Multiple Components of Photodynamic Therapy Can Phosphorylate Akt?

Therapeutic Enhancement of Verteporfin-mediated Photodynamic Therapy by mTOR Inhibitors

Photodynamic therapy (PDT) with photosensitizer verteporfin is a clinically approved vascular disrupting modality that is currently in clinical trial for cancer treatment. In this study, we evaluated PDT in combination with either mTORC1 inhibitor rapamycin or mTORC1/C2 dual inhibitor AZD2014 for therapeutic enhancement in SVEC endothelial cells. Verteporfin-PDT alone induced cell apoptosis by activating the intrinsic apoptotic pathway. However, it increased the expression of anti-apoptotic protein MCL-1 and the phosphorylation of S6, a downstream molecule of mTOR signaling. In contrast, mTOR inhibitors rapamycin and AZD2014 did not induce apoptosis in SVEC cells. They suppressed MCL-1 expression and S6 phosphorylation and imposed a potent inhibition on cell proliferation. PDT in combination with mTOR inhibitors activated the intrinsic apoptotic pathway and resulted in increased apoptosis. Combination treatments also led to sustained inhibition of cell proliferation. Although AZD2014 was more effective for cell growth inhibition and PDT enhancement than rapamycin at the higher concentrations examined in the study, both inhibitors effectively enhanced PDT response, suggesting that inhibition of mTORC1 is crucial for PDT enhancement. Our results indicate that mTOR inhibitors mechanistically cooperate with PDT for enhanced cell death and sustained growth inhibition, supporting a combination approach for therapeutic enhancement.

mTOR Signaling Pathway in Cancer Targets Photodynamic Therapy In Vitro

The Mechanistic or Mammalian Target of Rapamycin (mTOR) is a major signaling pathway in eukaryotic cells belonging to the P13K-related kinase family of the serine/threonine protein kinase. It has been established that mTOR plays a central role in cellular processes and implicated in various cancers, diabetes, and in the aging process with very poor prognosis. Inhibition of the mTOR pathway in the cells may improve the therapeutic index in cancer treatment. Photodynamic therapy (PDT) has been established to selectively eradicate neoplasia at clearly delineated malignant lesions. This review highlights recent advances in understanding the role or regulation of mTOR in cancer therapy. It also discusses how mTOR currently contributes to cancer as well as future perspectives on targeting mTOR therapeutically in cancer in vitro.

Phenalenone-photodynamic therapy induces apoptosis on human tumor cells mediated by caspase-8 and p38-MAPK activation

Photodynamic therapy (PDT) is a rising and hopeful treatment for solid tumors and others malignancies. PDT uses harmless visible light to activate a tumor-associated photosensitizer (PS). The excited PS generates cytotoxic reactive oxygen species (ROS) that induce damage and death of tumor cells. It is known that certain phytoalexins and phytoanticipins derived from plants often display a PS-like activity due to a phenalenone (PN) moiety-an efficient singlet oxygen photosensitizer-in its skeleton. The aim of this study is to explore the phototoxic properties of PN on the human cell line tumor-derived HL60 (acute promyelocytic leukemia) and to identify the cell-specific targets of ROS involved in the tumor cell death. Our results reveal that PN acts as an excellent PS, showing a potent antitumor cell activity in presence of light. PN-PDT generates intracellular ROS, via oxidation reaction mechanisms type I and II, resulting in an induction of apoptosis. Moreover, both extrinsic (through direct activation of caspase-3) and intrinsic (through mitochondrial depolarization) pathways of apoptosis are induced by PN-PDT. Using pharmacologic inhibitors, we also find that PN-PDT activates caspase-8/tBid and p38-MAPK, triggering the activation of the apoptotic pathways. Although, survival pathways are also promoted through PI3 K/Akt and JNK activation, the net result of PN-PDT is the tumor cell death. The present work identifies to PN, for the first time, as a potent photosensitizer in human tumor cell lines and proposes a mechanism by which ROS induces apoptosis of tumor cell.

