Photodynamic therapy with redaporfin targets the endoplasmic reticulum and Golgi apparatus

Abstract

Preclinical evidence depicts the capacity of redaporfin (Redp) to act as potent photosensitizer, causing direct antineoplastic effects as well as indirect immune-dependent destruction of malignant lesions. Here, we investigated the mechanisms through which photodynamic therapy (PDT) with redaporfin kills cancer cells. Subcellular localization and fractionation studies based on the physicochemical properties of redaporfin revealed its selective tropism for the endoplasmic reticulum (ER) and the Golgi apparatus (GA). When activated, redaporfin caused rapid reactive oxygen species-dependent perturbation of ER/GA compartments, coupled to ER stress and an inhibition of the GA-dependent secretory pathway. This led to a general inhibition of protein secretion by PDT-treated cancer cells. The ER/GA play a role upstream of mitochondria in the lethal signaling pathway triggered by redaporfin-based PDT Pharmacological perturbation of GA function or homeostasis reduces mitochondrial permeabilization. In contrast, removal of the pro-apoptotic multidomain proteins BAX and BAK or pretreatment with protease inhibitors reduced cell killing, yet left the GA perturbation unaffected. Altogether, these results point to the capacity of redaporfin to kill tumor cells via destroying ER/GA function.

Cell death in photodynamic therapy: From oxidative stress to anti-tumor immunity

“…Surprisingly, redaporfin-based PDT failed to elicit the activation of ATF4 and CHOP, the two transcription factors downstream of eIF2α phosphorylation despite other signs of ER stress being observed, namely at the level of ATF6 and IRE1. Overall, a partial reduction in protein synthesis was observed and gene knockout (KO) of EIF2AK1 (but not that of EIF2AK2, EIF2AK3 or EIF2AK4) sensitized the cells to redaporfin-dependent phototoxicity [34,35].…”

“…In both cases, increased levels of cytosolic Ca 2+ were observed, likely reflecting the direct damage at the ER. Upon Ca 2+ inhibition, for instance with the Ca 2+ chelator BAPTA, reduced cell toxicity was detected [35]. Hypericin-PDT demonstrated destruction of the anti-apoptotic BCL-XL [82] but also the activation of the PERK-eIF2α arm for ER stress.…”

“…In contrast, removal of the pro-apoptotic proteins BAX and BAK or pre-treatment with the pancaspase inhibitor Z-VAD-fmk, reduced cell killing but left the GA perturbation unaffected. These effects were mitigated by the lipophilic antioxidant tocopherol, thus indicating that they were ROS-mediated [34,35]. PDT with protoporphyrin IX, or polyamines-targeting derivatives, were shown to accumulate at the cells cytoplasm but also mediate cell death by activating apoptosis via the intrinsic pathway.…”

Lipophilicity of Bacteriochlorin-Based Photosensitizers as a Determinant for PDT Optimization through the Modulation of the Inflammatory Mediators

“…Each of these photosensitizers was incubated with a specific probe for mitochondria (MitoTracker), lysosomes (LysoTracker) and endoplasmic reticulum (ER-Tracker). The intracellular localization of F 2 BOH and F 2 BMet in different cell lines has been published before [21][22][23]41]. The more hydrophilic bacteriochlorin is accumulated in lysosomes, whereas the amphiphilic bacteriochlorin is mostly found in the ER (and Golgi), with a smaller localization in the mitochondria.…”

“…In addition, the introduction of fluorine and chlorine atoms into the PS structure leads to a change in their polarity, which in turn can increase the rate of transport of biologically-active compounds through lipid membranes [29][30][31][32][33][34].It is widely recognized that PDT regimes can trigger rapid inflammatory responses that are essential for the activation of antitumor immunity [35][36][37], improving long-term tumor control and offering protection against metastasis [38]. Unlike most chemotherapies, which mainly lead to apoptotic cell death, PDT may also lead to necrosis or immunogenic cell death (ICD), which can result in controlled inflammation, which in turn leads to further stimulation of the immune system [7,37,[39][40][41]. The generation of the post-PDT antitumor response involves the participation of various mechanisms based on the secretion of cytokines and mediators associated with the inflammatory process, increased level of neutrophils in the blood combined with neutrophil recruitment to the treated areas, as well as induction of acute-phase proteins and activation of the complement system [7,35,40,42].…”