porphycene is a tetrapyrrole molecule activated by light in the 600 - 950 nm range . irradiation with activating light leads to the production of highly energized photochemical radicals . based on in vitro studies , the production of singlet molecular oxygen is probable . however , this has not been yet completely established by in vivo studies . the term &# 34 ; singlet molecular oxygen &# 34 ; and &# 34 ; smo &# 34 ;, as used herein , are thus defined as meaning these highly energized photochemical radical products of in vivo photoactivation of porphycenes , including but not limited to singlet molecular oxygen radicals . singlet molecular oxygen causes cell destruction and necrosis in nearby tissues . however , porphycene and alkylated porphycenes are not soluble in water and pharmaceutically suitable solvents . they are thus not amenable to injection in aqueous media . porphycene compounds , including porphycene and tetra - alkyl substituted porphycenes of formulas i and ii are useful in the methods and compositions of this invention . ## str3 ## in the compounds of formula i , r 1 , r 2 , r 3 , and r 4 are hydrogen or a lower alkyl having from 1 to 6 carbons . ## str4 ## in the compounds of formula ii , r 5 , r 6 , r 7 , and r 8 are hydrogen or a lower alkyl having from 1 to 6 carbons . the term &# 34 ; alkyl &# 34 ; as used herein includes both straight and branch - chained saturated aliphatic groups . the compounds of formula i and ii can be prepared by reductive coupling corresponding lower alkyl substituted 5 , 5 &# 39 ;- diformyl - 2 , 2 &# 39 ;- bipyrroles or coupling 5 , 5 &# 39 ;- di -( lower alkyl )- carbonyl - 2 , 2 &# 39 ;- bipyrroles according to procedures described by vogel et al , angew . chem . 99 : 909 - 917 ( 1987 ) porphycenes are related to the porphyrins . however , porphycenes have several advantages as compared to the porphyrins which make them particularly suitable as phototherapeutic agents . due to the chemical structure of porphycenes they are more efficient generators of smo than the porphyrins , producing smo faster and in greater quantity than comparable porphyrins . each porphycene molecule can produce multiple smo moieties upon irradiation . the penetration of the therapeutically important red light having a frequency above 600 nm through tissues is limited by melanine absorption and light scattering . this filter and shielding effect decreases with increasing wavelength . since porphycenes absorb more strongly than the porphyrins in the higher - than - 600 nm region , lower doses of porphycenes and / or lower dosages of light are thus required for porphycene treatment than are necessary with porphyrin treatment , to achieve a given phototherapeutic result . liposomes are onion - like structures having a series of lipid layers spaced from one another by aqueous material , with the outermost layer being lipid . unilamellar bodies , a single lipid bilayer enclosing an aqueous compartment , are also known , and are described in u . s . pat . nos . 4 , 452 , 747 and 4 , 448 , 765 , which are incorporated herein by reference in their entireties . in the lipid vesicles , the substance dissolved in the solvent is enclosed by phospholipid bilayer membrane . the lipid membrane has a thickness of typically 3 to 5 nm , and the vesicles have a diameter from 15 to 120 nm . the size of the vesicles can be determined by laser light scattering , ultracentrifugation , gel - filtration or electron scanning microscopy . unlike porphyrins , porphycenes are generally insoluble in water and polar solvents . although emulsions or solutions of porphycenes for injection can be made , they are less physiologically compatible , and therefore less desirable than incorporation of the porphycene within liposomes . in accordance with the invention herein , porphycenes can be made physiologically compatible by incorporation into liposomes . porphycene compound - containing liposomes are administered into a patient having cancer . radiation is then used to selectively activate the porphycene compound , resulting in necrosis and death of the cancerous tissue . in a mouse model , tetra - n - propylporphycene was seen to concentrate preferentially in tumor tissue as compared to skin or muscle tissue at 24 hours post - injection . there was little or no porphycene uptake by the brain . drug clearance was via the liver rather than by the kidneys . the phototherapeutic approach to cancer treatment herein involves binding or concentrating one or more porphycene compound in tumor tissue . porphycene compounds are substantially less toxic or hazardous in their unexcited state than cytotoxins incorporating ribosomal inhibiting proteins . this physiologically tolerated substance is then exposed to activating radiation with a low likelihood of hazard . this novel therapeutic approach has a variety of advantages . the chemical agent , a porphycene , is minimally toxic in the unexcited state . each prophycene molecule can be repeatedly photoactivated and lead each time to cell - lethal events . the source of the cell - lethal agent is endogenous within the patient . smo is likely to play a major role in the cell - lethal events . the half - life of the smo toxin is approximately 4μ seconds in water at room temperature , allowing contact with the target cell