Improve Therapeutic Outcomes with Nanomaterials That Penetrate Tumors
Targeted nanoparticles containing therapeutic cargo are being engineered by many groups to improve the therapeutic index of chemotherapy. However, nanoparticle delivery into the tumor microenvironment is limited by vascular permeability, diffusion through stroma, and off-target binding known as the 'binding site barrier'. We have explored several strategies to increase delivery of therapeutic cargo into the tumor microenvironment, including the use of local hyperthermia, two-component nanoparticle cocktails that cooperate to amplify deposition of cargo, and computational modeling of the transport process to guide engineering design. We observed the most profound effects on drug delivery and therapeutic outcome in collaboration with Erkki Ruoslahti (Sanford Burnham) who discovered an active tumor penetration pathway in 2009. His laboratory uncovered tumor-penetrating peptides that home to tumors and leverage a consensus R/KXXR/K C-terminal peptide motif to bind neuropilin-1, stimulate transport from inside blood vessels into a target tissue, and rapidly deliver therapeutic cargo deep into the tumor itself. This class of peptides could increase the delivery and impactof a variety of therapeutic cargo including small molecules, antibodies, and nanoparticles - but not siRNA. We sought to build on this discovery to enable targeted siRNA delivery.
Through a screening approach, we developed a tumor-penetrating nanocomplex (TPN) made by combining a tumor-penetrating peptide together with a membrane-translocating peptide and N-terminal myristoyl group (Fig. 6). Tandem peptides complexed with siRNA form nanoparticles that penetrate into tumor space and act in the cytoplasm of tumor cells to silence mRNA. Nanoparticle trafficking studies suggest that TPNs enter cells through a receptor-mediated process influenced by both macropinocytosis and lipid-rafts, followed by escape from endosomal entrapment that is enhanced by N-myristoylation, and release of siRNA at acidic pH. In collaboration with William Hahn (Dana Farber), we used TPNs in vivo to demonstrate that inhibitor of DNA binding 4 (ID4) is a novel oncogene in 32% of high-grade ovarian cancers. In a follow-up collaboration, we used TPNs to rapidly establish the role of PSMC2, which encodes an essential subunit of the 19S proteasome, in cancers with copy number alterations in vivo. Moving forward, we seek to extend siRNA delivery to other human malignancies, in part by updating TPN formulation to enable systemic rather than intraperitoneal delivery.
Tumor penetrating nanocomplexes for oncogene credentialing and intervention. (A) Schematic of LyP-1 binding and internalization. (B) Structure of tandem peptides and tumor penetrating nanoparticles (TPNs). (C) TPN-mediated knockdown is inhibited by free peptide competing for targeting receptor. (D) Microscopy image of TPN endosomal escape (left) and escape of transportan with and without myristic acid (right). (E) Fraction of TPN extravasation from tumor vasculature compared to untargeted control. (F) Orthotopic tumor treatment with TPN/siID4 (red), as compared to untargeted TPN/siID4 (blue), TPN loaded with control siRNA (green), saline (black). (Ren et al, STM 2012; Ren et al., ACS Nano 2012; Nijhawan et al., Cell 2012)