Cellular uptake and relative efficiency in cell inactivation by photoactivated sulfonated meso-tetraphenylporphines

Specific photodamage on HT-29 cancer cells leads to endolysosomal failure and autophagy blockage by cathepsin depletion

Endolysosomes perform a wide range of cellular functions, including nutrient sensing, macromolecule digestion and recycling, as well as plasma membrane repair. Because of their high activity in cancerous cells, endolysosomes are attractive targets for the development of novel cancer treatments. Light-activated compounds termed photosensitizers (PS) can catalyze the oxidation of specific biomolecules and intracellular organelles. To selectively damage endosomes and lysosomes, HT-29 colorectal cancer cells were incubated with nanomolar concentrations of meso-tetraphenylporphine disulfonate (TPPS2a), an amphiphilic PS taken up via endocytosis and activated by green light (522 nm, 2.1 J.cm-1). Several cellular responses were characterized by a combination of immunofluorescence and immunoblotting assays. We showed that TPPS2a photosensitization blocked autophagic flux without extensive endolysosomal membrane rupture. Nevertheless, there was a severe functional failure of endolysosomes due to a decrease in CTSD (cathepsin D, 55%) and CTSB (cathepsin B, 52%) maturation. PSAP (prosaposin) processing (into saposins) was also considerably impaired, a fact that could be detrimental to glycosphingolipid homeostasis. Therefore, photosensitization of HT-29 cells previously incubated with a low concentration of TPPS2a promotes endolysosomal dysfunction, an effect that can be used to improve cancer therapies.

Evaluating a targeted Palbociclib-Trastuzumab loaded smart niosome platform for treating HER2 positive breast cancer cells

In this study, we present a targeted and pH-sensitive niosomal (pHSN) formulation, incorporating quantum dot (QD)-labeled Trastuzumab (Trz) molecules for the specific delivery of Palbociclib (Pal) to cells overexpressing human epidermal growth factor receptor 2 (HER2). FTIR analyses confirmed the successful preparation of the pHSNs and their bioconjugation. The labeled Trz-conjugated Pal-pHSNs (Trz-Pal-pHSNs) exhibited a size of approximately 170 nm, displaying a spherical shape with a neutral surface charge of -1.2 mV. Pal encapsulation reached ∼86%, and the release pattern followed a two-phase pH-dependent mechanism. MTT assessments demonstrated enhanced apoptosis induction, particularly in HER2-positive cells, by Trz-Pal-pHSNs. Fluorescence imaging further validated the internalization of particles into cells. In conclusion, Trz-Pal-pHSNs emerge as a promising platform for personalized medicine in the treatment of HER2-positive breast cancer.

Optical Properties and Kinetics: New Insights to the Porphyrin Assembly and Disassembly by Polarized Resonance Synchronous Spectroscopy

With their unique photochemical properties, porphyrins have remained for decades the most interested chemicals as photonic materials for applications ranging from chemistry, biology, medicine, to photovoltaic. Porphyrins can self-assemble into higher order structures. However, information has been scant on the kinetics and structural evolution during porphyrin assembly and disassembly. Furthermore, quantitative understanding of the porphyrin optical activities is complicated by the complex interplay of photon absorption, scattering, and fluorescence emission that can concurrently occur in porphyrin samples. Using meso-tetrakis(4-sulfonatophenyl)porphyrin as the model molecule, reported herein is a combined UV-vis extinction, polarized Stokes-shifted fluorescence, and polarized resonance synchronous spectroscopic (PRS2) study of porphyrin assembly and disassembly in acidic solutions. Although porphyrin assembly and disassembly occur instantaneously upon the sample preparation, both processes last at least a few months before reaching their approximate equilibrium states. The two processes were monitored in situ by quantifying the porphyrin fluorescence and scattering depolarizations as well as its extinction, absorption, scattering, and fluorescence emission cross sections. In addition to a series of new insights to the porphyrin assembly and disassembly, the methodology described in this work opens the door for the in situ study of the structural and optical properties of photonic materials comprising molecular assembly.

Photochemical internalization in bladder cancer - development of an orthotopic in vivo model

The possibility of using photochemical internalization (PCI) to enhance the effects of the cytotoxic drug bleomycin is investigated, together with photophysical determination and outlines of a possible treatment for intravesical therapy of bladder cancer. In vitro experiments indicated that the employment of PCI technology using the novel photosensitizer TPCS_2a® can enhance the cytotoxic effect of bleomycin in bladder cancer cells. Furthermore, experiments in an orthotopic in vivo bladder cancer model show an effective reduction in both the necrotic area and the bladder weight after TPCS_2a based photodynamic therapy (PDT). The tumor selectivity and PDT effects may be sufficient to destroy tumors without damaging the detrusor muscle layer. Our results present a possible new treatment strategy for non-muscle invasive bladder cancer, with the intravesical instillation of the photosensitizer and bleomycin followed by illumination through an optic fiber by using a catheter.

Gold mining for PDT: Great expectations from tiny nanoparticles

Among many and various products, born by the modern nanotechnology, gold nanoparticles roused a special interest of biomedical researchers. Unique features of the nanoparticles allow to use them not only as effective transporters for therapeutic agents but also as basic components of nanocomposite preparations intended for targeted photodynamic and photothermal therapy of tumours. In the review, physical, chemical and biological properties of gold nanoparticles which can promote PDT efficiency of a designed nanocomposite, are briefly characterized, and promising trends in creation of gold-containing composite photosensitizers are analysed.

Hyaluronan-decorated polymer nanoparticles targeting the CD44 receptor for the combined photo/chemo-therapy of cancer

In the attempt to develop novel concepts in designing targeted nanoparticles for combination therapy of cancer, we propose here CD44-targeted hyaluronan-decorated double-coated nanoparticles (dcNPs) delivering the lipophilic chemotherapeutic docetaxel (DTX) and an anionic porphyrin (TPPS₄). dcNPs are based on electrostatic interactions between a negative DTX-loaded nanoscaffold of poly(lactide-co-glycolide), a polycationic shell of polyethyleneimine entangling negatively-charged TPPS₄ and finally decorated with hyaluronan (HA) to promote internalization through CD44 receptor-mediated endocytosis. DTX/TPPS₄-dcNPs, prepared through layer-by-layer deposition, showed a hydrodynamic diameter of around 180 nm, negative zeta potential and efficient loading of both DTX and TPPS₄. DTX/TPPS₄-dcNPs were freeze-dried with trehalose giving a powder that could be easily dispersed in different media. Excellent stability of dcNPs in specific salt- and protein-containing media was found. Spectroscopic behavior of DTX/TPPS₄-dcNPs demonstrated a face-to-face arrangement of the TPPS₄ units in non-photoresponsive H-type aggregates accounting for an extensive aggregation of the porphyrin embedded in the shell. Experiments in MDA-MB-231 cells overexpressing the CD44 receptor demonstrated a 9.4-fold increase in the intracellular level of TPPS₄ delivered from dcNPs as compared to free TPPS₄. Light-induced death increased tremendously in cells that had been treated with a combination of TPPS₄ and DTX delivered through dcNPs as compared with free drugs, presumably due to efficient uptake and co-localization inside the cells. In perspective, the strategy proposed here to target synergistic drug combinations through HA-decorated nanoparticles seems very attractive to improve the specificity and efficacy of cancer treatment.

