Photodynamic properties of amphiphilic derivatives of aluminum tetrasulfophthalocyanine.

Photodynamic therapy (PDT) is a promising treatment modality that has recently been accepted in clinics as a curative or palliative therapy for cancer and other nonmalignant conditions. Phthalocyanines (Pc) are attractive photosensitizers for PDT because of their enhanced photophysical and photochemical properties. The overall charge and solubility of Pc play a major role in their potential usefulness for PDT. A series of amphiphilic derivatives of tetrasulfonated aluminum Pc (AlPcS4) was prepared by substituting one of the four sulfonate groups with aliphatic side chains of 4, 8, 12 and 16 carbon atoms. The photodynamic properties of the derivatives were compared with those of AlPcS4 and the adjacent disulfonated aluminum Pc. Parameters studied included reversed-phase high-performance liquid chromatography (HPLC) retention times, capacity to generate singlet oxygen (1O2), in vitro cell uptake and phototoxicity, as well as PDT response of transplantable EMT-6 tumors in mice. The monomerized AlPcS4 derivatives showed similar or higher capacities to generate 1O2 as compared with the parent AlPcS4 as measured from relative L-tryptophan photooxidation yields. A549 cell uptake of the AlPcS4 derivatives decreased in the following order: AlPcS4(C16) > AlPcS4(C12) > AlPcS4(C8) > AlPcS4(C4). Human low-density lipoprotein at high concentrations (40 micrograms/mL) completely prevented uptake, whereas at 4 micrograms/mL uptake was decreased for the more lipophilic compounds and yet remained unaffected for the more hydrophilic dyes. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, A549 cell survival was assessed; it showed that photocytotoxic activity varied directly with the HPLC retention times, i.e. more hydrophilic compounds were less phototoxic. As 1O2 yields were similar for the four substituted AlPcS4 derivatives, it was postulated that the increased cytotoxic activity was caused by enhanced subcellular localization as a result of the long aliphatic side chains. These amphiphilic compounds proved to be photodynamically potent against the EMT-6 mouse mammary tumor model implanted in Balb/c mice. At dye doses of 0.2 mumol/kg and a fluence of 400 J/cm2 complete tumor regression was observed with no morbidity. The substitution of AlPcS4 with long aliphatic chains on the macrocycle greatly enhances its photodynamic efficacy both in vitro and in vivo.

Interstrand cross-link induction by UV radiation in bromodeoxyuridine-substituted DNA: dependence on DNA conformation.

DNA interstrand cross-links (ICL) can be induced both by natural products (e.g., psoralens with UVA) and by chemical agents, some of which are used in chemotherapy (e.g., Carboplatin and mitomycin C). Here, we report the formation of ICL by UV radiation in brominated DNA, but only for very specific conformations. The quantum yields for strand break and cross-link formation depend on the wavelength with a maximum near 280 nm. It is known that the photosensitization of DNA by bromodeoxyuridine (BrdUrd) results mainly from the electron affinity of bromine, leading to the irreversible formation of 2'-deoxyuridin-5-yl radicals (dUrd*) upon the addition of an electron from an adjacent adenosine. It is well documented that the photolytic loss of the bromine atom is greatly suppressed in single-stranded DNA versus that in double-stranded DNA. To study this behavior, we have used two models of BrdUrd-mediated sensitization: one consists of a DNA duplex containing a bulge, formed by five mismatched bases, including the BrdUrd, and the other consists of completely duplex DNA. UV irradiation induces much higher levels of single-strand breaks (ssb) in the completely duplex DNA at the BrdUrd site compared to the DNA with a bulge. However, in completely duplex DNA, ssb appear only in the brominated strand, whereas in the bulged duplex DNA, ssb occur on both strands. Most importantly, we also observe formation of interstrand cross-links in bulged duplex DNA in the BrdUrd region. Thus, we propose that UV irradiation of cells containing BrdUrd incorporated randomly into duplex DNA will create many ssb, whereas BrdUrd present in DNA bulges or open regions in double-stranded DNA (transcription bubbles, replication forks) will lead to potentially lethal damage in both strands in the form of ICL. These findings may help explain the potent clinical antiviral activity of IdUrd and BrdUrd (e.g., IdUrd is used to treat eye infections caused by the herpes virus) and suggest that ICL formation may be a very specific probe for identifying single-stranded regions in the DNA of living cells. In addition, this model system provides an excellent means of introducing ICL for studies on their repair and biological consequences.

