A novel mellitin‐derived peptide nanoparticle delivery system for STAT3 siRNA mediated killing of B16 melanoma cells

Exogenously delivered siRNA has the potential to form a new class of cancer therapeutics based on sequence specific silencing of oncogene expression. Previous work has shown that the transcription factor, Signal Transducer and Activator of Transcription 3 (STAT3), is constitutively activated in the B16 melanoma cell line and mediates resistance to apoptosis by driving expression of anti‐apoptotic genes. In this study, we sought to establish the efficacy of novel peptide‐based siRNA delivery agents derived from the bee‐venom component, melittin, for STAT3 knockdown in B16 cells. Modifications to melittin (GIGAVLKVLTTGLPALISWIKRKRQQ) include truncation of its N‐terminus to reduce cytotoxicity and addition of basic residues to its C‐terminus to improve electrostatic binding to siRNA. The resulting peptide, p5RHH (VLTTGLPALISWIRRRHRRHC), complexes siRNA to form a nanoparticle delivery system, and mediates sequence specific knockdown of GFP in B16‐GFP cells. Confocal microscopy reveals that Cy3 labeled oligonucleotides are taken up by cells with diffuse cytoplasmic staining after 2 hours. Notably, p5RHH‐mediated transfection of 50nM STAT3 siRNA reduces B16 viability by 25% without vector associated cytotoxicity. These results indicate that p5RHH is a high efficiency, low toxicity siRNA transfection agent with implications for cancer therapy. Supported by Sigma‐Aldrich Predoctoral Fellowship.