Ground and excited state interactions of metalloporphyrin PtTMPyP4 with polynucleotides [poly(dG-dC)]2 and [poly(dA-dT)]2

The ground- and excited-state interactions of Pt(ii) meso-tetrakis(4-N-methylpyridyl)porphyrin (PtTMPyP4) with polynucleotides [poly(dG-dC)]2 and [poly(dA-dT)]2 have been investigated using UV/visible, circular dichroism, and steady-state and time-resolved emission spectroscopy. PtTMPyP4 intercalates into [poly(dG-dC)]2 with K∼ 10(6) M(-1). When bound to [poly(dG-dC)]2 in aerated solution there is a six-fold emission enhancement with 18 nm red-shift in emission maximum. Emission lifetimes are biexponential. In the presence of [poly(dA-dT)]2 at least two distinct groove-binding modes are observed, depending on the binding ratio. In [poly(dA-dT)]2 the emission intensity increases by a maximum factor of 17 with no shift in the emission spectrum. Three exponentials were required for lifetime fitting. The lower extent of emission enhancement in the presence of [poly(dG-dC)]2 suggests that a slow electron transfer may take place to guanine, which is significantly less efficient than that previously observed for PtTMPyP4 in the presence of guanosine 5'-monophosphate (GMP). The results are compared to those previously recorded with free base H2TMPyP4.

Spectroscopic study of associated systems formed between water-soluble cationic porphyrins or their copper (II) complexes and nucleic building blocks

The association process between two water soluble cationic porphyrins, 5,10,15,20-tetrakis[4-(trimethyl-ammonio)phenyl]-21H,23H-porphine tetra-p-tosylate (H2TTMePP) and 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine tetra-p-tosylate (H2TMePyP), as well as their Cu (II) complexes, with five series of nucleic agents has been studied using UV-VIS spectroscopy in aqueous solutions. During the titration with nucleic compounds the bathochromic effect of porphyrins absorption spectra can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using a curve-fitting procedure (KAC of the order of magnitude of 103–105 mol−1). It has been shown that the interactions of H2TTMePP with nucleic agents are much stronger than interactions of H2TMePyP, which is most likely related to the kind and the size of the porphyrin substituent groups partaking in the process of stacking. The strength of the observed associated systems increases generally in a series: nucleic base

Toward a 3D cellular model for studying in vitro the outcome of photodynamic treatments: accounting for the effects of tissue complexity

Clinical therapies have traditionally been developed using two-dimensional (2D) cell culture systems, which fail to accurately capture tissue complexity. Therefore, three-dimensional (3D) cell cultures are more attractive platforms to integrate multiple cues that arise from the extracellular matrix and cells, closer to an in vivo scenario. Here we report the development of a 3D cellular model for the in vitro assessment of the outcome of oxygen- and drug-dependent therapies, exemplified by photodynamic therapy (PDT). Using a synthetic self-assembling peptide as a cellular scaffold (RAD16-I), we were able to recreate the in vivo limitation of oxygen and drug diffusion and its biological effect, which is the development of cellular resistance to therapy. For the first time, the production and decay of the cytotoxic species singlet oxygen could be observed in a 3D cell culture. Results revealed that the intrinsic mechanism of action is maintained in both systems and, hence, the dynamic mass transfer effects accounted for the major differences in efficacy between the 2D and 3D models. We propose that this methodological approach will help to improve the efficacy of future oxygen- and drug-dependent therapies such as PDT.

Singlet oxygen in antimicrobial photodynamic therapy: photosensitizer-dependent production and decay in E. coli

Several families of photosensitizers are currently being scrutinized for antimicrobial photodynamic therapy applications. Differences in physical and photochemical properties can lead to different localization patterns as well as differences in singlet oxygen production and decay when the photosensitizers are taken up by bacterial cells. We have examined the production and fate of singlet oxygen in Escherichia coli upon photosensitization with three structurally-different cationic photosensitizers, namely New Methylene Blue N (NMB), a member of the phenothiazine family, ACS268, a hydrophobic porphyrin with a single cationic alkyl chain, and zinc(II)-tetramethyltetrapyridinoporphyrazinium salt, a phthalocyanine-like photosensitizer with four positive charges on the macrocycle core. The kinetics of singlet oxygen production and decay indicate different localization for the three photosensitizers, whereby NMB appears to localize in an aqueous-like microenvironment, whereas ACS268 localizes in an oxygen-shielded site, highly reactive towards singlet oxygen. The tetracationic zinc(II) tetrapyridinoporphyrazine is extensively aggregated in the bacteria and fails to produce any detectable singlet oxygen.