Targeting Phosphatidylinositol 3-Kinase Signaling Pathway for Therapeutic Enhancement of Vascular-Targeted Photodynamic Therapy

Vascular-targeted photodynamic therapy (PDT) selectively disrupts vascular function by inducing oxidative damages to the vasculature, particularly endothelial cells. Although effective tumor eradication and excellent safety profile are well demonstrated in both preclinical and clinical studies, incomplete vascular shutdown and angiogenesis are known to cause tumor recurrence after vascular-targeted PDT. We have explored therapeutic enhancement of vascular-targeted PDT with PI3K signaling pathway inhibitors because the activation of PI3K pathway was involved in promoting endothelial cell survival and proliferation after PDT. Here, three clinically relevant small-molecule inhibitors (BYL719, BKM120, and BEZ235) of the PI3K pathway were evaluated in combination with verteporfin-PDT. Although all three inhibitors were able to synergistically enhance PDT response in endothelial cells, PDT combined with dual PI3K/mTOR inhibitor BEZ235 exhibited the strongest synergism, followed in order by combinations with pan-PI3K inhibitor BKM120 and p110α isoform-selective inhibitor BYL719. Combination treatments of PDT and BEZ235 exhibited a cooperative inhibition of antiapoptotic Bcl-2 family protein Mcl-1 and induced more cell apoptosis than each treatment alone. In addition to increasing treatment lethality, BEZ235 combined with PDT effectively inhibited PI3K pathway activation and consequent endothelial cell proliferation after PDT alone, leading to a sustained growth inhibition. In the PC-3 prostate tumor model, combination treatments improved treatment outcomes by turning a temporary tumor regrowth delay induced by PDT alone to a more long-lasting treatment response. Our study strongly supports the combination of vascular-targeted PDT and PI3K pathway inhibitors, particularly mTOR inhibitors, for therapeutic enhancement. Mol Cancer Ther; 16(11); 2422-31. ©2017 AACR.

Enhanced apoptotic effects by downregulating Mcl-1: evidence for the improvement of photodynamic therapy with Celecoxib

Tumor cells exposed to sub-lethal photodynamic therapy (PDT) cause cellular rescue responses that lead to resistance to the therapy, including expression of angiogenic factors and survival molecules. However, the mechanisms contributing to the resistance are yet to be fully understood. Here, we show for the first time that Mcl-1, an anti-apoptotic protein, plays an important role in protecting cells from PDT-induced apoptosis. In contrast to the reduction in the anti-apoptotic proteins Bcl-2 and Bcl-xl, sub-lethal PDT induces an increase in Mcl-1 expression. Silencing Mcl-1 sensitizes tumor cells to PDT-induced apoptosis, and ectopic expression of Mcl-1 significantly delays Bax translocation to mitochondria and inhibits caspase-3 activity following PDT. Mcl-1 expression is associated closely with activated AKT signaling following PDT. AKT can regulate Mcl-1 expression through GSK-3β and NF-κB at the protein and transcriptional levels, respectively. Inhibition of AKT by Wortmannin or siRNA significantly reduces the levels of Mcl-1 mRNA and protein and enhances PDT-induced apoptosis. Treatment with Celecoxib, a non-steroidal anti-inflammatory drug (NSAID), is shown to downregulate Mcl-1 expression, and enhances PDT-induced apoptosis both in vitro and in vivo. This down-regulation is closely related to the inhibition effect of Celecoxib on the AKT/GSK-3β pathway, and was blocked upon addition of GSK-3β inhibitor LiCl or the proteasome inhibitor MG132. These results suggest that Mcl-1 is a potential target for improving the antitumor efficiency of PDT. A loss in Mcl-1 by inhibiting AKT promotes PDT-induced apoptosis through the mitochondrial pathway. This also provides a novel rationale for utilizing Celecoxib to improve the efficacy of PDT.

