Hypericum perforatum L. extract – Novel photosensitizer against human bladder cancer cells

The polar methanolic fraction (PMF) of the Hypericum perforatum L. extract has recently been developed and tested as a novel, natural photosensitizer for use in the photodynamic therapy (PDT), and photodynamic diagnosis (PDD). PMF has been tested on HL-60 leukemic cells and cord blood hemopoietic progenitors. In the present study, the efficacy of PMF as a phototoxic agent against urinary bladder carcinoma has been studied using the T24 (high grade metastatic cancer), and RT4 (primary low grade papillary transitional cell carcinoma) human bladder cancer cells. Following cell culture incubation, PMF was excited using 630 nm laser light. The photosensitizer exhibited significant photocytotoxicity in both cell lines at a concentration of 60microg/ml, with 4-8 J/cm(2) light dose, resulting in cell destruction from 80% to 86%. At the concentration of 20microg/ml PMF was not active in either cell line. These results were compared with the results obtained in the same cell lines, under the same conditions with a clinically approved photosensitizer, Photofrin. Photofrin was used in the maximum clinically tolerable dose of 4microg/ml, and it was also excited with 630 nm laser light. In the T24 cell Photofrin exhibited slightly less photocytotocixity, compared with PMF, resulting in 77% cell death with 8J/cm(2) light dose. However, against the RT4 cells Photofrin resulted in minimal cell death (9%) with even 8J/cm(2) light dose. Finally, the type of cell death induced by PMF photoactivation was studied using flow cytometry and DNA laddering. Cell death by PMF photodynamic action in these two bladder cell lines is caused predominently by apoptosis. The reported significant photocytotoxicity, selective localization, natural abundance, easy, and inexpensive preparation, underscore that the PMF extract hold the promise of being a novel, effective PDT photosensitizer.

Photophysical properties of Hypericum perforatum L. extracts--novel photosensitizers for PDT

We report the preparation of the methanolic extract (ME), and polar methanolic fraction (PMF) from the plant Hypericum perforatum L. The extracts contain various photosensitizing constituents such as naphthodianthrone derivatives (in 1.37% w/w), and chlorophylls (in 0.08% w/w). Upon light emission these constituents can be activated, providing photodynamic properties to the extracts, and making them a potent, new class, natural photosensitizers for use in photodynamic therapy (PDT), and photodynamic diagnosis (PDD). The absorbance spectra of the extracts are similar to the spectrum of hypericin, the main naphthodianthrone identified within, with two major bands at 548 and 590 nm. The fluorescence spectra in ethanol exhibit two main bands around 595 and 640 nm, in accordance with the spectrum of pure hypericin. The fluorescence intensity of PMF at 595 nm is only eight times less than the intensity of pure hypericin at the same wavelength, even though its hypericin concentration is only 0.57% w/w. The dependence of the PMF fluorescence signal on the pH of the medium, alone and in comparison with the signal of hypericin, has been investigated. PMF signal fades steadily, and smoothly both in acidic, and basic environment.

Does Hypericum perforatum L. extract show any specificity as photosensitizer for HL-60 leukemic cells and cord blood hemopoietic progenitors during photodynamic therapy?

Autologous bone marrow transplantation is a therapeutic modality that increases the survival rates for children with malignancies with poor prognosis but relapse rates are high and attributed partially to the existence of residual malignant cells. Photodynamic treatment (PDT) has been developed among purging strategies. We investigated the effect of the methanolic extract (ME) and its polar methanolic fraction (PMF) of Hypericum perforatum L., as a new photosensitizer for the leukemic cell line HL-60 and cord blood (CB) hemopoietic progenitors as well as the subcellular localization of the photosensitizer.

METHODS

ME and PMF were prepared after extraction of the dry herb with methanol (ME), followed by liquid-liquid extraction with petroleum ether (PMF). Cells were incubated with the extracts before irradiation with Nd-Yvo Laser. Various concentrations of PMF or ME as well as irradiation doses were tested. Following irradiation, cell viability was determined by trypan blue in continuous liquid cultures for HL-60 cells and in clonogenic assays for CB cells. The subcellular localization of the photosensitizer was determined by confocal microscopy.

