Tumor vascular targeting using a tumor-tissue endothelium-specific monoclonal antibody as an effective strategy for cancer chemotherapy

[DDS and Me]

With the success of the human genome project, the focus of life science research has shifted to the functional and structural analyses of proteins, such as proteomics and structural genomics. These analyses of proteins including newly identified proteins are expected to contribute to the identification of therapeutically applicable proteins for various diseases. Thus, pharmaco-proteomic-based drug discovery and development for protein therapies, including gene therapy, cell therapy, and vaccine therapy, is attracting current attention. However, there is clinical difficulty in using almost all bioactive proteins, because of their very low stability and pleiotropic actions in vivo. To promote pharmaco-proteomic-based drug discovery and development, we have attempted to develop drug delivery systems (DDSs), such as the protein-drug innovation system and the optimal cell therapeutic system. In this review, we introduce our original DDSs.

Incorporation of adult organ-derived endothelial cells into tumor blood vessel

In this study, we attempted to assess the incorporable potential of vascular endothelial cells derived from adult organ blood vessels into tumor blood vessels. Two kinds of adult organ-derived vascular endothelial cells, human aorta endothelial cells (HAEC) and umbilical vein endothelial cells (HUVEC), were administered into murine tumors inoculated to SCID mice. Many human blood vessel networks were visualized in the murine tumors. These cells in solid tumor not only survived and proliferated, but also incorporated into tumor endothelium. These results suggest that adult organ-derived vascular endothelial cells possess the potential to form the neovascular network in various tissues such as vascular endothelial progenitor-like cells in vivo. We propose that these cells can be regarded as a congenic (autologous) vector for vascular regeneration cell therapy and tumor vascular targeting gene therapy.

Suppression of tumor angiogenesis through the inhibition of integrin function and signaling in endothelial cells: which side to target?

Tumor angiogenesis is an essential step in tumor progression and metastasis formation. Suppression of tumor angiogenesis results in the inhibition of tumor growth. Recent evidence indicates that vascular integrins, in particular alpha V beta 3, are important regulators of angiogenesis, including tumor angiogenesis. Integrin alpha V beta 3 antagonists, such as blocking antibodies or peptides, suppress tumor angiogenesis and tumor progression in many preclinical tumor models. The potential therapeutic efficacy of extracellular integrin antagonists in human cancer is currently being tested in clinical trials. Selective disruption of the tumor vasculature by high doses of tumor necrosis factor (TNF) and interferon gamma (IFN-gamma), and the antiangiogenic activity of nonsteroidal anti-inflammatory drugs are associated with the suppression of integrin alpha V beta 3 function and signaling in endothelial cells. Furthermore, expression of isolated integrin cytoplasmic domains disrupts integrin-dependent adhesion, resulting in endothelial cell detachment and apoptosis. These results confirm the critical role of vascular integrins in promoting endothelial cell survival and angiogenesis and suggest that intracellular targeting of integrin function and signaling may be an alternative strategy to extracellular integrin antagonists for the therapeutic inhibition of tumor angiogenesis.

The biology of the combretastatins as tumour vascular targeting agents

The tumour vasculature is an attractive target for therapy. Combretastatin A-4 (CA-4) and A-1 (CA-1) are tubulin binding agents, structurally related to colchicine, which induce vascular-mediated tumour necrosis in animal models. CA-1 and CA-4 were isolated from the African bush willow, Combretum caffrum, and several synthetic analogues are also now available, such as the Aventis Pharma compound, AVE8062. More soluble, phosphated, forms of CA-4 (CA-4-P) and CA-1 (CA-1-P) are commonly used for in vitro and in vivo studies. These are cleaved to the natural forms by endogenous phosphatases and are taken up into cells. The lead compound, CA-4-P, is currently in clinical trial as a tumour vascular targeting agent. In animal models, CA-4-P causes a prolonged and extensive shut-down of blood flow in established tumour blood vessels, with much less effect in normal tissues. This paper reviews the current understanding of the mechanism of action of the combretastatins and their therapeutic potential.

Targeted drug conjugates: principles and progress

Reports of targeting drugs using antibodies have appeared in the literature since 1958, but exciting clinical results in this field have only been reported in the last few years. Progress in this field has occurred largely through an understanding how drug-immunoconjugates work. The objective of this review is to draw together the fundamental principles on which this field of work is based, to examine the evidence supporting those principles, and the effectiveness and selectivity of targeted drug conjugates. The activity of many drug-immunoconjugates can now largely be accounted for by the underlying principles. Excellent development work, both with conventional anti-cancer agents and very potent drugs have led to a number of interesting clinical trials. In the best Phase I and II trials, good evidence of effectiveness have been reported, which suggest that drug-immunoconjugates may now be heralding a new era for chemotherapy.

Effective cancer targeting using an anti-tumor tissue vascular endothelium-specific monoclonal antibody (TES-23)

Immunoconjugate targeting of solid tumors has not been routinely successful because the endo-thelial cells of blood vessels act as a physical barrier against the transport of macromolecules, such as antibodies. In the present study, we attempted to achieve tumor vascular targeting with an anti-tumor tissue endothelium-specific monoclonal antibody (TES-23). TES-23, an IgG1 monoclonal antibody raised against rat KMT-17 fibrosarcoma-derived endothelial cells, was covalently conjugated with neocarzinostatin (NCS) in a previous study. The TES-23-NCS conjugate induced tumor hemorrhagic necrosis, and showed marked anti-tumor effects against rat KMT-17 fibrosarcoma. This result prompted us to investigate whether this approach would be applicable to various other types of solid tumors. One hour after injection of (125)I-labeled TES-23 into BALB / c mice bearing Meth-A fibrosarcoma and Colon 26 adenocarcinoma, the tumor accumulation of TES-23 was greater than that of the control IgG. In the present study, we report the anti-tumor effects of this monoclonal antibody in mice bearing Meth-A fibrosarcoma. Mice treated with the immunoconjugate showed improved survival with no side effects. This result indicates that common antigens may be found in different kinds of tumor endothelial cells, and that TES-23 might recognize these antigens.