Photodynamic therapy (PDT) is a surface oriented, locally cytotoxic intervention being investigated for oncologic therapy. Surfaces such as the pleura or the peritoneum are frequency involved with primary or metastatic cancer, and the chance for cure in such situations is low due to the inability to eradicate all the disease. A series of investigations has been performed at the National Cancer Institute since 1985 studying the possible use of PDT for large cavity treatment. This report details the original methodology, immediate results, and overall feasibility of the delivery of intrapleural PDT to patients after debulking of primary and malignant neoplasms in the chest which were considered to be 'non-curative' by standard surgical techniques alone. From this original feasibility study, an ongoing Phase I trial has developed to determine the maximum amount of this therapy which can be delivered safely to the thorax.

Since 1975, Phase I/II studies have demonstrated the successfulness of hematoporphyrin derivative photodynamic therapy (PDT) in the treatment of various malignancies of the skin, eye, bladder, lung, and head and neck. Moreover, in 1981 two cases of traditional Western cutaneous Kaposi's sarcoma (TKS) have been treated with photodynamic therapy with both early and late complete response. To date, attempts to cure and palliation of the more aggressive AIDS-related oral Kaposi's sarcoma with conventional radiation, chemotherapy or immunotherapy, or surgical excision have been limited and often associated with debilitating mucositis and further immunosuppression. Certain aspects of photodynamic therapy may be efficacious for treatment of mucocutaneous Kaposi's sarcoma: (1) the selective retention of hematoporphyrin derivative by neoplastic lesions (endothelial cell tumors); (2) a tumor- specific cytotoxic agent (i.e., free oxygen radical); (3) absence of systemic toxicity from immunosuppression; (4) the potential for retreatment without increasing side effects; and (5) porphyrin-mediated photoinactivation of enveloped viruses. Herein presented are seven cases of AIDS-related KS (EKS) with diffuse, superficial, and nodular mucocutaneous lesions treated with dihematoporphyrin derivative and photodynamic therapy with subsequent dramatic early partial and complete responses.

We report on 15 patients with multifocal carcinoma in situ of the bladder, treated with whole bladder wall photodynamic therapy (PDT). The total light dose, measured in situ (scattered plus nonscattered light) was 100 J/cm2 in the first six patients and 75 J/cm2 in the remaining nine patients. Follow-up ranges were from 6 to 27 months (average 15 months). Two cystectomies had to be performed in the first treatment group because of permanent shrunk bladders. Pathology of the resection specimens showed extensive granulation and fibrosis throughout the whole bladder wall. In the second treatment group, the maximal bladder capacity measured three months after PDT had increased on the average of 63% compared to the initial pretreatment values. No increased fibrosis could be detected on microscopical examination of random biopsies. Four recurrences necessitated cystectomy after 5 to 9 months, two in each treatment group. Three out of these originated in patients with a previous history of invasive bladder cancer. The preliminary data demonstrate the importance of in-situ light dosimetry for minimizing local side effects of PDT as well as the importance of strict inclusion criteria to optimize the therapeutic ratio.

Photodynamic therapy (PDT) is a promising alternative in the treatment of pancreatic cancer in man, due to the low sensitivity of the normal pancreas to PDT as shown in preclinical studies. Investigations on four human pancreatic cancer lines (MIA PaCa-2, PaCa 1, PaCa 3, and CAPAN 2) in vitro demonstrated a considerable variety in PDT-sensitivity proportional to the degree of differentiation, which was related to photosensitizer-uptake (PhotofrinTM). The well differentiated pancreatic tumor line Capan 2 showed a close relationship between high cell density and increased PDT-resistance. The Photofrin uptake of Capan 2 at high cell densities could be increased by short trypsinization prior to photosensitizer exposure. The data supports the hypothesis that a complex intercellular organization reduces the cell surface available for photosensitizer uptake and may cause the relative PDT resistance of normal pancreatic tissues and highly differentiated tumors.

Twenty-one carcinomas of the oral cavity in 18 patients were treated by photodynamic therapy (PDT). Patients were sensitized with Photosan III (2 mg/kg body weight), a modified HPD. Forty-eight hours after application of Photosan III, the tumor and surrounding tissues were irradiated with red laser light (200 mW/cm2, 120 J/cm2). MRI controls were carried out 24 hours after irradiation. Three to five days after irradiation, tumors were removed by conventional surgery. All specimens underwent histological examination. Histologically, hemorrhagic necroses of the irradiated tumors was found in all cases. The depth of necrosis varied from 2 to 8 mm. By MRI controls it was possible to detect edemas as change of signal resonance. PDT is a reliable therapy to reduce oral cancer selectively. Cancer destruction is limited by penetration depth of the laser light.

