Synthesis and photophysical properties of new fluorinated benzo[c]xanthene dyes as intracellular pH indicators

Two new fluorinated benzo[c]xanthene dyes were synthesized by reaction of fluorinated 1,6-dihydroxynaphthalenes with 2,4- (and 2,5)-dicarboxy-3'-dimethylamino-2'-hydroxybenzophenone. The two critical fluorinated 1,6-dihydroxynaphthalene intermediates were prepared via a regioselective route. The fluorinated benzo[c]xanthene dyes exhibit desired lower pK(a) values (6.4 and 7.2, respectively) than their parent compound (pK(a)=7.5) while the pH-dependent dual-emission characteristics are well retained. Their cell-permeable esters have been prepared for intracellular applications.

Characterization of extracellular chitinolytic activity in biofilms

Extracellular enzymes produced by bacterial biofilms tend to become an integral, permanent part of the biofilm/substratum system. Thus, characterizing extracellular enzyme activity is an essential component of understanding biofilm ecology. Methods have been presented for characterizing three aspects of extracellular enzyme activity in biofilms: promoter activity of the structural gene, local catalytic activity, and kinetics of collective substrate degradation. The abundance of intracellular transcript derived from a structural gene is only indirectly related to the magnitude of catalytic activity of the corresponding enzyme. This relationship may be particularly tenuous in the case of extracellular enzymes, which must be transported out of the cell in order to become active. Fluorogenic substrates that allow direct detection of an increasingly greater variety of enzyme activities are becoming available. There are technical problems, originating from surface roughness and intrinsic fluorescence, associated with microscopic examination of biofilms on natural materials. Thin films provide one option for acquiring data about biofilms colonizing relevant materials.

Rapid and simple single nanogram detection of glycoproteins in polyacrylamide gels and on electroblots

The fluorescent hydrazide, Pro-Q Emerald 300 dye, may be conjugated to glycoproteins by a periodic acid Schiff's (PAS) mechanism. The glycols present in glycoproteins are initially oxidized to aldehydes using periodic acid. The dye then reacts with the aldehydes to generate a highly fluorescent conjugate. Reduction with sodium metabisulfite or sodium borohydride is not required to stabilize the conjugate. Though glycoprotein detection may be performed on transfer membranes, direct detection in gels avoids electroblotting and glycoproteins may be visualized within 2-4 h of electrophoresis. This is substantially more rapid than PAS labeling with digoxigenin hydrazide followed by detection with an antidigoxigenin antibody conjugate of alkaline phosphatase, or PAS labeling with biotin hydrazide followed by detection with horseradish peroxidase or alkaline phosphatase conjugates of streptavidin, which require more than eight hours to complete. Pro-Q Emerald 300 dye-labeled gels and blots may be poststained with SYPRO Ruby dye, allowing sequential two-color detection of glycosylated and nonglycosylated proteins. Both fluorophores are excited with mid-range UV illumination. Pro-Q Emerald 300 dye maximally emits at 530 nm (green) while SYPRO Ruby dye maximally emits at 610 nm (red). As little as 300 pg of alpha 1-acid glycoprotein (40% carbohydrate) and 1 ng of glucose oxidase (12% carbohydrate) or avidin (7% carbohydrate) are detectable in gels after staining with Pro-Q Emerald 300 dye. Besides glycoproteins, as little as 2-4 ng of lipopolysaccharide is detectable in gels using Pro-Q Emerald 300 dye while 250-1000 ng is required for detection with conventional silver staining. Detection of glycoproteins may be achieved in sodium dodecyl sulfate-polyacrylamide gels, two-dimensional gels and on polyvinylidene difluoride membranes.

An improved, luminescent europium-based stain for detection of electroblotted proteins on nitrocellulose or polyvinylidene difluoride membranes

SYPRO Rose Plus protein blot stain is an improved europium-based metal chelate stain for the detection of proteins on nitrocellulose and poly(vinylidene difluoride) (PVDF) membranes. Staining is achieved without covalently modifying the proteins. The stain may be excited with a 254 nm (UV-C), 302 nm (UV-B), or 365 nm (UV-A) light source and displays a sharp emission maximum at 612 nm. The emission peak has a full width at half-maximum of only 8 nm. The stain exhibits exceptional photostability, allowing long exposure times for maximum sensitivity. Since the dye is composed of a europium complex, it has a long emission lifetime, potentially allowing time-resolved detection, greatly reducing background fluorescence. Proteins immobilized to a nitrocellulose or PVDF membrane by electroblotting, dot-blotting, or vacuum slot-blotting are incubated with SYPRO Rose Plus protein blot stain for 15-30 min. Membranes are rinsed briefly, visualized with UV epi-illumination and the luminescence of the europium dye is measured using a 490 nm long-pass or 625 +/- 15 nm band-pass filter in combination with a conventional photographic or charge-coupled device (CCD) camera system. Alternatively, the dye may be visualized using a xenon-arc illumination source. The stain is readily removed from proteins by incubating membranes at mildly alkaline pH. The reversibility of the protein staining procedure allows for subsequent biochemical analyses, such as immunoblotting and biotin-streptavidin detection using colorimetric, direct fluorescence or fluorogenic visualization methods.

