Photosensitization and redox signaling

Conjugated Polymer-Photosensitizers for Cancer Photodynamic Therapy and Their Multimodal Treatment Strategies

Conjugated polymers (CPs) have emerged as promising candidates for photodynamic therapy (PDT) in cancer treatment due to their high fluorescence quantum yield, excellent photostability, and remarkable reactive oxygen species (ROS) generation capability. This review systematically summarizes molecular design strategies to augment CP photosensitivity efficiency, including: (1) constructing donor-acceptor (D-A) alternating structures, (2) incorporating aggregation-induced emission (AIE) moieties, (3) employing heavy-atom effects, and (4) designing hyperbranched architectures. In addition, considering the limitations of monotherapy like tumor heterogeneity, we will further discuss the synergistic treatment strategies of CP-mediated PDT in combination with other therapeutic modalities, including photothermal therapy (PTT)-PDT, immunotherapy-PDT, chemotherapy-PDT, Chemiluminescence (CL)-PDT, diagnostic technology-PDT, and chemodynamic therapy (CDT)-PDT. These multimodal approaches leverage complementary mechanisms to achieve enhanced tumor eradication efficacy.

Inhibition of NF-κB in Tumor Cells Exacerbates Immune Cell Activation Following Photodynamic Therapy

Although photodynamic therapy (PDT) yields very good outcomes in numerous types of superficial solid cancers, some tumors respond suboptimally to PDT. Novel treatment strategies are therefore needed to enhance the efficacy in these therapy-resistant tumors. One of these strategies is to combine PDT with inhibitors of PDT-induced survival pathways. In this respect, the transcription factor nuclear factor κB (NF-κB) has been identified as a potential pharmacological target, albeit inhibition of NF-κB may concurrently dampen the subsequent anti-tumor immune response required for complete tumor eradication and abscopal effects. In contrast to these postulations, this study demonstrated that siRNA knockdown of NF-κB in murine breast carcinoma (EMT-6) cells increased survival signaling in these cells and exacerbated the inflammatory response in murine RAW 264.7 macrophages. These results suggest a pro-death and immunosuppressive role of NF-κB in PDT-treated cells that concurs with a hyperstimulated immune response in innate immune cells.

Calorie restriction modulates redox-sensitive AP-1 during the aging process

Oxidative stress is claimed to be a major cause of aging. Recent data suggest that calorie restriction (CR) prolongs life span by its ability to retard aging, possibly by regulating the intracellular redox status through its antioxidative actions. Currently, there is little information showing the influences of age and CR on the redox-sensitive transcription factor activator protein-1 (AP-1). In the present study, we investigated how age affects the status of AP-1 and whether CR modulates the age effect. For our study, we used the kidney from male Fischer 344 rats, ages 6, 12, 18, and 24 months fed ad libitum (AL) or a CR diet. Results from our study showed that AP-1 binding activity markedly increases with age, while CR keeps this activity at the level of 6-month-old rats. We found that c-Jun and c-Fos protein levels increase during aging, and that aging induces phosphorylation of c-Jun, which might enhance AP-1 transcriptional activity. For CR's action, we found that in the nucleus of aged rats, AP-1 activation was blunted by decreasing c-Jun and c-Fos levels and inhibiting c-Jun protein phosphorylation. Results also indicated that matrix metalloproteinase-13 and heme oxygenase-1, which have an AP-1 binding site in their promoter regions, have a similar tendency toward AP-1 binding activity. Based on the data of these findings, we concluded that AP-1 activity increases in rat kidney with age and that CR reduces AP-1 activity.

Cell signaling (mechanism and reproductive toxicity): redox chains, radicals, electrons, relays, conduit, electrochemistry, and other medical implications

This article deals with a novel, simple, integrated approach to cell signaling involving basic biochemical principles, and their relationship to reproductive toxicity. Initially, an overview of the biological aspects is presented. According to the hypothetical approach, cell signaling entails interaction of redox chains, involving initiation, propagation, and termination. The messengers are mainly radicals and electrons that are generated during electron transfer (ET) and hydrogen atom abstraction reactions. Termination and initiation processes in the chain occur at relay sites occupied by redox functionalities, including quinones, metal complexes, and imines, as well as redox amino acids. Conduits for the messengers, comprising species with nonbonding electrons, are omnipresent. Details are provided for the various electron transfer processes. In relation to the varying rates of cell communication, rationale is based on electrons and size of radicals. Another fit is similarly seen in inspection of endogenous precursors of reactive oxygen species (ROS); namely, proteins bearing redox moieties, lipid oxidation products, and carbohydrate radicals. A hypothesis is advanced in which electromagnetic fields associated with mobile radicals and electrons play a role. Although radicals have previously been investigated as messengers, the area occupies a minor part of the research, and it has not attracted broad consensus as an important component. For the first time, an integrated framework is presented composed of radicals, electrons, relays, conduits, and electrical fields. The approach is in keeping with the vast majority of experimental observations. Cell signaling also plays an important role in reproductive toxicity. The main classes that cause birth defects, including ROS, radiation, metal compounds, medicinals, abused drugs, and miscellaneous substances, are known to participate in the signaling process. A unifying basis exists, in that both signaling and reproductive toxicity are characterized by the electron transfer-reactive oxygen species-oxidative stress (ET-ROS-OS) scheme. This article also incorporates representative examples of the extensive investigations dealing with various medical implications. There is considerable literature pointing to a role for cell communication in a wide variety of illnesses.

