Development and characterisation of capsaicin-encapsulated polymeric hydrogel nanocarrier for in vitro cancer therapy

Abstract

Cancer-related death has reached approximately 10 million worldwide, thus increasing demand for efficacious and safe anticancer therapy in order to ensure a better cancer care outcome. Capsaicin is one of a few promising compounds to fulfil this need due to its anticancer property, but its short half-life of 8 minutes limits its application in anticancer therapy. Encapsulation of capsaicin into nanoparticles is a possible solution to this problem, as they protect drugs from being degraded due to their sustained-release properties. Chitosan and κ-carrageenan was chosen for this purpose due to the ability of chitosan to passively target cancer cells and κ-carrageenan’s ability to protect drugs from degradation in the human body upon injection. Firstly, the nanoparticles were screened for a desired physicochemical characteristic such as smaller size, smaller polydispersity and higher positive charge using one-factor-at-a-time (OFAT) screening method. The screened nanoparticle containing capsaicin are then studied for their drug release behaviour using the dialysis bag method. Then, it was studied for its stability for 12 weeks in storage at 30°C and 75% RH. Lastly, the anticancer effect of the nanoparticles towards SiHa (uterine) cancer), MCF-7 (breast cancer) and HeLa (cervical) were investigated using MTT assay. The screening process reduced the size and PDI of the synthesised nanoparticles from 433.6±19.523 nm and 0.354±0.019 to a size and PDI as low as 189.6±5.39 nm and 0.218±0.0191 respectively, with capsaicin encapsulation. Zeta potential value was largely maintained significantly (p<0.05) above +30 mV throughout the process. Loading the nanoparticles with capsaicin does not change these characteristics but causes nanoparticle swelling to occur at a higher magnitude, although statistically insignificant. At 300μg/mL, the capsaicin was encapsulated at an efficiency of up to 27.298±4.030% and capacity of 13.284±3.025%. Capsaicin release from the nanoparticle occurs at a slower rate than free capsaicin, indicating sustained-release properties. Mathematical model fitting implies that the release mechanism is biphasic in nature involving capsaicin dissolution and diffusion through the polymeric network. Stability studies indicate that the nanoparticles are only stable for 1 week before significant changes in physicochemical characteristics occur, although this is in the case of storage in 30 °C and 75% relative humidity condition, which is not typical for nanoformulations. Cytotoxicity study results reveals that while free capsaicin is cytotoxic towards the three cell lines at concentrations under 400 μM, capsaicin-loaded nanoparticles are generally not different from empty nanoparticles, showing that nanoparticle encapsulation masks the anticancer effect of capsaicin. The current study demonstrates that the issue of hydrophobicity of capsaicin remains as a major issue for capsaicin-encapsulated nanoparticles to exert cytotoxic effect, and hence this problem must be addressed. The current study concludes that the current nanoformulation will require a massive overhaul aiming for increased encapsulation or reduction of polymeric material used to improve cytotoxicity. Improvement on the stability of the nanoparticle is possible in future research by introducing an additional cross-linking step to improve nanoparticle integrity. The current study is significant due to it being the first attempt at encapsulating capsaicin in a chitosan-carrageenan nanoparticle.