Anticancer drug delivery: Investigating the impacts of viscosity on lipid-based formulations for pulmonary targeting

Abstract

Pulmonary drug delivery via aerosolization is a non-intrusive method for achieving localized and systemic effects. The aim of this study was to establish the impact of viscosity as a novel aspect (i.e., low, medium and high) using various lipid-based formulations (including liposomes (F1-F3), transfersomes (F4-F6), micelles (F7-F9) and nanostructured lipid carriers (NLCs; F10-F12)) as well as to investigate their impact on in-vitro nebulization performance using Trans-resveratrol (TRES) as a model anticancer drug. Based on the physicochemical properties, micelles (F7-F9) elicited the smallest particle size (12–174 nm); additionally, all formulations tested exhibited high entrapment efficiency (>89 %). Through measurement using capillary viscometers, NLC formulations exhibited the highest viscosity (3.35–10.04 m²/sec). Upon using a rotational rheometer, formulations exhibited shear-thinning (non-Newtonian) behaviour. Air jet and vibrating mesh nebulizers were subsequently employed to assess nebulization performance using an in-vitro model. Higher viscosity formulations elicited a prolonged nebulization time. The vibrating mesh nebulizer exhibited significantly higher emitted dose (ED), fine particle fraction (FPF) and fine particle dose (FPD) (up to 97 %, 90 % and 64 µg). Moreover, the in-vitro release of TRES was higher at pH 5, demonstrating an alignment of the release profile with the Korsmeyer-Peppas model. Thus, formulations with higher viscosity paired with a vibrating mesh nebulizer were an ideal combination for delivering and targeting peripheral lungs.

Introduction

Lung cancer is the second most prevalent cancer in both men and women, accounting for approximately 18 % of cancer-related deaths in developed nations (Siegel et al., 2023). Typically, systemic chemotherapy is offered, which delivers anticancer drugs to non-targeted sites marked by systemic side-effects and poor efficacy (Mangal et al., 2017). Conversely, administration of anticancer drugs via inhalation enables the deposition of large concentrations of chemotherapeutic agents directly to the lungs (localized effect), enhancing anti-tumour action and reducing systemic side-effects (Tatsumura et al., 1983).

Pulmonary targeting may be achieved using nanoparticles (NPs) which have been demonstrated to outperform conventional dosage forms in terms of efficacy, reduction in adverse effects and enhanced stability due to their small size, increased surface area and effective targeting (Roa et al., 2011,Yousaf et al., 2021, Subramanian et al., 2016
). NPs can be classified into various types based on their composition. The majority of NPs are made from lipids, polymers, proteins and carbohydrates, examples include: liposomes (Elhissi, A., 2017, Khan et al., 2023, Bnyan et al., 2020), micelles (Andrade et al., 2011), transfersomes (Khan et al., 2021b, Bnyan et al., 2019), dendrimers (Bai et al., 2007), solid lipid nanoparticles (SLNs) (Bai et al., 2007) and nanostructured lipid carriers (NLCs) (Khan et al., 2021a).

Resveratrol (3,5,4́ trihydroxystilbene) a novel anti-cancer agent, is a polyphenol stilbenoid comprising of two phenol rings joined together by ethylene bridges. It exists in two isomeric forms, cis and trans resveratrol, however the trans form (TRES) is considered more biologically active although less stable. It is highly photosensitive and converts to cis form when exposed to UV and visible light (Neves et al., 1999). Studies have also shown that TRES is unstable at higher pH level and temperature which results in conversion to cis form or degradation (Francioso et al., 2014). Additionally, TRES undergoes substantial liver metabolism and has limited water solubility, resulting in low bioavailability (Neves et al., 1999).

It is important to consider the physicochemical properties of NPs and anticancer drugs when developing inhalation formulations as they may affect the drug’s residence time in the lungs (Abdulbaqi et al., 2021). Drug loaded NPs are administered to the lungs as a liquid formulation (solution/dispersion) or solid (dry powders) aerosol system via dry powder inhalers (DPIs), pressurized metered dose inhalers (pMDIs), nebulizers and soft mist inhalers. pMDIs and soft mist inhalers deliver low drug doses, whereas nebulizers and DPIs can deliver high drug doses typically needed for anticancer drugs to effectively target tumour cells (Rosiere et al., 2019). To ensure effective delivery and prevent issues such as coughing and lung irritation, it is crucial to optimize factors such as pH, viscosity, surface tension and osmolality of the formulations (Labiris and Dolovich, 2003, Cipolla et al., 2013). Hence, an appropriate selection of formulation excipients and nebulizer are key parameters to be considered for optimum outcomes. Deposition of formulations in the lungs takes place by three mechanisms: inertial impaction, sedimentation and diffusion. Particles with an aerodynamic diameter greater than 5 μm deposit by inertial impaction, as they are unable to change their flow track within the airway, hence they deposit in upper respiratory tract. Particles sized between 0.5 and 5 μm deposit through sedimentation in the lower respiratory tract (central and alveolar region). This process yields a notable concentration of fine particles within this region often denoted to as the fine particle fraction (FPF). However, particles under 1 μm deposit by Brownian diffusion in to the peripheral areas of lungs (Darquenne and Prisk, 2004, Khan et al., 2016). In order to understand the mechanism of particle deposition in lungs, the British Pharmacopoeia has recommended an artificial lung model known as the two-stage impinger or twin impinger (TSI). The TSI is comprised of upper and lower stages (with a cut off diameter of 6.4 μm), which mimics the upper and lower respiratory tract and enables the determination of deposited drug into the lungs (Hallworth and Westmoreland, 1987).

In this study, various types of lipid-based formulations: liposomes (F1-F3), transfersomes (F4-F6), micelles (F7-F9), and NLCs (F10-F12) were prepared according to their viscosity (i.e., low, medium and high) by employing different compositions and combinations of phospholipids (SPC), surfactants (Tween 80), solid lipid (glycerol dibehenate; GBD) and liquid lipid (propylene glycol dicaprylate; PGD) using anticancer trans-resveratrol (TRES) as the model drug. These formulations were characterized in terms of particle size, drug entrapment, viscosity, and in-vitro drug release. The performance of nebulizers was evaluated using a TSI, to deliver the anticancer drug to the pulmonary system. The goal or novelty was to investigate how each formulation’s viscosity affected the nebulization performance in terms of nebulization time, sputtering time, mass output and aerosol output rate using two types of nebulizers: air jet and vibrating mesh. Finally, the deposition of TRES in the nebulizer reservoir and stages of TSI were examined to identify the best nebulizer type.

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Materials

Trans-resveratrol (TRES; >97 %) was purchased from Manchester organics, UK. Soybean phosphatidylcholine (SPC; Lipoid S-100; 94 % purity) was acquired from Lipoid, Switzerland. Tween 80 was purchased from Sigma Aldrich, UK. Glycerol dibehenate (GDB; Compritol 888 ATO) was obtained as a free sample from Gattefosse, France. Propylene glycol dicaprylate (PGD; Miglyol 840) was a generous gift from Oleo chemicals, UK. Analytical grade ethanol, formic acid (98 %), and HPLC grade acetonitrile (99.8 %) were obtained from Fischer scientific, UK.

Anila Mathew Thevarkattil, Sakib Yousaf, Chahinez Houacine, Wasiq Khan, Ruba Bnyan, Abdelbary Elhissi, Iftikhar Khan, Anticancer drug delivery: Investigating the impacts of viscosity on lipid-based formulations for pulmonary targeting, International Journal of Pharmaceutics, 2024, 124591, ISSN 0378-5173, https://doi.org/10.1016/j.ijpharm.2024.124591.