Since 1981, more than fifty spontaneous tumors of dogs and cats were treated by photodynamic therapy with hematoporphyrins in the surgery department of the University of Milan. Therapeutic results proved to be successful and promising in certain forms of cancer and will be compared in the future with the effectiveness of other photosensitizer drugs like phatolocyanines derivatives. Applied hematoporphyrins phototherapy methods included: (1) injection of hematoporphyrins derivative (HpD) and irradiation with laser light at 631 nanometers, using a Rhodamine B dye laser; (2) injection of the active component of hematoporphyrin derivative (DHE) and irradiation with a Rhodamine B dye laser; and (3) injection of DHE and irradiation with laser light at 628 nanometers using a gold vapor laser. More frequently treated tumor sites were oral and nasal cavities. Other localizations were mucous membranes of the glans and stomach. Nineteen histological types were diagnosed in treated tumors.

The effects of the photosensitizers, PhotofrinTM and benozoporphyrin derivative monoacid ring A (BPD) on a variety of hematopoietic cell functions have been studied, both in the presence and absence of light activation. A marked increase in hematopoiesis was observed in the bone marrow and spleens of DBA/2 mice administered high dose Photofrin but not BPD. This was manifested in an increased relative spleen weight, nucleated spleen cell number and circulating white blood cell concentration 7 days following Photofrin injection. We have shown that BPD and light doses just below phototoxic ranges stimulate the growth of human colony forming committed myeloid progenitors as well as pluripotent stem cells grown in long term marrow culture. Studies on the effect of BPD on the function of T lymphocytes in the absence of light has also demonstrated a stimulatory effect. The dose range in which this is observed is considerably broader than that observed with light activation. The mechanisms involved in this stimulatory effect have been studied and are discussed.

We examined the effect of ultrasound on the murine leukemia L1210 cell line in culture, in the presence of different photosensitizing agents: mesoporphyrin and tetraphenylporphines bearing 1 - 4 sulfonate groups. These agents could enhance ultrasound-induced cell damage when added to the incubation medium; sensitizers present only in the intracellular space were inactive in this regard. All of the porphine sulfonates were equally effective sensitizers to ultrasound but the product with 2 adjacent-SO₃H groups was the most effective photodynamic sensitizer. Ultrasound-induced cytotoxicity was associated with outer membrane damage and could be detected by measuring hydrophobic- or charge-associated whole-cell partitioning or by measurement of inhibition of active transport of a non-metabolized amino acid.

The porphyrin derivative Photofrin-Il (PH-Il) is associated with positive photodynarnic therapy (PDT) responses (1,5) . However several properties of this photosensitizer, such as minimal absorption above 600 nm, chemical impurity and prolonged in-vivo retention, are not optimal. New photosensitizers are being synthesized and evaluated in an attempt to improve the efficacy of PDT (6) . Compounds with increased absorption further in the near infrared will improve photon utilization and depth of light penetration within tissue (7) . Derivatives of porphyrins, chlorins and phthalocyanines are among the compounds being examined (8, 9) . One second generation compound, mono-l--aspartyl chiorin e6 (NPe6), is an hydrophilic chlorin which exhibits promising in-vitro and in-vivo photosensitizing properties (8, 10-14) . N2e6 is chemically pure and has significant absorption at 664 nm. The photosensitizer appears to localize in the lysosomal compartment in cells and has in-vivo tissue distribution properties similar to PH-Il (12,14) . NPe6 mediated PDT is effective against a mouse mammary carcinoma when short time intervals (4-6 hours) between drug injection and light exposure are used (8) . Clearance of N2e6 from blood accounts for the minimal tumor and skin photosensitivity when a 24 hr interval between drug administration and light treatment is used. In the current study, we evaluated in-vivo metabolic properties of NPe6 and quantified PDT responsiveness as a function of the time interval between drug administration and light treatment.