Differentiation of chitinase-active and non-chitinase-active subpopulations of a marine bacterium during chitin degradation

The ability of marine bacteria to adhere to detrital particulate organic matter and rapidly switch on metabolic genes in an effort to reproduce is an important response for bacterial survival in the pelagic marine environment. The goal of this investigation was to evaluate the relationship between chitinolytic gene expression and extracellular chitinase activity in individual cells of the marine bacterium Pseudoalteromonas sp. strain S91 attached to solid chitin. A green fluorescent protein reporter gene under the control of the chiA promoter was used to evaluate chiA gene expression, and a precipitating enzyme-linked fluorescent probe, ELF-97-N-acetyl-beta-D-glucosaminide, was used to evaluate extracellular chitinase activity among cells in the bacterial population. Evaluation of chiA expression and ELF-97 crystal location at the single-cell level revealed two physiologically distinct subpopulations of S91 on the chitin surface: one that was chitinase active and remained associated with the surface and another that was non-chitinase active and released daughter cells into the bulk aqueous phase. It is hypothesized that the surface-associated, non-chitinase-active population is utilizing chitin degradation products that were released by the adjacent chitinase-active population for cell replication and dissemination into the bulk aqueous phase.

New ratiometric fluorescent calcium indicators with moderately attenuated binding affinities

Mono-halogenated derivatives of the calcium indicators fura-2 and indo-1 were synthesized and their spectroscopic properties evaluated. Halogenation ortho or para to the bridging oxygen in the BAPTA nucleus had a more pronounced weakening effect on binding affinity than in the meta position in the fura derivatives. Two new excitation ratioable fluorescent calcium indicators, benzothiaza-1 and 2, were also synthesized. Kd values of 400 nM to 5.3 microM [Ca2+] were observed in these families of new probes.

Background-free, high sensitivity staining of proteins in one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gels using a luminescent ruthenium complex

SYPRO Ruby dye is a permanent stain comprised of ruthenium as part of an organic complex that interacts noncovalently with proteins. SYPRO Ruby Protein Gel Stain provides a sensitive, gentle, fluorescence-based method for detecting proteins in one-dimensional and two-dimensional sodium dodecyl sulfate-polyacrylamide gels. Proteins are fixed, stained from 3h to overnight and then rinsed in deionized water or dilute methanol/acetic acid solution for 30 min. The stain can be visualized using a wide range of excitation sources commonly used in image analysis systems including a 302 nm UV-B transilluminator, 473 nm second harmonic generation (SHG) laser, 488 nm argon-ion laser, 532 nm yttrium-aluminum-garnet (YAG) laser, xenon arc lamp, blue fluorescent light bulb or blue light-emitting diode (LED). The sensitivity of SYPRO Ruby Protein Gel Stain is superior to colloidal Coomassie Brilliant Blue (CBB) stain or monobromobimane labeling and comparable with the highest sensitivity silver or zinc-imidazole staining procedures available. The linear dynamic range of SYPRO Ruby Protein Gel stain extends over three orders of magnitude, which is vastly superior to silver, zinc-imidazole, monobromobimane and CBB stain. The fluorescent stain does not contain superfluous chemicals (formaldehyde, glutaraldehyde, Tween-20) that frequently interfere with peptide identification in mass spectrometry. While peptide mass profiles are severely altered in protein samples prelabeled with monobromobimane, successful identification of proteins by peptide mass profiling using matrix-assisted laser desorption/ionization mass spectrometry was easily performed after protein detection with SYPRO Ruby Protein Gel stain.