Synthesis, characterization and in vitro photodynamic antimicrobial activity of basic amino acid-porphyrin conjugates

Photodynamic antimicrobial chemotherapy (PACT), as a novel and effective modality for the treatment of infection with the advantage of circumventing multidrug resistance, receives great attention in recent years. The photosensitizer is the crucial element in PACT, and cationic porphyrins have been demonstrated to usually be more efficient than neutral and negatively charged analogues towards bacteria in PACT. In this work, three native basic amino acids, l-lysine, l-histidine and l-arginine, were conjugated with amino porphyrins as cationic auxiliary groups, and 13 target compounds were synthesized. This paper reports their syntheses, structural characterizations, oil-water partition coefficients, singlet oxygen generation yields, photo-stability, as well as their photo inactivation efficacies against methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Pseudomonas aeruginosa in vitro. The preliminary structure-activity relationship was discussed. Compound 4i, with porphyrin bearing four lysine moieties, displays the highest photo inactivation efficacy against the tested bacterial strains at 3.91 μM with a low light dose (6 J/cm(2)), and it is stable in serum and lower cytotoxicity to A929 cells. These basic amino acid-porphyrin conjugates are potential photosensitizers for PACT.

Delivery of lipophilic porphyrin by liposome vehicles: preparation and photodynamic therapy activity against cancer cell lines

Porphyrin photosensitizers are mostly used components in photodynamic therapy (PDT). The poor solubility of porphyrins in aqueous medium is the problem to be solved for the in vivo applications. The delivery of photosensitizers to the tumor cells using liposome vehicles can help to overcome this problem. In this work, we have first functionalized the protoporphyrin IX with lipophilic oleylamine arms and encapsulated it into 1,2 dioleyl-sn-glycero-phosphatidylcholine (DOPC) liposomes. The appropriate sizes of liposomes are about 140 nm and have the characteristic Soret and Q band absorptions at 405 nm (Soret), 507 nm, 541 nm, 577 nm and 631 nm (Q bands), respectively. In the photodynamic activity studies, the liposomal porphyrins were irradiated with light (375 nm, 10 mW) in the presence of cancer cell lines, HeLa and AGS. We have found that both liposomal porphyrins and oleylamine conjugated porphyrins are much more effective than PpIX. This result can be attributed to the drug delivery characteristic of the liposomes which plays effective role in endocytosis. We also found that, in AGS cells, liposomal PpIX-Ole induced apoptosis more than HeLa cells under light conditions.

Mechanisms of porphyrinoid localization in tumors

The photosensitizing and pharmacokinetic properties of porphyrin-type compounds have been investigated for nearly a century. In the last decade, two porphyrin derivatives were approved in the U.S.A. and in several other countries for the photodynamic treatment of various lesions. An overview of the different mechanisms for preferential porphyrinoid localization in malignant tumors is presented herein. Several uptake pathways are possible for each photosensitizer, which are determined by its structure, mode of delivery and tumor type. Comparisons of the different mechanisms and correlations with the structure of the sensitizer are presented. Current delivery systems for porphyrin sensitizers are described, as well as recent strategies for enhancing their tumor-specificity, including conjugation to a carrier system that selectively targets a tumor-associated receptor or antigen.

In vitro and in vivo photosensitization by protoporphyrins possessing different lipophilicities and vertical localization in the membrane

Photodynamic therapy (PDT) is being evaluated in clinical trials for treatment of various oncologic and ophthalmic diseases. The main cause for cell inactivation and retardation of tumor growth after photoactivation of sensitizers is very short-lived singlet oxygen molecules that are produced and have limited diffusion distances. In this paper we show that the extent of biological damage can be modulated by using protoporphyrin, which was modified to increase its lipophilicity, and which also places the tetrapyrrole core deeper within the membrane by the carboxylate groups being anchored at the lipid:water interface. The uptake of the parent molecule (PPIX) and its diheptanoic acid analogue (PPIXC6) by WiDR and CT26 cells was investigated by fluorescence microscopy and by fluorescence intensity from the cells. The uptake of PPIXC6 increased almost linearly with incubation length for over 24 h, whereas for PPIX only 1 h was needed to reach maximal intracellular concentration. Fluorescence microscopy of both cell lines indicated that both drugs were distributed diffusely in the plasma membrane and cytoplasm, but remained outside the nucleus. The efficiency of in vitro inactivation of WiDr and CT26 cells increased with the length of the alkylcarboxylic chain. Tumors in mice that were treated with PPIX-PDT grew more slowly than control tumors. However, tumors that were given PPIXC6 followed by light exposure showed a significant delay in their growth.

The history of PDT in Norway Part one: Identification of basic mechanisms of general PDT

Photodynamic therapy (PDT) is now an established treatment of malignant and premalignant dysplasias. A number of first and second generation photosensitizers have been studied in Norway. The aim has been to improve PDT efficiency and applicability. Many critical details regarding the mechanisms of PDT were elucidated by researchers in Norway. In this review we focus on the most important findings related to these basic mechanisms, such as generation of singlet oxygen, estimations of its lifetime, the oxygen effect itself, the subcellular localization of photosensitizers with different properties, their photodegradation during PDT and their tumour selectivity.

