Anti-cancer vaccination by transdermal delivery of antigen peptide-loaded nanogels via iontophoresis

Abstract

Transdermal vaccination with cancer antigens is expected to become a useful anti-cancer therapy. However, it is difficult to accumulate enough antigen in the epidermis for effective exposure to Langerhans cells because of diffusion into the skin and muscle. Carriers, such as liposomes and nanoparticles, may be useful for the prevention of antigen diffusion. Iontophoresis, via application of a small electric current, is a noninvasive and efficient technology for transdermal drug delivery. Previously, we succeeded in the iontophoretic transdermal delivery of liposomes encapsulating insulin, and accumulation of polymer-based nanoparticle nanogels in the stratum corneum of the skin. Therefore, in the present study, we examined the use of iontophoresis with cancer antigen gp-100 peptide KVPRNQDWL-loaded nanogels for anti-cancer vaccination. Iontophoresis resulted in the accumulation of gp-100 peptide and nanogels in the epidermis, and subsequent increase in the number of Langerhans cells in the epidermis. Moreover, tumor growth was significantly suppressed by iontophoresis of the antigen peptide-loaded nanogels. Thus, iontophoresis of the antigen peptide-loaded nanogels may serve as an effective transdermal delivery system for anti-cancer vaccination.

Introduction

Anti-cancer vaccination is expected to become an effective anti-cancer therapy (Aranda et al., 2013). Induction of an immune response against a specific tumor requires the administration of antigen proteins or peptides derived from cancer cells directly into the skin or muscle. Intradermal injection is especially an effective administration method, because the antigen presenting Langerhans cells (LCs) exist in the epidermis (Tay et al., 2013). However, injection of antigen solution with a needle is invasive. Moreover, as intradermal injection is also difficult, special techniques are required for assured administration of the antigen solution into the epidermis. Iontophoresis has attracted attention in this regard as an effective and non-invasive transdermal delivery technology that can overcome the barriers associated with intradermal injection (Schoellhammer et al., 2014, Wong, 2014, Gratieri et al., 2013). In fact, non-invasive transdermal delivery of insulin by iontophoresis has been reported (Dixit et al., 2007). Iontophoresis is known as an effective technology for the physical stimulation of transdermal permeation of charged substances by the application of a small electric current (Schoellhammer et al., 2014, Wong, 2014, Gratieri et al., 2013). However, substances, such as antigen proteins and peptides, delivered by iontophoresis can also diffuse into the skin and muscle. As accumulation of the antigen in the skin is required for effective exposure to Langerhans cells, devices that can concentrate the antigen within restricted regions of the skin may be useful for effective induction of immune responses mediated by antigen capture of Langerhans cells. Carriers such as liposomes and nanoparticles, which are used in the intravenous administration of drugs, can also be valuable in the transdermal delivery of antigens into the skin. Recently, we succeeded in the iontophoretic transdermal delivery of hydrophilic macromolecules, such as siRNA and CpG oligoDNA, and liposomes (Kigasawa et al., 2011, Kigasawa et al., 2010, Kajimoto et al., 2011). Based on a mechanistic analysis, transdermal penetration of such macromolecules and nanoparticles induced by applying a small electric current was attributed to cleavage of the intercellular junction via Ca²⁺-mediated activation of cellular signaling (Hama et al., 2014). Thus, it is expected that iontophoresis can deliver antigen-loaded carriers into the epidermis, where Langerhans cells exist.

It was previously reported that Langerhans cells extend their dendrites to capture antigens located within the stratum corneum (Kubo et al., 2009). Thus, effective exposure of antigens by Langerhans cells may be accomplished by accumulation of antigen-loaded carriers within the surface region of the epidermis via iontophoresis. With regard to carriers, accumulation of nanogels exhibiting small (<100 nm) and rigid core structures is more preferable in the stratum corneum than liposomes that exhibit flexible structures (Hama et al., 2014), because rigid nanogels can hook into the intercellular space.

Based on these considerations, we hypothesize that cancer antigen-loaded nanogels accumulated in the surface region of the epidermis by iontophoresis should exhibit the ability to be captured by Langerhans cells, resulting in the subsequent induction of an anti-cancer effect via activation of an immune response. To validate our hypothesis, we herein examine the iontophoretic delivery of nanogels modified with antigen peptides into the epidermis, and the subsequent effect on tumor growth of mouse melanoma.