labels. Radioisotope labeling is preferred, as it can be readily detected in vivo.

The compounds which are alone or are conjugates with a specific binding substance can be labeled with radioisotopes by coordination of a suitable radioactive cation in the porphyrin system. Useful cations include technetium and indium. In the conjugates, the specific binding substances can also be linked to label.

ADMINISTRATION AND USE

In general, the pyropheophorbide compounds of the invention are administered to a host such as a human suffering from cancer in therapeutically effective amounts by any suitable means such as injection which may be IV or IM or may be administered transdermally. The pyropheophorbide compounds of the invention accumulate in tumor cells to a much higher degree than they accumulate in surrounding normal tissues. After being provided with sufficient time so as to accumulate in the tumor tissue, the pyropheophorbide compounds are exposed to a particular wavelength of light which causes the compounds to become cytotoxic, thus destroying the tumor or diseased tissue which the pyropheophorbide compounds have accumulated in. This is accomplished without causing irreversible damage to surrounding normal tissues wherein there has not been an accumulation of the pyropheophorbide compounds.

The compounds and their conjugates with target-specific substances of the invention are useful, in general, in the manner known in the art for hematoporphyrin derivative and for Photofrin II compositions. These compositions are useful in sensitizing neoplastic cells or other abnormal tissue to destruction by irradiation using visible light—upon photoactivation, the compositions have no direct effect, nor are they entered into any biological event; however the energy of photoactivation is believed to be transferred to endogenous oxygen to convert it to singlet oxygen. This singlet oxygen is thought to be responsible for the cytotoxic effect. In addition, the photoactivated forms of porphyrin fluorescence which fluoresce can aid in localizing the tumor. Thus, the dimer and trimer compounds of the invention are not consumed or altered in exerting their biological effects.

Typical indications, known in the art, include destruction of tumor tissue in solid tumors, dissolution of plaques in blood vessels (see, eg., U.S. Pat. No. 4,517,762), treatment of tropical conditions such as acne, athlete's foot, warts, papilloma, and psoriasis and treatment of biological products (such as blood for transfusion) for infectious agents, since the presence of a membrane in such agents promotes the accumulation of the drug. Other uses include treating humans suffering from atherosclerosis and inactivating bacterial or viral infections.

The compositions are formulated into pharmaceutical compositions for administration to the subject or applied to an in vitro target using techniques known in the art generally. A summery of such pharmaceutical compositions may be found, for example, in Remington's Pharmaceutical Sciences, Mack Publishing Co., Easton, PA, latest edition. The compositions, labeled or unlabeled, can be administered systemically, in particular by injection or can be used topically.

Injection may be intravenous, subcutaneous, intra-muscular, or even intraperitoneal. Injectables in be prepared in conventional forms, either as liquid solutions or suspensions, solid form suitable for solution or suspension in liquid prior to injection, or as emulsions. Suitable excipients normal for example, water, saline, dextrose, glycerol and the like. Of course, these compositions may also contain minor amounts of nontoxic auxiliary substances such as wetting or emulsifying agents, pH buffering agents and so forth.

Systemic administration can also be implemented through implantation of a slow release or sustained release system, by suppository, or, if properly formulated, orally. Formulations for these mode of administration are well known in the art, and a summary of such methods may be found, for example, in Remington's Pharmaceutical Sciences (supra).

If the treatment is to be localized, such as for the treatment of superficial tumors or skin disorders, the compositions may be typically administered using standard topical compositions involving lotions, suspensions, or pastes.

The quantity of compound to be administered depends on the choice of active ingredient, the condition to be treated, the mode of administration, the individual subject, and the judgment of the practitioner. Depending on the specificity of the preparation, smaller or larger doses may be needed. For compositions which are highly specific to target tissue, such as those which comprise conjugates with a highly specific monoclonal immunoglobulin preparation or specific receptor ligand, dosages in the range of 0/05-1 mg/kg are suggested. For compositions which are less specific to the target tissue, larger doses, up to 1-10 mg/kg may be needed. The foregoing ranges are merely suggestive, as the number of variables in regard to an individual treatment regime is large and considerable excursions from these recommended values are expected. Further, because of slight solubility in water, certain compounds of the invention may be administered directly in saline or 5% glucose solution, thus avoiding the complications of detergents or other solubilizing agents.