Photochemical internalization of therapeutic macromolecular agents: a novel strategy to kill multidrug-resistant cancer cells

Drug resistance is a major problem for chemotherapy. Entrapment of anticancer drugs in endolysosomal compartments or active extrusions by plasma membrane proteins of the ATP-binding cassette (ABC) superfamily are important resistance mechanisms. This study evaluated photochemical internalization (PCI) of membrane-impermeable macromolecules that are not the target of ABC drug pumps for treating multidrug-resistant (MDR) cancer cells. We used the drug-sensitive uterine fibrosarcoma cell line MES-SA and its MDR, P-glycoprotein (P-gp)-overexpressing derivative MES-SA/Dx5 with the photosensitizer disulfonated meso-tetraphenylporphine (TPPS(2a)) and broad spectrum illumination. The PCI of doxorubicin, the ribosome-inactivating protein gelonin and adenoviral transduction were assessed in both cell lines, together with the uptake and excretion of TPPS(2a) and of two fluid phase markers easily detectable by fluorescence [lucifer yellow (LY) and fluorescein isothiocyanate (FITC)-dextran], as a model of gelonin uptake. Both cell lines were resistant to PCI of doxorubicin, but equally sensitive to PCI of gelonin, even though the endocytosis rates of LY and FITC-dextran were significantly lower in the MDR cells. In control studies, MES-SA/Dx5 cells were more resistant to photodynamic therapy (TPPS(2a) + light only). This was not mediated by P-gp, as there were no differences in the uptake and efflux of TPPS(2a) between the cell lines. After adenoviral infection, PCI enhanced gene delivery in both cell lines. In conclusion, PCI of macromolecular therapeutic agents that are not targets of P-gp is a novel therapeutic strategy to kill MDR cancer cells.

Photochemical treatment with endosomally localized photosensitizers enhances the number of adenoviruses in the nucleus

BACKGROUND

In the present study the physical targeting technique photochemical internalization (PCI) has been used in combination with adenovirus. We have previously shown that PCI enhances transgene expression from AdhCMV-lacZ, and the aim of the present study was to further increase the understanding of photochemically mediated adenoviral transduction.

METHODS

Two colorectal carcinoma cell lines, WiDr and HCT116, were pre-incubated with the photosensitizer TPPS(2a) or methylene blue derivates (MBD) followed by infection with adenovirus and light exposure. Transgene expression was measured by flow cytometry. Real-time polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH) were used to quantify the level of viral DNA in the nuclei. Real-time PCR was also used to measure the level of beta-galactosidase mRNA in samples infected with AdhCMV-lacZ.

RESULTS

Exposing TPPS(2a)-treated cells to light enhanced the quantity of viral DNA in the nucleus, the mRNA level of the transgene and the transgene expression compared to non-illuminated cells. The increased transgene expression was independent of the promoter used, but dependent on the time of light exposure and the cellular localization of the photosensitizer.

CONCLUSIONS

The enhanced transgene expression observed after photochemical treatment is most likely not a result of one event, but more an interplay between various mechanisms. An increased level of adenoviral DNA in the nucleus and a dependency of endosomal localization of the photosensitizer to obtain enhanced transgene expression suggested that endosomal rupture facilitated the transport of adenoviruses to the nucleus.

Porphyrin Effects on Zwitterionic HPS Micelles as Investigated by Small-Angle X-ray Scattering (SAXS) and Electron Paramagnetic Resonance (EPR)

In this work, small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) studies on the interaction of three anionic mesotetrakis (4-sulfonatophenyl) porphyrins, TPPS4, FeTPPS4, and ZnTPPS4, at concentrations in the 2-10 mM range, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) at pH 4.0 and 9.0 are reported. The SAXS results demonstrate that, upon addition of all species of porphyrins, the HPS micelle of prolate shape reduces its axial ratio from 1.8 +/- 0.2 (in the absence of porphyrin) to 1.5 +/- 0.1. Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.5 A to 18.0 +/- 0.2 A. This shows that the micellar hydrophobic core is affected by porphyrin incorporation, independent of the type of porphyrin and pH. Concurrently, EPR results demonstrate an increase in the micellar packing as noticed from the increase in motional restriction for both nitroxides. Furthermore, increase of the porphyrin concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of an interaction between surface-charged micelles. Such a finding gives strong evidence that the negatively charged porphyrin molecule must accommodate in the HPS micelle dipole layer close to the inner positive charges (near the hydrophobic core), inducing a surface charge (probably a negative one associated with the HPS sulfonate external groups) in the original zwitterionic (overall neutral) micelle. Such a porphyrin location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values that are quite large compared to the binding of cationic drugs to HPS micelles (Caetano, W.; Barbosa, L. R. S.; Itri, R.; Tabak, M. J. Coll. Int. Sci. 2003, 260, 414).

Diorganotin(IV) and triorganotin(IV) complexes of meso-tetra(4-sulfonatophenyl)porphine induce apoptosis in A375 human melanoma cells

The cytotoxic effect of several diorganotin(IV) and triorganotin(IV)-meso-tetra(4-sulfonatophenyl)porphine derivatives was tested and only the (Bu(2)Sn)(2)TPPS and the (Bu(3)Sn)(4)TPPS showed cytotoxicity on A375 human melanoma cells. To examine the pathway of (Bu(2)Sn)(2)TPPS or (Bu(3)Sn)(4)TPPS induced A375 cell death, DNA fragmentation analysis, Annexin V binding and PI uptake as well as caspases activation analysis by Western blot were carried out. A375 cells treated exhibited several typical characteristics of apoptosis. Both the (Bu(2)Sn)(2)TPPS and the (Bu(3)Sn)(4)TPPS compounds activate caspase-8 and caspase-9 leading to caspase-3 activation. Thus, we propose that these two porphirin derivatives lead to the apoptosis of human melanoma cells via both death receptor-mediated and mitochondrial apoptotic pathways.

PCI-enhanced adenoviral transduction employs the known uptake mechanism of adenoviral particles

The development of methods for efficient and specific delivery of therapeutic genes into target tissues is an important issue for further development of in vivo gene therapy. In the present study, the physical targeting technique, photochemical internalization (PCI), has been used together with adenovirus. The combination of PCI and adenoviral transduction has previously been shown to be favorable compared to adenovirus used alone, and the aim of this study was to verify the role of the adenoviral receptors and identify the uptake pathway used by adenoviral particles in photochemically treated cells. All examined cell lines showed augmented transduction efficiency after PCI-treatment, with a maximum of 13-fold increase in transgene expression compared to conventionally infected cells. Blocking of CAR induced a complete inhibition of PCI-enhanced transgene expression. However, photochemical treatment managed to enhance the transduction efficiency of the retargeted virus AdRGD-GFP showing also that the virus-CAR interaction is not vital for obtaining a photochemical effect on adenoviral transduction. Blocking the alpha(V)-integrins reduced the gene expression significantly in photochemically treated cells. Subjecting HeLa cells expressing negative mutant-dynamin to light treatment after infection gave no significant increase in gene transfer, while the gene transfer were enhanced seven-fold in cells with wild-type dynamin. Furthermore, chlorpromazine inhibited photochemical transduction in a dose-dependent manner, whereas Filipin III had no effect on the gene transfer. In summary, the data presented imply that adenoviral receptor binding is important and clathrin-mediated endocytosis is the predominant uptake mechanism for adenoviral particles in photochemically treated cells.

