Targeted photodynamic therapy via receptor mediated delivery systems.

Targeted photodynamic therapy (PDT) offers the opportunity of enhancing photodynamic efficiency by directly targeting diseased cells and tissues. While antibody-conjugates have received the most attention, cellular transformations offer numerous other potent targets to exploit during the delivery of photosensitizers (PSs) for PDT. Alterations in receptor expression, increased levels of specific cell surface membrane lipids and proteins as well as changes in the cellular microenvironment all occur in diseased cells. Along with other biochemical and physiological changes that occur during diseased and malignant cell transformation, these factors have been utilized in order to improve the efficacy of PDT. Attempts have been made to either increase the uptake of the dye by the target cells and tissues or to improve subcellular localization so as to deliver the dye to photosensitive sites within the cells. This review discusses various PS bioconjugates that utilize these factors and summarizes the results obtained to date.

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.

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.