while providing minimal migration in the lethal form to neighboring healthy tissue cells . preferably , the singlet oxygen molecules rupture chemical bonds in the target cell wall , which results in the destruction of the target cell . lethal attack commences promptly upon irradiation in the immediate vicinity of the singlet oxygen producer , which disrupts the cell wall and destroys the integrity of the target cell . unreacted smo decays rapidly to ground state oxygen , giving oxygen molecules as its primary decay product . the therapist ( e . g ., physician and radiologist ) can select the time and duration of therapy , repeating the irradiation treatment at intervals , with the same agent molecules bound to the target cell . booster doses of the singlet oxygen producer may be given . the dosage of the cytotoxic agent may be varied according to the size and location of the target tissues which are to be destroyed , and the method of administration . generally , the dosage will be in the range of 0 . 5 to 20 . 0 milligrams of porphycene compound per kilogram of body weight , more preferably in the range of 0 . 5 to 5 . 0 milligrams per kilogram . the liposomes incorporating one or more porphycenes may be administered intravenously , intraarterially , or directly proximal to the tumor . irradiation will generally take place not less than 1 hour nor more than 4 days after introduction of the cytotoxic agent . more usually , phototherapy will be administered from 3 hours to 48 hours after administration of the cytotoxic agent . exposure to non - therapeutic light sources should be avoided immediately following phototherapy , to minimize light toxicity . a variety of phototherapy and irradiation methodologies are well known to those skilled in the art , and may be used in conjunction with the novel compounds herein . for example , at beginning at about 620 nm , radiation can penetrate human tissue to a depth of up to about 2 cm . unfocused light may be administered to a patient topically . appropriate draping can be used to limit the penetration area of the light if desired . light sources which are appropriate for such use are well known to the art , and may vary from white light sources with appropriate filters , to lasers . preferred wavelengths are from 600 to 950 nm , more preferably 700 to 950 nm . the total amount of light which is applied to a tumor will vary with the methods used and the location of the tumor , but will generally be in the range of 50 to 1 , 000 j / cm 2 , more usually in the range of 100 to 350 j / cm 2 . in a preferred embodiment , focused radiation is administered internally in a patient , using flexible fiberoptic catheters or other endoscopic devices to deliver the necessary radiation to the site of the bound porphycenes . fiberoptic catheters are available commercially . this invention is further illustrated by the following specific but non - limiting examples . temperatures are given in degrees centigrade and percentages as weight percents unless otherwise specified . procedures which have been previously carried out are presented in the past tense , and procedures which are being constructively reduced to practice in this application are presented in the present tense . 2 , 7 , 12 , 17 - tetra - n - propylporphycene ( tpp ) ( formula i ) is produced by the methods of e . vogel et al , angew . chem . 99 : 909 - 912 ( 1987 ). repeating the procedure , but replacing the 5 , 5 &# 39 ;- diformyl - 4 , 4 &# 39 ;- di - n - propyl - 2 , 2 &# 39 ;- bipyrrole with 5 , 5 &# 39 ;- diformyl - 2 , 2 &# 39 ;- bipyrrole ; 5 , 5 &# 39 ;- diformyl - 4 , 4 &# 39 ;- dimethyl - 2 , 2 &# 39 ;- bipyrrole ; 4 , 4 &# 39 ;- diethyl - 5 , 5 &# 39 ;- diformyl - 2 , 2 &# 39 ;- bipyrrole ; 4 , 4 &# 39 ;- di - n - butyl - 5 , 5 &# 39 ;- diformyl - 2 , 2 &# 39 ;- bipyrrole ; 5 , 5 &# 39 ;- diformyl - 4 , 4 &# 39 ;- di - n - pentyl - 2 , 2 &# 39 ;- bipyrrole ; and 5 , 5 &# 39 ;- diformyl - 4 , 4 &# 39 ;- di - n - hexyl - 2 , 2 &# 39 ;- bipyrrole , yields the corresponding porphycene ; 2 , 7 , 12 , 17 - tetramethylporphycene ; 1 . 5 mg of 2 , 7 , 12 , 17 - tetra - n - propylporphycene ( tpp ) ( e . vogel et al , angew . chem . 99 : 909 - 912 ( 1987 )) and 80 mg dipalmitoyl - phosphatidylcholine ( dppc ) ( crystalline dl - α - dppc , sigma ) were dissolved in a binary mixture of chcl 3 : ch 3 oh ( 9 : 1 , v / v ). after gentle magnetic stirring for approximately 10 minutes , the solvent was removed by rotary evaporation under reduced pressure . the film was resuspended in 5 ml of phosphate - buffered saline ( pbs , ph 7 . 4 ) with vigorous stirring , and then sonicated at 55 ° c . for 30 minutes . the dispersion thus obtained was allowed to cool to 25 ° c ., and was centrifuged for 5 minutes at 3 , 000 rpm . a small aliquot of the supernatant was assayed for endoliposomal tpp content . the liposomes appeared to have an average external radius of approximately 26 nm by electron microscopy . repeating the procedures of example 2 but replacing the tetra - n - propylporphycene with one or more products of example 1 yields liposomes incorporating porphycene ; 2 , 7 , 12 , 17 - tetramethylporphycene ; 2 , 7 , 12 , 17 - tetraethylporphycene ; 2 , 7 , 12 , 17 - tetra - n - butylporphycene ; 2 , 7 , 12 , 17 - tetra - n - pentylporphycene ; 2 , 7 , 12 , 17 - tetra - n - hexylporphycene ; and mixtures thereof . female balb / c mice had a ms - 2 fibrosarcoma transplanted in the right hind leg . by the seventh day after transplantation , the tumors had reached a diameter of approximately 0 . 