Background-free, high sensitivity staining of proteins in one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gels using a luminescent ruthenium complex

SYPRO Ruby dye is a permanent stain comprised of ruthenium as part of an organic complex that interacts noncovalently with proteins. SYPRO Ruby Protein Gel Stain provides a sensitive, gentle, fluorescence-based method for detecting proteins in one-dimensional and two-dimensional sodium dodecyl sulfate-polyacrylamide gels. Proteins are fixed, stained from 3h to overnight and then rinsed in deionized water or dilute methanol/acetic acid solution for 30 min. The stain can be visualized using a wide range of excitation sources commonly used in image analysis systems including a 302 nm UV-B transilluminator, 473 nm second harmonic generation (SHG) laser, 488 nm argon-ion laser, 532 nm yttrium-aluminum-garnet (YAG) laser, xenon arc lamp, blue fluorescent light bulb or blue light-emitting diode (LED). The sensitivity of SYPRO Ruby Protein Gel Stain is superior to colloidal Coomassie Brilliant Blue (CBB) stain or monobromobimane labeling and comparable with the highest sensitivity silver or zinc-imidazole staining procedures available. The linear dynamic range of SYPRO Ruby Protein Gel stain extends over three orders of magnitude, which is vastly superior to silver, zinc-imidazole, monobromobimane and CBB stain. The fluorescent stain does not contain superfluous chemicals (formaldehyde, glutaraldehyde, Tween-20) that frequently interfere with peptide identification in mass spectrometry. While peptide mass profiles are severely altered in protein samples prelabeled with monobromobimane, successful identification of proteins by peptide mass profiling using matrix-assisted laser desorption/ionization mass spectrometry was easily performed after protein detection with SYPRO Ruby Protein Gel stain.

Ultrasensitive fluorescence protein detection in isoelectric focusing gels using a ruthenium metal chelate stain

SYPRO Ruby IEF Protein Gel Stain is an ultrasensitive, luminescent stain optimized for the analysis of protein in isoelectric focusing gels. Proteins are stained in a ruthenium-containing metal complex overnight and then rinsed in distilled water for 2 h. Stained proteins can be excited by ultraviolet light of about 302 nm (UV-B transilluminator) or with visible light of about 470 nm. Fluorescence emission of the dye is maximal at approximately 610 nm. The sensitivity of the SYPRO Ruby IEF protein gel stain is superior to colloidal Coomassie blue stain and the highest sensitivity silver staining procedures available. The SYPRO Ruby IEF protein gel stain is suitable for staining proteins in nondenaturing or denaturing carrier ampholyte isoelectric focusing and immobilized pH gradient gel electrophoresis. The stain is compatible with N,N'-methylenebisacrylamide or piperazine diacylamide cross-linked polyacrylamide gels as well as with agarose gels and high tensile strength Duracryl gels. The stain does not contain extraneous chemicals (formaldehyde, glutaraldehyde, Tween-20) that frequently interfere with peptide identification in mass spectrometry. Successful identification of stained proteins by peptide mass profiling is demonstrated.

A luminescent ruthenium complex for ultrasensitive detection of proteins immobilized on membrane supports

SYPRO Ruby protein blot stain provides a sensitive, gentle, fluorescence-based method for detecting proteins on nitrocellulose or polyvinylidene difluoride (PVDF) membranes. SYPRO Ruby dye is a permanent stain composed of ruthenium as part of an organic complex that interacts noncovalently with proteins. Stained proteins can be excited by ultraviolet light of about 302 nm or with visible light of about 470 nm. Fluorescence emission of the dye is approximately 618 nm. The stain can be visualized using a wide range of excitation sources utilized in image analysis systems including a UV-B transilluminator, 488-nm argon-ion laser, 532-nm yttrium-aluminum-garnet (YAG) laser, blue fluorescent light bulb, or blue light-emitting diode (LED). The detection sensitivity of SYPRO Ruby protein blot stain (0.25-1 ng protein/mm(2)) is superior to that of amido black, Coomassie blue, and india ink staining and nearly matches colloidal gold staining. SYPRO Ruby protein blot stain visualizes proteins more rapidly than colloidal gold stain and the linear dynamic range is more extensive. Unlike colloidal gold stain, SYPRO Ruby protein blot stain is fully compatible with subsequent biochemical applications including colorimetric and chemiluminescent immunoblotting, Edman-based sequencing and mass spectrometry.

Fluorescent molecular probes V: a sensitive caspase-3 substrate for fluorometric assays

(Z-Asp-Glu-Val-Asp)-Rhodamine 110 [(Z-DEVD)2-Rh 110] was prepared and characterized as a sensitive fluorogenic substrate for the determination of caspase-3 activity.