Transgene delivery and gelonin cytotoxicity enhanced by photochemical internalization in fibroblast-like synoviocytes (FLS) from rheumatoid arthritis patients

The objective of this study was to determine if photochemical internalization (PCI) of gelonin can improve the treatment outcome as compared to photodynamic therapy (PDT) and gene transduction of fibroblast-like synoviocytes (FLS)in vitro. For this purpose synovial tissue was obtained under synovectomy of rheumatoid arthritis (RA) patients. Primary single cell suspensions were treated with the photosensitizer meso-tetraphenylporphine (TPPS2a) and light exposure (PDT) followed by evaluation of the cell survival by flow cytometry. PCI of gelonin was performed on FLS in passages 4 and 5 after removal from patients followed by measurements of protein synthesis 24 h after treatment. Additionally FLS were transduced with an adenovirus encoding the E.coli. lacZ gene and treated with PCI to evaluate the effect on the transduction rate. As a result all the cells in the primary cell suspension were susceptible to PDT but CD 106- (FLS) and CD14-positive (monocytes) cells were more sensitive to inactivation by PDT than CD2- (T-cells) and CD19-positive (B-cells) cells. With respect to protein synthesis FLS became up to 4-fold more sensitive to light when combining the photochemical treatment with the gelonin incubation. The fraction of virally transduced FLS was approximately doubled by means of PCI. In conclusion our experiments showed that PCI increased the cytotoxic effect of gelonin and adenoviral transduction of FLS derived from RA patients.

Dynamics of interactions of photosensitizers with lipoproteins and membrane-models: correlation with cellular incorporation and subcellular distribution

The incorporation and subcellular localization of photosensitizers are critical determinants of their efficiency. Here, we correlate these properties with the interactions of photosensitizers with membrane-models and low density lipoproteins (LDL) in acellular systems. Focus was given on dynamics aspects. Two amphiphilic photosensitizers, deuteroporphyrin (DP) and aluminum phthalocyanine sulfonated on two adjacent isoindole units (AlPcS2a) were selected. The phthalocyanine was bound to LDL with an overall association constant around 5 x 10(7)M(-1). Biphasic association kinetics was indicative of two types of sites. The release of the phthalocyanine into the bulk aqueous medium occurred within less than a second. A similar behavior was found previously for deuteroporphyrin although its affinity was somewhat higher (5.5 x 10(8)M(-1)). Both compounds were previously characterized by high affinity for membrane-models and quick exchange with the bulk solution. However, they strongly differed by their rate of transfer through the lipid bilayer, in the range of seconds for the porphyrin, several hours for the phthalocyanine. In the case of the porphyrin, fluorescence microscopy on human fibroblasts showed diffuse labeling with no significant modification of the distribution upon vectorization by LDL. In contrast, the phthalocyanine was localized in intracellular vesicles. Vectorization by LDL favored lysosomal localization although little effect was found on the overall uptake as shown by extraction experiments. The role of lipoproteins in the cellular localization of photosensitizers is significantly more important for photosensitizers not freely diffusing through bilayers. The dynamics of the interactions of photosensitizers with membranes appears as an important determinant of their subcellular localization.

Spectroscopic study of a water-soluble iron(III) meso-tetrakis(4-N-methylpyridiniumyl) porphyrin in aqueous solution: effects of pH and salt

The equilibrium behavior of cationic iron(III) meso-tetrakis(4-N-methyl-pyridiniumyl) porphyrin, Fe(III)TMPyP, in aqueous solution was studied as a function of pH by optical absorption, EPR and (1)H NMR spectroscopies. The presence of several Fe(III)TMPyP species in solution was unequivocally demonstrated: monomeric porphyrin species (a monoaqueous five-coordinated complex, a diaaqueous six-coordinated complex and a monoaqueous-hydroxo six-coordinated complex), a micro-oxo dimer and a bis-hydroxo complex. The addition of salt to the porphyrin solution leads to a simplification of the equilibrium as a function of pH. In this case, only three species were observed in solution: a monomeric porphyrin species, a micro-oxo dimer and a bis-hydroxo complex. Optical absorption, EPR and (1)H NMR spectra contributed to the characterization of these species. Four critical pH values (pK) for Fe(III)TMPyP were obtained in pure buffer and only three pK values were observed in the presence of NaCl. The addition of salt favors the presence of the dimeric species in solution and simplifies the equilibrium in the acidic pH range.

Photochemical Internalization Enhances the Cytotoxic Effect of the Protein Toxin Gelonin and Transgene Expression in Sarcoma Cells¶

Further advantages in the treatment of soft-tissue sarcomas will only be achieved by tailoring the adjuvant therapy after surgery. The photochemically directed release of macro-molecules from endosomes and lysosomes into the cytosol is a novel technology, named photochemical internalization (PCI), that has been evaluated for treatment of sarcoma cells in vitro. Two human synovial sarcoma cell lines (SW 982 and CME-1) were treated with the photosensitizer meso-tetraphenylporphine with two sulfonate groups on adjacent phenyl rings (TPPS2a) and a plasmid encoding enhanced green fluorescent protein (EGFP) complexed to poly-L-lysine to investigate the influence of PCI on gene transfer and with 5 micrograms/mL gelonin to investigate PCI of a Type-I ribosome-inactivating protein toxin. In addition, both cell lines were transduced with an Adenovirus serotype 5 encoding the Escherichia coli lacZ gene (AdHCMV-lacZ, expressing beta-galactosidase) and treated with TPPS2a and light to evaluate the effect of PCI on the transduction rate. Photochemically induced transfection with the reporter gene EGFP in CME-1 cells increased from 0% of cells at no light to 40% of the cells after 60 s of light exposure. In contrast, the SW 982 cells showed no enhanced expression of the gene. The fraction of virally transduced cells was about doubled in both cell lines by means of PCI, although the transduction was more efficient in the CME-1 cells. Both cell lines became up to four-fold more sensitive to light when combining photochemical treatment with gelonin incubation. Our experiments showed that PCI induced the endocytic escape of therapeutic substances in cells derived from human soft-tissue sarcomas.