Vessel constriction and platelet aggregation are observed within the first minutes of light exposure to photosensitized tissues and lead to blood flow stasis, tissue hypoxia, and nutrient depravation. The mechanism for these vessel changes remains unknown, although the release of eicosanoids is implicated. We propose the following hypothesis: Photodynamic therapy results in specific perturbations of endothelial cells which results in a combination of membrane damage, mitochondrial damage, and rearrangement of cytoskeletal proteins. This results in cellular stress which leads to interruption of tight junctions along the endothelium and cell rounding. Cell rounding exposes the basement membrane proteins causing activation of platelets and leukocytes. Activated platelets and leukocytes release thromboxane and other eicosanoids. These eicosanoids induce vasoconstriction, platelet aggregation, increases in vessel permeability, and blood flow stasis.

Type II photo-oxidation depends on and consumes oxygen. Several factors, including the concentration of photosensitizer and the radiation fluence rate, determine the rate of oxygen consumption in tissue undergoing Photodynamic Therapy. If the tissue capillary density is sparse, as it is in many human tumors, our calculations indicate that for cells sufficiently distant from the nearest capillary, fluence rates commonly used in PDT (50 - 200 mW/cm²) deplete ³O₂ levels below those necessary for ¹O₂ formation. The calculations suggest that under these conditions reduced fluence rates and radiation dose fractionation should be more effective than continuous radiation at high fluence rates in producing ¹O₂ throughout the treated tissue volume. These predictions are supported by results obtained in vivo. The data and their interpretation have implications for PDT dosimetry and offer the possibility of improved therapeutic ratio.

Multidrug resistance in cancer chemotherapy is a well established phenomenon. One of the most common phenotypical changes in acquired or intrinsic multidrug resistance in human tumor cells is the overexpression of the mdrl gene product P-glycoprotein, which acts as an active efflux pump. Increased levels of P-glycoprotein are associated with resistance to a variety of anticancer drugs commonly used in tumor chemotherapy like anthracyclins, vinca- alcaloids, epipodophyllotoxins or actinomycin D. We investigated the efficacy or photodynamic therapy in the treatment of tumor cells expressing the multidrug resistance phenotype. Our data show that multidrug resistant cells are highly cross resistant to the phototoxic stain rhodamine 123 but exhibit only low degrees of cross resistance (2 - 3 -folds) to the photosensitizers Photosan-3, Clorin-2, methylene blue and meso-tetra (4- sulfonatophenyl) porphine (TPPS4). Resistance is associated with a decrease in intracellular accumulation of the photosensitizer. Verapamil, a membrane active compound known to enhance drug sensitivity in multidrug resistant cells by inhibition of P-glycoprotein, also increases phototoxicity in multidrug resistant cells. Our results imply that tumors expressing the multidrug resistance phenotype might fail to respond to photochemotherapy with rhodamine 123. On the other hand, multidrug resistance may not play an important role in photodynamic therapy with Photosan-3, Chlorin-2, methylene blue or TPPS4.

C3H mice bearing SCCVII squamous cell carcinoma were treated with photodynamic therapy (PDT) 24 hours after receiving Photofrin (25 mg/kg, i.v.). Single cell suspensions obtained by the enzymatic digestion of tumors excised either 30 minutes or 4 hours after PDT were analyzed for the content of host immune cells and colony forming ability of malignant cells. The results were compared to the data obtained with non-treated tumors. It is shown that there is a marked increase in the content of cells expressing Mac-1 (monocytes/macrophages or granulocytes) in the tumor 30 minutes post PDT, while a high level of other leucocytes are found within the tumors by 4 hours after PDT. As elaborated in Discussion, the infiltration rate of host immune cells, dying of malignant tumor cells, and yet unknown death rate of host cells originally present in PDT treated tumor occurring concomitantly during this time period complicates this analysis. The results of this study suggest a massive infiltration of macrophages and other leucocytes in PDT treated SCCVII tumor, supporting the suggestion that a potent immune reaction is one of the main characteristics of PDT action in solid tumors. It remains to be determined to what extent is the activity of tumor infiltrating immune cells responsible for its eradication by PDT.

A decrease in the effectiveness of photosensitized killing of neoplasm cells was observed in the presence of chlorin-e₆ at a reduced concentration of oxygen. But when metronidazole (MZ) was injected in vitro as well as in vivo, a significant increase in the photosensitized killing of Ehrlich carcinoma cells by chlorin-e₆ was observed. Moreover, contrary to the hematoporphyrin derivative (HpD), MZ increases the effectiveness of photodynamic therapy (PDT) by using chlorin-e₆ not only in the hypoxic but also in the aerobic conditions. The interaction between MZ and the excited photosensitizer may account for an increased phototoxicity of chlorin-e₆. The formation of cytotoxic nitroimidazole radicals as a result of photochemical processes of type 1 is discussed. This property of the photosensitizer may be successfully used in working out a method of potentiating PDT in combination not only with nitroimidazoles, but also with other electron acceptor compounds (EACp), e.g., quinone antitumor antibiotics.