RESULTS

Laser photoirradiation in the presence of both PMF and ME induces the killing of HL-60 cells. This effect is dose dependent. No CFU-GM and BFU-E growth was observed from CB mononuclear cells under the tested experimental conditions. Confocal microscopy revealed that the extracts localize mainly in the cytoplasm of the cells.

CONCLUSIONS

PDT with both PMF and ME induces the killing of HL-60 leukemic cells and the optimal conditions of treatment were determined. This effect of PDT/PMF was also exerted on CB progenitor cells indicative of the non-selective uptake of the photosensitizer by malignant cells. Though this suggests that PDT/PMF cannot be helpful in autologous bone marrow purging, these novel extracts can however be beneficial in the PDT treatment of tumors given their photostability, low toxicity and low cost.

Impaired accumulation of a cationic photosensitizing agent by a cell line exhibiting multidrug resistance

Transport and accumulation of copper benzochlorin iminium salt (CDS1), a cationic photosensitizing agent, were examined using the P388/ADR murine leukemia, which exhibits the MDR (multidrug resistance) phenotype, and the wild-type parent cell line, P388. The recent availability of radioactive CDS1 permitted kinetic studies at drug levels in the submicromolar range. Exclusion of CDS1 by P388/ADR cells could be demonstrated, indicating that this agent is a substrate for the outward transport system associated with MDR. These results have implications with regard to the efficacy of cationic photosensitizers against this common neoplastic phenotype. The CDS1 was readily accumulated by P388 cells and by P388/ADR cells when the outward transport system was inhibited. Under these conditions, CDS1 was tightly bound and could not be washed out even when the outward transport system was reactivated.

Iminium salt benzochlorins: structure-activity relationship studies

An iminium salt of copper(II) octaethylbenzochlorin (CDS1) is an effective new photosensitizer despite the fact that it does not produce singlet oxygen, does not fluoresce and the triplet state lifetime can only be less than 20 ns. A number of octaethylbenzochlorin derivatives were synthesized in order to determine the structural component(s) that is(are) responsible for the photodynamic action of these new photosensitizers. Studies utilizing the N-(4-[5-nitro-2-furyl]-2-thiazolyl)formamide-induced urothelial tumor revealed that the coexistence of the copper inside the aromatic ring and the iminium group at the meso position are required for the photodynamic effect.

Iminium salt of copper benzochlorin (CDS1), a novel photosensitizer for photodynamic therapy: mechanism of cell killing

The mechanism of cell killing by CDS1, an iminium salt of octaethylbenzochlorin with copper in the aromatic ring, in combination with light from a noncoherent light source was investigated. Using a standard clonogenic assay and the AY-27 FANFT tumor line, photoactivation of CDS1 was shown to be cytotoxic. The photodynamic cell killing ability of CDS1 required the presence of molecular oxygen. The reactive species generated by light activation of CDS1 were effectively quenched by N,N'-diphenyl-p-phenylenediamine. Additionally, the photodynamic effect of CDS1 was not enhanced by deuterium oxide. To characterize the reactive oxygen species generated by the photoactivation of CDS1 the well-characterized erythrocyte ghost model was used. Superoxide dismutase and catalase were potent inhibitors of CDS1-induced lipid peroxidation of erythrocyte membranes. Sodium azide only partially inhibited lipid peroxidation. These findings differed from the known singlet oxygen generator, tin (II) etiopurpurin dichloride (SnET2). Sodium azide was a potent inhibitor of SnET2-induced lipid peroxidation, whereas superoxide dismutase and catalase were totally ineffective. Based on these results, we conclude that CDS1 requires the presence of molecular oxygen for cell killing to occur but appears to act primarily through a non-singlet oxygen mechanism.