The effect of porphyrins on normal and transformed mouse cell lines in the presence of visible light

Photodynamic therapy consists of the uptake of a photosensitizing dye, often a porphyrin, by tumor tissue and subsequent irradiation of the tumor with visible light of an appropriate wavelength matched to the absorption spectrum of the photosensitizing dye. This class of molecules produces reactive oxygen species when activated by light, resulting in a direct or indirect cytotoxic effect on the target cells. Photodynamic therapy has been used in the treatment of cancer but the technology has a potential for the treatment of several disease conditions mainly because of its selectivity. However, it is not clear why the porphyrins are retained preferentially by abnormal tissue. This paper describes a study of the effect of the association of porphyrin and visible light on two mouse fibroblast cell lines: A31, normal cells and B61, an EJ-ras transformed variant of A31. Two water-soluble porphyrins were used, a positively charged one, tetra(N-methyl-4-pyridyl)porphyrin chloride, and a negatively charged one, tetra(4-sulfonatophenyl)porphyrin-Na salt (TPPS4) in order to assess the effect on cell survival. The results suggest that the B61 cell line is more sensitive to incubation with the anionic porphyrin (TPPS4) followed by light irradiation and that the anionic porphyrin is more efficient in killing the cells than the cationic porphyrin.

Interaction of Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins with ionic and nonionic surfactants: aggregation and binding

Interactions of the water soluble Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins, FeTPPS(4) and ZnTPPS(4), with ionic and nonionic micelles in aqueous solutions have been studied by optical absorption, fluorescence, resonance light-scattering (RLS), and 1H NMR spectroscopies. The presence of three different species of both Fe(III)- and Zn(II)TPPS(4) in cationic cetyltrimethylammonium chloride (CTAC) solution has been unequivocally demonstrated: free metalloporphyrin monomers or dimers (pH 9), metalloporphyrin monomers or aggregates (possibly micro-oxo dimers) bound to the micelles, and nonmicellar metalloporphyrin/surfactant aggregates. The surfactant:metalloporphyrin ratio for the maximum nonmicellar aggregate formation is around 5-8 for Fe(III)TPPS(4) both at pH 4.0 and 9.0; for Zn(II)TPPS(4) this ratio is 8, and the spectral changes are practically independent of pH. In the case of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and non-ionic polyoxyethylene lauryl ether (Brij-35) and t-octylphenoxypolyethoxyetanol (Triton X-100), the nonmicellar aggregates were not observed in the pH range from 2.0 to 12.0. Binding constants were calculated from optical absorption data and are of the order of 10(4) M(-1) for both CTAC and HPS, values which are similar to those previously obtained for the porphyrin in the free base form. For Brij-35 and Triton X-100 the binding constant for ZnTPPS(4) at pH 4.0 is a factor of 3-5 lower than those for CTAC and HPS, while in the case of FeTPPS(4) they are two orders of magnitude lower. Our data show that solubilization of ZnTPPS(4) within nonpolar regions of micelles is determined, in general, by nonspecific hydrophobic interactions, yet it is modulated by electrostatic factors. In the case of FeTPPS(4), the electrostatic factor seems to be more relevant. NMR data indicated that Fe(III)TPPS(4) is bound to the micelles predominantly as a monomer at pH 4.0, and at pH 9.0 the bound aggregated form (possibly micro-oxo dimers) remains. The metalloporphyrins were incorporated into the micelles near the terminal part of their hydrocarbon chains, as evidenced by a strong upfield shift of the corresponding peaks of the surfactants.

Analytical Application of Oligopyrrole Macrocycles

Progress of modern analytical chemistry is closely related with advancement in other fields such as organic chemistry and biochemistry. Successful solution of current scientific problems is inconceivable without close cooperation of different chemical disciplines. As an example of such hot and very intricate theme research in the field of molecular recognition of biologically active compounds can serve, where numerous methods of analytical chemistry, organic chemistry and biochemistry can suitably be utilized, elaborated and brought into consonance. This multidisciplinary overlap logically leads to the advent of new scientific fields with their own tools, methodologies and subjects of exploration - bioanalytical chemistry and nanotechnology. This review covers different aspects of analytical application of oligopyrrole macrocycles (mainly porphyrins and sapphyrins). These compounds are widely used in analytical chemistry due to their outstanding optical properties. In our contribution oligopyrrole macrocycles are considered as signaling and structural parts of chemical receptors and selectors in various applications. Introduction of different moieties into meso-position of macrocyclic rings allows to obtain e.g., sterically well-organized receptors for recognition of biologically important analytes, new chromatographic materials, and powerful tools in electrochemical research. Finally, future trends in the field are outlined briefly.

Mitochondrial localization and photodamage during photodynamic therapy with tetraphenylporphines

The subcellular localization sites of TPPS4 and TPPS1 and the subsequent cellular site damage during photodynamic therapy were investigated in CT-26 colon carcinoma cells using spectroscopic and electron microscopy techniques. The association of both porphyrins with the mitochondria was investigated and the implications of this association on cellular functions were determined. Spectrofluorescence measurements showed that TPPS4 favors an aqueous environment, while TPPS1 interacts with lipophilic complexes. The subcellular localization sites of each sensitizer were determined using spectral imaging. Mitochondrial-CFP transfected cells treated with porphyrins revealed localization of TPPS1 in the peri-nuclear region, while TPPS4 localized in the mitochondria, inducing structural damage and swelling upon irradiation, as shown by transmission electron microscopy. TPPS4 fluorescence was detected in isolated mitochondria following irradiation. The photodamage induced a 38% reduction in mitochondrial activity, a 30% decrease in cellular ATP and a reduction in Na(+)/K(+)-ATPase activity. As a result, cytosolic concentrations of Na(+) and Ca(2+) increased, and the level of K(+) decreased. In contrast, the lipophilic TPPS1 did not affect mitochondrial structure or function and ATP content remained unchanged. We conclude that TPPS4 induces mitochondrial structural and functional photodamage resulting in an altered cytoplasmic ion concentration, while TPPS1 has no effect on the mitochondria.

Targeted intracellular delivery of photosensitizers to enhance photodynamic efficiency

Photodynamic therapy (PDT) is a novel treatment, used mainly for anticancer therapy, that depends on the retention of photosensitizers (PS) in tumour cells and irradiation of the tumour with appropriate wavelength light. Photosensitizers are molecules such as porphyrins and chlorins that, on photoactivation, effect strongly localized oxidative damage within target cells. The PS used for PDT localize in various cytoplasmic membranous structures, but are not found in the most vulnerable intracellular sites for reactive oxygen species, such as the cell nucleus. The experimental approaches discussed in the present paper indicate that it is possible to design highly efficient molecular constructs, PS carriers, with specific modules conferring cell-specific targeting, internalization, escape from intracellular vesicles and targeting to the most vulnerable intracellular compartments, such as the nucleus. Nuclear targeting of these PS-carrying constructs results in enhanced photodynamic activity, maximally about 2500-fold that of free PS. Future work is intended to optimize this approach to the point at which tumour cells can be killed rapidly and efficiently, while minimizing normal cell and tissue damage.