Two types of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing meso- chlorin e₆ monoethylene diamine disodium salt (Mce₆) were synthesized. The Mce₆ was bound via pendant enzymatically degradable oligopeptide side chains (G-F-L-G) in one copolymer and was attached through noncleavable side chains (G) in the other. Preliminary experiments have been undertaken to compare their localization/retention behavior and their tumorcidal activity in vivo (A/J mice; C1300 neuroblastoma). Results of localization/retention experiments indicated that the Mce₆ bound to the noncleavable copolymer was retained in the tumor and other tissues for a prolonged time period compared with free Mce₆ or the Mce₆ bound to the cleavable copolymer. Light activation of the Mce₆ from the cleavable copolymer rendered a substantially more potent biological response in vivo than did the permanently bound Mce₆. It is hypothesized and indirectly supported by photophysical data that both of the polymer-photosensitizer complexes are aggregated (or conformationally altered) under physiological conditions due to their hydrophilic/hydrophobic properties. In buffer at pH 7.4, the quantum yield of singlet oxygen generation by free Mce₆ is three-fold higher than by the Mce₆ bound to a noncleavable copolymer; adding detergent (CTAB), increased the quantum yield of singlet oxygen generation to a value consistent with that of the free Mce₆. In vivo, if a sufficient time lag is allowed after drug administration for tumor cell lysosomal enzymes to cleave the Mce₆ from the polymer containing degradable side chains, the Mce₆ would be released in free form and behave with properties akin to the free drug. Due to the difference in cellular uptake mechanisms for free and bound drugs (and the targeting potential of the copolymer), a much higher local concentration in the tumor compared with surrounding tissue can be achieved with the polymer bound drug than the free photosensitizer. Side effects characteristics of current PDT treatment such as light ultrasensitivity in skin may be reduced by improving localization selectivity.

Photons are one of the three major reactants in the photodynamic reaction that yields toxic photoproduct for cell killing. Dosimetry of light is a major concern when planning a photodynamic therapy (PDT) protocol. This paper presents a very simple approach toward the tissue optics with a practical conclusion about how tissue optics affects planning of day-to-day PDT dosimetry. The paper does not address all the complexities of real tissue dosimetry, such as heterogeneous tissues, variable absorption due to changing tissue blood content, and variable tissue oxygen levels. The paper outlines the optical behavior in a homogeneous tissue, which is a starting point for understanding light dosimetry.

The kinetics of light absorbing compounds can be followed continuously in vivo by the use of reflection photometry to measure the changes in total optical attenuation of tissue. This method was employed in anesthetized DBA mice with SMT tumors. The pharmacokinetics in the tumor tissue of two closely related pheophorbides were followed continuously for the first two hours following tail vein injection2. The results of these measurements were correlated with the response of the tumors to photodynamic therapy and the plasma clearance. MPM (methyl pheophorbide methyl ether) cleared the tumor tissues with kinetics that matched the plasma clearance (20 min). MPH (methyl pheophorbide hexyl ether) showed steady accumulation and retention while the plasma was clearing the sensitizer. When the tumors were subsequently exposed to light (665 nm) the MPM tumor was not responsive even at short times (10 min) post injection. A response was produced in these two mice only when they were exposed to the treatment light and simultaneously injecting the MPM at high doses. MPH treated mice responded to treatment at 24 hours post injection. Reflection measurements of tissue attenuation at that time indicated that significant quantities2 of MPH were still present.

The determination of photosensitizer concentration in tissue will allow improved planning of photodynamic therapy. Laser-induced fluorescence (LIF) has been used to measure fluorescence of drugs in tissue. This study was designed to determine if in-vivo fluorescence intensities could be correlated with tissue concentration of chloroaluminum phthalocyanine tetrasulfonate in rat tissues. Following LIF measurement, the animals were euthanized and the concentration of AlPcs in different tissues were determined using chemical extraction technique. In-vivo fluorescence intensities were correlated with the extracted AlPcs for several tissues. A linear relationship between concentration and in-vivo fluorescence intensity was found for all tissues examined with correlation coefficient being highest in tissues such as liver, spleen, kidney and tumor. The correlation coefficient in skin, leg muscle and tongue was lower.

