Ultraviolet radiation (UVR) has a significant impact on human skin and is the major environmental factor for skin cancer formation. It is also believed that 80% of the signs of skin aging are attributed to UVR. UVR induces inflammatory changes in the skin via the increase in oxidative stress, DNA damage vascular permeability, and fluctuation in a myriad of cytokines. Acutely, UVR causes skin inflammation and DNA damage, which manifest as sunburn (erythema). ST266 is the secretome of proprietary amnion-derived cells that have been shown to reduce inflammation and accelerate healing of various wounds by promoting migration of keratinocytes and fibroblasts in preclinical animal studies. We hypothesized that ST266 has anti-inflammatory effects that can be used to reduce ultraviolet (UV) erythema and markers of inflammation. In this study, we examined the in vivo effects of ST266 on post UV-irradiated skin by measuring erythema, level of cyclobutane pyrimidine dimer (CPD), and expression level of xeroderma pigmentosum, complementation group A (XPA). We demonstrated that ST266 has the potential to reduce the acute effects of UV-induced skin damage when applied immediately after the initial exposure. In addition, ST266 is shown to reduce erythema, increase XPA DNA repair protein, and decrease damaged DNA.

Photodynamic Therapy (PDT) is an emerging field in the treatment of various skin cancers. PDT uses photosensitizing drugs that destroy malignant cells only when activated with light. Previous studies have shown the efficacy of the DNA analog 4-thiothymidine (4tT) in photosensitizing rapidly-dividing malignant cells. Its phototoxic activity and low off-target effects make this thiobase a highly promising PDT candidate. However, the depth of tissues able to be treated with 4tT is limited by its absorption cutoff at ∼365 nm. A thiobase photosensitizer able to absorb longer wavelengths of light is needed because longer wavelengths are able to reach more invasive skin cancers. Recently, we have found that doubling the sulfur substitution of the nucleobase increases its photoreactivity and simultaneously shifts its absorption spectrum into the near-visible region (∼395 nm) where light is able to penetrate more than 100% deeper into tissues. Our initial screening with epidermoid carcinoma cells (A431) yielded two effective thiobase photosensitizers, dithiothymine (dtThy) and dithiouracil (dtUra). MTT assays revealed optimal concentrations of dtThy and dtUra, which do not significantly impact cell survival in the absence of UVA light (360-400 nm). With the addition of UVA light, the dtThy and dtUra treated cells demonstrated 42% (p<0.05) and 33% (p<0.05) decrease in survival, respectively, while the UVA exposure had no significant effect on untreated cells. Our novel agents are highly effective against skin cancer and have the ability to be photoactivated in deeper human tissues than the recently reported 4tT photosensitizer. This study fuels the possibility of investigating these new thiobase photosensitizers as UVA chemotherapeutic agents against skin cancer.

BACKGROUND:Photodynamic therapy (PDT) has been shown to be effective in the treatment of malignancies of a variety of organ systems, including the lungs, bladder, gastrointestinal tract and skin. Cutaneous lesions serve as ideal targets of PDT because of the accessibility of the skin to light. To achieve optimum results, the photosensitizer must be delivered effectively into the target layers of the skin within a practical timeframe, via noninvasive methods. AIM:To determine whether topical application of a second-generation photosensitizer, silicon phthalocyanine (Pc) 4 [SiPc(OSi(CH3)2 (CH2)3 N(CH3)2)(OH)], results in effective penetration of the skin barrier. METHODS:Penetration of Pc 4 was evaluated using standard Franz-type vertical diffusion cell experiments on surrogate materials (silicone membranes) and laser-scanning confocal microscopy of normal skin biopsy samples from human volunteers. RESULTS:The Franz diffusion data indicate that Pc 4 formulated in an ethanol/propylene glycol solution (70/30%, v/v) can penetrate the membrane at a flux that is appreciable and relatively invariant. Using the same formulation, Pc 4 uptake could be detected in human skin via laser-scanning confocal microscopy. CONCLUSION:After topical application, Pc 4 is absorbed into the epidermis in as little as 1 h, and the absorption increased with increasing time and dose. Pc 4 can be effectively delivered into human skin via topical application. The data also suggest that the degree of penetration is time- and dose-dependent.