8 cm . each mouse was intravenously injected with 2 mg ./ kg . of 2 , 7 , 12 , 17 - tetra - n - propylporphycene ( tpp ) incorporated into small umilamellar liposomes of dipalmitoyl - phosphatidylcholine ( dppc ), prepared according to the procedures of example 2 , on the seventh day after transplantation . at this time the diameter of the tumor was approximately 0 . 8 cm . 24 hours after tpp injection , the tumor area was exposed to 600 - 690 nm . light isolated by optical filtration from the emission of a 250 w quartz - halogen lamp through a set of optical filters ( teclas , lugano , switzerland ). the light beam was focused into a bundle of optical fibers having an external diameter of 6 mm . the tip of the fiber was kept at a distance of 1 cm from the tissue surface . the lamp was operated at a dose - rate of 230 mw / cm 2 , and the total delivered light dose was 150 j / cm 2 or 300 j / cm 2 . an equal area of normal skin on the left hind leg was irradiated in each mouse immediately after tumor irradiation using an identical protocol . irradiation of tpp - untreated mice under the experimental conditions caused no detactable damage to the tumor area or to normal skin . irradiation of the mice with 300 j / cm 2 at 24 hours after tpp injection caused the onset of massive tumor necrosis , with eschar formation complete within 3 days . the depth of necrosis continued until bone was reached , at about 7 days . an equally deep necrosis , however less extensive , was obtained upon administration of 150 j / cm 2 of red light . most irradiated tpp - treated mice developed some photoinduced damage at the level of the normal skin . such damage mainly consisted of erythema , the extent of which was generally limited ( diameter less than 0 . 3 cm ) and which disappeared within about one week . some photosensitivity was also observed at the irradiated normal skin of the left hind leg . at each of 3 hours and 24 hours after injection , six mice were sacrificed by exposure to ether vapor , and the serum or specific tissue were removed . about 2 ml of blood was taken intracardially and centrifuged for 15 minutes at 3 , 000 rpm to remove the erythrocytes . the serum was collected , diluted with 2 % aqueous sds and assayed for tpp content spectrophotofluorimetrically ( λ ex = 560 nm ). the fluorescence emitted in the 580 - 740 nm interval was converted into tpp concentration by interpolation with a calibration plot . the tumor and predetermined normal tissues were removed , washed twice with pbs , and a weighed amount of tissue ( approximately 200 mg ) was finely minced and homogenized in a potter vessel with 4 ml chloroform . the dispersion was centrifuged at 3 , 000 rpm for 15 minutes ; the supernatant was collected and its tpp content was estimated spectrophotofluorimetrically as described above . rehomogenization of the sediment under the same conditions gave less than 3 % of the tpp extracted in the original step . a serum sample ( 0 . 75 ml ) was added with an equal volume of pbs and then eluted at room temperature through a column ( 1 . 7 × 140 cm ) of sephacryl s - 300 which had been previously equilibrated with ph 7 . 4 na 2 hpo 4 - kh 2 po 4 buffer at ionic strength 0 . 1 , according to the procedures of reddi et al , brit . j . canc . 56 : 507 - 600 ( 1987 ), the disclosure of which are incorporated herein by reference . the recovery of tpp from serum and various tissues of the tumor - bearing mice at 3 hours and 24 hours after injection are shown in table 1 . the samples from each animal were analyzed separately , and are table values represent the average recovery data from the single tissues of 6 mice . the maximum deviation from the reported values was ± 20 %. no tpp - type fluorescence was observed in the tumor and healthy tissues obtained from mice not injected with tpp . the recovery from the tumor was approximately 1 μg / g ( microgram per gram ) of tissue . the 24 - hour ratios of tpp concentration between tumor and ( healthy , peri - tumoral ) muscle was approximately 17 : 1 . this indicates that the selective concentration of tpp into tumor cells was good . the ratio of concentration of tpp in the tumor and that in healthy skin was approximately 3 : 1 . this indicates a relatively low risk of general photosensitivity . table a______________________________________recovery aftersite 3 hours * 24 hours * ______________________________________serum 122 . 53 25 . 56liver 13 . 03 11 . 09skin 0 . 29 0 . 44muscle 0 . 14 0 . 09brain & lt ; 0 . 01 & lt ; 0 . 01spleen 6 . 8 5 2 . 94kidneys 1 . 25 not determinedtumor 0 . 69 1 . 50______________________________________ * μg ( micrograms ) per gram of tissue or per ml of serum
the therapeutic compositions of this invention comprise one or more porphycene compounds incorporated within liposomes . the method of this invention for treating cancer comprises administering a therapeutically effective amount of a porphycene derivative to a patient , and exposing an affected body area of the patient to a therapeutically sufficient amount of light having a wavelength of from 600 to 950 nm .