Multistimuli-Responsive Bilirubin Nanoparticles for Anticancer Therapy.

Although stimuli-responsive materials hold potential for use as drug-delivery carriers for treating cancers, their clinical translation has been limited. Ideally, materials used for the purpose should be biocompatible and nontoxic, provide "on-demand" drug release in response to internal or external stimuli, allow large-scale manufacturing, and exhibit intrinsic anticancer efficacy. We present multistimuli-responsive nanoparticles formed from bilirubin, a potent endogenous antioxidant that possesses intrinsic anticancer and anti-inflammatory activity. Exposure of the bilirubin nanoparticles (BRNPs) to either reactive oxygen species (ROS) or external laser light causes rapid disruption of the BRNP nanostructure as a result of a switch in bilirubin solubility, thereby releasing encapsulated drugs. In a xenograft tumor model, BRNPs loaded with the anticancer drug doxorubicin (DOX@BRNPs), when combined with laser irradiation of 650 nm, significantly inhibited tumor growth. This study suggests that BRNPs may be used as a drug-delivery carrier as well as a companion medicine for effectively treating cancers.