Erkki Ruoslahti

Nanoparticles coated with the tumor-penetrating peptide iRGD reduce experimental breast cancer metastasis in the brain

Metastasis is the main killer in cancer; consequently, there is great interest in novel approaches to prevent and treat metastatic disease. Brain metastases are particularly deadly, as the protection of the blood-brain barrier obstructs the passage of common anticancer drugs. This study used magnetic resonance imaging (MRI) to investigate the therapeutic effects of nanoparticles coated with a tumor-penetrating peptide (iRGD) against a preclinical model of breast cancer brain metastasis. Single doses of iRGD nanoparticle were administered intravenously, and the effect on tumor growth was observed over time. iRGD nanoparticles, when applied in the early stages of metastasis development, strongly inhibited tumor progression. Overall, this study demonstrated for the first time that a single dose of iRGD nanoparticle can have a significant effect on metastatic tumor progression and nonproliferative cancer cell retention when applied early in course of tumor development. These data suggest that iRGD nanoparticles may be useful in preventatively reducing metastasis after a cancer diagnosis has been established.Key messagesbSSFP MRI can be used to track nonproliferative iron-labeled cells and tumor development over time.iRGD-NW, when applied early, has a significant effect on metastatic tumor progression.Retained signal voids represent a subpopulation of nonproliferating tumor cells.Reduced cell retention and tumor burden show a role for iRGD-NW in metastasis prevention.iRGD target is universally expressed; thus, iRGD-NW should be clinically translatable.

Cell surface nucleolin antagonist causes endothelial cell apoptosis and normalization of tumor vasculature

Nucleolin is specifically transported to the surface of proliferating endothelial cells in vitro and in vivo. In contrast to its well defined functions in the nucleus and cytoplasm, the function of cell surface nucleolin is poorly defined. We have previously identified the nucleolin-binding antibody NCL3 that specifically binds to cell surface nucleolin on angiogenic blood vessels in vivo and is internalized into the cell. Here, we show that NCL3 inhibits endothelial tube formation in vitro as well as angiogenesis in the matrigel plaque assay and subcutaneous tumor models in vivo. Intriguingly, the specific targeting of proliferating endothelial cells by NCL3 in subcutaneous tumor models leads to the normalization of the tumor vasculature and as a result to an increase in tumor oxygenation. Treatment of endothelial cells with anti-nucleolin antibody NCL3 leads to a decrease of mRNA levels of the anti-apoptotic molecule Bcl-2 and as a consequence induces endothelial cell apoptosis as evidenced by PARP cleavage. These data reveal a novel mode of action for anti-angiogenic therapy and identify cell surface nucleolin as a novel target for combinatorial chemotherapy.

Engineering strategy to improve peptide analogs: from structure-based computational design to tumor homing

We present a chemical strategy to engineer analogs of the tumor-homing peptide CREKA (Cys-Arg-Glu-Lys-Ala), which binds to fibrin and fibrin-associated clotted plasma proteins in tumor vessels (Simberg et al. in Proc Natl Acad Sci USA 104:932–936, 2007) with improved ability to inhibit tumor growth. Computer modeling using a combination of simulated annealing and molecular dynamics were carried out to design targeted replacements aimed at enhancing the stability of the bioactive conformation of CREKA. Because this conformation presents a pocket-like shape with the charged groups of Arg, Glu and Lys pointing outward, non-proteinogenic amino acids α-methyl and N-methyl derivatives of Arg, Glu and Lys were selected, rationally designed and incorporated into CREKA analogs. The stabilization of the bioactive conformation predicted by the modeling for the different CREKA analogs matched the tumor fluorescence results, with tumor accumulation increasing with stabilization. Here we report the modeling, synthetic procedures, and new biological assays used to test the efficacy and utility of the analogs. Combined, our results show how studies based on multi-disciplinary collaboration can converge and lead to useful biomedical advances.

DEPLETION OF TUMOR-ASSOCIATED MACROPHAGES WITH CLODRONATE-LOADED PLGA NANOPARTICLES

Tumor-associated macrophages (TAMs) play an important role in tumor progression and metastasis. In this study, we developed a TAM-targeting poly lactic-co-glycolic acid (PLGA) nanoparticle (NP) that encapsulates a bisphosphonate drug, clodronate. Clodronate-loaded NPs killed macrophages more efficiently than the drug alone in vitro. The NPs functionalized with a TAM-targeting tissue-penetrating peptide, LyP-1, selectively accumulated in CD11b-positive (macrophage-rich) regions in mouse 4T1 breast tumor xenografts. Furthermore, clodronate-loaded LyP-1-functionalized NPs reduced the number of macrophages selectively in the 4T1 tumors, and modestly inhibited tumor growth. Our results support the idea that LyP-1-functionalized clodronate-loaded PLGA NPs could be a promising anti-tumor agent.