Nanoemulsion Formulations in Targeted Delivery of Cancer Therapeutics

Introduction

One of the major problems faced in most of the cancer therapies is to efficiently deliver the therapeutics to the site of tumor and keep the side effects to the minimum. Although the systemic administration of therapeutics has been heavily dependent on their physical and chemical properties including their size, diffusibility, and binding affinity to the plasma proteins, tumors have a crowded and diversified vascular system with a net drift towards outside. This hinders the targeted drug delivery to the site of the tumor. Furthermore, the conventional ways to deliver anticancer therapeutics generate a number of issues such as development of multidrug resistance (MDR) in carcinoma cells, high toxic effects on non-tumor cells, and poor specific indices (Wong et al., 2007). Moreover, most of the drugs that are developed for the cancer treatment are highly hydrophobic. To overcome the problem of hydrophobic drug incorporation and their effective delivery to the targeted tumor sites, nanocarriers have emerged out as potent drug delivery carriers. Due to their numerous advantageous properties in the field of drug delivery, the use of nanocarriers has significantly increased in the past few years. Nanocarriers are drug delivery systems, usually composed of colloids and have their particle size generally less than 500 nm (Neubert, 2011). Nanocarriers such as liposomes, dendrimers, nanoparticles, nanocapsules, and nanoemulsions have the ability to exploit the tumor microenvironment and increase the therapeutic efficiency of the loaded anticancer drug (Din et al., 2017).

Among all nanocarriers systems, nanoemulsions are colloidal drug carrier systems having a submicron droplet size, generally lying in the range of 10 to 1000 nm (Jaiswal et al., 2015). The structure of nanoemulsions resembles spherical nanoscaled heterogeneous dispersion composed of two immiscible liquids. They can be either of oil-in-water (O/W) type, water-in-oil (W/O) type, or bi-continuous type. Nanoemulsions have multiple advantageous properties to be used as novel drug carrier systems. First of all, the small size of nanoemulsions makes them capable of crossing highly vascularized surrounding environment of the tumor and accumulate there with an ease. Moreover, their spherical structure provides them a large surface area which may aid in greater adsorption. Secondly, the lipophilic core of the O/W nanoemulsions allows them to encapsulate highly hydrophobic drugs. Additionally, they are non-toxic, stable, non-irritant, can effectively increase the bioavailability of the drug, and can be used for site-specific targeting (Tiwari et al., 2006; Jaiswal et al., 2015). Above all, since the drug release pattern is maintained and controlled for a long duration, dose and frequency of shots may be lowered during the entire treatment process (Lovelyn & Attama, 2011). Figure 1 represents typical structure of a nanoemulsion drug delivery system. These properties make nanoemulsions novel carrier for the controlled and targeted delivery of cancer therapeutics. The current chapter aims to discuss the formulations of nanoemulsions for the controlled and targeted delivery of anti-cancer therapeutics and their applications in the treatment of various types of cancers. At last, the chapter summarizes various ongoing and completed clinical trials for using nanoemulsion formulations effectively and safely in the practical world.

Figure 1.

Structure of a nanoemulsion drug delivery system