Abstract
Enhanced protoporphyrin IX (PpIX) production in tumors derived from the administration of 5-aminolevulinic acid (ALA) enables the use of ALA as a prodrug for photodynamic therapy (PDT) and fluorescence-guided tumor resection. Although ALA has been successfully used in the clinic, the mechanism underlying enhanced ALA-induced PpIX production in tumors is not well understood. Human epidermal growth receptor 2 (Her2, Neu, ErbB2) is a driver oncogene in human cancers, particularly breast cancers. Here we showed that, in addition to activating Her2/Neu cell signaling, inducing epithelial-mesenchymal transition and upregulating glycolytic enzymes, transfection of NeuT (a mutated Her2/Neu) oncogene in MCF10A human breast epithelial cells significantly enhanced ALA-induced PpIX fluorescence by elevating some enzymes involved in PpIX biosynthesis. Furthermore, NeuT-transformed and vector control cells exhibited drastic differences in the intracellular localization of PpIX, either produced endogenously from ALA or applied exogenously. In vector control cells, PpIX displayed a cell contact-dependent membrane localization at high cell densities and increased mitochondrial localization at low cell densities. In contrast, no predominant membrane localization of PpIX was observed in NeuT cells and ALA-induced PpIX showed a consistent mitochondrial localization regardless of cell density. PDT with ALA caused significantly more decrease in cell viability in NeuT cells than in vector cells. Our data demonstrate that NeuT oncogene transformation enhanced ALA-induced PpIX production and altered PpIX intracellular localization, rendering NeuT-transformed cells increased response to ALA-mediated PDT. These results support the use of ALA for imaging and photodynamic targeting Her2/Neu-positive tumors.
Highlights
Photodynamic therapy (PDT) is a FDA-approved treatment modality using photoactivatable drugs called photosensitizers to generate therapeutic effects through the production of reactive oxygen species following light activation [1]
Effects of Her2/Neu oncogene, a driver oncogene in human cancers, on aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence, PpIX intracellular localization and cell sensitivity to ALA-mediated photodynamic therapy (PDT) were studied in the present study
Our results demonstrate that transfecting MCF10A human breast epithelial cells with NeuT oncogene caused cell transformation by activating Her2/Neu signaling, inducing epithelial-mesenchymal transition (EMT), and altering glucose metabolism
Summary
Photodynamic therapy (PDT) is a FDA-approved treatment modality using photoactivatable drugs called photosensitizers to generate therapeutic effects through the production of reactive oxygen species following light activation [1]. ALA itself does not possess any photosensitizing activity. It is metabolically converted in the heme biosynthesis pathway to protoporphyrin IX (PpIX), a heme precursor metabolite with photosensitizing and fluorescent properties [2, 3]. Heme biosynthesis pathway is a ubiquitous cell metabolic pathway existing in almost all mammalian cells. It begins with the formation of ALA in mitochondria, continues with consecutive enzymatic cascades in the cytosol, and ends with the chelation of PpIX and ferrous iron to form heme back in mitochondria. Administration of exogenous ALA bypasses the step of endogenous ALA synthesis where pathway negative feedback control is located, resulting in increased PpIX production [2, 3]
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