(137e) High Diffusive Peptides for Drug Carriers in Tumor Extracellular Matrix

Current therapies against solid cancers fail in part due to their inability to penetrate through the tumor microenvironment and reach the cancer cells at therapeutic doses. Increasing penetration promotes tumor regression and improves the therapeutic index of compounds. Tumor penetration of the therapeutics are limited by three major transport steps - the vascular, transvascular, and interstitial barriers. The hyper-permeable vasculature and dysfunctional lymphatic system of tumors result in elevated interstitial fluid pressure of the tumor extracellular matrix (ECM). This reduces the convective transport through the ECM, thus, diffusion is the primary mode of transport for therapeutic agents. Diffusivity of molecules through the ECM depends on their size and their interaction with the components of ECM. These interactions are driven by the surface physicochemical properties (i.e., charge and hydrophobicity) of the therapeutics.

To address challenges presented by current surface chemistries, we used peptide-presenting phage libraries as a high-throughput approach to screen and identify peptide coatings with physicochemical properties able to facilitating improved diffusive transport through the tumor microenvironment. We constructed a phage library, where random seven amino acid peptide sequences are displayed on the surface of T7 phage. Here, each phage expresses a different peptide sequence and each phage effectively serves as a formulation with unique surface chemistry. These libraries display random peptides on the surface of phages and effectively serve as a collection of peptide-based surface chemistries with a permutation of amino acids possessing varying physicochemical properties (i.e. 10⁵ – 10⁹ different sequences). Individual clones were selected through iterative screening of these phage libraries against the selective pressure of ECM components found in solid tumors and identification through next-generation DNA sequencing and analysis, and their transport was measured by diffusion assays.

We identified a net-neutral charge, hydrophilic peptide, P4, that diffused 90 times faster compared to a negative control through in vitro tumor ECM, achieving approximately half of its unhindered diffusivity in PBS. Using the selected peptide as a model we validated that hydrophilicity, charge and the order of the amino acid sequence can impact diffusive transport through the tumor ECM. The uptake of the selected clone is ~200 times higher compared to the negative control in ex vivo BxPC3 pancreatic tumor xenograft. We also verified the ability of the peptide as surface coatings to improve diffusive transport of nanoparticles through the tumor microenvironment towards improved drug delivery. The selected peptide was conjugated onto fluorescent nanoparticles, and the diffusivity in ex vivo pancreatic tumor tissues was quantified by multiple particle tracking. After peptide coating, the nanoparticles exhibited ~40-fold improvement in diffusivity and greater number of mobile particles compared to particles functionalized with the gold standard— poly(ethylene) glycol or iRGD-peptide ligands. The diffusivity is of similar order as that achieved by PEGylated or iRGD-peptide-coated particles, which are generally used for improved penetration of drugs in the tumor environment.