<p>Enhanced Efficacy of Photodynamic Therapy by Coupling a Cell-Penetrating Peptide with Methylene Blue</p>

Abstract

Introduction: Photodynamic therapy (PDT), which induces tissue damage by exposing tissue to a specific wavelength of light in the presence of a photosensitizer and oxygen, is a promising alternative treatment that could be used as an adjunct to chemotherapy and surgery in oncology. Cell-penetrating peptides (CPPs) with high arginine content, such as protamine, have membrane translocation and lysosome localization activities. They have been used in an extensive range of drug delivery applications. Methods: We conjugated cell-penetrating peptides (CPPs) with methylene blue (MB) and then purification by FPLC. Synthesis structure was characterized by the absorbance spectrum, FPLC, Maldi-TOF, and then evaluated cell viability by cytotoxicity assay after photodynamic therapy (PDT) assay. An uptake imaging assay was used to determine the sites of MB and MB-Pro in subcellular compartments. Results: In vitro assays showed that MB-Pro has more efficient photodynamic activities than MB alone for the colon cancer cells, owing to lysosome rupture causing the rapid necrotic cell death. In this study, we coupled protamine with MB for high efficacy PDT. The conjugates localized in the lysosomes and enhanced the efficiency of PDT by inducing necrotic cell death, whereas PDT with non-coupled MB resulted in only apoptotic processes. Discussion: Our research aimed to enhance PDT by engineering the photosensitizers using CPPs coupled with methylene blue (MB). MB alone permeates through the cell membrane and distributes into the cytoplasm, whereas coupling of MB dye with CPPs localizes the MB through an endocytic mechanism to a specific organelle where the localized conjugates enhance the generation of reactive oxygen species (ROS) and induce cell damage.

Membrane Internalization Mechanisms and Design Strategies of Arginine-Rich Cell-Penetrating Peptides

“…Deshpande et al [ 113 ] proved that the attachment of an arginine-rich CPP octaarginine (R 8 ) and transferrin (Tf) to the surface of DOX-loaded liposomes improved the targeting of A2780 ovarian carcinoma cells and controlling tumor growth in an A2780 ovarian xenograft model. Besides ovarian carcinoma [ 114 ], the arginine-rich CPPs also showed their application potential in the therapy of other cancers, such as colorectal cancer [ 115 , 116 , 117 ], lung cancer [ 36 , 118 , 119 , 120 , 121 , 122 , 123 ], oral cancer [ 75 , 124 , 125 ], breast cancer [ 122 , 126 , 127 , 128 , 129 ], prostate cancer [ 130 , 131 , 132 , 133 ], pancreatic cancer [ 134 , 135 ], renal carcinoma [ 121 , 136 ], etc.…”

Synthesis of Methotrexate-Loaded Dumbbell-Shaped Titanium Dioxide/Gold Nanorods Coated with Mesoporous Silica and Decorated with Upconversion Nanoparticles for Near-Infrared-Driven Trimodal Cancer Treatment

“…MB is used as a photosensitizer stimulated under NIR light irradiation to produce ROS radicals, including 1 O 2 and OH • . 61 The absorbance of MB reduced drastically with increasing irradiation time. The MB degraded completely for AuNRs-TiO 2 @mS: UCNP nanocomposites after 30 min of laser irradiation.…”

“…To assess the photocatalytic degradation activity of AuNRs-TiO 2 @mS: UCNP nanocomposites, methylene blue (MB) was performed under laser irradiation (Figure d). MB is used as a photosensitizer stimulated under NIR light irradiation to produce ROS radicals, including 1 O 2 and OH • . The absorbance of MB reduced drastically with increasing irradiation time.…”

Organelle-Targeted Photosensitizers for Precision Photodynamic Therapy

“…More than that, researchers have also built a nanodiagnostic and therapeutic system that combines specific receptor recognition and acid activatable capabilities. − Ju et al designed and synthesized a new NEt 2 Br 2 BDP, and it was encapsulated in cRGD–PEG-PLA and mPEG–PLA nanomicelles to form a αvβ3 integrin-rich tumor cells target and pH-activatable cRGD-NEt 2 Br 2 BDP nanoparticles (Figure a) . cRGD-NEt 2 Br 2 BDP nanoparticles can reach the lysosome through αvβ3 receptor-mediated endocytosis in αvβ3 high-expression cancer cells.…”

“…To achieve lysosomal accumulation through the endocytic pathway, PSs also modified tamoxifen to target the estrogen receptor 93 or were modified with cell-penetrating peptides 94 for enhancing tumor penetration. Modification of these ligands enables the PSs nanocomposites to effectively migrate to the lysosome, resulting in significant damage to cancer cells.…”