Nanocarriers in topical photodynamic therapy

ABSTRACT

Introduction

Photodynamic therapy (PDT) has gained significant attention due to its superiority over conventional treatments. In the context of skin cancers and nonmalignant skin diseases, topical application of photosensitizer formulations onto affected skin, followed by illumination, offers distinct advantages. Topical PDT simplifies therapy by providing easy access to the skin, increasing drug concentration within the target area, and confining residual photosensitivity to the treated skin. However, the effectiveness of topical PDT is often hindered by challenges such as limited skin penetration or photosensitizer instability. Additionally, the hypoxic tumor environment poses further limitations. Nanocarriers present a promising solution to address these challenges.

Areas covered

The objective of this review is to comprehensively explore and highlight the role of various nanocarriers in advancing topical PDT for the treatment of skin diseases. The primary focus is to address the challenges associated with conventional topical PDT approaches and demonstrate how nanotechnology-based strategies can overcome these challenges, thereby improving the overall efficiency and efficacy of PDT.

Expert opinion

Nanotechnology has revolutionized the field of PDT, offering innovative tools to combat the unfavorable features of photosensitizers and hurdles in PDT. Nanocarriers enhance skin penetration and stability of photosensitizers, provide controlled drug release, reduce needed dose, increase production of reactive oxygen species, while reducing side effects, thereby improving PDT effectiveness.

GRAPHICAL ABSTRACT

KEYWORDS:

• Nanocarriers
• nanotechnology
• nonmalignant skin diseases
• skin cancer
• topical photodynamic therapy

Article highlights

• While various types of nanoparticles hold potential as nanocarriers, this review focuses on those that have demonstrated particular effectiveness in addressing the challenges of topical photosensitizer (PS) delivery. By concentrating on these frequently encountered nanocarriers, we aim to provide a comprehensive overview of the most promising and well-studied options for topical PDT applications. These selected nanocarriers warrant in-depth exploration due to their proven ability to enhance therapeutic efficacy in PDT.

• Different kinds of nanocarriers have been used for topical PDT, including liposomes, lipid nanoparticles, polymeric nanoparticles, dendrimers, and inorganic nanocarriers. These nanocarriers have demonstrated the ability to overcome unfavorable properties of photosensitizers (PSs), like enhancing skin penetration, solubility, and stability of PSs. As a result they improve the therapeutic efficacy of topical PDT.

• Nanocarriers reduce treatment-related side effects, the required dose and the frequency of PDT treatment. Consequently, they contribute to increased patient compliance.

• Nanocarriers facilitate efficient topical PDT. In contrast to systemic PDT, they confine potential photosensitivity reactions solely to the site of application, avoiding general photosensitivity.

• Topical PDT with photosensitizer-loaded nanocarriers yields favorable cosmetic outcomes, with no scarring or functional impairment.

• To further enhance the therapeutic outcomes in cancer treatments, a current trend involves the development of novel multifunctional nanoplatforms (single-atom catalyst-, graphitic carbon nitride-, near-infrared-II- and other hollow-nanoplatforms, multifunctional nanoparticles, organic radical photosensitizers, etc.) that combine photosensitizing agents with other therapeutic or diagnostic agents, such as chemotherapeutic drugs or imaging agents. In that way they enable multi-modal therapies, such as PDT-PTT synergistic therapy, chemo/photo immunotherapy, and others. These multifunctional nanoplatforms contribute to more effective therapeutic outcomes.

• Newly developed nanomaterials are able to relieve the hypoxic conditions in tumor microenvironment.

• Newly developed nanomaterials often serve as nanotheranostics, enabling precise tumor diagnosis and enhancing tumor elimination outcomes, potentially leading to improved or even complete eradication.

• Nanotechnology strategies aimed at enhancing tumor immunotherapy have the potential to increase the therapeutic outcomes in cancer treatments.

• Prior to the clinical application of photosensitizer-loaded nanocarriers several challenges need to be addressed. These include further optimization of their properties, evaluation of their in vivo effectiveness and safety, as well as enhancement of their regulatory aspects.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.