Novel method for screening bacterial colonies for phosphatase activity

Current methods for screening large numbers of bacterial colonies for phosphatase activity, rely heavily on the use of colorimetric assays. While such methods have been applied extensively in the laboratory, they are not without their drawbacks. We here describe a precipitating fluorescent probe that can be used to screen phosphatase activity in bacterial colonies. This probe can be incorporated directly into agar plates used to culture the organisms of interest. The approach offers several advantages over current methodologies including the ability to monitor the development of phosphatase activity with colony development, and the ability to distinguish between activity arising from cell-bound and cell-free enzyme. This enzyme probe was successfully used to detect and isolate phosphatase-producing bacteria from activated sludge.

A novel acidotropic pH indicator and its potential application in labeling acidic organelles of live cells

BACKGROUND

Ratio imaging has received intensive attention in the past few decades. The growing potential of ratio imaging is significantly limited, however, by the lack of appropriate fluorescent probes, for acidic organelles in particular. The classic fluorescent dyes (such as fluoresceins, rhodamines and coumarins) are not suitable for studying acidic organelles (such as lysosomes) because their fluorescence is significantly decreased under neutral or acidic conditions. This has motivated us to develop probes that can be used in ratio imaging that are strongly fluorescent even in acidic media.

RESULTS

The compound 2-(4-pyridyl)-5-((4-(2-dimethylaminoethyl-aminocarbamoyl) methoxy)phenyl)oxazole (PDMPO) was prepared and characterized as a new acidotropic dual-excitation and dual-emission pH indicator. It emits intense yellow fluorescence at lower pH and gives intense blue fluorescence at higher pH. This unique pH-dependent fluorescence property was readily explored to selectively stain lysosomes and to determine the pH of the organelle in an emission-ratio-imaging mode. PDMPO is selectively localized to lysosomes and exhibits a pH-dependent dual excitation and emission.

CONCLUSIONS

PDMPO selectively labels acidic organelles (such as lysosomes) of live cells and the two distinct emission peaks can be used to monitor the pH fluctuations of live cells in ratio measurements. Additionally, the very large Stokes shift and excellent photostability of PDMPO make the compound an ideal fluorescent acidotropic probe. The unique fluorescence properties of PDMPO might give researchers a new tool with which to study acidic organelles of live cells.

5-(Pentafluorobenzoylamino)fluorescein: A selective substrate for the determination of glutathione concentration and glutathione S-transferase activity

5-(Pentafluorobenzoylamino)fluorescein (PFB-F), a new thiol-reactive molecule was synthesized to improve the detection limits and specificity of the assays for glutathione S-transferase (GST) activity and glutathione (GSH). A rapid assay method to measure GSH concentration or GST activity and the simultaneous analysis of multiple samples is possible because the glutathione adduct, GS-TFB-F, is separated from PFB-F by thin-layer chromatography (TLC) and can be quantitated by a fluorescence scanner. The detection limits for GSH and for GST activity using TLC were found to be as low as 10 pmol/microl and 1 ng/microl using equine liver GST, respectively. Determination of GSH concentration or GST activity in bovine pulmonary artery endothelial (BPAE) cell lysates gave a linear response for samples corresponding to 500-2500 cells. PFB-F could also measure GST activities of GST fusion proteins and prove to be a suitable substrate for determining the activities of human GST isozymes and other sources of mammalian GST. The selectivity of PFB-F with GSH was proven by comparing trace amount of the adducts that formed with cysteine and beta-galactosidase to that formed with GSH. The HPLC profile of a reaction mixture where cell lysate was used in place of purified GST, also shows only two main peaks, corresponding to GS-TFB-F and unreacted PFB-F. The selectivity of PFB-F for GSH was further confirmed by exposing BPAE cells to dl-buthionine-[S,R]-sulfoximine (BSO). Our results of GS-TFB-F determination indicate that 12-, 24-, or 36-h incubations with BSO caused 2-, 6-, or 7.6-fold reductions in GSH levels, respectively.

Single cell analysis and selection of living retrovirus vector-corrected mucopolysaccharidosis VII cells using a fluorescence-activated cell sorting-based assay for mammalian beta-glucuronidase enzymatic activity