Those skilled in the art of photodynamic therapy and compounds related m the present invention will be better able to determine an appropriate dosage and overall dosage regime when taking a number of factors into consideration. For example, the size, weight and condition of the patient must be considered as must be the responsiveness of the patient and their disease to the particular therapy. It is believed that even relatively small doses administered a single time can have a beneficial effect Further, extremely large doses could of course, be toxic. Accordingly, rather than providing specific information on dosage amount and intervals between dosing, attention should be paid to conventional factors used at determining such dosing while considering that the pyropheophorbide compounds of the invention have a greater degree of toxicity with respect, to tumor cells and therefore can generally be adminstered in smaller amounts than the conventional compounds used in connection with photodynamic therapy.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make the pyropheophorbide compounds and pharmaceutical compositions of the invention and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperature, etc.), but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight; temperature is in degrees Centigrade, and pressure is at or near atmospheric.

EXAMPLE 1

Methyl pyropheophorbide-a (2): Methyl pheophorbide-a (1, 1.0 g) was obtained from alga Spirulina destridratada by following the procedure described in K. M. Smith, D. A. Golf and D. J. Simpson, J. Am. Chem. Soc, 1985, 107, 4941-4954; and R. R. Pandey, D. A. Bellnier, K. M. Smith and T. J. Dougherty, Photochem. Photobiol, 1991, 53, 65-72 both of which are incorporated herein by reference The methyl pheophorbide-a was heated under reflux in collidine (100 ml) for 90 min during slow passage of a stream of nitrogen. See G. W. Kenner, S. W. McCombie and R. M. Smith. J. Chem. Soc. Perkin Trans. 1973, 1, 2517-2523, incorporated herein by reference. The solution is evaporated (0.1 mm Hg) and the residue was recrystallized from dichloromethane/methanol. Yield 820 mg; 91%, m.p. 217-219° C. lit. 220-225° C.; H. Fisher and A. Stern, Die Chemie des Pyrrole, vol II, Part 2, pp. 64 and 74, Akademische Verlag, Leipzig incorporated herein by reference. Vis: (max) 410 (112 000); 508 (11 000); 536 (9 600) 610 (8 200) 666 (45 000); NMR, ppm; 9.50. 9.38, 8.52 each s, 3H, 3 meso. H); 7.95-8.05 (m, 1H, CH═CH₂); 6.30 and 6.15 (each s, 1H, CH-CH₂), 5.27 to 5.12 (q, 2H, 10-CHz); 4.50 (m, 8-HO; 4.28 (m, 7-H); 3.70 (q, 2H, CH₂CH₂) 3.68 (s, 3H, CHCHCO₂CH₃); 3.62, 3.40, 3.22(each s, 3H, 3CH₃); 2.70 (7a-H); 2.31(7a′-H); 2.56 (7b-H); 2.29 (7b′-H); 1.82 (d, 3H, 8-CH₃); 1.70 (t, 3H, CH₃CH₃); −1.70 (s, 2

Pyropheophorbide-a (3); Methyl pyropheophorbide-a (2, 250 mg) was dissolved in distilled tetrahydrofuran (50 ml) and 4N HCl (125 ml) was added in one lot. The reaction mixture stirred under nitrogen atmosphere at room temperature for 4 hours. The reaction was monitored by analytical tlc (silica plates), using 10% methanol/dichloromethane as a mobile phase. The reaction mixture was then poured in ice water, extracted with dichloromethane. The dichloromethane layer was washed several times with water (3×200 ml). The organic layer was separated and dried over anhydrous sodium sulfate. Evaporation of the solvent gave a residue, which was crystallized from dichloromethane/hexane. Yield, 225 mg. The purity of the compound was ascertained by tlc and the structure was confirmed by NMR spectroscopy. The NMR data were similar as described for 2 except the resonances for the —OCH₃ protons of the propionic ester (—CH₂CH₂CO₂CH₃) were missing.