Effect of aggregation of a cationic phthalocyanine in micelles and in the presence of human serum albumin

The photophysical properties of tetrakis(1,1-dimethyl-2-trimethylammonium)ethylphthalocyaninato zinc(II) tetraiodide (I) – a water-soluble cationic phthalocyanine – are presented in the presence of human serum albumin (HSA) and in micelles of sodium dodecylsulfate ( SDS ) and hexadecyltrimethylammonium chloride ( CTAC ). Spectrophotometric measurements showed that the surfactants SDS and CTAC induce monomerization of I, although the latter less efficiently than the former. This effect is less pronounced in the presence of HSA. The strength of this effect is evaluated through dimerization constants, which are Kd = (5 ± 1) × 105 m−1 in SDS , (1.5 ± 0.5) × 106 M −1 in CTAC , and (1.8 ± 0.9) × 106 M −1 in HSA. Fluorescence experiments confirm that aggregation of I drops as the concentration of surfactant is raised. Triplet quantum yields also decreased upon aggregation and were Φ T = 0.59, 0.16, and < 0.01 in SDS , CTAC , and HSA, respectively. These results indicate that the affinity of I for the environment is not just due to ionic interactions; hydrophobic interactions play an equally important role.

Triplet-state dynamics of a metalloporphyrin photosensitiser (PtTMPyP4) in the presence of halides and purine mononucleotides

The photophysical properties of Pt(II) meso-tetrakis(4-N-methylpyridyl)porphyrin (PtTMPyP4) have been investigated in the presence of purine mononucleotides using emission and transient UV/visible/near-IR spectroscopy. While both adenosine 5'-monophosphate (AMP) and guanosine 5'-monophosphate (GMP) form 1:1 and 1:2 complexes with PtTMPyP4, the effect on the triplet lifetime is different. With AMP, complexation gives rise to an enhancement of lifetime and quantum yield due to shielding from dissolved oxygen and a slight decrease in the non-radiative decay rate. When complexed with GMP, quenching is observed consistent with photoinduced electron transfer from guanine to triplet-excited PtTMPyP4, due to both dynamic quenching of the porphyrin and to short-lived emission from 1:1 (67 ns) and 1:2 (400 ns) complexes. No charge-separated photoproducts are observed by transient UV/vis/near-IR absorption spectroscopy on the nanosecond timescale, suggesting that rapid reverse electron transfer may prevent type 1 DNA damage.

Kinetics of singlet oxygen photosensitization in human skin fibroblasts

The roles played by singlet oxygen ((1)O(2)) in photodynamic therapy are not fully understood yet. In particular, the mobility of (1)O(2) within cells has been a subject of debate for the last two decades. In this work, we report on the kinetics of (1)O(2) formation, diffusion, and decay in human skin fibroblasts. (1)O(2) has been photosensitized by two water-soluble porphyrins targeting different subcellular organelles, namely the nucleus and lysosomes, respectively. By recording the time-resolved near-IR phosphorescence of (1)O(2) and that of its precursor the photosensitizer's triplet state, we find that the kinetics of singlet oxygen formation and decay are strongly dependent on the site of generation. (1)O(2) photosensitized in the nucleus is able to escape out of the cells while (1)O(2) photosensitized in the lysosomes is not. Despite showing a lifetime in the microsecond time domain, (1)O(2) decay is largely governed by interactions with the biomolecules within the organelle where it is produced. This observation may reconcile earlier views that singlet oxygen-induced photodamage is highly localized, while its lifetime is long enough to diffuse over long distances within the cells.

DNA binding studies of a new dicationic porphyrin. Insights into interligand interactions

Cationic porphyrins have an affinity for DNA and potential for applications in the fields of photodynamic therapy and cellular imaging. This report describes a new dicationic porphyrin, 5,15-dimethyl-10,20-di(N-methylpyridinium-4-yl)porphyrin, abbreviated H2tMe2D4. Although tetrasubstituted, H2tMe2D4 presents modest steric requirements and forms in reasonable yield by a "2+2" synthetic method. Accordingly, studies of the zinc(II)- and copper(II)-containing derivatives, Zn(tMe2D4) and Cu(tMe2D4), have also been possible. Methods used to characterize DNA-binding motifs include absorption, emission, linear, and circular dichroism spectroscopies, as well as viscometry. An unusually detailed picture of porphyrin uptake emerges. As the ratio of DNA to porphyrin increases during a typical titration, H2tMe2D4 or Cu(tMe2D4) initially aggregates on the host and then shifts to intercalative binding at close quarters before finally dispersing into non-interacting intercalation sites of the host. Emission studies of the copper(II) porphyrin have been very valuable. The existence of a measurable signal is diagnostic of intercalative binding, and the saturation behavior establishes that internalization typically monopolizes approximately three base pairs. In the moderate loading regime, emission data are most telling because dipole-dipole interactions between near-neighbor porphyrins tend to confuse other spectroscopic assays. The third ligand, Zn(tMe2D4), behaves differently in that the uptake is a strictly cooperative process. The mode of binding also varies with the base content of the DNA host. When the DNA is rich in A=T base pairs, the porphyrin remains five-coordinate and binds externally; however, Zn(tMe2D4) loses its axial ligand and binds by intercalation if the host contains only G[triple bond]C base pairs.