On the role of phosphatidylinositol 3-kinase, protein kinase b/Akt, and glycogen synthase kinase-3β in photodynamic injury of crayfish neurons and glial cells

Photodynamic treatment that causes intense oxidative stress and cell death is currently used in neurooncology. However, along with tumor cells, it may damage healthy neurons and glia. To study the involvement of signaling processes in photodynamic injury or protection of neurons and glia, we used crayfish mechanoreceptor consisting of a single neuron surrounded by glial cells. It was photosensitized with alumophthalocyanine Photosens. Application of specific inhibitors showed that phosphatidylinositol 3-kinase did not participate in photoinduced death of neurons and glia. Akt was involved in photoinduced necrosis but not in apoptosis of neurons and glia. Glycogen synthase kinase-3β participated in photoinduced apoptosis of glial cells and in necrosis of neurons. Therefore, phosphatidylinositol 3-kinase/protein kinase Akt/glycogen synthase kinase-3β pathway was not involved as a whole in photodynamic injury of crayfish neurons and glia but its components, Akt and glycogen synthase kinase-3β, independently and cell specifically regulated death of neurons and glial cells. According to these data, necrosis in this system was a controlled but not a non-regulated cell death mode. The obtained results may be used for the search of pharmacological agents selectively modulating death and survival of normal neurons and glial cells during photodynamic therapy of brain tumors.

Chain-dependent photocytotoxicity of tricationic porphyrin conjugates and related mechanisms of cell death in proliferating human skin keratinocytes

Photodynamic therapy (PDT) is a poor treatment option for nodular basal cell carcinomas and squamous cell carcinomas. As a result, the search for new photosensitizers with better effectiveness is of current interest. The photocytotoxicity of conjugates (P-R) of a water-soluble tri-cationic porphyrin (P-H) having similar efficiency of production of singlet oxygen, the PDT cytotoxin, has been assessed in vitro. Links between uptake, intracellular localization, photooxidative stress, photocytotoxicity and ability to induce programmed cell death are established. Conjugates bearing methyl (P-Me), Di-O-isopropylidene-(-d-galactopyranosyl (P-OGal) or N,N'-dicyclohexylureidooxycarbonyl (P-DDC) chains are efficiently taken-up by proliferating NCTC 2544 keratinocytes. The relative order of photocytotoxicity is P-OGal >P-DDC=P-Me≫P-H. The photocytotoxic potential of P-Me, P-OGal and P-DDC equals that of endogenous protoporphyrin IX induced by δ-aminolevulinic acid or its esters, the pro-drugs currently employed for PDT of skin lesions. Microfluorometry shows that P-Me, P-OGal, and P-DDC localize in endocytotic or pinocytotic vesicles but not in mitochondria or nucleus. Absence of annexin V binding, caspase activation or chromatin condensation suggests that cell photosensitization by P-R does not induce apoptosis. On the other hand, P-OGal photocytotoxicity correlates with appearance of multiple vesicles that have hallmarks of autophagy compartments, being decorated with the marker LC3 in cells transfected with an expression vector encoding GFP-LC3. p38 and JNK phosphorylation and inhibition of ERK1/2 phosphorylation suggest close relationship between mortality of NCTC 2544 keratinocytes and MAPK pathway impairment. Given their potentially easy formulation, water-soluble P-R are promising powerful photosensitizers for PDT of skin lesions.

Targeted inhibition of the EGFR pathways enhances Zn-BC-AM PDT-induced apoptosis in well-differentiated nasopharyngeal carcinoma cells

