Dr. Ruoslahtis main scientific contributions are in
the field of cell adhesion. He was one of the discoverers of fibronectin. His
laboratory subsequently discovered the RGD cell attachment sequence in
fibronectin and isolated cellular RGD receptors, now known as integrins. The RGD
discovery has led to the development of drugs for diseases ranging from vascular
thrombosis to cancer.
Dr. Ruoslahti current studies deal with peptides that
specifically target a diseased tissue, particularly its blood vessels. The
peptides can be used to deliver drugs and nanoparticles to sites of disease,
such as a tumor. The molecules targeted by such disease-specific peptides are of
interest regarding their possible role in the disease and potential targets for
Vascular Zip Codes
Our laboratory screens large collections ("libraries")
of random peptides to identify those that bind to specific targets in tissues.
The peptides in the library are displayed on the surface of phage (a virus that
infects bacteria), and the screening is done in vivo. When the library is
injected into the circulation of a mouse, phage particles that display peptides
capable of binding to a selected target tissue, such as a tumor, accumulate at
the target where they can be collected and their peptide identified. The process
primarily probes the vasculature of the target tissue, unless the vasculature is
very leaky. The method has revealed a wealth of specific features, or "vascular
zip codes", in the vessels of individual tissues and tumors. We have identified
peptides that specifically home to tumors because they recognize
angiogenesis-associated or tumor-type specific markers in tumor blood vessels.
We even have peptides that distinguish the vessels of pre-malignant lesions from
those of fully malignant tumors. Homing peptides have also revealed a zip code
system of molecular changes in tumor lymphatics.
We have used synthetic homing peptides identified by
phage display to target drugs, biologicals, and nanoparticles into tumors. The
targeting can increase the efficacy of a drug while reducing its side effects.
Even a non-specifically toxic compound can be converted into a compound that
affects only the targeted tissue. We also identify the target molecules
(receptors) for the peptides. The receptors of our tumor-homing peptides often
play a functionally important role in tumor vasculature, and because of this are
candidates for drug development.
A few years ago we discovered peptides that not only home to tumor vessels, but are transported through the vascular wall and deep into tumor tissue. The key feature of these peptides is a R/KXXR/K sequence motif we have named C-end Rule (CendR) motif or element. In tumor-penetrating peptides, the CendR element is cryptic. These peptides penetrate into tumor tissue in a 3-step process: (i) The peptide binds to a primary receptor on tumor endothelium. In iRGD, the RGD motif recognizes the αvβ3/αvβ5 integrins; the primary receptor for the LyP-1 family of peptides is cell surface p32/gC1qR. (ii) The peptide is then cleaved by a protease to expose the CendR element at the C-terminus of the peptide; and, (iii) the CendR element mediates binding to neuropilin-1 (NRP-1), to induce vascular and tissue permeability. The CendR transport pathway triggered through NRP-1 resembles macropinocytosis, but differs from it in being receptor-mediated. Importantly, the responsiveness of the pathway to triggering through NRP-1 is regulated by the nutrient status of cells and tissues. Its physiological function is likely to be to transport nutrients into tissues that lack them. Our ability to trigger the pathway specifically in tumors makes it useful in delivering drugs into tumors.
Targeting the brain
We have recently also applied the phage screening to the identification of peptides that target brain diseases. So far, we have a peptide that specifically recognizes sites of brain injury, and a panel of peptides that are specific for Alzheimer’s brain. This topic will be an expanding focus of the laboratory in the near future.
A major focus is to use homing peptides as targeting elements to deliver nanoparticles into tumors and other sites of disease. Nanoparticles are considered a promising new approach in medicine because they can be designed to perform more functions than a simple drug. The vasculature is an excellent target for nanoparticles because tumor vessels are readily available for circulating particles. In collaboration with several chemistry and bioengineering laboratories, we have constructed multifunctional nanoparticles for tumor targeting. These particles can be directed into tumors in a highly selective manner as demonstrated by histology, non-invasive imaging, and tumor treatment results. We have constructed nanoparticles with the ability to amplify their own homing to tumors, and are currently working on nanoparticles coated with tumor-penetrating peptides. Recently, we have also worked on nanoparticles that target brain diseases or atherosclerotic plaques. The general goal is to engineer nanoparticles with multiple functions. In addition to the specific targeting, such functions include avoidance of the reticuloendothelial system, self-amplification of the targeting, exit from vessels into tissue, ability to send signals for imaging, and controlled drug delivery.
Schematic representation of the CendR trans-tissue transport pathway.
Note that CendR effect enhances the tissue penetration of molecules (depicted here as a black dots) that are co-administered with the peptide, as well as of cargo coupled to the peptide. The inset shows an electron microscopic image of a CendR endocytic vesicle that is budding from the cell surface into the cytoplasm and contains CendR peptide-coated gold nanoparticles (dark dots) See Ruoslahti, Adv. Drug Deliv. Rev. 2016.
Ruoslahti E.Tumor penetrating peptides for improved drug delivery.
Adv Drug Deliv Rev. 2016 Apr 1. pii: S0169-409X(16)30094-1. doi: 10.1016/j.addr.2016.03.008. [Epub ahead of print] Review. PMID: 27040947
Ruoslahti, E. Peptides as targeting elements and tissue penetration devices for nanoparticles. Adv. Mat. (review article) 24:3747-3756. (2012). [Epub ahead of print] PMCID: PMC3947925