Article pubs.acs.org/Biomac
Enhanced Photodynamic Efficiency Achieved via a Dual-Targeted Strategy Based on Photosensitizer/Micelle Structure Jiangsheng Xu, Fang Zeng,* Hao Wu, Caiping Hu, and Shuizhu Wu* College of Materials Science and Engineering, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China S Supporting Information *
ABSTRACT: The applications of photodynamic therapy (PDT) are usually limited by photosensitizer’s side effect and the singlet oxygen’s short half-life. Herein, we demonstrate a dual-targeting (both cellular and subcellular targeting) strategy to enhance the PDT efficacy. A cationic porphyrin derivative (MitoTPP) was synthesized as the mitochondriontargeting photosensitizer, and the dual-targeting PDT system was then fabricated by encapsulating MitoTPP into the acidresponsive and folic acid (FA)-modified polymer micelles. Under acidic pH, the micelles swell as a result of protonation of tertiary amines and disruption of the nucleobase pairing, thereby causing the release of the photosensitizer. Confocal microscope observation shows that the dual-targeting and micelle-based PDT system can preferably enter folate receptor (FR)positive cancer cells, and upon cellular internalization, the MitoTPP molecules are released from the micelles and selectively accumulate in mitochondria. Under light irradiation, the singlet oxygen generated by the photosensitizer causes the oxidant damage to the mitochondrial and subsequently the apoptosis of the cells, as evidenced by the loss of mitochondrial membrane potential. Cell viability assays indicate that dual-targeting micelle-based systems exhibit enhanced cytotoxicity toward FR-positive cells. This study may provide a new approach for effectively enhancing the action of PDT systems.
1. INTRODUCTION
The mitochondria are energy factories of the cell, playing important roles in energy metabolism of various biochemical processes.15,16 They are also the executioners of programmed cell death (apoptosis). So far two major apoptotic pathways have been characterized: the death receptor-mediated, or extrinsic pathway, and the mitochondria-mediated apoptosis or intrinsic pathway. The role played by mitochondria in apoptosis makes these cellular organelles desired targets for therapeutic drugs.17−21 Currently, several strategies for the delivery of biologically active molecules to the mitochondria of live mammalian cells are widely used: (1) tethering a mitochondrial localization peptide sequence, which utilizes protein import pathway; (2) attaching a lipophilic cation group, which utilizes the high membrane potential (180 mV) across the inner mitochondrial membrane; and (3) using lyposome-based carrier (e.g., vesicle) for transporting large or vulnerable cargo.16,22 As for the lipophilic cation approach, Murphy, Chang, and so on have designed a series of triphenylphosphonium-based bioactive molecules with excellent mitochondria targeting capability.16,23,24 The delocalized positive charge in these lipophilic cations enables them to permeate lipid bilayers easily and to accumulate several hundred-fold within mitochondria because of the large mitochondrial membrane potential (∼180 mV, negative
Photodynamic therapy (PDT) has received considerable attention as a safe, minimally invasive treatment for a number of malignant and nonmalignant diseases.1−4 As an alternative means to kill drug- and radio-resistant tumor cells, PDT involves three main components: a photosensitizer (PS), molecular oxygen, and light. PDT depends on the retention of PS in tumor cells and their activation within the tumor through irradiation with the light of appropriate wavelength.5−8 Cytotoxic effects in PDT are driven by reactive oxygen species (ROS), prevalently singlet oxygen, which is a highly reactive species. The singlet oxygen produces localized oxidative lesions that can lead to the initiation of various stress signaling pathways and, ultimately, cell death.9−12 However, severe limitations do exist for PDT. On one hand, singlet oxygen tends to inflict damage on all types of cells without any specificity, because both the malignant cells and normal cells are able to accumulate PSs and thereby causing photodamage to both of the cells. On the other hand, singlet oxygen has a very short lifetime in biological systems (