In the present paper we address the question if fluorescence diagnostics can be used to monitor and possibly predict the outcome of photodynamic therapy (PDT) using the tumor seeking agents Photofrin and (delta) -aminolevulinic acid (ALA). The degree of selective uptake may vary from patient to patient and it would be interesting to use the drug-related fluorescence signal as a tool to tailor the treatment strategy. Clearly, the fluorescence intensity cannot be directly related to the tissue drug contents because of varying absorption and scattering properties of the tissue. However, because of the real-time capability of fluorescence it is interesting to see how far the fluorescence information can be utilized for optimizing the light delivery. Patients with basal cell carcinoma and spread metastatic breast cancer in the skin were treated. Two different doses, 1 and 2 mg/kg b.w. of Photofrin (Quadra Logic, Vancouver, Canada) were used. The treatment laser was a Nd:YAG pumped dye laser (Multilase Dye 600, Technomed International, Paris/Bron, France). The system provides 1064 nm IR and 532 nm green light from the Nd:YAG laser as well as red light in the region 620 - 670 nm from a dye laser. The treatment procedure was preceded by fluorescence measurements for allowing comparisons between the diagnostic signals and the treatment outcome. At the end of the treatment, fluorescence was again monitored to assess the degree of bleaching manifested by the appearance of an additional red peak. Our data on the connection between fluorescence signals, delivered dose and observed treatment outcome are presented and the potential of imaging fluorescence monitoring in PDT dosimetry is discussed.

Copper vapor/dye systems are used for photodynamic therapy because they can produce several watts of light at 630 nm with high efficiency. In contrast to continuous wave argon/dye laser systems, the pulsed Cu/dye systems have a peak power 10,000 higher than the average power. Because no commercial spherical diffusing fibers guaranteed at these peak powers were available to us, we developed high power diffusers ourselves. The probes, with diameters up to 3.7 mm on 600 micrometers fibers, have an improved thermal behavior. The output is 50 - 60% of the laser beam input. Tested with input powers up to 6 W, no damage occurred for exposure times over 15 minutes. The isotropy of the probes varied between within 1% and 25% (sd) on average. We have successfully started photodynamic therapy in patients with carcinoma in situ in the bladder using these probes.

The location of photosensitive dye within a cell will affect the efficacy of photodynamic therapy (PDT). This report demonstrates that during the first 3 hours of dye (Photofrin porfimer) uptake from a liquid medium, the dye is diffusely distributed within the cell. After 24 hours of dye uptake, the dye is localized in specific sites within the cell. Fluorescence spectroscopy demonstrated that the 3-hour dye's emission peak near 635 nm was slightly blue shifted for the localized 24-hour dye. This paper demonstrates that the diffuse dye (at 3 hours) is more effective for PDT than the localized dye (at 24 hours). The amount of diffuse dye within the cell that is required to achieve an LD₅₀ (50% lethal dose) is 1.5-fold to 4.5- fold less than the amount of localized dye required, using the same light exposure. The range of 1.5 - 4.5-fold refers to the results for four cell lines.

A reiteration method based on a modified discrete lattice model is presented to determine the absorption and transport scattering coefficients according to the fit of the calculated radial distribution curve of diffuse reflectance to the measured one. The modified discrete lattice model which includes the effects of specular reflection and the reduced incident intensity serves to exactly calculate the probability P(x,y,m) that a normally incident photon is emitted from the lattice point(x,y) at mth step on the surface of a semi-infinite medium with the index of refraction n before reiteration. In the reiteration procedure, various parameters to absorption and transport scattering coefficients as input data in an optimal sequences are used to calculate the radial distribution of diffuse reflectance R((rho) ) on the basis of P(x,y,m). The parameters correspondent to the radial distribution of diffuse reflectance which fits the measured curve are adopted to be the absorption and transport scattering coefficients of the medium. Steady state diffuse reflectance measurements are performed on Intralipid/ink phantoms with various concentrations. It costs only a few minutes to determine the absorption and transport scattering coefficients from the radial distribution of diffuse reflectance by this method in a personal microcomputer. The good agreement between the results of this method and those obtained from the transmission measurements of scattering and absorption demonstrates the potential of this technique in clinical applications.