Mutations in the acid beta-glucuronidase gene lead to systemic accumulation of undegraded glycosaminoglycans in lysosomes and ultimately to clinical manifestations of mucopolysaccharidosis VII (Sly disease). Gene transfer by retrovirus vectors into murine mucopolysaccharidosis VII hematopoietic stem cells or fibroblasts ameliorates glycosaminoglycan accumulation in some affected tissues. The efficacy of gene therapy for mucopolysaccharidosis VII depends on the levels of beta-glucuronidase secreted by gene-corrected cells; therefore, enrichment of transduced cells expressing high levels of enzyme prior to transplantation is desirable. We describe the development of a fluorescence-activated cell sorter-based assay for the quantitative analysis of beta-glucuronidase activity in viable cells. Murine mucopolysaccharidosis VII cells transduced with a beta-glucuronidase retroviral vector can be isolated by cell sorting on the basis of beta-glucuronidase activity and cultured for further use. In vitro analysis revealed that sorted cells have elevated levels of beta-glucuronidase activity and secrete higher levels of cross-correcting enzyme than the population from which they were sorted. Transduced fibroblasts stably expressing beta-glucuronidase after subcutaneous passage in the mucopolysaccharidosis VII mouse can be isolated by cell sorting and expanded ex vivo. A relatively high percentage of these cells maintain stable expression after secondary transplantation, yielding significantly higher levels of enzymatic activity than that generated in the primary transplant.

A stable nonfluorescent derivative of resorufin for the fluorometric determination of trace hydrogen peroxide: applications in detecting the activity of phagocyte NADPH oxidase and other oxidases

The enzymatic determination of hydrogen peroxide can be accomplished with high sensitivity and specificity using N-acetyl-3, 7-dihydroxyphenoxazine (Amplex Red), a highly sensitive and chemically stable fluorogenic probe for the enzymatic determination of H2O2. Enzyme-catalyzed oxidation of Amplex Red, which is a colorless and nonfluorescent derivative of dihydroresorufin, produces highly fluorescent resorufin, which has an excitation maximum at 563 nm and emission maximum at 587 nm. The reaction stoichiometry of Amplex Red and H2O2 was determined to be 1:1. This probe allows detection of 5 pmol H2O2 in a 96-well fluorescence microplate assay. When applied to the measurement of NADPH oxidase activation, the Amplex Red assay can detect H2O2 release from as few as 2000 phorbol myristate acetate-stimulated neutrophils with a sensitivity 5- to 20-fold greater than that attained in the scopoletin assay under the same experimental conditions. Furthermore, the oxidase-catalyzed assay using Amplex Red results in an increase in fluorescence on oxidation rather than a decrease in fluorescence as in the scopoletin assay. In comparison with other fluorometric and spectrophotometric assays for the detection of monoamine oxidase and glucose oxidase, this probe is also found to be more sensitive. Given its high sensitivity and specificity, Amplex Red should have a broad application for the measurement of H2O2 in a variety of oxidase-mediated reactions and very low levels of H2O2 in food, environmental waters, and consumer products.

Detection and isolation of gene-corrected cells in Gaucher disease via a fluorescence-activated cell sorter assay for lysosomal glucocerebrosidase activity

Gaucher disease type 1 results from the accumulation of glucocerebroside in macrophages of the reticuloendothelial system, as a consequence of a deficiency in glucocerebrosidase (GC) activity. Recent improvements in the methodologies for introducing foreign genes into bone marrow stem cells have prompted several groups to test the efficacy of gene transfer therapy as a curative treatment for Gaucher disease. Limitations of this approach include the potential for insufficient engraftment of gene-corrected cells and incomplete transduction of hematopoietic stem cells using retroviral gene transfer. Overcoming these obstacles may be critical in the case of treatment for Gaucher disease type 1, because GC transduced cells have not been shown to have a growth advantage over noncorrected cells. Here, we describe the development and application of a novel, fluorescence-activated cell sorter based assay that directly quantitates GC activity at the single cell level. In a test of this application, fibroblasts from a Gaucher patient were transduced, and high expressing cells sorted based on GC activity. Reanalysis of cultured sorted fibroblasts reveals that these cells maintain high levels of enzymatic activity, compared with the heterogeneous population from which they were sorted. The assay is sufficiently sensitive to distinguish GC activity found in Gaucher patient monocytes from that in normal controls. Furthermore, preliminary results indicate that increased GC activity can be detected in transduced, CD34+ enriched peripheral blood mononuclear cells isolated from a Gaucher patient. This method should be a useful addition to current gene therapy protocols as a means to quantitatively assess gene correction of relevant cell populations and potentially purify transduced cells for transplantation.

