Induction of Cancer Cell Death by Hyaluronic Acid-Mediated Uptake of Cytochrome C

Effective cancer treatment needs both, passive and active targeting approaches, to achieve highly specific drug delivery to the target cells while avoiding cytotoxicity to normal cells. Protein drugs are useful in this context because they can display excellent specificity and potency. However, their use in therapeutic formulations is limited due to their physical and chemical instability during storage and administration. Polysaccharides have been used to stabilize proteins during formulation and delivery. To accomplish both, stabilization and targeting simultaneously, the apoptosis-inducing protein cytochrome c (Cyt c) was modified with the polysaccharide hyaluronic acid (HA) because its corresponding receptor CD44 is overexpressed in many cancers. Cyt c-HA bioconjugates were formed using low and high molecular weight HA (8 kDa and 1 MDa) with a resultant Cyt c loading percentage of 4%. Circular dichroism and a cell-free caspase assay showed minor structural changes and high bioactivity (more than 80% caspase activation) of Cyt c, respectively, after bioconjugate formation. Two CD44-positive cancer cells lines, HeLa and A549 cells, and two CD44-negative normal cell lines, Huvec and NIH-3T3 cells, were incubated with the samples to assess selectivity and cytotoxicity. After 24 h of incubation with the samples, cancer cell viability was reduced at least 3-fold while CD44-negative control cell lines remained minimally affected. Fluorescence imaging confirmed selective internalization of the Cyt c-HA construct by CD44-positive cancer cell lines. These results demonstrate the development of a drug delivery system that incorporates passive and active targeting which is essential for cancer treatment.