Plasma membrane is known to have a high degree of selectivity for molecular trafficking, and it does not allow the penetration of peptides larger than 3 amino acids. Previously known exceptions of large peptides that penetrate the plasma membrane are the Arginine rich peptides such as human immunodeficiency virus (HIV)-tat peptides. However, the mechanism of cell penetration of these peptides is largely unknown. Bax Inhibiting Peptides (BIP) are penta-peptides derived from the Bax binding domain of Ku70. At present, three types of BIP have been developed. Those are: VPMLK, VPTLK, and VPALR. All of these three BIPs directly bind Bax and inhibit Bax-mediated cell death in cultured cells as well as in animal study. Surprisingly, BIPs are cell permeable and autonomously enter the cytoplasm of the cells within 1 hr. Therefore BIPs are recognized as new members of cell penetration peptides. In this study, we investigated the mechanism of cell penetration of BIPs. DAMI cells (a human megakaryocyte cell line) and HeLa cells were used to investigate the detailed mechanism of cell penetration of BIPs. To detect the cell entry of BIPs, fluorescent dyes (fluorescein or tetramethylrodhamine) were conjugated to the N-terminus of BIPs and the cytoplasmic localization of BIPs was confirmed by confocal microscopy. Cell Penetration activities of BIPs were detected at 1 uM concentration in the culture medium. The significant accumulation of BIPs in the cytoplasm were detected within 1 hour of incubation both at 4 °C and 37 °C, suggesting that ATP-independent mechanism of cell penetration of BIP exists. However, cellular uptake of BIPs reaches plateau at 100 uM at 4 °C, whereas it increases in a dose dependent manner up to 1 mM at 37 °C without any sign of cytotoxicity. These results suggest that there are at least two mechanisms contributing to the cell penetration of BIPs that are, “ATP-independent (4 °C)” and “ATP-dependent (37 °C)” mechanisms. In addition to BIPs, we generated a series of mutated BIPs that do not bind Bax but retain cell-penetrating activities. We performed competition assay using fluorescence dye-labeled and non-labeled BIP (and the mutant BIPs), and the preliminary results suggest that there is a specific receptor for each peptide for its delivery into the cells. Our data also indicates that BIPs can deliver a cargo molecule (e.g. fluorescent dye) with at least the same molecular weight. Unlike other cell penetrating peptides, BIP has minimum toxicity due to its nature to inhibit Bax-mediated cell death. Along with the new data showing that BIP protects cells from pathological damages in cell culture and animal model, we will discuss the potential application of BIPs as a new type of drug delivery tool.

Phthalocyanine (Pc) 4, like many photosensitizers for photodynamic therapy (PDT), localizes to intracellular membranes, especially mitochondria. Pc 4-PDT photodamages Bcl-2 and Bcl-xL, antiapoptotic proteins interacting with the permeability transition pore complex that forms at contact sites between the inner and outer mitochondrial membranes. These complexes and the inner membrane are unique in containing the phospholipid cardiolipin. Nonyl-acridine orange (NAO) is a specific probe of cardiolipin. Here we show evidence for fluorescence resonance energy transfer from NAO to Pc 4, defining a binding site for the photosensitizer. This observation establishes an innovative tool for exploring the localization of other photosensitizers and additional fluorescent, mitochondrion-localizing drugs having appropriate spectral properties.

In response to photodynamic therapy (PDT), many cells in culture or within experimental tumors are eliminated by apoptosis. PDT with photosensitizers that localize in or target mitochondria, such as the phthalocyanine Pc 4, causes prompt release of cytochrome c into the cytoplasm and activation of caspases-9 and -3, among other caspases, that are responsible for initiating cell degradation. Some cells appear resistant to apoptosis after PDT; however, if they have sustained sufficient damage, they will die by a necrotic process or through a different apoptotic pathway. In the case of PDT, the distinction between apoptosis and necrosis may be less important than the mechanism that triggers both processes, since critical lethal damage appears to occur during treatment and does not require the major steps in apoptosis to be expressed. We earlier showed, for example, that human breast cancer MCF-7 cells that lack caspase-3 are resistant to the induction of apoptosis by PDT, but are just as sensitive to the loss of clonogenicity as MCF-7 cells stably expressing transfected procaspase-3. Many photosensitizers that target mitochondria specifically attack the antiapoptotic protein Bcl-2, generating a variety of crosslinked and cleaved photoproducts. Recent evidence suggests that the closely related protein Bcl-xL is also a target of Pc 4-PDT. Transient transfection of an expression vector encoding deletion mutants of Bcl-2 have identified the critical sensitive site in the protein that is required for photodamage. This region contains two alpha helices that form a secondary membrane anchorage site and are thought to be responsible for pore formation by Bcl-2. As specific protein targets are identified, we are becoming better able to model the critical events in PDT-induced cell death.