Antiviral activities of photoactive perylenequinones

Nine perylenequinones (PQ), including some familiar naturally occurring pigments, were compared for their light-mediated antiviral efficacies. Calphostin C was the most active compound against the two target viruses, herpes simplex virus type 1 and Sindbis virus. Hypocrellins A and B were also very active. However, three cercosporin-like PQ were substantially less active in spite of their high quantum yields of singlet oxygen, whereas phleichrome, another efficient singlet oxygen producer, showed no detectable antiviral activity. One other PQ, which was a very weak singlet oxygen producer, also showed no antiviral activity. None of the active compounds showed significant antiviral activity in the dark. Thus, for some groups of PQ there was correlation between quantum yield of singlet oxygen (1O2) and antiviral efficacy, but there are evidently other structural features of PQ that influence activity.

A fluorogenic substrate for beta-glucuronidase: applications in fluorometric, polyacrylamide gel and histochemical assays

We have developed a fluorogenic substrate, ELF-97 beta-D-glucuronide, that provides significant advantages over existing substrates in detecting beta-glucuronidase activity. ELF-97 beta-D-glucuronide allows the detection of enzymatic activity in situ, yielding a hydrolytic product that exhibits maximal fluorescence within the physiological pH range. This substrate yields a hydrolytic product that demonstrates a more than 100 nm Stokes shift, which minimizes interference from autofluorescence in plant tissue. With the commercial enzyme, ELF-97 beta-D-glucuronide can detect less than 2 x 10(-4) U/ml of beta-glucuronidase activity in solution, and 5 x 10(-4) U per lane in polyacrylamide gels. Assays using transgenic Arabidopsis, whole leaf extracts of GUS-positive, but not GUS-negative plans, show significant GUS activity upon incubation with ELF-97 beta-D-glucuronide. Furthermore, the ability of this substrate to form insoluble precipitates at the sites of enzymatic activity makes it suitable for in situ localization of GUS activity in tissue samples of higher plants.

Enzyme-generated intracellular fluorescence for single-cell reporter gene analysis utilizing Escherichia coli beta-glucuronidase

We report the development of a new fluorescence-activated cell sorter (FACS)-based reporter gene system utilizing the enzymatic activity of the E. coli beta-glucuronidase (gus) gene. When loaded with the Gus substrate fluorescein-di-beta-D-glucuronide (FDGlcu), individual mammalian cells expressing and translating gus mRNA liberate sufficient levels of intracellular fluorescein for quantitative analysis by flow cytometry. This assay can be used to FACS sort viable cells based on Gus enzymatic activity, and the efficacy of the assay can be measured independently by using a fluorometric lysate assay. Furthermore, both the beta-glucuronidase and the previously described E. coli beta-galactosidase enzymes have high specificities for their cognate substrates, allowing each reporter gene to be measured by FACS independently.

Hypocrellins as photosensitizers for photodynamic therapy: a screening evaluation and pharmacokinetic study

Hypocrellin compounds were selected as potential photosensitizers for photodynamic therapy (PDT) owing to their high quantum yields of singlet oxygen (1O2), and facility for site-directed chemical modification to enhance phototoxicity, pharmacokinetics, solubility, and light absorption in the red spectral region, among other properties. Parent hypocrellins A and B share an absorption peak at 658 nm. These molecules may therefore be considered useful progenitors of derivatives which absorb more strongly in the red, considering that the ideal sensitizer should absorb in the 650-800 nm range, beyond the absorption range of hemoglobin and melanin, and where light penetration in tissues is maximized through reduced scattering. A series of pure, monomeric hypocrellin derivatives was tested for properties of dark cytotoxicity and photosensitizing potential by clonogenic assay in monolayer cultures of EMT6/Ed murine tumor cells. Their respective toxicities are reported on a molar basis. The in vitro screening assay has, to date, resulted in the selection of four hypocrellin derivatives for further development as photosensitizers for PDT. Cellular uptake for photosensitizing doses of selected compounds was determined by fluorimetry. Dose escalation studies in rodents indicate that potentially photosensitizing doses promote no demonstrable systemic toxicity.

Novel therapeutic and diagnostic applications of hypocrellins and hypericins

Hypocrellins and hypericins, structurally related plant pigments isolated from Hypocrella bambuase and Hypericum respectively, are known photodynamic agents. This review summarizes certain significant advances in the photophysics, photochemistry and photobiology of these pigments in the last 2 years and discusses their prospects as novel therapeutic and diagnostic agents in the future. Recently, certain unique properties of hypocrellins and hypericins have been explored for a variety of therapeutic and diagnostic applications. In particular, substantial progress has been made in both anticancer and antiviral applications (especially anti-human immunodeficiency virus). The promising anticancer and antiviral results obtained both in vitro and in vivo have led to intensive investigation into their photo-physical and photochemical processes, especially kinetic studies of their intramolecular proton transfer. These compounds offer the potential for a highly sensitive fluorescent redox sensor for investigation of a variety of cellular events. The biomedical advances of hypocrellins and hypericins have been further promoted by significant progress in their chemical synthesis and the recent commercialization of hypocrellins A and B and hypericin.