Copper benzochlorin, a novel photosensitizer for photodynamic therapy: effects on a transplantable urothelial tumor

An iminium salt of octaethylbenzochlorin with copper in the aromatic ring, CDS1, was tested for its tumoricidal effects on the AY-27 N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide tumor line. CDS1 was found to be an effective photosensitizer in vivo when used in combination with either a xenon arc lamp or a pulsed alexandrite laser. Hemodynamically, CDS1 and light caused a rapid decrease in tumor blood flow. Skin photosensitization was found to be minimal when drug-injected mice were illuminated in a solar simulator.

Observations on the synthesis and in vivo photodynamic activity of some benzochlorins

An improved synthesis of benzochlorins is reported. Demetallation of the meso-hydroxymethylvinyl derivative of octaethylporphyrin, followed by treatment with sulfuric acid results in cyclization to generate the corresponding octaethylbenzochlorin in high yield. Prolonged treatment with acid generates the sulfonated derivative. These sensitizers were shown to be efficient photodynamic agents in vivo. Animals bearing a transplanted N-[4-(5-nitro-2-furyl)-2-thiazoly]formamide induced urothelial tumor were treated with either the benzochlorin or its sulfonated derivative. Irradiation of tumors 24 h later resulted in a significant tumoricidal effect in a short term assay. We conclude that benzochlorins warrant further examination as potential agents for use in photodynamic therapy.

Synthesis and in vivo photodynamic activity of some bacteriochlorin derivatives against bladder tumors in rodents

Bacteriochlorins have been suggested as potential photosensitizers for use in photodynamic therapy. We have shown that bacteriochlorin-like macrocycles can be generated through cyclization of either 5,10- or 5,15-bis[(ethoxycarbonyl)vinyl]porphyrins; however, the resulting products are rapidly decomposed on exposure to air. More stable systems can be generated by Diels-Alder reactions between dienophiles such as dimethyl acetylenedicarboxylate or tetracyanoethylene, and vinylporphyrinones. Although spectroscopic properties of these latter products resemble those of porphyrinones rather than bacteriochlorins, in vivo studies using the N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide-induced rat bladder tumor (AY-27) transplanted into Fisher CDF (F344)/CrlBr rats demonstrated a powerful photodynamic response.

Tin etiopurpurin dichloride-sensitized lipid photooxidation of erythrocyte membranes

Tin(IV) etiopurpurin dichloride (SnET2 x 2Cl) is a photosensitizer which has been shown to be an effective photodynamic agent for the treatment of transplantable animal tumors in vivo. The purpose of this study was to understand the effect of SnET2 x 2Cl on membrane lipid peroxidation. When erythrocyte membranes were exposed to visible light in the presence of SnET2 x 2Cl, lipid peroxidation was observed. An accumulation of lipid hydroperoxides and an increase in lipid fluorescence were also observed. Thin layer chromatography of lipid extracts from photooxidized membrane revealed photoperoxide products derived from phospholipid. Investigations into the mechanism(s) of lipid peroxidation by SnET2 x 2Cl and light-sensitized membranes were also performed. Results indicate that singlet oxygen (1O2) plays a major role in lipid peroxidation.

Synthesis and in vivo activity of some porphyrindione derivatives with potential in photodynamic therapy

A number of synthetic bacteriochlorins were prepared from porphyrindiones. The potential of these compounds as sensitizers for photodynamic therapy was examined using the FANFT-induced urothelial cell carcinoma (AY-27) transplanted into rats. In a number of cases, tumor regression was significant following treatment with both drug and light.

Diels-Alder adducts of vinyl porphyrins: synthesis and in vivo photodynamic effect against a rat bladder tumor

Benzoporphyrin derivatives have been proposed as potential photosensitizers for photodynamic therapy. We have prepared a number of benzoporphyrin derivatives and tested their effect, in combination with red light, on the N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) induced rat bladder tumor (AY-27) transplanted into Fischer CDF(F344)/CrlBr rats. Tetracyanoethylene (TCNE) adducts showed very little activity, which may be attributable to their poor tumor uptake or to chemical instability of the adduct under physiological conditions. However, dimethyl acetylenedicarboxylate (DMAD) adducts tested showed greater cytotoxic effect than hematoporphyrin derivative and similar activities to metallopurpurins when tested under the same protocol.