Epidermal growth factor receptor (EGFR), a receptor often expressed in nasopharyngeal carcinoma (NPC) cells, is one of the recently identified molecular targets in cancer treatment. In the present study, the effects of combined treatment of Zn-BC-AM PDT with an EGFR inhibitor AG1478 were investigated. Well-differentiated NPC HK-1 cells were subjected to PDT with 1 microM of Zn-BC-AM and were irradiated at a light dose of 1 J/cm(2) in the presence or absence of EGFR inhibitor AG1478. Specific protein kinase inhibitors of downstream EGFR targets were also used in the investigation. EGFR, Akt, and ERK were found constitutively activated in HK-1 cells and the activities could be inhibited by the EGFR inhibitor AG1478. A sub-lethal concentration of AG1478 was found to further enhance the irreversible cell damage induced by Zn-BC-AM PDT in HK-1 cells. Pre-incubation of the cells with specific inhibitors of EGFR (AG1478), PI3k/Akt (LY294002), or MEK/ERK (PD98059) before light irradiation were found to enhance Zn-BC-AM PDT-induced formation of apoptotic cells. The efficacy of Zn-BC-AM PDT can be increased through the inhibition of EGFR/PI3K/Akt and EGFR/MEK/ERK signaling pathways in NPC cells. Combination therapy with Zn-BC-AM PDT and EGFR inhibitors may further be developed for the treatment of advanced NPC.

Down-regulation of Bcl-2 and Akt induced by combination of photoactivated hypericin and genistein in human breast cancer cells

Presented experiment considers combination of genistein and photodynamic therapy with hypericin with a view to achieve higher therapeutic outcome in human breast adenocarcinoma cell lines MCF-7 and MDA-MB-231, both identified in our conditions as photodynamic therapy resistant. Since genistein is known to suppress Bcl-2 expression, we predicted that photodynamic therapy with hypericin might benefit from mutual therapeutic combination. In line with our expectations, combined treatment led to down-regulation of Bcl-2 and up-regulation of Bax in both cell lines as well as to suppression of Akt and Erk1/2 phosphorylation induced by photoactivated hypericin in MCF-7 cells. Although Akt and Erk1/2 phosphorylation was not stimulated by photodynamic therapy with hypericin in MDA-MB-231 cells, it was effectively suppressed in combination. Variations in cell death signaling favoring apoptosis were indeed accompanied by cell cycle arrest in G(2)/M-phase, activation of caspase-7, PARP cleavage and increased occurrence of cells with apoptotic morphology of nucleus. All these events corresponded with suppression of proliferation and significantly lowered clonogenic ability of treated cells. In conclusion, our results indicate that pre-treatment with tyrosine kinase inhibitor genistein may significantly improve the effectiveness of photodynamic therapy with hypericin in MCF-7 and MDA-MB-231 breast cancer cells.

Targeting the 90 kDa heat shock protein improves photodynamic therapy

The geldanamycin derivative, 17-allylamino-17-demethoxygeldanamycin (17-AAG), binds to the amino-terminal ATP binding pocket of the 90 kDa heat shock protein (Hsp-90) and inhibits this chaperone from stabilizing client proteins involved with the malignant phenotype. We examined the effects of a combined modality protocol involving photodynamic therapy (PDT) and 17-AAG in mouse mammary carcinoma cells and tumors. PDT increased the expression of the anti-apoptotic and pro-angiogenic proteins survivin, Akt, HIF-1alpha, MMP-2 and VEGF in tumor tissue and this expression decreased significantly when 17-AAG was included in the treatment regimen. Tumor bearing mice treated with PDT and 17-AAG had improved long-term tumoricidal responses when compared with individual treatment protocols. We conclude that Hsp-90 plays an active role in modulating tumor responsiveness following PDT and targeting Hsp-90 with 17-AAG enhances the therapeutic effectiveness of PDT.

The effect of photodynamic therapy on tumor angiogenesis

Photodynamic therapy (PDT), the activation of a photosensitive drug in tumor tissue with light of specific wavelength, has been used effectively to treat certain solid tumors. Though therapeutic responses are encouraging, PDT-mediated oxidative stress can act as an angiogenic switch that ultimately leads to neovascularization and tumor recurrence. This article explores the effect of PDT on angiogenesis in different tumor models. Overexpression of proangiogenic vascular endothelial growth factor, cyclooxygenase-2 and matrix metalloproteases has often been reported post-illumination. Recent clinical studies have demonstrated that inhibiting angiogenesis after chemotherapy and radiotherapy is an attractive and valuable approach to cancer treatment. In this review, we report the effective therapeutic strategy of combining angiogenesis inhibitors with PDT to control and treat tumors.