Photosensitization with anticancer agents. 20--EPR studies on the photodynamic action of phleichrome: formation of semiquinone radical and activated oxygen species on illumination with visible light

When phleichrome was illuminated with visible light, the semiquinone radical, singlet oxygen, and superoxide anion radical were detected. The formation of the semiquinone radical and activated oxygen species and the transformations and competitions between them depend on quinone and oxygen concentration, duration and intensity of illumination, and the nature of the substrate. In anaerobic solution, the semiquinone radical was predominantly photoproduced via the self-electron transfer between the excited and ground species. In contrast, in aerobic solution, singlet oxygen is the principal product in the photosensitization of phleichrome. In addition to singlet oxygen, superoxide anion radical is also generated by the quinones upon illumination in aerobic solution, but to a lesser extent. The generation of the superoxide anion is significantly enhanced by the presence of electron donors.

Photosensitization with anticancer agents 19. EPR studies of photodynamic action of calphostin C: formation of semiquinone radical and activated oxygen on illumination with visible light

When calphostin C was illuminated with visible light, the semiquinone radical, singlet oxygen, and superoxide anion radical were detected. The formation of the semiquinone radical and activated oxygen species and the transformations and competitions between them depend upon the quinone and oxygen concentrations, time and intensity of illumination, and the nature of the substrate. In anaerobic solution, the semiquinone radical was predominantly photoproduced via the self-electron transfer between the excited and ground species. In aerobic solution, singlet oxygen is the principal product in the photosensitization of calphostin C. In addition to singlet oxygen, superoxide anion radical is also generated by the quinones upon illumination in aerobic solution, but to a lesser extent than singlet oxygen. The superoxide anion is produced via the reduction of oxygen by the semiquinone radical, and this process is significantly enhanced by the presence of electron donors.

Design, synthesis and investigation of mechanisms of action of novel protein kinase C inhibitors: perylenequinonoid pigments

A series of perylenequinonoid pigments (PQPs) and related compounds were synthesized and screened for the inhibition of protein kinase C (PKC), a key enzyme involved in cellular differentiation and proliferation, and a potential target for anticancer and antiviral chemotherapeutic drugs. This study has established PQPs as efficient PKC inhibitors, and elucidated aspects of the light-enhanced action mode of the PKC inhibitors. Comparative studies between natural and synthetic PQPs led to the recognition of the effect of certain structural features of PQPs on PKC inhibition, including the skeleton of the 3,10-dihydroxy-4,9-perylenequinonoid chromophore and the configuration of the two side chains at positions 1 and 12. Calphostin C was identified as a superior PKC inhibitor of the POP class, and with the latter as a representative structure, we investigated the mechanism of PKC inhibition by PQPs via electron paramagnetic resonance spectroscopy in conjunction with the spin-trapping technique, absorption and fluorescence spectroscopy, photochemical and photobiological studies, and enzyme methodology. Multiple modes of action are suggested for PKC inhibition, comprising the following steps: (1) the binding of PQPs to the PKC regulatory domain via complexation; (2) the photobonding between mercapto groups of PKC cysteine residues and the PQP quinonoid moiety; and (3) the PQP-sensitized photodamage of PKC via Type I and/or Type II photosensitization.

Phototherapeutic potential of alternative photosensitizers to porphyrins

Because of promising clinical results obtained with photodynamic therapy, more and more photosensitizers continue to be isolated (from natural sources), synthesized and evaluated, the development of which is considered to be a key factor for the successful clinical application of photodynamic therapy. Porphyrins and their analogs (as classical types of phototherapeutic agents) have been extensively reviewed. In this review, we have attempted to summarize the phototherapeutic potential (in particular, anticancer and antiviral aspects) of nonporphyrin photosensitizers (as a new generation of phototherapeutic agents) in more detail, which have been relatively much less reviewed hitherto. They include anthraquinones, anthrapyrazoles, perylenequinones, xanthenes, cyanines, acridines, phenoxazines and phenothiazines. They have shown certain phototherapeutic advantages over the presently used porphyrins. Some anthraquinones, perylenequinones, cyanines, phenoxazines and phenothiazines exhibit strong light absorption in the 'phototherapeutic window' (600-1000 nm), high photosensitizing efficacy and low delayed skin photosensitivity. Some of the nonporphyrin photosensitizers (such as rhodamine 123, merocyanine 540 and some cyanine cationic dyes) demonstrate higher selectivity for tumor cells. They can also be explored in connection with selective carcinoma photolysis strategy based on mitochondrion-, lysosome- or DNA-directed localization mode.

