Unprecedented behavior of (9R)-9-hydroxystearic acid loaded keratin nanoparticles on cancer cell cycle

High level expression of histone deacetylase 1 (HDAC1) plays a pivotal role in the pathobiology of cancer [1]. The endogenous fatty acid (9R)-9-hydroxystearic acid, 9R, is a natural HDAC1 inhibitor, which exerts its antiproliferative activity by arresting cancer cells growth in G0/G1 phase [2]. However, one of its major limitations is the unfavorable pharmacokinetic that hampers its therapeutic effectiveness. To overcome this constraint, 9R keratin nanoparticles (9R@Ker) were prepared and described here for the first time. Keratin was selected as carrier because possesses excellent biocompatibility and low toxicity to cells, thus resulting very promising material for drug delivery applications [3]. The formation of 200 nm nanoparticles (NPs) was induced by hydrophobic interactions between 9R and the hydrophobic protein domains, affording water-stable NPs with no need of toxic cross-linking agents. NPs were characterized in terms of particles size distribution, zeta potential, morphology, thermogravimetric behavior and drug release profile. Moreover, in vitro uptake and cytotoxicity was evaluated using human colorectal adenocarcinoma cells (HT29). Our data revealed that 9R@Ker are efficiently internalized by tumor cells, altering membrane lipidic composition. In vitro results demonstrate that the activity of 9R as free or loaded onto NPs is similar in terms of anti-proliferative effect. Remarkably, some significant differences were observed in the cell cycle analysis, showing that while free 9R caused a growth arrest in the G0/G1 phase, 9R@Ker induced a S phase arrest, thus promoting apoptosis (Fig.1). Additional studies are ongoing to better elucidate the underpinning biochemical mechanism of action of our newly developed delivery system.