The present invention provides novel, serum-stable lipid particles comprising one or more active agents or therapeutic agents, methods of making the lipid particles, and methods of delivering and / or administering the lipid particles. More particularly, the present invention provides serum-stable
nucleic acid-lipid particles (SNALP) comprising a
nucleic acid (e.g., one or more interfering
RNA molecules), methods of making the SNALP, and methods of delivering and / or administering the SNALP (e.g., for the treatment of
cancer). In particular embodiments, the present invention provides tumor-directed lipid particles that preferentially target
solid tumors. The tumor-directed formulations of the present invention are capable of preferentially delivering a
payload such as a
nucleic acid to cells of
solid tumors compared to non-cancerous cells.