The bystander effect in photodynamic inactivation of cells

Treatment of MDCK II cells with the lipophilic photosensitizer tetra(3-hydroxyphenyl)porphyrin and light was found to induce a rapid apoptotic response in a large fraction of the cells. Furthermore, the distribution of apoptotic cells in microcolonies of eight cells was found to be different from the binomial distribution, indicating that the cells are not inactivated independently, but that a bystander effect is involved in cell killing by photodynamic treatment. The observation of a bystander effect disagrees with the common view that cells are inactivated only by direct damage and indicates that communication between cells in a colony plays a role in photosensitized induction of apoptosis. The degree of bystander effect was higher for cells dying by necrosis than for cell dying by apoptosis.

125I brachytherapy k-edge dose enhancement with AgTPPS4

Photon activation is a radiotherapy technique in which an element is added to the absorbing medium to raise the probability that a photoelectric interaction will occur, thus causing an increase in the absorption of ionizing radiation. Binding energies of key elements within an absorbing medium are closely matched with the incident photon energies to maximize the production of free electrons and subsequent absorption of their kinetic energies. The purpose of this research was to quantify potential dose enhancement using a silver tetraphenyl sulfonato porphyrin (AgTPPS4) in tumors as a photon activator for use with interstitial 125I brachytherapy. A three-dimensional Monte Carlo dosimetry model was developed using the EGS4 coding system. The photon source was modeled using spectral gamma emissions from models 6702 or 6711 brachytherapy seeds for comparison. Absorbed dose within the tumor volume was calculated for AgTPPS4 concentrations ranging between 0 and 20 mmol/kg tumor weight. These theoretical studies demonstrated linear increases in dose absorbed by the tumor with corresponding increases in AgTPPS4 concentration. The required AgTPPS4 concentration (RSC) to achieve at least a ten percent absorbed dose increase is approximately 6.5 mmol/kg tumor weight for model 6702 seeds. In vivo biodistribution and in vitro toxicity studies were conducted to determine if the theoretically derived RSC could be achieved biologically. Cell toxicity studies showed that TPPS4 porphyrin derivatives were cytotoxic at concentrations required to provide significant brachytherapy dose enhancement. Reverse phase HPLC confirmed that toxicity was due to intrinsic properties of the TPPS4 molecule, not the presence of free silver, drug impurities, or metabolites. Further research is necessary to develop a nontoxic molecular carrier for delivering silver to the DNA of tumor cells.

Photosensitization of cells with different metastatic potentials by liposome-delivered Zn(II)-phthalocyanine

The phototoxicity of liposome-incorporated Zn(II)-phthalocyanine (ZnPc) and its water-soluble tetrasulphonated derivative (ZnPcTS) was studied in the tumorigenic but nonmetastatic (RE4) and the highly metastatic (4R) transformed rat embryo fibroblasts. Upon irradiation with 585-605 nm light in the presence of ZnPc, the cell survival drastically decreased, while it was unaffected by ZnPcTS. Enzymatic assays showed that ZnPc induced about a 60% decrease in the activity of the mitochondrial enzymes NADH and succinate dehydrogenase after 3 min of irradiation, while no significant reduction in the activity of lactate dehydrogenase and lysosomal N-acetyl-beta-glucosaminidase was observed. The transport of thymidine, deoxyglucose and alpha-aminoisobutyric acid through the plasma membrane was strongly inhibited after irradiation. Similarly, the intracellular ATP content was significantly reduced. The reduction of DNA biosynthesis showed a time dependence quite similar to the photo-induced decrease in cell survival. No repair of cellular functions affected by ZnPc was observed in the 2 cell lines. These results indicate that, under our experimental conditions, hydrophobic ZnPc exerts its cytotoxic activity mainly by impairing those functions localized in the plasma membrane of the cells.

Effect of chemical structure and hydrophobicity on the pharmacokinetic properties of porphycenes in tumour-bearing mice

The efficiency and selectivity of tumour targeting by several tetra-n-propylporphycene (TPPn) and tetrakis(methoxyethyl)porphycene (TMPn) derivatives have been studied by administering 3.76 micromol/kg of aqueous or liposomal porphycene formulations to BALB/c mice bearing an i.m. implanted MS-2 fibrosarcoma. These 2 parameters have been studied as a function of the type of substituents linked to the 9-position of the macrocycle by amide, ester or ether functional groups. The pharmacokinetic properties appear to be controlled mainly by the degree of porphycene hydrophobicity, as evaluated by measuring their retention times in a C 18 column for HPLC. Thus, the post-injection time (T50) at which the porphycene concentration in the plasma decreases to 50% of the initial value ranged from a few minutes for the less hydrophobic to several hours for the more hydrophobic porphycenes. An increase in hydrophobicity also was accompanied by an enhanced efficiency and selectivity of tumour targeting. The less hydrophobic porphycenes showed a maximum tumour uptake of 0.5-2 nmol/g of tissue at 10-20 min after administration with a tumour/peri-tumoural concentration ratio around 2-3, while those with higher hydrophobicity reached tumour concentrations of 7-8 nmol/g at 24-48 hr after administration with concentration ratios higher than 20.

Photodynamic effects of meso-tetra (4-sulfonatophenyl)porphine on human leukemia cells HEL and HL60, human lymphocytes and bone marrow progenitor cells

Meso-tetra(4-sulfonatophenyl)porphine (TPPS4), in combination with a light dose of 14 J cm-2, has a profound negative effect on the proliferation and viability of leukemia cells HL60 (human promyelocytic leukemia) and HEL (human erythroleukemia), the viability of normal lymphocytes and the colony-forming activity of human bone marrow progenitor cells. However, normal leukocytes (monocytes, granulocytes) are, to a large extent, resistant to photodynamic treatment (PDT). Whilst DNA fragmentation suggesting apoptosis is induced in HL60 cells, accumulation in the interphase of the cell cycle (G0/G1, G2/M) is mainly operative in the TPPS4-mediated PDT of HEL cells. The "dark" effect of TPPS4 on the cell viability is below 15% up to a concentration of 40 microM.