A series of silicon and aluminum phthalocyanines is being investigated in this laboratory for their potential as photosensitizers for photodynamic tumor therapy (PDT). Of these, one of the silicon phthalocyanines [SiPc(OH)OSi(CH₃)₂(CH₂)₃N(CH₃)₂] (Pc IV) has proven to be highly efficient in a series of in vitro assays and in PDT in vivo. When compared to sulfonated or non-sulfonated aluminum phthalocyanine and/or Photofrin II, Pc IV produced greater effects at lower concentrations in a clonogenic assay with V79 cells, and in photoenhancement of lipid peroxidation in human erythrocyte membranes. Physiological responses of treated cells in vitro appeared similar to those produced by PDT with other sensitizers; however, the responses, such as the induction of apoptosis in murine lymphoma, occurred with greater efficiency when Pc IV served as photosensitizer. In order to evaluate the efficacy of Pc IV in vivo, the dye was suspended in corn oil or incorporated into liposomes and injected intraperitoneally into C3H mice bearing RIF-1 tumors. Pharmacokinetic studies showed efficient uptake of Pc IV into the tumor, as well as into liver and kidney. For PDT, tumors were irradiated with 675 nm light from an argon-pumped dye laser. Treatment of tumors up to 100 mm³ with 1.0 mg/kg Pc IV and 135 J/cm² produced ablation of the tumor within 48 hours. Tumors > 200 mm³ could be ablated with 2.0 mg/kg Pc IV. The data suggest that Pc IV may be a highly efficient photosensitizer for tumor PDT.

The synthesis and characterization of a tetradibenzobarrelenoocta-n-butoxyzinc phthalocyanine, as well as the phthalocyanines t-butyldimethylsiloxy-N(3(beta) -acetoxy-23, 24-dinor-5-cholenoyl)-4-amino-n-butyldimethylsiloxysilicon phthalocyanine and bis- N(3(beta) -acetoxy-23,24-dinor-5-cholenoyl)-4-amino-n-butyldimethylsiloxysilicon phthalocyanine are reported. The zinc phthalocyanine is soluble, open at its center and highly hindered. It has a deep red absorption and a long triplet state lifetime. The silicon phthalocyanines have red absorptions and ligands bearing functions that have a resemblance to a part of the core of the low density lipoprotein fraction of blood serum. The zinc phthalocyanine has the potential to be a good photosensitizer, and the silicon phthalocyanines or related compounds have the potential to be preferentially accumulated by tumor cells. All three compounds are of interest for photodynamic therapy studies.

Two types of photosensitizers are compared here for their singlet oxygen production and in vivo sensitizing capacity: Mg²⁺ and Zn²⁺-tetrabenzoporphyrin, which have a strong Q band at the HeNe laser line; and Cd-texaphyrin, with absorption at 770 nm. The singlet oxygen quantum yields in homogeneous solutions were determined by employing a singlet oxygen-destroyable fluorescent target. Photosensitizers of bacterial and human leukemic cells were carried out with these sensitizers, in comparison with HPD and Photofrin II. The new sensitizers were found to have high quantum yields for production of singlet oxygen in solutions. They also have comparable photosensitizing capacities of bacterial cells.

In order to evaluate the effect of substituents in photosensitizing activity, a series of long wavelength absorbing photosensitizers related to pyropheophorbides, bacteriopheophorbides, and benzoporphyrin derivatives were synthesized. Pheophorbide dimers, covalently joining two molecules of pyropheophorbide-a and bacteriopheophorbide-a with lysine as a cross-link were also prepared. The syntheses and spectroscopic properties of these compounds are discussed. Some of these compounds were tested for in vivo photosensitizing activity vis-a-vis Photofrin II^TM, using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. The preliminary in vivo results suggest that replacement of substituents at peripheral positions of the macrocycles causes a significant difference in photosensitizing efficacy.

In the first part of this paper, syntheses of water-soluble photosensitizers for use in photodynamic therapy are described. Vinylporphyrins and vinylchlorins react with N.N- dimethylmethyleneammonium iodide (Eschenmoser's reagent) to give 2- (dimethylaminomethyl)vinyl derivatives which can be readily quaternized with methyl iodide to give highly water-soluble quaternary ammonium salts. Deuteroporphyrin-IX dimethyl ester undergoes direct substitution with dimethylaminomethyl at the nuclear 2- and 4-positions. The second part of this report describes the syntheses of bacteriochlorin analogues of natural chlorophyll derivatives; these are obtained by osmium tetraoxide oxidation of chlorins to give vic-dihydroxybacteriochlorins. Acid catalyzed pinacol-pinacolone rearrangements of a number of vic-dihydroxybacterochlorins to given ketobacteriochlorins are described, and the chemistry of the rearrangement is investigated. Biological studies of all sensitizers described will be reported elsewhere.