Distinct transduction mechanisms of cyclooxygenase 2 gene activation in tumour cells after photodynamic therapy

Photodynamic therapy (PDT) is a minimally invasive treatment for cancer and several noncancerous proliferating cell diseases. PDT relies on the uptake of a photosensitizing compound by the pathologic tissue followed by a selective irradiation with visible light, which leads to oxidative stress-mediated cell death. However, some studies showed that PDT induces the release of proangiogenic factors, such as vascular endothelial growth factor, and/or cyclooxygenase-2 (COX-2), thereby promoting cancer cell regrowth following PDT. In this work, we focused on the molecular mechanisms regulating COX-2 expression after low-dose PDT in two cancer cell lines, namely HeLa and T24. We report that PDT induces COX-2 expression in these cells and this expression is mainly due to nuclear factor kappa B (NF-kappaB)-dependent transcription of cox-2 gene without any post-transcriptional regulation. However, the transduction mechanism leading to NF-kappaB activation and subsequent cox-2 gene transcription differs in both cell types. In T24, NF-kappaB activation occurs through a protein kinase C (PKC)alpha- and phosphoinositide-3-kinase (PI3K)-dependent I kappa B kinase (IKK) complex activation, whereas in HeLa cells, NF-kappaB activation is mediated by PKC- and PI3K-independent IKK complex activation.

Role of NADPH oxidases in the control of vascular gene expression

All vascular cells, including endothelial cells and smooth muscle cells, express components of the leukocyte NADPH oxidase such as p22phox, p47phox, and Rac. Endothelial cells and fibroblasts also express the leukocyte NADPH oxidase subunit gp91phox/nox2, whereas in smooth muscle cells nox1 and nox4 are found. The different vascular NADPH oxidases represent important sources for the basal as well as the agonist-induced superoxide anion (O(2) .-) generation in the vasculature. In vascular smooth muscle cells, activation of the NADPH oxidases and the subsequent formation of O(2) .- has been demonstrated for various agents including angiotensin II, thrombin, lysophosphatidylcholine, and tumor necrosis factor alpha. By influencing the activity of p38 mitogen-activated protein kinase and AKT, NADPH oxidase-derived O(2) .- increases the expression of several pro-arteriosclerotic genes, such as monocyte chemoattractant protein-1, tissue factor, and vascular endothelial growth factor. Thus, the vascular NADPH oxidases play an important role in mediating the signal transduction cascade of pro-arteriosclerotic stimuli.

Activation of the stress-activated JNK and p38 MAP kinases in human cells by Photofrin-mediated photodynamic therapy

We have examined the possible role of the stress-activated JNK and p38 protein kinases in cellular sensitivity following Photofrin-mediated photodynamic therapy (PDT). Previously we reported that immortalized Li-Fraumeni syndrome (LFS) cells are more resistant to Photofrin-mediated PDT compared to normal human fibroblasts (NHF) at equivalent cellular Photofrin levels. In the current work we report that Photofrin-mediated PDT increased the activity of JNK1 and p38 within 30 min in both cell types. However, the increased activity of JNK1 and p38 was transient in the sensitive NHF cells and returned back to near basal levels by 3 h after PDT. In contrast, the resistant LFS cells exhibited a more prolonged activation of JNK and p38, which lasted for at least 11 h and 7 h after PDT, respectively. Blocking of the p38 pathway in LFS cells by transient infection with a recombinant adenovirus expressing a dominant negative mutant of p38 or in HeLa cells by stable transfection with a dominant negative mutant of p38 had no effect on cell survival following PDT. These data suggest that although Photofrin-mediated PDT is able to induce JNK1 and p38 in human cells, the p38 pathway alone does not play a major role in the sensitivity of LFS cells to Photofrin-mediated PDT.

Singlet oxygen-induced signaling effects in mammalian cells

Singlet oxygen, an electronically excited form of molecular oxygen, may be generated photochemically or in dark reactions in vivo. Singlet oxygen is not only toxic to cells and impairs signaling events but is also capable of eliciting a cellular stress response. The signaling processes initiated in this response include the activation of mitogen-activated protein kinases. Two possible activation mechanisms of signaling pathways by singlet oxygen are the generation of positive regulators as well as the inactivation of negative regulators.