Using X-rays in photodynamic therapy: an overview

Abstract

Photodynamic therapy is a therapeutic option to treat cancer and other diseases. PDT is used every day in dermatology, and recent developments in the treatment of glioblastoma, mesothelioma or prostate have demonstrated the efficacy of this modality. In order to improve the efficacy of PDT, different strategies are under development, such as the use of targeted PS or nanoparticles to improve selectivity and the design of light devices to better monitor the light dose. Due to the low penetration of light into tissue, another way to improve the efficacy of PDT to treat deep tumors is the use of upconversion NPs or bi-photon absorption compounds. These compounds can be excited in the red part of the spectrum. A relatively new approach, which we will call PDTX, is the use of X-rays instead of UV-visible light for deeper penetration into tissue. The principle of this technique will be described, and the state-of-art literature concerning this modality will be discussed. First, we will focus on various photosensitizers that have been used in combination with X-ray irradiation. To improve the efficacy of this modality, nanoparticles have been designed that allow the conversion of high-energy ionizing radiation into UV-visible light; these are potential candidates for the PDTX approach. They will be discussed at the end of this review.

X-ray induced photodynamic therapy (PDT) with a mitochondria-targeted liposome delivery system

“…For example, red light (620-750 nm) required to activate verteporfin (VP, a PDT drug) penetrates only up to 3 mm allowing to treat superficial lesions only. The X-ray-induced PDT has emerged as an attractive alternative as it is able to overcome limited penetration depth of activating light in traditional PDT [24][25][26][27][28]. Unlike visible or near-infrared (NIR) light, X-rays have excellent tissue penetration capability.…”

Photoimmunotherapy of Ovarian Cancer: A Unique Niche in the Management of Advanced Disease

“…Although in its infancy, bioluminescent PDT (BL-PDT) has been reported to treat tumors in pre-clinical models. Other approaches used to circumvent the short-comings of limited light penetration are X-ray based PDT [168,169] and the use of upconversion nanoparticles [170].…”

Optical and x-ray technology synergies enabling diagnostic and therapeutic applications in medicine

“…154,155 Alternatively, organic molecules such as porphyrins, bacteriochlorins, phthalocyanines, and smaller cyclic structures that absorb UV/violet-blue light operate through generation of biologically active free radicals or excited-state oxygen. [156][157][158] Direct x-ray excitation is dominant in metals and scintillators, and there are multiple excitation mechanisms in photocatalysts and photosensitizer molecules. The choices to achieve maximum energy transfer here are not obvious because of the complexity of initiating events and the cascade of secondary events in the energy-transfer process.…”

“…The latter is a relatively new line of research (Figs. 11 and 12), achieving radiosensitization with the benefits of specificity and packaging of optical agents, 157,158 and a number of efforts in materials chemistry have produced some extremely promising in vivo tumor killing results in the last few years. The key to advancing this approach to human use is to have nanoparticle agents that have low toxicity and are produced for human use, which is seemingly costly and currently uncertain.…”