Methyl-2-{1((0-hexyl)ethyl)-devinyl pyropheophorbide (4); pyropheophorbide-a 200 mg) was dissolved in 30% HBr/acetic acid (5.0 ml) and the reaction mixture was stirred in a glass stoppered flask (rubber septum can also be used) at room temperature for 2.5 hours. The solvent was removed under high vacuum (1 mm Hg) and the resulting 1-bromo ethyl derivative was washed with water (3×200 ml) till the aqueous phase is neutral and then dried over anhydrous sodium sulfate. Evaporation of the solvent gave a residue, which was chromatographed over Alumina Grade III (6% water/neutral Alumina) and eluted with dichloromethane. The first fraction was a mixture of the starting material and the desired product (minor quantity). Further elution with same solvent gave the desired product. The appropriate eluates were combined. Evaporation of the solvent afforded a sticky solid, which can be crystallized from dichloromethane/hexane. Yield 0%. (see Scheme-1), Vis,(max); 408 (90 000); 471 (3 200). 506 (8600); 536 (8,500); 604 (7,250); 660 (41 500). NMR, ppm; 9.79 9.51, 8.53 (each s, 1H) meso H_ 5.90 (q, 2H, —CH (O-hexyl)CH₃; 5.08-5.30 (q, 2H, 10-CH₂); 4.47 (m, 8H); 4.29 (m, 7-HO; 3.75 (q, 2H, CH₂CH₃); 3.67 (s, 3H, CH₂CH₂CO₂CH₃), 3.67 (s, 6H, 2 X CH₃); 3.38 and 3.27 (each s, CH₃); 2.68 (7a-H) 2.28 (7a′-H), 2.55 (7b-H); 2.20 (7b′-H); 1.80 (d, 3H, CH₂CH₃); −1.70 (s, 2H, 2 NH); for the hexyl group; 3.72 (t, 2H, O—CH₂CH₂); 1.73 (2H, CH₂); 1.25 [bs, merged, 6H, (CH₂)₃]; 0.78 (t, 3H, CH₃) (see FIG. 1)

2-{1(O-hexyl)ethyl) devinyl pyropheophorbide-a (5): Pyropheophorbide-a (3,200 mg) was reacted with 30% HBr/acetic add and than with n-hexanol by following the method as discussed for 4 and the desired product was isolated in 60 to 65% yield. The structure was confirmed by NMR spectroscopy.

EXAMPLE 2

Tumor Treatment

When 2-[1-(O-hexyl)ethyl] devinyl pyropheophorbide-a-structure (5) in Scheme 1: S-RO-where R=(CH₂)₃CH₃ and m=H, (formula IIa) synthesized as indicated (5.0 mg) is dissolved in Tween 80 (0.1 ml) and mixed with 10 ml Hacks Balanced Salt Solution (HBSS), a solution of approximately 0.5 mg/ml in 0.1% Tween 80 is produced after filtration through a 0.22 μM Millipore filter. Ten DBA/2 mice with 0.4-0.5 mm diameter subcutaneous SMT-F tumors in the axilla are injected intravenously with 0.3 mg/kg body weight of the above solution (after diluting in HBSS so that the injected volume per mouse is approximately 0.2 ml). Approximately 24 h later the tumor area (having been shaved and depilated prior to tumor implant) is exposed to laser light at 660-670 nm for 30 min at a power of 75 m^W/cm² to deliver 135 Joules/cm². Alternately, a Xenon arc lamp filtered to emit a broader band width near 670 nm and approximately 283 Joules/cm² can be used.

The day after light treatment all the tumors are seen in be flat (non-palpable) and slight skin blanching over the area is noted. This progresses to frank tumor necrosis over the next few days. At 7 days post treatment all tumors remain non-palpable and necrotic. At 30 days post treatment six of the 10 tumors remain non-palpable, and one remains tumor-free to 90 days post treatment.

EXAMPLE 3

Side Clearance

Six albino Swiss mice (HalCR) are injected intravenously with a doe of 0.1 mg/kg body weight of the compound of formula IIa prepared as is Example 1. After approximately 24 h, the hind foot of the animal is exposed to the same dose or either laser light at 660-670 nm (135 Joules/cm²) or the Xenon arc lamp (283 Joules/cm²) as above The reaction of the foot is scored for damage over the next few days to determine the maximum effect, which in this case is a value 0.3 equivalent to slight edema. If the internal between the injection and light treatment is extended to approximately 48 h, the foot reaction is zero (no damage incurred), indicating either clearance or metabolism of the sensitizer.

Data obtained as a result of experiment carried out is put forth below in Table 1.