Photodynamic efficacy of naturally occurring porphyrins in endothelial cells in vitro and microvasculature in vivo

Photodynamic therapy (PDT) has been described in terms of cellular and vascular effects. The precise mechanisms of cellular and vascular damage are still unknown. In this study, the photodynamic inactivation of endothelial cells in vitro and damage to the microvasculature in vivo by naturally occurring porphyrins (uroporphyrin III (UP), coproporphyrin III (CP) and protoporphyrin IX (PP)) were investigated. The chick chorioallantoic membrane model (CAM model) was used, which is convenient for the study of damage to the microcirculation induced by PDT. The hydrophilic porphyrins UP and CP exhibited low cytotoxicity towards endothelial cells. Only small amounts of UP and CP were taken up, resulting in weak inactivation after irradiation. In contrast, the more lipophilic PP showed a marked cytotoxicity. Considerable amounts of PP were accumulated in the cells, leading to pronounced inactivation after light exposure. For the three porphyrins, damage to the microvasculature was observed. The damage caused by the hydrophilic porphyrins UP and CP was strongly dependent on the drug and light dose. For vascular injury, the efficacy was graded as UP < CP < PP.

Aggregation phenomena in the complexes of iron tetraphenylporphine sulfonate with bovine serum albumin

Binding of Fe(III) meso-tetrakis(p-sulfonatophenyl)-porphyrin (FeTPPS4) to bovine serum albumin (BSA) was studied by UV-VIS absorption, fluorescence quenching, circular dichroism, 1H NMR, and ESR. At excess of BSA, the bound form of FeTPPS4 is a high-spin monomer exhibiting a Soret band at 417 nm, a broad NMR peak at 10.3 ppm, an ESR signal at g = 5.7-5.9, and a strong enhancement of magnetic relaxation of water protons. In the intermediate concentration range, a formation of nonparamagnetic bound aggregates of FeTPPS4 occurs (up to 10-15 molecules at pH 6.0) with a Soret band at 414 nm and NMR peaks at 7.0, 8.1, and 12.7 ppm. In the physiologic pH range, BSA binds the monomeric form of FeTPPS4 with an association constant of about 10(8) M-1, the affinity to oxo-dimers in solution being much lower. BSA itself is also subject to aggregation with an average aggregation number of 4-8 in the physiological pH range. It is assumed that aggregation phenomena may play an important role, both in the relaxation efficiency of metalloporphyrins as MRI contrast agents and in the blood transport of porphyrin drugs by albumins.

Correlation of subcellular and intratumoral photosensitizer localization with ultrastructural features after photodynamic therapy

Photodynamic therapy (PDT) of cancer typically involves systemic administration of tumor-localizing photosensitizers followed 48-72 h later by exposure to light of appropriate wavelengths. Knowledge about the distribution of photosensitizers in tissues is still fragmentary. In particular, little is known as to the detailed localization patterns of photosensitizers in neoplastic and normal tissues as well as the relationship between such patterns and the actual targets for the photosensitizing effect. This review focuses on ultrastructural features seen in treated cells and tumors. An attempt is made to correlate these findings with the subcellular/intratumoral localization pattern of the photosensitizers in tumor cell lines in vitro and in tumor models in vivo. Several subcellular sites are main targets of PDT with different sulfonated aluminum phthalocyanines (AIPcSn) in the human tumor cell line LOX. Nuclei are not among the primary targets. Overall, the ultrastructural changes correlate well with the data about the subcellular localization patterns for each analogue of AIPcSn in the same cell line. Similar findings are also obtained for the family of sulfonated mesotetraphenylporphines (TPPSn) in the NHIK 3025 cell line. The mechanisms involved in the killing of tumors by PDT seem to be a complex interplay between direct and indirect (via vascular damage) effects on neoplastic cells according to the intratumoral localization pattern of the applied dye. Several factors can affect the localization pattern of a drug, such as its chemical character, the mode of drug delivery, the time interval between drug administration and light exposure, and tumor type. Furthermore, whether local immune reactions (such as macrophages) and apoptosis (programmed cell death) are involved in the destruction of neoplastic cells by PDT in vivo is still an enigma. A general model for PDT-induced tumor destruction is suggested.

H NMR and electronic absorption spectroscopy of paramagnetic water-soluble meso-tetraarylsubstituted cationic and anionic metalloporphyrins

The ionization, mu-oxo-dimerization and axial ligation equilibria of free bases, iron(III) and manganese(III) derivatives of meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS4) and meso-tetrakis(4-N-methyl-pyridiniumyl)porphyrin (TMPyP) in aqueous solution are studied by 1H NMR and electronic absorption spectroscopy. At physiological pH, Fe(III) complexes of TMPyP and TPPS4 exist predominantly as dimers and may undergo transition to low spin species upon binding to biomolecules, whereas Mn(III) complexes are essentially monomeric. Dicyano and bis-imidazole complexes of FeTMPyP and FeTPPS4 are low spin monomer adducts in the pH range 2.0 to 11.2. No low spin dimeric complexes were found. The low spin monocyano and high spin mono-imidazole complexes of FeTMPyP are formed in acidic and alkaline media, respectively. T1-relaxation enhancement of water protons at 200 MHz induced by FeTPPS4 falls dramatically in the sequence high spin >> dimeric > low spin form.

Correlation of distribution of sulphonated aluminium phthalocyanines with their photodynamic effect in tumour and skin of mice bearing CaD2 mammary carcinoma

A chemical extraction assay and fluorescence microscopy incorporating a light-sensitive thermoelectrically cooled charge-coupled device (CCD) camera was used to study the kinetics of uptake, retention and localisation of disulphonated aluminium phthalocyanine (A1PcS2) and tetrasulphonated aluminium phthalocyanine (A1PcS4) at different time intervals after an i.p. injection at a dose of 10 mg kg-1 body weight (b.w.) in tumour and surrounding normal skin and muscle of female C3D2/F1 mice bearing CaD2 mammary carcinoma. Moreover, the photodynamic effect on the tumour and normal skin using sulphonated aluminium phthalocyanines (A1PcS1, A1PcS2, A1pcS4) and Photofrin was compared with respect to dye, dye dose and time interval between dye administration and light exposure. The maximal concentrations of A1PcS2 in the tumour tissue were reached 2-24 h after injection of the dye, while the amounts of A1PcS4 peaked 1-2 h after the dye administration. A1PcS2 was simultaneously localised in the interstitium and in the neoplastic cells of the tumour, whereas A1PcS4 appeared to localise only in the stroma of the tumour. The photodynamic efficiency (light was applied 24 h after dye injection at a dose of 10 mg kg-1 b.w.) of the tumours was found to decrease in the following order: A1PcS2 > A1PcS4 > Photofrin > A1PcS1. Furthermore, photodynamic efficacy was strongly dependent upon dye doses and time intervals between dye administration and light exposure: the higher the dose, the higher the photodynamic efficiency. The most efficient photodynamic therapy (PDT) of the tumour was reached (day 20 tumour-free) when light exposure took place 2 h after injection of A1PcS2 (10 mg kg-1). A dual intratumoral localisation pattern of the dye, as found for A1PcS2, seems desirable to obtain a high photodynamic efficiency. The kinetic patterns of uptake, retention and localisation of A1PcS2 and A1PcS4 are roughly correlated with their photodynamic effect on the tumour and normal skin.

