Kallikrein-kinin in infection and cancer

Mechanism of tumor-targeted delivery of macromolecular drugs, including the EPR effect in solid tumor and clinical overview of the prototype polymeric drug SMANCS

This review article describes three aspects of polymeric drugs. The general mechanism of the EPR (enhanced permeability and retention) effect and factors involved in the effect are discussed, in view of the advantages of macromolecular therapeutics for cancer treatment, which are based on the highly selective EPR-related delivery of drug to tumor. Also described are advantages of more general water-soluble polymeric drugs as primary anticancer agents, using SMANCS as an example. Last, SMANCS/Lipiodol is discussed with reference to the type of formulation for arterial injection with most pronounced tumor selective delivery, as well as its advantages, precautions, and side effects from the clinical standpoint.

Enhanced vascular permeability in solid tumor involving peroxynitrite and matrix metalloproteinases

Peroxynitrite (ONOO(-)), which is generated from nitric oxide (NO) and superoxide anion (O(2)(.-)) under pathological conditions, plays an important role in pathophysiological processes. Activation of matrix metalloproteinases (MMPs) contributes to tumor angiogenesis and metastasis. NO mediates the enhanced vascular permeability and retention (EPR) effect in solid tumors, and ONOO(-)activates proMMP to MMP in vitro. In this study, we examined the role of ONOO(-)in the EPR effect in solid tumors and normal tissues as related to MMP activation. Authentic ONOO(-), at 50 nmol or higher concentrations, induced the enhanced vascular permeability in normal dorsal skin of mice. ONOO(-)scavengers ebselen and uric acid significantly suppressed the EPR effect in mouse sarcoma 180 (S-180) tumors. Indirect evidence for formation of ONOO(-)in S-180 and mouse colon adenocarcinoma (C-38) tumors included strong immunostaining for nitrotyrosine in the tumor tissue, predominantly surrounding the tumor vessels. MMP inhibitor BE16627B (66.6 mg / kg i.v., given 2 times) or SI-27 (10 mg / kg i.p., given 2 times) significantly suppressed the ONOO(-)-induced EPR effect in S-180 tumors and in normal skin. Soybean trypsin inhibitor (Kunitz type), broad-spectrum proteinase inhibitor ovomacroglobulin, and bradykinin receptor antagonist HOE 140 also significantly suppressed the ONOO(-)-induced EPR effect in normal skin tissues. These data suggest that ONOO(-)may be involved in and promote the EPR effect in tumors, which could be mediated partly through activation of MMPs and a subsequent proteinase cascade to generate potent vasoactive mediators such as bradykinin.

Tumor vascular permeability and the EPR effect in macromolecular therapeutics: a review

Most solid tumors possess unique pathophysiological characteristics that are not observed in normal tissues or organs, such as extensive angiogenesis and hence hypervasculature, defective vascular architecture, impaired lymphatic drainage/recovery system, and greatly increased production of a number of permeability mediators. The phenomenon now known as the enhanced permeability and retention (EPR) effect for lipid and macromolecular agents has been observed to be universal in solid tumors. Primarily, enhanced vascular permeability will sustain an adequate supply of nutrients and oxygen for rapid tumor growth. The EPR effect also provides a great opportunity for more selective targeting of lipid- or polymer-conjugated anticancer drugs, such as SMANCS and PK-1, to the tumor. In the present review, the basic characteristics of the EPR effect, particularly the factors involved, are described, as well as its modulation for improving delivery of macromolecular drugs to the tumor. Tumor-specific vascular physiology is also described.