Light-induced reactions of different hydrophilic meso-tetraphenyl porphyrins (TPPS₄, TPPC₄, T4MP_yP) were investigated during PDT treatment. These measurements were carried out in vitro using micro-spectrofluorometry and were correlated with measurements in buffer solutions. In the case of the anionic TPPS₄, before light exposure, a neutral free base and a protonated species could be detected simultaneously in the cells. During irradiation, the protonated species first disappeared. Due to the fact that a coexistence of a protonated and unprotonated species requires a pH value around 5, TPPS₄ was at first located in the lysosomes (pH 5) and was released into the cytoplasm during irradiation as a result of lysosomal rupture. Further light exposure led to a drastic fluorescence formation in the nuclei, in particular the nucleoli of the cells, which was concomitant with a renewed observation of a fluorescence emission spectrum similar to that of the protonated species. In the case of the anionic TPPC₄, a similar fluorescence increase was observed during irradiation. However, the formation of a protonated species played a less important role. The cationic T4MP_yP again showed fluorescence increase during irradiation. Two Soret-bands separated by about 20 nm could be detected. The red-shifted band may be due to a special intercalation of T4MP_yP in nucleic acids.

The use of the photosensitizer Photofrin' (dihematoporphyrin ether, DHE)' in the photodynarnic treatment of human disease is becoming well known and widely used. While a number of photosensitizers may be used for photodynamic therapy (PDT), the porphyrins, in particular Photofrin', have received the most attention. This is specifically true for human trials.25 Clinical studies in photodynamic therapy (PDT) have utilized lasers to take advantage of coupling efficiencies to optical fibers allowing light to be delivered to many areas of the body. This is particularly true in endoscopic PDT. Both interstitial and superficial delivery techniques can be applied using one of a variety of delivery fibers available. A fiber with an optically flat end with a lens to produce a spot with a homogeneous intensity is used for superficial applications. Diffusers of various lengths, at the tip of a fiber, produce a cylindrical isotropic pattern and are suited for either intraluminal or interstitial illuminations, Previous studies have measured space irradiance produced by cylindrical fibers to determine the extent to which conditions of use would affect light distribution.6 Further, those studies attempted to assess the impact of variations in light distribution on the therapeutic effect. The therapeutic effect, however, was based upon the use of the cylindrical fiber as an interstitial implant and conclusions, therefore, were made in that context. The manner in which energy is distributed in air by fiberoptics can be described in terms of those surfaces through which the energy flux (energy per unit area per unit time) is everywhere constant. Since the therapeutic light dose has units of energy per unit area, these surfaces are properly called 'isodose-rate' surfaces. A field of treatment that conforms to an isodose-rate surface receives an incidental uniform light dose in a time interval (sec) given by the numerical ratio of the light dose (Joules/cni2) to the dose rate (watts/cm2). The isodose-rate surfaces in the air of the microlens and the sphere diffuser are simple surfaces, namely planes perpendicular to the light beam and spheres centered on the light source, respectively. The isodose-rate surfaces of the cylinder diffuser do not have a simple cycometry. In the following, these surfaces are presented for a line source which is a good approximation of the cylinder diffuser.

New results are presented on the pharmacokinetics of the fluorescing fraction of Photofrin II in patients with an early cancer in the oesophagus or the buccal cavity. The light-induced fluorescence signal shows a relatively high contrast between tumor and surrounding normal tissue at short times after i.v. injection. The magnitude of this contrast appears to correlate with the staging of the cancer, the more invasive tumors showing the highest contrast. Some early results on the ex vivo fluorescence analysis of biopsies taken on patients injected with the new sensitizer meta-tetra(hydroxyphenyl)chlorin (mTHPC) demonstrate the selectivity of this efficient second generation photosensitizer for advanced lung cancer. mTHPC appears to have good properties for photodetection and has a rather high rate of photobleaching. The significant of the latter is discussed in relation to simplifying light application in PDT.