Structure-activity relationship of porphines for photoinactivation of bacteria

The antibacterial photodynamic effects of uncharged (o-tetrahydroxyphenyl porphine [THPP], m-THPP and p-THPP), cationic (5,10,15,20-tetra[4-N-methylpyridyl]porphine [TMPyP]) and anionic (5,10,15,20-tetra[4-sulfonatophenyl porphine] [TPPS4]) porphines on Staphylococcus aureus and Escherichia coli bacteria inactivation were examined. The results show that uncharged porphines provoked antibacterial photodynamic activity on S. aureus, and also on E. coli in the presence of the membrane-disorganizing peptide polymixin B nonapeptide (PMNP). The TMPyP compound was highly photoactive toward gram-positive bacteria but only marginally effective on gram-negative cells, whereas TPPS4 showed no activity on either gram-positive or gram-negative bacteria. The photoactivity of TMPyP is due to the electrostatic attraction between the positively charged sensitizer molecule and the negatively charged membrane of the gram-positive target cells. For TPPS4, the inactivity toward gram-positive bacteria is due to electrostatic repulsion between the charged sensitizer molecule and the cell membrane. For gram-negative bacteria, the inactivity is conceivably due to preferential (electrostatic) binding to the positively charged PMNP, which is an adjuvant for membrane disorganization, but has no effect on cell viability. For hydrophobic sensitizers, the photoactivity depends on the state of aggregation. The extent of deaggregation of the different THPP isomers was determined by fluorescence measurements of bound sensitizers and could be positively correlated with their photoinactivation capacity. We conclude that the structure-activity relationships of these porphines are affected by their net charge and by aggregation.

The influence of the cysteine protease inhibitor L-trans-epoxysuccinyl-leucyl amido(4-guanidio)butane (E64) on photobiological effects of tetra(4-sulfonatophenyl)porphine

Human cervix carcinoma cells of the line NHIK 3025 were exposed to light after 18 h incubation with tetra(4-sulfonatophenyl)porphine (TPPS4) in the absence or presence of the cysteine protease inhibitor L-trans-epoxysuccinyl-leucyl amido(4-guanidino)butane (E64) followed by 1 h in sensitizer-free medium. E64 changed the photochemical properties of TPPS4 in NHIK 3025 cells, i.e., TPPS4 fluorescence yield was enhanced 2.5-fold and photochemically induced lysosomal rupture and loss of cell bound TPPS4 were inhibited. Additionally, E64 slightly (10%) reduced the sensitivity of the NHIK 3025 cells to photoinactivation. This is not likely to be due to its inhibitory effect on protease activity, but correlates with its inhibition of lysosomal rupture. The present results indicate that the release of lysosomal cysteine proteases from the lysosomal compartments are of little or no importance in the photochemical inactivation of NHIK 3025 cells when TPPS4 is used as photosensitizer.

Binding of meso-tetra(4-sulfonatophenyl)porphine to haemopexin and albumin studied by spectroscopy methods

1. The interaction of haemopexin and albumin with TPPS4 was studied by measuring the absorption and fluorescence spectra. Haemopexin was found to have one strong TPPS4 binding center (Ka = 3 x 10(7) M-1). 2. Haem-haemopexin complex appears to have no specific binding site for TPPS4. Occupation of the specific binding center of haemopexin molecule by a haem abolishes TPPS4 binding. 3. Albumin was found to possess one strong TPPS4 binding center (Ka = 3 x 10(6) M-1) besides two or three weak binding sites (Ka = 2 x 10(5) M-1). 4. Haem-albumin complex possesses only one weak TPPS4 binding site (Ka = 7 x 10(5) M-1). These observations suggest identity of primary binding sites of TPPS4 and haem on albumin molecule.

No correlation between DNA strand breaks and HPRT mutation induced by photochemical treatment in V79 cells

DNA strand breaks, measured by alkaline elution, and hypoxanthine guanine phosphoribosyltransferase (HPRT) mutation were studied in V79 cells after photochemical treatment (PCT) or exposure to X-rays. Cells were incubated with the photosensitizers Photofrin II (PII) and three closely related porphyrins tetra-(3-hydroxyphenyl) porphyrin (3THPP), meso-tetra-(4-sulfonatophenyl) porphine (TPPS4) and meso-tetra-(N-methyl-4-pyridyl) porphine (TMPyPH2). These dyes are assumed to act on cellular targets mainly via singlet oxygen when excited by light. While the hydrophilic TPPS4 and TMPyPH2 did not photoinduce mutants to any significant extent, both lipophilic dyes, 3THPP and PII, were significantly mutagenic when excited by light. On the other hand, TPPS4 was the most efficient sensitizer of alkali-labile DNA strand breaks, while TMPyPH2 did not induce any significant amount of either type of DNA damage. Surprisingly, no correlation between the two parameters was found for PCT, either after exposures inactivating 50% of the cells or after exposures inactivating 90% of them. The lack of correlation between the yields of DNA strand breaks and of mutants could not be explained by differences in the intracellular localization pattern of the dyes.

Stereochemical factors in the transport and binding of photosensitizers in biological systems and in photodynamic therapy

The uptake and biological activity of porphyrins and phthalocyanines in tumours were correlated with the geometrical features of the photosensitizer molecules. The data suggest that a critical distance of approximately 1.2 nm between oxygen atoms (originating in SO3-, COO- or OH substituents) characterizes a biologically active photosensitizer for photodynamic therapy. We propose that tubulin, which is available in large amounts during mitosis, is the main receptor molecule which binds these photosensitizers. Basic amino acid residues or tightly bound cations in tubulin or homologous proteins may act as binding sites on the receptor molecule.