In Vivo Tumor Photosensitizing Activity of Pyrophosphorbide Ethers1
	Time			Normal Foot Response3
Injected Dose	Interval		Tumor Response2	Time Interval	Maximum
(mg/kg)	(hours)	Wavelength	Day 1	Day 7	Day 30	Day 90	(hours)	Reaction
Formula II
R5 = —O—(CH2)5CH3
R7 = —CO2H
0.05	24	659	0/40	—	—	—
0.1	24	659	6/6	6/6	1/6	1/6	24	0.3
0.3	24	659	5/5	4/5	0/5	—	48-72	0
0.3	24	655	0/10	—	—	—	—	—
0.3	24	665	10/10	10/10	2/10	0/10	—	—
0.3	24	670	10/10	10/10	6/10	1/10	—	—
0.3	24	680	8/10	0/10	—	—	—	—
Formula II
R5 = —O—(CH2)5CH3
R7 = —CO2CH3
0.3	24	660	6/6	6/6	3/6	3/6	—	—
0.1	24	660	5/5	3.5	0/5	—	—	—
Formula II
R5c = —O—CH3
R7 = —CO2CH3
0.1	24	660	0/6	—	—	—	—	—
0.5	3	660	0/6	—	—	—	—	—
Formula I
R1 = —CH2O(CH2)5CH3
R3 = —CO2CH3
0.3	24	660	6/6	2/6	0/6	—	—	—
1SMT-F tumor is DBA/2 mice; 135 J/cm2 light from laser at 75 mW/cm2
2Number of non-palpable tumors/Number treated tumors post light treatment on Day indicated
3White Albino Swiss motor: foot exposed using same conditions as for tumor treatment. Score of 0.3 = light edema; 0 = no reaction.

The data put forth in Table 1 clearly demonstrates that the pyropheophorbide compounds of the invention are activated by light having a wavelength or about 660 nm. Further, when the compound were administered by injection and subjected to light having a wavelength of about 660 nm, the treatment was found to be highly effective with respect to reducing tumor size in as little as seven days.

Further, the data of Table 1 show compounds of the invention clear skin over a period or 24-48 hours after administration. This is a desirable feature in that the patient is not subjected to prolonged cutaneous photosensitivity. The data of Table 1 also show that the hexyl ethers of formula II are preferred over methyl ethers in terms of effecting tumor growth when used in photodynamic therapy.

While the present invention has been described with reference to specific compounds, formulations and methods, it is to be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt to a particular individual, method of administration, process of synthesizing, etc., which are within the scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.

Claims

1. A compound of formula I: ##STR00007##

2. The compound as claimed in claim 1, wherein R₁ is —CH₂—O—hexyl.

3. The compound as claimed in claim 1, wherein R₂ is —CH₃.

4. The compound as claimed in claim 1, wherein R₃ is —CO₂CH₃.

5. A method to effect the destruction of target virus, cells or tissue, comprising:

contacting said target with an effective amount of compound of claim 1, and irradiating with light absorbed by said compound.

6. A pharmaceutical composition useful in treatment of a target virus, cells or tissue, comprising:

an effective amount of the compound of claim 1 in admixture with a pharmaceutically acceptable excipient.

7. A compound or formula ii: ##STR00008##

8. The compound as claimed in claim 7, wherein R₅ is —O—hexyl.

9. The compound as claimed in claim 7, wherein R₇ is —CO₂CH₃.

10. The compound as claimed in claim 7, wherein R₅ is —O—(CH₃)₅CH₃ and R₇ is selected from the group consisting of —CO₂CH₃ and —CO₂H.

11. A method to effect the destruction of target virus, cells or tissue, comprising:

contacting said target with an effective amount of compound of claim 7; and irradiating with light absorbed by said compound.

12. A pharmaceutical composition useful in treatment of a target virus, cells or tissue, comprising:

an effective amount of the compound of claim 7 in admixture with a pharmaceutically acceptable excipient.

13. A method of treating a human with abnormal cells which replicate at an abnormally high rate, comprising the steps of:

administering to the human a therapeutically effective amount of a compound of formula ii: ##STR00009##

14. The method as claimed in claim 13 wherein the compound is administered in an amount in the range of 0.01 mg/kg to 1.0 mg/kg of body weight.

15. The method as claimed in claim 14 wherein the compound of formula ii is administered at timed intervals in the range of from every 3 hours to every 72 hours for over a period of from 1 day to 30 days.

16. The method as claimed in claim 15, wherein R₅ is —O—hexyl and R₇ is —CO₂H.

17. The method can claimed in claim 16 wherein the wavelength of the light is in the range of 600 to 700 nm.

18. The method at claimed in claim 17 wherein the wavelength or the light is about 600 nm.