Structure-photodynamic activity relationships of substituted zinc trisulfophthalocyanines.

To identify optimal features of metalated sulfophthalocyanine dyes for their use as photosensitizers in the photodynamic therapy of cancer, we synthesized a series of alkynyl-substituted trisulfonated phthalocyanines and compared their amphiphilic properties to a number of parameters related to their photodynamic potency. Varying the length of the substituted alkynyl side-chain modulates the hydrophobic/hydrophilic properties of the dyes providing a linear relationship between their n-octanol/water partition coefficients and retention times on reversed-phase HPLC. Aggregate formation of the dyes in aqueous solution increased with increasing hydrophobicity while monomer formation was favored by the addition of serum proteins or organic solvent. Trisulfonated zinc phthalocyanines bearing hexynyl and nonynyl substituents exhibited high cellular uptake with strong localization at the mitochondrial membranes, which coincided with effective photocytotoxicity toward EMT-6 murine mammary tumor cells. Further increase in the length of the alkynyl chains (dodecynyl, hexadecynyl) did not improve their phototoxicity, likely resulting from extensive aggregation of the dyes in aqueous medium and reduced cell uptake. Aggregation was evident from shifts in the electronic spectra and reduced capacity to generate singlet oxygen. When monomerized through the addition of Cremophor EL all sulfonated zinc phthalocyanines gave similar singlet oxygen yields. Accordingly, differences in the tendency of the dyes to aggregate do not appear to be a determining factor in their photodynamic potency. Our results confirm that the latter in particular relates to their amphiphilic properties, which facilitate cell uptake and intracellular localization at photosensitive sites such as the mitochondria. Combined, these factors play a significant role in the overall photodynamic potency of the dyes.

Regulation of GTP-binding protein alpha q (Galpha q) signaling by the ezrin-radixin-moesin-binding phosphoprotein-50 (EBP50).

Although ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) is a PDZ domain-containing protein known to bind to various channels, receptors, cytoskeletal elements, and cytoplasmic proteins, there is still very little evidence for a role of EBP50 in the regulation of receptor signal transduction. In this report, we show that EBP50 inhibits the phospholipase C (PLC)-beta-mediated inositol phosphate production of a Galpha(q)-coupled receptor as well as PLC-beta activation by the constitutively active Galpha(q)-R183C mutant. Coimmunoprecipitation experiments revealed that EBP50 interacts with Galpha(q) and to a greater extent with Galpha(q)-R183C. Agonist stimulation of the thromboxane A(2) receptor (TP receptor) resulted in an increased interaction between EBP50 and Galpha(q), suggesting that EBP50 preferentially interacts with activated Galpha(q). We also demonstrate that EBP50 inhibits Galpha(q) signaling by preventing the interaction between Galpha(q) and the TP receptor and between activated Galpha(q) and PLC-beta1. Investigation of the EBP50 regions involved in Galpha(q) binding indicated that its two PDZ domains are responsible for this interaction. This study constitutes the first demonstration of an interaction between a G protein alpha subunit and another protein through a PDZ domain, with broad implications in the regulation of diverse physiological systems.

Attenuation of photodynamically induced apoptosis by an RGD containing peptide.

Research efforts have focused on the improvement of already established photodynamic therapy (PDT) protocols. The use of adjunct therapies is one such route. The integrin class of receptors mediates extracellular matrix signals through a complex maze of intertwining cellular pathways. The Arg-Gly-Asp (RGD) motif is known to bind to several of the 25 known integrin receptor types. Soluble RGD peptides under most circumstances induce apoptosis in a number of cell lines In this study, the effect of an RGD-containing peptide on the photodynamic action of aluminium disulfophthalocyanine (A1PcS(2adj)) was investigated. Adenocarcinoma lung cancer cells (A549) and murine mammary cancer cells (EMT-6) were treated with A1PcS(2adj) in the presence of soluble RGD. At elevated RGD concentrations (10 mM) apoptosis was induced by the peptide alone. It was shown that at lower concentrations, RGD abrogated the apoptotic effect of PDT in both cell lines, as assessed by an MTT cytotoxicity assay, nucleosomal DNA laddering and the formation of apoptotic bodies. RGD protection against apoptosis was more pronounced in the A549 receptor positive cell line which exhibits over 70% cell survival when using 100 microM RGD peptide under LD90 conditions. Different parameters were investigated to clearly establish that the attenuation of cell killing was not solely due to quenching of the excited species by the peptide. Indeed, the phenomenon is not photophysical but biological.