Recent Progress in Upconversion Photodynamic Therapy.

Hailong Qiu,Meiling Tan,Jonathan Lovell,Tymish Ohulchanskyy,Guanying Chen

doi:10.3390/nano8050344

Abstract

Photodynamic therapy (PDT) is a minimally invasive cancer modality that combines a photosensitizer (PS), light, and oxygen. Introduction of new nanotechnologies holds potential to improve PDT performance. Upconversion nanoparticles (UCNPs) offer potentially advantageous benefits for PDT, attributed to their distinct photon upconverting feature. The ability to convert near-infrared (NIR) light into visible or even ultraviolet light via UCNPs allows for the activation of nearby PS agents to produce singlet oxygen, as most PS agents absorb visible and ultraviolet light. The use of a longer NIR wavelength permits light to penetrate deeper into tissue, and thus PDT of a deeper tissue can be effectively achieved with the incorporation of UCNPs. Recent progress in UCNP development has generated the possibility to employ a wide variety of NIR excitation sources in PDT. Use of UCNPs enables concurrent strategies for loading, targeting, and controlling the release of additional drugs. In this review article, recent progress in the development of UCNPs for PDT applications is summarized.

Highlights

Photodynamic therapy (PDT) is a clinical treatment modality that involves the administration of photo-triggered chemicals known as photosensitizers (PS)
A similar result was reported by Zhao’s group [76]. These results clearly indicate that a Upconversion nanoparticles (UCNPs)-photosensitizer can be used as PDT agents for efficient therapy, and as dual-modal theranostic probes for accurate diagnosis with imaging followed by the therapy
While UCNPs offer outstanding optical properties and tunable surface chemistries, several issues still remain and need to be addressed before they can be of general practical use in the clinical setting: (i) Current inorganic UCNPs typically have a low upconversion quantum yield of less than 3%, which sets a strong limit for the use of harvested NIR excitation light to produce UV-visible light for the activation of PS

Summary

Introduction

Photodynamic therapy (PDT) is a clinical treatment modality that involves the administration of photo-triggered chemicals known as photosensitizers (PS). The light frequency conversion efficiency in this case is orders of magnitude higher than that of a nonlinear two-photon absorption mechanism [16], and, NIR light upconversion can be achieved with an excitation density of 10−1–102 W/cm provided by an inexpensive low energy continuous-wave (CW) diode laser This conversion can be readily realized in lanthanide-doped upconversion nanoparticles (UCNPs) which are able to emit shorter wavelength photons under excitation by NIR light. Compared with traditional downconversion fluorescent probes, such as quantum dots and organic dyes, UCNPs have prominent advantages such as narrow emission peaks, large stokes shifts, low toxicity, and good photostability, as well as absence of the autofluorescence in the anti-Stokes spectral region, where the upconversion emission is manifested All these features significantly improve the signal-to-noise ratio in optical bioimaging. This review aims to summarize the progress achieved to date on the use of luminescent UCNPs for photodynamic therapy in cancer treatment

Principles of Photosensitization

Emission Wavelengths Offered by Lanthanide-Doped UCNPs for PDT Application

Surface Modification and Bioconjugation of Lanthanide Doped UCNPs

In Vitro and In Vivo PDT by Lanthanide Doped UCNPs

Findings

Conclusions and Perspectives