Lianglin Zhang

Biomimetic amplification of nanoparticle homing to tumors

Nanoparticle-based diagnostics and therapeutics hold great promise because multiple functions can be built into the particles. One such function is an ability to home to specific sites in the body. We describe here biomimetic particles that not only home to tumors, but also amplify their own homing. The system is based on a peptide that recognizes clotted plasma proteins and selectively homes to tumors, where it binds to vessel walls and tumor stroma. Iron oxide nanoparticles and liposomes coated with this tumor-homing peptide accumulate in tumor vessels, where they induce additional local clotting, thereby producing new binding sites for more particles. The system mimics platelets, which also circulate freely but accumulate at a diseased site and amplify their own accumulation at that site. The self-amplifying homing is a novel function for nanoparticles. The clotting-based amplification greatly enhances tumor imaging, and the addition of a drug carrier function to the particles is envisioned.

Progressive vascular changes in a transgenic mouse model of squamous cell carcinoma

Phage display was used to identify homing peptides for blood vessels in a mouse model of HPV16-induced epidermal carcinogenesis. One peptide, CSRPRRSEC, recognized the neovasculature in dysplastic skin but not in carcinomas. Two other peptides, with the sequences CGKRK and CDTRL, preferentially homed to neovasculature in tumors and, to a lesser extent, premalignant dysplasias. The peptides did not home to vessels in normal skin, other normal organs, or the stages in pancreatic islet carcinogenesis in another mouse model. The CGKRK peptide may recognize heparan sulfates in tumor vessels. The dysplasia-homing peptide is identical to a loop in kallikrein-9 and may bind a kallikrein inhibitor or substrate. Thus, characteristics of the angiogenic vasculature distinguish premalignant and malignant stages of skin tumorigenesis.

Systematic Surface Engineering of Magnetic Nanoworms for in vivo Tumor Targeting

In the design of nanoparticles that can target disease tissue in vivo, parameters such as targeting ligand density, type of target receptor, and nanoparticle shape can play an important role in determining the extent of accumulation. Herein, a systematic study of these parameters for the targeting of mouse xenograft tumors is performed using superparamagnetic iron oxide as a model nanoparticle system. The type of targeting peptide (recognizing cell surface versus extracellular matrix), the surface coverage of the peptide, its attachment chemistry, and the shape of the nanomaterial [elongated (nanoworm, NW) versus spherical (nanosphere, NS)] are varied. Nanoparticle circulation times and in vivo tumor-targeting efficiencies are quantified in two xenograft models of human tumors (MDA-MB-435 human carcinoma and HT1080 human fibrosarcoma). It is found that the in vivo tumor-targeting ability of the NW is superior to that of the NS, that the smaller, neutral CREKA targeting group is more effective than the larger, positively charged F3 molecule, that a maximum in tumor-targeting efficiency and blood half-life is observed with approximately 60 CREKA peptides per NW for either the HT1080 or the MDA-MB-435 tumor types, and that incorporation of a 5-kDa polyethylene glycol linker improves targeting to both tumor types relative to a short linker. It is concluded that the blood half-life of a targeting molecule-nanomaterial ensemble is a key consideration when selecting the appropriate ligand and nanoparticle chemistry for tumor targeting.

Mitochondrial/Cell-Surface Protein p32/gC1qR as a Molecular Target in Tumor Cells and Tumor Stroma

A tumor homing peptide, LyP-1, selectively binds to tumor-associated lymphatic vessels and tumor cells in certain tumors and exhibits an antitumor effect. Here, we show that the protein known as p32 or gC1q receptor is the receptor for LyP-1. Various human tumor cell lines were positive for p32 expression in culture, and the expression was increased in xenograft tumors grown from the positive cell lines. Fluorescence-activated cell sorting analyses with anti-p32 antibodies showed that p32-positive cell lines expressed p32 at the cell surface. These cells bound and internalized LyP-1 peptide in proportion to the cell-surface expression level, which correlated with malignancy rather than total p32 expression in the cells. Like the LyP-1 peptide, p32 antibodies highlighted hypoxic areas in tumors, where they bound to both tumor cells and cells that expressed macrophage/myeloid cell markers and often seemed to be incorporated into the walls of tumor lymphatics. Significant p32 expression was common in human cancers and the p32 levels were often greatly elevated compared with the corresponding normal tissue. These results establish p32, particularly its cell-surface-expressed form, as a new marker of tumor cells and tumor-associated macrophages/myeloid cells in hypoxic/metabolically deprived areas of tumors. Its unique localization in tumors and its relative tumor specificity may make p32 a useful target in tumor diagnosis and therapy.

Peptide Targeting of Tumor Lymph Vessels

In addition to having a blood vasculature, most normal organs and pathologic conditions involve a second vascular system, the lymphatic vasculature, and many tumors induce the growth of new lymphatic vessels. However, compared to the blood vasculature, very little is known about the lymphatic vessels in tumors. We have used the in vivo phage display technology to map tumor‐specific differences in the lymphatic vasculature, and identified peptides that specifically home to tumor lymphatics. Each of these peptides recognizes lymphatic vessels in a different set of tumors, and some of them also recognize tumor cells. Furthermore, these peptides can differentiate lymphatic vasculature of a premalignant lesion from that of a full‐blown tumor, indicating tumor stage–specific differences in the lymphatic vessels. None of the lymphatic homing peptides recognizes blood endothelial cells, nor do they home to any normal organ. Of interest, some of our homing peptides are able to penetrate the target cells in a cell type–specific manner. These peptides appear to be able to concentrate in the target tissue, making them particularly efficient delivery vectors for the targeting of therapeutic moieties and imaging agents. Conjugation of the lymphatic homing peptides to drugs provides an opportunity to specifically deliver therapeutic agents into tumors using a route not previously exploited. The surprising degree of selectivity of these lymphatic homing peptides suggests extensive molecular specialization of tumor lymphatic vessels, positing the existence of a molecular lymphatic “zip code” system, as has been previously demonstrated for the tumor blood vasculature.