Photodynamic therapy of lung cancer, where are we?

Abstract

Lung cancer remains the leading threat of death globally, killing more people than colon, breast, and prostate cancers combined. Novel lung cancer treatments are being researched because of the ineffectiveness of conventional cancer treatments and the failure of remission. Photodynamic therapy (PDT), a cancer treatment method that is still underutilized, is a sophisticated cancer treatment that shows selective destruction of malignant cells via reactive oxygen species production. PDT has been extensively studied in vitro and clinically. Various PDT strategies have been shown to be effective in the treatment of lung cancer. PDT has been shown in clinical trials to considerably enhance the quality of life and survival in individuals with incurable malignancies. Furthermore, PDT, in conjunction with the use of nanoparticles, is currently being researched for use as an effective cancer treatment, with promising results. PDT and the new avenue of nanoPDT, which are novel treatment options for lung cancer with such promising results, should be tested in clinical trials to determine their efficacy and side effects. In this review, we examine the status and future potentials of nanoPDT in lung cancer treatment.

Keywords: lung cancer; nanoPDT; nanomaterials; nanomedicine; nanotechnology; photodynamic therapy; photosensitizer.

FIGURE 1

The mechanism of photodynamic therapy (PDT). The photosensitizer (PS) is absorbed when the PS is in its ground state. It goes into its first excited singlet state because of photoactivation. This state can be broken down by emitting fluorescence, or it can cross over to the more stable excited triplet state. Type I is when the PS in its excited triplet state reacts with biomolecules (such as lipids, proteins, and nucleic acids), and the radical mechanism is used to transfer hydrogen atoms. It generates free radicals and radical ions (the type of radical varies depending on the target molecule, such as lipids, proteins, or nucleic acids), which react with oxygen to produce reactive oxygen species. Type II reactions are based on a phenomenon known as triplet–triplet annihilation. In these reactions, the PS in its excited triplet state reacts with oxygen in its triplet ground state. This results in the formation of highly reactive and cytotoxic singlet oxygen.

FIGURE 2

Cell death pathways activated during PDT, according to PS localization. The PS can localize in the cytoplasm and mitochondria and induce apoptosis. Autophagy occurs when there is damage to the lysosomes or endoplasmic reticulum. Necrosis occurs during plasma membrane localization.

FIGURE 3

Nanodrug delivery systems used for site-targeted distribution and improved bioavailability. Protein and polysaccharide nanoparticles, liposomes, dendrimers, inorganic/metallic nanoparticles, nanocrystals, and carbon nanotubes are all examples of nanoparticles used in nanomedicine.