Photosensitization with anticancer agents. 15. Perylenequinonoid pigments as potential photodynamic therapeutic agents: formation of semiquinone radicals and reactive oxygen species on illumination

Visible light illumination of solutions of perylenequinonoid pigments generates the corresponding semiquinone radicals, singlet oxygen, superoxide anion radical, hydroxyl radical and hydrogen peroxide. In anaerobic solution, the semiquinone radicals are predominantly photoproduced via the self-electron transfer between the excited and ground state species. In aerobic solution, singlet oxygen is the principal product in the photosensitization of perylenequinonoid pigments. The 3,10-dihydroxy-4,9-perylenequinonoid chromophore was shown to be the necessary structural requirement for the generation of singlet oxygen, and the side-chains of the quinones had little effect on the production of singlet oxygen. This conclusion is useful in the development of more efficient photodynamic therapeutic agents than natural perylenequinonoid pigments themselves. Such agents should ideally contain the 3,10-dihydroxy-4,9-perylenequinonoid chromophore to produce singlet oxygen together with appropriate elaborated side-chains to permit the selective localization of the sensitizer in tumor tissue. In addition to singlet oxygen, superoxide anion radical is generated by the perylenequinones on illumination in aerobic solution, but to a lesser extent than singlet oxygen, via the reduction of oxygen by the corresponding semiquinone radicals. This latter process is significantly enhanced by the presence of electron donors.

Photosensitization with anticancer agents. 16. The photo-oxidation of hypocrellin A. A mechanism study using 18O labelling

Hypocrellin A was selected as a representative structure to investigate the mechanism of photo-oxidation of perylenequinonoid pigments (PQPs). It was found that singlet oxygen plays a key role in the photo-oxidation of PQPs. The following processes were determined to be involved in the photo-oxidation of PQPs using 18O atom labelling. After the PQP is photoexcited, it tautomerizes and dissociates to produce the anion, which reacts with singlet oxygen generated during irradiation, resulting in the formation of an endoperoxide. The endoperoxide then rearranges to form a dioxetane which undergoes cycloreversion to produce the final product, a di-alpha-naphthoquinone. The factors affecting the photo-oxidation of hypocrellin A were also investigated, including the pH of the solution, nature of the solvent, irradiation wavelength and hydration phenomena. Of these factors, the extremely strong effect of pH on the photo-oxidation of hypocrellin A may be used as a basis for the selective localization of hypocrellin A in tumor tissue. On the basis of the proposed mechanism for the photo-oxidation of PQPs, it may be possible to design and synthesize an optimal tumor-selective PQP photosensitizer for the photodynamic therapy of human tumors.

Photosensitization with anticancer agents. 18. Perylenequinonoid pigments as potential photodynamic therapeutic agents: preparation and photodynamic properties of amino-substituted hypocrellin derivatives

Perylenequinonoid pigments have demonstrated several photodynamic therapeutic advantages over the commonly used hematoporphyrin derivatives. Certain new amino-substituted hypocrellin B derivatives have been prepared, and both direct and reductive aminations of hypocrellin B are described. The photophysical and photochemical properties of the amino-substituted hypocrellin B derivatives were investigated, and their significantly enhanced red absorptivities and strong 1O2-generating functions qualify them as promising photodynamic therapeutic agents. In addition, the superoxide anion radical was also determined to be implicated in the photosensitization of the amino-substituted hypocrellin B derivatives.

Photosensitization with anticancer agents. 17. EPR studies of photodynamic action of hypericin: formation of semiquinone radical and activated oxygen species on illumination

When hypericin was illuminated with 580 nm light in aqueous solution, the semiquinone radical, singlet oxygen, and superoxide anion radical were detected. The formation of the semiquinone radical and activated oxygen species and the transformation and competition between them depend on the quinone and oxygen concentrations, irradiation time and intensity, and the nature of substrate. In anaerobic solution containing a high concentration of the quinone, the semiquinone radical was predominantly photoproduced. In contrast, in aerobic solution, singlet oxygen is the principal product in the photosensitization of hypericin. Besides singlet oxygen, superoxide anion radical is generated by the quinone on illumination in aerobic solution via the reduction of oxygen by the semiquinone radical, but to a lesser extent than singlet oxygen. The generation of superoxide anion radical is significantly enhanced by the presence of electron donors.